Hydraulic fracturing — almost always shortened to fracking — is the process of pumping fluid into a rock formation at pressures high enough to crack it. Once the rock fractures, a granular material called proppant (usually frac sand) is carried into the cracks so they stay propped open after pumping stops. Those open fractures create pathways that let oil and natural gas flow toward the wellbore.
Fracking is what unlocked the U.S. shale boom. Many of the most valuable hydrocarbon resources are trapped in low-permeability rock such as shale, where the oil and gas cannot move easily on their own. Drilling a well into that rock isn't enough — without stimulation it would barely produce. Fracking, paired with horizontal drilling, makes these formations economic.
Frac fluid is roughly 98–99% water and sand. The remaining 0.5–2% is a small number of chemical additives — typically 3 to 12 of them — each with a specific job such as reducing friction or killing bacteria.
Why fracking is needed
In a conventional reservoir, oil and gas have already migrated out of the source rock into a porous, permeable trap. The fluids flow readily, and a simple vertical well can produce them. Unconventional reservoirs — shale and tight formations — are different: the hydrocarbons are still locked inside the dense source rock itself. The rock holds plenty of oil and gas, but its permeability is so low that the fluids cannot move to the well without help.
Hydraulic fracturing solves that problem by manufacturing permeability. By cracking the rock and propping the fractures open, operators create a network of flow paths connecting the reservoir to the wellbore. Combined with a long horizontal lateral that exposes thousands of feet of pay zone, fracking turns rock that was once considered uneconomic into productive wells.
What actually happens downhole
A modern frac job is done in stages along a horizontal well — often 30 to 60 or more. For each stage, crews perforate the casing to open a section of reservoir, then pump frac fluid at high pressure to crack the rock, follow it with a proppant-laden slurry, and finally release the pressure so the proppant holds the new fractures open. Then they isolate that stage and move to the next.
The induced fractures are typically tens to a few hundred feet tall — not thousands. In most plays they occur thousands of feet below any drinking-water aquifer, separated by layers of impermeable rock and protected by cemented steel casing. Documented groundwater incidents are usually traced to surface spills or faulty well cementing, not to fractures reaching aquifers.
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Frequently asked
No. Drilling creates the wellbore; fracking is a separate completion step done after the well is drilled and cased. Fracking stimulates the rock so it will produce, while drilling simply makes the hole.
Roughly 98–99% of frac fluid is water and sand. The rest is a handful of additives such as friction reducers, biocides, scale and corrosion inhibitors, gels and surfactants. In the U.S., operators disclose the additives used on each well through FracFocus.
Fractures are created thousands of feet below aquifers and separated from them by impermeable rock and cemented casing. The contamination cases that have occurred are generally linked to surface spills or poor cementing, not to the fractures themselves.