Mineral dissolution and precipitation reactions in porous media can have large impacts on formation properties, including porosity and permeability. However, the rate and impact of these reactions are not well understood. Large variations in estimates of reactive surface area result in orders of magnitude discrepancies in simulated reaction rates. In addition, a lack of understanding of what controls mineral reactions at the pore scale translates into limited predictive capabilities of subsurface permeability evolution. In this work, multi-scale imaging is combined with laboratory experiments and pore-to-core scale reactive transport simulations to enhance understanding and simulation of mineral reaction rates in porous media and corresponding changes in porosity and permeability. Mineral reactive surface areas and pore network structures, extracted from 2D SEM, 3D X-ray CT, and FIB-SEM imaging, are used in pore and continuum scale reactive transport simulations. Image-obtained accessible surface area yields a more accurate depiction of mineral reaction rates in porous media, as validated through core-flood experiments. The need for more robust approximations of surface area, however, depends on the timescale of interest and reactivity of the mineral phase. Less robust approximations of surface area are adequate for less reactive phases for simulations with short time scales. Similarly, simulations with long time scales are little impacted by surface area values for very reactive phases. Pore network modeling of dissolution and precipitation reveals that permeability evolution depends on the spatial distribution of reactions within the pore network.

Improving understanding of mineral reaction rates and permeability evolution in porous media

ACS Spring Meeting 2021

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