A gas hydrate is a crystalline solid which consists of a gas molecule surrounded by a cage of water molecules.
From physical appearance point of view, it could be considered similar to ice. This substance releases gaseous methane when it melts. The following figure shows burning of methane releasing from a piece of gas hydrate:
Gas hydrates can be found in large amounts in the permafrost (frozen region) at the bottom of the sea floor in porous rocks or in sand in the adjacency of water.
Gas hydrate needs special conditions to be stable. Generally it can be stable at low temperature and high pressure. A typical pressure and temperature can be 50 bar and 10 C .
The worldwide amounts of carbon bound in gas hydrates is estimated to be twice the amount of carbon to be found in all known fossil fuels on Earth . This shows the importance of development of this unconventional source of natural gas.
Especially gas hydrates are potentially huge resource of natural gas for the United States. The U.S. Geological Survey (USGS) estimated that there are about 85 trillion cubic feet (TCF) of technically recoverable gas hydrates in northern Alaska. The Minerals Management Service estimated a mean value of 21,000 TCF of in-place gas hydrates in the Gulf of Mexico . We can compare these values to 1,300 TCF of technically recoverable U.S. conventional natural gas reserves .
Although hydrates are such a great energy resource potential, there are two unfavorable major concerns about them in sea-floor sediments:
1) While a conventional oil and gas drilling is under going in offshore, due to the pressure changes, if the solid gas hydrate dissociates suddenly and releases its trapped methane, it could disrupt the marine sediments and compromise pipelines and production equipment on the seafloor. Hence gas hydrates can be a significant hazard for drilling and production operations.
2) Methane is a powerful greenhouse gas. It may cause 15 to 20 times more warming than carbon dioxide . However methane does not remain in the atmosphere for a long time. Within around 10 years methane is transferred to CO2 which is the main greenhouse gas.
There is a direct relationship between climate change and stability of gas hydrates. A warming climate could result in dissociation of gas hydrates and releasing methane to the atmosphere. Released methane will increase global warming and this cycle results in more dissociation of gas hydrates.
Although gas hydrates contain huge amounts of natural gas, unfortunately they have had no confirmed commercial production yet. Producing natural gas from gas hydrates will require that we find economical ways for safely extracting the methane, while minimizing environmental impacts. Even though some progress has been made in this area, there are much more to be understood.
Some of the challenges in production from gas hydrate resources are: maintaining commercial gas flow rates with high water production rates, operating at low temperature and low pressures in the wellbore, controlling formation sand production into the wellbore and ensuring the structural integrity of the well and potential environmental impacts and safety concerns. Consequently significant scientific work must be completed before gas hydrate can be considered a producible natural gas resource .
Even though Methane production from gas hydrates seems to be complicated, if new technologies can be applied economically to the development of gas hydrate as a source of natural gas, the U.S. could significantly decrease its dependence on foreign energy supplies. Hence, developing gas hydrates into a commercially viable source of energy is a goal of the U.S. Department of Energy (DOE). There is a special research group in Department of Energy which is studying gas hydrates carefully. The National Methane Hydrates R&D Program is housed at the National Energy Technology Laboratory (NETL) of the Department of Energy. The main goal of the DOE methane hydrate research and development (R&D) program is to develop knowledge and technology to allow commercial production of methane from gas hydrates by 2015 . Three major field research projects are currently under the study in the U.S., one offshore project in the Gulf of Mexico and two onshore projects in northern Alaska .
Over the long term, the development of new natural gas resources such as Gas Hydrates can play a major role in ensuring enough future supplies of natural gas and moderating energy prices for American consumers.
Last, for those who are interested, this video gives a short interesting introduction to gas hydrates: