The Gippsland Basin in southeastern Victoria is Australia's major crude oil and natural gas producing province. To the end of 1986 the basin had supplied 88 per cent of Australia's cumulative crude oil production and 48 per cent of cumulative natural gas production. Crude oil and natural gas were first discovered onshore in 1924, near Lakes Entrance, Victoria. Since then over 125 onshore wells have been drilled, resulting in the discovery of one (1) subeconomic and six (6) uneconomic petroleum accumulations. More than 80 exploration and step-out wells have been drilled offshore, resulting in the discovery of eleven (11) economic, twenty-six (26) subeconomic and six (6) uneconomic petroleum accumulations.
The petroleum in the Gippsland Basin mainly occupies structural and structural/stratigraphic traps within the Oligocene, Eocene, Paleocene and Late Cretaceous marine, marginal marine and continental clastic sequences. The petroleum is believed to be of land-plant origin; crude oil results from thermal breakdown of exinite, and natural gas from thermal cracking of vitrinite and exinite.
The crude oils are generally very light and paraffinic, ranging from 40 to 60oAPI. Some heavier oils discovered at shallow depths range from 14.6 to 26.5oAPI and are thought to have been biologically degraded. The condensates range from 48 to 63oAPI. The natural gases are generally low in condensate content. Some gas reservoirs contain a high proportion of carbon dioxide.
Production of natural gas and oil commenced in 1969 and 1970 respectively. Cumulative production to 31 December 1986 was 344.66 x 106m3 of oil, 9.68 x 106m3 of condensate, 41.75 x 106m3 of LPG and 66.14 x 109m3 of sales gas. The oil and gas produced is transported from the twelve offshore production facilities (platforms) by pipeline to gas and crude oil stabilisation plant at Longford, Victoria for processing, and then to storage and distribution centres.
Estimated remaining recoverable petroleum reserves in the Gippsland Basin as at 31 December 1986 are 202.44 x 106m3 of oil, 22.44 x 106m3 of condensate, 44.89 x 106m3 of liquid petroleum gas, and 206.39 x 109m3 of sales gas.
