Poor Timing in the Canadian Arctic: Risks to Petroleum Trapping and Preservation in Three Successive Petroleum Systems
Apparently promising petroleum systems with adequate source rocks, burial, reservoirs, and traps are present in the Canadian Arctic Islands. Basin history evaluation and petroleum generation modeling, however, indicate that petroleum potential was compromised by unfavorable timing of generation relative to trap formation, overmaturation, and destruction or remigration of accumulations during post-trapping deformation and uplift.
Silurian shales in the lower Paleozoic Franklinian passive margin sequence generated petroleum about 380 Ma during rapid burial beneath Devonian strata shed from the Caledonides, too early to fill traps formed by Late Devonian to Early Mississippian Ellesmerian deformation. The Ellesmerian fold-and-thrust belt was rifted in Carboniferous time to form the intracontinental Sverdrup Basin, where Pennsylvanian to Permian source rocks generated petroleum beginning in the Triassic. Overmaturity suggests that resulting accumulations were mostly destroyed by subsequent burial beneath thick Mesozoic to Cenozoic strata.
A proven Mesozoic petroleum system contains about 17 trillion cubic feet (TCF) and 500 million barrels (MMBO) of discovered recoverable gas and oil respectively, according to industry reports. Modeling indicates that Triassic oil-prone source rocks began to generate about 70 Ma, partially predating traps formed during Eurekan deformation driven by motion between Greenland and Arctic Canada as the Labrador Sea opened from 62 to 34 Ma. Petroleum was generated, but ongoing Eurekan deformation damaged traps and seals, especially in the eastern part of the basin, and caused widespread erosion and uplift; observed maturity levels indicate 1 to 2 km of erosion. The dominance of gas, despite the oil-prone nature of the source strata, implies that uplift and erosion may have caused gas to expand and displace oil from traps, and that ongoing gas generation may have refilled them. On Sverdrup Rim, the rift shoulder on the north side of Sverdrup Basin formed by Early Cretaceous sea floor spreading, Cretaceous erosion removed much of the prospective Triassic to Jurassic section. However, potential remains for petroleum generated from deeply buried Cretaceous and younger source rocks on the adjoining Canada Basin continental slope.
A mean of 4.9 TCF and 427 MMBO of remaining undiscovered gas and oil was estimated for Mesozoic strata in the Sverdrup Basin, mostly in stratigraphic traps, and 3.6 TCF and 424 MMBO for the Sverdrup Rim.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009