P98-O8
The Effect of Trapped Critical Fluid Saturations
on Reservoir Permeability and Conformance
D.Brant Bennion, F. Brent Thomas, A.K. M. Jamaluddin, T. Ma
Hycal Energy Research Laboratories Ltd.
Junel998CIMATM
Abstract
Hysteretic effects refer to dte difference between relative
penneability and residual saturation values as a given fluid phase
satW'ation is increased or decreased. The difference between
initial, trapped, mobile and irreducible saturations are clarified.
Hysteretic effects can impact a number of reservoir production
scenarios in both favourable and unfavourable fashions.
Hysteretic effects can operate positively in such processes as
anti-water ooning technology (A W AT), mobility control in
cyclic projects, such as a water alternating gas treatment or
cyclic dtermal stimulation operations, or in heterogeneous
carbonates in a process known as the successive displacement
process (SOP). Adverse effects include phase trapping and
aitical vs trapped saturation hysteresis effects. Discussion on
die favourable use ofhystaetic effects for conformance control
processes, such as gas or water shut-off, are also presented.
Introduction
The concept of relative permeability was introduced to
modify DarciesLaw, describingsingle phaseflow in a porous
media, for the extremely complex multiphase flow effects
occurringwhenmorethan a singleimmisciblephaseis present.
Relative penneability values strongly control the flow
mechanics,pressureand productionresponseof virtually every
producing oil or gas property and. therefore, a proper
understandingof how they are influenced is important in the
processof reservoiroptimization. Relative penneabilitiesare
expressedas functionsof water (for water-oil systems)or total
liquid saturation(for gas-liquid systems),and have beenwelt
documentedin the literature! to be strong functions of such
parameters as pore system geometry and tortousity2,
wettability1,4,S,initial phase saturations6, temperature7,viscosity
of fluids', interfacial tension9 and hysteresis effectslO,II,12.
What is Hysteresis?
Hysteresis refers to the directional saturation phenomena
exhibited by many relative permeability and capillary pressure
curves. In many porous media, relative penneability values are
a non-unique function of saturation, having different values
when a given phase saturation is being increased than when it is
being reduced. This phenomena is illustrated for an oil-water
casein Figure 1. Commencing with a condition of 100% water
saturation ("A"), an oilflood is conducted. reducing die water
saturation to point "B" along relative penneability pad1A-B. In
a water-wet porous media, this process is often referred to as
primary drainage (drainage referring to a process where die
wetting phase saturation is being reduced). Reflooding with
water, referred to as an imbibition process in a water-wet porous
media (a situation where the wetting phase saturation is being
increased), we move to point "C" along relative permeability
path B-C. It can be ~
that the initial condition of 100% water
saturation is not re-achieved due to capillary trapping, resuhing
in a residual oil saturation being obtained. A subsequent
drainage watertlood (C-B) results in different relative
penneability paths being traced, in comparison to the equivalent
imbibition process (B-C).
This phenomena is known as
hysteresis. In general, hysteresis is more pronounced in the
non-wetting phase than in the wetting phase, but may occur in
both phases with up to two orders of magnitude difference in
relative permeability at equivalent saturations being observed.
In most cases, the relative permeability for a given phase is
greater when its saturation is increased rather than decreased.
This phenomena can be used to advantage in situations such as
1
mE
EFFECT
OF
TRAPPED
CRmCAL
FLUID
SA
nJRA
1lONS
a cyclic stearn injection process, since it will enhance oil
mobility and retard high water production rates on a return flow
cycle.
Two dominant mechanisms cause die saturation hysteresis.
In die primary and secondary drainage case, a portion of die
hysteresis is due to die disparity between die initial condition of
1000/0water saturation and die trapped irreducible oil saturation.
This is commonly refelTed to as trap hysteresis. The difference
in relative penneability curves caused by die motion between die
same endpoint saturation states is due to microscale hysteretic
effects, or sometimes called drag hysteresis. It is believed to be
primarily due to a phenomena known as contact angle hysteresis.
