After one year's operation, the Troll Pilot seabed separation system has been given top marks for increasing production capacity on Troll C and improving the environment.
On 25 August 2001, scarcely two years after the Hydro-operated oil platform Troll C came on stream, Troll Pilot was put into full operation. The system, which is installed on the seabed at a depth of 340 metres some 3.5 kilometres from the platform, uses the gravitation method to separate produced water from the oil and gas stream emanating from four of the 39 wells currently in operation on Troll C. The water is then reinjected into the reservoir, while the separated oil and gas are piped up onto the platform.
Produced water accompanies the oil and gas up from the reservoir. As the fields gradually become more mature, the volume of produced water increases. "The benefits of reducing the volume of water by means of seabed separation are twofold: increased oil production capacity and lower discharges," explains Terje Horn, responsible for seabed equipment on Troll. He describes Troll Pilot as a major success.
High regularity
"The operational regularity of Troll Pilot has been almost 100 percent this year while the environmental gain has been quite significant. Samples reveal that the injection water after separation contains only 15 ppm (parts per million) oil. By way of comparison, the State Pollution Control Authority has imposed a discharge limit of 40 ppm, while Hydro's internal target is 30 ppm. This water would normally have been released into the sea having undergone normal treatment on the platform," says Horn.
He adds that the Troll Pilot results confirm that the nearer to the reservoir separation takes place, the easier it is to separate oil and water.
The geological structure of Troll make the field especially suitable for seabed separation. Because of its thin oil layers, the field produces a lot of water early in the production phase.
Troll Pilot was developed by ABB Offshore Systems in conjunction with Hydro.
Next biggest oil producer
Troll is not only Norway's largest gas field, it is also the second largest oil field on the Norwegian shelf in terms of recoverable reserves. The two oil platforms - Troll B and Troll C - came on stream in 1995 and 1999, with Hydro as operator.
The seabed separation system Troll Pilot is not the first pioneer project on the Troll field. A historical breakthrough occurred in the mid-1990s, when Hydro proved it was possible to recover the thin layers of oil under the gas by means of advanced horizontal drilling and also, more recently, by drilling multilateral wells.