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The objective of this study was to improve our ability to predict CO2-SO2 geologic storage. SO2 is an impurity of industrial CO2 gas streams which is expected to intensify brine acidification resulting in enhanced mineral reaction. Short-term H2SO4-brine-rock experiments were combined with reaction path modelling to identify reactions and evaluate the pH and temperature dependency of reaction rates. In addition, available reactive surface area was investigated to enhance our ability to upscale to reservoir scale. Kinetically controlled reaction path models that included CO2, SO2 and O2 were generated and then run at reservoir conditions for 100 y. The models predicted a rapid buffering of the SO2 induced acidification. Compared to pure CO2 storage the CO2-SO2-O2 reservoir models resulted in enhanced carbonate reaction extents and a greater porosity increase, which have significant ramifications for the safety of the seal and the storage capacity of the storage formation.