Seepage coupling model of in-seam gas extraction and its applications

Abstract

In order to reveal the mechanism of gas flow during gas extraction,the correlation between deformation and gas seepage in coal seam was studied.Based on gas seepage characteristics,a coupling model was established.The dynamic processes such as gas seepage in fractures,the adsorption gas desorption and diffusion in micro pores and the coal deformation were investigated,as well as the dynamically varied permeability.Numerical simulation study on the model was carried out in specific geological conditions.The results show that the gas pressure drops quickly in the early stage,and after a period of extraction the pressure declines steadily, and the closer to the location of borehole the faster gas pressure drops,and effective extraction radius is about 3m.In-seam borehole spacing at 6mreaches a stable pure metahne flow rate up to 5—7m3/min in field drainage test.