摘要
下扬子地区上二叠统大隆组—吴家坪组富有机质页岩是一套重要的烃源岩,是中国页岩气调查的重点层位。页岩的形成条件和发育模式与古沉积环境关系紧密。为此,对下扬子地区望江拗陷上二叠统大隆组—吴家坪组典型页岩样品进行了元素分析,恢复了页岩沉积环境的古气候、古水深、古盐度、古生产力、氧化还原特征。研究结果表明:(1)大隆组硅质页岩V/(V+Ni)均值为0.47,Sr/Ba均值为303.4,Sr/Cu均值为5.83,Rb/K均值为0.022,指示研究区大隆组硅质页岩沉积期为较为温暖湿润的气候,水体环境为咸水、弱氧化环境,古水深总体较深,分析大隆组硅质页岩主要发育在深水陆棚相环境,具备较高的古生产力,并有利于有机质的保存,为页岩气勘探有利层位。(2)吴家坪组炭质页岩V/(V+Ni)均值为0.80,Sr/Ba均值为343.6,Sr/Cu均值为9.83,Rb/K均值为0.0092,指示研究区吴家坪组炭质页岩沉积期为偏干旱气候,水体为咸水、还原环境,古水深较浅,分析吴家坪组炭质页岩沉积环境为滨海沼泽相环境,古生产力较低,有机质保存条件较差,导致有机质含量偏低。
Organic-rich shales in the Upper Permian Dalong Formation–Wujiaping Formation of Lower Yangtze area are important source rocks,and the key horizon for shale gas survey in China.The forming conditions and development models of shale are closely related to paleo-sedimentary environment.Element analysis was conducted on typical shale samples from the Formations,to reconstruct the paleo-climate,paleo-water depth,paleo-salinity,paleo-productivity,and redox characteristics of sedimentary environment.The following results are obtained:(i)The average V/(V+Ni),Sr/Ba,Sr/Cu and Rb/K values of siliceous shales in the Dalong Formation are 0.47,303.4,5.83,and 0.022,respectively,indicating that the siliceous shales were deposited in a relatively warm and humid climate,with a saline and weakly oxidizing water environment where the paleo-water was generally deep.The siliceous shales are believed to have developed mainly in a deep-water continental shelf environment with high paleo-productivity.They are conducive to organic matter preservation,showing a favorable horizon for shale gas exploration.(ii)The average V/(V+Ni),Sr/Ba,Sr/Cu and Rb/K values of carbonaceous shales in the Wujiaping Formation are 0.80,343.6,9.83,and 0.0092,respectively,indicating that the carbonaceous shales was deposited in an arid climate with saline and reducing environment where the paleo-water was relatively shallow.The carbonaceous shales are believed to have deposited in a littoral swamp environment with low paleo-productivity and poor organic matter preservation conditions,resulting in low organic matter content.
作者
刘恒
童召军
乔洪国
王朔
LIU Heng;TONG Zhaojun;QIAO Hongguo;WANG Shuo(The First Exploration Team of Shandong Coalfield Geologic Bureau,Qingdao,Shandong 266400,China)
出处
《天然气勘探与开发》
2023年第2期74-83,共10页
Natural Gas Exploration and Development
基金
山东省煤田地质局第一勘探队2022-2023年度局科研专项“急倾斜地层防斜打快技术研究”(编号鲁煤地科字(2022)24号)。
关键词
元素分析
沉积环境
大隆组—吴家坪组页岩
下扬子地区
Element analysis
Sedimentary environment
Shales in Dalong Formation–Wujiaping Formation
Lower Yangtze area