Contact angle hysteresis is pictorially illustrated in Figure 2. It
refers to die fact that, as immiscible interfaces advance in a
porous media, die effective angle of die advancing interface,
which is related by wettability and capillary dynamics to die
relative ease of the fluid displacement in die porous media, is
diff~t
between advancing and receding phaseconditions. This
difference, which appears to be a Strong factor of die degree of
surface roughness and tortuosity which exists in die system. is
believed to be die root cause of hysteretic microscale relative
penneability effects.
To further complicate the issue, not only is the relative
permeability value a function of the direction of the saturation
changes, it is also a strong function of the terminal saturation
endpoint reached before the direction of the saturation reversal
occurs. This is illusb"ated in Figure 3. It can be seen that the
relative penneability path, if a saturation reversal occurs at an
intermediate saturation level (and not an endpoint saturation),
will result in the relative penneability curves tracing intemIediate
paths between the secondary drainage and imbibition curves
called a scanning curve. Since these curves have virtually an
infinite number of values, measurement would be expensive and
technically difficult. They are usually detennined using
analytical models such as those developed by Killough'}.
Saturation Definitions
To provide a discussion on hysteretic effects, a proper
definition of a number of commonly confused saturation
conditionsis ~~ry.
Inilial Fluid Saturalio1lS. This represents the hue fraction of the
rock actually occupied by oil, gas and water at initial reservoir
conditions. There are a number of methods for detennining
these values'4, which are crucial to proper evaluation of relative
permeability. It should be noted that the initial saturation
conditions do not, in many situations, represent the irreducible
saturation conditions with which they are often confused. In
some reservoirs, the initial water, gas, or condensate saturation
may exist at some value which is considerably less than the
irreducible or mobile value's (Figure 4).
ON
RESERVOIR
PERMEABn.IrY
-
AND
---
CON
FORMANCE
P98-O8
---
--
Critical Fluid Saturations. This represents the minimum phase
saturation which must occur when the minimum phase saturation
is being increased the first time such that connectivity of the
phase is established and fmite relative permeability exists, so
that the phase can begin to flow in the porous media. This should
not be confused with the trapped or irreducible saturation.
Examples of a critical fluid saturation would be the point of first
free gasmobility in a sub- bubblepoint depleted black oil system,
the point of first liquid hydrocarbon condensate production in a
sub-dewpoint reb"ogradecondensate gas system, or the point of
fIrSt water production as water saturation is increased in a
desiccated or subirreducible water saturation system (Figure 4).
Trapped or Irreducible Fluid Saturation. This represents d1e
saturation value obtained when a fluid saturation is reduced from
a large mobile value to an immobile value. This is also d1e
irreducible saturation as is commonly detennined from a primary
drainage capillmy pressure test or a waterflood to ultimate 8M
(Figure 4).
Mobile Fluid Saturation. This value is subtly different from the
critical saturation as it is the value to which the saturation must
be increased after a b'apped or iITeducible saturation is obtained
by a displacement process. The value is generally identical to (in
an ideal situation) or larger than the b'apped or irreducible
saturation (Figure 4).
How Hysteretic Effects Can Affect Reservoir Confonnance
and Production
Hysteretic effects may positively or negatively influence
reservoir performance.Some examplesof each situation are
given for illustrative purposes.
Positive Effects
Mobility Control. Hysteretic relative permeability effects have
often been used as a mobility control agent to preferentially
reduce d1e mobility of one phase over another to achieve
superior conformance control and ultimate sweep efficiency,
particulary in the presence of adverse viscosity ratios. A prime
example of this technology is the water alternating gas treatment
or WAG process used to reduce the mobility of injected gas in
a horizontal gas injection project. The interfering effects
between the gas and liquid phases are used to selectively retard
the speed of gas migration. Since the water, due to its higher
viscosity, tends to preferentially channel into the higher
penneability channels of the reservoir, it tends to screen off
these better quality zones and selectively reduces the
permeability to gas. Due to hysteresis and mobility effects, it is
more difficult for the gas to displace the water from this zone
than to be preferentially redirected into zones of lower
penneability, which tends to improve the overall conformance
and sweep efficiency of a horizontal gas injection project,
particularly in thick pay zones or zones containing highly
p.B. BENNIONF.LrnoMAS A.K.M~D~
T. ~
variablepermeabilityor high penneabilitystreaks(Figure 5)
(i.e. 5% water, 95% oil)
Water Coning Reduction. Hysteretic relative penneability
effects are the basis of anti-water coning technology used in
some heavy oil reservoir situations. Due to the extremely
adverse viscosity ratio between many heavy oils and active
bottom water present in some of these systems, rapid water
coning, high water cuts and marginal or \meconomic production
occurs. It has often been found in such situations that the
presence of a mobile gas phase saturation appears to
preferentially reduce the water phase penneability over the oil
phase pemteability. This tends to selectively reduce the water
cut, and may improve the economics of a marginal well by the
simple injection of a slug of inert gas in the near wellbore
region. A particular application of this tedmology was patented
in the 1980's by the Alberta Oil Sands Technology Research
Authority (AOSTRA) under the trade name A W AT (Anti-Water
Coning Technology). Figure 6 provides an iUustrative set of
gas-water relative penneability curves showing the basis for this
Figure 8(b) Immiscible gas cap encroachment as gas injection
for pressure support continues. This results in stable gravity
drainage of oil, in some cases down to fairly low oil sablration
values of20-2S%. This establishes a roDe of high gas saturation
in d1egravity drained rone.
technology.
Enhanced Cyclic Production. The use of a simulation model
with hysteretic relative permeability capability is sometimes the
only method of accurately predicting the perfOmlance of some
cyclic projects, particularly cyclic steamfloods in heavy oil
applicationsl6. This is illustrated in relative penneability curves
as pictured in Figure 7. It can be seen that the higher water
phase relative penneability on the water injection cycle aids in
increasing the ease of injectivity of the hot water and steam
condensateinto the fonnation. The lower oil phasepermeability,
as its saturation is being reduced, allows the hot water/steam to
bypass some oil and penetrate deeper into the formation which
improves the contact and size of the heated zone. Conversely, on
the production cycle, oil production rate is enhancedas the water
mobility is reduced, since its saturation is being reduced, and the
oil phase relatively permeability may be significantly increased.
This results in enhanced production of oil rather than rapid
production of the less viscous water phase.
Successive Displacement Process (SDP). The successive
displacement process is a recently researched process which
appears to utilize saturation hysteresis effects as a basis for
enhanced oil production as a by-product of an immiscible gas
and water displacement process. The mechanism is not entirely
understood, but is pictorially illustrated in Figures 8(a) to 8(d).
The prime application for the SOP has been observed in vertical
displacements in heterogenouscarbonate formations with strong
bottom water drives with immiscible gas injection projects for
pressure support. The mechanism of the process is illustrated as
follows:
Figure 8(a) Initial saturation conditions. The oil wet carbonate
media. generally a reef type sb"Ucturewith considerable vertical
relief, exhibits oil wet behaviour with a low initial water
saturation encapsulated in the central portion of the pore system
Figure 8(c) Gascap b/owdown and oil sandwich displacemenJ.
The depressurization of the gascap results in the active aquifer
displacing up a sandwich of unrecovered oil from the baseof the
reservoir. As the oil bank penetrates the highly gas saturated
zone, hysteretic saturation and relative penneability effects result
in a very high trapped gas saturation (generally in excess of
500/e)being retained in the oil encroached zone.
Figure 8(d) Aquifer encroachment. Following the displaced oil
sandwich is the active water front. Due to the high trapped gas
saturation. die encroaching water appears to be redirected by
hysteretic relative penneability effects to peneb"ateportions of
the pore space not previously accessedduring the gas drainage
process. This results in a measurable reduction in die residual oil
saturation (to perl1apsas low as 100/0)over that obtained during
the conventional gasdrainage process, and represents significant
incremental recovery which may be obtained from what was
diought to be a depleted reservoir during the blowdown cycle.
This phenomenahas been documentedin a number of
reservoirapplicationsin the literature 17.18,19,20.
Negative Effects
Phase Trapping. Phase b'apping has been well documented in
the literature as a mechanism of substantially reduced
productivity in many reservoir applications20.21.Phase trapping
is causedby a combination of both adverse saturation hysteresis
effects and associated adverse relative permeability effects as
illustrated in Figure 9. Common situations where phaseb'apping
may occur are the use of water-based drilling, completion.
stimulation or kill fluids in overbalanced conditions in low initial
water saturation condition gas reservoirs or strongly oil wet oil
reservoirs (bod1 of which exhibit extremely low initial water
saturations). Hydrocarbon phase traps may be established
through the use of oil-based drilling, completion or stimulation
fluids in gas reservoir applications or retrograde condensate
dropout effects during the production of rich gas condensate
reservoirs.
MasshleCritical and TrappedSaturation Hysteresis. In some
reservoirs,dte difference between dte initial critical mobile
saturationlevel, when the phasessaturationis being increased
anddte npped saturationvalue,whenthat phasessaturationis
being reduced, can be significant. This is schematically
illustratedas Figure 10. An example would be in a black oil
depletion processwhere dtc reservoir pressureis dropped a
4
mE ~
OFTRAPP~ CRmCAL ~
SATURATK>NSON RESERVOIR
PERMEABIUTYANDCONFORMANCE
significant degree below die satwation pressure. This will result
in die liberation of a large amount of free solution gas. The
critical gas saturation will rapidly be exceeded and gas will begin
to flow but, as pressure continues to drop, die value of die
mobile gas satwation will also tend to rise. If die pressure
decline is dlen halted, and we attempt to flow back into die
highly gas saturated zone, a much higher "b'apped" gas
satl.uationdian die initial critical value will usually be obtained.
This may significantly reduce die mobility of die oil phase,
resulting in a large loss in potential productivity.
Laboratory Case Studies lIustrating Water, Gas and
CondensateTrap Phenomena
Table I provides a summary of basic water trap tests which
were conducted on two low penneability core samples which
exhibited sub-ireducible
initial
water saturations of
approximately 23%. It can seenthat a significant phasetrap was
established in the low penneability porous media by the
introduction of a non-damaging inert 3% KCI phase and 3500
kPa of dlreshold pressure was required to cause initial gas
mobilization through samples of approximately 5 cm in length.
This resulted in regain penneabilities at the original threshold
pressure with reductions ranging from 78 to 85% of the original
gas phase penneability measurements. It provides a good
indication of the severe type of damage which can be associated
wid! significant invasion depd1Sor minimal drawdown gradients
associated wid1 water-blocking phenomena that may occur in
low permeability porous media.
Table 2 provides analogous examples for d1edepletion of a
low penneability black oil reservoir. As gases evolve from
solution as pressure is effectively dropped. the b'8pped aitical
gas saturation increasesuntil the mobile critical gas saturation is
acltieved. In the higher permeability samples observed in Core
# I, it can be seen that the aitical gas saturation is achieved at a
much lower saturation value of approximately 5.5% in
comparison to the lower permeability sample suite where aitical
gas mobility was not obtained until a saturation in excess of 16%
had been physically realized. Once again, significant reductions
in apparent oil phase permeability are noted due to the
establishment and entrapment of a trapped critical gas saturation
value in the near wellbore or frac face region.
