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The AAPG/Datapages Combined Publications Database

Tulsa Geological Society

Abstract


Limestones of the Mid-Continent, 1984
Pages 201-246

Recognition of Favorable Reservoir Trends in Upper Pennsylvanian Cyclic Carbonates in Western Kansas

W. Lynn Watney

Abstract

The Missourian age, Lansing-Kansas City Groups in the subsurface of western Kansas constitute an important target for explorationists. Many recent oil discoveries in these units are scattered over a wide area of the west ranges of the state. An understanding of the geologic setting of these discoveries is critical to defining present trends and generating future analogous prospects. Prospect development is facilitated by the examination of the rocks in core and cuttings followed by a mapping program that reveals details of each cycle. In turn, structures can then be evaluated with respect to favorable trends of reservoir development.

Regional mapping of lithofacies components, combined with conventional isopach and structural maps, reveals each cycle displays regular variations in thickness, facies and reservoir development. These variations are affected by differential subsidence on a gently, southerly dipping platform. Broad, positive areas on this platform closely correspond with previously active uplifts. Subtle flexures along the platform were sometimes loci for the formation of ooid shoals, when waves and currents were focused on these areas during late regressive phases of the cycles.

Although different cycles are remarkably similar, variations in the characteristics of the cycles occur. These variations are inferred to be the result of changes in the extent of platform inundation, rates of regression, terrigenous clastic influx and differential subsidence. As a result of subaerial exposure, early diagenesis by fresh and CaCO3-undersaturated waters has strongly influenced the formation and redistribution of porosity in the carbonate reservoirs. One cycle, the "K" zone, is described from cores and wireline logs and evidence for freshwater diagenesis and subaerial exposure are reviewed. The "K" zone (Swope Limestone) is briefly compared to three other cycles in the Kansas City Group.


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