Hydro has started water injection on the Visund field. Hydro now operates four platforms - Oseberg Sør, Oseberg Øst, Snorre B og Visund - with full reinjection of produced water, waste water and cuttings
"Produced water is reinjected in a well and used as pressure in the reservoir. On the other wells on Visund, gas will continue to be used to force out oil and gas deposits," says Arnleiv Dale, leader of the Visund unit.
Stone, gravel and sludge containing oil residues - as well as waste water - will be returned to beneath the seabed. Use of chemicals is reduced, and emissions of carbon dioxide and nitrous oxide are much lower than usual.
Less water than expected
Since Visund was first put into operation, the wells have produced less water than originally expected. Therefore, there has been too little water to process for the installed pump capacity on the platform. Processed water has been emitted to the sea, but measurements show that the content of oil residues is far below the limits of 40 parts per million set by Norwegian authorities.
"We have produced so litte water on Visund that it has not been possible to reinject it. Emissions have therefore also been very limited and well within Hydro's own standards as well as external standards," says Dale.
Other wells, including two recently put into production on Visund North, now produce enough water that the pumps are well supplied.
Gas as pressure
The Visund project has carried out a research program in cooperation with Hydro's research center in Bergen on the use of gas as pressure instead of water.
"This gave good results, and we decided to use gas instead of water, in that the water volume was low. We also considered using water from a reservoir in the Utsire formation, but that was not realized because of technical and geological reasons," says Dale.
'Green' platform
Hydro wanted Visund to be a "green" platform. When water reinjection becomes a reality, emissions of process water will be reduced to a minimum. The project is a milestone for the field, which is 27 kilometers northeast of Gullfaks.
Visund was developed with a floating drilling, processing and accommodation platform. The field produces on average 48,000 barrels per day. Development of gas resources has started and exports of gas are to begin around 2005. Subsea development on Visund North began production in February 2002.