五峰组—龙马溪组页岩地化特征及沉积环境——以四川盆地西南缘为例  

Geochemical characteristics and sedimentary environment of the Wufeng-Longmaxi shales: A case study from southwestern margin of the Sichuan basin

作　　者：拜文华[1,2] 王强 孙莎莎[1,2] 梁峰[1,2] 张琴 昌燕[1,2] BAI Wenhua;WANG Qiang;SUN Shasha;LIANG Feng;ZHANG Qin;CHANG Yan(PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;National Energy Shale Gas R&D Experiment Center,Langfang,Hebei 065007,China;School of Geoscienences,Chengdu University of Technology,Chengdu,Sichuan 610059,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]国家能源页岩气研发实验中心,河北廊坊065007 [3]成都理工大学地球科学学院,四川成都610059

出　　处：《中国矿业大学学报》2019年第6期1276-1289,共14页Journal of China University of Mining & Technology

基　　金：国家“十三五”重大专项(2017ZX05035);中国石油天然气股份公司重大专项配套项目(XN11711)

摘　　要：通过对四川盆地西南缘永善-绥江一带3条露头剖面系统的页岩样品地球化学及微量元素分析测试,从五峰组、龙马溪组下部、龙马溪组中部3个层段分析了页岩微量元素、稀土元素的垂向变化规律,探讨了页岩沉积的氧化还原条件、古气候、古盐度、古水深,进一步研究了主力勘探目的层段--龙马溪组下部沉积相展布.认为龙马溪组下部页岩沉积水体为贫氧还原环境,利于形成黑色富有机质页岩,是页岩气勘探的最有利甜点段;五峰组-龙马溪组总体处于干热气候和微咸水环境,有机质古生产力较高.研究结果表明:五峰组属于滞留盆地沉积,水体深度在70~100 m,观音桥层沉积水体变浅为20~50 m,龙马溪组下部的沉积水深70~150 m,为深水陆棚沉积,龙马溪组中部沉积水深变浅,属于浅水陆棚.龙马溪组下部属于钙质深水陆棚沉积,富有机质黑色页岩厚度在37~76 m,平均为53 m,TOC平均为2.71%,具有较好的页岩气发育的物质基础.五峰组黑色页岩厚度平均为8.1 m,TOC平均为1.87%,可作为次要勘探目标层位.To deepen the understanding of the sedimentary environment of the Wufeng-Longmaxi formations, samples from three outcrop sections in Yongshan-Suijiang area along the southwestern Sichuan basin were collected for the geochemistry and trace element analysis. Wufeng-Longmaxi formations were divided into Wufeng formation, the lower Longmaxi section, and the mid Longmaxi section. The vertical variations of trace element and rare earth element in the shale samples were analyzed. The redox conditions, paleoclimate, paleosalinity and paleo-water depth of the shales were discussed and sedimentary facies distributions of the lower Longmaxi section were further studied in this paper. The results indicate that the anoxic(reduction) environment of the lower Longmaxi is beneficial for black shale deposition, and the lower Longmaxi is the sweet spot for shale gas exploration and development. The Wufeng-Longmaxi formations are generally in a hot dry climate and a brackish water environment with a high organic productivity. The results also show that the paleo-water depths of Wufeng formation deposited in restricted basin, with paleo-water-depth ranging from 70 to 100 m, and the paleo-water-depths of the Guanyinqiao and the lower Longmaxi range from 20-50 m and 70-100 m, respectively. The mid Longmaxi and the lower Longmaxi belong to the shallow water shelf deposit and calcareous deep water shelf deposit, respectively. The thickness of organic rich black shale is about 37 to 76 m, with an average of 53 m, and the average of TOC is 2.71%, which demonstrate that the lower Longmaxi is of solid material basis for shale gas development. The Wufeng formation has an average thickness of 8.1 m and an average TOC of 1.87%, which can be regarded as a co-prospecting exploration interval.

关 键 词：四川盆地西南缘 五峰组-龙马溪组 黑色页岩 地球化学特征 微量元素 古水深 沉积环境 

分 类 号：P618.13[天文地球—矿床学]