In an update, the exploration firm said the Ensco 72 drilling unit had been mobilised to the Wick prospect drilling location.
Once drilling at Wick is completed, the rig will then be mobilised to the Colter location, with the appraisal well scheduled to be drilled in the first quarter of 2019.
Colter will appraise a historic discovery that lies immediately to the south of Europe's largest onshore oil field at Wytch Farm. The discovery was made in 1986 by well 98/11-3, which encountered a 10.5-metre oil column in the Sherwood Sandstone reservoir, the same play that has proven to be productive at Wytch Farm where over 450mln barrels (mmbbl) have been produced to date.
UOG said the new well would be drilled updip of 98/11-3 targeting significant potential that has been identified following reprocessing of 3D seismic data.
The gross unrisked mid-case oil contingent resources in the section proven up by the 98/11-3 well have been estimated at 4mln barrels, with gross unrisked mean-case prospective resources estimated at 15mln barrels in the rest of the structure.
Brian Larkin, chief executive of United, said: “As well as appraising a historic discovery at Colter, which we believe could hold in aggregate up to 19mmbbls of gross contingent and prospective resources, shareholders can look forward to further high impact activity across our portfolio of late stage European development projects and frontier exploration offshore Jamaica.”
“This includes advancing the Podere Maiar gas discovery on the Podere Gallina licence onshore Italy towards the first production; results from the ongoing processing and interpretation work of the recently acquired 3D seismic over the Colibri target on the Tullow Oil operated Walton-Morant licence, offshore Jamaica; and further progress in de-risking the Crown discovery in the North Sea."
Colter, in which United holds a 10% stake, is located in the Wessex basin, a geological area along the Southern coast on England that stretches into the English Channel and is rich in hydrocarbons.
In late-morning trading Wednesday, UOG shares were steady around 3.9p.