Natural Gas and the Environment

Natural gas well drilling operation

Source: Bureau of Land Management (public domain)

Natural gas has many qualities that make it an efficient, relatively clean burning, and economical energy source. However, there are environmental and safety issues associated with the production and use of natural gas.

Natural gas is a relatively clean burning fossil fuel

Burning natural gas for energy results in fewer emissions of nearly all types of air pollutants and carbon dioxide (CO2) per unit of heat produced than coal or refined petroleum products. About 117 pounds of carbon dioxide are produced per million British thermal units (Btu) equivalent of natural gas compared to more than 200 pounds of CO2 per million Btu of coal and more than 160 pounds per million Btu of distillate fuel oil. These clean burning properties have contributed to the increased use of natural gas for electricity generation and the increased use of natural gas as a transportation fuel for fleet vehicles in the United States.

Natural gas is mainly methane—a strong greenhouse gas

Natural gas is made up mostly of methane, which is a potent greenhouse gas. Some natural gas leaks into the atmosphere from oil and natural gas wells, storage tanks, pipelines, and processing plants. These leaks were the source of about 29% of total U.S. methane emissions, but only about 2% of total U.S. greenhouse gas emissions in 2013¹. The oil and natural gas industry tries to prevent natural gas leaks. In areas where natural gas is produced but can't be transported economically, natural gas is flared or burned at well sites. This is considered to be safer than releasing methane into the atmosphere, and CO2 is not as potent a greenhouse gas as methane.

Natural gas exploration, drilling, and production can negatively affect the environment

When geologists explore for natural gas deposits on land, they may have to disturb vegetation and soils with their vehicles. A natural gas well on land may require an area to be cleared and leveled to host a pad where a natural gas well can be drilled. Well drilling activities produce air pollution and may disturb people, wildlife, and water resources. Pipelines are needed to transport the natural gas from the wells, and this usually requires clearing land to bury the pipe. Natural gas production can also result in the production of large volumes of contaminated water. This water has to be properly handled, stored, and treated so that it does not pollute land and water.

Although the natural gas that people use as a fuel is processed so that it is mainly methane, unprocessed natural gas from a well may contain many other compounds, including hydrogen sulfide, a very toxic gas. Natural gas with high concentrations of hydrogen sulfide is usually flared. Natural gas flaring produces CO2, carbon monoxide, sulfur dioxide, nitrogen oxides, and many other compounds depending on the chemical composition of the natural gas and depending on how well the natural gas burns in the flare. Natural gas wells and pipelines often have engines to run equipment and compressors that produce additional air pollutants and noise.

Advances in drilling and production technologies have positive and negative impacts on the environment

New drilling and natural gas recovery technologies have greatly reduced the area that has to be disturbed to produce natural gas. Horizontal and directional drilling techniques make it possible to produce more natural gas from a single well than in the past, so fewer wells are needed to develop a natural gas field. Hydraulic fracturing (commonly called hydrofracking, fracking, or fracing) of shale, sandstone, and carbonate rock formations is opening up large reserves of natural gas that were previously too expensive to develop. Fracking involves pumping liquids under high pressure into a well to fracture the rock, which allows natural gas to escape from the rock. There are some potential environmental concerns associated with the production of natural gas using this technique:

• The fracturing of wells requires large amounts of water. In some areas of the country, significant use of water for shale gas production may affect the availability of water for other uses, and can affect aquatic habitats.
• If mismanaged, hydraulic fracturing fluid—that may contain potentially hazardous chemicals—can be released by spills, leaks, faulty well construction, or other exposure pathways. These releases can contaminate surrounding areas.
• Hydraulic fracturing also produces large amounts of wastewater, which may contain dissolved chemicals and other contaminants that require treatment before disposal or reuse. Because of the quantities of water used and the complexities inherent in treating some of the wastewater components, treatment and disposal of the wastewater is important.
• According to the U.S. Geological Survey, hydraulic fracturing "causes small earthquakes, but they are almost always too small to be a safety concern. In addition to natural gas, fracking fluids and formation waters are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater into the subsurface can cause earthquakes that are large enough to be felt and may cause damage."
• Natural gas may be released to the atmosphere during and after well drilling, the amounts of which are being investigated.

Strict safety regulations and standards are required for natural gas production, transportation, distribution, and storage

Because a natural gas leak can cause an explosion, there are strict government regulations and industry standards in place to ensure the safe transportation, storing, distribution, and use of natural gas. Because natural gas has no odor, natural gas companies add a strong-smelling substance called mercaptan to the natural gas so that people will know if there is a leak. If you have a stove that burns natural gas, you may smell the rotten egg scent of natural gas when the pilot light goes out.