BURNS, BRIAN J., and JOHN K. EMMETT, Esso Australia Ltd., Melbourne Central, Melbourne, Victoria, Australia
A regional geochemical study of the oil and gas in the Gippsland basin was undertaken to better define the maturation window and to identify the key source units in the basin. Detailed GCMS analysis of forty source rocks was used to calibrate the biomarker derived maturity against the measured vitrinite reflectance. This calibration was then applied to the biomarker data on 40 additional oils and it was found that the oil window was from Rv 0.9-1.3% with peak generation in the Rv 1.1-1.3% range. Isotopic analysis of the major gas fields in the basin confirm their origin from overmature source rocks at maturities of Rv 1.25-2.0%.
Biomarker studies of the oils revealed that they form a single oil family, with some local variations, and that the source is from terrestrial higher plant material, dominated by gymnosperms, and occurring in a mildly oxidizing environment with very little bacterial reworking of the primary organic input. Coals and carbonaceous shales correlate with the oils and these source units are best developed in a lower coastal plain depositional setting which formed behind a wave-dominated shoreline. Upper Cretaceous sediments form the main mature source units. Thick lacustrine deposits of P. mawsonii (Late Cretaceous) age are believed to be part of a large early-rift lake but their poor source rating and poor correlations with any of the oils excludes them from consideration as a potential so rce for the Gippsland oils.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)