Feasibility of carbon dioxide geological storage in abandoned coal mine: A fully coupled model with validated multi-physical interactions

It has gained wide attention that Carbon dioxide (CO₂) is to be injected into abandoned coal mines for geological storage of CO₂-enhanced coalbed methane recovery. Although abundantly evidences in literature indicate that the injection of CO₂ will cause lots of interactions among the mechanical characteristics of coal and the properties of CO₂ flow, further studies on these multi-physical interactions are still necessary. In this work, a series of laboratory experiments to elucidate the multi-physical interactions of CO₂ adsorption, softening effect of coal and the non-Darcy gas flow were conducted. Based on the experimental results, theoretical and empirical models to describe these coal-CO₂ interactions were meticulously proposed and validated, the results turned out to be satisfactory. Consequently, the compressive strength and elasticity modulus of coal decrease exponentially with the increased injection CO₂ pressure. The gas flow in coal obeys the Izbash non-Darcy model, and coal permeability can be well modified by the volumetric stress. By taking these coal-CO₂ interactions into account, this study established of a fully coupled model for coal deformation and CO₂ conservation. The model was then implemented into the numerical simulations of CO₂ storage in abandoned coal mine by using the finite element method. A series of scenario-based numerical simulations was conducted to investigate the feasibility and limitation of CO₂ storage in abandoned coal mine. The conducted experiments, models and numerical simulation will offer implications on the multi-physical interactions between coal and gas especially in CO₂ storage in abandoned coal mines.