GEOTHERMAL PROSPECTIVITY OF LOW-TEMPERATURE REGIONS IN NEW ZEALAND

Abstract

Based on fluid geothermometry of discharges from cold and hot springs, wells and underground mines; and hydrocarbon well measurements and projections, the estimated temperatures at depth in low-temperature regions, outside the Taupo Volcanic Zone and Ngawha, vary from about 55 to 250oC. The minimum estimated recoverable heat energy (calculated at 10% of accessible heat) from aqueous solutions, in these low-temperature geothermal resources, is 3.1 PJ/a, which is but a tiny fraction of heat energy that can be harnessed conductively from the rock. e.g. GSHP at shallow depths of <300m. Based on the total recoverable heat energy, maximum temperature at depth and the ratio of heat energy provided by conventional and unconventional sources of heat, the six main regions with the highest to lowest geothermal prospectivity are: Coromandel, Auckland, Hauraki Rift Zone, Western Waikato, Bay of Plenty and Taranaki, These six regions hold about 75% (at >20oC) of the recoverable heat energy estimated from aqueous solutions in low-temperature regions.