Hot dry rock geothermal systems: Geochemical applications of transient field experiments

Abstract

Although geochemical investigations of Hot Dry Rock geothermal reservoirs may be useful to both their short and long term operation, most applications of geochemistry require a knowledge of the chemical processes occurring in the various parts of the reservoir during circulation. This contribution describes chemical transient experiments that can indicate qualitatively the distribution of aqueous species concentrations in the reservoir. These experiments include both non-steady-state (reservoir inflation and deflation) and steady-state (Fresh Water Flush, and recirculation) hydraulic types. The method of data interpretation in terms of water-rock interactions and mixing with indigenous fluids in the reservoir is described with the aid of a conceptual physical/geochemical model of the reservoir derived from several field studies. The limitations of the technique are discussed and some examples of data interpretation are given, although these are dealt with more fully elsewhere (McCartney 1984, 1986a, 1986b).