What is fracking — and why is it so controversial?

"Fracking" is short for "hydraulic fracturing" — it's a process by which water, sand, and chemicals are injected underground at very high pressures to crack open rock layers and release the oil or gas trapped inside.

Technically, fracking isn't new: Companies have been using this technique for decades to extract oil and gas from hard-to-exploit rock formations. Halliburton first used hydraulic fracturing back in 1949 as a way of increasing the flow of gas from wells in Kansas.

In recent years, however, fracking has become much more widespread. In the mid-2000s, US companies figured out how to combine fracking with methods like horizontal drilling to extract oil and gas from vast underground shale rock formations at a reasonable price. There's a lot of oil and gas in shale, so this breakthrough led to a drilling boom in states like North Dakota, Texas, and Pennsylvania.

The "fracking boom" has reshaped the American energy landscape. Domestic production of oil and natural gas has risen sharply, leading to cheaper energy and a reduced reliance on imports.

Advocates often argue that fracking is creating jobs, boosting manufacturing, and helping to tackle global warming by reducing the amount of coal we use. Opponents often argue that the industry is poorly regulated, the global warming benefits are overhyped, and that fracking has led to increased air and water pollution around the country.

How does fracking work, exactly?

Using hydraulic fracturing and horizontal drilling to extract oil or gas from shale rock involves a number of steps. Let's walk through a basic fracking operation for natural gas in, say, the Marcellus Shale in Pennsylvania:

1) First, a "wellbore," or hole, needs to be drilled all the way down to the layer of gas-rich shale. This shale layer can sit more than 5,000 feet underground and drilling can take as long as a month. The well is lined with a steel casing to prevent the contamination of nearby groundwater.

2) Once the drill reaches down to the shale layer, it slowly turns and begins drilling horizontally, for a mile or more along the rock.

3) A "perforating gun" loaded with explosive charges is lowered to the bottom of the well and punctures tiny holes in the horizontal section of the casing that's deep down in the shale layer.

4) Now comes the actual fracking, or "completion" stage: A mixture of water, sand, and chemicals is pumped into the well at extremely high pressures and goes through the tiny holes in the casing. The fluids crack open the shale rock. The sand holds those cracks open. And the chemicals help the natural gas seep out.

5) The "flowback" stage: The water and chemicals flow back out of the well and are taken for disposal or treatment.

6) Finally, natural gas begins flowing from the shale and up out of the well, where it's eventually shipped to consumers via pipeline. A typical well can produce gas for 20 to 40 years, pumping out thousands of cubic feet of gas each day.

That's a very rough overview of the fracking process. There are plenty of variations, depending on the geology of the region or the technologies used. (Often other particles besides sand are used, for instance. And here's a partial listing of some of the different techniques used in North Dakota, for example.)

Where is fracking taking place in the United States?

This interactive map from the Post Carbon Institute shows the location of more than 63,000 shale oil wells and shale gas wells around the country. Much of the activity is concentrated in Texas, North Dakota, Louisiana, and the Marcellus Shale region in the East:

These aren't the only oil and gas wells in the United States (shale represents about 29 percent of total oil production and 40 percent of gas). But they're the ones that tend to rely heavily on fracking.

The Energy Information Administration has its own map of the major shale formations around the country, including the Bakken in North Dakota, Eagle Ford in Texas, and the Marcellus up in Pennsylvania and West Virginia.

How has fracking boosted US oil and gas production?

Since the late 2000s, the amount of oil and natural gas produced in the United States has risen dramatically, thanks to fracking, horizontal drilling, offshore drilling, and other advanced techniques. Supplies are projected to grow further in the years ahead:

Crude oil: By November 2013, the United States was producing 7.8 million barrels of crude oil each day, the most in a quarter-century. Oil production is now expected to keep growing until it reaches a peak of 9.6 million barrels per day in 2019:





Natural gas: US natural gas production has also reached new historical highs, to 24 trillion cubic feet in November 2013. Supplies are currently expected to grow until at least 2040:

Note that these predictions are far from perfect — ten years ago, few were predicting the fracking boom.

How has fracking affected the US economy?

