The first of eight topside modules for the Mariner field was installed on the weekend.
The Saipem 7000 vessel hoisted the 10,000-tonne utility module onto the steel jacket on Saturday.
The processing module is next in line for lifting.
Once completed, the Mariner A platform will weigh more than 38,000 tonnes.
Uno Holm Rognli, Mariner project director for Statoil, said: “We are well under way with piecing together the giant puzzle that will become the Mariner platform.
“The installation supports 1,500 jobs from now until start up in the second half of 2018.”
Mariner, about 95miles east of Shetland, is currently expected to yield 250million barrels over its 30-year production life, and create 700 long-term jobs.
The company plans to drill an appraisal well and an exploration well in the coming weeks to determine whether they can raise their estimate.
