Dynamics of two-phase transport properties in reacting porous media

Abstract:

Progress of (multi-component) chemical reactions in porous media may cause pore-space alteration and change in hydraulic properties such as porosity and permeability (Figure 1). Pore size evolution affects two-phase flow properties such as capillary pressure-saturation relation (Figure 2). Moreover, in the case of solute transport, presence of the two phases affects solute mixing and dispersion (Figure 3) within each phase.

This study presents a comprehensive reactive pore-scale model to simulate changes in the above-mentioned flow and transport hydraulic proprieties, under two-phase flow, due to the dissolution/precipitation in the presence of multi-component chemical reactions. The pore space is represented using a large number of interconnected pore elements of different sizes. Flow and transport of chemical components are simulated within each pore element by taking into account advective and diffusive transport processes, as well as both equilibrium and kinetic type chemical reactions.

We will show how regime of flow and reaction (characterized using Péclet number and Damköhler number) results in different responses such as uniform dissolution, shaper front dissolution as well as formation of channels or wormholes. Each of these reaction regimes affects pore-size distribution differently controlling two-phase hydraulic proprieties.

Figure descriptions:

Figure 1: Porosity-hydraulic conductivity relation, due to dissolution, for different flow rates (Péclet Number). Maximum conductivity is obtained under regime of high Péclet Number due to uniform dissolution throughout the sample. Conductivity values are normalized using the initial conductivity.

Figure 2: Water content-capillary (i.e., saturation*porosity) capillary pressure relation for a sample at three different stages of dissolution. Dissolution causes increase in porosity (i.e., initial water content) and lowers the capillary entry-pressure due to the increase of pore sizes.

Figure 3: Relation between wetting phase saturation and solute dispersivity for three different samples with different pore size variances (Low, Medium, and High). It is shown that change in saturation significantly affects the value of solute dispersion depending on the pore size distribution.