|
1 Exxon Production Research Company, Houston, TX 77252, USA
2 Esso Australia Ltd., 127 Kent Street, Sydney NSW 2000, Australia
The Gippsland Basin is Australia’s most prolific oil and gas province, with initial reserves estimated at 3.6 billion barrels crude/condensate, 0.6 billion barrels liquid petroleum gas (LPG) and 8.3 TCF dry gas. It is located in southeastern Australia, mainly offshore. Significant hydrocarbons were first discovered in 1964, in large structures at the top of the Late Cretaceous-Eocene Latrobe Group. All of the large structures have now been drilled, with current exploration concentrating on fault-dependent and combined stratigraphic structural traps within the Latrobe Group. Hydrocarbon, source rock and maturation data suggest that there is a widespread and uniform non-marine source of Late Cretaceous age. The concentration of hydrocarbons at the top of the Latrobe Group is due to the presence of large structures, an excellent cap seal, and the relatively sandy nature of the underlying, intra-Latrobe section. The distribution of oil versus gas at this level is largely explained by maturation variations and migration pathways within the basin. Vertical migration of up to 2 km is required in most cases. The distribution of oil versus gas is also influenced by minor source rock variations, fresh water washing, biodegradation, and the variable quality of fault seal. Recent exploration studies have concentrated on locating stratigraphic and combination traps, especially within the Latrobe Group. Prediction and subsequent discovery of these traps is a challenging task that has been aided by sequence-stratigraphic and seismic-stratigraphic analysis of the rock record. This has allowed the prediction of reservoir, source and seal geometries and distributions. The techniques used to construct this chronostratigraphic framework are presented, together with examples of its application within fields and on a regional basis.
