Investigations in Upscaling Transport and Geochemistry in Porous Media: Modeling CO2 Sequestration at the Pore, Continuum and Reservoir Scales

Abstract

Geological Carbon Sequestration has been identified as one of the most promising technologies to bridge the gap between energy security and climate change mitigation. However, many questions arise about the ability to safely keep the injected CO2 in deep formations. In order to answer these questions and provide practical guidance for engineers and policymakers the use of computational models is employed on a daily basis. These models strive to accurately represent physical and chemical phenomena using functional relationships at scales much larger than the scales at which they have been originally derived. It is the intention of this dissertation to present several new methods and techniques in order to accurately represent physical and geochemical phenomena at different spatial and temporal scales. In Chapter 2 a new average pressure definition, herein called the first-order macro-scale pressure, is used to numerically upscale capillary pressure and relative permeability. The results from Chapter 2 show that the first-order marco-scale pressure does a much better job at developing unique and well-behaved upscaled curves than the commonly used intrinsic phase pressure definition. In Chapter 3 a new method to upscale mass transfer between two phases, which relies on the assumption of capillary equilibrium, is explored. The new method for upscaling mass transfer across phases is shown to do much better at representing the actual evolution of mass transfer across phases than assuming equilibrium flash calculations at larger scales. In Chapter 4 a methodology to upscale geochemical changes at the pore-scale is introduced in order to account for changes in porosity and intrinsic permeability at the continuum-scale. The methodology is used to find upscale porosity vs. permeability curves and show how they change depending on different inflowing pH conditions, pressure boundary condition and boundary mixing conditions. Ultimately, the curves found and presented in this chapter are derived for their use in continuum scale models. A detailed analysis of how each scenario produces different evolution is presented. In Chapter 5 a reservoir scale model, which relies on multi-scale assumptions to model certain physical phenomena at larger scales, is used to assess the risk of leakage in a potential geological site with abandoned wells. The results of Chapter 5 are used to derive policy recommendations that try to bridge the gap between uncertainty in leakage scenarios and practical rule making. At the end of Chapter 5 a list of recommendation to policy makers based on the computational results. Finally, in Chapter 6 an extension of the work presented in Chapter 5 is done by exploring the possible benefits and limitations of using pressure-monitoring wells to detect potential leakage events. It is shown that monitoring for pressure perturbations compared to monitoring for CO2 plumes provide a better option for leakage detection.