Fracture sealing by mineral precipitation: The role of small‐scale mineral heterogeneity

Abstract

Fractures are often leakage pathways for fluid in low‐permeability rocks that otherwise act as geologic barriers in the subsurface. Flow of fluids in chemical disequilibrium with fracture surfaces can lead to mineral precipitation and fracture sealing. To directly evaluate the role of small‐scale mineral heterogeneity on mineral precipitation, we measured CaCO3 precipitation in a transparent analog fracture that included randomly distributed small‐scale regions of CaCO3 on one of the borosilicate surfaces. Steady flow of a well‐mixed CaCl2‐NaHCO3 solution ( log(ΩnormalCaCO3) = 1.44) resulted in significant mineral precipitation during the 82 day experiment. Localized mineral precipitation reduced flow within regions of the fracture, but small‐scale reaction‐site heterogeneity allowed preferential flow to persist through pathways that contained 82% less area of CaCO3 regions than the fracture‐scale average. This resulted in a significant reduction in measured precipitation rate; excluding these effects results in more than an order‐of‐magnitude underestimation of fracture sealing timescales.

Mineral Precipitation in Fractures: Using the Level‐Set Method to Quantify the Role of Mineral Heterogeneity on Transport Properties

“…To assess the potential importance of representing surface evolution as a 3‐D process, we compared simulation results using the 1‐D vertical growth model and the 3‐D level‐set method for the same initial fracture. To further assess the ability of the different modeling approaches to predict fracture alteration in heterogeneous fractures, we reproduced conditions from a mineral precipitation experiment in a transparent rough‐walled fracture (Jones & Detwiler, ). During this experiment, a supersaturated CaCO 3 solution ( = 27.5) was injected into a 15 × 15 cm at 0.5 ml/min.…”

“…Experimental measurement of the CaCO 3 distribution at early ( t ∗ = 0.1) and late time ( t ∗ = 1.3) from the experiment presented in Jones and Detwiler (). The measurement highlights the lateral growth of CaCO 3 throughout the experiment.…”

“…To do this, we simulate dissolved ion transport using a reactive transport model and model the precipitation process using (1) a 1‐D vertical growth surface alteration method (e.g., Detwiler & Rajaram, ; Hanna & Rajaram, ; Szymczak & Ladd, ) and (2) a 3‐D level‐set surface alteration method. To better understand the effects of three‐dimensional growth on reactive transport, we compare the results from (1) and (2) to recent experiments of precipitation in a heterogeneous fracture (Jones & Detwiler, ). In addition, we quantify the influence of different transport conditions on the evolution of reactive transport in heterogeneous fractures and demonstrate the inherent scale dependence of the mineral precipitation process.…”

Dissolution and precipitation of fractures in soluble rock

“…The measured flow through the fracture deviates from idealized Navier-Stokes flow, but the deviation has only a small effect on the evolution of permeability on the macro-scale. Jones and Dogwiler (2016) used two glass plates with rough surface, which where seeded with isolated regions of calcite.…”

Experimental postseismic recovery of fractured rocks assisted by calcite sealing

“… Mechanical time‐dependent recovery of microscale cracks by backsliding on wing crack geometries [ Brantut , ]. Microscale pressure solution processes accompany the backsliding. “Self‐healing”—sometimes called “healing,” not to be confused with the term healing for large‐scale restrengthening or recovery—involves surface energy‐driven closure of microscale cracks [e.g., Brantley et al , ; Brantley , ]. Sealing by mineral precipitation, resulting in fracture sealing that often consist of calcite or quartz (experiments by, e.g., Lee and Morse [], Morrow et al [] Dobson et al [], and Jones and Detwiler []). Deviatoric stress does not directly influence this mechanism, but deviatoric stress may indirectly cause fracture opening or closure. Fracture closure by pressure solution creep.…”