New mathematical model of the influence of coal matrix swelling and shrinkage on reservoir permeability

Coal seam permeability variation is affected by many constraints, of which the effective stress and swelling-shrinkage of the coal matrix are the major factors in the process of coal adsorption and desorption. In these two aspects, according to the volume invariance principle and the MATCHSTICK model, it brought out a new model that predicts permeability variations and effectively avoids the permeability simulation error problem using uncertain parameters in classic models. Research results show that the permeability changes with coal seam pressure consists of 3 kinds of theory models. We should as far as possible make the permeability curves present the trend of slow decline, stable and rapid increase during coalbed methane production. At last, it proved that the derived model is correct and practical through the comparison with classic P&M model and S&D model simulation and validation of field test data.