249428 Aspects of Fluid Compressibility, Swelling, and Time-Dependent Boundary Conditions for CO2 Sequestration in Saline Aquifers

Monday, October 29, 2012: 4:55 PM
304 (Convention Center )
Philip Cheng, Department of Chemical and Environmental Engineering, Yale University, New Haven , CT and Abbas Firoozabadi, Department of Chemical and Environmental Engineering, Yale University, New Haven, CT

A number of theoretical studies have examined the onset and subsequent development of density- driven convective flow for carbon dioxide (CO2) sequestration in saline aquifers. These studies employ a similar set of assumptions and boundary conditions, some of which may not be justified. For instance, the brine/water is taken to be incompressible (i.e., is described by a divergence-free velocity field), and the interface between the COand brine/water remains fixed in position and saturated at a constant COconcentration. Our work involves a theoretical study of these specific aspects. We have performed a linear stability analysis to verify that fluid incompressibility may indeed be a good approximation. The stability analysis shows that fluid compressibility has only a small effect on the critical time and critical wavelength which characterize the onset of the density-driven convection. However, the assumption of a fixed interface may not be realistic. Dissolution of COinto water can lead to swelling that may increase the volume of the aqueous phase by as much as seven percent. Furthermore, a fixed interfacial concentration can be achieved only if very large amounts of CO2 are injected into the aquifer. Doing so can potentially lead to excess pressure buildup and COleakage from the aquifer. We have performed numerical simulations of experiments where COis mixed with water in diffusion-convection cells. Our model includes a moving interface where the time-varying CO2 concentration is computed rigorously from an equation of state and thermodynamic principles. Incorporation of these features allow for closer agreement between our numerical results and experimental pressure evolution curves.

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