Review of Crude Oil Properties

Specific gravity

Solution gas-oil ratio

Density of oil- Calculation from composition (C3

+)- Calculation from composition (C1 ~ C3

+)- Calculation if composition is not known

Bubble point pressure

Formation volume factor

Isothermal compressibility

Viscosity

Formation Volume Factor BO

Definition (FVF, BO ):

BO > 1- temperature high in reservoir- Gas is dissolved in oil under reservoir conditions.

Shrinkage factor: 1/Bo

ro

sc

VBV

Vr : Volume of oil at reservoir T and PVsc : Volume of oil at standard condition

(14.7 psia and 60F)Units: barrels of oil at reservoir conditions per barrel of stock-tank oil (res bbl/STB), always at 60F

Formation Volume Factor, Bo

Above bubble point pressure, …

Below bubble point pressure, …

Chart #22Estimation from Correlation Chart

You need: Gas-oil ratio Gas gravity Tank oil gravity Temperature

Ex. 2.11: Estimation of Bo from Correlation ChartWe have an oil with the following properties:g =0.786, o =40.7API, T=220F, read Bo values from

correlation chart under various Rs conditions.

Solution: Estimation from chart #22

Rs = 600 SCF/STB, Bo = 1.35

Rs = 1000 SCF/STB, Bo = 1.52

Two Phase (Total) Formation Volume Factor, Bt

Definition: Volume in barrels one stock tank barrel and its initial complement of dissolved gas occupies at reservoir condition (res bbl / STB).

Bo : single phase formation volume factorBg : gas formation volume factorRsoi : initial solution gas-oil ratio in reservoirRso : solution gas-oil ratio

( )t o g soi soB B B R R

Two Phase Formation Volume Factor, Bt

Above bubble point pressure,

Rsoi = Rso , Bt = Bo

Below bubble point pressure

Bt > Bo

( )t o g soi soB B B R R

Estimation of Bt from Correlation Charts

Chart #20

You need: Gas-oil ratio Gas gravity Tank oil gravity (API) Temperature Pressure

Ex. 2.12, Estimation of Bt from Correlation Chart

We have an oil with the following properties: g = 0.786, o =40.7API, T = 220F, P = 2000 psia. Read Bt values under various Rs conditions from correlation chart.

Solution:

Estimation from chart #20

Rso = 600 SCF/STB, Bt = 1.50

Rso = 1000 SCF/STB, Bt = 2.00

Isothermal Compressibility

1o

T

dVcV dp

co : oil compressibility

v: volume

p: pressure

Definition: change of volume per change of pressure under constant temperature condition.

Simplified calculation:

2 1

2 1

1o

V VcV p p

V: V1 , V2 , or the average

Isothermal Compressibility

p < pb : Villena-Lanzi correlation for black oil

p > pb : Vasquez and Beggs correlation

,

ln( ) 0.664 1.430ln( ) 0.395ln( ) 0.390ln( )0.455ln( ) 0.262ln( )

o b

sob o API

c p p TR

6 6

,

31.0(10) ( ) 6600(10) , 500 ( ) 5300, 763 ( ) 5300, 78 ( ) 3301.5 , ( / ) 1947, 6.0 ( ) 52.0, 0.58 1.20

o b

o API g

c psia p psig p psig T FGOR gas oilratio SCF STB API

5,(5 17.2 1180 12.61 1433) /( 10 )o sob g o APIc R T

,

126 ( ) 9500, 1.006 ( / ) 2.2269.3 , ( / ) 219915.3 ( ) 59.5, 0.511 1.351

o

o API g

p psig B bbl STBGOR gas oilratio SCF STB

API

Viscosity

Above pb , viscosity increases with p

Below pb , viscosity decreases with p

Viscosity ~ f(T, P, composition)

Viscosity Estimation Correlation

p < pb , dead oil (No solution gas):

p < pb , live oil (with solution gas)

10 10 ,

od

log [log ( 1)] 1.8653 0.025086 0.5644log( )where dead oil viscosity, cp, T = temperature, deg F

od o API T

0.515 0.338so

o,API

where A= 10.715(R 100) , 5.44( 150)conditions:0<p(psig)<5250, 70<T( F)<295, 16< ( ) 5820<GOR, gas-oil ratio (SCF/STB)<2070

