Oil Correlations

Subtopics:

Al-Marhoun 1985 (Saudi Arabian Oil)

The Al-Marhoun correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), and oil formation volume factor (Bo) for Saudi Arabian oils. Seventy-five bottom hole fluid samples from 62 reservoirs in Saudi Arabia were used in the development of these correlations. The author claims that the correlations should be valid for all types of gas-oil mixtures that share similar properties as those used in the derivation. According to the author, the average errors and standard deviations were lower with the Al-Marhoun correlation than with the Standing and Glaso correlations for Saudi Arabian crude oils.

Bubble Point Pressure

Where:

Solution Gas Oil Ratio

The bubble point pressure equation is reversed to solve for the solution gas-oil ratio. The variable x must be solved for using the quadratic equation.

Where:

Oil Formation Volume Factor

Gas Saturated

Where:

Undersaturated

The oil compressibility (co) used in this equation is obtained from the Vasquez and Beggs correlation.

Reference

"Pressure-Volume-Temperature Correlations for Saudi Crude Oils", M.A. Al-Marhoun, SPE 13718, 1985.

De Ghetto et al (Heavy and Extra-Heavy Oils)

The De Ghetto et al correlation contains modified PVT correlations for estimating bubble point pressure, solution gas oil ratio (Rs), oil formation volume factor (Bo), oil compressibility (co), and oil viscosity (mo) for heavy (10 < °API < 22.3) and extra-heavy oils (°API < 10). The oils used for developing the correlation came from AGIP’s reservoir fluid samples taken from the Mediterranean Basin, Africa, and the Persian Gulf. When comparing published correlations, De Ghetto et al decided that the Vasquez and Beggs correlation estimated the oil formation volume factor (Bo) with minimal error, and therefore no further modification was needed. Note that in contrast with other correlations, the De Ghetto et al correlation requires the pressure and temperature at the separator.

Bubble Point Pressure

Heavy Oils

A modified Vasquez and Beggs solution gas oil ratio (Rs) correlation is reversed to solve for the bubble point pressure as follows:

Where:

Extra-Heavy Oils

A modified Standing solution gas oil ratio (Rs) correlation is reversed to solve for the bubble point pressure as follows:

Solution Gas Oil Ratio

Heavy Oils

A modified Vasquez and Beggs solution gas oil ratio (Rs) correlation was developed as follows:

Where gg(psp) is calculated the same as above for bubble point pressure.

Extra-Heavy Oils

A modified Standing solution gas oil ratio (Rs) correlation was developed as follows:

Oil Formation Volume Factor

Gas Saturated

A modified Vasquez and Beggs oil formation volume factor (Bo) correlation was developed as follows:

Where:

Coefficient

go<= 30°API

go > 30°API

C1

4.677x10-4

4.670x10-4

C2

1.751x10-5

1.100x10-5

C3

-1.811x10-8

1.377x10-9

Undersaturated

Oil Compressibility

Gas Saturated

The derivatives dBo/ dRs and dRs / dp were taken from the Vasquez and Beggs correlation.

Undersaturated

Modified Vasquez and Beggs oil compressibility (co) correlations were developed as follows:

Heavy Oils

Extra-Heavy Oils

Where gg(psp) is calculated the same as above for bubble point pressure.

Oil Viscosity

Dead Oil

Modified Egbogah-Jack’s oil viscosity (mo) correlations were developed as follows:

Heavy-Oils

Extra-Heavy Oils

Gas Saturated

Modified Kartoatmodjo’s oil viscosity (mo) correlations were developed as follows:

Heavy-Oils

Where:

Extra-Heavy Oils

Where:

Undersaturated

Heavy Oils

A modified Kartoatmodjo’s oil viscosity (mo) correlation was developed as follows:

Extra-Heavy Oils

A modified Labedi’s oil viscosity (mo) correlation was developed as follows:

Reference

"Pressure-Volume-Temperature Correlations for Heavy and Extra Heavy Oils", Giambattista De Ghetto, Francesco Paone, and Marco Villa, SPE 30316, 1995.

Glaso (North Sea Oil)

The Glaso correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), and oil formation volume factor (Bo) for North Sea oils. The author claims that the correlation should be valid for all types of oil & gas mixtures after correcting for non-hydrocarbons in the surface gases, and the paraffinicity of the oil. According to the author, the correlation more accurately predicts the oil properties of North Sea oils than the Standing correlation.

