MILLER, MARK B., Murphy Exploration and Production Company, New Orleans, LA

ABSTRACT: Lithofacies Mapping and Reservoir Potential of the Kekiktuk Formation, North Slope, Alaska

The Mississippian Kekiktuk Formation is subdivided into three lithofacies in the subsurface representing in ascending order, a lacustrine/swamp/floodplain environment (Zone 1), a braided plain (Zone 2), and a meandering fluvial system (Zone 3). Each zone is identified on logs and can subsequently be mapped in the North Slope/Beaufort Sea area. Truncation by the Lower Cretaceous unconformity (LCU) in combination with basement onlap defines each zone's limit.

In the subsurface, a northern sediment source is evident; however, outcrops in the Northeastern Brooks Range reflect sediments locally derived and coarser grained than in the subsurface. These two areas were separated by a basement high and no clear correlation of lithofacies between the subsurface and outcrops is evident.

Reservoir quality is controlled by lithofacies, burial history, and grain size. Zone 2 offers the best reservoir potential while Zone 1 offers the least. Proximal, coarse-grained sandstones in contact with the LCU exhibit better reservoir quality than the distal, fine-grained, and deeply buried sandstones that were not truncated by the LCU. Most of the porosity in the Kekiktuk is primary in origin and reduced principally by compact ion and quartz cementation. Porosity is enhanced by chert dissolution where sandstones are truncated by the LCU. The truncation zone extends from Endicott field to Mikkelsen Bay and parallels the upthrown (north) side of the northwest-southeast trending Mikkelsen fault. Recognition of this truncation zone in conjunction with lithofacies, burial history, and basin setting can help determine the location of potential reservoir quality rocks.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.