PVTPVTPressure Volume TemperaturePressure Volume Temperature

Adrian C ToddAdrian C Todd

Heriot-Watt UniversityHeriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING

Heriot-Watt UniversityHeriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING

PVT - ScopePVT - Scope

Reservoir fluid analysis provides key data to Reservoir fluid analysis provides key data to the petroleum engineer.the petroleum engineer.

Quality of the testing is important to ensure Quality of the testing is important to ensure realistic values used in design.realistic values used in design.

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

PVT AnalysisPVT Analysis

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

Reservoir calculationsReservoir calculations

Well flow calculationsWell flow calculations

Surface facilitiesSurface facilities

PVT AnalysisPVT Analysis

Correlation between pressure and volume at Correlation between pressure and volume at reservoir temperature.reservoir temperature.

Various physical constants in reservoir Various physical constants in reservoir calculations; viscosity, density, compressibility.calculations; viscosity, density, compressibility.

Effect of separator conditions on Bo & GOR. etc.Effect of separator conditions on Bo & GOR. etc.

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

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

Dry gasDry gas::

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

Wet gasWet gas::

as above plus information on liquid drop out, quantities and compositions.as above plus information on liquid drop out, quantities and compositions.

Oil system:Oil system:

Bubble point pressure, composition of reservoir and produced fluids, Bo, Bubble point pressure, composition of reservoir and produced fluids, Bo, GOR, Bt and viscosity. All as function of pressure. Co.GOR, Bt and viscosity. All as function of pressure. Co.

Below Pb considerations.Below Pb considerations.

PVT AnalysisPVT Analysis

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

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.

Desirable to take samples early in the life of Desirable to take samples early in the life of the reservoir.the reservoir.

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

Sub-Surface SamplingSub-Surface Sampling Can only be representative Can only be representative

when pressure at sampling when pressure at sampling point is above or equal to point is above or equal to the saturation pressure.the saturation pressure.

At pressure close to At pressure close to saturation pressure serious saturation pressure serious possibility of sample possibility of sample integrity being lost.integrity being lost.

In recent years In recent years considerable advance in considerable advance in downhole fluid samplingdownhole fluid sampling

Surface SamplingSurface Sampling

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

Fluids recombined in the laboratory on the Fluids recombined in the laboratory on the basis of the produced GORbasis of the produced GOR

Vertical and Vertical and Horizontal Horizontal SeparatorsSeparators

Separator Gas SamplingSeparator Gas Sampling

Separator Liquid Sampling by Gas Separator Liquid Sampling by Gas DisplacementDisplacement

Separator Liquid Sampling by Water Separator Liquid Sampling by Water DisplacementDisplacement

Wellhead Wellhead samplingsampling A low cost option.A low cost option.

Only possible for very Only possible for very undersaturated undersaturated sytsems. sytsems.

Still single phase at Still single phase at wellhead.wellhead.

Sampling Wet Gas and Gas Condensate Sampling Wet Gas and Gas Condensate SystemsSystems

Use and value of any PVT study dependant on the Use and value of any PVT study dependant on the quality of the sample collected.quality of the sample collected.

Sampling wet gas and gas condensate fluids can Sampling wet gas and gas condensate fluids can give rise to errors. give rise to errors.

During sampling procedure it is possible to alter During sampling procedure it is possible to alter the conditions so that samples are not the conditions so that samples are not representative.representative.

An important consideration is the phase An important consideration is the phase behaviour.behaviour.

Phase Behaviour.Phase Behaviour. Fluids uniquely Fluids uniquely

described by phase described by phase diagram.diagram.

Within the phase Within the phase diagram system is diagram system is two phase.two phase.

Whereas outside the Whereas outside the phase envelope phase envelope single phasesingle phase

Single phase

Two phase

Phase Behaviour.Phase Behaviour. The separation of oil and The separation of oil and

gas as predicted by the gas as predicted by the phase diagram results in phase diagram results in each phase having its own each phase having its own phase diagram.phase diagram.

The oil exists at its bubble The oil exists at its bubble point .point .

The gas exists at its dew The gas exists at its dew point.point.

