| Abstract |
The principal role of geology in geothermal exploration is to obtain as much information as practical on: • The lithology of the anticipated reservoir. • The nature of hydrothermal alteration of the reservoir rocks, and hence the nature of the fluids which were responsible for it. If the alteration exposed on the surface indicates temperatures over 100°C, or there are disequilibrium assemblages present, then there has been some erosion of the system, which can affect the hydrological model and also the interpretation of the geophysics. • Permeability controls in the anticipated reservoir, and hence the location of permeable zones. • Possible heat source of the system, any indications of active volcanism, and some idea of the age of the system. • Assessment of geological risk to the project such as volcanic, seismic, and slope stability. During development of the resource the same topics are addressed, but at a greater level of detail and with less uncertainty. Although most of the surface geological data are collected prior to drilling, and most of the subsurface data during the development drilling phase, the geologist's task does not stop when the power plant is commissioned. There will be a continuing need to have input to the conceptual resource model as it develops in response to production, to interpret the results of reservoir monitoring (e.g. subsidence), and to guide the course of on-going resource management, most particularly the drilling of make up wells. |