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Assessment of the effects of carbon dioxide injection on the reservoir formation, caprock and wellbore integrity

Omar, Abdirizak Ali
Climate change is currently one of the most serious issues affecting the planet earth and its population. The continuously increasing concentration of carbon dioxide (CO2) in the atmosphere is a major culprit. In efforts to mitigate climate change, Carbon Capture and Storage (CCS) projects have been initiated whereby CO2 is captured and injected into deep geological formations. However, a major point of concern is the safety and risk involved in the geological sequestration of CO2. To reduce this risk, it is important to characterize the formations and understand the effects of CO2 injection on them. This study aims to understand the effects of CO2 injection on the reservoir, caprock and wellbore cement integrity. TOUGHREACT is used for numerical simulation of CO2 injection into a hydrocarbon and a geothermal reservoir. The effect of CO2 on wellbore cement is also modeled. Results showed that in the carbonate hydrocarbon reservoir, the injected CO2 was mainly stored by seal trapping and solubility trapping. There was a reduction in the caprock porosity and permeability indicating an improvement in its seal properties. In the geothermal reservoir, injected CO2 was mainly stored via solubility trapping and mineral trapping. There was some free CO2 in cases of high injection rates which was stored by seal trapping. The modeling of the cement plug showed that CO2 presence caused cement degradation. In the presence of a micro-silica additive, CO2 penetrated less into the plug and there was relatively less degradation. Under high temperature conditions, the degradation was more prominent. However, it was noted that in general, the cement degradation is a very slow process due to its self-inhibiting nature.