This behaviour has This behaviour has important implications on important implications on well samplingwell sampling

Sampling Wet Sampling Wet Gas and Gas Gas and Gas Condensate Condensate ReservoirsReservoirs

Potential locations Potential locations for reservoir for reservoir samplingsampling

Sampling Wet Gas and Sampling Wet Gas and Gas Condensate Gas Condensate ReservoirsReservoirs

LocationLocation

1. Reservoir1. Reservoir

2.Bottom-hole2.Bottom-hole

3.Well Head3.Well Head

4. Separator4. Separator For.For.

1. Ideal1. Ideal

2. 1-phase2. 1-phase

3. Cost 3. Cost

4. Cost, 1-phase, 4. Cost, 1-phase, buffer,sampling volume buffer,sampling volume

AgainstAgainst

1. Impossible1. Impossible

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

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

4.Gas/liquid volumes,, separator conditions, 4.Gas/liquid volumes,, separator conditions, Representative ?, Representative ?,

Sampling Wet Gas and Sampling Wet Gas and Gas Condensate Gas Condensate Reservoirs-Flowing well.Reservoirs-Flowing well.

Well behaviour can Well behaviour can significantly influence significantly influence nature and nature and characteristics of fluids characteristics of fluids produced.produced.

Flowing well gas Flowing well gas condensate - mist flowcondensate - mist flow

Sampling Wet Gas Sampling Wet Gas and Gas Condensate and Gas Condensate Reservoirs-Shut in well Reservoirs-Shut in well after flow.after flow.

Well acts as a separatorWell acts as a separator

Liquid rains down and Liquid rains down and accumulates at bottom accumulates at bottom of well.of well.

Pressure builds up in Pressure builds up in the well and disturbed the well and disturbed formation.formation.

Some gas goes back Some gas goes back into solution.into solution.

Well flow after shut in.Well flow after shut in. Large variations in compositions Large variations in compositions

of produced fluids.of produced fluids.

Early period lean gas produced. Early period lean gas produced. High GORHigh GOR

When fluids produced from bottom When fluids produced from bottom of well. Liquids much lower GOR.of well. Liquids much lower GOR.

Then fluids from disturbed Then fluids from disturbed reservoir zonereservoir zone

Eventually fluids from undisturbed Eventually fluids from undisturbed reservoirreservoir

Sampling Wet Gas and Gas Sampling Wet Gas and Gas Condensate ReservoirsCondensate Reservoirs

In assessing quality of samples In assessing quality of samples important to know how long it will important to know how long it will take for unrepresentative samples take for unrepresentative samples to be displaced from reservoir.to be displaced from reservoir.

Volumetrics required on wells, Volumetrics required on wells, facilities and near well volumesfacilities and near well volumes

Separator Sampling PointsSeparator Sampling Points A very practical issue is the A very practical issue is the

location of sampling points on location of sampling points on separators.separators.

Often located for convenience Often located for convenience for accessibility.for accessibility.

Important to recognise that the Important to recognise that the gas and liquid in a separator gas and liquid in a separator are at their saturation are at their saturation pressure.pressure.

Small changes will result in Small changes will result in liquid drop out and gas being liquid drop out and gas being producedproduced

Liquid in gas line

Gas in liquid line

Iso kinetic sampling

Sampling DetailsSampling Details

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

Date and timeDate and time

Cylinder identificationCylinder identification

Location of sampling points.Location of sampling points.

Temperature and pressureTemperature and pressure

GOR in separatorGOR in separator

Any special details ( HAny special details ( H22S in sample, etcS in sample, etc

Equipment for PVT AnalysisEquipment for PVT Analysis

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

Apparatus for measuring gas and liquid volumesApparatus for measuring gas and liquid volumes

Apparatus for performing separator testsApparatus for performing separator tests

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

High pressure viscometerHigh pressure viscometer

Gas chromatograph or equivalent. Gas chromatograph or equivalent.

Equipment for PVT Analysis-Subsurface Equipment for PVT Analysis-Subsurface SamplesSamples

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

Equipment for PVT Analysis-Gas Condensate Equipment for PVT Analysis-Gas Condensate SamplesSamples

PVT TestsPVT Tests

To provide data for reservoir calculationsTo provide data for reservoir calculations

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

For surface facility designFor surface facility design

The reservoir calculations are the main driving force for the various The reservoir calculations are the main driving force for the various tests.tests.

Over recent years reservoir simulation capability has generated the Over recent years reservoir simulation capability has generated the need to extend compositional description from C7+ to in some cases need to extend compositional description from C7+ to in some cases C29+.C29+.

PVT report provides source of all reservoir engineering properties for PVT report provides source of all reservoir engineering properties for behaviour over exploration, development and productionbehaviour over exploration, development and production

Main PVT TestsMain PVT Tests

Flash vaporisation or relative volume test.Flash vaporisation or relative volume test.

