2. 34
I- the log and the tool used.
II- Data Quality Control: ....................................................3
1- SP ................................................................................4
2- GR ...............................................................................4
3- HCAL ..........................................................................4
4- HALS...........................................................................5
5- RHOZ ..........................................................................6
6- PEFZ............................................................................7
7- TNPH...........................................................................7
8- RXOZ, DSOZ, RSOZ..................................................7
III- Zoning..........................................................................8
1- Zone 1 (TD=2491 to 2428m)......................................8
2- Zone 2 (2428 to 2417m) .............................................8
3- Zone 3 (2417 to 2387m) .............................................9
4- Zone 4 (2387 to 2362.5m) ..........................................9
5- Zone 5 (2362.5 to 2338m) ..........................................9
6- Zone 6 (2338 to 2300m) ...........................................11
7- Zone 7 (2300 to 2222m) ...........................................11
IV- General Log Description:...........................................11
V- Rw , Sw Calculations ..................................................12
Sw and Sh Calculation Table ........................................12
HART and HDI and RXOZ Calculation Table............13
VI- Conclusion: ................................................................13
4. 36
The tool run in the well is a BSP-PEX-DSLT-HALS, which provide total Gamma-Ray,
Neutron porosity from HGNS, Formation Density, PEF, Caliper, Micro-resistivity from
TLD and formation resistivity from HALS and SP from BSP.
HALS DSLT TLD HGNS BSP
The log section is extended from 2222.0 M to 2496.5 M. interpreting this log using the
basic tool principles and measurements will provide an understanding of the importance
and significance of the data that Wireline Engineer delivers to the clients.
Data Quality Control:
We have to be sure that all the curves used are valid.
This section is for identifying any anomalies or unsuspected behaviors.
This toolstring run on a vertical well and maximum temperature recorded is 85 DEGC,
which is within tool specification. According to parameter used, mud type is Water Based
Mud, matrix for clean zone set to LIMESTONE, and high saline mud of 58000 ppm. No
Barite correction is used.
5. 37
1-SP
In a fresh mud environment where Rmf > Rw, shale should have little to no SP deflection
while in clean sandstones there should be a significant negative SP deflection. In an
environment where Rmf < Rw, shale should show little to no SP deflection while in clean
sandstones there should be significant positive SP deflection. If Rmf = Rw little SP will
be developed and the SP log will have very little character. Hence the SP should indicate
shaliness, in which case, it should follow the GR curve. However, this is not the case in
this log. This can be due to floating reference. Therefore the SP curve presented is not
valid for interpretation.
2-GR
GR sensor in the HGNS measures the formation total GR, due to nuclear natural
component (Uranium, Thorium, Potassium). It is a good indicator of shale. It reads high
in a shale zone and low in the clean zone. The value is not very important; the most
important thing is the shape of the curve.
GR reads high in shale (around 190 GAPI), and in the clean zone GR is reading about 40
GAPI. The GR curve behaves well in the proposed shale zones (Validated by other logs
discussed below). The gamma ray curve on this log is believed to be valid.
3-HCAL
The caliper reads good value of 8.5in. The caliper pointed out some events in the log.
There is washout just on the top part (2222-2995m) was picked up by the caliper. The
washouts are especially in the shale zone because as known, shale is fragile rock and
could be broken easily by the drilling bit. And there are small mud-cake zones in shaly
sand (2417-2428m). Thus the HCAL is a valid curve for this interpretation.
6. 38
4-HALS
The HALS curves evaluate the resistivity of the formation at different depth of
investigation: Laterolog Deep Resistivity (HLLD) and Laterolog Shallow Resistivity
(HLLS). The laterolog tool works better in a conductive mud in high formation resistivity.
Using the tool planner and as input RT=1000Ωm and Rxo=40Ωm and the resistivity of
mud Rmud=0.1Ωm, we obtain the next graph:
Tool Planner for Laterolog
This graph demonstrates that the laterolog tool is suitable for this environment.
A known tool behavior is that the curves overlays in shale. As it is shown in the next log,
confirmed by the GR curve.
7. An other known tool behavior is high reading in hydrocarbons zone (2338-2358m), as
shown in the next log portion
5-RHOZ
This log is used as a porosity determinant as the bulk density of the formation is related
to the porosity. Limestone compatible scale was used for this log, hence it should have a
value of 2.71g/cc in a zero porosity formation or rock unit. The density curve should
therefore increase or decrease based on the bulk density of the intercepted rocks. For
shale with higher density, the density curve is expected to be higher compared to
8. sandstone, limestone or dolomite. This is very true for this density log and it matches
with the GR and HALS curve responses in the impermeable/shale zones.
