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REPUBLIC OF YEMEN
     MINISTRY OF OIL AND MINERAL RESOURCES
PETROLEUM EXPLORATION AND PRODUCTION AUTHORITY




A STUDY ON THE RESERVOIR ROCKS OF QISHN
        FORMATION (Masila Block 14)




     By: Dr. Eng. Mohammed Darsi Abdulrahman Nedham
     Doctor of Science (Geologist), PEPA ’s Office (Aden)




                                                 Aden (June 2oo3)
WHAT MASILA BLOCK AND QISHN FORMATION
        MEANS FOR CANADIAN NEXEN INC.?
     First of all, and before I am going to write any word as an introduction to my study on
     the reservoir rocks of Qishn Formation in Masila Block (14). I would like to draw the
     attention of all people, who work as decision makers in the Ministry of Oil and
     Minerals (MOM) and the Petroleum Exploration and Production Authority (PEPA) on
     the great importance of answering the above-mentioned question.

     We must know, that Masila Block (See, Fig. (1)) has a great meaning for Nexen
     Company, because of the following reasons:
1.   Approximately 44% of Nexen's overall production comes from the Masila Block
     (Yemen), which representing just over one third of the company's cash flow.
2.   Nexen has a 52% working interest in and operate the Masila Project, which is the
     largest single source of oil production in Yemen and has grown steadily since
     discovery in 1990.
3.   To date, the 15 fields that comprise the Project have produced over 665 million
     gross barrels of oil from total gross recoverable reserves of just over one billion
     barrels.
4.   Nexen has the right to produce oil from the Masila fields until 2011 and the right
     to negotiate a five-year extension.
5.   During 2002, $402 million ($209 million net) was invested to drill and equip 74
     new development wells and expand existing infrastructure. Gross production was
     maintained throughout the year at approximately 226,900 barrels per day.
6.   The economics of Masila production are attractive. Historic finding and
     development costs are approximately US $2 per barrel and operating costs have
     averaged US $1 per barrel, resulting in excellent returns for shareholders!

     All the above mentioned reasons makes Nexen not just take care of Masila Block and
     Qishn Formation, (I mean the Qishn clastic member, which is the main producing
     reservoir in this area and the main subject of this study), but also to work actively on
     exploring outside the Masila Block. In my opinion, the strategic point of view and the
     excellent steps taken by the heads of Nexen Inc. led to the following main result and
     present fact:

     (Nexen, NOW, hold interests in seven exploration licenses (Block 50 Block 51
     Northern Blocks 11, 12, 36, 54 and 59) comprising over 20 million acres of
     undeveloped land, the majority of which are located in northeastern Yemen close to
     the Saudi Arabian border. (See Fig. (2))

     Due to what mentioned above I am sure that we in Yemen are highly in need for
     building not just the high qualified Yemeni oil team but also for building the first
     National Oil Exploration Company. Am I right? Now, it is the suitable time for
     Yemeni specialists, who found a great chance to work with those kind of high-
     qualified and experienced foreign specialists, to learn from the newest in their field of
     specialization. Our scientific cooperation and friendship must continue with all and
     forever. If we really want to see the whole plains clearly, we must climb the highest
     mountain.                                   i
Fig. (1) Masila Location (Nexen Inc., Data)




                                       <

Fig. (2) Nexen Blocks in Yemen (Nexen Inc., Data)


                       ii
INTRODUCTION

     Masila Block 14 is operated by Canadian Occidental Petroleum Yemen on behalf of
     its partners Occidental Peninsula, Inc. and Consolidated Contractors International,
     Ltd., (CANADIAN NEXEN PETROLEUM YEMEN as known now), and is located
     in the Hadhramaut region, in east-central Republic of Yemen. Oil was first discovered
     on the Block in late 1990 with Commerciality declared in late 1991. Oil production at
     Masila began in July 1993.

     There are now 15 oil fields known in Masila, Block 14: (See, Fig. (3)) 1. Camaal (C),
     2. North Camaal (NC), 3. Sunah (S), 4. Northeast Sunah (NES), 5. Heijah (HJ), 6.
     Hemiar (HR), 7. South Hemiar (S.HR), 8. West Hemiar (W.HR), 9. Tawila (T), 10.
     Haru (HU), 11. Nazeia (NZ), 12. Dahban (D), 13. Bainoon (ND), 14. Qataban (QAT),
     and 15. Gabal-Isbeel, containing 56 pools within the Masila Block. Total proven
     ultimate recoverable oil reserves are approaching 900 million STB. Proven, probable
     and possible reserve estimates are in excess of one billion barrels of recoverable oil.

     The Masila fields are in the Jurassic- to Lower Cretaceous-aged, Saar Graben. Almost
     90% of the Masila reserves are reservoired in the Qishn Formation of the Lower
     Cretaceous Upper Qishn Clastics Member. Oil is also found in at least seven other
     reservoirs consisting of Lower Cretaceous and Middle to Upper Jurassic age clastics
     and carbonates as well as fractured granitic basement.

     In this study I used real subsurface data related to 93 wells, penetrated the productive
     and non-productive fields of the studied area. All above-mentioned wells penetrated
     Qishn formation the main subject of this study, where I made geostatistical
     calculations and analysis, to explain the process of sedimentation mathematically for
     Qishn formation generally and its subdivision in detail. Showing the maximum,
     minimum and the average of Qishn formation thickness, its members, sub members,
     units and sub units in detail for every well, for every productive field and for Masila
     Block as a whole.

     The most important thing I have done during my study to the pervious and the present
     data, informations and published materials on the reservoir rocks of Qishn Formation
     is that I focused on the main producing horizon (the Upper Qishn Clastics Member).
     The Upper Qishn represents an upward transgressive sequence from braided river
     deposits into tidally influenced shorelines, overlain by subtidal and shelf deposits.

     Important Notices:
1.   Yemeni reserves of raw oil were estimated to be about 4 billion barrels, of which
     1380 million barrels are found in Marib, 1580 billion barrels in Masila, 250
     million barrels in Shabwah, and 750 million barrels in Gannah.
2.   Arab investment in Yemen heading toward $1 billion Yemen, Economics,
     9/23/1997



                                                iii
Fig. (3) Masila Block Oil Fields (Nexen Inc., Data)




                        iv
MAIN TOPICS OF THIS STUDY

     The main topics of this study on the reservoir rocks of Qishn Formation (Masila
     Block 14) are the following:

1.          To show the great importance of Masila (Block 14) and the
            reservoir rocks of Qishn Formation for Nexen Inc.

2.          To give a brief on the whole pervious activities done on studying
            the Geological Research History Work of the eastern part of the
            Republic of Yemen (the study area and the adjacent areas).

3.          To follow Qishn formation location on the whole surface, to study
            it in the sub surface of the studied area and to highlight the upper
            Qishn clastics rocks stratigraphy.

4.          To study the Qishn Formation in Masila Block 14 as whole and in
            detail, its subdivision, ages, sequence stratigraphy, general
            lithology, lithology, its drilling parameters averages, mud
            parameters, its Paleogeography, and its sedimentation thicknesses
            in the study area by making 20 tables on Qishn formations and it
            sub sequences.

5.           To explain the petroleum system of Qishn Formation, its source
            rocks, maturation, migration, reservoir rocks, traps and seals.




                                                v
NATURE OF THIS STUDY
     Prompted largely by this interest, my research study plan on studying the reservoir
     rock of Qishn Formation was concentrated on its achievement on the following
     important point:

1.   Study and examination of all primary information connected with the subject from
     various sources.
2.   Sorting of this information in accordance with its importance.
1.   Making number of tables and maps.
2.   Checking of all data and making necessary tests on them.
3.   Follow-up of the historical development of the reservoir rocks of Qishn Formation
     through the making of varying geostatistical and mathematical calculation for the
     interested section of Qishn formation and its subdivision from its bottom till the
     surface.




                              AIM OF THIS STUDY

     The study was aimed at the problems outlined in the previous two sections. This study
     is the first investigation work-study, done by me on the reservoir rocks of Qishn
     formation of Masila Block 14, which aims to:

1.   Help understanding of the great importance of the studied area.
2.   Help understanding of the pervious and present geological activities in the area.
3.   Help understanding of the reservoir rocks of Qishn formation, surface, sub surface
     geology and the upper Qishn stratigraphy.
4.   Help understanding of Qishn formation sequence stratigraphy.
5.   Help understanding of Qishn formation (Masila, Block 14) petroleum system.
6.   Give new discussions points, recommendations and conclusions.




                                               vi
CONTENTS
        WHAT MASILA BLOCK AND QISHN FORMATION MEANS FOR
        CANADIAN NEXEN INC.? --------------------------------------------------------------i
        INTRODUCTION --------------------------------------------------------------------------iii
        MAIN TOPICS OF THIS STUDY ------------------------------------------------------v
        NATURE OF THE PROBLEM ---------------------------------------------------------vi
        AIM OF THIS STUDY --------------------------------------------------------------------vi
        CONTENTS ---------------------------------------------------------------------------------vii
        LIST OF FIGURES ------------------------------------------------------------------------ix
        LIST OF TABLES --------------------------------------------------------------------------x

        CHAPTER 1: THE EASTERN PART OF THE REPUBLIC OF YEMEN
        GEOLOGICAL RESEARCH HISTORY WORK
            1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT
            AREAS -------------------------------------------------------------------------------1
1.1.1              INRODUCTION
1.1.2              PERVIOUS WORKS BASED ON MY
                   CLASIFICATION AND DIVISION

        CHAPTER 2: THE RESERVOIR ROCKS OF QISHN FORMATION
        (MASILA, BLOCK 14) – GEOLOGY
             2.1 INTRODUCTION --------------------------------------------------------------3
             2.2 QISHN FORMATION RESERVOIR GEOLOGY
             2.3 UPPER QISHN CLASTICS – STRATIGRAPHY -------------------------9

        CHAPTER 3: QISHN FORMATION AND ITS SUBDIVISION (IN DETALS)
            3.1 INTRODUCTION -------------------------------------------------------------10
            3.2 QISHN FORMATION IN THE OUTCROP
            3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS)
                   3.3.1 Qishn Carbonate Member ------------------------------------------21
                          3.3.1.1 Qishn Carbonate Member - Age
                          3.3.1.2 Qishn Carbonate Member - Lithology in General
                          3.3.1.3 Qishn Carbonate Member - Lithological Description
                          3.3.1.4 Rate of Penetrations for Qishn Carbonate Member
                          3.3.1.5 Gases in Qishn Carbonate Member
                          3.3.1.6 Drilling Parameters for Qishn Carbonate Member
                          3.3.1.7 Qishn Carbonate Member – Subdivision ------------24
                                  3.3.1.7. 1 C1
                                  3.3.1.7.2 C2
                                  3.3.1.7.3 RS (Red Shale)
                                  3.3.1.7.4 C3
                   3.3.2 Qishn Clastic Member ----------------------------------------------26
                          3.3.2.1 Qishn Clastic Member - Age
                          3.3.2.2 Qishn Clastic Member - Lithology in General
                          3.3.2.3 Qishn Clastic Member - Lithological Description


                                                     vii
3.3.2.4 Rate of Penetrations for Qishn Clastic Member
                       3.3.2.5 Gases in Qishn Clastic Member
                       3.3.2.6 Oil Shows in Qishn Clastic Member
                       3.3.2.7 Drilling Parameters for Qishn Clastic Member
                       3.3.2.8 Qishn Clastic Member – Subdivision ----------------29
                               3.3.2.8.1 Upper Qishn Clastic Sub Member ----------30
                                       3.3.2.8.1.1 S1 ------------------------------------31
                                               3.3.2.8.1.1.1 S1A
                                               3.3.2.8.1.1.2 S1B
                                               3.3.2.8.1.1.3 S1C
                                       3.3.2.8.1.2 S2 ------------------------------------33
                                               3.3.2.8.1.2.1 S2A
                                               3.3.2.8.1.2.2 S2B
                                               3.3.2.8.1.2.3 S2C
                                               3.3.2.8.1.2.4 S2D
                                       3.3.2.8.1.3 S3 ------------------------------------35
                               3.3.2.8.2 Lower Qishn Clastic Sub Member -------- -36
                                       3.3.2.8.2.1 LQ1
                                       3.3.2.8.2.2 LQ2
                                       3.3.2.8.2.3 LQ3
                                       3.3.2.8.2.4 LQ4

CHAPTER 4: QISHN FORMATION PETROLEUM SYSTEM -----------------40
    4.1 INTRODUCTION
    4.2 SOURCE ROCKS
    4.3 MATURATION
    4.4 MIGRATION
    4.5 RESERVOIR ROCKS
    4.6 TRAPS AND SEALS

CHAPTER 5: DISSCUSION POINTS, RECOMMENDATIONS AND
CONCLUSION
    5.1 DISSCUSION POINTS --------------------------------------------------------41
    5.2 RECOMMENDATIONS ------------------------------------------------------42
    5.3 CONCLUSIONS ----------------------------------------------------------------43

ACKNOWLEDGEMENTS -----------------------------------------------------------------44
REFERENCES -------------------------------------------------------------------------------45
ABOUT THE AUTHOR --------------------------------------------------------------------46




                                            viii
LIST OF FIGURES

Fig. (1) Masila Location ---------------------------------------------------------------------ii
Fig. (2) Nexen Blocks in Yemen -----------------------------------------------------------ii
Fig. (3) Masila Block Oil Fields ------------------------------------------------------------iv
Fig. (4) Regional Stratigraphy (showing our study area) --------------------------------4
Fig. (5) Regional Frame Work (showing Masila Block Location due to Say’un al-
Masila Basin -----------------------------------------------------------------------------------5
Fig. (6) Regional Setting (showing Masila Block Location, due to Masila High) ---6
Fig. (7) Stratigraphy of Masila (showing Qishn Clastics Member and its related
subdivision) -----------------------------------------------------------------------------------7
Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2, Camaal-3
and Sunah-3 wells -----------------------------------------------------------------------------8
Fig. (9) Qishn Carbonate Member, Thickness Map -------------------------------------22
Fig. (10) Qishn Carbonate Member, Three Dimension Model -------------------------23
Fig. (11) Qishn Clastics Member, Thickness Map ---------------------------------------27
Fig. (12) Qishn Clastics Member, Three Dimension Model ----------------------------28
Fig. (13) Qishn Formation, Thickness Map -----------------------------------------------38
Fig. (14) Qishn Formation, Three Dimension Model -----------------------------------39




                                               ix
LIST OF TABLES
     Qishn Formation of Masila Block, its Subdivision Tops and Thicknesses
     Table (1) Qishn Carbonate of Masila, Block 14 Thicknesses ----------------------11
     Table (2) Qishn Carbonate (C1) of Masila, Block 14 Thicknesses --------------------14
     Table (3) Qishn Carbonate (C2) of Masila, Block 14 Thicknesses --------------------15
     Table (4) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses --------------------15
     Table (5) Qishn Carbonate (C3) of Masila Block 14, Thiknesses ---------------------16
     Table (6) Qishn Clastics of Masila, Block 14 Thicknesses --------------------------19
     Table (7) Upper Qishn Clastics of Masila, Block 14 Thicknesses -----------------20
     Table (8) Upper Qishn Clastics (S1A) of Masila, Block 14 Thicknesses -------------21
       Table (9) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses -----------22
     Table (10) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses -----------22
     Table (11) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses -----------23
     Table (12) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses -----------24
     Table (13) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses -----------24
     Table (14) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses -----------25
     Table (15) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses -------------25
     Table (16) Lower Qishn Clastics of Masila, Block 14 Thicknesses ---------------26
      Table (17) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses ----------26
      Table (18) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses ----------27
     Table (19) Qishn Formation of Masila, Block 14 Thicknesses ---------------------27


     Important Notice:
     All above-mentioned tables done by me based on my study to:
1.   The Masila Block Field Development Location Map in General.
2.   Sunah, Heijah, Camaal, Hemiar, … ,Haru and Naziah Fields
3.   The Geological Summary of the Masila Block
4.   The Masila Block Stratigraphic Column
5.   The Geological Sections done by me for Sunah-1, Naar-1, Maljan-1, Ressib-1,
     Deelun-1 Wells.
6.    Masila Block Formation Tops and Thicknesses (The table done in 1993, 1997 and
     updated in 2002, by Nexen Inc.)
7.   An old table done by me as a part of my study to Masila Block in the past. The
     main aim of the above mentioned table is to give interested persons in Masila
     Block general informations (such as: Block Area, Productive and non-productive
     fields, No. of wells in every Productive and non-productive fields and the
     Sedimentary Cover) and also geological informations (such as: the stratigraphical
     sections, thicknesses, lithology, source rocks characteristics and reservoir rocks
     characteristics)




                                               x
CHAPTER 1
              THE EASTERN PART OF THE REPUBLIC OF
                 YEMEN GEOLOGICAL RESEARCH
                        HISTORY WORK

        1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT
        AREAS

1.1.1           INRODUCTION
        The Republic of Yemen is beside the richest hydrocarbon province in the world. Oil
        only discovered in the early 1980’s in the offshore (Sharmah Well). It is known, that
        Nexen Inc. (formerly known as Can Oxy Company) discovered oil in Masila Block in
        1990 in the Qishn Clastics Member of Qishn Formation.


        The Masila Block has 1250 km2 in size. The Estimated Reserves is 1.1 billion barrels
        recoverable and the Cumulative Production is 600,000,000 barrels (Due to March
        2002 wells production reports), where the daily production was 230,000 b/d.

        1.2 PERVIOUS WORKS BASED ON MY CLASIFICATION AND DIVISION

        According to my new classification and first division to the whole geological research
        history work in the Republic of Yemen to four stages (See Yemen Times Newspaper.
        Issue 2-January 10th through January 16 2000, Vol. IX Culture Page, Issue 10 -
        March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April 10
        through April 16 2000, Vol. X, Culture Page). It is so clear now, that:

        1. On the First Stage (The First Systematic Geological Observation Stage or
        Carter’s Stage), 1852-1901:

        No kind of geological studies had been detected in the Masila area.

        2. On the Second Stage or the Hinterland Studies Stage, (1902-1946) and the
        Third Stage (The First Systematic more detailed Stratigraphic and Geological
        Studies Stage or Beydoun, Z.R.'s Stage, (1947-1967):

        The Petroleum Concessions Ltd, one of the Iraq Petroleum Company and associated
        companies (IPC and Associated companies) had carried out little exploration work in
        the area between 1937 and 1960. During that time they made geological field
        mapping, investigation, supplemented by aerophoto studies, photogeologic and
        mapping covering the entire territory were carried out.



                                                  1
3. On The Third Stage (The First Systematic more detailed Stratigraphic and
Geological Studies Stage or Beydoun, Z.R.'s Stage), 1947-1967:

During this stage the adjacent areas started to be studied by scientist and oil
companies. Bunker, D.G. wrote about the southwest Borderlands of Rub al Khali, in
1953. From 1961 to early 1967, Pan American International Oil Company through a
subsidiary, Pan American Hadhramawt Oil Company (PAHOC) drilled four wells
(Hoowarin, Tarfayt and Core Hole 88 reached Precambrian basement and the forth
was abandoned in the Cretaceous sediments).

4. The Forth Stage or The Yemeni Geologists Stage (1968 – until Today):

During this stage many important scientific works happened in Yemen, which at the
end led to the creation of the concision map of Yemen, the birth of Masila Block and
its oil discoveries.

It is known that, the Petroleum and Minerals Board (the PMB) was established, in
1970 in former South Yemen. During the period from 1970 to 1973, the joint of
former South Yemen-Algerian Petroleum Company (SYAPCO) drilled Taur-1 in
1974 and Taur-2 was commenced. In 1974, a group of experts from Cuba assumed the
drilling operation from SYAPCO and with former PMB completed Taur-2, Taur-3
and drilled Thamud-1 and Hathout-1. In September 1976, the functions of the PMB
were broadened and the Petroleum Exploration Board (the PED) was created (The
Petroleum Exploration and Production Board, Aden Branch – As known now), was
led different activities on studding the geology of this area. As a result of their work
on the Yemeni sector of Rub al Khali basin, wells as Taur-2, Taur-3 and Hathout-1
was drilled. A group of the P.E.D.’s Engineers, Technician and workers, work hard on
this area, their work is highly appreciated.

Between 1975 and 1979, as a part of its assistance program, TechnoExport, the former
Soviet Technical Assistance Organization, had recorded aeromagnetic surveys
covering most of former South Yemen and also a gravity survey had been conducted
over specific areas of interest.

On Mar. 27 1979, B. Kuzin and Mohammed Ba’abad made a Stratigraphic
Correlation, for wells drilled in that area correlative with wells located in the adjacent
area at that's time.

The field investigation had been augmented from time to time by Czechoslovakian
and German technical personnel.

Agip SpA (from 1978 to 1980): conducted landsite airphoto interpretation and a field
mapping project along the coastal outcrop belt as part of its offshore exploration effort
in the Sayhut Block. On 1981 Agip recorded 110 km of seismic on the coastal plain
east of Mukalla.

Petroleo Brasileiro SA (Petrobras): shot a regional seismic program and drilled three
unsuccessful test wells in the area to the north of the Masila Block in Jeza syncline
and relinquished the area in 1987.
                                             2
CHAPTER 2
 THE RESERVOIR ROCKS OF QISHN FORMATION
       (MASILA, BLOCK 14) – GEOLOGY

2.1 ITRODUCTION
It is known, that oil trapped in sands of the Qishn Formation, the main subject of this
study, in the following structures: Camaal, North, Sunah, North East Sunah, Heijah,
Hemiar, South Hemiar, West Hemiar, Tawila, Haru, Nazeia, Dahban, North Dahban,
Qataban, and Gabal-Isbeel.
Note 3: Oil has also been discovered in the Kohlan Formation (at Sunah; for
example), in addition there have been significant oil shows from fractured basement
(at Sunah; for example) and the Saar Formation (at Camaal; for example). In my
opinion ongoing exploratory drilling is expected to inhance present discoveries and to
find oil in additional horizons and traps.
Subsidence in the Masila area began with a marine transgression in Upper Jurassic
time over the Pre Cambrian basement peneplain. The Kohlan Formation sands were
deposited as a transgressive lag that passes gradationally upwards into the shallow
marine carbonates of Shuqra Formation. A period of rifting in the late Jurassic led to
restricted conditions and deposition of the Madbi shales, the oil source rocks for the
discoveries. The Madbi shales are overlain by the deep-water limestones of the Naifa
Formation of uppermost Jurassic to lowermost Cretaceous age. Lower Cretaceous
shales and carbonates of the Saar Formation and the clastics and carbonates of the
Qishn Formation, the main subject of this study, were deposited. The Upper
Cretaceous and the Lower Tertiary sediments are predominantly clastic with
interbedded carbonates becoming more carbonate rich into the Tertiary.
The Masila area has undergone several periods of rifting, resulting in a complexly
faulted basement structure. Uppers Jurassic rift basins are bounded by the basement
high blocks over which the Jurassic has been eroded and is either thin or absent.
Subsequent periods of rifting led to reactivation of the basement faults and normal
faulting through the Cretaceous (the Lower Cretaceous age of Qishn Formation) and
the Tertiary section over the basement highs.


2.2 QISHN FORMATION RESERVOIR GEOLOGY
The Qishn reservoir sandstones have both high porosity (18-21%), and high
permeability (<10 Darcies). They are relatively homogenous and continuous in the
lower section and are more heterogeneous in the middle-upper section. The uppermost
marine sandstones are mature and very homogeneous. The major field accumulations
are tilted, normal, fault block structures located over basement paleohighs, and are
dependent upon juxtaposition against overlying Qishn carbonates. The carbonate-
dominated pre-Qishn section, including the source rock, is not present on the paleo-
highs, and is thickest in the basement lows.



                                           3
This Study




Fig. (4) Regional Stratigraphy, showing our study area
                (Beydoun et al., 1998)




                            4
This study




Fig. (5) Regional Frame Work, showing Masila Block Location due to
              Say’un al-Masila Basin (Nexen Inc., Data)




                                5
Fig. (6) Regional Setting, showing Masila Block Location due to
                 Masila High (Nexen Inc., Data)




                               6
Fig. (7) Stratigraphy of Masila, showing Qishn Clastics Member and its
                  related subdivision (Nexen Inc., Data)




                                  7
Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2,
           Camaal-3 and Sunah-3 Wells (Nexen Inc., Data)




                                  8
1. The Upper Qishn Clastics of Cretaceous age are the primary producing reservoirs
in the Masila Block Development area.

2. Cretaceous Qishn Clastics Member, Yemen, was deposited in a rift basin connected
to the Paleo-Indian Ocean - an ideal set-up for tidal amplification and domination.
Recoverable hydrocarbon reserves are 1.1 bbl. Facies associations are consistent with
an estuarine system – sand shoals, tidally influenced point bars, mud flats, etc.
Lower Qishn onlap resulted in deposition of tidal estuarine to bay-facies. A sequence
boundary truncates the Lower Qishn at the base of the S3, a low-accommodation
braidplain deposited close to the shoreline. A flooding surface at the top of the S3
heralds S2 progradational, tide-dominated deltaic deposits. Delta progradation
culminated in clastic dolomitic deposits on the coastal plain. With subsequent
transgression, S1C deposits show rising water table and a nonmarine flooding surface,
overlain by tidal-flat/inlet deposits. Ongoing transgression resulted in wave-
ravinement overlain by shallow shelf clastics and deeper shelf carbonates of the S1B.
The overlying S1A comprises bioturbated, clastic shelf deposits related to a drop in
sea level. Accommodation was relatively high, except for low accommodation
associated with regional sheet sandstone of the S3. Qishn Clastic sediments meet the
criteria of a macrotidal, tide-dominated estuary, yet a more appropriate analog is the
Tigress-Euphrates River and delta flowing into the Arabian Gulf. Is the latter a tidally
influenced delta flowing into a gulf - or a large bayhead delta? Application of existing
terminologies - estuaries, syn-rift clastics, deltaic, strait, Gulf, bay - is confusing to the
practicing explorationist, particularly when attempting to convey a mental image of
the environmental setting of the reservoir.


2.3 UPPER QISHN CLASTICS – STRATIGRAPHY
The Upper Qishn Clastics have been proven productive over the Sunah, Heijah,
Camaal and other productive structures. The interval is defined as the predominantly
sandstone section abruptly overlying the shalier Lower Qishn Clastics and underlying
the sealing Qishn Carbonates. It ranges in thickness from 61 meter in Heijah-1 to 76
m in Sunah-1.

Important Notice: We are highly in need to make a restudy on all Upper Qishn
Clastics samples cored in productive structures. Through standard core analysis and
special core analysis and petrographic analysis, we can give a full more detailed
restudy on the Upper Qishn Clastics reservoir geology and petrophysics.

The Upper Qishn Clastics is subdivided into three lithostratigraphic units, which in
descending order are SI, S2 and S3. Each sequence contains reservoir quality sands
and in my opinion it must be correlated not just in specific structures, but amongst all
above mentioned Upper Qishn Clastics productive structures.




                                              9
CHAPTER 3
         QISHN FORMATION AND ITS SUBDIVISION
                     (IN DETALS)
    3.1: INTRODUCTION
    It is known that Qishn Formation (Lower Cretaceous Age) is synonym to Lower
    Cretaceous part of Little, 1925. It is equivalent to Shuaiba Formation (Present in the
    Kingdom of Saudi Arabia and the United Arab Emirates). In this study I used 93 wells
    penetrated Qishn Formation in different productive and non-productive fields of
    Masila Block, where I concentrated my study on the reservoir rocks of Qishn
    formation. (See, Table (1))


    3.2 QISHN FORMATION IN THE OUTCROP
•     In Mahra Province at Ras Sharwayn near Qishn town as the name implies. Thickness 411
      m, from base upwards mainly limestone and marl.
•     Near Al-Mukalla at Jabal ar Rays. Thickness 32 m, from base upwards mainly sandstone,
      marls and limestone.
•     In Wadi Masila near Qalana (Thickness 628 m, for the first section 338 m and for the
      second section 290 m), from base upwards mainly sandstones, dolomites and lime-
      mustone for the first section mainly marls and marly limestone.
•     In Masila – Thickness 498 m. Mainly limestone, with several sandstone, marl and shale
      zones in the lower part.
•     Jabal Ghuba (near Brum) – Thickness 63 m. mainly of sandstones and gypsiferous marls
      and siltstone and some conglomeratic layers, is capped by the fossiliferous limestone
      carrying orbitolinas.
•     Jabal Billum – the Jurassic Qishn contact is marked by sandy dolomitic limestone.
•     Al-Mintaq – The base is marked by a thick conglomerate or sandstone with some pebbles
      generally locally derived from the under lying Jurassic or basement, this marks the advent
      of the Cretaceous Sea.


    3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS)
     It is known, that Qishn formation in Yemen is subdivided into three members:

    1. Qishn Carbonate Member
    2. Qishn Clastic Member
    3. Sa’af Member

    Due to my study to the above mentioned area I gave more attention to the following
    subdivision of Qishn Formation:

    3.3.1 Qishn Carbonate Member
    3.3.2 Qishn Clastic Member



                                                  10
3.3.1 Qishn Carbonate Member: (See, Table (1), Figs. (9) and (10))

3.3.1.1 Qishn Carbonate Member - ge: (Barremian to Aptian but in the extreme east
may go down to Late Hauterivian and up to ?Early Albian Age)

3.3.1.2 Qishn Carbonate Member - Lithology in General: Principally carbonates as
the name implies but includes subordinate shales and occasional sands and generally
reflect a nertic environment.

3.3.1.3 Qishn Carbonate Member - Lithological Description: In my study area,
Qishn Carbonate Member ’s lithology is mainly of Lime-Mudstone to Lime-
Wackstone with thin streaks of Shale.

Limestone: Mudstone to Wackstone, occasionally Packstone, white to grayish white,
pale yellow brown, cryptocrystalline to occasionally microcrystalline, moderately
hard to hard, chalky, argillaceous grading to marly Limestone, with pyrite crystals.

Shale: Dark bluish grey, olive grey, reddish brown, firm, fissile, calcareous in places,
with abundant pyrite.


              Table (1) Qishn Carbonate of Masila, Block 14 Thicknesses
                           (Done by: Dr. Mohammed Darsi)

               Field                 Qishn Car.   Qishn Car.     Qishn Car.
               Name                  Thickness    Thickness      Thickness
                                      (Max. (ft    (Min. (ft     (Aver. (ft
Sunah                                455 (S-11)   144 (S-8 D2)     367.6
NE Sunah                            424 (NES-1)    418(NES-2)       421
Heijah                              377 (HJ-11)     340 (HJ-6)     356.3
Camaal                               402 (C-14)    128 (C-21)      343.1
North Camaal                         419 (NC-2)    392 (NC-1)      405.5
Hemiar                               422 (HR-1)    407 (HR-2)      413.9
S.Hemiar                           546 (S.HR-1)   117 (S.HR-3)     360.3
W.Hemiar                           415 (W.HR-3)   117(W.HR-1)       308
Tawila                                373 (T-9)     129 (T-11)     285.4
Masila Block (Thickness Max.)      546 (S.HR-1)   418 (NES-2)       421
Masila Block (Thickness Min.)         373 (T-9)   117 (S.HR-3      285.4
                                                   & W.HR-1)
Masila Block (Thickness Ave.)          425.7          243.6        361.1




                                           11
1 .1 0

                                                                                       1 .0 0
  45
                                                                                       0 .9 0

                                                                                       0 .8 0

  40                                                                                   0 .7 0

                                                                                       0 .6 0

                                                                                       0 .5 0
  35                                                                                   0 .4 0

                                                                                       0 .3 0

                                                                                       0 .2 0
  30
                                                                                       0 .1 0

                                                                                       0 .0 0

  25                                                                                   -0 .1 0

          20          30          40          50         60          70
               Fig. (9) Qishn Carbonate Member, Thickness Map
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)




                                        12
1 .1

                                                                                       1 .0

                                                                                       0 .9

                                                                                       0 .8

                                                                                       0 .7

                                                                                       0 .6

                                                                                       0 .5

                                                                                       0 .4

                                                                                       0 .3

                                                                                       0 .2

                                                                                       0 .1

                                                                                       0 .0

                                                                                       -0 .1



      Fig. (10) Qishn Carbonate Member, Three Dimension Model
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)




                                        13
3.3.1.4 Rate of Penetrations for Qishn Carbonate Member:
Average ROP in Limestone 28 Min/M.
Average ROP in Shale 22 Min/M.

3.3.1.5 Gases in Qishn Carbonate Member:
Background gas levels averaged 0.1 units.

3.3.1.6 Drilling Parameters for Qishn Carbonate Member:
WOB 20-25 klbs
RPM 90-100
SPM 540 gpm
SPP 1500 psi

MW 9.4 PPG
FW 42-43


3.3.1.7 Qishn Carbonate Member - Subdivision: In Masila Block, Qishn Carbonate
Member subdivided into the following units:

        3.3.1.7. 1 C1 (See, Table (2))
        3.3.1.7.2 C2 (See, Table (3))
        3.3.1.7.3 RS (Red Shale) (See, Table (4))
        3.3.1.7.4 C3 (See, Table (5))


           Table (2): Qishn Carbonate (C1) of Masila, Block 14 Thicknesses
                           (Done by: Dr. Mohammed Darsi)


               Field                             Qishn Carbonate (C1)
               Name                   C1 Max.            C1 Min.      C1 Ave.
                                   (Thickness (ft (Thickness (ft    (Thickness (ft
Sunah                                133 (S-11)          82 (S-3)        93.7
NE Sunah                            129 (NES-2)       114 (NES-1)       121.5
Heijah                                86 (HJ-2)         62 (HJ-5)        73.7
Camaal                               117 (C-14)         91 (C-19)         88
North Camaal                         105 (NC-2)         98 (NC-1)       101.5
Hemiar                               123 (HR-5)        100 (HR-2)       113.3
S.Hemiar                            118 (S.HR-1)     117 (S.HR-2)        78.3
W.Hemiar                           111 (W.HR-3) 109 (W.HR- 2)            73.3
Tawila                                 94 (T-2)          87 (T-8)        65.9
Masila Block (Thickness Max.)        133 (S-11)     117 (S.HR-2)        121.5
Masila Block (Thickness Min.)         86 (HJ-2)         62 (HJ-5)        65.9
Masila Block (Thickness Ave.)           112.9              95.6          89.9




                                         14
Table (3): Qishn Carbonate (C2) of Masila, Block 14 Thicknesses
                           (Done by: Dr. Mohammed Darsi)

              Field                               Qishn Carbonate (C2)
              Name                  C2 Max.              C2 Min.         C2 Ave.
                                 (Thickness (ft       (Thickness (ft   (Thickness (ft
Sunah                               190 (S-6)            175(S-3)          135.9
NE Sunah                          183 (NES-1)          178 (NES-2)         180.5
Heijah                             168 (HJ-9)           147 (HJ-6)         161.8
Camaal                             191 (C-20)            117 (C-2)         135.8
North Camaal                       172 (NC-2)           163 (NC-1)         167.5
Hemiar                             187 (HR-2)           175 (HR-7)          181
S.Hemiar                           183 (S.HR)           183 (S.HR)          122
W.Hemiar                         177 (W.HR-3)         167 (W.HR-2)         114.7
Tawila                              145 (T-9)       138 (T-1,2,8 & 14)     102.8
Masila Block (Thickness Max.)      191 (C-20)          183 (S.HR)           181
Masila Block (Thickness Min.)       145 (T-9)            117 (C-2)         102.8
Masila Block (Thickness Ave.)         177.3                160.3           144.7




           Table (4) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses
                          (Done by: Dr. Mohammed Darsi)

               Field                           Qishn Carbonate (RS)
               Name                   RS Max.          RS Min.        RS Ava.
                                   (Thickness (ft  (Thickness (ft   (Thickness (ft
Sunah                                  59 (S-7)        49 (S-9)          55.5
NE Sunah                             48 (NES-1)      37 (NES-2)          42.5
Heijah                               53 (HJ-11)       37 (HJ-7)          49.6
Camaal                                83 (C-20)       36 (C-16)          52.6
North Camaal                          60 (NC-2)       54 (NC-1)           57
Hemiar                                54 (HR-6)  51 (HR-3,4,5 & 8)      51.75
S.Hemiar                           183 (S.HR-1)     54 (S.HR-2)          97.7
W.Hemiar                            57 (W.HR-1)     54 (W.HR-3)          55.3
Tawila                                98 (T-11)   49 (T-3,7 & 10)        47.2
Masila Block (Thickness Max.)      183 (S.HR-1)    54 (S.HR-2 &          97.7
                                                      W.HR-3)
Masila Block (Thickness Min.)       48 (NES-1)        36 (C-16)          42.5
Masila Block (Thickness Ave.)           77.2             46.8            56.6




                                         15
Table (5) Qishn Carbonate (C3) of Masila, Block 14 Thicknesses
                          (Done by: Dr. Mohammed Darsi)

               Field                               Qishn Carbonate (C3)
               Name                     C3 Max.           C3 Min.        C3 Ava.
                                     (Thickness (ft    (Thickness (ft  (Thickness (ft
Sunah                                    87 (S-1)          75(S-9)          82.5
NE Sunah                               79 (NES-1)       74 (NES-2)          76.5
Heijah                                 80 (HJ-11)        58 (HJ-12)         71.2
Camaal                                  80 (C-10)         12 (C-20)         66.7
North Camaal                            82 (NC-2)        77 (NC-1)          79.5
Hemiar                                  71 (HR-1)     65 (HR-5 & 6)         67.9
S.Hemiar                              64 (S.HR-2)       61 (S.HR-3)         62.3
W.Hemiar                              73 (W.HR-3)       60 (W.HR-1)         64.7
Tawila                                   90 (T-8)         31 (T-11)         69.5
Masila Block (Thickness Max.)            90 (T-8)        77 (NC-1)          82.5
Masila Block (Thickness Min.)         64 (S.HR-2)         12 (C-20)         62.3
Masila Block (Thickness Ave.)              78.4               57            71.2



3.3.2 Qishn Clastic Member: (See, Figs. (11), (12) and Table (6))

3.3.2.1 Qishn Clastic Member – Age: (Generally Hauterivian – Early Barremian,
especially in the eastern province, to Barremian - Early Aptian in the west (?))

3.3.2.2 Qishn Clastic Member - Lithology in General: Principally clastics as the
name implies, includes coarse clastics in some sections as well as fine sands, silts and
mudstones, shales, as well as marls.

3.3.2.3 Qishn Clastic Member - Lithological Description: In my study area, Qishn
Clastic Member is mainly of Sandstone with Claystone streaks and traces of
Anhydrite. A trace of Coal was logged also.

Sandstone: Quartz, colourless, grayish white, brownish grey, medium grained,
moderately sorted to well sorted in places, subrounded to subangular, poor to
moderate intergranular porosity, with calcareous cement.

Claystone: Light grayish green, reddish brown, soft to firm, blocky, slightly silty,
subfissile in places graded to Shale. Towards the base Claystone was replaced by
Clay, which was highly washable.

Traces Anhydrite: Off white to white, colourless, amorphous, occasionally
crystalline, soft, locally hard, calcareous in places.

Coal: Black, firm to moderately hard, laminated, vitreous luster, earthy and pyretic.


                                           16
2 .0 0

                                                                                       1 .8 0
 45
                                                                                       1 .6 0

                                                                                       1 .4 0
 40                                                                                    1 .2 0

                                                                                       1 .0 0

                                                                                       0 .8 0
 35
                                                                                       0 .6 0

                                                                                       0 .4 0
 30
                                                                                       0 .2 0

                                                                                       0 .0 0

 25                                                                                    -0 .2 0

        35      40      45       50      55      60      65      70      75

             Fig. (11) Qishn Clastics Member, Thickness Map
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)




                                        17
2 .0 0

                                                                                       1 .8 0

                                                                                       1 .6 0

                                                                                       1 .4 0

                                                                                       1 .2 0

                                                                                       1 .0 0

                                                                                       0 .8 0

                                                                                       0 .6 0

                                                                                       0 .4 0

                                                                                       0 .2 0

                                                                                       0 .0 0

                                                                                       -0 .2 0




        Fig. (12) Qishn Clastics Member, Three Dimension Model
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)




                                        18


             Table (6) Qishn Clastics of Masila, Block 14 Thicknesses
(Done by: Dr. Mohammed Darsi)

               Field                   Qishn        Qishn         Qishn
               Name                   Clastics     Clastics      Clastics
                                     (Max. (ft     (Min. (ft    (Aver. (ft
Sunah                                 816 (S-6)  232 (S-8 D2)     713.6
NE Sunah                            741 (NES-1) 719 (NES-2)        730
Heijah                              598 (HJ-11)  396 (HJ-12)      524.8
Camaal                               690 (C-22)    78 (C-14)      593.9
North Camaal                         741 (NC-2)   654 (NC-1)      697.5
Hemiar                               666 (HR-1)    80 (HR-8)      372.3
S.Hemiar                           658 (S.HR-1) 229(S.HR-3)        512
W.Hemiar                           627 (W.HR-1) 608 (W.HR-3)       615
Tawila                                506 (T-5)     0 (T-15)      427.5
Masila Block (Thickness Max.)         816 (S-6)  719 (NES-2)       730
Masila Block (Thickness Min.)         506 (T-5)     0 (T-15)      372.3
Masila Block (Thickness Ave.)           671.4        332.9        576.3



3.3.2.4 Rate of Penetrations for Qishn Clastic Member:
Average ROP in Sandstone 15 Min/M, with maximum of 7 Min/M.
Average ROP in Claystone 20 Min/M.
Average ROP in Anhydrite 25 Min/M.

3.3.2.5 Gases in Qishn Clastic Member:
Background gas levels slightly increased through some sections ranging from 0.5 to
1.0 API units. A gas peak was recorded at some wells with a maximum of 14.1 unit.
The chromatographic analysis of which broke down in some wells as follows:
C1= 0.77U; C2= 0.11U; C3= 0.98U; C4= 0.2 U

3.3.2.6 Oil Shows in Qishn Clastic Member:
A good oil shows was observed through the sandstones of the Qishn Clastics Member
of the Qishn Formation. Light brown oil stain, bluish white and bright fluorescence,
and straw yellow chloroethane cut of dull to bright intensity.

3.3.2.7 Drilling Parameters for Qishn Clastic Member:
WOB 23 klbs; RPM 93; SPM 698 gpm; SPP 2350 psi

MW 9.3-9,4 PPG; FW 43-48

3.3.2.8 Qishn Clastic Member – Subdivision:
The Qishn Clastic Member is subdivided into two sub members:

        3.3.2.8.1 Upper Qishn Clastic Sub Member
        3.3.2.8.2 Lower Qishn Clastic Sub Member

                                          19

3.3.2.8.1 Upper Qishn Clastic Sub Member: (See, Table (7))
Production is mainly from the Lower Cretaceous of the Upper Qishn Clastic Sub
Member, a sandstone-dominated sequence that reflects deposition during an overall
transgression.

           Table (7) Upper Qishn Clastics of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)

                 Field                U. Qishn          U. Qishn     U. Qishn
                 Name                  Clastics         Clastics      Clastics
                                      (Max. (ft         (Min. (ft    (Aver. (ft
Sunah                                   260 (S-6)       221 (S-3)       240
NE Sunah                              327 (NES-2)     321 (NES-1)       324
Heijah                                 216 (HJ-7)      177 (HJ-5)      196.4
Camaal                                 289 (C-15)       78 (C-14)      244.1
North Camaal                           237 (NC-2)      215 (NC-1)       226
Hemiar                              266 (HR-1 & 4)      80 (HR-8)      171.5
S.Hemiar                           235 (S.HR-1 & 2)   229 (S.HR-3)      233
W.Hemiar                             212 (W.HR-3)     208 (W.HR-2)     210.3
Tawila                                  218 (T-6)      169 (T-12)      178.3
Masila Block (Thickness Max.)         327 (NES-2)     321 (NES-1)       324
Masila Block (Thickness Min.)       212 (W.HR-3)        78 (C-14)      171.5
Masila Block (Thickness Ave.)             251.1           188.7        224.8



Upper Qishn Clastic Sub Member subdivided into three units:

                 3.3.2.8.1.1 S1
                 3.3.2.8.1 .2 S2
                 3.3.2.8.1.3 S3


               3.3.2.8.1.1 S1
Important Notice: The base of S1, which it is the top of S2 is marked by the
correlative lowest bed of S1 sequence, a thin basal conglomeratic, muddy, calcareous
sandstones, with abundant shale clasts and shells.


                3.3.2.8.1 .2 S2
Important Notice: The base of S2 is marked by the correlative shales of S2-D, which
directly overly the thick sand S3.


              3.3.2.8.1.3 S3
 Important Notice: S3 abruptly overlies the Lower Qishn Clastics section of shales
and sands.


                                          20

3.3.2.8.1.1 S1
The S1 sequence is composed of upper porous quartzose sand and lower, tight,
muddy, calcareous sand. The upper quartzose sand marks the top of the Upper Qishn
Clastics and its oil-bearing sand, which ranges in pay thickness from 2.8 m in
Camaal-2 to 9.1 m in Sunah-2. The S1 sequence is widespread and thicking of the S1
sand occurs off the crest of the structures. (My pervious studies to Camaal fields
prove this fact)

The S1 sand is a fine to medium grained, moderately to well sorted and poorly
cemented quartzose sand interbedded with thin calcite cemented sands. The
Mineralog shows 10% of clay potassium feldspar. Based on the presence of low angle
planner cross-bedding with rippled tops, shell lags at the base of cross-bedded units
and glauconite company researchers suggest deposition in a shallow marine
environment.

S1 is subdivided into three sub-units:

3.3.2.8.1.1.1 S1A: (See, Table (8))
It is marine sandstone, forms at the top of this regional open marine shale, and is
characterized by an overall coarsening-upward sequence. The top of the S1A is
marked by another thin,regional, open marine shale.


          Table (8) Upper Qishn Clastics (S1A) of Masila Fields Thiknesses
                          (Done by: Dr. Mohammed Darsi)

               Field                               Upper Qishn Clastics
               Name                   S1A Max.          S1A Min.          S1A Ava.
                                    (Thickness (ft   (Thickness (ft     (Thickness (ft
Sunah                                   42 (S-2)         27 (S-3)            33.3
NE Sunah                              41 (NES-1)       39 (NES-2)             40
Heijah                                 30 (HJ-1)    20 (HJ-2 & 11)           23.6
Camaal                                  39 (C-9)        18 (C-10)            31.7
North Camaal                           28 (NC-2)        26 (NC-1)             27
Hemiar                                 12 (HR-5)         7 (HR-8)             9.6
S.Hemiar                             24 (S.HR-2)      19 (S.HR-3)            21.3
W.Hemiar                             29 (W.HR-1)      11 (W.HR-3)            22.3
Tawila                              18 (T-5 & 10)     10 (T-8 & 9)           12.8
Masila Block (Thickness Max.)           42 (S-2)       39 (NES-2)             40
Masila Block (Thickness Min.)         12 (HR-5)         7 (HR-8)              9.6
Masila Block (Thickness Ave.)             29.2              19.7             24.6



3.3.2.8.1.1.2 S1B: (See, Table (9))
It is marine sandstone. The top of the S1B is marked by a regional, open-marine
-shale.


                                           21


        Table (9) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses
(Done by: Dr. Mohammed Darsi)

               Field                                    Upper Qishn Clastics
               Name                       S1B Max.           S1B Min.          S1B Ava.
                                       (Thickness (ft     (Thickness (ft     (Thickness (ft
Sunah                                      38(S-1)            21 (S-7)            27.6
NE Sunah                                 33 (NES-1)         29 (NES-2)             31
Heijah                                    30 (HJ-5)          23 (HJ-6)            25.6
Camaal                                     39 (C-8)           20 (C-4)            28.3
North Camaal                               28 (NC)            28 (NC)              28
Hemiar                                 35 (HR-3 & 5)         29 (HR-6)            32.6
S.Hemiar                                 31 (S.HR-1)        23 (S.HR-2)           27.3
W.Hemiar                                22 (W.HR-3)        18 (W.HR-2)            20.3
Tawila                                    44 (T-14)           27 (T-8)            31.5
Masila Block (Thickness Max.)             44 (T-14)         29 (NES-2)            32.6
Masila Block (Thickness Min.)           22 (W.HR-3)        18 (W.HR-2)            20.3
Masila Block (Thickness Ave.)                33.3               24.2               28



Important Notice: The proximal clastic-dominated followed by carbonate-dominated
(coquinas) shelf deposits of the S1B and finally subtidal sandstone bars of the S1A are
produced as a result of continued transgression.


3.3.2.8.1.1.3 S1C: (See, Table (10))
It is deposit of tidal flats; tidal channels and fine-grained bay fill deposits.


       Table (10) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)

               Field                                  Upper Qishn Clastics
               Name                       S1C Max.        S1C Min.         S1C Ava.
                                       (Thickness (ft (Thickness (ft     (Thickness (ft
Sunah                                      40 (S-5)        17 (S-6)           29.3
NE Sunah                                 29 (NES-2)      27 (NES-1)            28
Heijah                                    27 (HJ-2)       12 (HJ-1)           17.9
Camaal                                    34 (C-19)        15 (C-4)           23.9
North Camaal                              44 (NC-2)       36 (NC-1)            40
Hemiar                                    13 (HR-2)    10 (HR-3,4 & 7)        11.3
S.Hemiar                               8 (S.HR-1 & 3)    7 (S.HR-2)            7.6
W.Hemiar                                16 (W.HR-3)     12 (W.HR-2)            14
Tawila
Masila Block (Thickness Max.)            44 (NC-2)         36 (NC-1)              40
Masila Block (Thickness Min.)         8 (S.HR-1 & 3)       7 (S.HR-2)             7.6
Masila Block (Thickness Ave.)               26.4                17               21.5
                                             22

Important Notice: The two sub-units, the tidal S1C and the marine S1B, overlie the S2
sub-unit.
3.3.2.8.1.2 S2:
S2 is a thick muddy paleosols unit that can form a vertical flow barrier, which is
interpreted to be a non-marine expression of a relative rise of sea level. It is a fluvial
to marginal marine, characterized by tidally influenced channels and tidal deposits.
The S2 is normally about 25 m thick, and arranged in an overall fining upward
sequence.

The S2 sequence of interbedded sands and shales is further subdivided into for
sequences, which in descending order are S2A, S2B, S2C and S2D. Each sub-
sequence contains reservoir quality sands over different parts of the study area. In
contrast to S1, the S2 reservoir sands show less continuity, and S2A and S2B show
the lowest continuity.

Lithofacies in S2 include tidal channel reservoir sandstones, crevasse splay reservoir
sandstones and tidal flat non-reservoirs of interbedded silty mudstones and muddy
sandstones.


S2 is subdivided into four sub units:

3.3.2.8.1.2.1 S2A: (See, Table (11))



       Table (11) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)


               Field                                    Upper Qishn Clastics
               Name                       S2A Max.          S2A Min.           S2A Ava.
                                       (Thickness (ft    (Thickness (ft      (Thickness (ft
Sunah                                      89 (S-6)          60 (S-8)             71.5
NE Sunah                                 84 (NES-2)        74 (NES-1)              79
Heijah                                    92 (HJ-7)        68 (HJ-12)             80.5
Camaal                                    43 (C-21)         15 (C-17)             23.7
North Camaal                               24 (NC)           24 (NC)               24
Hemiar                                   161 (HR-4)         27(HR-8)              93.9
S.Hemiar                                83 (S.HR-2)       80 (S.HR-3)             81.3
W.Hemiar                                84 (W.HR-3)       72 (W.HR-2)             76.7
Tawila                                     98 (T-5)         64 (T-13)             74.7
Masila Block (Thickness Max.)            161 (HR-4)       80 (S.HR-3)             93.9
Masila Block (Thickness Min.)              24 (NC)          15 (C-17)             23.7
Masila Block (Thickness Ave.)                84.2              53.8               67.3

                                             23

3.3.2.8.1.2.2 S2B: (See, Table (12))



       Table (12) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses
(Done by: Dr. Mohammed Darsi)

               Field                                    Upper Qishn Clastics
               Name                   S2B Max.             S2B Min.           S2B Ava.
                                    (Thickness (ft       (Thickness (ft     (Thickness (ft
Sunah
NE Sunah
Heijah
Camaal                                  49 (C-19)           20 (C-7)
North Camaal                            26 (NC-2)          22 (NC-1)              24
Hemiar                                                                             0
S.Hemiar                               31 (S.HR-3)        29 (S.HR-1)             30
W.Hemiar                               20 (W.HR-1)        6 (W.HR-3)             14.3
Tawila
Masila Block (Thickness Max.)            49 (C-19)        29 (S.HR-1)             30
Masila Block (Thickness Min.)          20 (W.HR-1)        6 (W.HR-3)               0
Masila Block (Thickness Ave.)              31.5               19.3               17.1



3.3.2.8.1.2.3 S2C: (See, Table (13))



       Table (13) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)

               Field                                    Upper Qishn Clastics
               Name                      S2C Max.           S2C Min.           S2C Ava.
                                       (Thickness (ft     (Thickness (ft     (Thickness (ft
Sunah
NE Sunah
Heijah
Camaal                                   58 (C-13)            26 (C-2)              42
North Camaal                             39 (NC-1)           35 (NC-2)              37
Hemiar
S.Hemiar
W.Hemiar
Tawila
Masila Block (Thickness Max.)            58 (C-13)           35 (NC-2)              42
Masila Block (Thickness Min.)            39 (NC-1)            26 (C-2)              37
Masila Block (Thickness Ave.)               48.5                30.5               18.5



                                             24
3.3.2.8.1.2.4 S2D: (See, Table (14))


       Table (14) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)
Field                                 Upper Qishn Clastics
               Name                   S2D Max.          S2D Min.            S2D Ava.
                                    (Thickness (ft    (Thickness (ft      (Thickness (ft
Sunah
NE Sunah
Heijah
Camaal                                10 (C-9)         1 (C-10 & 15)           5.5
North Camaal                          5 (NC-2)            4 (NC-1)             4.5
Hemiar
S.Hemiar
W.Hemiar
Tawila
Masila Block (Thickness Max.)         10 (C-9)            4 (NC-1)             5.5
Masila Block (Thickness Min.)         5 (NC-2)         1 (C-10 & 15)           4.5
Masila Block (Thickness Ave.)            7.5                 2.5               2.3



3.3.2.8.1.3 S3: (See, Table (15))

The S3 sequence is massive sand section about 15 m thick, marking the base of the
Upper Qishn Clastics section. Lithofacies in S3 are the same as S2, except that the
meandering tidal channel facies is dominant. The sand grains are subrounded, weakly
to moderately consolidated with minor calcareous and silica cement. The Mineralog
shows about 10% clay content and less than 5% potassium-feldspare. Clays are
primarily illite/smecitite with lesser kaolinite.

        Table (15) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses
                         (Done by: Dr. Mohammed Darsi)

               Field                               Upper Qishn Clastics
               Name                    S3 Max.            S3 Min.          S3 Ava.
                                    (Thickness (ft    (Thickness (ft    (Thickness (ft
Sunah                                   88 (S-8)          67 (S-3)           78.3
NE Sunah                              146 (NES)         146 (NES)            146
Heijah                                 64 (HJ-2)         34 (HJ-5)           48.8
Camaal                                 89 (C-15)         52 (C-2)            65.8
North Camaal                          47 (NC-2)         36 (NC-1)            41.5
Hemiar                                56 (HR-1)         32 (HR-2)            24.1
S.Hemiar                             68 (S.HR-2)       63 (S.HR-1)           65.3
W.Hemiar                             73 (W.HR-3)       53 (W.HR-1)           62.7
Tawila                                 84 (T-13)         43 (T-12)           59.4
Masila Block (Thickness Max.)         146 (NES)         146 (NES)            146
Masila Block (Thickness Min.)         47 (NC-2)         32 (HR-2)            24.1
Masila Block (Thickness Ave.)             79.4              58.4             65.8
                                           25

3.3.2.8.2 Lower Qishn Clastic Sub Member: (See, Table (16))
The Lower Qishn Clastics are the shales and sands found between the Upper Qishn
Clastics and the Saar Formation. The sands are tidal channel in origin and have
limited areal extent. The sands are fine to medium grained and quartzose.

