Numerical simulation research on heat of adsorption on coal-gas interaction

Both coalbed methane development and carbon dioxide geological storage involve adsorption-desorption effects at gas-solid interface. A large number of studies have confirmed that gas molecules release heat or absorb heat in the process of adsorption or desorption on the solid surface，which leads to the temperature rise or fall of the gas-solid system. However，the commonly used research method is to evaluate the gas adsorption capacity of coal under the condition of temperature-pressure equilibrium. However，the process of gas production or gas injection in coal reservoir is an unbalanced process，which will produce a large amount of adsorption heat to change the temperature of coal body，which is contradictory to the assumption of constant temperature in most studies. In order to study the influence of adsorption heat on coal-gas interaction，the adsorption heat was introduced into the coupling relationship of solid deformation-gas flow-adsorption/desorption. The adsorption deformation of coal was defined as a temperature function，and the heat storage term of coal-gas system was divided into fracture system and matrix system. Taking solid strain as the coupling term and considering the heat exchange process between coal and the environment，a deformation-seepage-diffusion coupling calculation model considering adsorption heat was established. The simulated coal surface temperature can fit well with the experimental data in literature. In addition，according to the simulation results of carbon dioxide storage，the decrease of gas injection efficiency caused by adsorption heat is about 16.8%. Under the influence of adsorption heat，the gas injection pressure should be increased to 7.2 MPa，which provides a reference for the evolution of coal seam temperature during coalbed methane exploitation.