Table 3 provides a summary of the illustration of the critical
condensate saturation accumulation phenomena. It can be seen
that for the higher quality sample tested that critical condensate
saturation values and permeability reduction effects are
relatively insignificant in comparison to a similar effect observed
in lower quality porous media, where large scale reductions in
effective gas phase permeability and relatively high values of
trapped critical condensate saturation are achieved. The
permeability vs gas saturation data of Table 2 has been plotted
on Cartesian coordinates and appears as Figure 11. The
oenneabilitv vs condensate saturation data of Table 3 has been
P98~8
plotted in a similar fashionand appearsasFigme 12.
Using Hysteretic Relative Permeability EffectsforConfonnance
Control Purposes. Some examples have already been presented
as to how hysteretic relative penneability effects may influence
confonnance control. Potential applications include:
Gas Shut Off
Gas phase relative permeability may be
preferentially affected by selective b"eatmentswith an immiscible
fluid. The selective injection of water based fluid, possibly a
surfactant, into the upper portion of a high gas cut well may
result in the hysteretic trap of a higher water saturation in the
zone of high gas saturation and penneability, and result in a
transient or permanent reduction in gas-oil ratio. Inclusion of a
surfactant may generate a high viscosity stable foam system
when contact is made with zones of high gas saturation. This
will result in a large portion of the pore system which is
available for mobile gas to flow being occluded by the immobile
foam phase and, once again. result in a preferential reduction in
the gas phase penneability. Treatments of d1is type tend to be
somewhat transient in effect due to gradual degradation of the
foam system over time by adsorption (particularly in clastic
formations) and dispersion effects. This process is illustrated
schematically as Figure 11.
WaJer Shut Off Hysteretic effects can also be used to aid in
water shutoff. Reference has already been made to the A W AT
process when non-condensible gas injection is used to
preferentially reduce water cuts by a selective reduction in the
relative penneabilitY to water over the oil value. In zones
containing pure water. which cannot be readily isolated by
casing and selective completion. a similar effect can be
accomplished by the direct zone specific injection of an
immiscible non condensible gas into the water saturated zone.
This will establish a zone of high trapped gas saturation and
may. depending on the rock geometry and relative penneabilitY
characteristics. significantly reduce the inflow characteristics of
water from die affected zone. The establishment of a trapped gas
saturation in the oil saturated strata is obviously undesirable and
should be avoided as this may substantially also impair the
penneabilitY to oil.
Oil injection (although opposite of what we want to
accomplish is most producing wells) may also be an effectual
WOR reducing technique in certain situations where free bottom
water with an active drive in present. The objective of this
technique is to inject produced oil, or some other low viscosity
hydrocarbon, directly into the wet zone underneath the
producing zone. Hysteretic effects will trap an irreducible oil
saturation in this zone which may reduce the effective
permeability to water by as much as 95%, depending on the
relative permeability characteristics of the porous media.
D.B. BENNION. F.B nIOMAS. A.K.M. JAMALUDDIN. T. MA
Conclusions
3
Salathiei. R.A., "Oil Recovery by Surface Film Drainage in
Mixed Wettability Rocks", SPE 4014 presented at die SPE
47d1annual meeting, San Antonio, California, Oct 8, 1972.
4
Leach, R.O., et aI, "A Laboratory and Field Study of
Wettability Adjustment in Waterflooding", JPT, 44, 206,
1962.
s
Denenkas,N.O., "The Effect of Crude Oil Componentson
Rock Wettability", TransAIME, 216,330,1959.
6
Caudle, B.H., et aI, "Further Developments in die
LaboratoryDeterminationof RelativePermeability",Trans
AIME. 192,145,1951.
A discussion on cyclic hysteresis effects in the exploitation
of oil and gas producing properties indicates that:
Significant saturation and relative permeability hysteresis
occurs in many reservoir systems. The degree of hysteresis
is usually more pronounced in the non-wetting phase, but
may be significant in both phases.Researchstudies suggest
that the degree of hysteresis is related to the magnitude of
contact angle hysteresis which is, in turn, a function of the
amount of surface roughness in a given reservoir system.
