Dae-Gee Huh

Sequestering carbon dioxide into complex structures of naturally occurring gas hydrates

Large amounts of CH4 in the form of solid hydrates are stored on continental margins and in permafrost regions. If these CH4 hydrates could be converted into CO2 hydrates, they would serve double duty as CH4 sources and CO2 storage sites. We explore here the swapping phenomenon occurring in structure I (sI) and structure II (sII) CH4 hydrate deposits through spectroscopic analyses and its potential application to CO2 sequestration at the preliminary phase. The present 85% CH4 recovery rate in sI CH4 hydrate achieved by the direct use of binary N2 + CO2 guests is surprising when compared with the rate of 64% for a pure CO2 guest attained in the previous approach. The direct use of a mixture of N2 + CO2 eliminates the requirement of a CO2 separation/purification process. In addition, the simultaneously occurring dual mechanism of CO2 sequestration and CH4 recovery is expected to provide the physicochemical background required for developing a promising large-scale approach with economic feasibility. In the case of sII CH4 hydrates, we observe a spontaneous structure transition of sII to sI during the replacement and a cage-specific distribution of guest molecules. A significant change of the lattice dimension caused by structure transformation induces a relative number of small cage sites to reduce, resulting in the considerable increase of CH4 recovery rate. The mutually interactive pattern of targeted guest–cage conjugates possesses important implications for the diverse hydrate-based inclusion phenomena as illustrated in the swapping process between CO2 stream and complex CH4 hydrate structure.

Effect of Interlayer Ions on Methane Hydrate Formation in Clay Sediments

Natural methane hydrates occurring in marine clay sediments exhibit heterogeneous phase behavior with high complexity, particularly in the negatively charged interlayer region. To date, the real clay interlayer effect on natural methane hydrate formation and stability remains still much unanswered, even though a few computer simulation and model studies are reported. We first examined the chemical shift difference of 27Al, 29Si, and 23Na between dry clay and clay containing intercalated methane hydrates (MH) in the interlayer. We also measured the solid-state 13C MAS NMR spectra of MH in Na-montmorillonite (MMT) and Ca-montmorillonite (MMT) to reveal abnormal methane popularity established in the course of intercalation and further performed cryo-TEM and XRD analyses to identify the morphology and layered structure of the intercalated methane hydrate. The present findings strongly suggest that the real methane amount contained in natural MH deposits should be reevaluated under consideration of the compositional, structural, and physical characteristics of clay-rich sediments. Furthermore, the intercalated methane hydrate structure should be seriously considered for developing the in situ production technologies of the deep-ocean methane hydrate.

Abnormal methane occupancy of natural gas hydrates in deep sea floor sediments

Natural gas hydrates were recovered from near-seafloor sediments and analysed to compare two distinctive methane inclusion phenomena. We document the first observation of abnormal methane occupancy in sediment-rich NGH deposits.

Experimental Study on Two-phase Flow in Artificial Hydrate-bearing Sediments

ABSTRACT It is important to investigate gas-water multiphase flow in methane hydrate-bearing sediment. In this work, we measured relative permeability of gas and water in artificial methane hydrate bearing sediment by the unsteady state method, and determined the effects of hydrate saturation on relative permeability curves. The results show that the relative permeability shifted left with increasing hydrate saturation.

Phase and kinetic behavior of the mixed methane and carbon dioxide hydrates

Large amounts of CH4 are stored as hydrates on continental margins and permafrost regions. If the CH4 hydrates could be converted into CO2 hydrate, they would serve double duty as CH4 sources and CO2 storage sites in the deep ocean sediments. As preliminary investigations, both the phase behavior of CH4 hydrates and kinetic behavior of CO2 hydrate were measured at versatile conditions that can simulate actual marine sediments. When measuring three-phase equilibria (H-LW-V) containing CH4 hydrate, we also closely examined pore and electrolyte effects of clay and NaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium line shift to a higher pressure region. In addition, the kinetic data of CO2 hydrate in the mixtures containing clay and NaCl were determined at 2.0 MPa and 274.15 K. Clay mineral accelerated an initial formation rate of CO2 hydrate by inducing nucleation as initiator, but total amount of formed CO2, of course, decreased due to the capillary effect of clay pores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO2 consumption decrease.

Preliminary Study on Petrophysical Properties of Artificial Gas Hydrate Bearing Sediments

ABSTRACT The permeability and resistance of 4 artificial sediments samples were measured with saturation of gashydrate changed. It is observed that the reduction patterns of permeability of the samples in this study are similar with increasing gas-hydrate saturation, which shows the possibility of existence of correlation with permeability and gas-hydrate saturation. In the measurements of resistance, the resistance of the gas hydrate sediments shows totally different value depending on saturated fluid.