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Subsidence Caused by Fluid Withdrawal: The Need for
a SystemsApproach
Alexander E. Gurevich
1,0940MeadowglenLane,#371,Houston,TX 77042-3368;
e-mail:[email protected]
GeorgeV. Chilingarian
Departmentof Cioil Engineering,
Uniuersityof SouthernCalifurnia,UniaersityPark,
LosAngeles,California90089-2531
Firyal Bou-Rabee
Collegeof Science,
GeologyDepartment,
Kuwait Uniaersity,P.O.Box5969,Kuwait13060
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ABSTRACT
Community Health & Safety
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Current understanding of the processesinduced by fluid withdrawal
from a petroleum reservoir or aquifer is incomplete, partly becausesubsidence processesand related effects are viewed individually rather than as
part of a single, complex system. Compaction due to pressure decreasein a
reservoir or aquifer causessubsidenceof overlying formations and the
land surface. This deformation also leads to fracturing. Additional fractures can be created by pressure increasescaused by fluid injection.
Fracturing can result in upward migration of gas and other fluids, connection between adjacent reservoirs and aquifers, and changes in water composition due to the cross-flow of waters from different aquifers. Land subsidence can reduce the depth to the water table, causing seepageof water
and light hydrocarbons floating on the water table into basements of
buildings, and uplifting basementsresulting in structural damage.Usually
these processesand phenomena are studied separately; however, because
they are related, they should be jointly investigated. A conceptual outline
of the causes and consequencesof fluid withdrawal is a preliminary step
in developing a more comprehensive systems approach to the phenomena
of land subsidence. A comprehensive systems approach requires that new
techniques be developed for characterizing mechanical properties and
deformation processesof large massesof heterogeneousrocks, monitoring
changes in rock properties in the field, and developing hierarchical models
of rock deformation.
SusstogttcE
CeuseoBv FlutoWrnonnwnl
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Pressuredecline
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Community Health & Safety
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Gompactionof
reservoir/aquifer
Subsidence
Loweringof surface,
steepening
of slopes
,
J
Fracturing,
increased
permeability
Ground
lissures
l
I
I
ll erittr"deformation,
ll p"t"rr",""
t
Inducedearthquakes
ll,, t*,"r,"r tl
"*""*
structures
I
-
E
!
I
Slippage
on faults
Flowbetween
reservoirs/aquifers
Firesandblastsat
landsurface
tn
properties
of soils
Uplift& deformationof
surfacestructures
Seepageof water,oil,
and gas intobasements
Figure 1. Relation between Pressuredecline (emboldened box), compa"ction(single boxes) in reientoirs and aquifers, subsidence-related
processesoccurring in earth materials overlying_reservoir-sand
iquifers (double boies), and surfaceeffects of subsidence(shadowed
boxes).
SubsidenceCausedby Fluid Withdrawal: The Need for
a SystemsApproach
GrassrootsCoalition
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Alexander
Gurevich
Community
Health &E.
Safety
Full
Disclosure
1.0940
Meadowglen
e-mail:[email protected]
Lane,#3L7,Houston,TX 77042-3368;
George V. Chilingarian
Departmentof Cioil Engineering,Uniaersityof SouthernCalifurnia,UniaersityPark,
LosAngeles,Califurnia90089-2531
Firyal Bou-Rabee
Collegeof Science,
GeologyDepartment,
Kuwait Uniaersity,P.O.Box5959,Kuwait 13050
ABSTRACT
Current understanding of the processesinduced by fluid withdrawal
from a petroleum reservoir or aquifer is incomplete, partly becausesubsidence processesand related effectsare viewed individually rather than as
part of a single, complex system.Compaction due to pressuredecreasein a
reservoir or aquifer causessubsidenceof overlying formations and the
land surface.This deformation also leads to fracturing. Additional fractures can be created by pressure increasescaused by fluid injection.
Fracturing can result in upward migration of gas and other fluids, connection between adjacent reservoirs and aquifers, and changesin water composition due to the cross-flow of waters from different aquifers. Land subsidence can reduce the depth to the water table, causing seepageof water
and light hydrocarbons floating on the water table into basements of
buildings, and uplifting basementsresulting in structural damage.Usually
these processesand phenomena are studied separately;however, because
they are related, they should be jointly investigated.A conceptual outline
of the causesand consequencesof fluid withdrawal is a preliminary step
in developing a more comprehensivesystemsapproach to the phenomena
of land subsidence.A comprehensivesystemsapproach requires that new
techniques be developed for characterizing mechanical properties and
deformation processesof large massesof heterogeneousrocks, monitoring
changesin rock properties in the field, and developing hierarchical models
of rock deformation.
