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塔中地区奥陶系天然气成因多样,Ⅰ号坡折带中东部奥陶系天然气以高干燥系数、甲烷同位素值重为特征,与塔深1井寒武系原油裂解气接近,应主要来自寒武系原油裂解气成因。寒武系贫H_2S、高成熟原油裂解气在喜马拉雅山期时,气侵奥陶系油气藏,得到了以下主要证据的支持:1)天然气甲烷δ~(13)C值大多比Chung et al.(1988)天然气模式甲烷δ~(13)C值计算值高3‰以上,2)干燥系数与甲烷δ~(13)C值大体上具有正相关关系,3)天然气干燥系数与H_2S含量大体上具有负相关关系。这些特征表明,存在贫H_2S、相对富~(13)C甲烷为主的干气与富H_2S、相对贫~(13)C甲烷的湿气混合作用。奥陶系中H_2S-δ~(34)S值为14‰~20‰,远低于中深1井寒武系原地热化学硫酸盐还原作用(TSR)成因的H_2S(33‰),支持了奥陶系中H_2S并不是来源于寒武系古油气藏。于是提出,来自寒武系贫H_2S的干气在喜马拉雅山期对良里塔格组和鹰山组油气藏发生了气洗,油气藏的气/油比值增大、导致了原油蜡含量增高、甲烷δ~(13)C值发生正偏移。
The natural gas of Ordovician in the Tazhong area is various in origin. The Ordovician natural gas in the eastern part of No.1 slope break zone is characterized by high dry coefficient and methane isotope value. It is close to that of the Cambrian crude oil in Tashen-1 well and should mainly come from cold Wu Department of crude oil pyrolysis gas causes. In the Himalayan period, the Cambrian-depleted H_2S pyrolysis gas of high mature crude oil gas-infiltrated the Ordovician oil-gas reservoirs. The main evidences are as follows: 1) The δ 13 C values of natural gas methane are mostly higher than those of Chung et al. (13) C value of natural gas above methane is above 3 ‰, 2) the coefficient of dryness has a positive correlation with δ 13 C of methane, and 3) the coefficient of natural gas drying and the content of H 2 S in general Has a negative correlation. These characteristics indicate that there is a mixed wet gas with H 2 S-depleted, relatively rich (13) C-methane-based dry gas and H 2 S-rich and relatively lean (13) C methane. The value of H 2 S-δ ~ (34) S in Ordovician ranges from 14 ‰ to 20 ‰, which is much lower than the H 2 S (33 ‰) of the original geothermal sulphate reduction (TSR) The Ordovician H_2S is not derived from the Cambrian paleo-oil and gas reservoirs. Therefore, it is suggested that the dry gas from the Cambrian H_2S-depleted gas flushes the Lianglitage Formation and Yingshan Formation reservoirs in the Himalayas, and increases the gas / oil ratio of the reservoirs, resulting in an increase in the wax content of the crude oil, Methane δ ~ (13) C value positive shift occurs.