Water volume FAQ

Q: Where does the water in a coal seam gas development come from?

A: The water comes from coal seams – not from the aquifers that are tapped for town water and domestic water and for most agricultural water (some agricultural bores actually tap the coal seams). Natural gas is trapped on the surface of the coal – it is said to be ‘adsorbed’ onto the coal, and held there by pressure from the groundwater in the coal beds. To release the gas from the coal the pressure is decreased to the point where it is no longer sufficient to hold the gas on the coal. This is done by pumping water from the coals, which decreases the pressure and releases the gas.

Q: How much water is extracted?

A: The amount of water that must be removed varies from coal seam to coal seam, depending on the permeability of the coal and surrounding geologic formations. Coals with lower permeability do not require as much water to be pumped to reduce the pressure on the coal. This is why some CSG operations produce lower volumes of water, such as Queensland’s Bowen Basin and in NSW.

The bulk of the water that a well produces is at the start of the pumping phase. As the water is pumped from the coal formation, the pressure is released from the seam, and the gas begins to flow. For instance, at its peak, CSG extraction from Camden in the Sydney Basin produced a maximum of 30 megalitres (ML) of water per year from all gas well. But in 2012 it produced only 4.8 ML in total.  In Queensland, water production has – to date – averaged about 30,000 litres per well per day.

Q: Comparatively speaking, how much water is that?

A: The Great Artesian Basin (GAB) contains 65 million Gigalitres (GL) of water. The CSG industry, over the proposed life of the current projects will produce 1,701 GL of water from the coal seams, or less than 0.03% (3 parts per 10,000) of the GAB’s water supply.

Recent studies collating data from each of the major Queensland CSG producers, have found water production from the Surat Basin CSG operations will average 55 Gigalitres (GL) per annum (pa). By comparison, 452 GL pa is used in Queensland for agriculture, industry, urban, stock and domestic purposes.

Q: How will CSG water production affect aquifers?

A: CSG production extracts water from coal seams rather than from normal aquifers. But producing water from the coal seams will change the pressure balance between water in those seams and the water in overlying and underlying aquifers. While this could induce some water flows between these aquifers and the coal seams, intervening rock layers will impede and limit any such flows. The distance between coal seams targeted for CSG production and overlying aquifers used for cropping and drinking water is between 200 and 800 metres.

In some areas where the impact could be considerable, the uppermost coals would not be tapped for CSG production. Interconnection between coal seams and other aquifers is often very slight. But there could be localised effects on aquifers and bores in some parts of the Surat Basin where about half of this extraction is expected to occur. In some cases, some aquifers could be depleted by 6 to 20 metres.

However, making treated CSG water available for beneficial use will actually reduce the need to tap the main aquifers in some areas, and some treated CSG water is already being reinjected into aquifers.

Q: What are make-good obligations?

A: In Queensland, CSG companies are legally required to make good any depletion of bore-water that could affect landholder activities.

Options include:

  • Deepening a pump
  • Increasing the size of a pump
  • Drilling a new bore into a different aquifer
  • Supplying water from a different location
  • A financial arrangement.

Any measure taken to deal with the problem must be by agreement with the landholder. The burden of proof rests on the government and the CSG company, not the landholder. The priority is reinstating water supply in the shortest possible time.

Q: What is done with the produced CSG water?

A: The water produced from the coal seams is mildly salty (brackish). It comes from deeper geological layers, and is generally not usable for agricultural purposes without desalination treatment or blending with fresher (less saline) water.

Importantly, of the CSG water produced annually:

  • 59% is treated and made available for agricultural purposes
  • 24% is treated and reinjected into underground aquifers
  • 14% is treated and used for industrial purposes such as mining, roads and construction
  • 3% remains as brine or salt.[1]

Q: What is the difference between megalitres, gigalitres and kilolitres?

  • 1 gigalitre (GL) = 1 000 000 000 litres
  • 1 megalitre (ML) = 1 000 000 litres
  • 1 kilolitre (KL) = 1000 litres

[1] Department of Trade and Investment Queensland, 2014. Queensland Resources Under Construction: Queensland LNG


 

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