A New Method for Determining Coal Seam Permeability based on a Gas–Solid Coupling Model and PSO + LM Hybrid Optimization Algorithm

Previous underground test methods for coal seam permeability are usually based on radial flow theory, which ignores the impact of coal deformation and permeability dynamic evolution. Thus, these methods have some limitations in theoretical reliability, result stability and method applicability. Therefore, this paper derives a gas–solid coupling model considering pore sorption strain. Based on this model and a hybrid optimization algorithm, which combines particle swarm optimization (PSO) and Levenberg–Marquardt (LM) algorithm, a novel method for determining coal seam permeability, namely the GP method, is proposed. The feasibility and reliability of this method were verified by numerical experiments and field tests, respectively. The findings indicate that the proposed PSO + LM algorithm was superior to PSO algorithm and LM algorithm in terms of convergence and computational efficiency. In field application, the test value of the GP method was closer to the true value of coal seam permeability, and its theoretical model can better reflect the change of borehole gas flow, whether compared with the traditional radial flow method from the global perspective or compared with other classical permeability models from the local perspective. Therefore, the GP method has the potential to become an effective test method for coal seam permeability. This study has certain reference significance for the acquisition of mechanical parameters and gas parameters.