海相细粒陆源碎屑岩主要沉积构造类型及页岩气意义^*

Main sedimentary structure types of marine fine-grained terrigenous clastic rocks and their significance for shale gas

摘要

沉积构造不仅能揭示海相细粒陆源碎屑岩的形成环境和沉积时的古水动力条件,还影响到页岩气储集层的渗透性及可压裂性。文中通过系统总结国内外相关研究成果,明确了海相细粒陆源碎屑岩沉积构造的主要类型及成因。海相细粒陆源碎屑岩主要发育物理成因、化学成因和生物成因3类沉积构造: 物理成因构造主要有流动成因构造和软沉积物变形构造,前者包括交错纹理、水平层理(纹理)、块状构造、递变纹理和复合纹理,后者包括滑塌—滑移构造、负载构造、火焰状构造、球—枕构造、包卷层理、扭曲纹理、碎裂纹理和坠石; 化学成因构造包括碳酸盐结核和黄铁矿结核; 生物成因构造主要有生物遗迹构造和生物扰动构造。该3类沉积构造主要为细粒浊流沉积、等深流沉积和远洋—半远洋沉积成因,少数为沉积物变形成因。沉积构造类型直接影响页岩气储集层的渗透性、水力裂缝的生成及延展方向。

Abstract

Sedimentary structures can not only provide insights into the formation environment and hydrodynamics of marine fine-grained terrigenous clastic rocks,but also significantly influence the permeability and fracturability of shale gas reservoirs. Based on comprehensive analysis of relevant materials at home and abroad,the types and origins of marine fine-grained terrigenous clastic rocks were systematically summarized. The rocks exhibit physical,chemical and biological structures. The physical structures mainly include flow structures and soft-sediment deformation structures. Flow structures include cross lamination,horizontal bedding or lamination,massive structure,graded lamination,and composite lamination. Soft-sediment deformation structures include slumps and slides,load structures,flame structures,ball-and-pillow structures,convolute lamination,contorted lamination,disrupted lamination,and dropstones. Chemical structures comprise carbonate concretes and pyrites,with biogenic structures primarily consisting of trace fossils and bioturbation. The three major types of sedimentary structures are mainly the result of fine-grained turbidites,contourites,and pelagites-hemipelagites,with a few arising from sediment deformation. Variations in sedimentary structures directly influence the permeability of shale gas reservoirs and affect the generation and propagation direction of hydraulic fractures.

关键词

海相细粒陆源碎屑岩 / 水平纹理 / 交错纹理 / 递变纹理 / 软沉积物变形 / 沉积构造 / 可压裂性

Key words

marine fine-grained terrigenous clastic rocks / parallel lamination / cross lamination / graded lamination / soft-sediment deformation structures / sedimentary structure / fracturability

基金资助

*中国石油天然气股份有限公司科技管理部“十四五”科技重大专项(编号: 2021DJ1901)资助