Mineral Precipitation in Fractures: Using the Level‐Set Method to Quantify the Role of Mineral Heterogeneity on Transport Properties. Issue 5 (22nd May 2019) - Jones, Trevor A.
Abstract: We used a depth‐averaged reactive transport model to simulate transport of a supersaturated fluid through fractures and considered two models of precipitation‐induced surface alterations: (1) a localized 1‐D alteration of the surface and (2) a 3‐D alteration of the surface using the level‐set method. Comparing simulation results to a simple analytical solution for precipitation in a homogeneous (aperture and mineralogy) fracture demonstrated both models predict the alteration process reasonably well. However, comparing simulation results from both models to results from a recent experimental study of precipitation in a mineralogically heterogeneous fracture (Jones & Detwiler, 2016, https://doi.org/10.1002/2016GL069598 ) demonstrated that the ability of the 3‐D model to predict mineral growth across the aperture and in the fracture plane leads to much better agreement with the experimental observations. To quantify the role of reaction kinetics on the precipitation process, we ran additional simulations using the 3‐D evolution model for reaction rate constants ranging over 3 orders of magnitude. When the kinetics were much faster than the advective flux through the fracture, precipitation was focused near the inlet, which led to a transition from preferential flow near the inlet to more uniform flow near the outlet. When reaction kinetics were slow relative to advection, reaction sites grew uniformly throughout the fracture leading to the eventual formation of a single preferential flow path from inlet to outlet. Regardless of reaction rate, localization of precipitation reactions led to significant increases (3 to 20 times) in the time scale required to seal the fracture relative to a mineralogically homogeneous fracture. Key Points: Precipitation leads to three‐dimensional fracture surface alterations Lateral growth of reactive minerals focuses flow into regions with limited reactive surface area Local mineralogy affects transport alterations at the fracture scale