Coal seam gas
[Music plays and text appears: Unearthing coal seam gas – What is coal seam gas, how is it extracted and what are some of the challenges involved?]
[Image appears of a farmland landscape on the surface of a cross section of land. Camera zooms down the cross section of land to a map of Australia and text appears: 1997 over Queensland]
Narrator: Coal seam gas has been part of Australia’s energy mix since it was first produced in Queensland in 1997, and development of the resource has been steadily increasing since then.
[A blue coal seam line appears on the rotating cross section of land and text appears: Coal seam]
Coal seam gas is mainly methane found within coal deposits trapped underground by water pressure.
[A line appears on the cross section of land moving through the rock to the coal seam and text appears: Surface, 300 m, 1000 m and Aquifer Aquitard]
To access the gas, a well is drilled – anywhere from 300 to 1000 metres deep through various layers of rock – to the coal seam.
[Camera zooms in on the well in the cross section of land and then a small block pops out of the side to show the cement and steel casing of the well]
To protect groundwater from being contaminated the well is lined with cement and steel casings.
[Camera zooms down to show water in the coal seam, text appears: Formation Water]
Water already in the coal seam is pumped out to release the trapped gas.
[Text appears: Hydraulic Fracturing and camera zooms in on well shaft to show perforations in well shaft]
If water and gas don’t flow freely, hydraulic fracturing, also known as fracking, may be used to increase the rate of flow. Hydraulic fracturing involves perforating the casing at different levels along the well, to gain access to the coal.
[Image shows water moving down the well shaft and into the coal seam. A single water drop appears and text appears: 1% chemical additives, 99% water & proppant]
Water containing chemical additives is pumped under high pressure down the well, opening up existing fractures and creating new ones.
[Camera zooms in on the coal seam to show sand in the water and then zooms out to show the well shaft and the water and sand moving up the well shaft]
Proppant, such as sand is then added to the water that flows through to the fractures. The sand keeps the cracks open allowing the gas to flow to the well and up to the surface.
[Camera zooms up the well shaft to the well head at the surface. Image shows the well head with a truck and a pumping station. Text appears: Produced Water = hydraulic fracturing fluid + formation water]
Produced water and gas are pumped to the surface, and separated at the well head.
[Camera zooms out to reveal the whole cross section of land with arrows pointing left to three hexagons showing what happens to the gas and arrows pointing right to six hexagons to show what happens to the water]
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.
[Camera zooms in on the cross section of land again and shows the well. Image appears of a cube of the Aquifer and Aquitard layer: text appears: On one cube Aquifer and the other cube Aquitard . Over decades and thousands of years
A source of concern is that hydraulic fracturing fluids may leave the coal seam and enter fresh water aquifers, which are layers of porous permeable rock that allow water to flow through easily.
This risk is reduced by layers of rock with low permeability, known as aquitards, which limit water flow and can act as a barrier.
[Camera zooms back to surface of cross section of land and image shows a truck with fluid spilling from the rear]
Contamination of groundwater is more likely to occur as a result of accidental surface spills or leaks of produced water and hydraulic fracturing fluids.
[Camera zooms out to show the coal seam and the layers either side. Text appears to label the layers: Aquifer, Aquitard, Coal Seam, Aquitard, Aquifer]
Another impact is the lowering of water levels in aquifers. Removing large amounts of water from the coal seam decreases the water pressure within the rock layer containing coal deposits. Water in the aquifers can then move towards the coal seam. Just how fast and far this happens depends on the type of and connectivity between the aquifers and aquitards.
[Camera zooms up the well shaft to the surface again and then zooms in on a chimney spewing flame]
[Camera zooms out to show the cross section of land]
Other potential environmental impacts include the industry’s greenhouse gas footprint, fragmenting of local habitat, changes to agricultural landscapes and rural communities.
[Text appears: Research to inform decisions, Visit the CSIRO and GISERA websites for more information and latest research. www.csiro.au, www.gisera.org.au’]
CSIRO is conducting research to better understand the impacts of coal seam gas development and develop sound technologies and practices to ensure socially and environmentally responsible development.
[CSIRO logo and text appears: Big ideas start here, www.csiro.au]
Unearthing coal seam gas – GISERA video