Shares in Empyrean Energy rose after the explorer said it received a major upgrade to its Sugarloaf project in Texas.The AIM-listed stock rose 3.41% to 3.41p by 12:25 on Wednesday after it said proved and probable reserves were up by 94%.The Sugarloaf project is operated by Marathon Oil company which Empyrean had a 3% interest in.Sugarloaf had 231 wells in production, with 54 of those drilled and undergoing completion.Empyrean attributed the rise to a successful appraisal of the Austin Chalk well and a shift from contingent resource status into a reserve status.Chief executive Tom Kelly said the project continues to grow and represented a viable and attractive investment proposition even at current lower oil prices.