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The variation in the carbon isotope composition of the cap rock of Texas and Louisiana sulphur wells was investigated by means of a simultaneous collection mass spectrometer. These rocks showed anomalously large depletions in C-13. The isotope depletion in the decarboxylation of pyruvic acid, both by chemical means and by bacteria, was measured and the isotope composition of the carbon dioxide released was found to be similar to that of the cap rock. The hypothesis is advanced that the carbonate of the cap rock may have originated by the precipitation of carbon dioxide released in the bacterial decarboxylation of an organic substrate. / Thesis / Master of Science (MSc)

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. 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. To prevent the leakage, the possible leakage paths and the mechanisms triggering the paths must be examined and identified. It is known that the leakage paths can be due to CO2 - rock interaction and CO2 &ndash / well interaction. 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 Sayindere cap rock by laboratory experiments. It is also aimed to model and simulate the experiments using ToughReact software. Sayindere 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 Sayindere 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 Sayindere 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 Sayindere cap rock integrity must be monitored in the field if application is planned.

The dependency on fossil fuels faces resource limitations and sustainability concerns. This situation requires new strategies for greenhouse gas emission management and the development of new sources of energy. This thesis explores fundamental concepts related to carbon geological storage, including CO2-CH4 replacement in hydrate-bearing sediments. In particular it addresses the following phenomena: - Interfacial tension and contact angle in CO2-water-mineral and CH4-water-mineral systems. These data are needed to upscale pore phenomena through the sediment porous network, to define multiphase flow characteristics in enhanced gas recovery operations, and to optimize the injection and storage CO2 in geological formations. - Coupled processes and potential geomechanical implications associated to CH4-CO2 replacement in hydrate bearing sediments. Results include physical monitoring data gathered for CH4 hydrate-bearing sediments during and after CO2 injection. - Performance of cap rocks as trapping structures for CO2 injection sites. This study focuses on clay-CO2-water systems and CO2 breakthrough through highly compacted fine-grained sediments. Long term experiments help evaluate different sediments according to their vulnerability to CO2, predict the likelihood and time-scale of breakthrough, and estimate consequent CO2 leaks.