General coal seam gas frequently
asked questions
December 2011
What is coal seam gas (CSG)?
Coal Seam Gas (CSG), or coal bed methane (CBM)
as it’s sometimes known, is a form of natural gas,
typically extracted from coal seams at depths of
300‑1000 metres. It is a colourless, odourless, mixture
of a number of gases, but is mostly made up of methane
- it’s usually more than 95 per cent pure methane.
CSG was made over 200 million years ago when coal
was being formed, and has been held in the coal since
then by water pressure. To get at the gas you first need
to remove the water. This reduces the pressure in the
coal seam enabling the gas to flow.
What is the difference between CSG and
conventional natural gas?
There are different forms of natural gas and
they are generally called either conventional or
unconventional gas.
Conventional natural gas and CSG are chemically similar.
CSG is almost pure methane; conventional natural gas is
around 90 per cent methane with ethane, propane and
butane mostly making up the remainder.
The main difference between conventional natural
gas and CSG is the type of reservoir from which they
are produced.
Conventional natural gas reservoirs largely consist of
porous sandstone formations capped by impermeable
rock. The gas is stored in the sandstone at high
pressure and so can flow to the surface, through
production wells, at a high-flow rate, often without the
need to pump.
CSG is contained in the fine structures or natural
fractures of coal seams. Movement of CSG to the
surface through gas wells normally requires extraction
of formation water through natural or induced
fractures in the coal. Water extraction reduces the
pressure in the coal seam, allowing methane to be
released from the coal. Over time, water production
decreases and gas production increases from
each well.
What is the difference between
underground coal gasification (UCG),
CSG, shale and tight gas production?
CSG, shale and tight gas are different types of
unconventional natural gas.
Coal seam and shale gas are found in different types
of geological systems. Coal seam gas is found in
systems containing coal and the gas is contained
within fine structures and fractures in the coal. Shale
gas is generally extracted from clay-rich sedimentary
rock and the gas is either contained within fine
structures in the rock or can exist as gas bubbles in
the pores of the rock. Tight gas exist in rock pores
that have very low permeability and can only migrate
through it with great difficulty.
UCG occurs where gas is not readily available, but
can be created by the combustion of coal to make a
synthetic gas, which is commonly known as syngas
and is made up of carbon monoxide, hydrogen
and methane. The conversion of coal into synthetic
gas takes place underground, where the coal was
originally found.
CSG is often called an unconventional natural gas,
because it’s not stored in these ‘conventional’
sandstone reservoirs.
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What can CSG be used for?
Is CSG a cleaner fuel source?
Similarly to natural gas, CSG can be used in
household stoves, heaters and hot water systems.
It can also be used for industrial processes and for
electricity generation.
To date, the best available data on the greenhouse
gas (GHG) footprint of CSG suggests that is likely to
be a less GHG-intensive source of energy for electricity
production than coal, by approximately 15-50 per cent.
In other words, it’s estimated that for a given amount
of electricity production, CSG will create approximately
15‑50 per cent less GHG emissions than coal.
Specifically:
•Coal seam gas accounts for almost 10 per cent (9 per
cent) of Australia’s gas production, and is used to
generate about 6 per cent of Australia’s electricity.
•In Queensland, 90 per cent of the gas used in homes
and industry is coal seam gas, and over 25 per cent
of Queensland’s electricity is generated using coal
seam gas.
•Queensland’s production of CSG first exceeded that
of conventional natural gas in 2002 – it’s now ten
times that of conventional natural gas.
It is important to note that these data are based
on comparative studies, not direct measurements.
Direct measurements are useful because the GHG
footprint from gas or coal depends on the particulars
of each individual resource asset, the way that it’s
managed and the final use of the fuel. A greater
understanding of the situation for Australia requires
further research.
•CSG has been a growing part of the nation’s energy
supplies since 1996.
•It’s estimated that up to 80 per cent of Queensland’s
coal seam gas may be exported, where it’s most
likely to be used to generate electricity.
How much CSG is there?
Australia in general and Queensland in particular has
large reserves of coal seam gas.
The known reserves keep growing because the more
you look the more you tend to find.
Proven and probable reserves comprise 28,000 PJ.
That’s enough to meet Queensland’s existing electricity
needs for about 50 years.
The possible reserves may be as great as 300,000 PJ.
That’s enough to meet all of Queensland’s current
electricity generation needs for 500 years, or those of
Australia for about 120 years.
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