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.%水文地质条件是煤层气富集、成藏以及产出过程中的重要控制因素.通过分析延川南地区水化学与水动力条件,结合排采数据,明确了延川南地区煤层的水文地质条件分布特征,研究其对煤层气含气性、成藏等影响,并划分出相应的成藏模式.研究结果表明,延川南地区2号煤层水属于碳酸氢钠型(NaHCO3)和氯化钙型(CaCl2),谭坪构造带以NaHCO3为主,矿化度较低,为4×103 mg/L左右,偏酸性,甲烷碳同位素分馏作用强,为–36‰左右,水头高普遍高于700 m;万宝山构造带以CaCl2型为主,矿化度较高,为4×104 mg/L左右,偏碱性,甲烷碳同位素分馏作用弱,为–32‰左右,水头高一般低于700 m.研究区存在3种水文条件:万宝山为高压封闭滞留区,谭坪为弱径流区,研究区中北部局部断层发育的渗流区.煤层气成藏模式主要为承压水动力和断层封堵复合型煤层气藏.
展开▼
