Drilling has started on the Dunquin well of the west coast of Ireland by a group of exploration companies.
The drilling operations are expected to take several months to complete.
ExxonMobil, which holds a 27.5% interest in the well, is the main operator.
Irish company Providence holds a 16% interest, while other co-venturers are Eni, with a 27.5% stake, Repsol, with a 25% stake and Sosina, with a 4% stake.
The well is 150 km offshore and around 1,600 deep. The Eirik Raude semi-submersible drilling unit is being used for the work.
''This is a landmark well given that it is the first to be drilled in the central part of the deep-water southern Porcupine Basin and is designed to test a new and potentially material Lower Cretaceous carbonate exploration play concept,'' commented the company's chief executive Tony O'Reilly.
''The well is the second of six wells being drilled as part of Providence's Irish concerted multi-basin, multi-well drilling programme which kicked off in November 2011 with the Barryroe appraisal well,'' he added.