Economic Feasibility Evaluation of CO2 Huff-and-Puff for Enhanced Recovery in Low-Productivity Coalbed Methane Wells

CO2 enhanced coalbed methane recovery (CO2-ECBM) using huff-and-puff technology has attracted increasing attention as a promising approach to enhance the productivity of low-productivity coalbed methane (CBM) wells while simultaneously enabling CO2 storage. However, the economic feasibility of this method and the optimal soaking time remains unclear. In this study, an economic evaluation model for CO2 huff-and-puff CBM projects was developed based on the discounted cash flow method, incorporating key factors such as CBM price, government subsidies, carbon trading price, CH4 separation cost, and CO2 purchase and injection costs. Three representative scenarios were designed to evaluate the impacts of policy support and market conditions. The effects of CO2 injection volume and soaking time on net cash flow (NCF), net present value (NPV), and dynamic payback period (DPP) were systematically investigated. The results indicate that CO2 huff-and-puff is economically viable for enhancing CBM recovery. Increasing CO2 injection volume markedly improves CH4 production and project revenue, but also leads to higher initial investment and a longer payback period. The economic performance exhibits a non-monotonic dependence on soaking time, with an optimal range that maximizes NPV. Specifically, the optimal soaking time ranges from 30 to 60 days for injection volumes up to 2000 t, and from 60 to 90 days for higher injection volumes. External economic factors exert a strong influence on project performance: higher carbon trading prices and lower CO2 purchase costs markedly improve profitability, while government subsidies effectively increase net returns and shorten the payback period. In the absence of subsidies, higher injection volumes are required to maintain economic viability. Overall, this study provides a comprehensive economic evaluation framework for CO2 huff-and-puff CBM projects, identifies key operational and economic parameters for optimizing project performance, and offers theoretical support for field-scale applications. Nevertheless, the economic evaluation is based on deterministic numerical simulation results and simplified market assumptions. Long-term operational risks and geological heterogeneity are not explicitly considered, which may limit the applicability of the results under field conditions.