Experimental evaluation of energy supplement methods in the Yanchang Oilfield shale reservoir

Shale oil development in the Yanchang Oilfield is characterized by rapid production decline and low productivity, and supplementing the energy requirements and enhancing the recovery of oil are major challenges for shale reservoir development. In this study, physical simulations of cyclic water flooding, CO2 immiscible huff and puff, CO2 miscible huff and puff, and gas–water alternate drive processes were conducted on Chang 7 shale reservoir samples from the Yanchang Oilfield. The mechanism behind micro-displacement was analyzed by online NMR detection technologies, which showed that the displacement should be kept above the minimum miscible pressure during CO2 huff and puff. Furthermore, our analyses showed the highest recovery rate was that of water–gas alternate flooding is due to its higher utilization of small pores. Overall, CO2–water alternating flooding or CO2 miscible huff and puff is recommended to obtain higher recovery rates, based on our results. Considering the economic benefits and construction conditions, cyclic water flooding can be used first and then converted to other modes. This study can provide theoretical support for different ways of supplementing energy and provides scientific guidance for gas injection pilot test in similar reservoirs.