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Title Scaling of solutal convection in porous media
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Publication Date
Date Accessioned
Degree PhD
Discipline/Department Petroleum Engineering
Degree Level doctoral
University/Publisher University of Texas – Austin
Abstract Convective dissolution trapping is an important mechanism for CO₂ mitigation because of its high security and long-term storage capacity. This process is a problem of solutal convection in porous media, which is a classic example of symmetry breaking and pattern formation. The convective solute flux and geometry of the convective pattern are thought to be controlled by the molecular Rayleigh number, Raₘ, i.e., the ratio of the buoyant driving forces over diffusive dissipation. The dimensionless convective solute flux, Sh (Sherwood number), is thought to increase with Raₘ approximately linearly, as Sh ~ Raₘ. The spacing of the convective fingers, δ, relative to the domain height, H, is thought to decrease approximately as [mathematical equation]. However, there is little experimental verification of these fundamental scaling laws for solutal convection in porous media. To understand the controlling physics of CO₂ convective dissolution in aquifers and verify relevant fundamental scaling laws, I conduct convective dissolution experiments using analog fluids in a porous medium. By changing the controlling parameters, including permeability and maximum density difference, corresponding convective velocity, dissolution flux, and finger pattern are measured for each combination. The experimental results shows that these fundamental scaling laws do not hold for the experiments in porous media composed of glass beads. Instead, I observe that the dissolution flux levels off as Raₘ increases and that the finger spacing increases rather than decreases with increasing Raₘ. The classic scaling analysis breaks down because it does not consider the dominant dissipative mechanism in porous media, mechanical dispersion. Its influence on convection is captured by a dispersive Rayleigh number, Ra [subscript d] = H / αT, where αT is the transverse dispersivity. In experimental studies, dispersion dominates molecular diffusion, i.e., Ra [subscript d] ≤ Raₘ and therefore selects the finger spacing. Increasing the bead size of the porous medium increases Raₘ but decreases Ra [subscript d], leading to a coarsening of the convective pattern. The dissolution flux is controlled by Raₘ, which captured the buoyant driving force in the convection. However, the inherent anisotropy of mechanical dispersion leads to an asymmetry in the convective pattern that eventually limits the dissolution flux in the high Raₘ limit, resulting in the breakdown of the classic convective solute flux scaling. This anisotropy induced asymmetry and corresponding flux reduction are verified by a numerical simulation study. The results show that mechanical dispersion, which was ignored before, plays an important role in quantifying solutal convection in porous media. Since dispersivity generally increases with the scale of observations, knowledge obtained from the counter-intuitive results can be applied to predict mass transfer in large-scale applications such as CO₂ convective dissolution storage in aquifers.
Subjects/Keywords Solutal convection in porous media; Convective dissolution; Convection; Dissolution; Porous media; Dispersion; Mechanical dispersion; Transverse dispersion; Molecular diffusion; Experiments in porous media; Direct numerical simulation; CO2 sequestration; CO2 convective dissolution trapping; CO2 dissolution trapping; Pattern formation; Symmetry breaking; Convection-diffusion; Longitudinal dispersion; CO₂ sequestration; CO₂ convective dissolution trapping; CO₂ dissolution trapping
Contributors DiCarlo, David Anthony, 1969- (advisor); Hesse, Marc (advisor); Lake, Larry (committee member); Mohanty, Kishore (committee member); Balhoff, Matthew (committee member)
Language en
Country of Publication us
Record ID handle:2152/68164
Repository texas
Date Indexed 2020-10-15
Grantor The University of Texas at Austin
Issued Date 2017-12-08 00:00:00
Note [department] Petroleum and Geosystems Engineering;

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…Scaling of Solutal Convection in Porous Media Yu Liang, Ph.D. The University of Texas at Austin, 2017 Supervisor: David DiCarlo Co-Supervisor: Marc Hesse Convective dissolution trapping is an important mechanism for CO2 mitigation because of its…

…Background ............................................................................................3 2.1 CO2 Issues and Mitigation Methods ......................................................3 2.2 CO2 Saline Aquifer Storage and Trapping Mechanisms…

…164 Appendix P: CO2 Leakage and Trapping Mechanisms .......................................169 Glossary ...............................................................................................................172 Bibliography…

…Hesse, 2008; Metz et al., 2005). .................................................................167 xv List of Figures Figure 2.1: Illustration of fluid dynamics and trapping mechanisms for CO2 geological storage in saline aquifers, including…

…structural trapping, capillary (residual) trapping, solubility trapping (dissolution trapping) and mineral trapping (Emami-Meybodi et al., 2015). ........................6 Figure 2.2: A sketch of CO2 convective dissolution…

…5.8: When transverse dispersion (white arrows) is large enough, it dominates the convective patterns and therefore selects the finger width. Transverse dispersivity in counter-current flow is larger than transverse dispersivity in co-current…

…123 Figure 7.1: Longitudinal (yellow arrow) and transverse (while arrow) dispersion in one-side solutal convection in porous media. At the top and the bottom regions, convection occurs as co-current flow, longitudinal dispersivity…

…167 Figure O.2: Major options for CO2 geological storage (Metz, 2005). .................168 Figure P.1: Storage security depends on a combination of different trapping mechanisms (Metz, 2005)…

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