FRANKFURT, Germany—Europe’s natural gas crisis isn’t letting up. Reserves are low. Prices are high. Utility customers are facing expensive bills. Major Russian supplier Gazprom isn’t selling gas like it used to. It all raises the question: How exactly is Europe, which imports most of its energy, going to make it through the winter without a gas disaster, especially if the season turns out to be colder or longer than usual? Here’s how the European Union, home to 447 million people, will try to deal with the crisis: The Problem Is Low Storage Levels Utilities turn to gas stored in underground caverns to handle sudden additional demand for gas for heating or electricity. Europe started 2021 with gas storage only 56 percent full, compared with 73 percent a year earlier. The reasons vary: cold weather last winter, lack of Russian deliveries on the spot market and robust demand in Asia for …