阿姆河右岸区块碳酸盐岩气藏H_2S成因与分布规律

Origin and distribution laws of H_2S in carbonate gas reservoirs in the Right Bank Block of the Amu Darya River

土库曼斯坦阿姆河右岸区块内的气藏天然气中普遍含有H2S,尤其是西北部气藏H2S含量相对较高,深入研究其成因和分布规律,才能最大限度地减少和控制由此产生的危害。根据该区地质条件和天然气组分特征,结合H2S形成机理,分析认为:①天然气中的H2S主要来源于硫酸盐热化学还原反应。由于西北部卡洛夫—牛津阶碳酸盐岩储层顶部为石灰岩和膏盐岩互层,并直接被膏盐层覆盖,具有发生硫酸盐热化学还原反应的物质条件,故其H2S含量高;东南部无石灰岩和膏盐岩互层,且有泥岩段将石灰岩储层与上覆膏盐岩层分隔,故其H2S含量低。②H2S含量的高低整体上受沉积相带的控制。在深水高伽马泥岩分布区及开阔台地深水沉积区,H2S含量普遍较低;而在无高伽马泥岩分布区H2S含量普遍较高。③东南部较大的逆断裂破坏了高伽马泥岩层的封隔性,使H2S分布规律更复杂化。

H2S is commonly contained in the natural gas produced from the reservoirs in the Right Bank Block of the Amu Darya River,Turkmenistan,especially in the northwest part of this block where its content is relatively high.A thorough analysis of its origin and distribution is necessary for eliminating and controlling as much as possible its negative effects.Based on an analysis of the geological conditions,gas components and mechanism of H2S formation,the following 3 conclusions are drawn.First,the H2S in the natural gas is mainly sourced from thermochemical sulfate reduction.The top of the Callovian-Oxfordian carbonate reservoirs in the western block consists of interbedded limestone and salt and is directly overlain by salt layers.They just provide material conditions for thermochemical sulfate reduction,resulting in a higher content of H2S.In contrast,there are no such interbedded limestone layers and salt layers in the southeastern block.Moreover,a mudrock layer separates the limestone from the overlying salt layer,resulting in a lower H2S content.Second,the content of H2S is mainly controlled by sedimentary facies zones.It is commonly lower in areas where deep water mudrocks with high Gamma ray occur,as well as in areas with open platform deep water deposits.In contrast,it is generally higher in areas where no mudrocks with high Gamma ray occur.Third,large reverse faults damage the sealing ability of the mudrocks with high Gamma ray in the eastern block,resulting in a more complex distribution of H2S.