Differential vaporisation test.Differential vaporisation test.

Separator tests.Separator tests.

Viscosity measurements.Viscosity measurements.

Compositional measurements.Compositional measurements.

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

Determination of the correlation between pressure and volume Determination of the correlation between pressure and volume at reservoir temperature.at reservoir temperature.

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

The gas remains in equilibrium with the oil through out the test.The gas remains in equilibrium with the oil through out the test.

The behaviour below the bubble point does not reflect The behaviour below the bubble point does not reflect reservoir behaviour, where gas has greater mobility than the reservoir behaviour, where gas has greater mobility than the oil.oil.

This test determines the This test determines the Bubble PointBubble Point pressure pressure corresponding to the reservoir temperature.corresponding to the reservoir temperature.

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

Liberated gas remains in Liberated gas remains in equilibrium with oilequilibrium with oil

Flash Vaporisation (Relative Volume ) TestFlash Vaporisation (Relative Volume ) TestBy plotting P versus V, a break in the slope is obtained at the Bubble Point pressure.

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

Tests at constant pressure Tests at constant pressure and varying temperature and varying temperature enables thermal expansion enables 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

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

Above bubble point compressibility of Above bubble point compressibility of oil at reservoir temperature can be oil at reservoir temperature can be determined.determined.

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

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

Main objectives:Main objectives:

Reservoir bubble point Reservoir bubble point pressure.pressure.

Together with Together with information from separator information from separator tests, formation volume tests, formation volume factor above bubble point.factor above bubble point.

Differential Vaporisation Differential Vaporisation Below bubble point in reservoir gas liquid separation in Below bubble point in reservoir gas liquid separation in

the reservoir is a constant changing system.the reservoir is a constant changing system.

A test has been design to attempt to simulate this A test has been design to attempt to simulate this process.process.

In the In the differential vaporisationdifferential vaporisation test liberated gas is test liberated gas is removed from the cell step wise.removed from the cell step wise.

At each step below bubble point, volumes densities , At each step below bubble point, volumes densities , gas expansion and compressibility determined.gas expansion and compressibility determined.

Bubble point starting point.Bubble point starting point.

Differential VaporisationDifferential Vaporisation

Differential liberation process

Flash liberation process

Differential VaporisationDifferential Vaporisation

Differential VaporisationDifferential Vaporisation

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

Final step to 60Final step to 60ooF.F.

Remaining oil Remaining oil Residual OilResidual Oil

Differential Vaporisation vs.Flash VaporisationDifferential Vaporisation vs.Flash Vaporisation

Flash liberation considered to take place Flash liberation considered to take place between reservoir and surface.between reservoir and surface.

Differential liberation considered to be Differential 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.

Differential tests carried out to obtain oil Differential tests carried out to obtain oil formation volume factors and GOR’s to predict formation volume factors and GOR’s to predict behaviour below bubble point pressure.behaviour below bubble point pressure.

Separator TestsSeparator Tests Objective to determine impact of separator conditions on Bo, Objective to determine impact of separator conditions on Bo,

GOR, and produced fluid physical properties.GOR, and produced fluid physical properties.

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

Carried out to give an indication of oil shrinkage and GOR Carried out to give an indication of oil shrinkage and GOR when fluids produced to surface.when fluids produced to surface.

There are not uniques values for Bo & GOR. They depend on There are not uniques values for Bo & GOR. They depend on separator conditions.separator conditions.

Starting point for the test is the bubble point pressure.Starting point for the test is the bubble point pressure.

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

Separator TestsSeparator Tests

PVT Cell pressure kept at bubble point

Separator TestsSeparator Tests

PVT Cell pressure kept at bubble point

Separator TestsSeparator Tests

PVT Cell pressure kept at bubble point

Separator TestsSeparator Tests

PVT Cell pressure kept at bubble point

Separator TestsSeparator Tests

PVT Cell pressure kept at bubble point

V resV res

ViscosityViscosity

Measured at different pressures above and Measured at different pressures above and below bubble point pressure.below bubble point pressure.

Below bubble point pressure carried out under Below bubble point pressure carried out under differential conditions.differential conditions.

Rolling ball or capillary tube methods of Rolling ball or capillary tube methods of measurementmeasurement

Hydrocarbon analysisHydrocarbon analysis Analysis from C1 to an upper C number based on Analysis from C1 to an upper C number based on

paraffin series.paraffin series.

