Post on 16-Apr-2015
description
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 1
The Petrophysical Characteristics and their Effect on the Reservoir Fluids for Mheiherrat Formation at the Central Part of
the Gulf of Suez, Egypt
M.Ghorab
Egyptian Petroleum Research Institute
ABSTRACT
The present work for determined the petrophysical characteristics of the
Mheiherrat Fomation which is formed generally of carbonates and other case from
sandstone. These include twelve wells (HH 84-1, GG 85-1, WFA-1, WFB-1, GS
216-1, GS 206-1A, GS 207-1A, GS 197-2, GS 196-1A, TANKA-1, TANKA-3 and
TANKA-4) were selected for applying the present technique of the reservoir
performance for Mheiherrat Formation in the considered area.
In this respect, shale volume is needed for correcting the porosity
and water saturation results for the biased effects of shale. It is considered as
an indicator of reservoir quality, in which the lower shale content usually reveals
a better reservoir.
These petrophysical parameters (Фe, Vsh, Sw, Swir, Swre, Sh, Shr and
Shm) are represented horizontally in the form of iso-parametric maps to illustrate
their areal distribution within the evaluated formation across the area of study. The
result of this study illustrate that, the hydrocabon quality increases gradullay
outward the area of study where the movable hydrocarbon shows low content
where it varies from 0% to32% at GS 216-1 well.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 2
INTRODUCTION Mheiherrat Formation in WFB-1 well possess many sandy dolomite
intervals. These intervals are composed of dolomite, sandy dolomite, grading into
sandstone. It contains quartz and feldspars with shale intercalation. The dolomite
is sandy and glauconitic with local vuggy porosity. The resistivity curves are
deflected towards high levels with positive separation. The glauconite is
prevailing in these intervals. The limestone of this formation is dolomitic, sandy
and shaly in parts. In some limestone intervals, the glauconite is present. The
marl is light gray, silty, calcareous and grading to limestone. A thick sandstone
bed is also present in GS 207-1A well. It is described as white, light brown, fine
grained, subrounded-subangular, poor to fair sorting, high matrix/grain ratio, highly
calcareous, grading into high sandy limestone and occasionally glauconitic with
yellow florescence ,figure( 2 ).
The core description for limestone and sandy limestone intervals in GS
207-1A well is as follows: the limestone is gray, with no visible porosity,
glauconitic slightly sandy with no oil shows. The sandstone streaks is highly
calcareous. Dark brown oil strains (OSTN) are reported in many sandy limestone
streaks, described as well sorted and slightly pyritic.
1- Shale Volume Determination:
The shale content is determined using different shale indicators, the
minimum of all these methods has been used in this interpretation. The following
methods were used to define the shale volumes in the present work.
1- Gamma-Ray Method: Gamma-ray log is considered one of the best tools used for identifying and
determining the shale volume. This is principally due to its sensitive response for
the radioactive materials normally concentrated in the shaly rocks. The following
equation is used to determine the shale volume:
IGRGR GRGR GR
=−
−log min
max min (1)
Where: IGR is the Gamma-ray index,
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 3
GRlog is the Gamma-ray reading for each zone, and
GRmin and GRmax are the minimum Gamma-ray value
(Clean sand or carbonate) and the maximum Gamma-ray
Value (shale), respectively.
Then, the shale volume can be calculated from the Gamma-ray index, by
the following formulae (Dresser Atlas, 1979).
1- Older rocks (Paleozoic and Mesozoic), consolidated:
Vsh = 0.33 [2(2 x IGR) − 1.0] (2)
2- Younger rocks (Tertiary), unconsolidated:
Vsh = 0.083 [2(3.7 x IGR) − 1.0] (3)
Accordingly, the second formula was applied in the present work.
2- Neutron Method: It can be used in case of high clay content and low effective porosities,
from the formula:
VNN
Xshsh
≤ =( )( )
logΦ
Φ (4)
Where: (ΦN) log is the neutron log reading for each studied zone,
and (ΦN)sh is the neutron log reading in front of a shale
zone.