SuestoeNcE
CAUSED
Bv FluroWrrnoRRwRl:
TnENeeoFon A SvsreusAppnoRcH 479
INTRODUCTION
La n d subsidence over reserv o irs a n d
aquifers from which fluids are withdrawn is a
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ph
e n o menon known all over t h e wo rld ,
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including such countries as the United States
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of America, Mexico, Venezuela,Italy, the forFull Disclosure
mer Soviet Union, Italy, fapan, and Kuwait
(Saxena,7979; Jol'rrson, 7997; Chilingarian and
others, 1995).Fluid withdrawal causesa chain
of interrelated consequences.The immediate
result is a decreasein fluid pressurethat causes compaction of the aquifer or reseryoir and
consequent subsidenceof overlying formations and the land surface.Bending of rock
formations due to subsidenceresults in compression, extension, and sheat which lead to
fracturing of rocks,damageto well bores,and,
sometimes, to induced earthquakes.Land subsidence damages surface structures, such as
buildings, pipelines, etc. Local subsidence
su p e r p osed on an unchanged re g io n a l
ground-water-flow system reduces the depth
to the water table. This higher water table can
cause water and oil floating on the water to
seep into basements,especiallyif thesebasements were damaged by subsidence.Further
damage can be causedby uplift of basement
floors associatedwith rising water tables.
Rock fracturing allows upward migration of
fluids, especiallygas. Gas and oil from reservoirs can seep to the surface creating fire hazar d s. Saline water can contamin a t e f re s h
drinking water of the overlying aquifers.
Fissuresin the ground can very noticeably
increase infiltration of surface water into subsurface aquifers and may contaminate ground
water. In multireservoir oll/gas fields, fracturi ng ca n connect adjacent reser v o irs a n d
aquifers and influence production.
The processescausing subsidenceand the
phenomena resulting from it should be considered parts of a single system. Information
on rock properties, geologic structure, and
fluid withdrawal parametersshould be consi de r e d in subsidence inves t ig a t io n s .
Currently in the oil and gas industry, emphasis is placed on reservoir compaction and
subsidence;other facetsof the processusually
480
are ignored.A systemsapproach(fig. 1) allows
interrelations among all subsidence issues to
be considered.This allows unknown components of the system to be estimated or predicted when information may exist for only some
of the components.A systems approach may
be crucial to plan fluid production safely,to
remediate sites, and to evaluate lawsuits and
other litigation. Key details of a legal casemay
be revealedonly if the subsidenceprocessis
analvzed in its entiretv.
This paper emphajizes the importance of a
multidisciplinary systems approach to planning fluid withdrawal and estimating and
mitigating subsidence.It draws on our previous work (Gurevich, L969; Gurevich and others, 7972, 7987; Gurevich and Chilingarian,
1993),but is preliminary. In this paper we (1)
present, as fully as possible, all subsidence
phenomena/processes,consequencesrelated
to fluid removal from aquifers and petroleum
reservoirs,and the complete strucfure of their
cause-and-effectrelations, and (2) outline
media properties and methods of exploration
that are necessaryto guarantee a successful
systems approach to subsidenceand related
processesand hazards.
Not all statementsin this paper are substantiated by published information, empirical
data, or calculations.However, while we continue to arralyzethe subject in more detail for
later publication, we hope to initiate discussion of this very important topic among scientists in traditionally disparate fields.
TYPESOF DEFORMATION CAUSED
BY FLUID WITHDRAWAL
Deformations of Rocks
Pressuredecreasecauses compaction of
rocks within and immediately above and
below a reservoir or aquifer (Geertsma,1957,
7973).Becausepressure change is usually not
transmitted a great distance acrossreservoir
o r a q u if e r b o u n d a rie s , mo s t c o mp a c t i o n
occurs within the reservoir or aquifer. As a
result of compaction, the reservoir or aquifer
bottom subsides only slightly, and overlying
f o rma t io n s s u b s id e t o a g re a t e r d e g r e e .
LnNoSuesrDENcE
RESEARcH
CnsESruoresANDCURRENT
phic, and igneous rocks bonds are strong.
