威远地区五峰组-龙马溪组页岩纹层发育特征及地质意义

Development characteristics and geological significance of laminae in Wufeng-Longmaxi shales in Weiyuan area

为了精细研究海相富有机质页岩纹层组成、结构、构造及地质意义,选取四川盆地威远页岩气田五峰组—龙马溪组页岩为研究对象,对比分析页岩纹层发育特征,定量表征页岩纹层形成的古环境等参数。首先,通过钻井岩心、大薄片鉴定和X射线衍射(XRD),阐述研究区页岩纹层发育的类别;其次,结合氩离子抛光.扫描电镜(SEM),直接观察不同矿物特征;最后,利用高分辨率二维原位X射线荧光光谱(2DXRF)等实验技术,定量分析页岩纹层差异性及其地质意义。研究结果表明:四川盆地威远页岩气田五峰组—龙马溪组一段页岩纹层按组分划分为硅质纹层、钙质纹层、黏土质纹层和有机质纹层4类,主要识别出硅质I+有机质纹层组、钙质+黏土质纹层组和硅质Ⅱ+黏土质纹层组3类纹层组;威远地区页岩纹层和纹层组在纵向上的分布具有明显的分段性,揭示纹层尺度下水体动力条件和氧化还原特征等古环境演化。通过多种技术联用进行页岩纹层发育特征的精细研究,将为页岩油气的勘探开发提供重要的地质理论基础。

In order to finely study the laminae composition,texture,structure and geological significance of marine organic-rich shale,Wufeng—Longmaxi Formation in the Weiyuan Shale Gas Field in the Sichuan Basin was selected as the object.The development characteristics of shale laminae were compared and analyzed quantitatively to characterize the difference of shale laminae.Firstly,the types of shale laminae developed in the study area were described by drilling cores,large section identification and X−ray diffraction(XRD).Secondly,the characteristics of different minerals were directly observed by combining with Ar−SEM(argon ion polishing scanning electron microscopy).Finally,high-resolution two-dimensional in situ X−ray fluorescence spectroscopy(2D-XRF)and other analyses were used to quantitatively analyze the geological significance of shale laminae differences.The results show that Wufeng—Longmaxi Formation first member in the Weiyuan Shale Gas Field in the Sichuan Basin contains four types,including siliceous laminae,calcareous laminae,clay laminae and organic laminae.Three types of laminasets mainly exist,including siliceous I+organic laminasets,calcareous+clay laminasets and siliceousⅡ+clay laminasets.The distribution of shale laminae and laminasets in the Weiyuan area has obvious segmentation with the depth,which reveals the evolution of paleoenvironment such as hydrodynamics and redox conditions of water columns at the lamina scale.The fine research on the development characteristics of shale laminae by various technologies will provide an important geological basis for the exploration and development of shale oil and gas.