3- Resistivity Method: It can be utilized to calculate the shale volume in case of high clay contents
and low (Rt) values from the relation:
V RRtsh
sh≤log
(5)
If this ratio is more than (0.5) (i.e., 0.5 ≤ Vsh ≤ 1), then:
Vsh ≤ (Rsh / Rt) = X (6)
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 4
If this ratio is less than (0.5) (i.e., Vsh ≤ 0.5), then:
VRRt
R RtR R
Xshsh cl
cl sh≤ −
−
−
⎡
⎣⎢⎢
⎤
⎦⎥⎥
=log
log/B1
(7)
Where: Rsh is the resistivity of a shale zone,
Rcl is the resistivity log reading for a clean zone,
Rtlog is the resistivity log reading for each zone, and
B is a constant, ranging in value between 1 and 2.
B-2-2- Correction of Shale Volume: The value of (X) obtained previously must be corrected by valid formula to
obtain the optimum value usable in the log interpretation.
The first formula is:
V Xsh = − − +17 3 38 0 7 2. . ( . ) (Clavier et al., 1971) (8)
The second formula is:
V XXsh =
−0 515
..
(Steiber, 1973) (9)
Then the different zones were classified into clean, shaly and shale zones
according to the following bases:
- If Vsh < 10 % This means clean zone,
- If Vsh from 10 to 35 % This means shaly zone, and
-If Vsh > 35 % This means shale zone.
ISO-PARAMETRIC MAPS OF SHALE FOR MHEIHERRAT FORMATION:
The shale percentage map (Fig. 14) illustrates an increase of shale content
in the southeastern and northwestern parts of the area which, reaches its highest
value of 30% at GG 85-1 well in the south eastern corner of the studied area while
it decreases to 7% at TANKA-4 well locality in the southwestern part.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 5
2- Porosity Determination:
Porosity is the volume of non-solid portion of the rock that is filled with
fluids, as divided by the total volume of the rock. Primary porosity is the porosity
developed during the original sedimentation process by which the rock is created.
Porosities in the reservoir rocks usually range from 5 % to 30 %, in which
the porosity of carbonate rocks is somewhat less than that of sandstones. In
general, porosities tend to be lower in deeper and older rocks due to the
cementation and overburden pressure stress on the rock. Shale porosity
decreases more with depth than sand, this is because the shale is compressed
more easily than sand. These basic trends of porosity changes vs. depth are not
noticeable clearly in the carbonates as compared to the sandstone and shale,
where porosity is more affected by the depositional environments and secondary
processes, both unrelated to the depth of burial.
Secondary porosity is created by processes, which synthesize vugs or
coverns in rocks by ground water (Crain, 1986). In most cases, secondary
porosity results in such higher permeability than primary granular porosity.
However, the porosity derived directly from logs without correction for shale
content is termed apparent or total porosity. In a zone of no shales, the total
porosity in this case equals the effective porosity.
2-1- Total Porosity (Φt):
• Porosity from One-Log Method. It can be determined from the sonic, density and neutron logs, in both clean
and shaly zones.
1-Porosity From Sonic Log: The total porosity can be diversified, according to the clean and shaly
zones.
a- In Clean Zones:
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 6
In the shale free formations, the determination of the total porosity depends
on Wyille’s et al. (1958) formula as:
ΦΔ Δ
Δ ΔSma
f ma
T TT T
=−
−log (10)
If the compaction factor is considered, then:
ΦΔ Δ
Δ ΔSma
f ma
T TT T CP
=−
−×log 1 (11)
In such a case: CPT Csh=
×Δ100
(12)
where: C is a constant normally equals 1.0 (Hilchie, 1978).
b- In Shaly Zones: In the shaly formations, the total porosity is determined from the formula of
Dresser Atlas (1979) as:
ΦΔ Δ
Δ ΔΔ ΔΔ ΔS
ma
f mash
sh ma
f ma
T TT T CP
V T TT T
=−
−×
⎡
⎣⎢
⎤
⎦⎥ −
−−
⎡
⎣⎢
⎤
⎦⎥
log 1 (13)
2-2-Porosity From Density Log: a- In Clean Zones:
The porosities derived from density log (ΦD) are calculated from the
relation:
ΦDma b
ma f=
−−
ρ ρρ ρ
(Wyille, 1963) (14)
where: ρma is the matrix density.
b- In Shaly Zone: According to Dresser Atlas (1979), as follow:
ΦDma b
ma fsh
ma sh
ma fV=
−−
⎡
⎣⎢
⎤
⎦⎥ −
−−
⎡
⎣⎢
⎤
⎦⎥
ρ ρρ ρ
ρ ρρ ρ
(15)
where: ρsh is the shale zone density.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 7
2-3-Porosity From Neutron Log: Neutron logs give directly the porosity values on the log track in clean
formations. Correction of the log data for the different factors affecting it must
be taken into consideration. These factors include bore hole size, mud cake
thickness, borehole and formation water salinities, pressure and temprature.
