Simulation study on nonlinear permeability characteristics of coalbed methane mining driven by mixed N₂/CO₂ pressure

Area of Science:

• Geosciences
• Energy Science
• Environmental Engineering

Background:

• Coalbed methane (CBM) recovery and CO2 geological storage are critical for sustainable energy.
• N2/CO2 flooding offers a dual benefit for CBM production and carbon capture.

Purpose of the Study:

• To develop and validate a coupled model for ternary gas (N2, CO2, CH4) displacement and adsorption in coal.
• To investigate the impact of N2/CO2 injection ratios on CBM recovery and CO2 storage.

Main Methods:

• Utilized the characterization volume element method to model gas adsorption, desorption, and seepage in coal.
• Established and verified a coupling model for N2, CO2, and CH4 ternary gas displacement adsorption, considering heat conduction and coal deformation.

Main Results:

• CO2 injection significantly enhances CH4 production and causes coal body adsorption and expansion.
• An optimal injection ratio of 60% CO2 and 40% N2 was identified to maximize CBM recovery and CO2 storage.
• Higher CO2 ratios increase adsorption heat and coal temperature, while excessive N2 can lead to well breakthrough.

Conclusions:

• The N2/CO2 injection ratio critically influences CBM recovery and CO2 sequestration efficiency.
• The study provides a theoretical framework for optimizing mixed injection strategies in CBM reservoirs.
• Findings support sustainable energy development and greenhouse gas emission reduction efforts.