NATURAL GAS HYDRATE: FUTURE ENERGY RESOURCE?

Estimates of the amount of natural gas in gas hydrate deposits of the world range from about 3,100 to 7,650,000 trillion cubic meters. While the published gas hydrate resource estimates show considerable variation, current estimates of the amount of methane in the world’s gas hydrate accumulations are in rough accord at about 20,000 trillion cubic meters. If these estimates are valid, the amount of methane in gas hydrates is almost two orders of magnitude larger than the estimated total remaining recoverable conventional natural gas resources. The fact that gas hydrates are believed to contain a vast storehouse of gas is the main reason they are often considered an important potential future energy resource. Even though gas hydrates are known to occur in numerous marine and Arctic settings, little is known about the technology needed to produce gas hydrates. Most of the existing gas hydrate "resource" assessments do not address the problem of gas hydrate recoverability. Proposed methods of gas recovery from hydrates usually deal with dissociating or "melting" in-situ gas hydrates by heating the reservoir beyond hydrate formation temperatures, or decreasing the reservoir pressure below hydrate equilibrium conditions. First order thermal stimulation computer models have shown that gas can be produced from hydrates at sufficient rates to make gas hydrates a technically recoverable resource. However, the economic cost associated with these types of enhanced gas recovery techniques would be prohibitive. Among the possible techniques for production of natural gas from in-situ gas hydrates, the most economically promising method is considered to be the depressurization technique. It has been suggested that the production history of the West Siberian Messoyakha field demonstrates that gas hydrates are an immediate producible source of natural gas, and that production can be started and maintained by simple reservoir depressurization. More recently, preliminary reservoir modeling studies of gas hydrate accumulations in northern Alaska have also shown that gas production from hydrates can be established as a by-product of reservoir depressurization associated with conventional free-gas production.