AGE DETERMINATION OF CRUDE OILS IN THE BARROW SUB- BASIN USING PALAEOCLIMATE RELATED VARIATIONS IN HIGHER PLANT BIOMARKERS

Abstract

Variations in higher-plant-derived biomarkers in sedimentary sequences reflect changes in the palaeoclimatic conditions at the time of deposition. It is thought that changes in climate affect the distribution of higher plant populations growing on the hinterland, thus changing the contribution of these plants into the sediments. These variations can be measured using the abundances of three aromatic hydrocarbons: retene, cadalene and iP-iHMN. This was done for a Jurassic sedimentary sequence from the Koolinda–1 well in the Barrow Sub-basin, The obtained profile was related to an absolute time-scale. Measurement of the higher-plant-derived biomarkers in crude oils from the Barrow Sub-basin enabled accurate measurement of the age of their source rocks by using the Koolinda–1 profile as a reference. Most of these oils correlate with the Jurassic W. spectabilis dinoflagellate zone in the Oxfordian. Within this zone the oils fall into four age groups, reflecting four oil-prone intervals each separated by approximately 0.2 My. The oils that have been generated from each group can be found in specific reservoirs in the sub-basin, showing a pattern of migration away from the depocentre with decreasing age of the source rock. This method of determining the source rock age of crude oils enables detailed oil-source rock correlations. On a basin-wide scale it can provide insight into the location of major source rocks and migration pathways.