In-situ stress measurements and stress distribution characteristics of coal reservoirs in major coalfields in China: Implication for coalbed methane (CBM) development

Coal reservoir permeability decreases exponentially with the increase in effective in-situ stress (EIS, (σH + σh + σv)/3 − Po). Vertically, four distinct vertical bands of coal permeability can be found in the EMOB, SQB and WGP, defined by the compression and deformation of the coal-matrix under certain stress regimes: in shallow coal seams (EMOB, < 800 m; SQB, < 650 m; WGP, < 500 m), coal reservoirs are within a strike-slip faulting stress regime (σH > σh > σv) where σH and σh tend to increase, and coal permeability decreases exponentially with an increasing depth; in intermediate coal seams (EMOB, 800-1000 m; SQB, 650-825 m; WGP, 500-750 m), the σv > σH > σh stress regime plays a major role, with relatively high coal permeability. For deep coal seams (EMOB, > 950 m; SQB, > 825 m; WGP, > 750 m), CBM development conditions deteriorate due to a state of “extremely low permeability and extremely high in-situ stress”.