Co-Evolution of Fracture Permeability and Friction in Rocks From the EGS Collab Experiment 1 Site

Fracture permeability is a dynamic property under conditions of varying stress and responds to fluid overpressures applied during hydraulic stimulation. We use samples from the SIGMA-V site (Sanford Underground Research Facility (SURF), SD) to measure the co-evolution of fracture permeability and friction throughout phases of the seismic cycle. This is accomplished a slide-hold-slide and pore pressure stepping experiments completed in double direct shear. Fracture reactivation results in permeability enhancement only after sufficiently long interseismic repose periods. The magnitude of permeability increase from each reactivation, following the long hold periods, is critically dependent on the degree of fracture healing achieved in each pre-slip hold period. Shear dilation and permeability enhancement only results following a threshold repose period. Permeability enhances continuously with each pressure step with the highest permeability increase rate being with the first reactivation event. Our study establishes a direct linkage between fracture permeability and friction evolution throughout the seismic cycle and hydraulic shear, which applies across different fracture surface roughnesses.