Recent reports by the joint venture, which also includes Australian Worldwide Exploration, suggested full product sales would begin in March. Full production is now not expected until late April.

Commissioning of the onshore plant is now about 60% complete, while remedial works on the Yolla A plaform are progressing, Origin.

But there have been further delays. Offshore, the accommodation support vessel the Safe Astoria was connected to the Yolla A Platform this month, about three weeks later than expected.

Origin said the vessel was fully operational, with project staff undertaking critical remedial work on the platform to prepare for commissioning.

A start-up date for steady gas production will also be a month behind schedule, due to additional integrity assurance work and slower than expected progress of some commissioning work at the onshore plant.

Origin now expects sales gas will be introduced to the Victorian grid in late February for final commissioning of the plant.

This means the project would become fully operational about one month later than previously advised, with product sales starting in March and full production expected from late April.

BassGas is a partnership between Origin Energy as operator (42.5%), AWE (30%), CalEnergy (15%) and Wandoo Petroleum (12.5%)