TECHNOLOGY Geographic location considered in PVT calculation program

Abdel M. Elsharkawy,
Dawood El-Mater
Kuwait University
Kuwaitz

A computer program was developed to calculate hydrocarbon fluid properties from a

variety of geographical locations. For any given area of the world, one correlation may

be better than another.

The program's calculations are based on published pressure-volume-temperature (PVT)

correlations. The program will run on an IBM compatible personal computer.

The following correlations were used for crudes of different parts of the world:

Standing (1947), California crudes
Glas
Al-Marhoun (1988), Saudi Arabia crudes
Dokla and Osman (1992), U.A.E. crudes
Petrosky and Farshad (1993), Gulf of Mexico crudes
Farshad, et al. (1992), Colombian crudes
Obomanu and Okpobiri (1987), Nigerian crudes
Vasquez and Beggs (1980), general
Kartoatmodjo and Schmidt (1994), general.

The properties calculated include solution gas/oil ratio, oil formation volume factor,

crude oil viscosity, gas deviation factor, gas formation volume factor, and gas

viscosity.

The program includes most of the well known correlations as well as the recently

developed ones for estimating properties of saturated crude oil in several different

areas of the world. The mathematical functions represent the best fit for estimating

the gas properties from empirical data.

view example problem

The fluid properties obtained can be used for formation evaluation of hydrocarbon

reservoirs, reserve calculations, reservoir performance predictions, production

operations, and production facility design.

The program can also be used in research work for assessing published correlations that

predict the properties of a given crude whose laboratory PVT data are known.

Program input data include the number of data points, calculation option for saturated

crudes, reservoir pressure, API crude oil gravity, gas specific gravity, reservoir

temperature.

Output from the program can be stored in a data file for later use or printed on the

screen.

Crude oil properties

In the program, Standing's correlations1 are used to calculate PVT properties for

California crudes. Standing's correlations are the most commonly used correlations in

petroleum engineering textbooks. Most petroleum engineers use Standing's correlations

to predict PVT properties of low API crudes in absence of empirical data.2 3

The program uses Vasquez and Beggs correlations4 to calculate PVT properties of crudes

from areas whose particular correlations have not been developed or are unknown.

Vasquez and Beggs correlations are based on 600 PVT laboratory analyses from different

oil fields representing a variety of locations in the world.

GlasSea crudes. For this correlation to be general, Glas

The program uses Al-Marhoun's correlations7 to calculate the PVT properties of Middle

East crudes. The bubble-point pressure correlation is recommended for Saudi Arabian

crudes. Recent studies by Elsharkawy6 and Al-Fattah8 showed that Al-Marhoun's

correlation for oil formation volume factor offers the best accuracy among the other

correlations.

Dokla and Osman's correlations9 are used to calculate PVT properties for United Arab

Emirates crude oils. However, the gas oil ratio correlation has a physical

deficiency.10 11

Obomanu and Okpobiri's correlations12 estimate the PVT properties of the Nigerian

crudes. It is important to note that in Equations 17-19, solution gas/oil ratio (Rs) is

in standard cu m/standard cu m, pressure is in 1,000 Pascals, and temperature is in

Kelvin.

View Equations[102232 bytes ]

Farshad, et al.'s, correlations13 are used in the program to calculate PVT properties

of Colombian crudes, and Petrosky and Farshad14 correlations are used to calculate PVT

properties for Gulf of Mexico crudes.

The program uses Kartoatmodjo and Schmidt's correlations15 to calculate solution

gas/oil ratio and oil formation volume factor for crudes that do not have a local

correlation to describe their behavior. These correlations were developed from a large

data bank representing 740 different crude oil samples and are much more up to date

than the ones developed by Vasquez and Beggs.

The program uses Beggs and Robinson16 correlations to calculate crude oil viscosity

because it was found that this correlation represents the best fit for saturated

crudes.17

Gas properties

Pseudocritical pressure and temperature of gas are calculated using Suttan's

correlations.18 The pseudoreduced pressure and temperature are calculated after the

program determines the pseudocritical values.

Dranchuk and Abou-Kassem's correlation19 was found to properly fit the equation of

state.20 Therefore, Dranchuk and Abou-Kassem's equation of state is used to calculate

the gas deviation factor.

