Impact of Dynamic Elastic Modulus on Coal Permeability: Modeling and Analysis

Abstract

Coalbed methane is a kind of high-quality clean energy. The underground gas drainage can achieve the efficient utilization of coalbed methane. Permeability is the key factor affecting gas drainage. At present, permeability research mainly considers the effect of gas adsorption-induced matrix swelling deformation as well as the effective stress. However, experiments indicate that the variation of pore pressure has an impact on the mechanical properties of coal, which further changes the coal permeability. Due to the differences between the theory and experimental results, firstly, the dynamic elastic modulus model was established in this paper. Then, an experiment was conducted to prove that the elastic modulus of coal-containing gas decreases with the increasing gas pressure. On this basis, a permeability model considering internal swelling deformation was constructed. Finally, the rationality of the model was validated through the laboratory experiment. Finally, through analyzing the influence of key parameters on the evolution law of permeability, we find that the parameters have three different impacts on permeability. The new permeability model is more accurate in predicting coalbed methane production capacity. The result can provide a theoretical basis for the research of the multifield coupling process during gas drainage.