The project supported graduate students working on experimental and numerical modeling of rock fracture, with the following objectives: (a) perform laboratory testing of fluid-saturated rock; (b) develop predictive models for simulation of fracture; and (c) establish educational frameworks for geologic sequestration issues related to rock fracture. These objectives were achieved through (i) using a novel apparatus to produce faulting in a fluid-saturated rock; (ii) modeling fracture with a boundary element method; and (iii) developing curricula for training geoengineers in experimental mechanics, numerical modeling of fracture, and poroelasticity.4
EXECUTIVE SUMMARYCarbon storage technologies offer a means of reducing CO 2 emissions and mitigating climate change. These new technologies will require a workforce educated in geomechanics. To this end, the project supported graduate students working on geomechanical simulation of fluid-driven fractures with the following objectives:1. Measure elastic and inelastic response of fluid-saturated rock 2. Develop predictive models for simulation of fluid-driven fractures 1. Deformation and damage of a porous, fluid-saturated rock under drained and undrained conditions were investigated. A plane-strain apparatus was modified in order to conduct tests with water-saturated rock specimens and to measure the pore pressure within the rock. Transducers within the apparatus were calibrated at the various loading states and the compliances of the system were determined. Plane strain compression and conventional triaxial compression tests were performed at different confining pressures under air-dry, drained, and undrained conditions. The behavior of the rock was evaluated within the framework of linear poroelasticity. Dilatant hardening and contractant softening was investigated from undrained experiments, where pore pressure was measured throughout the failure process. The parameters that govern the inelastic deformation of fluid-saturated rock, i.e. dilatancy angle β, friction coefficient µ, poroelastic coefficient K eff , shear modulus G, and inelastic hardening modulus H, were calculated for the drained response. The constitutive model predicts the undrained inelastic response of the rock fairly well, almost up to the peak load if compared with the undrained test that had the same effective mean stress at the onset of inelasticity. Knowledge of dilatant hardening behavior is essential for the proper assessment of underground structures, such as long-term CO 2 storage facilities.2. The boundary element method (BEM) is based on the boundary integral representation equivalent to the differential equation governing a specific physical problem. Such representation is possible when the so-called fundamental solution of the governing differential equation is available. The fundamental solution satisfies the differential equation everywhere in the domain except one point where it is singular. In the case of linear isotropic and homogeneous elasticity, the fundamental solution...