Texas oil producers and refiners remained shut for a fifth day on Wednesday after several days of blistering cold, and the governor ordered a ban on natural gas exports from the state to try to speed the restoration of power. The cold snap, which has killed at least 21 people and knocked out power to more than 4 million people in Texas, is not expected to let up until this weekend. Governor Greg Abbott directed Texas natural gas providers not to ship outside the state until Sunday and asked the state energy regulator to enforce his export ban.