caracterización de yacimientos

7/17/2019 caracterizacin de yacimientos

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SECTION 2 RESERVOIR CHARACTERIZATION

WHYISRESERVOIRCHARACTERIZATIONNEEDED?

EXPERT'S OPINIONS

"WF success is dependent on reservoir geology"

"Geology is never known as well as it needs to be known"

"Many WF fall below expectations because of the flaws in reservoir characterization

"Most WF fail because of inaccurate reservoir characterization"

One needs to develop an in-depth qualitative understanding and an accurate quantitativedescription of the reservoir state at the:

1. At the start of waterflood project2. At any time during the recovery process3. At the time of waterflood aandonment

!he following features specify the reservoir state:

1. Pressure and Temperature

2. Rock Properties"patial #3-$% description #mapping% of all reservoir and non-reservoir roc& properties:

'ithology( )orosity( )ermeaility( Anisotropy( *ompressiility( +eterogeneity

*ompartmentali,ation( "tratification( aults( ractures( *onnectivity( *ontinuityechanical strength( etc.

3. Fluid Properties$etailed 3-$ description of Oil( /as( and 0ater properties:

iscosity( $ensity( "olution /as-oil ratio( *ompressiility( luid distriution(*hange of *omposition with )ressure!emperature variation( njection water andormation water interaction( etc.

4. Rock/Fluid Interactive Properties4elative )ermeaility( *apillary )ressure( 0ettaility( 0ater4oc& interaction( etc.


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S e c t i o n 2

t should e clearly understood that accurate quantification of all of the aove features is almostimpossile.

4eservoir characteri,ation is therefore a dynamic process( requiring continual updating andupgrading due to:

data ecoming availale only in a piecemeal manner(

data applicaility and reliaility is often uncertain and improves with time(

etter interpretation techniques continue to ecome availale(

newer insights are gained with time( and

unanticipated prolems surface during the productive life requiring a

differentfresh loo&.

5o one discipline alone generates( manipulates( and utili,es all the aove data. +ence( reservoircharacteri,ation is a multi-disciplinary effort. !he following disciplines participate in the process:

/eophysics

/eology

)etrophysics

+ydrology

4eservoir 6ngineering)roduction 6ngineering$rilling 6ngineeringacilities 6ngineering

'aoratory "pecialists

A synergistic approac as proven e!!icient and productive" saving lots o! time" e!!ort"money" and su#se$uent !inger%pointing #et&een various disciplines.

!he total scope of a reservoir characteri,ation project is depicted in igure 2-1.

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R e s e r v o i r C h a r a c t e r i z a t i o n

Figure 2-1

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S e c t i o n 2

RESERVOIRHABITAT

A reservoir is a su-surface( 3-dimensional roc& ody with special attriutes such that

hydrocarons can accumulate. !hese attriutes are:

)orosity - void space for the fluids

)ermeaility - interconnected pore space to provide flow communication

!rapping echanism - cap roc& aove and oilwater contact elowpinch-outs

*ommon reservoir roc&s are formed of limestone( dolomite( and sandstone.

4eservoirs come in various shapes and si,es. !he most common are:

$omes

Anticlines

aulted "tructures

"tratigraphic - unconformity

"tratigraphic - sand lenses( shoe-string sands

4eefs

!hese shapes influence the developmentproduction process( not only during the primarydepletion ut also during the displacement type of O4 #mproved Oil 4ecovery% processes.

!raps with moderate to high relief are commonly developed under peripheral water

injection schemes.

!raps with low relief are generally developed under pattern flood schemes. Other factors

may favor the pattern flood 7 low permeaility( high heterogeneity( low well cost( shorterproject life.

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All reservoirs are under the influence of two PR'(()R'sources:

)ore #4eservoir% )ressure

Overurden )ressure #or 4oc& 68ternal Overurden "tress%

Figure 2-2

!hree types of reservoir pressure systems are

encountered. !hese are shown elow:

5ormal )ressure 4eservoir

)49 .;< 8 $epth

Anormally +igh #/eo-)ressure% 4eservoir

)4= .;< 8 $epth

"u-5ormal )ressure 4eservoir

)4> .;< 8 $epth

#5ote: )ressure /radient of salty formation water is assumed at .;< psift.%

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S e c t i o n 2

PRESSURE - DEPTH PLOTS

!he pressure gradient from a )ressure ? $epth plot( such as one the shown here( is indicativeof the type of fluid present as a continuous phase in the pore space of a reservoir.

/as /radient > .1 psift

Oil /radient 9 .3 to .; psift

0ater /radient = .;3; psift

!he presence of more than one fluid in the reservoir is indicated y the

change of pressure gradient. !he intersection of pressure trends shows theposition of the contact etween the fluids.

4! and $! data #"chlumerger%( "! data #+alliurton%( or ! data #@a&er +ughes%is e8tremely useful for this purpose.

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RESERVOIR TEMPERATURE

4eservoir temperature is otained y:

1. $irect measurement using wireline thermometer2. *alculation from regional thermal gradient and &nown depth

A generali,ed $epth versus !emperature plot is shown elow. !he thermal gradient( slope of thiscurve( in most of the oil-producing areas of the world in the range of 1-2 degrees per 1 ft of depth.

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S e c t i o n 2

*uring te primary recovery pase" reservoir temperature usually remainsessentially constant. All reservoir processes are assumed isothermal.

*uring a &ater!lood" three changes are rought aout due to the injection of colderwater in a hot reservoir.

1. !he reservoir roc& around the injection well gets colder. 0ith continuous injection(the region of cooled roc& e8pands outward away from the injector. !he resultingthermal shoc& causes roc& contraction( therey inducing roc& crac&ing and fracturesin the reservoir.

2. +igh-pressure injection water increases pore pressure in the vicinity of the well andtherey decreases the in-situ stress level. !his reduced stress level can e sufficientto cause shear failure of the roc& and slippage of faults. As the water-front movesoutward away from the injection well( the region of shear failure and fault slippagecontinues to grow.

3. !emperature decrease in the vicinity of the well results in a region of increasedviscosity. !his region e8pands as water front moves outward into the reservoir.

n many waterflood projects( continual improvement in well injectivity has een noted.)ressure transient well tests have confirmed presence of large negative s&ins and increasedformation permeaility.

!he comined effect of the three is rather hard to predict without simulating the thermal andgeo-mechanical ehavior of the reservoir.

EFFECT OF STRESS CHANGE DURING A WF ON PERFORMANCE

$uring a 0 process( the effective stress #)overurden- )reservoir% around an injector changes due toincrease in reservoir pressure and a decrease in reservoir temperature. !his change hasresulted in one or more of the following changes in many 0 projects:

1. "hear failure of roc& resulting in hairline fractures

2. 6longation of e8isting fractures

3. "lippage of faults

;. 0ellore failure due to caving of wellore wall and slipping of faults

n comparison( the effective stress increases due to decrease in reservoir pressure. !his changehas resulted in reservoir compactionand surface susidence in many projects.

