OSLO, Feb 11 (Reuters) - A potential strike at Norway’s Mongstad refinery next week could affect the export of crude oil from the offshore Johan Sverdrup and Troll fields, the Safe labour union said on Thursday. Wage talks are due between the union and employers on Monday, and a dozen Mongstad workers will go on strike the following day if the negotiations break down, Safe said last month. (Reporting by Terje Solsvik, Gwladys Fouche)