Shares in Rose Petroleum tanked on Tuesday, after the oil explorer said it had chosen the Cisco Dome region for the first of its six new horizontal wells on the Mancos Shale in Utah.The group said it can no longer use the 1-34 vertical well for the horizontal leg of the project as it would be required to secure permit for a whole new location, stepping away from the current location only to drill back towards it.The London-listed company said the decision was made following analysis of previous core results, which were in line with the group's expectations, adding it expected the first of the new well to be nearing completion by the end of 2015."We plan to target the new location with better well control and excellent surface infrastructure with the gathering system and processing plant nearby," Matthew Idiens, the group's chief executive, said.Rose Petroleum shares were down 24.85% to 0.883p at 11:29 on Tuesday.