Regional Stratigraphic and Core-Based Characterization of the Upper Pennsylvanian Cline Shale, Midland Basin and Eastern Shelf, Texas

Reed Roush¹, H. Scott Hamlin¹, and Harry Rowe¹

¹The Bureau of Economic Geology Jackson School of Geosciences The University of Texas at Austin

Abstract

The Cline Shale is an organic rich mudrock deposited in the Midland Basin during late Pennsylvanian time. The Cline has recently seen increased exploration and production activity as an unconventional resource play. This poster describes Cline facies using core analysis, and outlines the geographic distribution of the Cline Shale using wireline logs and cores. The study area was a restricted deepwater basin during the late Pennsylvanian; slow sedimentation rates and periodic oceanic oxygen depletion controlled the accumulation and preservation of organic matter. Preliminary data show the Cline shale has TOC values ranging from 1.3% to 3.0%.

Over 400 wireline well logs were used to define the stratigraphy of the Upper Pennsylvanian interval in the Eastern Shelf and Midland Basin. The top contact is located between 2780 feet subsea on the Eastern Shelf, and 7855 feet subsea in the basin center. The Cline Shale is between 150 to 461 feet thick in the central part of the Midland Basin, and up to 544 feet thick north of the Horseshoe Atoll.

High-resolution (2-inch interval) x-ray fluorescence (XRF) geochemical data were collected from five Cline cores. The XRF data delineate both composition and depositional conditions, i.e. periods of oceanic oxygen depletion, throughout the interval at sub-facies resolution. XRF data show an inverse correlation between calcium content, associated with carbonate content, and aluminum content, associated with clay content. The data also detect intervals with elevated concentrations of redox sensitive elements such as vanadium. The detailed chemostratigraphy coupled with wireline logs and core descriptions are used to present a detailed composite section, including a facies scheme, within the Cline Shale.

AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014