Experimental and Numerical Investigation of Carbon Sequestration in Saline Aquifers

Abstract

This paper was part of a student paper session at the conference.It was included in the proceedings as STUDENT13. Abstract 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. Introduction Anthropogenic greenhouse gases emission become a threat for the earth in the means of global warming. Climate modeling studies proposed that earth's temperature increased about 0.3–0.6 °C during the last 150 years. Along others, carbon dioxide is known to be the major contributor to global warming with the % 64 of the enhanced greenhouse effect.1 In excess of 27 billion tones of carbon dioxide per year worldwide are generated by combustion of fossil fuels such as oil, natural gas, and coal, virtually all of which is discharged into atmosphere.2 Disposal and long-term sequestration of CO2 is a proposed approach to reducing global warming. Geological formations, such as oil fields, coal beds, and aquifers are likely to provide opportunities for disposal and long-term sequestration of CO2. Aquifers represent the most widely available and the second largest, naturally occurring potential store for CO2. CO2 can be sequestrated in saline aquifers by three mechanisms: solubility trapping through dissolution in the formation water, mineral trapping through geochemical reactions with the aquifer fluids and rocks, and hydrodynamic trapping of CO2 plume. These mechanisms lead to storage of CO2 as free-phase gas in pore spaces, dissolved phase CO2 in formation water and CO2 converted to rock matrix. Geological disposal of CO2 into saline aquifers would ideally be made at supercritical conditions (31.04 °C and 1070.7 psi), in order to avoid adverse effects of prior separation of CO2 into liquid and gas phases in the injection system. The desire of supercritical injection limits minimum aquifer depths to approximately 800m to sustain a supercritical regime.1 Although supercritical injection and storage of CO2 would be ideal, for all practical reasons, it is not a necessary condition.