By: Chris Smitt, Director of Water Resources
Shale gas and coal seam gas are often confused with one another and many people believe they are one and the same. However, they are quite different and the discussion below aims to help differentiate the two and outline what water management options are important to consider.
WHAT IS COAL SEAM GAS?
Coal seam gas (CSG) is methane formed from the decay of organic matter over time, formed in the same way as coal and oil. Methane is held within the coal seam by water pressure in the seam. Extracting the gas requires depressurising the coal seam by removing the water, and may include other techniques to increase the permeability of the seam (e.g. fracking).
Therefore, the main driver for water management within the CSG industry is disposal of CSG Water. Current options that industry are using for CSG water management are:
- Irrigation (after treatment)
- Dust Suppression
- Beneficial Aquifer Injection (after treatment)
WHAT IS SHALE GAS?
Shale gas is methane held within shale layers, rather than a coal seam. Shale is much harder than coal and always requires fracturing (‘fracking’) to allow the gas to flow.
Hydraulic fracturing involves pumping large volumes of a fluid, usually water with some chemicals, at high pressure, down the well causing the shale beds or coal seam to fracture to increase the permeability and allow the gas to flow more freely.
It is estimated that a shale gas well requires between 9,000 m3 – 29,000 m3 of water per well, of which approximately 10-40 percent of the fluid returns to the surface. This is referred to as “flowback” water.
Therefore, the main driver for water management within the shale gas industry is the availability of water for fracking and then the removal and disposal of the water.
Current options for shale gas water management “flowback” are:
- Reuse without treatment. Reusing untreated water is frequently performed in the US, but continued reuse will lead to problems as the high level of contaminants may plug the gas wells with residual chemicals, precipitates or shale fines.
- Deep well injection. Simply drilling another well to store the water, however, is not without problems. In March, Ohio state regulators said a dozen earthquakes in the state’s northeast were almost certainly induced by injection of gas-drilling wastewater and analysts say this option will be almost impossible in Europe due to stricter legislation.
- On-site treatment for reuse. This option is used to remove most TSS (total suspended solids), acid-producing bacteria and scaling materials like barium, calcium, iron, magnesium and strontium, which are likely to clog the well if returned to the gas reservoir. Having removed most TSS, typically from 500-1000 mg/l to 50 mg/l, this treated water is then mixed with fresh water and re-used for fracking. As everything is done on site, this option has negligible transport costs.
- On or off-site treatment for discharge as fresh water, which can, of course, be used for fracking. The main objective is to remove TDS (total dissolved solids) in flowback, which can reach extremely high levels of both concentration and variability. Flowback from fracking operations in the Haynesville shale, which covers southwestern Arkansas, northwest Louisiana and East Texas, has been found to contain anywhere between 500-250,000 mg/l.
Currently, the Australian CSG market is more mature than the Shale gas market in this geographic region, with 100 percent of unconventional gas production comprising of CSG, although there are large shale gas reserves in SA, northern QLD, the NT and WA, see Figure 1. In the US, the shale gas market is more developed (see Figure 2) and supplies ~15% of gas consumption. Currently, EHS Support is helping clients with their upstream water requirements for both CSG and shale gas projects in SA, NT and QLD as well as in the Marcellus Shale region in the USA.
Chris is a principal hydrogeologist with over 14 years’ experience in both private and public sector within Australia and the Middle East. His main areas of interest are hydrogeology, managed aquifer recharge (MAR) and climate change impacts on water resources… Read More