Hydraulic Transport Through Calcite Bearing Faults With Customized Roughness: Effects of Normal and Shear Loading

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 conducted fluid transport experiments on Carrara marble fractures with a novel customized surface topography. Transmissivity measurements were conducted under mechanical loading conditions representative of deep geothermal reservoirs (normal stresses from 20 to 70 MPa and shear stresses from 0 to 30 MPa). A numerical procedure simulating normal contact and fluid flow through fractures with complex geometries was validated toward 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 and (ii) the standard deviation of heights (hRMS) and macroscopic wavelength of the surface asperities control fracture transmissivity. Transmissivity evolution is nonmonotonic, with more than 4 orders of magnitude difference for small variations of macroscopic wavelength and hRMS roughness. 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 increases its transmissivity while inducing small shear displacements does not.

Competing Controls of Effective Stress Variation and Chloritization on Friction and Stability of Faults in Granite: Implications for Seismicity Triggered by Fluid Injection

“…The transition from net compaction to dilation with decreasing effective confining stress indicates that a lower effective confining stress can reduce cataclasis and its impact on grain-size reduction by weakening the effect of compaction and thus accentuating fault dilation, contributing to an elevated porosity, and thereby changing the velocity dependence of friction. This observation is consistent with the results of Acosta et al (2020Acosta et al ( , 2022 in terms of the permeability evolution of calcite bearing faults. The fault shear induces dilatancy at low effective stress but contributes to more compaction at high effective stress.…”

Transient evolution of permeability and friction in a slowly slipping fault activated by fluid pressurization

“…Friction and permeability of faults are known to change during slip due to the rearrangement and destruction of asperities. Permeability may increase due to shear induced dilation 6 or decrease as a result of gouge formation 35 or irreversible changes in surface roughness 36 . During slip, frictional strength is affected by the state of the contact area between the displacing surfaces 4 , 32 , 33 .…”

From Fluid Flow to Coupled Processes in Fractured Rock: Recent Advances and New Frontiers

“…These have the disadvantage of being highly idealized, planar features but have the advantage of having controllable surface properties that permit repeatable property investigations. In many cases, the surfaces are polished with a specified grit giving a uniform level of roughness (e.g., Noiriel & Deng, 2018), or the surfaces can be milled to give structured roughness (e.g., Acosta et al, 2020). These studies are beneficial in comparing different rock types and mineralogy (Fang et al, 2018).…”