Gel reaction and permeability modification for CO2 leakage remediation and flood conformance

Moneke, Kenechukwu
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Carbon Capture and Storage (CCS) program, also known as CO2 sequestration, has been proposed as a long-term process to mitigate emissions of greenhouse gases such as CO2 in the atmosphere. One of the biggest challenges associated with the CO2 sequestration process is the migration and leakage of the CO2 due to the formation of leakage pathways which weakens the integrity of the reservoir caprock. To ensure the CO2 storage effectiveness and minimize the environmental and economic risk, it is important to monitor the subsurface CO2 migration and apply a treatment method if leakage is detected. One of the potential treatment methods to mitigate the leakage challenge in the CCS program is the use of chemical sealants such as silicate gel. The concentrated potassium silicate solution (i.e. silicate gel) reacts with the dissolved CO2 species to form a silica gel barrier which prevents the captured CO2 from escaping into the atmosphere and reduces the reservoir permeability. This thesis aims to evaluate the potential of silica gel as leakage prevention and remediation measure during the CO2 sequestration process. The use of the silica gel as a permeability modifier, conformance control agent and an effective cap rock sealant was also investigated. The mother solution used in these experiments is Betol K28T diluted with deionized water (50 wt.%) which acts as the silicate gel being investigated. Bulk gelation experiments were initially performed to measure the gel time at different silicate content, acid concentrations, salinities, and temperatures. The results were then fit to an existing model for gelation time and then used as a predictive tool for the core flood experiments. Core flood experiments were then performed to investigate the reaction transport of silicate gel in porous media, compare the results obtained from gelation in porous media to the gelation results from the earlier bulk experiments and finally, investigate the capability of the gel in permeability reduction and sealing of the core. These core flood experiments were conducted in two conditions: ambient condition with an acetic acid solution as a CO2 substitute and the High-Pressure High-Temperature (1500 psi, 600C, 30,000ppm) condition with CO2 saturated brine. From the core flood experiments, it is shown that using potassium silicate reagents (Betol K28T) to form a silica gel barrier is an applicable strategy for mitigating the risk of CO2 leakage Reduction in the core permeability (up to 90%) of the Benthemier sandstone core was observed during barrier formation. However, to further validate the use of the silica gel to form a chemical barrier under CO2 storage conditions, additional modeling and experiments using micromodel chips and field-scale conditions are recommended