鄂西地区二叠系大隆组含气页岩岩相类型及储层特征

Lithofacies Types and Reservoir Characteristics of Gas-Bearing Shale of Permian Dalong Formation in Western Hubei

为研究鄂西地区上二叠统大隆组含气页岩岩相类型和储层特征,本文以鄂西地区恩施市恩地2井钻井岩心为研究对象,利用X-射线衍射全岩矿物分析(XRD)、总有机碳(TOC)质量分数测定、镜质体反射率(R_(o))测定、干酪根镜检、场发射扫描电镜(FE-SEM)观察、CO_(2)和N2吸附实验、页岩含气量测定、微量元素测定等方法开展精细研究。结果显示:鄂西地区二叠系大隆组主要发育的岩相类型包括硅质岩相、黏土质硅质岩相和混合质硅质岩相,其中黏土质硅质岩相是大隆组有机碳质量分数最高的岩相类型;大隆组页岩孔隙类型多样,微孔和介孔贡献了页岩主要的孔隙体积和孔比表面积;高有机碳和高黏土矿物有利于页岩气的聚集和页岩中微小孔隙(孔径<50 nm)系统的建立,微孔和介孔中的吸附气是总含气量的重要组成部分。以含气量和有机碳质量分数为指标建立鄂西二叠系大隆组页岩评价标准,黏土质硅质岩相和混合质硅质岩相为Ⅱ_(1)类优势岩相类型,硅质岩为Ⅱ_(2)类页岩气优势岩相类型,恩地2井1 241.0~1 250.4 m井段为页岩气“甜点段”。页岩微量元素和有机碳质量分数关系表明大隆组高有机质含量是高古生产力和水体还原环境的共同结果,其中高古生产力是有机质富集的主要原因。

To study the lithofacies types and reservoir characteristics of gas-bearing shale in the Upper Permian Dalong Formation in western Hubei area,the drilling cores of Endi 2 Well were taken as the research object and analyzed by whole rock X-ray diffraction,organic carbon content,vitrinite reflectance,kerogen microscopy,field emission scanning electron microscopy,carbon dioxide and nitrogen physical adsorption experiments,shale gas content and trace elements.The results show that the main lithofacies types of the Permian Dalong Formation in western Hubei include siliceous rocks,clayey siliceous rocks and mixed siliceous rocks,and the clayey siliceous lithofacies has the highest average organic carbon content.The shale of Dalong Formation has multiple pore types.Micropores and mesopores contribute to the main pore volume and specific surface area of shale.High organic carbon and clay mineral content are conducive to the accumulation of shale gas and the establishment of micro-pore system(pore size<50 nm)in shale,and the adsorbed gas in micropores and mesopores is an important part of the total gas content.This paper established the evaluation criteria of Permian Dalong Formation shale in western Hubei based on gas content and TOC.The results show that clayey siliceous lithofacies and mixed siliceous lithofacies areⅡ_(1) class advantageous lithofacies types,siliceous lithofacies areⅡ_(2) class advantageous lithofacies types,and the 1241.0-1250.4 m section of Endi 2 Well is the“sweet section”of shale gas.The relationship between trace elements and organic carbon content of shale shows that the high organic matter content of Dalong Formation is the joint result of high productivity and water reduction environment,and the high ancient productivity is the main reason for the enrichment of organic matter.