Coal seam gas
What is coal seam gas?
Coal seam gas (CSG) is a natural gas which is mainly composed of methane. It is found in underground coal seams which are generally located 200 to 1,000 metres below the surface.
How does it form?
CSG is a by-product of ancient plant matter that has formed under pressure over millions of years by the same natural processes that produce coal. The gas collects by bonding to the surface of coal particles in the fractures or ‘cleats’ of underground coal seams. A combination of water and ground pressure traps the gas below the surface.
How is it extracted?
To extract the gas, wells about the diameter of a dinner plate are drilled down, through the geological layers into the coal seams. After the hole is drilled to the required depth, a steel casing is installed and cement is pumped to fill the space between the casing and the well bore. When the cement hardens, it provides a barrier between the extraction zone and the surrounding geological area. The wells enable some of the water contained within the seams to be pumped to the surface. This pumping reduces the groundwater pressure, allowing the gas to flow up the wells.
A CSG well site, when in operation, covers a fenced area that is typically half the size of a netball court. During the construction phase, a larger area is cleared to provide access for drilling rigs and other equipment. Once in operation the land around a well site can be used as it previously was for grazing and cropping.
If the coal seams are not highly permeable, meaning that they do not allow water and gas to flow freely, they can be hydraulically fractured (this involves pumping into the coal seams a mixture made up predominantly of water and sand with a small amount of approved chemicals) to increase the rate of gas flow from the coal seams. Both the gas and associated water are extracted via the CSG well.
At the surface they are separated and pumped to relevant treatment facilities via separate pipelines. The CSG is pumped to a gas processing facility where any remaining water is removed. Once completely dry the gas is compressed and then transported via high pressure pipeline to residential, industrial and commercial customers.
The water is sent to a water treatment facility where it is treated via filtration and reverse osmosis to remove dissolved salts and impurities. This treated water can then be applied to beneficial uses such as replenishing aquifers, provision to land holders for irrigation and release into waterways.
What is it used for once extracted?
CSG is used to supply residential, commercial and industrial gas customers, as well as being used as a fuel for gas-fired power stations. Origin currently owns and operates a number of gas-fired power stations across Australia. The Darling Downs Power Station, which is a combined cycle gas-fired power station, is one of the cleanest baseload power stations in Australia in terms of carbon emissions.
Today, CSG provides over 90% of Queensland's gas needs and 15% of the state's electricity generation.
CSG can also be transformed to Liquefied Natural Gas (LNG) through cooling and pressurisation. LNG is expected to become a major new export commodity for Queensland and has the potential to provide countries in Asia with cleaner sources of energy.
Origin’s CSG operations
Origin has interests, in its own right and through joint ventures, in CSG reserves located in the Bowen, Surat and Galilee Basins in Queensland, Australia. It wholly owns the following CSG assets in Queensland:
Origin is also a joint venture partner in Australia Pacific LNG with ConocoPhillips and Sinopec. Australia Pacific LNG holds Australia's largest CSG reserves and is the leading producer of CSG in Australia.
Origin operates the following Queensland CSG facilities on behalf of Australia Pacific LNG:
- Spring Gully
Origin also has interests in the Fairview and Kenya gas processing facilities.
-161°C. CSG is turned into LNG so it can be shipped offshore.