RECONSTRUCTING THE GEOLOGICAL HISTORY OF AUSTRALIAN CRUDE OILS USING AROMATIC HYDROCARBONS

Abstract

The distributions of methylated naphthalenes in crude oils carry within them detailed information regarding the geological history of the oils. The effects of thermal stress, mixing, biodegradation and migration contamination all leave recognisable imprints, which can be deconvoluted. An extended suite of crude oils from several locations in Australia was analysed for their methylated naphthalene content. It was shown that three ratios of selected isomers, each reflecting the same underlying sedimentary reactions, are linearly related to each other when thermal stress has been the only factor controlling the distribution of methylated naphthalenes. This internal consistency allows for an assessment of maturity independent of source, age and location of the crude oil. When the relationships between the three ratios are not linear, secondary processes such as mixing, biodegradation or migration contamination have affected the crude oil. Close examination of the distribution of methylated naphthalenes can reveal the extent to which either of these processes has affected the oil.