Australia's biggest offshore explorer announced this week it would broaden its exploration efforts in Australia and overseas from 2013 and "materially" increase its exploration budget over the next two to three years.

A couple of statistics about Woodside's exploration program in recent years highlight the significance of the change in strategy.

First, Woodside has made a massive investment in exploration in the Carnarvon Basin in recent years, with a total of 20 exploration wells in the past two years alone.

Most of this activity has been in the search for additional gas for Pluto LNG. In 2012, the company plans to drill only three wells with this objective.

Secondly, Woodside's focus on the Carnarvon Basin has been at the expense of exploration drilling in every other area except the Browse Basin.

It's been five years since the company drilled an exploration well outside the Carnarvon Basin or Browse Basin. And the last time the company made a big frontier effort was almost a decade ago in the Bight Basin, with the Gnarlyknots well in 2003.

The new strategy is a return to the Woodside of old and the type of frontier exploration on which the company's fortunes were founded.

The shift back to frontier targets began this week with the announcement of plans for exploration in the Rowley Sub-basin of the Roebuck Basin, a frontier area despite its location between the Northern Carnarvon and Browse basins.

Woodside and Shell were awarded three permits (WA-462-P, WA-464-P and WA-466-P) over the Rowley Sub-basin in November.

These areas, which are on the continental slope in water depths of 250-3000m, were part of the 2010 acreage release. Bids closed in May last year, effectively before the arrival of Woodside's new CEO and changes across the company.

Woodside also has previous experience with the Rowley Sub-basin. One of the new permits, WA-464-P, includes part of former permit WA-297-P, where Woodside drilled the unsuccessful Huntsman-1 wildcat in 2006.

The well did not reach the Triassic formations that are the source of the gas riches of north western Australia, and in fact the Triassic of the Roebuck Basin remains untested.

(Woodside said at the time Huntsman-1 was within the Northern Carnarvon Basin, but Geoscience Australia has always regarded the location was part of the western Rowley Sub-basin).

Whatever the original thinking behind Woodside's new acreage acquisition in the Roebuck, the company is embracing its new frontier opportunity with a passion.

Woodside and its partner Shell are focusing formidable resources on the area with plans to acquire 11,000 square kilometres of 3D seismic this year ahead of exploration drilling next year.

Managing director Peter Coleman said this week the company was "most excited" by the Rowley Sub-basin acreage, which "contain very large structures with multi-Tcf potential, but at this stage they are also very high risk."

While the Northern Carnarvon Basin and the Roebuck Basin are immediate neighbours, they have major differences.

The major difference is the lack of proven source rocks in the Roebuck Basin.

Geoscience Australia's project leader for the acreage release program, Tom Bernecker, has previously told Energy News Premium that "in the Carnarvon Basin, explorers have made major inroads in understanding the petroleum systems, particularly the Triassic system where the source of most of the basin's huge gas reserves occurs.

"In the Roebuck Basin these systems have not been identified. There is some evidence to tie the Phoenix-1 gas discovery in the Bedout Sub-basin to the same Triassic system in the Carnarvon, but there needs to be much more work and exploration drilling."

The Roebuck has a different evolutionary history to its neighbours and is more structurally dissected and complex. It missed out on the Jurassic rifting that characterised the Carnarvon and Browse Basins and does not have the Jurassic sediments that are rich sources of oil in the North West Cape.

The new Woodside-Shell campaign, with its vast 3D seismic survey, will provide a huge leap in understanding about this frontier area.

Carnarvon Petroleum and joint venture partner Finder Exploration are also trying to tame the Roebuck with an exploration program over four permits (WA-435-P through to WA-438-P) in shallow water closer to shore. These permits include BP's Phoenix-1 discovery in 1980.

Even with an increased focus on overseas exploration, Woodside will have the budget to consider other new frontiers in Australian waters.

The Bight Basin, considered by many to be Australia's best hope for a major new oil province, is now tied up BP.

Other frontiers with the potential for big rewards include the Mentelle Basin, a fragment of continental crust at a tectonic plate "triple point" where Australia broke away from India and Antarctica.

The Mentelle has been subject to extensive pre-competitive work by Geoscience Australia. A Mentelle permit was included in the 2010 acreage released but was not awarded.

Another big frontier opportunity may come up this year in the Capel and Faust basins, another continental fragment about 800km east of Brisbane.

Geoscience Australia has invested heavily in pre-competitive work in this area, which it believes it has strong similarities to the Gippsland Basin.

It is one of many frontiers in Australia waiting to be tested. With the change in Woodside's exploration strategy, the odds of some of these finally being tested have improved dramatically.