WASHINGTON -- Fracking, the controversial drilling technique that is driving America's energy boom, has been around for decades. But it was only in the last decade that the process of blasting underground rocks with water and chemicals was refined enough to deliver a long sought oil and gas bounty and stir a furious debate over its health and environmental consequences.
The fracking revolution began in an underground rock formation known as the Barnett Shale outside of Fort Worth, Texas. That's where a wildcatter named George Mitchell, the son of an immigrant Greek goat herder, began searching in the 1980s for the right cocktail of water, sand and chemicals that would crack shale a mile underground and free the natural gas trapped inside. His company finally found the formula in the late 1990s, and it took a few years after that for others in the American oil industry to catch on to the transformative power of the new techniques.
"It took a long time to get to the starting line, but once we got there it's really gone pretty fast," said Pulitzer-Prize winning author and historian Daniel Yergin.
"This is a technical triumph, what George Mitchell did," said Jim Henry, a 78-year-old drilling pioneer in Midland, Texas.
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Formally known as hydrau
lic fracturing, fracking starts with a rig on the surface drilling through layers of earth and rock to a hydrocarbon-rich rock formation, often one to two miles below the ground. Instruments guide the drilling crew to what's known as the "kickoff point" within the deep formation. That's where the crew instructs the drill bit to move sideways, drilling a horizontal shaft that can stretch thousands of feet.
That's called horizontal drilling, and it allows the rig to tap a huge area. It makes the wells far more economical than the traditional method of just drilling straight down into the earth.
Next a perforating gun with explosive charges is lowered by wire to the rock formation. It sets off a charge that pierces the pipe and creates minuscule fractures within the shale rock.
Then the fracking really starts. Between 3 million and 6 million gallons of chemical-spiked water is injected down the well to the rock formation at enormous pressure, thousands of pounds per square inch.
The force of the water is like a baseball hitting a piece of glass and shattering it, except the rock can take days to crack. Sand is sent down the pipe to prop open the paper-thin cracks.
"The fracking fluid is 99 percent sand and water and 1 percent additives," said Robert Montgomery, a production engineer in Williamsport, Pa., with Anadarko Petroleum.
Oil and gas flow through the cracks into the hole the drill has made, and pressure brings it to the surface.
The exact makeup of the chemical cocktail depends on the driller and the well. It's often protected as a trade secret. The list often includes hydrochloric acid, used at the start of the fracking process to dissolve debris.
Other common chemicals include ethylene glycol (used in antifreeze) to help stabilize the mixture, glutaraldehyde to kill bacteria in the pipe, potassium chloride to reduce friction so the water goes faster and dimethylformamide to fight corrosion.
Some polluted water rises back to the surface, at times with low levels of radiation. It can be stored in a pit or tanks, and there are increasing efforts to recycle and reuse it.
The waste is often trucked to disposal wells and injected thousands of feet underground.
Kevin Hurst, a former assistant director for energy research and development in the Obama White House, said there needs to be more research about the health and environmental impacts of the shale boom.
There is a widespread perception of the risks, but a lack of information on how likely those risks are and the consequences, said Hurst, who chaired a recent working group taking a look at what's scientifically known about fracking for the Union of Concerned Scientists.
Among the key issues is whether the chemicals contaminate groundwater. The drilling industry maintains they don't, noting that the water table is typically only a few hundred feet underground while the chemicals are injected more than a mile below the surface. Cement is used to seal the steel drilling pipe from surrounding earth and rocks, with the cement thickest at the water table.
The Environmental Protection Agency in 2011 linked fracking chemicals to groundwater contamination in central Wyoming. But this past summer the EPA withdrew from further investigation and turned the investigation over to the state of Wyoming, which had beencritical of the EPA's testing methodology and conclusions, and questioned whether the contamination came from fracking. The EPA also backed off a claim of water contamination in Texas, and closed a high-profile investigation in Pennsylvania.
Preliminary results of a Department of Energy study in western Pennsylvania found no evidence of groundwater contamination. Results of a broader EPA study aren't expected until 2016.