Geochemical behavior of a hot dry rock geothermal reservoir
— Charles O. Grigsby, Fraser E. Goff, Trujillo, Patricio E., Jr., and Dale A. Counce

Technical feasibility of the Hot Dry Rock (HDR) concept of geothermal- energy extraction was proved in 1978 (Tester and Albright, 1978). Since that time a series of experiments has been conducted in the first (Phase I) reservoir to assess reservoir performance. The geochemistry of fluids obtained during these early experiments has been discussed by Grigsby and others (1983) and Goff and Grigsby (1982). These authors noted that the chemistry of fluids was subtly different from the natural hydrothermal fluids originating in the nearby Baca geothermal field, Valles caldera. After additional experiments, and after obtaining samples of pore fluid from deeper wells at Fenton Hill, the differences between these two fluids are even more noteworthy than previously thought. Because of the attention now being focused on the Valles caldera due to geothermal activities and the growing Continental Scientific Drilling Program, it is appropriate that the fluid chemistry of the Fenton Hill pore fluids be contrasted here with the Baca geothermal waters.