CSG is a natural gas held within the coal formations by groundwater pressure. A well (similar to a water bore) is drilled to depressurise the coal formation by extracting groundwater. As the pressure is reduced, the gas is gradually released together with groundwater. There is more water than gas in the initial period but over time, the proportion of water gradually declines to being practically negligible and only gas is produced.
The impact of depressurisation from groundwater removal spreads in all directions from the site of extraction. It also creates a pressure difference between the target formations and those above and below, as illustrated in this diagram. This pressure difference encourages groundwater to flow towards the site of extraction and potentially impacts the availability of groundwater at the source.
In Queensland's Surat Basin CSG fields, many wells are placed approximately 700 to 1,000 metres apart to depressurise large areas of CSG reservoirs and maximise gas extraction. This also creates potentially widespread and cumulative impacts from groundwater extraction that must be assessed and managed.
Last updated: 31 Oct 2023