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POROSITY

)orosity is the measure of the void spaces in a roc& where fluids #oil( gas( and water%

reside under reservoir conditions of pressure and temperature.

Total Void SpacePorosity = =

Total Bulk Volume

PV BV - GV = =

BV BV

0here: @ 9 !otal @ul& olume/ 9 !otal /rain olume) 9 !otal )ore olume

)orosity is dependent upon roc& type( grain si,e distriution( shape of grains and their

arrangement( nature and degree of cementation( deposition history( and digenetic changes.

Rock Type +ommon Porosity Range" ,

'imestone 3-12

"andstone 12-2B

)orosity may e defined on the asis of:

T-TA which accounts for all the availale void space

'FF'+TI0'which accounts for only that void space which is interconnected and which

participates in the fluid movement in the reservoir. All reservoir-engineering calculationsare ased on this value as it pertains to pore space of economic interest.

igure 2-3 shows the type of porosity in a thin section.

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S e c t i o n 2

Figure 2-3

0e need maps showing distriution of effective porosity under reservoir conditions ofpressure( temperature( and stress.

METHODS FOR POROSITY MEASUREMENT

1. $irect laoratory measurements on cores cut from the reservoir

2. ndirect calculation from physical measurement ofa roc& property #that can ecorrelated with porosity% using logs

DIRECT LABORATORY MEASUREMENTS

*ore samples of various si,es are used. *ore plugs are used for homogeneous roc&s

#sandstones( in general% while full si,e cores may often e used for limestone.

$irect measurements on cores in the laoratory under either reservoir conditions or

room #ench-top% conditions.

or clean and dry cores( the following methods are used:

"aturation ethod ? the core sample is 1C saturated with a liquid of &nown density.

D@oyleDs 'awD ethod ? the simplest( the fastest( and the least e8pensive method.

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Figure 2-4

!he decision to duplicate reservoir conditions or room conditions in the laoratorydepends on the nature of roc&. f effective porosity is stress dependent #such as 4oc&*%( reservoir conditions must e duplicated. f effective porosity is not stress dependent

#such as 4oc& A%( room condition measurement would e satisfactory.

Figure 2-5

et Pressure -ver#urden Pressure Reservoir Pressure

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S e c t i o n 2

POROSITY FROM WIRELINE LOGS

0ell logs are depth records of a physical property of the reservoir roc&(

which can e related to porosity through some physical or empirical relationship.

ost common relationships relate )orosity to $ensity( Acoustic elocity( and

5eutron )opulation.

*omparison of log-derived porosity with core-measured porosity selects the

logging tool that is est suited for a particular area.

!here are various practical reasons for the choice of logging over coring.

1. 'og measurements are under reservoir conditions of pressure( temperature(and stress.

2. 'ogging is cheaper and faster than coring. +ence( logs are run on all wells utonly a small numer of wells are cored.

3. )orosity information is availale shortly after logging.

;. A continuous porosity profile is made availale.

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PERMEABILITY

)ermeaility is the measure of the ease of flow of fluids through the interconnected pore

space.

t is the single most important property( since it governs the rate of fluid flow. +ence( the

economics of a project.

*arcys a&" an empirical relationship( provides the asis for quantifying permeaility.

t relates flow rate through a porous medium to the properties of roc& and fluid( and to theapplied pressure differential( y the following e8pression:

i oK A (P - P )

q =

0here: q 9 low 4ate( ccsecE 9 )ermeaility( darcy

)i 9 nlet )ressure( psig)O 9 Outlet )ressure( psig

9 luid iscosity( cp

' 9 *ore 'ength( cm

4eservoir permeaility varies over a wide range.

Rock Type Permea#ility Range" 5* Average" 5*

'imestone .1-----2 1-1

"andstone 1-----3 -2

)ermeaility is the property of the roc& alone and is independent of the type of fluid so long

as it totally fills the effective pore volume #1C saturation% and flows through the roc& in alaminar manner.

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S e c t i o n 2

arious methods are used for measuring permeaility:

1. 'aoratory easurement

2. 0ell !ests

3. )orosity - )ermeaility *orrelations

;. )otential 'ogging Approach

LABORATORY MEASUREMENT

*ore samples of various si,es are used. "mall plugs are used for a homogeneous roc&

#sandstones( in general% while full si,ecores are used for a heterogeneous roc& #limestoneand dolomite%.

4oc& #Asolute% permeaility is routinely measured in the laoratory under room pressure

and temperature conditions. or stress sensitive cores( measurements must e made undereffective reservoir pressure.

or routine measurements of permeaility( an apparatus named )ermeameter and shown

in the figure elow( is the apparatus commonly used.

Figure 2-6

/as #air( nitrogen( helium% is used as the test fluid as it is more convenient and

tests are rapidly conducted. f water is used as the test fluid( formation water orsynthesi,ed rine is used.

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A full diameter core is used for hori,ontal and vertical permeaility measurements.

6ori7ontal Permea#ility

E#8% 7 in a pre-selected direction

#parallel to edding plane%

E#F% 7 in the direction at F degrees

to the pre-selected direction

0ertical Permea#ility

E#,% is measured in the directionperpendicular to the edding plane.

Oriented coresG duplicating their geographical placement in the reservoir provide very

important data on the directional permea#ilitytrends in a reservoir.

!hrough identification of permeaility trends #grain orientation in clastic roc&s

and fractures( joints( fossil alignments in caronate roc&s% this data assists ininjectionproduction wells placements to optimi,e sweep efficiency of adisplacement project.

any waterfloods fail due to the limited &nowledge of the anisotropic character

of the reservoir roc&.

or stress sensitive roc&s #friale( unconsolidated%( laoratory measurements are made

under simulated reservoir conditions of pressure #net overurden pressure%. "incetemperature has no significant effect( tests are made at room temperature.

G ld !echnology ew !echnology# $ownhole %hotos& '(age )ogs *FM'+FM,-

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S e c t i o n 2

PERMEABILITY FROM WELL TESTS

0ell tests are very important sources for permeaility #E oh to e e8act% values for a

reservoir. !he value is considered more representative as the well test is representative of amuch larger portion of the reservoir than is a core.

!he measurements can e easily interpreted into effective Eoh #md-ft% of a reservoir within

its radius of influence. !he estimated value is valid under reservoir conditions of pressure(temperature( and saturations.

*ommon well tests are:

)ressure @uild Hp

)ressure all off

)ermeaility data from well test analysis is continually integrated with that otained from the

core analysis data. !he ojective is to evolve a consistent reservoir description.

PERMEABILITY FROM WIRELINE LOGS

5o wireline log is availale at the present time that directly measures permeaility in a

reservoir.

