中扬子西部下古生界页岩沉积古环境  

Sedimentary Paleoenvironment of the Lower Paleozoic Shale in the Western Middle Yangtze

作　　者：沈均均[1] 杨丽亚 王玉满[3] 李辉[4] 王鹏万 周林[6] 刘计勇[6] 孟江辉[1] SHEN JunJun;YANG LiYa;WANG YuMan;LI Hui;WANG PengWan;ZHOU Lin;LIU JiYong;MENG JiangHui(Hubei Cooperative Innovation Center of Unconventional Oil and Gas of Yangtze University,Wuhan 430100,China;Exploration and Development Research Institute of SINOPEC Zhongyuan Oilfield Branch,Puyang,Henan 457001,China;PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;China Oilfield Services Limited Production Optimization,Tianjin 300459,China;PetroChina Hangzhou Institute of Petroleum Geology,Hangzhou 310023,China;Exploration and Production Research Institute,Jianghan Oilfield Company,SINOPEC,Wuhan 430070,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,武汉430100 [2]中国石化中原油田分公司勘探开发研究院,河南濮阳457001 [3]中国石油勘探开发研究院,北京100083 [4]中海油田服务股份有限公司油田生产事业部,天津300459 [5]中国石油杭州地质研究院,杭州310023 [6]中国石化江汉油田分公司勘探开发研究院,武汉430070

出　　处：《沉积学报》2025年第1期314-334,共21页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42372168);非常规油气省部共建协同创新中心开放基金项目(UOG2022-36);国家科技重大专项(2017ZX05035001-002)。

摘　　要：【目的】下古生界筇竹寺组和龙马溪组是中上扬子地区页岩气勘探开发的重点层系,而对两套页岩有机质富集的控制因素一直缺乏系统对比研究。【方法】以中扬子西部两套海相页岩为例,对其在被动大陆边缘和克拉通坳陷内沉积学及地球化学特征进行对比分析,探讨有机质差异富集主控因素及形成模式。【结果】两套页岩高总有机碳(Total Organic Carbon,TOC)段均位于底部,形成于陆源输入量低、古生产力水平高和保存条件好的环境,且筇竹寺组底部古生产力水平和底水还原程度更高,导致其TOC含量更高。此后,筇竹寺期盆地拉张裂陷作用持续减弱,龙马溪期前陆挠曲—迁移作用逐渐增强,两套页岩均表现出陆源输入量增大和保存条件变差的特点,但古生产力水平变化却截然不同:筇竹寺期,洋流活动随着海平面下降而减弱,古生产力水平随之降低,而龙马溪期,挠曲—迁移作用导致扬子海盆北部障壁开口逐渐打开,洋流涌入规模逐渐扩大,受海平面下降影响较弱,古生产力水平随之升高。因此,纵向上,筇竹寺组TOC含量降低主要受古生产力水平降低、保存条件变差和陆源输入量增大共同控制,而龙马溪组则主要受后两个因素控制。横向上,两套页岩由被动大陆边缘过渡至克拉通坳陷内,海平面高度和洋流活跃程度均呈降低趋势,保存条件和古生产力水平同时变差,TOC含量随之降低。受此控制,筇竹寺组页岩气勘探开发重点应向西南落实,而龙马溪组则应转向西北方向,二者难以同时兼顾。【结论】该研究对于深入理解下古生界海相页岩沉积古环境演化特征、有机质富集机理及指导页岩气勘探实践均具有积极意义。[Objective]The Lower Paleozoic Qiongzhusi Formation and Longmaxi Formation are the key strata for shale gas exploration and development in southern China.The organic matter content in the shale is a key index for determining the degree of gas enrichment.However,there has been a lack of systematic comparative study on the en-vironmental control factors of organic matter enrichment in the two shales.[Methods]Using core/outcrop,X-ray dif-fraction,thin section,organic matter content,and element analysis data,the sedimentological and geochemical changes of the two shale layers were compared and analyzed.The differences in the sedimentary paleoenvironment between the two layers for similar geological backgrounds were systematically discussed,and the sedimentary pa-leoenvironment changes from passive continental margin to cratonic depression were compared and analyzed.The main controlling factors and differences of organic matter enrichment in two sets shale formations were clarified,and the corresponding enrichment models were established.[Results](1)Vertically,the bottoms of the Qiongzhusi For-mation(Q1 member)and Longmaxi Formation(LM1-LM5)are dominated by organic rich bio siliceous rock siliceous shale deposits,and the total organic carbon(TOC)content of the former is higher than that of the latter.At the top,with the continuous decline of sea level,TOC and biogenic silicon content showed a downward trend,whereas clay or carbonate rock mineral content exhibited an upward trend.Horizontally,under the control of paleogeomorphology,TOC and biogenic silicon content decreased from passive continental margin to cratonic depression in different sedimentary periods.(2)The high TOC shale sections at the bottom of both shales were formed in environments with low terrestrial input,high paleoproductivity,and good preservation conditions.Moreover,the paleoproductivity level and bottom water reduction degree of the Q1 member were higher than those of LM1-LM5,resulting in higher TOC content.With the continuous decline of sea level

关 键 词：笻竹寺组 龙马溪组 黑色页岩 有机质 沉积古环境 富集主控因素 

分 类 号：P531[天文地球—古生物学与地层学]