Evidence for a deep gas hydrate stability zone associated with submerged permafrost on the Canadian Arctic Beaufort Shelf, Northwest Territories

• Main Authors: Riedel, Michael, Taylor, G., Taylor, A. E., Dallimore, S. R.
• Format: Report
• Language: English
• Published: Natural Resources Canada 2015
• Subjects: Arctic; Beaufort Shelf; Northwest Territories; Beaufort Sea; permafrost; wedge*
• Online Access: https://oceanrep.geomar.de/id/eprint/29901/; https://oceanrep.geomar.de/id/eprint/29901/1/cr_2015_08_gsc.pdf; https://doi.org/10.4095/296987

The presence of offshore permafrost in the Canadian Beaufort Sea region has previously been identified from seismic and borehole data. The consequence of such permafrost is the possibility of an underlying gas-hydrate stability zone. In this study the authors present the first evidence for the widespread occurrence of gas hydrate in the offshore portion of the Beaufort Shelf using 3-D seismic data. A reflector of opposite polarity relative to the seafloor was identified at a depth of about 1000 m below seafloor that mimics some of the behaviour of the traditionally seen bottom-simulating reflectors in marine gas-hydrate regimes; however, the reflection identified is not truly bottom simulating, as its depth is rather controlled by the rapidly thinning wedge of submerged permafrost. The depth of the reflector decreases with increasing water depth, as predicted from thermal modelling. The reflection crosscuts strata and marks a zone of enhanced reflectivity underneath, possibly originating from free gas that accumulated at this phase boundary over time as the permafrost and associated gas-hydrate stability zones were thinning in response to the transgression. The presence of a clear and widespread gas-hydrate stability field beneath the permafrost has widespread implications on the region, including deep-drilling hazards associated with the presence of free gas, possible overpressure, and lateral migration of fluids and associated expulsion at the seafloor.