Fluid transport properties and friction constitutive parameters of fractures are key factors in mediating energy production and safety of waste storage within the Earth’s crust. Together, they control permeability, influence recovery rates of water, energy and fuels and impact the longevity of waste isolation. In our current work, we have developed experimental and analytical methods to study the evolution of flow and elastodynamic properties in fractured rocks undergoing shear and effective stress perturbations. Here, we propose to leverage the cross-disciplinary collaboration that we have developed under the current project and expand on the successful techniques generated in the past few years. Our goals include understanding the fundamental mechanisms that govern fluid flow, friction, and elastic properties of fractured rock. Specifically, we will conduct experiments to: (I) decouple the influence of fracture aperture distribution and roughness from unclogging on the elastic and flow properties, explore these behaviors for (II) shear-reactivation of fractures, and develop complex analyses that: (III) assimilate these data, illuminate key mechanistic feedbacks and address upscaling of our results to field scale. The work we propose addresses societally-relevant issues such as induced seismicity, probes frontier scientific problems related to nonlinear elasticity and the coupling between transport and elastodynamic properties and utilizes machine learning techniques to maximally illuminate correlations from the mechanism-rich geophysical data. Our proposed plan includes unusually well-controlled lab experiments to measure friction and flow. We will use new techniques including synchrotron X-ray computed tomography of fracture properties and will combine time-dependent microstructural and ultrasonic imaging of fractures under dynamic stressing to probe causative mechanisms linking permeability and stiffness. The primary elements of our proposed work include: 1) active and passive ultrasonic measurements to determine the elastodynamic response of fractured samples and simulated faults, 2) permeability studies of fractured samples subject to elastic loading and inelastic deformation, 3) measurement of friction constitutive properties under steady state shear and during stick-slip sliding, and 4) physics-based and data-driven modeling to predict hydraulic properties and controls on induced seismicity. The laboratory program will include a subset of simple tests with isolated measurement of one variable, but the majority of our work will focus on coupled processes as
revealed by simultaneous monitoring of the evolution of elastodynamic properties, permeability, and friction constitutive behavior during elastic loading and inelastic deformation. We will follow a systematic approach by studying both intact rock and comparing it to well-characterized fractures (with and without infilling) under a range of stress and saturation conditions. The role of microstructure and shear fabric will be illuminated by our laboratory data and also by studies that involve synchrotron X-ray imaging.