Bo od

so

A

B R

API

pour ,Conditions: 59 < T( F) < 176, -58 < T ( F) < 59, 5.0 < < 58.0o API

Viscosity Estimation Correlation Chart

Chart #19

Dead oil Live oil

Viscosity Estimation Correlation

p > pb

1.187 -5

o,API

( / )

where m= 2.6p exp[-11.513-8.98(10) p]oil viscosity at the bubble point pressure, cp

conditions:126< p(psig) <9500, 15.3< ( ) 59.50.511 1.351

9.3<GOR, gas-oil ratio (SCF/

mo ob b

ob

g

p p

API

o

STB)<21990.117< ( ) 148.0cp

Type of Oil

Black oil

Volatile oil

Black Oil

Pressure path in reservoir

Separator

Black Oil

Contain more relatively heavier components

Critical T is far away from reservoir T

Rso < 2000 scf/STB

Bo < 2.0 res bbl/STB

Not always black, but usually dark colors

Volatile Oil

Pressure path in reservoir

Separator

Comparison: Black and Volatile Oil

Pressure path in reservoir

Separator

Volatile Oil

Contain more intermediate components (ethane to hexane)

Critical T is close to reservoir T

2000 < Rso < 3300 scf/STB

Bo > 2.0 res bbl/STB

2. Fluid and Rock Properties

2.1 Rock properties2.2 Gas properties2.3 Liquid properties

Oil properties:

Specific gravity

Bubble point pressure

Formation volume factor

Solution gas-oil ratio

Density

Total Formation volume factor

Isothermal compressibility

Oil viscosity, …

Gas properties:

z factor

Formation volume factor

Gas viscosity

Specific gravity, …

Questions: How do we obtain raw data on these properties?

Reservoir Sample Collection

Bottom-hole sample or subsurface sample

Put in figures

Reservoir Sample Collection

Put in figures

Separator samples, surface samples, recombination samples

2. Fluid and Rock Properties

2.1 Rock properties2.2 Gas properties2.3 Liquid properties2.4 Reservoir fluid properties – PVT study

Reservoir Fluid Studies – PVT study

Oil Properties

Gas properties

Quantities of separator gas, stock- tank gas, and stock-tank oil

Important properties in material balance equation

Reservoir Fluid Studies – PVT study

Oil properties:

Bubble point pressure

Formation volume factor

Solution gas-oil ratio

Total Formation volume factor

Isothermal compressibility

Oil viscosity, …

Gas properties:

z factor

Formation volume factor of gas

Gas viscosity

Specific gravity, …

PVT Study Procedures

Composition measurement

Flash vaporization

Differential vaporization

Separator tests

Viscosity measurement

Composition Analysis

Usually determine the composition of C1 - C6 , and lump all others to heptanes plus.

Heptanes plus composition

We get: mole fraction of each component.

Flash Vaporization

Put in figures

p decrease gradually

p1 >pb , Vt,1 p2 >pb, Vt,2 p3 , Vt,3 p4 , Vt,4p5 , Vt,5

Flash Vaporization

Put in figures

Start at Tr , Pr >= Pb Pressure is reduced gradually. Agitation to keep liquid-gas equilibrium. No gas or liquid is removed from the cell.

Also called: flash vaporization, flash liberation, pressure-

volume relations, constant composition expansion, flash expansion.

What we Get from Flash Vaporization?

Put in figure 10-2Determination of: pb Vsat specific volume = Vsat / mass relative volume:

V / Vsat , (Vt /Vb )F:

Ex. 2.13: The data from a flash vaporization on a black oil at 220 deg F is given below. Determine the bubble point pressure and prepare a table of pressure and relative volume for the reservoir fluid study.

Solution:1. Plot pressure against total volume, determine

pb = 2620 psig, Vb = 63.316 cc2. Determine relative volume = Vt / Vb

Ex. 2.13: The data from a flash vaporization on a black oil at 220 deg F is given below. Determine the bubble point pressure and prepare a table of pressure and relative volume for the reservoir fluid study.

Differential Vaporization

p decrease gradually until atmospheric P

p1 >=pb , Vo,1 p2 , Vo,2 p3 , Vo,3

Differential Vaporization

Start at Tr , P >= Pb Pressure is reduced gradually. Agitation to keep liquid-gas equilibrium. Gas expelled from cell while keeping p constant. Gas quantity and properties determined. Vo determined at each p until atmospheric p residual oil at T = 60 deg F and P = Pa Called: differential liberation, differential expansion

What we Get from Differential Vaporization

r r sc

sc sc r

V p TzV p T

Vo at various p (Reservoir conditions) Vresidual oil (standard condition): Vo,scRelative volume = Vo / Vresidual oil (= BoD )

Oil:

Gas:

Vg at cell condition (Reservoir conditions): Vr Vg at standard condition: Vg,scAlso know: pr , psc , Tr , Tsc z factor Bg

cu ft0.0282scf

rg

r

zTBp

How is Gas-oil Ratio (Rso ) Determined?