The oil and gas boom — driven by fracking — has had all sorts of effects on the US economy. Here are a few of the big ones:

More jobs in some states: More drilling means more jobs. The oil and gas industry added 169,000 positions between 2010 and 2012 — growing ten times faster than the nation as a whole. Texas, North Dakota, and Pennsylvania have seen some of the biggest gains:

Higher economic growth: The oil and gas industry is a fairly small portion of the overall US economy, but analysts tend to agree that the fracking boom has helped bolster the country's growth a bit. JP Morgan estimates that the oil and gas boom added 0.3 percentage points to economic growth in 2013. Other models suggest that the boom could add 0.5 percentage points to growth each year for the next decade.

Lower energy prices (sometimes): Oil is still quite expensive — because the price of crude oil depends on global supply and demand factors. But US natural gas prices have fallen significantly since the mid-2000s (though they rebounded during the cold 2013 winter, as heating demand surged). That's saved consumers money. It also means that power plants are more likely to use natural gas for electricity.

The decline of coal power: Many electric utilities have taken advantage of cheap prices to switch from coal to natural gas as their preferred power source. That switch has reduced a variety of air pollutants, as well as carbon-dioxide emissions that contribute to global warming. This trend is hurting the coal industry — and one reason why one-fourth of the nation's coal power plants have closed since 2011.

A boost for US manufacturing: America's glut of cheap natural gas is also luring some manufacturers to the United States. Factories being built in Texas and Pennsylvania will convert natural gas into ethylene, a key ingredient in plastics and antifreeze. (That said, it's unclear how many companies this will affect — as a note from Morgan Stanley points out, energy is still a small fraction of costs for most industries.)

Lower imports: The United States is importing far less oil and natural gas than it used to — one reason why the trade deficit has dropped to its lowest level since 1998. Indeed, many companies are now arguing that US government should loosen its restrictions on selling American oil and gas abroad.

Does fracking pollute the water and air?

It can. As fracking operations have spread out across the United States, they've triggered protests over air and water pollution. Here's an overview of some of the key concerns:

Groundwater contamination: One big concern is whether the chemicals used in fracking or the natural gas itself could contaminate people's drinking water. (There's the worry, for instance, that natural gas leaks could make people's tap water flammable.)

There are two big ways this might happen. One is through accidents or contamination near the surface. In recent years, fracking wells have blown out in states like North Dakota. In another incident, thousands of gallons of fracking fluid leaked out of a storage tank in Dimock, Pennsylvania. And poorly constructed wells with cement problems can allow fluids or gas to migrate upward. The Environmental Protection Agency is currently conducting a big study into this type of contamination and how to prevent it.

A second question is whether chemicals or natural gas could somehow migrate from the fracked shale layer thousands of feet up into the groundwater — even if the wells are perfectly constructed. This second possibility is considered unlikely, since there are dozens of layers of rock separating the shale from groundwater. Still, the EPA had been studying one (relatively shallow) well in Wyoming where chemicals appeared to have seeped into the water.

Wastewater pollution: A separate issue is what happens with all that water after it has been used to crack open shale and is pumped back up to the surface. The oil and gas industry produces billions of gallons of this murky wastewater each year, which typically contains chemicals that were added for the fracking process.

In many states, this wastewater is pumped back underground into separate "injection wells." But when there aren't enough injection wells available, the water is either stored in tanks and holding ponds or sent off to treatment plants. That raises the risk of either accidental spills or improper treatment. In 2013, three treatment plants in Pennsylvania were fined for dumping waste into the Allegheny River.

Air pollution: Once an area of shale has been fracked, natural gas begins flowing up out of the well. Most of this methane is typically captured, but some of it can escape into the air or leak out of pipelines — and methane is a potent greenhouse gas, heating the planet.

Separately, another report found that certain chemical gases such as benzene can escape into the air, posing health risks for nearby residents in Colorado. In 2012, the EPA began requiring oil and gas companies to limit these emissions and capture the escaped gas.

What chemicals are used in fracking?

Oil and gas companies typically add chemicals to the water used for fracking. Those chemicals can help decrease friction or prevent corrosion and so forth. They typically make up about 0.5 percent to 2 percent of the fluid volume.

Different operations require different chemicals, but all told some 2,500 different fracking chemicals have been identified. A good list can be found here. Some of the additives used are quite ordinary, including salt and citric acid. Others, like benzene, are toxic. (One congressional investigation identified at least 650 toxic additives that have been used.)

