Experimental Research on Enhanced Oil Recovery Methods for Gas Injection of Fractured Reservoirs Based on Microfluidic Chips.

Gas injection is an effective method to enhance oil recovery of low-permeability and tight reservoirs, while the complicated fractures distributed in the formation have a noticeable effect on the performance of gas injection. In this study, three methods of gas injection were employed to conduct microfluidic experiments using micromodels simulating fractured reservoirs. The sweep efficiency and oil displacement efficiency of pores and throats, fractures, and the whole region were measured respectively to evaluate the oil displacement effects of the different gas injection methods. Moreover, the microscopic displacement process and the morphology of residual oil in porous media were analyzed to investigate the behavior of gas activated oil. The experimental results show that there are three stages of gas displacing oil: the oil in fractures was displaced first, then the oil in the pores and throats around the fracture was displaced, and finally the gas channeling occurred in fractures. Moreover, the sweep efficiency and oil displacement efficiency showed a tendency of increasing fast first and then reaching a steady state. Simultaneous injection of gas and water showed an optimal enhanced oil recovery effect among these three injection methods. Gas can invade deep throats, and those are difficult for water to sweep. However, the higher viscosity of water endowed it a smaller mobility than gas. And, the channeling in the two-phase mixing region was inhibited more obviously. The overall sweep efficiency and oil displacement efficiency increased about 18.4% and 13.4%, respectively.