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Petroleum Geochemistry of Woodford-Sourced Oils From the Mid-Continent Region, USA


330 crude oils from Oklahoma, Kansas, and Nebraska, with biomarker and carbon isotope values characteristic of UD-LM Woodford Shale source rocks were assessed using cluster and principal component analyses. These oils have relatively depleted carbon isotope compositions, strong upwelling signatures, profuse green algae input, and abundant isorenieratanes, biomarkers for extremely anoxic conditions in shallow water (Photic Zone Euxinia). The oil reservoirs range from Cambrian to Cretaceous. Five oil families were identified, their geographic occurrences mapped and probable source facies interpreted. Family 1 oils only occur in Kansas and Nebraska, from the Sedgwick Basin NW along the NE side of the Central Kansas Uplift. Long range migration of Family 1 oils to the NW into Nebraska appears to have occurred along the NE flank of the Central Kansas Uplift. Oil Families 2, 3, and 4 were likely generated from different vertical organofacies of the Woodford; Family 5 oils appear to have been sourced from the UM Caney Fm. Family 4 oils are produced in Oklahoma and Kansas, but not Nebraska. Family 4 oils originated in the Anadarko and Arkoma basins, with long-range migration in two directions: 1) NNW from the Anadarko Basin, west of the Nemaha Uplift, into Kansas along the SW flank of the Central Kansas Uplift; 2) NNE from the Arkoma Basin along the Cherokee Platform, east of the Nemaha Uplift, reaching Vernon Co., Missouri and the Forest City Basin. Horizontal Woodford completions in the ‘Stack’ play are members of this family. Family 3 has the most positive carbon isotopes, the lowest upwelling signatures, and the highest paralic indications. These oils occur in distinct regions with apparent migration trends:1) In a northerly direction from north-central Oklahoma into eastern-central Kansas and the Salina Basin along, and on the western flank of the Nemaha Uplift; 2) In a NE direction within the Hugoton Embayment of SW Kansas, from mature Woodford sources in the Anadarko Basin of the Oklahoma and Texas panhandles. Maturity-dependent oil biomarker ratios were evaluated to calculate a vitrinite reflectance equivalent (%VRE) for each oil. The range in oil thermal maturity (related to source rock maturity at the time of expulsion) is from <0.7% VRE to >0.9% VRE. Only Family 3 & 4 oils are at levels which are generally best suited for unconventional production (>0.85% VRE).