Three chemical tracer experiments and one extended injection of fluid low in concentration of dissolved species have beer? carried out during the Long Term Flow Test (LTFT) of the Fenton Hill Hot Dry Rock (HDR) reservoir. The tracer tests results illustrate the dynamic nature of the flow system, with more fluid traveling through longer residence time paths as heat is extracted. The total fracture volumes calculated from these tests allow us to determine the fate of unrecovered injection fluid, examine the pressure-dependence of fracture volume, and, through a comparison to the hydraulic performance, postulate a model for the nature of the pressure drops through the system. The Fresh Water Flush (FWF) test showed that while no dissolved specie behavior is truly conservative (no sources or sinks), several breakthrough curves are well explained with a pore fluid displacement model. Other dissolved components are clearly influenced by dissolution or precipitation reactions. Finally, the transient response of the chemistry during the FWF to an increase in production well pressure showed that some fractures connected to the production well preferentially open when pressure is raised.

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Copyright 1993, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.