| Description |
Carbon dioxide (CO2) sequestration is a technology being implemented with the potential to mitigate anthropogenic CO2 emissions. CO2 injection into underground brine-saturated formations requires a good understanding of the ensuing mineralogical changes. Core floods and batch reactor studies involving three different rock types such as sandstone, limestone, and dolomite were conducted at realistic sequestration conditions in this study. Inductively Coupled Plasma Mass Spectrometer (ICP-MS) was used to obtain effluent brine concentrations as brine and CO2 were injected/reacted with the different rock types. Analysis of the cores by X-ray Diffraction (XRD), Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN), and Micro-Computed Tomography (Micro-CT) complemented the aqueous-phase compositional measurements. Selected porosity and permeability measurement were also performed using a helium porosimeter. Core flooding revealed the importance of iron chemistry in CO2 sequestration in sandstone formations. Significant dissolution of iron bearing minerals was observed with slight increase in porosity. This would have implications in the near well bore injection region. Dissolution with wormhole creation was seen in limestone and dolomite experiments. The changes in mineralogy were modeled using TOUGHREACT, a reactive transport geochemical simulator. The experimental changes observed due to changes in flow rates could not easily be reproduced in the model indicating a more complex underlying processor, even at this scale. The batch experiments confirmed the types of mineral dissolutions observed in the core studies. Additionally, these experiments helped quantity the effect of surface area (higher surface area leading to more dissolution) and revealed that the heterogeneity of limestone and dolomite permit reactions to occur in the interior. In contrast, sandstone reactions appeared limited to the surface. Surface area measurements showed that the new porosity generated was characterized by a smaller pore size distribution in comparison to the unreacted one. |
