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Oil Correlations Subtopics:

Vasquez and Beggs (Generally Applicable) Al-Marhoun 1985 (Saudi Arabian Oil) Beggs and Robinson De Ghetto et al. (Heavy and Extra-Heavy Oils) Glaso (North Sea Oil) Hanafy et al. (Egyptian Oil) Khan et al. (Saudi Arabian Oil) Ng and Egbogah Petrosky and Farshad (Gulf of Mexico) Standing (California Oil) Velarde et al. (Reduced Variable Approach) Oil Correlation Limits

Vasquez and Beggs (Generally Applicable)

Vasquez and Beggs is a generally applicable correlation containing equations for solution gas oil

ratio, oil formation volume factor, and oil compressibility. 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 oil gravity over 30°API and one

at and below 30°API.

Bubble Point Pressure

Solution Gas Oil Ratio

Oil FVF – Saturated

Oil FVF – Undersaturated

Compressibility – Saturated

Compressibility – Undersaturated

Coefficient γo ≤ 30o API γo > 30o API

A1 0.0362 0.0178

A2 1.0937 1.1870

A3 25.7240 23.9310

C1 0.0362 0.0178

C2 1.0937 1.1870

C3 25.7240 23.9310

Al-Marhoun 1985 (Saudi Arabian Oil)

The Al-Marhoun correlation contains equations for estimating bubble point pressure, solution gas oil

ratio, and oil formation volume factor for Saudi Arabian oils. 75 bottomhole 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. Note that temperature is measured in Rankine.

Bubble Point Pressure

Solution Gas Oil Ratio

where:

a = - 2.278475 * 10-9

b = 7.02362 * 10-3

c = - 64.13891 – p

Oil FVF – Saturated

Oil FVF – Undersaturated

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

Beggs and Robinson

Beggs and Robinson developed an empirical correlation for determining the viscosity of dead oil.

The correlation originated from analyzing 460 dead oil viscosity measurements. The data set from

which the results were obtained ranged from 16°API to 58°API and 70°F to 295°F. The correlation

tends to overstate the viscosity of the crude oil when dealing in temperature ranges below 100°F to

150°F.

Viscosity

where:

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, oil formation volume factor (FVF), oil compressibility, and oil viscosity

for heavy (10° < API < 22.3°) and extra-heavy oils (API < 10°). The oils used for developing the

correlation came from 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 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.

Heavy Oils (10° < API < 22.3°)

Bubble Point Pressure

Solution Gas Oil Ratio

Oil FVF – Saturated

where:

A1, A2, and A3 are Vasquez and Beggs constants for API ≤ 30o:

A1 = 4.677*10-4

A2 = 1.751*10-5

A3 = -1.811*10-8

Oil FVF – Undersaturated

Compressibility – Saturated

Compressibility – Undersaturated

Viscosity – Dead Oil

Viscosity – Saturated

Viscosity – Undersaturated

Extra Heavy Oils (API < 10°)

Bubble Point Pressure

Solution Gas Oil Ratio

Oil FVF – Saturated

where:

A1, A2, and A3 are Vasquez and Beggs constants for API ≤ 30o:

A1 = 4.677*10-4

A2 = 1.751*10-5

A3 = -1.811*10-8

Oil FVF – Undersaturated

Compressibility - Saturated

Compressibility – Undersaturated

Viscosity – Dead Oil

Viscosity – Saturated

Viscosity – Undersaturated

Glaso (North Sea Oil)

The Glaso correlation contains equations for estimating bubble point pressure, solution gas oil ratio,

and oil formation volume factor for North Sea oils. The author claims that the correlation should be

valid for all types of oil and 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 Pressure

Solution Gas Oil Ratio

where:

x = 10log(x)

a = -0.30218

b = 1.7447

c = 1.7669 – log(p)

Oil FVF – Saturated

Oil FVF – Undersaturated

Note: The oil compressibility used in this equation is obtained from the Vasquez and

Beggs correlation.

Hanafy et al. (Egyptian Oil)

The Hanafy et al. correlation contains equations for estimating bubble point pressure, solution gas

oil ratio, oil formation volume factor, oil compressibility, oil viscosity, and oil density for Egyptian oils.

