Modeling Coupled Reactive Transport Through Fault Zones: A Critical Review

Fault zones significantly influence the migration of fluids in the subsurface and can be important controls on the local as well as regional hydrogeology. Hence, understanding the evolution of fault porosity/permeability is critical for many engineering applications (like geologic carbon sequestration, enhanced geothermal systems, groundwater remediation, etc.), as well as geological studies (like sediment diagenesis, seismic activities, hydrothermal ore deposition, etc.). The highly heterogeneous pore structure of fault zones along with the wide range of hydrogeochemical heterogeneity that a fault zone can cut through make conduit fault zones a dynamic reactive transport environment that can be highly complex to accurately model. In this article, we present a critical review of the possible ways of modeling reactive fluid flow through fault zones, particularly from the perspective of chemically driven “self-sealing” or “self-enhancing” of fault zones. Along with an in-depth review of the literature, we consider key issues related to different conceptual models (e.g., fault zone as a network of fractures or as a combination of damaged zone and fault core), modeling approaches (e.g., multiple continua, discrete fracture networks, pore-scale models), and kinetics of water/rock interactions. Inherent modeling aspects related to dimensionality (e.g., one-dimensional vs. two-dimensional) and the dimensionless Damköhler number are explored. Moreover, we use a case study of the Little Grand Wash Fault zone from central Utah as an example in the review. Finally, critical aspects of reactive transport modeling like multiscale approaches and chemomechanical coupling are also addressed in the context of fault zones.