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Michael T. Whalen1
(1) University of Alaska Fairbanks, Fairbanks, AK
Abstract: Outcrop to subsurface correlation and reservoir analysis of Lisburne Group carbonates: northeastern Brooks Range and Prudhoe Bay, Alaska
Carbonate rocks of the Lisburne Group (Carboniferous) are exposed in the Brooks Range and form significant petroleum reservoirs in the subsurface at Prudhoe Bay. The Lisburne Group represents a south facing carbonate ramp deposited on a formerly passive continental margin. A wealth of subsurface data and core, courtesy of ARCO, Alaska, along with outcrop gamma ray spectrometry of the Alapah Formation (Lower Lisburne), northeastern Brooks Range, is providing refined correlations between the surface and subsurface and insights into reservoir development.
The Lisburne Group thickens and records deeper water facies to the south. More proximal facies in Prudhoe Bay commonly have a higher siliciclastic component, more shallow water and evaporitic facies, and are more thoroughly dolomitized in relation to coeval outcrop sections. In both the outcrop and subsurface the Alapah contains cyclic meter scale parasequences. Parasequences are commonly shaly or argillaceous at their base, mostly subtidal dominated in outcrop, and peritidal dominated in the subsurface. Basal argillaceous units and upper evaporite-related facies probably serve as efficient permeability barriers that compartmentalize Alapah parasequence-scale reservoirs. The location of reservoir intervals in the subsurface appears to be controlled by dolomitization in the lower parts of parasequences.
Outcrop gamma ray analysis has identified poorly exposed argillaceous units in the northeastern Brooks Range and provides important tie points for correlation with subsurface data. Parasequences in the outcrop commonly shoal upward from argillaceous or fine-grained carbonate facies to porous, coarse-grained shoal deposits with higher reservoir quality. Paleogeographic variations in facies stacking patterns thus imply that reservoir properties of proximal parasequences might vary considerably compared to distal parasequences. Understanding of these variations will be crucial to further exploration of Lisburne plays along the foothills of the Brooks Range in the National Petroleum Reserve in Alaska
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana