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  • 1
    Publication Date: 2018-05-31
    Description: Mud volcanism and fluid seepage are common phenomena on the continental margin in the Gulf of Cadiz, North East Atlantic Ocean. Over the past 2 decades more than 50 mud volcanoes have been discovered and investigated interdisciplinarily. Mud volcano fluids emanating at these sites are sourced at great depths and migration is often mediated by strike slip faults in a seismically active region. The geochemical signals of the mud volcano fluids are affected by widespread various processes such as clay mineral dehydration, but also the recrystallization of ancient carbonate rocks and the alteration of oceanic crust have been suggested (Hensen et al., 2015). We developed a novel fully-coupled, basin-scale, reaction-transport model with an adaptive numerical mesh to simulate the fluid genesis in this region. An advantage of this model is the coupling of a realistic geophysical and geochemical approach, considering a growing sediment column over time together with instant compaction of sediments as well as diffusion and advection of dissolved pore water species and chemical reactions. In this proof of concept study, we looked at various scenarios to identify the processes of fluid genesis for 4 mud volcanoes, representing combinations in different subsurface settings. We can reproduce the fluid signatures (chloride, strontium, 87Sr/86Sr) of all mud volcanoes. Furthermore, we can give additional evidence that alteration of oceanic crust by fluid flow is a likely process affecting the fluid composition.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
    Publication Date: 2019-03-29
    Description: Marine transform faults and associated fracture zones (MTFFZs) cover vast stretches of the ocean floor, where they play a key role in plate tectonics, accommodating the lateral movement of tectonic plates and allowing connections between ridges and trenches. Together with the continental counterparts of MTFFZs, these structures also pose a risk to human societies as they can generate high magnitude earthquakes and trigger tsunamis. Historical examples are the Sumatra-Wharton Basin Earthquake in 2012 (M8.6) and the Atlantic Gloria Fault Earthquake in 1941 (M8.4). Earthquakes at MTFFZs furthermore open and sustain pathways for fluid flow triggering reactions with the host rocks that may permanently change the rheological properties of the oceanic lithosphere. In fact, they may act as conduits mediating vertical fluid flow and leading to elemental exchanges between Earth’s mantle and overlying sediments. Chemicals transported upward in MTFFZs include energy substrates, such as H2 and volatile hydrocarbons, which then sustain chemosynthetic, microbial ecosystems at and below the seafloor. Moreover, up- or downwelling of fluids within the complex system of fractures and seismogenic faults along MTFFZs could modify earthquake cycles and/or serve as “detectors” for changes in the stress state during interseismic phases. Despite their likely global importance, the large areas where transform faults and fracture zones occur are still underexplored, as are the coupling mechanisms between seismic activity, fluid flow, and life. This manuscript provides an interdisciplinary review and synthesis of scientific progress at or related to MTFFZs and specifies approaches and strategies to deepen the understanding of processes that trigger, maintain, and control fluid flow at MTFFZs.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2016-02-02
    Description: A bottom-simulating reflector (BSR) occurs west of Svalbard in water depths exceeding 600 m, indicating that gas hydrate occurrence in marine sediments is more widespread in this region than anywhere else on the eastern North Atlantic margin. Regional BSR mapping shows the presence of hydrate and free gas in several areas, with the largest area located north of the Knipovich Ridge, a slow-spreading ridge segment of the Mid Atlantic Ridge system. Here, heat flow is high (up to 330 mW m-2), increasing towards the ridge axis. The coinciding maxima in across-margin BSR width and heat flow suggest that the Knipovich Ridge influenced methane generation in this area. This is supported by recent finds of thermogenic methane at cold seeps north of the ridge termination. To evaluate the source rock potential on the western Svalbard margin, we applied 1D petroleum system modeling at three sites. The modeling shows that temperature and burial conditions near the ridge were sufficient to produce hydrocarbons. The bulk petroleum mass produced since the Eocene is at least 5 kt and could be as high as ~0.2 Mt. Most likely, source rocks are Miocene organic-rich sediments and a potential Eocene source rock that may exist in the area if early rifting created sufficiently deep depocenters. Thermogenic methane production could thus explain the more widespread presence of gas hydrates north of the Knipovich Ridge. The presence of microbial methane on the upper continental slope and shelf indicates that the origin of methane on the Svalbard margin varies spatially.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2017-06-20
    Description: Vast amounts of methane hydrates are potentially stored in sediments along the continental margins, owing their stability to low temperature – high pressure conditions. Global warming could destabilize these hydrates and cause a release of methane (CH 4) into the water column and possibly the atmosphere. Since the Arctic has and will be warmed considerably, Arctic bottom water temperatures and their future evolution projected by a climate model were analyzed. The resulting warming is spatially inhomogeneous, with the strongest impact on shallow regions affected by Atlantic inflow. Within the next 100 years, the warming affects 25% of shallow and mid-depth regions containing methane hydrates. Release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column. The impact of methane release on global warming, however, would not be significant within the considered time span.
    Type: Article , PeerReviewed
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  • 5
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    In:  [Poster] In: 13. International Conference on Gas in Marine Sediments (GIMS13), 19.-22.09.2016, Tromsø, Norway .
