Injection energy utilization efficiency and production performance of oil shale in-situ exploitation

Oil shale in-situ conversion is an effective and promising exploitation method. The most concerned problem of oil shale in-situ conversion is how to exploit maximum oil and gas by injecting the least energy. However, the relationship between injection energy utilization efficiency and productivity under different operational conditions remain unclear. In this paper, based on a multiphase flow, heat transfer and chemical reaction numerical model, evolution of kerogen pyrolysis with reservoir temperature distribution is thoroughly analyzed. Aims at injection energy utilization efficiency and productivity, effects of injection energy rate, well shut-in measure, reservoir pressure and well spacing on the production performance of the oil shale in-situ exploitation are investigated. Results show that the useless heating region exists during kerogen pyrolysis, which significantly reduces the energy utilization efficiency. A shut-in measure can slightly improve the energy utilization efficiency but lower oil output, thus not a very effective measure to solve the useless heating problem. Under the same energy injection rate, a higher injection temperature and lower injection flow rate will simultaneously obtain higher oil production rate, oil output, and energy utilization efficiency. Furthermore, a larger reservoir pressure and well spacing of 40 m–50 m are recommended to obtain higher oil production rate and output. Results provide meaningful suggestions for optimizing operational parameters in view of injection energy utilization efficiency and oil output.