The interest in Dory comes at a time when the east coast gas market is hurtling towards a shortage and when new opportunities are being put on the table thanks to a decision by the Gippsland Basin Joint Venture partners, ExxonMobil and BHP Billiton, to get out of the Bass Strait oil business.

Once Australia's premier basin, the Gippsland hasn't seen much in the way of drilling since Apache Energy's failed attempts in 2008, but if new players can be enticed in the region could be about to get a new shake.

Aside from near-field exploration and appraisal drilling around the existing GBJV facilities looking for incremental production from thin reservoirs, the offshore Gippsland Basin has fallen on hard times with a few juniors pecking around newer, less proven plays and a complete freeze on onshore exploration until at least 2020.

Besides the South East Remora-1 oil and gas discovery, north of the Marlin platform, there's been little in the way of encouraging drilling, but US-based Liberty has recently been shopping around VIC/P70 in the offshore basin and Energy News understands a farm-in could be close to fund re-drilling of the Dory prospect.

Energy News has been told negotiations for a farm-in are advancing for the permit, which sits over the transition between the shallower Central Platform and the Anemone Canyon where waters are between 500m and 2000m.

The area was previously held by Apache as its once-feted VIC/P45 and VIC/p59.

The US-based company drilled a handful of wells in the basin in 2008, but only Dory-1 was any kind of success with Madfish-1 and Elver-1, also in VIC/P59 and Coelacanth-1 in Vic/P45 both dusters.

Given earlier disappointments at Wasabi-1 in Vic/P58 and the Speke South-1 in VIC/P42, Apache ended all plans for what could have been two dozen wells in the basin and walked away, eventually quitting Australia completely.

But Liberty was undaunted. It had previously held the area so reapplied for it and went back to the very basics of geology and geophysics, trying to understand where Apache had gone wrong and work out how many of the remaining prospects were still valid.

Initially Liberty was thinking about developing a crop of existing, smaller Golden Beach discoveries and exploring for further Golden Beach gas.

However, it quickly became apparent that Apache had missed something when mapping the permit and the Dory and Fangtooth structures were not only part of one very large Top Latrobe structural and erosional closure, but the structure was connected to the GBJV's Blackback field, a 150sq.km target bisected by the Selene Canyon.

As Liberty has been telling people at PESA functions on the east coast, it soon became clear that Dory wasn't just the small gas discovery Apache believed, but that the US independent could have nicked the toe of a sleeping giant.

Apache's exploration team mapped the prospect using fairly conventional PSTM, however the process doesn't really work in the Gippsland Basin due to the high velocity channels and a very rugosed seabed that makes it almost impossible to map.

It became clear that Dory-1 and Madfish-1 has been drilled into false pull-ups, and that what Dory represents is a potential lookalike of the 4.4Tcf Pluto discovery made by Woodside Petroleum on the North West Shelf.

Liberty says that despite extensive NWS exploration spanning 30 years, the discovery of Pluto was delayed by depth conversion difficulties below the slope, so from that standpoint where is no reason to believe that all the best of the Gippsland Basin has been found.

Liberty also says the push down at Dory is similar to Pluto in the Carnarvon Basin, and the explorer believes Dory also sits under the shelf break, which has reduced the recognised size of the structure.

Part of the issue was the sparse 2D seismic in the area prior to 2003. Both ExxonMobil's 2003 Tuskfish 3D and Apache's 2007 Elver 3D showed the presence of Fangtooth, a large depth closure in very deep water to the east of Dory-1, but neither structure had closure in time.

Velocity smoothing reduced the apparent intensity of anomalies that had led to the mapping of Dory and Fangtooth as separate structures, and appears to define them as much flatter, more extensive structures than previously recognised, and it removes the saddle between the two prospects.

The result is a drill-ready prospect that could host as much as three trillion cubic feet of gas, as evidenced by the 30m gas column in the westernmost end of a large gas accumulation.

The challenging technical work was labour intensive and required detailed depth conversion study of the seismic, but the technique velocity technique developed by ExxonMobil for the adjacent Blackback field and Liberty is confident that it is applicable at Dory.

The result is what Liberty has mapped as what may be the largest gas field in a basin that has produced some four billion barrels and 11Tcf to date.

Liberty says Dory is likely to contain 2000PJ and 53MMbbl of condensate in permeability reservoirs.

Selling the Gippsland Basin is a hard task, but a prospect is of a sufficient size it should attract attention, particularly as the east coast is facing a supply shortfall, and there is not much in the way of additional, conventional supply on the horizon.

Cooper Energy and Santos are developing new gas at Orbost, via the Sole and Basker-Manta-Gully fields, but they will add just a few hundred petajoules as the market needs it.

Queensland's gas is heading offshore, the New South Wales CSG fields remain undeveloped and controversial, the Northern Territory is facing a fraccing ban, and while the Cooper Basin unconventionals such as Real Energy's Tamarama-1are in the background, as Beach Energy showed recently with a writedown of its Nappameri Trough reserves, shale gas is not easy to develop.

In the offshore Otway Basin, WHL Energy is yet to make much headway with its La Bella gas discovery and Beach and 3D Oil have the large 1Tcf plus Flanagan prospect, which in itself appears to be a tertiary wedge offering striking similarity to the charge mechanism on the North West Shelf gas province, but it is another wildcat play at a time when the zeal for investing in risky drilling is lacking.

That said, if Dory is confirmed, it could solve the east coast's gas issues within a few years because it is a Top Latrobe target, similar to the premium reservoirs that were developed in the first flush of exploration in the 1960s and 1970s and not the less ideal Golden Beach or Emperor horizons where the reservoir is not as good and the CO2 levels are higher.

If successfully tested, Dory should be a fairly straightforward development.

Liberty has a commitment well due by November 2017, however a lack of rigs off eastern Australia, much less suitable rigs, means the company is looking at swapping out the commitment for more technical work to further derisk the prospect.

The company sees a huge opportunity is still in the Gippsland, beyond just Dory.

VIC/P70 also contains the Archer-1 Intra-Latrobe oil discoveries and multiple Golden Beach gas discoveries Anemone-1 (120PJ and 14MMbbl), Angler-1 (140PJ and 6MMbbL) and Archer (155PJ and 8MMbbloil, with untested upside in Archer Deep and other follow-up targets.

A lot of people have given up, or have been thwarted by the drillbit, but persistence has so far paid off for Liberty, it remains to be seen if nature will play ball.