Chapter 6: Oil System Correlations

The calculation of reserves in an oil reservoir or the determination of its performance requires knowledge of the fluid’s physical properties at elevated pressure and temperature. Of primary importance are those properties including bubblepoint pressure, solution gas/oil ratio (GOR), and formation volume factor (FVF). In addition, viscosity and surface tension must be determined for calculations involving the flow of oil through pipe or porous media. Ideally, these properties are determined from laboratory studies designed to duplicate the conditions of interest; however, experimental data are quite often unavailable because representative samples cannot be obtained or the producing horizon does not warrant the expense of an in-depth reservoir fluid study. In these cases, pressure-volume-temperature (PVT) properties must be determined by analogy or through the use of empirically derived correlations. This chapter reviews methods for the determination of bubblepoint pressure, solution GOR, oil FVF, isothermal compressibility, dead (gas-free) oil viscosity, gas-saturated (bubblepoint) oil viscosity, undersaturated oil viscosity, and gas/oil, oil/water, and gas/water surface tension. Table 6.1 (Refs. 1 through 28 ) summarizes the recommended methods for general use determination of each property. These recommendations are based on the correlation performance derived from a common data set or the author’s experiences drawn from using various correlations for a number of years. In  Appendix A , Tables A-1 through A-12 (Refs. 29 through 65 ) contain a comprehensive and descriptive list of available correlations because specific applications could require the use of methods other than those listed in Table 6.1 .