04 fluid properties

7/29/2019 04 Fluid Properties

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Copyright 2007, , All rights reserved

Fluid Properties

Basic Fluid Parameters Used in Reservoir Engineering

(Viscosity, Compressibility, Volume Factor, GOR, PhaseDiagrams)


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Copyright 2007, , All rights reserved 2

What is Petroleum?

Petroleum: a natural yellow-to-black liquid hydrocarbonfound at and beneath the earths surface,

Hydrocarbon: an organic compound made up of carbon and

hydrogen atoms.


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Crude Oils

Light CrudePalo Pinto Field

North Texas

Heavy CrudeHumble Oil FieldSouthwest Texas


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Crude Oils

Extra Heavy Oil(Orinoco Belt, Venezuela)


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Petroleum ProductsA Barrel of Crude Oil Provides:

Gasoline - 19.5 gallons

Fuel Oil - 9.2 gallons

Jet Fuel - 4.1 gallonsAsphalt - 2.3 gallonsKerosene - 0.2 gallonsLubricants - 0.5 gallonsPetrochemicals,other products - 6.2 gallons

One Barrel =42 gallons


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Hydrocarbon

Combination of C and H

CH

H

H

H

CH

H

H

C

H

H

H

CH

H

H

C

H

H

C

H

H

H

METHANE

ETHANE

PROPANE


7/51Copyright 2007, , All rights reserved 7

Other elements in Reservoir Fluids

Water (Salinity)

H2S

CO2 N2

Hg (Mercury)



API Gravity

5.131API

5.141SG

or

5.131SG

5.141API

Where

SG: Specific Gravity

API: API Gravity (60degF)



Viscosity ()

A measure of resistance to flow

Symbols: o, g, w

Units: cp Sources: Lab measurements, correlations

Range and typical values

0.25 to 10,000 cp, Black oil

0.5 to 1.0 cp, Water

0.012 to 0.035 cp, Gas



Variation of Viscosity with Pressure

Pressure

Pb



Fluid Compressibility (Co, Cg, Cw)

Fractional change in volume due to a unit change in pressure

Symbol: co, cg, cw

Units: psi-1, microsips (1 microsip = 1x10-6 psi-1)

Source: Lab measurements, correlations



Oil Formation Volume Factor (Bo)

Pb

Oil at Surface

Gas at Surface

Oil in Place

SurfaceatVolumeOil

PlaceinVolumeOilBo



Gas-Oil Ratio (GOR)

Pb

Oil at Surface

Gas at Surface

Oil in Place

SurfaceatVolumeOil

SurfaceatVolumeGasGOR



Exercise

There is 1,000,000 bbls of recoverable oil in reservoir. If yourecover all of the oil to the surface, how much stock tankvolume of oil and gas (standard condition) you can obtain?

Assume: Bo = 1.2, GOR = 600, reservoir is saturated and nofree gas is drained.

If the oil price is $75/bbl and gas price is $10 /mscf, howmuch revenue can you get? (you do not have to considerproduction cost in this exercise).



GOR is different from Gas in Solution (Rs)

GOR is the ratio of ALL the gas at surface and the oil atsurface, while Rs is the ratio of gas in solution in the oil in thereservoir



GOR RsSurface

Reservoir

Bg

GWR

GOR

Rs

VoVg3

Vg2

Vg1

BoBw

o

ggg

V

3V2V1VGOR



Gas-Oil Ratio(for Pr < Pb and no Free Gas Cap)

where:GOR Production gas oil ratio

Rs Gas in solution in oil

Bo and Bg Oil and gas volume factorsmo and mg Oil and gas viscosities

krg/kro Gas/oil-relative permeability-ratio



Hydrocarbons Classification

BlackOil

VolatileOil

RetrogradeGas

WetGas

DryGas

InitialProducingGas/Liquid

Ratio, scf/STB

3200 > 15,000* 100,000*

Initial Stock-Tank Liquid

Gravity, API

< 45 > 40 > 40 Up to 70 NoLiquid

Color of Stock-

Tank Liquid

Dark Colored Lightly

Colored

Water

White

No

Liquid

*For Engineering Purposes



Hydrocarbons Classification

BlackOil

VolatileOil

RetrogradeGas

WetGas

DryGas

PhaseChange inReservoir

Bubblepoint Bubblepoint Dewpoint NoPhase

Change

NoPhase

Change

HeptanesPlus, MolePercent

> 20% 20 to 12.5 < 12.5 < 4* < 0.8*

OilFormationVolume

Factor atBubblepoint

< 2.0 > 2.0 - - -




Hydrocarbon Behavior

(Single Component / Constant Temperature)


22/51Copyright 2007, , All rights reserved

DIFFERENTIAL GAS LIBERATIONGas phase removal process in a hydrocarbon system, when gas is formed below the bubble point pressure.During the process the composition of the system continuously changes.

