阿姆河右岸区块气藏酸气的成因与分布影响因素

Origin and Distribution Factors of Sour Gases in Natural Gas Reservoirs in the Amu Darya Right Bank Block,Turkmenistan

土库曼斯坦阿姆河右岸区块气藏属于酸性气藏,气体碳同位素组成特征显示,该研究区块的二氧化碳(CO_2)属于无机成因;而烃源岩、储层、有机质镜质体反射率、酸性气体含量等资料显示,研究区的硫化氢(H_2S)为硫酸盐热化学还原反应的产物。通过对常规酸性气体分布影响因素的分析,包括构造、断裂、盖层质量、沉积相、储层类型、埋深、岩相、硫源等进行归纳可以得出,影响研究区酸性气体分布的因素主要有:土库曼斯坦阿姆河右岸区块的基底断裂有利于CO_2分布;盖层质量越好,越有利于CO_2富集;生物堤礁带、点礁和逆掩断裂带的气藏具有中等CO_2含量;上侏罗统基末利—提塘阶膏盐岩是形成H_2S的重要硫源,但不是充分条件,中—下侏罗统海滨相碎屑岩作为研究区主力烃源岩是H_2S气藏的主要硫源,中—上侏罗统卡洛夫—牛津阶碳酸盐岩和上侏罗统基末利—提塘阶巨厚膏岩层有利于H_2S保存;溶解态SO_4^(2-)源影响H_2S分布;构造、断裂导致H_2S分布更为复杂;研究区孔隙(洞)型储层与H_2S分布具有良好的相关关系;研究区H_2S多分布在地温高于100℃的地层中;开阔台地深水沉积相不利于H_2S形成,点礁和逆掩断裂带属于低H_2S含量带,生物堤礁带属于中—高H_2S含量带。通过研究区的同位素、沉积相、岩性、温度、断裂分布等因素的全面分析,初步提出了其CO_2和H_2S的成因,且较为全面地讨论了酸气分布的影响因素,并指出为确定更细致的酸性气体成因和分布因素仍需进行必要的后续研究工作。

Through the analysis of original carbon isotopes in the blocks on the right bank of the Amu Darya River, Turkmenistan, it can be firstly concluded that the carbon dioxide （CO2） in the sour gas reservoirs belongs to the inorganic-origin gas. The origin of hydrogen sulfide （H2S） in the Amu Darya Right Bank Block is thermochemical sulfate reduction from the detailed analysis of hydrocarbon source rocks data, reservoir characteristics, vitrinite reflectance of organic matter, and sour gas content. Then, the factors affecting the distribution of sour gases in the Amu Darya Right Bank Block were investigated by the analysis of conventional sour gas distribution factors including geological structure, fracture and fault, caprock integrity, sedimentary facies, reservoir types, lithofacies, the source of sulfur and so on. The following basic findings were achieved： ① The basement rift in the study area is conductive to the distribution of CO2. The caprock integrity contributes to the concentration of CO2. The gas reservoirs in the biological dike reefs, patch reefs and overthrust zones usually have medium CO2 content. ② The geological structure and fracture caused the complexity of the distribution of H2S. The gypsum-salt rock in upper Jurassic-Tithonian is an important sulphur source, and the main hydrocarbon source rocks are also the major sulfur source of H2S gas reservoirs. Furthermore, the giant gypsum layers in the middle-upper Jurassic Callovian-Oxfordian and the upper Jurassic-Tithonian are conductive to preservation of H2S, and the small openings and holes in the reservoir is also correlative to the distribution of H2S. ③ The H2S in the study area is mostly distributed in the formations with the geothermal temperature of higher than 100 ℃. The open platform deep-water sedimentary facies are harmful to the formation of H2S. The patch reef and overthrust zones belong to the belts of low H2S content, however, the biological dike reef zones belong to the belts of medium-high H2S content. However, the origin and distribution factors of sour gases in natural gas reservoirs were obtained. At the same time, it was pointed out that more necessary and accurately quantitative research is still needed to determine the origin and distribution of acid gases in the Amu Darya Right Bank Block, Turkmenistan.