Unconformities--Key to Major Oil Accumulations, North Slope, Alaska: ABSTRACT

Abstract

The entrapment of oil and gas at an unconformity at Prudhoe Bay, North America's largest oil field, is well known. It now appears that other large oil and gas accumulations such as those in the Kuparuk River sandstones west of Prudhoe Bay are trapped at an unconformity. Prudhoe Bay field is on a large anticline on which the reservoir rocks have been truncated by an unconformity. The unconformity places organically rich Cretaceous shales in juxtaposition with Sadlerochit reservoir rocks. Cretaceous shales above the unconformity also provide the updip seal for the oil accumulation. Oil in the Jurassic Kuparuk River sandstones is trapped on a large structural nose by truncation of the reservoir rocks. The Cretaceous shales above the unconformity provide the seal and possibly the source for the oil. Uplift of the Barrow arch in Late Jurassic and Early Cretaceous time resulted in a regional unconformity. The truncation of older rocks by this unconformity, and the seal provided by the overlying shales are key factors to exploration of this arch which extends for more than 300 mi (483 km) along the Beaufort Sea coast. The delicate relations of source, reservoir, and trap, which are commonly controlled by one or more unconformities, are important to exploring this rich petroleum province. End_of_Article - Last_Page 684------------