The Fortescue field is the last of the "giant" oil fields discovered to date in the offshore Gippsland basin, southeastern Australia. This field is a stratigraphic oil accumulation on the western flank of the giant Halibut-Cobia oil field. The Fortescue field discovery well, West Halibut-1, was drilled in 1978--some 11 years after the Halibut discovery--as a follow-up to the dry Fortescue-1 wildcat. The occurrence of a stratigraphic trap in a sand-prone section is a unique feature of the Fortescue field. Fortescue reservoirs are Eocene sandstones that are interpreted as having been deposited in coastal plain, upper shoreface, and lower shoreface environments. Fortescue reservoirs are stratigraphically younger than, and hydraulically separated from, those in the underlying Halibut-Cobia field. Pressure data have conclusively demonstrated that there are at least three separate hydraulic systems within Fortescue field. Reserves are estimated at 280 MMSTB on the basis of an original oil in place estimate of 415 MMSTB.

Fortescue field was developed by two 21-conductor platforms, Fortescue A and Cobia A, which also developed the underlying Cobia reserves. These platforms were commissioned in 1983. At the conclusion of development drilling in early 1986, 28 productive wells had been drilled into the field.

Peak production of 100,000 BOPD from the combined development facilities was achieved in 1984 and sustained until 1986. Production received a boost in 1989 from two infill wells that were drilled following interpretation of the available reservoir data.

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Following these successes, a 3D seismic survey was acquired over Fortescue, Halibut-Cobia, and Mackerel fields in 1990. A revised detailed reservoir description based on these data is expected to allow identification of additional infill and workover opportunities and to help mitigate production declines in these mature fields.