De f o rma t io n b e g in s e la s t ic a lly a n d i s
reversible, but soon its potential is exhausted
and irreversible, rate- and stage-dependent
deformation begins. Very slow deformation is
almost plastic; grains have enough time to
regroup, breaking and rebuilding bonds here
and there. At higher deformation rates,
microfracturing and brittle microdeformations
becomeinevitable. At still higher rates, brittle
deformation is predominant. The response of rock
Compactionof
to stress also is effected by
Pressuredecline
reservoir/aquifer
in c re a s e s in c u m u l a t i v e
deformation (deformation
stage).Rocks with different
Loueringof surtace,
mechanical properties folsteepeningof slopes
low the sequenceof deformation mechanismsdifferently. Deformation due to
pressure decreasecaused
b y f lu id wit h d ra w a l i s
rapid comparedto geologic
Brittle
deformation,
processes;
therefore,brittle
Inducedearthquakes
fracturing
deformation may constitute a very appreciablepart
of the total process.
Slippageon faults
Compaction of a reservoir or aquifer is not limited to the rearrangement
o f c o n s t it u e n t g r a i n s . I n
consolidated sandstones,
e s p e c ia lly in s a n d s t o n e s
t h a t a re h e t e ro g e n e o u s ,
Firesand blastsat
considerablecompaction
land surface
can create microfractures
a n d ma c ro f ra c t u r e s t h a t
might partially neutralize
Seepageof water,oil,
and gas into basements the decreasein permeability causedby compaction.
From the onset of compaction, deformation of
overlying formations cannot be considered purely
elastic.As has been noted
Figure 1. Relation between pressure decline (emboldenedbox), com(Gurevich and Chilingarian,
paction (single boxes) in reservoirs and aquifers, subsidence-related
processesoccurring in earth materials overlying reservoirs and 7993),data on well-bore
aquifers (double boxes),and surface effects of subsidence(shadowed deformation presented by
boxes).
Poland and Davis (7969)
Structural analysis indicates that in multireservoir oil or gas fields less permeable
rocks (cap rocks) between compacting reserGrassrootsCoalition
voirs can be damaged more than rocks in formations above the shallowest reservoir.
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Deformation
causedby compaction and
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subsidence
is
a
Full Disclosure complex process.Clastic rock
is a medium built of grains. In poorly consolidated, terrigenous rocks, grains have weak
bonds. In consolidated, carbonate,metamor-
AppRoRcn 481
THENeeoFon A SvsrEHits
SuesrorNcE
Bv FluroWrrHoRRwnL:
CAUSED
suggested that subsidencebegins gradually in
beds immediately overlying the reservoir or
aquifer whereas land surface and shallow
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for m a ti ons are unaffected. D u rin g t h is
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process, different rock beds and thin strata
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can separate,
opening existing bedding joints
a n dDisclosure
cr eating new ones (Gur e v ic h ' a n d
Full
Chilingarian, 1993).Gradually, the deformation processexpands upward. Therefore,from
the very beginning of subsidence,deformation
is not uniform in a vertical section and contains elastic, plastic, and brittle componentsin
proportions that change with time and with
the rate and total amount of deformation.
Compaction and subsidencealso depend on
the permeability of reservoir or aquifer rocks.
In poorly permeable rocks, pressure decrease
is uneven. Pressuredecreaseis greatestin the
immediate vicinity of producing wells and
lessensrapidly with distance from the well,
especially early during fluid withdrawal. The
bulk strength of rock formations overlying a
compacting reservoir or aquifer provides lateral support (bridging effect) that prevents
them from settling immediately. Land subsidence begins when horizontal extensionof the
pressure depletion zone becomesapproximately five times greater than the thicknessof
the above-lying formations (Kotov and others,
797I). Subsidence,therefore, does not take
place in the initial stage of fluid production,
but deformation due to the initial pressure
d e cr e a se can still occur. Loca l p re s s u re
decreasein the fluid changes compression of
the rock grains in the depleted volume of
reservoir or aquifer. The overburden weight is
not yet active becauseof the bridging effect,
bu t i ncrease in grain volume c a u s e d b y
decreasedfluid pressure can produce additional stress at grain contacts (effectivestress)
and causesome rearrangementand microfracturing. Pressure decreasesof more than 100
kg/ cmz are common during oil and gas production and consequent increasein effective
stress may be substantial. Becausegrains of
different minerals have different elastic moduli and becausegrain packing varies, differential stressesthat theoreticallycould develop at
grain contacts might break bonds between
482
grains and create microfractures. This preliminary deformation could increase the amount
of sand removed during initial production of
the fluid and, thus, reduce rock stressaround
the well bore and somewhat loosen the rock.
Processesactive during the early stages of
fluid production prepare the reservoir or
aquifer rocks for compaction, which begins as
soon as pressure depletion zones reach the
size necessary to activate the overburden.
This nonuniform deformation probably contributes to localization of fracturing during
process.
the full-scalecompaction-subsidence
Bending of rock layers in addition to lateral
displacements produces cross-bedding fractures, increasesthe aperture of faults, and
causesslippage along faults. Earthquakes
induced by fluid withdrawal or injection are a
well-known phenomenon (McGarr, 1993).
Lateral displacementdue to subsidencecauses earthquakes (Lee, 1979;Kosloff and others,
1980).Analyzing subsidence-inducedearthquakes at the Wilmington, California, oil
f ie ld , Ric h t e r (1 9 5 8 ),Ma y u g a (1 9 6 5 ) a n d
Kovach (1974) noted that slippage occurred
along nearly horizontal planes.
Fracturing increasescross-beddingpermeability and, thus, creates or enhancesvertical
connectivity of adjacent reservoirs or aquifers.
SurfaceDeformation
De f o rma t io n d u e t o c o mp re s s i o n a n d
extensionat and near the land surfacecauses
fissuresin the soil and damages buildings,
pipelines,and other structures.Subsidenceof
15 to 20 ft or more may cause swamping of
subsurfacestructures. Regional water tables
that approximately parallel the land surface
can remain at nearly the same altitude after
local subsidence lowers the land surface. The
effect is to decreasethe depth to water. If the
water table rises (relative to land surface)
higher than the bottom of a building, the
uplift pressure on the structure is noticeably
increased.If a basement is in heterogeneous
soils or rocks, uplift may not be uniform,
causing a distorting stress (fig. 2) and consequent damage to the structure. This dam-
RESEARoH
LnNoSuasrDENcE
CnsESruorrsANDCURRENT
a g e ca n be combined with da ma g e f ro m
d e for mation of the land surfa c e . Ra is e d
water tables (relative to land surface) can
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especially,this can lead to hydrocollapse,
which
can&be
considerable in loessal soils,
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and
additional deformation of surface and
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subsurfacestructures.
Shallower water tables, especially during
heavy rains when additional water table rise
occurs, can cause water to leak into basements through damaged walls. If light oil,
gasoline, or other hydrocarbons are floating
on the water table, these contaminants can
seep into the damaged basement creating
serious hazards and fire danger. The authors
observed domal deformation of floors of and
seepageof crude oil into the underground
garage of a multistory apartment building in
the Fairfax area of Los Angeles.
Deformation in the Caseof Heterogeneity
in Rock Properties
Lateral heterogeneity of a reservoir or
aquifer can cause hydraulic compartmentalization that can significantly affect deformation associatedwith subsidencein the following way. Hydraulic compartmentalization is
most often causedby heterogeneouslithology
and sealing faults. In a reservoir or aquifer
divided into hydraulically separatecompartments, fluid can be withdrawn from one compartment without affecting pressures in adjace n t compartments. B ecaus e p re s s u re
decreaseoccurs only on one side of a seal,
compaction and subsidenceoccur only on one
side of the seal.This can creategreat stressin
a fault zone and can cause a noticeable and
sud d e n slip along sealing fau lt s . Mu c h
greater surface damage can result from this
kind of differential subsidencethan from uni- fo r m s ubsidence due to compa c t io n in a
regionally uniform reservoiror aquifer.
CROSS.BEDDING FLOW
Seepageof oil and gas to the surface is a
widespread and well known phenomenon
Figure 2. Illustration showing the effect of
water table rise in heterogeneous soil. The
basement of the building is partly in sand, partly in clay. Uplift due to a shallower water table
after subsidence initially affects the part of the
basement that is surrounded by sand.
Therefore, the buoyancy force provides a rotating/bending moment (M) (equal to the buoyancy force multiplied by the action radius, R) that
can damagethe building.
(Link, 1952;Hovland and Judd, 1988;Clarke
and Cleverly, 7991).Cross-bedding fracturing
enhancesold migration paths and createsnew
paths that hydraulically connect reservoirs or
aquifers in the vertical section and the surface.
