Shell has said safety is its "foremost priority" after calls for North Sea activities to be restricted in the wake of the oil leak. The company has been tackling the release of more than 200 tonnes of oil near the Gannet Alpha platform.
A relief valve was closed by divers on Friday.
Environmental organisation WWF Scotland said operations should be restricted pending an infrastructure audit. Shell said safety was always paramount.
The company said in a statement: "Safety is Shell's foremost priority at all times.
"As part of that commitment, in 2004 Shell initiated a $1.2bn (£728m) project to upgrade our assets in the North Sea. This has been completed.
"This year alone, we plan to invest approximately $600m (£363m) in our assets in the region.
"The 2003 audit, eight years ago, was one of the things that led to the huge investment programme."
The oil giant said oil had been seeping from the valve at a rate of less than one barrel a day before it was closed.
The situation will continue to be monitored.
The leak - about 300ft (91m) below the surface - had been discovered earlier this month.
The Gannet Alpha oil platform is 113 miles (180km) off Aberdeen.
Source: BBC News