An improved oil recovery prediction method for volatile oil reservoirs

To describe the complex phase transformation in the process of depletion exploitation of volatile oil reservoir, four fluid phases are defined, and production and remaining volume of these phases are calculated based on the principle of surface volume balance, then the recovery prediction method of volatile oil reservoir considering the influence of condensate content in released solution gas and the correction method of multiple degassing experiments data are established. Taking three typical kinds of crude oil(black oil, medium–weak volatile oil, strong volatile oil) as examples, the new improved method is used to simulate constant volume depletion experiments based on the corrected data of multiple degassing experiment to verify the reliability of the modified method. By using "experimental data and traditional method", "corrected data and traditional method" and "corrected data and modified method", recovery factors of these three typical kinds of oil are calculated respectively. The source of parameters and the calculation methods have little effect on the recovery of typical black oil. However, with the increase of crude oil volatility, the oil recovery will be seriously underestimated by using experimental data or traditional method. The combination of "corrected data and modified method" considers the influence of condensate in gas phase in both experimental parameters and calculation method, and has good applicability to typical black oil and volatile oil. The strong shrinkage of volatile oil makes more "liquid oil" convert to "gaseous oil", so volatile oil reservoir can reach very high oil recovery by depletion drive.