Natural Gas Q & A

What is natural gas?

Natural gas is a fossil fuel formed underground over millions of years from the remains of plants, animals and microorganisms. Like all fossil fuels, it is “non renewable”—there is a finite amount of it, and once it is depleted, there is no more available for future needs. Non-renewable resources are consumed much faster than nature can create them.

Natural gas is generally found a mile or more beneath the earth’s surface, but is sometimes found at shallower depths.

natural gas graphic

Natural gas is a combustible mixture of hydrocarbon gases, consisting primarily of methane—but also containing smaller amounts of other marketable hydrocarbons such as ethane, propane and butane, along with impurities such as hydrogen sulfide and carbon dioxide. Many of these gases, like methane, are greenhouse gases (GHGs): they trap heat in the atmosphere and contribute to global warming.

What is methane?

Methane is the primary component of natural gas—typically about 70% to 90% by volume. It is a molecule, CH4, made up of one carbon atom and four hydrogen atoms. The combustion of methane produces heat, water (H20) and carbon dioxide (CO2). Methane is a powerful greenhouse gas, many times more potent than carbon dioxide, which is currently the largest contributer to man made climate change. Think of greenhouse gases as creating a heavy blanket in our atmosphere, trapping too much of the sun’s heat on our planet.

methane molecule graphic


What makes natural gas smell like rotten eggs?

Methane is odorless, colorless, and tasteless. That awful odor comes from mercaptan, which is added to the gas, so that you can smell a gas leak in your home or on your block.

What is shale gas?

Shale is fine-grained, organic-rich, sedimentary rock. Shale can be a ‘source-rock’ for oil and natural gas.

Millions of years ago, the remains of ancient life were trapped in layers of mud, preventing normal decay. That mud was buried under the earth and exposed to high temperatures and pressures, chemically transforming the sediment to rock and the trapped particles into natural gas. As shale was formed, clays in the mud compressed and layered—that’s what makes it difficult for the trapped oil and gas to rise through the formation.

Today natural gas producers use horizontal drilling and hydraulic fracturing—injecting water, sand or other “proppants” (materials that keep fractures open) and chemicals down the wellbore—to break up the shale and release the trapped oil and gas.

Most of the shale gas in North America is concentrated in ancient sedimentary basins in distinct geographical areas. There are currently over twenty active shale plays in the United States, and fourteen states make up about 85% of onshore unconventional natural gas reserves.

Shale plays map

Why is shale gas the focus of so much attention these days?

The availability of new technologies for extracting shale gas means that our “energy landscape”—the mix of fuels we use to power our lives—is changing radically.

In 2001, shale gas accounted for only 2% of total U.S. natural gas production. In one decade—because of technological developments in horizontal drilling and hydraulic fracturing–that number has grown to 30%.

The U.S. Energy Information Administration projects that shale gas production will increase significantly between 2009 and 2035. By 2035, shale gas is projected to reach nearly half of total domestic natural gas production.

The brisk and far-reaching scope of shale gas extraction has led to profound public concern about the negative impacts of irresponsible gas development on human health and our air, water and land.

What is fracking?

During the hydraulic fracturing process, commonly referred to as “fracking,” millions of gallons of water, combined with sand and chemicals – some of them toxic–are injected down a well bore under intense pressure to create tiny fissures in the shale, allowing the trapped oil or natural gas to flow into the well.

Hydraulic fracturing is not new. It has been used in oil and gas wells for decades. What’s new is the combination of hydraulic fracturing with horizontal drilling in onshore production. With horizontal drilling technology, the well bores turn sideways – think of a bendable straw – to reach much further into and along the shale formation. It’s this recent combination of technologies that has made it profitable to produce shale gas in areas that were once prohibitively expensive for gas industry development.

Why is natural gas a potentially “cleaner” fuel?

Natural gas may have a significant role to play in achieving a cleaner, less carbon-intensive energy future for the United States –but only if it is possible to develop it responsibly.

Natural gas has the potential to be good for our air because it means we are burning less coal. Natural gas burns cleaner than either coal or oil, with lower emissions at the smokestack of greenhouse gases, smog-forming pollutants, mercury, sulfur dioxide, soot and other contaminants.

And – unlike coal-fired plants – modern gas turbines can adapt their output quickly, making them better suited than coal plants as supplements to intermittent wind and solar energy generation. Output from these technologies can vary over the course of a day or a season, thus the importance of deploying commercially viable technologies that can quickly fill in the gaps.

But natural gas exploration, drilling and transport may outweigh these cleaner-at-the-power-plant benefits. That’s because of leaking toxic air pollutants and methane, a potent greenhouse gas and the major component of natural gas, all along the chain of extraction and production. The scope of such leaks is unknown; but communities near oil and gas activity are suffering from sometimes debilitating air pollution. And research on rates of methane leakage is ongoing.

How does natural gas affect coal?

Coal fired power plants are closing at a rapid clip as a shift in the US energy landscape takes hold. Do these retirements have anything to do with natural gas?

Yes. While some coal companies complain that EPA regulations are to blame, coal plant shutdowns are actually happening because of market conditions, not environmental standards.

According to Grist’s David Roberts, “One market condition has to do with demand for power, which has slowed/plateaued due to the recession and recent mild weather. Another is the falling price of renewables. But the big one, the cudgel to coal’s head, is natural gas prices.” As natural gas prices continue to outcompete coal, utilities are using more of it.

“So what can we expect for coal-plant retirements given these market conditions?” asks Roberts. “20 to 25 percent of U.S. coal generation capacity [will retire], in a matter of less than a decade. It’s an extraordinary shift — far bigger than anything the EPA could engineer.”

Burning coal for energy releases huge amounts of climate-warming carbon dioxide and other dangerous air pollutants, including mercury.

Is natural gas development dangerous?

Unfortunately, current production practices have resulted in unacceptable impacts on air, water, landscapes, people and communities. Irresponsible natural gas development presents serious risks to people’s health and the environment in several ways, including:

  • Human exposure to toxic chemicals and the waste products of gas extraction;
  • Contamination of groundwater and surface water from spills, problems with well construction and operation and failures at waste storage facilities;
  • Global warming impacts through the release of methane—a powerful greenhouse gas;
  • Deleterious air pollution—both local and regional—from equipment and activities involved in drilling, production and pipeline transportation; and
  • Negative impacts on the quality of life in communities.
Workers inspect a natural gas valve at a fracking site in
Pennsylvania’s Marcellus Shale region. (1)


Are natural gas production and greenhouse gases related?

Methane (CH4), the primary component of natural gas, is a greenhouse gas many times more potent than carbon dioxide (CO2), now the principal contributor to man-made climate change.

Methane has a very high global warming potential – much higher than CO2. Pound for pound, methane can trap heat about 25 times more effectively than carbon dioxide over a 100-year timeline. Over a shorter timeline, the impact of methane is even greater. This is because methane breaks down relatively quickly in the atmosphere. So its global warming impacts are greatest in near-term decades.

Methane can leak at many points along the development process. Very small leaks at the point of production, along the pipeline system or at the local distribution system, can actually undo the greenhouse-gas benefits of switching from coal to natural gas.

A less-known aspect of methane is that it also adds to ozone (O3) levels, another greenhouse gas and air pollutant. In relation to health, ozone exposure can have many effects, ranging from minor ones on the respiratory system to premature mortality. Ozone is not emitted directly but is formed through the reaction of volatile organic compounds (VOCs), such as methane, and nitrogen oxides (NOx) in the presence of sunlight.

Natural gas compressor station

Just how much methane is released into the atmosphere during these processes is uncertain because the measured data is limited and drilling and completion processes have evolved rapidly in recent years. The Environmental Protection Agency (EPA) has estimated the methane leak rate at a little more than two percent. But a recent study by the National Oceanic and Atmospheric Administration (NOAA) suggested it might be twice that in northern Colorado. Other studies suggest it could be higher still.

In order to reduce leaks, it is important to find where they are occurring and how much gas is being lost to the atmosphere. Climate impacts from methane leakage – and other key public health and environmental risks – could be reduced by strong regulatory standards and improved industry practices. For example, during natural gas development, most of the gas is leaked into the air at the beginning of the well’s life. To cut down on this loss, by 2015 the EPA will require “green-completions” for many new gas wells in the U.S. Unfortunately, the new federal rules won’t cover all new gas wells or existing oil and gas wells– where a lot of natural gas can also be lost when bringing a well online.

Are there other air pollution issues related to natural gas production?

Yes. Leaks and venting at natural gas well sites and processing plants release other pollutants besides methane that can threaten air quality and public health, including the following hazardous air pollutants (HAPs):

  • Exposure to benzene can cause skin and respiratory irritation, and long-term exposure can lead to cancer and blood, developmental and reproductive disorders;
  • Long-term exposure to toluene can cause skin and respiratory irritation, headaches, dizziness, birth defects and damage the nervous system;
  • Ethylbenzene can cause irritation of the throat and eyes, and dizziness and long-term exposure can cause blood disorders;
  • High levels of xylene exposure have numerous short-term impacts, including nausea, gastric irritation and neurological effects, and long-term exposure can negatively impact the nervous system; and
  • Exposure to n-hexane can cause dizziness, nausea and headaches, while long-term exposure can lead to numbness, muscular atrophy, blurred vision and fatigue.

The EPA notes that areas with natural gas development can have increased levels of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). The air quality impacts of these emissions vary based on local conditions, but they can be significant, even in rural areas. For example, wintertime ozone levels in excess of the nation’s health-based air quality standards have been recorded in parts of Wyoming and Utah, where natural gas and oil production are the only significant industrial activities.

A fracking site in Bradford County, Pennsylvania. (2)

Engines and other combustion sources used throughout the industry also produce emissions that can affect air quality.

In 2009, a Southern Methodist University study estimated that the combined amounts of VOCs and nitrogen oxides (NOx) emissions from oil and natural gas production in the Barnett Shale of North Texas were comparable to amounts of those emissions from the roughly four million cars and trucks in the Dallas Fort-Worth metro area. The Barnett Shale is a geological formation underlying 5,000 square miles of Texas, including at least 17 counties, and the city of Forth Worth.

What is Ozone—and what does that have to do with gas production?

Ground level ozone—O3– is the main component of smog. Ground level ozone is created by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). Some of the major sources of ozone precursors are emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents.

Oil and gas development produces significant amounts of smog-forming pollution and is directly linked to ozone problems in states like Wyoming, where previously pristine air quality has deteriorated to levels that violate the nation’s health-based air quality standards for ozone; Wyoming families are now experiencing unhealthy levels of ozone concentrations on some days comparable to some of the nation’s most polluted urban areas.

Without rigorous pollution control measures, the problem of ozone pollution will worsen as the pace of oil and gas development surges across the country.
The U. S Energy Information Administration projects that shale gas production will triple between 2009 and 2035, and that by 2035 shale gas will account for nearly 46% of domestic energy production, touching communities across the country, from Pennsylvania and Ohio to Texas, North Dakota and Colorado.

In certain communities close to oil and gas development, there is inadequate ozone monitoring to provide the data needed to let people know whether or not the air they are breathing is safe.

Petitioners have respectfully urged the EPA to take actions that will provide important public health protections for communities faced with ozone pollution from gas development.

Ozone levels in the air climb during hot, sunny days, but high ozone concentrations have also been measured in winter months in parts of Wyoming and Colorado where there are high emissions of VOCs and NOx associated with oil and gas development. Ozone can travel great distances carried by the wind.

Ozone is a powerful oxidant that can irritate the airways, causing a burning sensation, coughing, wheezing, and shortness of breath. Ozone has been linked to a host of maladies, including premature mortality, heart failure, increased hospital admissions and emergency room visits for respiratory causes among children and adults with pre-existing respiratory disease, such as asthma and inflammation of the lung, and possible long-term damage to the lungs.

Children, the elderly, and people with existing respiratory conditions are the most at risk from ozone pollution. Children are more vulnerable to the damaging effects of ozone because their lungs are still developing—and children tend to be more active outdoors, even when ozone levels are high.

Ozone also damages crops and ecosystems. Ozone is one of the most phytotoxic air pollutants. It damages vegetation in national parks and wilderness areas, especially in mountain regions–and, as well, valuable crops.

Ozone pollution also contributes to climate change. According to the Intergovernmental Panel on Climate Change (IPCC), ozone is the third-largest contributor to climate change after carbon dioxide and methane.

What are EPA's 'New Source Performance Standards?

These standards for the oil and natural gas sector (often referred to as NSPS) will limit harmful ozone precursors and air toxics. They are an important first step in reducing air pollution—as they cover only new sources. (These new standards will also limit the emission of methane, a potent greenhouse gas that contributes to climate change.)

The NSPS use cost-effective, proven technologies—as demonstrated in states like Colorado and Wyoming—that in many cases plug leaks of NOx and VOCs through the gas development system. These new performance standards reduce pollution, conserve a valuable source of energy, and in some cases actually save producers money.

Drill rig set up for winter natural gas drilling in Wyoming


What is flaring?

Flaring is a method of burning off gas at the well-head that produces harmful pollution. It also wastes a finite energy resource. Producers flare natural gas to eliminate the dangers of venting gas that the developer cannot use on-site or put into a pipeline. Flaring can also be used to protect pipes or vessels from becoming over-pressured. Natural gas is frequently flared when there is no pipeline infrastructure in place to transport the gas to market.

Gas flare in La Porte, Texas. (3)

Burning natural gas produces both carbon dioxide – a greenhouse gas – and nitrogen oxides (NOx), a pollutant that contributes to the formation of smog or ground-level ozone. Depending on how efficiently the gas is combusted, flaring can also lead to emissions of soot, unburned hydrocarbons, carbon monoxide and other contaminants that can be dangerous to human health.

On top of these serious health and environmental impacts, flaring wastes natural gas – a finite, domestic energy resource that could otherwise be used to heat our homes and power our country. The U. S. is currently wasting more of the fuel than it has in years, with flaring rising 223% from 2007 to 2011, making it the fastest growing offender in the world.

The World Bank recently issued an analysis showing that the United States is behind only Russia, Nigeria, Iran and Iraq in terms of the amount of gas we burned in flares in 2011. In the U.S, in 2011, this amounted to 7.1 billion cubic meters of gas flared. This could have powered many American homes.

Regulators and producers need to take measures to reduce flaring wherever possible. Infrastructure can be built to capture the gas instead. It should be noted, however, that if the choice is between venting and flaring, flaring is the better option so as to avoid releasing uncombusted methane – a highly potent greenhouse gas – directly into the atmosphere.

The best option of all, though, is to capture the natural gas and bring it to market responsibly.

A new federal requirement for “green completions,” which capture natural gas and other emissions following the completion of drilling the gas well but before production begins, can help reduce the practice of venting methane directly into the atmosphere. This new requirement will take effect by 2015.

The U.S. Government Accountability Office (GAO), with supporting data from EPA, estimates that around 40% of the natural gas vented and flared on onshore federal leases could be captured at a profit to the operator with currently available technologies. Recouping these losses could increase federal royalty payments by $23 million annually.

Nighttime view of widespread drilling throughout Northwestern North Dakota
Nighttime view of widespread drilling throughout Northwestern North Dakota.

More on flaring in North Dakota here.

Are air quality risks the only worry about natural gas production?

No. Natural gas development involves other important activities of concern:

  • Water management—Careful use of water is especially important in areas prone to drought and in sensitive ecosystems;
  • Wastewater management—Wastewater must be handled, stored, transported and either disposed of or recycled in ways that protect people and the environment. Spills and leaks in waste containment facilities are a major problem in the industry;
  • Well integrity—Poor construction and operation of wells – especially in casing, cementing and pressure management – can lead to the contamination of drinking water; and
  • Local community and land impacts—Communities can be overwhelmed by the impacts of gas development activities, such as infrastructure development, truck traffic, lights and noise, and burdens on local government resources. Land disturbance and ecosystem impacts from intensive development can also be a major problem.
Pipeline construction and sand tankers in Wyalusing, PA (5)

Is natural gas production regulated?

Currently there are no federal regulations in place that regulate natural gas production. Notably, many states have made efforts to regulate natural gas production on a local level, and some have been successful. In June 2013, Illinois Governor Pat Quinn signed legislation to regulate fracking in his state, requiring chemical disclosure and water testing around fracking sites. In February 2014, Colorado approved regulations on the natural gas industry focused on reducing methane emissions. The Colorado regulations – which were backed by four of the largest natural gas developers in the state – include requirements to use leak-proof valves and conduct regular inspections for methane leaks.

What sensitive areas should remain off limits to natural gas development?

An advisory committee to the Department of Energy noted that some areas are so unique and/or sensitive that they should be declared off limits to drilling. The committee recommended using science-based processes for identifying these areas. Communities can–and should–choose to ban fracking in sensitive areas.

North Dakota’s Bakken shale — a primary area for fracking (6)


Can hydraulic fracturing cause earthquakes?

Reports of earthquakes connected to shale gas wastewater disposal have surfaced in Oklahoma, Ohio, Arkansas and elsewhere. These earthquakes have ranged in magnitude from 1.0-4.7 on the Richter scale.

Two studies have tied a recent increase in significant earthquakes to reinjection of wastewater fluids from unconventional oil and gas drilling. More from Climate Progress

While hydraulic fracturing does have micro-seismic impacts, the earthquakes that have gained attention are not the result of the hydraulic fracturing process. Rather, they are linked to the deep well injection of wastewater that is produced after a well is hydraulically fractured. In deep well injection, wastewater is taken away and injected into special disposal wells that are regulated under EPA rules. While the frequency of these events has increased, most of the tremors have been very small (earthquakes below magnitude 3.0 generally are too small to feel) and, for the most part, have not posed safety risks.

Modern natural gas well detail

Nevertheless, the incidence of earthquakes points to the need for better rules for injection wells, including improved analysis of the geology surrounding injection wells, better monitoring of injection well pressures and requirements that injection well operators to take corrective measures – including shutting down the wells if there are signs of trouble.

Where can I learn more?

1) Air Pollution Issues Associated with Natural Gas and Oil Operations

Alvarez, R., & Paranhos, E., June 2012.

This document reviews key sources of air pollution and points to air policy concerns and considerations related to oil and gas industries. It discusses both environmental and public health impacts relations to ambient air and greenhouse gas pollution.

2) EPA Natural Gas Air Pollution Standards

EPA Air and Radiation, April 17, 2012

Standards recently established for oil and gas industry activities limit smog-forming volatile organic compound (VOCs) and other toxic air pollutants that affect human health. Information on emissions, regulatory actions, and technical material is presented by the EPA, and EDF’s summary highlights additional key points of interest.

3) Natural Gas Operations from a Public Health Perspective

Colborn et al, 2011. TEDX.

This study was the first of its kind to complete a thorough analysis of chemicals used in hydraulic fracturing fluids. Although concentrations and volumes of these substances were not in the scope of the study, it provides a glimpse into general health risks possible from direct consumption or absorption.

4) IEHN: Extracting The Facts

5) IEA: Golden Rules for a Golden Age of Gas

6) SEAB Interim 90-Day Report + SEAB 2nd 90-Day Report

7) PNAS Paper: Greater focus needed on methane leakage from natural gas infrastructure

8) Do Shale Gas Activities Play a Role in Rising Ozone Levels?

Craft, E., Texas Clean Air Matters, EDF blog. July 2012.

This blog post summarizes what is currently known about the relationship between shale gas development and rising ozone levels. Ground-level ozone, or “smog,” is emitted in significant amounts from equipment used in drilling, production, processing, and transporting of natural gas and oil. The many health effects associated with ozone, such as respiratory disease, put children and the elderly at greatest risk from pollution.

Photo sources:

(1) Getty Images

(2) Ralph Wilson, AP file

(3) Texas Tribune

(4) Star Tribune

(5) Scott Cannon,

(6) CNN, courtesy of Continental Resources



TOPICS: Natural Gas

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