Quantitative Analysis of Fracture Roughness and Multi-Field Effects for CO 2 -ECBM Projects

Carbon Dioxide-Enhanced Coalbed Methane (CO 2 -ECBM), a progressive technique for extracting coalbed methane, substantially boosts gas recovery and simultaneously reduces greenhouse gas emissions. In this process, the dynamics of coalbed fractures, crucial for CO 2 and methane migration, significantly affect carbon storage and methane retrieval. However, the extent to which fracture roughness, under the coupled thermal-hydro-mechanic effects, impacts engineering efficiency remains ambiguous. Addressing this, our study introduces a pioneering, cross-disciplinary mathematical model. This model innovatively quantifies fracture roughness, incorporating it with gas flow dynamics under multifaceted field conditions in coalbeds. This comprehensive approach examines the synergistic impact of CO 2 and methane adsorption/desorption, their pressure changes, adsorption-induced coalbed stress, ambient stress, temperature variations, deformation, and fracture roughness. Finite element analysis of the model demonstrates its alignment with real-world data, precisely depicting fracture roughness in coalbed networks. The application of finite element analysis to the proposed mathematical model reveals that (1) fracture roughness ξ markedly influences residual coalbed methane and injected CO 2 pressures; (2) coalbed permeability and porosity are inversely proportional to ξ ; and (3) adsorption/desorption reactions are highly sensitive to ξ . This research offers novel insights into fracture behavior quantification in coalbed methane extraction engineering.