The work, valued at about $71 million, was an option under the original $982-million contract that ConocoPhillips awarded to Kvaerner group in March 2011 for engineering, procurement, and construction of the topsides.
The topsides comprise a combined living quarter and utility module and a combined process and wellhead module, with a total weight of 15,500 tons.
In addition, Kvaerner is building two bridges, one bridge support module, and a flare.
Offshore hook-up of the bridges is expected to take place later this year, followed by the topside modules in 2014.
The Eldfisk field in the Greater Ekofisk Area has been in production since 1979.