About This Item
Share This Item
Middle and Upper Devonian reefs outcrop spectacularly for some 220 mi (350 km) along the northern margin of the Canning basin, in a series of rugged limestone ranges. They extend into the subsurface of the basin, and may originally have continued for some 750 mi (1,200 km) in a belt girdling the Precambrian Kimberley block, to join with similar reefs known in the onshore Bonaparte Gulf basin. There is also evidence that they once extended into the Carnarvon basin, 930 mi (1,500 km) to the south.
The Canning basin reefs show similarities to the Devonian reefs of Canada, and for the past 25 years, they have been regarded as prime targets for oil exploration. However, the first potentially commercial discovery was not made in the basin until 1981, when oil was recovered from an Upper Devonian (Famennian) reef complex in the Blina 1 well. This well yielded flows of up to 905 bbl per day from the reefal carbonates.
Recent encouragement of oil exploration in Devonian reefs has also been obtained in the Bonaparte Gulf basin, in this case as a result of mineral-exploration activities. More than 20 drill holes, exploring for lead-zinc, encountered significant showings of oil and bitumen in Upper Devonian reefal carbonates and overlying Carboniferous carbonates, in a belt some 95 mi (150 km) long. They are probably the most extensive near-surface oil showings known in Australia. There appears to be a genetic relationship between secondary porosity development, base-metal deposition, and oil emplacement (in that order) in these carbonates.
There are strong grounds for optimism that further reef-associated oil discoveries will be made in the northern Canning basin, and the outlook is also promising for similar discoveries in the Bonaparte Gulf basin and the offshore area adjoining the Kimberley block.
End_of_Article - Last_Page 981------------