Permeability-driven optimization of carbon dioxide injection timing in enhanced coalbed methane recovery
Lei Yang, Chaojun Fan, Mingkun Luo, Haiou Wen, Lijun Zhou, Quanle Zou, Hao Sun, Dezhen Wang
Abstract
Abstract Reducing greenhouse gas emissions and improving unconventional gas recovery are pressing challenges worldwide. This study investigates the leading role of coal permeability in CO 2 -enhanced coalbed methane recovery (CO 2 -ECBM) using an improved thermo-hydro-mechanical (THM) coupling model. The model is validated and applied to the simulation of CO 2 -ECBM process under varying permeability. The direct positive relationship between both cumulative CH 4 production and cumulative CO 2 injection with coal permeability, and operating duration of CO 2 -ECBM is negatively correlated with coal permeability. The delay in the injection start time will extend the operating duration of CO 2 -ECBM and overcome the problem of early CO 2 breakthrough. An increase in both delayed start time for injection and coal permeability progressively boosts CH 4 production, while diminishing CO 2 sequestration. The optimal start timing for CO 2 injection is contingent upon primary objectives, such as CO 2 sequestration or CH 4 production. For the primary constraint of CO 2 sequestration, the optimal starting time should be before the peak gas production. For the primary constraint of CH 4 production, the optimal starting time should be after the peak gas production. In analyzed instances, the optimal timing for CO 2 injection exhibits an inverse correlation with coal permeability. The results provide practical insights for CO 2 injection optimization and field applications.