Collaborative Research: Use of Novel True Triaxial Tests and Shear Band Theory to Determine Failure Properties of Compactive Porous Sandstones

来自威斯康星大学麦迪逊分校和西北大学的一个研究小组将实验观察和剪切带分析相结合，以研究高孔隙度岩石的破坏特性。剪切带分析是对岩石等材料在施加应力作用下的破坏集中在一个窄带内而不是均匀分布的一种观察到的行为的数学描述。在高孔隙度致密砂岩上进行的真三轴试验中，测试样品受到三个独立且通常不相等的主应力，模拟实际现场条件。试验对每个主应力采用新的加载路径。这些路径在实验室实验中是前所未有的，旨在促进本构关系的制定，并与剪切带分析的理论预测进行比较。本研究的结果将首次系统地验证剪切带理论在各种应力条件下的适用性。更好地理解岩石力学行为及其与致密多孔砂岩破坏的关系，对于解释现场观测结果以及作为复杂地质力学和地球物理问题数值模拟的输入至关重要。其中包括地震力学、地下储存设施的设计、能源回收和二氧化碳的封存。这些物质的破坏往往发生在狭窄的范围内，因此会极大地改变岩层捕获或传输流体的能力。在涉及流体注入（例如二氧化碳封存或液体废物隔离）和流体提取（例如油田作业）的应用中，这些狭窄的故障区域可能会减少流经它们的流量，并干扰流体循环。这些破坏区也可以为沿其增强的流动提供管道。这样的水流会破坏用来捕获流体的岩层，阻止它们到达地表或与浅层地下水相互作用。

A research team from the University of Wisconsin-Madison and Northwestern University is combining experimental observations and shear band analysis in order to investigate the failure properties of high porosity rock. Shear band analysis is a mathematical description of the observed behavior of materials such as rocks by which their failure under applied stresses is concentrated in a narrow band rather than being uniformly distributed. True triaxial tests, in which test samples are subjected to three independent and typically unequal principal stresses simulating realistic field conditions, are being conducted on high-porosity compactive sandstones. The tests employ novel loading paths for each of the principal stresses. These paths, unprecedented in laboratory experiments, are designed to facilitate formulation of constitutive relations and comparison with the theoretical predictions of shear band analysis. The results of this research will provide the first systematic test of the applicability of shear band theory for the full range of stress conditions.A better understanding of rock mechanical behavior and its relation to failure of compactive porous sandstones is essential for interpreting field observations and as input for numerical simulations of complex geomechanical and geophysical problems. These include earthquake mechanics, design of underground storage facilities, energy recovery and sequestration of carbon dioxide. Failure in these materials tends to occur in narrow bands and therefore can drastically alter the ability of the rock formation to trap or transmit fluids. These narrow zones of failure may reduce flow across them and interfere with fluid circulation in applications involving fluid injection (e.g. for carbon dioxide sequestration or liquid waste isolation) and fluid extraction (e.g. for oil field operations). These failure zones can also provide conduits for enhanced flow along them. Such flow can disrupt rock formations intended to trap fluids and prevent them from reaching the surface or interacting with shallow groundwater.