However, the CNL neutron log in the usable data is designed to minimize the
effect of the borehole parameters (Schlumberger, 1989). If shales intervene,
their effect must be corrected through the following equation:
ΦNc=ΦNlog-VshxΦNsh (16)
Porosity from Density-Neutron Combination:
The combination of neutron and density is considered as a good
approach for calculating the comparable porosity in clean and shaly zones.
1- in clean zones:-
Φ(N-D)= ΦN+ΦD/2
(17)
2- 1n shaly zones:
Φ(N-D)=√(ΦNc2+ΦDc
2)/2 (18) where:
Φ ΦΦ
NC NNsh
shV= − ⎡
⎣⎢⎤
⎦⎥× ×
0 450 30
.. (19)
Φ ΦΦ
DC DNsh
shV= − ⎡
⎣⎢⎤
⎦⎥× ×
0 45013
.. (20)
For clean and shaly zones, the values of porosity obtained from sonic,
density, neutron logs and the dia-porosity density-neutron methods are termed
ΦS, ΦD, ΦN and ΦD-N respectively, and their average (Φt) is calculated for each
zone to get the optimum total corrected porosity value .
\ISO-PARAMETRIC MAPS OF POROSITY FORMHEIHERRAT FORMATION:
Generally the porosity distribution of Mheiherrat Formation decreases
gradually southeastern ward (Fig. 15) in which the minimum porosity value is (9%)
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 8
is represented at WFB-1 well in the southeast part till reaches its maximum value
(31%) at TANKA-4 well.
3- Determination of Fluid Saturation:
This part exploits the formerly deduced petrophysical parameters to
calculate the fluid saturation and to complete the information needed about the
reservoir characters. The determination of the fluid saturation involves principally
the discrimination between the various fluid components (water and
hydrocarbons) filling up the pores of the flushed and uninvaded zones.
3-1- Calculation of Rock Variables and Exponents: -
The rock variables and exponents include the cementation
factor "m", the saturation factor "n" and the tourtosity exponent "a". The
importance of these factors lies in the need for the optimum estimation
of the total water saturation. In the present work, Pickett's method
(1963) was utilized for calculating these parameters.
The Pickett crossplot can provides some useful information on
formation characteristics. This plot utilizes a basic rearrangement of the Archie
equation,
Swn = aRw / Φm Rt
(21)
logRt = -mlogΦ + log(aRw) - nlogSw, (22)
if Sw = 100% this reduces to:-
logRt=-mlogΦ+log(aRw) (23)
this is a straight line plot on log-log grid for Rt Vs Φ where Y= mx+b is the
equation of a line. The slope of the 100% water saturation line determine "m"
whereas the value of "aRw" is derived from the intercept of such a line with the
porosity axis at Φ = 1, of course if Rw is known "a" can be calculated, as shown in
Fig. (6). A crossplot of this type works best in clean formations of a resonably wide
porosity range and constant Rw in the zone, (figures from 3 to 13) contains the
Pickett's plot of Mheiherrat Formation for the study area.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 9
Data from the studied wells are averaged for each formation to
obtain a good value of "a" and "m". The porosity exponent "m" equals the
saturation exponent "n", as shown by Pickett (1973). Table (1) shows the different
values for these parameters and their average values for each formation in the
studied wells.
TABLE (1) THE ESTIMATED VALUES OF THE EXPONENTS "a" and "m"
FOR THE STUDIED FORMATION IN THE DIFFERENT WELLS.
GS
197-2
GS
216-1
GS
207-1A
TANKA
-4
TANKA
-3
GS
206-1A
GG
85-1
GS
196-1A
WFA
-1
WFB
-1
TANKA
-1
HH
84-1
AVERAG
E
.1 87 83 .1 .2 .1 66 96 73 68 .3 96
MH
EIIH
ER
.5 .1 .3 .0 .4 .2 .2 .4 .3 .0 .1 .2
3--2- Water Saturation:
1) Uninvaded Zone Water Saturation (Sw):
Archie’s formula was chosen to determine the water saturation (Sw) in the
clean zones, on the other hand, the average of Simandoux equation (1963) and
Schlumberger equation (1972) was used for the shaly zones.
a- Clean Zones : The uninvaded zone water saturation determination from resistivity logs in
the non-shaly formations with homogeneous inter-granular porosity is based on
Archie's equation (1942), as follows:
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 10
S a RRw m
w
t
n
= ×⎡
⎣⎢
⎤
⎦⎥Φ
1/
(24)
Where: Φ is the formation porosity,
a is the tortuosity factor .
m is the cementation factor . and
n is the saturation exponent.
b- Shaly Zones : It is determined utilizing the average of the Simandoux and Schlumberger
equations, shown as fallows:
Simandoux method 1/Rt = ((Vsh/Rsh)Sw) +( (Φm/aRw)Swn) (25)
• Schlumberger equation
1 1 2 22
RV
R aRS
t
shV
sh
m
ww
nsh
= +⎡
⎣⎢⎢
⎤
⎦⎥⎥×
−( / ) //Φ (26)
where : Rsh is the resistivity of a thick shale unit.
2) Flushed-Zone Water Saturation (Sxo):
The estimation of Sxo is essential for the definition of the residual
hydrocarbon saturation (Shr) in clean and shaly zones.
The flushed zone water saturation is determined as follows:
a) Clean Zones: It is calculated using the Archie's equation (1942), as follows:
S a RRxo m
mf
xo
n
= ×⎡
⎣⎢
⎤
⎦⎥Φ
1/
(27)
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 11
b) Shaly Zones: It is determined utilizing the average of the Simandoux and Schlumberger
equations, shown as fallows:
Simandoux method :1/Rxo=((Vsh/Rsh)Sw)+((Φm/aRw)Swn)
(28)
Schlumberger equation: 1 1 2 22
RV
R aRS
xo
shV
sh
m
mfxo
nsh
= +⎡
⎣⎢⎢
⎤
⎦⎥⎥×
−( / ) //Φ (29)
3- Irreducible Water Saturation:
It is a thin film of water around the grains of rocks, which can not
be move out with oil or water. It can be estimated by crains method
(1986) from the general formula:
Swir=(ΦtxSw)/ΦE (30)
B-4-3- Hydrocarbon Saturation:
The hydrocarbon saturation is calculated through the formula:
Sh = 1 − Sw (31)
Such hydrocarbons are normally differentiated into their residual (Shr) and
movable (Shm) habitates, as shown:
Shr = 1 − Sxo (32)
Shm = Sh − Shr (33)
ISO-PARAMETRIC MAPS OF MHEIHERRAT FORMATION:
The water saturation map (Fig. 16) shows that, the water proportion attains
its maximum value of 81% at TANKA-3 well and the minimum value of 48% at GS
196-1A well localities. The irreducible water map Fig. (18) illustrates generally
high irreducible water component with general trend of increasing towards the
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 12
central part of the area. The reducible water type increases in the opposite
direction of the irreducible one as shown in Fig. (19).
The hydrocarbon saturation map (Fig. 17) reveals its maximum record of
52% at GS 196-1A well and the minimum value of 19% at TANKA-3 well with a
general trend of increasing towards the northeast direction in the opposite
direction of the water saturation trend for that body. The residual hydrocarbon is
generally higher than the movable one that increases gradually towards the north
direction (Fig. 20). Figure (21) reflects that the movable hydrocarbon increase to
the east of the study area, which varies from 25% at WFB-1 well in the east of the
study area to 0% at TANKA-4 well in the west.
Total Porosity Distribution Map of Mheiherrat Member:
Generally, the porosity distribution of Mheiherrat Member decreases
gradually southeasternward (Fig. 14), in which the minimum porosity value (9%) is
represented at WFB-1 well in the southeastern part, till reaches its maximum
value (31%) at TANKA-4 well.
SUMMARY AND CONCLUSIONS The present work deals with the computerized well-log analysis for twelve
wells (HH 84-1, GG 85-1, WFA-1, WFB-1, GS 216-1, GS 206-1A, GS 207-1A, GS
197-2, GS 196-1A, TANKA-1, TANKA-3 and TANKA-4.), which are distributed in
the centeral part of the Gulf of Suez, Egypt. Such an analysis was carried out for
Mheiherrat Formation selected in the Lower Miocene sequence. These formation
are very important from the point of view of the petroleum exploration in this
province.
