The British oil and gas explorer, which holds a 16.6% interest in the discovery, said the 210/30a-4 appraisal will attempt to discover deeper oil in the structure.
The well is being drilled to the south-east of the original 2008 discovery and subsequent 2010 sidetrack wells, using semi-submersible rig Transocean prospect.
The project is expected to take about 40 days, subject to weather and operational requirements.
Sterling operates Cladhan with a 39.9% stake along with EnCore, Wintershall on 33.5% and Dyas UK holding the remaining 10% interest.
