New progress in research on CO₂-enhanced coalbed methane

CO₂-Enhanced Coalbed Methane (CO₂-ECBM) integrates CO₂ and CH₄ greenhouse gas emission reduction with enhanced coalbed methane (CBM) recovery. It holds significant potential for achieving China’s “dual carbon” goals (carbon peaking and carbon neutrality) and safeguarding national energy security. However, constrained by insufficient fundamental research and existing technical bottlenecks, its practical application remains largely at the pilot and demonstration stage. This paper reviews recent progress in the mechanisms, evaluation methods, and technological frameworks of CO₂-ECBM, discusses key scientific challenges and technological pathways for geological CO₂ sequestration in coal mine goafs, and provides a forward-looking assessment of the prospects and developmental trends of engineering applications based on representative case studies. The findings indicate that: (1) Mechanistic studies—the essential theoretical foundation of CO₂ sequestration and CH₄ enhancement lies in the synergistic effect of adsorption–displacement and energy-boosted replacement. The process is characterized by a continuous fluid migration under multi-field, multiphase, and multiscale coupling, with CO₂ injectivity and its regulatory mechanisms serving as prerequisites for engineering-scale deployment. (2) Technological frameworks—a five-tier progressive site selection and suitability evaluation system, the KUANGDA method for storage capacity estimation, and in situ monitoring techniques such as downhole sensors, tracers, and transient electromagnetics have been successfully applied in China’s pioneering CO₂-ECBM pilot projects. Moreover, advances in multi-field coupled numerical simulations for engineering forecasting and performance evaluation, as well as the development of multi-source data fusion–based stereoscopic monitoring systems integrating “aerial, satellite, surface, and well” data, have driven a paradigm shift from static estimation toward “dynamic coupling analysis–engineering-accurate prediction–iterative technological optimization.” (3) Engineering applications—technological innovations include liquid/supercritical CO₂ injection systems, synergistic production–injection schemes such as “stepwise intermittent injection with pressure-limited enhancement” and “intermittent drainage,” and vertical well group injection–production technologies. These have facilitated stable and efficient supercritical CO₂ injection through strategies such as multi-source adaptability, flexible multiphase transport, stepwise pressurization, and intelligent regulation. Furthermore, experimental and numerical studies on mineral carbonation using coal-based solid wastes and the reconstruction of strata sealing in coal mine goafs have advanced toward integrated “mineralization–sealing reconstruction” technologies, thereby expanding the engineering application scope of CO₂-ECBM. The study concludes that single-well CO₂ huff-and-puff, CO₂-enhanced fracturing, and vertical/directional well group injection–production are currently the three principal technical modes of CO₂-ECBM. Among these, large-scale deployment is most likely to be realized through horizontal well group–based supercritical CO₂ injection, given its superior injectivity and operational stability.