With a potential capacity of sequestrating 4,000 – 23,000 Gt of CO2, geological carbon sequestration which works by storing captured and compressed CO2 into geological formations such as saline aquifers has been attracting elevating attention during the past two to three decades as a strategy for mitigating global warming. After being injected into the target formations that are comprised of porous media, the bulk CO2 phase will firstly become disconnected and trapped in the pore space during the reinvasion of the background flow (‘capillary trapping’); with further invasion of brine capillary trapped CO2 are dissolved (‘dissolution trapping’), reducing the risk of CO2 leakage from the aquifers. Therefore, to improve the security of geological carbon sequestration, it is of importance to understand the evolution of capillary trapped CO2 during the process of dissolution trapping, both qualitatively and quantitatively.
Due to the opaque formations of porous media, direct optical access of in-situ fluid configuration is impossible, while with the advances of microtomographic imaging (MCT) information of fluid and the inner structure of porous media can now be visualized as microtomographic data. With subsequent data processing, physical properties of the system such as the volume and the surface area of fluid can be obtained for further data analysis. In this talk, I will be presenting the time-evolution of CO2 clusters ‘tracked’ using MCT throughout a series of dissolution experiments that were conducted under the conditions for geological carbon sequestration. To quantitatively understand the process of CO2 dissolution, the mass transfer coefficient k which measures the rate of CO2 mass transferred into the brine is calculated and presented for the dissolution experiments; the complexities for calculating k are also discussed. With the calculated k, method of back calculating the in-situ CO2 concentration field is also proposed.
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