Multiphase flow properties of sealing caprocks for CO₂ geological storage




Guiltinan, Eric Joseph

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At the pore-scale, intermolecular forces are responsible for wetting, solubility, phase separation, and interfacial tension. These forces along with the pore structure, in porous media, and aperture distributions, in fractures, govern the physics of multiphase fluid flow and result in continuum scale parameters such as residual saturation and relative permeability. However, these forces are often overlooked and poorly understood. In this dissertation we explore how the pore-scale contributes to multiphase flow with an emphasis on geologic CO₂ sequestration and caprock integrity. First, we explore the wettability of organic shales, a likely caprock, for CO₂ storage. We provide the first reservoir condition brine/supercritical CO₂ contact angle measurements on an organic shale and find the organic shale to be water wet with little effect of organic content and thermal maturity. This means that capillary forces can hold back large CO₂ columns in these caprocks. Second, we investigate how pore structure controls the breakthrough pressure of mudstones through the use of resedimentation experiments combined with mercury intrusion porosimetry. We offer novel insights into the relationship between the coarse grained percolating network and the fine grained void ratio and show that the breakthrough pressure is related to the fine grained void ratio through a power-law. Third, we incorporate intermolecular forces into a numerical model to explore how heterogeneous wetting distributions contribute to the flow of CO₂ in fractures. We discover that the heterogeneous wetting contributes to residual saturation in fractures by providing opportunities for the predominately non-wetting CO₂ to surround the wetting phase. The wetting distribution also contributes to breakthrough time and the evolution of unsteady relative permeability. These results provide fundamental insight into how pore scale forces control continuum scale multiphase flow.


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