The Pluto-1 well intersected a 209m gross gas column and analysts are saying the discovery could be as much as 2.5 trillion cubic feet of high quality gas.

Pluto is 15km from ChevronTexaco's similar-sized Wheatstone discovery and 110km south-west of the North Rankin production platform.

Both companies are partners in the North West Shelf venture and their combined discoveries could provide enough gas to feed a four to five million tonnes per year LNG train over 20 years.

Woodside, the operator of the NWS project, last year commissioned the $2.4 billion fourth LNG production train and a new gas trunkline connecting the gasfields to the Burrup Peninsula at Karratha.

Then early this month, Woodside announced it had signed a letter of intent for the fifth train engineering, procurement and construction management contract with Foster Wheeler WA Pty Ltd and WorleyParsons Services Pty Ltd.

A sixth train, which could be in production by early next decade, would lift the Shelf's LNG capacity to more than 20 million tonnes a year.

The Pluto discovery saw Woodside shares jumped 50 cents, or 2%, to $24.80. Woodside opened at $25.00 today and reached $25.03 by midday AEDT.