| Title | Chemical Structure of the Ngatamariki Geothermal Field, Taupo Volcanic Zone, NZ |
|---|---|
| Authors | Jeremy O'Brien, E Mroczek, C Boseley |
| Year | 2011 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | soil, co2, flux, shallow, temperature, survey, geothermal, San Jancinto, Nicaragua |
| Abstract | A review of the chemistry of the Ngatamariki geothermal field has enabled the source fluid composition and the natural state reservoir processes to be characterized. The cation and anion relationships and chloride enthalpy mixing models show that Ngatamariki shallow fluids are related to the deep fluids by dilution (mixing). The processes are in agreement with the conceptual model developed by Mighty River in 2010. Deep fluid composition at Ngatamariki was characterised from 5 deep exploration wells and shows typical neutral chloride composition with ~950 mg/l Cl and silica and Tnkc geothermometer temperatures of ~280 C. Gas chemistry from the geothermal wells suggests that the Ngatamariki fluids have degassed evenly across the field and record equilibrium geothermometry temperatures of 275 C. As the fluids ascend out of the reservoir they enter an intermediate aquifer through a zone in the central part of the field which appears to be the main upflow from the reservoir to the surface. These fluids can be classified into three distinct types of water within the aquifer 1) Local groundwater, 2) Dilute geothermal fluids mixed with groundwater and 3) a steam heated groundwater. Based on the enthalpy chloride relationship of samples taken from wells drilled into the upflow suggest that the fluids are 60% deep reservoir fluid mixed with regional cold groundwater. These fluids then variably mix with ~140 C steam heated ground waters as they travel towards the Orakonui stream springs where they discharge at the surface. |