* Nigerian oil minister Emmanuel Ibe Kachikwu said he was "not ruffled" by the recent oil price decline and OPEC member nations needed to focus on their production costs * "OPEC needs to just focus on itself and focus on what it needs to do and forget what is happening in shale ... Every OPEC producer must work hard to be a least-cost producer," he said * Oil prices were trading at $64.40 per barrel on Thursday, just over 9 percent below the highs this year above $71 per barrel reached in January * Nigeria, Africa's largest oil exporter, produces 2.07 million barrels per day (bpd), including 1.71 million bpd of crude and 362,000 bpd of condensates, a ministry spokesman said. -Reuters