It can sometimes be difficult to get a full list of chemicals used. Many fracking companies are now listing the compounds they employ on their websites, and some states like Texas have public disclosure laws, but these rules can vary from state to state.

Does fracking use a lot of water?

Fracking requires a lot of water to crack open the shale rock. A typical well can use between 2 million to 7 million gallons over the course of its lifetime.

How much is that all together? In 2011, water used for shale wells represented about 0.3 percent of all US freshwater consumption. But the percentages can vary by region — in Texas, it's about 1 percent.

That raises the question of whether it can stress local water supplies. In dry regions of Texas or Colorado, fracking operations can put a fair bit of stress on local water sources. But that's not universal. In the Marcellus region in the East, by contrast, studies have found that there's no danger of a water shortage.

How is fracking regulated in the United States?

Fracking is currently regulated by the states, who have very different rules on everything from the disclosure of chemicals to wastewater treatment to well casings.

You can find a number of useful maps showing the state of play for different fracking regulations at Resources for the Future. This map, for instance, shows how different states regulate the injection of wastewater underground. Missouri has no regulations, whereas North Carolina has a statewide ban:

One major issue is whether the US federal government should get more involved in fracking regulations. Currently, the Environmental Protection Agency has issued rules requiring oil and gas companies to limit air pollution from fracking operations, and it is currently studying groundwater contamination. But, for now, the feds have tread lightly. And Congress has exempted fracking from certain provisions of the Clean Water Act.

Some states and localities, meanwhile, have proposed blanket bans on fracking. New York state, for instance, has had a moratorium since 2010. Here's a longer list of regulations in the United States.

Can fracking cause earthquakes?

Fracking itself has rarely been linked to earthquakes (though Ohio is investigating this). But the disposal of all the wastewater used in fracking has been known to cause tremors.

Once a well is fracked, there are thousands of gallons of wastewater left over. Companies often dispose of that chemical-laced water by pumping it into separate underground "injection wells." As the water pressure builds up in those wells, that can shift rocks around. If those rocks lie near a geologic fault, that could trigger a tremor. At least, that's the theory.

One study by the U.S. Geologic Survey found that earthquakes were on the rise in areas where wastewater injection was increasing. A follow-up study found that wastewater injection likely caused a 2011 earthquake in Oklahoma.

It's worth noting that not all injection wells are associated with earthquakes, and many of these events were minor tremors. Still, there are plenty of questions about whether these earthquakes could get stronger as fracking expands.

How much oil and gas does the US have?

As of 2011, the United States had 220 billion barrels of oil and 2,203 trillion cubic feet of natural gas that was "technically recoverable."

This is oil and gas that we currently have the technology to access. But that doesn't mean we'll actually extract all that oil and gas. A lot depends on economic conditions. If prices go higher, then it will become more profitable for companies to drill for more oil and gas. But if prices fall, it becomes less profitable and they might just leave it in the ground.

That's why many analysts focus on a different measure, known as "proved reserves" — the stuff we could recover given existing technology and economic conditions. By that measure, there are 29 billion barrels of oil and 348.8 trillion cubic feet of natural gas available.

To put that all into perspective, the United States consumed about 7 billion barrels of oil and 26 trillion cubic feet of natural gas in 2012. So that means we have anywhere from a 13 years' supply of natural gas to an 84 years' supply. It all depends.

What do we use oil and gas for?

Lots of things. About 93 percent of the fuel we use for transportation comes from oil. And natural gas is currently used to provide about one-third of the nation's electricity. Here's a more precise breakdown:

Oil: The U.S. currently consumes about 15 million barrels of crude oil each day — after it's processed by oil refineries. Roughly 87 percent is turned into fuel for cars, trucks, and airplanes. Some of the oil is refined into home heating fuel. The rest is used for a wide array of industrial purposes (to make chemicals, paints, plastics, greases, asphalt, and so forth).

Natural gas: The United States consumed about 25 trillion cubic feet of natural gas in 2012. About 36 percent of that was used to generate electricity at power plants. Another 28 percent was used to heat homes and buildings. And the rest was used for various industrial purposes (generating electricity or heat to help produce everything from steel to paper to food).

What's the debate over US oil and gas exports?

For the past few decades, the United States has been a major importer of oil and natural gas. But thanks to the fracking boom, the country is now in a position to sell some of its newfound abundance to other countries. But that would require changing certain laws — and doing so is controversial.

