Numerical study on in-situ mining oil shale by high-temperature steam injection in long-distance horizontal wells

Abstract This article proposes an in-situ steam-assisted thermal decomposition method for oil shale using long-distance horizontal wells.Firstly, this article establishes a coupled thermal–hydraulic hydrothermal mechanical model considering the anisotropy of oil shale to study the in-situ pyrolysis process of oil shale by steam injection in horizontal wells. Then Optimization analysis was conducted on the effects of fracture spacing, fracture length, and horizontal well length on extraction efficiency. Finally, An economic analysis was conducted on the new extraction method. The research results indicate that: (1) Compared with the traditional vertical well mining mode (1injection and 8 production well, with a well spacing of 50 m), the newly proposed long-distance horizontal well configuration (1 injection and 2 production well) has higher heating efficiency. (2) When the fracture spacing is less than 25 m, the heating efficiency is no longer significantly improved. Increasing the length of fractures has a significant effect on improving heating efficiency. (3) When the length of the horizontal well exceeds 450 m, the extraction cost no longer significantly decreases. Increasing the length of fracturing fractures can significantly reduce extraction costs. When the fracture spacing is less than 30 m, the extraction cost no longer significantly decreases. This study provides theoretical reference and data support for the efficient in-situ thermal decomposition of oil shale.