One way to reduce the amount of CO2 in the atmosphere for the mitigation of climate change is to capture the CO2 and inject it into geological formations such as depleted oil and gas reservoirs, aquifers, oceans and unmined coal beds. The most important public concern about carbon capture and storage (CCS) is whether stored CO2 will leak into groundwater sources and finally into the atmosphere or not, since CO2 at high concentration is hazardous. During underground CO2 storage, the containment of CO2 will be crucially dependent on the cap rock integrity above the CO2. Thus, it is important to assess how the CO2 might impact cap rocks, since this could control the ultimate longevity of CO2 storage. Although supercritical CO2 is normally inert, when it dissolves in water or brine, it makes water acidic. This acidic water can react with the surrounding rock minerals and thus geochemical reactions, dissolution of primary minerals and precipitation of secondary minerals, take place. These reactions can alter the porosity and the permeability and furthermore affect the sealing capacity of cap rocks. The objective of this research is to identify the geochemical reactions of the dissolved CO2 in the synthetic formation water with the rock minerals of the Sayındere cap rock by laboratory experiments. It is also aimed to model and simulate the experiments using ToughReact software. Sayındere formation is the cap rock of the Caylarbasi, a southeastern petroleum field in Turkey. The mineralogical investigation and fluid chemistry analysis of the experiments show that calcite was dissolved from the cap rock core as a result of CO2- water- rock interaction. Using the reactive transport code TOUGHREACT, the modeling of the dynamic experiment is performed. Calcite, the main primary mineral in the Sayındere is dissolved first and then re-precipitated during the simulation process. The decreases of 0.01 % in the porosity and 0.03% in permeability of the packed core of the Sayındere cap rock are observed in the simulation. The simulation was continued for 25 years without CO2 injection. However, the results of this simulation show that the porosity and permeability are increased by 0.001 % and 0.004 %, respectively due to the CO2-water-rock mineral interaction. This shows that the Sayındere cap rock integrity must be monitored in the field if application is planned.


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