Natural Gas Reserves
The combustible part of natural gas (NG) consists mainly of methane (CH4) with some admixture of heavier hydrocarbons (ethane, propane, and butane). However, frequently noncombustible gases are found mixed with NG, namely, N2 and CO2. For example, the recently discovered gas fields off the coast of the Indonesian archipelago contain up to 70% by volume CO2. On the average, NG contains 74.4% by weight of carbon, 24.8% hydrogen, 0.6% nitrogen, and 0.2% oxygen.
On the average, the heating value of NG is 23,500 Btu/lb (55 MJ/kg), or 1032 Btu per cubic foot (38.5 MJ/m3).
Natural gas is a very desirable fuel for several reasons. First, it is easy to combust because, being a gas, it readily mixes with air. Thus, the combustion is rapidly completed, and the boiler or furnace volume is smaller than that required for oil or coal combustion. Second, the combusted gas can directly drive a gas turbine with applications in power generation. Third, gas combustion does not produce particulate and sulfurous pollutants. Fourth, NG produces one-half the amount of CO2 per unit heating value as does coal, and it produces three-quarters as much as oil.
The USGS estimate of the world’s natural gas reserves is 6.75 E(15) cubic feet. Taking the heating value of NG as 1032 Btu/ft3, the world’s NG reserves amount to 6966 Q, comparable to those of oil.
The world’s rate of consumption of NG in 1995 amounted to 77.5 Q. If that rate were to continue in the future, the world’s proven gas reserves would be depleted in about 85–90 years.
If gas consumption keeps increasing at a rate of 2.45%/y, the lifetime of the world’s gas reserves would be only about 50 years.
The gas reserves are distributed among the major reservoirs as follows (in percent): Middle East (24.3), Russia, including Siberia (23), North America, including the United States, Canada, and Mexico (17.4), Asia and Pacific (7.9), Caspian Basin (6.8), North and West Africa (5.4), West Europe, including the North Sea (5.2), South and Central America (3.6), and others (6.4).
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