Accessing these reserves will provide Australia with large quantities of gas to meet domestic needs and for export to international markets. However, this access requires use of world's best practice safety, engineering and environmental standards to ensure impacts are minimised.
What is coal seam gas (CSG)?
Coal seam gas, or coal bed methane (CBM), is a form of natural gas, typically extracted from coal seams at depths of 300–1000 metres. It is a colourless, odourless, non-toxic mixture of a number of gases but mostly made up of methane (generally 95–97 per cent pure methane). Coal seam gas has been part of Australia's energy mix since it was first produced in Queensland in 1997. Australia is now operating CSG production fields in the Surat and Bowen Basins of Queensland to meet Queensland domestic needs and for the export market.
What is shale gas?
Shale gas is mainly methane trapped within shale rock layers at depths greater than about 1500 metres. Although Australia has vast reserves of shale gas, the industry is largely in exploration phase.
How are CSG and shale gas different to conventional natural gas?
Conventional natural gas, CSG and shale gas are chemically similar. CSG/shale gas is nearly pure methane; conventional gas is around 90 per cent methane with ethane, propane, butane and other hydrocarbons making up the remainder. The difference between CSG/shale gas and conventional gas is the type of geological rock they are found in.
Conventional gas reservoirs largely consist of porous sandstone formations capped by impermeable rock, with the gas stored at high pressure. Conventional gas flows to the production well and to the surface under high pressure. Australia's reserves are mostly offshore.
CSG is found attached to the coal in coal seams, trapped underground by water pressure. To extract CSG, water already in the coal seam, known as formation water, needs to be pumped out to release the gas.
Shale gas occurs within rock formations under high pressure. These rock formations have extremely low porosity making it difficult for gas to flow to wells. Hydraulic fracturing is always used in shale gas wells to increase the flow of gas from the reservoir.
More on CSG
What can CSG be used for?
Similar to natural gas, CSG and shale gas can be used in household stoves, heaters and hot water systems, industrial processes and electricity generation.
Is CSG a greenhouse gas?
Methane is a greenhouse gas that produces carbon dioxide (another greenhouse gas) when burned or oxidised, and greenhouse gases contribute to global warming. But, methane has higher potential to warm the atmosphere than carbon dioxide, so its greenhouse impact can be reduced by burning it for energy production rather than releasing it to the atmosphere.
Methane produces fewer greenhouse gas emissions in energy production than coal and oil-based fossil fuels — 30-60 per cent fewer emissions compared to coal-fired power generation. However, the actual greenhouse benefits relative to coal or oil depend on ensuring leakage of methane from wells and other infrastructure is minimal.
What are the benefits of CSG?
Australia has relatively large supplies of coal seam gas resources (especially in areas of Queensland and NSW). These have the potential to provide a secure supply of energy for Australia and international markets over the coming decades. Production of gas generates revenue for industry and government, which has social and economic benefits for Australia.
How is CSG extracted?
To access the gas, a well is drilled — anywhere from 300 to 1000 metres deep through various layers of rock — to a coal seam. To protect groundwater from being contaminated the well is lined with three cement and steel casings near the surface.
Water already in the coal seam, called formation water, is pumped out to release trapped gas. If water and gas don't flow freely, hydraulic fracturing, also known as fracking may be used to increase the rate of flow. This involves perforating the well casing to gain access to the coal. Water containing a proppant (a gritty material like sand) and chemical additives is pumped under high pressure down the well, opening up existing fractures in the coal known as cleats. Proppant is then added to the water that flows through to the fractures. The sand keeps the fractures open allowing the gas to flow to the well and up to the surface.
Produced water (see below) and gas are pumped to the surface, and separated at the well head. The extracted gas is then processed and transported for domestic and international use. The produced water is treated to remove salts and other chemicals, and then either re-used or disposed of according to state government regulations.
What is produced water or CSG water?
In hydraulic fracking, produced water (also known as coal seam gas water or associated water) is the combination of hydraulic fracturing fluid and formation water, which is water that is already present in the coal seam. The gas and produced water are separated at the surface.
What happens to the water after it is brought to the surface and separated from the gas?
Produced water is treated to remove salts and other chemicals and then either re-used or disposed of according to state government regulations.
What are some of the other potential environmental impacts of CSG extraction?
Removing large amounts of formation water from a coal seam decreases the water pressure within layers containing CSG. Where a coal seam is near the surface, connectivity between the seam and a confined aquifer (where water is under pressure) or alluvium (loose material on the surface) can lead to a lowering of water pressure or the water table.
Access to and use of freshwater sources for hydraulic fracturing can compete with other water users, including agriculture and human water use. Using non-potable sources of water for hydraulic fracturing can reduce these impacts. The industry's potential greenhouse gas footprint, possible fragmenting of local habitat, changes to agricultural landscapes and economic and social impacts on rural communities, are other potential environmental impacts.
What are fugitive emissions?
Fugitive emissions refer to greenhouse gases (such as methane) that can escape into the atmosphere during mining and production of fossil fuels such as black coal, crude oil and natural gas. Methane is also released naturally, seeping from coal seams or from biological processes occurring in wetlands, swamps, rivers and dams.
What impact can they have?
Methane is a very powerful greenhouse gas, with about 27-times the greenhouse warming potential of carbon dioxide. Releasing fugitive emissions of methane during extraction of CSG can therefore have a negative impact on global warming. According to the Department of Industry, Science, Energy and Resources latest estimates (2018–19), fugitive emissions from the fossil fuel industry account for 9.8 per cent of Australia's national greenhouse gas inventory.
How much methane escapes during production of unconventional gas?
In 2013, CSIRO measured emissions from 43 CSG production wells in Queensland and NSW in the first study to measure fugitive emissions from CSG wells in Australia. Only three showed no emissions. The remainder had some level of emission, but generally the rates were very low, especially when compared to the volume of gas produced from the wells.
As a rule of thumb, if fugitive emissions are below 1–2 per cent, natural gas has lower greenhouse gas emissions compared with coal (based on current technologies). Above about 4 per cent fugitive emissions, the greenhouse benefits are lost. The average emissions rate for this CSG study were approximately 0.02 per cent of the total gas produced.
It's important to note that this was a pilot study of fewer than one per cent of the existing CSG wells in Australia. The study measured emissions only from the well pad and adjacent equipment, although low levels of fugitive emissions were detected from most of the well studied, and no emissions were found to emanate from the well casing. Many of the leaks detected were easily fixed.