Abstract

The Devonian-Mississippian age reservoirs in the STACK/SCOOP play segments of the Anadarko Basin in Oklahoma are a complex succession of very low permeability shale and low permeability mixed carbonate and siliciclastic strata. In the last decade, prolific horizontal drilling and unconventional completion practices have demonstrated significant heterogeneity in the composition of oils produced from STACK/SCOOP reservoirs. This study discusses some aspects of this heterogeneity and offers geoscientific explanations of our observations.

Geochemical data from 172 produced oils across 13 counties and 4 different reservoir formations are reviewed. Calculated thermal maturity (Rc%) from alkylated polycyclic aromatic hydrocarbons shows a strong positive correlation with depth and measured vitrinite reflectance. Terpane biomarkers show that oils from STACK West carry a different signature than STACK East and SCOOP oils, likely reflecting a decreasing water depth with consequent limited access to organic-rich upwellings. Light hydrocarbons show that oils in STACK West are also significantly more aromatic than STACK East and SCOOP, indicating lower terrigenous input. Oils from the SCOOP Springer system are depleted in paraffinic compounds to other SCOOP oils and have a unique bicyclic sesquiterpane signature. These geochemical fingerprints suggest that the SCOOP Springer oils are from an argillaceous, non-Woodford source.