Reactive transport under stress: Permeability evolution in deformable porous media

Abstract

We study reactive transport in a stressed porous media, where dissolution of the solid matrix causes two simultaneous, competing effects: pore enlargement due to chemical deformation, and pore compaction due to mechanical weakening. We use a novel, mechanistic pore-scale model to simulate flooding of a sample under fixed confining stress. Our 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. We explain this behavior 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.Our results also elucidate that the impact of stress depends on the dissolution regime. Under wormholing conditions (slow injection, i.e. high Damkohler number, Da), the development of a sharp dissolution front and high porosity contrast accentuates the bottleneck effect. This reduces transport heterogeneity, promoting wormhole competition. Once the outlet starts eroding, the extreme focusing of transport and hence dissolution-characteristic of wormholing-becomes dominant, diminishing the bottleneck effect and hence the impact of stress at breakthrough. In contrast, at high flow rates (low Da), incomplete reaction upstream allows some of the reagent to traverse the sample, causing a more uniform dissolution. The continuous dissolution and its partial counteraction by compaction at the outlet provides a steady, gradual increase in the effect of stress. Consequently, the impact of stress is more pronounced at high Da during early stages (low permeability), and at low Da close to breakthrough. Our work promotes understanding of the interplay between dissolution and compaction and its effect on the hydromechanical property evolution, with important implications for processes ranging from diagenesis and weathering of rocks, to well stimulation and carbon geosequetration.This further enhances their conductivity relative to other, less conductive regions, leading eventually to runaway permeability increase [12,4,18,39].In many cases, for instance in the subsurface, the medium is under appreciable stress, such that dissolution ("chemical deformation") also induces mechanical deformation. Chemomechanical deformation and the coupled changes in the transport and mechanical properties is key in many applications, such as enhanced energy recovery and carbon geosequestration [35,26,11,32,44,7]. A large body of literature exists on rough fractures, due to their importance, e.g. dominance of fracture flow, and their quasi two-dimensional (2-D) nature, which simplifies experimental setup and imaging as well as numerical simulations [e.g. 22, 14, 15, 19, 2]. Relatively fewer works addressed porous media such as soils [8] and rocks [e.g. 46, 11, 47, 16, 6, 29, 32, 23], mostly focusing on the evolution of the mechanical properties.The evolution of transport properties i...

Wormholing in Anisotropic Media: Pore‐Scale Effect on Large‐Scale Patterns

“…Here is the acid capacity number, defined as the ratio between the number of molecules in a unit volume of mineral to the number of molecules of reactant in a unit volume of the incoming fluid, with θ accounting for the reaction stoichiometry. To account for a finite amount of soluble solid, once locally solid is fully dissolved between adjacent pores, these pores are merged (see Roded et al., 2018).…”

Reactive Flow and Homogenization in Anisotropic Media

“…Then, the total volume of mineral dissolved from a single channel surface during a time step Δ t can be calculated using In order to keep the model tractable, we assume that each cylindrical channel dissolves uniformly along its length. The corresponding change in channel radius is then The model also accounts for a finite amount of soluble solid, and if locally between adjacent channels solid is fully dissolved, channel merging is accounted for by the associated hydraulic conductivity increase (see Roded et al, 2018).…”

“…The model also accounts for a finite amount of soluble solid, and if locally between adjacent channels solid is fully dissolved, channel merging is accounted for by the associated hydraulic conductivity increase (see Roded et al, 2018).…”

“…Additionally, as the relaxation time of the flow field is much faster than that of solute, these fields can be calculated sequentially at each time step. The geometrical properties are then updated at the end of each time step to be used in the subsequent step (Ameli et al, 2014; Hoefner & Fogler, 1988; Roded et al, 2018; Szymczak & Ladd, 2009).…”

Geochemical modeling of changes in caprock permeability caused by CO2–brine–rock interactions under the diffusion mechanism

“…The 2D reactive transport simulations conducted by Wolf et al have found a distinct inner region of 2000 m radial distance under the dominating impact of dissolved CO 2 [23]. Near the injection well, increasing the stress which impact mainly depends on the dissolution regime inhibited the permeability enhancement, increasing the injected volume required to reach a certain permeability [24]. Wang et al have predicted a maximum 3.2% permeability increase of the reservoir and a maximum 1.1% permeability increase of the caprock after 1000 years of exposure to CO 2 -rich brine under the convection mechanism [25].…”