Shares in Canadian oil & gas explorer Antrim Energy more than doubled after it said it had found a potentially large oilfield off the coast of the Irish Republic.The stock rose 4.6p or 142.3% to 7.9p at 14:46 in London after Antrim said a prospective resources report on its Frontier Exploration Licence 1/13 had estimated that it contained 1.1bn barrels of oil equivalent.FEL 1/13 includes about six blocks collectively known as the Skellig block, in which Antrim has a 25% working interest.Antrim acquired a licencing option over Skellig in 2011 and it farmed out a 75% interest in the option to Kosmos Energy and converted it into FEL 1-13 in 2013.PW