| Title | Dilution and Boiling in the Wairakei Field Due to Exploitation 1959-1982 |
|---|---|
| Authors | Brown, K. L., R. W. Henley, R. B. Glover, E. K. Mroczek and H. Plum |
| Year | 1988 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | |
| Abstract | Chemical data obtained from production and exploration wells during exploitation of the Wairakei Geothermal field are reviewed and interpreted in conjunction with physical data for the field. Two processes have dominated the chemistry during exploitation; (a) adiabatic boiling due to depressurisation and (b) dilution due to blowdown of near surface steam heated waters. Adiabatic boiling dominated the period up to the mid I9601s and was accompanied by the development of extensive steam-dominated zones in the upper part of the field. As pressure stabilised due to a reduction in the amount of mass discharge, dilution became dominant. These trends are monitored by assuming a simple boiling/dilution model which allows easy comparison between different wells and between the same well in different years. The dilution trends for the main production area show that the cooler surface waters flow preferentially along fault systems and the cooling effect of these diluting waters is reflected in lower silica temperatures in these areas. The water discharged in 1982 from the production areas of the Wairakei field is diluted by about 7% compared with fluid discharged in 1961, and the 1961 fluid is diluted by about 14% compared with what is believed to be the deep recharge fluid. The current dilution trends are expected to continue, but with the large size of the available reservoir, and the decline in mass withdrawal for power production, the rate of dilution should be reduced. |