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  • 2020-2023  (6)
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  • 1
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    Numerical Simulation of Hydrate Formation in the LArge-scale Reservoir Simulator (LARS) (2022)
    In:  Energies
    Details
    Publication Date: 2022-03-09
    Description: The LArge-scale Reservoir Simulator (LARS) has been previously developed to study hydrate dissociation in hydrate-bearing systems under in-situ conditions. In the present study, a numerical framework of equations of state describing hydrate formation at equilibrium conditions has been elaborated and integrated with a numerical flow and transport simulator to investigate a multi-stage hydrate formation experiment undertaken in LARS. A verification of the implemented modeling framework has been carried out by benchmarking it against another established numerical code. Three-dimensional (3D) model calibration has been performed based on laboratory data available from temperature sensors, fluid sampling, and electrical resistivity tomography. The simulation results demonstrate that temperature profiles, spatial hydrate distribution, and bulk hydrate saturation are consistent with the observations. Furthermore, our numerical framework can be applied to calibrate geophysical measurements, optimize post-processing workflows for monitoring data, improve the design of hydrate formation experiments, and investigate the temporal evolution of sub-permafrost methane hydrate reservoirs.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 2
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    Gas hydrates in nature and in the laboratory: necessary requirements for formation and properties of the resulting hydrate phase (2022)
    In:  ChemTexts
    Details
    Publication Date: 2022-04-20
    Description: Clathrate hydrates—also known as gas hydrates—are ice-like compounds consisting of gas and water molecules. They occur wherever elevated pressures and low temperatures prevail; and where enough water and hydrate-forming gas molecules are available. Therefore, natural gas hydrates occur at all active and passive continental margins, in permafrost regions, in some deep lakes, and under unfavorable circumstances, also, in pipelines. This article provides an overview of the (thermodynamic) requirements and various models for the nucleation and growth of gas hydrates and the different gas hydrate structures that may occur and which have been detected in nature. Furthermore, this study also shows the influence of the properties of the enclosed gas molecules such as size and shape on the structure and thermodynamic properties of the resulting hydrate phase. Finally, the complexity of a natural environment with regard to the various influences of sediments, microbial activity, and salinity of the pore fluid on hydrate formation is also discussed.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 3
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    Gashydrate – Eine Einführung in Grundlagenforschung und Anwendung (2021)
    Springer
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    Publication Date: 2022-01-18
    Description: Gashydrate, auch „brennendes Eis“ genannt, sind faszinierende, eisähnliche Feststoffe, die aus Wasser- und Gasmolekülen aufgebaut sind und weltweit an allen aktiven und passiven Kontinentalhängen und in Permafrostgebieten vorkommen. Doch ihr unauffälliges Erscheinungsbild täuscht: Die Einschlussverbindungen können beachtliche Mengen Methangas enthalten. Daher besteht einerseits die Hoffnung auf einen möglichen neuen Energieträger und andererseits die Sorge um eine nicht zu unterschätzende Quelle an klimaschädlichem Methangas. Gashydrate, hat die neueste Forschung gezeigt, bieten zudem in vielen Bereichen industrieller Anwendung eine durchaus vielversprechende Alternative zu konventionellen Verfahren. Das vorliegende Buch gibt eine Einführung in die physikalisch-chemischen Grundlagen der Hydratbildung und die Strukturen der Gashydratphasen. Basierend auf diesem grundlegenden Verständnis erklärt es die natürlichen Gashydratvorkommen und zeichnet mögliche Methoden des Abbaus und der Gewinnung von Methangas auf. Es beleuchtet Risiken, die von den Gashydratvorkommen in der Natur ausgehen könnten, und führt in die Möglichkeiten der Nutzung dieser Einschlussverbindungen in verschiedenen industriellen Anwendungsbereichen wie z.B. der Aufbereitung von Abwässern oder der Speicherung von Gasen ein. Zielgruppe dieser kompakten Einführung in die verschiedenen Aspekte der Gashydratforschung sind Studierende der Chemie und Geowissenschaften, Ingenieure, Techniker oder auch Wissenschaftler.
