Mærsk Endeavour,all year Maersk Exerter,all year
Transocean Shelf Explorer,all year Noble Byron Welliver,all year ENSCO 71,from late December
Drilling rigs used by Mærsk Olie og Gas in the drilling of production wells in various fields and in exploratory drilling
Amerada Hess Noble Kolskaya,all year
Drilling rig used by Amerada Hess in cooperation with DONG E&P for drilling production wells in the South Arne Field
DONG E&P
ENSCO 70,from mid-April
Drilling rig used by DONG E & P as operator and in partnership with other operators to drill exploration wells in various licence areas
Statoil Efterforskning og Produktion
Statoil did not perform drilling operations in the Danish sector, but kept the drilling rig
Noble George Sauvageaumoored at the Siri Field until mid-February (awaiting weather conditions permitting its relocation).
OTHER MOBILE OFFSHORE INSTALLATIONS Mærsk Olie og Gas
Seaway Falcon,until the beginning of February
Pipelaying barge used for installing pipelines in connection with the Halfdan project
SSCV Thialf,7 days in September
Crane barge used to install the Halfdan platform
Box 3.2 Mobile Offshore Installations in the Danish Sector in 2000
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Mobile offshore installations include drilling rigs, pipe-laying barges, crane barges and accommodation platforms/flotels, as well as ships used in connection with oil and gas exploration or production, e.g. during the construction of a fixed offshore installation. Box 3.2 lists all mobile offshore installations operating in the Danish sector in 2000.
Some of the major incidents related to health, safety and environment recorded on the installations in 2000 are described below.
Tanker loading incident at South Arne
In the Siri and South Arne Fields, subsea facilities for storing the crude oil produ-ced have been established. In both fields, the storage tanks were provided with a buoy loading system of the SAL type (Single Anchor Loading).
In the SAL system, the pipeline from the storage tanks is connected via a swivel to a riser for fluid transfer, which is hooked up to the tanker’s loading system.
The swivel is fixed to a suction anchor placed at the seabed, which also serves as the attachment point for the mooring line that keeps the tanker on position during the loading operation. The seabed swivel allows the flow and mooring lines to weathervane freely with the tanker.
During a transfer of crude oil from the South Arne storage tank to the Nordic Savonitashuttle tanker on 7 May 2000, approx. 640 m3of oil was accidentally dis-charged into the sea. The oil spillage was caused by a leakage in the SAL system’s hose connection between the subsea swivel and the tanker’s loading point. The leakage was due to improper operation of the system.
The oil spillage was discovered by the standby vessel Esvagt Gamma, which was assisting in the transfer of oil from the storage tank in the South Arne Field to the tanker. As soon as the leakage had been observed, the loading operation was stopped and the oil spill preparedness activated.
In this way, it was possible to collect about 240 m3of the oil spill, corresponding to about 38%. The rest of the oil dissolved in the sea and/or evaporated.
After the incident, Amerada Hess ApS met with representatives of the company that had supplied the SAL system, representatives from the standby vessel and the tanker to analyze the incident. Based on this analysis, Amerada Hess ApS changed a number of the SAL system’s design features and operating procedures. Together with the Danish Environmental Protection Agency, the Danish Energy Agency has followed the company’s evaluation of the incident.
During the process of evaluating the incident, close contact was also maintained with Statoil, the operator of the Siri Field. Statoil is expected to make similar changes to the design and operation of the SAL system installed in the Siri Field.
Leakage in the Kraka-Dan Pipeline
During a routine subsea inspection of the 9 kilometre long 10" pipeline between the Kraka A and Dan FA platforms, Mærsk Oil og Gas AS discovered gas bubbles seeping up from the seabed.
The pipeline was exposed at the location concerned, and inspection revealed a small hole in the pipeline. It was therefore decided to make a provisional repair of the hole by installing an encirclement sleeve. After a pressure test, oil transport through the pipeline was resumed at reduced pressure.
Closer inspection showed that the hole in the pipeline was very likely caused by a high level of bacterial activity in the pipeline. The operator is therefore currently considering whether to replace certain sections of the pipeline.
In light of the Kraka pipeline incident, the Danish Energy Agency and Mærsk Oil og Gas AS have agreed that in 2001 the company is to perform internal inspec-tion using intelligent piggingof a number of the company’s multi-phase interfield pipe-lines in the North Sea.
Subsidence in the Tyra Field
The extraction of hydrocarbons from the Tyra Field reduces fluid pressure in the hydrocarbon-bearing chalk layers. This pressure reduction causes compaction of the overlying layers and consequent subsidence of the seabed surface. As a result, platforms installed on the subsiding seabed will experience a gradual rise in sea level and a corresponding rise in the level at which the waves impact the structure.
The changing load pattern makes it necessary to reassess the structural strength of the platforms, and such analysis may reveal a need to modify the structural parts of the platforms to ensure that they have the necessary strength to withstand the changed load regime.
The seabed in the Tyra Field has been subsiding since production began in the mid-1980s, and the overall subsidence is now about 2 metres. Work to reinforce the Tyra West A platform began in 1999 when three hollow structural elements were filled with concrete.
The ongoing analyses are expected to result in further reinforcement of the plat-forms in the coming years. The seabed subsidence may also make it relevant to change the applications for which the platforms are used. Thus, it may be neces-sary to relocate equipment from the cellar decks of the platforms due to the impaired safety of personnel and equipment.
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Reinforcement of the Older Platforms in the Dan Field
Some of the platforms in the Dan Field date back to the 1970s. Calculations have shown these platforms to lack the sufficient strength to withstand maximum wave loads under all conditions. The Danish Energy Agency has therefore required that the Dan B complex be demanned under weather conditions involving wave heights beyond a certain maximum level.
However, recent analyses have shown that it is possible to reinforce the platform structure to such a degree that sufficient safety is ensured at loads equal to 50 years of wave impact, which is a commonly accepted design criterion. Such structural changes were implemented in 2000 when 28 structural elements were reinforced with high-strength concrete.
After the structural properties of the platforms have been improved, the Danish Energy Agency has granted its approval for maintaining the manning level of the Dan B complex in weather conditions that previously required evacuation of the platforms.
New Drilling Rigs in Danish Territory
In 2000, the operator company ENSCO put two jack-up drilling rigs into service in the Danish sector. The accommodation facilities on these rigs did not meet Danish regulatory requirements, for example, with regard to the size and functionality of their recreational facilities. By cooperating, the company and the Danish Energy Agency came up with solutions to reduce the most important non-compliances without any major impact on operations.
At the same time, solutions were found that are presumed to ensure full compli-ance with Danish rules and regulations. However, this involves conversion work on a scale that cannot be implemented while the rigs are in operation.
Permissions for use were obtained for the rigs on condition that the most impor-tant non-compliances were rectified immediately. Furthermore, an agreement was entered into with ENSCO to the effect that the major construction works would be carried out in summer 2001 and spring 2002.
DEVELOPMENT IN CO EMISSIONS