A Modeling Study of the Role of Selected Minerals in Enhancing CO2 Mineralization During CO2 Aquifer Storage

摘要

CO2 mineralization is a process whereby the CO2 that is injected into a geological formation dissolves into the formation water, reacts with the in situ minerals and ions, and precipitates as carbonate minerals. This process governs the long-term fate of the injected CO2 and ensures a safe storage once CO2 has been converted into minerals. In a previous study involving the modelling of the long-term fate of CO2 in the Utsira aquifer storage, the authors observed that CO2 mineralization was not possible if mineral reactions were limited to Calcite and Dolomite precipitation and dissolution. Indeed, to mineralize CO2, non carbonate minerals that are present in the formation have to: - dissolve in order to buffer the pH decrease resulting from the CO2 injection; - provide cations such as Ca2+, Mg2+, Fe2+ to the formation water; - not release bicarbonate (HCO3 –) to the formation water. Then the released cations react with HCO3 – resulting from the dissolution of the injected CO2 and precipitate new carbonate minerals. In this study, the CO2 mineralization process is modelled, taking into consideration various possible reactive pathways. In the first step, the different reactive pathways are investigated in terms of reactive potential, CO2 mineralization potential and consequences on the porous network. In the second step, simulation of flow and dissolution of CO2 together with geochemical reactions is performed to examine the mineralization process in space and time for two different time scales: - 1000 years with a finer grid to examine how chemistry interacts with the CO2 dissolution process; and - 18,000 years with a coarser scale to reach geochemical equilibrium in the aquifer.This work shows that a limited amount of non-carbonate reactive minerals (for a given time scale) can contribute to the mineralization of CO2 that is significant for an industrial CO2 storage project. As such, the identification of the reactive pathways leading to CO2 mineralization is a key step to evaluate the long-term fate of the injected CO2 in a geological storage project.