Online

Foroutan, Maziar

Civil and Environmental Engineering

2021

Ph. D.

Carbon dioxide Capturing, and Sequestration (CCS) is a promising technique that helps mitigate the amount of CO2 emitted into the atmosphere. CCS process mainly involves capturing CO2 at the industrial plant, followed by transportation and injection into a suitable geological storage, under supercritical conditions. Saline aquifers are among the best geological storage candidates due to their availability, high storage capacity and injectivity. Despite the CCUS technology promise, several public safety concerns remain to be address, including but not limited to reservoir/wellbore stability and integrity, CO2 leakage, ground deformation (uplift) and induced seismicity. The injected supercritical CO2 is trapped through different mechanisms in the host reservoir including (i) structural and stratigraphic trapping, (ii) residual trapping, (iii) solubility trapping, and (iv) mineral trapping. Dissolution of CO2 into the formation brine creates an acidic environment, which is highly reactive. The potential mineral dissolution in reservoir rocks can enhance the storage capacity and reservoir injectivity, while the secondary precipitation of minerals can decrease the storage capacity and injectivity. However, the geochemical processes triggered by CO2 injection can potentially degrade the mechanical properties of the reservoir rock, which can consequently disturb the wellbore-stability, reservoir integrity, and lead to significant reservoir compaction. Furthermore, injecting CO2 changes the stress-regime by increasing pore-pressure in the reservoir and its surroundings, which can potentially reactivate the existing faults, leading to induced seismicity. In this research, experiments were performed to evaluate the variation of porosity and pore-connectivity of intact sandstone specimens upon injecting CO2-enriched brine. In addition, the permeability evolution during the CO2-enriched brine injection process was evaluated under different reservoir condition. The mechanical impacts of injecting CO2-enriched brine were evaluated by comparing the mechanical properties (i.e., elastic, strength, seismic and time dependent properties) before and after injecting CO2-enriched brine. In addition, to evaluate the response of fractured reservoirs to CO2 injection, CO2-enriched brine was injected into a limestone and varyingly cemented (i.e., calcite and quartz cemented) sandstone specimens that were artificially fractured. The experimental results were used to numerically simulate CO2 injection into a core-scale porous medium to investigate the changes in CO2 concentration and mass transfer mechanism under different porosity, permeability, and injection pressure values. The experimental results of injecting CO2-enrihed brine to the intact (non-fractured) specimens revealed permeability enhancement and mechanical weakening caused by mineral dissolution. The extent of changes in permeability and mechanical properties of rock specimens varied under different reservoir conditions (i.e., pressure, salinity, and temperature). The mechanical weakening increased the possibility of induced seismicity, which consequently resulted in decreasing the allowable injection pressure of CO2. However, the permeability increase resulted in enhancing CO2 mass transfer and accelerating the solubility trapping in the brine aquifer.