Natural gas is a generic term commonly applied to those gases found in or near deposits of crude petroleum. It is not connected with the production of oil and should always be regarded as a separate and independent entity. Natural gas is piped under pressure from the gas fields to the consumer centers, and these pipelines now serve a considerable portion of the United States.
Natural gas is the richest of the gases and contains from 80 to 95 percent methane with small percentages of the other hydrocarbons. The heating value of natural gas varies from 1000 to 1200 Btu/ft3, with the majority of gases averaging about 1000 Btu/ft3. The caloric value will depend upon the locality.
Natural gas can be divided into three basic types:
1. Associated gas
2. Nonassociated gas
3. Dissolved gas
Associated gas is a free (undissolved) natural gas found in close contact with crude petroleum. Nonassociated gas is also a free gas but is not found in contact with the crude petroleum deposit. As the name suggests, dissolved gas is found in solution in the crude petroleum.