chap 14- pvt

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PVTPVTPressure Volume TemperaturePressure Volume Temperature

Adrian C Todd Adrian C Todd

Heriot-Watt University Heriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING

Heriot-Watt University Heriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING



PVT - ScopePVT - Scope

q

Reservoir fluid analysis provides key data toReservoir fluid analysis provides key data tothe petroleum engineer.the petroleum engineer.

q Quality of the testing is important to ensureQuality of the testing is important to ensure

realistic values used in design.realistic values used in design.

q Sample quality is the first quality issue.Sample quality is the first quality issue.



PVT AnalysisPVT Analysis

q Provides data for field evaluation and designProvides data for field evaluation and design

® Reservoir calculationsReservoir calculations

® Well flow calculationsWell flow calculations

® Surface facilitiesSurface facilities




q Correlation between pressure and volume atCorrelation between pressure and volume atreservoir temperature.reservoir temperature.

q Various physical constants in reservoir Various physical constants in reservoir

calculations; viscosity, density, compressibility.calculations; viscosity, density, compressibility.q Effect of separator conditions on Bo & GOR. etc.Effect of separator conditions on Bo & GOR. etc.

q Chemical composition of the volatile components.Chemical composition of the volatile components.



PVT AnalysisPVT Analysisq Scope of the analysis depends on the nature of the fluid.Scope of the analysis depends on the nature of the fluid.

q Dry gasDry gas::

®composition, specific gravity, Bg, z, and viscositycomposition, specific gravity, Bg, z, and viscosity

q Wet gasWet gas::

®as above plus information on liquid drop out, quantities andas above plus information on liquid drop out, quantities and

compositions.compositions.

q Oil system:Oil system:

®Bubble point pressure, composition of reservoir and producedBubble point pressure, composition of reservoir and producedfluids, Bo, GOR, Bt and viscosity. All as function of pressure.fluids, Bo, GOR, Bt and viscosity. All as function of pressure.

Co.Co.

®Below Pb considerations.Below Pb considerations.




q Gas condensate:Gas condensate:

®Reflect wet gas and oil.Reflect wet gas and oil.

®Dew point pressureDew point pressure

®Compressibility above Pd.Compressibility above Pd.

®Impact of dropping below PdImpact of dropping below Pd



SamplingSampling

q Clearly the sample has to representative of Clearly the sample has to representative of

the reservoir contents or the drainage area.the reservoir contents or the drainage area.

q Desirable to take samples early in the life of Desirable to take samples early in the life of

the reservoir.the reservoir.

q Either sub-surface or surface sampling.Either sub-surface or surface sampling.



Sub-Surface SamplingSub-Surface Sampling

q Can only beCan only be

representative whenrepresentative whenpressure at samplingpressure at sampling

point is above or equal topoint is above or equal to

the saturation pressure.the saturation pressure.

q At pressure close to At pressure close tosaturation pressuresaturation pressure

serious possibility of serious possibility of

sample integrity beingsample integrity being

lost.lost.q In recent yearsIn recent years

considerable advance inconsiderable advance in

downhole fluid samplingdownhole fluid sampling



Surface SamplingSurface Sampling

q Samples of oil and gas taken from separator Samples of oil and gas taken from separator connected with the well.connected with the well.

q Fluids recombined in the laboratory on theFluids recombined in the laboratory on the

basis of the produced GORbasis of the produced GOR



Vertical andVertical and

HorizontalHorizontalSeparatorsSeparators



Separator Gas SamplingSeparator Gas Sampling



Separator Liquid Sampling by GasSeparator Liquid Sampling by Gas

DisplacementDisplacement



Separator Liquid Sampling by Water Separator Liquid Sampling by Water

DisplacementDisplacement



Wellhead samplingWellhead sampling

q A low cost option. A low cost option.

q Only possible for veryOnly possible for very

undersaturatedundersaturated

sytsems.sytsems.

q Still single phase atStill single phase at

wellhead.wellhead.