6-PEFZ
PEFZ is the Photoelectric Absorption Measurement of the formation, and can give the
minerals contained by the formation, and confirms also the density readings. The PEF is
reading about 1.8 to 2 in clean sandstone zone; which let us assume that this reading is
valid. So it can be used for confirming formation lithology.
7-TNPH
Neutron tools see the hydrogen ion concentration (hydrogen index) in rocks and relate it
to porosity. The hydrogen index (H.I) varies from one rock to the other depending on
amount of pore spaces present to hold fluids and the amount of hydrogen present in the
fluids. Shale, with lots of bound water is seen by the neutron porosity log as very porous,
hence higher values were recorded in shale all through the log. Based on this and the
aforementioned shale density property, the neutron porosity curve and the density curve
usually crossover in shale zones. This is also true for this log, hence the curve is valid.
8-RXOZ, DSOZ, RSOZ
Micro-resistivity evaluates the shallow resistivity of the formation; Mud Cake resistivity,
and thickness in water based mud. The reading of RXOZ in shale zone without washout
is almost the same as HALS reading and there is no mudcake at the depth of (2309-
2338m). Which let the micro-resistivity usable in this log but not in the zone 1 due to the
washout.
9. II- Zoning:
The logged interval is divided into the following seven major zones based on the log
response to the intercepted lithologic units. An attempt will be made to describe the
lithologic units within each of the zones.
(REVIEW lithology plot)
1- Zone 1 (TD=2491 to 2428m)
Using the crossplot RHOZ vs. TNPH we can say
that this zone has mainly a limestone lithology
even though the gamma ray curves tend to show
this zone as Sandstone with impurity knowing that
PEF in this zone is about 2.5 in average.
The subzone from 2472 to 2466m, we can notice a
shale zone where GR is reading high
(195 GAPI - 200 GAPI), resistivity curves are overlaying and reading between 1 and 2Ωm.
And also we can find washouts (caliper readings a little bit higher than the pervious value),
also the density and porosity are high who induce to affirm that this is a shale rock. In this
zone there are also some spikes in the resistivity curves followed by porosity curve at 2454m
and 2473m (high resistivity and low porosity); this could be thin beds of dolomite (it is also
confirmed by the few points in the dolomite region in the crossplot above).
2- Zone 2 (2428 to 2417m)
In this zone the resistivity curves are overlaying and reading high, the gamma ray also is
reading high about 140 to 200 GAPI; which is a good indicator of shaly zone. In the other
hand by looking at the density curve that is on the right of the porosity or by using the
crossplot we can affirm that the matrix type is dolomite.
10. 3- Zone 3 (2417 to 2387m)
Here the gamma ray is reading low values except some places, the resistivity is constant and
is the same as the one of the zone 4 which is clean sandstone, the density curve is in the left
of the porosity, and the PEF is reading about 2. Taking on consideration the pervious
information we can affirm that this zone is sandstone with some shale on it.
4- Zone 4 (2387 to 2362.5m)
This is the water zone; it is a part of the sandstone
reservoir rock. It is observed in this zone that the
resistivity curves show low resistivity values
(indicative of water). The invasion diameter curves
shows prominent invasion (permeability) in these
sandstone units. The PEF curve is reading about 2
and the density curve is on the left of the porosity
which is indicator of sandstone and confirmed by
the crossplot. Therefore this zone is classified as
water bearing sandstone.
5- Zone 5 (2362.5 to 2338m)
This zone is Transitional and Hydrocarbon zone.
The resistivity profile on the lower sand unit
(2362.5-2359.5) is seen to show a sort of
progression of increasing resistivity but reduced
separation with decreasing depth compared to the
units below. This zone is interpreted as a
transitional zone. The sandstone unit above this
subzone is noticed to have a distinct high resistivity
characteristic (about 700Ωm). The resistivity value
of this subzone represents the highest value
encountered in the whole
11. logged interval. These resistivity curves are also seen to not overlay (shallow not
overlaying deep curves), suggesting that there is invasion. This is due to the resistivity
difference between the mud (WBM) and the fluid in the virgin zone (Oil). Also the low
reading of Neutron porosity indicates a reduction in the concentration of H.I in this
section (there is not a lot of hydrogen in oil). Normally, the density in the Hydrocarbon
zone should be less than that of water zone but this is not really the case here. The oil
could be indicative of biodegradation or leakage among other reasons.
