Geochemical modelling of formation damage risk during CO2 injection in saline aquifers
Abstract
This study provides an understanding of the impact of geochemical reactions during and after CO2 injection into a potential storage site. The results of calculations of geochemical reactivity of reservoir rock and of cap rock during and after CO2 injection were performed using a geochemical simulator, with the calculations showing that for these conditions up to 0.5 moles of CO2 can be dissolved per kg of water. The risk of dissolution of primary cements was considered and identified. In addition, the potential of carbonation reactions to permanently sequester CO2 was considered, although these reactions were shown to be very slow relative to other processes. The implications for security of storage are that while dolomite nodules exist in the sandstone formation, these do not contribute significantly to the overall rock strength, and hence the risk of dissolution of the formation or caprock causing significant leakages pathways is very low. Further calculations were performed using a commercial reservoir simulation code to account for brine evaporation, halite precipitation and capillary pressure re-imbibition. The impact on injectivity was found not to be significant during continuous and sustained injection of CO2 at a constant rate. Capillary pressure effects did cause re-imbibition of saline brine, and hence greater deposition, reducing the absolute porosity by up to 13%. The impact of the halite deposition was to channel the CO2, but for the configuration used there was not a significant change in injection pressure.
