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Australia has vast resources of unconventional gas including coal seam gas, shale gas, and tight gas. The gas is found in complex geological systems and can be difficult to produce, requiring innovative technological solutions for extraction.
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.
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 developing coal seam gas production fields in the Surat and Bowen Basins of Queensland to meet Queensland domestic needs and for the export market.
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.
Conventional natural gas and CSG are chemically similar. CSG is almost 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. Australia’s conventional gas reserves are mostly offshore. Conventional gas flows to the production well and to the surface under high pressure. CSG is found in coal seams attached to the coal and is 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 but having 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.
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. Greenhouse gases contribute to global warming; however, methane has higher potential to warm the atmosphere than carbon dioxide and so burning methane for energy production rather than releasing it to the atmosphere reduces its greenhouse impact. Methane produces less greenhouse gas emissions in energy production than coal and oil-based fossil fuels, producing 30–60 per cent less greenhouse gas 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.
Australia has relatively large supplies of coal seam gas resources (especially in areas of Queensland and NSW) that 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 that have social and economic benefits for Australia.
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 is pumped out to release trapped gas. If water and gas don’t flow freely, hydraulic fracturing, also known as fraccing may be used to increase the rate of flow. Hydraulic fracturing involves perforating the well casing to gain access to the coal. Water containing a proppant and chemical additives is pumped under high pressure down the well, opening up existing fractures in the coal known as cleats. Proppant, such as sand 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 description below for more information) and gas are pumped to the surface, and separated at the well head. The extracted gas is processed and transported for domestic and international use. Produced water is treated to remove salts and other chemicals and then either re-used or disposed of according to state government regulations.
Produced water (also known as coal seam gas water or associated water) is the combination of hydraulic fracturing fluid (if hydraulic fracturing has occurred) and formation water, which is water that is already present in the coal seam. The gas and produced water are separated at the surface.
Produced water is treated to remove salts and other chemicals and then either re-used or disposed of according to state government regulations.
Removing large amounts of formation water from a coal seam decreases the water pressure within layers containing coal seam gas. Where coal seams come near the surface, connectivity between the seam and confined aquifers or alluvium can lead to a lowering of water pressure in aquifers or water tables in alluvium. In shale gas production, access to and use of freshwater sources for hydraulic fracturing can compete with other water users including agriculture and human water use. Utilisation of non-potable sources of water for hydraulic fracturing can reduce these impacts. Other potential environmental impacts include the industry’s potential greenhouse gas footprint, possible fragmenting of local habitat, changes to agricultural landscapes and economic and social impacts on rural communities.
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 biological processes occurring in wetlands, swamps, rivers and dams.
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 coal seam gas can therefore have a negative impact on global warming. According to the Department of Environment’s latest estimates (2012-13), fugitive emissions from the fossil fuel industry account for 8 per cent of Australia’s national greenhouse gas inventory.
To provide quantitative information on emissions from CSG operations, CSIRO and the federal Department of the Environment initiated a project to measure emissions from a range of production wells in Queensland and NSW. This is the first study to measure fugitive emissions from CSG wells in Australia. Methane emissions were measured at 43 CSG wells – six in NSW and 37 in Queensland. Of the 43 wells examined, only three showed no emissions. The remainder had some level of emission but generally the emission 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 study equated to approximately 0.02 per cent of the total gas produced. However, it’s important to note that: this is only a pilot study, encompassing less than 1 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, no emissions were found to emanate from the well casing. Many of the leaks detected were easily fixed.
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Last updated: Last updated: 25 February 2015
Printed from: What is unconventional gas? (http://csiroaucd2-cdc.it.csiro.au/en/Research/Energy/Hydraulic-fracturing/What-is-unconventional-gas)