15meos_PPT_16x9_Black Oil Property Correlations - State of the Art

SPE-172833-MS

Black Oil Property Correlations - State of the Art

Muhammad Ali Al-Marhoun

Reservoir Technologies, Saudi Arabia

Paper # SPE-172833-MS• Black Oil Property Correlations - State of the Art • Muhammad Ali Al-Marhoun

Slide 2

Outline

Introduction

Literature Review

Black Oil Properties Bubblepoint Pressure & Solution Gas Oil Ratio

Oil Formation Volume Factor

Oil Density at Reservoir Conditions

Oil Compressibility above & below bubble point

Oil Viscosity

Adjustment of Differential Data to Separator Conditions

Conclusions


Slide 3

This paper gives the best correlations to estimate black oil properties based on statistical accuracy and physical behavior.

Hundreds of reservoir-fluid studies of black oil samples representing all areas of the world producing black oils were gathered from different published and unpublished sources to perform statistical error analysis.

All black oil property correlations available in the petroleum literature were compared with this world wide database.

Introduction


Slide 4

Black oil reservoirs consist of large, heavy, nonvolatile hydrocarbon molecules and the fluid is a liquid at reservoir conditions. They are roughly identified as having

Initial solution gas oil ratio of less than 2,000 scf/STB

Very dark green or brown to black in color Stock-tank oil gravities below 45°API

C7+ composition greater than 20 mole percent

Oil formation volume factor of less than 2.00 bbl/STB

Identification of black oil reservoirs


Slide 5

For the PVT database used in this study, the best correlations are presented for the following Black Oil Properties:

Solution Gas Oil Ratio

Bubblepoint Pressure

Oil Formation Volume Factor

Oil Density at Reservoir Conditions

Oil Compressibility above bubble point

Oil Compressibility below bubble point

Oil Viscosity at bubble point

Oil Viscosity above bubble point

Dead Oil Viscosity

Black oil properties


Slide 6

Solution gas oil ratio is the ratio of the volume of the liberated gas from solution to the volume of the remaining stock tank oil both volume corrected to 14.7 psi and 60°F.

Fig. 1 - Typical Solution Gas Oil Ratio Curve.

5432 )460(1

aa

o

a

b

a

gs TpaR

where a1 = 1.4903 x10+3

a2 = 2.626

a3 = 1.3984

a4 = -4.3963

a5 = -1.86

Solution gas oil ratio, Rs


Slide 7

Oil formation volume factor is the volume of the reservoir liquid at conditions under consideration per unit volume of stock tank oil at 14.7 psi and 60°F. It is usually expressed as bbl/STB.

Fig. 2 - Typical Oil Formation Volume Factor Curve.

60160/1 4321 TaTRaRaRaB osogssob

where a1 = 0.177342 x10-3

a2 = 0.220163 x10-3

a3 = 4.292580 x10-6

a4 = 0.528707 x10-3

Oil formation volume factor, Bo


Slide 8

The specific gravity of oil is defined as the ratio of density of the oil to that of water both at the same specified pressure and temperature.

An equation for oil relative density at any pressure is expressed as

Fig. 3 - Typical Oil Relative Density Curve.

ogsoop BRx /)1018.2( 4

w

o

o

Oil density at reservoir conditions, ρo


Slide 9

By definition, the single phase isothermal compressibility or the reciprocal bulk modulus of elasticity is defined as the unit change in volume with pressure. It is usually expressed as 1/psi.

Fig. 4 - Typical Oil Compressibility Curve above Pb.

)460/(/)(/ln 4

3

321 Tappaaac obbobo

where a1 = -14.1042

a2 = 2.7314

a3 = - 56.0605 x 10-6

a4 = 0

Correlations of Co above bubblepoint


Slide 10

Introduction and definitions

Perrine definition of Co below Pb

Paradox of Perrine definition

New definition of Co below Pb

The constant composition curve

Consistency of Co definitions

Estimation of Co below Bubblepoint

Correlations of Co below bubblepoint

Different Definitions of Oil Compressibility Curves


Slide 11

According to Perrine definition, the Co below Pb should include

1. The change in liquid volume

2. The change in the amount of dissolved gas is

Therefore, the Perrine defining equation of oil compressibility below Pb is

Typical oil compressibility curve

in petroleum literature.

T

o

P

B

T

s

P

R

T

sg

T

o

o

op

RB

p

B

Bc

1

Perrine definition of Co below Pb


Slide 12

Below Pb, Experimental data shows that live oil density increases as pressure decreases.

Using Perrine definition co increases with the increase in density

Such behavior cannot happen in nature; observed physical behavior is density and compressibility have opposite trend.

