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  • Springer  (7)
  • China Geological Survey  (5)
  • ASLO (Association for the Sciences of Limnology and Oceanography)  (2)
  • GEOMAR Helmholtz-Zentrum für Ozeanforschung
  • 1
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    The Character and Formation of Elongated Depressions on the Upper Bulgarian Slope (2018)
    Springer
    In:  Journal of Ocean University of China, 17 (3). pp. 555-562.
    Details
    Publication Date: 2021-02-08
    Description: Seafloor elongated depressions are indicators of gas seepage or slope instability. Here we report a sequence of slope-parallel elongated depressions that link to headwalls of sediment slides on upper slope. The depressions of about 250 m in width and several kilometers in length are areas of focused gas discharge indicated by bubble-release into the water column and methane enriched pore waters. Sparker seismic profiles running perpendicular and parallel to the coast, show gas migration pathways and trapped gas underneath these depressions with bright spots and seismic blanking. The data indicate that upward gas migration is the initial reason for fracturing sedimentary layers. In the top sediment where two young stages of landslides can be detected, the slope-parallel sediment weakening lengthens and deepens the surficial fractures, creating the elongated depressions in the seafloor supported by sediment erosion due to slope-parallel water currents.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1007/s11802-018-3460-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Linked sediment and water-column methanotrophy at a man-made gas blowout in the North Sea: Implications for methane budgeting in seasonally stratified shallow seas (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). S367-S386.
    Details
    Publication Date: 2019-02-01
    Description: Large quantities of the greenhouse gas methane (CH4) are stored in the seafloor. The flux of CH4 from the sediments into the water column and finally to the atmosphere is mitigated by a series of microbial methanotrophic filter systems of unknown efficiency at highly active CH4-release sites in shallow marine settings. Here, we studied CH4-oxidation and the methanotrophic community at a high-CH4-flux site in the northern North Sea (well 22/4b), where CH4 is continuously released since a blowout in 1990. Vigorous bubble emanation from the seafloor and strongly elevated CH4 concentrations in the water column (up to 42 µM) indicated that a substantial fraction of CH4 bypassed the highly active (up to ∼2920 nmol cm−3 d−1) zone of anaerobic CH4-oxidation in sediments. In the water column, we measured rates of aerobic CH4-oxidation (up to 498 nM d−1) that were among the highest ever measured in a marine environment and, under stratified conditions, have the potential to remove a significant part of the uprising CH4 prior to evasion to the atmosphere. An unusual dominance of the water-column methanotrophs by Type II methane-oxidizing bacteria (MOB) is partially supported by recruitment of sedimentary MOB, which are entrained together with sediment particles in the CH4 bubble plume. Our study thus provides evidence that bubble emission can be an important vector for the transport of sediment-borne microbial inocula, aiding in the rapid colonization of the water column by methanotrophic communities and promoting their persistence close to highly active CH4 point sources.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10388
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Effects of climate change on methane emissions from seafloor sediments in the Arctic Ocean: A review (2016)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 61 (S1). pp. 301-309.
    Details
    Publication Date: 2019-09-24
    Description: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and seaair exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/lno.10307
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Gas migration through Opouawe Bank at the Hikurangi margin offshore New Zealand (2016)
    Springer
    In:  Geo-Marine Letters, 36 (3). pp. 187-196.
    Details
    Publication Date: 2019-09-23
    Description: This study presents 2D seismic reflection data, seismic velocity analysis, as well as geochemical and isotopic porewater compositions from Opouawe Bank on New Zealand’s Hikurangi subduction margin, providing evidence for essentially pure methane gas seepage. The combination of geochemical information and seismic reflection images is an effective way to investigate the nature of gas migration beneath the seafloor, and to distinguish between water advection and gas ascent. The maximum source depth of the methane that migrates to the seep sites on Opouawe Bank is 1,500–2,100 m below seafloor, generated by low-temperature degradation of organic matter via microbial CO2 reduction. Seismic velocity analysis enabled identifying a zone of gas accumulation underneath the base of gas hydrate stability (BGHS) below the bank. Besides structurally controlled gas migration along conduits, gas migration also takes place along dipping strata across the BGHS. Gas migration on Opouawe Bank is influenced by anticlinal focusing and by several focusing levels within the gas hydrate stability zone.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1007/s00367-016-0441-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Charakterisierung von Gashydratlagerstätten und Überwachung des Erdgasförderprozesses : Abschlussbericht SUGAR II : (A: Methoden zur Exploration und Überwachung von Gashydrat-Lagerstätten) : Laufzeit des Vorhabens: 1.7.2011-30.6.2014, Förderkennzeichen BMBF 03G0819A (2015)
    GEOMAR Helmholtz-Zentrum für Ozeanforschung
    In:  GEOMAR Helmholtz-Zentrum für Ozeanforschung, Kiel, Germany, 48 pp.
