What is Natural Gas?
Natural gas, like other fossil fuels (coal and oil), is formed from the ancient decaying remains of plants and animals. Over millions of years, pressure and heat change some of this organic matter into natural gas trapped as bubbles beneath and in layers of rock. Natural gas formed in this way is known as thermogenic gas.
The primary component of natural gas is our old friend methane, CH4, usually around 70 to 90%. Natural gas also contains ethane, propane, butane and may have some carbon dioxide, oxygen, nitrogen, hydrogen sulphide and trace amounts of rare gases (e.g. A, He, Ne, Xe).
Natural gas is also created through biogenic processes. ("Biogenic" means produced by living organisms.) In this type of process, small microorganisms (bacteria) chemically break down (digest) organic matter to produce methane. These microorganisms are anaerobic, meaning they thrive in environments that have no oxygen. They live in shallow sediments, marshes, bogs and landfills, as well as the intestines of most animals, including humans.
One example of biogenic methane (or biogas) is landfill gas. New technologies allow this gas to be harvested and added to the supply of natural gas.
Anaerobic processes for producing methane may also be managed in a digester (an airtight tank) or a covered lagoon (a pond used to store manure) for waste treatment.
Natural gas can be a confusing term. We put "gas" in our car, but this is not "natural gas." The "gas" we use in our BBQs is propane (which is also known as liquid petroleum gas, or LPG), commonly found in natural gas, but not natural gas itself.
And while we're at it, another interesting thing about natural gas...in its natural form, natural gas is odorless. The "rotten egg" smell is added before it gets to the end user for safety reasons to help detect leaks. (Yes, someone chose that smell.) The odorant is called mercaptan.
Units of Measure
Like other gases, natural gas is commonly measured as a volume expressed as hundreds of cubic feet (ccf), thousands of cubic feet (Mcf), millions of cubic feet (MMcf) or billions and trillions of cubic feet (Bcf and Tcf, respectively).
Another way natural gas may be measured is by its energy or heat content, expressed as British Thermal Units, or BTUs. A BTU is the amount of natural gas required to heat one pound of water one degree. One cubic foot of natural gas contains about 1,027 BTUs, and thus 1 ccf contains about 102,700 BTUs. Residential natural gas is usually sold in ccfs. A therm, sometimes used for billing purposes, is exactly 100,000 BTUs.