Coal
seam gas (CSG) exploration and development requires the abstraction of
significant amounts of water. This is so because gas desorbtion in coal seams
takes place only after aquifer pressure has been reduced by prolonged pumping of
aquifer water. CSG waters have a specific geochemical signature which is a
product of their formation process. These waters have high bicarbonate, high
sodium, low calcium, low magnesium, and very low sulphate concentrations.
Additionally, chloride concentrations may be high depending on the coal
depositional environment. This particular signature is not only useful for
exploration purposes, but it also highlights potential environmental issues that
can arise as a consequence of CSG water disposal. Since 2002 L&M Coal Seam
Gas Ltd and CRL Energy Ltd, have been involved in exploration and development of
CSG in New Zealand.
Anticipating disposal of CSG waters as a key issue in CSG development, they have
been assessing CSG water quality along with exploration work. Coal seam gas
water samples from an exploration well in Maramarua closely follow the
geochemical signature associated with CSG waters. This has helped to identify
CSG potential, while at the same time assessing the chemical characteristics and
water generation processes in the aquifer. Neutral pH and high alkalinity
suggest that these waters could be easily managed once the sodium and chloride
concentrations are reduced to acceptable levels.