As the fields on the Norwegian shelf age, the reservoir pressure (pore pressure) is also reduced and production decreases. This pressure reduction – depletion - poses various challenges.
Often, alternative drilling methods will be necessary, for example managed pressure drilling (MPD).
MPD has in many cases proven to be a good, efficient method, in part because it makes it possible to reduce the pressure the formation is exposed to and to change the back pressure in the well more quickly.
The well control incident at the Gullfaks C facility on 19 May of this year occurred in a well that was drilled with MPD. It is still unclear what caused the incident.
The PSA has been in daily contact with Statoil, and is assessing the company's work on re-establish barriers and secure well 34/10C-0-6A at Gullfaks C. This close follow-up will continue for as long as the PSA finds it necessary.
In June, Statoil decided to carry out an internal investigation of the incident. An assessment of Statoil's investigation and its results will be included in the PSA's follow-up.
Statoil has also confirmed that it not will drill new wells in special pressure zones until it has carried out an overall review and assessment of relevant well incidents.
The PSA will prioritise follow-up of the incident in well 34/10-C-06A on Gullfaks C as regards ascertaining the causes of the incident. In connection with this, a separate audit activity will be carried out with the goal of assessing the operator's choice of methods, application of experience and establishment of plans, including the choice and follow-up of measures to ensure safety while drilling on depleted fields. Planning of this audit activity started as early as 2009, but the incident on Gullfaks C has somewhat changed the goal and scope of the activity.
The work will contribute a basis for the PSA's evaluations of direct and underlying causes of the incident and the operator's handling of the incident. It will also form a basis for evaluations of possible future measures.
A central topic for the audit activity will be the overall assessment the operating company will carry out regarding the risk associated with drilling operations in such areas, and how it compensates for this through risk-reducing measures.
Another goal will be to assess Statoil's decision basis and work on planning balanced-pressure drilling, both in general and specifically in relation to Gullfaks.
The audit activity directed toward drilling in depleted zones will start after the summer.