Gippsland Basin

Note: refer to the Acreage Release basins page for updated information on the Gippsland Basin.

Basin Details and Geological Overview

The Gippsland Basin, one of Australia's most prolific hydrocarbon provinces, is situated in southeastern Australia and is located about 200km east of the city of Melbourne. Most of the commercial oil and gas discoveries are reservoired within the siliciclastics of the Late Cretaceous to Paleogene Latrobe Group. Remaining reserves are estimated at 400 MMbbl of liquids and 6 Tcf of gas (unpublished data, Victorian Department of Primary Industries).

A network of pipelines brings produced hydrocarbons to the onshore petroleum processing facilities near Longford. A 457mm (18 inch) gas pipeline from these facilities delivers Gippsland gas along the eastern seaboard of Australia to Sydney in New South Wales. A new network of gas pipelines distributes Gippsland Basin gas to customers in Victoria, Tasmania, New South Wales and South Australia. Increasing gas market demand in the SE Australian region together with deregulation and reform of the upstream and downstream gas industry during recent years has also provided the impetus for renewed exploration activities. This has resulted in an increase in exploration activities in the Gippsland basin with an additional commercial gas discoveries (East Pilchard, Longtom).

Petroleum exploration

Structural elements

The Gippsland Basin is geographically restricted (46 000km²), with approximately two-thirds of the basin located offshore. It is bounded to the north by Paleozoic basement of the Eastern Uplands, to the west by uplifted Lower Cretaceous fault-blocks and to the southwest by the Bassian Rise, which separates it from the Bass Basin to the west. In spite of the limited geographic extent of the Gippsland Basin, more than 300 exploration wells have been drilled within it and approximately 90 000 line km of 2D seismic data and more than forty 3D seismic surveys have been acquired. Consequently, exploration within the Gippsland Basin is mature in comparison to other Australian basins, though it is actually relatively under-explored in comparison to many other prolific basins around the world.

As part of the Early Cretaceous rift system between Antarctica and Australia, the Gippsland Basin initial rift architecture consisted of a rift valley complex. Continued rifting into the Late Cretaceous generated a broader depocentre (the Central Deep; flanked by fault-bounded platforms and terraces to the north and south. The Rosedale and Lake Wellington Fault systems marked the northern margin of the Central Deep and Northern Terrace respectively, with the Darriman and Foster Fault systems defining the southern margin of the Central Deep, and the northern boundary of the Southern Platform. To the east, the Central Deep is characterised by rapidly increasing water depths; these exceed 3000 m in the Bass Canyon. The eastern boundary of the basin is defined by the Cape Everard Fault System, a prominent north-northeast-striking basement high. The western onshore extent of the basin is traditionally placed at the Mornington High. However, the Latrobe Group’s extent is effectively defined by the outcrops of the Lower Cretaceous Strzelecki Group.

In the late Eocene, a compressional period began to affect the Gippsland Basin, initiating the formation of a series of northeast to east-northeast-trending anticlines (Smith, 1988). Compression and structural growth peaked in the middle Miocene and resulted in partial basin inversion. All the major fold structures at the top of the Latrobe Group, which became the hosts for the large oil and gas accumulations, such as Barracouta, Tuna, Kingfish, Snapper and Halibut, are related to this tectonic episode.

Stratigraphy

The Gippsland Basin contains in excess of 10km of Cretaceous to Neogene sediments. The succession is non-marine clastics, to marginal marine clastics, marine clastics and uppermost marine carbonates.

Key References