Hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures

Abstract

Thermo‐hydro‐mechanical‐chemical simulations at the pore scale are conducted to study the hydraulic sealing of siliciclastic rock fractures as contact zones grow driven by pressure dissolution. The evolving fluid‐saturated three‐dimensional pore space of the fracture results from the elastic contact between self‐affine, randomly rough surfaces in response to the effective confining pressure. A diffusion‐reaction equation controls pressure solution over contact zones as a function of their emergent geometry and stress variations. Results show that three coupled processes govern the evolution of the fracture's hydraulic properties: (1) the dissolution‐driven convergence of the opposing fracture walls acts to compact the pore space; (2) the growth of contact zones reduces the elastic compression of the pore space; and (3) the growth of contact zones leads to flow channeling and the presence of stagnant zones in the flow field. The dominant early time compaction mechanism is the elastic compression of the fracture void space, but this eventually becomes overshadowed by the irreversible process of pressure dissolution. Growing contact zones isolate void space and cause an increasing disproportion between average and hydraulic aperture. This results in the loss of hydraulic conductivity when the mean aperture is a third of its initial value and the contact ratio approaches the characteristic value of one half. Convergence rates depend on small‐wavelength roughness initially and on long‐wavelength roughness in the late time. The assumption of a characteristic roughness length scale, therefore, leads to a characteristic time scale with an underestimation of dissolution rates before and an overestimation thereafter.

A Review of Critical Conditions for the Onset of Nonlinear Fluid Flow in Rock Fractures

“…Many factors can affect the magnitude of permeability of fractured rock masses, including fracture length [28][29][30][31], aperture [32][33][34], surface roughness [35,36], dead-end [37], number of intersections [38,39], hydraulic gradient [40], boundary stress [41,42], anisotropy [43][44][45][46], scale [47][48][49][50], stiffness [51], coupled thermo-hydro-mechanical-chemical (HTMC) processes [52][53][54][55], and precipitation-dissolution and biogeochemistry [56]. The discrete fracture network (DFN) model, which can consider most of the above parameters, has been increasingly utilized to simulate fluid flow in the complex 2 Geofluids fractured rock masses [57][58][59][60], although it cannot model the aperture heterogeneity of each fracture [61][62][63].…”

Evolution of fracture normal stiffness due to pressure dissolution and precipitation

“…The pressure dissolution model is based on a closed-form approximation to a reaction-diffusion equation in a water-quartz environment for spherical contacts (Lehner and Leroy, 2004;Bernabé and Evans, 2007), extended to arbitrarily shaped contacts (Lang et al, 2015):…”

“…Building on previous work (Lang et al, 2015), the present study presents coupled hydro-mechanical-chemical simulations at the pore scale to assess changes in fracture normal stiffness under the effects of pressure solution and precipitation, for a water-quartz system. Specifically, instantaneous fracture closure curves are generated, for specific points in time during the dissolution and precipitation process, and related to changes in the rock surface morphology ( Figure 1).…”

Analytical Solutions for Water–gas Flow Through 3d Rock Fracture Networks Subjected to Triaxial Stresses

“…They reported that pure normal loading may not be the main reason for the fast closure of a fracture, and the damages of contact between the two walls of a fracture during normal loading play an important role. Lang et al 43 simulated the hydraulic sealing due to pressure solution in siliciclastic rock fractures. Their results show that under pressure solution, the contact zone grows and leads to flow channeling.…”