HYDROCARBON PVT PROPERTIES

PISTON

GASLIQUID

PISTON

LIQUIDLIQUID

LIQUID

PISTON

GASLIQUID

(B) GAS EXTRACTION (C) GAS EXTRACTION(A)

PRESSURE DECREASE

PISTON PISTON


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FLASH EXPANSIONGas is formed from the liquid when de pressure is reduced, keeping in contact with the crudeoil. The total composition of the system remains constant.

GAS

PISTON

LIQUID

LIQUID

PISTON

PISTON

LIQUID

GAS

PRESSURE DECREASE

LIQUID

PISTON

Pb



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Typical PVT Data for Differential Vaporization of anUndersaturated Oil at Constant Temperature (305F)


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Five Reservoir Fluids

Black Oil

Volatile Oil

Retrograde Gas

Wet Gas

Dry Gas


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The Reservoir Fluid Type

Determined using the pressure-temperature phase diagram.

Requires knowledge of the reservoir to surface pressure-temperature path.

Estimated using field data with rules of thumb.


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Phase Diagram Typical Black Oil

Black Oil

Criticalpoint

Pressure,psia

Separator

Pressure pathin reservoir

Dewpoint line

% Liquid

Temperature, F


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Phase Diagram of a Typical Volatile Oil

Pressure

Temperature, F

Separator

% Liquid

Volatile oil


3

2

1 Criticalpoint


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Phase Diagram of a Typical Retrograde Gas

3

Separator

% Liquid

Pressure path

in reservoir1

2Retrograde gas

Critical point

Pressure

Temperature


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Phase Diagram of Typical Wet Gas

Pressur

e

Temperature

% Liquid

2

1


Wet gas

Criticalpoint

Separator


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Phase Diagram of Typical Dry Gas

Pressu

re

Temperature

% Liquid

2

1

Pressure path

in reservoir

Dry gas

Separator

Th Fi R i Fl id


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Black Oil

Criticalpoint

Pressure,psia

Separator


Dewpoint line

% Liquid

Temperature, F

Pressure

Retrograde Gas Wet Gas Dry Gas

The FiveReservoirFluids

Pressure

Temperature

Separator

% Liquid

Volatile oil


3

2

1Criticalpoint

3

Separator

% Liquid


1

2Retrograde gas

Critical

point

Temperature

Pressure

Temperature

% Liquid

2

1


Wet gas

Criticalpoint

Separator

Black Oil Volatile Oil

Pressure

Temperature

% Liquid

2

1


Dry gas

Separator

The Five Reservoir Fluids

Th G


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Three Gases

Dry gas - gas at surface is same as gas in reservoir

Wet gas - recombined surface gas and condensaterepresents gas in reservoir

Retrograde gas - recombined surface gas and condensaterepresents the gas in the reservoir but not the total reservoirfluid (retrograde condensate stays in reservoir)

C t f N t ll i P t l


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Components of Naturally occurring PetroleumFluids

Component Composition,mole percent

Hydrogen sulfide 4.91Carbon dioxide 11.01Nitrogen 0.51Methane 57.70

Ethane 7.22Propane 4.45i-Butane 0.96n-Butane 1.95i-Pentane 0.78n-Pentane 0.71

Hexanes 1.45Heptanes plus 8.35100.00

Properties of heptanes plusSpecific Gravity 0.807Molecular Weight 142 lb/lb mole

I iti l P d i GLR C l t With C7


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Initial Producing GLR Correlates With C7+

0

20000

40000

60000

80000

100000

0 10 20 30 40 50

Heptanes plus in reservoir fluid, mole %

Initialprodu

cing

ga

s/liquidratio,

scf/STB

Dewpoint gas

Bubblepoint oil

I iti l P d i GLR C l t With C7


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Initial Producing GLR Correlates With C7+

10

100

1000

10000

100000

1000000

0.1 1 10 100


Initialproduc

ing

gas

/liquidratio,scf/STB

Dewpoint gasBubblepoint oil

R t d G


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Retrograde Gas

2000

3000

4000

5000

10 11 12 13 14 15


Initialprodu

cing

ga

s/liquidratio,

scf/STB

Th G Wh t th diff ?


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Three Gases What are the differences?

Dry gas - gas at surface is same as gas in reservoir

Wet gas - recombined surface gas and condensate representsgas in reservoir

Retrograde gas - recombined surface gas and condensaterepresents the gas in the reservoir But not the total reservoirfluid (retrograde condensate stays in reservoir)