The compressibility correlation assumes constant compressibility after the bubble point. This

correlation is independent of oil gravity and reservoir temperature. 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

Rs = 0 when p ≤ 157.28

Oil FVF – Saturated

Oil FVF – Undersaturated

Density – Saturated

Density – Undersaturated

Compressibility – Saturated

Note: This equation uses the Vasquez and Beggs correlation.

Compressibility – Undersaturated

Oil Viscosity

Khan et al. (Saudi Arabian Oil)

The Khan et al. correlation contains equations for estimating oil viscosity at, above, and below the

bubble point for Saudi Arabian oils. The study used data from 75 bottomhole 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. For this correlation, oil gravity must be less than 1 (10° API).

Oil Viscosity (API < 10°)

p = pb

where:

p > pb

p < pb

Ng and Egbogah

The Ng and Egbogah correlation contains two methods for calculating dead oil viscosity 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 Oil

-50°C < Tpp < 15°C

Live Oil – Saturated

where μod is defined using the modified Beggs and Robinson correlation.

Live Oil - Undersaturated

Petrosky and Farshad (Gulf of Mexico)

The Petrosky and Farshad correlation contains equations for estimating bubble point pressure,

solution gas oil ratio, oil formation volume factor, and oil compressibility 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 FVF – Saturated

Oil FVF – Undersaturated

Compressibility – Saturated

where dRs / dp is from Vasquez and Beggs.

Compressibility – Undersaturated

where 2.464 * 10-5 < co < 3.507 * 10-5

Standing (California Oil)

The Standing correlation contains equations for estimating bubble point pressure, solution gas oil

ratio, and oil formation volume factor 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 FVF – Saturated

Oil FVF – Undersaturated

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

Velarde et al. (Reduced Variable Approach)

The Velarde et al. correlation contains equations for estimating bubble point pressure, solution gas

oil ratio, and oil formation volume factor. The bubble point pressure correlation was based on 728

data sets. The solution gas oil ratio was based on 2097 data sets.

Bubble Point Pressure

Solution Gas Oil Ratio (p = pb)

Solution Gas Oil Ratio (p < pb)

Note: All pressures in the above equations are measured in psig.

Reduced Variable Approach

The reduced solution gas oil ratio is defined as the solution gas oil ratio divided by the solution gas

oil ratio at the bubble point. The reduced pressure is defined as the pressure divided by the bubble

point pressure. Using the above relationship the reduced solution gas oil ratio and the solution gas

oil ratio at the bubble point are used to solve for the actual solution gas oil ratio at any pressure

below the bubble point.

A Coefficients B Coefficients C Coefficients

A0 = 9.73 x 10-7 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

Oil FVF – Saturated

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

Once this initial value is known, ρpo 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 ρpo.

Oil FVF – Undersaturated

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

Note: All pressures in the above equations are measured in psia.

Correlation Limits

Variable Rs Correlation Limits pbp Correlation Limits

T 70 - 307 oF 74 - 327 oF

pb 106 - 5312 psia 70 - 6700 psia

Bob 1.040 - 2.082 bbl/stb N/A

Rs or Rsb 102 - 1808 scf/stb 10 - 1870 scf/stb

γg 0.561 - 1.101 0.556 - 1.367

γo 11.6 - 53.4 oAPI 12 - 55 oAPI

Oil Correlation Limits

Correlation T (oF) p (psia) pb (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 1038.49 - 36 - 5003 1.032 - 1.35 7 - 4272

Oil) 7411.54

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 γo μo (cp) μos (cp) μod (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 2.4 - 354.6

2.1 - 295.9

7.7 - 1386.9

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) 0.13 - 77.4

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 Tsp (oF) psp (psia)

De Ghetto et al. (Heavy and Extra-Heavy Oils) 59 - 177.8 14.5 - 752.2

Correlation ρo (g/cm3) ρob (g/cm3)

Hanafy et al. (Egyptian Oils) 0.648 - 1.071 0.428 - 0.939

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