Bubble Point Correlation

Where:

Solution Gas Oil Ratio

The bubble point pressure equation is reversed to solve for the solution gas oil ratio (Rs). The variable x must be solved for using the qua

Where:

Oil Formation Volume Factor

Gas Saturated

Where:

Undersaturated

The oil compressibility (co) used in this equation is obtained from the Vasquez and Beggs correlation.

Reference

"Generalized Pressure-Volume-Temperature Correlations", Oistein Glaso, Journal of Petroleum Technology, 1980.

Hanafy et al (Egyptian Oil)

The Hanafy et al correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), oil formation volume factor (Bo), oil compressibility (co), oil viscosity (mo), and oil density (ro)  for Egyptian oils. The compressibility correlation assumes constant compressibility after the bubble point. This correlation is independent of oil gravity (go) and reservoir temperature (T). The PVT data used in the derivation of the correlations was gathered from the Gulf of Suez, Western Desert, and Sinai regions. The authors claim that the correlations can be used to estimate oil properties for a wide range of crude oils ranging from heavy to volatile oils. However our observations are that it appears to be closer to the properties of light oils.

Bubble Point Pressure

Solution Gas Oil Ratio

To prevent the calculation of a negative solution gas oil ratio (Rs), 0 is returned for pressures less than 157.28 psia.

Oil Formation Volume Factor

Gas Saturated

Undersaturated

Oil Density

Note that the density is calculated in metric units (g / cm3).

Gas Saturated

Undersaturated

Oil Compressibility

Undersaturated

This correlation uses only the oil density (rob) at the bubble point. Therefore the oil compressibility (co) is constant for pressures greater than the bubble point.

Gas Saturated

The derivatives dBo/ dRs and dRs / dP were taken from the Vasquez and Beggs correlation.

Oil Viscosity

This correlation calculates the oil viscosity (mo) at any pressure using the corresponding oil density (ro).

Reference

"A New Approach for Predicting the Crude Oil Properties", H.H. Hanafy, S.M. Macary, Y.M. ElNady, A.A. Bayomi and M.H. El Batanony, SPE 37439, 1997.

Khan et al (Saudi Arabian Oil)

The Khan et al correlation contains equations for estimating oil viscosity (mo) at, above, and below the bubble point for Saudi Arabian oils. The study used data from 75 bottom hole samples, which were taken from 65 Saudi Arabian reservoirs. The authors claim that this correlation gives the most accurate predictions for Saudi Arabian crude oils, as compared to the Beggs and Robinson, Beal, and Chew and Connally correlations.

Oil Viscosity at the Bubble Point

For this correlation oil gravity (go) must be less than 1 (10°API).

Where:

Oil Viscosity above the Bubble Point

Oil Viscosity below the Bubble Point

Reference

"Viscosity Correlations for Saudi Arabian Crude Oils", S.A. Khan, M.A. Al-Marhoun, S.O. Duffuaa, and S.A. Abu-Khamsin, SPE Paper No. 15720, 1987.

Ng and Egbogah

The Ng and Egbogah correlation contains two methods for calculating dead oil viscosity (mod) using a modified Beggs and Robinson viscosity correlation and a correlation that uses the pour point temperature. Pour point temperature is the lowest temperature at which the oil is observed to flow when cooled and examined under conditions prescribed in ASTM D97. The purpose of introducing the pour point temperature into the correlation is to reflect the chemical composition of crude oil into the viscosity correlation. To obtain the viscosity for live oils, the dead oil correlations are used with the Beggs and Robinson viscosity correlation. The data used to derive the correlations was taken from the Reservoir Fluids Analysis Laboratory of AGAT Engineering Ltd., using a total of 394 oil systems.

Dead Oils

Modified Beggs and Robinson Viscosity Correlation

Pour Point Visc

Note the range for pour point temperature (Tpp) in this equation is from -50 to 15 °C.

Live Oils

Gas-Saturated

Where:

Undersaturated

Where:

Reference

"An Improved Temperature-Viscosity Correlation for Crude Oil Systems", J.T.H. Ng and E.O. Egbogah, Petroleum Society of CIM 83-34-32, 1983.

Petrosky and Farshad (Gulf of Mexico Oil)

The Petrosky and Farshad correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), oil formation volume factor (Bo), and oil compressibility (co) for Gulf of Mexico oils. The correlation was developed using fluid samples taken from offshore regions in Texas and Louisiana (Galveston Island eastward through Main Pass). The authors claim that these correlations provide improved results over other correlations for the Gulf of Mexico, including those published by Standing, Vasquez and Beggs, Glaso, and Al-Marhoun.

