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Abstract

The Frisco Formation is a middle Lower Devonian limestone within the Hunton Group (Upper Ordovician-Lower Devonian). In the Anadarko basin, the Frisco Formation consists of skeletal packstones and grainstones whose main components are pelmatozoans, bryozoans, brachiopods, and, locally, corals. Depositional intergranular porosity has been mostly obliterated through syntaxial cementation on pelmatozoans, and mechanical and chemical compaction. Secondary porosity, which formed during subaerial exposure of the Frisco, occurs locally near the top of the formation in the form of partly leached grains, vugs, and solution channels. This secondary porosity is best developed close to areas where the formation was completely eroded—areas which commonly correspond to Middle Devonian paleostructures.

Hydrocarbon accumulations in the Frisco Formation are mainly in stratigraphic traps situated downdip from areas where the formation has been severely truncated. The Woodford Shale (Upper Devonian-Lower Mississippian) unconformably overlies the Frisco Formation throughout most of the study area and provides a source, trap, and seal for reservoirs within the Frisco.

Geophysical identification of Frisco Formation porosity is possible using Relative Amplitude (RAM) processing. Where the Woodford Shale overlies nonporous, high-velocity Frisco or older Hunton strata, the resulting reflection coefficient causes a well-developed amplitude peak on RAM-processed seismic sections. However, where the Frisco Formation is porous, a lower reflection coefficient between the two formations produces a relative amplitude diminishment and subsequent break-up of the Woodford-Frisco peak.

Use of RAM-processed seismic sections, in conjunction with available geologic data, permits identification of porosity and approximation of the subcrop pattern of the Frisco in areas where well control is sparse. The West El Reno field, Canadian County, Oklahoma, produces gas and condensate from an outlier of the Frisco Formation, and provides a template for this technique.

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