Report: TR 2013/08
Author: I Cheptum (University of Auckland)
New Zealand is endowed with a wide range of geothermal resources ranging from high to low enthalpy resources. However, the exploration and development of the vast low enthalpy geothermal resources have been limited because of the abundance of high enthalpy geothermal resources (Thain et al., 2006).
There are several sources of low-enthalpy heat in New Zealand. Reyes and Jongens (2005), noted that heat can be from hot spring systems with discharge temperatures of less than 90 °C in the North and South Islands, edges or boundaries of high-enthalpy geothermal systems in the Taupo Volcanic Zone (TVZ) and Northland.
Temperature ranging from 120 to 160 °C waters at depths greater than 3.5 km is observed in abandoned hydrocarbon wells and natural heat flow from about 15 m below the surface to deeper levels. There are approximately 105 low-temperature geothermal systems in New Zealand, with approximately 30 of them found within the Waikato region (Luketina, 2012).
Among the 30 known small geothermal systems in the region is Ohinewai geothermal field. The purpose of this study is to do a preliminary assessment of Ohinewai low enthalpy geothermal system and give the size of the resource in the prospect.
The field survey was conducted in the area of study and it involved sampling of water from the water bores in the resource area. The preliminary geochemical analyses are looked into and their interpretation is presented in this report.
|1.2||Waikato regional geothermal systems||1|
|1.3||Aim of the study||2|
|2||Ohinewai geothermal field||2|
|2.3||Geological cross section of Ohinewai field||5|
|3||Background work to the study||6|
|5||2: Analytical methods||10|
|6.1||Classification of geothermal waters||12|
|6.1.1||Cl-SO4-HCO3 ternary diagram||12|
|6.2||Na-K-Mg ternary diagram||13|
|6.3||Cl-B-HCO3 ternary diagram||15|
|7||Discussion and conclusions||21|
|Appendix 1: Geothermal water quality site description sheet||26|