Soft Matter and Complex Systems Seminar

Reactive transport and dissolution in porous media is a fundamental process in many earth systems, including for example weathering and diagenesis of rocks, hydrocarbon recovery and CO2 sequestration. Reactive transport is a complex, nonlinear process: the transport and reactive properties and hence the rate and spatial distribution of fluid flow and reaction strongly depend on the microstructure, which in turn keeps evolving in time with the reaction. Further complexity arises due to the fact that in most geological conditions the subsurface medium is under large stress and dissolution of the solid matrix causes two simultaneous, competing effects: void space enlargement due to chemical deformation and mechanical compaction due to mechanical weakening.
We study reactive transport and permeability evolution in a stressed porous media, using mechanistic pore-scale model and simulate flooding of a sample under fixed confining stress. The simulations show that increasing the stress inhibits the permeability enhancement, increasing the injected volume required to reach a certain permeability, in agreement with recent experiments. This behavior is explained by stress concentration downstream, in the less dissolved (hence stiffer) outlet region. As this region is also less conductive, even its small compaction has a strong bottleneck effect that curbs the permeability. The results also elucidate that the impact of stress depends on the dissolution regime and Damköhler number, where interestingly at the wormholing regime stress reduces transport heterogeneity and promoting wormhole competition.