Geothermal Systems

Geothermal fields are found throughout the world in a range of geological settings, and are increasingly being developed as an energy source. Each of the different types of geothermal system has distinct characteristics which are reflected in the chemistry of the geothermal fluids and their potential applications. However, they all have in common a heat source at a few kilometres depth, and it is this which sets water, present in the upper sections of the Earth’s crust, into convection. Most geothermal resources can be used for space heating applications (eg. urban district heating schemes, fish farming, greenhouse heating), but it is only the hotter systems (>~180°C) which are used to generate electricity through the production of steam (see Rowley, 1982, for a review of systems worldwide). Since aqueous geochemistry is involved in all stages of the exploration, evaluation, and production of a geothermal field, an understanding of the chemistry of the fluids is essential for the development of a resource. The chemistry of the geothermal waters and gases contains important information about the hydrology of the field and conditions in the reservoir. These aspects of geothermal fluid chemistry are discussed in the following chapters. However, before looking at specific aspects of geothermal chemistry, it will be useful to first place the fluids in context by briefly describing the different types of geothermal system.