The present-day in-situ stress field within coalbed methane reservoirs, Yuwang Block, Laochang Basin, south China

Understanding in-situ stress variation is extremely important for coalbed methane (CBM) exploration and development; however, precise information on the present-day in-situ stress field in the Yuwang Block of Laochang Basin is unclear. In the present study, the horizontal maximum (S-Hmax) and minimum (S-hmin) principal stress, and vertical stress (S-v) in coal seams of Yuwang Block were systematically analyzed based on measured injection/falloff data and geomechanical models. The results indicated that, in the Yuwang Block, vertically, shallow coal seams (less than 800 m below ground level, bgl) mainly experienced the strike-slip faulting stress regime (S-Hmax > S-v > S-hmin); whereas deep layers (more than 800 m bgl) were characterized by the dominant normal faulting stress regime (S-v > S-Hmax > S-hmin). Laterally, with the No.9 coal seam case study, relatively lower stress magnitudes were mainly located around Yuwang and Well L-4 regions. Coal permeability obtained from injection-falloff well tests decreased exponentially with the increased effective stress, suggesting that coal permeability in the Yuwang Block was in-situ stress controlled. In addition, differential stress and presence of natural fractures within coal seams significantly affected the geometry and pattern of hydraulic fractures. In coal seams of Yuwang Block, the present-day in-situ stress field contributed to generate complex hydraulic fracture networks. The study results provided geological references for CBM development in the Yuwang Block of Laochang Basin.