Derrick shift clarified
Locking wedges had not been attached to the drilling derrick which shifted about a metre on Statoil's Sleipner A platform on 29 January.
This conclusion is drawn in the report from the internal commission of inquiry into the incident on the North Sea installation.
The investigation also found that procedures for moving the drilling rig are formulated in an unfortunate way, and that roles and responsibilities could be defined more clearly.
"A culture which tacitly accepts deviations from routines/procedures appears to have developed," says the report, which has been submitted to the Norwegian Petroleum Directorate.
Hurricane-force winds gusting up to about 108 knots were blowing when the derrick shifted on the skids used to move it between drilling slots.
The inquiry report will form the basis for an action plan, and Statoil's Sleipner operations organisation has already taken initiatives to ensure that similar incidents do not recur.
"These immediate measures have tightened the rule that wedges must always be used, and that the responsible person must document all locking of the derrick after it has been moved," says inquiry team leader Rune Nedrehagen.
"We're also notifying other operators and drilling contractors off Norway about the need to pay attention to this aspect."
The incident caused delays to the Sleipner A drilling programme and minor damage to a good deal of equipment.