Experimental and Numerical Investigation of Carbon Sequestration in Saline Aquifers

Because of the global warming threat posed by greenhouse gases, mainly by CO₂, some strategies were proposed. Along those, disposal and long term storage of greenhouse gases is important for reducing global warming. Aquifers represent the most widely available and the second largest, naturally occurring potential store for CO₂. Although there are a number of mathematical modeling studies related to injection of CO₂ in deep saline aquifers, experimental studies are limited and most studies focus to sandstone aquifers as opposed to carbonate ones.

Potential CO₂ sequestration capacity of a carbonate aquifer formation located in S. East Turkey was evaluated using computerized tomography (CT) monitored experiments. Porosity changes along the core plugs, drilled from Midyat aquifer formation located in south-east Turkey, and the corresponding permeability changes are reported for differing CO₂ injection rates, pressures and temperatures with differing salt concentrations. CT monitored experiments are designed to model fast near well bore flow and slow reservoir flows. It was observed that permeability initially increased and decreased for slow injection cases. As the salt concentration decreased the porosity and thus the permeability decrease was less pronounced. Orientation of the core plugs was observed to be influential in rock-fluid-carbon dioxide interactions. For vertically aligned cores high injection rates resulted in an increase then decrease of permeability. On the other hand horizontally aligned cores represented a decrease in permeability due to CaCO₃ precipitation. It was observed that CO₂ sequestration by solubility trapping is larger compared to mineral trapping. The results are discussed using a finite difference, non-isothermal compositional numerical simulator where solution and dissolution of carbonates via chemical reactions are considered. The calibrated model was then used to analyze field scale injections and to model the CO₂ sequestration capacity of a potential carbonate aquifer formation located in S. East Turkey.