Carnarvon Petroleum (20%), the only listed player in the joint venture, this morning revealed that the Roc-1 well defined gross 3C resources of 372 billion cubic feet and 18 million barrels of condensate and there is almost as much again updip with additional prospective resource of 328Bcf and 16MMbbl.

Current 1C resources are a sub-commercial 42Bcf and 2MMbbl with further prospective resources of 87Bcf and 4MMbbl, while the best case scenario is for 270Bcf and 13MMbbl and a further 193MMbbl and 16MMbbl, RISC calculated.

Carnarvon managing director Adrian Cook says that, as it stands, the field at the 2C level falls just short of the estimated minimum economic field size of around 325Bcf and 17MMbbl, but the drilling of Roc-2, targeting hydrocarbon zones higher in the structure could change all that.

The wide range in volumetric analysis is a reflection of the un-appraised nature of the discovery some the subsurface uncertainties caused by the fact that the Roc structure in a flank position.

Roc-2 will attempt to confirm the lateral extent of the upper gas bearing sands and the extent of the predicted gas and condensate column in the reservoir quality Caley Sandstone intersected water wet below the interpreted gas water contact.

Success at Roc-2, which has an 80% chance of geological success, is expected to move prospective resources into contingent resources and prove the base for a viable field development, with the main risk being the extent to which the reservoir is present.

Operator Quadrant Energy (40%) has yet to make public its own figure, but Cook said Carnarvon's estimates were "consistent" with Quadrant's own estimates.

JV partner Finder Exploration earlier this year said there were around 300Bcf in Roc-1, but that Roc-2 could potentially show 1.2 trillion cubic feet of gas-in-place with 40-60 barrels of condensate per million cubic feet.

Roc-2 is planned for the second half of the year to try to resolve the upside and get Roc-1 over the line, although there is the possibility of a hub development with the nearby Phoenix South and possibly the earlier Phoenix discoveries.

Phoenix South-1 well discovered high quality light oil in the Barrett member in lower Triassic reservoir, but it did not reach the Caley member that contains the condensate rich gas discovered in the Roc-1 well.

Cook said Phoenix South-1 warrants future appraisal work, but that the partners need to balance the competing needs for exploration, appraisal and development, and that Roc is currently the most attractive option.

The Roc field sits within the WA-435-P and WA-437-P joint venture.

"The Roc structure is a particularly compelling appraisal proposition," Cook said.

"We are confident about several important elements in the structure, including the quality of the gas and condensate discovered in the Roc-1 well, the quality of the reservoir rocks that contain the discovered hydrocarbons, the outer extent of the structure via the gas water contact and the size of the structure as mapped on modern 3D seismic data."

Roc-2 will attempt to prove that the gas and condensate exists down to the gas water contact, and hopefully improve overall resources towards the high side estimate.

"Roc-2 has been assessed as a relatively low risk appraisal well with a successful outcome being a significant step forward in supporting a development hub for gas and liquids (oil and condensate) that also opens up the province to additional development and appraisal projects," Cook said.

Cook also confirmed that the JV was also working to understand the regional significance of "compelling" hydrocarbon shows recorded in the deeper section of the Roc-1 well, that were observed down to the well's total depth.

"The science clearly shows us there are prolific hydrocarbon generating source rocks within the Bedout sub-basin and our new 3D seismic data stretching beyond the Roc structure is showing us there are a significant number of large structures warranting further exploration within the area," he said.

Roc-1 encountered a gross 40m (net 13m) hydrocarbon column below 4384m, overlying a further 80m of reservoir quality sands.

Roc-2 will be drilled 5-6km to the east of Roc-1, about 65m updip, where the deeper zone may be hydrocarbon-bearing, and will involve coring about 120m of reservoir. The well will be designed to allow for flow-testing.

Carnarvon and Finder will each be carried for the first $8 million of costs.

Cook said Quadrant was working on a variety of technical projects this year that will assist in future drilling activities and opportunities in the emerging Bedout Sub-basin.

Any development at Roc is likely to involve a floating production storage and offtake vessel for condensate production and a sales gas pipeline to shore to supply the domestic gas market.

First production could happen from 2020, with capital costs estimated at $US1.6 billion ($A2.12 billion).

JX Nippon has 20% of the JV.

Carnarvon shares were up 5% to $0.084 this morning.