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Natural Gas

Natural gas is a combustible, gaseous mixture of simple hydrocarbon compounds, usually found in deep underground reservoirs formed by porous rock. The gas was formed when sand, mud, and rock buried plants and tiny sea animals. Layers of organic and inorganic matter built up until pressure and heat from the earth turned them into petroleum and natural gas [1].

“Natural gas” is used to describe a combustible mixture of hydrocarbon gases composed almost entirely of methane, but also including other gases such as ethane, propane, butane, and pentane [1]. Figure 1 outlines the typical makeup of natural gas before it is refined.

Figure 1: Composition of Natural Gas

Typical Composition of Natural Gas
Methane	CH4	70-90%
Ethane	C2H6	0-20%
Propane	C3H8
Butane	C4H10
Carbon Dioxide	CO2	0-8%
Oxygen	O2	0-0.2%
Nitrogen	N2	0-5%
Hydrogen Sulphide	H2S	0-5%
Rare gases	A, He, Ne, Xe	trace

Source: NaturalGas.org

Natural gas is easily transported by pipeline; the US possesses an impressive 280,000 miles of natural gas transmission pipelines and 1.4 million miles of distribution pipelines, most moving natural gas from high-production areas, like the Gulf of Mexico, to various market areas [2, 3].

The US relies on natural gas for nearly 25% of its total energy needs [2]. About 95% of the natural gas used in the United States is derived from domestic sources and the rest is imported from Canada [4]. The US possesses the world’s sixth largest proved reserves of natural gas, but this accounts for only approximately 3% of the global total of 4,900 trillion cubic feet [4, 5]. In 2004, estimates concluded that there is enough natural gas available worldwide to last 60 years at current consumption rates. Figure 2 outlines technically recoverable resources of natural gas in the US.

Figure 2: Recoverable Natural Gas

Natural Gas Technically Recoverable Resources
Natural Gas Resource Category (Trillion Cubic Feet)	As of January 1, 2000
Nonassociated Gas
Undiscovered	247.71
Onshore	121.61
Offshore	126.1
Deep	81.56
Shallow	44.52
Inferred Reserves	232.7
Onshore	183.03
Offshore	47.68
Deep	7.72
Shallow	39.96
Unconventional Gas Recovery	369.59
Tight Gas	253.83
Shale Gas	55.42
Coalbed Methane	60.35
Associated-Dissolved Gas	140.89
Total Lower 48 Unproved	990.89
Alaska	32.32
Total U.S. Unproved	1023.21
Proved Reserves	167.41

Total Natural Gas	1190.62

Source: NaturalGas.org

Only about 24% of natural gas used in the US is used to generate electricity; about 50% is used for heating homes and commercial facilities; the remaining 26% is used for industrial processes and other purposes [1, 6]. However, natural gas for electricity generation is on the rise.

In 2004, 758 billion KWh of electricity was generated from natural gas [7]. Generation takes place in cogeneration and combined-cycle turbine system power plants. These are high-efficiency technologies; both capture waste heat that is otherwise wasted – a combined-cycle power plant uses waste heat to produce more electricity, while a cogeneration system uses the waste heat to provide heat or steam to a building or facility [1].

There are numerous benefits to natural gas. In comparison to other fossil fuels, it is more convenient, clean, reliable, and affordable [1]. It is the cleanest burning of any fossil fuel, producing primarily carbon dioxide, water vapor, and small amounts of nitrogen oxides when burned. Natural gas plants produce none of the solid waste associated with coal units, less than 1% of the sulfur dioxide and particulate emissions, and 85% less nitrogen oxide than a coal plant with pollution control equipment [1]. Furthermore, natural gas is relatively inexpensive; from a cost-effective perspective, natural gas is a highly efficient source of energy with new power plants approaching conversion efficiencies of 45 percent. In its natural state, natural gas is easy to transport through pipelines, so domestic natural gas is simpler to transport [4].

The natural gas industry has already gone through the deregulation which now is occurring in the electric industry. Deregulation has increased availability and sources of gas, while driving down prices [1]. Although natural gas-only-fired power plants account for only 19% of all fuels used to generate electricity nationwide, 92% of the new electric capacity built in the last 10 years use natural gas as their primary, and in many cases, only fuel [2]. Natural gas is indeed on the rise: it is expected that homes, businesses, industries, and electric power generators will increase their combined consumption of natural gas by 20% between now and 2030 [2]. Because of this projected growth, there have been calls to expand the current natural gas transmission and distribution infrastructure [2, 3].