There are more discouraging signs from Nova Scotia's depleting Sable offshore natural gas project as a report from majority owner ExxonMobil concluded natural gas production at Sable is down by 35 per cent since planned maintenance two months ago.

The company said it does not know when full production will resume.

"Sable is producing at about 65 per cent of normal levels," Merle MacIsaac, an ExxonMobil spokesperson, said in an emailed statement to CBC News.

"During our planned maintenance in September we identified some additional work to be done before returning to full production. The timetable for returning to full production has not yet been determined."

The production slowdown was revealed this week in documents filed by Nova Scotia Power.

The electrical utility told regulators on Tuesday that it was having difficulty securing a supply of natural gas because of production cuts at Sable and the failure of EnCana's Deep Panuke project to come on stream this year, as expected.

"This has caused significant cuts to Nova Scotia Power’s contracted gas. Both the delay at Deep Panuke and reduced production at Sable have resulted in increased costs as Nova Scotia Power has sourced other fuel to replace the contracted gas," the utility stated.

The lifespan of the Sable natural gas fields has been the subject of speculation as output from its five offshore wellheads has gradually lessened in recent years. When it went into production in late 1999, a 25-year lifespan was projected.  

In 2010, Exxon announced it would wind down Sable.

The Nova Scotia government has also seen its royalties plummet. Projected royalties for 2012 are estimated to be about $27 million, down from $110 million in 2011, according to the provincial budget released in April.