About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 4. (April)

First Page: 682

Last Page: 682

Title: West Sak and Ugnu Sands: Low-Gravity Oil Zones of the Kuparuk River Area, North Slope, Alaska: ABSTRACT

Author(s): Michael R. Werner

Article Type: Meeting abstract

Abstract:

Low-gravity oil in Upper Cretaceous and Tertiary shallow marine and deltaic sands of the North Slope have been known since 1969. The majority of the oil occurs in two intervals informally named the West Sak sands (Maestrichtian) and the overlying Ugnu sands (Maestrichtian-Paleocene). These zones are oil-bearing primarily in the Kuparuk River and Milne Point units where they occur at depths ranging from 2,000 to 4,500 ft (610 to 1,370 m) subsea.

The West Sak consists of very fine-grained, unconsolidated sands with interbedded siltstone and mudstone that were deposited in an inner-shelf to delta-front environment. The oil in the West Sak is a less heavy to intermediate crude with gravities ranging 16°-22° API. The Ugnu consists of fine to medium-grained, unconsolidated sands with interbedded siltstone, mudstone, and coal that were deposited in fluvial and delta-plain environments. The oil in the Ugnu sands is bitumen and extra heavy crude with gravities between 8° and 12° API.

The total oil in place in the West Sak and Ugnu sands is estimated to be as large as 40 billion bbl. Geochemical work on these oils indicates that they have the same source as the oils in the deeper Kuparuk and Sadlerochit reservoirs but have been biodegraded.

End_of_Article - Last_Page 682------------

Copyright 1997 American Association of Petroleum Geologists