The distribution of dimethylcarbazoles in oils from the Pearl River Mouth Basin, South China Sea

C2-carbazole isomers have been investigated in crude oils from the Hui-Liu Structure Ridge (HLSR) in the Pearl River Mouth Basin (PRMB), South China Sea. The NH shielded isomer, as well as the NH partially shielded isomers, was detected in high abundance and the NH exposed isomers in lower abundance. A small-enrichment trend of 1,8-dimethylcarbazole (DMC) was observed in crude oils along the western part of HLSR (WPHLSR), which may indicate little effect of migration on the C2-carbazole distributions. Two strikingly different distribution patterns of NH partially shielded isomers were observed in the reservoirs along the WPHLSR: one with a preference of 1,3-and 1,6-DMCs and the other with a preference of 1,4-and 1,5-DMCs. All of the oils occurring in the Upper reservoirs have a preference of 1,3-and 1,6-DMCs, whereas those trapped in the Lower reservoirs show a preference of 1,4-and 1,5-DMCs, which may indicate there are two petroleum migration systems in the WPHLSR. © Science Press 2007.