PETROLEUM IN WESTERN AUSTRALIA: A REVIEW OF EXPLORATION, PRODUCTION, AND FUTURE PROSPECTS

Abstract

Modern petroleum exploration has been in progress in Western Australia since 1952, and has been concentrated mainly in the Perth, Carnarvon, Canning, and Bonaparte Gulf Basins. Two large onshore fields have been developed, the Barrow Island oilfield in the Carnarvon Basin (found in 1964), and the Dongara gasfield in the Perth Basin (found in 1966). Small gasfields have also been developed at Mondarra, Gingin, and Walyering in the Perth Basin, but Gingin and Walyering are now virtually depleted.

Major gas-condensate fields have been found offshore. These are the North Rankin, Goodwyn, West Tryal Rocks, and Angel fields in the northern Carnarvon Basin, and the Scott Reef field in the Browse Basin. They were found during the period 1971 to 1973, but none has yet been developed.

Since 1968 the accent has been on offshore exploration, and this reached a peak in 1972. Exploration activity, both onshore and offshore, is currently declining, owing to the lack of recent success and the unfavourable exploration climate prevailing in Australia today.

Original reserves in the Dongara gasfield amounted to about 13 billion cubic metres, of which nearly 2.1 billion have now been produced. Current gas production from Dongara and the small adjoining Mondarra field is about 2.2 million cubic metres per day, and production will continue at about this rate until 1981, after which it will begin declining. Production will fall steeply in 1987, when existing contracts expire. At that time about 90% of the reserves will have been depleted.

The original in-place reserves of the Barrow Island oil-field amounted to some 750 million barrels, and it is expected that about 240 million will be recovered. Current oil production is around 37,000 barrels per day, compared with the peak of 48.000 barrels per day reached in 1970. Nearly 43% of the original reserves have now been produced.

Total reserves of the major fields in the offshore northern Car-narvon Basin (in the proved and probable categories) are more than 345 billion cubic metres of gas and 320 million barrels of condensate. Of these amounts more than 220 billion cubic metres of gas and 180 million barrels of condensate are in the North Rankin field, which is the largest gasfield in Australia and is a giant by world standards. This is followed by Goodwyn (about 65 billion cubic metres of gas and 90 million barrels of condensate), West Tryal Rocks (more than 30 billion cubic metres of gas) and Angel (about 30 billion cubic metres of gas and 50 million barrels of condensate).

Further drilling will be required before gas reserves of the Scott Reef field can be estimated, but the results of the first well and the size of the structure indicate that they could be very large. It is clear that future exploration in Western Australia will be mainly concentrated offshore, in the Carnarvon, Browse, Bonaparte Gulf, and Perth Basins. However, there are still some prospective onshore areas in the Perth, Carnarvon, and Canning Basins.

The chances of finding giant oilfields in Western Australia have declined markedly in recent years, as It seems that the generative sequences are mainly gas prone, and most of the obvious structures have now been drilled. However, the prospects are good for further large gas discoveries, and there is a reasonable chance that significant oil reserves will also be found.