North Sea oil and gas firm EnCore Oil spudded its central Tudor Rose well on Wednesday afternoon.
EnCore, operator and 40% owner on the field, said well 14/30a-5 was being drilled by the Transocean Sedco 704 semi-submersible rig.
Tudor Rose, an oil accumulation, was discovered in 1983. The discovery well found an 80 feet oil column within Tertiary age Beauly Sands.
Endeavour Energy, a 20% equity holder in the licence, said latest analysis on the field indicated that the accumulation could have more than 500million barrels of oil in-place.
The well is expected to take 20 to 30 days to complete, subject to weather conditions and operational requirements, under the management of ADTI.
The other equity holders in the field are EnQuest 20% and Nautical Petroleum 20%.