The mobility of continental shale oil by gas flooding and influencing factors based on displacement-nuclear magnetic resonance instruments

The efficient development of shale oil is a challenging problem for researchers. Conventional experiments for characterizing fluid distribution encounter a bottleneck because of the special composition, complex pore structure, and unclear fluid occurrence in shale oil reservoirs. Targeting continental shale in eastern China, we used high-temperature and high-pressure displacement instruments combined with nuclear magnetic resonance instruments for the first time to evaluate the shale oil mobility under different gases (CH4, CO2, and N-2) flooding for simulating "huff-n-puff" in the field. Results found that the gas flooding can significantly improve the mobility of shale oil. Compared with CH4 and N-2, CO2 had obvious advantages in improving the mobility of shale oil. Under an injection pressure of 6.0 MPa, the experimental average movable ratio was 22.3%, and the theoretical maximum movable ratio was 39.3%. Organic matter abundance, mineral composition, sedimentary structures, and pore structure determine the movable ratio of gas flooding by affecting the permeable channel, phase state of the injected gas, and gas-oil contact. Gas flooding has broad prospects in the exploitation of continental shale oil considering difficult development and abundant gas source in the eastern basin of China.