Geology Reference
In-Depth Information
fined crude oil will produce about 19 gallons of gasoline. Most gas is used by cars
and light trucks, but it also fuels boats, farm equipment, and recreational vehicles.
Natural gas is a pure form of fossil fuel composed of methane, or CH
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, a chemical
compound made up of one carbon atom and four hydrogen atoms. Natural gas is
lighter than air, has no natural odor (we mix it with mercaptan, a chemical with a
strong sulfur odor, as a warning of leakage), is often found near petroleum deposits
deep underground, and is highly flammable.
The first discoveries of natural gas were made in what is now Iran, 6,000 to
2,000 years BCE (Before the Common Era). Natural gas seeps there were probably
ignited by lightning, and fueled the “eternal fires” of the fire-worshipping ancient
Persians.
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To find gas deposits today, geologists study seismic surveys—using echoes sent
by a vibrating pad under a specially built truck—to identify natural gas deposits
deep below ground. At a promising site, a drill rig bores test wells. Once a product-
ive deposit is found, gas is pumped to the surface and is sent to storage tanks by
pipeline.
Once stored, natural gas is measured by volume: a cubic foot (cf) of gas is equi-
valent to the amount of gas that fills a one cubic foot volume, under set conditions
of temperature and pressure. A “therm” is equivalent to 100 cf; and “mcf” is equi-
valent to 1,000 cf. To help compare fuels, energy content is measured in BTUs, or
British Thermal Units. One BTU is the amount of heat required to raise one pound
of water (about a pint) one degree Fahrenheit at its point of maximum density. One
cubic foot of natural gas releases approximately 1,000 BTUs of heat energy (and
one barrel of oil equals 6,000 cubic feet of natural gas).
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Natural gas requires minimal processing. “Wet” natural gas contains liquid hy-
drocarbons and nonhydrocarbon gases, such as butane and propane, which are
known as byproducts. Once the byproducts are removed, the methane is classified
duction and use of natural gas creates fewer emissions than oil and coal.
Conventional natural gas wells tap into large free-flowing reservoirs of trapped
gas that can be accessed by a single, vertical well. In “shale gas” and “tight gas”
fields, the gas is trapped in tiny bubbles embedded in dense (or tight) rock form-
