Origin of the Drake Anticline and the Giant Drake Gas Field, Melville Island, Nunavut, CA

Keith Dewing

The two largest conventional gas fields in CA are located on Sabine Peninsula of Melville Island in the central Canadian Arctic Islands. The Drake gas field was drilled on the closure on an anticline defined both by surface mapping and subsurface seismic data. The field is hosted in Jurassic-aged sandstones of the Heiberg Group. Ultimate recoverable reserves are estimated at 5.3 tcf. Exploration stopped in 1985 and the fields have never been produced. Modern processing and interpretation methods were applied to more than 3400 line-kilometres of legacy seismic data from onshore Sabine Peninsula. The success of the reprocessing improved the imaging and hence the interpretation of the Devonian through Cretaceous succession. Processing consisted of three main steps: 1) Principal component decomposition was used to remove both coherent and random noise, 2) data were migrated following the principals of Kirchhoff migration through the use of a 3-D geostatistical velocity model and 3) seismic bandwidth extension was conducted in order to increase vertical resolution. The north-south oriented Sabine Peninsula has three tectono-stratigraphic assemblages: 1) thrust-faulted and folded lower Paleozoic strata in the lower part; 2) normally-faulted upper Paleozoic carbonate and clastic strata in the middle; 3) folded Mesozoic to Tertiary clastic strata in the upper part of the succession. Cretaceous sills and dykes locally intrude the succession. The central part of Sabine Peninsula is underlain by a graben containing upper Paleozoic sediments and overlies folded lower Paleozoic sediments. The graben fill is only intersected once by drilling but the graben likely contains late Carboniferous to early Permian sediments of the Canyon Fiord, Belcher Channel, and Raanes formations. Reflections within the graben are intersected by normal faults, terminating at or near the top of the upper Paleozoic succession and do not extend into the Mesozoic succession. Upper Paleozoic beds are not folded as part of the Drake anticline as Mesozoic and younger beds. However the Lower Cretaceous Christopher Formation thins over the Drake anticline, indicating that the anticline formed during, or just prior to its deposition. We propose that evaporites were present in the upper Paleozoic graben, analogous to the evaporitic Fosheim Sub-basin on northern Ellesmere Island. As evaporites were removed in the Early Cretaceous, either due to dissolution or salt withdrawal, the overlying Mesozoic strata were deformed into a rollover anticline.