"ome newer tools such as 54 and *4 are currently under active research and

development. !hey are proving promising in some applicationsI especially after the logresponse is conditioned to the availale core data.

0henever successful( significant savings will e reali,ed in terms of cost and time.

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FORMATIONCOMPRESSIBILITY

4eservoir roc&s( just li&e reservoir fluids( are compressile and e8pand as pore pressure

decreases due to production and therey provide a source of e8pulsive energy.

n reservoir engineering calculations( roc& compressiility is reported on the pore volume

asis. ts value is otained from:

'aoratory easurements

*orrelations

+all

an $er Enapp

n the oil reservoirs( total compressiility is given y:

*t9 *o"oJ *w"wJ *g"gJ *f

when ) = )@)

*t9 *K"wJ *w"wJ *f

when ) > )@)

gas compressiility dominates all others

roc& compressiility is usually ignored *r >> *g

*t9 *g"g as *g== *oor *wor *f

n the aquifer( total compressiility is given y:

*t9 *wJ *f

or most competent roc&s( the value ranges etween 2 7 2 8 67< #1psi%. or

unconsolidated roc&( this value can e8ceed 1 6-< #1psi%.

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S e c t i o n 2

ROCKWETTABILITY

0ettaility is the tendency of one liquid #oil or water% to preferentially spread over the

surfaces of a roc&( when two or more fluids #oil( gas( and water% are present together.

/as is always the non-wetting fluid. +ence( it preferentially occupies the centers

of the larger pores.

4eservoir roc&s are made up of minerals #silica and caronates% that are natively

water-wet. +ence( all reservoirs should initially e water- wet.

any reservoirs e8hiit a large range of wetting tendency #from strongly water-wet to

neutral-wet to strongly oil-wet%I therefore( the change must have occurred some timeafter oil accumulation.

A numer of possile reasons for the alteration have een suggested: #1% some

crude oils contain surface-active ingredients and polar compounds( and #2% someare rich in asphaltenes and wa8-li&e material.

n some reservoirs( wettaility depends on structural position 7 high structural areas

are often oil-wetI upper flan& wells are of neutral wettailityI areas closer to O0* areoften water-wet.

*O5!A*! A5/'6 is a common measure of roc& wettaility. t is measured in the

laoratory y using samples of reservoir fluids and a crystal of the roc& that ma&es upthe pore surfaces in the reservoir. After equilirium is estalished( the contact angle ismeasured through the water phase.

Figure 2-7

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!he contact angle scale elow shows the ranges that classify roc& wettaility.

ost reservoir roc&s e8hiit intermediate wettaility. +owever( many reservoirs e8hiitstrongly water-wet or oil-wet ehavior.

A numer of other laoratory techniques are also utili,ed. AmottDs method is very popular - ituses a representative core that is either otained under preserved conditions or is pic&ledwith reservoir fluids for a long time to insure that native state is re-stored.

!he method sujects the core to an imiition-drainage process( which duplicates the

reservoir processes of oil accumulation and waterflood displacement.

Accurate assessment of reservoir wettaility is very important as it has a pronounced effect on:

1. nitial $istriution of Oil and 0ater2. *onnate 0ater "aturation

3. luid low through the 4eservoir;. 4esidual Oil "anitation

. )roduction )erformance


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S e c t i o n 2

2. CONNATE WATER SATURATION

*onnate water saturation in the water-wet roc& is around 2 to 3C and around to 1C in anoil-wet roc&.

Figure 2-8

3. FLUID FLOW THROUGH THE RESERVOIR

St!"#$% W&t-Wt R!()

0ater prefers to wet solid surfaces and therey advances along the walls of the pore spaces.0ith continual advancement( it pushes oil from the edges until water cusps in at the pore e8it. tthen retains some oil as disconnected( isolated droplets in the pore centers. !his oil saturation iscalled D4esidual Oil "aturation to 0ater - "orwL.

Figure 2-9

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St!"#$% O*$-Wt R!()

0ater prefers to move through the pore centers pushing oil ahead of it. 0ith continualadvancement( it drags oil from the edges until it estalishes a continuous path through thepores. t then retains oil as a connected film covering the solid surfaces. !his oil saturation iscalled D4esidual Oil "aturation to 0aterflood - "orwD.

Figure 2-10

+. RESIDUAL OIL SATURATION TO WATERFLOOD

"orw for a water-wet roc& is of the order of 2 - ;C and in the 3-;C for an oil-wet roc&.

"orw is not a function of water throughput or applied pressure differential for a water-wet roc&(ut is strongly dependent on the twofor an oil-wet roc&.

,. PRODUCTION PERFORMANCE

!he ideali,ed production performance #oil recovery and water-cut versus time% of a stronglywater-wet and oil-wet reservoir is compared elow.

St!"#$% W&t-Wt R!()

'arge oil recovery prior to water rea&through

4elatively small increase in oil recovery post rea&through

0ater-cut increases sharply after water rea&through

!otal oil recovery is essentially independent of the volume of water injected and theapplied flooding pressure gradients

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S e c t i o n 2

Figure 2-11

St!"#$% O*$- Wt R!()

'ower oil recovery prior to water rea&through

"ustantial increase in oil recovery post rea&through

0ater-cut increases gradually after water rea&through

!otal oil recovery is dependent on the volume of water injected and the applied flooding

pressure gradients

Figure 2-12

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W&t$!! (!/% *0 ""t !" !() tt&*$*t%

!he generali,ed plot of 68pected Hltimate 4ecovery versus roc& wettaility shows that forsimilar oilwater viscosity ratio floods( recovery is higher from a water-wet roc& than an oil-wetroc&. t also shows that recovery from a neutral-wet roc& could even e higher than the two

e8treme cases.

Figure 2-13

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S e c t i o n 2

FLUIDDISTRIBUTIONINARESERVOIR

One of the most important factors responsile for the success of a waterflood is the fluidsaturation #oil( water( gas% and their distriution in the reservoir at the start of the project.

"aturation distriution is seldom &nown #e8cept under the initial conditions prior to production%and its accuracy is always a suspect. !here are many reasons for this:

1. nitial static distriution is not e8actly &nown( especially in a mi8ed lithology reservoir.

2. 4eservoir development prior to waterflood is not uniform. +ence( the productionperformance is varies oth areally and vertically. 4egional drift of fluids inside thereservoir is hard to quantify.

3. 6ven with a dedicated effort( the sampling inadequacy poses a major handicap.

"ince this information is essential as the starting point in a waterflood project( it has to eotained with reasonale degree of accuracy. 4esources required are: a multi-disciplinary team(a dedicated effort( and commitment of time( money( and resources.

At t4 0t&t ! &t$!!

6stimate of saturation averages is rather straightforward. +owever( it requires that:

1. good estimates are availale for pore volume and original oil-in-place(

2. accurate production records have een &ept(

3. water influ8 rates can e estimated with accuracy( and

;. reservoir drive mechanisms can e assessed. *lassical reservoir engineering methodsare employed.