Oil and more particularly gas can leak
upward from a reservoir. If such migration
occurred naturally, prior to fluid extraction
(such as in the area of the La Brea tar pits in
Los Angeles), migration may intensify after
p ro d u c t io n b e g in s . V e rt ic a l mig r a t i o n o f
hydrocarbons and, sometimes,leakage though
damaged wells frequently creates a series of
smaller pools above the major reservoirs.
F ra c t u rin g in d u c e d b y s u b s id e n c e m a y
increaseleakagefrom these pools. Therefore,
seepagecan increaseeven though pressurein
major reservoirsdecreasesdramatically. Cas,
due to its low density, can migrate upward
through substantially opened fractures and
damaged wells even from reservoirs containing gas at less than hydrostatic pressure
(Gurevich, 1969;Gurevich and others, 7993).
In areassubject to earthquakes,seeping
hydrocarbon gases can affect mechanical
properties of soil. Depending on the chemical
and biochemical processesinitiated by gas, the
soil may become mechanically stronger, or
may become more easily liquefied during
vibrations causedby an earthquake.
THENero Fon A SvsreusAppnoRcn 483
SuesloeNcE
CAUSED
Bv Fr-uroWrruoRnwnL:
Fractures can connect two or more reservoir s in an oil or gas field. The a u t h o rs
observed a California field where adjacent
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courseHealth
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FIELD EXPLORATION
Lithology, degree of lithification, arrangement of rocks of different lithology (bedding
r e la ti on s, etc.), and tectonic defo rma t io n
determine the mechanicalproperties of rocks.
Geologic analysis of a rock volume that contains a reservoir or aquifer from the viewpoint of deformational properties and the
consequent translation of geologic data into
mechanical data, are the basis for prediction
of deformation due to fluid withdrawal or
injection. Deformational behavior of rocks
and formations should be examined and analyzed with respect to stress rates and deformation. Stressesthat changeslowly compared
to the potential rate of grain rearrangement
can produce plastic deformation of the rock.
Faster stress change will cause brittle deformation and fracturing. Initial stressesin rock,
caused by overburden weight and tectonic
stress, will strongly affect distribution of
stressesand the deformation produced by
subsidence.
Deformation within a homogenousgeologic stratum dependson the mechanicalproperties of that stratum and the adjacentstrata.
For example, the presenceof a rock with very
low shear strength (thin layer of a cIay,mudstone, a rock rich in mica, etc.) can causeslippage in this weak layer at much lower shear
stressthan in the caseof a relatively uniform
formation. Most deformation would occur in
this thin weak layer and the rest of formation
would suffer only minor shear deformation.
Tlhepresenceof rocks with low shear strength
should be investigatedthoroughly.
Fr acture distribution and dime n s io n s
(aperture, length, height) depend on tectonic
structure, (anticline,flexure, fault zone),stress
regime, secondarymineralization, and weathering, and, therefore, on geologic history.
484
A major part of subsidencedeformation can
o c c u r o n e x is t in g ma c ro f ra c t u re s a n d
microfracfures, leaving blocks of unfractured
rock nearly intact.
Geologic formations are complex, discrete
bodies that can be represented only approximately as continuous media. To understand
deformation of large volumes of rock with
varying lithology, deformational models at
multiple scalesmust be developed. Also, a
"dictionary" should be developed to translate
t h re e -d ime n s io n a l g e o lo g y in t o a t h r e e dimensional description of mechanicalproperties.This dictionary could be used as a basis
for developing a hierarchical chain of deforma t io n a l b e h a v io r mo d e ls t h a t m i m i c s
changes in deformational mechanisms as
cumulative deformation increasesand as
deformation rates vary.
MONITORING
The following characteristics should be
monitored simultaneously with studv of their
interrelations.
.Surfacevertical and horizontal deformations
b y le v e lin g s u rv e y s , s a t e llit e (G l o b a l
Positioning System) techniques,and other
similar techniques.
oDeformationsin well bores by existing techniques (i.e.,logging the position of radioactive bullets).
.Changes in the permeability of reservoir or
aquifer rocks either indirectly through
changesin productivity or directly by measuring permeability of cores obtained from
new well bores.
eMicroseismicactivity recorded at several
a u t o ma t ic mic ro s t a t io n s f o r lo ca t i n g
microearthquakes to monitor and predict
deformation and also to use as a warning
for effects on production.
oGasseepageand gas composition by automa t ic d e t e c t o rs p o s it io n e d a t p rob a b l e
seepagelocations (fault zones, flexures,
zonesof extensiondue to subsidence).
oPosition of the water table and other piezometric surfaces.
