Simulation and optimization of hydraulic fracturing in deep coal-rock reservoirs

Deep coalbed methane (CBM) reservoirs represent a promising yet technically challenging frontier in unconventional gas development, owing to their ultra-low permeability, pronounced heterogeneity, and complex in situ stress conditions. However, conventional hydraulic fracturing designs developed for shallow seams often fail to deliver satisfactory stimulation performance in deeper formations. To overcome these limitations, this study proposes an integrated workflow that combines high-resolution 3 dimensions geological modeling, numerical simulation, and statistical optimization to enhance stimulation effectiveness in deep CBM reservoirs. A high-resolution geological and fracture model of Block M was constructed to accurately represent spatial heterogeneity and natural fracture distribution. Based on this model, a series of numerical simulations were conducted under varying operational conditions, and response surface methodology was employed to evaluate the effects of key fracturing parameters on the stimulated reservoir volume (SRV).The results indicate that the optimized scheme enhances the effective SRV by 24.13% compared to the baseline design, while effectively maintaining fracture height containment. However, economic evaluation reveals that the scheme with the largest SRV does not correspond to the most economically optimal option. By comparing the SRV-maximized and economically optimal scenarios, a trade-off analysis was performed to identify a technically and economically balanced solution. Moreover, economic evaluation results confirmed the technical feasibility and cost-effectiveness of the proposed stimulation strategy under deep reservoir conditions. Overall, this work provides a scalable, data-driven approach to guide hydraulic fracturing optimization in deep CBM development, aligning geological constraints with engineering decisions.