Woodside Petroleum has announced a 10% decrease in proved and probable (2P) gas reserves estimate for its Greater Pluto region off Western Australia.

Following a review, the company reported an increase of 1P total reserves by around 10% for the region.

Woodside’s review, which has excluded production to date this year, is said to follow completion of integrated subsurface studies that cover 4D seismic and well performance data.

The Greater Pluto region consists of Pluto-Xena, Pyxis, Larsen, Martell, Martin, Noblige and Remy fields.

The company has used a probabilistic method to calculate an updated estimate. Earlier, a deterministic method was used to calculate the reserves and resource estimates for the Pluto-Xena fields.

As part of the review, Pyxis Hub reserves have been reclassified from undeveloped to developed, after obtaining ready for start-up (RFSU) in October for the Pyxis and Pluto North wells.

With the targeted RFSU of the Xena-2 well and the Pluto water handling project, further reclassification of reserves from undeveloped to developed is anticipated next year.

Woodside CEO Meg O’Neill said: “The 4D seismic survey undertaken in 2020, together with the performance of the wells in these fields, has enabled us to narrow the 1P and 2P reserves range.

“The Greater Pluto region is a significant and valuable resource for Woodside. Having already produced more than 440 million barrels of oil equivalent from the Pluto and Xena reserves since start-up in 2012, the Greater Pluto region has 2P Total reserves of approximately 360 million barrels of oil equivalent for production in the years ahead.”

The company has also reduced the Greater Pluto 2C Contingent Resource by around 7% from 234.MMboe to 218.4MMboe.

As a result of removing late life compression from the reference development plan, the decrease consists of the reclassification of 6.2 MMboe from 2P undeveloped reserves to 2C contingent resource.

As an operator, Woodside has a 90% stake in the WA-34-L production licence that includes Pluto, Xena and Pyxis fields.

Woodside, as an operator, owns a 100% stake in the WA-404-P exploration permit that consists of Larsen, Martell, Martin, Noblige and Remy fields.