          Table (16) Lower Qishn Clastics of Masila, Block 14 Thicknesses
(Done by: Dr. Mohammed Darsi)

            Field                 L. Qishn              L. Qishn            L. Qishn
            Name                   Clastics             Clastics             Clastics
                                  (Max. (ft             (Min. (ft           (Aver. (ft
Sunah                              556 (S-6)         0 (S-8 D2)               473.6
NE Sunah                         420 (NES-1)       392 (NES-2)                 406
Heijah                           391 (HJ-11)        206 (HJ-12)               328.4
Camaal                             441 (C-1)      0 (C-14 & 20)               349.8
North Camaal                      504 (NC-2)        439 (NC-1)                471.5
Hemiar                            410 (HR-2)     0 (HR-5,6,7 & 8)             200.8
S.Hemiar                        423 (S.HR-1)        0 (S.HR-3)                 279
W.Hemiar                        416 (W.HR-1)      396 (W.HR-3)                 406
Tawila                            332 (T-12)          0 (T-15)                249.1
Masila Block (Thickness Max.)      556 (S-6)        439 (NC-1)                473.6
Masila Block (Thickness Min.)     332 (T-12) 0 (C-14,20; HR-5,6,7,8;          200.8
                                                 S.HR-3 & T-15)
Masila Block (Thickness Ave.)        432.6              158.8                 351.4

Lower Qishn Clastic Sub Member is subdivided into four units:

        3.3.2.8.2.1 LQ1: (See, Table (17))

        Table (17) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses
                          (Done by: Dr. Mohammed Darsi)

               Field                                                    Lower Qishn Clastics
               Name                    LQ1 Max.              LQ1 Min.          LQ1 Ava.
                                     (Thickness (ft       (Thickness (ft     (Thickness (ft
Sunah                                   350 (S-6)            232 (S-7)           272.3
NE Sunah                              267 (NES-1)          258 (NES-2)           262.5
Heijah                                 238 (HJ-11)          139 (HJ-5)           191.7
Camaal                                 241 (C-10)           175 (C-11)           189.1
North Camaal                           279 (NC-2)           242 (NC-1)           260.5
Hemiar                                 275 (HR-3)           239 (HR-4)           128.5
S.Hemiar                              262 (S.HR-1)         261 (S.HR-2)          174.3
W.Hemiar                             383 (W.HR-1)         219 (W.HR-3)            248
Tawila                                  167 (T-9)            139 (T-2)           136.3
Masila Block (Thickness Max.)        383 (W.HR-1)          261 (S.HR-2)          272.3
Masila Block (Thickness Min.)           167 (T-9)           139 (HJ-5)           128.5
Masila Block (Thickness Ave.)             273.6                211.6              207



                                          26
        3.3.2.8.2.2 LQ2: (See, Table (18))
        Table (18) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses
                          (Done by: Dr. Mohammed Darsi)

               Field                                  Lower Qishn Clastics
               Name                    LQ2 Max.            LQ2 Min.          LQ2 Ava.
                                     (Thickness (ft      (Thickness (ft    (Thickness (ft
Sunah                                  287 (S-7)           197 (S-9)           201.3
NE Sunah                              153 (NES-1)         134 (NES-2)                  143.5
Heijah                                 164 (HJ-1)         136 (HJ-10)                  136.7
Camaal                                  244 (C-1)           130 (C-2)                  160.7
North Camaal                           225 (NC-2)         197 (NC-1)                    211
Hemiar                                 151 (HR-4)          131 (HR-3)                   72.3
S.Hemiar                             161 (S.HR-1)        153 (S.HR-2)                  104.7
W.Hemiar                             177 (W.HR-3)        133 (W.HR-1)                  156.7
Tawila                                 168 (T-12)          117 (T-11)                  112.8
Masila Block (Thickness Max.)           287 (S-7)           197 (S-9)                   211
Masila Block (Thickness Min.)         151 (HR-4)           117 (T-11)                   72.3
Masila Block (Ava. Thickness)             192.2               147.6                    144.4

        3.3.2.8.2.3 LQ3
        3.3.2.8.2.4 LQ4
Important Notice:
It must be known that above mentioned fields majorities occupy separate normal
fault-bounded structures, aligned along a NE-SW oriented structural high trend (called
the Masila High). These faults were formed by late stage reactivation of faults initially
created during Late Jurassic to Early Cretaceous active rifting. On the highs a
relatively thin veneer of Lower Cretaceous sandstones and carbonates rest
unconformably upon granitic or metamorphic basement. In the adjacent paleo-lows, a
significantly thicker stratigraphic section exists in which carbonates predominate.
(See, Table (19), Figs. (13) and (14)) as a conclusions.

                          Table (19) Qishn Formation of Masila, Block 14 Thicknesses
                                                     (Done by: Dr. Mohammed Darsi)

             Field                  Qishn               Qishn             Qishn                1 .8 0
             Name                 Formation           Formation         Formation
                                   (Max. (ft           (Min. (ft        (Aver. (ft             1 .7 0
Sunah
   40                             1227 (S-6)      376 (S-8 D2)           1081.2                1 .6 0
NE Sunah                         1165 (NES-1)    1137(NES-2)              1151
Heijah                            975 (HJ-11)     750 (HJ-12)             881.1
                                                                                               1 .5 0
Camaal                            1071 (C-1)       480 (C-14)              937                 1 .4 0
North Camaal                     1160 (NC-2)      1046 (NC-1)             1103
Hemiar                           1088 (HR- 1)      494 (HR-8)             786.1
                                                                                               1 .3 0
S.Hemiar                        1204 (S.HR-1)    346 (S.HR-3)             872.3                1 .2 0
W.Hemiar                        1023 (W.HR-3)    744 (W.HR-1)              923
   30
Tawila                             871 (T-12)       0 (T-15)              712.9
                                                                                               1 .1 0
Masila Block (Thickness Max.)     1227 (S-6)          1137                1151                 1 .0 0
Masila Block (Thickness Min.)     871 (T-12)        0 (T-15)              712.9
Masila Block (Thickness Ave.)        1087.1            597                938.6
                                                                                               0 .9 0
                                           27                                                  0 .8 0
                                                                                               0 .7 0
   20                                                                                          0 .6 0
                                                                                               0 .5 0
                                                                                               0 .4 0
                                                                                               0 .3 0
                                                                                               0 .2 0
   10                                                                                          0 .1 0
                                                                                               0 .0 0
                                                                                               -0 . 1 0
            20           30         40           50                60             70
Fig. (13) Qishn Formation, Thickness Map
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)


                                                                                       1 .8 0
                                                                                       1 .7 0
                                                                                       1 .6 0
                                                                                       1 .5 0
                                                                                       1 .4 0
                                                                                       1 .3 0
                                                                                       1 .2 0
                                                                                       1 .1 0
                                        28
                                                                                       1 .0 0
                                                                                       0 .9 0
                                                                                       0 .8 0
                                                                                       0 .7 0
                                                                                       0 .6 0
                                                                                       0 .5 0
                                                                                       0 .4 0
                                                                                       0 .3 0
                                                                                       0 .2 0
                                                                                       0 .1 0
                                                                                       0 .0 0
                                                                                       -0 .1 0
Fig. (14) Qishn Formation, Three Dimension Model
(Taking in account the whole eastern part of the Republic of Yemen, the western part
   of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the
       Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi)




                                         29

                                                                 CHAPTER 4
      QISHN FORMATION PETROLEUM SYSTEM
4.1 INTRODUCTION
The petroleum system of the Masila Block (14) is related to an Upper Jurassic source
rock sequence essentially deposited as deep marine deposits in a synrift setting (in
some areas prerift sag). Qishn Clastic Member as a primary reservoir and the main
subject of our study to the reservoir rocks of Qishn Formation, is a postrift reservoir.
In detail, the petroleum system of our studied area is related to the presence of the
following factors:

4.2 SOURCE ROCKS
The Upper Jurassic (Kimmeridgian) source rock of the Madbi Formation is organic-
rich black shales deposited in the deeper portions of rifts in the Late Jurassic. Madbi
Formation is the main potential source rocks for the reservoir rocks of Qishn
Formation.

4.3 MATURATION
Source rocks began generating in the central rift basin in latest Cretaceous to
earliest Paleogene time and the process were largely completed by the end of
Paleogene time. Degree of maturation: (Oil Window) 0.6. Type of kerogen: 1 and 2
type of organic mater types.

4.4 MIGRATION
In the Masila Basin, oil and gas migrated along faults to horst blocks. Numerous horst
uplifts occur; however migration resulted in hydrocarbon accumulations, where sealed
by Early Cretaceous carbonate (Qishn Carbonate Member). Heavy oil is known to
occur marginal to the accumulation sites.

4.5 RESERVOIR ROCKS
In the Masila Basin, the Early Cretaceous estuarine sandstones of the Qishn
Formation (Berremian/Aptian), mainly the Upper and Lower Qishn Clastics Members
are the primary reservoir. Porosity average: 18 % – 21 %. Permeability average: 140 –
2000 mD

4.6 TRAPS AND SEALS
The Qishn Carbonate Member (Aptian) provides the seal for the underlying Qishn
Clastic Member in the Masila Basin.




                                           30
                                                                    CHAPTER 5
DISSCUSION POINTS, RECOMMENDATIONS AND
              CONCLUSIONS
5.1 DISSCUSION POINTS
1.   Masila Block’s Fields are located within the Sirr-Sayun Rift Basin that formed
     during the Upper Jurassic when the Africa-Arabian Plate separated from the India-
     Madagascar Plate. The Sirr-Sayun Basin is a few hundred kilometres wide and
     several hundred kilometres long, and is oriented northwest southeast. The basin is
     bounded on the west by Jahi - Mukalla High, to the south by the South Hadramaut
     Arch, to the east by the Ras Fartak High and partially interrupted to the northwest
     by the Sayun High. The Masila Block is situated on an intragraben terrace, and is
     ideally located to access migrating hydrocarbons from mature deeper buried
     Jurassic Madbi source rocks.

2.   I found that one of the most famous, more complex and interesting topic
     problems, which faces any researcher who would like to make any kind of
     academic works. Such as any kind of geological studies on Masila Block 14
     reservoir rocks of Qishn formation or any other geological research studies on the
     whole area, is that:
                 a. We have a huge material in the Database Center of the Petroleum
                 Exploration and Production Authority (P.E.P.A) and its offices around the
                 country.
                 b. We till now don’t have any full-blooded Geo-Scientific Research
                 Centers and the suitable laboratories, where we can make new restudies on
                 all data and materials located now in our Databases Centers.

     What we can do now? … In my opinion the first step we should take it, as a right
     step in the right direction, is that P.E.P.A. ’s Database Center must be open for all
     Yemeni nationality scientific researchers 24 hour per day. Because this step will
     encourage young Yemeni scientists and researchers to make a lot of studies used the
     above mentioned materials. I am sure, GOD and then History will keep the names of
     those Yemeni peoples, who work as decision-makers and give their time and life for
     their country and its young generation.

     Important Notice:
     I would like to drew the reader of this study attention on the following most important
     mater, that one of the most important problem which make it so difficult to write on
     the Yemeni Geology as a whole or partly is that the whole Yemen was divided to
     blocks. In my opinion dividing Yemen, as a whole to blocks is the real reason, which
     lead to the development of company-centered informal stratigraphic nomenclature
     schemes. Companies’ main principal objective was to facilitate operations within the
     individual company’s concession area rather than facilitating scientific research and
     any ultimate communication in journals. So to solve this question, we must
     scientifically divide just the sedimentary basins in Yemen to blocks in accordance to
     their categorisation. (No, for dividing Yemen as a whole to blocks. I said it in the
     past, say it now and will say it).
                                                 31

     5.2 RECOMMENDATIONS
     1. In the absence of the more detailed and accurate studies on the reservoir rocks of
     Qishn Formation, I suggest the following known steps as an emergency solution to
     our case of study:
a.             Modelling of the Qishn Formation as whole and
                       specially the Qishn Clastic Member and its related
                       subdivision in detail. This must included:
                   •   The gross thickness
                   •   Facies proportions and distribution (vertically and laterally)
                   •   Porosity modelling (vertically and laterally for each facies)
                   •   Permeability (vertically and laterally for each facies).

             b. To model each of above-mentioned parameters, modelling steps must
             included the following:
                    • Declustering the well data
                    • Examine data and clean up if necessary
                    • Identify and mathematically describe trends that exist
                    • Remove trends from the data
                    • Perform variogram analysis and determine variogram model
                    • Simulate the parameter in 3-D space
                    • Re-introduce the trends that were removed earlier

              c. The geostatistical surfaces resieved as results of our pervious steps must be
                compared to maps generated by conventional geologic mapping methods in
                              order to highlight the differences between the two techniques.

     2. We are highly in need to make a restudy on all Upper Qishn Clastics samples cored
     in productive structures. Through standard core analysis and special core analysis and
     petrographic analysis, we can give a full more detailed restudy on the Upper Qishn
     Clastics reservoir geology and petrophysics.

     3. NOW, It is recommended that a very highly qualified team must lead local and
     regional studies on the Yemeni Sedimentary Basin by keeping contacts with all
     International Geoscientific Centers in and out side Yemen.


     Important Notice:
     We in the Republic of Yemen must give a high attention to the Environmental Geo-
     sciences. It is known that the global warming issue poses a number of potential
     challenges and opportunities for the oil industry. Ongoing negotiations are defining
     not only targets for greenhouse gas reduction but also mechanisms to enable countries
     and companies to respond. A broad range of options exists to reduce or sequester
     emissions. So it is recommended to discuss some of the important technical,
     economic, and political questions that surround the ultimate viability of this option.



                                                32

     5.3 CONCLUSIONS
1.   One of the main conclusions of this study is that Qishn Formation as a whole and
     also its subdivision mostly thin to the south and to the east. This important
conclusion, I received it as a result of my geostatistical and mathematical analysis
     study on every Qishn Formation ’s subdivision in detail.

2.   As a result of this study, it is easy now to understand the great importance of
     studying:
                 a.               The Masila Block (14) as a part of Say’un Al-
                                  Masila basin.
                 b.               The pervious and present geological activities of
                                  the whole eastern part of the Republic of
                                  Yemen.
                 c.               The Qishn formation in the outcrop, the
                                  reservoir rocks of Qishn formation in the
                                  subsurface and the upper Qishn stratigraphy.
                 d.               The Qishn formation sequence stratigraphy.
                 e.               The Qishn formation (Masila, Block 14)
                                  petroleum system.

3.   If we really want to be Excellent and long vision decision makers, we must
     identify the best mechanism or trend, that could be used to study the reservoir
     rocks of Qishn Formation and by the way to predict the better-developed methods.

4.   In my opinion, the best mechanism or trend is that we must use the latest multi
     functional geological soft ware application which can gave the more accurate
     scientific solutions to our geological problems saving time and money.

5.   We in the Petroleum Exploration and Production Authority, as a main part of the
     Ministry of Oil and Mineral Resources, must build a strong long vision strategy on
     studying the oil exploration and production future prospect. Because the first
     lesson I learned from this study, is that we must take in account our great Yemeni
     grandchildren interests, by making long-term studies on our sedimentary basins.

6.   I believe in that Yemeni Geology, which took some care in the past and attracts
     many experts in the present time, is not going just to surprise all with its oil and
     gas discoveries, but also with its rich and useful data in the near future.


     Important Notice:
     Here, I would like to inform interested readers of this study, that I planned to continue
     this work by publishing a paper on my mathematical description to the reservoir rocks
     of Qishn Formations and its subdivision, based on its geostatistical data.




                                                 33


                            ACKNOWLEDGEMENTS
In this respect, I would like to extend my thanks to the Petroleum Exploration and
Production Authority – (San’a), for their great trust on asking me to work on this
study, especially Mr. Nabeel Al-Kaosi, Dr. Ahmed Ali Abdellah and Dr. Mohammed
Ahmed Al-Zubairi (P.E.P.A – San’a). Mr. Abdullah Salem Ta’lab and Mr. Nagib
Saeed Tabet (P.E.P.A – ADEN). Mr. Tawfik Ahmed Ismail and Mr. Mohammed
Mahyoub (P.E.P.A ’s Office in CPF – Masila Block 14).

I would like to express my deep gratitude and sincere thanks to Mr. Victor W. Dudus
(The Operation Geologist), Mr. L. A. Len Flexhaug (The Petrophysicist) and Al Jones
(The Construction Superintendent) Canadian Nexen (CPF, Masila Block 14), for their
help and support on fulfilling this study.

I have to thank Miss. Wafa and Miss. Fatimah Salem Khamis, for help and support.

Special thanks go to that kind of people, who work hard and in silence on building a
bright future for our lovely Yemen, from both sides, the Yemeni Ministry of Oil &
Mineral Resources (The Petroleum Exploration and Production Authority) side,
the Nexen Inc. (Canadian Nexen Petroleum Yemen) side.

Someone said that "many people will walk in & out of your life, but only true friends
will leave footprints in your heart." I'm so glad that all above mentioned people lift
theirs in mine. Hope it is the right step in the right direction!




                                          34
                               REFERENCES
1. Beydoun, Z.R., Bamahmoud, M.O., and Nani, A.S.O., 1993. The Qishn Formation,
Yemen: lithofacies and hydrocarbon habitat. Marine and Petroleum Geology, 10 (4):
364-372.

2. Beydoun, Z.R., and others, 1998, International lexicon of stratigraphy, v. III,
Republic of Yemen, (2nd ed.): International Union of Geological Sciences and
Ministry of Oil and Mineral Resources, Republic of Yemen Publication no. 34, 245 p.

3. Bosence, D.W.J., ed., 1997, Special issue on Mesozoic rift basins of Yemen:
Marine and Petroleum Geology, v. 14, no. 6, p. 611-730.

4. Brannin, Joe, and others, 1999, Geological evolution of the central Marib-Shabwa
basin, Yemen: GeoArabia, v. 4, no. 1, p. 9-34.

5. Nedham, M. Darsi, 2000. The Geological Research History Work in the Republic
of Yemen during the period from 1852 until Today (Three papers). Yemen Times
newspaper. Issue 2-January 10th through January 16 2000, Vol. IX, Culture Page,
Issue 10 - March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April
10 through April 16 2000, Vol. X, Culture Page.

6. Productivity Prediction from Well Logs in Variable Grain Size Reservoirs
Cretaceous Qishn Formation, Republic of Yemen, Michael L. Cheng and Marco A.
Leal: Canadian Petroleum Ltd., Calgary, Canada David McNaughton: Mincom Inc.,
Houston, Texas U.S.A.

7. Putnam, P.E., 1997, Upper Qishn (Lower Cretaceous) reservoirs at Masila, Yemen,
CSPG-SEPM Joint Convention Core Conference, J. Wood and B. Martindale
(compilers), p. 429-448.

8. Putnam, P.E., Kendall, G.A., and Winter, D. A. 1997, Estuarine deposits of the
upper Qishn Formation (Lower Cretaceous) in the Masila region of Yemen, American
Association of Petroleum Geologists Bulletin, v.81, p. 1306-1329.

9. The Masila Fields, Republic of Yemen, W.A. King1, B.R. Mills1, Scott Gardiner2,
and A.A. Abdellah3. (1) Nexen Inc. (Formerly Canadian Occidental Petroleum Ltd.),
Calgary, AB T2P 3Z1, Canada, (2) Nexen Inc. (formerly Canadian Occidental
Petroleum Ltd.), 1801 - 635 8th Avenue S.W, Calgary, AB T2P 3Z1, Canada, (3)
Petroleum Exploration and Production Authority (PEPA), Yemen Ministry of Oil and
Mineral Resources (MOMR), Yemen

10. Tide-Dominated Sedimentation in an Arid Rift Basin - Cretaceous Qishn Clastics,
Masila Block, Republic of Yemen, Dale A Leckie and Tom Rumpel. Nexen Inc,
Calgary, AB T2P 3P7, Canada, and phone: 403699-5902, Dale_leckie@nexeninc.com

11. Local, Regional, International and Global ’s World Web Site Internet Resources

                                         35


                        ABOUT THE AUTHOR
* Dr. Eng. Mohammed Darsi Abdulrahman Nedham, born on November 17, 1963,
Crater (Aden). 5 Languages (Arabic, English, Russian, Chinese and German
Languages). Petroleum Engineer, Geologist; Married have 2 sons. Education:
Graduated from the Earth Science College of Jilin University as a Doctor of Science
in Mineralogy, Petrology and Ore Deposit on May 29 2002 and also graduated from
the Russian among People Friendship University in 1991 as a Petroleum Engineer,
Geologist (M.S. degree) on June 29 1991. Appointments: Petroleum Exploration and
Production Board, Aden Branch, Ministry of Oil and Mineral Resources; Petroleum
Engineer; Senior Geologist; Representative; Coordinator. Publications: 10 scientific
papers, 6 published in the Yemen Times Newspaper, 3 in China (2 in World Geology
and 1 in the Journal of Geoscientific Research of Northeast Asia) and the last one in
Russia. Two registered Patents. 18 Certificate from different institutes, centers,
organizations and clubs. Membership: Fellow, Geological Association of Canada,
American Association of Petroleum Engineers and other memberships. Dr. Eng.
Mohammed Darsi Abdulrahman Nedham began his professional career by working as
petroleum engineer, geologist in the Petroleum Exploration and Production Board
(Aden Branch). His scientific interest is concentrated on the Geological Research
History Work, Earth science software application and basin-modeling problems. The
most important thing, Dr. Darsi is ONE of the Who is Who in the 21st Century for
2001 and 2002 (First and Second Publication), choosed by the International
Geographical Centre, Cambridge, England.




                                         36

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A Study On The Reservoir Rocks Of Qishn Formation (Masila Block 14)

  • 1. REPUBLIC OF YEMEN MINISTRY OF OIL AND MINERAL RESOURCES PETROLEUM EXPLORATION AND PRODUCTION AUTHORITY A STUDY ON THE RESERVOIR ROCKS OF QISHN FORMATION (Masila Block 14) By: Dr. Eng. Mohammed Darsi Abdulrahman Nedham Doctor of Science (Geologist), PEPA ’s Office (Aden) Aden (June 2oo3)
  • 2. WHAT MASILA BLOCK AND QISHN FORMATION MEANS FOR CANADIAN NEXEN INC.? First of all, and before I am going to write any word as an introduction to my study on the reservoir rocks of Qishn Formation in Masila Block (14). I would like to draw the attention of all people, who work as decision makers in the Ministry of Oil and Minerals (MOM) and the Petroleum Exploration and Production Authority (PEPA) on the great importance of answering the above-mentioned question. We must know, that Masila Block (See, Fig. (1)) has a great meaning for Nexen Company, because of the following reasons: 1. Approximately 44% of Nexen's overall production comes from the Masila Block (Yemen), which representing just over one third of the company's cash flow. 2. Nexen has a 52% working interest in and operate the Masila Project, which is the largest single source of oil production in Yemen and has grown steadily since discovery in 1990. 3. To date, the 15 fields that comprise the Project have produced over 665 million gross barrels of oil from total gross recoverable reserves of just over one billion barrels. 4. Nexen has the right to produce oil from the Masila fields until 2011 and the right to negotiate a five-year extension. 5. During 2002, $402 million ($209 million net) was invested to drill and equip 74 new development wells and expand existing infrastructure. Gross production was maintained throughout the year at approximately 226,900 barrels per day. 6. The economics of Masila production are attractive. Historic finding and development costs are approximately US $2 per barrel and operating costs have averaged US $1 per barrel, resulting in excellent returns for shareholders! All the above mentioned reasons makes Nexen not just take care of Masila Block and Qishn Formation, (I mean the Qishn clastic member, which is the main producing reservoir in this area and the main subject of this study), but also to work actively on exploring outside the Masila Block. In my opinion, the strategic point of view and the excellent steps taken by the heads of Nexen Inc. led to the following main result and present fact: (Nexen, NOW, hold interests in seven exploration licenses (Block 50 Block 51 Northern Blocks 11, 12, 36, 54 and 59) comprising over 20 million acres of undeveloped land, the majority of which are located in northeastern Yemen close to the Saudi Arabian border. (See Fig. (2)) Due to what mentioned above I am sure that we in Yemen are highly in need for building not just the high qualified Yemeni oil team but also for building the first National Oil Exploration Company. Am I right? Now, it is the suitable time for Yemeni specialists, who found a great chance to work with those kind of high- qualified and experienced foreign specialists, to learn from the newest in their field of specialization. Our scientific cooperation and friendship must continue with all and forever. If we really want to see the whole plains clearly, we must climb the highest mountain. i
  • 3. Fig. (1) Masila Location (Nexen Inc., Data) < Fig. (2) Nexen Blocks in Yemen (Nexen Inc., Data) ii
  • 4. INTRODUCTION Masila Block 14 is operated by Canadian Occidental Petroleum Yemen on behalf of its partners Occidental Peninsula, Inc. and Consolidated Contractors International, Ltd., (CANADIAN NEXEN PETROLEUM YEMEN as known now), and is located in the Hadhramaut region, in east-central Republic of Yemen. Oil was first discovered on the Block in late 1990 with Commerciality declared in late 1991. Oil production at Masila began in July 1993. There are now 15 oil fields known in Masila, Block 14: (See, Fig. (3)) 1. Camaal (C), 2. North Camaal (NC), 3. Sunah (S), 4. Northeast Sunah (NES), 5. Heijah (HJ), 6. Hemiar (HR), 7. South Hemiar (S.HR), 8. West Hemiar (W.HR), 9. Tawila (T), 10. Haru (HU), 11. Nazeia (NZ), 12. Dahban (D), 13. Bainoon (ND), 14. Qataban (QAT), and 15. Gabal-Isbeel, containing 56 pools within the Masila Block. Total proven ultimate recoverable oil reserves are approaching 900 million STB. Proven, probable and possible reserve estimates are in excess of one billion barrels of recoverable oil. The Masila fields are in the Jurassic- to Lower Cretaceous-aged, Saar Graben. Almost 90% of the Masila reserves are reservoired in the Qishn Formation of the Lower Cretaceous Upper Qishn Clastics Member. Oil is also found in at least seven other reservoirs consisting of Lower Cretaceous and Middle to Upper Jurassic age clastics and carbonates as well as fractured granitic basement. In this study I used real subsurface data related to 93 wells, penetrated the productive and non-productive fields of the studied area. All above-mentioned wells penetrated Qishn formation the main subject of this study, where I made geostatistical calculations and analysis, to explain the process of sedimentation mathematically for Qishn formation generally and its subdivision in detail. Showing the maximum, minimum and the average of Qishn formation thickness, its members, sub members, units and sub units in detail for every well, for every productive field and for Masila Block as a whole. The most important thing I have done during my study to the pervious and the present data, informations and published materials on the reservoir rocks of Qishn Formation is that I focused on the main producing horizon (the Upper Qishn Clastics Member). The Upper Qishn represents an upward transgressive sequence from braided river deposits into tidally influenced shorelines, overlain by subtidal and shelf deposits. Important Notices: 1. Yemeni reserves of raw oil were estimated to be about 4 billion barrels, of which 1380 million barrels are found in Marib, 1580 billion barrels in Masila, 250 million barrels in Shabwah, and 750 million barrels in Gannah. 2. Arab investment in Yemen heading toward $1 billion Yemen, Economics, 9/23/1997 iii
  • 5. Fig. (3) Masila Block Oil Fields (Nexen Inc., Data) iv
  • 6. MAIN TOPICS OF THIS STUDY The main topics of this study on the reservoir rocks of Qishn Formation (Masila Block 14) are the following: 1. To show the great importance of Masila (Block 14) and the reservoir rocks of Qishn Formation for Nexen Inc. 2. To give a brief on the whole pervious activities done on studying the Geological Research History Work of the eastern part of the Republic of Yemen (the study area and the adjacent areas). 3. To follow Qishn formation location on the whole surface, to study it in the sub surface of the studied area and to highlight the upper Qishn clastics rocks stratigraphy. 4. To study the Qishn Formation in Masila Block 14 as whole and in detail, its subdivision, ages, sequence stratigraphy, general lithology, lithology, its drilling parameters averages, mud parameters, its Paleogeography, and its sedimentation thicknesses in the study area by making 20 tables on Qishn formations and it sub sequences. 5. To explain the petroleum system of Qishn Formation, its source rocks, maturation, migration, reservoir rocks, traps and seals. v
  • 7. NATURE OF THIS STUDY Prompted largely by this interest, my research study plan on studying the reservoir rock of Qishn Formation was concentrated on its achievement on the following important point: 1. Study and examination of all primary information connected with the subject from various sources. 2. Sorting of this information in accordance with its importance. 1. Making number of tables and maps. 2. Checking of all data and making necessary tests on them. 3. Follow-up of the historical development of the reservoir rocks of Qishn Formation through the making of varying geostatistical and mathematical calculation for the interested section of Qishn formation and its subdivision from its bottom till the surface. AIM OF THIS STUDY The study was aimed at the problems outlined in the previous two sections. This study is the first investigation work-study, done by me on the reservoir rocks of Qishn formation of Masila Block 14, which aims to: 1. Help understanding of the great importance of the studied area. 2. Help understanding of the pervious and present geological activities in the area. 3. Help understanding of the reservoir rocks of Qishn formation, surface, sub surface geology and the upper Qishn stratigraphy. 4. Help understanding of Qishn formation sequence stratigraphy. 5. Help understanding of Qishn formation (Masila, Block 14) petroleum system. 6. Give new discussions points, recommendations and conclusions. vi
  • 8. CONTENTS WHAT MASILA BLOCK AND QISHN FORMATION MEANS FOR CANADIAN NEXEN INC.? --------------------------------------------------------------i INTRODUCTION --------------------------------------------------------------------------iii MAIN TOPICS OF THIS STUDY ------------------------------------------------------v NATURE OF THE PROBLEM ---------------------------------------------------------vi AIM OF THIS STUDY --------------------------------------------------------------------vi CONTENTS ---------------------------------------------------------------------------------vii LIST OF FIGURES ------------------------------------------------------------------------ix LIST OF TABLES --------------------------------------------------------------------------x CHAPTER 1: THE EASTERN PART OF THE REPUBLIC OF YEMEN GEOLOGICAL RESEARCH HISTORY WORK 1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT AREAS -------------------------------------------------------------------------------1 1.1.1 INRODUCTION 1.1.2 PERVIOUS WORKS BASED ON MY CLASIFICATION AND DIVISION CHAPTER 2: THE RESERVOIR ROCKS OF QISHN FORMATION (MASILA, BLOCK 14) – GEOLOGY 2.1 INTRODUCTION --------------------------------------------------------------3 2.2 QISHN FORMATION RESERVOIR GEOLOGY 2.3 UPPER QISHN CLASTICS – STRATIGRAPHY -------------------------9 CHAPTER 3: QISHN FORMATION AND ITS SUBDIVISION (IN DETALS) 3.1 INTRODUCTION -------------------------------------------------------------10 3.2 QISHN FORMATION IN THE OUTCROP 3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS) 3.3.1 Qishn Carbonate Member ------------------------------------------21 3.3.1.1 Qishn Carbonate Member - Age 3.3.1.2 Qishn Carbonate Member - Lithology in General 3.3.1.3 Qishn Carbonate Member - Lithological Description 3.3.1.4 Rate of Penetrations for Qishn Carbonate Member 3.3.1.5 Gases in Qishn Carbonate Member 3.3.1.6 Drilling Parameters for Qishn Carbonate Member 3.3.1.7 Qishn Carbonate Member – Subdivision ------------24 3.3.1.7. 1 C1 3.3.1.7.2 C2 3.3.1.7.3 RS (Red Shale) 3.3.1.7.4 C3 3.3.2 Qishn Clastic Member ----------------------------------------------26 3.3.2.1 Qishn Clastic Member - Age 3.3.2.2 Qishn Clastic Member - Lithology in General 3.3.2.3 Qishn Clastic Member - Lithological Description vii
  • 9. 3.3.2.4 Rate of Penetrations for Qishn Clastic Member 3.3.2.5 Gases in Qishn Clastic Member 3.3.2.6 Oil Shows in Qishn Clastic Member 3.3.2.7 Drilling Parameters for Qishn Clastic Member 3.3.2.8 Qishn Clastic Member – Subdivision ----------------29 3.3.2.8.1 Upper Qishn Clastic Sub Member ----------30 3.3.2.8.1.1 S1 ------------------------------------31 3.3.2.8.1.1.1 S1A 3.3.2.8.1.1.2 S1B 3.3.2.8.1.1.3 S1C 3.3.2.8.1.2 S2 ------------------------------------33 3.3.2.8.1.2.1 S2A 3.3.2.8.1.2.2 S2B 3.3.2.8.1.2.3 S2C 3.3.2.8.1.2.4 S2D 3.3.2.8.1.3 S3 ------------------------------------35 3.3.2.8.2 Lower Qishn Clastic Sub Member -------- -36 3.3.2.8.2.1 LQ1 3.3.2.8.2.2 LQ2 3.3.2.8.2.3 LQ3 3.3.2.8.2.4 LQ4 CHAPTER 4: QISHN FORMATION PETROLEUM SYSTEM -----------------40 4.1 INTRODUCTION 4.2 SOURCE ROCKS 4.3 MATURATION 4.4 MIGRATION 4.5 RESERVOIR ROCKS 4.6 TRAPS AND SEALS CHAPTER 5: DISSCUSION POINTS, RECOMMENDATIONS AND CONCLUSION 5.1 DISSCUSION POINTS --------------------------------------------------------41 5.2 RECOMMENDATIONS ------------------------------------------------------42 5.3 CONCLUSIONS ----------------------------------------------------------------43 ACKNOWLEDGEMENTS -----------------------------------------------------------------44 REFERENCES -------------------------------------------------------------------------------45 ABOUT THE AUTHOR --------------------------------------------------------------------46 viii
  • 10. LIST OF FIGURES Fig. (1) Masila Location ---------------------------------------------------------------------ii Fig. (2) Nexen Blocks in Yemen -----------------------------------------------------------ii Fig. (3) Masila Block Oil Fields ------------------------------------------------------------iv Fig. (4) Regional Stratigraphy (showing our study area) --------------------------------4 Fig. (5) Regional Frame Work (showing Masila Block Location due to Say’un al- Masila Basin -----------------------------------------------------------------------------------5 Fig. (6) Regional Setting (showing Masila Block Location, due to Masila High) ---6 Fig. (7) Stratigraphy of Masila (showing Qishn Clastics Member and its related subdivision) -----------------------------------------------------------------------------------7 Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2, Camaal-3 and Sunah-3 wells -----------------------------------------------------------------------------8 Fig. (9) Qishn Carbonate Member, Thickness Map -------------------------------------22 Fig. (10) Qishn Carbonate Member, Three Dimension Model -------------------------23 Fig. (11) Qishn Clastics Member, Thickness Map ---------------------------------------27 Fig. (12) Qishn Clastics Member, Three Dimension Model ----------------------------28 Fig. (13) Qishn Formation, Thickness Map -----------------------------------------------38 Fig. (14) Qishn Formation, Three Dimension Model -----------------------------------39 ix
  • 11. LIST OF TABLES Qishn Formation of Masila Block, its Subdivision Tops and Thicknesses Table (1) Qishn Carbonate of Masila, Block 14 Thicknesses ----------------------11 Table (2) Qishn Carbonate (C1) of Masila, Block 14 Thicknesses --------------------14 Table (3) Qishn Carbonate (C2) of Masila, Block 14 Thicknesses --------------------15 Table (4) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses --------------------15 Table (5) Qishn Carbonate (C3) of Masila Block 14, Thiknesses ---------------------16 Table (6) Qishn Clastics of Masila, Block 14 Thicknesses --------------------------19 Table (7) Upper Qishn Clastics of Masila, Block 14 Thicknesses -----------------20 Table (8) Upper Qishn Clastics (S1A) of Masila, Block 14 Thicknesses -------------21 Table (9) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses -----------22 Table (10) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses -----------22 Table (11) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses -----------23 Table (12) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses -----------24 Table (13) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses -----------24 Table (14) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses -----------25 Table (15) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses -------------25 Table (16) Lower Qishn Clastics of Masila, Block 14 Thicknesses ---------------26 Table (17) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses ----------26 Table (18) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses ----------27 Table (19) Qishn Formation of Masila, Block 14 Thicknesses ---------------------27 Important Notice: All above-mentioned tables done by me based on my study to: 1. The Masila Block Field Development Location Map in General. 2. Sunah, Heijah, Camaal, Hemiar, … ,Haru and Naziah Fields 3. The Geological Summary of the Masila Block 4. The Masila Block Stratigraphic Column 5. The Geological Sections done by me for Sunah-1, Naar-1, Maljan-1, Ressib-1, Deelun-1 Wells. 6. Masila Block Formation Tops and Thicknesses (The table done in 1993, 1997 and updated in 2002, by Nexen Inc.) 7. An old table done by me as a part of my study to Masila Block in the past. The main aim of the above mentioned table is to give interested persons in Masila Block general informations (such as: Block Area, Productive and non-productive fields, No. of wells in every Productive and non-productive fields and the Sedimentary Cover) and also geological informations (such as: the stratigraphical sections, thicknesses, lithology, source rocks characteristics and reservoir rocks characteristics) x
  • 12. CHAPTER 1 THE EASTERN PART OF THE REPUBLIC OF YEMEN GEOLOGICAL RESEARCH HISTORY WORK 1.1 PERVIOUS ACTIVITIES IN MASILA BLOCK AND ITS ADJACENT AREAS 1.1.1 INRODUCTION The Republic of Yemen is beside the richest hydrocarbon province in the world. Oil only discovered in the early 1980’s in the offshore (Sharmah Well). It is known, that Nexen Inc. (formerly known as Can Oxy Company) discovered oil in Masila Block in 1990 in the Qishn Clastics Member of Qishn Formation. The Masila Block has 1250 km2 in size. The Estimated Reserves is 1.1 billion barrels recoverable and the Cumulative Production is 600,000,000 barrels (Due to March 2002 wells production reports), where the daily production was 230,000 b/d. 1.2 PERVIOUS WORKS BASED ON MY CLASIFICATION AND DIVISION According to my new classification and first division to the whole geological research history work in the Republic of Yemen to four stages (See Yemen Times Newspaper. Issue 2-January 10th through January 16 2000, Vol. IX Culture Page, Issue 10 - March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April 10 through April 16 2000, Vol. X, Culture Page). It is so clear now, that: 1. On the First Stage (The First Systematic Geological Observation Stage or Carter’s Stage), 1852-1901: No kind of geological studies had been detected in the Masila area. 2. On the Second Stage or the Hinterland Studies Stage, (1902-1946) and the Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage, (1947-1967): The Petroleum Concessions Ltd, one of the Iraq Petroleum Company and associated companies (IPC and Associated companies) had carried out little exploration work in the area between 1937 and 1960. During that time they made geological field mapping, investigation, supplemented by aerophoto studies, photogeologic and mapping covering the entire territory were carried out. 1
  • 13. 3. On The Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage), 1947-1967: During this stage the adjacent areas started to be studied by scientist and oil companies. Bunker, D.G. wrote about the southwest Borderlands of Rub al Khali, in 1953. From 1961 to early 1967, Pan American International Oil Company through a subsidiary, Pan American Hadhramawt Oil Company (PAHOC) drilled four wells (Hoowarin, Tarfayt and Core Hole 88 reached Precambrian basement and the forth was abandoned in the Cretaceous sediments). 4. The Forth Stage or The Yemeni Geologists Stage (1968 – until Today): During this stage many important scientific works happened in Yemen, which at the end led to the creation of the concision map of Yemen, the birth of Masila Block and its oil discoveries. It is known that, the Petroleum and Minerals Board (the PMB) was established, in 1970 in former South Yemen. During the period from 1970 to 1973, the joint of former South Yemen-Algerian Petroleum Company (SYAPCO) drilled Taur-1 in 1974 and Taur-2 was commenced. In 1974, a group of experts from Cuba assumed the drilling operation from SYAPCO and with former PMB completed Taur-2, Taur-3 and drilled Thamud-1 and Hathout-1. In September 1976, the functions of the PMB were broadened and the Petroleum Exploration Board (the PED) was created (The Petroleum Exploration and Production Board, Aden Branch – As known now), was led different activities on studding the geology of this area. As a result of their work on the Yemeni sector of Rub al Khali basin, wells as Taur-2, Taur-3 and Hathout-1 was drilled. A group of the P.E.D.’s Engineers, Technician and workers, work hard on this area, their work is highly appreciated. Between 1975 and 1979, as a part of its assistance program, TechnoExport, the former Soviet Technical Assistance Organization, had recorded aeromagnetic surveys covering most of former South Yemen and also a gravity survey had been conducted over specific areas of interest. On Mar. 27 1979, B. Kuzin and Mohammed Ba’abad made a Stratigraphic Correlation, for wells drilled in that area correlative with wells located in the adjacent area at that's time. The field investigation had been augmented from time to time by Czechoslovakian and German technical personnel. Agip SpA (from 1978 to 1980): conducted landsite airphoto interpretation and a field mapping project along the coastal outcrop belt as part of its offshore exploration effort in the Sayhut Block. On 1981 Agip recorded 110 km of seismic on the coastal plain east of Mukalla. Petroleo Brasileiro SA (Petrobras): shot a regional seismic program and drilled three unsuccessful test wells in the area to the north of the Masila Block in Jeza syncline and relinquished the area in 1987. 2
