Study on effect of geo-stress on coal permeability and its controlling mechanism

According to the great significance for the study on the effects of geo-stress on coal initial permeability and the expansion fractures during hydraulic frac turing, based on the controlling factors of stress state in coalbed methane (CBM) reservoir, the influence of geo-stress on the permeability and its controlling mechanis m, the paper summarizes the recent progress about geo-stress vs.permeability.The results show that the influencing factors of geo-stress state include three aspects: te ctonism, burial depth and coal lithotypes, dominating by the first and second aspects.The geo-stress generally captured by hydraulic fracturing method and experimenta | test.The current researches focused on the effects of in-situ tectonic stress field characteristics, laboratory and numerical simulation of different geo-stress on coal res ervoir permeability. The essence of its controlling mechanism is the pore-fissure structure deformation in CBM reservoir dynamics.The regional stress field that develope d a regional fissure system controls the regional distribution of coal permeability, whereas the local tectonic zone controls the anisotropic permeability in different block s.The permeability decreases exponentially with increasing the effective vertical stress, the effective maximum horizontal principal stress and the effective minimum hori zontal principal stress.Compared with the geo-stress difference, the coefficient of stress difference is the major factor that affects the expansion of hydraulic fracturing a long the direction of maximum principal stress.