Oil compressibility below Pb increases with

density according to Perrine definition!!

Paradox of Perrine definition


Slide 13

The new definition of Co

below Pb is

The slope dBo/dp should be

taken along the constant

composition curve at the

pressure of interest Locus of Co below Pb (Green

curve)

New definition of Co below Pb


Slide 14

Bo curve below the original Pb is a changing composition curve.

Therefore, the slope of the Bo below the original Pb at any pressure is negative if taken along Bo curve.

To calculate Co, the slope of Bo should be taken along a constant composition curve at pressure of interest as shown in figure.

The pressure of interest where Co is to be evaluated is a new bubble point pressure.

The constant composition curve is Bo curve above the new bubble point pressure with a trend similar to Bo curve above the original bubble point pressure.

The slope of dBo/dp below Pb is

taken along constant composition

curve at pressure of interest.

The constant composition curve


Slide 15

Perrine definition

Co is not consistent with the observed physical behavior.

The new definition

Co is consistent with the observed physical behavior.

Co increases with the decrease of density below as well as above bubble point pressure

Co is continuous from atmospheric pressure to infinity.

Co function is differentiable everywhere except at bubble point where it forms a cusp

Consistency of Co definitions


Slide 16

3

1 2 3 4

1 2 4

ln / ( ) / /( 460)

ln / /( 460)

o ob b b ob

o ob

c a a a P P a T

c a a a T

)460/(/)(/ln 43

321 TaPPaaac obbobo

At original bubble point pressure, oil compressibility could be

estimated by replacing p by pb

Above original bubble point pressure, oil compressibility could

be estimated the following correlation:

21ln o

ob

ac a

Estimation of Co below bubblepoint


Slide 17

2

1 2

2

2

(1/ 1/ )

ln /

ln ln (1/ 1/ )

ln( / ) (1/ 1/ )

op ob

o ob

op ob op ob

op ob op ob

a

op ob

c a a

c c a

c c a

c c e

Below the original bubble point pressure, oil compressibility

could be estimated in terms of oil compressibility at the original

bubble point pressure

Estimation of Co below bubblepoint


Slide 18

The oil viscosity measures the oil’s resistance to flow.

Fig. 8 - Typical Oil Viscosity Curve.

Oil viscosity, μo


Slide 19

The bubblepoint viscosity can be estimated to an accuracy of 30% with

where

and a1 = 10.715

a2 = 100

a3 = -0.515

a4 = 5.44

a5 = 150

a6 = -0.338

odob

3

21

a

S aRa

6

54

a

S aRa

Oil viscosity at bubblepoint pressure, μob


Slide 20

The viscosity above bubblepoint can be estimated to an accuracy of 2% with

where a1 = = 0.151292 x10-3

b

2

1oblnln ppa obo

Oil viscosity above bubblepoint pressure

Fig. 8 - Typical Oil Viscosity Curve.


Slide 21

The dead oil viscosity can be estimated to an accuracy of 35% with

where a1 = 54.56805426

a2 = -7.179530398

a3 = -36.447

a4 = 4.478878992

)ln(ln)(ln)ln(lnlnln api4api321od TaaTaa

Dead oil viscosity, μod


Slide 22

The adjusted differential solution gas-oil ratios at pressures below bubblepoint are evaluated from the following equation:

The adjusted differential oil formation volume factor at pressures below bubblepoint pressure are evaluated from the following equation:

At atmospheric pressure, if equation yields a value for Boi < 1, then Boi for all pressures are calculated by

sbdsbfsdisi RRRR /

obdobfodioi BBBB /

1/1 obdobfodiobdobfoi BBBBBB

Adjustment of differential to separator test


Slide 23

The following conclusions were drawn from this evaluation study:

The bubblepoint pressure and solution gas oil ratio exhibited high errors with original coefficients, but when new coefficients are recalculated an improvement occurred.

All correlations available in literature to estimate the oil formation volume factor at bubblepoint pressure show low errors and a good degree of harmony towards the data used.

The selected correlation of isothermal oil compressibility gives an accurate and unique value independent of different separator tests or consistent field data.

Bubblepoint oil viscosity and dead oil viscosity correlations exhibited very high errors for all correlations available in literature. Therefore more research is needed in this area.

The performance of most of the correlations for viscosity above bubblepoint pressure are adequate.

The adjustment of differential liberation data to separator conditions successfully gives the expected values for all the PVT properties at both bubble point and atmospheric pressures.

Conclusions

Thank You

Slide 24

15meos_PPT_16x9_Black Oil Property Correlations - State of the Art

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