(47a) CO2/brine Interacting with Cedar Keys-Lawson Formation Rocks ­Under CO2 Sequestration Conditions

Atmospheric CO₂ and other greenhouse gases have been considered to be 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 options, 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, unmineable coal seams, 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 Cretaceous rocks of Florida have been recognized as the potential suitable reservoirs for CO₂ storage. For example, the upper member of the Upper Cretaceous Lawson Formation, together with the lower part of the Paleocene Cedar Key Formation, due to, they composed of porous dolostone seals by the thick anhydrites of the overlying middle Cedar Keys Formation. Many of the porous interval within the Cedar Keys-Lawson storage reservoir display lateral continuity and have average porosity up to 20 %. The estimated CO₂ storage capacity for the reservoir is approximately 97 billion ton of CO₂, which suggests the Lawson and Cedar Keys Formations composite potentially support CO₂ sequestration for large-scale power plants within this area. Obtaining 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 Cedar Keys-Lawson sandstone exposure to CO₂ and brine under sequestration conditions were studied. Samples were exposed to the simulated in-situ reaction conditions for up to 24 months. Four core samples of Cedar Keys-Lawson sandstone and a synthetic brine at the temperature of 55 °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 up to 24 months. In addition, the permeability obtained from the core oriented parallel to the bedding plane is much larger than that measured from the core oriented 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 change 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.