Abstract:

The talk will include a tutorial on modeling reactive transport.

Fractures are ubiquitous features in porous media and exert a strong control on subsurface flow, mixing, and reactive transport by introducing preferential pathways and strong velocity contrasts that fundamentally reorganize how fluids spread, mix, and react. Despite their recognized importance, the mechanisms by which fracture connectivity controls the spatial localization of reactions and the emergence of reaction hotspots at the pore scale remain incompletely understood.

Here, we investigate how increasing fracture connectivity reorganizes pore-scale flow, mixing and reaction dynamics using direct numerical simulations of flow coupled with reactive random walk particle tracking. We consider a bimolecular irreversible reaction occurring during the displacement of one reactant by another in two-dimensional heterogeneous porous media with progressively developed fracture networks. Reaction localization is quantified using a time-integrated product-based formulation that captures cumulative reaction activity and enables robust identification of persistent reaction hotspots.

Our results show that increasing fracture connectivity shifts transport from matrix-dominated pathways toward fracture-controlled preferential flow, leading to higher particle tortuosity, elongated mixing interfaces, and a redistribution of reaction activity across space. In unfractured media, reactions are concentrated in localized high-intensity pore-scale hotspots associated with sharp concentration gradients. As fracture density increases, reaction activity becomes more spatially distributed along fracture-aligned pathways, forming elongated reaction zones without increasing peak reaction intensity. At the global scale, fractured systems exhibit faster early-time product formation due to enhanced mixing and reactant contact, but all configurations converge toward similar asymptotic product masses. This convergence reflects faster reactant depletion and earlier reaction extinction in fractured systems, indicating that fractures primarily accelerate reaction kinetics rather than increase total reaction yield.

BIO: Dr Perez earned his PhD in Civil and Environmental Engineering in 2019 from the Polytechnic University of Catalonia (Barcelona, Spain), graduating with summa cum laude honors. Before joining Oregon State University, he worked as Assistant Research Professor at the Desert Research Institute (Reno, NV), following a postdoctoral associate position from 2019 to 2021.