Sampling Wet Gas and Gas CondensateSampling Wet Gas and Gas Condensate

SystemsSystems

q Use and value of any PVT study dependantUse and value of any PVT study dependant

on the quality of the sample collected.on the quality of the sample collected.

q

Sampling wet gas and gas condensate fluidsSampling wet gas and gas condensate fluidscan give rise to errors.can give rise to errors.

q During sampling procedure it is possible toDuring sampling procedure it is possible to

alter the conditions so that samples are notalter the conditions so that samples are not

representative.representative.

q An important consideration is the phase An important consideration is the phase

behaviour.behaviour.



Phase Behaviour.Phase Behaviour.

q

Fluids uniquelyFluids uniquelydescribed by phasedescribed by phase

diagram.diagram.

q

Within the phaseWithin the phase

diagram system isdiagram system is

two phase.two phase.

q Whereas outsideWhereas outside

the phase envelopethe phase envelopesingle phasesingle phase

Single phase

Two phase



Phase Behaviour.Phase Behaviour.q The separation of oilThe separation of oil

and gas as predictedand gas as predicted

by the phase diagramby the phase diagramresults in each phaseresults in each phase

having its own phasehaving its own phase

diagram.diagram.

q The oil exists at itsThe oil exists at itsbubble point .bubble point .

q The gas exists at itsThe gas exists at its

dew point.dew point.

q This behaviour hasThis behaviour has

important implicationsimportant implications

on well samplingon well sampling



Sampling WetSampling Wet

Gas and GasGas and Gas

CondensateCondensate

ReservoirsReservoirs

q

Potential locationsPotential locationsfor reservoir for reservoir

samplingsampling

S GS li W t G d



Sampling Wet Gas andSampling Wet Gas and

Gas CondensateGas Condensate

ReservoirsReservoirsq LocationLocation

q 1. Reservoir 1. Reservoir

q 2.Bottom-hole2.Bottom-hole

q 3.Well Head3.Well Head

q 4. Separator 4. Separator q For.

q 1. Ideal

q 2. 1-phase

q 3. Cost

q 4. Cost, 1-phase,

buffer,sampling volume

q Against Against

q 1. Impossible1. Impossible

q 2. Representative ? Technology, Cost, Handling.2. Representative ? Technology, Cost, Handling.

q 3. 2-phase ? Representative ?,3. 2-phase ? Representative ?,

q 4.Gas/liquid volumes,, separator conditions,4.Gas/liquid volumes,, separator conditions,

Representative ?,Representative ?,



Sampling Wet Gas andSampling Wet Gas and


Reservoirs-Flowing well.Reservoirs-Flowing well.

q Well behaviour canWell behaviour can

significantly influencesignificantly influence

nature andnature and

characteristics of fluidscharacteristics of fluidsproduced.produced.

q Flowing well gasFlowing well gas

condensate - mist flowcondensate - mist flow

S li W t GS li W t G



Sampling Wet GasSampling Wet Gas

and Gas Condensateand Gas Condensate

Reservoirs-Shut in wellReservoirs-Shut in well

after flow.after flow.q Well acts as a separator Well acts as a separator

q Liquid rains down andLiquid rains down and

accumulates at bottomaccumulates at bottom

of well.of well.

q Pressure builds up inPressure builds up in

the well and disturbedthe well and disturbed

formation.formation.q Some gas goes backSome gas goes back

into solution.into solution.



