Coal Seam Gas (CSG) and Shale Gas reservoirs are relatively new gas sources which have revolutionised natural gas markets over the past two decades, increasing global supply and stabilising gas prices.
The CSG industry in Australia is growing exponentially, accounting for over 30 per cent of the country’s total gas produced in 2016.
Australia's eastern states all have world class reserves of CSG, however only Queensland is developing a sizeable production, due to pioneering efforts of local stakeholders and progressive government regulations.
New South Wales and Victoria have taken a more conservative approach, with NSW temporarily freezing CSG exploration in 2014, and Victoria maintaining a moratorium on onshore gas development since 2012.
Northern and Western Australia contain large shale gas reservoirs (such as the Beetaloo Sub-Basin), with the Northern Territory lifting it’s moratorium on onshore gas exploration in 2018.
Coal Seam Gas Well. Source: https://smallcaps.com.au/comet-ridge-lines-up-coal-seam-gas-wells-production-testing/
Water management is typically different between CSG and shale gas production.
The hydraulic fracturing, or fracking, process is always required for shale gas production; however only required in approximately 30 per cent of CSG cases.
Hydraulic fracturing is the controvercial process of pumping water (plus sand and dilute chemicals) deep underground, into a coal seam or shale, to cause structural fractures which create a path for the gas to transfer out.
This fracking process consumes large volumes of water, which often requires upfront treatment to remove unwanted contaminants.
Up to 70 per cent of the injected water returns to the surface with additional contamination, and thus requires further treatment before it can be discharged into the environment.
Drilling down to access the coal seams and shales also penetrates underground water reservoirs and aquifers, causing large amounts of additional contaminated water to rise to the surface.
Typical Coal Seam Gas and Associated Water Prodcution Curves.
The bulk water is produced in the initial stages of gas production, known as the dewatering phase, with smaller but steady flows continuing in later phases.
The contaminants typically found in CSG and shale gas waters are leached elements from the ground, and thus depend on the type of soil and rocks in the region.
Elements such as dissolved salts (sodium and chloride), hardness (calcium and magnesium), trace metals (iron, manganese, lead, copper), alkalinity (carbonates), nitrates, and hydrocarbons are all common.
It is important that these elements are treated to ensure that surrounding waterways and aquifers are not contaminated.
Several technologies can be used to treat CSG and shale gas water, depending on the type and level of contamination:
Suspended particulates (dirt, sand) are removed using media or cartridge filters.
Dissolved salts are removed with technologies such as reverse osmosis or ion exchange.
Bacterial contaminants are neutralised using chloramination or ultraviolet (UV) treatments.
Coal Seam Gas Associated Water. Source: https://www.advisian.com/en/global-perspectives/coal-seam-gas-water---the-challenge-of-upstream-interfaces
The importance of water treatment in the CSG industry is demonstrated by the Reedy Creek Water Treatment Facility (WTF), which treats 40 million litres of water per day from over 600 CSG wells in Queensland's Surat Basin.
The WTF uses a combination of filtration, chloramination, and reverse osmosis to treat the CSG water such that it can be discharged into nearby creeks and aquifers.
A recent CSIRO study investigated the environmental effects of the CSG industry in the Surat Basin, and found nearby creeks and aquifers showed no signs of contamination due to the Reedy Creek WTF.
More information about the CSIRO study can be found here.