Unconventional Sources of Geothermal Energy in NZ

Abstract

Essentially, New Zealand is one big geothermal system with pockets of subsurface high temperatures where heat can be mined economically. However, with developments in Enhanced Geothermal System (EGS) technology, previously uneconomical geothermal sources may now be exploited. There are conventional and non-conventional sources of geothermal energy in New Zealand. Conventional sources include high enthalpy geothermal systems in the Taupo Volcanic Zone and Ngawha used for power generation, waste-water from high enthalpy producing fields and hot spring systems scattered all over the country. Non-conventional sources of geothermal energy include peripheries of high-enthalpy geothermal systems in the TVZ, 2500 m depth in high-heat flow sedimentary basins and rapidly rising regions of the country such as the Raukumara Peninsula and the Southern Alps, >3500m depth outside high heat flow regions using hot dry rock (HDR) technology and natural conductive heat flow where constant heat at 15m and deeper can be extracted by ground source heat pumps. For some of the unconventional sources of geothermal energy, such as heat from sedimentary basins and hot dry rock (HDR), permeability or the volume of circulating fluids may be marginal but could be overcome by present technology. It is estimated that the total annual extractable geothermal energy, for direct use of heat and for power generation, is about 144 PJ. Essentially only 8.5% of the geothermal resources that could be harnessed for direct heat utilisation have been exploited; and only 24% of the various sources of geothermal power have been tapped. Only about 15% of the geothermal resources of New Zealand have been exploited.