Regional stratigraphic and core-based characterization of the Cline Shale, Midland Basin, Texas

The Cline Shale is an organic-rich mudrock that was deposited in the Midland Basin during the latest Pennsylvanian. Deposits of the Cline Shale are restricted to basinal facies and contain great lateral and vertical heterogeneity. The basinal deposits are bounded by the Eastern Shelf to the east, the Horseshoe Atoll to the north, the Central Basin Platform to the west, and the Ozona Arch to the south. The boundaries do not only vary in morphology, but also in sediment type. High-resolution (2 to 3-inch spacing) x-ray fluorescence (XRF) data were obtained from four cores in the basin. The data were interpreted within a chemofacies framework using agglomerative hierarchal clustering analysis, a statistical grouping method, calibrated with mineralogy and organic matter measurements. The high-resolution XRF chemofacies framework was used to core-calibrate a regional dataset of wire-line logs to determine quantitative lithofacies cutoffs from gamma ray logs of carbonates, organic matter-poor siliciclastics, and organic matter-rich siliciclastics. The lithofacies were mapped throughout the Southern Midland Basin. The maps were created for the Lower Cline, Middle Cline, and Upper Cline, three distinct units within the Cline Shale. An integrated core-based dataset was also used to glean relationships between mineralogy, porosity, permeability, organic content, thermal maturity, and grain density within the Cline Shale on the foot-scale. The results of this study have allowed the synthesis of core-based chemofacies trends analysis and regional composite lithofacies distributions in the Lower Cline, Middle Cline, and Upper Cline.