An inquiry report on a problem well on Statoil's Huldra field in the North Sea on 20 October is critical, but concludes that alarm and response systems functioned well.
Gas began flowing into the well while completion work was being carried out from the Mærsk Gallant rig. High downhole pressure activated the topside blowout preventer (BOP).
The report by an internal inquiry team drawn from Statoil and rig owner Mærsk describes the incident as very serious. It could have had even more far-reaching consequences had the safety systems failed to function.
"We take the report and its conclusions seriously," says Morten Ruth, project director for the Huldra development in Exploration & Production Norway.
"This well was under very high pressure, which makes the drilling operation extremely complex. We had therefore taken a number of steps before spudding, and had installed a new BOP."
According to Mr Ruth, the latter unit had the capacity to shut the well completely with all its downhole equipment.
The report concludes that requirements for safe and acceptable operation were not adequately met, and that signals from the well were misinterpreted by the drilling supervisors.
Mr Ruth says that such signals can be very difficult to understand in high-pressure wells. Once the danger signs had been spotted, however, the well was swiftly sealed in accordance with safety procedures.
The inquiry team has not been able to identify deficiencies in the emergency response to the incident. Leadership, alerts and demobilisation functioned satisfactorily and with a high degree of professionalism.