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Vibrational behavior and host-guest interaction of C 7 D 14 molecule (the most representative large molecular guest hydrate) in 51268 cage of structure H hydrate. [Display omitted] • The Raman spectral confusion of 512 cage and 435663 cage have been clarified by Density Functional Theory and in situ Raman spectra, which provides a theoretical basis for the accurate determination of sH hydrate. • The stretching vibration Raman spectrum of C 7 D 14 in the 51268 cages of sH is reported for the first time, which provides a basis for regulating the formation of macromolecular hydrate. • A high precision Raman spectral resolution method of Raman wavenumber for multi-hydrocarbon supramolecular was raised. • Repulsion and attraction among guest and host molecules cooperatively stabilizes the cluster structure. • Raman spectral calibration equation for hydrate under different temperature and pressure was proposed. The formation of complex multi-guest clathrate hydrates, which are more stable than single-guest ones, has expanded the clathrate hydrate stability phase space. Multi-guest clathrate hydrate may lead to the formation of sI, sII, and sH structures, introducing a variety of possible guest occupancy and crystal composition; the occupancy of sH cages in particular remains poorly understood. We report the occupancy of methane (CH 4) in the 512 and 435663 cages of sH measured via in situ Raman spectrum and density functional theory, identifying the corresponding peak position for the C–H stretching mode at 2909.80 cm−1 and 2912.40 cm−1, respectively. The in situ Raman spectrum of C 7 D 14 in the 51268 cages of sH is also reported for the first time. Vibrational-mode analysis shows that repulsion and attraction among guest and host molecules cooperatively stabilizes the cluster structure. In addition, our work provides an accurate method of distinguishing sI and sH hydrates by in situ Raman spectroscopy, offering a spectroscopic basis for the study of crystal transformation dynamics in polymorphous clathrate hydrates. [ABSTRACT FROM AUTHOR]

Gas hydrates have been considered promising in gas storage, gas separation, and water desalination. The hydrates' technical application is affected by the long kinetics time. Of interest is gas hydrates show strong facilitation in dissociated water containing a high concentration of micro-nanobubbles. Here, it was discovered that the nano-particles present in the dissociated water were identified as nano-bubbles, characterized by nanoparticle track analyzer and infrared spectrum. The presence of bubbles increased the nucleation probability, likely attributed to the provision of nucleation sites. Results indicated that the ability of facilitation was related to the nanobubble types: the bubble solution with the same guest molecules exhibited similar facilitation to dissociated water; specifically, the average induction time was shortened by 27.48 %, the nucleation probability was increased by 50 % compared to deionized water. Moreover, the time hydrate filled the field of view with high bubble concentration was reduced by 60 % compared with low bubble concentration. The facilitation effect mechanism could be related to the presence of gas-dense regions inside the bubbles, based on the Raman results. This finding may offer valuable insights for the application of hydrate-based energy storage technology and shed light on the potential role of bubbles in causing memory effects. • Nano-bubbles are generated as a result of gas hydrate dissociation. • These bubbles have the potential to facilitate hydrate nucleation, with the specific bubble type influencing the process. • The bubbles play a role in promoting hydrate growth, reducing the growth time by 60 %. • The existence of high-pressure zones within the bubbles may be confirmed. [ABSTRACT FROM AUTHOR]

Several trial productions have been conducted on marine natural gas hydrate reservoirs, demonstrating its enormous potential as an alternative energy source. Nonetheless, sustained and efficient production still remains challenging, with crucial issues on low gas production efficiency and blockages. The large amount of hydrate decomposition and resulting heat absorption can lead to prolonged subzero conditions close to the well; this can readily induce ice formation and blockage. This study aims to investigate the issue of ice blockages caused by insufficient energy supply during the recovery process. A systematic analysis of the energy consumption and ice blockage quantification at each stage of the traditional multi-stage direct depressurization and constant speed depressurization methods is conducted. A hybrid optimized scheme is proposed, which enhances energy utilization efficiency by appropriately utilizing reservoir sensible heat during the initial stage of production. Additionally, a multi-stage constant speed depressurization method is introduced in the later stages to mitigate production fluctuations and reduce blockage duration. Results showed a 69.5 % increase in energy efficiency and an average 67.1 % decline in gas blockage duration with comparable gas productivity. The proposed method could be a viable solution to mitigate challenges of icing blockages and fluctuating production during trial tests of marine hydrate reservoirs, achieving improved energy efficiency and sustainable production. • Ice blockage in hydrate reservoirs reduced production efficiency during direct and constant-speed depressurization methods. • Proposed a hybrid method to address gas production fluctuations caused by ice blockage through energy consumption analysis. • Multi-stage analysis revealed 70% energy efficiency improvement and 67% reduced ice blockage duration with the hybrid method. [ABSTRACT FROM AUTHOR]