Aquifer chemistry and mineral saturation in selected high temperature geothermal areas

Abstract

Aquifer fluid compositions have been assessed from analytical data on water and steam samples collected at the wellhead from 28 production wells in eight geothermal areas from five countries (Hveragerdi, Krafla, Námafjall, and Nesjavellir in Iceland; Kizildere in Turkey; Momotombo in Nicaragua; Olkaria in Kenya and Zunil in Guatemala). The state of mineral saturation of the aquifer water with respect to the following minerals was studied: anhydrite, calcite, clinochlore-daphnite, clinozoisite-epidote, grossular, low-albite, microcline (the stable K-feldspar at low temperatures), prehnite, pyrite, pyrrhotite, quartz, wairakite and wollastonite. The aquifer water is close to equilibrium with calcite, quartz, low-albite and microcline. Most of the water is relatively close to wollastonite saturation. The same applies to clinozoisite, prehnite and wairakite although the scatter of the data points is larger than for the previously listed minerals. The waters are saturated or undersaturated with respect to anhydrite and grossular. Oversaturation is indicated for the clinochlore component of chlorite and the epidote component of the epidote solid solution....