Kuhs, Werner F.

[["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.issue","1-4"],["dc.bibliographiccitation.journal","Marine Geology"],["dc.bibliographiccitation.lastpage","14"],["dc.bibliographiccitation.volume","244"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Abegg, Fritz"],["dc.date.accessioned","2018-11-07T10:57:49Z"],["dc.date.available","2018-11-07T10:57:49Z"],["dc.date.issued","2007"],["dc.description.abstract","The state of preservation of natural gas hydrate samples, recovered from 6 sites drilled during ODP Leg 204 at southern summit of Hydrate Ridge, Oregon Margin, has been investigated by X-ray diffraction (XRD) and cryo-scanning-electron-inicroscopy (cryo-SEM) techniques. A detailed characterization of the state of decomposition of gas hydrates is necessary since no pressurized autoclave tools were used for sampling and partial dissociation must have occurred during recovery prior to the quench and storage in liquid nitrogen. Samples from 16 distinct horizons have been investigated by synchrotron X-ray diffraction measurements at HASYLAB/ Hamburg. A full profile fitting analysis (\"Rietveld method\") of synchrotron XRD data provides quantitative phase determinations of the major sample constituents such as gas hydrate structure I (sI), hexagonal ice (Ih) and quartz. The ice content (Ih) in each sample is related to frozen water composed of both original existing pore water and the water from decomposed hydrates. Hydrate contents as measured by diffraction vary between 0 and 68 wt.% in the samples we measured. Samples with low hydrate content usually show micro-structural features in cryo-SEM ascribed to extensive decomposition. Comparing the appearance of hydrates at different scales, the grade of preservation seems to be primarily correlated with the contiguous volume of the original existing hydrate; the dissociation front appears to be indicated by micrometer-sized pores in a dense ice matrix. (c) 2007 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.margeo.2007.05.003"],["dc.identifier.isi","000250150800001"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50340"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","0025-3227"],["dc.title","Appearance and preservation of natural gas hydrate from Hydrate Ridge sampled during ODP Leg 204 drilling"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","L13608"],["dc.bibliographiccitation.issue","13"],["dc.bibliographiccitation.journal","Geophysical Research Letters"],["dc.bibliographiccitation.volume","34"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Klein, Hannah"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T11:00:39Z"],["dc.date.available","2018-11-07T11:00:39Z"],["dc.date.issued","2007"],["dc.description.abstract","Due to experimental difficulties grain size distributions of gas hydrate crystallites are largely unknown in natural samples. For the first time, we were able to determine grain size distributions of six natural gas hydrates for samples retrieved from the Gulf of Mexico and from Hydrate Ridge offshore Oregon from varying depths. High-energy synchrotron radiation provides high photon fluxes as well as high penetration depth and thus allows for investigation of bulk sediment samples. The gas hydrate crystallites appear to be (log-) normally distributed in the natural samples and to be of roughly globular shape. The mean grain sizes are in the range from 300-600 mu m with a tendency for bigger grains to occur in greater depth, possibly indicating a difference in the formation age. Laboratory produced methane hydrate, starting from ice and aged for 3 weeks, shows half a log-normal curve with a mean value of similar to 40 mu m. This one order-of-magnitude smaller grain sizes suggests that care must be taken when transposing grain-size sensitive (petro-)physical data from laboratory-made gas hydrates to natural settings."],["dc.identifier.doi","10.1029/2006GL029134"],["dc.identifier.isi","000248024000002"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50975"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Geophysical Union"],["dc.relation.issn","0094-8276"],["dc.title","First determination of gas hydrate crystallite size distributions using high-energy synchrotron radiation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","116"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Marine and Petroleum Geology"],["dc.bibliographiccitation.lastpage","125"],["dc.bibliographiccitation.volume","27"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Pape, Thomas"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Heeschen, Katja U."],["dc.contributor.author","Abegg, Friedrich"],["dc.date.accessioned","2018-11-07T08:48:06Z"],["dc.date.available","2018-11-07T08:48:06Z"],["dc.date.issued","2010"],["dc.description.abstract","Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities. The crystallographic structures were established by X-ray diffraction, using both conventional X-ray sources and high-energy synchrotron radiation. The microstructures were examined by cryo-stage Field-Emission Scanning Electron Microscopy (FE-SEM). Good sample preservation was warranted by the low ice fractions shown from quantitative phase analyses. Gas hydrate structure II samples from the Green Canyon in the northern GOM had methane concentrations of 70-80% and up to 30% of C-2-C-5 of measured hydrocarbons. Hydrocarbons in the crystallographic structure I hydrate from the Chapopote asphalt volcano in the southern GOM was comprised of more than 98% methane. Fairly different microstructures were