Coal seam gas
Coal seam gas (CSG) is a type of unconventional gas. It is a natural gas, consisting primarily of methane, which is found in coal deposits.
Coal seam gas collects in the coal seams by bonding to the surface of coal particles. The coal seams are generally filled with water, and it is the pressure of the water that keeps the gas as a thin film on the surface of the coal.
CSG is extracted through wells drilled into coal seams. The initial phase of CSG production usually involves the extraction of water from the coal seams in order to reduce the pressure and release gas from the coal.
If the pressure within the seam is high, the gas may flow to the surface unaided. Conversely, the gas may have to be pumped to the surface if the pressure is lower.
When CSG comes to the surface, water in the gas is separated.
The water is then treated to ensure it meets water quality standards, before it is injected into underground water systems, called aquifers, used for other purposes such as irrigating crops, watering livestock or for commercial use, for water supplies or added to watercourses.
CSG in use
CSG has been used safely to power Queensland homes for the past 15 years.
It is used in the same ways as natural gas including fuelling natural gas appliances, such as heaters and stoves, and generating electricity.
Electricity generated from CSG is a cleaner energy source as it produces around half the emissions of electricity generated by coal.
LNG is simply CSG that has been cooled to minus 161°C so it becomes a liquid, reducing it to 1/600 of its original size so it is able to be transported safely and economically to Queensland’s export markets.
Queensland’s CSG reserves will provide the basis for the developing LNG industry which will become one of the state’s major exports.
Read more about the LNG industry.
Other unconventional gas
There are other types of unconventional gases which are referenced by the type of reservoir from which they are extracted. For example, shale gas is found in shale deposits and tight gas is found in relatively impermeable geological formations.
Shale gas and tight gas refer to natural gas that has been trapped in low-fracture, low permeability formations that generally do not have a natural flow. These formations are located below 2,000 metres, much deeper than CSG resources.
Specialised technologies are needed to produce gas from these kinds of reservoirs such as directional drilling and hydraulic fracturing. The use of horizontal drilling technology also allows for multiple wells to be drilled from one well pad which can reduce the surface footprint.
The development of shale and tight gas resources is in its infancy in Australia. Whilst Queensland has these resources, activities are generally at the exploration stage.