Oil and gas producer Nexus Energy says it has found the source of a fault that has halted production for a month but more work is required before output can be resumed.

At 1553 AEDT Nexus shares were 0.5 cents, or 2.7 per cent, higher at 19 cents after the news.

The company on Monday said its offshore intervention program was completed safely after an electrical fault caused a production interruption on January 9.

Nexus said the vessel involved in the work near its Longtom gas project off Victoria returned to port on Monday for demobilisation.

"The location of the electrical fault that has caused the interruption to gas production at the Longtom field since January 9 has been identified as being within the Santos Ltd offshore facilities," Nexus said in a statement.

Nexus said the results of the work would be assessed and another offshore program would be required before gas production resumed.

"Nexus will provide further updates as appropriate," the company said.

Nexus has energy assets in the Gippsland Basin off the south east coast of Victoria, and the Browse Basin off the north west coast of Western Australia.