Crack propagation and stress evolution in fluid-exposed limestones

Abstract

Crack initiation and propagation in rocks exposed to injected fluids must be understood better for sustainable sequestration and geo-energy applications. One specific challenge is the characterization of the fluid-induced changes in the stress state and mechanical properties when multiple cracks grow and interact with each other. We conduct crack propagation tests on brine-exposed and supercritical \(\hbox {CO}_2\)-exposed Indiana limestone samples under uniaxial compression conditions. By analyzing the displacement and strain fields using Digital Image Correlation and the first arrival time and amplitude of the transmitted shear waves, we characterize the effect of crack propagation and interaction events on stress and toughness. We build 3-D simulation models of crack propagation under uniaxial compression using the extended finite element method to analyze the 3-D stress and deformation fields in high resolution. We quantify the evolution of crack-tip’s J-integral value with the crack length for wing cracks and shear cracks in samples exposed to mixtures of brine and supercritical \(\hbox {CO}_2\) at subsurface conditions. Experimental and simulation results are synthesized to gain insights into crack propagation, shear-to-tensile failure transition, and interaction of cracks in fluid-exposed rocks. Crack length and J-integral analysis quantifies the impact of fluid exposure on the fracture toughness.