尼泊尔低喜马拉雅推覆带油源对比及油气成藏  

Oil-source correlation and hydrocarbon accumulation in the Lesser Himalayan belt of Nepal

作　　者：杨平[1,2] 谭富文 施美凤[1,2] 王正和 李忠雄[1,2] 占王忠 Sudhir RAJ AURE[3] Ganesh N.TRIPATHI YANG Ping;TAN Fuwen;SHI Meifeng;WANG Zhenghe;LI Zhongxiong;ZHAN Wangzhong;Sudhir RAJAURE;Ganesh N.TRIPATHI(Chengdu Center,China Geological Survey,Chengdu,Sichuan 610081,China;Key Laboratory of Sedimentary Basin and Oil and Gas Resources,Ministry of Natural Resources,Chengdu,Sichuan 610081,China;Petroleum Ex ploration Promotion Project(PEPP),Department of Mines and Geology,Kathmandu,Nepal)

机构地区：[1]中国地质调查局成都地质调查中心,中国四川成都610081 [2]自然资源部沉积盆地与油气资源重点实验室,中国四川成都610081 [3]Department of Mines and Geology,Kathmandu,Nepal

出　　处：《地质学报》2021年第11期3426-3441,共16页Acta Geologica Sinica

基　　金：商务部援外项目“援尼泊尔油气资源调查”(编号CGSA001)资助的成果。

摘　　要：尼泊尔低喜马拉雅推覆带油气苗来源不清极大地影响了该区油气勘探。在地质-地球物理综合调查的基础上,利用油气地球化学、碳同位素及生烃史模拟对尼泊尔代莱克地区油源和成藏过程进行了研究。结果表明:(1)尼泊尔代莱克地区油苗产于Padukasthan断裂,可分两期,第一期呈含油断层泥产出,氯仿沥青"A"为149~231μg/g,R_(o)为0.81%,氯仿沥青"A"的δ^(13)C相对较重(-26.24‰~-27.10‰),族组分具有正碳同位素序列,发黄绿色荧光,为典型的低熟煤成油,第二期呈液态油产出并遭受微生物降解,金刚烷I_(MD)指数为0.33~0.45,R_(o)为1.24%~1.53%,3,4-DMD含量46%~47%,全油δ^(13)C为-29.50‰~-29.45‰,族组分碳同位素趋于一致,发蓝色荧光,为海相成因高熟油;(2)第一期油来源于Surkhet群的Melpani组和Gondwana群煤系烃源岩,为Ⅲ型有机质低熟阶段的产物,第二期来源于Surkhet群的Swat组浅海陆棚相黑色页岩,为Ⅱ;型有机质生油高峰的产物,两期油与Lakharpata群过成熟黑色泥岩和Siwalik群未熟泥岩没有亲缘关系;(3)尼泊尔低喜马拉雅推覆带具有"多源多期、推覆增熟、砂体控储、披覆控聚"的油气成藏模式,油气成藏过程可划分为沉积浅埋、构造圈闭形成、深埋油藏形成、气藏形成和晚期改造定型5个演化阶段;(4)尼泊尔低喜马拉雅推覆有利于Gondwana群、Surkhet群深埋增温、持续快速生烃和晚期成藏,对比邻区巴基斯坦的含油气盆地,尼泊尔低喜马拉雅推覆带及相邻类似地区具备良好的油气成藏条件。The unclear source of oil and gas seeps has impeded the exploration work in the Lesser Himalayan thrust belt in Nepal.In an attempt to address this problem we have carried out comprehensive geological and geophysical surveys,petroleum geochemical investigation,carbon isotope analysis and hydrocarbon-generation history simulation with an aim to explore the source of oil and gas in the Dailekh area of Nepal.Accordingly the following conclusions are drawn:(1)The oil seeps along the Padukasthan(PT)fault can be divided into two types.The first type occurred as oil-bearing fault gouge,with chloroform bitumen"A"concentration of 149~231μg/g and vitrinite reflectance(R_(o))value of 0.81%.The carbon isotopic compositions of chloroform bitumen"A"are heavy withδ^(13)C values ranging from-26.24‰to-27.10‰,which represents a normal carbon isotope sequence.The source rock are yellow-green on the fluorescence thin section.These characteristics show that it is a typical low-maturity coal-derived oil.The second type occurred as a liquid crude oil that has undergone microbial degradation.The analysis result shows the maturity index of adamantine(IMD)from 0.33 to 0.45,R_(o)value from 1.24%to 1.53%,dimethyl biadamantane(3,4-DMD)contents of 46%~47%,δ^(13)C values of crude oil from-29.50‰to-29.45‰.The carbon isotopic compositions tend to be consistent.The source rocks display blue fluorescence.These futures are indicative of a marine-facies origin in high-mature stage.(2)The source rock of the first oil-type are the coal-bearing layers from the Melpani Formation of Surkhet Group and the Gondwana Group.The oil is a low-mature stage product of the organic matter type III.The second oil-type originated from the shelf facies black shale of the Swat Formation of the Surkhet Group and formed during hydrocarbon-generation peak of organic matter type II_(MD).Both oil-types have no genetic relationship with the over mature black mudstone of the Lakharpata Group and the immature mudstone of the Siwalik Group.(3)The hydrocarbon accumula

关 键 词：推覆带 油气地球化学 碳同位素 油源对比 成藏模式 尼泊尔 

分 类 号：P618.13[天文地球—矿床学]