12. 6- Zone 6 (2338 to 2300m)
This zone is above the reservoir rock and it is characterized by a high resistivity with no
invasion, all the depth of investigation overlay. The porosity is low in this rock and the
density is high. Also the gamma ray reading is high (about 140 to 180GAPI). Considering
this we can affirm that this rock is a shale cap rock.
7- Zone 7 (2300 to 2222m)
This thick zone is characterized by high gamma ray reading. The GR increased from the
underlying zone to a value of about 185 GAPI. The GR value for the interval ranges
between 178-191 GAPI suggesting a total shale zone. The Caliper reading indicates a
small scale washout at the base of this zone but grades into a big-scale washout at the
uppermost part (2240-2222m) which is a characteristic feature of shale. The HALS
curves overlay all through this zone and the HDI curve is reading low indicating a non
permeable (no invasion). Also the relatively low resistivity value in this zone suggests a
conductive system which is interpreted as the shale-bound water. The MCFL invalidity
(mentioned in DQC section) is observed in this zone. The density value increased to over
2.6g/cc while the neutron porosity increased to about 0.3pu which are the expected values
for shale lithology. However, this ‘increase’ in the shale porosity is false as shale has no
true porosity but contain a lot of bound water. Based on all this responses, we can
confidently infer that this zone is principally a shale zone.
III- General Log Description:
The general lithology of this log is sandstone rock with presence of shale and minerals.
There is hydrocarbon (oil) in this well in a sandstone zone when resistivity was
increasing and the porosity stayed constant. The hydrocarbon zone is between (2358.5 &
2338m), below this zone is the water zone. The oil-water contact is at 2362.5m.
13. w
n m
S
aRw
Rt
IV-Rw, Sw Calculations
To start with, ten points will be selected in all. Five points from the clean water zone while
five points will be selected from the hydrocarbon zone. The selected point from the clean
water zone will be utilized in computing the water resistivity. Since the water saturation in
the water zone = 1, we modify the Archie’s equation as follow. So from Archie’s equation
Where m=n=2
Rw = Ө2
eff*Rt.
Points Depth(ft)
Fluid
type
ρb
(g/cc)
Ө
(%)
Өeff
(%)
Rt
(Ω-
m)
Rw
(Ω-m)
Sw
(%)
Sh
(%)
1 2366 Water 2.36 12.61 17.2 8 0.2366 1 0
2 2370 Water 2.3 11.05 18.2 6.5 0.2153* 1 0
3 2375 Water 2.3 13.20 20 6 0.24 1 0
4 2380 Water 2.43 9.58 13.9 8 0.1545 1 0
5 2385 Water 2.44 13.13 14 5 0.098 1 0
6 2340 Oil 2.43 8.27 13 290 0.2153 0.209 79.04056
7 2345 Oil 2.37 12.04 17 550 0.2153 0.1163 88.36164
8 2350 Oil 2.43 11.42 14.9 450 0.2153 0.1468 85.31988
9 2355 Oil 2.35 12.56 18 620 0.2153 0.1035 89.6473
10 2360 Oil 2.35 13.25 18.2 140 0.2153 0.215 78.45301
Sw and Sh Calculation Table
The selected water resistivity is 0.2153 Ω-m and we used that to compute the
hydrocarbon saturation in the hydrocarbon zone.
14. P
oi
nt
s
Depth(m) Fluid type HART HDI RXOZ
1 2366 Water 8.1316 33.9277 1.9867
2 2370 Water 7.3878 31.1953 1.8210
3 2375 Water 6.9908 30.3953 2.0684
4 2380 Water 8.8547 27.1406 2.3739
5 2385 Water 4.6607 32.7503 1.2061
6 2340 Oil 1099.0272 26.3145 6.4606
7 2345 Oil 739.3747 25.1674 4.8338
8 2350 Oil 586.6102 27.4814 4.2098
9 2355 Oil 654.2325 26.1207 4.7172
10 2360 Oil 171.0135 27.2354 2.9407
HART and HDI and RXOZ Calculation Tabl
The HDI (diameter of invasion) is almost constant; a little bit lower in the oil zone, but it
is higher in the reservoir rock than any where else. RXOZ are higher in the oil zone.
V- Conclusion:
In this project, the process of interpreting a log has been done. Started with a quick DQC
of the curves involved in the log, the invalid curves has been identified. The next step
was to do a general zoning of the log so that the lithology of each zone can be determined
and hydrocarbon zone can be seen (zone 6). Then by taking into account 10 points from
clean zone, the hydrocarbon saturation is calculated and the result is averagely 84.16%.
