Nigeria has approved 28 companies to buy natural gas that is currently being flared at oil fields, a long-running problem the country has talked about fixing for years and is now trying—again—to turn into something usable. The permits were issued under the Nigerian Gas Flare Commercialization Program, the upstream regulator said this week. Forty-two companies applied to capture gas from 49 flare sites in the Niger Delta. Fourteen bidders did not meet the requirements and were not approved. The regulator estimates that between 250 million…