"If we decide to drill an exploration well, it is unlikely to happen before 2014-15," Shell said in its inaugural Shell New Zealand Great South Basin newsletter released yesterday.
After analysing drill data from the 1970s and 1980s, Shell was still examining its own hydrographic survey data during the rest of this year, noting that "only gas can be expected to be found in the Shell-operated licence area".
"The Great South Basin venture signals the return of Shell New Zealand as an operator in real greenfield exploration," the newsletter said.
Aside from using four independent marine mammal observers during hydrographic surveying, Shell had environmental, health and social impact assessment studies under way, and was meeting special interest groups, the newsletter said.
This week, executives from Anadarko, which plans up to two test drilling programmes for oil and gas off Oamaru next year, are meeting representatives of Dunedin businesses.
This month, Anadarko committed to test-drilling the first of possibly two deep-water oil and gas exploration holes off Oamaru's coast in 14 months.
The projects, drilling in 1100m of water, could cost $50 million to $100 million.
A new drill ship, the Noble Bob Douglas, is expected to visit New Zealand for its maiden voyage and first work programme of up to three holes within 14 months.
One hole is expected to be drilled in November or December next year off Oamaru, then another off Taranaki.
Then, depending on earlier results, a second appraisal hole might be drilled off Oamaru, at the Caravel prospect.
New Zealand's oil and gas exports totalled $2 billion for the year to June, the fourth largest sector behind dairy, meat and wood products and generated about $700 million in royalties and tax.