Well flow after shut in.Well flow after shut in.

q Large variations inLarge variations in

compositions of producedcompositions of producedfluids.fluids.

q Early period lean gasEarly period lean gas

produced. High GORproduced. High GOR

q When fluids produced fromWhen fluids produced from

bottom of well. Liquids muchbottom of well. Liquids much

lower GOR.lower GOR.

q

Then fluids from disturbedThen fluids from disturbedreservoir zonereservoir zone

q Eventually fluids fromEventually fluids from

undisturbed reservoir undisturbed reservoir



Sampling Wet Gas and GasSampling Wet Gas and Gas

Condensate ReservoirsCondensate Reservoirs

q In assessing quality of samplesIn assessing quality of samples

important to know how long it willimportant to know how long it will

take for unrepresentative samples totake for unrepresentative samples to

be displaced from reservoir.be displaced from reservoir.

q Volumetrics required on wells,Volumetrics required on wells,

facilities and near well volumesfacilities and near well volumes



Separator Sampling PointsSeparator Sampling Pointsq A very practical issue is A very practical issue is

the location of samplingthe location of sampling

points on separators.points on separators.

q Often located for Often located for

convenience for convenience for

accessibility.accessibility.

q Important to recogniseImportant to recognise

that the gas and liquid inthat the gas and liquid in

a separator are at their a separator are at their

saturation pressure.saturation pressure.q Small changes will resultSmall changes will result

in liquid drop out and gasin liquid drop out and gas

being producedbeing produced

Liquid in gas line

Gas in liquid line

Iso kinetic sampling



Sampling DetailsSampling Details

q Important to record and keep note off following.Important to record and keep note off following.These records to go with samplesThese records to go with samples

q Date and timeDate and time

q Cylinder identificationCylinder identification

q Location of sampling points.Location of sampling points.

q

Temperature and pressureTemperature and pressureq GOR in separator GOR in separator

q Any special details ( H Any special details ( H22S in sample, etcS in sample, etc



Equipment for PVT AnalysisEquipment for PVT Analysis

q Apparatus for transfer and recombination of Apparatus for transfer and recombination of separator oil and gas samples.separator oil and gas samples.

q Apparatus for measuring gas and liquid Apparatus for measuring gas and liquid

volumesvolumesq Apparatus for performing separator tests Apparatus for performing separator tests

q PVT cell and displacing pumps.PVT cell and displacing pumps.

q High pressure viscometer High pressure viscometer

q Gas chromatograph or equivalent.Gas chromatograph or equivalent.

E i t f PVT A l i S b fE i t f PVT A l i S b f



Equipment for PVT Analysis-SubsurfaceEquipment for PVT Analysis-Subsurface

SamplesSamples



Equipment for PVT Analysis-Surface SamplesEquipment for PVT Analysis-Surface Samples

f G C



Equipment for PVT Analysis-Gas CondensateEquipment for PVT Analysis-Gas Condensate

SamplesSamples

PVT T tPVT T t



PVT TestsPVT Tests

q To provide data for reservoir calculationsTo provide data for reservoir calculations

q To provide physical property data for well flow calculationsTo provide physical property data for well flow calculations

q For surface facility designFor surface facility design

q The reservoir calculations are the main driving force for theThe reservoir calculations are the main driving force for the

various tests.various tests.

q Over recent years reservoir simulation capability has generatedOver recent years reservoir simulation capability has generated

the need to extend compositional description from C7+ to inthe need to extend compositional description from C7+ to in

some cases C29+.some cases C29+.

q PVT report provides source of all reservoir engineeringPVT report provides source of all reservoir engineering

properties for behaviour over exploration, development andproperties for behaviour over exploration, development and

productionproduction



Main PVT TestsMain PVT Tests

q

Flash vaporisation or relative volume test.Flash vaporisation or relative volume test.q Differential vaporisation test.Differential vaporisation test.

q Separator tests.Separator tests.

q Viscosity measurements.Viscosity measurements.

q Compositional measurements.Compositional measurements.

q

Special studies: e.g. Interfacial tension.Special studies: e.g. Interfacial tension.



