The Evolution of Parameters During CBM Drainage in Different Regions

Abstract

Draining while mining is an important method for preventing gas outburst and achieving clean energy, and understanding the evolution of the parameters (gas pressure, strain and permeability) during coalbed methane (CBM) drainage while mining is important for improving extraction efficiency (which is very low at present). Physical simulations of CBM drainage were conducted, and the gas pressures were achieved. The values of the permeability and strain could be calculated. The parameters (gas pressure, permeability and strain) trends were achieved during the drainage process. In terms of timing, during the initial stages of CBM drainage, the gas pressures declined quickly, the permeability decreased sharply, and the volumetric strain increased quickly. During the later stages, the gas pressures decreased slowly, the permeability recovered slowly over time, and the volumetric strain increased slowly. In terms of space, the gas pressure declined more quickly nearer the effective borehole. The permeability initially declined more quickly nearer the effective borehole and then increased during the later stages. During CBM drainage in the stress relief region, the volumetric strain of the stress concentration region was the largest. The volumetric strain of the stress relief region was larger than that of original region I, but this trend reversed as time progressed. The volumetric strain of original region II was the smallest. The relationship between the total strains during CBM drainage in different regions was as follows: the total strain during CBM drainage in the stress concentration region > in the stress relief region > in original region I > in original region II.