Natural gas is a fossil energy source that formed deep beneath the earth's surface. Millions years ago and over long periods, the remains of plants and animals built up in thick layers on the earth’s surface and ocean floors, sometimes mixed with sand, silt and calcium carbonate. Over time, these layers were buried under sand, silt and rock. Pressure and heat changed some of this carbon and hydrogen-rich material into coal, some into oil (petroleum) and some into natural gas. Natural gas should not be confused with gasoline, which is a petroleum product. Natural gas from underground reservoirs is a nonrenewable energy source, which means we cannot make more in a short time.
In some places, natural gas moved into large cracks and spaces between layers of overlying rock. The natural gas found in these types of formations is called conventional natural gas. In other places, natural gas occurs in the tiny pores (spaces) within some formations of shale, sandstone, and other types of sedimentary rock. This natural gas is referred to as shale gas or tight gas, and it is sometimes called unconventional natural gas. Natural gas also occurs with deposits of crude oil, and this natural gas is called associated natural gas. Natural gas deposits are found on land and some are offshore and deep under the ocean floor. Coalbed Methane is a type of natural gas found in coal deposits.
Natural gas production, transportation, distribution, and storage require strict safety regulations and standards. Because a natural gas leak could cause an explosion, strict government regulations and industry standards are in place to ensure the safe transportation, storage, distribution, and use of natural gas. Because processed natural gas has no odor, natural gas companies add a strong, rotten egg-like smelling substance called mercaptan to natural gas so that people can smell leaks.