Occurrence of global natural hydrogen and profitable preservation

Occurrence and abundance of molecular hydrogen in natural geologic reservoirs are enigmatic, due to its various sources, diverse migration pathways and complicated biological and chemical reactions. Natural gas samples containing hydrogen from producing wells in several sedimentary basins in China were collected in this study, and gas abundances and isotopic compositions of these gases were compared with those in global petroliferous basins and deep intrusive rocks. Several geochemical indicators were suggested for identifying sources, migration and accumulation mechanisms of hydrogen in the subsurface environment. Hydrogen contents in natural gas deposits have contributions from various sources with the following high-to-low order: microbial degradation > serpentinization > deep mantle volatile release > radiation-induced water decomposition > thermal cracking of organic matter. A hydrogen-rich reservoir in Kansas, USA, is specifically analyzed to determine its formation mechanism. This study suggests that future exploration of geological hydrogen resources may focus on the igneous rock bodies with overlying dense sedimentary rocks in the continental rift systems.