New Correlations For Formation Volume Factors Of Oil And Gas Mixtures
Authors: Al-Marhoun M.A. 
Published: March 2010

This paper presents new correlations for formation volume factors (FVF) at, above and below bubblepoint pressure for oil and gas mixtures as empirical functions of solution gas oil ratio, gas relative density, oil relative density pressure, and reservoir temperature. The correlations are developed from a total of 11 728 experimentally obtained FVF at above and below bubblepoint pressure on oil-gas mixtures collected from fields allover the world. The data encompassed a wide range of gas-oil ratios, oil and gas relative densities, pressure and reservoir temperature.

The newly developed correlations outperform the existing correlations for FVF of oil and gas mixtures based on high correlation coefficient and on low values of average per cent relative error, average absolute per cent relative error and standard deviation.

Introduction

The evaluation of FVF at, above and below bubblepoint pressure of oil-gas mixtures is an important tool in reservoir performance calculations and the design of various stages of oilfield operations. The following presents a review of the development of FVF correlations. The empirical equations that form these published correlations are provided in the Appendix.

Oil FVF at Bubblepoint Pressure

In 1947, Standing(1,2) proposed a correlation for determining the formation volume factor of a gas-saturated oil. A total of 105 experimentally determined data points on 22 different crude oil gas mixtures from California fields were utilized in arriving at the correlation.

In 1980, Vazquez and Beggs(3,4) presented relationships for determining the formation volume factor. A total of 6004 data points were obtained from fields all over the world.

In 1980, Glas Φ (5) presented a correlation for calculating the formation volume factor. A total of 41 data points, obtained mostly from the North Sea Region, were used in the correlation.

In 1988, Al-Marhoun(6) presented a correlation for calculating the formation volume factor. A total of 160 experimentally determined data points on 69 different crude oils from the Middle East were used in the correlation.

Oil FVF Above Bubblepoint Pressure

In 1947, Calhoun(7) presented a chart correlation for calculating the undersaturated oil compressibility. The following equation is proposed here instead of chart reading:

Equation 1 (available in full paper)

In 1980, Vazquez and Beggs(3,4) presented a correlation for determining the undersaturated oil compressibility. A total of 2000 data points obtained from fields all over the world were used in the correlation.

The undersaturated oil compressibility is utilized in the following equation to calculate oil FVF above bubblepoint pressure:

Equation 2 (available in full paper)

Total FVF Below Bubblepoint Pressure

In 1980, Glass Φ (5) presented a correlation for calculating the total formation volume factor below bubblepoint pressure, A total of 36 data points from 15 crude samples, obtained mostly from the North Sea Region, were used in the correlation.

In 1988, Al-Marhoun(6) presented a correlation for calculating the total formation volume factor. A total of 1556 experimentally determined data points on 69 different curde oils from the Middle East were used in the correlation.