LnNoSuesrDENcE
RESEARcH
CnseSruoresANDCURRENT
oComposition of water from producing and
observationwells.
ferent in the laboratory than in nature.
.Laboratory tests are conducted using uniform samples, whereas in-situ processes
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tored parameters would be different for shalmedia where redistribution of pressure,
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lowHealth
aquifers
than for deep oil or gas reservoirs,
stress,and deformation significantly affects
can have great pressure decreases.The
Fullwhich
Disclosure
material response (Gurevich , 7987).
set of monitored parameters would vary on a
Correlation of empirical statistics of in-situ
case-by-case
basis.
deformation with geologic and physical
characteristicsis necessaryto determine
more realistic parameters for simulation
TECHNIQUES TO BE DEVELOPED
models. This will increasethe accuracy of
So me new techniques are n e e d e d t o
predictions of, for example, subsidence,
improve understanding of subsidence-related fracturing, induced earthquakes, and gas
processesto allow collectionof field data at
seepage.Correlations between geologic
monitoring locations and to improve prediccharacteristicsand deformation parameters
tion capability.
could be made on the basis of a complete
cause-and-effect
geological/physicalmodel
oOften, reservoir pressuresare maintained bv
of deformation processes.A set of geologic
waterflooding or gas injection to reduce thl
characteristicsselectedas analogs to physip o ssibility of subsidencein u rb a n a n d
cal values of this model, together with
industrial areas during oil and gas produchydrodynamic parametersof the fluid withtion. Beyond the protected areas,pressure
drawal or injection can be used for correladecreaseand subsidencecan occur and can
tion techniques.Data on many reservoirs or
be substantial enough to causeearthquakes.
aquifers should be used to provide reliable
Pressure increase in underground gas storresults and develop geologic indices for
ag e reservoirs (usually aban d o n e d o il
accurateprediction of subsidenceand its
fields) due to gas injection can lead to the
consequences.
same result. In seismicallv active zones .Improved models and sets of models for
there is a danger that theie small earths imu la t in g a n d p re d ic t in g s ub s i d e n c e
quakes could trigger a major earthquake;
should be developed, continuing the curtherefore, it is necessaryto develop techrent trend of evolution of subsidencesimuniques for (1) indirect and direct measurelation models.
ment of stressin heterogeneousrocks during subsidence, (2) evaluating tensile and
Total relative deformation of rocks during
shear strength of heterogeneousformations subsidenceis small. Therefore, it is difficult to
( as opposed to the method s u s e d in a reliably establish the mechanism responsible
homogenous rock bodies), (3) measuring for deformation by mathematical modeling
changes in rock strength during deforma- becauseadjusting numerical values of para-tion, and (4) maintaining and reducing meters and coefficientsis merely a data-fitting
str e ss to a level below the f o rma t io n process that does not reveal incomplete or
strength to avoid earthquakes.
incorrect models of the mechanisms involved.
media
and
their
behaviors
are very More attention should be paid to developing
-rGeologic
complex. Laboratory experimentsand tests a d e q u a t e u n d e rs t a n d in g o f d e f o r m a t i o n
do not reproducein-situ compactionor sub- mechanisms and processesin huge massesof
sidence processesand cannot simulate them ro c k wit h h e t e ro g e n e o u s g e o log i c a n d
accurately. Deformation rates in the labora- mechanical properties. As a result, more realtory are much greater than in situ and, istic, complete,and accuratemodels of in-situ
therefore, deformation mechanismsare dif- deformation will be developed.
SueslorNlcE
CAUSED
Bv FluroWrnoRRwnL:
THENreo Fon A Svsrevs Appnoncn 485
Deformation and mechanisms of deforma- REFERENCES
CITED
V
tion are not uniform in time and space.
Initi ally, pressure depletion oc c u rs o n ly Chilingarian, G. V., E. C. Donaldson, and T. F. yen, *, tggS,
/
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Subsidencedue to fluid withdrawal: Amsterdam, Elsevier,
around producing wells. Due to small lateral
498p.
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size of these zones (the lower the permeabili- Clarke, R. H., and R. W Cleverly, 1991, Petroleum seepage
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ty, theHealth
smaller
the lateral size), initially there
and post-accumulationmigration, inW. A. England and A.
