Reactive infiltration instability (RII) drives the development of many
natural and engineered flow systems. These are encountered e.g. in hydraulic
fracturing, geologic carbon storage and well stimulation in enhanced oil
recovery. The surface area of the rocks changes as the pore structure evolves.
We combined a reactor network model with grey scale tomography to seek the
morphological interpretation for differences among geometric, reactive and
apparent surface areas of dissolving natural porous materials. The approach
allowed us to delineate the experimentally convoluted variables and study
independently the effects of initial geometry and macroscopic flowrate.
Simulations based on North Sea chalk microstructure showed that geometric
surface not only serves as the interface for water-rock interactions but also
represents the regional transport heterogeneities that can be amplified
indefinitely by dissolutive percolation. Hence, RII leads to channelization of
the solid matrix, which results in fluid focusing and an increase in geometric
surface area. Fluid focusing reduces the reactive surface area and the
residence time of reactants, both of which amplify the differences in question,
i.e. they are self-supporting. Our results also suggested that the growing and
merging of microchannels near the fluid entrance leads to the macroscopic "fast
initial dissolution" of chemically homogeneous materials.Comment: 37 pages, 12 figure
