Dissolution kinetics of Devonian carbonates at circum-neutral pH, 50 bar pCO2, 105 °C, and 0.4 M: The importance of complex brine chemistry on reaction rates

• Dissolution kinetics of rocks in natural brines was slower than synthetic brines.
• Single ionic species in mmol concentrations could exert strong influences on rates.
• Demonstrated the importance of complex brine chemistry on dissolution rates.
• Reactive transport models should input kinetic data from site specific experiments.
• Measured dolomite dissolution kinetics at elevated pressures and temperatures.

The dissolution kinetics of carbonate rocks sampled from the Keg River Formation in Northeast British Columbia were measured at 50 bar pCO2 and 105 °C, in both natural and synthetic brines of 0.4 M ionic strength. Natural brines yielded reaction rates of −12.16 ± 0.11 mol cm−2 s−1 for Log RCa, and −12.64 ± 0.05 for Log RMg. Synthetic brine yielded faster rates of reaction than natural brines. Experiments performed on synthetic brines, spiked with 10 mmol of either Sr or Zn, suggest that enhanced reaction rates observed in synthetic brines are due to a lack of trace ion interaction with mineral surfaces. Results were interpreted within the surface complexation model framework, allowing for the discrimination of reactive surface sites, most importantly the hydration of the >MgOH surface site. Dissolution rates extrapolated from experiments predict that CO2 injected into the Keg River Formation will dissolve a very minor portion of rock in contact with affected formation waters.