Gas, made from coal in gasworks, caused significant pollution in cities until 1969 when natural gas was piped from Bass Strait to Melbourne, Moomba to Adelaide, Roma to Brisbane and in 1976 from Moomba to Sydney. This natural gas is now called conventional gas to distinguish it from unconventional gas.
Conventional gas migrates from its source rock until it is trapped in a reservoir, sometimes with petroleum, by an impermeable ‘cap’ rock. Drilling vertically through the cap rock allows the gas to flow out naturally so fracking is not required. Impacts on the environment are less than unconventional gas because a minimal amount of water is brought to the surface and fewer wells and other infrastructure are required.
Unconventional gas, such as coal seam gas, has a different recovery process from conventional gas, requiring many more wells, pipelines and processing infrastructure.
Drilling a well releases toxic chemicals, found naturally in the coal seams, into the huge amount of water stored in the coal seam. Before the gas will flow, this water must be extracted from the coal seam and brought to the surface.
If the coal seam is above the Great Artesian Basin, nearby bores in shallower aquifers with good quality irrigation water will dry up. The water sucked out of an aquifer on one property, could be somebody else’s irrigation allocation on the other side of the river.
Fracturing the coal seam (fracking) is used to increase the flow of the gas if it does not flow naturally. During the fracking process, chemicals, sand and water are blasted into the well to fracture the coal seam and further natural occurring chemicals in the coal seam are released.
Gas and water brought to the surface are piped to large central processing plants where they are separated. The gas is then piped to market and huge amounts of salty water, often containing toxic chemicals, are piped to massive ponds lined with several layers of plastic. This water is treated in a reverse osmosis (RO) plant designed to remove most of the salts, chemicals, toxins and heavy metals, such as lead and uranium.
The treated water is called ‘beneficial water’ by the government and mining companies and ‘RO water’ by most other people. Owing to the volume, particularly at the beginning of a well’s life, the mining companies are desperate to get rid of it. ‘RO water’ is used by industry; supplements town water supplies and creeks; waters gravel roads for dust suppression; and irrigates stock feed crops and planted native hardwood forests.
The remaining salty toxic sludge is stored in plastic lined ponds. One of the major concerns of people opposed to coal seam gas is the regulation, disposal and monitoring of this toxic salty sludge as it has the potential to contaminate aquifers. Despite great effort there is no safe way to store this sludge long term, or to put it to “beneficial use”.
When gas is extracted from coal seams below the Great Artesian Basin, drillers penetrate the impermeable strata underlying the Basin then drill into the coal seams below. When the gas no longer flows from the wells they are capped with steel piping and cement to stop the water in the Great Artesian Basin leaking into the coal seams below. However, leakage is inevitable as wells are man-made structures, which will deteriorate with time in a salty environment.
COAL SEAM GAS VERSES COAL
Mining companies, armed with industry funded research, say that conventional gas is running out and that unconventional gas is a low carbon energy source, a transition between coal and renewables. The industry claims to pay state royalties, and create jobs and business opportunities in rural areas where unemployment is high.
However, today the science is being questioned, but the industry is well underway. Initially the carbon footprint of coal seam gas was said to be seventy percent less than coal. This changed to fifty percent when it was revealed that the initial comparison was made with brown coal which is not mined or used in Queensland or New South Wales. Again this figure has been disputed when studies showed if fugitive emissions from coal seam gas are taken into account from the beginning of the extraction process, its full life cycle emissions are nearly the same as that produced by black coal. Therefore by exporting coal seam gas instead of coal, a foreign country gets the benefits of reduced emissions while Australia’s emissions increase due to infrastructure leaks.