Research on shale acid fracturing reservoir simulation technology: A critical review

The production potential of shale reservoirs is significantly influenced by the application of reservoir stimulation technology. Compared to conventional hydraulic fracturing reservoir reforming techniques, acid fracturing emerges as a promising alternative due to its remarkable permeability enhancement effects, reduced difficulty in fracturing deep shale formations, enhanced propensity for intricate seam network formation, and effective propping without the need for proppant. This comprehensive review presents an in-depth analysis of the existing literature on shale acidizing. The review delves into the specific changes observed in shale's mineral composition, microstructure, mechanical properties, gas adsorption characteristics, and wettability following acidification. It critically analyses various numerical simulation methods (e.g., FEM, XFEM, BEM, FDM, DEM, etc.) and models (e.g., Two-scale continuum model, Fractal model, Lumped model, etc.) employed in shale acidification and fracturing simulations. Field case studies demonstrate that acid fracturing is highly effective in shale reservoirs with high carbonate mineral content and well-developed natural fractures, yet it yields limited long-term benefits in silica-dominated reservoirs. Future research should focus on optimizing acid system designs, developing multiphysics coupled models, and investigating synergistic effects between CO₂ fracturing and acid fracturing to advance efficient shale reservoir stimulation technologies. In conclusion, this review synthesizes the current challenges encountered in shale acid fracturing theoretical research and field applications, while simultaneously identifying key areas for future research endeavors.