Australian oil discovery holds 171 million barrels

Australian companies Quadrant Energy and Carnarvon Petroleum announced surprised results of a drilling operation at its so-called Phoenix blocks off the coast of Western Australia state last week. At its first well, dubbed Dorado, the joint venture partners announced they ran through a 393-foot column of oil while searching for natural gas.

That would quantify as a major oil discovery, with initial estimates of 150 million barrels of commercial prospects possible. On Monday, Carnarvon Managing Director and CEO Adrian Cook said the best estimate now was 171 million barrels of oil at Dorado.

"Oil fields of this significant scale are not often found, with the last large field discovery on the North West Shelf being around 30 years ago," he said in a statement.

Carnarvon in a letter to shareholders last week said Dorado was a high-risk prospect that's paid off because of the low drilling costs. According to consultant group Wood Mackenzie, the next deciding factor would be the quality of oil discovered at Dorado. Conventional oil would be the best-case scenario for the joint venture partners. An ultra-light form of oil called condensate would be more capital intensive.

Carnarvon's best-estimate reserve scenario found only 16 million barrels existed as condensate.

"These volumetric results reiterate the significance of the Dorado discovery and we look forward to maturing this resource and finding additional neighboring resources in our future drilling programs," Cook said.

For development, Wood Mackenzie said floating infrastructure would be the best option considering the low cost.

Quadrant Energy had no public statement on the reserve estimate at Dorado.