!he average oil saturation in the reservoir at the start of a 0 is primarily related to theprimary drive mechanism( as shown y the figure elow:

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Figure 2-14

apping of saturations is possile if:

1. A history-matched reservoir simulation model is availale. Accuracy hinges on reservoirdescription( however.

2. A well logging program is the est approach. Eey wells are selected and appropriatelogs are run to calculate saturation distriutions around producers.

3. *oring of new wells is another approach. +owever( the coring program #cutting( retrieval(preservation( storage( testing% has to e designed such that meaningful interpretation ispossile.

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S e c t i o n 2

FLUID DISTRIBUTION IN A RESERVOIR UNDER INITIAL 5STATIC6 CONDITIONS

!he simplified #ideali,ed% model elow depicts the initial distriution of fluids in a reservoir.

Figure 2-15

!his distriution is controlled y equilirium etween the gravitational and capillary forces.

/ravitational orce: t causes fluid segregation into gas aove( oil in the middle andwater at the ottom.

! "#orce = $%&'' ( - )

*apillary orce: t causes the wetting fluid #water in general% to occupy the smaller pores

while the non-wetting fluids #oil and gas% occupy the larger pores.

"! "S *

#orce = +

A realistic model of $epth vs. 0ater "aturation is shown in the figure elow:

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Figure 2-16

!he length of oil-water transition ,one is a function of pore si,e distriution. f pores are

of uniform si,e #higher permeaility reservoirs%( transition ,one length is very small. ora wide pore si,e distriution #lower permeaility reservoirs%( transition ,one may coverthe entire reservoir thic&ness.

!he oil-water transition ,one is of great interest in designing a waterflood project.

!here is no single definition of oil-water contact #O0*%. An aritrary choice is made

depending upon the local practice and the purpose of the analysis.

5O!6: *apillary orces have a major effect on initial distriution of water in the

reservoir. +O0664( they will have minimal effect on water movement during awaterflood where viscous forces and high )ressure /radients dominate.

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S e c t i o n 2

5etodsused for estalishing initial fluid distriution are:

1. $irect ethod

)roduction testing: well is production or $"! tested over successively &nown depth

intervals

2. ndirect ethods

*oring: conventional core analysis is of limited use.

'ogging: resistivity and porosity logs are used.

4!$!: spot pressures are measured at &nown depths along the well path. Only

fluid contacts are estalished.

'aoratory *apillary )ressure !ests: representative preserved cores are used to

measure capillary pressure - water saturation data utili,ing the following methods:

)orous $iaphragm ethod

ercury njection ethod

*entrifuge ethod

!est is made under conditions that duplicate the reservoir process of interest -$rainage or miition.

$rainage: !he wetting phase fluid is displaced from the pores y the non-wetting

fluid #nitial oil migration in the reservoir%.

miition: !he non-wetting phase fluid is displaced from the pores y the

wetting phase fluid #waterflooding in a water-wet reservoir%.

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CAPILLARYPRESSUREDATAFORWATERFLOODING

0aterflooding results in increasing water saturation in the reservoir as oil is displaced.

!he laoratory-derived capillary pressure curve measured under the condition of increasing

wetting phase saturation is called MmiitionM and is the data that is needed as input to reservoirsimulator to model the waterflood process.

!he figure elow shows a typical imiition capillary pressure curve for a water displacementprocess in roc&s with different wettaility preferences.

INTERMEDIATE WETTABILITY ROC7

Figure 2-17

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S e c t i o n 2

STRONGLY WATER-WET ROC7

0 in a water-wet roc& is an miition process as "w increases.

Figure 2-18

STRONGLY OIL-WET ROC7

0 in an oil-wet roc& is a $rainage process as "o decreases.

\Figure 2-19

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RELATIVEPERMEABILITY

elative per(eability curves are the /road (aps/ to production rate and hydrocarbon recovery.0ence& it is of para(ount i(portance that data is as representative as possible.

4eservoir pore space is generally filled with two #oil and water% or with three fluids #oil(water and gas%. low of any one fluid in the presence of other fluids is treated y the conceptof relative permeaility.

4elative permeaility is defined as the ratio of the 6ffective )ermeaility to a fluid to theAsolute )ermeaility of the roc&. !he value ranges etween and 1 #or to 1C%.

!his is the most important &ey data for all calculations dealing with water drive reservoirs(waterflood projects( and water coning - +ence( it is imperative that the data used is reliale.!he following guidelines are recommended.

1. 6ither use a preserved core or ma&e sure that wettaility is re-stored in the laoratory.

2. 6ither use the reservoir live fluids #cumersome% or use fluids with laoratory oil-water viscosity ratio matched to the reservoir condition viscosity ratio.

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, o+! +"

K KK = K =

K K


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S e c t i o n 2

OIL-WATER RELATIVE PERMEABILITY

A typical oil-water relative permeaility relationship is shown in the figure elow:

Figure 2-20

"wc 9 *onnate #rreducile% 0ater "aturation

"orw 9 4esidual Oil "aturation #where Ero 9 % at "wma8 #a8imum 0ater "aturation%

#Erw%"orw 9 6nd )oint 4elative )ermeaility to 0ater

#Ero%"wc 9 6nd )oint 4elative )ermeaility to Oil

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"ince hysteresis plays an important role( the relative permeaility is also influenced y thedirection of change. !he figure elow is a typical e8ample of this ehavior.

Figure 2-21

!he water #wetting phase% relat ive permeaility is generally not direction dependent -

it is a function of its saturation alone.

!he oil #non-wetting phase% relative permeaility is highly direction dependent. At any

given water saturation( it is lower for the imiition process than for the drainage process.

any times hysteresis effect is not modeled in reservoir simulations.

METHODS OF MEASUREMENTS

4elative permeaility data is measured in the laoratory y one of the following methods:Hnsteady "tate ethod( "teady "tate ethod( and *entrifuge ethod.

!hese testing methods differ from each other in the quantity and quality of the generated data(and therefore in the time required and the cost incurred.

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S e c t i o n 2

I8!t&"t Dt&*$0 ! D*(t Mt4!0

Unsteady State Method

!he e8perimental procedure is depicted elow. +ere( water is injected into a 1C saturated#with oil and connate water% core at a constant pressure differential. !he oil and water

production rates are continually measured until only the injected water is produced.

Figure 2-22

Advantage: !a&es only a few hours to complete the test.

$isadvantage: *alculations to convert production data into relative permeaility

data are involved.

Steady State (Penn. State) Method

!he e8perimental procedure is depicted elow. +ere( water and oil at a &nown ratio areinjected into a 1C saturated #with oil and connate water% core until saturation and pressuredifferential across the core staili,e. !his step is repeated with different &nown oil and water

injection ratios.

Figure 2-23

Advantage: *alculations to convert production data into relative permeaility are simple.

