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 is carried out vertically or, more
commonly, by drilling horizontally to the rock layer. The process can create
new pathways to release gas or can be used to extend existing channels.
What are the advantages of fracking?
Fracking allows drilling firms to access
difficult-to-reach resources of oil and gas. In the US it has significantly
boosted domestic oil production and driven down gas prices. It is estimated to
have offered gas security to the US and Canada for about 100 years, and has
presented an opportunity to generate electricity at half the CO2 emissions of
coal.
The industry suggests fracking of shale gas could
contribute significantly to the UK's future energy needs. A report by the
Energy and Climate Change Committee in April said shale gas in the UK may help
to secure energy supplies, but may not bring down gas prices.
Shale gas is
natural gas trapped in impermeable shale rock, as opposed to conventional
natural gas deposits, which are trapped below a layer of impermeable rock.
Therefore simply drilling down to it is not enough. The rock has to be cracked
open at high pressure or ‘fractured’ to get the gas out. Fracking involves
drilling up to around 2,500 metres vertically, then laterally out for 1,000
-3,000 metres. The gap between the borehole liner and the surrounding rock is
then sealed up with concrete. The well casing is perforated to allow fracking
fluid to get into the rock, and gas to get out. Then, on a typical well, up to
10 million litres of water containing lubricating fluids and other additives,
and sand, are pumped into the borehole under extremely high pressures. This
opens up cracks in the shale for up to 50 metres. The cracks are kept open by
the sand particles when the pressure is released, so the shale gas can escape.
A well head is then installed to capture the released gas. The drilling and
fracking equipment is then taken away.
Risks:
Contaminating groundwater (methane dissolves in the aquifer)
Release of greenhouse gases: methane
Very large consumption of energy
Improper or insufficient cement casing leads to methane
leaks
More than 750 chemicals are used:
-they
reduce friction and shorten drilling time
-increase
the viscosity and serve as antibacterial agents
Fracturing fluids remaining underground have the potential
to migrate into shallow ground water sources over time
What is
Fracking?
Fracking is
shorthand for hydraulic fracturing, a type of drilling that has been used
commercially for 65 years. Today, the combination of advanced hydraulic
fracturing and horizontal drilling, employing cutting-edge technologies, is
mostly responsible for surging U.S. oil and natural gas production.
Hydraulic
fracturing involves safely tapping shale and other tight-rock formations by
drilling a mile or more below the surface before gradually turning horizontal
and continuing several thousand feet more. Thus, a single surface site can
accommodate a number of wells. Once the well is drilled, cased and cemented,
small perforations are made in the horizontal portion of the well pipe, through
which a typical mixture of water (90 percent), sand (9.5 percent) and additives
(0.5 percent) is pumped at high pressure to create micro-fractures in the rock
that are held open by the grains of sand. Additives play a number of roles,
including helping to reduce friction (thereby reducing the amount of pumping
pressure from diesel-powered sources, which reduces air emissions) and prevent
pipe corrosion, which in turn help protect the environment and boost well
efficiency.
