The chloride and C02 chemistry at the Wairakei geothermal field, New Zealand has been modelled using an extended version of the geothermal simulator TOUGH2 which solves the equations for the transport of reacting chemical species in multi-phase fluids. Reactions involving the speciation of aqueous COZ to H2C03 and HCO, are included in the model. Because COz speciation in water is pH dependent, a reaction involving the most important weak acid buffer at Wairakei (HdSi04) has also been included. A ëHenryís Lawí reaction expresses the equilibrium between the aqueous and vapour components of C02. The chloride is treated as a conservative, non-reacting species which is present only in the liquid phase. Results from the model are compared with measured chloride and CO2 data from Wairakei covering the period 1959 to 1987.

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Copyright 1996, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.