Simple layout of a PVT FacilitySimple layout of a PVT Facility



Flash Vaporisation ( Relative Volume ) TestFlash Vaporisation ( Relative Volume ) Test

q Determination of the correlation between pressureDetermination of the correlation between pressure

and volume at reservoir temperature.and volume at reservoir temperature.

q The system never changes during the test.The system never changes during the test.

q The gas remains in equilibrium with the oil throughThe gas remains in equilibrium with the oil through

out the test.out the test.

q The behaviour below the bubble point does notThe behaviour below the bubble point does not

reflect reservoir behaviour, where gas has greater reflect reservoir behaviour, where gas has greater

mobility than the oil.mobility than the oil.

q This test determines theThis test determines the Bubble Point Bubble Point pressurepressure

corresponding to the reservoir temperature.corresponding to the reservoir temperature.



Flash VaporisationFlash Vaporisation

(Relative Volume ) Test(Relative Volume ) Test

q Liberated gas remains inLiberated gas remains in

equilibrium with oilequilibrium with oil

Fl h V i ti (R l ti V l ) T tFl h V i ti (R l ti V l ) T t



Flash Vaporisation (Relative Volume ) TestFlash Vaporisation (Relative Volume ) Test

By plotting P versus V, a break in the slope is obtained at

the Bubble Point pressure.



Flash VaporisationFlash Vaporisation

(Relative Volume ) Test(Relative Volume ) Test

q Tests at constant pressureTests at constant pressure

and varying temperatureand varying temperature

enables thermal expansionenables thermal expansion

coefficient to be obtained for coefficient to be obtained for

well flow calculations.well flow calculations.

( )12

2 2 1

1 1 2 2

V VThermal expansion,V T T

V volume at T , V volume at T

−β =−

= =




q Above bubble point compressibility of Above bubble point compressibility of oil at reservoir temperature can beoil at reservoir temperature can be

determined.determined.

q No free gasNo free gas

( )2 1

2 1 2

2 2

1 1

V Vc

V P P

V =volume at pressure P

V =volume at pressure P

−=

−




q Main objectives:Main objectives:

® Reservoir bubble pointReservoir bubble point

pressure.pressure.

® Together withTogether withinformation from separator information from separator

tests, formation volumetests, formation volume

factor above bubble point.factor above bubble point.



Differential VaporisationDifferential Vaporisation

q Below bubble point in reservoir gas liquidBelow bubble point in reservoir gas liquid

separation in the reservoir is a constantseparation in the reservoir is a constantchanging system.changing system.

q A test has been design to attempt to simulate A test has been design to attempt to simulate

this process.this process.q In theIn the differential vaporisationdifferential vaporisation test liberatedtest liberated

gas is removed from the cell step wise.gas is removed from the cell step wise.

q At each step below bubble point, volumes At each step below bubble point, volumesdensities , gas expansion and compressibilitydensities , gas expansion and compressibility

determined.determined.

q

Bubble point starting point.Bubble point starting point.





Differential liberation process

Flash liberation process





ff



Differential VaporisationDifferential Vaporisationq 8-10 pressure reduction steps at reservoir temperature.8-10 pressure reduction steps at reservoir temperature.

q

Final step to 60Final step to 60oo

F.F.q Remaining oilRemaining oil Residual Oil Residual Oil



Differential Vaporisation vs.Flash VaporisationDifferential Vaporisation vs.Flash Vaporisation

q

Flash liberation considered to take placeFlash liberation considered to take placebetween reservoir and surface.between reservoir and surface.

q Differential liberation considered to beDifferential liberation considered to be

representative of the process in the reservoir representative of the process in the reservoir below bubble point pressure.below bubble point pressure.

q Differential tests carried out to obtain oilDifferential tests carried out to obtain oil

formation volume factors and GOR’s toformation volume factors and GOR’s to

predict behaviour below bubble pointpredict behaviour below bubble point

pressure.pressure.

