Geochemical modelling of CO2 storage
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The injection of CO2 into the reservoir acidifies the brine, which in turn drives mineral dissolution and precipitation processes. This thesis explores how far geochemical modelling can be applied to evaluate the CO2-brine-rock interactions during CO2 storage in North Sea saline formations. First, modelling requirements and the capabilities and limitations of the numerical codes used in this study (PHREEQC, GEM, TOUGHREACT and MoReS) were identified. Solubility of CO2 in brine by different models at conditions relevant to CO2 storage was compared. Batch modelling of three sandstone core samples from target CO2 storage formations was performed to compare the numerical codes and assess mineral trapping capacity of the formations. Finally, reactive transport modelling of Rannoch formation at reservoir scale was studied. The simulation results of GEM and MoReS were compared. It was shown that current codes can model geochemical reactions with acceptable simplifications and the choice of simulator is not critical for the model predictions. It was demonstrated how thermodynamic data and activity models can affect the modelling results. It was also found that the models are sensitive to relative mineral composition, grid discretization, permeability models, and kinetic parameters. Mineral trapping is comparable to solubility trapping in Rannoch formation.