When the Valhall offshore complex is upgraded in 2009, it will no longer be generating its own power but will be supplied using HVDC Light technology, from the mainland almost 300km away. The result will be safer, more cost-effective energy production and substantially less greenhouse gases.
The major redevelopment of BP’s Valhall production complex, which includes the construction of a new production and living-quarters platform, will enable the facility to maintain output right through to the middle of the 21st century.
An important feature of the upgrade project is the replacement of existing offshore gas turbines, currently providing power for the five-bridge linked complex, with power from the shore (PFS) electricity delivered directly from the Norwegian mainland 300km away.
Oil is supplied from the platform in the Ekofisk field to Teesside in the UK, while gas is delivered into Norpipe through which it is transported to Germany.
Since the facility was installed in 1981-82, reserves have grown from 247 million barrels to 1,050 million barrels. It is estimated that 529 million barrels remain to be produced, although the company hopes that it may be able to extract considerably more than this. Output is running at 150,000 barrels of oil per day, 200,000 barrels of other liquids per day and 5 million m3 of gas per day.
The installation has been experiencing reservoir compaction, seabed subsidence, which has increased water depth by about 5.4 metres over the years. This was a factor in deciding to replace the original production and compression platform with a new production-hotel facility designed to meet the site needs until 2050.
COST AND ENVIRONMENTAL SAVINGS
Power supply is critical to the performance of the Valhall facility, and with such a long life ahead of it, it is essential to meet strict economic and environmental criteria.
At present power is generated on the field by gas turbines. These will be replaced by a 292km powerlink direct from the shore – an unprecedented distance for an offshore installation.
ABB’s HVDC Light technology will be used to transmit the power from the mainland. This involves taking AC power at 300kV from the Norwegian grid, converting it to high voltage direct current (HVDC), and transmitting it at 150kV through a subsea power cable to the platform, and converting back to AC at 11kV for use on the field. The total power requirement is 78MW-.
This solution is not only costeffective but it also offers clear environmental benefits - at peak it will eliminate an annual 300,000 tonnes of CO2 and 250 tonnes of nitrogen oxide, compared with a combined-cycle power plant operating with low NOx gas turbines.
Grid power in Norway is for the most part clean power generated by hydroelectric plants.
Reducing CO2 output will also cut costs. This is because such emissions from offshore installations are taxed in Norway. Another benefit is that ABB’s HVDC Light system offers very high availability of 98.5–99 per cent – and requires much lower maintenance than on-platform gas turbines.
An onshore converter station is to be built at Lista near Norway’s southern tip, and on the platform, conversion of the HVDC power will take place in a dedicated module designed to protect equipment from the effects of salty, humid air.