Study On Oil Fingerprint Of Seawater In Typical Sea Area

With the rapid development of global economy, as the main energy of the modern society, demand for oil is increasing rapidly in the world. Along with the increase of oil demand, maritime transportation and offshore oil exploration is developing quickly. This contributes to risk of oil spill accident. Oil fingerprinting is an important technology in oil source identification. China has formed a relatively complete oil spill identification system and stable characteristic ratios under weathering are required in the oil identification. Some ratios have been often used in the oil spill identification and show good stability. But these ratios in different oil often show little difference. The results are not very scientific when these ratios are used, and even lead to wrong judgment. Characteristic ratios’consistency of different oils is studied in the article. Oil spill identification should consider the stability and difference of characteristic ratios and the impact of the background environment on characteristic ratios determination. With Jieshi Bay and Zhoushan waters as the object of research, their oil fingerprint of sea water and their source of petroleum hydrocarbon is studied. The main conclusions are shown as follows:(1) The characteristic ratios’stability of different oil is obviously different, but characteristic ratios of steranes and terpanes show good stability. For the four different oils, some characteristic ratios of n-alkanes, sterane and terpane classes show obvious consistency. These ratios include CPI, C3iaβ(S/(S+R)), C32aP(S/(S+R)), C33aP(S/(S+R)), C34αβ(S/(S+R)) and C29aaa(S/(S+R)). The PAHs distribution and ratios show obvious difference between these four different oils, and there is little consistency problem. To avoid wrong judgment in the oil spill identification, not only the stability of characteristic ratios should be taken into account, but also the consistency of different characteristic ratios in different oils.(2) For the Jieshi Bay seawater, the characteristic parameters of n-alkanes show good consistency at different time. The GC-MS spectrograms show relatively consistence for previous peak, and the main peak is n-C16. The relative content of n-C18, Pr and Ph is obviously high, which suggests that Jieshi Bay seawater were contaminated by petroleum hydrocarbons. In the spring, sea contribution is significantly higher than the terrestrial contribution, while in the autumn, terrestrial contribution becomes high. The value of Pr/Ph, n-C17/Pr and n-C18/Ph are less than 1 and CPI is between 1 and 2, which suggests petroleum hydrocarbons contaminations. Terpane and sterane characteristic ratios are very similar between different stations of the Jieshi bay. The value of C31αβ(S/(S+R)), C32αβ(S/(S+R)) and C29aaa(S/(S+R)) are very similar with oils.(3) For seawater in Zhoushan, n-alkanes distribution patterns are divided into double peak-cluster, which means contribution of terrestrial and marine origin, and middle peak dominant cluster, which means contribution of phytoplankton. The relative content of n-C11 in many stations is high and Pr of some stations is obviously high which indicates contamination of petroleum hydrocarbons. N-alkane distribution of coastal area waters changed greatly affected by different sources and can be divided into back peak, double peak and middle peak distribution. They indicate different sources of hydrocarbon. The value of Pr/Ph are less than 1, indicating the existence of oil pollution. Terrestrial origin contribution is higher than marine origin in Zhoushan sea area and some stations are contaminated by oil. CPI ranges from 0.84 to 1.10 and some stations show mild even carbon advantage. CPI ranges from 1.02 to 1.24 in coastal area of Zhoushan, which suggests the contamination of oil.Sterane and terpane distribution are not consistent in Zhoushan sea area which suggest that oil contamination is more complex in Zhoushan than Jieshi Bay. The relative abundance of sterane and terpane are much higher in coastal area, indicating that coastal area are more affected by oil contamination.18a(H)-oleanane is found in Zhoushan sea area, which exists in oil. For coastal area, C31αβ(S/(S+R)), C32αβ(S/(S+R)) and C29aaa(S/(S+R)) show high maturity. C31αβ(S/(S+R)), C32αβ(S/(S+R)) and C29ααα(S/(S+R)) range widely in Zhoushan sea area. Sterane and terpane ratios show obvious difference between different stations.