Core-calibrated regional facies distributions of the Cline Shale, Midland Basin, TX
Abstract
The Cline Shale is an organic-rich mudrock deposited in the Midland Basin during the uppermost Pennsylvanian (Canyon and Cisco time). The Cline Shale facies are constrained by the Central Basin Platform to the west, the Horseshoe Atoll to the north, the Eastern Shelf to the East, and the Ozona Arch to the South. It sits stratigraphically above the Pennsylvanian Strawn Formation and below the Permian Wolfcamp Formation. The Cline Shale is approximately 250 feet to 400 feet thick in the Midland Basin. It is both regionally and locally heterogeneous; investigating these heterogeneities is the first step to understanding the potential of this unconventional resource play.
Three cores from the basin center and one core from the toe of the Eastern Shelf slope were used in this study. X-ray fluorescence (XRF) data points were analyzed on a two to three inch resolution for the composition of 29 different elements. Using the XRF as a reference, 86 samples were drilled from the four cores and were analyzed for x-ray diffraction (XRD) and total organic carbon (TOC); these samples were used as calibrations for mineralogy and organic matter content. Agglomerative hierarchical cluster analysis, a multivariable statistical method, was used to group the dataset into statistical clusters. Each cluster was interpreted as a geologic facies based on empirically derived cutoffs of mineralogy and organic matter content. This core analysis reveals previously unrecognized facies stacking patterns and vertical organic matter distributions.
From this core study, we distinguished core-calibrated gamma ray (GR) facies cutoffs. Gamma ray (GR) logs were first normalized to the same maximum and minimum values. The facies are: GR<75 API = carbonate, 75
AAPG Datapages/Search and Discovery Article #90214 © 2015 Southwest Section AAPG Annual Convention, Wichita Falls, Texas, April 11-14, 2015