Distribution of nitrogen compounds and migration of the oils in the Xifeng Oilfield, Ordos Basin, NW China

The Xifeng Oilfield is the largest new-discovered one in the Ordos Basin, NW China. Distribution of the nitrogen compounds in crude oils of the oilfield shows that the migration fractionation of neutral nitrogen compounds in the crude oils are present in the lateral and vertical directions of the oilfield. However, the small variance in the absolute concentration and isomer parameter values of neutral nitrogen compounds in oils from the subsection of Chang-8 oil layer of the Yanchang Formation indicates the short migration distance of the oils. The migration fractionation features of neutral nitrogen compounds in the oils show that the charging direction of crude oil is mainly from the northeast of the oilfield to the southwest and partially from the south to the north for oils from the subsection of the Chang-8 of the Yanchang Formation. It is also observed by means of the migration fractionation of neutral nitrogen compounds in the oils that vertical migration direction of crude oil is downward for Chang-8 oil leg and upward for Chang-3 oil leg and Yan-8 oil leg. This oil migration direction of Xifeng Oilfield is consistent with the distribution of subsurface fluid pressure of the studied area. These oil migration pathways suggest that the oils of Xifeng Oilfield are mainly derived from the subsection of Chang-7 of the Yanchang Formation.