Utilization of Pyrrolic Compounds as Indicators of Secondary Migration for Woodford Oils in the Anadarko Basin, Oklahoma, USA

Migration pathways and distances of the oils in reservoir are thought to affect the distribution of pyrrolic compounds such as carbazole, its alkyl derivatives (alkylated carbazoles) and benzocarbazoles, although other factors, including maturity and depositional environments may also affect the distribution of these organic nitrogen compounds. In this study, 14 oil samples produced from conventional reservoirs in Pauls Valley, south Oklahoma were investigated using organic geochemical techniques. The sterane and hopane fingerprints suggest that most of the oils were sourced from the Devonian Woodford shale. Maturity parameters consistently indicate that the maturity level of the studied samples are all of similar maturity (Rc = similar to 0.7%), suggesting the distribution of the organic nitrogen organic compounds is possibly reflecting variations in relative migration distances. The distribution of alkylcarbazoles revealed a preferential enrichment during migration, with the nitrogen-shielded alkylcarbazole tending to be enriched relative to the nitrogen-semi-shielded alkylcarbozoles particularly in oils produced close to the Arbuckle uplift to the east. Correspondingly, another family of pyrrolic compounds, benzocarbazoles, whose distributions also indicated that the Pauls Valley Woodford oils came from deeper part of the Anadarko Basin as the benzo-[a]/([a]+[c])-carbazole ratios decrease eastwards. In more specific migration systems, although the pyrrolic compound indicators are potentially disturbed by the structural complexes, the general migration directions suggest that the studied oils in Pauls Valley Hunton uplift were sourced from the deep basin area, and migrate upwards in porous sediments due to the buoyancy. This study investigates the feasibility of using pyrrolic compounds to estimate relative migration distances and will aid in the interpretation of migration history by using the distribution of carbazole, alkylated carbazoles, benzocarbazoles isomers in the Anadarko and Ardmore Basin petroleum systems.