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Wednesday, February 21 2018

5:30 PM - 8 PM
Wednesday, Feb 21, 2018 5:30 p.m.
Intl. Dinner

Petroleum-Systems Framework of Significant New Oil Discoveries in a Giant Cretaceous Clinothem in Arctic Alaska

Dave Houseknecht

U.S. Geological Survey

Recent oil discoveries in a Cretaceous clinothem in Arctic Alaska prove the potential for hundred-million to billion-barrel oil accumulations in Nanushuk Formation topsets and Torok Formation foresets–bottomsets. Oil-prone source rocks and the clinothem are draped across the Barrow arch, a structural hinge between the Colville foreland basin and Beaufort Sea rifted margin. Stratigraphic traps lay in a favorable thermal maturity domain along multiple migration pathways across more than 30,000 km2 (10,000 mi2). Sediment flux from Chukotka filled the western Colville foreland basin and spilled over the Beaufort rift shoulder, forming east- and north-facing shelf margins. Progradational shelf-margin trajectories change abruptly to “sawtooth” trajectories at mid-clinothem, the result of reduction in sediment influx. Two stratigraphic trap types are inferred in Nanushuk basal topsets in the eastern part of the clinothem. (1) Lowstand (or falling stage) systems tracts, inferred to reflect forced regression, include a narrow, thick progradational stacking pattern perched on a sequence boundary on the upper slope. (2) Highstand-progradational systems tracts include a broad, thin wedge of shingled parasequences above a toplap surface. Both include stratigraphically isolated sandstone sealed by mudstone. Trap geometries in Torok foreset and bottomset facies in the eastern part of the clinothem include basin-floor fan, slope-apron, and slope-channel deposits that pinch out up-slope and are sealed by mudstone. Significant potential exists for the discovery of additional oil accumulations in these stratigraphic trap types in the eastern part of the clinothem. Less potential may exist in the western part because sequence-stratigraphic successions, and therefore trap geometries, are poorly defined.