What is natural gas?
Natural gas is a gas that occurs deep beneath the earths surface. Natural gas consists mainly of methane, a gas (or compound) with one carbon atom and four hydrogen atoms. Natural gas also contains small amounts of hydrocarbon liquids and nonhydrocarbon gases. Natural gas can be used as a fuel or to make materials and chemicals.
How was natural gas formed?
Millions of years ago, the remains of plants and animals (diatoms) decayed and built up in thick layers, sometimes mixed with sand and silt. Over time, these layers were buried under sand, silt, and rock. Pressure and heat changed some of this organic material into coal, some into oil (petroleum), and some into natural gas. In some places, the natural gas moved into large cracks and spaces between layers of overlying rock. Natural gas is also contained in tiny pores (spaces) within some formations of shale, sandstone, other types of sedimentary rock, and in coal.
How do we get natural gas?
Did you know?
Because natural gas is colorless, odorless, and tasteless, mercaptan (a chemical that smells like sulfur) is added before distribution, to give natural gas a distinct unpleasant odor (it smells like rotten eggs). This added smell serves as a safety device by allowing it to be detected in the atmosphere in cases where leaks occur.
The search for natural gas begins with geologists, who study the structure and processes of the earth. They locate the types of rock that are likely to contain natural gas deposits. Some of these areas are on land, and some are offshore and deep under the ocean floor.
Today, geologists use seismic surveys to find the right places to drill wells. Seismic surveys use echoes from a vibration source at the earths surface (usually a vibrating pad under a truck built for this purpose) to collect information about the rocks beneath. Sometimes it is necessary to use small amounts of dynamite to provide the vibration needed.
If a site seems promising, an exploratory well may be drilled to collect data on the formation to find out if it contains enough natural gas to be produced economically. Once a formation is proven for economical production, one or more production wells are drilled down into the formation, and natural gas flows up through the wells to the surface. In the United States and in a few other countries, natural gas is produced directly from shale and other types of rock formations that contain natural gas in pores within the rock. The rock formation is fractured by forcing water, chemicals, and sand down a well. This releases the natural gas from the rock, and the natural gas flows up the well to the surface. Wells drilled to produce oil may also produce associated natural gas.
The natural gas withdrawn from a well is called wet natural gas because it usually contains liquid hydrocarbons and nonhydrocarbon gases. Methane and other useful gases are separated from the wet natural gas near the site of the well or at a natural gas processing plant. The processed gas is called dry or consumer-grade natural gas. This natural gas is sent through pipelines to underground storage fields and/or to distribution companies, and then to consumers.
Coal may contain coalbed methane, which can be captured when coal is mined. Coalbed methane can be added to natural gas pipelines without any special treatment. Another source of methane is biogas that is produced in landfills and in machines called digesters.
Most of the natural gas consumed in the United States is produced in the United States. Some natural gas is imported from Canada and Mexico in pipelines. A small amount of natural gas is also imported as liquefied natural gas.