Numerical investigation of natural gas-enhanced autothermic pyrolysis for optimizing in-situ conversion in oil shale

The autothermic pyrolysis in-situ conversion process for oil shale (ATS) offers the advantages of low development costs and the capability to exploit deep oil shale resources. However, oil shale formations with low oil content encounter the challenge of insufficient heat-generating donors in the thermal cracking residue, making it difficult to sustain the autogenous thermal reaction through oxidative exotherm. In this study, we propose a natural gas-assisted autogenous thermal in-situ conversion technology (H-ATS) designed to develop low oil content shale, and we analyze its mechanism through numerical simulation across oil shales with varying oil contents. The results show that introducing 2.0% natural gas into the injected air successfully triggers the autogenous thermal reaction in low-oil-content shale, achieving an energy efficiency of 3.70. For medium oil content shale, a 2.0% natural gas addition, and for high oil content shale, a 4.0% addition, significantly reduces the gas compression energy required, enhancing energy efficiency to 8.11 and 13.04, respectively—representing improvements of 29.47% and 19.19% over the ATS process alone. This study evaluates the applicability of H-ATS technology across various oil shale formations, providing a new approach for the commercialization of in-situ conversion technology.