(126a) CO2/Brine Interaction with Reservoir Rock Under CO2 Sequestration Conditions

The atmospheric CO₂ as well as other greenhouse gases have been considered as the main contributors to global climate change. To alleviate the effect of anthropogenic CO₂ on global climate change, many strategies are under development that can potentially remove CO₂ from the atmosphere. Among, many strategies, carbon capture and storage (CCS) is identified as the key strategy for reducing the atmospheric concentration of CO₂ from power plants and energy-intensive industries. In particular, CCS technologies could eliminate CO₂emissions from power plants that use fossil fuels by separating CO₂from plant flue gas and purifying, compressing, and transporting it via pipeline to underground geologic formations for permanent storage. The potential options for CO₂ storage include underground geological formations such as saline aquifers, depleted oil and gas reservoirs, unminable coal seams, hydrate storage, and CO₂ within enhanced geothermal systems. CO₂ storage in saline aquifers is recognized as one of the highest estimated storage capacities within underground geological formation. The Mount Simon formation in the Midwest region of the U.S. is considered as a potential candidate host reservoir for carbon storage. The Mount Simon formation is a deep saline aquifer and is a primary reservoir target for large scale carbon dioxide injection tests due to its proximity to CO₂ sources, large CO₂ storagecapacity, favorable depth, thickness, permeability, porosity, and the presence of the thick overlying seals such as, Eau Claire formation. The Midwest Geological Sequestration Consortium (MGSC) has selected the Mount Simon formation as the reservoir at its major demonstration project. Obtain the knowledge of possible geochemically-induced changes to the permeability and porosity of host CO₂ storage sandstone will enable us to gain a deeper insight of the long-term reservoir behavior under the CO₂ storage conditions.

An experimental study of the interaction of CO₂/brine/rock on saline formations in a static system under CO₂ storage conditions was conducted. Chemical interactions in the Mount Simon sandstone exposure to CO₂ and brine under sequestration conditions were studied. Samples were exposed to the simulated in-situ reaction conditions for six months. Two core samples of Mount Simon sandstone (one is parallel to the bedding plane and the other is perpendicular to the bedding plane) were used. An Illinois Basin model brine at the temperature of 85 °C and CO₂ pressure of 23.8 MPa (3,500 psig) were applied to the reactors. CT, XRD, SEM, and brine, porosity, and permeability analyses were conducted prior and after the experiments.

The permeability and porosity measurements obtained from the sandstone sample showed a decrease after core was exposed to CO₂-saturated brine for six months. In addition, the permeability obtained from the core orientated parallel to the bedding plane is much larger than that measured from the core orientated perpendicular to the bedding plane. The combination of mineral dissolution and mineral precipitation occurring in the sample pores and cracks with the net effect of blocking of flow resulting in the observed the decrease in permeability. This observation suggests that mineral dissolution and mineral precipitation could occur in the host deposit altering its characteristics for CO₂ storage over time. In addition, the observed significantly difference in permeability obtained from the different orientation of core implies that during the CO₂ storage stage the CO₂ is more likely to flow toward the parallel than the perpendicular direction.