Neptune-5 is the third appraisal well to have been drilled since Woodside acquired its interest in the Neptune Field with Neptune-4 being plugged and abandoned and Neptune-3 recording two reservoirs with a total 150ft net oil pay.

Previously Woodside has had a fairly dry run in the Gulf of Mexico including the P&A of the Bison-1 wildcat, the Voss exploratory well and Roatan-1.

In contrast to Woodside's mixed fortune in the region BHP Billiton (BHPB) has had a run of success in the ultra-deepwater area with several oil discoveries including its second exploratory well on the Chinook prospect which intersected 79m of net oil pay.

The net column at Neptune-5 is significantly larger than those recorded in the similar Miocene reservoir sandstone intervals of previous Neptune wells and preliminary evaluation of the fluids indicates the presence of relatively good quality oil.

The well spudded in July using the BHP Billiton-operated drillship CR Luigs and has been drilled to a total depth of 19,142ft in water depths of 6,215ft.

Currently, the well is being sidetracked and the joint venture is assessing options for other associated operations at the well. Woodside's acting managing director, Keith Spence, said that the Neptune-5 result is very promising.

"This is a very large oil column with well developed sands. The data will greatly assist our evaluation of the commercial viability of the field."

The Neptune discovery is located in the Atwater Foldbelt region of the Central Gulf of Mexico. This area includes the Mad Dog and Atlantis fields, which are currently being developed by other joint ventures.

Woodside Energy has a 20% working interest in the leases containing the Neptune Field and BHPB 50%.