Corallian Energy and partners will focus on the Colter South discovery off Bournemouth after their main target to the north disappointed.
UK firm Corallian, operator with a 49% stake, booked Ensco-72 jack-up rig to drill the main Colter prospect in the Wessex Basin earlier this year.
Last month, partners said the well “unexpectedly” kept to the southern side of the Colter prospect’s boundary.
Despite missing its primary target, the company kept drilling and struck oil and gas, making a “separate discovery to the original appraisal target”.
Colter South could yield 15 million barrels of oil, though more analysis is needed to firm up the estimate.
A sidetrack well targeting the main Colter prospect on the northern side of the boundary has now been drilled.
But preliminary results show that the Colter prospect is smaller than expected and would not be worth developing.
Partners had hoped to find 23m barrels in Colter, but feel the 15m barrel Colter South discovery “remains an opportunity”.
Sachin Oza, co-chief executive of Reabold Resources, which owns 32.9% of operator Corallian, said: “We were delighted to make an oil discovery with the Colter well, and with the sidetrack effectively giving us two wells worth of data, the operator is now in a position to undertake the necessary work to determine the optimum forward plan.
“This offsets the disappointment around the lack of commerciality within the northern Colter fault terrace.”
Brian Larkin, chief executive of United Oil and Gas, which has a 10% interest in Colter, said: “The Colter appraisal campaign has delivered a new discovery and significantly increased our understanding of the Colter prospect.
“While we are obviously delighted by the discovery of Colter South, which with an estimated mean recoverable volume of 15 mmbbls is an exciting discovery and appears to have exceeded our pre-drill requirements for commerciality, Colter North has not delivered in the way that we would have hoped.
“However, even this latest result has delivered some interesting additional data which points to further targets and prospectivity within the licence area.”
Corallian suffered a blow in January when its Wick exploration well in the Moray Firth was revealed to be a failure.
It was thought to hold 26m barrels.