Historically C6 & C7+. Much higher analysis capability.Historically C6 & C7+. Much higher analysis capability.

C+ characterised by specific gravity and apparent C+ characterised by specific gravity and apparent molecular weight.molecular weight.

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

Higher C+ characterisation helpful to process Higher C+ characterisation helpful to process engineers re. solid phase formation. engineers re. solid phase formation.

Wax and AshphaltenesWax and Ashphaltenes

Solid phase formation series concern.Solid phase formation series concern.

Heavy components at low temperatures can Heavy components at low temperatures can form solid phases.form solid phases.

Wax in transfer lines and process facilities.Wax in transfer lines and process facilities.

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.

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

Wax Wax Crystallization Crystallization TemperatureTemperature

Different tests used:Different tests used:

Filtering and measuring Filtering and measuring resistance to flow at resistance to flow at different temperatures.different temperatures.

Appearance temperature Appearance temperature is considered to be is considered to be affected by super cooling.affected by super cooling.

The disappearance The disappearance temperature is considered temperature is considered to be the equilibrium value.to be the equilibrium value.

Core Laboratories

Wax Wax Crystallization Crystallization TemperatureTemperature

Core Laboratories

Summary of results provided by an oil sample Summary of results provided by an oil sample PVT test.PVT test.

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

Compressibility coefficient.Compressibility coefficient.

Coefficient of thermal expansion.Coefficient of thermal expansion.

Relative total volume of oil and gas, VRelative total volume of oil and gas, Vtt

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

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

Summary of results provided by an oil sample Summary of results provided by an oil sample PVT test.PVT test.

Gas formation volume factor or gas expansion factorGas formation volume factor or gas expansion factor

Gas compressibility factor. Gas compressibility factor.

Specific gravity of gasSpecific gravity of gas

Liquid densityLiquid density

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

Oil formation volume factorOil formation volume factor

Solution gas- oil ratio. Shrinkage of separator oil to tank oilSolution gas- oil ratio. Shrinkage of separator oil to tank oil

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

Volumetric relationship of fluids in an oil Volumetric relationship of fluids in an oil PVT testPVT test

Reference point bubble point

Volumetric relationship of fluids in an oil Volumetric relationship of fluids in an oil PVT testPVT test

Reference point Stock Tank Conditions

Volumetric relationship of fluids in an oil PVT testVolumetric relationship of fluids in an oil PVT test

Interfacial Tension, IFTInterfacial Tension, IFT

Impact of IFT now considered an important Impact of IFT now considered an important aspectaspect

particularly for gas condensatesparticularly for gas condensates

IFT has a significant impact on the behaviour IFT has a significant impact on the behaviour of residual condensate saturation and of residual condensate saturation and associated relative permeability.associated relative permeability.

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

Interfacial Tension MeasurementsInterfacial Tension Measurements

Most common method pendant dropMost common method pendant drop

2

L Vegd

l

2

L Vegd

l

l = shape factor a function of ds/de

Interfacial Tension MeasurementsInterfacial Tension Measurements For very low IFT size of tube too small to suspend drop.For very low IFT size of tube too small to suspend drop.

Thin wire can be usedThin wire can be used

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

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

Retrograde CondensationRetrograde Condensation

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

Gas condensate cells have a window to Gas condensate cells have a window to visualise dew point.visualise dew point.

Not possible to determine by change of slope Not possible to determine by change of slope of compressibilities of gas and liquid..of compressibilities of gas and liquid..

Gas CondensateGas Condensate

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

down samples and recombining the resultant liquid and down samples and recombining the resultant liquid and gas phase compositions.gas phase compositions.

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

Purpose to determine z value above dew point.Purpose to determine z value above dew point.

Determine dew point pressureDetermine dew point pressure

Dew point observed as drops on window

Gas Condensate- Constant Volume DepletionGas Condensate- Constant Volume Depletion

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

Series of pressure expansionsSeries of pressure expansions

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

Gas Condensate- Constant Volume DepletionGas Condensate- Constant Volume Depletion

Liquid volume produced below dew point Liquid volume produced below dew point generates a liquid drop out curve.generates a liquid drop out curve.

Gas Condensate-Special tests IFT and Gas Condensate-Special tests IFT and Full Compositional dataFull Compositional data

Hg

Condensate

Gas

Hg

Density cell

High pressuresampling

Stirrer

Gas Condensate-Special tests IFT and Gas Condensate-Special tests IFT and Full Compositional dataFull Compositional data

Hg

Condensate

Gas

Hg

Density cell

High pressuresampling

Hg

Pendant drop

Interface

Rising film methodRising film method

Vapour

Liquid

1 cm

Rising film thickness

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

Very thin meniscusheight

Vapour

Liquid

1 cm

Understanding PVT Rep[ortsUnderstanding PVT Rep[orts Purpose of the PVT report:Purpose of the PVT report:

Although can be used for applications from reservoir to surface Although can be used for applications from reservoir to surface facilities. Reservoir engineering provides the main basis.facilities. Reservoir engineering provides the main basis.

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

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

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

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

Specific to a particular fluidSpecific to a particular fluid

Example PVT report.Example PVT report.

Example PVT report.Example PVT report.

Example PVT report.Example PVT report.

Example Example PVT PVT report.report.

Separator TestSeparator Test

Separator Separator TestTest

Separator TestSeparator Test

READ THE FOOTNOTES

Fluid Properties above bubble pointFluid Properties above bubble point Relative Volume Test - Flash Vaporisation TestRelative Volume Test - Flash Vaporisation Test

Relative Relative Volume Test - Volume Test - Flash Flash Vaporisation Vaporisation TestTest

P

V

Pb

Vsat

BBoo above bubble point above bubble point

o

vol. reservoir oilB

vol. stock tank oil

o

vol. bubble point oil vol. reservoir oilB

vol. stock tank oil vol. bubble point oil

From separator test

Above bubble pointAbove bubble point

Density above bubble point obtained by Density above bubble point obtained by combining data from separator test and combining data from separator test and relative volume tests.relative volume tests.

oo ob rel

1 1

v v v

oo ob rel

1 1

v v v

Above bubble pointAbove bubble point

Compressibility above bubble point can be Compressibility above bubble point can be obtained from relative volume testobtained from relative volume test

o

T

1 vC

v p

o

T

1 vC

v p

oavg T

1 vC

v p

Total Formation Volume Below Bubble Total Formation Volume Below Bubble PointPoint

Total formation Total formation volume factor, Bvolume factor, Btt

Of little Of little significance, but significance, but sometimes used in sometimes used in MB based MB based calculationscalculations

Bo BT

Total Formation Volume Below Bubble Total Formation Volume Below Bubble PointPoint If we multiply BIf we multiply Bobob x v x vrelrel. we get B. we get Btt over the total over the total

pressure range above and below the bubble pressure range above and below the bubble point pressure.point pressure.

Differential liberation testsDifferential liberation tests

Differential liberation testsDifferential liberation tests 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 Ratio Calculation of Gas-Oil Ratio Below the Bubble pointBelow the Bubble point

The GOR resulting from the separator tests and The GOR resulting from the separator tests and those from the differential test have different values.those from the differential test have different values.

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

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.

In practise, reservoir pressure drop is a differential In practise, reservoir pressure drop is a differential process but the pressure drop through the tubing process but the pressure drop through the tubing and separator is a flash process.and separator is a flash process.

Calculation of Gas-Oil Ratio Calculation of Gas-Oil Ratio Below the Bubble pointBelow the Bubble point

The 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 Ratio Calculation of Gas-Oil Ratio Below the Bubble pointBelow the Bubble point The differential GOR is converted The differential GOR is converted

in the following manner:in the following manner:

s diffR 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 Below the Bubble pointBelow the Bubble point

Formation volume factors between bubble point and Formation volume factors between bubble point and surface also show a distinct difference between flash and surface also show a distinct difference between flash and differential.differential.

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

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

BVB

V . V / V

Viscosity DataViscosity Data

Pressures below bubble point match differential

test

ViscosityViscosity

Composition of Reservoir FluidComposition of Reservoir Fluid

Composition of Separator GasComposition of Separator Gas

Composition of Separator GasComposition of Separator Gas

Gas Gas Condensate Condensate PVT ReportPVT Report

Gas Gas Condensate Condensate PVT ReportPVT Report

Liquid Drop Out Liquid Drop Out CurveCurve

44%

High Pressure / High Temperature, HP/HT High Pressure / High Temperature, HP/HT FluidsFluids

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

High pressure and temperature accumulations foundHigh pressure and temperature accumulations found

Conventional PVT facilities do not enable testing Conventional PVT facilities do not enable testing these fluids.these fluids.

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

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