Modelling air injection in shale oil reservoirs: physical process and recovery mechanism

In this paper, reservoir simulation approach is conducted for qualitative analysis on EOR mechanisms of air injection in shale oil reservoirs. Effects of oxygen molecular diffusion, reaction enthalpy, activation energy, reaction scheme, and flowing well-bore pressure on the well performance of air injection are examined in detail. Results show that oxygen molecular diffusion has great effect on spontaneous ignition temperature, heat transfer and oil recovery, which should be considered in simulating air injection in shale oil reservoir for better understanding the real mechanisms. Reaction enthalpy and activation energy can significantly affect ignition temperature, but not on the production performance. High oil recovery can be favourably achieved when the crack reaction dominates, while the combustion reaction exhibits a negative effect on production performance. The development scheme with lower flowing well-bore pressure is more favourable for the air injection process. In-situ combustion and heat transfer cannot sustain due to the air low injectivity. More hydraulic fractures as well as an improved understanding of fracture and its distribution is helpful for enhancing air injectivity to better perform synergic recovery mechanisms of air injection in shale reservoirs. [Received: January 2, 2017; Accepted: June 25, 2018]