Numerical Simulation of CO2 Flooding of Coalbed Methane Considering the Fluid-Solid Coupling Effect

Area of Science:

• Geosciences
• Petroleum Engineering
• Environmental Science

Background:

• Carbon dioxide (CO2) flooding for enhanced coalbed methane (CO2-ECBM) recovery offers a dual benefit of CO2 sequestration and increased natural gas production.
• This process integrates complex phenomena including multi-phase fluid flow, coal-rock deformation, competitive gas adsorption, and diffusion within a dual-porosity system (matrix and fractures).

Purpose of the Study:

• To develop and apply a mathematical model simulating CO2-ECBM, accounting for coupled processes like competitive adsorption, diffusion, seepage, and flow-deformation interactions.
• To investigate the spatial variability of reservoir permeability changes resulting from coal matrix shrinkage during CO2 injection and methane production.

Main Methods:

• A dual-porosity model representing coal reservoirs was constructed to simulate the CO2-ECBM process.
• A mathematical model was employed to analyze competitive adsorption, diffusion, seepage, and the interplay between fluid flow and coal-rock deformation.

Main Results:

• Permeability alterations induced by coal matrix shrinkage exhibited significant spatial heterogeneity across the reservoir.
• The highest permeability values were observed in proximity to the production well.
• The extent of permeability recovery diminished with increasing distance from the production well.

Conclusions:

• CO2-ECBM is a viable strategy for both carbon storage and enhanced methane recovery.
• Understanding the coupled flow and geomechanical processes, particularly matrix shrinkage-induced permeability changes, is crucial for optimizing CO2-ECBM operations.
• Reservoir management strategies should consider the spatially variable permeability distribution for efficient gas extraction.