More out of Gullfaks

September 9, 1998, 01:00 CEST

New studies show that the recovery factor for Statoil's Gullfaks field in the Norwegian North Sea can be substantially increased.

"With sufficiently good knowledge of the reservoir, a factor of 65 per cent is a realistic goal for the Brent group," says Hafsteinn Agustsson, project manager for Gullfaks oil drainage.

Statoil currently expects to recover 54 per cent of the stock tank oil originally in place (Stooip) in this field, which has roughly 80 per cent of its reserves in the Brent group.

Efforts are now being focused on identifying undrained pockets of oil which have been "bypassed" over the 11 years since Gullfaks came on stream.

More of these pockets than expected have been found by the drainage project since work began in January, Mr Agustsson reports.

"A number of relevant observations have been made recently with the aid of 'four-dimensional' seismic," he explains. This method involves comparing the results of three-dimensional surveys carried out at different periods.

The fourth dimension of time provides information on the way oil and water have flowed through the reservoirs, and where residual deposits are located.

This approach represents a revolution in portraying the reservoir and fluid movement, Mr Agustsson emphasises. It is being combined with improved geological description plus advanced reservoir and production technology in a bid to recover an extra 190 million barrels of oil from Gullfaks.

After the trawl of the Brent group - which includes a total of four formations - a similar job is planned in the Lunde, Statfjord and Cook formations.

The two-year oil drainage project is being pursued jointly by the Gullfaks operations organisation and Statoil's research centre in Trondheim.