NATURAL GAS is the name given to the inflammable gas which occurs in porous, sub-surface, imperviously capped earth formations. Petroleum is found in many instances with the gas. Brine waters are generally present. The occurrence of natural gas is wide-spread both geographically and geologically. Geo graphically, natural gas is produced in North America, South America, Europe, Asia, and Africa. The major producing fields of North America are : Texas, California, Louisiana, Oklahoma, West Virginia, and Pennsylvania ; in Canada, the provinces of Al berta and Ontario; in Mexico, the States of Vera Cruz, Tamau lipas, and Tabasco; in South America, Venezuela, Colombia, Peru, Argentina, Ecuador, and Trinidad; in Europe, the Soviet Union, Rumania, and Poland; in Asia, Iraq, Iran, Netherlands East In dies, Bahrein Island, British India, and Japan; and in Africa, Egypt. Geologically, these deposits of natural gas are variously found in the Carboniferous, Devonian, Silurian, Ordovician, Cam brian, Tertiary, Cretaceous, and Jurassic systems.
Chemical Composition.—Natural gas is for the most part composed of the hydrocarbons of the paraffin series. However, its composition varies considerably in the different fields. Carbon dioxide, nitrogen, hydrogen sulphide, and helium are sometimes present. Natural gas of the East American or Appalachian field is almost entirely made up of methane, ethane, propane, the bu tanes, and the vapours of pentane, hexane, heptane, and octane. The gas from some parts of Texas, Oklahoma, and Kansas is high in nitrogen content and some of these high nitrogen gases contain helium. The content of nitrogen is so high in some of the gas from the wells of West Texas, that the gas is non-combustible. Practically all the so-called "sour" gas contains hydrogen sul phide and organic sulphur compounds. Some natural gas of Cali fornia, Colorado, Utah, New Mexico, and Washington contains high percentages of carbon dioxide. Natural gas suitable for pro ducing solid carbon dioxide is obtained in several States and natural "dry ice" plants have been built in all these States except New Mexico, to utilize this gas. The rated capacity of these plants totals 8o to ioo tons daily.
Natural gas wells are, and have been for the most part, remote from the gas-consuming markets. Fusion-welded and "Dresser coupling" steel lines are used in the transportation of gas. Many of these lines are more than loo miles in length—one line is i,000 miles long. The pressure of transportation varies from 200 to more than 400lbs.—one line transports gas at i,3oolbs. pressure. When and where natural well pressures are inadequate to effect delivery, compressing stations are installed. One large gas-trans porting company has 72,700 installed horse-power compressing capacity. Many of the transporting lines are 20 to 2 2 inches in diameter—one is a 36-inch line. During the winter months when consumption is large, temperatures are low, and transporting pressures are high, it has been necessary to install dehydrating plants on the large lines to eliminate stoppage of lines due to the formation of crystalline hydrates. The hydrate of methane contains 6 molecules of water, while those of ethane, propane, and iso-butane contain 7 molecules of water. These hydrates are stable at all temperatures below 66° F. The other hydrocarbons of natural gas do not form hydrates. The wholesale metering of gas in the large transporting lines is effected with orifice meters. The average deviation of natural gas from Boyle's law at 6o° F. is approximately 8% at 30olbs. pressure and 20% at 1,30o pounds.
Natural gas as distributed is for the most part refined. It has been processed for the elimination of suspended and finely di vided solids and water. On practically all the large transporting systems, gasoline and liquefied .petroleum gas recovery plants are installed. In some few instances natural gas is processed to re move its content of hydrogen sulphide and organic sulphur com pounds. The so-called "dry" natural gas of commerce is mainly made up of the hydrocarbon methane associated with varying quantities of ethane, propane, and the butanes. The total heating value per cubic foot, measured at 6o° F. and 3o inches mercury pressure, varies from ',coo to 1,200 British thermal units. The specific gravity (air= z) varies from .56 to .67. The explosive limits are 4.8 to 15.