ORGANIC BIOMARKER CLASSIFICATION OF OIL FAMILIES IN SOUTHERN OKLAHOMA

In the mid-continent, The West Velma and Sholem Alechem fields are located in the Sho-Vel-Tum region and host oils whose source rocks remain unresolved. In this study, a suite of oils sampled from a range of producing depths in the Sho-Vel-Tum region are characterized based on their organic biomarker signatures and correlated with regional source rocks to accurately assign the oil source(s). The Sho-Vel-Tum region is one of southern Oklahoma’s prolific hydrocarbon-producing fields and has produced more than 100 MMBO.

Previous studies have indicated that the Woodford Shale is the main source rock in this region of southern Oklahoma; however, due to the complex subsurface structures, a contribution from other source rocks is possible. These other potential source rocks include; the Upper Ordovician limestones of the Viola Group, the Lower Pennsylvanian black shales of the Springer Formation and Morrow Group, the Lower Mississippian Osage Limestone and the shales of the Ordovician Simpson Group.

Twelve oil samples were perforated from the Deese C, E and D intervals between 3416-4704 ft in the West Velma and Sholem Alechem fields. The organic matter sources and depositional conditions for these source rocks and oils should result in diagnostic biomarker signatures that were measured using gas chromatography and mass spectrometry (GC-MS). The biomarker signatures, specifically the n-alkanes, hopanes and steranes, of these oils were correlated with the known source rocks in the area to determine the source(s) of these oils.

The initial biomarker data indicates that these oils were sourced from lithologies that were deposited under reducing marine conditions. Additionally, our preliminary results concluded that the Woodford Shale is the primary source rock; however, there are indications of mixing of sources in our oils that may be confined to certain perforation depths. The outcomes of this study will aid in targeting the proper source rocks in this complicated region, ultimately increasing exploration efficiency.