Finally, the gas viscosity is calculated using Lee, Gonzalze and Eakin's semiempirical

method.20 21

Editor's note: To obtain the program PVT.EXE, Journal subscribers can send a blank 31/2

diskette formatted to MS DOS and a self-addressed, postage paid or stamped return

diskette mailer to: Production Editor, Oil & Gas Journal, 3050 Post Oak Blvd., Suite

200, Houston, TX 77056, USA.

Subscribers outside the U.S. should send the diskette and return mailer without return

postage to the same address. This mail offer will expire Apr. 30, 1996.

view equations continued[27769 bytes ]

References

Standing, M.B., "A Pressure-Volume-Temperature Correlation for Mixtures of
California Oils and Gases," Drill. & Prod. Prac., API, 1947, pp. 275-87.
Ostermann, R.D., Ehlig-Economides, C.A., and Owalabi, O.O., "Correlations for the
Reservoir Fluid Properties of Alaskan Crudes," Paper No. SPE 11703, SPE California
Regional Meeting Ventura, Mar. 23-25, 1983.
Suttan, R.P., and Farshad, F F., "Evaluation of Empirically Derived PVT Properties
for Gulf of Mexico Crude Oils,," SPERE, February 1990, pp. 79-86.
Vasquez, M.E., and Beggs, H.D., "Correlations for Fluid Physical Property
Prediction," JPT, June 1980, pp. 968-70.
GlasMay 1980, pp. 785-95.
Elsharkawy, A.M., Elgibaly A.A., and Alikhan A.A., "Assessment of the PVT
Correlations for Predicting the Properties of the Kuwaiti Crudes," Paper No. ADSPE 58,
6th Abu Dhabi International Petroleum Exhibition Conference, Nov. 16-19, 1994.
Al-Marhoun, M.A., "PVT Correlations for Middle East Crude Oils," JPT, May 1988,
pp. 650-66.
Al-Fattah, S.M., and Al-Marhoun, M.A., "Evaluation of Empirical Correlations for
Bubble Point Oil Formation Volume Factor," J. Pet. Science & Eng., Vol. 11, 1994, pp.
341-50.
Dokla, M.E., and Osman M.E., "Correlation of PVT Properties for UAE Crudes," SPE
Formation Evaluation, March 1992, pp. 41-46.
Al-Yousef, H.Y., and Al-Marhoun, M.A., "Discussion of PVT Properties for UAE
Crudes," SPE Formation Evaluation, March 1993, pp. 80-81.
Dokla, M.E., and Osman, M.E., "Author's Reply to Discussion of Correlation of PVT
Properties for UAE Crudes," SPE Formation Evaluation, March 1993, pp. 81.
Obomanu, D.A., and Okpobiri, G.A., "Correlating the PVT Properties of Nigerian
Crudes," J. of Energy Resources Technology, Trans. ASME, Vol. 109, December 1987, pp.
214-17.
Farshad, J.L., Leblanc, J.L., Garber, J.D., and Osorio J.G., "Empirical PVT
Correlations for Colombian Crude Oils," Paper No. SPE 24538, 1992.
Petrosky, G.E., and Farshad, F.F., "Pressure-Volume-Temperature Correlations for
Gulf of Mexico Crude Oils," Paper No. SPE 26644, SPE 68th Annual Technical Conference
and Exhibition, Houston, Oct. 3-6, 1993.
Kartoatmodjo, F. and Schmidt, Z., "Large data bank improves crude oil physical
property correlations," OGJ, July 4, 1994, pp. 51-55.
Beggs, H.D., and Robinson, J.R., "Estimating the Viscosity of Crude Oil System
JPT," September 1975, pp. 1104-41.
Al-Ameer, O.A, "Evaluation of Crude-oil Viscosity Correlations," Kuwait
University, September 1994.
Suttan, R.P., "Compressibility Factors for High-Molecular Weight Reservoir Gases,"
Paper No. SPE 14265, SPE Annual Technical Conference and Exhibition, Los Vegas, Sept.
22-25, 1985.
Dranchuk, P.M., and Abou-Kassem, J.H., "Calculation of Z factors for Natural Gases
Using Equation of State," JPT, July-September 1975, pp. 34-36.
Al-Otaiby, S.G, " Assessment of the Gas Physical Property Correlations," Kuwait
University, June 1994.
Lee, A.T., Gonzalze, M.H., and Eakin, B.E., "The Viscosity of Natural Gases," JPT,
August 1966, pp. 997-1000.