Statoil confirmed a gas leak had occurred on its Asgard field.
The leak, which was discovered on Friday night, lasted 20 minutes on the Deepsea Bergen rig.
A total of 25 tonnes of gas leaked out during well preparations.
No one was hurt in the incident.
A Statoil spokesman said the Norwegian operator had launched an investigation into the incident.
It is the latest in string of safety incidents for the firm.
Last week, PSA, the Norwegian safety body, found Statoil in breach of regulations in relation to an offshore fire. A fire broke out on a North Sea platform after crude oil pumped against a closed valve for nearly an hour – with the temperature rising from 33 degrees Celsius to 344C. Read more here.
Separately, Respol Sinopec was forced to shutdown North Sea production after an oil sheen was spotted on Saturday. Read more here.