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.
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