针对页岩受力脆性破坏的力学机理认识不清的问题,在分析层理页岩特征的基础上,应用岩石断裂力学理论,结合广义胡克定律,建立了纵向力学非均质性的层理页岩脆性破裂模型,分析了层理页岩破裂模式的主要影响因素。研究表明:层理页岩的脆性破裂模式主要分为剪切破坏和拉伸破坏,外界应力条件下硬岩岩层易发生拉伸破坏,软岩岩层易发生剪切破坏;岩层杨氏模量越大、泊松比越小,岩层越易发生拉伸破坏,反之易发生剪切破坏;最小水平主应力越大、水平主应力差越小,越倾向于发生剪切破坏;页岩层间力学性质的差异性是页岩发生脆性破裂的根本原因,页岩层间差异越大,岩石脆性特征越强,越有利于压裂。该研究可为页岩脆性评价和水力压裂方案制订提供理论指导。
To address the problem of poorly understood mechanical mechanism of stress-caused brittle failure in shale, the brittle fracture model of laminated shale with longitudinal mechanical inhomogeneity was established by applying the theory of rock fracture mechanics and combining it with generalized Hooke's law on the basis of analyzing the characteristics of laminated shale, and the main influencing factors of the fracture mode of laminated shale were analyzed. The study shows that the fracture modes of laminated shale are mainly divided into shear failure and tensile failure, hard rock formations are prone to tensile failure, while soft rock formations are prone to shear failure under external stress conditions; the larger the Young's modulus of the rock formation and the smaller the Poisson's ratio, the more prone the formation is to tensile failure and vice versa; the larger the minimum horizontal principal stress and the smaller the horizontal principal stress difference, the more prone the formation is to shear failure; the variability of mechanical properties between shale layers is the fundamental reason for the brittle fracture of shale; the greater the variability between shale layers, the more brittle the rock is, and the more favorable it is for fracturing. This study can provide theoretical guidance for shale brittleness evaluation and hydraulic fracturing scheme development.
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