Depositional Facies and Reservoir Quality, Devonian Carbonate Mounds, Frisco Formation, Oklahoma

Abstract

Devonian carbonate mounds of the Frisco Formation in Oklahoma are important petroleum reservoirs in a number of oil and gas fields that produce from Hunton Group carbonates. Though these reservoirs have produced large volumes of petroleum, little is known about their origin, distribution and diagenetic history. Outcrops and cores were described, sampled and analyzed petrographically to establish fabric and mound lithofacies and determine post-depositional diagenetic modification. The preservation and evolution of mound porosity was controlled by depositional facies. Post depositional alteration reduced primary porosity. Syntaxial calcite cement on pelmatozoan grains occluded primary porosity, whereas fine granular cement reduced the porosity in bryozoan zooecia. Some primary porosity is preserved in the axial canals of crinoid stems and zooecia of bryozoan fragments. Primary porosity provided conduits for corrosive fluids that formed secondary dissolution porosity during pre-Woodford subareal exposure. Core analysis reveals Fitts Field is producing from stacked mound deposits. Stratified bryozoa-rich reservoir of flanking facies preserves the best reservoir quality. In contrast, the muddier beds of the mound core and pelmatozoan- rich beds in flanking facies can be low porosity and low permeability.