Regional variability of Caney Shale elemental composition, mineralogy, and petrophysical properties, Ardmore Basin, Oklahoma

Abstract

The Mississippian-age Caney Shale of the Ardmore Basin, Oklahoma, consists of four chemofacies based on geochemical analyses of well drill cuttings. Chemofacies 1 and 3 represent a dominant detrital source into the basin, and chemofacies 2 is associated with periods of shallow-water conditions favorable to carbonate mineral formation. Chemofacies 4 represents intervals that are interpreted to have formed by reducing-bottom water conditions during deposition, with pyrite formation in an anoxic setting. The elemental proxies used to indicate carbonate minerals and detrital fluxes correlate with X-ray diffraction (XRD) derived mineralogical analyses. Based on XRD, the Caney Shale is primarily composed of mixed-clays, quartz, and carbonate minerals. The mixed-clay fraction consists of illite and kaolinite, while the carbonate fraction is composed of calcite and ankerite. These results are also consistent with ρmaa-Umaa mineralogical analysis, constrained by XRD results, which revealed 3 rock types: mixed-clays, quartz, and carbonate. Rock-type models and vertical proportion curves illustrate an abundance of carbonate deposits within the central Ardmore Basin, suggesting a shallow-water environment and likely multiple shorefaces delivering sediment across the basin. A decreasing upward GR log response paired with an increasing upward carbonate abundance can be interpreted as transgressive sequences that correspond to 4 stratigraphic zones within the Caney Shale. Chemofacies also correlate with the transgressive sequences, suggesting that chemofacies are related to deposition. 3D total porosity models show an average porosity of approximately 20% per zone of the Caney Shale, with maximum porosity values of 61% occurring in Zone 4. Brittleness index models show brittleness within the quartz rock type, and greater ductility within the mixed clay rock type. This basin-scale characterization provides an understanding of Caney Shale elemental composition, mineralogy, and petrophysical properties and their regional variability.