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The AAPG/Datapages Combined Publications Database

Southeast Asia Petroleum Exploration Society (SEAPEX)

Abstract


Offshore South East Asia Conference, 1978
Pages 54-65

Exploration of Part of the Northwest Shelf of Australia (A Case History)

J. S. Thomas, E. O. Nestvold, A. Crostella

Abstract

In the period between 1963 and the present, Woodside Petroleum Development Pty. Ltd. has carried out an extensive exploration programme over a large part of the Northwest Shelf of Australia.

A number of oil and gas discoveries have been made and three of the gas discoveries could possibly be commercial. Studies on development projects for the gas fields began in 1972 but were delayed at the time by uncertainties concerning Government petroleum policies. A further development proposal was submitted to Government in April, 1976 and is currently under discussion. Exploration activities have continued throughout the period.

The current view of the regional geology of the area is of a continental margin formed by the breakup of the Gondwanaland mass in late Palaeozoic to early Mesozoic times. A major period of tectonic activity extending from late Carboniferous to Middle Jurassic resulted in a series of basins trending roughly parallel to the present coastline. Subsequent sinking of the shelf area has resulted in the burial of these structures and the development of drape closures. Seaward tilting in the Tertiary has resulted in a thick wedge of mainly carbonate sediments being laid down.

Oil and gas has been found in the Cretaceous and Upper Jurassic post-breakup sediments but the major hydrocarbon accumulations are found in Middle Jurassic to Upper Triassic gas-bearing sands in the high blocks of the pre-breakup section. Delineation of structural features below the ‘Main Unconformity’ by reflection seismic is difficult and considerable problems have been encountered in the interpretation of the geo-physical results.

Future work in the area depends largely on economic developments in the world gas market and the Government’s attitude to the development of mineral resources in general.


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