The ins and outs of fracking
Hydraulic fracturing, or “fracking,” is a method of extracting oil and gas deposits that are inaccessible by conventional drilling. Fracking has become increasingly common over the past decade and is largely responsible for the current energy boom in the United States.
A well is drilled in an oil and gas basin. Wells are drilled several thousand feet down to reach a shale formation and then extend horizontally to penetrate as much of the shale as possible with a single well.
After the well is drilled a perforating gun with explosive charges is lowered by wire to the rock formation.
The perforating gun sets off charge that pierces pipe, creating tiny fractures within the shale rock.
3 million to 6 million gallons (11 million to 23 million liters) of water are trucked to the well site.
Mixture of water, sand and chemicals is pumped into the well.
Water mixture is pumped into well under extremely high pressure and in huge quantities.
The force of water creates fissures in the oil- or gas-bearing shale. Rock can take days to crack.
Sand flows into the fissures to prop them open so that the oil or gas from the shale can be released.
Oil or gas flows up and out of the well along with much of the water used to pressurize the well.
The water is separated from the oil or gas and is stored to be trucked away, treated or injected deep underground in disposal wells.
The gas or oil is stored for delivery to refineries or markets.
What's in the fracking water?
The mix of the chemical cocktail depends on the driller and the well, but often includes
- Hydrochloric acid Used at start of fracking to dissolve debris
- Ethylene glycol Helps stabilize the mixture (used in antifreeze)
- Glutaraldehyde Kills bacteria in pipe
- Potassium chloride Reduces friction so water flows faster
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Sources: McClatchy-Tribune, ProPublica, FracFocus, Dallas Morning News, McClatchy Washington Bureau
©MCT2013
Graphic: Mitchell Brooks, The Sacramento Bee, and Danny Dougherty, McClatchy Washington Bureau