延川南地区水文地质条件及煤层气成藏

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。

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.