FROM BOUNDARIES TO BARRELS: SEQUENCE STRATIGRAPHY AND PETROLEUM RESOURCE ASSESSMENT OF FEDERAL LAND IN NORTHERN ALASKA

Alaska North Slope exploration has focused increasingly during the past decade on stratigraphic objectives, resulting in the discovery of at least ten oil fields ranging in size from 50 to >400 million barrels of recoverable oil. While small by Prudhoe Bay standards (~15 billion barrels), these fields dwarf most North America discoveries of the past quarter century.

Most onshore areas of northern Alaska not yet explored for stratigraphic traps are Federal Lands, including the National Petroleum Reserve – Alaska and the “1002 area” of the Arctic National Wildlife Refuge. Most prospective are Jurassic-Early Cretaceous strata of the Beaufortian megasequence and Cretaceous-Tertiary strata of the Brookian megasequence. Assessment of the petroleum potential of these strata requires estimation of stratigraphic trap attributes based on sequence stratigraphy and interpretation of depositional systems.

Beaufortian strata were deposited in marine depositional systems adjacent to an active rift margin. Stratigraphic traps occur within transgressive systems tracts that comprise incised shoreface sandstones capped by condensed mudstone. Brookian strata were deposited in a generally prograding clastic wedge associated with orogenic uplift of the Brooks Range. Stratigraphic traps occur within lowstand systems tracts that comprise amalgamated, turbidite sandstones capped by condensed mudstone deposited during subsequent transgression. Additional stratigraphic trap types, including incised valley fill deposits in both Beaufortian and Brookian strata, are likely to be recognized as exploration continues.

Although subtle in comparison to the structural and combination traps that previously were the focus of North Slope exploration, these stratigraphic traps likely contain billions of barrels of oil and will be a focal point of Federal energy and land-use policy decisions in coming years.