$isadvantage: !his procedure ta&es a long time.

34


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C"t*9# Mt4!

!his is a much faster method. t measures relative permeaility of the phase that is producedduring the test.

Figure 2-24

C!8&*0!" ! t4 Mt4!0

1. 0ater-oil relative permeaility data from the steady state method covers the entire range ofsaturation change.

2. "ince the saturation range is 'imited in the unsteady-state method( e8trapolation of the data isneeded.

3. $ata otained from the centrifuge method is aout the same within the e8perimental accuracy.

;. Agreement etween gas-oil relative permeaility data from gas-flood and centrifugemethod is quite good.

. !he centrifuge data provides a etter estimate of residual liquid saturation as thedisplacement process may e sujected to higher pressure gradients.

. 35


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S e c t i o n 2

Figure 2-25

Te steady%state metod is generally considered to #e superior to te oter t&o metods.

36


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4oc&&etta#ility has a pronounced influence on the shape of the relative permeaility curvesand on the end-point values. igure elow demonstrates this.

Strongly Water - Wet Rock

St rongly Oi l - Wet Rock

wc

rw "O40

ro "0*

0 rw ro

" > 1C

" :.3

E :.N

" :C at E 9 E

. 37

wc

rw "O40

ro " 0*

0 rw ro

" 9 2-;:C

" 9 :.1 - :.2

E :.B

" :C at E 9 E


38/82

S e c t i o n 2

aintaining a core in its native #un-altered% state for "*A' laoratory tests is very important.0hile it is a pains-ta&ing activity and an e8pensive underta&ing( it is asolutely essential to theaccuracy of recovery forecasting #project performance% and the project profitaility.

Te '8traction process- where core is cleaned off its oil and water and dried - may alter thenative wettaility of the core.

Te Restoration process- where the e8tracted cores are saturated with water and oil - maypartially restore the wettaility character. 4estoration may get etter if the core is aged with time.

Figure 2-26

OIL-GAS-WATER RELATIVE PERMEABILITY"imultaneous flow of oil( gas( and water occurs at only a small comination of saturations dueto the moility #E+ 1% contrast etween the fluids. !he fluid distriution is rapidly arranged as:

0A!64 O' @A5E /A"

0O O/4el )erm 4el )erm

38


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A typical three-phase diagram is shown elow:

Figure 2-27

'aoratory tests to otain this data are very cumersome and e8pensive. +ence( anumer of DproailisticD models have een developed to estimate three-phase data that isneeded for the reservoir simulation studies. !hese models #"toneLs *orrelation% require theroutinely availale two-phase water-oil and gas-oil relative permeaility data.

I8!t&"t Dt&*$0 ! I"*(t Mt4!0:

Data f rom Analogos Reser!oi r

A fairly good source if similarity of reservoir type( depositional sett ing( fluid propert ies(and development strategy is estalished.

P"l ished #orrelat ions

any pulished correlations #etween relative permeaility and capillary pressure% areavailale. !heir use is highly questionale.

. 39


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S e c t i o n 2

$ield Prodct ion %istory

)roduction history of a reservoir can also e utili,ed in estimating the field average or wellaverage effective permeaility relationship( provided the drive mechanism is well understood.ts use is however limited ecause the data ecomes availale after the fact.

+A)TI-999

Fluid !lo& #eavior and oil recovery estimate are a direct !unction o! terelative permea#ility relationsip.

-ne must make sure to utili7e te relationsips &ic are o#tained!rom care!ully designed la#oratory tests on cores &ic are kno&n tomaintain &etta#ility caracter during te coring" sipment" storage" andtesting processes.

CURRENT THOUGHTS ON OIL-WATER RELATIVE PERMEABILITY MEASUREMENT

"teady-"tate method is etter than the Hnsteady-"tate method as it provides data over the

entire saturation range.

Hnsteady-"tate method results in too high residual oil saturation ecause of insufficient

flooding.

!he *entrifuge method provides a etter estimate of the residual oil saturation.

S!"" reco##en$s a co#%ination #etho$ &here Stea$'-State #etho$ (rovi$es

re)ative (er#ea%i)it' $ata an$ Centri*uge #etho$ (rovi$es the resi$ua) oi) saturation+

4elative permeaility should e made under reservoir conditions using imiition procedure

on representative preserved or restored-state #aged% cores.

n the past( non-preserved cores were often used. !hese cores generally e8hiited water-

wet ehavior due to changes introduced during coring( retrieval( storage( and testingprocesses. ield e8amples elow show significant changes in the residual oil saturationvalues( suggesting higher displacement efficiencies.

*urrent Old

@rent 1C 2BC

$unlin 1 2 - 3"chiehallion 1; 2F

"an

rancisco

1 =9;

'e&hwair 2B

aui 1 2B

40


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2olu(etric sweep efficiencies need re3assess(ent in older waterfloods where displace(entefficiencies were based on older esti(ates of residual oil saturations.

. 41


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S e c t i o n 2

RESERVOIRHETEROGENEITY

Figure 2-28

Figure 2-29

42


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+eterogeneity is the spatial variation of the reservoir properties. t can occur at various levels.

'arge "cale +eterogeneity may e due to:

4eservoir *ompartmentali,ation

)resence of aults

)resence of racture clusters

'arge )ermeaility *ontrast

"mall "cale heterogeneity is due to:

"hape and si,e of the sediments

$eposition history of the sediments

"usequent changes due to digenesis and tectonics

0eterogeneity is the (ost difficult attribute to 4uantify5 but has the greatest effect on theefficiency of the WF processes.

0hile all reservoir properties may vary( oth areally and vertically( change in permeailityvalues are most drastic #many fold changes are encountered%.

!herefore( vertical heterogeneity is in general much greater than areal heterogeneity.

Figure 2-30

. 43


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S e c t i o n 2

!wo methods were introduced during the ;Ds and Ds for the quantification of verticalheterogeneity on a scale of #homogeneous% to 1. #heterogeneous%. !hese are:

1. 'oren, *oefficient

2. $y&stra P )arsonLs )ermeaility ariation actor

!hese were utili,ed in estimating vertical sweep efficiency of a 0 project.

Areal heterogeneity was handled y conventional interpolation and e8trapolation methods( such as:

1. !he Assumed !rends

2. !he nverse $istance ethod

3. !he nverse $istance "quared ethod

*urrently( numerous geostatistical techniques are eing employed.

GEOSTATISTICAL TECHNI;UES

!he conventional technique for mapping a property value is to contour the &nown valuesandor the estimated values( while incorporating geological trends( depositional features( andpersonal e8perience of the user. +ence( these techniques are highly sujective.

!he newest technique with a great deal of promise and non-sujectivity is geostatist icaltreatment. t uses spatial correlations #variograms are relations of measured valuesquantifying variation with distance and direction% to estimate the value of the property at allQRS locations. Additional soft data is incorporated honoring geological trends(depositional features( and personal e8perience of the user.

