Migration Fractionation Effects of Pyrrolic Nitrogen Compounds of Crude Oil in Weizhuang Area, Gaoyou Sag

The fractionation of pyrrolic nitrogen compounds has been applied widely on studying secondary hydrocarbon migration. As for a biodegraded crude oil, the effect of biodegradation on pyrrolic nitrogen compounds should be studied. The normal crude oil occurs in the reservoirs of Wei 2, Wei 9 and Wei 11 in Weizhuang area of Gaoyou sag, but the oil with little biodegradation occurs in reservoirs of Wei 5, Wei 6 and Wei 8. By comparison among concentration of nitrogen compounds, relative contents of pyrrolic N-H shielded carbazoles and parameters of C₂₁^-/C₂₂⁺, Pr/nC₁₇, the results show that slight biodegradation has little effects on the relative contents and distribution of pyrrolic nitrogen compounds, but has certain effect on its concentration. Hence, variation of relative contents of pyrrolic nitrogen compounds would imply the secondary migration direction of hydrocarbon. The results indicate that hydrocarbon originated from the deep depression zone and Cheluo saddle and injected westward and southwestward in Weizhuang area.