Abstract

The central part of the Jurassic/Cretaceous Eromanga Basin and the underlying Permian/Triassic Cooper Basin together comprise the largest and most prolific onshore hydrocarbon province in Australia. Production comes from common multiple stacked pools at many horizons in both basins.

Permian carbonaceous lithofacies of the Cooper Basin have previously been thought to be the main source of the oil found in the Eromanga Basin. The Triassic Arraburry Formation, the main seal to the Cooper Basin, has focussed hydrocarbon migration to its zero edge. This has resulted in oil exploration within the Eromanga Basin being concentrated on prospects along the margin of the Cooper Basin. However, new information based on biomarker signatures of oils from Permian and Jurassic reservoirs of the central Patchawarra Trough and the Gidgealpa southern dome (including a significant palaeo-oil column) reveals that much of the oil in the Eromanga Basin may have a significant lateral migrational component and be of Jurassic (i.e. intra-Eromanga) origin. The Jurassic of the Gidgealpa southern dome is an example of the Birkhead-Hutton(!) petroleum system. Analyses of oils within the Jurassic of the Gidgealpa southern dome indicate that two major oil generation episodes have occurred within its drainage area.

Most major Eromanga Basin oil accumulations are trapped by diagenetic capillary seals related to a provenance change and are not full to structural spill point. Many accumulations are leaking and may be acting as permeability seals. The common palaeo-oil columns of many Eromanga Basin accumulations may be related to a change of wettability of the seal.