J. Fleet, eds., Petroleum migration: Geological Society of
is no
subsidence,but deformation and predeFull
Disclosure
London Special Publication 59, p.265-271.
formational changes in rock strength do Geertsma, 1957,The effect of fluid-pressure decline on vol1.,
occur. As depletion zones spread over the
umetric changes of rocks: Transactions of AIME, v.210, p.
331-339.
larger area of reservoir or aquifer, compaction
Geertsma,J.,1973,A basic theory of subsidencedue to reserbecomesnoticeable and subsidencebegins,
voir compaction: the homogeneous case: Verh. Kon. Ned.
but due to rock strength changesaround proGeol.Mijnbouwk. Gen.,v.28, p.43-62.
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migration: Leningrad,Nedra Publishers,112p.
deformation is not uniform. As has been men- Gurevich,
A. E., 1989, Tasks for further development of
tioned, there is also evidence that deformageofluid dynamics: Yakutsk, Russia, Yakutsk University,
30 P.
tion due to subsidence begins at depth and
Gurevich, A. E., and G. V. Chilingarian,1993, Subsidenceover
can cease to be elastic even before surface
producing oil and gas fields, and gas leakage to the surdeformation occurs.
face:Journal of Petroleum Scienceand Engineering, v.9, p.
239-250.
The complete deformation model, therefore,
Gurevich,A. E., L. N. Kapchenko,and N. M. Kruglikov, 1972,
may be based on a "sliding" model of deforT h e o r e t i c a l p r i n c i p l e s o f p e t r o l e u m h y d r og e o l o g y:
mation mechanisms such that at each particuLeningrad,Nedra Publishers,272 p.
lar physicat point (i.e., a grid cell in a mathe- Gurevich, A. E., and others, 1987,Formation fluid pressure:
Leningrad, Nedra Publishers,223 p.
matical model), the deformation law (algoGurevich, A. E., B. L. Endres, J. O. Robertson, fr., and G. V.
,/
rithm in a mathematical model) should
Chilingarian, 1993, Gas migration from oil and gas fields
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describe real deformation processesmore
Kosloff, D., R. F. Scott,and f. Scranton, 1980,Finite element
accurately.If the distribution of types of deforsimulation of Wilmington oil field subsidence:1..Linear
modeling: Tectonophysics,v. 65, p. 339-368.
mation mechanisms acting concurrently is statistically uniform, another approach can be Kotov. I. G., V. A. Mironenko, and L. I. Serdyukov, 7977, On
r/
the influence of rock layers overlying unl aquifer on the
suggested. Integrating the effects of all deforelastic regime of water percolation: Jotirnal of Applied
Mechanics and TechnicalPhysics,v.2, p.172-1.76.
mational mechanisms involved could yield a
for Wilmington oil
composite model with a generalizedmecha- Kovach, R. L., 1974,Source mechanism
field, California, subsidenceearthquakes:Bulletin of the
nism. Parametersof this model may be made
SeismologicalSocietyof America, v.64, p.699-711..
V
dependent on the rate and total amount of Lee, L. L., 1979,Subsidenceearthquakeat a California oil
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deformation to provide necessaryflexibility
subsidence:New York, ASCE, p. 549-564.
for this "bulk" model. Models of these two Link, W. K., 1952, Significance of oil and gas seeps in world
oil exploration:AAPG Bulletin, v.36, p.1505-1539.
types may bridge the gap between current
models of deformations in a laboratory sam- Mayuga, M. N., 1970,Geology and development of California
giant; the Wilmington oil field, in Geology of giant petroples and in huge volumes of rocks in situ.
leum fields: AAPG Memoir 14, p. 158-184.
To
select
an
M
c
G a r r , A . , e d . , 1 9 9 3 , I n d u c e d s e i s m i c i t y : Ne w Yo r k,
optimal
simulation
approach,
Springer-Verlag, 460p.
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v
oped (Gurevich, 1989).Partial simulations of
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separate elements of the total processmake it
GeologicalSocietyof America,p.1'87-269.
possible to select best approximations of the Richter, C. F., 1958, Elementary seismology: San Francisco,
Freeman,768p.
actual process and tb simplify simulation of Saxena,S. K., ed., 1979,Evaluation and prediction of subsithe total processwithout losing accuracy.
dence: New York, ASCE,594 p.
486
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