The Pennsylvania Guide to Hydraulic Fracturing, or "Fracking"

Background

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Susan Phillips / WHYY

Drill rig in Susque­hanna County Pennsylvania

Hydraulic frac­tur­ing or “frack­ing” is a tech­nol­ogy used to extract nat­ural gas that lies within a shale rock for­ma­tion thou­sands of feet beneath the earth’s surface.

Com­bined with another tech­nique called “hor­i­zon­tal drilling,” nat­ural gas com­pa­nies are able to drill for pre­vi­ously untapped reserves. Hor­i­zon­tal drilling allows one sur­face well to tap gas trapped over hun­dreds of acres. Once the con­ven­tional ver­ti­cle drill hits the shale for­ma­tion, it turns hor­i­zon­tally in sev­eral direc­tions, much like the spokes of a wheel. The well is then cased with steel and cement. Explo­sives are places at inter­vals along the hor­i­zon­tal sec­tion of the well to per­fo­rate the steel cas­ing. Under very high pres­sure, a com­bi­na­tion of water, sand and chem­i­cals is sent deep into the earth to cre­ate cracks and fis­sures in the shale rock. Those fis­sures are held open by the sand, allow­ing the nat­ural gas to flow through those cracks, into the well bore and up to the surface.

Click on the image to the left to view Penn State Pub­lic Broadcasting’s inter­ac­tive web­site explain­ing the hydraulic frac­tur­ing process.

Indus­try says the process is safe and does not pol­lute drink­ing water sup­plies. But a grow­ing move­ment of envi­ron­men­tal­ists, sci­en­tists and res­i­dents worry that the chem­i­cals used in the frack­ing process will leak into aquifers. Waste­water from the process returns to the sur­face con­t­a­m­i­nated with some of those chem­i­cals, as well as buried salts and nat­u­rally occur­ring radioac­tive mate­r­ial. That waste­water needs to be treated, or buried in con­tain­ment wells.