Gas hydrates (or methane hydrates) have a structure consisting of a guest gas (methane in most cases) molecule inside a “basket” made of water molecules, and are known to exist in permafrost areas and within the deep seafloor ground due to temperature and pressure. Natural gas hydrates include sand-layer type natural gas hydrates present in the gaps of sand several hundred meters below the seafloor, and surface-layer type (shallow) natural gas hydrates present as clumps in the seafloor surface layers, or as nodules (granular), lenses, plates, or veins in the mud on the seafloor. In any case, the methane gas generated after decomposition is the main component of natural gas, and use is expected as a next-generation energy source for achieving a low-carbon society.

The researchers measured the strength and stiffness (rigidity) of massive natural gas hydrates (ice-like solid substances consisting of water molecules and natural gas molecules) excavated off the Joetsu coast of the Sea of Japan for the first time.

Natural gas hydrates are stable under low temperature and high pressure, but decompose into natural gas and water under normal temperature and atmospheric pressure. This has made it extremely difficult to measure the strength and rigidity of natural gas hydrates. The researchers are developing a device to evaluate the physical properties of natural gas hydrates collected while maintaining the deep seafloor water pressure. In the present research, the researchers and Meiji University collaborated to conduct experiments to measure the strength and rigidity of collected natural gas hydrates from the deep seafloor surface layers. The hardness and mechanical stability of massive natural gas hydrates in the mud on the deep seafloor had not previously been clarified. The strength and rigidity of natural gas hydrates are key physical properties for examining specific mining or drilling techniques (crushing, breaking, collecting, etc.) of shallow natural gas hydrates and assessing the mechanical stability of the seafloor ground during natural gas hydrate recovery. The results of this research are expected to play an important role in deep seafloor resource development and environmental assessment.