Reservoir-condition pore-scale imaging of dolomite reaction with supercritical CO2 acidified brine: Effect of pore-structure on reaction rate using velocity distribution analysis

To investigate the impact of rock heterogeneity and flowrate on reaction rates and dissolution dynamics, four millimetre-scale Silurian dolomite samples were pre-screened based on their physical heterogeneity, defined by the simulated velocity distributions characterising each flow field. Two pairs of cores with similar heterogeneity were flooded with supercritical carbon-dioxide (scCO(2)) saturated brine under reservoir conditions, 50 degrees C and 10 MPa, at a high (0.5 ml/min) and low (0.1 ml/min) flowrate. Changes to the pore structure brought about by dissolution were captured in situ using X-ray microtomography (micro-CT) imaging. Mass balance from effluent analysis showed a good agreement with calculations from imaging. Image calculated reaction rates (r(eff)) were 538 times lower than the corresponding batch reaction rate under the same conditions of temperature and pressure but without mass transfer limitations. For both high (Peclet number = 2600-1200) and low (Peclet number = 420-300) flow rates, an impact of the initial rock heterogeneity was observed on both reaction rates and permeability-porosity relationships.