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  • AGU (American Geophysical Union)  (10)
  • ECO2 Project Office  (5)
  • ACS (American Chemical Society)  (3)
  • GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel  (3)
  • 1
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    Testing a thermo-chemo-hydro-geomechanical model for gas hydrate-bearing sediments using triaxial compression laboratory experiments (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 18 (9). pp. 3419-3437.
    Details
    Publication Date: 2020-02-06
    Description: Natural gas hydrates are considered a potential resource for gas production on industrial scales. Gas hydrates contribute to the strength and stiffness of the hydrate-bearing sediments. During gas production, the geomechanical stability of the sediment is compromised. Due to the potential geotechnical risks and process management issues, the mechanical behavior of the gas hydrate-bearing sediments needs to be carefully considered. In this study, we describe a coupling concept that simplifies the mathematical description of the complex interactions occurring during gas production by isolating the effects of sediment deformation and hydrate phase changes. Central to this coupling concept is the assumption that the soil grains form the load-bearing solid skeleton, while the gas hydrate enhances the mechanical properties of this skeleton. We focus on testing this coupling concept in capturing the overall impact of geomechanics on gas production behavior though numerical simulation of a high-pressure isotropic compression experiment combined with methane hydrate formation and dissociation. We consider a linear-elastic stress-strain relationship because it is uniquely defined and easy to calibrate. Since, in reality, the geomechanical response of the hydrate-bearing sediment is typically inelastic and is characterized by a significant shear-volumetric coupling, we control the experiment very carefully in order to keep the sample deformations small and well within the assumptions of poroelasticity. The closely coordinated experimental and numerical procedures enable us to validate the proposed simplified geomechanics-to-flow coupling, and set an important precursor toward enhancing our coupled hydro-geomechanical hydrate reservoir simulator with more suitable elastoplastic constitutive models.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 2
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    3-D basin-scale reconstruction of natural gas hydrate system of the Green Canyon, Gulf of Mexico (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 18 (5). pp. 1959-1985.
    Details
    Publication Date: 2020-02-06
    Description: Our study presents a basin-scale 3D modeling solution, quantifying and exploring gas hydrate accumulations in the marine environment around the Green Canyon (GC955) area, Gulf of Mexico. It is the first modeling study that considers the full complexity of gas hydrate formation in a natural geological system. Overall, it comprises a comprehensive basin re-construction, accounting for depositional and transient thermal history of the basin, source rock maturation, petroleum components generation, expulsion and migration, salt tectonics and associated multi-stage fault development. The resulting 3D gas hydrate distribution in the Green Canyon area is consistent with independent borehole observations. An important mechanism identified in this study and leading to high gas hydrate saturation (〉 80 vol. %) at the base of the gas hydrate stability zone (GHSZ), is the recycling of gas hydrate and free gas enhanced by high Neogene sedimentation rates in the region. Our model predicts the rapid development of secondary intra-salt mini-basins situated on top of the allochthonous salt deposits which leads to significant sediment subsidence and an ensuing dislocation of the lower GHSZ boundary. Consequently, large amounts of gas hydrates located in the deepest parts of the basin dissociate and the released free methane gas migrates upwards to recharge the GHSZ. In total, we have predicted the gas hydrate budget for the Green Canyon area that amounts to ∼3,256 Mt of gas hydrate which is equivalent to ∼340 Mt of carbon (∼7 x 1011 m3 of CH4 at STP conditions), and consists mostly of biogenic hydrates.
    Type: Article , PeerReviewed
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  • 3
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    Shallow gas migration along hydrocarbon wells – An unconsidered, anthropogenic source of biogenic methane in the North Sea (2017)
    ACS (American Chemical Society)
    In:  Environmental Science & Technology, 51 (17). pp. 10262-10268.
    Details
    Publication Date: 2020-02-06
    Description: Shallow gas migration along hydrocarbon wells constitutes a potential methane emission pathway that currently is not recognized in any regulatory framework or greenhouse gas inventory. Recently, the first methane emission measurements at three abandoned offshore wells in the Central North Sea (CNS) were conducted showing that considerable amounts of biogenic methane originating from shallow gas accumulations in the overburden of deep reservoirs were released by the boreholes. Here, we identify numerous wells poking through shallow gas pockets in 3D seismic data of the CNS indicating that about one third of the wells may leak, potentially releasing a total of 3-17 kt of methane per year into the North Sea. This poses a significant contribution to the North Sea methane budget. A large fraction of this gas (~42 %) may reach the atmosphere via direct bubble transport (0-2 kt yr-1) and via diffusive exchange of methane dissolving in the surface mixed layer (1-5 kt yr-1), as indicated by numerical modeling. In the North Sea and in other hydrocarbon-prolific provinces of the world shallow gas pockets are frequently observed in the sedimentary overburden and aggregate leakages along the numerous wells drilled in those areas may be significant.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 4
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    Best Practice Guidance for Environmental Risk Assessment for offshore CO2 geological storage (2015)
    ECO2 Project Office
    In:  ECO2 Deliverable, D14.1 . ECO2 Project Office, Kiel, Germany, 53 pp.
    Details
    Publication Date: 2019-03-11
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 5
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    An abyssal hill fractionates organic and inorganic matter in deep-sea surface sediments (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 42 (18). pp. 7663-7672.
    Details
    Publication Date: 2017-04-10
    Description: Current estimates suggest that more than 60% of the global seafloor are covered by millions of abyssal hills and mountains. These features introduce spatial fluid-dynamic granularity whose influence on deep-ocean sediment biogeochemistry is unknown. Here we compare biogeochemical surface-sediment properties from a fluid-dynamically well-characterized abyssal hill and upstream plain: (1) In hill sediments, organic-carbon and -nitrogen contents are only about half as high as on the plain while proteinaceous material displays less degradation; (2) on the hill, more coarse-grained sediments (reducing particle surface area) and very variable calcite contents (influencing particle surface charge) are proposed to reduce the extent, and influence compound-specificity, of sorptive organic-matter preservation. Further studies are needed to estimate the representativeness of the results in a global context. Given millions of abyssal hills and mountains, their integrative influence on formation and composition of deep-sea sediments warrants more attention.
    Type: Article , PeerReviewed
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  • 6
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    Linked halokinesis and mud volcanism at the Mercator Mud Volcano, Gulf of Cadiz (2011)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 116 . B05101.
    Details
    Publication Date: 2018-04-27
    Description: Mud volcanoes are seafloor expressions of focused fluid flow that are common in compressional tectonic settings. New high-resolution 3-D seismic data from the Mercator mud volcano (MMV) and an adjacent buried mud volcano (BMV) image the internal structure of the top 800 m of sediment at both mud volcanoes, revealing that both are linked and have been active episodically. The total volumes of extruded mud range between 0.15 and 0.35 km3 and 0.02–0.05 km3 for the MMV and the BMV, respectively. The pore water composition of surface sediment samples suggests that halokinesis has played an important role in the evolution of the mud volcanoes. We propose that erosion of the top of the Vernadsky Ridge that underlies the mud volcanoes activated salt movement, triggering deep migration of fluids, dissolution of salt, and sediment liquefaction and mobilization since the end of the Pliocene. Since beginning of mud volcanism in this area, the mud volcanoes erupted four times while there was only one reactivation of salt tectonics. This implies that there are other mechanisms that trigger mud eruptions. The stratigraphic relationship of mudflows from the MMV and BMV indicates that the BMV was triggered by the MMV eruptions. This may either be caused by loading-induced hydrofracturing within the BMV or due to a common feeder system for both mud volcanoes. This study shows that the mud volcanoes in the El Arraiche mud volcano field are long-lived features that erupt with intervals of several tens of thousands of years.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
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    Report on range of long-term scenarios to be simulated (2012)
    ECO2 Project Office
    In:  ECO2 Deliverable, D12.2 . ECO2 Project Office, 6 pp.
    Details
    Publication Date: 2019-03-11
    Description: In order to proceed with speculative modelling of the impacts of potential leakage of geologically stored carbon, it is necessary to develop plausible scenarios. Here a range of such scenarios are developed based on a consensus of the possible geological mechanisms of leakage, namely abandoned wells, geological faults and operational blowouts. Whilst the resulting scenarios remain highly speculative, they do enable short term progress in modelling and provide a basis for further debate and refinement.
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 8
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    CCT2 Report on model interfacing and evaluation strategy (2012)
    ECO2 Project Office
    In:  ECO2 Deliverable, D12.1 . ECO2 Project Office, 14 pp.
    Details
    Publication Date: 2019-03-11
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 9
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    Gas release experiment (2012)
    GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
    In:  In: RV Celtic Explorer EUROFLEETS cruise report CE12010 - ECO2@NorthSea : 20.07. – 06.08.2012, Bremerhaven - Hamburg. , ed. by Linke, P. GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Kiel, pp. 28-32.
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    Publication Date: 2014-02-20
    Type: Book chapter , NonPeerReviewed
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  • 10
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    Fluxes of CO2 from natural seep sites and Sleipner storage site (2014)
    ECO2 Project Office
    In:  ECO2 Deliverable, D2.2 . ECO2 Project Office, Kiel, Germany, 43 pp.
    Details
    Publication Date: 2019-03-11
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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