  • 14. CHAPTER 2 THE RESERVOIR ROCKS OF QISHN FORMATION (MASILA, BLOCK 14) – GEOLOGY 2.1 ITRODUCTION It is known, that oil trapped in sands of the Qishn Formation, the main subject of this study, in the following structures: Camaal, North, Sunah, North East Sunah, Heijah, Hemiar, South Hemiar, West Hemiar, Tawila, Haru, Nazeia, Dahban, North Dahban, Qataban, and Gabal-Isbeel. Note 3: Oil has also been discovered in the Kohlan Formation (at Sunah; for example), in addition there have been significant oil shows from fractured basement (at Sunah; for example) and the Saar Formation (at Camaal; for example). In my opinion ongoing exploratory drilling is expected to inhance present discoveries and to find oil in additional horizons and traps. Subsidence in the Masila area began with a marine transgression in Upper Jurassic time over the Pre Cambrian basement peneplain. The Kohlan Formation sands were deposited as a transgressive lag that passes gradationally upwards into the shallow marine carbonates of Shuqra Formation. A period of rifting in the late Jurassic led to restricted conditions and deposition of the Madbi shales, the oil source rocks for the discoveries. The Madbi shales are overlain by the deep-water limestones of the Naifa Formation of uppermost Jurassic to lowermost Cretaceous age. Lower Cretaceous shales and carbonates of the Saar Formation and the clastics and carbonates of the Qishn Formation, the main subject of this study, were deposited. The Upper Cretaceous and the Lower Tertiary sediments are predominantly clastic with interbedded carbonates becoming more carbonate rich into the Tertiary. The Masila area has undergone several periods of rifting, resulting in a complexly faulted basement structure. Uppers Jurassic rift basins are bounded by the basement high blocks over which the Jurassic has been eroded and is either thin or absent. Subsequent periods of rifting led to reactivation of the basement faults and normal faulting through the Cretaceous (the Lower Cretaceous age of Qishn Formation) and the Tertiary section over the basement highs. 2.2 QISHN FORMATION RESERVOIR GEOLOGY The Qishn reservoir sandstones have both high porosity (18-21%), and high permeability (<10 Darcies). They are relatively homogenous and continuous in the lower section and are more heterogeneous in the middle-upper section. The uppermost marine sandstones are mature and very homogeneous. The major field accumulations are tilted, normal, fault block structures located over basement paleohighs, and are dependent upon juxtaposition against overlying Qishn carbonates. The carbonate- dominated pre-Qishn section, including the source rock, is not present on the paleo- highs, and is thickest in the basement lows. 3
  • 15. This Study Fig. (4) Regional Stratigraphy, showing our study area (Beydoun et al., 1998) 4
  • 16. This study Fig. (5) Regional Frame Work, showing Masila Block Location due to Say’un al-Masila Basin (Nexen Inc., Data) 5
  • 17. Fig. (6) Regional Setting, showing Masila Block Location due to Masila High (Nexen Inc., Data) 6
  • 18. Fig. (7) Stratigraphy of Masila, showing Qishn Clastics Member and its related subdivision (Nexen Inc., Data) 7
  • 19. Fig. (8) Regional cross section between Tawila-1, Tawila-17, Heijah-2, Camaal-3 and Sunah-3 Wells (Nexen Inc., Data) 8
  • 20. 1. The Upper Qishn Clastics of Cretaceous age are the primary producing reservoirs in the Masila Block Development area. 2. Cretaceous Qishn Clastics Member, Yemen, was deposited in a rift basin connected to the Paleo-Indian Ocean - an ideal set-up for tidal amplification and domination. Recoverable hydrocarbon reserves are 1.1 bbl. Facies associations are consistent with an estuarine system – sand shoals, tidally influenced point bars, mud flats, etc. Lower Qishn onlap resulted in deposition of tidal estuarine to bay-facies. A sequence boundary truncates the Lower Qishn at the base of the S3, a low-accommodation braidplain deposited close to the shoreline. A flooding surface at the top of the S3 heralds S2 progradational, tide-dominated deltaic deposits. Delta progradation culminated in clastic dolomitic deposits on the coastal plain. With subsequent transgression, S1C deposits show rising water table and a nonmarine flooding surface, overlain by tidal-flat/inlet deposits. Ongoing transgression resulted in wave- ravinement overlain by shallow shelf clastics and deeper shelf carbonates of the S1B. The overlying S1A comprises bioturbated, clastic shelf deposits related to a drop in sea level. Accommodation was relatively high, except for low accommodation associated with regional sheet sandstone of the S3. Qishn Clastic sediments meet the criteria of a macrotidal, tide-dominated estuary, yet a more appropriate analog is the Tigress-Euphrates River and delta flowing into the Arabian Gulf. Is the latter a tidally influenced delta flowing into a gulf - or a large bayhead delta? Application of existing terminologies - estuaries, syn-rift clastics, deltaic, strait, Gulf, bay - is confusing to the practicing explorationist, particularly when attempting to convey a mental image of the environmental setting of the reservoir. 2.3 UPPER QISHN CLASTICS – STRATIGRAPHY The Upper Qishn Clastics have been proven productive over the Sunah, Heijah, Camaal and other productive structures. The interval is defined as the predominantly sandstone section abruptly overlying the shalier Lower Qishn Clastics and underlying the sealing Qishn Carbonates. It ranges in thickness from 61 meter in Heijah-1 to 76 m in Sunah-1. Important Notice: We are highly in need to make a restudy on all Upper Qishn Clastics samples cored in productive structures. Through standard core analysis and special core analysis and petrographic analysis, we can give a full more detailed restudy on the Upper Qishn Clastics reservoir geology and petrophysics. The Upper Qishn Clastics is subdivided into three lithostratigraphic units, which in descending order are SI, S2 and S3. Each sequence contains reservoir quality sands and in my opinion it must be correlated not just in specific structures, but amongst all above mentioned Upper Qishn Clastics productive structures. 9
  • 21. CHAPTER 3 QISHN FORMATION AND ITS SUBDIVISION (IN DETALS) 3.1: INTRODUCTION It is known that Qishn Formation (Lower Cretaceous Age) is synonym to Lower Cretaceous part of Little, 1925. It is equivalent to Shuaiba Formation (Present in the Kingdom of Saudi Arabia and the United Arab Emirates). In this study I used 93 wells penetrated Qishn Formation in different productive and non-productive fields of Masila Block, where I concentrated my study on the reservoir rocks of Qishn formation. (See, Table (1)) 3.2 QISHN FORMATION IN THE OUTCROP • In Mahra Province at Ras Sharwayn near Qishn town as the name implies. Thickness 411 m, from base upwards mainly limestone and marl. • Near Al-Mukalla at Jabal ar Rays. Thickness 32 m, from base upwards mainly sandstone, marls and limestone. • In Wadi Masila near Qalana (Thickness 628 m, for the first section 338 m and for the second section 290 m), from base upwards mainly sandstones, dolomites and lime- mustone for the first section mainly marls and marly limestone. • In Masila – Thickness 498 m. Mainly limestone, with several sandstone, marl and shale zones in the lower part. • Jabal Ghuba (near Brum) – Thickness 63 m. mainly of sandstones and gypsiferous marls and siltstone and some conglomeratic layers, is capped by the fossiliferous limestone carrying orbitolinas. • Jabal Billum – the Jurassic Qishn contact is marked by sandy dolomitic limestone. • Al-Mintaq – The base is marked by a thick conglomerate or sandstone with some pebbles generally locally derived from the under lying Jurassic or basement, this marks the advent of the Cretaceous Sea. 3.3 QISHN FORMATION IN THE SUBSURFACE (IN DETAILS) It is known, that Qishn formation in Yemen is subdivided into three members: 1. Qishn Carbonate Member 2. Qishn Clastic Member 3. Sa’af Member Due to my study to the above mentioned area I gave more attention to the following subdivision of Qishn Formation: 3.3.1 Qishn Carbonate Member 3.3.2 Qishn Clastic Member 10
  • 22. 3.3.1 Qishn Carbonate Member: (See, Table (1), Figs. (9) and (10)) 3.3.1.1 Qishn Carbonate Member - ge: (Barremian to Aptian but in the extreme east may go down to Late Hauterivian and up to ?Early Albian Age) 3.3.1.2 Qishn Carbonate Member - Lithology in General: Principally carbonates as the name implies but includes subordinate shales and occasional sands and generally reflect a nertic environment. 3.3.1.3 Qishn Carbonate Member - Lithological Description: In my study area, Qishn Carbonate Member ’s lithology is mainly of Lime-Mudstone to Lime- Wackstone with thin streaks of Shale. Limestone: Mudstone to Wackstone, occasionally Packstone, white to grayish white, pale yellow brown, cryptocrystalline to occasionally microcrystalline, moderately hard to hard, chalky, argillaceous grading to marly Limestone, with pyrite crystals. Shale: Dark bluish grey, olive grey, reddish brown, firm, fissile, calcareous in places, with abundant pyrite. Table (1) Qishn Carbonate of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Car. Qishn Car. Qishn Car. Name Thickness Thickness Thickness (Max. (ft (Min. (ft (Aver. (ft Sunah 455 (S-11) 144 (S-8 D2) 367.6 NE Sunah 424 (NES-1) 418(NES-2) 421 Heijah 377 (HJ-11) 340 (HJ-6) 356.3 Camaal 402 (C-14) 128 (C-21) 343.1 North Camaal 419 (NC-2) 392 (NC-1) 405.5 Hemiar 422 (HR-1) 407 (HR-2) 413.9 S.Hemiar 546 (S.HR-1) 117 (S.HR-3) 360.3 W.Hemiar 415 (W.HR-3) 117(W.HR-1) 308 Tawila 373 (T-9) 129 (T-11) 285.4 Masila Block (Thickness Max.) 546 (S.HR-1) 418 (NES-2) 421 Masila Block (Thickness Min.) 373 (T-9) 117 (S.HR-3 285.4 & W.HR-1) Masila Block (Thickness Ave.) 425.7 243.6 361.1 11
  • 23. 1 .1 0 1 .0 0 45 0 .9 0 0 .8 0 40 0 .7 0 0 .6 0 0 .5 0 35 0 .4 0 0 .3 0 0 .2 0 30 0 .1 0 0 .0 0 25 -0 .1 0 20 30 40 50 60 70 Fig. (9) Qishn Carbonate Member, Thickness Map (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 12
  • 24. 1 .1 1 .0 0 .9 0 .8 0 .7 0 .6 0 .5 0 .4 0 .3 0 .2 0 .1 0 .0 -0 .1 Fig. (10) Qishn Carbonate Member, Three Dimension Model (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 13
  • 25. 3.3.1.4 Rate of Penetrations for Qishn Carbonate Member: Average ROP in Limestone 28 Min/M. Average ROP in Shale 22 Min/M. 3.3.1.5 Gases in Qishn Carbonate Member: Background gas levels averaged 0.1 units. 3.3.1.6 Drilling Parameters for Qishn Carbonate Member: WOB 20-25 klbs RPM 90-100 SPM 540 gpm SPP 1500 psi MW 9.4 PPG FW 42-43 3.3.1.7 Qishn Carbonate Member - Subdivision: In Masila Block, Qishn Carbonate Member subdivided into the following units: 3.3.1.7. 1 C1 (See, Table (2)) 3.3.1.7.2 C2 (See, Table (3)) 3.3.1.7.3 RS (Red Shale) (See, Table (4)) 3.3.1.7.4 C3 (See, Table (5)) Table (2): Qishn Carbonate (C1) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Carbonate (C1) Name C1 Max. C1 Min. C1 Ave. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 133 (S-11) 82 (S-3) 93.7 NE Sunah 129 (NES-2) 114 (NES-1) 121.5 Heijah 86 (HJ-2) 62 (HJ-5) 73.7 Camaal 117 (C-14) 91 (C-19) 88 North Camaal 105 (NC-2) 98 (NC-1) 101.5 Hemiar 123 (HR-5) 100 (HR-2) 113.3 S.Hemiar 118 (S.HR-1) 117 (S.HR-2) 78.3 W.Hemiar 111 (W.HR-3) 109 (W.HR- 2) 73.3 Tawila 94 (T-2) 87 (T-8) 65.9 Masila Block (Thickness Max.) 133 (S-11) 117 (S.HR-2) 121.5 Masila Block (Thickness Min.) 86 (HJ-2) 62 (HJ-5) 65.9 Masila Block (Thickness Ave.) 112.9 95.6 89.9 14
  • 26. Table (3): Qishn Carbonate (C2) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Carbonate (C2) Name C2 Max. C2 Min. C2 Ave. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 190 (S-6) 175(S-3) 135.9 NE Sunah 183 (NES-1) 178 (NES-2) 180.5 Heijah 168 (HJ-9) 147 (HJ-6) 161.8 Camaal 191 (C-20) 117 (C-2) 135.8 North Camaal 172 (NC-2) 163 (NC-1) 167.5 Hemiar 187 (HR-2) 175 (HR-7) 181 S.Hemiar 183 (S.HR) 183 (S.HR) 122 W.Hemiar 177 (W.HR-3) 167 (W.HR-2) 114.7 Tawila 145 (T-9) 138 (T-1,2,8 & 14) 102.8 Masila Block (Thickness Max.) 191 (C-20) 183 (S.HR) 181 Masila Block (Thickness Min.) 145 (T-9) 117 (C-2) 102.8 Masila Block (Thickness Ave.) 177.3 160.3 144.7 Table (4) Qishn Carbonate (RS) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Carbonate (RS) Name RS Max. RS Min. RS Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 59 (S-7) 49 (S-9) 55.5 NE Sunah 48 (NES-1) 37 (NES-2) 42.5 Heijah 53 (HJ-11) 37 (HJ-7) 49.6 Camaal 83 (C-20) 36 (C-16) 52.6 North Camaal 60 (NC-2) 54 (NC-1) 57 Hemiar 54 (HR-6) 51 (HR-3,4,5 & 8) 51.75 S.Hemiar 183 (S.HR-1) 54 (S.HR-2) 97.7 W.Hemiar 57 (W.HR-1) 54 (W.HR-3) 55.3 Tawila 98 (T-11) 49 (T-3,7 & 10) 47.2 Masila Block (Thickness Max.) 183 (S.HR-1) 54 (S.HR-2 & 97.7 W.HR-3) Masila Block (Thickness Min.) 48 (NES-1) 36 (C-16) 42.5 Masila Block (Thickness Ave.) 77.2 46.8 56.6 15
  • 27. Table (5) Qishn Carbonate (C3) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Carbonate (C3) Name C3 Max. C3 Min. C3 Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 87 (S-1) 75(S-9) 82.5 NE Sunah 79 (NES-1) 74 (NES-2) 76.5 Heijah 80 (HJ-11) 58 (HJ-12) 71.2 Camaal 80 (C-10) 12 (C-20) 66.7 North Camaal 82 (NC-2) 77 (NC-1) 79.5 Hemiar 71 (HR-1) 65 (HR-5 & 6) 67.9 S.Hemiar 64 (S.HR-2) 61 (S.HR-3) 62.3 W.Hemiar 73 (W.HR-3) 60 (W.HR-1) 64.7 Tawila 90 (T-8) 31 (T-11) 69.5 Masila Block (Thickness Max.) 90 (T-8) 77 (NC-1) 82.5 Masila Block (Thickness Min.) 64 (S.HR-2) 12 (C-20) 62.3 Masila Block (Thickness Ave.) 78.4 57 71.2 3.3.2 Qishn Clastic Member: (See, Figs. (11), (12) and Table (6)) 3.3.2.1 Qishn Clastic Member – Age: (Generally Hauterivian – Early Barremian, especially in the eastern province, to Barremian - Early Aptian in the west (?)) 3.3.2.2 Qishn Clastic Member - Lithology in General: Principally clastics as the name implies, includes coarse clastics in some sections as well as fine sands, silts and mudstones, shales, as well as marls. 3.3.2.3 Qishn Clastic Member - Lithological Description: In my study area, Qishn Clastic Member is mainly of Sandstone with Claystone streaks and traces of Anhydrite. A trace of Coal was logged also. Sandstone: Quartz, colourless, grayish white, brownish grey, medium grained, moderately sorted to well sorted in places, subrounded to subangular, poor to moderate intergranular porosity, with calcareous cement. Claystone: Light grayish green, reddish brown, soft to firm, blocky, slightly silty, subfissile in places graded to Shale. Towards the base Claystone was replaced by Clay, which was highly washable. Traces Anhydrite: Off white to white, colourless, amorphous, occasionally crystalline, soft, locally hard, calcareous in places. Coal: Black, firm to moderately hard, laminated, vitreous luster, earthy and pyretic. 16
  • 28. 2 .0 0 1 .8 0 45 1 .6 0 1 .4 0 40 1 .2 0 1 .0 0 0 .8 0 35 0 .6 0 0 .4 0 30 0 .2 0 0 .0 0 25 -0 .2 0 35 40 45 50 55 60 65 70 75 Fig. (11) Qishn Clastics Member, Thickness Map (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 17
  • 29. 2 .0 0 1 .8 0 1 .6 0 1 .4 0 1 .2 0 1 .0 0 0 .8 0 0 .6 0 0 .4 0 0 .2 0 0 .0 0 -0 .2 0 Fig. (12) Qishn Clastics Member, Three Dimension Model (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 18 Table (6) Qishn Clastics of Masila, Block 14 Thicknesses
  • 30. (Done by: Dr. Mohammed Darsi) Field Qishn Qishn Qishn Name Clastics Clastics Clastics (Max. (ft (Min. (ft (Aver. (ft Sunah 816 (S-6) 232 (S-8 D2) 713.6 NE Sunah 741 (NES-1) 719 (NES-2) 730 Heijah 598 (HJ-11) 396 (HJ-12) 524.8 Camaal 690 (C-22) 78 (C-14) 593.9 North Camaal 741 (NC-2) 654 (NC-1) 697.5 Hemiar 666 (HR-1) 80 (HR-8) 372.3 S.Hemiar 658 (S.HR-1) 229(S.HR-3) 512 W.Hemiar 627 (W.HR-1) 608 (W.HR-3) 615 Tawila 506 (T-5) 0 (T-15) 427.5 Masila Block (Thickness Max.) 816 (S-6) 719 (NES-2) 730 Masila Block (Thickness Min.) 506 (T-5) 0 (T-15) 372.3 Masila Block (Thickness Ave.) 671.4 332.9 576.3 3.3.2.4 Rate of Penetrations for Qishn Clastic Member: Average ROP in Sandstone 15 Min/M, with maximum of 7 Min/M. Average ROP in Claystone 20 Min/M. Average ROP in Anhydrite 25 Min/M. 3.3.2.5 Gases in Qishn Clastic Member: Background gas levels slightly increased through some sections ranging from 0.5 to 1.0 API units. A gas peak was recorded at some wells with a maximum of 14.1 unit. The chromatographic analysis of which broke down in some wells as follows: C1= 0.77U; C2= 0.11U; C3= 0.98U; C4= 0.2 U 3.3.2.6 Oil Shows in Qishn Clastic Member: A good oil shows was observed through the sandstones of the Qishn Clastics Member of the Qishn Formation. Light brown oil stain, bluish white and bright fluorescence, and straw yellow chloroethane cut of dull to bright intensity. 3.3.2.7 Drilling Parameters for Qishn Clastic Member: WOB 23 klbs; RPM 93; SPM 698 gpm; SPP 2350 psi MW 9.3-9,4 PPG; FW 43-48 3.3.2.8 Qishn Clastic Member – Subdivision: The Qishn Clastic Member is subdivided into two sub members: 3.3.2.8.1 Upper Qishn Clastic Sub Member 3.3.2.8.2 Lower Qishn Clastic Sub Member 19 3.3.2.8.1 Upper Qishn Clastic Sub Member: (See, Table (7))
  • 31. Production is mainly from the Lower Cretaceous of the Upper Qishn Clastic Sub Member, a sandstone-dominated sequence that reflects deposition during an overall transgression. Table (7) Upper Qishn Clastics of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field U. Qishn U. Qishn U. Qishn Name Clastics Clastics Clastics (Max. (ft (Min. (ft (Aver. (ft Sunah 260 (S-6) 221 (S-3) 240 NE Sunah 327 (NES-2) 321 (NES-1) 324 Heijah 216 (HJ-7) 177 (HJ-5) 196.4 Camaal 289 (C-15) 78 (C-14) 244.1 North Camaal 237 (NC-2) 215 (NC-1) 226 Hemiar 266 (HR-1 & 4) 80 (HR-8) 171.5 S.Hemiar 235 (S.HR-1 & 2) 229 (S.HR-3) 233 W.Hemiar 212 (W.HR-3) 208 (W.HR-2) 210.3 Tawila 218 (T-6) 169 (T-12) 178.3 Masila Block (Thickness Max.) 327 (NES-2) 321 (NES-1) 324 Masila Block (Thickness Min.) 212 (W.HR-3) 78 (C-14) 171.5 Masila Block (Thickness Ave.) 251.1 188.7 224.8 Upper Qishn Clastic Sub Member subdivided into three units: 3.3.2.8.1.1 S1 3.3.2.8.1 .2 S2 3.3.2.8.1.3 S3 3.3.2.8.1.1 S1 Important Notice: The base of S1, which it is the top of S2 is marked by the correlative lowest bed of S1 sequence, a thin basal conglomeratic, muddy, calcareous sandstones, with abundant shale clasts and shells. 3.3.2.8.1 .2 S2 Important Notice: The base of S2 is marked by the correlative shales of S2-D, which directly overly the thick sand S3. 3.3.2.8.1.3 S3 Important Notice: S3 abruptly overlies the Lower Qishn Clastics section of shales and sands. 20 3.3.2.8.1.1 S1
  • 32. The S1 sequence is composed of upper porous quartzose sand and lower, tight, muddy, calcareous sand. The upper quartzose sand marks the top of the Upper Qishn Clastics and its oil-bearing sand, which ranges in pay thickness from 2.8 m in Camaal-2 to 9.1 m in Sunah-2. The S1 sequence is widespread and thicking of the S1 sand occurs off the crest of the structures. (My pervious studies to Camaal fields prove this fact) The S1 sand is a fine to medium grained, moderately to well sorted and poorly cemented quartzose sand interbedded with thin calcite cemented sands. The Mineralog shows 10% of clay potassium feldspar. Based on the presence of low angle planner cross-bedding with rippled tops, shell lags at the base of cross-bedded units and glauconite company researchers suggest deposition in a shallow marine environment. S1 is subdivided into three sub-units: 3.3.2.8.1.1.1 S1A: (See, Table (8)) It is marine sandstone, forms at the top of this regional open marine shale, and is characterized by an overall coarsening-upward sequence. The top of the S1A is marked by another thin,regional, open marine shale. Table (8) Upper Qishn Clastics (S1A) of Masila Fields Thiknesses (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S1A Max. S1A Min. S1A Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 42 (S-2) 27 (S-3) 33.3 NE Sunah 41 (NES-1) 39 (NES-2) 40 Heijah 30 (HJ-1) 20 (HJ-2 & 11) 23.6 Camaal 39 (C-9) 18 (C-10) 31.7 North Camaal 28 (NC-2) 26 (NC-1) 27 Hemiar 12 (HR-5) 7 (HR-8) 9.6 S.Hemiar 24 (S.HR-2) 19 (S.HR-3) 21.3 W.Hemiar 29 (W.HR-1) 11 (W.HR-3) 22.3 Tawila 18 (T-5 & 10) 10 (T-8 & 9) 12.8 Masila Block (Thickness Max.) 42 (S-2) 39 (NES-2) 40 Masila Block (Thickness Min.) 12 (HR-5) 7 (HR-8) 9.6 Masila Block (Thickness Ave.) 29.2 19.7 24.6 3.3.2.8.1.1.2 S1B: (See, Table (9)) It is marine sandstone. The top of the S1B is marked by a regional, open-marine -shale. 21 Table (9) Upper Qishn Clastics (S1B) of Masila, Block 14 Thicknesses
  • 33. (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S1B Max. S1B Min. S1B Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 38(S-1) 21 (S-7) 27.6 NE Sunah 33 (NES-1) 29 (NES-2) 31 Heijah 30 (HJ-5) 23 (HJ-6) 25.6 Camaal 39 (C-8) 20 (C-4) 28.3 North Camaal 28 (NC) 28 (NC) 28 Hemiar 35 (HR-3 & 5) 29 (HR-6) 32.6 S.Hemiar 31 (S.HR-1) 23 (S.HR-2) 27.3 W.Hemiar 22 (W.HR-3) 18 (W.HR-2) 20.3 Tawila 44 (T-14) 27 (T-8) 31.5 Masila Block (Thickness Max.) 44 (T-14) 29 (NES-2) 32.6 Masila Block (Thickness Min.) 22 (W.HR-3) 18 (W.HR-2) 20.3 Masila Block (Thickness Ave.) 33.3 24.2 28 Important Notice: The proximal clastic-dominated followed by carbonate-dominated (coquinas) shelf deposits of the S1B and finally subtidal sandstone bars of the S1A are produced as a result of continued transgression. 3.3.2.8.1.1.3 S1C: (See, Table (10)) It is deposit of tidal flats; tidal channels and fine-grained bay fill deposits. Table (10) Upper Qishn Clastics (S1C) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S1C Max. S1C Min. S1C Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 40 (S-5) 17 (S-6) 29.3 NE Sunah 29 (NES-2) 27 (NES-1) 28 Heijah 27 (HJ-2) 12 (HJ-1) 17.9 Camaal 34 (C-19) 15 (C-4) 23.9 North Camaal 44 (NC-2) 36 (NC-1) 40 Hemiar 13 (HR-2) 10 (HR-3,4 & 7) 11.3 S.Hemiar 8 (S.HR-1 & 3) 7 (S.HR-2) 7.6 W.Hemiar 16 (W.HR-3) 12 (W.HR-2) 14 Tawila Masila Block (Thickness Max.) 44 (NC-2) 36 (NC-1) 40 Masila Block (Thickness Min.) 8 (S.HR-1 & 3) 7 (S.HR-2) 7.6 Masila Block (Thickness Ave.) 26.4 17 21.5 22 Important Notice: The two sub-units, the tidal S1C and the marine S1B, overlie the S2 sub-unit.
  • 34. 3.3.2.8.1.2 S2: S2 is a thick muddy paleosols unit that can form a vertical flow barrier, which is interpreted to be a non-marine expression of a relative rise of sea level. It is a fluvial to marginal marine, characterized by tidally influenced channels and tidal deposits. The S2 is normally about 25 m thick, and arranged in an overall fining upward sequence. The S2 sequence of interbedded sands and shales is further subdivided into for sequences, which in descending order are S2A, S2B, S2C and S2D. Each sub- sequence contains reservoir quality sands over different parts of the study area. In contrast to S1, the S2 reservoir sands show less continuity, and S2A and S2B show the lowest continuity. Lithofacies in S2 include tidal channel reservoir sandstones, crevasse splay reservoir sandstones and tidal flat non-reservoirs of interbedded silty mudstones and muddy sandstones. S2 is subdivided into four sub units: 3.3.2.8.1.2.1 S2A: (See, Table (11)) Table (11) Upper Qishn Clastics (S2A) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S2A Max. S2A Min. S2A Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 89 (S-6) 60 (S-8) 71.5 NE Sunah 84 (NES-2) 74 (NES-1) 79 Heijah 92 (HJ-7) 68 (HJ-12) 80.5 Camaal 43 (C-21) 15 (C-17) 23.7 North Camaal 24 (NC) 24 (NC) 24 Hemiar 161 (HR-4) 27(HR-8) 93.9 S.Hemiar 83 (S.HR-2) 80 (S.HR-3) 81.3 W.Hemiar 84 (W.HR-3) 72 (W.HR-2) 76.7 Tawila 98 (T-5) 64 (T-13) 74.7 Masila Block (Thickness Max.) 161 (HR-4) 80 (S.HR-3) 93.9 Masila Block (Thickness Min.) 24 (NC) 15 (C-17) 23.7 Masila Block (Thickness Ave.) 84.2 53.8 67.3 23 3.3.2.8.1.2.2 S2B: (See, Table (12)) Table (12) Upper Qishn Clastics (S2B) of Masila, Block 14 Thicknesses
