NOK 2.5 billion to subsea compression
The partners in the Ormen Lange field in the Norwegian Sea are to spend NOK 2.5 billion on developing a subsea compression station. With a compression station at a sea depth of 860 meters, the developers will be able to halve the costs of development and operation compared to the costs of a platform solution.
In a full-size pilot program, a subsea compressor will be tested in a pool at Ormen Lange’s processing facility at Nyhamna.
The work to qualify the technology has been taking place since 2003. The detailed planning will continue for the next two years, before the actual test phase at Nyhamna commences in 2009.
By the end of 2011, the pilot program should have qualified the technology – which can be extremely important for future oil and gas developments.
A great step forward
“The partners have concluded that the technology is sufficiently mature for us to carry out a full-scale test. It is rare that a development project has this much funding available for qualifying new technology. But then again, this is a solution which will mean a great step forward for the oil industry,” says Tom Røtjer, Hydro's project director for the Ormen Lange project.
According to the main plan for the Ormen Lange field, a compression platform will be installed once the natural pressure in the reservoir is no longer sufficient to transport the gas to land.
“If we succeed with this project, we will be able to replace a 25,000-tonne platform with a subsea installation weighing around 3,500 tonnes. The development costs for future offshore compression for the Ormen Lange field will potentially be reduced by 50 per cent, which means a saving of many billion NOK. In addition, we will be able to halve operating costs over a 20-year period,” Røtjer says.
Testing at Nyhamna
The outlined subsea compression station includes four compressor trains. During the testing at Nyhamna, one compression train module will be placed in a water-filled reservoir that was blasted out during development of the site for the land-based gas processing facility.
“The pool is an important part of the testing facility to be built at Nyhamna, with the aim of qualifying subsea compression. The testing facility must simulate operating conditions out on the Ormen Lange field. In addition, it will be used to verify procedures for installation and removal of the subsea compression modules,” Røtjer explains.
The reservoir is 30 metres long, 20 metres wide, and 12 metres deep. The compression train to be tested in this pool has a gas capacity equivalent to 25 per cent of the actual land-based processing facility at Nyhamna.
It is envisaged that this compression train will later be used out on the field.
“The testing facility will also be used for future completion and verification of all modules prior to installation out on the Ormen Lange field,” Røtjer says.
Installation in 2015?
According to the plan, a decision regarding whether a platform or subsea station will be built for compressing the gas will be taken in 2011.
Installation on the field is planned for around 2015, but the need for compression will depend on the properties of the gas reservoir.
If a subsea solution is chosen, the subsea compression station will be placed between the two templates that are installed on the sea floor 120 kilometres west of Kristiansund.
The compression station will cover an area of the sea floor measuring 60 metres in length by 40 metres in width. Each of the compression modules to be installed in this station will weigh around 200 tonnes.
With a capacity of 52 megawatts, the compression station’s electricity needs will be equivalent to the consumption of 20,000 households.
The subsea compression station will be supplied with power through a submarine cable, to be laid from Nyhamna.
|Licence holders on the Ormen Lange field:
In the summer of 2006, Aker Kværner Subsea AS was chosen as EPC contractor (engineering, procurement and construction) for the pilot station with a subsea compression system.
Vetco Aibel AS was chosen as EPC contractor for the long step-out power supply for the pilot compression station.
The technology that is being qualified by the Ormen Lange partners will potentially be of great significance for future gas and condensate field developments, both on the Norwegian continental shelf and elsewhere.
“By using a subsea compression facility in order to increase pressure in the well stream, it will be easier to transport gas and condensate over long distances to a land-based processing facility, or to existing platforms. This is also an efficient way of increasing recovery rates from existing subsea fields.”
“A big advantage of using a subsea compression station is that the development can be divided into two phases – first, an early phase where compression is not required for pressure support during transportation, and then a later phase when the pressure in the reservoir drops, and a compression station can be installed to increase the pressure and thereby maintain the production rate from the subsea wells,” Røtjer explains.