石油学报 ›› 2022, Vol. 43 ›› Issue (5): 605-616,636.DOI: 10.7623/syxb202205003

• 地质勘探 • 上一篇    下一篇

潜江凹陷古近系盐间地层沉积环境与有机质富集——以潜江组三段下亚段10号韵律为例

蔡媛1, 孔祥鑫1,2, 姜在兴1,2, 葛涛元1,2, 陈凤玲3, 吴世强3, 张亮3   

  1. 1. 中国地质大学(北京)能源学院 北京 100083;
    2. 中国地质大学(北京)教育部海相储层演化与油气富集机理重点实验室 北京 100083;
    3. 中国石油化工股份有限公司江汉油田分公司勘探开发研究院 湖北武汉 430223
  • 收稿日期:2021-10-19 修回日期:2022-02-14 发布日期:2022-05-28
  • 通讯作者: 孔祥鑫,男,1990年5月生,2020年获中国地质大学(北京)博士学位,现为中国地质大学(北京)能源学院讲师,主要从事细粒沉积学与非常规油气储层研究。Email:kongxiangxin@cugb.edu.cn
  • 作者简介:蔡媛,女,2000年8月生,现为中国地质大学(北京)能源学院本科生,主要从事沉积学研究。Email:13311581943@139.com
  • 基金资助:
    国家自然科学基金面上项目(No.41772029)、中国博士后科学基金项目(2020M680624)和中国地质大学(北京)大学生创新创业训练计划项目(S202111415094)资助。

Sedimentary environment and organic matter enrichment of Paleogene inter-salt strata in Q ianjiang sag: a case study from 10th rhythmite of the Lower Member 3 of Q ianjiang Formation

Cai Yuan1, Kong Xiangxin1,2, Jiang Zaixing1,2, Ge Taoyuan1,2, Chen Fengling3, Wu Shiqiang3, Zhang Liang3   

  1. 1. School of Energy Resources, China University of Geosciences, Beijing 100083, China;
    2. MOE Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Enrichment Mechanism, China University of Geosciences, Beijing 100083, China;
    3. Research Institute of Exploration and Development, Sinopec Jianghan Oilfield Company, Hubei Wuhan 430223, China
  • Received:2021-10-19 Revised:2022-02-14 Published:2022-05-28

摘要: 潜江凹陷潜江组发育多套富有机质的盐间细粒沉积岩,是潜在的页岩油勘探目标,对盐湖环境有机质富集机制的认识不清制约了页岩油成藏机理的研究。以潜江组三段(潜三段)下亚段10号韵律盐间层为研究对象,综合岩心、岩石薄片、X射线衍射矿物分析与常量、微量、稀土元素分析等地质资料,探讨了潜江凹陷盐间地层有机质的富集机理。根据物质组成和岩相类型,将潜三段下亚段10号韵律盐间层划分为3段,其中,上段、下段由层状白云质泥岩和钙芒硝岩组成,总有机碳(TOC)平均含量为0.83%;中段由纹层状白云质泥岩和纹层状灰质泥岩组成,TOC平均含量为1.35%。盐间层中段黄铁矿的晶体形态、元素地球化学特征反映热液活动参与其沉积。盐间层中段沉积期,古气候相对湿润,水体还原性较强、盐度偏低、生物生产力高;盐间层上段和下段形成于干热古气候条件,沉积水体还原性较弱、盐度高、生物生产力低。潜江凹陷盐间层有机质的富集是热液活动和气候变化共同作用的结果。其中,热液活动为表层水体带来营养物质,利于盐湖生物繁盛和生产力水平提高;古气候的干湿变化通过改变盐湖水体的氧化还原性和盐度,进而影响沉积有机质的保存。

关键词: 盐湖, 热液, 有机质富集, 潜江凹陷, 沉积环境

Abstract: Multiple inter-salt layers composed of organic-rich fine-grained sedimentary rocks are developed in the Qianjiang Formation, which is a potential target for shale oil exploration in Qianjiang sag. However, the unclear understanding of the mechanism of organic matter enrichment in salt lakes restricts the study of shale oil accumulation mechanism. The geological data including core, thin section, X-ray analysis and major, trace, rare earth elements were integrated to study the enrichment mechanism of organic matter in the inter-salt stratum of the 10th rhythmite of the Lower Member 3 of Qianjiang Formation. According to the mineral composition and lithofacies types, the inter-salt stratum of the 10th rhythmite of the Lower Member 3 of Qianjiang Formation can be divided into three sections. The upper and lower sections are composed of bedded dolomitic mudstone and glauberite, with average TOC content of 0.83%, while the middle section is composed of laminated marlstone and laminated dolomitic mudstone, with an average TOC content of 1.35%. The crystal morphology of pyrite and geochemical characteristics of elements indicates that inter-salt layers in the Qianjiang sag has recorded hydrothermal activity. During the sedimentary period of the middle section of inter-salt layers, the climate was relatively humid, with a strong reducing condition, low salinity and high biological productivity. The upper and lower sections of inter-salt layers were formed in a dry and hot climate, with a weak reducing condition, high salinity and low biological productivity. This study indicates that the enrichment of organic matter in inter-salt layers of Qianjiang sag was resulted from the hydrothermal activity and climate change. The hydrothermal activity played an important role in improving the biological productivity in salt lakes, which brought nutrients to the surface waters.The dry-wet changes of paleoclimate can affect the preservation of sedimentary organic matter by controlling the changes of redox and salinity of the salt lake.

Key words: salt lake, hydrothermal activity, organic matter enrichment, Qianjiang sag, sedimentary environment

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