Only a fraction of the natural gas export projects being developed around the globe will become reality as high costs and weakening gas prices torpedo those that until recently promised huge returns on investment. Large natural gas field discoveries on and offshore have prompted several countries to plan liquefied natural gas (LNG) export projects, including in North America, Australia, East Africa and the east Mediterranean. But high development costs and low profit margins in the gas sector mean most of the projects will fail, Royal Dutch Shell's director of projects and technology told Reuters in an interview. "There is always so much talk about these big LNG projects around the world…