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RESERVOIRCOMPARTMENTALIZATION ITSASSESSMENT

any reservoirs are compartmentali,ed into separate loc&s. 6ach loc& may have its own oil-water contact and may contain an oil of different composition than the other loc&s.

@arriers such as faults shown elow may divide the reservoir into loc&s that:

ay not communicate with one another at all( or

ay not communicate at the eginning ut may start communicating under the

production-induced pressure differentials etween the loc&s.

Figure 2-31

!he project economics is impacted if compartmentali,ation information is not correct. nitialdevelopment planning #numer of wells and their locations and surface facilities requirements%is dependent on this.

nitially( only the static data of various &inds is availale. t must e analy,ed to gain someinsight into the inter-loc& communication. 'ater on( dynamic #pressure and production%data ecomes availale which is far more conclusive.

. 45


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S e c t i o n 2

!he commonly employed methods are descried elow in detail.

1. 4!$! data

!hese data provide gas gradients in the gas cap( oil gradient in the oil leg( watergradient in the water leg( and depth of free water level in each loc&.

2. )! data

!he oil density data under reservoir conditions #from )! analysis% is comparedfrom wells in various loc&s. !he difference in density at similar depths can only e8ist ifthere is no inter-loc& communication.

3. 0ell !est $ata

nterpretation of long-term pressure drawdownuildup test yields information on thepresence of lateral arriers within the well drainage radius. 0hile such information isnon-unique( inferences may e drawn.

;. /* ingerprinting

Oil samples from various wells are analy,ed for *1 - *12 components. !heseanalyses are compared statistically using cluster analysis to loo& for similarities anddifferences etween loc&s.

. Oil aturity nde8ing

@oth oil samples and solvent-e8tracts of cores are analy,ed for geo-chemical attriutesthat are related to hydrocaron maturity. !hese attriutes are compared to loo& forsimilarities and differences etween the loc&s.


47/82


VERTICALHETEROGENEITY- LORENZCOEFFICIENT

'ist the data #&( % fore each interval of thic&ness h. *alculate &h and h and arrange in a

descending &h order. !he following quantities are then calculated.

1. *umulative ractional )ore olume #h htot%

2. *umulative ractional low *apacity #&h &htot%

A linear scale plot of 2 vs. 1 is made #shown elow%.

Figure 2-32

!he value of ' for the successful floods is in the range of .2 to .;

. 47

1.

$


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S e c t i o n 2

VERTICALHETEROGENEITY- PERMEABILITYVARIATION: V

$y&stra P )arson introduced a statistical measure of reservoir heterogeneity and correlated itwith ertical "weep 6fficiency.

'ist data #&% for each sample. Arrange in descending order of permeaility #&%. or each value(calculate the C of numer of values that are larger. )lot )erm vs. MC higherM on log proailitypaper P fit straight line. "uch a plot is shown elow.

Figure 2-33

!his correlation was developed for *alifornia sandstone reservoirs and is applicale in a range ofmoility ratio floods at various stages #at various water-cuts% in stratified reservoirs. t is widelyused for this purpose in conventional forecasting of volumetric sweep efficiency of waterflooding.

6oth ) and 2 values are non3uni4ue since various property distributions can result inthe sa(enu(erical value.

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ote-rdering o! property values in descending or ascending order is notre!lective o! real situation. 6ence" tis metod sould not #e used !or layering tereservoir !or !lo& calculations.

!he figure elow shows:

On the right( the actual permeaility profile of a reservoir

On the left( the permeaility profile arranged in ascending order

Figure 2-34

t is ovious that the two representations will manifest different ehavior in a 0 project.

t should e noted that for "!A!"!*A' )H4)O"6"( often different permeaility ,ones arearranged in descending &-h order #descending permeaility if each ,one is defined y the samethic&ness( h% in order to calculate cumulative permeaility thic&ness( or cumulative flowcontriution. or e8ample( to set-up 'oren, and $y&stra-)arsons calculations( ,ones must eordered li&e this.

. 49


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S e c t i o n 2

AREALHETEROGENEITY

Areal heterogeneity has een handled y conventional interpolation and e8trapolation means.!hese are descried elow:

THE ASSUMED TRENDS METHOD

)roperty distriution is contoured on the asis of a &nown trend. t is quite an effective method inthe hands of a person who is well versed in the regional depositional !rends.

THE INVERSE DISTANCE METHOD

!he un&nown value is estimated on the asis of weight factors associated with the entire dataset. !he weight factors are calculated such that the influence of a &nown data point is inverselyproportional to its distance from the point of the un&nown value.

i

i -

i=. i

.

d=

.

d

0here: dj 9 distance etween the measured value and location of interestn 9 numer of neary points

i 9 weight factor

Q 9 un&nown value at point 8

!

/ i i

i=.

V = V

50


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THE INVERSE DISTANCE S;UARED METHOD

!he un&nown value is estimated on the asis of weight factors associated with the entire dataset. !he weight factors are calculated such that the influence of a &nown data-point is inverselyproportional to the square of its distance from the point of the un&nown value.

i

i

i=. i

.

d=

.

d

01i 9 1

Figure 2-35

. 51


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S e c t i o n 2

RESERVOIRCONNECTIVITY& PAYCONTINUITY& FLOODABILITY

4eservoir continuity and pay connectivity are the two most important factors that controldisplacement processes such as waterflooding.

igure 2-3< shows two major prolems in a waterflooding project( especially in lenticular andfluvial reservoirs.

)ossile indicators of these prolems include:

)oor nter-0ell *orrelation

'ow 5et to /ross !hic&ness 4atio

'ower than e8pected 0ell njectivity or )roductivity

'arge $ifference in 4eservoir )ressure from )@H P )O !ests

Kuantitative assessment is difficult at est ecause of the directional nature of flow. !heconcept of !looda#le payis demonstrated elow:

Figure 2-36

loodale )ay A: )ay that completely participates in the flood. All the availalepore space is contacted y the encroaching fluid.

)artially loodale )ay @: )ay that partially participates in the flood. "ome of the porespace is not contacted and the resident hydrocarons arepartially trapped y the encroaching fluid.

5on-loodale )ay *: )ay that does not effectively participate in the flood process.!he resident hydrocarons remain essentially trapped andunrecovered.

!he pay continuity is quantified y the following 6quation:

52

A

'i

7i

+i

@

*


53/82


66*!6 +')64*65! *O5!5H!R 9

!O!A' +'

!here are two common methods for estalishing the pay continuity in a reservoir. !hese fallunder two categories:

1. !racer tests

2. ultiwell pressure interference tests

A tracer used in a waterflood project should meet most of the following criteria: safe( easy tohandle( environmentally friendly( water solule( essentially insolule in oil( non-adsorent onroc& and metals( chemically inert( detectale in small amounts( ine8pensive.

