鄂西渝东下古生界海相页岩饱和烃组成特征及其指示意义  

Characteristics of saturated hydrocarbons from Lower Paleozoic marine shales in western Hubei-eastern Chongqing area and their indications

作　　者：徐姝慧 何生[1] 朱钢添 刘若冰[2] 陆亚秋[3] 魏思乐 Xu Shuhui;He Sheng;Zhu Gangtian;Liu Ruobing;Lu Yaqiu;Wei Sile(Key Laboratory of Tectonics and Petroleum Resources,Key Laboratory of Ministry of Education,China University of Geosciences, Wuhan, Hubei 430074,China;Research Institute of Exploration Company,SIN OPEC, Chengdu,Sichuan 610041, China;Research Institute oo Exploration and Development 〇 o Jianghan Oilfield Company, SINOPEC, Qianjiang,Hubei 433124, China)

机构地区：[1]中国地质大学(武汉)构造与油气资源教育部重点实验室,湖北武汉430074 [2]中国石化勘探分公司勘探研究院,四川成都610041 [3]中国石化江汉油田分公司勘探开发研究院,湖北潜江433124

出　　处：《石油与天然气地质》2018年第2期217-228,共12页Oil & Gas Geology

基　　金：国家自然科学基金面上项目(41672139);国家"十三五"油气重大专项(2016ZX05034002-003;2017ZX05005001-008);中央高校基本科研业务费专项资金资助项目(CUGQYZX1707);高等学校学科创新引智计划资助项目(B14031)

摘　　要：鄂西渝东区下寒武统水井沱组(牛蹄塘组)、上奥陶统五峰组和下志留统龙马溪组海相富有机质页岩是我国南方页岩气勘探的重要层位。研究表明,研究区水井沱组经历的最高古地温介于280~300℃,现今R_o为3.90%~4.50%;五峰组和龙马溪组最高古地温介于200~220℃,现今R_o为2.45%~3.00%,有机质处于高演化过成熟阶段。然而,页岩样品氯仿抽提物饱和烃组成仍较为完整,存在碳数分布多具双峰型的正构烷烃、部分类异戊二烯烷烃和甾萜类化合物。该现象说明在地层条件下页岩中较严格受限的液态烃向气态烃的热力转化即环化缩聚和加氢裂解受到限制,从而造成常见饱和烃生物标志化合物的基本碳骨架在地温为200~300℃和热力作用时间为50~180 Ma的条件下仍然可以保存。研究表明,过成熟页岩中的饱和烃生物标志化合物没有完全失去其指示成熟度和生源的意义。根据页岩样品中的正构烷烃碳数和双峰型分布特征以及C_(23)三环萜烷/C_(30)藿烷指标判断,水井沱组页岩有机质成熟度更高,有机质来源中以原核生物的母质贡献占优,而五峰组和龙马溪组页岩有机母质来源中主要为细菌和藻类。Organic-rich marine shales in the Lower Cambrian Shuijingtuo（ Niutitang） Formation,the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation of western Hubei-eastern Chongqing area are very attractive targets for shale gas exploration in southern China. This research shows that the maximum paleogeotemperature experienced by the Shuijingtuo Formation ranges from 280 ℃ to 300 ℃,while the maximum paleogeotemperature of the Wufeng Formation and the Longmaxi Formation ranges from 200 ℃ to 220 ℃. The organic matter of the three formations is over-mature,with the vitrinite reflectance（ Ro） for the Shuijingtuo Formation varying from 3. 90% to 4. 50%,while that for the Wufeng Formation and the Longmaxi Formation from 2. 45% to 3. 00%. However,nearly a complete series of n-alkanes mostly with bimodal distributions,isoprenoid alkenes,steranes,and terpanes have been observed in saturated hydrocarbons from the sampled shales’ chloroform extract. This demonstrates that the conversion from liquid hydrocarbons to gaseous hydrocarbons（ i. e. cyclo-polycondensation and hydrocracking） has been restricted within the shale strata,and thus the carbon skeleton of typical saturated hydrocarbon biomarkers could preserve at 200 ℃ to 300 ℃ for 50 to 180 Ma. What is also shown by the research is that some saturated hydrocarbon biomarkers in over-mature shales have not lost their ability to indicate maturity and biogenesis completely. Judging from the carbon number range and bimodal distributionsof n-alkanes,and C23 tricyclic terpane/C30 hopance ratios in the sampled shales,the shales in the Shuijingtuo Formation have a higher level of organic maturity and the prokaryote is a major source of their organic matter,while the organic parent substance for Wufeng shales and Longmaxi shales are mainly derived from bacteria and alga.

关 键 词：有机质 过成熟 饱和烃 页岩 下古生界 鄂西渝东 

分 类 号：TE122.1[石油与天然气工程—油气勘探]