Conventional Hydrothermal Resources Compared with Alternative Geothermal Resources
Large scale commercial developments of geothermal fields for heat and/or electricity generation are based on hydrothermal resources in New Zealand. However, internationally there is now interest in the development of a wider range of resources, many of which are at the demonstration stage or have undergone a measure of development, though at subsidised levels. This includes: Geopressured Resources, Hot Sedimentary Aquifers and Enhanced or Engineered Geothermal Systems
There is a general view in New Zealand that our hydrothermal systems will be more attractive commercially than any of these alternatives. Due to the accessible energy being at relatively shallow depths and the success rate at which productive wells are drilled, all of which work together to reduce the total project cost of wells. However, this view should be tempered by the recognition that the prime hydrothermal systems are limited in location, that demand for energy exists outside these areas and that large-scale heat demand can be an adequate commercial driver for investment in such projects. Within the next 20 years most of our prime available hydrothermal resources will be under development, after which developers will be looking to the next tier of possible projects. However, there are some immediate prospects for development for large scale heating or cooling purposes.
The graph below compares temperatures of a range of alternative geothermal developments around the world with the Boiling Point for Depth (BPD) curve often encountered at shallow depths in New Zealand fields. Also shown on the graph are some of the gradients observed in several New Zealand fields which were considered disappointing at the time, but which in fact compare favourably with many of these alternative resources world-wide.