Drilling companies suggest trillions of cubic feet of shale gas may be recoverable from underneath parts of the UK through a process known as “fracking”.
Hydraulic fracturing, or fracking, is a technique designed to recover gas and oil from shale rock. But how does it work and why is it controversial?
What is fracking?
Fracking is the process of drilling down into the earth before a high-pressure water mixture is directed at the rock to release the gas inside.
Water, sand and chemicals are injected into the rock at high pressure which allows the gas to flow out to the head of the well.
The process can be carried out vertically or, more commonly, by drilling horizontally to the rock layer and can create new pathways to release gas or can be used to extend existing channels.
The term fracking refers to how the rock is fractured apart by the high pressure mixture.
How does fracking work?
Fracking starts with a well (1) bored several thousand meters vertically through aquifers (groundwater rocks, 2), and then horizontally into an oil or gas deposit (3). Once the hole’s been drilled, it’s cased with a continuous steel pipe sunk down (and then sideways) the entire length of the hole, which is cemented into place to make a kind of giant “drinking straw” through which oil and gas can be extracted (4). A special perforation gun is lowered down through the pipe and small explosive charges make holes at various points so the fracking fluidcan be pumped in at high pressure, from trucks on the surface (5). This creates many small cracks in the deposit through which the trapped oil or gas can escape (6).
Although the name “hydraulic” fracturing suggests only water is used, fracking fluid actually contains three main ingredients:
- Water—anything from a few tens of thousands of gallons to millions of gallons per well, which does the fracturing.
- Proppant—gritty sand or small ceramic balls that lodge in the fractured rock, holding the cracks open so oil or gas can flow through. The water and proppant typically make up around 99 percent of fracking fluid. The yellow dots in the artwork above, at stage 6, represent the proppant.
- Fracking chemicals—including lubricating and gelling agents and antimicrobial chemicals. These help to carry the proppant and improve the quantity and quality of oil or gas recovered. They usually account for less than 1 percent of fracking fluid.
Once the rock is fractured, pumping stops, so the pressure is released. The gas or oil trapped underground flows back to the surface with some of the water and chemicals from the fracking fluid and other deposits flushed up from underground, making up what is technically called flowback. Fracking can also release what’s called produced water(“released water” might be a better name for it), which is naturally occurring water trapped in something like a shale formation. Produced water also carries trapped minerals, naturally radioactive materials, and so on. Since flowback and produced water both potentially contain toxic chemicals and flushed out salts and other harmful substances, they’re classed as contaminated wastewater. Some of this toxic mix might be reused on other fracking operations, while the rest must be treated and stored since it’s too contaminated to be released into rivers or seas.
And the bad…
fracking creates serious leaksLeaky stuffOne estimate shows that between 4 and 8 percent of shale gas leaks away of methane, a greenhouse gas which is around 25 times more powerful than CO2. Eventually methane breaks down to CO2 and water vapour, both major greenhouse gases themselves
it can cause small earthquakes
it needs vast amounts of waterTypically between 5 and 15 million litres of water per well, not good in an arid area like Texas in the USA or the Karoo in South Africa plus sand and many different chemicalsMost of the commonly-used ones are harmless but the list runs into many hundreds, many of which are toxic. The fracking companies tend to be secretive about their particular injection fluid ‘recipes’ so it’s hard to know what’s going on. The sand and chemicals aid in keeping the fractures open so the gas can come out
some of this fluid may contaminate groundwater (drinking water underground) and the waste fracking fluids — called ‘flowback’ — can cause more pollution because they bring up from deep below stuff like salt, hydrogen sulphide gas and even radioactive radium
fracking also makes it possible to get methane out of deep coal seams and can be used to extract more oil from old oilwells and oilfields. Using more fossil fuel is not good when you think about pollution and greenhouse gases
because the USA has increased its use of shale gas to generate electric power by such a large amount, it is now using much less coal. Sounds good, doesn’t it? But that coal is still being mined and sold to Europe which doesn’t have so much gas. So as carbon emissions have gone down in the US, they’ve gone up in countries like Britain and Germany which have started guzzling cheap American coal. It’s an unfortunate fact that electricity-generating companies will always burn whatever fossil fuel is cheapest. For now, shale gas is cheap in the US whilst coal is cheapest in much of Europe. So the mining of coal — the filthiest but cheapest fuel for most countries — continues to go up. This ‘law of the jungle’ where the cheapest fuel is always burned to make the cheapest electricity (never mind the pollution) is, to be fair, not entirely the fault of the generating companies. It’s that no-one wants to pay more than they have to for energy and so they look for the cheapest supply.