Chemistry and Materials in Geothermal Systems

The development of a geothermal fluid is traced, from its origin as meteoric water precipitating on the earth's surface, as it flows through the soils and rocks of geological formations, to the point where it returns to the surface as a hot spring, geyser, well, or other form. Water of magmatic origin is also included. The tendency of these hydrothermal fluids to form scale by precipitation of a portion of their dissolved solids is noted. A discussion is presented of types of information required for materials selection for energy systems utilizing geothermal fluids, including pH, temperature, the speciation of the particular geothermal fluid (especially its chloride, sulfide, and carbon dioxide content), and various types of corrosive attack on common materials. Specific examples of responses of materials to geothermal fluids are given.