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气体压裂作为一种新型的无水压裂技术,对页岩气开采具有重要意义。为探究不同层理方向页岩气体压裂破坏机制,以彭水黑色页岩为试样,首先系统地分析其力学各向异性特征,并利用自行改造组装的高压气体压裂系统分别对轴向平行层理页岩和轴向垂直层理页岩开展气体压裂试验,研究层理方向对页岩的变形、强度、声发射特征和破坏形态的影响,揭示页岩气压致裂破坏的机制,讨论不同加载方式下层理效应对页岩破坏强度的影响。研究表明:(1)黑色页岩的拉、压力学特征受层理方向影响明显,平行层理面加载页岩与垂直层理面加载页岩的抗压强度、抗拉强度、弹性模量、剪切模量之比分别为:138.22%,44.37%,169.17%,173.27%,泊松比受层理影响小。页岩平行层理面加载时,容易沿层理面产生张拉破坏;垂直层理面加载时,在层理本身发生剪切滑移破坏。(2)轴向垂直层理面页岩的破坏气压、破坏时间分别是轴向平行层理面页岩的4.2和3.35倍,前者沿层理弱面发生拉伸破坏,后者以拉伸破坏为主,也有剪切破坏发生,其破裂面凹凸起伏明显。所有变形曲线呈非线性变化,垂直层理面页岩的变形大,其变形曲线出现异常拐点,侧向变形曲线呈下凹趋势;轴向平行层理试样的变形曲线相对光滑,侧向变形曲线呈上凹趋势。AE能率反映了轴向垂直层理页岩破坏更加剧烈。(3)加载方式对页岩强度的层理效应系数影响显著,影响最大的是气体压裂试验,最小的是单轴压缩试验。
As a new type of waterless fracturing technology, gas fracturing is of great significance for shale gas exploration. In order to explore the fracturing mechanism of shale gas in different bedding directions, the Pengsha black shale was used as a sample to systematically analyze its mechanical anisotropy characteristics. By utilizing the high-pressure gas fracturing system that was self-rebuilt and assembled, The gas fracturing tests were conducted on the parallel stratified shale and the axial vertical stratified shale to study the effect of bedding orientation on the deformation, intensity, acoustic emission characteristics and failure modes of shales, revealing the mechanism of shale gas fracturing failure, The effect of different layer loading on shale failure intensity is discussed. The results show that: (1) The tensile and compressive characteristics of black shale are significantly affected by bedding direction. Compressive strength, tensile strength and elastic modulus of shale loaded with shale and vertical bedding plane in parallel bedding plane are higher, The shear modulus ratios were 138.22%, 44.37%, 169.17% and 173.27%, respectively. The Poisson’s ratio was less affected by bedding. When the parallel shale plane of shale is loaded, it is easy to cause tensile failure along the bedding plane. When the vertical bedding plane is loaded, shear-slip damage occurs in the bedding itself. (2) The failure pressure and failure time of the shale in the axial vertical bedding plane are respectively 4.2 and 3.35 times that of the axial parallel bedding shale. The former is tensile and destructive along the weak face of the layer, and the latter is damaged by tensile Mainly, there are shear damage occurred, the rupture surface bumpy obvious. All of the deformation curves showed a nonlinear change. The shale deformation of the vertical bedding plane was large, and the deformation curve showed an abnormal inflection point, the lateral deformation curve showed a concave tendency. The deformation curve of the axial parallel bedding sample was relatively smooth and the lateral deformation Curve showed a concave trend. The AE energy rate reflects the more severe vertical shale shale destruction. (3) The loading method has obvious influence on the bedding effect coefficient of shale strength, the most influential is the gas fracturing test, the smallest is the uniaxial compression test.