Bubble Point Pressure

Where:

Solution Gas Oil Ratio

Where:

Oil Formation Volume Factor

Gas Saturated

Undersaturated

Oil Compressibility

Gas Saturated

The derivatives dBo/ dRs and dRs / dP were taken from the Vasquez and Beggs correlation.

Undersaturated

Note that this equation is valid for an oil compressibility (co) between 2.464x10-5 to 3.507x10-5.

Reference

"Pressure-Volume-Temperature Correlations for Gulf of Mexico Crude Oils", G.E. Petrosky Jr. and F.F. Farshad, SPE 26644, 1993.

Standing (California Oil)

The Standing correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), and oil formation volume factor (Bo) for California oils. 105 experimentally determined data points on 22 different oil-gas mixtures from California were used in the development of the correlations.

Bubble Point Pressure

Solution Gas Oil Ratio

Oil Formation Volume Factor

Gas Saturated

Undersaturated

The oil compressibility (co) used in this equation is obtained from the Vasquez and Beggs correlation.

Reference

"A Pressure-Volume-Temperature Correlation for Mixtures of California Oil and Gases", M.B. Standing, Drill. & Prod. Prac., API, 1947.

Vasquez and Beggs (Generally Applicable)

Vasquez and Beggs is a generally applicable correlation containing equations for solution gas oil ratio (Rs), oil formation volume factor (Bo), and oil compressibility (co). The correlation was developed from data obtained from over 600 laboratory PVT analyses gathered from fields all over the world. The data used in the development of the correlation covers a wide range of pressures, temperatures, and oil properties. The correlation divides the data into two groups, one for an oil gravity (go) over 30 API and one at and below 30 API.

Bubble Point Pressure

Where:

Coefficient

go<= 30°API

go > 30°API

C1

0.0362

0.0178

C2

1.0937

1.1870

C3

25.7240

23.9310

Solution Gas Oil Ratio

The coefficients  C1,  C2, and  C3 are the same as for the bubble point pressure equation above.

Oil Formation Volume Factor

Gas Saturated

Where:

Coefficient

go<= 30°API

go > 30°API

C1

4.677x10-4

4.670x10-4

C2

1.751x10-5

1.100x10-5

C3

-1.811x10-8

1.377x10-9

Undersaturated

Oil Compressibility

Gas Saturated

The derivatives dBo/ dRs and dRs / dP were taken from the Vasquez and Beggs correlation.

Undersaturated

Reference

"Correlations for Fluid Physical Property Prediction", M.E. Vasquez and H.D. Beggs, JPT 968 - 70, June 1980.

Velarde et al (Reduced Variable Approach)

The Velarde et al correlation contains equations for estimating bubble point pressure, solution gas oil ratio (Rs), and oil formation volume factor (Bo).  The bubble point pressure correlation was based on 728 data sets.  The solution gas oil ratio (Rs) was based on 2097 data sets.

Bubble Point Pressure

Where:

Solution Gas Oil Ratio at the Bubble Point Pressure

Starting from the bubble point pressure equation shown above, re-arrangement yields the following solution for the solution gas oil ratio (Rs):

Solution Gas Oil Ratio

The correlation for the solution gas oil ratio (Rs) below the bubble point uses a reduced variable approach, which yields the reduced solution gas oil ratio (Rsr) as follows:

Where:

A Coefficients

B Coefficients

C Coefficients

A0 = 9.73x10-7

B0 = 0.022339

C0 = 0.725167

A1 = 1.672608

B1 = 1.004750

C1 = 1.485480

A2 = 0.929870

B2 = 0.337711

C2 = 0.164741

A3 = 0.247235

B3 = 0.132795

C3 = 0.091330

A4 = 1.056052

B4 = 0.302065

C4 = 0.047094

The reduced solution gas oil ratio (Rsr) is defined as the solution gas oil ratio (Rs) divided by the solution gas oil ratio at the bubble point (Rsb) as follows:

Similarly, the reduced pressure is defined as the pressure divided by the bubble point pressure.

Using the above relationship the reduced solution gas oil ratio (Rsr) and the solution gas oil ratio at the bubble point (Rsb) are used to solve for the actual solution gas oil ratio (Rs) at any pressure below the bubble point.

Oil Formation Volume Factor

Gas Saturated

Where:

In the above equation an initial estimate of rpo is calculated as follows:

After this initial value is known, rpo is calculated through a 10 step iteration process using the following equations.  The values from the ninth and tenth iterations are averaged to yield a final value for rpo.

