Natural gas is retrieved from underground shale deposits through a process called hydraulic fracturing (also known as hydrofracking, fracking, hydro-fracturing, or fraccing).
During hydrofracking, millions of gallons of water mixed with industrial chemicals and proppant (sand or ceramic particles) are blasted into the well bore to release natural gas. In the Marcellus Shale formation in the northeastern U.S., for example, fracking a single well can require 1 million to 5 million gallons of this water mixture.
Waste water that comes back up out of a shale gas well goes by two names: flowback and produced water. These terms are often used interchangeably, but they have slightly different meanings.
Flowback. After the hydraulic fracturing procedure is completed, pressure in the well is released. The direction of fluid flow reverses, and water and excess proppant flow back up through the wellbore to the surface. Both the process and the returned water are commonly referred to as “flowback.”
Produced water. After drilling and fracturing of a well are completed, water may come up out of the well along with the natural gas. Some of this water is returned fracturing fluid and some is water that occurs naturally in the geological formation. These produced waters move back through the wellhead with the gas.
The amount of flowback and produced water varies greatly among wells, and not all shale formations produce a lot of water. Two that apparently are producing little or no water are the Lewis, mostly in the San Juan Basin of New Mexico and Colorado, and the Fayetteville in Arkansas.