湘西前陆坳陷区五峰-龙马溪组黑色岩系沉积环境与有机质富集机制:以TD2井为例  

Sedimentary Environment and Organic Matter Accumulation of Black Rock Series of Wufeng-Longmaxi Formations in Foreland Depression,Western Hunan Province:An Example from Well TD2 in Changde Area

作　　者：蔡全升[1,2,3,4] 胡明毅 杨智[5] 邱小松[5] 张保民[4] 李海[4] 胡忠贵[2] 邓庆杰[2] Cai Quansheng;Hu Mingyi;Yang Zhi;Qiu Xiaosong;Zhang Baomin;Li Hai;Hu Zhonggui;Deng Qingjie(Cooperative Innovation Center of Unconventional Oil and Gas,Yangtze University(Ministry of Education&Hubei Province),Wuhan 430100,China;School of Geosciences,Yangtze University,Wuhan 430100,China;Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences,Wuhan 430074,China;Wuhan Center of China Geological Survey,Wuhan 430023,China;Research Institute of Petroleum Exploration&Development,PetroChina,Beijing 100083,China)

机构地区：[1]长江大学非常规油气省部共建协同创新中心,湖北武汉430100 [2]长江大学地球科学学院,湖北武汉430100 [3]中国地质大学构造与油气资源教育部重点实验室,湖北武汉430074 [4]中国地质调查局武汉地质调查中心,湖北武汉430023 [5]中国石油勘探开发研究院,北京100083

出　　处：《地球科学》2024年第7期2330-2345,共16页Earth Science

基　　金：中石油科技创新基金项目(No.2021DQ02-0101);湖北省教育厅青年基金项目(No.Q20211304);长江大学非常规油气省部共建协同创新中心开放基金项目(No.UOG2022-08);构造与油气资源教育部重点实验室项目(No.TPR-2021-13)。

摘　　要：受地层剥蚀和强烈构造活动的影响,对中扬子东南缘前陆坳陷区五峰-龙马溪组黑色岩系关注较少,该区黑色岩系沉积特征与有机质富集规律尚不清楚.利用近年来新获取的常德TD2井岩心资料,基于岩石学、沉积学以及地球化学分析,对湘西前陆坳陷区五峰-龙马溪组黑色岩系的发育特征、沉积环境及有机质富集机制开展了深入研究.结果表明,湘西前陆坳陷区TD2井五峰-龙马溪组黑色岩系厚度较大,TOC>2%的富有机质页岩厚约21 m,岩性以硅质页岩与碳质页岩为主,基于岩性差异自下而上可划分为四个沉积单元,富有机质页岩主要集中凯迪阶至鲁丹阶下部,而鲁丹阶上部-埃隆阶下部黑色岩系TOC含量普遍偏低且呈间断发育.综合研究认为,前陆坳陷区五峰-龙马溪组黑色岩系的形成主要受构造、海平面以及陆源碎屑供给等因素的综合控制.凯迪晚期-鲁丹早期,受区域构造挤压和全球海平面上升的影响,湘西地区经历了显著的构造沉降及相对海平面上升等事件,极大地促进了坳陷区强还原条件的形成以及古生产力的提高,使得该时期研究区黑色岩系中的有机质大量富集.然而,随着鲁丹晚期区域构造挤压活动的加剧,研究区由构造沉降向构造隆升转变,持续的构造抬升与风化作用增强,导致了研究区陆源碎屑供给大量增加和相对海平面不断下降,并最终使得研究区富有机质页岩的形成发育在埃隆早期被终结.值得注意的是,埃隆早期的全球冰川型海平面上升在研究区也有响应,促进了龙马溪组黑色页岩的二次发育.据此,提出了湘西前陆坳陷区奥陶-志留纪之交富有机质页岩的发育模式,以期为该区五峰-龙马溪组页岩气勘探及奥陶-志留纪之交重大地质事件沉积响应研究提供参考.As the main sediments across the Yangtze area during the Ordovician-Silurian(O-S)transition,the Upper Ordovician Wufeng Formation and Lower Longmaxi Formation are widely distributed in the Yangtze Sea,and they are also the main targets for marine shale gas exploration in the South China.However,little attention has been paid to the Wufeng-Longmaxi black rock series in the foreland basin,southeastern Yangtze Block,due to the lack of complete and fresh outcrops caused by intensive erosion and tectonic damage.In this paper,by utilizing the newly obtained drilling cores of the Well TD2 located in the Hunan Province,the sedimentary environment and organic matter accumulation of the Wufeng-Longmaxi black rock series in the foreland basin were investigated based on the systematically petrological and geochemical analysis.The organic-rich shale of the Wufeng-Longmaxi formations is dominated by siliceous shale and carbonaceous shale,in which plenty of terrigenous clast and even thin sandstone can be observed.The black shale with TOC>2%is about 21 m in thickness.Four sedimentary cycles can be recognized from the O-S black series and they exhibit different lithological and geochemical variation characteristics.The organic shale generally developed in the Late Katian to the Early Rhuddanian,while the black rock series developed during the Late Rhuddanian to Early Aeronian have low TOC content and are discontinuous.Based on the analyses of lithology,mineral composition and geochemistry,tectonism,sea-level and terrigenous supply should be the primary controlling factors for the deposition of the O-S black shale in the foreland basin,Yangtze area.During the Late Katian to Early Rhuddanian,the study area experienced significantly tectonic subsidence and sea-level rise caused by regional tectonic compression and global sea-level rise,then strongly reducing conditions were formed and paleoproductivity was improved in the deep-depression area,which promoted the enrichment of organic matter in black rock series during this stage.Nev

关 键 词：前陆坳陷 五峰-龙马溪组 黑色岩系 沉积特征 有机质富集 湘西地区 石油地质 

分 类 号：P618.13[天文地球—矿床学]