RESEARCHES ON THE CHARACTERISTICS OF THE NEUTRAL NITROGEN COMPOUNDS AND THE OIL MIGRATION IN ORDOVICIAN CRUDE OIL FROM TAHE OIL FIELD, TARIM BASIN

In Tahe oil field,the oil accumulation formed in several stages.The heavy oil and the light oil are together in presence in the Ordovician reservoirs.In heavy oil,not only the absolute concentrations but also the ratio indicators of neutral nitrogen compounds are too low to distinguish the oil migration path.The distribution of the neutral nitrogen compounds in the light oil shows that the oil migrates from the south to the north and from the east to the west.In these two orientations,the absolute concentration of carbazole(CA) decreases,the ratio of methycarbazoles(MCA) and the dmethycarbazoles(DMCA) increases,and the ratio of benzo carbazole,a/(a+c),decreases.At the fault belt in the No.3 Block in Tahe oil field,the absolute concentration of carbazole is high,the ratio of MCA to DMCA is low,and the value of a/(a+c) is relative high.These features show that it is through the fault that the hydrocarbon migrates from the source rock to the reservoirs.In this way,the oil migration paths are short,and the hydrocarbon can accumulate in the late stages.Therefore,the crude oil is lighter in No.3 Block than in the blocks of No.4 and No.6 in Tahe oil field.