The Mackerel oil field, located offshore in the Gippsland basin, Australia, was discovered in April 1969. The field, which is a topographic-erosional feature, contains oil in high-quality Eocene-Paleocene reservoir sands which lie beneath an unconformity at the top of Latrobe Group, and is sealed by calcareous shales and mudstone of the Oligocene Lake's Entrance Formation. The initial definition of the field was based on 235 km of seismic data which had been shot in an irregular grid involving seven different surveys and on a total of four exploration wells. At the end of 1974, 145 km of high-resolution seismic data were shot over Mackerel to better define the top of Latrobe unconformity and the internal reservoir configuration. In 1976 a detailed pre-development structur l interpretation was undertaken and a stratigraphic model of the field was constructed from detailed analysis of the seismic data.

The pre-development seismic structural and stratigraphic mapping was used to determine the final platform location and to choose the initial development well locations. These well locations were picked to gain early structural control on the top of Latrobe, to test the interpretation in the problem areas, and to investigate the internal geometry of the reservoir units.

Development drilling started in July 1977, and these well results have provided feedback to both the structural and stratigraphic models, which are being continuously updated. The pre-development mapping of the Mackerel field was successful in delineating the basic size and shape of the field and its internal stratigraphic configuration and in identifying all the geophysical and geologic problems which were subsequently encountered in the development drilling. Thus a rigorous seismic interpretation provided the geologists and engineers with a sound basis for field development planning.

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