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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 65 (1981)

Issue: 5. (May)

First Page: 926

Last Page: 926

Title: Depositional Environments and Reservoir Properties of Sandstones of Lower Cretaceous Nanushuk and Upper Cretaceous Colville Groups, Umiat Test Well 11, National Petroleum Reserve, Alaska: ABSTRACT

Author(s): James E. Fox, P. W. Lambert, J. K. Pitman

Article Type: Meeting abstract

Abstract:

Delta-front sandstones of the Grandstand Formation, Killik Tongue of the Chandler Formation, and the Ninuluk Formation (Nanushuk Group) are moderately well to well-sorted, very fine to fine-grained, angular to subangular chert-arenite and phyllarenite. A source terrane of low-grade metamorphic rocks, sandstones, and cherty limestone was southwest of Umiat and the delta prograded northeasterly. Weighted average porosity and permeability of cored sandstones are 15.6% and 167 md for the Grandstand Formation, 16.4% and 96.2 md for the Killik Tongue of the Chandler Formation, and 12.6% and 10.7 md for the Ninuluk Formation.

The Seabee Formation (Colville Group) is predominantly marine shale, interbedded with several sandstone units. These marine sandstones are moderately well to well-sorted, very fine to medium-grained, angular to subangular phyllarenite, metarenite, and volcanic litharenite. Volcanic rock fragments and volcanic plagioclase feldspar are abundant. Abundant chlorite and smectite reduce permeability; weighted average permeability is 3.1 md and weighted average porosity is 11.5%.

The Tuluvak Tongue of the Prince Creek Formation (Colville Group) is composed of interbedded delta-plain and delta-front facies of a northeasterly prograding delta. Sandstones from the Tuluvak Tongue are moderately well to well-sorted, very fine to medium-grained, angular to subangular phyllarenite, feldspathin phyllarenite, and volcanic litharenite. Abundant authigenic smectite reduces permeability; weighted average permeability is 3.9 md and weighted average porosity is 14.6%.

Composition of the sandstones has a major effect on porosity and permeability. Sandstones that have a higher content of compressible grains (mainly phyllite), and sandstones that have greater matrix and cement content generally have lower porosity and permeability. Expandable clay matrix is essentially absent in the Nanushuk Group sandstones. Porous and permeable Nanushuk Group sandstones should exist in those depositional areas that received only sparse amounts of metamorphic rock debris and in areas where energy conditions at the site of deposition facilitated sorting and winnowing of the sediment.

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