Natural gas: If companies want to ship natural gas to other countries, they need to get a permit from the Department of Energy to do so (they get one automatically if the United States has a free trade agreement with that country). More and more companies are applying for export permits these days and building shipping terminals.

Opponents of these plans say that increased exports could lead to increases in the price of natural gas for Americans, hurting consumers and domestic manufacturers. See here for more detail.

Oil: Ever since the 1970s, it has been illegal for companies to export crude oil abroad (with a few exceptions). In the wake of the fracking boom, many oil companies want to revise these laws, claiming that these restrictions are depressing prices and hurting their business. Opponents of exports argue, among other things, that this could raise gasoline prices for some drivers in the Midwest. See here for more detail.

Can the US become independent from foreign oil?

Not likely — in part because "oil independence" is a bit of a myth.

Right now, the United States imports 40 percent of the oil that it consumes. That number is expected to shrink to about 32 percent in the decades ahead, thanks to increased production and the fact that we're driving more efficient vehicles. But it still means plenty of imports:

Even if we could reduce our imports all the way to zero, however, the United States still wouldn't be totally independent of foreign countries. That's because oil prices are set on the global market. So instability in the Middle East or rapid growth in China would still drive up global oil prices — leading to price spikes here in the United States.

Can natural gas help tackle global warming?

In theory, yes — though there are large caveats here.

Natural gas is a fossil fuel, and when we burn it for electricity, we produce carbon-dioxide emissions that contribute to global warming. But natural gas is much cleaner on this score than coal is, producing just half the carbon dioxide per unit of energy. So when we replace coal with natural gas, we're contributing somewhat less to global warming.

That's what's happening in the United States. The glut of cheap shale gas has persuaded many electric utilities to switch from coal to natural gas. That was one reason why U.S. carbon-dioxide emissions fell 10 percent between 2005 and 2013 (the recession and increased efficiency also helped).

There's a catch, however: The whole process of fracking for and transporting natural gas can lead to emissions of methane, another potent greenhouse gas. No one's quite sure how big those methane leaks are — there's a lot of disagreement among researchers. But those leaks could potentially undermine the climate benefits of natural gas, unless companies find ways to fix them. Here's a rundown of potential fixes.

In the long run, however, natural gas is still a source of greenhouse-gas emissions, and efforts to avoid drastic global warming will likely require the world to sharply curtail its use of gas in the next few decades. So natural gas, by itself, isn't a solution for global warming. (See here for more detail on this.)

Do other countries use fracking?

A few countries have been using fracking for some time — particularly Canada. But shale fracking hasn't yet caught on anywhere the way it has in the United States.

Plenty of countries abroad have their own shale gas and shale oil resources. That includes China, which appears to have nearly twice as much shale gas underground as the United States does:

But fracking has been slow to spread overseas, for a variety of reasons. Some countries, like France and the Netherlands, have banned fracking for fear of water contamination. Others, like Austria, have such strict regulations that drilling is uneconomical.

Even countries in favor of fracking have seen sluggish progress, in part because working with shale can be extremely difficult and complicated. In Poland, there's still plenty of work that has to be done to understand the region's geology. And, in China, the spread of fracking has been hampered by a variety of factors — complex geology, a dearth of water supplies in key regions, and a burdensome layer of regulations that hamper innovation.

You didn't answer my question!

This card stack is very much a work in progress. It will continue to be updated as events unfold, new research gets published, and fresh questions emerge.

So if you have additional questions or comments or quibbles or complaints, send a note to Brad Plumer: brad@vox.com.

What else should I read about fracking?

The US Energy Information Administration's website has a wealth of detail on the USoil and gas industry. You can find the answer to most questions about production or consumption there.

The International Energy Agency's report on "Golden Rules for a Golden Age of Gas" offers a comprehensive overview of fracking issues around the world, as well as a guide to questions about pollution and regulation.

Carl T. Montgomery and Michael B. Smith of NSI Technologies have written a nice, readable history of hydraulic fracturing.

ProPublica has constant coverage of various pollution issues related to fracking in the United States.

How have these cards changed?

This is a running list of substantive updates, corrections, and additions to this card stack. These cards were last updated on April 10, 2014. Here is a summary of edits: