SYDNEY — Burma, once the richest countries in Southeast Asia, today is mired in deep poverty — its economy ruined by nearly 50 years of economic mismanagement under military rule. And yet, over the last few years Burma has also emerged as a significant producer of energy in Southeast Asia. Thanks to large fields of recoverable natural gas located offshore, Burma now earns substantial foreign exchange revenues. At present, most of these revenues ($1 billion to 1.5 billion per year, depending on price fluctuations) come from Thailand. Gas from Burma, piped onshore from the Gulf of Martaban, generates around 20 percent of Bangkok's electricity supply.