Investigation of Coupled Processes in Fractures and the Bordering Matrix via a Micro‐Continuum Reactive Transport Model

Abstract

In multi‐mineral fractured rocks, the altered porous layer on the fracture surface resulting from preferential dissolution of the fast‐reacting minerals can have profound impacts on subsequent chemical‐physical alteration of the fractures. This study adopts the micro‐continuum approach to provide further understanding of reactive transport processes in the altered layer (AL), and mass exchanges with the bordering matrix and fracture. The modeling framework couples the Darcy‐Brinkman‐Stokes (DBS) solver in COMSOL Multiphysics and the geochemical modeling capability of CrunchFlow. Three‐dimensional steady state simulations with systematically varied chemical‐physical parameters of the AL were performed to examine the impacts of individual factors and processes. Our simulation results confirm previous observations that dissolution of the fast‐reacting mineral (i.e., calcite) is largely controlled by diffusion across the AL. We also show that dissolution of the slow‐reacting mineral (i.e., dolomite), which controls AL development and fracture enlargement, increases with surface area and has a complex dependence on different local rate‐limiting processes. In particular, advection can result in evident spatial variations in the local dissolution rates of dolomite, although it does not affect the bulk chemistry significantly. The difference in the spatial patterns between simulations with and without advection in the AL is more noticeable in the locations with smaller apertures, with up to 20% difference in local reaction rates. Therefore, it is important to include a full depiction of advection, diffusion, and reactions for accurately capturing local dynamics that control long‐term fracture evolution.

Fe Oxidation and Species Distribution at the Rock–Fluid Interface of Marcellus Shale Reacted with Hydraulic Fracturing Fluid

“…Figure shows vertical profiles of the calcite volume fraction and local porosity at the location highlighted by the red line in Figure . With the porosity increase, permeability in the matrix increased, leading to non-negligible advective transport in the matrix that facilitated reactions . For an initial matrix porosity of 3%, the porosity increased to ∼18%, which corresponded to an increase in permeability for close to four orders of magnitude.…”

“…With the porosity increase, permeability in the matrix increased, leading to non-negligible advective transport in the matrix that facilitated reactions. 28 For an initial matrix porosity of 3%, the porosity increased to ∼18%, which corresponded to an increase in permeability for close to four orders of magnitude. For the initial matrix porosity of 20%, the porosity increases to 35%, resulting in an increase in permeability for over five orders of magnitude.…”

“…In this study, a microcontinuum reactive transport model was used to illustrate the mineral reaction front migration and test the impacts of matrix properties. The reactive transport model has been detailed in previous studies, ,− and the simulation setup for this study is described here.…”

Quantification of the Impact of Acidified Brine on Fracture-Matrix Transport in a Naturally Fractured Shale Using in Situ Imaging and Modeling

“…Flow and transport processes between fractures and matrix and host rock material have been quantitatively described with a range of numerical and analytical modeling approaches. Large fracture networks have been modeled with multiple interacting continua approaches (e.g., dual porosity, dual permeability), − or large discrete fracture networks where the fractures are explicitly defined. , Simulation of flow in a small number of fractures can be accomplished using explicit flow field modeling by solving the Navier–Stokes equation when fracture geometry can be constrained or approximated, , or using hybrid or microcontinuum approaches. , …”

Improved micro-continuum approach for capillary-dominated multiphase flow with reduced spurious velocity

“…Therefore, single-phase fluid dynamics modeling across the multiscale porous medium is well established within the micro-continuum framework, and is widely used in simulations of reactive flow in fractures and mineral precipitation. 35,[39][40][41][42] The multiphase micro-continuum DBS framework has recently modeled multiphase flows in a multiscale porous medium. Horgue et al 43 and Soulaine et al 14,18 proposed two-phase micro-…”