Undersaturated

The oil compressibility (co) used in this equation is obtained from the Vasquez and Beggs correlation.

Correlation Limits

Variable

Rs Correlation Limits

Pbp Correlation Limits

T

70 to 307 °F

74 to 327 °F

pbp

106 to 5312 psia

70 to 6700 psia

Bob

1.040 to 2.082 Rbbl / stbbl

N/A

Rs or Rsb

102 to 1808 scf / stbbl

10 to 1870 scf / stbbl

gg

0.561 to 1.101

0.556 to 1.367

go

11.6 to 53.4 °API

12 to 55 °API

Reference

"Correlation of Black Oil Properties at Pressures Below Bubble Point Pressure – A New Approach", J. Velarde, T.A. Blasingame and W.D. McCain, Jr., The Petroleum Society 93 - 97, 1997.

Oil Correlation Limits

Correlation

T (°F)

p (psia)

pbp (psia)

Bo (Rbbl / stbbl)

Rs (scf / stbbl)

Al-Marhoun 1985

(Saudi Arabian Oil)

75 – 240

 

107 – 4315

1.02 – 2.42

24 – 1901

De Ghetto et al

(Heavy and Extra-Heavy Oils)

131.4 – 250.7

1038.49 – 7411.54

208.86 – 4021.96

1.057 – 1.362

17.21 – 640.25

Glaso

(North Sea Oil)

80 – 280

400 – 4000

150 – 7127

1.087 – 2.588

90 – 2637

Hanafy et al

(Egyptian Oil)

1038.49 – 7411.54

 

36 – 5003

1.032 – 1.35

7 – 4272

Khan et al

(Saudi Arabian Oil)

75 – 240

14.7 – 5015

107 – 4315

 

24 – 1901

Ng and Egbogah

70 – 295

 

 

 

 

Petrosky and Farshad

(Gulf of Mexico Oil)

114 – 288

1700 – 10692

1574 – 6523

1.1178 – 1.6229

217 – 1406

Standing

(California Oil)

60 – 260 (pbp)

100 – 260 (Bo)

 

200 – 6000

1.024 – 2.15

20 – 1425

Vasquez and Beggs

(Generally Applicable)

 

140.7 – 9514.7

 

 

 

Velarde et al

(Reduced Variable Approach)

See Velarde et al

 

See Velarde et al

See Velarde et al

See Velarde et al

 

Correlation

gg

go (°API)

Tsp (°F)

Psp (psia)

mo (cp)

Al-Marhoun 1985

(Saudi Arabian Oil)

0.752 – 1.367

14.3 – 44.6

 

 

 

De Ghetto et al

(Heavy and Extra-Heavy Oils)

0.623 – 1.517

6 – 22.3

59 – 177.8

14.5 – 752.2

2.4 – 354.6

Glaso

(North Sea Oil)

0.65 – 1.276

22.3 – 48.1

 

 

0.119 – 106.6

Hanafy et al

(Egyptian Oil)

0.752 – 1.367

14.3 – 44.6

 

 

0.13 – 71

Khan et al

(Saudi Arabian Oil)

 

 

 

 

 

Ng and Egbogah

 

5 – 58

 

 

 

Petrosky and Farshad

(Gulf of Mexico Oil)

0.5781 – 0.8519

16.3 – 45

 

 

 

Standing

(California Oil)

0.5 – 1.5

16.5 – 63.8

 

 

 

Vasquez and Beggs

(Generally Applicable)

0.511 – 1.351

15.3 – 59.5

 

 

 

Velarde et al

(Reduced Variable Approach)

See Velarde et al

See Velarde et al

 

 

 

 

Correlation

mod (cp)

mos (cp)

mob (cp)

ro (g / cm3)

rob (g / cm3)

Al-Marhoun 1985

(Saudi Arabian Oil)

 

 

 

 

 

De Ghetto et al

(Heavy and Extra-Heavy Oils)

7.7 – 1386.9

2.1 – 295.9

 

 

 

Glaso

(North Sea Oil)

 

 

 

 

 

Hanafy et al

(Egyptian Oil)

 

 

 

0.648 – 1.071

0.428 – 0.939

Khan et al

(Saudi Arabian Oil)

 

0.13 – 77.4

0.13 – 17.9

 

 

Ng and Egbogah

 

 

 

 

 

Petrosky and Farshad

(Gulf of Mexico Oil)

 

 

 

 

 

Standing

(California Oil)

 

 

 

 

 

Vasquez and Beggs

(Generally Applicable)

 

 

 

 

 

Velarde et al

(Reduced Variable Approach)