In many places throughout the world there is a remarkable new source of energy—methane gas (CH4), a major component of natural gas, concentrated in the form of hydrates—whose extent, characteristics, and economic feasibility are now being explored.
Methane hydrates look somewhat like large ice crystals. On the seafloor they appear to be frozen solidly in place as the gas is bound into a water-methane structure by a function of pressure (water depth) and temperature. Generally, water depths would be greater than 1,500 feet and, depending on pressure, the temperature between 32- and 68-degrees Fahrenheit. As one or both of these formative conditions is reduced, methane is released as a gas, increasing in volume 160 times. The source of the gas is decay of organic matter deep beneath the seafloor.
Harvesting this resource could provide enormous amounts of energy to supplement current global production of crude oil and natural gas. Some experts believe that global quantities of methane may be greater than the total of all other fossil fuel resources worldwide. Research programs in the United States, Canada, Japan, India, and South Korea are actively searching for and assessing new hydrate zones.
The creation and occurrence of hydrates has been known for a long time, however, it was not until the past two decades that they have been discovered throughout the world. One of the best-studied zones is off the coast of South Carolina. The amount of methane available there indicates that an optimum harvest could supply the entire nation with all its natural gas needs for a century.
As with almost all good news, there is a downside. Methane is 25 times more potent as a greenhouse gas than carbon dioxide. Any that escapes as a result of mining operations can adversely affect the atmosphere. On land this is already a problem as the Arctic warms. There, thawing permafrost is releasing methane stored from the decomposition of organic materials into the atmosphere. Unfortunately, it is unlikely that an efficient means can be developed to capture this gas.
It is therefore a matter of considerable concern how to safely harvest the far more dense concentrations of methane found on the seafloor. Relieving either pressure or temperature of the hydrate crystals will produce the gas. Heating the hydrates in place requires considerable energy so this may not be feasible. Alternatively, if the pressure can be successfully reduced, how are the hydrate gases safely captured from more than 1,500 feet down in the sea
Another problem with methane hydrates is that in certain places on the seafloor their unintentional "thawing" can result in underwater landslides, perhaps creating a tsunami. This would happen where thick zones of hydrates lie beneath sediments on slopes. When the crystals "melt," they provide a lubricating action that permits the overlying sediment layers to slough off and slide downhill. If the melting is rapid and the area is large enough, then the seafloor slippage can be catastrophic. While deliberate hydrate mining would not be done in such areas, it will be a concern for those who exploit these resources.
It is unlikely that most methane hydrate structures on the seafloor will be released naturally. The global sea level is rising, thus increasing pressure at depth and ocean warming will not significantly affect the depths at which the hydrates are found. Interestingly, legends of massive methane burps or eruptions abound to account for mysterious disappearances of ships including some of those in the so-called Bermuda Triangle. In most cases it is very difficult to see how nature could create the conditions for this to occur. One possible exception could be offshore drilling that might warm underlying hydrate zones on seafloor slopes.
It may take years of investment in research and development before commercial methane hydrate harvesting can be done. The current global energy crisis, however, and the steady and largely irreversible increase in crude oil prices provide strong incentives to produce methane from the seafloor. The Japanese government estimates that methane will compete with oil priced above $54 a barrel once a viable hydrate harvesting process is found.
If burping the ocean to get gas can be done at the right price and with minimal environmental impact, then there will be a new source of energy for the world. Granted, just like petroleum, methane from the sea is not a renewable resource, but it could be a major part of an overall national energy strategy to help power up our nation. And there is an awful lot of it under our coastal waters.