    Publication Date: 2016-10-13
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
    Publication Date: 2019-02-01
    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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  • 7
    Publication Date: 2019-02-01
    Description: Highlights • BSR position does not match BGHS as predicted based on regional TP conditions. • Use steady state and transient models to determine extent of hydrate stability. • Investigate the influence of topographic focusing on hydrate stability. • Variable thermal properties of sediment impact hydrate stability. The Danube Fan in the western Black Sea shows many features indicating the presence of gas and gas hydrates, including a bottom simulating reflection (BSR), high-amplitude anomalies beneath the BSR and the presence of gas flares at the seafloor. The BSR depth derived from 3D P-cable seismic data of an older slope canyon of the fan (the S2 canyon) suggests that the BSR is not in equilibrium with the present-day topography. The Danube Fan was abandoned ∼7.5 ka, and the S2 canyon was likely incised ∼20 ka, suggesting that the gas hydrate system has had at least 7.5 ka years to equilibrate to the present-day conditions. Here we examine the extent and position of the hydrate stability zone through constructing both steady and transient state models of a 2D profile across the S2 canyon. This was done using inputs from mapping of the 3D P-cable seismic data and geochemical analysis of core samples. Using these models, we investigate the effects of different factors including variable thermal properties of heterogeneous sediments in the vicinity of the canyon and, topographic focusing on the geothermal gradient on the extent of the hydrate stability zone. Our results indicate that both factors have a significant effect and that the hydrate system may actually be in, or approaching equilibrium.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 8
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    In:  [Poster] In: Gordon Research Conference on Natural Gas Hydrate Systems, 28.02.-04.03.2016, Galvestone, TX, US .
    Publication Date: 2016-03-08
    Description: Gas migration pathways in the Gulf of Mexico are strongly influenced by the extensive formation and time evolution of salt canopies, welds and sheets. This multi-level salt system (known as the Louann Salt formation) deposited mostly within Callovian age (upper Middle Jurassic) and mobilized during late Miocene up to Pliocene-Pleistocene times controls the extension and direction of petroleum components migration over the entire history of the basin which, in return, has a major impact on potential gas transportation into the gas hydrate stability zone (GHSZ). In the context of gas hydrate formation, presence of extensive salt deposits tends to bend gas migration pathways from vertical (typical for the Gulf of Mexico region) towards rather horizontal and dispersed. However, amalgamation of two or more salt structures often results in re-focusing of the flow towards the local topographic subsalt heights. Together with the formation of local sediment discontinuity structures such as faults developing at the rims and tops of rootless salt deposits related to further stages of allochthonous salt mobilization, new high-permeability migration pathways develop and act as direct connection for the thermogenic gas to the GHSZ. Our study presents the 3D modeling solution quantifying and exploring the gas hydrate accumulation potential in the marine environment experiencing salt tectonics such as the Green Canyon, Gulf of Mexico. This modeling study evaluates the potential of bio- and thermogenic gas hydrate formation within Pliocene-Pleistocene reservoir layers based on full basin re-construction which accounts for depositional and transient thermal history of the basin, source rock maturation, petroleum generation, expulsion and migration, salt tectonics and associated faults development. Based on a numerical study calibrated with the existing field data, we present a new distribution pattern of gas hydrates attributed to both microbial and thermogenic origin. We present here an explanation for a formation mechanism of large gas hydrate amounts (〉 70 vol. %) wide-spread at the base of the stability zone as a result of the gas hydrate-free gas recycling process enhanced by very high Neogene sedimentation rates in the region. We suggest that the rapid development of secondary intra-salt mini-basins situated on top of the allochthonous salt deposits and following sediment subsidence caused a consequent dislocation of the GHSZ lower boundary and led to efficient gas hydrate dissociation process followed by a free gas re-charge into the GHSZ.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
    Publication Date: 2017-03-28
    Description: Gas hydrate deposits are abundant in the Black Sea region and confirmed by direct observations as well as geophysical evidence, such as continuous bottom simulating reflectors (BSRs). Although those gas hydrate accumulations have been well-studied for almost two decades, the migration pathways of methane that charge the gas hydrate stability zone (GHSZ) in the region are unknown. The aim of this study is to explore the most probable gas migration scenarios within a three-dimensional finite element grid based on seismic surveys and available basin cross-sections. We have used the commercial software PetroMod TM(Schlumberger) to perform a set of sensitivity studies that narrow the gap between the wide range of sediment properties affecting the multi-phase flow in porous media. The high-resolution model domain focuses on the Danube deep-sea fan and associated buried sandy channel-levee systems whereas the total extension of the model domain covers a larger area of the western Black Sea basin. Such a large model domain allows for investigating biogenic as well as thermogenic methane generation and a permeability driven migration of the free phase of methane on a basin scale to confirm the hypothesis of efficient methane migration into the gas hydrate reservoir layers by horizontal flow along the carrier beds.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
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    In:  [Talk] In: International Gas Hydrate Conference (ICGH9), 25.06.-30.06.2017, Denver, USA .
    Publication Date: 2017-03-28
    Description: Numerical modeling of natural gas hydrate systems requires an innovative and complex approach. The variability of parameters present in natural geological settings and the lack of wide spread high-quality 3D seismic data are the main factors limiting large-scale numerical simulations. Here, we present the outcome of a joint academic-industry project on testing the feasibility of a newly developed simulation-module included in the commercial software PetroMod TM for modeling the formation of natural gas hydrate deposits at two locations in the Gulf of Mexico. The project aimed at the scientific assessment of required input data quality and validity, choice of the computational methods, and calibration with the field data.
    Type: Conference or Workshop Item , NonPeerReviewed
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