Hydrocarbon Habitat of Kugmallit Formation, Oligocene, Beaufort Sea, Canada

Andrew Bullock

The Kugmallit Formation is the primary reservoir for oil and gas accumulations in the offshore Beaufort Sea. Hydrocarbons occur in two main structural/stratigraphic configurations: either in deltaic sands along a northeast-southwest-trending belt of growth faults or in distal delta sands and submarine fan deposits draped over shale swells situated basinward of the growth fault zone.

The growth fault zone was created as a result of the northward progradation of the Kugmallit Formation from the stable Devonian platform into the Kugmallit Trough. The rate of deposition was only marginally greater than subsidence rates, thus producing fault blocks with thick sand sequences bounded by major growth faults. The Amauligak structure is located on such a fault block and is estimated to contain 800 million to 1.1 billion bbl of recoverable oil.

Shale swells are of either lutokinetic or tectonokinetic origin. The lutokinetic diapir zone occurs in the eastern Beaufort Sea area, basinward of the growth fault zone. In some places, diapiric growth has been syndepositional, resulting in a crestal thinning of reservoirs.

In the western Beaufort Sea area, thrusting and folding associated with strike-slip movement have produced a series of asymmetrical linear ridges. Hydrocarbon accumulations in this zone are limited due to the lack of Kugmallit reservoir and deterrents to migration. The major oil discoveries such as Kopanoar, 292 million bbl of recoverable oil, occur in the transition zone between the tectonokinetic and lutokinetic zones. Reservoirs of submarine fan origin, sourced from the Kugmallit deltaic environment, are stacked over the crest of the Kopanoar structure and are full to spillpoint.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.