Japan Geoscience Union Meeting 2021

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[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS26] Gas hydrates in environmental-resource sciences

Sun. Jun 6, 2021 1:45 PM - 3:15 PM Ch.12 (Zoom Room 12)

convener:Hitoshi Tomaru(Department of Earth Sciences, Chiba University), Akihiro Hachikubo(Kitami Institute of Technology), Atsushi Tani(Department of Human Environmental Science, Graduate School of Human Development and Environment, Kobe University), Shusaku Goto(Institute for Geo-Resources and Environment National Institute of Advanced Industrial Science and Technology), Chairperson:Hitoshi Tomaru(Department of Earth Sciences, Chiba University), Shusaku Goto(Institute for Geo-Resources and Environment National Institute of Advanced Industrial Science and Technology)

2:05 PM - 2:25 PM

[MIS26-02] Experimental Verification of CH4-CO2 Replacement Occurring in Natural Gas Hydrates for Energy Recovery and CO2 Sequestration

★Invited Papers

*Yongwon Seo1 (1.Ulsan National Institute of Science and Technology, Republic of Korea)

Keywords:natural gas hydrates, replacement, CO2 sequestration, phase behavior, structural transformation

CH4 recovery using CO2 injection into natural gas hydrates is very attractive because it can perform dual functions of energy production and CO2 sequestration. In this study, the CH4-CO2 replacement that occurs in various gas hydrate structures (sI, sII, and sH) was investigated with a primary focus on phase behaviors and structural transformation. To verify the influence of CO2 injection on the thermodynamic stability of gas hydrates, phase equilibria of the initial CH4 hydrate (sI), CH4 + C3H8 hydrate (sII), and CH4 + 2,2-dimethylbutane (neohexane, NH) hydrate (sH) were compared with those of the corresponding gas hydrates replaced with CO2. After the replacement reaction was completed, significant shifts in the hydrate equilibrium curves of each system were observed, which indicates that the substantial extent of the replacement was achievable through CO2 injection. The initial and replaced hydrates were analyzed via 13C NMR spectroscopy and powder X-ray diffraction (PXRD) to examine cage-dependent guest distributions and possible structural transition. To identify heat generation or absorption during the replacement process and to elucidate its influence on the thermal properties of the replaced hydrates, the changes in heat flow and dissociation enthalpies (ΔHd) were measured using a high-pressure micro-differential scanning calorimeter (HP μ-DSC). The replacement behaviors were strongly dependent on the structure of initial gas hydrates. The overall experimental results provide further insights into the cage-specific occupation of external gas molecules and thermodynamic stability for the real replacement occurring in natural gas hydrate reservoirs for CH4 recovery and CO2 sequestration.