identified for those different hydrates: Pores measuring 200-400 nm in diameter were present in structure I gas hydrate samples; no such pores but dense crystal surfaces instead were discovered in structure II gas hydrate. The stability of the hydrate samples is discussed regarding gas composition, crystallographic structure and microstructure. Electron microscopic observations showed evidence of gas hydrate and liquid oil co-occurrence on a micrometer scale. That demonstrates that oil has direct contact to gas hydrates when it diffuses through a hydrate matrix. (C) 2009 Elsevier Ltd. All rights reserved."],["dc.identifier.doi","10.1016/j.marpetgeo.2009.03.004"],["dc.identifier.isi","000272308200010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/21128"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Sci Ltd"],["dc.relation.issn","0264-8172"],["dc.title","Microstructures of structure I and II gas hydrates from the Gulf of Mexico"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","555"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","Geo-Marine Letters"],["dc.bibliographiccitation.lastpage","562"],["dc.bibliographiccitation.volume","32"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Enzmann, Frieder"],["dc.contributor.author","Walz, Peter"],["dc.contributor.author","Huthwelker, Thomas"],["dc.contributor.author","Tuckermann, Juergen"],["dc.contributor.author","Schwarz, J.-Oliver"],["dc.contributor.author","Pape, Thomas"],["dc.contributor.author","Peltzer, Edward T."],["dc.contributor.author","Mokso, Rajmund"],["dc.contributor.author","Wangner, David"],["dc.contributor.author","Marone, Federica"],["dc.contributor.author","Kersten, Michael"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Stampanoni, Marco"],["dc.contributor.author","Brewer, Peter G."],["dc.date.accessioned","2018-11-07T09:02:48Z"],["dc.date.available","2018-11-07T09:02:48Z"],["dc.date.issued","2012"],["dc.description.abstract","Despite much progress over the past years in fundamental gas hydrate research, frontiers to the unknown are the early beginning and early decomposition of gas hydrates in their natural, submarine environment: gas bubbles meeting ocean water and forming hydrate, and gas starting to escape from the surface of a hydrate grain. In this paper we report on both of these topics, and present three-dimensional microstructure results obtained by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM). Hydrates can precipitate when hydrate-forming molecules such as methane exceed solubility, and combine with water within the gas hydrate stability zone. Here we show hydrate formation on surfaces of bubbles from different gas mixtures and seawater, based on underwater robotic in situ experiments in the deep Monterey Canyon, offshore California. Hydrate begins to form from the surrounding water on the bubble surfaces, and subsequently grows inward into the bubble, evidenced by distinct edges. Over time, the bubbles become smaller while gas is being incorporated into newly formed hydrate. In contrast, current understanding has been that hydrate decomposition starts on the outer surface of hydrate aggregates and grains. It is shown that in an early stage of decomposition, newly found tube structures connect well-preserved gas hydrate patches to areas that are dissociating, demonstrating how dissociating areas in a hydrate grain are linked through hydrate that is still intact and will likely decompose at a later stage."],["dc.identifier.doi","10.1007/s00367-012-0276-0"],["dc.identifier.isi","000311025300018"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/24765"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Springer"],["dc.publisher.place","New york"],["dc.relation.conference","10th International Conference on Gas in Marine Sediments (GIMS)"],["dc.relation.eventlocation","Listvyanka, RUSSIA"],["dc.relation.issn","1432-1157"],["dc.relation.issn","0276-0460"],["dc.title","Microstructure characteristics during hydrate formation and dissociation revealed by X-ray tomographic microscopy"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","L23612"],["dc.bibliographiccitation.issue","23"],["dc.bibliographiccitation.journal","Geophysical Research Letters"],["dc.bibliographiccitation.volume","35"],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Enzmann, Frieder"],["dc.contributor.author","Szeder, Thore"],["dc.contributor.author","Huthwelker, Thomas"],["dc.contributor.author","Stampanoni, Marco"],["dc.contributor.author","Marone, Federica"],["dc.contributor.author","Hintermuller, Christoph"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Kersten, Michael"],["dc.date.accessioned","2018-11-07T11:07:59Z"],["dc.date.available","2018-11-07T11:07:59Z"],["dc.date.issued","2008"],["dc.description.abstract","We report the 3D microstructure analyses of natural gas hydrates sampled from Gulf of Mexico. The samples were characterized by synchrotron radiation X-ray cryotomographic microscopy (SRXCTM) using the 'TOMCAT' beam line at the Swiss Light Source (SLS). The SRXCTM demonstrates its applicability to unlock some microscopic features of the marine hydrates, in particular of crystallite size and grain boundary network. The gas hydrate domains are surrounded by a network of pores of typically a few micrometers, which are largely due to decomposition. Out of the SRXCTM data, the porosity, total volume of the voids, the void surface area and number of the total gas-filled voids have been calculated. The results reveal the capability of SRXCTM to access the 3D microstructure which is of fundamental