Fi ld Id tifi ti


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Field Identification

BlackOil

VolatileOil

RetrogradeGas

WetGas

DryGas

InitialProducingGas/Liquid

Ratio, scf/STB

3200 > 15,000* 100,000*

Initial Stock-Tank Liquid

Gravity, API

< 45 > 40 > 40 Up to 70 NoLiquid

Color of Stock-

Tank Liquid

Dark Colored Lightly

Colored

Water

White

No

Liquid


L b t A l i


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Laboratory Analysis

BlackOil

VolatileOil

RetrogradeGas

WetGas

DryGas

PhaseChange inReservoir

Bubblepoint Bubblepoint Dewpoint NoPhase

Change

NoPhase

Change

HeptanesPlus, MolePercent

> 20% 20 to 12.5 < 12.5 < 4* < 0.8*

OilFormation

VolumeFactor atBubblepoint

< 2.0 > 2.0 - - -


P i P d ti T d


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Primary Production Trends

GOR

GOR

GOR

GOR

GOR

Time Time Time

TimeTimeTimeTimeTime

TimeTime

No

liquid

No

liquid

DryGas

WetGas

RetrogradeGas

VolatileOil

BlackOil

API

API

API

API

API

E i


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Exercise

One of the wells in the Merit field, completed inDecember 1967 in the North Rodessa formation,originally produced 54API stock-tank liquid at a gas/oilratio of about 23,000 scf/STB. During July 1969, thewell produced 1987 STB of 58API liquid and 78,946Mscf of gas. By May 1972, the well was producingliquid at a rate of about 30 STB/d of 59API liquid and

gas at about 2,000 Mscf/d. What type of reservoir fluidis this well producing?

Plot of Exercise


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Plot of Exercise

00 12 24 36 48 60 72

50

5152

53

54

55

60

59

58

57

56

100000

90000

80000

70000

60000

50000

40000

30000

1000020000

Months since start of 1967

Producing

g

as/oilratio,s

cf/STB

Stock-tank

liqu

idgravity,API

Exercise Solution


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Exercise Solution

Retrograde Gas Condensate

Initial GLR over 3,200 scf/STB and producing gas-liquid ratioand stock tank oil gravity increasing with production, thus fluidis retrograde gas condensate

Initial GLR over 15,000 scf/STB, thus fluid can be treated aswet gas

GLR apparently started increasing immediately, indicating thatpi = pd and the possibility of an oil zone


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EMPIRICAL CORRELATIONS


STANDING CORRELATION


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P 10 0.0125 o API 1.205

Rs = g x when P Pb18 10 0.00091 T

Bo = 0.972 + 0.00014 F 1.175

Rs: Gas in solution, SCF/STB;

Bo: Oil volumetric factor , Bbl/STB;

P: Pressure, psi;

T: Temperature F;

g: Gas Specific gravity (air = 1);o: Oil Specific gravity (water = 1) ;o API: Oil API Gravity

o: Oil density, lb/ft3

STANDING CORRELATION

gF = Rs + 1.25 To

0.6

Rs(Solution Gas, SCF/STB) and Bo (Oil volume factor, Bbl/STB) calculation

OIL DENSITY


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62.4 o + 0.0764 g Rs / 5.615

o = Bo

OIL DENSITY

Where o= Oil density, lb/ft3 @ P,T


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GAS VOLUMETRIC FACTOR, Bg

zT

Bg = 0.028269 (vol./vol.)P

The gas volumetric factor, Bg, can be determined using followingequation, which is derived from state equation (PV = znRT)

P: pressure, psia,

T: temperatureo

R (=o

F + 460)and z: supercompressibility factor.


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g= gSC / Bg ,

Gas density at P and T

Where gSC

= 0.0764 g



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GAS

PISTON

LIQUID

LIQUID

PISTON

PISTON

LIQUID

GASLIQUID

PISTON

RESERVOIRCONDITION

Pr, Tr

BUBBLEPRESSURE

Pb

CONDITION AT A GIVENPOINT IN THE PIPE

P, T

STANDARDCONDITIONS

14.7 psi, 60oF

HOW TO DETERMINE FREE GAS AND CRUDE OIL VOLUME AT A GIVEN PRESURE AND

TEMPERATURE CONDITION

1 2 3 4

VgSC

Vo SC

GOR = Vg SC / Vo SC

Vg P,T

Vo P,T

Vo (P,T)= Bo x VoSC

Vg (P,T)= Bg X (GOR - Rs) x VoSC

P

T

LIQUID GAS

TWO PHASES

1

2

3

4

60o F

14.7 psi


EXERCISE


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A well is producing 35 oAPI oil at a rate of 1000 STB/day, with a GOR of 500 SCF/STB.Gas specific gravity is 0.65 (air = 1).

1) Calculate the oil and gas flow rates in ft3/sec. in a point of the tubing where the pressureis 800 psi and the temperature is 140 oF.. Assume Z= 0.9.

Use empirical correlations for Bo, Bg, Rs Calculations

2) Calculate the oil and gas densities for the same conditions. Sol# Rs=152, F=307.9, Bo=1.089Bg=.0189

Qo(800psi, 140 F) = Bo x Qo(STB/day) ,AnsQ0=1089 bpdQg(800psi, 140 F) = BgxQo(STB/day)x(GOR Rs)

1 bbl = 5.615 ft3 y 1day=86400 sec

EXERCISEAPPLICATION OF FLUID PROPERTIES CALCULATIONS

04 fluid properties

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