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ABSTRACT: Reservoir Description of the Lisburne Field, Prudhoe Bay, Alaska

Jeremy Jameson

The principle reservoir unit in the Lisburne oil field is the Wahoo Formation, a Pennsylvanian cyclic, shallow-water carbonate. Four major geological factors control Wahoo reservoir behavior: (1) depositional stratification and cyclicity, (2) multiple stages of porosity development, (3) the subunconformity alteration zone (SAZ) and (4) faulting and fracturing.

Wahoo Formation is highly stratified, consisting of 16 upward-shoaling depositional cycles (20-40 ft thick), deposited in a mosaic of shoal and lagoonal environments. Most parts of the field have 30-40 pay layers of variable thickness and lateral extent. Pore types and reservoir quality of layers vary considerably because porosity formed in three distinct episodes of diagenesis. The first episode was associated with localized dissolution at the close of some cycles. Extensive dolomitization of the upper Wahoo then followed as a regional aquifer was buried during the Permian-Triassic. Shallow burial alteration of dolomites immediately beneath the pre-Upper Permian unconformity created the SAZ, a thin fractured zone of ankerite.

The youngest stage of porosity development is associated with deep burial and probably hydrocarbon maturation. Extensive dissolution opened faults and created moldic porosity on the eastern side of the field. Faults provide vertical and lateral communication across the reservoir.

These four geological factors control Lisburne reservoir behavior as well as development planning.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990