Sakhalin II CGBS Oil & Gas Platform

Plattformen Lun-A uOverall dimension caissons: 88,0 m x 105,0 m 980 run/m form. Shafts: diameter bottom =26,0 m, diameter top =16,0 m.

Located 15 km off the north-eastern coast of Sakhalin Island, in a water depth of 48 metres, the Lunskoye (LUN-A) is a drilling and production platform, with minimum processing facilities for the Sakhalin Island Energy offshore development programme in Eastern Russia. Oil/condensate and gas separation, including gas treatment for transport to the LNG plant will be done onshore at the onshore processing facility. This platform will produce the majority of the gas for the LNG plant.
The Piltun-Astokhskoye-B (PA-B) is a drilling, processing and production platform that will extract oil and associated gas from the Piltun reservoir. The platform will be located in a water depth of 32 m.
           
Progress
At the end of January, the final tower of the huge gravity base structure of the Piltun Oilfield was nearing completion. The adjacent Lunskoye platform  was completed in December 2003 which was built in the same graving dock. The dock dimensions are 330 m by 220 m, with a depth of 18 m. In all 1.5 mil t of excavated materials were required to be moved to create the dock, which will be reinstated on completion.
Removal of the bund wall will require further excavation of 650,000 cu m, which will be undertaken predominantly by a cutter hopper suction dredger. This is due to start immediately following extraction of the steel sheet pile wall in April. This will flood the concrete gravity base structure basin where the two structures are located in advance of their tow out to Sakhalin Island.
The project is managed and supervised by teams of experienced personnel provided by main contractor Quattrogemini in Finland, slipform contractor Gleitbau in Austria and engineering design contractor Aker Kvearner AS in Norway.
In parallel the topsides are under construction at the Samsung Heavy Industries yard in South Korea. Total contractor man-hours for the two topsides (Lunskoye and Piltun) are averaging an impressive 10,000 hours per day.
Once completed the two concrete gravity base structures will be floated out of the dock and towed to the Lunskoye and Piltun fields, ballasted and sunk accurately onto preinstalled drill templates, finally resting on the sea bed. This operation will take place in June and July of 2005, with the topside platforms transported on barges during 2006 and positioned on top of the legs. Production is scheduled to start in early 2007.

Procedure
Work on the Lunskoye concrete gravity base structure started in March 2004 with the preparation of the base re-bar and concrete formwork. Slipforming of the Unit 1 caisson cell walls consisting of 500 lm of formwork and 250 jacks started in May last year. The 12 m high walls were slipformed at a rate of 1.2 m per 24hours, in four units. The base caisson was completed and as the top slab was installed work on the shafts commenced. The riser and storage shafts were completed at the beginning of November, while the utility shaft was half complete and slip forming of the drill shaft had just started. Slipform rates for the shafts varied between 2.50 and 1.84 m per 24 hours depending upon the difficulty of geometric performance and embedments. The platform was completed to start with the slipform operations in December last year.
The construction of the PA-B concrete gravity base structure progressed in parallel. The base casson, slipformed at a rate of 1 m per 24 hrs, was completed by mid November. And as the shafts were split into four operations such that two shafts were completed by the New Year, the third in the last week of January while the last was completed in February this year. All in all 6,200 cu m of concrete, of differing grades between 45 N to 85 N strength, varying from high density to lightweight has been poured, with 40,000 t of reinforcement fixed in a total formed area in excess of 110,000 sq m.

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