Dependence of Pore-to-Core Up-scaled Reaction Rate on Flow Rate in Porous Media

Due to inherent heterogeneities in structure, mineral placement and fluid velocity in rock, bulk reaction rates realized during reactive flow through porous media may differ significantly from that predicted by laboratory-measured rate laws. In particular, rate laws determined in batch reactor experiments do not capture any of the flow dependence that will be experienced in the porous medium. Based on network flow model simulations of anorthite and kaolinite reactions in two sandstone pore networks under acidic conditions commensurate with CO2 sequestration, we compute up-scaled reaction rates at the core scale and investigate the dependence of the observed reaction rates on flow rate. For the anorthite reaction which, under these acidic conditions is far from equilibrium and dominated by pH, we find a power law dependence of reaction rate on flow rate. For the kaolinite reaction, which is near equilibrium, a more complex dependence emerges, with the up-scaled rate tending to rapidly increasing net precipitation at low-flow rates, then reversing and tending toward net dissolution at high-flow rates.