Failure analysis of the edge-notched beam test on fluid-exposed Berea Sandstone

Abstract

Injection of fluids during wastewater disposal and geologic carbon sequestration causes induced stress and changes in rock’s elastic and failure properties, such as elastic moduli and fracture toughness. An accurate understanding of such changes in the response requires modeling and analysis of fluid-induced changes in rock’s stress and deformation states for which core-scale mechanical loading tests are often employed. Using experiments and simulations of Single Edge Notched Beam (SENB) test on water-exposed and supercritical (sc) CO_2-exposed Berea sandstones, we quantify the effect of pore fluid on tensile crack propagation, spatial distributions of shear and tensile stresses, and fracture toughness and J-integral properties. We use Digital Image Correlation (DIC) to monitor the changes in local stress and deformation fields during crack initiation and propagation. A representative numerical simulation model of dynamic crack propagation under SENB loading is built using the extended finite element method. Results are analyzed using the stress path analysis to identify shear and tensile stress concentration regions, which provide precursory information for failure events during the test. Stress profiles along and across the growing crack are analyzed and compared with Irwin’s classical solutions to understand the impact of SENB loading. Evolution in stress intensity factor and crack length shows subcritical crack growth prior to Griffith-like failure at the structure scale.