Research on multi-parameter collaborative control method for enhancing coalbed methane recovery by hot flue gas displacement.

The article focuses on investigating the interaction between geological and engineering factors affecting the efficiency of hot flue gas displacement for enhanced coalbed methane (CBM) recovery. A thermo-hydro-mechanical (THM) coupled numerical model was developed to simulate the displacement process using binary gas mixtures primarily composed of nitrogen (N₂) and carbon dioxide (CO₂). The study introduces an enhanced harvesting index (EHI) to evaluate recovery efficiency dynamically and employs the response surface method to analyze the effects of single and combined factors such as initial permeability, gas pressure, injection pressure, gas composition, and temperature. Results indicate that high-permeability and high-gas-pressure regions show higher early-stage recovery efficiency (pre-EHI) but experience rapid declines later, while adjusting the N₂/CO₂ ratio and injection pressure can optimize recovery depending on geological conditions. Optimization maps for typical mining areas suggest tailored injection strategies, such as increasing CO₂ proportion in later stages for high-permeability seams and following a "first increase then decrease" CO₂ ratio principle for low-permeability seams, to maximize methane extraction and maintain gas flow rates.