Natural gas hydrates - A promising source of energy

摘要

Gas hydrates are clathrate physical compounds, in which the molecules of gas are occluded in crystalline cells, consisting of water molecules retained by the energy of hydrogen bonds. All gases can form hydrates under different pressures and temperatures. The crystalline structure of solid gas hydrate crystals has a strong dependence on gas composition, pressure, and temperature. Presently, three crystalline structures are known (Sloan, 1990, 2007) to form at moderate pressure, and nearly ten structures in the pressure range above 100 MPa. For example, methane hydrate can be stable at a pressure of 20 nPa to 2 GPa, and at temperatures changing from 70 to 350 K (Makogon, 1997). Formation of gas hydrate occurs when water and natural gas are present at a low temperature and a high pressure. Such conditions often exist in oil and gas wells, and pipeline equipment. Hydrate plugs can damage gas transport system equipment. The petroleum industry spends about one billion US dollars a year to prevent hydrate formation in wells, pipelines and equipment. Natural deposits of gas hydrates also exist on Earth in colder regions, such as permafrost, or sea bottom areas. Natural gas hydrates are an unconventional energy resource. Potential reserves of gas in hydrated posits distributed offshore and on land are over 1.5 x 10~(16) m~3 (Makogon, 1982). About 97% of natural gas hydrates have been located offshore, and only 3% on land. At present time, there are several successful federal research programs in a number of countries for research and development of gas hydrate deposits. Over 230 gas hydrate deposits were discovered, over a hundred wells drilled, and kilometers of cores studied. Gas hydrate resource is distributed conveniently for development by most every country. Effective tools for the recovery of gas from hydrate deposits, and new technology for development of gas hydrate deposits are being developed. There is a commercial production of natural gas from hydrates in Siberia. Researchers continue to study the properties of natural gas hydrates at reservoir conditions, and develop new technologies for exploration and production of gas from hydrate deposits in different geological formations.