Hydraulic Transport Properties of Calcite Bearing Faults with Customized Roughness: Revisiting Hydro-Shear Stimulation Techniques

Abstract

Understanding fluid flow in rough fractures is of high importance to large scale geologic processes and to most anthropogenic geo-energy activities. Here, we present the work conducted by Acosta et al. (2020) regarding fluid transport experiments on Carrara marble fractures with a novel customized surface topography. Transmissivity (fracture permeability) measurements were conducted under normal stresses from 20 to 50 MPa and shear stresses from 0 to 30 MPa. An open-source numerical procedure was developed to simulate normal contact and fluid flow through fractures with complex geometries. It was validated towards experiments. Using it, we isolated the effects of roughness parameters on fracture fluid flow. Under normal loading, we find that i) the transmissivity decreases with normal loading and is strongly dependent on fault surface geometry ii) the standard deviation of heights (hrms) and macroscopic wavelength of the surface asperities control fracture transmissivity. Transmissivity evolution is non-monotonic, with more than 4 orders of magnitude difference for small variations of macroscopic wavelength and roughness. Experiments show that reversible elastic shear loading has little effect on transmissivity, it can increase or decrease depending on contact geometry and overall stress state on the fault. Irreversible shear displacement (up to 1 mm offset) slightly decreases transmissivity and its variation with irreversible shear displacements can be predicted numerically and geometrically at low normal stress only. Finally, irreversible changes in surface roughness (plasticity and wear) due to shear displacement result in a permanent decrease of transmissivity when decreasing differential stress. Generally, reduction of a carbonate fault’s effective stress significantly increases its transmissivity while inducing small shear displacements doesn’t. This highlights the need to reassess the hydro-shear stimulation technique in geo-energy activities, issue that is thoroughly discussed in this conference paper.