Oil correlations

Oil / condensate correlations

Oil condensate PVT correlations are described below.

PVT

Vasquez and Beggs: Developed from data obtained from fields all over the world and generally applicable for all oil types. Covers a wide range of pressures, temperatures, and oil properties.

Al-Marhoun: Developed for Saudi Arabian oils. Valid for all types of gas-oil mixtures ranging from 14 - 45 ºAmerican Petroleum Institute (API) gravity.

De Ghetto et al: Developed for heavy oils (10 < °API < 22.3) and extra-heavy oils (°API < 10) from the Mediterranean Basin, Africa, and the Persian Gulf. Requires separator pressure and temperature.

Glaso: Developed for North Sea oils and it is suitable for oil mixtures ranging from 22-48 ºAPI. Valid for all types of oil and gas mixtures after correcting for non-hydrocarbons in the surface gases and the paraffinicity of the oil.

Hanafy et al: Developed for Egyptian oils gathered from the Gulf of Suez, Western Desert, and Sinai regions. Independent of oil gravity and reservoir temperature. Although authors claim that the correlations are applicable to a wide range of crude oils ranging from heavy to volatile oils (14.3 – 47 ºAPI), it appears to be more applicable for light oils.

Petrosky and Farshad: Developed for Gulf of Mexico oils gathered from offshore regions in Texas and Louisiana. Applicable for oil mixtures ranging from 16 - 45 ºAPI. Provides improved results for the Gulf of Mexico oils compared to Standing, Vasquez and Beggs, Glaso, and Al-Marhoun correlations.

Standing: Developed for California oils. Applicable for oil mixtures ranging from 16 - 64 ºAPI.

Velarde et al: Developed for black oils, applicable for oil mixtures ranging from 12 - 55 ºAPI.

Constant Properties: Allows you to enter values for oil compressibility, the solution gas-oil ratio, and the oil formation volume factor at initial reservoir conditions.

Custom Table: Allows you to enter laboratory measurements for oil compressibility, the solution gas-oil ratio, and the oil formation volume factor.

Viscosity

Beggs and Robinson: Developed from data obtained from fields all over the world and generally applicable for all oil types. Covers a wide range of pressures, temperatures, and oil properties.

Hanafy et al: Developed for Egyptian oils gathered from the Gulf of Suez, Western Desert, and Sinai regions. Independent of oil gravity and reservoir temperature. Although the authors claim that the correlations are applicable to a wide range of crude oils ranging from heavy to volatile oils (14.3 – 47 ºAPI), it appears to be more applicable for light oils.

Khan et al: Developed using oil samples collected from Saudi Arabian reservoirs. Gives more accurate predictions for Saudi Arabian oils, compared to the Beggs and Robinson.

Ng and Egbogah: This 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, which is the lowest temperature at which the oil is observed to flow when cooled. 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. This correlation is applicable for oil mixtures ranging from 5 - 58 ºAPI.

Constant Properties: Allows you to enter the value for oil viscosity at initial reservoir conditions.

Custom Table: Allows you to enter laboratory measurements for oil viscosity.

Vasquez and Beggs (generally applicable)

Vasquez and Beggs is a generally applicable correlation containing equations for the solution gas oil ratio, oil formation volume factor, and oil compressibility. The correlation was developed from data obtained from over 600 laboratory pressure volume temperature (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.

Note: This is the default setting for oil correlations.

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 B_ob is the formation volume factor at the bubble point pressure

Compressibility – saturated

where R_sob 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 dataset 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:

x = y T^-1.163

y = 10^z

z = 3.0324 - 0.02023 G

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 the bubble point pressure, solution gas oil ratio, and the 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 the 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 pressure volume temperature (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 sandface 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 the 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 the bubble point pressure, solution gas oil ratio, and the oil formation volume factor for California oils. There were 105 experimentally determined data points on 22 different oil-gas mixtures from California 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 the bubble point pressure, solution gas oil ratio, and the oil formation volume factor. The bubble point pressure correlation was based on 728 datasets. The solution gas oil ratio was based on 2097 datasets.

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