Deep-Water
Foraminifera and Petroleum Geology of the Oligocene Kugmallit
Submarine Fan Complex in the Beaufort Sea, Arctic Canada
McNeil, D.H.1, J.R. Dietrich2,
D.R. Issler2, J. Dixon1, K. Hu1 (1) Geological
Survey of Canada, Calgary, AB (2) Geological Survey
of Canada, Calgary,
Thirteen exploration wells have been
drilled in the Kugmallit deep-water play of the Beaufort Sea resulting in six
significant discoveries. Potential reserves are large - 2 billion barrels of
oil and more than 30 TCF of natural gas, but the play has
been delayed by a record of thin sandstones, discontinuous reservoirs on large
shale-cored anticlines, and 50 to 100 meters of water, seasonally ice covered.
New seismic data and the proposed Mackenzie Valley pipeline, however, now
make this prospect more favourable. Nine of the wells
penetrate the extensive Oligocene Kugmallit submarine
fan complex deposited on the lower slope and continental rise. Deep-water
agglutinated foraminifera occur abundantly in most of these deposits, dominated
by Bathysiphon, Reticulophragmium,
and Recurvoides. Some species, such as R. projectus occur only in the deep water facies,
but many other species ranged onto the upper slope and outer shelf during the
Oligocene. The “tops” for agglutinated species are diachronous
and young distally. Sediment of the Kugmallit
Sequence underwent rapid subsidence in the Late Cenozoic concurrent with
deposition of the >2.5 km thick Pliocene-Pleistocene Iperk
Sequence. As a result, all the reservoirs occur below the top of an
overpressure zone located at the base of the Iperk.
Thermal maturity, determined by foraminiferal colouration (FCI), is generally low through the Kugmallit fan deposits, but increases with present day
borehole temperatures, for example 100oC=FCI 2.6 and 137oC=FCI 5.8. Evidence of
hydrocarbon-related diagenesis, indicated by
precipitation and dissolution of silica in agglutinated foraminifera, is
present in two significant discovery wells.