What’s the difference between natural gas, liquid natural gas, shale gas, shale oil and methane? An oil and gas glossary
- 23 Aug 2013, 00:00
- Robin Webster
Over the last few weeks, shale gas has shot into the
national consciousness - resulting in more discussion on the
airwaves about what, exactly, the UK's energy future is going to
look like. But it's easy to get lost in all the technical terms.
Here's our quick oil and gas glossary to help you sort your coal
bed methane from your LNG.
gas: Natural gas is a major energy source
around the world, accounting for
21 per cent of the world's energy supply in 2010.
Natural gas is an odourless, colourless gas, largely formed over
millions of years underground. It's made of a variety of compounds
(see below), but methane is by far the most significant.
Natural gas is a fossil fuel, releasing greenhouse
gases when burnt - but is less climate-polluting than coal,
half of its carbon emissions.
Typical makeup of natural gas. Source:
Unconventional gas: Unconventional
natural gas is trapped in deep underground rocks that are hard to
reach, such as shale rock or coal beds. Recent technological
advances have made it possible to get these new sources of energy
out of the ground.
Shale gas: Shale gas is extracted
from shale rock using fracking, or hydraulic fracturing, of the rock. Shale
rock is very common; the BGS estimates it makes up 35 per cent of the
world's surface rocks. It also suggests there are
1,300 trillion cubic feet of shale gas
in the north of England.
The application of the fracking process - which has
been used in the oil industry since the
mid nineteenth century - to shale gas
extraction has the potential to bring about a "a
sweeping transformation" of the energy
system around the world, according to the International Energy
Agency, as different countries develop the resource.
Methane: In the shale gas debate,
commentators sometimes make
a distinction between natural gas and methane. In fact,
as the chart above demonstrates, natural gas mostly is
When it's released directly in the atmosphere -
rather than being burnt - methane is a powerful greenhouse gas. It
25 times more climate-polluting than
carbon dioxide over a 100-year timescale. Some academics are
worried that methane
leaks during the fracking process - so
called fugitive emissions - will significantly increase the impact
of fracking on the climate.
Liquified Natural gas (LNG): In
order to feed the world's demand for natural gas, the gas needs to
be transported from where it's produced to where it's going to be
transporting gas is not that easy. LNG
is created by cooling natural gas to -160ºC,
creating a clear, colourless and non-toxic liquid, 600 times
smaller than natural gas. The
biggest exporter of LNG around the
Qatar, which sends it around the world
in enormous tankers.
Shale oil: Fracking can be used to
get not just gas out of the rock, but oil. The US-based Energy Information Administration estimates
that shale oil represents 10 per cent of the world's crude oil
resources. It's not clear how much the UK has got. The British
Geological Survey is working on a
survey of the shale oil resource in the
south of the country. But a spokesperson tells Carbon Brief it will
be "several if not many months" before the report is
Coal bed methane
(CBM): Methane occurs naturally underground within
coal reserves. It can be
extracted using a variety of
techniques. In comparison to shale gas, the amount of gas we might
get from CBM seems to be fairly small - maybe around three years of
UK natural gas supply, according to the
British Geological Survey.
Underground coal gasification (UCG):
UCG is an industrial
process where coal is converted into
gas while it's still underground. It
involves drilling boreholes into the
coal seam, injecting water and oxygen, and partially burning the
coal underground. UCG has
not been carried out in the UK since
trials in Derbyshire in the 1950s, but recently there's been an
increased interest in the technology.
UCG has the potential to open up large new areas of coal to
exploitation - a prospect that has