鄂尔多斯盆地东缘下石盒子组砂−泥薄互层岩石力学特性  

Mechanical properties of thinly interbedded sandstone-mudstone rocks in Lower Shihezi Formation from eastern Ordos Basin

作　　者：丛日超 杨睿月 胡家晨[1,2] 夏志浩 黄中伟 李根生[1] 井美洋[1] CONG Richao;YANG Ruiyue;HU Jiachen;XIA Zhihao;HUANG Zhongwei;LI Gensheng;JING Meiyang(State Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing 102249,China;CNOOC Energy Development Co.,Ltd.,Engineering Branch,Tianjin 300450,China)

机构地区：[1]中国石油大学(北京)油气资源与工程全国重点实验室,北京102249 [2]中海油能源发展股份有限公司工程技术分公司,天津300450

出　　处：《煤炭学报》2025年第3期1668-1682,共15页Journal of China Coal Society

基　　金：国家自然科学基金面上资助项目(52274014)。

摘　　要：阐明薄互层岩石力学性质是研究薄互层裂缝扩展规律和开展水力压裂方案设计的基础。然而,常规岩石力学实验难以精细表征薄互层岩石层间力学性质。针对上述问题,采用点矩阵纳米压痕、高分辨率扫描电镜和能量色散光谱技术(SEM-EDS)精细表征了鄂尔多斯盆地东缘下石盒子组砂-泥薄互层取心岩石中砂岩层与泥岩层的矿物特征及力学差异、分析了典型矿物的压痕特征和开裂模式;在此基础上通过巴西劈裂实验研究了倾角、夹层/弱面对砂-泥薄互层岩石抗拉强度和断裂模式的影响。研究结果表明:①砂岩层石英、长石、赤铁矿和方解石等脆性矿物含量较高,平均弹性模量为51.4GPa,平均硬度为1.74GPa,平均断裂韧性为5.4MPa·m^(0.5),分别是泥岩层的1.10、1.14、1.10倍。②三棱锥玻式金刚石压头条件下单矿物压痕近似呈等边三角形,多矿物压痕主要受软矿物影响,易于向软矿物相一侧压入。③石英、赤铁矿/方解石、层状硅酸盐矿物的压痕尺寸依次增大,脆性矿物压痕易于产生剪切裂纹和径向裂纹,延性矿物压痕易于产生材料剥落。④随倾角增加(0°~90°),砂-泥薄互层岩石巴西劈裂抗拉强度逐渐降低,破坏易沿着夹层/弱面产生;倾角从0°~90°的变化过程是砂-泥薄互层岩石的破坏模式由拉伸主导-剪切主导-拉伸主导的转变过程。研究区下石盒子组砂-泥薄互层岩石非均质性和各向异性显著,矿物组成及其力学性质差异是导致薄互层层间地质力学差异的重要因素。Mechanical properties of thinly interbedded rocks are fundamental for investigating the crack propagations and designing hydraulic fracturing treatments in multi-layered formations.However,conventional geomechanical tests face challenges in precisely characterizing the mechanical properties of individual interlayers.For the issues mentioned above,the grid nanoindentation,high-resolution scanning electron microscopy assist with energy-dispersive spectroscopy(SEM-EDS)techniques are employed to finely characterize the differences in mineral features and mechanical properties between the sandstone layer and mudstone layer within the thinly interbedded sandstone-mudstone core rocks that collected from the Lower Shihezi Formation in the eastern Ordos Basin.Furthermore,the indentation features and cracking patterns of typical minerals are analyzed.On this basis,the impact of inclination angle and interlayer/weak interface on the tensile strength and fracture pattern of the thinly interbedded sandstone-mudstone rocks is investigated through Brazilian splitting tests.Results indicate that①the sandstone layer exhibits the higher mechanical strength due to the higher content of brittle minerals such as quartz,feldspar,hematite,and calcite,with an average Young's modulus of 51.4 GPa,average hardness of 1.74 GPa,and average fracture toughness of 5.4 MPa∙m^(0.5),which are 1.10 times,1.14 times,and 1.10 times than that of mudstone layer,respectively.②When using a three-sided pyramid Berkovich diamond indenter,the indenta-tion of a single mineral exhibits an approximate equilateral triangle shape.In the case of multiple minerals,the indentation is primarily influenced by the softer mineral phase,making it easier to press into the softer mineral phase.③The indenta-tion sizes of quartz,hematite/calcite,and phyllosilicate minerals increase sequentially.Moreover,indentations on brittle minerals are prone to generate shear and radial cracks,while indentations on ductile minerals are more likely to produce chippings.④As the

关 键 词：薄互层岩石 点矩阵纳米压痕 SEM-EDS 压痕形貌 巴西劈裂 

分 类 号：P618[天文地球—矿床学]