Geochemical Characterization of the Woodford Shale, Southeastern Oklahoma
In this study a total of 56 rock samples from eight wells containing a Woodford Shale section, including a cored outcrop, in southeastern Oklahoma were analyzed. Analytical techniques performed on these samples included carbonate content, Rock Eval analysis, total organic carbon (TOC), and vitrinite reflectance (Ro). Additionally, crushed rock extracts were subjected to gas chromatography (GC), and gas chromatography-mass spectrometry (GCMS) for biomarker analyses.
TOC values ranged from 3.83% in the south to 11.42% in the north. Maturity increases towards the east of the study area indicated by Ro values ranging from 0.49% to 0.59%. The samples were dominated by kerogen Type II/III indicating a mixed organic matter source. Higher plant input occurred mainly towards the north indicated by the presence of eudesmane and by higher pristane/phytane ratios (>3.0). Depositional conditions were variable and primarily controlled by the extent of anoxia. Aryl isoprenoid ratios indicate that the persistence of photic zone anoxia was episodic.
Several biomarker ratios including pristane/phytane, hopanes/steranes, C23 tricyclic/C30 hopane, and C18 aryl isoprenoids permitted division of the Woodford Shale into different members (upper and middle) as suggested in previous studies.
The Relative Hydrocarbon Potential (RHP) parameter was also of use in characterizing depositional conditions relative to sea-level changes. This information will be further integrated and correlated with geochemical logs and available geological data in order to define regression-transgression cycles.
This study will definitely lead to a deeper understanding of this self-sourced reservoir, in terms of depositional environment, source, maturity, and type of hydrocarbons that are generated.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid