Estimation of Relative Migration Distances in the Anadarko Basin Based on the Distribution of Nitrogen Compounds in Crude Oils

Abstract

The organic nitrogen content of most oils ranges from 0.1 to 2.0%. Migration distance, thermal maturity and depositional environments can potentially affect the distribution of carbazole and benzocarbazole isomers in the oils. However, the extent of variation within these compounds during migration is still poorly understood. In this study, the relationship between the distribution of organic nitrogen compounds in Woodford oils and source rocks in the Anadarko Basin has been investigated. 22 Oil samples and 4 rock samples from the Woodford have been investigated. 12 Woodford oils and 1 rock sample are from the Pauls Valley-Hunton Uplift area and 10 Woodford oils and 3 rock samples are from the Cherokee Platform region. The maturity of oil samples from Pauls Valley-Hunton Uplift is in the range of 0.58 to 0.69 (Rc) estimated from the methylphenanthrene index (MPI). Such small range maturity variations minimize the maturity impact on the distribution of nitrogen compounds. The content of nitrogen shielded carbazoles is low near the Anadarko Basin but high in the Pauls Valley-Hunton Uplift. The benzo-[a]/[(a)+(c)] -carbazole ratio (BC) is increasing from the Pauls Valley-Hunton Uplift to the Anadarko Basin. This trend suggests the migration pathway is from the center of the Anadarko Basin to the Pauls Valley-Hunton Uplift. Oil samples from Cherokee Platform are produced horizontally from the Woodford Shale. The maturity of the source rock and oils is higher than that of Pauls Valley-Hunton Uplift samples. The oils have a low abundance of both the carbazole and benzocarbazole isomers. Biomarker distributions indicate the organic matter input in Cherokee Platform is different from that in the Pauls Valley-Hunton Uplift. The organic facies might potentially affect the distribution of nitrogen compounds. Another possibility is that the Cherokee Platform oils have already migrated long distances, leading to a depletion of the carbazole and benzocarbazole isomers. Future work will focus on elucidating organic facies, depositional environments and maturity of these samples by studying aliphatic and aromatic compounds. Such research will potentially aid in the interpretation of migration pathways by using the distributions of carbazole and benzocarbazole isomers in the Anadarko Basin petroleum system.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015