ABB's Subsis (subsea separation and injection system) project should reach the prototype test stage by late 1998.ABB has reached the halfway stage in a three-year project known as Subsis - subsea separation and injection system - which is scheduled to end in a prototype test in the third quarter of 1998.
It has a full-time dedicated project team of nearly 30 people led by Stig Gustafson, ABB's project manager for subsea processing.
Several dozens of millions of kroner are being invested in the current project. A large part of the funding and resources is being provided by ABB through its own corporate research system. The company brings to the project its experience in subsea production and its power expertise.
Expertise on the injection side is being supplied by Framo Engineering, under a frame agreement between the two companies whereby they will jointly promote the new technology worldwide.
The project is divided into three stages. The first, covering concept definition and finalization of a business plan, was completed last autumn. The second , involving R&D work and detailed design, was due to be finished at the end of March. Then follows the construction of a prototype, which is due to be tested by early in the third quarter 1998.
A number of key challenges are involved, Gustafson says, including the development of a separation system, a subsea power distribution system, and an oil-in-water monitoring system.
Processing will take the form of three-way separation of the oil, water and gas in the wellstream, after which the water will be disposed of and the oil and gas recombined for export. Where necessary, the processing facilities will also be able to separate out and dispose of sand in the wellstream.
As with most of the other elements in the project, the topside technology for supplying power already exists - the challenge is to marinize it.
The question of subsea power supply is being addressed in a separate industry-sponsored project known as Sepdis - subsea electrical power distribution system. The sponsors are Norske Shell, Norsk Hydro, Saga, Statoil, and the Norwegian Research Council.
ABB was selected last year to carry out a feasibility study, which it completed in February. In April the sponsors will decide whether to give the go-ahead for ABB/Framo to move onto the full-scale development of a prototype.
This will include the development of a 36 kv connector, for which detailed design is due to be finished in September. By November the physical hardware for a high-voltage cable penetrator should be available.
The requirements of such a system include frequency converters, transformers, switch gear, high-voltage penetrators, and high-voltage subsea mateable connectors.
The development of an oil-in-water monitor is essential to the option of disposing of the produced water into the sea. In cases where re-injection is not required for reservoir pressure maintenance, this option avoids the cost of drilling an injection well.
By mid year work on the conceptual development of a subsea oil-in-water monitor is due to be completed. No such instrument, capable of working in real-time, exists today, says Gustafson, but there is plenty of upside potential for one, and potential clients have expressed interest in both options.
The development of reliable electronic control facilities and instrumentation is also a key element. One of the most important functions will be to monitor the oil/water level in the separator in order to maintain the separation process at an optimal level.
Fibre-optic cables between the subsea units and the platform from which control is exercised will be used to ensure high-speed, broad-band communications immune to electrical noise. Voltage and hydraulic controls for the integrated power plants will be run through the same cable.
"We're now in a position to have a system view of a complete subsea separation station," Gustafson says. "It could be separate structures, or it could be one. The separator could be either vertical or horizontal, depending on the application - this will set the parameters for the choice of separator."
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