Numerical Investigation of Optimal Well Spacing Configuration for Enhanced CH ₄ Recovery and CO ₂ Sequestration: Geological Implications Analysis

Within the framework of the CO2-ECBM projects, the optimal arrangement of well spacing serves as a pivotal factor in maximizing CH4 production and optimizing the CO2 sequestration performance. This study centers on the Panyi mining area in Huainan city as its primary research focus. Initially, a comprehensive analysis was carried out employing fully coupled THMC mathematical models to simulate the CO2-ECBM process. Subsequently, the investigation systematically assessed the impact of well spacing on key performance indicators. To rigorously evaluate the engineering outcomes of the CO2-ECBM process, objective functions were meticulously formulated to quantify performance. Following this, an in-depth analysis was conducted to identify the optimal well spacing configurations corresponding to four distinct engineering objectives under varying injection pressures. Based on the findings, a dynamic design framework for well spacing and injection pressure was proposed, adhering to the principles of multiobjective optimization. For well spacings less than 210 m, both CH4 production and the CO2 injection volume demonstrate a positive correlation with increasing well spacing. Conversely, when well spacing exceeds 280 m, both volumes exhibit a decline as well spacing expands. Within the intermediate range of 210–280 m, variations in CH4 production and CO2 injection volumes with respect to well spacing are relatively minimal. As the CO2 injection pressure intensifies, the optimal well spacing required to achieve the four engineering objectives increases proportionally. Under identical injection pressures, the optimal well spacings, when ranked from smallest to largest, align with the following objectives: time-efficiency optimization, comprehensive consideration, production prioritization, and storage prioritization. It is worth noting that time-efficiency optimization should not serve as the primary engineering objective in the layout of CO2-ECBM technology due to potential trade-offs with other critical performance metrics. For projects with a strong emphasis on CH4 production, a strategy that combines a low injection pressure with moderate well spacing is recommended to strike a balance between production efficiency and operational feasibility. Conversely, for projects prioritizing CO2 sequestration, a high injection pressure paired with large well spacing is advisible to enhance sequestration capacity while maintaining system stability. The research findings provide robust theoretical support for the precise regulation of CO2-ECBM engineering parameters under complex geological conditions, thereby advancing the field’s capacity to optimize both energy recovery and environmental mitigation outcomes.