Hydraulic fracturing, commonly called fracking, is primarily used to extract oil and natural gas from underground rock formations that are too dense for fuel to flow through on its own. The technique works by injecting fluid at extremely high pressure to crack open rock deep below the surface, creating pathways for trapped energy resources to reach a well. Beyond fossil fuels, it also has applications in geothermal energy production and environmental cleanup.
How the Process Works
At its core, hydraulic fracturing forces open cracks in buried rock so that oil or gas can escape. A mixture of fluid, solid particles, and chemical additives gets pumped into a well at pressures high enough to fracture the surrounding rock. The fluid creates new cracks and widens existing ones, while solid particles (called proppants) wedge into those cracks to hold them open after the pressure is released. Once the fractures are propped open, oil or gas flows through them and up the well to the surface.
The fluid is mostly water, though some operations use oil, liquid carbon dioxide, or other base fluids depending on the geology. Sand is the most common proppant, but ceramic beads and resin-coated sand are used in deeper wells where the pressure would crush ordinary sand grains. Chemical additives make up a small fraction of the total fluid and serve practical roles: reducing friction so the mixture flows more easily, preventing bacterial growth that could clog the well, stopping mineral scale from building up, and stabilizing clay in the rock formation.
A single well can require anywhere from about 1.5 million to 16 million gallons of water, depending on the rock type, whether the well runs vertically or horizontally, and how many sections of the well are fractured.
Extracting Oil and Gas From Tight Rock
The most widespread use of hydraulic fracturing is pulling oil and natural gas from rock formations that have very low permeability, meaning fluids can’t pass through them easily on their own. Shale, tight sandstone, and certain coal beds all fall into this category. Without fracturing, the fuel locked inside these formations would stay put.
Shale formations are a prime example. Shale is so dense that gas molecules trapped in its pores have essentially no natural pathway to a wellbore. Horizontal drilling combined with hydraulic fracturing changed that equation dramatically starting in the 2000s, turning the United States into one of the world’s largest natural gas producers. The same combination unlocked vast reserves of tight oil in formations like the Bakken in North Dakota and the Permian Basin in Texas.
Recovering Methane From Coal Seams
Coal beds naturally contain methane, and hydraulic fracturing is used to boost the rate at which that gas can be recovered. Coal seam methane (often called coalbed methane) is held in place partly by water pressure within the coal. Fracturing the coal creates channels that allow both water and methane to drain toward the well more efficiently.
The process for coal seams typically uses simpler, lower-cost fluid systems compared to deep shale operations. In one documented operation, roughly 538 cubic meters of fracturing fluid and 25 cubic meters of sand were pumped into the reservoir at a maximum pressure of about 22 megapascals, which is considerably less intense than what deep shale wells require. The goal is the same: create enough permeability for gas to move freely to the surface.
Reviving Older, Low-Producing Wells
Hydraulic fracturing isn’t only for new wells. It’s also used to stimulate older wells whose production has dropped off or stalled entirely. Over time, a well’s output naturally declines as nearby rock depletes or as water floods the producing zone. Rather than drilling an expensive new well, operators can re-fracture the existing one to open fresh pathways and restore flow.
This approach has proven economically attractive because the cost of a fracturing treatment is relatively low compared to the revenue from renewed production. In Romania, for instance, researchers documented cases where gas wells considered finished due to flooding were brought back into production through hydraulic stimulation. Oil wells that had slowed to a trickle were similarly rejuvenated. For mature oil and gas fields around the world, re-fracturing extends the productive life of existing infrastructure rather than requiring new drilling.
Producing Geothermal Energy
A less well-known application of hydraulic fracturing is in enhanced geothermal systems, or EGS. Deep underground, rock is naturally hot, but it doesn’t always have enough water flowing through it to carry that heat to the surface for power generation. Fracturing creates artificial fluid pathways through hot rock so that water can be circulated down, heated, and brought back up to drive turbines.
The U.S. Department of Energy’s ARPA-E program has funded development of advanced fracturing methods specifically for geothermal use. One project aims to use electricity and water together to create a more extensive network of fractures, increasing the surface area where circulating water contacts hot rock. The developers estimate this approach could improve geothermal power plant efficiency by up to 500% compared to conventional methods. If scalable, EGS could turn hydraulic fracturing into a tool for renewable energy production in regions that lack natural hot springs or geysers.
Cleaning Up Contaminated Sites
A modified version of hydraulic fracturing is used in environmental remediation. At sites where soil or groundwater is contaminated, the underground material is sometimes too dense for cleanup technologies to work effectively. Fracturing the subsurface increases permeability so that techniques like soil vapor extraction, which pulls volatile pollutants out of the ground as gas, can reach contaminated zones that would otherwise be inaccessible. This application is far smaller in scale than energy production but represents a practical use of the same underlying physics.
Environmental Tradeoffs
The scale of hydraulic fracturing raises environmental concerns that are worth understanding alongside its uses. Water consumption is significant, with millions of gallons needed per well in regions that sometimes face drought. After fracturing, a portion of the injected fluid returns to the surface as wastewater, which contains both the original chemical additives and naturally occurring substances picked up from the rock, including salts, heavy metals, and sometimes low levels of radioactive material.
Disposing of this wastewater creates its own issue. Most of it gets injected into deep disposal wells, and this disposal process, not the fracturing itself, is the primary driver of induced earthquakes in areas like Oklahoma and parts of Texas. According to the U.S. Geological Survey, reports of hydraulic fracturing directly causing felt earthquakes are extremely rare. But wastewater injection wells operate for much longer periods and handle far larger volumes of fluid, raising underground pressure over wide areas and sometimes triggering seismic events that people can feel at the surface.
Surface-level concerns include the potential for spills during fluid transport, the release of methane from well sites, and the industrial footprint of well pads, roads, and pipelines in areas that were previously rural or undeveloped. These tradeoffs vary significantly by region, geology, and how carefully individual operations are managed.