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How does fracking work?

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Quick answer

Fracking is a way of releasing gas or oil trapped in dense shale rock. After drilling down and then sideways through the shale, crews pump water mixed with sand and chemicals into the well at very high pressure. This cracks the rock, and the sand holds the cracks open so fuel flows out.

Fracking, or hydraulic fracturing, works by pumping water, sand and small amounts of chemicals down a well at very high pressure to crack open dense shale rock deep underground. The sand props the new cracks open so trapped natural gas or oil can flow into the well and up to the surface.

Step by step

  1. A rig drills a vertical well one to three kilometres deep, then curves it to run horizontally through shale.
  2. Steel casing is cemented in place to seal the well from surrounding rock layers and groundwater aquifers.
  3. Perforating guns fire small shaped charges that punch holes through the casing and cement into the shale.
  4. High-pressure pumps force water, sand and additives through the holes, cracking the rock in stages along the well.
  5. Pressure is released, flowback water returns to the surface, and gas or oil flows through the sand-propped fractures.

Key things to understand

  1. Shale holds natural gas and oil in tiny pores that are too poorly connected for the fuel to flow out by itself.
  2. Operators drill down one to three kilometres, then turn and drill horizontally along the shale layer for long distances.
  3. Steel casing and cement line the well, and perforating charges punch holes through them into the surrounding rock.
  4. Fluid that is mostly water, with sand and small chemical additives, is pumped in fast enough to split the rock.
  5. When pumping stops, sand grains hold the fractures open, letting gas or oil flow back through the well to the surface.

Labelled diagram

  1. Wellhead

    Surface pumps inject high-pressure fluid and later collect returning gas or oil.

  2. Vertical well

    Cased and cemented borehole descending one to three kilometres to the shale.

  3. Horizontal section

    Runs sideways through the shale layer so more rock touches the well.

  4. Fractures

    High-pressure fluid splits the shale into networks of thin cracks.

  5. Proppant sand

    Grains wedge the cracks open so trapped fuel can flow out.

How a fracked well reaches gas in shale

Real-world examples

  • The Marcellus Shale under Pennsylvania became one of the largest natural gas sources in the United States.
  • Texas's Permian Basin produces large volumes of oil from horizontally drilled, fractured wells.
  • Fracking near Blackpool, England, was halted in 2019 after it triggered tremors felt by residents.
  • India's ONGC has drilled exploratory shale gas wells in the Damodar and Cambay basins.

Common mistake

✗ Myth: Fracking is just another word for drilling a gas well.

✓ Fact: Fracking is one stage that happens after a well is drilled and cased. It is the high-pressure injection that cracks the rock, and many conventional wells never need it.

People also ask

How does fracking get gas out of rock?
Shale traps gas in tiny, poorly connected pores. Fracking pumps water, sand and additives down a horizontal well at pressures high enough to split the rock. The new cracks connect many pores, and sand keeps them open, so gas can flow along them into the well and rise to the surface.
What chemicals are used in fracking?
Fracking fluid is mostly water and sand, with chemicals usually making up well under 2 percent. Additives can include friction reducers, gelling agents to carry sand, biocides to stop bacteria growing, scale inhibitors and acids to clean perforations. Many regions now require companies to disclose the substances they use.
Is fracking banned in the uk?
England paused fracking in 2019 after tremors at a Lancashire site, briefly lifted the pause in 2022, then reinstated it weeks later. Scotland and Wales have policies opposing it. No shale gas is currently commercially produced in Britain, and the rules depend on future government decisions.
Why is sand added to fracking fluid?
The sand acts as a proppant. Once the pumping pressure is released, the rock tries to close the fractures, and the sand grains wedge them open, leaving permeable pathways along which gas and oil can keep flowing.
Does fracking cause earthquakes?
Fracturing itself usually creates only tiny tremors, but it has occasionally triggered felt quakes on existing faults. Larger induced earthquakes, such as those in Oklahoma, have mainly been linked to disposing of large volumes of wastewater in deep wells.
What happens to the water after fracking?
Part of the injected fluid returns to the surface as flowback, mixed with salty, sometimes radioactive water from the rock. It is stored, treated, recycled for further wells, or injected into deep disposal wells, and spills are a key environmental risk.
Why is fracking controversial?
Critics point to heavy water use, possible groundwater contamination from faulty wells, methane leaks, induced earthquakes, truck traffic and continued fossil-fuel emissions. Supporters cite cheaper gas and energy security, and rules vary widely between countries.

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