Natural Gas. Rising Importance of Natural Gas

This fossil fuel now supplies about a quarter of the world's primary energy, the category that includes all fossil and biomass fuels as well as hydro, nuclear, solar, and geothermal electricity. Its importance will rise in the future because of its abundance and relatively clean combustion.

Much like crude oil, natural gas was known for millennia from "burning pillars" encountered by travellers in the Middle East. The only instance of the fuel's use in antiquity was the remarkable practice of burning it in order to evaporate brines in China's landlocked Sichuan province. This usage dates to at least the beginning of the Han dynasty (200 все) and it was made possible by the Chinese invention of percussion drilling, whereby heavy iron bits attached to long bamboo cables from bamboo derricks were raised rhythmically by men jumping on a lever.

Boreholes were only 1030 meters deep during the Han dynasty, but they reached 150 meters by the tenth century, and culminated in the one-kilometer-deep Xinhai well completed in 1835. Natural gas was distributed by bamboo pipelines, and the evaporation of brines took place in huge cast iron pans. Some of the piped gas was also used for lighting and cooking.

Rising Importance of Natural Gas. For decades after the beginning of modern oil production most of the natural gas that is commonly associated with crude oil deposits was flared (burned) on site because without compressors and steel pipes it could not be moved over longer distances. Only the availability of large-diameter pipelines and turbine- driven compressors, and the growing demand for clean household and industrial fuel and for convenient petrochemical feedstocks, led to increased natural gas extraction.

The United States pioneered the shift before World War II but the dense North American network of natural gas pipelines was built only after 1945 as new gas resources were tapped in states ranging from Pennsylvania to Wyoming and from Alaska to the Gulf of Mexico.

Beginning in the early nineteenth century many European countries produced relatively large volumes of town gas by gasification of coal whereby tire fuel, heated to high temperatures in the absence of air, releases a mixture of hydrogen, carbon monoxide, methane and ethylene. A virtually continent-wide shift toward natural gas (mostly just methane) began only during the J960s. The greatest milestones in this European transition were the discovery (in 1959) and the development of the giant Dutch gas field in Groningen, deliveries of Russian gas from giant fields in western Siberia (which began in 1978 via the world's longest gas pipeline), emergence of the North Sea as a major natural gas province, and the completion of the first gas pipeline connecting Africa and Italy (Transined from Algeria via Tunisia to Sicily in 1975).

Exploitation of huge Siberian and Central Asian fields also boosted Russia's domestic natural gas consumption. The rising demand for energy in the Middle East led to greatly reduced flaring of the gas in the region, and to its use in water desalination, chemical syntheses, and steelmaking.

As a result, the share of natural gas in the world's total primary energy supply rose from about 10 percent in 1950 to 25 percent by the year 2000 when more than 2.3 trillion cubic meters were extracted. U.S. and Russian shares of this total were, respectively, 25 percent and 53 percent and even Japan, where all natural gas is imported in expensive liquefied form from Brunei and from the Middle East, got nearly 15 percent of its primary energy from this fuel.

The two main reasons that explain this growing worldwide importance of natural gas are the relative abundance of the fuel and its clean combustion. The world's known reserves of conventional natural gas (the fuel that escaped from its parental rocks and accumulated in nonpermeable reservoirs, either associated with oil or alone) nearly tripled between 1975 and 2000, and in spite of the doubled extraction since 1970 the global reserve/production ratio is now above sixty years, compared to just over forty years In the early 1970s. Principal concentrations of gas reserves are in Russia (about one-third of the total), Iran (about 15 percent), Qatar (over 7 percent), and Saudi Arabia and United Arab Emirates (4 percent each).

The best available global assessment puts the world's known reserves of natural gas at nearly 150 trillion cubic meters in the year 2000 but the most likely total of recoverable resources is nearly three times as large and in addition there are enormous deposits of nonconventional natural gas. This category includes methane in coalbeds, and much larger deposits in tight reservoirs, high-pressure aquifers, and in methane hydrates.

Global resources of geopressured gas were estimated to be about 110 times the current proven reserves of the fuel, and methane hydrates (CH₄ trapped inside rigid lattice cages formed by frozen water molecules) in all coastal U.S. waters may contain as much as 1,000 times the volume of the U.S. conventional gas reserves. Eventual recovery of even a tiny share of these deposits would multiply the global gas supply.

Environmental Advantages. No fossil fuel is more environmentally friendly than natural gas, which is extracted either as a virtually puremethane (CH₄), or as a mixture of methane, ethane, and propane with the merest trace of sulfur (mostly as H₂S) that can be easily removed before the fuel is put into pipelines. Low energy density of the fuel—typically around 34 megajoules per cubic meter compared to 34 gigajoules per cubic meter for oil, or a thousandfold difference—obviously limits its use as a transportation fuel, but its stationary combustion produces no sulfur gases, and it proceeds with higher efficiency (up to 97 percent in the best gas furnaces) and emits less C0₂ per unit of energy than is the case with any other fuel.

Typical carbon emission ratios per gigajoule are about 25 kilograms for bituminous coal, 19 kilograms for refined fuels, and less than 14 kilograms for natural gas. At the same time, methane is itself a greenhouse gas. Though the losses from pipelines should not exceed more than 1-2 percent of the carried gas, pipelines in the former USSR leak 6-9 percent of total extraction.

Low air pollution emissions are the main reason why natural gas is increasingly preferred not only for household and industrial uses but also for electricity generation using stationary gas turbines. Combined- cycle plants that use waste heat to produce more electricity, and whose overall conversion efficiency is well above 50 percent, will be increasingly common as will be the use of natural gas to generate electricity indirectly via fuel cells.

This conversion should also eventually make the gas an important automotive fuel. Modular phosphoric acid fuel cells are already used for small-scale electricity generation and in experimental vehicles. Another option is to use methane to produce methanol (CH₃OH), a liquid at ambient temperature that can be stored and handled much like gasoline but is much less flammable. Finally, methane is also the most important feedstock, as well as energy source, for the synthesis of ammonia from its elements as well as for the production of many plastics.