Home / Our Science / Energy & Resources / Gas Hydrates / What are Gas Hydrates?

What are Gas Hydrates?

What are gas hydrates and why are they important?

What are Gas Hydrates?

hydrate

Gas hydrate is a solid ice-like form of water that contains gas molecules in its molecular cavities1. In nature, this gas is mostly methane. Methane gas hydrate is stable at the seafloor at water depths beneath about 500 m. The gas hydrate stability zone extends into the seafloor sediments down to a depth where temperature exceeds gas hydrate stability, usually some 10s to 100s of meters beneath the seafloor. At this depth, thin methane gas layers are often present causing strong reflections in seismic records. The reflections approximately follow a line of constant temperature. Temperature in the subsurface is a function of heat flow and depth, so the reflections usually mimic the shape of the seafloor. Hence, they are named bottom simulating reflections (BSRs).

Why are gas hydrates important?

Large quantities of gas hydrates exist on the world's continental margins. Methane from gas hydrates may constitute a future source of natural gas. This energy potential is probably the main motivation for many national gas hydrate programmes overseas, e.g., in Japan and the U.S.

Gas hydrates are also important for seafloor stability studies, because "melting" gas hydrate may cause seafloor "land" slides. Methane is a potent greenhouse gas. Methane released from gas hydrate may therefore play a significant role in climate change3.

It is important to distinguish between the climate change aspects of methane released naturally from gas hydrates and those of methane produced from gas hydrates for energy use. By burning methane or using it in fuel cells, the methane is converted to CO2. - just like burning coal or oil. Combustion of methane, however is more CO2 efficient than that of any other hydrocarbon, e.g., twice as efficient as burning coal. Hence, using methane from gas hydrate as an energy resource would be, compared to other hydrocarbons, relatively climate friendly.

Why New Zealand?

New Zealand's main conventional gas fields are being depleted. Gas production from gas hydrate may, in the long term, be a viable alternative. New Zealand's gas hydrate deposits are particularly interesting because they occur in geologic formations that favour "sweet spots" - areas of high gas hydrate concentration. The proximity of the North Island's East Coast gas hydrate province to major population centres would also greatly facilitate the installation of offshore gas pipelines and other infrastructure.

References

  1. Sloan, E.D. (1990), Clathrate hydrates of natural gases , 641 pp., Marcel Bekker, New York .
  2. Kvenvolden, K.A. (1988), Methane hydrate - a major reservoir of carbon in the shallow geosphere?, Chem. Geol. , 71 , 41-51.
  3. Kvenvolden, K.A. (1993), Gas hydrates - geologic perspective and global change, Rev. Geophys. , 31 , 173-187.