Fangjian Xue | Agnes Dubois FJX Resources | Schlumberger NExT

1. New Knowledge and Approach
on Drilling and Completion Optimization
of Carbonate Reservoirs
Fangjian ‘Jack’ Xue Agnes Dubois
FJX Resources Schlumberger NExT
June 15, 2022

2. 2
• Still various high-economic drilling opportunities in carbonate reservoirs
• Need correct knowledge and approach on carbonate heterogeneity to
reduce high uncertainty in operation
Understanding on carbonates drilling
Key words highlighted for focus in each slide
• Blue: geological reality
• Red: challenge and risk
• Pink: effort

3. 3
• New knowledge
• Optimal approach
• Worldwide Opportunities
Outline

4. 4
“String-beads”
Seismic images on uncollapsed caves in carbonate rocks
“Pair-beads”
Ordovician carbonate in Tarim Basin, western China.
(Courtesy of CNPC)
Miocene carbonates in Central Luconia Province, offshore
Sarawak, Malaysia. (Courtesy of PETRONAS)
B
+
-
A
Standard display/reference:
• American zero-phase polarity
• Petrel seismic color code (red for peak and blue for trough)
+
-

5. 5
 The nature of carbonate heterogeneity: extreme, extensive and inherent
The nature of carbonate heterogeneity is a mixture of pores & throats with different sizes from micrometers to
kilometers in 3 types.
 The First type is the matrix pores with size from vug in hundreds millimetres to micrometres in chalk. They
basically follow Darcy’s Law as clastic reservoirs and have been extensively studied and evaluated in detail
with well data.
 The second type is large voids with size from meters in caves to kilometers in cave networks. They can
only be identified in seismic. In this slide, the amplitude map of cave interpretation illustrates two cave
networks with dendritic patterns and connected length of several kilometers. The large voids, instead of
Darcy’s Law, follow turbulent law. Their extremely high permeability dominate reservoir performances, but
have been much under-evaluated and even unrecognized in reservoir evaluation due to limited knowledge
on them.
 The third type is fractures and faults, which have increase the connectivity in matrix porosity.
Now, we understanding, the nature of carbonate heterogeneity are extreme, extensive and inherent.

6. 6
o Uneven distribution of large voids within matrix porosity
o Highly uneven distribution of resources and reserves
o Complex fluid system due to property trapping
o Strong uneven water rising during production due to baffle zone
and/or flow conduits
The impact of carbonate heterogeneity on reservoir
characters and drilling efficiency
Tight Ordovician carbonates, Tarim Basin
Porous Miocene carbonates, Central Luconia
W W W
O O O
O: Oil well
W: Water well
 High mud loss and bit drop in drilling
 High uncertainty in drilling result: high productive well
close to dry hole
 High variation in production: water cut, recovery rate,
cumulative
Optimizing well path with seismic cave feature
to reduce 3H

7. 7
• New knowledge
• Optimal approach
• Worldwide Opportunities
Outline

8. 8
Advanced seismic approach to reveal “pair beads” as much as possible
Acquisition
Targeted
imaging
Conventional High
Density
Conventional 1L
Reservoir 2L 2L, 6S
Heterogeneity 2L, 2S ?
L for large cave feature, S for small cave feature
Once a cave feature is observed in seismic, it
means than more cave features exist around and
could be revealed with advanced seismic approach
Tarim Basin (Courtesy of CNPC)

9. 9
Characterizing matrix porosity and large void separately
L2
L3
L4
Matrix porosity characterization
•Surface/boundary interpretation
•Facies/property modeling
•Sweet spots (zone) in porous
carbonates (and clastics)
Cave (High Ø/k) characterization
•Direct cave interpretation
•Cave geobody modelling
•Connectivity analysis
•Sweet spots in tight carbonates
•Bitter spots in porous carbonates
+
beicip.asia
Xue et al., 2017

10. 10
Smart drilling and completion
Efforts
Reservoirs
Seismic Imaging &
Reservoir Characterization
Drilling
Optimization
Completions
Optimization
Matrix tight
carbonates
Heterogeneity imaging
Cave storage and connectivity,
flow unit
Directly drill into and
stop at top cave
Openhole
Matrix porous
carbonates
Heterogeneity imaging
Matrix porosity, cave conduits
Sweet-spot zone
Avoid cave conduits
Open/cased hole
Acidizing/fracking
Conventional
clastics
Reservoir imaging
Facies, reservoir-property, DHI
Sweet-spot zone Perforating,
fracking
Unconventional Conventional imaging
Structure, lithology, fault
Horizontal well path Multi-stage perf
and fracking
Different efforts for different reservoirs

11. 11
Smart drilling and completion
The different efforts for different reservoirs
• For tight carbonates, the drilling optimization is to drill directly into and stop at top cave, and then open-hole
completion.
• For porous carbonates, the optimization is to drill into sweet-spot zone and, at the same time, to avoid cave
conduits.
Hence, in smart carbonate drilling, advanced seismic approach is the focus to provide relevant sweet and
bitter spots for each individual drilling. It is the single well efficiency make the overall economic success.
Without revealing and characterizing “pair beads”, technical efforts on carbonates would be basically same as
on clastics, which would lead to low drilling efficiency in carbonate reservoirs.
• For unconventional, which is low heterogeneity, the technical effort should focus on drilling and completion
improvement. It is the well-pads area efficiency makes the overall economic success.
Tight carbonates and tight clastics are total different in drilling tactics.

12. 12
• New knowledge
• Optimal approach
• Worldwide Opportunities
Outline

13. 13
Worldwide
Seismic cave features have been recognized in thick carbonates worldwide from Barents Sea at north to
Australia at south. But they have been basically missed or misinterpreted in carbonate studies even they have
had large impacts on operation efficiency. For overall understanding, the nine cases are illustrated and
explained in three groups by their geological ages and settings.
• Cenozoic platform: usually shallow with high image quality, providing clear information on geological settings. “Pair
beads” are extensive in platform interior and lonesome at platform edge. Matrix are porous. “Pair beads” are mainly
identified as “bitter spots” in drilling and production.
• Paleozoic platform interior: usually deep with relatively low image quality. Matrix are usually tight. Analog to Cenozoic
platform interior, “pair beads” are widely distributed, which are highly prospective but only been studied and drilled in
Tarim. They are mostly distributed in the world, has the most undrilled potential and should be the focus for drilling
opportunities.
• Paleozoic platform edge: usual observable in seismic with distinct mound or build-up configuration. Matrix porosity are
highly variable. “Pair beads” are lonesome with vugs around. The mound features have been widely studied and drilled
due to favourite trapping and reservoir conditions.
With these cases, we could see various opportunities in carbonates worldwide. Four of them are selected as representative
references to illustrate why such opportunities and how to capture them.

14. 14
F14
(2012)
Karst
Fracture
Jintan
(2004)
F9
(2015)
1. Miocene Isolated Carbonate Platforms in Central Luconia, offshore Sarawak
Jintan
F6
Ali and Abolin,
1999
F9
+
-
F14
Different seismic interpretation on features related to mud-loss
Cave
Karst

15. 15
Luconia
More than 100 Miocene carbonate build-ups with various sizes. Most large ones have been drilled.
Gas-producing. High matrix porosity: Ø=5~35%. Mud loss is the main drilling hazards.
Different seismic interpretation on features related to large mud-loss
• The upper one is Cave network with dendritic patterns based on “pair beads” recognition in
section-view and dendritic distribution of direct cave interpretation in map-view,
• The lower ones are Combination of karst, fault and fracture based on vertical disruption of
reflection event in section view and dendritic attribute anomalies in slice-view.
In fact, “pair beads” could be observed in all the cases but unrecognized simply without knowledge
on them. These vertical disruption are more of noise or artifact relating to poor image quality. This is
the representative case illustrating the knowledge differentiation and opportunities to improve
operation efficiency on porous carbonates, especially large reef or isolated platform.

