School of Earth Sciences - Theses

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    Reactive barrier formation as CO2 leakage mitigation technology
    Castaneda-Herrera, Cesar Augusto ( 2017)
    Global climate change driven by the emission of carbon dioxide (CO2) to the atmosphere is one of the grand challenges of our time. Energy from the use of fossil fuels is the main source of anthropogenic CO2 emissions. While renewable energies are emerging, fossil sources are expected to continue providing a large portion of our energy needs into the foreseeable future. One way to mitigate emissions from fossil fuel usage is through Carbon Capture and Storage (CCS). This involves capturing CO2 by engineered methods and storing it in a high porosity-high permeability geological formation overlain by a low permeability shale (or caprock). It is expected that these formations will be able to hold CO2 for thousands of years. However, in some instances CO2 leakage through the caprock cannot be entirely precluded, e.g. through undetected zones of higher permeability including natural fractures. This thesis proposes the use of a chemical reactive barrier formation as a technology to mitigate and remediate CO2 leakage successfully. The proposed technology consists of injecting an alkaline sodium silicate solution that reacts with the leaking CO2 or CO2-saturated water, leading to silica gel formation. This work was conducted in three main research phases. Firstly, experimental and modelling studies were undertaken to evaluate the properties of the sodium silicate solution and geochemical viability of the chemical reaction. The second phase involved experiments in a flow-through unconsolidated sand-packed column at ambient conditions. During this phase, variables such as flow rate, temperature and incubation times were evaluated under different scenarios. Finally, core-flood experiments were carried out at reservoir conditions. CO2­saturated fluid and supercritical CO2 (scCO2) were injected into a sandstone saturated with silicate at high pressure and temperature. Reduction in permeability and the retention of silica in the column were used as measures of barrier formation in the last two experimental phases. The first phase of work showed that 7.15 wt% sodium silicate solution proved to be the most practical for applications in subsequent experiments. The modelling also showed that at this concentration the reaction is predicted to happen at different geochemical reservoir conditions. During the second phase, the formation of the silica barrier was found to be controlled by the mixing gradient of the two reactants, where the reaction resulted in reduction of permeability by at least one order of magnitude for mitigation and remediation scenarios. Moreover, the results of the core-flood experiments demonstrated that the formation of the silica barrier under CO2 reservoir conditions is possible and viable for a mitigations scenario. These results showed a significant reduction in permeability of two or three orders of magnitude and that the barrier was still strong a month after completing the test. In conclusion, results of this thesis suggest that the silica barrier formation is a promising technology to abate CO2 leakage from a geological carbon storage reservoir and provides useful findings for further research.