[1] A reactive transport model was developed to simulate reaction of carbonates within a pore network for the high-pressure CO 2 -acidified conditions relevant to geological carbon sequestration. The pore network was based on a synthetic oolithic dolostone. Simulation results produced insights that can inform continuum-scale models regarding reactioninduced changes in permeability and porosity. As expected, permeability increased extensively with dissolution caused by high concentrations of carbonic acid, but neither pH nor calcite saturation state alone was a good predictor of the effects, as may sometimes be the case. Complex temporal evolutions of interstitial brine chemistry and network structure led to the counterintuitive finding that a far-from-equilibrium solution produced less permeability change than a nearer-to-equilibrium solution at the same pH. This was explained by the pH buffering that increased carbonate ion concentration and inhibited further reaction. Simulations of different flow conditions produced a nonunique set of permeability-porosity relationships. Diffusive-dominated systems caused dissolution to be localized near the inlet, leading to substantial porosity change but relatively small permeability change. For the same extent of porosity change caused from advective transport, the domain changed uniformly, leading to a large permeability change. Regarding precipitation, permeability changes happen much slower compared to dissolution-induced changes and small amounts of precipitation, even if located only near the inlet, can lead to large changes in permeability. Exponent values for a power law that relates changes in permeability and porosity ranged from 2 to 10, but a value of 6 held constant when conditions led to uniform changes throughout the domain.Citation: Nogues, J. P., J. P. Fitts, M. A. Celia, and C. A. Peters (2013), Permeability evolution due to dissolution and precipitation of carbonates using reactive transport modeling in pore networks, Water Resour. Res., 49,[6006][6007][6008][6009][6010][6011][6012][6013][6014][6015][6016][6017][6018][6019][6020][6021]

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Summary A new macroscale pressure definition is investigated through a series of upscaling calculations for two-phase flow in porous media. This definition is taken from previous theoretical work by the authors and aims at correcting for systematic subscale heterogeneities including those generated by nonlinear dependencies on (heterogeneous) saturation distributionsTraditional intrinsic phase- averaged pressure leads to nonmonotone and multivalued upscaled constitutive functions (e.g., discontinuous upscaled-relative-per- meabilities exceeding unity). Using both analytical and numerical calculations, the new macroscale pressure definition is shown to lead to better-behaved upscaled functions.

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