Correlation and prediction of residual oil saturation for gas-injection-enhanced oil-recovery processes

A promising correlation has been developed that can be used to predict miscible or near-miscible residual oil saturation, S-orm, for a wide range of injected gases, crude oils, temperature, and pressure conditions. The correlation is based on the representation of the chemical and physical properties of the crude oil and the injected gas through Hildebrand solubility parameters. This approach has the advantage that characteristics of both the injected gas and crude oil are included in the correlation, in contrast to correlations based solely on properties of the injected gas. The correlation was developed using available experimental data for tertiary recovery of eight crude oils in carbonate and sandstone cores with common enhanced oil recovery (EOR) gases [CO2, N-2, CH4, CH4 + liquefied petroleum gas (LPG)]. Results for 45 coreflood tests at reservoir conditions collapsed along a band when S-orm was plotted as a function of the difference in solubility parameters between the injected gas and the crude oil. Results for a pure oil, decane, with CO2 lay along the same band. The success of this correlation scheme may be the result of the basic characterization of the fluids and of a relationship between solubility parameters and interfacial tension (IFT). Use of the correlation requires knowledge only of injected gas composition, injected gas density, oil average molecular weight, and temperature. This empirical correlation should have utility in screening studies as a simple means to forecast residual oil saturations as measured in coreflood tests. The correlation can be used to predict roughly the effects of changes in pressure, temperature, or injected gas composition on residual oil saturation. A new method to predict minimum miscibility pressure (MMP) based on the solubility parameter concept is also described.