湖相细粒沉积岩颗粒微观力学特征及类型划分

Micromechanical characteristics and classification of the grains of lacustrine fine-grained sedimentary rocks： A case study of shales in the 7 member of the Upper Triassic Yanchang Formation， Ordos Basin

解馨慧 邓虎成 胡蓝霄 李勇 毛金昕 刘佳杰 张鑫 李柏洋

Xinhui Xie Hucheng Deng Lanxiao Hu Yong Li Jinxin Mao Jiajie Liu Xin Zhang Boyang Li

细粒沉积岩蕴藏着丰富的油气资源，为了研究细粒沉积岩颗粒微观结构及力学特征，以鄂尔多斯盆地上三叠统延长组7段细粒沉积岩为例，开展了扫描电镜观察和纳米压痕实验分析，据此研究细粒沉积颗粒的几何特征和微观力学性质。研究认为：用粒径、扁平度、棱角性、硬度和弹性模量5个特征参数，可将细粒沉积岩划分为粒度+棱角型、扁平度+棱角型、扁平度+棱角+弹性模量+硬度型、弹性模量+硬度型、棱角+弹性模量+硬度型和粒度+棱角+弹性模量型6种主要颗粒类型；接着，根据颗粒类型的相对含量，进一步将颗粒类型划分为5种组合类型；最后，分析了细粒沉积颗粒类型与矿物类型之间的耦合关系。细粒沉积岩颗粒微观分类方案的建立，有助于理解细粒沉积岩微观结构特征，预测地质“甜点”空间分布，对细粒沉积岩的油气资源评价和效益开发具有重要的理论和科学意义。

Fine-grained sedimentary rocks contain abundant hydrocarbon resources. To examine the microscopic structural and micromechanical characteristics of their grains， we explore such rocks in the 7 member of the Upper Triassic Yanchang Formation （also referred to as the Chang 7 Member） in the Ordos Basin. Using scanning electron microscopy （SEM） and nanoindentation experiments， we delve into the geometric characteristics and micromechanical properties of the grains of these rocks. The results indicate that based on five characterization parameters， namely grain size， flatness， angularity， hardness， and modulus of elasticity， the fine-grained sedimentary rocks in the Chang 7 Member can be categorized into six major grain types： grain size and angularity predominating； flatness and angularity predominating； flatness， angularity， modulus of elasticity， and hardness predominating； modulus of elasticity and hardness predominating； angularity， modulus of elasticity， and hardness predominating， and grain size， angularity， and modulus of elasticity predominating. Five types of grain assemblages can be further identified based on the relative contents of the six types of grains. Additionally， the coupling relationships between the grain types and mineral types of the fine-grained sedimentary rocks are determined. The proposed scheme for microscopic grain classification of fine-grained sedimentary rocks assists in understanding the microscopic structural characteristics of fine-grained sedimentary rocks and predicting the spatial distributions of geological sweet spots， thus holding great theoretical and scientific significance for the hydrocarbon resource assessment and efficient hydrocarbon exploitation of fine-grained sedimentary rocks.

10.11743/ogg20240413