Publication Name: Second South-Eastern Australia Oil Exploration Symposium - Technical Papers
Authors: B. R. Brown
Date Published: December 1986
Number of Pages: 39
Reference Type: Book Section
Abstract:
During the past twenty-five years, since BHP acquired the Victorian offshore permits PEP 38 and PEP 39, over 71,000 km of seismic data have been collected and 136 exploration and appraisal wells drilled excluding junked wells. BHP and Esso have collected 48,000 km of seismic data and drilled 106 of the wells. There are now 12 platforms from which 224 wells have been drilled. The total cost of exploration by BHP and Esso has been $364 million. Over 3.2 billion barrels of oil and 0.8 billion barrels of condensate and gas liquid reserves have been discovered. Two billion barrels have been produced. Gas reserves are estimated at 8. 7 trillion cubic feet. The development of Gippsland Basin oil and gas reserves constitutes one of the most significant industrial developments in Victoria's 150 years and to date has provided the State with $1700 million in royalties.During the quarter century of exploration and production history, geological ideas have developed and Gippsland has been part of that evolution of thought. Plate tectonics has become the accepted theory for the disposition of the continents and oceans and the Gippsland Basin is recognised as typical of basins found on Atlantic type continental margins. The dominantly continental Latrobe Group has been subdivided by palynological zones. The seismic data, combined with palynological data and the faunal zonation of the marine Tertiary, has helped define the geological history of the basin. Potential source beds of the Gippsland Basin are known to lie within the largely continental organically-rich Latrobe Group rather than the overlying marine Tertiary sediments as was
originally predicted. An enormous amount of geophysical effort has been expended on the mapping of the basin and understanding the variations of seismic velocity of the sediments and their effects on depth mapping to 'Top of Latrobe' where over 90 per cent of the oil and gas reserves of the basin are concentrated.
The history of development of anticlinal structures in the basin is intermittent and lengthy. The earliest formed in the Early Eocene, notably at Tuna and Flounder. Another series of folds appears to have developed soon after deposition of the bulk of the Latrobe Group and others formed during the period of slow deposition in the Oligocene and Early Miocene. A further important episode occurred at 13 Ma and the last episode was in the Pliocene. The widespread development of 'Top of Latrobe' structures is important to the accumulation of oil and gas, and the time of sealing that surface appears to have a significant influence on the distribution of oil and gas. Early sealing appears to be most favourable for oil accumulation.
There Is little doubt that the major deposits were found in the first ten years of exploration of the 'Top of Latrobe' closures. The search is now expecting to yield fields with up to twenty million barrels, generally in the more complicated intra-Latrobe section. Exploration effort has not diminished and one of the longest drilling rogrammes in the Gippsland Basin, occupying the past four years, is still in progress and by far the largest seismic programme was completed in April 1985. Exploration is undergoing fine tuning and recently a number of small intra-Latrobe oil discoveries have been made at Tuna-4, Snapper-S and Whiptaii-1A.