In May of this year, China claimed a breakthrough in tapping an obscure fossil fuel resource: Researchers there managed to suck a steady flow of methane gas out of frozen mud on the seafloor. That same month, Japan did the same. And in the United States, researchers pulled a core of muddy, methane-soaked ice from the bottom of the Gulf of Mexico.The idea of exploiting this quirky fuel source would have been considered madness a couple of decades ago — both wildly expensive and dangerous. Until recently, methane-soaked ice was considered explosively unstable. In the Gulf of Mexico, traditional oil rigs have been tiptoeing around these icy deposits for years, trying to avoid them.