importance to model the petrophysical properties of natural gas hydrates."],["dc.description.sponsorship","GEOTECHNOLOGIEN [03G0604A]"],["dc.identifier.doi","10.1029/2008GL035460"],["dc.identifier.isi","000261669300001"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52692"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Geophysical Union"],["dc.relation.issn","1944-8007"],["dc.relation.issn","0094-8276"],["dc.title","Natural gas hydrate investigations by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM)"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","85"],["dc.bibliographiccitation.issue","1-4"],["dc.bibliographiccitation.journal","Marine Geology"],["dc.bibliographiccitation.lastpage","94"],["dc.bibliographiccitation.volume","274"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Hemes, Susanne"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","MacDonald, Ian"],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T08:40:22Z"],["dc.date.available","2018-11-07T08:40:22Z"],["dc.date.issued","2010"],["dc.description.abstract","Methane hydrates are present in marine seep systems and occur within the gas hydrate stability zone. Very little is known about their crystallite sizes and size distributions because they are notoriously difficult to measure. Crystal size distributions are usually considered as one of the key petrophysical parameters because they influence mechanical properties and possible compositional changes, which may occur with changing environmental conditions. Variations in grain size are relevant for gas substitution in natural hydrates by replacing CH(4) with CO(2) for the purpose of carbon dioxide sequestration. Here we show that crystallite sizes of gas hydrates from some locations in the Indian Ocean, Gulf of Mexico and Black Sea are in the range of 200-400 mu m; larger values were obtained for deeper-buried samples from ODP Leg 204. The crystallite sizes show generally a log-normal distribution and appear to vary sometimes rapidly with location. (C) 2010 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.margeo.2010.03.007"],["dc.identifier.isi","000279524100007"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/19216"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","0025-3227"],["dc.title","Grain size measurements of natural gas hydrates"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","207"],["dc.bibliographiccitation.issue","1-2"],["dc.bibliographiccitation.journal","Earth and Planetary Science Letters"],["dc.bibliographiccitation.lastpage","217"],["dc.bibliographiccitation.volume","299"],["dc.contributor.author","Klapp, Stephan A."],["dc.contributor.author","Murshed, M. Mangir"],["dc.contributor.author","Pape, Thomas"],["dc.contributor.author","Klein, Helmut"],["dc.contributor.author","Bohrmann, Gerhard"],["dc.contributor.author","Brewer, Peter G."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T08:37:59Z"],["dc.date.available","2018-11-07T08:37:59Z"],["dc.date.issued","2010"],["dc.description.abstract","In underwater hydrocarbon seepage environments, gas hydrates are considered to play a significant role as shallow gas reservoirs and buffers for light hydrocarbon expulsion. Here we report on mixed hydrate structures from the Chapopote Knoll in the southern Gulf of Mexico and discuss several options on how a mixture of structure I (sI) and structure II (sII) gas hydrate may occur in nature. Locally resolving microscopic methods are needed to characterize the coexistence of different hydrate structures at geological hydrate deposits; we used Raman spectroscopy, X-ray diffraction, and gas chromatography for our investigations. Gas hydrates were found within the matrix and pores of the asphalts extruded at the seafloor. Two of the three hydrate pieces investigated comprised only sI, formed mostly from methane. In contrast, one piece comprised an intimate mixture of both sI and sII with sII representing ca. 25 wt.% and sI ca. 75 wt.% of the hydrate present. The two structures were closely associated within individual grain agglomerates. The crystallites of sII were significantly larger than of sI, suggesting differences in the nucleation density or different crystallite ages. The structural coexistence may be a result of one or more processes: i) de-mixing into two hydrate structures during the growth from the gas phase, which provides an additional degree of freedom for lowering the free energy in the system; ii) fractionated crystallization with a subsequently changing molecular composition; iii) crystallization from separated gas bubbles with different hydrocarbon compositions and water; and iv) partial transformation from sII to sI after hydrate nucleation, ceasing when a thermodynamically stable state was reached. The presented work will affect future assessments of natural hydrate deposits at thermogenic hydrocarbon systems, as it shows that both hydrate types I and II can be present at a certain geological site, and may provide a lingering strength to the system if conditions fall below the sI stability limit. This suggests that present worldwide hydrate occurrences are likely to be underestimated. (C) 2010 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.epsl.2010.09.001"],["dc.identifier.isi","000284292100020"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/18668"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","1385-013X"],["dc.relation.issn","0012-821X"],["dc.title","Mixed gas hydrate structures at the Chapopote Knoll, southern Gulf of Mexico"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]