Fracking is a process of drilling sideways deep underground, then injecting fluid at high pressure to fracture shale (a kind of sedimentary rock) or coal formations releasing natural gas or oil trapped within.
Fracking is short for horizontal high-volume slickwater hydraulic fracturing. In the past such fracturing was only practised on
vertical wells.
Shale gas – natural gas trapped within shale formations.
Tight gas – retrieved from rocks of extremely low permeability, sandstone and limestone.
Coal seam gas (CSG) or coal bed methane (CBM) – natural gas extracted from coal beds.
Tight oil – oil from shale formations. Not usually called shale oil in order to avoid confusion with ‘oil shale’ (or kerogen, a substance requiring heating to be turned into fuel).
Potential problems
- Wastewater can release toxic volatile organic compounds (vocs) on evaporation.
- Escaping methane and vocs.
- Drilling rig 35 metres high.
- Lung-damaging ozone pollution when truck fumes mingle with vocs.
- 400 tanker trucks per site, carrying water and supplies.
- A single frack pad can drill up to 16 wells extending horizontally in different directions underground.
- Each drilling site is the size of a football field and is cleared of vegetation. Fracking areas are dotted with drilling sites – a 1,000 site spread is not uncommon.
- Aquifer - Any leakage could cause serious contamination.
- Casing of steel (malleable) surrounded by cement (rigid). Critics point out the combination cannot have the permanency claimed by industry. Industry claims casing failure rates of under 1%; independent researchers 6-7 %. In the long run, all casings will fail.
- Methane gas and toxic chemicals can contaminate the water supply.
- Frack fluid rises again, now mixed with heavy metals (like lead and arsenic) and radioactive substances leached from the rocks. Methane concentrations are 17 times higher in drinking-water wells near frack sites.
- Frack fluid pushed in great volumes at high pressure to crack the gas-bearing shale.
- Punctured casing allows fluid to burst through.
- Natural gas is released from the cracked rock.
How a well is fracked
- A huge rotary drill bores down from a frack pad to depths of 1.5 to 3 kilometres (though there are proposals to allow fracking at shallower depths). When it hits the gas or oil bearing shale it continues horizontally for a further kilometre or more.
- The uppermost parts are cased with cement and steel. The horizontal bore has a steel casing down which small explosive charges are set off by a perforating gun in order to punch holes.
- Now flush millions of litres of frack fluid – a slurry of water, sand and chemicals – under great pressure into the bore to make hairline cracks in the rock. The sand keeps the cracks propped open.
- The fluid is pumped back up for several days to open the bore to allow the gas or oil to flow up. Between 40% and 70% of the fluid stays behind.
- Each well can be fracked 10 times if required.
- For gas, cap the well until a pipeline is in place. For oil, fill up tankers.
- Now start on the next well from the same pad, extending in a different direction, and repeat the process.
- Non-productive wells are closed off by inserting cement plugs.
- Disposal of recovered frack fluid is a headache.
- Best practice is to reuse it. But often it is off-loaded on ill-equipped municipal treatment plants or even surreptitiously dumped.
- Frack fluid remaining in wells is freshwater contaminated with chemicals and effectively removed from the water cycle – millions of litres per well.
Slickwater – what’s in frack fluid
- 98.5% water
- 1% sand
- 0.5% chemicals
In the US over 600 chemicals have been tracked down by independent researchers – companies don’t disclose what they use. Known toxins, including carcinogens and neurotoxins, are among them.
Chemicals are used to reduce friction (that’s why it’s called slickwater); also acids, rust and scale inhibitors, anti-microbials, gelling agents and solvents.
If, say, 10 million litres of water are used to frack one well, then that makes 50,000 litres of chemicals. For a 1,000-well field, the amount of chemicals used is staggering, even allowing for recycling of frack fluid. Which is why industry is making promises (outside the US) of greatly reduced chemical use and even chemical-free fracking.
