Operator Eni Australia said at about 4:30am on Wednesday, free hydrocarbon gas was detected onboard the Four Vanguard FPSO.

"As a precautionary measure the operator of the facility, Australian FPSO Management [AFM/Premuda] decided to evacuate all non-essential personnel," Eni said.

"The evacuation has been successfully completed."

No injuries or damage to the facility have been registered, but production is currently shut in and will be restarted only when the causes of the incident are fully understood and addressed.

The Woollybutt field currently has a production potential of about 5000 barrels per day. Eni said the incident would not affect the current plan to tie back the recently successful well Woollybutt-4H in late May 2008.

AFM/Premuda is responsible for operating the FPSO Four Vanguard under a contract with Eni.

The Woollybutt partners are Eni (operator and 65%), ExxonMobil 20% and Tap Oil 15%.