    Language: German
    Type: info:eu-repo/semantics/book
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  • 4
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    A Review of Reactor Designs for Hydrogen Storage in Clathrate Hydrates (2021)
    In:  Applied Sciences
    Details
    Publication Date: 2022-01-19
    Description: Clathrate hydrates are ice-like, crystalline solids, composed of a three-dimensional network of hydrogen bonded water molecules that confines gas molecules in well-defined cavities that can store gases as a solid solution. Ideally, hydrogen hydrates can store hydrogen with a maximum theoretical capacity of about 5.4 wt%. However, the pressures necessary for the formation of such a hydrogen hydrate are 180–220 MPa and therefore too high for large-scale plants and industrial use. Thus, since the early 1990s, there have been numerous studies to optimize pressure and temperature conditions for hydrogen formation and storage and to develop a proper reactor type via optimisation of the heat and mass transfer to maximise hydrate storage capacity in the resulting hydrate phase. So far, the construction of the reactor has been developed for small, sub-litre scale; and indeed, many attempts were reported for pilot-scale reactor design, on the multiple-litre scale and larger. The purpose of this review article is to compile and summarise this knowledge in a single article and to highlight hydrogen-storage prospects and future challenges.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
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    Heterogeneous and Coexisting Hydrate Phases ─ Formation under Natural and Laboratory Conditions (2022)
    In:  Energy & Fuels
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    Publication Date: 2022-09-19
    Description: Natural gas hydrates are non-stoichiometric, crystalline solids composed of water and gas molecules. Dependent upon the source of the hydrate-forming gas, the structure and composition of the occurring natural gas hydrates may vary. In nature, the existence of structure I, structure II, and structure H hydrates containing predominantly methane but also other hydrocarbons, H2S, or CO2 could be verified. Interestingly, the number of reports on coexisting hydrate phases with different structures and compositions in natural gas hydrate reservoirs has increased in recent years. However, it has not yet been clearly clarified what leads to the formation of these coexisting hydrate phases. In the present study, we analyzed natural gas hydrate samples spatially resolved using Raman spectroscopy to check whether these natural samples only show heterogeneity with regard to their cage occupancy and composition or whether they already show coexistent phases. The samples available to us from the Hikurangi margin and the Cascadian margin showed strong fluctuations in cage occupancy and composition within the individual crystals but no coexisting phases. With complementary experiments, we were able to show that gas hydrates with a heterogeneous composition formed from a complex feed gas mixture. Furthermore, we were able to verify experimentally that coexisting phases may form when an initial methane hydrate phase was exposed to a complex gas mixture.
    Language: English
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  • 6
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    Numerical Simulation of Coastal Sub-Permafrost Gas Hydrate Formation in the Mackenzie Delta, Canadian Arctic (2022)
    In:  Energies
    Details
    Publication Date: 2022-07-12
    Description: The Mackenzie Delta (MD) is a permafrost-bearing region along the coasts of the Canadian Arctic which exhibits high sub-permafrost gas hydrate (GH) reserves. The GH occurring at the Mallik site in the MD is dominated by thermogenic methane (CH4), which migrated from deep conventional hydrocarbon reservoirs, very likely through the present fault systems. Therefore, it is assumed that fluid flow transports dissolved CH4 upward and out of the deeper overpressurized reservoirs via the existing polygonal fault system and then forms the GH accumulations in the Kugmallit–Mackenzie Bay Sequences. We investigate the feasibility of this mechanism with a thermo– hydraulic–chemical numerical model, representing a cross section of the Mallik site. We present the first simulations that consider permafrost formation and thawing, as well as the formation of GH accumulations sourced from the upward migrating CH4-rich formation fluid. The simulation results show that temperature distribution, as well as the thickness and base of the ice-bearing permafrost are consistent with corresponding field observations. The primary driver for the spatial GH distribution is the permeability of the host sediments. Thus, the hypothesis on GH formation by dissolved CH4 originating from deeper geological reservoirs is successfully validated. Furthermore, our results demonstrate that the permafrost has been substantially heated to 0.8–1.3 °C, triggered by the global temperature increase of about 0.44 ° C and further enhanced by the Arctic Amplification effect at the Mallik site from the early 1970s to the mid-2000s.
    Language: English
    Type: info:eu-repo/semantics/article
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