!racers used are of the following types: #1% water solule Alcohols( #2% inorganic salts such asAmmonium( "odium( )otassium( #3% fluorescent dyes( and #;% 4adioactive sustances such as!ritiated water.

"ingle well pressure #)@H)O% tests and multi-well pressure #)ulsenterference% tests are theest way to assess ,onal connectivity and connectivity( to locate fracturesfaults( and to assessdirectional property trends in a reservoir.

!here are many ways to estalish reservoir continuity $ualitatively( once reservoir data isavailale and production trends are estalished.

1. 4egional )ressure and )roduction !rends

2. 4atio of OO) estimate from olumetric and @6

f this ratio is 9 1( all pay is participating.

f this ratio is > 1( some pay is isolated and not participating.

3. 4atio of 6H4 #estimated ultimate recovery% from a simulation model study#utili,ing a history-matched model% and the decline curve analysis.

f the two values are close( all pay is participating. f simulation estimate is greater thanthe decline curve analysis( some pay is not connected to the producing wells.

*ontinuityconnectivity etween two wells can e $uantitatively measured and plottedversus the hori,ontal distance. igure 2-3N elow shows such a relationship for the eans"an Andres reservoir #under apattern waterflood earlier and now under a pattern *O2 - lood%in 0est !e8as.

. 53


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S e c t i o n 2

Figure 2-37

ote(ands may not #e correlative #et&een &ells" #ut tey may still #e connected:in te 3%* pore space;.

FLOODABILITY

loodailityof pay is a very important aspect in a 0 process. !o e floodale( a pay intervalmust e:

1. *ontinuous etween injector and producer

2. njection supported

3. 6ffectively completed in a producer

+ence( all the continuous pay is not necessarily floodale.

!he two-well schematic elow illustrates the difference etween continuity and floodaility.

54


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Figure 2-38

'ayers A( $( ( and + are geologically continuous. !hey together contain 23 of the inter-well porevolume.

'ayers * and + are injection supported.

'ayers $ and + are completed effectively in the producer.

'ayer + is the only one that is effectively floodale.

. 55


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S e c t i o n 2

EMPIRICALLAWSOFHETEROGENEITY

1. All reservoirs are heterogeneous in roc& and fluid properties

0hen we &now little aout them( we assume them to e homogeneous

2. !he more we get to &now them( the more heterogeneous they ecome

+eterogeneity is proportional to the amount of time( effort and money spent

3. +eterogeneity has major impact on reservoir ris&s and uncertainty related to:

olumes of hydrocarons-in-place

4ecovery 6fficiency

0ell )roductivity

4eservoir )erformance

;. Hnless you wal& a mile or two along the outcrop of the reservoir formation( you willhave little appreciation of roc& heterogeneity

56


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HYDROCARBONCLASSIFICATION

+ydrocarons are classified with respect to their state under the reservoir )ressure and!emperature conditions. "urface conditions #) P !% are also considered when classifyingthe production.

+ydrocaron systems in the reservoir are divided into five main categoriesI

1. $ry /as

2. 0et /as

3. /as *ondensate

;. olatile #high shrin&age% Oil

. @lac& #low shrin&age% Oil

A simple su-division on the asis of solution gas-oil ration is given elow.

Figure 2-39

@lac& Oils and olatile Oils are candidates for a 0 project. A volatile oil requires moreserious consideration due to its nature of rapidly changing into gas when pressure falls elowthe ule point pressure.

/as reservoirs #dry( rich( or condensate% are never intentionally waterflooded( as a largefraction of the gas is left trapped in the reservoir due to the water-wet nature of the roc&.

. 57


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S e c t i o n 2

CANDIDATE RESERVOIRS FOR WATERFLOODING

Figure 2-40

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PHASE BEHAVIOR

C$&00**(&t*!" ! & M9$t*-C!8!""t S%0t8

Figure 2-41

. 59


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S e c t i o n 2

D*"*t*!"0


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BLAC7 5LOW SHRIN7AGE6 OIL

C!"*t*!"0

*ritical point lies to the right of the *ricondenar

Kuality 'ines are closely spaced near the $ew )oint line

P!9(t*!" B4&/*! D9*"# P009 D$t*!"

)roduced fluids in the separators are in two phases

"ustantial amount of liquids recovery

/O4 >1( "*"!@

Oil /ravity > ; A)

*olor is lac& to dar& rowngreen

)roducing /O4 continues to increase with time( as shown on

the right

Oil gravity decreases gradually during most of the producing

life. 'ater in the life #when the producing gas ecomes wet%(gravity increases due to the addition of gas condensate to

the oil

P!9(t*!" B4&/*! D9*"# W&t$!!*"#

0aterflood projects have een initiated at various pressure levels ranging etween A and@. !heir performance differs from one another.

. 61


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S e c t i o n 2

VOLATILE 5HIGH SHRIN7AGE6 OIL

C!"*t*!"0

*ritical )oint lies to the right of the *ricondenar

4eservoir temperature is closer to the *ritical temperature

P!9(t*!" B4&/*! D9*"# P009 D$t*!"

)roduced fluids in the separators are in two phases

'ow liquid recoveries /O4 >1(N "*"!@

Oil /ravity ; $egrees A)

"ome color

= 2 4@"!@

)roducing /O4 increases with time ut far less than for the

@lac& Oils

Oil gravity increases gradually with the addition of condensates

from the gas into the produced oil phase

P!9(t*!" B4&/*! D9*"# W&t$!!*"#

0aterflood projects have een initiated at various pressure levels ranging etween A and@ule )oint )ressure #or not very far from there%.

62


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Figure 2-42+ ,o)u#e Re)ationshi( *or a %)ac oi) s'ste#+

. 63


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S e c t i o n 2

PVT PROPERTIESOFBLACKOIL

64


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4elationship @etween "urface 8 4eservoir *onditions

Figure 2-43

. 65


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S e c t i o n 2

T -il Formation 0olume Factor


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OILFIELDWATERS

FORMATION WATER

!he naturally occurring water in the reservoir pore space at discovery is called the formation

water or the interstitial water. "ince it has een associated with the particular reservoir roc& andcrude oil over a long period of time( it is in the state of complete chemical equilirium.

IN


68/82

S e c t i o n 2

WATER PROPERTIES

!he following physical properties are of interest:

1. $ensity of 0ater is 1. gmcc #3 )ound@@'%

2. Amount of $issolved 5atural /as in 0ater( 4sw"oluility of natural gas in water is quite lowAverage of 1 to 2 "*"!@

3. ormation olume actor of 0ater( @wAssume equal to 1. 4@@'"!@

;. *ompressiility of 0ater( *w

. iscosity of 0ater

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CHEMISTRYOFWATERMOVEMENTTHROUGHTHERESERVOIR

As the injection water #varying concentration of dissolved salts% moves through the reservoir( itcontacts the formation water and hydrocarons.

