Natural gas hydrate reservoirs have been strongly suggested as a potential energy resource. However, this potential is expected to be limited by geological factors, reservoir properties, and phase-equilibria considerations. Accordingly, sufficient understanding and accurate analyses for the complex surroundings in a natural gas hydrate system have to occur before methane recovery. In this paper, we discuss the formation and structure patterns of global natural gas hydrate, including the origins of hydrocarbon, crystal structures, and unique structure transition. We also summarize two important anomalies related to methane occupancy and chlorinity which were revealed very recently. Furthermore, we review the geological and chemical surroundings of the shallow hydrate deposits, the so-called brine patch discovered in the Cascadia Margin and Ulleung Basin, which are significantly related to tectonic conduits for methane gas and positive chlorinity.