Oil Correlations
Vasquez and Beggs (Generally Applicable)
Compressibility - Undersaturated
De Ghetto et al. (Heavy and Extra-Heavy Oils)
Heavy Oils (10° < API < 22.3°)
Compressibility - Undersaturated
Compressibility - Undersaturated
Compressibility - Undersaturated
Khan et al. (Saudi Arabian Oil)
Petrosky and Farshad (Gulf of Mexico)
Compressibility - Undersaturated
Velarde et al. (Reduced Variable Approach)
Solution Gas Oil Ratio (p = pb)
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
Coefficient
|
γo ≤ 30o API
|
γo > 30o API
|
C1 |
0.0362 |
0.0178 |
C2 |
1.0937 |
1.1870 |
C3 |
25.7240 |
23.9310 |
Solution Gas Oil Ratio
Oil Formation Volume Factor (FVF) – Saturated
Coefficient
|
γo ≤ 30o API
|
γo > 30o API
|
A1 |
4.677E-04 |
4.670E-04 |
A2 |
1.751E-05 |
1.100E-05 |
A3 |
-1.811E-08 |
1.337E-09 |
Oil FVF – Undersaturated
where Bob is the formation volume factor at the bubble point pressure
Compressibility – Saturated
where Rsob is the solution gas-oil ratio at the bubble point pressure
Compressibility – Undersaturated
Al-Marhoun (Middle East Oil)
The Al-Marhoun correlation contains equations for estimating bubble point pressure, solution gas oil ratio, and oil formation volume factor for Middle East oils. 75 bottomhole fluid samples from 62 reservoirs in the Middle East 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 Middle Eastern 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
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 62 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
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
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:
After 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. 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 (Middle East 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) |
107 - 327 |
|
36 - 5003 |
1.032 - 4.35 |
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 | γo (°API) | μo (cp) | μos (cp) | μod (cp) |
---|---|---|---|---|---|
Al-Marhoun (Middle East 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 |
17.8 - 47.7 |
0.13 - 71 |
|
|
Khan et al. (Saudi Arabian Oil) |
|
14.3 - 44.6 |
|
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 |