S t T t



Separator TestsSeparator Testsq Objective to determine impact of separator Objective to determine impact of separator

conditions on Bo, GOR, and produced fluid physicalconditions on Bo, GOR, and produced fluid physicalproperties.properties.

q Not the interest of facility designers.Not the interest of facility designers.

q Carried out to give an indication of oil shrinkage andCarried out to give an indication of oil shrinkage andGOR when fluids produced to surface.GOR when fluids produced to surface.

q There are not uniques values for Bo & GOR. TheyThere are not uniques values for Bo & GOR. They

depend on separator conditions.depend on separator conditions.q Starting point for the test is the bubble pointStarting point for the test is the bubble point

pressure.pressure.

q Fluid produced at surface conditons.Fluid produced at surface conditons. Stock tank oil Stock tank oil

S TS t T t



Separator TestsSeparator Tests

PVT Cell pressure kept at

bubble point

S t T tS t T t





bubble point

S t T tS t T t





bubble point

q V resV res

Vi itVi it



ViscosityViscosity

q

Measured at different pressures above andMeasured at different pressures above andbelow bubble point pressure.below bubble point pressure.

q Below bubble point pressure carried out under Below bubble point pressure carried out under

differential conditions.differential conditions.

q Rolling ball or capillary tube methods of Rolling ball or capillary tube methods of

measurementmeasurement

H d b l iH d b l i



Hydrocarbon analysisHydrocarbon analysis

q Analysis from C1 to an upper C number based Analysis from C1 to an upper C number based

on paraffin series.on paraffin series.

q Historically C6 & C7+. Much higher analysisHistorically C6 & C7+. Much higher analysis

capability.capability.

q C+ characterised by specific gravity andC+ characterised by specific gravity and

apparent molecular weight.apparent molecular weight.

q Latter by depression of freezing point.Latter by depression of freezing point.

q Higher C+ characterisation helpful to processHigher C+ characterisation helpful to process

engineers re. solid phase formation.engineers re. solid phase formation.

W d A h h ltW d A h h lt



Wax and AshphaltenesWax and Ashphaltenes

q

Solid phase formation series concern.Solid phase formation series concern.q Heavy components at low temperatures canHeavy components at low temperatures can

form solid phases.form solid phases.

q Wax in transfer lines and process facilities.Wax in transfer lines and process facilities.q Ashphaltene are larger molecules of hydrogen Ashphaltene are larger molecules of hydrogen

and carbon plus sulphur, oxygen or nitrogen.and carbon plus sulphur, oxygen or nitrogen.

q Ashphaltenes do not dissolve in oil but are Ashphaltenes do not dissolve in oil but aredispersed as colloids.dispersed as colloids.

WaxWax



CrystallizationCrystallization

TemperatureTemperature

q Different tests used:Different tests used:

q Filtering and measuringFiltering and measuring

resistance to flow atresistance to flow at

different temperatures.different temperatures.q Appearance temperature Appearance temperature

is considered to beis considered to be

affected by super affected by super

cooling.cooling.

q The disappearanceThe disappearance

temperature istemperature is

considered to be theconsidered to be the

equilibrium value.equilibrium value. Core Laboratories



WaxWax

CrystallizationCrystallizationTemperatureTemperature

Core Laboratories

Summary of results provided by an oil sampleSummary of results provided by an oil sample




PVT test.PVT test.

q Saturation pressure, -bubble point.Saturation pressure, -bubble point.

q Compressibility coefficient.Compressibility coefficient.

q

Coefficient of thermal expansion.Coefficient of thermal expansion.q Relative total volume of oil and gas, VRelative total volume of oil and gas, Vtt

q Cumulative relative volume of gas. VCumulative relative volume of gas. Vgg

q

Cumulative relative volume of oil. VCumulative relative volume of oil. Voo




Summary of results provided by an oil sampley p y p

PVT test.PVT test.

q

Gas formation volume factor or gas expansion factor Gas formation volume factor or gas expansion factor q Gas compressibility factor.Gas compressibility factor.

q Specific gravity of gasSpecific gravity of gas

q Liquid densityLiquid density

q Viscosity of liquids as a function of pressure.Viscosity of liquids as a function of pressure.

