The investigation conducted by the Petroleum Safety Authority Norway (PSA) into the Floatel Superior stability incident on 7 November 2012 has yielded new knowledge about securing anchors and transport at transit draft. It has also exposed challenges related to regulations, classification and design assumptions.
An unsecured anchor caused the hull of the Floatel Superior accommodation rig to be punctured in eight places on the night of 6-7 November 2012, leading to water intrusion in two tanks and a list of about 5.8 degrees.
The PSA has investigated this incident. See notification of orders after investigation of stability incident on Floatel Superior, 7 November 2012
Information has emerged in connection with the investigation which could be important for other players on the Norwegian continental shelf (NCS).
Securing anchors
One of the anchor bolsters on Floatel Superior lost three braces on the incident night as a result of damage which had arisen and developed over time.
Following these fractures, the remaining parts of the bolster were unable to prevent the anchor hitting the hull directly. The anchor hung free, and wave action caused to strike the hull repeatedly and cause seven holes.
A number of incidents have been reported which relate to anchors stowed in bolsters, both while the facility was in transit and during long-term stowage because of dynamic positioning (DP) operations and the like.
Keeping anchors in the bolsters over a long period, at or near the waterline, increases the risk of damage.
It is difficult to achieve a sufficiently stiff system for securing the anchors, particularly when using wire rope rather than chain. Wire rope is not an optimum choice for holding an anchor in place.
If anchors are to be stowed in bolsters during a storm, the investigation shows that careful calculations must be made of the loads which anchors and bolsters could experience during transport or operation.
Robustness
If the hull is to withstand direct blows from anchors, its dimensions might need to be considerable. Simply using a more robust bolster structure is not enough, but could be a way of protecting against anchor damage.
A number of bolsters on other facilities have an extra horizontal brace between the wear surface and the hull. This could delay the anchor striking the hull, but an unsecured anchor might also “sail” over it. The effect of the additional brace is then lost.
Another key element is the tension to be used in keeping the anchors in place. Industry practice has been to use 40-50 tonnes of winch tension on the anchor stowed in the bolsters. Even then, movement with consequent damage has been reported.
Additional measures are accordingly necessary. It has not been normal practice to secure or lash anchors on semi-submersibles, since the area between fairlead, anchor and bolster is hard to access.
To prevent similar incidents when the decision has been taken to stow anchors in the bolsters during transport and operation, great attention must be paid to winch tension.
This must be viewed in conjunction with the position of the anchor in relation to:
It is important that owners ensure that their facilities do not suffer damage if anchors have been stowed in the bolsters over a long period. Ensuring that new damage does not occur is also important.
Transport at transit draft
The PSA takes the view that Floatel Superior had suffered damage before it was taken into use on the NCS because it had been transported in higher waves than permitted by its operations manual and analyses. This damage had probably worsened in bad weather up to the incident night.
Semi-submersibles are normally transported at transit draft because they then experience minimum resistance and can be moved swiftly.
The hull designer applies assumptions concerning the weather and specifies limits for the conditions in which the facility can operate.
It is important that owners ensure that their facilities are and have been used in accordance with the weather assumptions at transit draft.
Should there be nonconformities, furthermore, possible effects on the hull of operating beyond the design assumptions should be analysed or inspected in order to establish the consequences of such operation for continued use of the facility.
Regulations, classification and design assumptions
The PSA’s investigation has shown that the combination of DP and classic mooring calls for adjustments to standards and classification rules to take account of a number of systems in a coherent manner. The PSA will follow this up with the classification societies.
Damage development on Floatel Superior can be traced throughout its operational history. The design and operating assumptions have been inadequately communicated and documented to take account of the reciprocal effects.
The investigation has demonstrated that earlier and more detailed follow-up of questions and observations from people involved could have halted or reduced development of the damage.
It is a general observation that clearer communication and better mutual understanding between those involved are important for reducing risk in complex systems.
.Offshore Installation Services (OIS), an Acteon company, has successfully completed its sixteenth rigless suspended well abandonment campaign involving multiple operators in the Southern North Sea. The multi-operator model for programs of this kind can deliver significant customer benefits in terms of cost-effectiveness. A total of nine mudline wells in categories 1, 2.1, 2.2 and 2.3 were abandoned during the operation including four on behalf of GDF SUEZ E&P UK Ltd. and two for RWE Dea.
The scope of work for OIS, part of Acteon’s activity and resource management business, included the initial approval processes; formulating the contracting strategy; developing detailed procedures; procurement; appointing specialist service providers; overall logistics; and recycling and disposing of the recovered wellheads.
OIS conducted the two-phase abandonment operation from a chartered DP2-class anchor-handling tug supply vessel (AHTS). During phase one, a proprietary twin low-pressure packer tool from Acteon sister company Claxton Engineering Services Ltd. was deployed through the vessel’s moon pool to set cement plugs across all the casing annuli. The second phase involved abrasive severance of the wells using Claxton Engineering’s SABRE cutting tool.
“We have a strong track record in providing commercially efficient decommissioning solutions which are particularly important for non-revenue-generating assets,” said OIS vice president of commercial and business development Tom Selwood. “Multi-operator campaigns such as this, enable operators to share the associated costs which, when combined with the rigless nature of our offering, makes this the most cost-effective way to comply with UK oil and gas decommissioning legislation.”
Max Proctor, GDF SUEZ E&P UK drilling manager, added, “We are committed to fulfilling our responsibility to the environment as an operator and are leading the way in the North Sea with the decommissioning of redundant wells. We started this campaign immediately after the request came from DECC for operators to fully abandon suspended wells by reviewing the history of the wells and confirming the status of each with an independent well examiner. OIS is a valued partner of GDF SUEZ and the success of this project is testament to the team’s strong technical skills and experience.”
Since 1996, the OIS team has successfully completed more than 100 well decommissioning projects without a single lost-time incident.
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Leading international oilfield services company Expro has been awarded a contract to provide equipment and services in support of a client’s offshore project in Latin America.
Located in the Santos Basin, in Brazil, the BS-4 block encompasses two post-salt wells and one pre salt well. Expro has been contracted to provide heavy oil well testing to post-salt wells and data management services through partner company Baker Hughes, in a contract valued at more than $10mn.
Expro will provide Queiroz Galvão Exploração e Produção SA (QGEP) with subsea equipment, Drill Stem Testing (DST), data acquisition, surface well testing, fluids services and wireline intervention services.
Expro has been providing extended well testing services internationally since 1983 and is recognised as a global leader in the delivery of fast track production facilities.
Jean Moritz, Expro’s Latin America region director, said: “We were invited to tender for this project because we offer high-quality integrated service packages. We have a good relationship with both Baker Hughes and QG and this is a great opportunity for Expro to introduce a full package well testing job in to Brazil.”
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