Pore-Scale Movability Evaluation for Tight Oil Enhanced Oil Recovery Methods Based on Miniature Core Test and Digital Core Construction

The movability of micro-remaining oil in microscale pores in tight reservoirs directly affects the recoverability of a reservoir fluid. Currently, core displacement and digital cores have been applied for the reservoir fluid movability and microstructure visualization. In this study, we present a practical framework for the pore-scale movability of tight oil, which combines core displacement tests and digital cores on real tight core samples. In this framework, the core displacement tests and miniature core displacement tests using three different displacement methods (water flooding, CH4 flooding, and CO2 flooding) are first performed. Then, through a series of CT (computed tomography) scanning results on the core displacement tests, a digital core model is constructed, and a distribution of micro-remaining oil is experimentally investigated. By combining the results of the miniature core displacement tests and the digital core model, the types and movability of tight oil at different times for the three methods are obtained. These results indicate that the remaining tight oil at pore scale can be classified into three different categories according to a shape factor (S) of the remaining oil, including block-like oil (4.85 > S > 1), flat-like oil (12.22 > S > 4.85) and film-like oil (S > 12.22). From CT scanning results, the method of water flooding can effectively unlock the type of block-like oil, while CH4 flooding and CO2 flooding can produce flat-like and film-like oil. Furthermore, CO2 flooding can significantly unlock more film-like oil than CH4 flooding.