q Oil formation volume factor Oil formation volume factor

q Solution gas- oil ratio. Shrinkage of separator oil toSolution gas- oil ratio. Shrinkage of separator oil totank oiltank oil

q Hydrocarbon analysis of reservoir and produced fluidsHydrocarbon analysis of reservoir and produced fluids

Volumetric relationship of fluids in an oilVolumetric relationship of fluids in an oil



pp

PVT testPVT test

Reference point

bubble point





PVT testPVT test

Reference point

Stock Tank Conditions

Volumetric relationship of fluids in an oil PVTVolumetric relationship of fluids in an oil PVT



Volumetric relationship of fluids in an oil PVTVolumetric relationship of fluids in an oil PVT

testtest

Interfacial Tension IFTInterfacial Tension IFT



Interfacial Tension, IFTInterfacial Tension, IFT

q Impact of IFT now considered an importantImpact of IFT now considered an important

aspectaspect

q particularly for gas condensatesparticularly for gas condensates

q

IFT has a significant impact on the behaviour IFT has a significant impact on the behaviour of residual condensate saturation andof residual condensate saturation and

associated relative permeability.associated relative permeability.

q IFT is very low as critical point approachedIFT is very low as critical point approached

Interfacial Tension MeasurementsInterfacial Tension Measurements




q Most common method pendant dropMost common method pendant drop

( )2

ρ − ρσ = L V

e gd

l

( )2 ρ − ρσ =

L V

e gd

l

l = shape factor a function of ds/de




Interfacial Tension Measurementste ac a e s o easu e e tsq For very low IFT size of tube too small to suspend drop.For very low IFT size of tube too small to suspend drop.

q Thin wire can be usedThin wire can be used

q Light scattering has been used.Light scattering has been used.

q Heriot-Watt method -rising film methodHeriot-Watt method -rising film method

Retrograde CondensationRetrograde Condensation



Retrograde CondensationRetrograde Condensation

q Saturation pressure is the dew point pressure.Saturation pressure is the dew point pressure.

q Gas condensate cells have a window toGas condensate cells have a window to

visualise dew point.visualise dew point.

q Not possible to determine by change of slopeNot possible to determine by change of slope

of compressibilities of gas and liquid..of compressibilities of gas and liquid..





q

Main aspects of PVT study:Main aspects of PVT study:® Constant mass expansionConstant mass expansion

® Constant volume depletionConstant volume depletion

® Specialised tests ( IFT)Specialised tests ( IFT)

® Compositions of oil & gasCompositions of oil & gas

T Compositions of fluids are generally made by blowingCompositions of fluids are generally made by blowing

down samples and recombining the resultant liquid anddown samples and recombining the resultant liquid and

gas phase compositions.gas phase compositions.

Gas Condensate Constant Mass StudyGas Condensate Constant Mass Study



Gas Condensate- Constant Mass StudyGas Condensate- Constant Mass Studyq No fluids removed from the cellNo fluids removed from the cell

q

Purpose to determine z value above dew point.Purpose to determine z value above dew point.q Determine dew point pressureDetermine dew point pressure

Dew point observed as drops on window

Gas Condensate- Constant Volume DepletionGas Condensate- Constant Volume Depletion



pp

q Carried out to simulate condition below dew pointCarried out to simulate condition below dew point

q Series of pressure expansionsSeries of pressure expansions

q Volume of cell returned to original volumeVolume of cell returned to original volume

Gas Condensate Constant Volume DepletionGas Condensate Constant Volume Depletion



Gas Condensate- Constant Volume DepletionGas Condensate- Constant Volume Depletion

q Liquid volume produced below dew pointLiquid volume produced below dew point

generates a liquid drop out curve.generates a liquid drop out curve.

