--> ABSTRACT: Sequence Stratigraphy of Oil- and Gas-Prospective Shelf and Shoreface Sandstones in the Kingak Shale, National Petroleum Reserve - Alaska (NPRA), by David W. Houseknecht, Kenneth J. Bird, and Christopher J. Schenk; #90906(2001)

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David W. Houseknecht1, Kenneth J. Bird2, Christopher J. Schenk3

(1) U.S. Geological Survey, Reston, VA
(2) U.S. Geological Survey, Menlo Park, CA
(3) U.S. Geological Survey, Denver, CO

ABSTRACT: Sequence Stratigraphy of Oil- and Gas-Prospective Shelf and Shoreface Sandstones in the Kingak Shale, National Petroleum Reserve - Alaska (NPRA)

The 1994 discovery of the Alpine oil field (>400 mmbo recoverable) has stimulated exploration for stratigraphic traps in the Kingak Shale (Jurassic - earliest Cretaceous) in the adjacent NPRA. Sequence stratigraphy and depositional facies of the Kingak have been interpreted from a regional 2-D seismic grid and well control.

The Kingak was deposited in marine shelf and shoreface systems on a continental margin influenced increasingly through time by episodic uplift along the Barrow Arch, an Arctic Ocean rift shoulder. Lower and Middle Jurassic strata define a depocenter in north-central NPRA, where a shelf developed through accumulation of depositional sequences comprising highstand (HST) and transgressive (TST) systems tracts. Shelf margins are defined by downlapping coalescence of TSTs, forming a basinal condensed section containing good source rocks. Upper Jurassic and lowermost Cretaceous (Neocomian) depositional sequences are thin to absent on the shelf, and pass basinward into thicker offlapping wedges that likely include lowstand systems tracts (LST).

Prospective Kingak intervals occur where sequence boundaries are expressed as exposure surfaces and/or transgressive surfaces of erosion (ravinements) developed on HSTs and overlain by TSTs. Marine shelf sandstones within HSTs locally display good reservoir quality (gas reservoirs near Barrow), whereas winnowed shoreface sandstones within TSTs display excellent reservoir quality (e.g., the Alpine reservoir). The latter are most commonly developed within relatively thin, Upper Jurassic depositional sequences, where lenses of transgressive shoreface sandstones accumulated in topographic lows on sequence bounding unconformities. Stratigraphic traps in the Kingak are sealed by marine shales deposited during maximum flooding of the shelf.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado