摘要
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。
Natural gases in the Ordovician of Tazhong area show very different geochemical characteristics.The gas in the middle and east part of the No.1 fault-slope zone is characterized by high gas dryness coefficient and δ13C isotope value,and is similar to the oil-cracking gas in the Cambrian in well TS1.The gas from the Cambrian was H2S-poor and charged into the petroleum pools of the middle and east part during the Himalayan orogeny,which is supported by the following lines of evidence:1) the gas has methane δ13C value of about 3% higher than anticipated from the natural gas plot by Chung et al.(1988) ; 2)a linear relationship between gas dryness coefficient and its δ13C value ; and 3) a inverse linear relationship between gas dryness and the concentration of H2S.These features suggest that there exists a mixing between H2S-poor,13C-rich methane-dominated dry gas and H2S-rich,13C-poor wet gas.H2S in the Ordovician has δ34S values from 14%~20%,being significantly lighter than the H2S in the ZS1 (33%o),supporting the different origin.The charge of the Cambrian dry gas may have resulted in increase in gas/oil ratios and wax content,gas dryness coefficient and positive shift in methane δ13C value.
出处
《地质科学》
CAS
CSCD
北大核心
2014年第4期1327-1336,共10页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家科技重大专项(编号:2011ZX05008-003)资助