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

威斯康星大学麦迪逊分校和西北大学的一个研究小组正在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。剪切带分析是一种数学描述的观察行为的材料，如岩石，其中他们的故障下施加的应力集中在一个狭窄的带，而不是均匀分布。在高孔隙度致密砂岩上进行真三轴试验，其中试样受到三个独立的、典型的不相等的主应力，模拟实际的现场条件。测试采用新的加载路径的每个主应力。这些路径，在实验室实验中前所未有的，旨在促进制定本构关系和比较剪切带分析的理论预测。该研究结果将首次系统地检验剪切带理论在全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野外观测和复杂地质力学和地球物理问题的数值模拟至关重要。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。这些材料的失效往往发生在窄带中，因此可以大大改变岩层捕获或传输流体的能力。这些狭窄的故障区域可能会减少穿过它们的流动，并干扰涉及流体注入（例如，用于二氧化碳封存或液体废物隔离）和流体提取（例如，用于油田操作）的应用中的流体循环。这些失效区域还可以提供用于增强沿它们的流动的管道沿着。这种流动会破坏旨在捕获流体的岩层，并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.