Reactive transport modeling in fractures and two-phase flow

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Noh, Myeong Hwan

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This study presents a mathematical model to simulate hydrodynamics and fluid-mineral reactions in a fracture within permeable media. Fluid convection, diffusion and precipitation / dissolution (PD) reactions inside a finite space are solved as a simplified representation of natural fracture mineralization. The problem involves mass transfer within the fluid accompanied by chemical reaction at the fracture surface. Mass-conservation equations for components in the fluid are solved, and these are coupled with chemical reaction at the fracture surface. The intent of this model is to show the time evolution of fracture aperture shrinkage patterns caused by the calcite cementation. We present the aperture width distribution along the fracture. In this study, we consider the precipitate as porous media and allow porosity and permeability in the cement. Therefore, the calcite cementation completely fills eventually. As a second subject, the reactive transport model of CO2 sequestration in aquifers is studied. Geologic formations are considered as a target for the sequesvi tration ofCO2 from stationary sources such as power plants or large industrial facilities. Deep saline aquifers have a large potential storage capacity for CO2 and they are ubiquitous in sedimentary formations. CO2 can be sequestered in geologic formations by three principal mechanisms: hydrodynamic trapping, solubility trapping and mineral trapping. Mineral trapping is the most stable way of CO2 sequestration in aquifers. Storage capacities of CO2 for each trapping mechanism are presented using GEM, a commercial program from Computer Modeling Group Ltd. We also present the anlaytical solutions for the miscible displacement and compare them with the numerical results. Developing methods for increasing the mineral trapping creates stable repositories of carbon dioxide and that decreases mobile hazards such as leakage of CO2 to the surface.