The worlds largest jack-up oil rig visited the Cromarty Firth in September 2016 and was discharged for taking on supplies before being sent to work in the Mariner Field.
First oil is expected to be produced from Mariner in 2018.
The pre-drilling campaign is expected to support about 500 jobs in the UK Continental Shelf (UKCS).
Mariner, which lies about 93 miles (150km) east of Shetland, is one of the largest projects currently under development in the UKCS.
The heavy oil field has reserves estimated at more than 250 million barrels of oil, with an average plateau production of about 55,000 barrels per day.