Diffusion and seepage mechanisms of high rank coal-bed methane reservoir and its numerical simulation at early drainage rate
To investigate the influence of drainage strategy on gas production with the coal-bed methane (CBM) reservoir in Southern Qinshui Basin,China as example,based on molecular dynamics and rock mechanics theory,the mechanisms of methane,diffusion and seepage in high rank coal were systematically investigated.Based on a constant permeability soft,a stress-dependent permeability model and a S-D permeability model considering the varying cleat compressibility,respectively,the influence of early drainage rate on gas production potential in high rank coal seams of different coal textures was investigated using a CBM numerical simulation soft called Simed.It demonstrates that the transportation of methane in coal seam involves desorption,diffusion,seepage in natural fractures and hydraulic fractures and the gas production will be sufficient only when all these four steps work coordinately.The diffusivity will increase and the conductivity will decrease due to the increase of effective stress and plugging in hydraulic fracture by pulverized coal during CBM depletion.Coal seam permeability is one of key factors influencing the gas production potential in the study area.High permeability will result in high gas production.Tectonically deformed coals are sensitive to early drainage rate but not sensitive to the fracture conductivity above a certain value.Intact and blocky coal seams are not very sensitive to early drainage rate but sensitive to fracture conductivity.A low rate of early drainage suits low permeability coal seam.A high drainage rate can be used to extract the coal and water continually from a high permeability coal seam during CBM depletion.
coal-bed methanediffusion and seepage mechanismsdrainage ratehigh rank coal
NETL
NSTL
万方数据
维普
