Groundwater conditions and relative CBM accumulation feature in Yanchuannan area

Groundwater plays a controlling role in enrichment, accumulation and yield of coalbed methane. With production data, hydrochemistry and geochemistry are taken into account to study hydrodynamic occurrence and hydrochemistry fea-ture, influence, CBM reservoir formation and saturation. Typical accumulations are proposed according to hydrogeochemis-try conditions. Two types of groundwater exist in Yanchuannan area. NaHCO₃ of acid low salinity (4×10³ mg/L) is located in Tanping belt. Isotope fractionation proves powerful and carbon value is -36‰. Water head reaches as high as more than 700 m. CaCl₂ of weak alkali and high salinity (4×10⁴ mg/L) is distributed in Wanbaoshan belt. Fractionation works subtle and the value is -32‰. Head is no more than 700 m. Three types of groundwater conditions occur as follows:high pressure stagnant flow in Wanbaoshan, weak runoff flow in Tanping and seepage in the north and midst dominated by faults. Confined water and fault block lead to accumulations.