四川盆地飞仙关组气藏硫化氢成因及其依据

四川盆地东北部下三叠统飞仙关组鲕滩气藏天然气烃类气体以甲烷为主，含量主要分布在75%～90%之间，C2＋含量为0～0.15%；非烃气体以H2S和CO2为主，含量分别为5%～20%和1%～10%。已有观点认为H2S为飞仙关组气藏附近的石膏经硫酸盐热化学还原作用（TSR）而成。随着川东北气区大中型高含硫化氢气田的发现，硫化氢成因机理的研究备受关注。应用金管、高压釜和石英管等实验方法模拟了硫化氢气体的生成，同时检测了模拟生成的硫化氢和石膏、硫磺等硫化物的硫同位素。实验结果表明:硫磺与正己烷在较低温度即可生成大量的硫化氢气体，而正己烷与硫酸钙的反应总体上比较困难，且生成的H2S量较少；富含黄铁矿的低成熟泥灰岩模拟生烃过程中可以生成与甲烷相当，甚至超过甲烷含量的硫化氢气体；含硫化合物与烃类反应生成的硫化氢的硫同位素值比原始物质的硫同位素值重。地层中的SO2－4是海相地层中H2S气体形成的最初来源。含硫烃源岩直接生成高硫化氢天然气和储层中单质硫与烃类的反应是川东北飞仙关组天然气中硫化氢形成的主要原因。

Genesis on Hydrogen Sulfide of Feixianguan Formation in Sichuan Basin

Hydrocarbons in oolitic reservoir gases of Feixianguan Formation in northeastern Sichuan Basin mainly consist of methane with 75%～90% of CH4, 0～0.15% of C2, and the nonhydrocarbon mainly consists of H2S and CO2, and their relative contents are 5%～20% and 1%～10%，respectively. The high sulfur bearing gas distribution area is identical to the gypseous distribution area. These is a view that the H2S in natural gases is formed by thermochemical sulfate reduction (TSR). As large middle gas reservoirs with high H2S contents have been found in the northeastern of Sichuan basin, the study on the genetic mechanism of H2S has become the hotsport. Based on the analysis and summary of the current research status of H2S genetic mechanism at home and abroad，these experiment techniques of Gold tube pyrolysis, hydrous pyrolysis and quartz tube pyrolysis have been used to simulate the dyhrocarbon generation of marl source rock, and the stable sulfur isotopic composition of pyrolysis H2S, CaSO4 and S have been measured. The results show that it is very easy that the reaction of sulphur and n hexane, and the quantity of generating H2S is very large under the lower temperature. Reverse, it is very difficult that the reaction of CaSO4 and n hexane, and the quantity of generating H2S is very small under the higher temperature. The content of H2S is as high as or even over the methane during the simulation experiment of immature marl with high organic matter content，better type and large amount of FeS2 of Feixianguan formation. The stable sulfur isotopic composition of H2S originated from the reactions of n hexane and sulphur as well as CaSO4 is higher than that of sulphur and CaSO4. The H2S in marine formation is originally sourcing from the SO2－ 4in formation. It is the main reason of H2S concentration in the Lower Triassic Feixianguan Fm. carbonate reservoirs in the East Sichuan Basin that the source rocks with high FeS2 generate H2S directly and the H2S origin from the reactions of hydrocarbon and sulphur in reservoirs.