Norway’s Petroleum Safety Authority (PSA) has revealed in its investigation of a fatality aboard the COSL Innovator, that the rig was not built to endure weather conditions that occurred on the night of 30 December, however, COSL Drilling Europe conducted its own heavy-hitter investigation, and disagrees.
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The COSL Innovator, from COSL. |
In December, the COSL Innovator semisubmersible drilling rig was struck while operating at Statoil’s Troll field in the Norwegian North Sea by a wave that killed Aker Solutions team leader Rune Morten Narvåg; injured four others; disconnected the rig from the well; smashed 17 windows; caused water intrusion, which led to extensive damage; and deformed the forward bulkhead on the box grinder, PSA said in its report.
The authorities also said that if more people were in their cabins, more lives could have been lost.
In the report, the PSA said the rig did not have an air gap of 1.5m between the underside of the lowest deck and the highest wave crest. At the time of the incident, the unit’s superstructure was not dimensioned to resist horizontal wave loads.
The PSA concluded that the wave that hit the COSL Innovator was steep, but that the weather conditions on the night of the incident were probably within the limits which the unit was designed for.
“Various air gap calculations exist for COSL Innovator, with different results, as well as a model test. The PSA considers that inadequate attention was paid to two key analyses during development of the design. This has probably been significant for the extent of the damage sustained in the incident,” the PSA said.
Meanwhile, COSL conducted an internal investigation, along with Statoil and Aker Solutions, and shared its results with the PSA last month.
In the internal investigation, COSL said that the COSL Innovator is in line with other rigs operating on the Norwegian Continental Shelf (NCS), and is designed and constructed according to current regulatory requirements and the practice of these. In addition, the rig has been subject to approval by DNV GL, and possesses an acknowledgment of compliance (AOC) issued by the PSA with assistance from the Norwegian Maritime Directorate.
“The practice of the current regulatory requirements does not take into account horizontal wave loader on the outer bulkhead,” COSL said. “We register that the report therefore represents the requirement for a new implementation of the regulations from the PSA's side. It is likely that such a change will have consequences for many of the rigs on the shelf, which will also have to document compliance in a similar way.”
COSL has a total of three drilling rigs of the same design on the NCS, the COSL Innovator, COSL Promoter and COSL Pioneer, that have a total operation time of 11 years in the North Sea.
“All rigs have on several previous occasions experienced significantly worse weather conditions than that occurred on December 30, 2015, without it has been experienced horizontal wave loader (mud flow) on the tire box,” COSL said.
The company has already made improvements to the COSL Innovator, and it is also working with DNV GL, Statoil, and Marintek to collaborate on additional tests to determine the rig’s design, and its air gap within the expected wave spectrum compared to the night of the incident.
COSL has until 1 October to comply with the PSA’s regulations.
Read more:
1 dead, 2 injured in Troll accident
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