Compound-specific isotope analysis as a tool for characterizing mixed oils: an example from the West of Shetlands area

The origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources, or when multiple episodes of charging are involved. In this study, oils from the Clair field, West of Shetland Islands, which are mixtures of nonbiodegraded oil added to biodegraded oil, are characterized by comparing the carbon isotope ratios of the gasoline-range hydrocarbons (GRH) of the oil to the GRH released from the pyrolysis of the asphaltenes in the oil. This comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir, information useful in assessing the source potential of the basin