Supplying electricity from land to natural gas compressors on the Troll A platform (photograph) in the Norwegian North Sea promises significant environmental benefits, according to Statoil ASA in an announcement earlier this summer.
Use of innovative technology eliminates emissions of carbon dioxide and nitrogen oxides from the platform and its associated 120 million cu m/day gas-treatment plant at Kollsnes near Bergen.
Turbines would otherwise have been needed offshore to drive the compressors, says the company, releasing some 230,000 tonnes/year of CO2 and 230 tonnes of NOx.
First application
High-voltage direct current (HVDC) transmission technology means that electricity can be supplied to Troll A from Kollsnes, where a transformer and DC rectifier are to be installed. Sent to the platform along specially developed DC cables, the power will pass to an AC rectifier and special motors.
The solution has been used before, says Statoil, but this represents its first application to an electrical drive system for compressors. ABB Process Industries Division of ABB AS has developed the system in cooperation with Statoil.
A contract to supply and install the submarine power cables and to build the electrical compressor drives has been awarded to ABB by the Troll licensees. Worth about 600 million kroner, this delivery also covers construction of the transformer and rectifier station at Kollsnes.
The new compressors, costing about 3 billion kroner, will offset declining reservoir pressures in Troll as gas production proceeds and drive output through the pipelines to land.
Troll lies on Blocks 31/2, 3, 5, and 6 and contains 60% of overall gas reserves off Norway. The development consists of the Troll A platform, the gas treatment plant at Kollsnes, and pipelines linking these two installations.
Troll still ranks as the largest gas find in the North Sea, and exploration of Block 31/2 has confirmed seismic data that showed that the structures extended into neighboring acreage.
Statoil operates the Troll development and holds a 20.8% interest.
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A diamond-wire cutting module developed by Sonsub Inc., Houston, has successfully cut a 12-in. pipeline in the Gulf of Mexico in 4,573 ft of water. The module (cutting frame shown at left) was deployed from Sonsub's HOS Innovator by an ROV to support recovery of a pipeline accidentally dropped while being laid. The module is part of Shell Gas Transmission LLC's diverless pipeline repair system, which in addition consists of an isolated hydraulic power unit and launch and recovery frame, a concrete and fusion-bonded-epoxy coating removal tool, a pipeline-end preparation tool, a pipeline caliper, and other support equipment. Sonsub, a Saipem Group company, designed and built these modules for the deepwater pipeline repair system.
