Clean water from Vigdis
Trials with a new treatment technology on Statoil’s Vigdis field in the North Sea have demonstrated its ability to remove up to 90 per cent of the oil contained in produced water.
The Vigdis licensees have now resolved to adopt this Epcon solution permanently. And the Heidrun field operated by Statoil in the Norwegian Sea also installed a test facility recently.
“Figures for the oil content in produced water from Vigdis have been high ever since it came on stream in 1997,” says process engineer Olav Dolonen in the Snorre operations unit.
“The Epcon method has yielded far better results than any other treatment system we’ve tried.
“It’s got the proportion of residual oil in the treated water down to 10-15 parts per million (ppm)– well below the official ceiling of 40 ppm.”
In addition to being efficient, the plant is inexpensive to install and robust in operation. Mr Dolonen accordingly believes it could be relevant for other fields.
Tied back to Statoil’s Snorre A platform, the subsea facilities on Vigdis currently produce some 70,000 barrels of oil per day and roughly 50,000 barrels of water.
Developed by Norway’s Epcon Offshore company, the new treatment solution is based on a combination of cyclone and flotation technology.
Flocculants are added along with nitrogen as a flotation gas before the water enters the plant.
The gas drives the oil droplets to the top of its tank before the clean water is drained off from the bottom. Separated oil goes to a degasification tank before returning to the process.
Approval for the Vigdis trial was given by the licensees before Statoil took over as operator from Norsk Hydro on 1 January 2003.