Industry sources have said they had been briefed on a $US70 million ($NZ91.5 million) one-hole drilling programme at a prospect within the GSB, to the south of the South Island and October was pencilled in for the start date.
However, Shell would neither confirm nor deny a drilling programme was in place. A spokeswoman said yesterday it was in a ''closed'' period for commenting on operations, because of the lead-up to the release of its quarterly financial result.
Shell New Zealand chairman Rob Jager said in a brief accompanying statement that no final decision had been made on rig selection or supply base.
''Planning continues on this [GSB] work programme and there are no further updates to report,'' he said yesterday.
While the most recent exploration drilling has been confined to the southern end of the Canterbury Basin off Oamaru, most recently one hole each in 2006 and 2014, the last drilling in the Great South Basin took place between 1976 and 1983.
Two holes out of eight showed some hydrocarbons, but neither was commercially viable.
Shell announced in December 2013 it was undertaking a 2-D shipborne seismic survey within a 21,200sq km area south of Dunedin, costing tens of millions of dollars.
One of Shell's GSB permits, covering 16,715sq km southeast of Dunedin, has Mitsui E&P Australia as a 17.07% stakeholder, OMV New Zealand 21.95% and Shell GSB at 60.98%.
Its second GSB permit is adjoining, and east of the first and covers 8507sq km. The partners in that are Mitsui E&P Australia (15%) OMV New Zealand (26%) and Shell GSB (59%).
Houston-based Anadarko has almost completed a shipborne seismic survey off Otago's coast, with its contracted research vessel, the 89m Polarcus Naila, in Dunedin for the past two days.
However, it is expected any decision by Anadarko to drill another test hole in the Canterbury Basin could be up to two year's away.
Anadarko contracted drill ship Noble Bob Douglas last year to drill off Taranaki then Oamaru, costing about $400 million, but came away empty-handed.
Since September last year, oil services giant Schlumberger Seaco has a permit covering a large swath of the Great South Basin, more than 370,000sq km, which is ''under evaluation''.