Therefore, tight, low penneability rocks with high surface
roughness may exhibit more hysteresis than their more
unifonn higher permeability counterparts, although specific
detennination on a reservoir by reservoir system is required.
5
,. Edmonson, T.A., "The Effect of Temperature on
Waterflooding",JCPT, 10,236, 1965.
2. The differencebetweeninitial, irreducible,critical, mobile
andtrappedfluid saturationshasbeendefmed.
3.
Hysteretic effects may also reduce productivity and
increaseproblems with water and gas coning in certain
situations due to adverseeffects associatedwith "trap"
saturationhysteresisor what is morecommonly referredto
as "phasetrapping".
Acknowledgments
Theauthorswish to expressappreciationto Vivian Whiting
for assistancein the preparationof the manuscriptand figures
andto the managementof Hycal EnergyResearchLaboratories
for the funding of this work and permissionto presentthe data.
References
Honarpour,M. et ai, "Relative Penneabilityof Petroleum
Reservoirs",CRC Press,1986,Boca Raton,Florida.
2.
Arps, J.J., et aI, "The Effect of Relative Penneability Ratio,
dte Oil Gravity and dte Solution Gas-Oil Ratio on the
Primary Recovery from a Depletion Type Reservoir", Trans
AlME. 204,120, 1955.
Lefebvre du Prey, E, " Deplacements Non-Miscibles dans
les Milluex Poreux Influence des Parameters Interfaciax sur
les Permeabilities Relatives", C.R. IV Coloq, ARTFP Pau,
Hysteretic effects may be advantageous in reducing water
coning problems, gas coning problems, enhancing
production from some cyclic projects (such as steam
injection) and reducing gas phase mobility in some
processes such as water alternating gasfloods (WAG) or
co-current injection projects. Residual oil saturation may be
substantially reduced in some heterogenous carbonate
formations due to hysteretic effects in what is known as the
successive displacement process (SDP).
4.
8.
1968.
9.
Leverett, M.C., "The Flow of Oil Water Mixnua Through
Unconsolidated Sands", Trans AIME, 132,149, 1939.
10. Geffen, T.M., "ExperimentalInvestigationof Factors
Affecting Laboratory Relative Permeability
Measurements",
TransAIME, 192,99,1951.
Osaba,J.S.,"The Effect ofWettability on Rock Oil-Water
Relative Penneability Relationships", Trans AIME,
192,91,1951.
12. Donaldson.E.C.. "MicroscopicObservationsof Oil-Water
Displacementin WaterWet andOil Wet Formations". SPE
3555.Presentedat die 46th annualSPE fall meeting.New
Orleans.Oct 3-6. 1971.
13. Killough, J.E. et aI, "Reservoir Simulation With History
DependentSaturationFunctions", Trans SPE of AIME,
261, pp. 37-45.
14. Bennion. D.B., et al, "Detennination of Initial Fluid
Saturations - A Key Factor in Bypassed Pay
Detennination", Presented at the PNEC 2nd annual
confermce on Profile Modification and Confonnance
Control, August, 1996,Houston,Texas.
15. Katz, D.L. et ai, "Absenceof ConnateWater in Michigan
GasReefReservoirs",AAPG Bulletin, Vol. 66, No.1, Jan.
1982.
16. Bennion,D.W., et aI, "The Effect of RelativePenneability
on the SteamStimulationProcess",JCPT, 1985.
6
mE EFFECTOFTRAPPFDCRmcAL FLUIDSATURATlONSONRESERVOIR
PERMEABD.JTY
AND CONFORMANCE
17. Batycky. J. and Irwin. D.. "Trapped Gas Saturationsin
LeducAge Reservoirs",JCPT,Feb.1998,Vol 37,No.2, pp
32.
