元坝、通南巴地区天然气地球化学特征与成藏关系研究

Relation between Geochemical Characteristics of Natural Gas and Hydrocarbon Accumulation in Yuanba and Tongnanba Areas

根据元坝、通南巴地区现有钻井的天然气地球化学特征及其成因分析,结合区域地质背景,研究结果表明:两个工区都以高热演化程度的甲烷为主、低含C2+的干气,且非烃含量较高;天然气母质主要为Ⅱ型有机质,是高热演化阶段的产物,同时研究区天然气是混源作用的结果。通过天然气ln(C1/C2)与ln(C2/C3)值分析表明,元坝地区长兴组-飞仙关组天然气是原油二次裂解的产物,通南巴地区上二叠统-下三叠统天然气是干酪根初次裂解的产物。研究认为元坝地区原生古油藏发生TSR反应(硫酸盐热化学还原反应),导致元坝地区长兴组-飞仙关组天然气中硫化氢含量较高;通南巴河坝地区没有原生古油藏发生TSR反应,造成通南巴地区上二叠统-下三叠统天然气不含硫化氢。

Based on the gas geochemistry characteristics of drilled wells and analysis of gas origin in Yuanba and Tongnanba Areas,and in combination with regional geological background,study results showed that two work areas were the same of high thermal evolution of methane,dry gas content was low heavy hydrocarbon,and the content of non-hydrocarbon was high.Gas parent material was typeⅡorganic matter that is the product from high thermal evolution stage.And at the same time,the gas origin was chaotic.The distribution range of ln(C1/C2) and ln(C2/C3) in gas obviously indicated that the gases in Changxing Formation and Feixianguan Formation were the products of secondary cracking of oil in Yuanba Area.And the gases in the Upper Permian and Lower Triassic were the result of first cracking of kerogen.It is considered that the thermochemical sulfate reduction(TSR)happens in native reservoirs in Yuanba Area,which causes high hydrogen sulfide content in Changxing Formation and Feixianguan Formation.The native reservoir in Tongnanba Area has no TSR,which is the reason the gas in Upper Permian and Lower Triassic excludes hydrogen sulfide.