Gas Condensate-Special tests IFT andGas Condensate-Special tests IFT and



Full Compositional dataFull Compositional data

Hg

Condensate

Gas

Hg

Density cell

High pressure

sampling

Stirrer

Gas Condensate-Special tests IFT andGas Condensate-Special tests IFT and



Full Compositional dataFull Compositional data

Hg

Condensate

Gas

Hg

Density cell

High pressure

sampling

Hg

Pendant drop

Interface

Rising film methodRising film method



Rising film methodRising film method

Vapour

Liquid

1 cm

Rising film

thickness

Rising film method - near critical pointRising film method - near critical point



Rising film method - near critical pointRising film method - near critical point

Very thin meniscus

height

Vapour

Liquid

1 cm

Understanding PVT Rep[ortsUnderstanding PVT Rep[orts



Understanding PVT Rep[ortsUnderstanding PVT Rep[orts

q Purpose of the PVT report:Purpose of the PVT report:

q Although can be used for applications from Although can be used for applications from

reservoir to surface facilities. Reservoir engineeringreservoir to surface facilities. Reservoir engineering

provides the main basis.provides the main basis.

q Provides much of black oil information.Provides much of black oil information.

q Material balance equation basis for report.Material balance equation basis for report.

q PVT report provides main data for MB equation.PVT report provides main data for MB equation.

q Both flash and differential separation assumed.Both flash and differential separation assumed.

q Specific to a particular fluidSpecific to a particular fluid



Example PVT report.Example PVT report.

Example PVT reportExample PVT report




E l PVT tE l PVT t




ExampleExample



Examplea p e

PVTPVT

report.report.

S t T tSeparator Test



Separator TestSeparator Test

SeparatorSeparator



Separator Separator

TestTest





READ THE FOOTNOTES



Fluid Properties above bubble pointFluid Properties above bubble point



Fluid Properties above bubble pointp p

q Relative Volume Test - Flash Vaporisation TestRelative Volume Test - Flash Vaporisation Test

RelativeRelative



Volume Test -Volume Test -

FlashFlash

VaporisationVaporisation

TestTest



P

V

Pb

Vsat

BB above bubble pointabove bubble point



BBoo above bubble pointabove bubble point

ovol. reservoir oilB

vol. stock tank oil=

o

vol. bubble point oil vol. reservoir oil

B vol. stock tank oil vol. bubble point oil= ×

From separator

test

Above bubble point Above bubble point



pp

q Density above bubble point obtained byDensity above bubble point obtained by

combining data from separator test andcombining data from separator test andrelative volume tests.relative volume tests.

o

o ob rel

1 1v v vρ = =

o

o ob rel

1 1v v v

ρ = =

Above bubble point Above bubble point



pp

q

Compressibility above bubble point can beCompressibility above bubble point can beobtained from relative volume testobtained from relative volume test

o

T

1 vCv p δ= − δ o

T

1 vC

v p

δ

= − δ

o

avg T

1 vCv p ∆= − ∆

Total Formation Volume Below BubbleTotal Formation Volume Below Bubble

P i



PointPoint

q

Total formationTotal formationvolume factor, Bvolume factor, B

tt

q Of littleOf little

significance, butsignificance, butsometimes used insometimes used in

MB basedMB based

calculationscalculations

Bo BT

Total Formation Volume Below BubbleTotal Formation Volume Below Bubble

P i tP i t



PointPointq If we multiply BIf we multiply B

obob x vx vrelrel. we get B. we get B

tt over theover the

total pressure range above and below thetotal pressure range above and below thebubble point pressure.bubble point pressure.

Differential liberation testsDifferential liberation tests



Differential liberation testsDifferential liberation tests



q Volume changes during differential liberationVolume changes during differential liberation

854-763=91scf/bbl residual oil



Residual oil not the same

composition as stock tank oil

Calculation of Gas-Oil RatioCalculation of Gas-Oil Ratio

Below the Bubble pointBelow the Bubble point




q The GOR resulting from the separator tests andThe GOR resulting from the separator tests and

those from the differential test have differentthose from the differential test have different

values.values.

q 796 ft796 ft33/B STO & 854 ft/B STO & 854 ft33/B residual oil/B residual oil

q The difference a result of the differential process of The difference a result of the differential process of

pressure draw down over the total pressure.pressure draw down over the total pressure.

q In practise, reservoir pressure drop is a differentialIn practise, reservoir pressure drop is a differential

process but the pressure drop through the tubingprocess but the pressure drop through the tubing

and separator is a flash process.and separator is a flash process.

Calculation of Gas-Oil RatioCalculation of Gas-Oil RatioBelow the Bubble pointBelow the Bubble point



Below the Bubble pointBelow the Bubble pointThe separator value is

correct.

We need to complete

GOR values below the

bubble point.

The GOR is made up of

two elements,

Differential in the

reservoir.

Flash in the wells and to

surface.

Differential liberation

Flash liberation

Calculation of Gas-Oil RatioCalculation of Gas-Oil Ratio

B l th B bbl i tBelow the Bubble point q Th diff ti l GOR iTh diff ti l GOR i



Below the Bubble pointBelow the Bubble point q The differential GOR isThe differential GOR is

converted in the followingconverted in the following

manner:manner:

( )s diff R liberated gas-oil ratio by differential liberation∆ =

( )3

s diff

ftR

bbl residual oil∆ =

3 3ft bbl residual oil ft

bbl residual oil bbl bubble point oil bbl bubble point oil× =

3 3ft bbl bubble point oil ft

bbl bubble point oil bbl stock tank oil bbl stock tank oil

× =

( )3

s flash

ftR

bbl stock tank oil= ∆

( )s si s flashR R R

= ∆

Differential test Separator test

( ) ( ) ( ) obs sb sflash flash diff

b resid

BR R R

V / V= − ∆

Calculation of Formation Volume Factor Calculation of Formation Volume Factor





q Formation volume factors between bubble point and surfaceFormation volume factors between bubble point and surface

also show a distinct difference between flash and differential.also show a distinct difference between flash and differential.

Calculation of Formation Volume Factor Calculation of Formation Volume Factor Below the Bubble pointBelow the Bubble point




q

V/Vresidual = relative volume at pressure, B/B resid.V/Vresidual = relative volume at pressure, B/B resid.

bbl Saturated oil bbl Residual oil bbl Saturated oil

bbl Residual oil bbl Bubble point oil bbl Bubble point oil× =

o

bbl Saturated oil bbl Bubble point oil bbl Saturated oilB

bbl Bubble point oil bbl Stock Tank oil bbl Stock Tank oil× = =

obo

resid b resid

BVB V . V /V=

obo

resid b resid

BVBV . V / V

=

Viscosity DataViscosity Data



Pressures below bubble

point match differential

test



ViscosityViscosity



Composition of Reservoir FluidComposition of Reservoir Fluid

Composition of Separator Gas



Composition of Separator Gas



p p

GasGas



CondensateCondensate

PVT ReportPVT Report

Gas



Condensate

PVT Report



Liquid Drop OutLiquid Drop Out



CurveCurve

44%

High Pressure / High Temperature, HP/HTHigh Pressure / High Temperature, HP/HTFluidsFluids



FluidsFluids

q Recent years exploration activity has moved deeper.Recent years exploration activity has moved deeper.

q High pressure and temperature accumulations foundHigh pressure and temperature accumulations found

q Conventional PVT facilities do not enable testingConventional PVT facilities do not enable testing

these fluids.these fluids.

q Ranges 250Ranges 250ooC and 20,000 psi.C and 20,000 psi.

q At these conditions role of water cannot be ignored. At these conditions role of water cannot be ignored.

chap 14- pvt

Documents

q q q q q q equipment

separator qq q q q q

q q q phase behaviour

q q pvt analysis q

q fluids

q q q pvt analysisq

cost q

q composition