    Details
    Publication Date: 2019-04-10
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2314/GBV:848039963
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    OceanRep: Report - other report
  • 6
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    SUGAR III - Submarine Gashydrat Ressourcen; Teil B: Exploration einer Feldtest-Lokation und geomechanisches Verhalten beim Gashydratabbau; Teilvorhaben GEOMAR: Charakterisierung der Gashydratvorkommen im Donautiefseefächer : öffentlicher Schlussbericht für die Technische Informationsbibliothek (TIB) an der Universität Hannover : Laufzeit des Vorhabens und Berichtszeitraum: 01.01.2015-31.03.2018. SUGAR III - submarine gas hydrate resources; part B: exploration of a field test location and geomechanical behavior during gas hydrate exploitation; subproject GEOMAR: characterization of gas hydrate accumulations in the Danube deep-sea fan, Förderkannzeichen: 03G0856A (2018)
    GEOMAR Helmholtz-Zentrum für Ozeanforschung
    In:  GEOMAR Helmholtz-Zentrum für Ozeanforschung, Kiel, 98 pp.
    Details
    Publication Date: 2019-05-03
    Description: GEOMAR's project was integrated into the large-scale collaborative project SUGAR-III with 19 partners from industry and academia that was also coordinated by GEOMAR. The ain of the project was to characterize the gas hydrate accumulations in the Danube deep-sea fan geophysically and geochemically, to develop a three-dimensional geological model of the deposit and simulate its formation over geological time scales using the hydrate module developed in the PetroMod software, to investigate the problem of geomechanical destabilization and sand production occurring during hydrate exploitation by means of high-pressure experiments, to further develop the SUGAR gas hydrate technologies on geophysical data analysis, geological basin modelling and geomechanical test units in collaboration with the industrial project partners.
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2314/GBV:1663478228
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    OceanRep: Report - other report
  • 7
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    Spatial and temporal modelling of thermal effects during CO2 injection into methane-hydrate reservoirs (2014)
    China Geological Survey
    In:  [Paper] In: 8. International Conference on Gas Hydrates (ICGH8), 28.07.-01.08.2014, Beijing, China . Proceedings of the 8th International Conference on Gas Hydrates (ICGH8-2014), Beijing, China, 28 July - 1 August, 2014 ; T3-56 .
    Details
    Publication Date: 2016-12-21
    Description: Injection of CO2 into CH4-hydrate bearing sediments, and the resulting in-situ replacement of CH4-hydrate by CO2-hydrate, has been proposed as a technique for the emission-free production of natural gas from gas hydrates. While the hydrate conversion is thermodynamically feasible, many studies conclude that the overall process suffers from mass transfer limitations and CH4 production is limited after short time. To improve CH4 production various technical concepts have been considered, including the injection of heated supercritical CO2 combining chemical activation and thermalstimulation. While the feasibility of the concept was demonstrated in high-pressure flow-through experiments and high CH4 production efficiencies were observed, it was evident that overall yields and efficiencies were influenced by a variety of processes which could not be disclosed through bulk mass and volume analysis. Here we present different numerical simulation strategies which were developed and tested as tools to better understand the importance of mass and heat transport relative to reaction and phase transition kinetics for CH4 release and production, or for CO2 retention, respectively. The modeling approaches are discussed with respect to applicability for experimental design, process development or prediction of CH4 production from natural gas hydrate reservoirs on larger scales.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Conference paper
  • 8
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    Experimental investigation of water permeability in quartz sand as function of CH4-hydrate saturation (2014)
    China Geological Survey
    In:  [Paper] In: 8. International Conference on Gas Hydrates (ICGH8), 28.07.-01.08.2014, Beijing, China . Proceedings of the 8th International Conference on Gas Hydrates (ICGH8) Beijing, China, 28 July - 1 August, 2014 ; T1-68 .