The available open-hole well-log data, used in the analysis of these unit,
are in the form of resistivity logs (deep and shallow), porosity tools (density,
neutron and sonic) and the gamma-ray log. Added, the composite logs and other
geologic data are given for the geological interpretation of the deduced
petrophysical model of the studied area. A qualitative interpretation for the
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 13
composite logs was done to get a preliminary idea about the lithology, porosity
and fluid saturations of the evaluated units.
Well-log system, followed, is started by the determination of the formation
temperature, then correcting the fluid and rock resistivities to the actual
temperature at correspondence depth and also the other environmental
corrections.
The shale percentage is increase in the southeastern and northwestern
parts of the area which, reaches its highest value of 30% at GG 85-1 well in the
south eastern corner of the studied area while it decreases to 7% at TANKA-4 well
locality in the southwestern part.
Generally the porosity of Mheiherrat Formation decreases gradually
southeastern ward in which the minimum porosity value is (9%) is represented at
WFB-1 well in the southeast part till reaches its maximum value (31%) at TANKA-
4 well.
The water saturation of Mheiherrat Formation shows that, the water
proportion attains its maximum value of 81% at TANKA-3 well and the minimum
value of 48% at GS 196-1A well localities. The irreducible water map of
Mheiherrat Formation shows high irreducible water component with general trend
of increasing towards the central part of the area. The reducible water type
increases in the opposite direction of the irreducible one .
The hydrocarbon saturation map of Mheiherrat Formation shows reveals
its maximum record of 52% at GS 196-1A well and the minimum value of 19% at
TANKA-3 well with a general trend of increasing towards the northeast direction in
the opposite direction of the water saturation trend for that body. The residual
hydrocarbon is generally higher than the movable one that increases gradually
towards the north direction .The movable hydrocarbon increase to the east of the
study area, which varies from 25% at WFB-1 well in the east of the study area to
0% at TANKA-4 well in the west.
However, it can be concluded that, the reservoir quality increases to the
east direction .
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 14
REFERENCES
Archie, G.E. (1942): "The Electrical Resistivity Logs as an Aid in Determining Some Reservoir Characteristics ";
Trans. AIME. \/01. 146.P.54- 67
Clavier, C., Huyle, W.R. and Meunier, D. (1971) : Quantitative Interpretation of
T.D.T. Logs; Part I and II, Journal of Petroleum Technology, No. 6.
Crain, E.R. (1986) : The Log Analysis Hand Book; Penn-Well, Publ. Co., Tulsa,
Oklahoma, U.S.A.
Dresser Atlas (1979) : “Log Interpretation Charts”; Houston, Dresser Industries,
Inc.
Hilchie, D.W. (1978) : “Applied Open Hole Interpretation”; Golden Colorado, D.W.
Hilchie, Inc.
Hilchie, D.W. (1982) : “Advanced Well Logging Interpretation”. Golden Colorado,
D.W. Hilchie, Inc.
EGPC (Egyptian General Petroleum Corporation) (1996) "Gulf of Suez oil fields (A comprehensive Overview)" EGPC, Cairo: 387.
Pickett, G.R; (1963): "Acoustic character logs and their applil:ation in formation evaluation"; Jour. Pet Tech., Trans.. AIME. Pickett,G.R. (1973):" Pattern recognition as a mean of formation evaluation". Paper presented at the 14th Annual logging Symposium. SPWLA, May.P.6-9. Schlumberger (1972) : “The Essentials of Log Interpretation Practice”,
Schlumberger Publication.
Schlumberger (1974) : “Log Interpretation, Volume II, Application”; Paris, France.
Schlumberger (198 7) : “Log Interpretation Manual”.
Schlumberger Ltd, (1989) : Log Interpretation Principles and Applications.
Simandoux, P.(1963) "Mesures dielectriques en milieu poreux, application a mesure des saturation en eau, etude du comportement des massifs argileux. revue de I institut francais du petrole", supplementary issue.
Steiber, R.G. (1973) : “Optimization of Shale Volumes in Open Hole Logs”; Jour.
Pet. Tech.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 15
Wyllie, M.R.J. (1963) : “The Fundamentals of Well Log Interpretation”; New York
Academic Press.
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 16
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 17
HEIHER
HEIH
FIG. (2) GENERALIZED STRATIGRAPHIC COLUMN
OF THE GULF OF SUEZ. (after EGPC,1996)
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 18
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 19
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 20
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 21
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 22
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 23
BALWOIS 2010 – Ohrid, Republic of Macedonia – 25, 29 May 2010 24