摘要
The GC /MS analytical data of the neutral nitrogen-containing component in forty-eight oil samples from the Bohai off-shore region show a significant influence of biodegradation in reservoir on the abundance and distribution of pyrrolic nitrogen compounds in oils. In comparison with the non-biodegraded oils from the same source rocks, the obvious biodegradation signal appeared in alkylcarbazoles and benzocarbazoles is observed in the slight-moderately biodegraded oils (level 3 to 4). With increasing extent of biodegradation, the abundance of nitrogen-containing compounds decreases gradually, and decline to round fifth of original concentration in the heavily degraded oils with level 6 to 8. For low-moderate degree of biodegraded oils(level 3 to 4), the N-H exposed methylcarbazoles is more susceptible to bacterial attack than the shielded type of isomer, with susceptibility order being 1-methylcarbazole < 4-methylcarbazole < 2-and 3-methylcarbazole. As biodegradation proceeds to higher degree, the 1-MC /4-MC ratio keeps relatively stable due to the presence of an almost consistent decreasing rate for the methylcarbazole isomers.