    Details
    Publication Date: 2014-11-21
    Description: Water permeability in gas hydrate bearing sediments is a crucial parameter for the prediction of gas production scenarios. So far, the commonly used permeability models are backed by very few experimental data. Furthermore, detailed knowledge of the exact formation mechanism leads to severe uncertainties in the interpretation of the experimental data. We formed CH4 hydrates from a methane saturated water solution and used Magnetic Resonance Imaging (MRI) to measure time resolved maps of the three-dimensional gas hydrate saturation. These maps were used for 3D Finite Elements Method (FEM) simulations. The simulation results enabled us to optimize existing models for permeabilities as function of gas hydrate saturation.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Conference paper
  • 9
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    Gas hydrate accumulations at the Alaska North Sloge: total assessment based on 3D petroleum system modeling (2014)
    China Geological Survey
    In:  [Paper] In: 8. International Conference on Gas Hydrates (ICGH8), 28.07.-01.08.2014, Beijing, China . Proceedings of the 8th International Conference on Gas Hydrates (ICGH8-2014), Beijing, China, 28 July - 1 August, 2014 ; T2-37 .
    Details
    Publication Date: 2014-11-21
    Description: The Alaska North Slope comprises an area of about 400,000 km2 including prominent gas and oil fields. Gas hydrates occur widely at the Alaska North Slope. A recent assessment by the USGS estimates 0.7-4.47 x 1012 m3 of technically recoverable gas hydrates based on well data and drilled hydrate accumulations. In spring 2012 a production field trial, testing CO2/N2 injection and depressurization, was conducted by USDOE/JOGMEC/ConocoPhillips at the Ignik Sikumi site. The 3D geological model of the Alaska North Slope developed by the USGS and Schlumberger is used to test the new gas hydrate module in the petroleum systems modeling software PetroMod®. Model results of the present extent of the gas hydrate stability zone (GHSZ) are in good agreement with results from well data. The model simulations reveal that the evolution of the GHSZ over time is primarily controlled by the climatic conditions regulating the extent of the permafrost during the last 1 Myr. Preliminary model runs predict the highest gas hydrate saturations near the major faults and at the bottom of the GHSZ, where thermogenic methane gas accumulates after migration through the most permeable stratigraphic layers (e.g. Sag River Sandstone Fm, Ivishak Fm). Gas hydrate saturations predicted for the Mount Elbert Stratigraphic Test Well and the Ignik Sikumi sites are basically controlled by the alternation of layers with different permeability and the fault properties (time of opening, permeability, etc). Further results including a total gas hydrate assessment for the Alaska North Slope will be presented during the conference.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Conference paper
  • 10
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    Gas hydrate dynamics at the Green Canyon Site, Gulf of Mexico - recovery prospects based on new 3-D modeling study (2014)
    China Geological Survey
    In:  [Paper] In: 8. International Conference on Gas Hydrates (ICGH8), 28.07.-01.08.2014, Beijing, China . Proceedings of the 8th International Conference on Gas Hydrates (ICGH8-2014), Beijing, China, 28 July - 1 August, 2014 ; T3-63 .
    Details
    Publication Date: 2019-09-23
    Description: Due to their favorable P-T conditions and organic-rich deposits, sub-seafloor sediments in the northern Gulf of Mexico are known to have a large potential for gas hydrate accumulations. The presence of gas hydrates within sediments of the Green Canyon block has been proven by various methods, incl. seismic imaging, geochemical analysis, and drilling conducted mainly as a part of Joint Industry Project (JIP) Phase II. Gas hydrates reported therein usually occur as tens up to hundreds of meters thick sections with moderate to high concentrations within a range of 50 – 70 vol. % of pore space, and hence, seem to offer a considerable natural deposit of methane gas. The main focus of this study was to explore the complex effects of a set of control- parameters responsible for hydrocarbon migration and storage within the Gas Hydrate Stability Zone (GHSZ) on the accumulation of gas hydrates. To investigate the processes of basin formation and its subsidence history, source rock maturation, hydrocarbon migration and expulsion, and to quantify the gas hydrate accumulation potential, 3-D numerical study has been conducted using PetroMod. The area of interest extends over ~14 km x 33 km and covers the edge of the Sigsbee Escarpment representing the main salt mobility front in the region. The simulation contains full depositional history of the Green Canyon block, incl. salt deposition and re-mobilization as well as its further implications for temperature field, fluids migration and sedimentary layers distribution. Methane generation has been resolved by in-situ POC degradation and deep thermogenic mobilization from two distinct hydrocarbon sources. As a result, we present a number of likely scenarios of gas hydrate formation and accumulation in the study area that have been calibrated against available data.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Conference paper
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