Predicting delta~(13) Cdic dynamics in CCS: A scheme based on a review of inorganic carbon chemistry under elevated pressures and temperatures

摘要

Stable carbon isotopes are important tools to assess potential storage sites for CO_2, as they allow the quantification of ionic trapping via isotope mass balances. In deep geological formations high p/T conditions need to be considered, because CO_2dissolution, equilibrium constants and isotope fractionation of dissolved inorganic carbon (DIC) depend on temperature, pressure and solute composition. After reviewing different approaches to account for these dependencies, an expanded scheme is presented for speciatior and carbon isotope fractionation of DIC and dissolution of CaCO_3 for pCO_2 up to 100 bar, pH down to 3 anc temperatures of up to 200 °C. The scheme evaluates the influence of respective parameters on isotope ratios during CO_2 sequestration. The pCO_2 and pH are the dominant controlling factors in the DIC7delta~(13)C/pH system. The fugacity of CO_2 has major impact on DIC concentrations at temperatures below 100 °C at high pCO_2. Temperature dependency of activities and equilibriumdominates at temperatures above 100 °C Isotope ratios of DIC are expected to be about 1-2%D more depleted in 13C compared to the free CO_2 al pCO_2 values above 10 bar. This depletion is controlled by carbon isotope fractionation between C02 anc H_2CO_3* which is the dominant species of DIC at the resulting pH below 5.