Methane hydrate is a solid substance in which methane (natural gas) is trapped in the crystal structure of ice. Methane hydrate occurs in marine sediments and crops out on the ocean floor where the pressure is sufficiently high and the temperature is sufficiently low. Technically, methane hydrate is called a clathrate which means that water molecules freeze into a lattice-like structure capable of trapping gas inside. These compounds can also occur in permafrost. The methane is produced from microbial decomposition of plankton which sinks to the ocean floor. See a short explanation from the U.S. Geological Survey (USGS) here. See also an article at Geology.com here. The map below shows the estimated global distribution of methane hydrates.
Estimates of the total resource vary widely. Gas units are often given in units of one trillion cubic feet (TCF). The USGS says that resources estimates from studies over the last 15 years vary from one million- to fifty million TCF of natural gas. The lower estimate is more than 4,000 times the annual US consumption of natural gas. The lower estimate is also at least twice as much as all other fossil fuels combined.
The big question now is: can these resources be technically and economically recovered?
Last year, the Department of Energy partnering with ConocoPhillips and Japan Oil, Gas and Metals National Corp. produced a steady flow of natural gas in the first field test of the new method that injects carbon dioxide into Alaskan permafrost. The carbon dioxide replaces the methane in the clathrate structure.
Last month, Japan became the first country to extract natural gas from methane hydrates in the sea bed. (See story in The Asahi Shimbun here.) According to that story, Japan Oil, Gas and Metals National Corp. was able to extract natural gas from a layer 330 meters below a 1,000-meter-deep floor of the Pacific Ocean. Water was pumped out of the methane hydrate sediment layer causing a drop in pressure which liberated the gas. Methane was collected by pipes. The Japanese government plans to establish production technology by fiscal 2018 and then begin production. “The seas around Japan are estimated to hold enough methane hydrate to produce as much natural gas as Japan consumes in 100 years.”
This is still emerging technology that could hold great promise, similar to the vast new resources made recoverable by the “fracking” revolution in shale oil and gas.
Methane hydrates probably played a part in the Paleocene-Eocene Thermal Maximum (PETM) which was a global temperature spike that happened about 55 million years ago.