川东二叠系龙潭组页岩岩相特征与沉积环境  

Lithofacies and sedimentary environment of shale of Permian Longtan Formation in eastern Sichuan Basin

作　　者：肖威 张兵[1] 姚永君 王艳[1] 杨洪宇 杨凯[1] XIAO Wei;ZHANG Bing;YAO Yongjun;WANG Yan;YANG Hongyu;YANG Kai(Key Laboratory of Earth Exploration and Information Technology,Ministry of Education,Chengdu University of Technology,Chengdu 610059,China;Chongqing GasMine,PetroChina Southwest Oil&Gas Field Company,Chongqing 400000,China)

机构地区：[1]成都理工大学地球勘探与信息技术教育部重点实验室,成都610059 [2]中国石油西南油气田分公司重庆气矿,重庆400000

出　　处：《岩性油气藏》2022年第2期152-162,共11页Lithologic Reservoirs

基　　金：国家自然科学基金“东特提斯三江构造带深部结构形态与属性特征研究”(编号:91755215)资助。

摘　　要：川东地区二叠系龙潭组属于过渡相—海相地层,页岩气勘探前景广阔。根据研究区页岩的矿物学、岩石学特征划分了岩相类型,利用地球化学数据重建了古沉积环境,并探讨了其有机质富集的控制因素,在此基础上建立岩相、有机质富集与沉积环境的耦合关系。研究结果表明:(1)川东龙潭组页岩主要发育硅质页岩、黏土质硅质混合页岩、黏土质钙质混合页岩和钙质硅质混合页岩等4种岩相,垂向上岩相分布可划分为早期相对富黏土阶段和晚期硅质含量相对较高阶段。(2)沉积环境分析表明,龙潭组沉积早期海平面低,主要处于氧化—次氧化环境,其U/Th平均为0.42,EF_(Mo)平均为6.66,V/(V+Ni)平均为0.77,古生产力较低,陆源输入大,硅质来源为陆源搬运;晚期海平面持续上升,主要处于还原环境,其U/Th平均为5.96,EF_(Mo)平均为148.01,V/(V+Ni)平均为0.79,古生产力高,陆源输入低,有大量生物成因硅富集。(3)龙潭组沉积时期有机质的富集具有明显的差异性,沉积早期受陆源输入强度和古生产力共同控制,大量陆源高等植物碎屑等被带入,造成其有机碳含量较高;沉积晚期仅受古生产力控制,陆源碎屑供给相对前期减弱,有机质多来源于海洋藻类植物。Permian Longtan Formation in eastern Sichuan Basin belongs to transitional-marine strata,with a broad shale gas exploration prospect.According to the mineralogical and petrological characteristics of shale in the study area,the lithofacies was divided,the paleosedimentary environment was reconstructed by using geochemical data,and the controlling factors of organic matter enrichment were discussed.On this basis,the coupling relationship among lithofacies,organic matter enrichment and sedimentary environment was established.The results show that:(1)The shale of Longtan Formation in eastern Sichuan Basin mainly develops four lithofacies:siliceous shale,clay siliceous mixed shale,clay calcareous mixed shale and calcareous siliceous mixed shale.The vertical distribution of lithofacies can be divided into early relatively clay rich stage and late relatively high siliceous content stage.(2)During the early stage of Longtan Formation,the sea level was low,it was mainly in oxidation-suboxidation environment.The average U/Th is 0.42,the average EF_(Mo) is 6.66,and the average V(/V+Ni)is 0.77.The paleoproductivity is low and the terrigenous input is large,and the siliceous source was terrigenous transport.During the late stage,the sea level continued to rise,it was mainly in reduction environment.The average U/Th is 5.96,the average EF_(Mo) is 148.01,and the average V/(V+Ni)is 0.79,with high paleoproductivity and little terrigenous input,and a large amount of biogenic silicon was enriched.(3)The organic matter enrichment in the sedimentary stage of Longtan Formation have obvious differences,it was jointly affected by terrigenous input and paleoproductivity in the early stage,and a large number of terrigenous higher plant debris were brought in,resulting in a high content of organic carbon.It was controlled by paleoproductivity in the late stage,and the supply of terrigenous debris was weaker than that in the early stage,with organic matter mostly from marine algae.

关 键 词：页岩岩相 陆源碎屑 古生产力 有机质富集 龙潭组 二叠系 川东 

分 类 号：TE122.1[石油与天然气工程—油气勘探] P618.13[天文地球—矿床学]