The Osagean Reeds Spring Formation (Lower Boone), Western Osage and Eastern Kay County, Oklahoma: Outcrop Analog and Reservoir Characterization
University of Arkansas, Department of Geosciences Fayetteville, Arkansas United States
The Reeds Spring Formation (Osagean, Lower Mississippian) is the maximum flooding interval of a carbonate sequence exposed on the Cherokee Platform, northeastern Oklahoma, and the equivalent of oil and gas reservoirs in the subsurface to the west and south-west. Outcrop character, particularly abundant, nodular, anastomosing, penecontemporaneous chert, interbedded with fine-grained carbonates, and the stratigraphic relationships with adjacent beds, provide an analog for core description and well log correlation. The Reeds Spring Formation reflects transportation of crinozoan detritus, spicules, and carbonate mud from the Burlington shelf, down-ramp into a deeper, shelf margin. Correlations suggest that the equivalent subsurface lithologies are characterized by shaly, fine-grained spiculitic, crinoidal wackestone deposited along the deep shelf margin environment. Subdivision of the formation, which exceeds 200 feet in the subsurface, offers more control for determining reservoir quality across the region studied (approximately 840 square miles). Criteria used to examine reservoir quality include volume clean carbonate, true porosity, and high resistivity signatures. Additionally, Formation Micro-Image (FMI) log evaluation revealed that chert does not develop in the Reeds Spring Formation where low gamma ray (< 40 API) and high resistivity (+90 ohm-m) signatures are absent. An anomalous amount of silt and clay content, identified by thin section and petrophysical analysis, reveals that the Reeds Spring Formation lacks vertically and laterally continuous reservoir grade rocks across western Osage and eastern Kay County, Oklahoma. There, the lower member of the Reeds Spring possesses the poorest reservoir quality, the middle member the best, and the upper member exhibits moderate quality.
AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects