Asphaltene profiling of crude and heavy fuel oils to assist in forensic oil spill investigations

Abstract

When oil is spilt, investigators compare the chemical profile of the spilt oil with suspected source oils through a process commonly referred to as oil fingerprinting. Oil fingerprints are currently generated exclusively from volatile fractions of oil whilst the non-volatile fraction is discarded. The non-volatile fraction contains asphaltenes, which are defined as the oil fraction that is not soluble in short chain n-alkanes. There is sufficient evidence in the literature to suggest that asphaltenes may offer probative information if they were included in oil spill investigations. This PhD research has investigated whether asphaltene profiling methods can in fact provide probative information that warrants their use alongside current oil fingerprinting methods. Asphaltene profiling methods were designed primarily as screening tools for the exclusion of obvious non-related oils prior to conducting conventional oil fingerprinting. A range of spectroscopic and thermal degradation methods were developed and tested using ten different crude and heavy fuel oils. The infrared spectroscopy and pyrolysis-gas chromatography-mass spectrometry methods were found to be the most suitable methods for oil spill investigations. Both methods were probative and capable of differentiating non-related oils, whilst grouping together oils from the same origin. A blind study was also conducted using these two methods. The original sample-set and five additional oils were analysed, and asphaltene profiles were interpreted. The four pairs of duplicated oils that were included in the blind study were correctly grouped together. The majority of non-related oils were differentiated except for two pairs of very closely-related oils which were not differentiated. Taking into account that asphaltene profiling was designed as a screening tool for use only in conjunction with conventional oil fingerprinting, the false inclusion of two pairs of non-related oils was not problematic. Conventional oil fingerprinting successfully differentiated these two pairs of oils following asphaltene profiling.

Date of Award	2018
Original language	English