What Is Fracking?

Fracking, the colloquial shorthand for hydraulic fracturing, is a well-stimulation technique in which a high-pressure fluid mixture is injected into a subsurface rock formation to create or enlarge fractures, allowing trapped hydrocarbons to flow toward a production well. The process has been applied commercially in the United States since 1947 and has been performed in more than 1.7 million wells, according to industry estimates. Its modern form, combined with horizontal drilling techniques developed in the 1980s and refined through the 1990s and 2000s, unlocked vast deposits of natural gas and oil in low-permeability shale formations that were previously uneconomical to extract. This combination drove a marked increase in domestic U.S. natural gas and oil production beginning around 2008 and reshaped global energy markets.

The technique is most commonly applied to shale and tight sandstone formations that have low natural permeability, meaning hydrocarbons cannot flow through the pore spaces without assistance. By creating networks of fractures extending outward from the wellbore, operators increase the effective drainage area of the well and the rate at which gas or oil can be recovered. The engineering challenge is to generate fractures of sufficient length and width while keeping them propped open so they do not close under the enormous compressive stresses of the surrounding rock.

The Hydraulic Fracturing Process

A hydraulic fracturing operation begins after a well has been drilled and cased with steel pipe cemented in place. The target interval is perforated with shaped charges to create pathways between the wellbore and the formation. Fracturing fluid, which consists primarily of water (typically 90 percent or more by volume) along with proppant and chemical additives, is pumped down the well at pressures sufficient to exceed the formation's fracture gradient and propagate cracks into the surrounding rock. Proppants, typically silica sand or engineered ceramic beads, are carried into the fractures by the fluid and remain behind when the fluid is recovered, holding the fractures open during production. The U.S. Geological Survey's documentation on hydraulic fracturing describes how wastewater recovery, wellbore integrity, and the potential for induced seismicity are among the key engineering and monitoring concerns associated with each well operation.

Environmental and Geological Considerations

Fracking operations generate significant volumes of wastewater, composed of the returned fracturing fluid plus formation brines that co-produce with the oil or gas. Disposal of this produced water, typically through deep injection into permitted disposal wells, has been linked to induced seismic activity in regions such as Oklahoma and southern Kansas, where disposal rates are high and subsurface geology is conducive to fault reactivation. Surface spills and improper well cementing represent pathways for contamination of shallow groundwater. The USGS research program on induced seismicity monitors seismic events near wastewater injection sites and develops protocols for operators to reduce risk. The U.S. Environmental Protection Agency's 2016 assessment found that hydraulic fracturing activities can, under some circumstances, affect drinking water resources, while emphasizing that the frequency and scale of such impacts are not yet fully characterized. The National Institute of Environmental Health Sciences page on hydraulic fracturing and health summarizes ongoing research into air quality, community health outcomes, and occupational exposures at active fracking sites.

Applications

Fracking has applications in a range of fields, including:

• Natural gas extraction from Marcellus, Barnett, and Haynesville shale formations
• Tight oil production from the Bakken, Permian Basin, and Eagle Ford formations
• Enhanced recovery from conventional oil and gas reservoirs with depleted pressure
• Geothermal energy development in enhanced geothermal systems
• Mining industry applications for in-situ resource recovery in hard rock formations