Reactive transport modelling in dual porosity media

Abstract

A pore-scale model is applied to investigate reactive mass transport in dual porosity media. We use a framework based on the Stokes-Brinkman flow to model reactive flow in porous media with multiscale features. The numerical method involves fluid flow in pore space as well as flow in the rock matrix with microporosity. Reactive transport simulations are performed in a simple fractured porous medium and carbonates. The results are compared against the predictions in regimes of Stokes flow where the microporosity of rocks is excluded. In the fractured porous medium, wormholing dissolution is observed while face dissolution occurs when microporosity is ignored for the same Péclet and Damköhler numbers. This is explained by the penetration of reactive fluid flow through the rock matrix by Stokes-Brinkman flow. Reactive transport is also simulated in a Ketton carbonate. We compare the simulation results with published dynamic micro-CT imaging experiments for dissolution. Inclusion of microporosity leads to more accurate predictions of the pore space structures. The effect of microporosity on pore structure and permeability-porosity relationships is also explored in the carbonate samples with a range of matrix permeability values. The results show that the impact of microporosity on rock permeability variations is dependent on the ratio of matrix permeability to the overall permeability of the porous medium. Greater errors in permeability predictions are observed in the cases with higher ratios. This paper illustrates the significance of microporosity in reactive transport and improves the understanding of reactive transport in porous domains with multiscale features.