  • 35. (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S2B Max. S2B Min. S2B Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah NE Sunah Heijah Camaal 49 (C-19) 20 (C-7) North Camaal 26 (NC-2) 22 (NC-1) 24 Hemiar 0 S.Hemiar 31 (S.HR-3) 29 (S.HR-1) 30 W.Hemiar 20 (W.HR-1) 6 (W.HR-3) 14.3 Tawila Masila Block (Thickness Max.) 49 (C-19) 29 (S.HR-1) 30 Masila Block (Thickness Min.) 20 (W.HR-1) 6 (W.HR-3) 0 Masila Block (Thickness Ave.) 31.5 19.3 17.1 3.3.2.8.1.2.3 S2C: (See, Table (13)) Table (13) Upper Qishn Clastics (S2C) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S2C Max. S2C Min. S2C Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah NE Sunah Heijah Camaal 58 (C-13) 26 (C-2) 42 North Camaal 39 (NC-1) 35 (NC-2) 37 Hemiar S.Hemiar W.Hemiar Tawila Masila Block (Thickness Max.) 58 (C-13) 35 (NC-2) 42 Masila Block (Thickness Min.) 39 (NC-1) 26 (C-2) 37 Masila Block (Thickness Ave.) 48.5 30.5 18.5 24 3.3.2.8.1.2.4 S2D: (See, Table (14)) Table (14) Upper Qishn Clastics (S2D) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi)
  • 36. Field Upper Qishn Clastics Name S2D Max. S2D Min. S2D Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah NE Sunah Heijah Camaal 10 (C-9) 1 (C-10 & 15) 5.5 North Camaal 5 (NC-2) 4 (NC-1) 4.5 Hemiar S.Hemiar W.Hemiar Tawila Masila Block (Thickness Max.) 10 (C-9) 4 (NC-1) 5.5 Masila Block (Thickness Min.) 5 (NC-2) 1 (C-10 & 15) 4.5 Masila Block (Thickness Ave.) 7.5 2.5 2.3 3.3.2.8.1.3 S3: (See, Table (15)) The S3 sequence is massive sand section about 15 m thick, marking the base of the Upper Qishn Clastics section. Lithofacies in S3 are the same as S2, except that the meandering tidal channel facies is dominant. The sand grains are subrounded, weakly to moderately consolidated with minor calcareous and silica cement. The Mineralog shows about 10% clay content and less than 5% potassium-feldspare. Clays are primarily illite/smecitite with lesser kaolinite. Table (15) Upper Qishn Clastics (S3) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Upper Qishn Clastics Name S3 Max. S3 Min. S3 Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 88 (S-8) 67 (S-3) 78.3 NE Sunah 146 (NES) 146 (NES) 146 Heijah 64 (HJ-2) 34 (HJ-5) 48.8 Camaal 89 (C-15) 52 (C-2) 65.8 North Camaal 47 (NC-2) 36 (NC-1) 41.5 Hemiar 56 (HR-1) 32 (HR-2) 24.1 S.Hemiar 68 (S.HR-2) 63 (S.HR-1) 65.3 W.Hemiar 73 (W.HR-3) 53 (W.HR-1) 62.7 Tawila 84 (T-13) 43 (T-12) 59.4 Masila Block (Thickness Max.) 146 (NES) 146 (NES) 146 Masila Block (Thickness Min.) 47 (NC-2) 32 (HR-2) 24.1 Masila Block (Thickness Ave.) 79.4 58.4 65.8 25 3.3.2.8.2 Lower Qishn Clastic Sub Member: (See, Table (16)) The Lower Qishn Clastics are the shales and sands found between the Upper Qishn Clastics and the Saar Formation. The sands are tidal channel in origin and have limited areal extent. The sands are fine to medium grained and quartzose. Table (16) Lower Qishn Clastics of Masila, Block 14 Thicknesses
  • 37. (Done by: Dr. Mohammed Darsi) Field L. Qishn L. Qishn L. Qishn Name Clastics Clastics Clastics (Max. (ft (Min. (ft (Aver. (ft Sunah 556 (S-6) 0 (S-8 D2) 473.6 NE Sunah 420 (NES-1) 392 (NES-2) 406 Heijah 391 (HJ-11) 206 (HJ-12) 328.4 Camaal 441 (C-1) 0 (C-14 & 20) 349.8 North Camaal 504 (NC-2) 439 (NC-1) 471.5 Hemiar 410 (HR-2) 0 (HR-5,6,7 & 8) 200.8 S.Hemiar 423 (S.HR-1) 0 (S.HR-3) 279 W.Hemiar 416 (W.HR-1) 396 (W.HR-3) 406 Tawila 332 (T-12) 0 (T-15) 249.1 Masila Block (Thickness Max.) 556 (S-6) 439 (NC-1) 473.6 Masila Block (Thickness Min.) 332 (T-12) 0 (C-14,20; HR-5,6,7,8; 200.8 S.HR-3 & T-15) Masila Block (Thickness Ave.) 432.6 158.8 351.4 Lower Qishn Clastic Sub Member is subdivided into four units: 3.3.2.8.2.1 LQ1: (See, Table (17)) Table (17) Lower Qishn Clastics (LQ1) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Lower Qishn Clastics Name LQ1 Max. LQ1 Min. LQ1 Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 350 (S-6) 232 (S-7) 272.3 NE Sunah 267 (NES-1) 258 (NES-2) 262.5 Heijah 238 (HJ-11) 139 (HJ-5) 191.7 Camaal 241 (C-10) 175 (C-11) 189.1 North Camaal 279 (NC-2) 242 (NC-1) 260.5 Hemiar 275 (HR-3) 239 (HR-4) 128.5 S.Hemiar 262 (S.HR-1) 261 (S.HR-2) 174.3 W.Hemiar 383 (W.HR-1) 219 (W.HR-3) 248 Tawila 167 (T-9) 139 (T-2) 136.3 Masila Block (Thickness Max.) 383 (W.HR-1) 261 (S.HR-2) 272.3 Masila Block (Thickness Min.) 167 (T-9) 139 (HJ-5) 128.5 Masila Block (Thickness Ave.) 273.6 211.6 207 26 3.3.2.8.2.2 LQ2: (See, Table (18)) Table (18) Lower Qishn Clastics (LQ2) of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Lower Qishn Clastics Name LQ2 Max. LQ2 Min. LQ2 Ava. (Thickness (ft (Thickness (ft (Thickness (ft Sunah 287 (S-7) 197 (S-9) 201.3
  • 38. NE Sunah 153 (NES-1) 134 (NES-2) 143.5 Heijah 164 (HJ-1) 136 (HJ-10) 136.7 Camaal 244 (C-1) 130 (C-2) 160.7 North Camaal 225 (NC-2) 197 (NC-1) 211 Hemiar 151 (HR-4) 131 (HR-3) 72.3 S.Hemiar 161 (S.HR-1) 153 (S.HR-2) 104.7 W.Hemiar 177 (W.HR-3) 133 (W.HR-1) 156.7 Tawila 168 (T-12) 117 (T-11) 112.8 Masila Block (Thickness Max.) 287 (S-7) 197 (S-9) 211 Masila Block (Thickness Min.) 151 (HR-4) 117 (T-11) 72.3 Masila Block (Ava. Thickness) 192.2 147.6 144.4 3.3.2.8.2.3 LQ3 3.3.2.8.2.4 LQ4 Important Notice: It must be known that above mentioned fields majorities occupy separate normal fault-bounded structures, aligned along a NE-SW oriented structural high trend (called the Masila High). These faults were formed by late stage reactivation of faults initially created during Late Jurassic to Early Cretaceous active rifting. On the highs a relatively thin veneer of Lower Cretaceous sandstones and carbonates rest unconformably upon granitic or metamorphic basement. In the adjacent paleo-lows, a significantly thicker stratigraphic section exists in which carbonates predominate. (See, Table (19), Figs. (13) and (14)) as a conclusions. Table (19) Qishn Formation of Masila, Block 14 Thicknesses (Done by: Dr. Mohammed Darsi) Field Qishn Qishn Qishn 1 .8 0 Name Formation Formation Formation (Max. (ft (Min. (ft (Aver. (ft 1 .7 0 Sunah 40 1227 (S-6) 376 (S-8 D2) 1081.2 1 .6 0 NE Sunah 1165 (NES-1) 1137(NES-2) 1151 Heijah 975 (HJ-11) 750 (HJ-12) 881.1 1 .5 0 Camaal 1071 (C-1) 480 (C-14) 937 1 .4 0 North Camaal 1160 (NC-2) 1046 (NC-1) 1103 Hemiar 1088 (HR- 1) 494 (HR-8) 786.1 1 .3 0 S.Hemiar 1204 (S.HR-1) 346 (S.HR-3) 872.3 1 .2 0 W.Hemiar 1023 (W.HR-3) 744 (W.HR-1) 923 30 Tawila 871 (T-12) 0 (T-15) 712.9 1 .1 0 Masila Block (Thickness Max.) 1227 (S-6) 1137 1151 1 .0 0 Masila Block (Thickness Min.) 871 (T-12) 0 (T-15) 712.9 Masila Block (Thickness Ave.) 1087.1 597 938.6 0 .9 0 27 0 .8 0 0 .7 0 20 0 .6 0 0 .5 0 0 .4 0 0 .3 0 0 .2 0 10 0 .1 0 0 .0 0 -0 . 1 0 20 30 40 50 60 70
  • 39. Fig. (13) Qishn Formation, Thickness Map (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 1 .8 0 1 .7 0 1 .6 0 1 .5 0 1 .4 0 1 .3 0 1 .2 0 1 .1 0 28 1 .0 0 0 .9 0 0 .8 0 0 .7 0 0 .6 0 0 .5 0 0 .4 0 0 .3 0 0 .2 0 0 .1 0 0 .0 0 -0 .1 0
  • 40. Fig. (14) Qishn Formation, Three Dimension Model (Taking in account the whole eastern part of the Republic of Yemen, the western part of Sultanate of Oman border and the Kingdom of Saudi Arabia border with the Yemeni sector of Rub al-Khali Basin; Done by: Dr. Mohammed Darsi) 29 CHAPTER 4 QISHN FORMATION PETROLEUM SYSTEM 4.1 INTRODUCTION The petroleum system of the Masila Block (14) is related to an Upper Jurassic source rock sequence essentially deposited as deep marine deposits in a synrift setting (in
  • 41. some areas prerift sag). Qishn Clastic Member as a primary reservoir and the main subject of our study to the reservoir rocks of Qishn Formation, is a postrift reservoir. In detail, the petroleum system of our studied area is related to the presence of the following factors: 4.2 SOURCE ROCKS The Upper Jurassic (Kimmeridgian) source rock of the Madbi Formation is organic- rich black shales deposited in the deeper portions of rifts in the Late Jurassic. Madbi Formation is the main potential source rocks for the reservoir rocks of Qishn Formation. 4.3 MATURATION Source rocks began generating in the central rift basin in latest Cretaceous to earliest Paleogene time and the process were largely completed by the end of Paleogene time. Degree of maturation: (Oil Window) 0.6. Type of kerogen: 1 and 2 type of organic mater types. 4.4 MIGRATION In the Masila Basin, oil and gas migrated along faults to horst blocks. Numerous horst uplifts occur; however migration resulted in hydrocarbon accumulations, where sealed by Early Cretaceous carbonate (Qishn Carbonate Member). Heavy oil is known to occur marginal to the accumulation sites. 4.5 RESERVOIR ROCKS In the Masila Basin, the Early Cretaceous estuarine sandstones of the Qishn Formation (Berremian/Aptian), mainly the Upper and Lower Qishn Clastics Members are the primary reservoir. Porosity average: 18 % – 21 %. Permeability average: 140 – 2000 mD 4.6 TRAPS AND SEALS The Qishn Carbonate Member (Aptian) provides the seal for the underlying Qishn Clastic Member in the Masila Basin. 30 CHAPTER 5 DISSCUSION POINTS, RECOMMENDATIONS AND CONCLUSIONS 5.1 DISSCUSION POINTS
  • 42. 1. Masila Block’s Fields are located within the Sirr-Sayun Rift Basin that formed during the Upper Jurassic when the Africa-Arabian Plate separated from the India- Madagascar Plate. The Sirr-Sayun Basin is a few hundred kilometres wide and several hundred kilometres long, and is oriented northwest southeast. The basin is bounded on the west by Jahi - Mukalla High, to the south by the South Hadramaut Arch, to the east by the Ras Fartak High and partially interrupted to the northwest by the Sayun High. The Masila Block is situated on an intragraben terrace, and is ideally located to access migrating hydrocarbons from mature deeper buried Jurassic Madbi source rocks. 2. I found that one of the most famous, more complex and interesting topic problems, which faces any researcher who would like to make any kind of academic works. Such as any kind of geological studies on Masila Block 14 reservoir rocks of Qishn formation or any other geological research studies on the whole area, is that: a. We have a huge material in the Database Center of the Petroleum Exploration and Production Authority (P.E.P.A) and its offices around the country. b. We till now don’t have any full-blooded Geo-Scientific Research Centers and the suitable laboratories, where we can make new restudies on all data and materials located now in our Databases Centers. What we can do now? … In my opinion the first step we should take it, as a right step in the right direction, is that P.E.P.A. ’s Database Center must be open for all Yemeni nationality scientific researchers 24 hour per day. Because this step will encourage young Yemeni scientists and researchers to make a lot of studies used the above mentioned materials. I am sure, GOD and then History will keep the names of those Yemeni peoples, who work as decision-makers and give their time and life for their country and its young generation. Important Notice: I would like to drew the reader of this study attention on the following most important mater, that one of the most important problem which make it so difficult to write on the Yemeni Geology as a whole or partly is that the whole Yemen was divided to blocks. In my opinion dividing Yemen, as a whole to blocks is the real reason, which lead to the development of company-centered informal stratigraphic nomenclature schemes. Companies’ main principal objective was to facilitate operations within the individual company’s concession area rather than facilitating scientific research and any ultimate communication in journals. So to solve this question, we must scientifically divide just the sedimentary basins in Yemen to blocks in accordance to their categorisation. (No, for dividing Yemen as a whole to blocks. I said it in the past, say it now and will say it). 31 5.2 RECOMMENDATIONS 1. In the absence of the more detailed and accurate studies on the reservoir rocks of Qishn Formation, I suggest the following known steps as an emergency solution to our case of study:
  • 43. a. Modelling of the Qishn Formation as whole and specially the Qishn Clastic Member and its related subdivision in detail. This must included: • The gross thickness • Facies proportions and distribution (vertically and laterally) • Porosity modelling (vertically and laterally for each facies) • Permeability (vertically and laterally for each facies). b. To model each of above-mentioned parameters, modelling steps must included the following: • Declustering the well data • Examine data and clean up if necessary • Identify and mathematically describe trends that exist • Remove trends from the data • Perform variogram analysis and determine variogram model • Simulate the parameter in 3-D space • Re-introduce the trends that were removed earlier c. The geostatistical surfaces resieved as results of our pervious steps must be compared to maps generated by conventional geologic mapping methods in order to highlight the differences between the two techniques. 2. We are highly in need to make a restudy on all Upper Qishn Clastics samples cored in productive structures. Through standard core analysis and special core analysis and petrographic analysis, we can give a full more detailed restudy on the Upper Qishn Clastics reservoir geology and petrophysics. 3. NOW, It is recommended that a very highly qualified team must lead local and regional studies on the Yemeni Sedimentary Basin by keeping contacts with all International Geoscientific Centers in and out side Yemen. Important Notice: We in the Republic of Yemen must give a high attention to the Environmental Geo- sciences. It is known that the global warming issue poses a number of potential challenges and opportunities for the oil industry. Ongoing negotiations are defining not only targets for greenhouse gas reduction but also mechanisms to enable countries and companies to respond. A broad range of options exists to reduce or sequester emissions. So it is recommended to discuss some of the important technical, economic, and political questions that surround the ultimate viability of this option. 32 5.3 CONCLUSIONS 1. One of the main conclusions of this study is that Qishn Formation as a whole and also its subdivision mostly thin to the south and to the east. This important
  • 44. conclusion, I received it as a result of my geostatistical and mathematical analysis study on every Qishn Formation ’s subdivision in detail. 2. As a result of this study, it is easy now to understand the great importance of studying: a. The Masila Block (14) as a part of Say’un Al- Masila basin. b. The pervious and present geological activities of the whole eastern part of the Republic of Yemen. c. The Qishn formation in the outcrop, the reservoir rocks of Qishn formation in the subsurface and the upper Qishn stratigraphy. d. The Qishn formation sequence stratigraphy. e. The Qishn formation (Masila, Block 14) petroleum system. 3. If we really want to be Excellent and long vision decision makers, we must identify the best mechanism or trend, that could be used to study the reservoir rocks of Qishn Formation and by the way to predict the better-developed methods. 4. In my opinion, the best mechanism or trend is that we must use the latest multi functional geological soft ware application which can gave the more accurate scientific solutions to our geological problems saving time and money. 5. We in the Petroleum Exploration and Production Authority, as a main part of the Ministry of Oil and Mineral Resources, must build a strong long vision strategy on studying the oil exploration and production future prospect. Because the first lesson I learned from this study, is that we must take in account our great Yemeni grandchildren interests, by making long-term studies on our sedimentary basins. 6. I believe in that Yemeni Geology, which took some care in the past and attracts many experts in the present time, is not going just to surprise all with its oil and gas discoveries, but also with its rich and useful data in the near future. Important Notice: Here, I would like to inform interested readers of this study, that I planned to continue this work by publishing a paper on my mathematical description to the reservoir rocks of Qishn Formations and its subdivision, based on its geostatistical data. 33 ACKNOWLEDGEMENTS
  • 45. In this respect, I would like to extend my thanks to the Petroleum Exploration and Production Authority – (San’a), for their great trust on asking me to work on this study, especially Mr. Nabeel Al-Kaosi, Dr. Ahmed Ali Abdellah and Dr. Mohammed Ahmed Al-Zubairi (P.E.P.A – San’a). Mr. Abdullah Salem Ta’lab and Mr. Nagib Saeed Tabet (P.E.P.A – ADEN). Mr. Tawfik Ahmed Ismail and Mr. Mohammed Mahyoub (P.E.P.A ’s Office in CPF – Masila Block 14). I would like to express my deep gratitude and sincere thanks to Mr. Victor W. Dudus (The Operation Geologist), Mr. L. A. Len Flexhaug (The Petrophysicist) and Al Jones (The Construction Superintendent) Canadian Nexen (CPF, Masila Block 14), for their help and support on fulfilling this study. I have to thank Miss. Wafa and Miss. Fatimah Salem Khamis, for help and support. Special thanks go to that kind of people, who work hard and in silence on building a bright future for our lovely Yemen, from both sides, the Yemeni Ministry of Oil & Mineral Resources (The Petroleum Exploration and Production Authority) side, the Nexen Inc. (Canadian Nexen Petroleum Yemen) side. Someone said that "many people will walk in & out of your life, but only true friends will leave footprints in your heart." I'm so glad that all above mentioned people lift theirs in mine. Hope it is the right step in the right direction! 34 REFERENCES
  • 46. 1. Beydoun, Z.R., Bamahmoud, M.O., and Nani, A.S.O., 1993. The Qishn Formation, Yemen: lithofacies and hydrocarbon habitat. Marine and Petroleum Geology, 10 (4): 364-372. 2. Beydoun, Z.R., and others, 1998, International lexicon of stratigraphy, v. III, Republic of Yemen, (2nd ed.): International Union of Geological Sciences and Ministry of Oil and Mineral Resources, Republic of Yemen Publication no. 34, 245 p. 3. Bosence, D.W.J., ed., 1997, Special issue on Mesozoic rift basins of Yemen: Marine and Petroleum Geology, v. 14, no. 6, p. 611-730. 4. Brannin, Joe, and others, 1999, Geological evolution of the central Marib-Shabwa basin, Yemen: GeoArabia, v. 4, no. 1, p. 9-34. 5. Nedham, M. Darsi, 2000. The Geological Research History Work in the Republic of Yemen during the period from 1852 until Today (Three papers). Yemen Times newspaper. Issue 2-January 10th through January 16 2000, Vol. IX, Culture Page, Issue 10 - March 6 through March 12 2000, Vol. X, Culture Page and Issue 15 - April 10 through April 16 2000, Vol. X, Culture Page. 6. Productivity Prediction from Well Logs in Variable Grain Size Reservoirs Cretaceous Qishn Formation, Republic of Yemen, Michael L. Cheng and Marco A. Leal: Canadian Petroleum Ltd., Calgary, Canada David McNaughton: Mincom Inc., Houston, Texas U.S.A. 7. Putnam, P.E., 1997, Upper Qishn (Lower Cretaceous) reservoirs at Masila, Yemen, CSPG-SEPM Joint Convention Core Conference, J. Wood and B. Martindale (compilers), p. 429-448. 8. Putnam, P.E., Kendall, G.A., and Winter, D. A. 1997, Estuarine deposits of the upper Qishn Formation (Lower Cretaceous) in the Masila region of Yemen, American Association of Petroleum Geologists Bulletin, v.81, p. 1306-1329. 9. The Masila Fields, Republic of Yemen, W.A. King1, B.R. Mills1, Scott Gardiner2, and A.A. Abdellah3. (1) Nexen Inc. (Formerly Canadian Occidental Petroleum Ltd.), Calgary, AB T2P 3Z1, Canada, (2) Nexen Inc. (formerly Canadian Occidental Petroleum Ltd.), 1801 - 635 8th Avenue S.W, Calgary, AB T2P 3Z1, Canada, (3) Petroleum Exploration and Production Authority (PEPA), Yemen Ministry of Oil and Mineral Resources (MOMR), Yemen 10. Tide-Dominated Sedimentation in an Arid Rift Basin - Cretaceous Qishn Clastics, Masila Block, Republic of Yemen, Dale A Leckie and Tom Rumpel. Nexen Inc, Calgary, AB T2P 3P7, Canada, and phone: 403699-5902, Dale_leckie@nexeninc.com 11. Local, Regional, International and Global ’s World Web Site Internet Resources 35 ABOUT THE AUTHOR
  • 47. * Dr. Eng. Mohammed Darsi Abdulrahman Nedham, born on November 17, 1963, Crater (Aden). 5 Languages (Arabic, English, Russian, Chinese and German Languages). Petroleum Engineer, Geologist; Married have 2 sons. Education: Graduated from the Earth Science College of Jilin University as a Doctor of Science in Mineralogy, Petrology and Ore Deposit on May 29 2002 and also graduated from the Russian among People Friendship University in 1991 as a Petroleum Engineer, Geologist (M.S. degree) on June 29 1991. Appointments: Petroleum Exploration and Production Board, Aden Branch, Ministry of Oil and Mineral Resources; Petroleum Engineer; Senior Geologist; Representative; Coordinator. Publications: 10 scientific papers, 6 published in the Yemen Times Newspaper, 3 in China (2 in World Geology and 1 in the Journal of Geoscientific Research of Northeast Asia) and the last one in Russia. Two registered Patents. 18 Certificate from different institutes, centers, organizations and clubs. Membership: Fellow, Geological Association of Canada, American Association of Petroleum Engineers and other memberships. Dr. Eng. Mohammed Darsi Abdulrahman Nedham began his professional career by working as petroleum engineer, geologist in the Petroleum Exploration and Production Board (Aden Branch). His scientific interest is concentrated on the Geological Research History Work, Earth science software application and basin-modeling problems. The most important thing, Dr. Darsi is ONE of the Who is Who in the 21st Century for 2001 and 2002 (First and Second Publication), choosed by the International Geographical Centre, Cambridge, England. 36