Exploration on Continental Shelf Off Northwest Australia

Abstract

Development of the Northwest shelf area into a proven hydrocarbon-bearing province has been relatively fast and successful thanks to recent advances in seismic technology and to close geologic-geophysical coordination. Work to date has located several geologic provinces and subbasins. The Dampier subbasin is especially attractive because of thick sandstone reservoirs and excellent shale source rocks, particularly in the Jurassic and Triassic sections. The Rankin trend has three separate accumulations, with separate gas and/or oil-water contacts proved by the drilling of North Rankin No. 1, Rankin No. 1, and Goodwyn No. 1. Thick sandstone sections in these wells had a westerly source. Similar features and environmental conditions are expected to extend into the adjoining Beagle Trough. The Browse basin, offshore from the ancient Precambrian-Proterozoic Kimberley block, contains more than 30,000 ft of Tertiary, Cretaceous, Jurassic, and Triassic sedimentary rocks. The Scott Reef gas discovery is on the outer rim of this basin and source sands of the productive Jurassic-Triassic section are indicated to have come from the northwest. Many upthrust-block trends within the basin are untested. Twelve wells drilled in the offshore Bonaparte basin resulted in significant evidence of hydrocarbons, although reservoir quality was poor. Outer margins of the Bonaparte basin may have well-developed reservoir sands, possibly from a northern source. The only area which lacks evidence of hydrocarbons is the offshore Canning basin; 40 wells have been drilled onshore without success or good evidence of hydrocarbons. The offshore Canning area is, however, very large and little is known of the detailed pre-Jurassic stratigraphy. Much more exploration is required and possibly the deeper Paleozoic sediments will be demonstrated to be objective targets.