Europe’s biggest gas supplier, Norway, is starting the annual maintenance on gas fields, processing plants, and pipelines, which will see Norwegian gas flows slashed through the middle of September. Some planned works have already begun this week, including the processing plant at Nyhamna. Others begin this weekend, with most maintenance expected to be completed by September 18. The giant Troll gas field in the North Sea—Europe’s biggest gas-producing field, and the Kollsnes onshore processing plant, will start maintenance on…