Geothermal gas equilibria

Comparison of theoretical and analytical equilibrium constants based on the reactions CH₄ + 2H₂O = CO₂ + 4H₂, 2NH₃ = N₂ + 3H₂ and iron(II)-aluminium-silicate + 2H₂S = FeS₂ + H₂ + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H₂O, CO₂, H₂S, NH₃, H₂, N₂ and CH₄. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.