(tripping ta&es place and water pic&s up some light ends( *O2 and +2"( as shown inthe figure elow.

Figure 2-44

(olu#ility o! natural gas in &ater is a function of temperature( pressure and !$".

. 69


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S e c t i o n 2

Figure 2-45

70


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ROCKANDFLUIDPROPERTIESFORANIDEALWATERFLOODPROJECT

1. +omogeneous and 5on-ractured 4eservoir

2. 5on-)artitioned( sotropic #E89 Ey%( and *ontinuous )ay

3. +igh )orosity P )ermeaility 4oc&

;. 'ow )ermeaility *ontrast etween 'ayers

. +igh EyEh4atio for +igh 4elief "tructures


72/82

S e c t i o n 2

CASESTUDYNO.

CHANGE IN GEOLOGIC CONCEPTS FORCE A CHANGE IN WATERFLOOD PLAN

!he "an Andres caronate reservoir in the $enver Hnit in 0asson "an Andres field( !e8aswas produced at ;-Acre well spacing under the solution gas drive recovery scheme. Awaterflood project was thereafter initiated to increase oil rate and recover additional oil.

@ased on the initial geological concept that reservoir is continuous with a common O0*( waterwas injected elow O0* in the edge wells. 0ater was e8pected to move laterally in the aquiferand push oil vertically upwards.

!he peripheral waterflood did not perform as e8pected:

1. )4 #injection-production ratio% could not e sustained( as injectivity in the edge wellswas low due to lower UEhL.

2. Oil response was erraticI some up-dip wells showed rate gain while others did note8perience any pressure or rate increase

A detailed geologic study incorporating pressure-production data showed that pay ,ones arenot only discontinuous #not floodale on the ;-Acre well spacing% ut also have differentO0*Ds.

@ased on the new geological concept( the peripheral plan was modified into a pattern flood andinfill wells were drilled on 2-Acre well spacing.

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!he pattern flood had a great success. After the waterflood reached its economic limit( a*O2-flood was initiated and the well spacing was further reduced to 1-Acre spacing. t is

currently an ongoing successful 6O4 project.

. 73


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S e c t i o n 2

CASESTUDYNO. !

NEW TECHNOLOGY AIDS RESERVOIR CHARACTERIZATION

)eripheral water injection in the /hawar Ara-$ reservoir( "audi Araia( efficiently displaced oil

from the flan&s of the reservoir to the crestal producers( until water rea&through occurred in anerratic manner in some flan& wells while others in similar structural locations continued toproduce dry oil. !his is depicted in the figure elow.

5o hard data was there to indicate faults and fractures in the reservoir. 5o well had evercrossed a fault( and well tests had not positively identified any fault or major discontinuity. naddition( there was a common elief #miss-elief% that faults in limestone and dolomitereservoirs cannot e8ist and will heal up if induced.

!o match flood fronts and water-cut history in wet wells( reservoir simulation models of the 1F


75/82


+ow would you classify these pressure systems at discovery

5ormal )ressure

/eo )ressure #Anormal%

"u-5ormal )ressure

PROBLEMNO. !

4! pressure data has een collected in an infill well in a stratified sandshale reservoir.nterpret this data for the effect of the shale layers on reservoir flow continuity. 0hat otherinformation can you deduce

. 75


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S e c t i o n 2

PROBLEMNO. "

6stimate oil-water contact in the reservoir shown elow. !he availale data is:

1. !he discovery well A found full oil #oil gradient 9 .3 psift% column with pressure of; psig at ; ft ss.

2. !he first delineation well @ was wet #water gradient 9 .; psift% with pressure of 1(Npsig at 1(B ft ss.

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PROBLEMNO. #

@elow are "amples ta&en from different layers in a reservoir( one sample is ta&en from eachlayer.

"amples were ta&en from 3 different wells

1% Average the data and develop a semi-log )ermeaility - )orosity correlation for the entire

reservoir.

2% "hould you use one )ermeaility - )orosity correlation for the entire reservoir

0ell V1 0ell V2 0ell V3

nterval )orosity!hic&ness

h #ft% md% md% md%

. .1 .2 .2

1 .1 1 .B .

3 .1 1 3.2 1.2

2 .2 1 12.< 3.

1 .2 1 . N.

. 77


78/82

S e c t i o n 2

PROBLEMNO. $ & %

@elow are "amples ta&en from different layers. "amples have een analy,ed from eachlayer. 3 different roc& types with different )erm-)orosity relationships #the same )orosity in thise8ample is used for simplicity% have een developed for this reservoir.

1% $etermine the 'oren, *oefficient of +eterogeneity for each roc& type.

2% f these roc& types can e identified easily in different areas of the field( then which areas willma&e the est candidate for 0aterflooding

0ell V1 0ell V2 0ell V3

nterval )orosity!hic&ness

h #ft% md% md% md%

. .1 .2 .2

1 .1 1 .B .

3 .1 1 3.2 1.2

2 .2 1 12.< 3.

1 .2 1 . N.

For PR-


79/82


dentify the following sand odies:

1. Attic oil

2. $ead 6nds #!rapped% oil

3. loodale oil

PROBLEMNO. '

6stimate permeaility value at the oservation well Q from the data given on four of the wellsin a waterflood pilot( y using all conventional methods.

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S e c t i o n 2

PROBLEMNO. (

*alculate continuity percent etween 0ells 1 and 2 in the reservoir with the stratification shownelow:

0hat will e the enefit of drilling nfill 0ell 3 on the continuity percent

PROBLEMNO. )

4ed 4eservoir( Average 4elative )ermeaility *haracteristics

!wo samples having porosity values of 12.3C and 22.NC have een tested to determine theirwater-oil relative permeaility characteristics. !hese are provided on the attached $ata sheet.

Kuestions

1. 0hat definition of asolute permeaility was used to prepare these curves

2. or the sample with 22.NC porosity( what are the effective permeailities to oil and water ata water saturation of ;F percent

3. $oes the roc& from which these samples were otained appear to e water-wet or oil-wet

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'aoratory 4elative )ermeaility 4esults

"ample 3A

)orosity #frac% 9 .22NAir )ermeaility #md% 9 23.B

)ermeaility to Oil at "wir #md% 9 21.;

"w Ero Erw.231 1. ..31B .


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S e c t i o n 2

PROBLEMNO.

*alculate injection water requirement for maintaining average reservoir pressure at 3( psigand temperature of 1W in order to provide for voidage replacement alance( at the timewhen oil production rate is ( "!@$ay( gas production rate is 1 "*$ay( and water

production rate is 1( "!@$ay.

luid properties and given elow:

Oil ormation olume actor 9 1.9 4@"!@

/as ormation olume actor - .1 4@"*

0ater ormation olume actor 9 1. 4@"!@

"olution /O4 at 3( psig P 1W 9 "*"!@

caracterización de yacimientos

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