SENSITIVITY OF COALBED PERMEABILITY AND ITS INFLUENCES ON PRODUCTION OF COALBED METHANE

Coal bed is characterized by a double porosity system composed of fissures and matrix.The fissures consist of cleats and epigenetic cracks and act as flow pathways of coalbed methane,while the matrix provides the main reservoir space for accumulation of coalbed methane.Coal bed permeability is an important parameter for evaluation of commercial development of coalbed methane.The pattern of permeability variation and its influences on performance of coalbed methane recovery need further study and verification.Based on summary and analysis of previous studies,the effective stress model of coalbed methane is studied and verified,and the influences of permeability variation on coalbed methane production are analyzed.The results show that coal bed permeability is under the dual impacts of fissure compression and matrix contraction and is characterized by decreasing at first and then increasing.Matrix contraction can improve coal bed permeability,thus can effectively enhance the recovery of coalbed methane.Therefore,its influences shall not be overlooked during production of coalbed methane.