18. Irwin, d. and Batyclcy,J., "The SuccessiveDisplacement
Process",SPERE,Nov. 1997.
19. Jensen,E.M. andGillund, G.N., "Windfall D3A Blowdown
Study", Amoco CanadaPetroleum.June 1988.
20. Bennion, D.B., et ai, "Water and Hydrocarbon Phase
Trapping in Porous Media, Diagnosis, Prevention and
Treatment",JCPT, September,1996.
21. Bennion,D.D., et ai, "Reductionsin the Productivityof Oil
and Oas ReservoirsDue to Aqueous PhaseTrapping",
JCPT,1994.
P9I-OI
Table I
Illustration of Water-Based PhaseTrap Potential
Table 2
Illustration of Oil PhasePermeability Reduction Due to
Critical Gas Saturation Accumulation
Sg
Core #1
(k.a) mD
Core #2
(k.J mD
Core #3
(k...) mD
4.51
2.86
1.99.
2.78
2.51
2.16
1.46.
0.0696
0.0672
0.0601
0.0552
0.0492
0.0312
0.0156
0.00
0.025
0.055
0.075
0.100
0.133
0.166
I. Criti~
.
gas saturation_value
Table 3
Illustration of Critical CondensateSaturation Accumulation Data
Core #1
(Gas Perm-mD)
Se
0.000
0.015
0.030
0.068
0.120
0.185
0.260
I. Critical
369.0
346.0
322.0.
condensate saturation
Core #1
(Gas Penn-roD)
0.63
0.49
0.32
0.18
0.10
0.060
0.020.
~
-
~1
1u.USTRATK>N
OF HYSTERESISEFFECTS
IN A WA1ER-~
oa...WATERDISP\ACBENT
~2
ILJ.USTRATION
OF CONTACTANGlE ~818
-
--.
-
Water SatlK8tion
~
~3
ItJ.U8TRATION OF A RElATIVE PERMEABILITY "SCANNING"
~
Water Saturatioo
:m
~4
IllUSTRATION OF VARIOUSSA~T1ON
TYPES
(Waw-Oi C- . W8t8r ~
0..,)
r
~
,J
~8
M..WSTRATK)N
OF EFFECTOF FREEGAS SATlmAOON
ON WATER& OIL PHASEIm.ATIVE ~
(AWAT)
AGme5
WAG PROCESSFOR MOBIlITY CONTROL
Water Sat\ntlon
~.
I.lUSTRATION OF THE SUCCESSIVEDISPlACEMENTPROCESS
AGURE7
ILlUSTRATIONOF CYCUC HYSTERESISEFFECTS
~ B8tANCED PRODUCTIONRATES
..
_.
1.8
~--~
~
I
-
.. .
_.
-.
~
'-..
,
0.00.0
Water Saturation
t.o
.
-
-
~
FIGURE 10
IU.USTRA T1ON OF CRITICAL AN!) TRAPPED SA TURA TION
HYSTERESIS EFFECTS
FIG~9
MECHANISMOF PHASETRAPPING
1.0
~
:c
m
~
:s
~
E
ct
~
';
~
~
~
GI
E
cf
.~
10
"i)
~
0.0
1.8
0.0
Liquid Satwation
~
,:
I
i
FIGURE
I
I
11
ILLUSTRATION OF OIL PHASE PERMEABIUTY REDUCTION
DUE TO CRmCAl GAS SATURATION ACCUMULAnON
FIGURE 12
ILLUSTRATION OF CRITICAL CONDENSATE SATURATION
ACCUMULATION DATA
~.
~
-t
.
0-"
c..a
I
o..a
'~
t~ '--c.'k
.
,...'
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.
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Sc
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f'~~ .. i r:: ~~'CC:-.C,.
iCC'C'ci~'
~13
UUSTRATION OF GAS SHt1TOFFTREATMENT