The world’s first sidetrack drilled by a mobile rig through the production string in a subsea-completed well has been successfully finished on Statoil’s Norne field in the Norwegian Sea.
Experience from this operation will be important for efforts to improve the recovery factor on existing offshore fields, and allows Statoil to drill further profitable sidetracks.
This method reduces drilling costs because the work can be carried out much more quickly than before.
“The lessons learnt mark an important step towards improving recovery both here and on other subsea-completed fields,” says Jan-Helge Furnesvik, acting operations vice president for Norne.
“We expect a recovery factor exceeding 60 per cent on Norne. The drilling technique we’ve now tested will help us to meet our goal of an average 55 per cent recovery from such fields.”
Sidetracks have previously been drilled from existing wells only after pulling the production liner and other downhole equipment.
Once the work is finished, the liner and equipment have to be run back into the well.
“Drilling a sidetrack without pulling the liner first has already been done from fixed installations,” explains Mr Furnesvik.
“We’ve now demonstrated on Norne that the special challenges presented by drilling in subsea-completed wells have been resolved.
“This successful operation was over in just 30 days, while a conventional sidetrack in a well of this type takes longer to drill and incurs higher equipment costs.”
Drilled by Transocean Arctic, the new Norne sidetrack is expected to flow almost 19,000 barrels of oil per day.