Palaeogeography of the Gippsland Basin Hydrocarbon Play Elements

Abstract

Fifty years of petroleum exploration in the offshore Gippsland Basin has seen the accumulation of an extensive well database that provides a superb resource for palaeogeographic reconstructions. In turn, the maps created can be used to succinctly explain how the key play elements of source, reservoir, seal, structure, maturation and migration were formed to make this relatively small basin at the south-east corner of Australia such a prolific hydrocarbon province. The Gippsland Basin is a tectonic-rift evolving to margin-sag basin whose initial rift deposition starts in the Valanginian with lacustrine and fluvial sediments, followed by the influx of large volumes of immature volcanoclastic sediments from the east. The oldest of these are latest Hauterivian or Barremian, but the greatest influx occurs from Aptian to Late Albian. After a 10 million year time gap a second extensional rift phase commences with the development of a deep-water rift-valley lake, that is terminated by the start of sea floor spreading in the Tasman Sea during the Santonian. The subsequent margin-sag basin from Campanian to Eocene is characterised by thick non-marine fluvial, coal measures and paralic coastal plain successions with a narrow easterly fringe of marine siliciclastics, that thin abruptly into starved outer-shelf and continental slope environments. Widespread marine sedimentation only occurs from Oligocene with the start of carbonate deposition. Biogenic carbonate production increases dramatically during early Neogene and this has produced the wide modern continental shelf. Key palaeogeographic maps are used to explain the hydrocarbon play elements from youngest to oldest. Because the completeness of the data declines deeper in the section this reverse order is preferred as the younger maps help explain the older maps, Maturation and migration of the hydrocarbons is late in the basin's history as for a long time the basin was cold. These aspects and the Mid-Miocene structuring are illustrated by the Miocene palaeogeography. Deposition of the regional seal is explained by the Oligocene to earliest Miocene palaeogeography. Development of the superb top of Latrobe Group reservoirs are best illustrated by a series of Eocene maps. Location of intra-Latrobe traps below lacustrine and marine seals are illustrated by Paleocene and Maastrichtian maps. Finally, the sources of the oil and gas in the basin can be explained by maps from the Santonian back to the Turonian.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015