Buoyancy Driven Flows in Porous Media with Applications to Geological Storage of Carbon Dioxide

Date
2019-04-15
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Abstract
This dissertation presents theoretical analyses and numerical experiments on buoyancy-driven convection in porous media in the context of geological storage of carbon dioxide (CO2) in deep saline aquifers. One of the main focuses of this study is to investigate the role of the concentration dependent base state density profile in the stability criterion of buoyancy-driven convection and hydrodynamics of the associated convective mixing in different fluid systems. In particular, scaling relations, which allow estimation of the onset of the convective instabilities and the generalization of the base state density dependence of the growth of the instabilities are of interest. Stability criterion of the buoyancy-driven convection in analogue fluid mixtures used in experimental studies of CO2 convective mixing are of particular interest. The density profile dependence of the growth of instabilities in both binary and ternary fluid mixtures is mathematically analyzed and scaling relations that relate the stability criterion of the diffusive boundary layer to the key parameters of the systems is proposed. It is shown that the characteristic behaviour of the base state density profile plays an important role in stability characteristics of the diffusive boundary layer and convective mixing beyond the onset of instability. The results have shown that the choice of an analogue system is critically important in correct representation of the onset of convective instabilities of CO2/water and design of experiments. In particular, it is shown that there are fundamental differences in the evolution of the buoyancy-driven instability and dynamics of convective mixing between CO2/water and typical EG-MeOH/water and PPG/water analogue systems. The developed concepts on the role of density profiles in the stability criterion of the buoyancy-driven convection are applied to multi-component fluid systems with applications to impure CO2 storage. The role of permitted impurities on the characteristic shape of the density profile evolved during the dissolution of impure CO2 in water is mathematically analyzed and a parameter space classification, which allows prediction of general stability behaviour of an impure CO2/water system is proposed. Specifically, a linear stability analysis is conducted to investigate the effect of H2S impurity in CO2 stream on the onset of buoyancy-driven convection associated with impure carbon CO2 storage in deep saline aquifers. Contrary to the common belief, it is shown that an impurity such as H2S has the potential to accelerate the buoyancy-driven instabilities. The theoretical analysis is extended, by means of high-resolution numerical simulations, to characterize the long-term behaviour of density-driven convection and the associated mixing. The key features of the convective dissolution beyond the onset is analyzed by evaluating the finger patterns and convective fluxes at different periods of the mixing process. It is shown that an impure CO2 stream may lead to different convective mixing dynamics at early and late periods of dissolution process depending on the fractional composition of the permitted impurity. Another focus of this study is to develop mathematical models that capture key features of fluid flow and transport in fractured porous media and to characterize the stability criteria of buoyancy-driven convection in fractured aquifers in the context of CO2 storage. Through performing a parametric analysis, by means of a linear stability analysis, the role of physical properties of a fracture network in the stability of the diffusive boundary layer in a saturated fractured porous medium is characterized. Important effects of fracture interporosity flow and fracture storativity on the stability behaviour of the system are demonstrated and scaling relations that can be used to estimate the onset of density-driven instabilities in a dual porosity porous system are reported as a function of the most common physical properties of the fractured porous medium. These findings improve our understanding of density-driven flow in porous media in the context of CO2 storage and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.
Description
Keywords
Buoyancy-driven flows, Solutal convection, Linear stability analysis, CO2 sequestration, Solubility trapping, Fractured porous media, Impure CO2 storage
Citation
Jafari Raad, S. M. (2019). Buoyancy driven flows in porous media with applications to geological storage of carbon dioxide (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.