Evidence for gas hydrate occurrences in the Canadian Arctic Beaufort Sea within permafrost-associated shelf and deep-water marine environments |
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| Institution: | 1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1- 3, D-24148, Kiel, Germany;2. Natural Resources Canada, Geological Survey of Canada–Calgary, 3303 33 Street NW, Calgary, Alberta, T2L 2A7, Canada;3. Imperial Oil Resources, 505 Quarry Park Blvd. S.E., W1C.113, Calgary, Alberta, T2P 3M9, Canada;4. Natural Resources Canada, Geological Survey of Canada–Pacific, 9860 West Saanich Rd, Sidney, BC, V8L4B2, Canada;5. Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon, 406-840, South Korea;1. Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, 0316 Oslo, Norway;2. The Center for Earth Evolution and Dynamics, University of Oslo, P.O. Box 1028, Blindern, 0315 Oslo, Norway;3. TGS, Lensmannslia 4, 1386 Asker, Norway;4. Department of Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway;1. Simula Research Laboratory, Fornebu, Norway;2. Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands;1. Research Centre for Arctic Petroleum Exploration (ARCEx), Department of Geosciences, University of Tromsø - The Arctic University of Norway, Dramsveien 201, NO-9037 Tromsø, Norway;2. North E&P AS, Tjuvholmen Allé 3, NO-0252 Oslo, Norway;3. First Geo AS, Karenslyst Allé 57, NO-0277 Oslo, Norway;4. MOL Norge AS, Trelastgata 3, NO-0191 Oslo, Norway;5. Centre for Arctic Gas Hydrate Environment and Climate (CAGE), Department of Geosciences, University of Tromsø - The Arctic University of Norway, Dramsveien 201, NO-9037 Tromsø, Norway;1. Trofimuk Institute of Petroleum Geology and Geophysics Siberian Branch of the RAS, Novosibirsk, 630090, Russia;2. Novosibirsk State University, Faculty of Geology, Novosibirsk, 630090, Russia;1. Department of Geoscience, Aarhus University, DK-8000 Aarhus C, Denmark;2. Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA;3. Department of Earth Science, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK;4. Dynamique des Fluides Géologiques, Univ. Paris Diderot, Sorbonne Paris Cité, Institute de Physique du Globe de Paris, UMR 7154 CNRS, F-75013 Paris, France;5. Department of Geosciences and Natural Resource Management, University of Copenhagen, DK-1350 Copenhagen K, Denmark |
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| Abstract: | The presence of a wedge of offshore permafrost on the shelf of the Canadian Beaufort Sea has been previously recognized and the consequence of a prolonged occurrence of such permafrost is the possibility of an underlying gas hydrate regime. We present the first evidence for wide-spread occurrences of gas hydrates across the shelf in water depths of 60–100 m using 3D and 2D multichannel seismic (MCS) data. A reflection with a polarity opposite to the seafloor was identified ～1000 m below the seafloor that mimics some of the bottom-simulating reflections (BSRs) in marine gas hydrate regimes. However, the reflection is not truly bottom-simulating, as its depth is controlled by offshore permafrost. The depth of the reflection decreases with increasing water depth, as predicted from thermal modeling of the late Wisconsin transgression. The reflection crosscuts strata and defines a zone of enhanced reflectivity beneath it, which originates from free gas accumulated at the phase boundary over time as permafrost and associated gas hydrate stability zones thin in response to the transgression. The wide-spread gas hydrate occurrence beneath permafrost has implications on the region including drilling hazards associated with the presence of free gas, possible overpressure, lateral migration of fluids and expulsion at the seafloor. In contrast to the permafrost-associated gas hydrates, a deep-water marine BSR was also identified on MCS profiles. The MCS data show a polarity-reversed seismic reflection associated with a low-velocity zone beneath it. The seismic data coverage in the southern Beaufort Sea shows that the deep-water marine BSR is not uniformly present across the entire region. The regional discrepancy of the BSR occurrence between the US Alaska portion and the Mackenzie Delta region may be a result of high sedimentation rates expected for the central Mackenzie delta and high abundance of mass-transport deposits that prohibit gas to accumulate within and beneath the gas hydrate stability zone. |
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| Keywords: | Gas hydrate Permafrost Free gas accumulation Geo-hazards |
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