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FRITZ, R. D., J. L. WILSON, P. L. MEDLOCK, and M. D. KUYKENDALL, MASERA Corporation, Tulsa, OK

ABSTRACT: Relationship of Facies and Sequence Stratigraphy to Paleokarst and Fracture Overprints in the Carbonates of the Arbuckle Group in the Evaluation of Exploration and Horizontal Drilling Potential

The mid-continent region, especially in Oklahoma and Arkansas, contains thick dolomite Paleozoic carbonate sections with karstic character. These sections commonly exhibit strong structural overprints, including intense fracturing, due primarily to Pennsylvanian orogenies.

The Arbuckle Group is composed of multiple parasequences that are the result of cyclic peritidal deposition on a broad shallow shelf. Sequence stratigraphy evaluation indicates that significant unconformities or disconformities occur within the Arbuckle Group along third-order sequence boundaries.

Arbuckle carbonates were subjected to very early dolomitization (Ordovician through Devonian). Sequences in which intercrystalline porosity was developed with little or no vuggy porosity usually have low permeability and effective porosity; however, these dolomitic sequences are quite susceptible to fracturing, and they may produce in structural traps. These fractured sequences in the Arbuckle also are particularly susceptible to karstification associated with multiple unconformities especially in areas where there has been significant orogenic activity, such as the Criner uplift in southern Oklahoma. Fracturing and subsequent karstification have significant influence on porosity development and can produce extremely heterogeneous reservoirs.

Exploration for oil and gas in the Arbuckle Group at best has been a difficult task. Problems with seal and source along with complex diagenetic and structural histories still plague efforts to understand Arbuckle reservoir development. There is new evidence that dolomitization, fracturing, and karstification may be related to particular sequence positions and their related facies and disconformities. Innovative advances in geologic concepts, such as sequence stratigraphy, and in techniques, such as horizontal drilling, may lead to new discoveries in the Arbuckle Group.

AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.