Effect of negative pressure on coalbed methane extraction and application in the utilization of methane resource

A constant negative pressure is used in the coal mines owing to a lack of research on the effect of negative pressure on methane extraction,resulting in the low methane concentration and difficult utilization,which is not condu- cive to the extraction and utilization of methane resource. In this study,a gas-solid coupling model of coalbed methane migration considering the pseudo-steady diffusion in coal matrix,seepage in fractures,permeability evolution and coal deformation is proposed. Comsol Multiphysics is used to conduct a numerical solution of the proposed model. The effects of the diffusion and seepage processes on the methane migration are analyzed,and the role of the negative pres- sure on methane extraction is studied. The methane concentrations of different negative pressures are calculated consid- ering the changing effect of negative pressure combined with the parallel relation between the methane migration and the air leak. The research results reveal that the negative pressure effect weakens gradually with the increasing methane extraction time and the reduction of the negative pressure can effectively increase the methane concentration. To change the present situation of the low methane concentration and utilization rate in coal mines,a new technical measure of methane extraction through parallel boreholes in groups is proposed to adjust the extraction negative pressure and increase the methane utilization rate.