Liquid Nitrogen Cryogenic Fracturing in Coalbed Methane Reservoirs: A Comprehensive Review

Summary Coalbed methane (CBM) reservoir fracturing is a critical method for enhancing CBM production. Liquid nitrogen (LN2) fracturing, a promising waterless fracturing technique, offers significant potential for improving reservoir stimulation. With this paper, we provide a comprehensive review of the multiphysics coupling mechanisms and key controlling factors involved in the application of LN2 cryogenic fracturing technology in coal reservoirs. The study highlights the synergistic interactions between thermal shock-induced damage mechanisms and LN2 phase-change dynamics, offering a detailed understanding of the fully coupled thermo-hydro-mechanical-damage (THMD) processes. Analysis reveals that coal properties—such as rank, mineral composition, pore structure, moisture content, and inherent fracture systems—along with reservoir conditions, including the in-situ stress field, temperature distribution, and reservoir pressure, as well as operational parameters (e.g., injection methods, timing, frequency, flow rate, and pressure), all play crucial roles in governing fracture initiation, propagation, and the resulting fracture morphology. Through multicycle freeze/thaw treatments, cumulative fatigue effects promote a stepwise enhancement in reservoir permeability. Numerical simulations and field practices demonstrate that optimization of fracturing parameters, grounded in geoengineering integration, can address critical challenges, including attenuation of heat transfer efficiency and nonuniform fracture propagation, ultimately facilitating the formation of complex, topologically intricate fracture networks. This review establishes a robust theoretical framework and offers practical insights for advancing the mechanistic understanding, process optimization, and large-scale implementation of LN2 fracturing technology in low-permeability coal reservoirs.