16. 16
ACP
DCP
2: Carbonate play in Tarim Basin, Western China
Lin et al 2012
• Deep: >5000m
• Tight: Øavg=1.2%
• “String beads” as
main drilling targets
• 3 SLB projects
2009~2014
O3
O1&2 O
Basin
1
2
3
Schematic map showing the paleogeography and the distribution of carbonate platform margins

17. 17
 In Tarim Basin, Ordovician platform carbonates are deep bellow 5000 meter. Matrix are tight
with average porosity about 1.2%, not productive. Production are mainly from vuggy reservoir at
platform edge and from cavernous reservoir at platform interior.
 “String beads” were firstly submitted in late 1990s as the main drilling targets.
 Schlumberger 3 successful integrated G&G project from 2009 to 2014. At that time, the
challenge is that most favorite “string beads” have been drilled. Drilling success rate had been
declined. But still many “string beads” have not been drilled. Effort in these 3 projects have
made large technical progress, significantly improved drilling efficiency in project areas and
provided valuable references to tight carbonate E&P worldwide.
2: Ordovician Carbonate play in Tarim Basin, Western China

18. 18
“String-beads”
“Pair-beads”
X
Y
Z
X Y Z
A
B
C
Project 1: Development tactics on cavernous reservoirs in Lugu area (2010)
Time map of cave interpretation
Seismic imaging, interpretation, connectivity analyses, HC prediction and drilling location on caves targets

19. 19
Lungu
• The first is Lungu project in 2009 to 2010, many new knowledge and approaches have
developed seismic cave features in carbonates:
• Seismic reprocessing had converged the long “string beads” into short “pair beads”, which
provide relatively more accurate information on location, size and shape of cave features.
• Direct cave interpretation approach was developed to map cave network in multi-level.
• Connectivity analysis is performed to predict hydrocarbon distribution and optimize drilling
locations.
• Two drilling before project completion resulted in high-productive wells, which had not
achieved for two years
This technical progress has opened the door to recognize “pair beads” worldwide.

20. 20
a:150m b c:80m e:80m
d:100m f
b
c
f
a
d
e
 The position difference of cave images between different PSDM seismic could reach more than 100m.
 These cave location difference had led to 15% drilling failure due to missing the cave targets
 The position errors could be reduce by velocity survey and subsequent PSDM update during drilling
The SGD project in Tarim had resulted in 0 % drilling failure due to missing cave targets
Cave location difference in section-view
Cave location difference in map-view
SGD-PSDM Base Model: cave in light blue, left upper
Original PSDM: cave in red, left lower
Project 2: Seismic Guided Drilling (SGD) in Halahatang area (2014)
A
B
C
Ordovician attached carbonate in Tarim Basin. (Courtesy of CNPC)

21. 21
Flow unit
• The cline in SGD project had requested not only drill into cave targets but also high productive
from them.
• To meet the high-standard request, flow unite approach was developed to predict remaining
unproduced oil-bearing caves.
• SGD drilling: Rate of high productive well increase for 33% (1/3) to 75% (3/4).
• The flow unit delineation provides the effective approach to improve drilling efficiency on tight
carbonates, specially in matured area.
Project 2: Seismic Guided Drilling (SGD) in Halahatang area (2014)

22. 22
Nan Nuan Field, Chumphon Basin
P:~10,000BO/D Cum ~5.3MMBO
Yinggehai-Song Hong Basin
Ham Rong Discovery
T: 6300BO/D, 8MMCFG/D
Beibuwan Basin, W10-N3 Field
P:~6000BO/D Cum>,1.5MMBO
Sinphuhorm Gas Field, Korat Basin
P:60 MMCFG/D Cum ~100BCF, Eur ~300BCF
Ha Long Bay, Vietnam
• High single-well productivity, but high uncertainty in drilling, only 3 fields and a few discoveries till now.
• Still high potential, wide distribution, remnant basement play, need advanced seismic approach and rolling E/D/P drilling.
E&P Cases
Topography
Dry
Dry
X
3: Permian carbonates play in SE Asia
Y
Ang Thong Marine Park
Minilog Island
Xe Bang Fai Cave, Laos
2
1
Gua Kanthan Cave, Perak,
Malaysia
(Courtesy of (PTTEP)

23. 23
Y dry
X 5.28 MMBO
P1 Nang Nuan oil field in B6/27 Block, Gulf of Thailand
Cave interpretation in Nang Nuan Field
-01
Dry
time
amplitude
X
5.28 MMBO
Y Dry
Quick screening (2017) with new knowledge of carbonate heterogeneity:
• Field has been suspended in 2007 due to high water cut
• High productive well X close to seismic cave features with large mud-loss in drilling. Dryhole Y away from cave features
• Most seismic cave features have not been drilled.
• Proposal for advanced reservoir study

24. 24
Y B
C
X
A B C
X
A
P1. Nang Nuan Oilfield in Block 6/27, Gulf of Thailand
Advanced reservoir study (2018).
• Three undrilled flow-units (A, B and C) delineated with for development drilling
• Flow unit B and C have large potentials comparable to X.(5.28 MMO Cum).
• Three potential areas defined for step-out exploration drilling within the block
5.28
X 5.3MMBO
amplitude
Y
Dry
>6?
>6?
B
C
A

25. 25
Permian carbonates in SE Asia
• Very high single-well productivity up to cum 5.3 MMBO, EUR 300 BCFG, but also very high uncertainty in
drilling result of high productive well with subsequent deviated dry hole.
• The reason is that Permian carbonate E&P in this region has been guided by concepts and models of
“fracture carbonates”, dolomitization, karst and reefs.
• The high uncertainty prevents operator’s subsequent E&P effort, resulting only 3 fields and a few
discoveries till now.
New understanding,
• the potential is high due to extensive cave features and continuous distribution as board platform interior in
Tethys Sea during Permian time.
• The intensive Cenozoic and Mesozoic tectonic movement have broken platform into complex remnant
basement play.
• Operation need advanced seismic approach to reduce drilling uncertainty and rolling E/D/P drilling to lower
economic threshold.

26. 26
The Great American Carbonate Bank -- GACB
(Sternbach, 2013)
• Evident “Pair beads”, no evident unconformity at carbonate top (~8000 ft), basically untested, below many mature fields/areas
• High economic but unrecognized drilling targets with great potential through most US mid-continental
4: Ordovician Ellenburger/Arbuckle carbonate play in North Texas
“Pair beads” in Ellenburger/Arbuckle carbonates
(Courtesy of Schlumberger)

27. 27
In reviewing of an old 3D seismic survey at northern Texas at 2018
• “Pair beads” have been recognized in Lower Ordovician Ellenburger carbonates.
• The top of Ellenburger is about 8000ft deep and conformable to overlaying formation. Treated as tight
basement, the Ellenburger carbonates have been penetrated only at top with a few wells.
• These thick cavernous reservoirs are basically unrecognized, becoming a deeper frontier play under
shallower mature fields, providing easy access, high productive and low-cost targets for drilling.
• Besides, they could be used for drilling-waste disposal and carbon storage.
The study area
• is at the shelf interior near shelf edge of “the Great American Carbonate Bank”,
• which is the Lower Ordovician – Upper Cambrian carbonate bank covering large areas of the midcontinent
US with local terms as Ellenburger, Arbuckle, Knox and Beekmantown carbonate in different regions.
• Lacking knowledge on “pair beads” has led to large unexplored potentials in this giant carbonate bank.
4: Ordovician Ellenburger/Arbuckle carbonate play in North Texas

28. 28
Summary and Conclusion:
New knowledge
• “Pair-beads” bright spots are the seismic images on cave features in carbonate rocks
• The nature of carbonate heterogeneity are extreme, extensive and inherent
• High heterogeneity has large and distinct impact on reservoir characters and drilling efficiency
Optimal approach
• Improving seismic imaging to reveal “pair beads” as much as possible
• Characterizing matrix porosity and large void separately to delineating sweet and bitter spots
• Increasing drilling efficiency with different technical efforts for different reservoirs
Worldwide opportunities
• Various opportunities remaining but unrecognized in carbonates, especially in Paleozoic play
• US Ordovician carbonates have high potential and economic value to drill
• Capturing these opportunities need correct knowledge and approaches on carbonate
heterogeneity

29. 29
Thanks and questions
Fangjian Xue: fxue@slb.com, fxue@fjxresources.com, 1-832-5479113
Agne Dubois: ADubois@slb.com
Contact