摘要
通过对四川盆地川中地区须家河组天然气的组分和碳氢同位素分析,结合前人对川西和川南地区须家河组及四川盆地其他层系天然气研究成果和区域地质背景,开展天然气成因和来源、氢同位素特征与指示意义等研究.结果表明,川中地区须家河组天然气以烃类气体为主,甲烷含量为67.89%~98.05%,重烃气(C2+)含量为0.42%~16.62%,非烃气体(CO2、N2)含量较低,除岳121井N2和CO2含量较高外,N2含量平均值为0.82%,CO2含量平均值为0.26%.元坝须家河组天然气干燥系数平均高达0.991,为干气;川中其他地区须家河组天然气干燥系数皆小于0.95,为湿气.天然气δ^13 C1值介于-43.8‰^-29.2‰之间,δ^13 C2值介于-33.5‰^-20.7‰之间,δ^13 C3值介于-33.6‰^-19.3‰之间,δ^13 C4值介于为-27.2‰^-22.2‰之间;天然气δD1值介于-191‰^-148‰之间,δD2值介于-165‰^-115‰之间,δD3值介于-153‰^-107‰之间.甲烷及其同系物(C2-4)基本上为碳氢同位素正序排列(δ^13 C1<δ^13 C2<δ^13 C3<δ^13 C4、δD1<δD2<δD3),与典型的有机成因烷烃气碳氢同位素特征一致.元坝须家河组天然气成熟度RO值为1.09%~1.78%,川中其他地区须家河组天然气成熟度RO值为0.64%~0.92%.川中须家河组天然气主要为来自须家河组煤系源岩的煤成气,元坝须二段天然气为来自须家河组煤系源岩的高成熟煤成气混入下寒武统(及下志留统)原油裂解气的混合气.四川盆地须家河组天然气甲烷δD值偏高,都大于-200‰.与来自淡水湖沼相烃源岩的吐哈盆地台北凹陷的煤成气相比,尽管两者成熟度相近,但甲烷δD值差异高达90‰,说明须家河组煤系源岩形成于水体咸化的沉积环境.
Based on the analysis of the components and carbon and hydrogen isotopes of gases from the Triassic Xujiahe and other formations in the Sichuan Basin,the gas origin,gas source and significance of hydrogen isotopes are studied by combining previous research results and regional geological background.The results show that gas from the Triassic Xujiahe Formation in the Sichuan Basin is mainly hydrocarbon gas.The content of methane is 67.89% -98.05%,and the content of heavy hydrocarbon(C2+)is 0.42%-16.62%.The content of non-hydrocarbon gas(CO2,N2)is low.Except the relatively high content of N2 and CO2 in the Well Yue121,the average content of N2 is 0.82%and the average value of CO2 is 0.26%.Gas from the Xujiahe Formation in Yuanba has average dryness coefficient as high as 0.991,which indicates the gas belongs to dry gas.While,gases from the Xujiahe Formation in other areas in the Central Sichuan Basin have dryness coefficient less than 0.95,indicative of wet gas.The δ13C1 value varies from -43.8‰to-29.2‰,δ13C2 value ranges from -33.5‰to-20.7‰, δ13C3 value is from -33.6‰ to -19.3‰ andδ13C4 value is from-27.2‰ to-22.2‰.TheδD1 value is from-191‰ to-148‰,δD2 value is from -165‰ to -115‰and δD3 value is from -153‰ to -107‰.Methane and its homologues(C2-4)become more enriched in 13C and D with increasing carbon number( δ13C1<δ13C2< δ13C3<δ13C4,δD1<δD2<δD3),which are consistent with the carbon and hydrogen isotopic characteristics of thermogenic gases.The thermal maturity ROof natural gas from Xujiahe Formation in Yuanba is 1.09%-1.78%,and the RO of the natural gas from Xujiahe Formation in other areas of Central Sichuan Basin is 0.64%-0.92%.Natural gas from the Xujiahe Formation in the central Sichuan Basin is mainly from the coal measure source rocks of the Xujiahe Formation.Natural gas from the 2nd member of Xujiahe Formation in Yuanba is mixed gas,a mixture of the high-mature coal-derived gas from the coal measure source rock of Xujiahe Formation and the Lower Cambrian(Lower Silurian)oil-cracked gas.The δD of methane from the Xujiahe Formation in the Sichuan Basin is relatively high,higher than -200‰.Compared to the coal-derived gas from the source rocks formed in limnetic facies with freshwater in the Taibei Sag,Turpan-Hami Basin,though at similar thermal maturity,the difference of the δD of methane can be as high as 90‰,indicating that the source rock of Xujiahe Formation is formed in an environment with water salinization.
作者
倪云燕
廖凤蓉
姚立邈
高金亮
张蒂嘉
Ni Yun-yan;Liao Feng-rong;Yao Li-miao;Gao Jin-liang;Zhang Di-jia(Key Laboratory of Petroleum Geochemistry China National Petroleum Corporation,Beijing 100083;PetroChina Research Institute of Petroleum Exploration & Development,Beijing 100083,China)
出处
《天然气地球科学》
EI
CAS
CSCD
北大核心
2019年第6期880-896,共17页
Natural Gas Geoscience
基金
国家自然科学基金(编号:41472120)
国家科技重大专项课题(编号:2016ZX05-007)联合资助
关键词
四川盆地
川中地区
须家河组
碳同位素
氢同位素
水体咸化
Sichuan Basin
Central Sichuan Basin
Xujiahe Formation
Carbon isotope
Hydrogen isotope
Water salinization
作者简介
倪云燕(1977-),女,浙江乐清人,高级工程师,博士,主要从事油气地球化学研究。E-mail:niyy@petrochina.com.cn.
