Dilution and Boiling in the Wairakei Field Due to Exploitation 1959-1982

Abstract

The exploration and consequent development of the ~airakei geothermal field has been central to both the evolution of geothermal technology in New Zealand and to the interpretation of the chemi stry of geothermal fluids in general. This paper exami nes the chemical changes which have occurred as a consequence of the massive withdrawal of hot water for power generation over a 30 year period. Concent rati on changes of conserved components such as ch 1 ori de are important as i ndi cators of the principal processes affecting the fluid; boiling, dilution or conductive heat transfer, and geothermomet ry a 1 so provi des important i nformati on. Early data are revi ewed to obtai n an estimate of the "deep" water feeding the field. Data for the succeeding 30 year period are used to assess the gross changes in the production field. This data analysis must filter out the chemical changes induced by local boiling and vapour loss. A technique is therefore proposed which permits comparison of data from individual wells and the field as a whole so that conclusions can be drawn concerning the principal changes and their relative rates. For reference, Figure 1 shows the location of thermal features and wells in the production area. Early in the history of Wairakei, an Eastern and Western production field were distinguished and these sector names are retained.