Influence of Fracture Parameters on the Development Performance of In Situ Oil Shale Conversion

Oil shale is an important unconventional fossil energy resource. In situ conversion represents a green and environmentally friendly extraction method. However, due to the low porosity and permeability of the reservoir, establishing artificial fracture networks is crucial for effective reservoir stimulation. Nevertheless, the mechanisms by which fracture networks influence development performance remain unclear. In this study, a coupled seepage–heat transfer–chemical model was developed, and a numerical model integrated with a discrete fracture network was constructed. Numerical simulations were performed to investigate the effects of main fracture permeability, fracture density, fracture tendency, and the Fisher constant K on development performance. The results indicate that high main fracture permeability leads to thermal short-circuiting of injected fluids, which promotes secondary cracking of oil products and reduces energy efficiency. A high fracture density accelerates pyrolysis in the early stage and enhances production migration in the later stage. A larger fracture tendency promotes pyrolysis while mitigating thermal short-circuiting, reducing secondary cracking, and improving energy efficiency. Moreover, a larger Fisher constant K enables uniform heating, promotes kerogen pyrolysis, reduces secondary cracking, and enhances energy efficiency. Correlation analysis reveals that the main fracture permeability is negatively correlated with daily energy efficiency, thereby acting as a limiting factor. In contrast, fracture density, fracture tendency, and the Fisher constant K positively correlate with daily energy efficiency, serving as key parameters that enhance energy efficiency. The optimal fracture configuration for maximizing energy efficiency includes lower main fracture permeability, moderate fracture density, larger fracture tendency, and a higher Fisher constant K. This study provides theoretical support for the stimulation of oil shale reservoirs.