Norway's Statoil has found more gas in Arctic waters, strengthening the business case for a $6.9 billion field and pipeline development already underway.

Statoil said on Wednesday it had discovered between five and nine billion cubic metres of recoverable gas near the Aasta Hansteen field in the Norwegian Sea, likely prolonging the production plateau for the development, which is expected to be around 130,000 barrels of oil equivalent per day.

"The Snefrid Nord discovery increases the resource base for the Aasta Hansteen field development project by around 15 percent," Irene Rummelhoff, Statoil's senior vice president of exploration Norway, said in a statement.

Production is scheduled to start up in the third quarter of 2017.

Aasta Hansteen, previously estimated to contain 47 billion cubic metres of gas, is one Statoil's biggest and northernmost current projects, expected to cost 32 billion crowns ($3.9 billion). The Polarled pipeline connecting it to the shore will cost another 25 billion crowns ($3 billion).

Still hoping to find more gas at Hansteen, named after a 19th century women's rights campaigner, Statoil will now drill another well in the nearby Roald Rygg prospect.

"Near-field exploration is the main focus of our Norwegian continental shelf exploration programme in 2015," Statoil said. "By proving additional timely resources, we extend the production life of our fields and create significant value."

Small discoveries near existing fields are among the cheapest developments because they can be tied into existing infrastructure at a relatively low cost, extending the lifetime of fields and lowering the unit cost.

The partners in the discovery are: Statoil with 51 percent, Wintershall, the oil and gas arm of chemicals group BASF, with 24 percent, OMV with 15 percent and ConocoPhillips with 10 percent.

Offshore