Characteristics of Nitrogen Compoundsin Crude Oil and Their Bearing on Oil Filling Processin Zhidan Oilfield, Ordos Basin

Oil charging, migration and accumulation into the tight reservoir of the Yanchang Formation in the Ordos Basin remain controversary. In order to solve the problem, oil charging direction of the Yanchang Formation in the Zhifang area of the Zhidan Oilfield was studied as a case using the neutral nitrogen compounds of crude oil as indicators. Results show that all the crude oil in the Yanchang Formation of the Zhifang area presents the same source and similar thermal evolutionary degree. They were gradually filled from the central part to the west and northeast. Along the direction of oil charging, the total of neutral nitrogen compounds in crude oil increases, the maturity of crude oil decreases, and the relative content of exposed compounds increases. The direction of crude oil charging is consistent with the thinning out of the source rock, and the migration distance is in fact very short. The research results are helpful to the study of the formation of oil fields in tight oil reservoirs of the Yanchang Formation.