,

,

g scsD

o sc

VR

V

,

,

(entire process)g scsDb

o sc

VR

VBubble point

gas-oil ratio:

How is Relative Total Volume Determined?

( )tD oD g sDb sDB B B R R

PVT Study Procedures

Composition measurement

Flash vaporization

Differential vaporization

Separator tests

Oil viscosity measurement

What we Get from Flash Vaporization?

Put in figure 10-2Determination of: pb Vsat specific volume = Vsat / mass relative volume:

V / Vsat , (Vt /Vb )F:

What we Get from Differential Vaporization

r r sc

sc sc r

V p TzV p T

Vo at various p (Reservoir conditions) Vresidual oil (standard condition): Vo,scRelative volume = Vo / Vresidual oil (= BoD )

Oil:

Gas:

Vg at cell condition (Reservoir conditions): Vr Vg at standard condition: Vg,scAlso know: pr , psc , Tr , Tsc z factor Bg

cu ft0.0282scf

rg

r

zTBp

,

,

g scsD

o sc

VR

V

,

,

(entire process)g scsDb

o sc

VR

VBubble point

gas-oil ratio:

( )tD oD g sDb sDB B B R R Total relative volume:

Gas-oil ratio:

Ex.2.14: The data from a differential vaporization on a black oil at 220 deg F are given below. Prepare a table of solution gas-oil ratios, relative oil volumes, and relative total volumes by this differential process. Also include z-factor and formation volume factors of the increments of gas removed.

Ex.2.14 Solution

,sD -6

,

All calculation will be shown for pressure at 2100 psig. 1. Calculate gas-oil ratio:

(0.21256 0.02265 0.01966) scfR 684 scf/residual bbl(39.572 cc residual oil)(6.29 10 bbl/cc)

1'. Calcul

g sc

o sc

VV

,sDb -6

,

oD

ate gas-oil ratio at bubble point:( ) 0.21256 scfR 854scf/residual bbl

(39.572 cc residual oil)(6.29 10 bbl/cc)2. Calculate relative oil volume:

59.952 reservoir ccB39.572 residual c

g sc

o sc

V allV

-6R R sc

sc sc R

res bbl1.515 c residual bbl

3. Calculate z-factorV p T (4.292 cc)(35.315 10 cu ft/cc)(2114.7 psia)(520 R)z= 0.851V p T (0.01966 scf)(14.65 psia)(680 R)

4. Calculate formation volume factor of gas

B

g

g

tD oD g

cu ft cu ft0.0282 0.0282 0.851 680 / 2114.7 0.00771scf scf

(another way of calculating B ?)

5. B B B ( )

res bbl 0.00771 cu ft/scf scf1.515 + (854 684)residual bbl 5.615 cu ft/bbl residual o

r

r

sDb sD

zTp

R R

tD

il bblres bblB 1.748

residual bbl

Ex.2.14 Solution

Separator Tests

Reservoir T, P >= Pb

Separator T, P

Stock tank T, P

Separator Tests

Volume of liquid expelled from the cellVolume of liquid arriving in the stock tankoSbB

Volume of separator gas +volume of stock-tank gasVolume of liquid in the stock tanksSbR

Selection of Separator Conditions

Optimum separator pressure: the pressure that

produces the maximum amount of stock-tank fluid.

minimum RsSb , BoSb , maximum API

Typical range: 100 to 120 psig

Ex 2.15. Given the following separator test data of a black oil, calculate gas-oil ratio and formation volume factor. Volume of oil at bubble-point pressure and reservoir temperature = 182.637 cc; volume of separator liquid at 100 psig and 75 deg F = 131.588cc; volume of stock-tank oil at 0 psig and 75 deg F = 124.773 cc; volume of stock-tank oil at 0 psig and 60 deg F = 123.906; volume of gas removed from separator = 0.52706 scf, volume of gas removed from stock tank = 0.07139 scf.

sSb

-6

182.637 cc 1.474 res bbl/STB123.906 ccvolume of gas from separator + volume of gas from stock tankR

volume of gas from stock tank0.52706 scf + 0.07139 scf

123.906 cc (6.29 10 bbl/cc)767.9

oSbB

scf/STB