Geochemical interpretation of discharge from Reykjanes wells RN-29 and RN-32, SW-Iceland

Abstract

In this report, chemically analysed data from Reykjanes wells RN-29 and RN-32 are used to compare the aquifer temperatures of these wells using selected chemical geothermometers. Calcite and amorphous silica scaling potential is assessed for selected wells. The downhole temperature measurements, the intersection of anhydrite, wairakite, epidote, prehnite and quartz mineral saturation indices and quartz geothermometer results are used to predict the reservoir temperature. From these parameters, the reservoir temperature of Reykjanes well RN-29 is considered to be around 290°C. Similarly, for Reykjanes well RN-32 the reservoir temperature is considered to be around 250°C. The speciation program WATCH was used to calculate amorphous silica and calcite saturation for variably boiled well water. The chemical composition of the fluids was compared with that of a standard sea water composition and the results had the same composition in chloride and total dissolved solids. Reykjanes well RN-29 is assumed to be an excess enthalpy well. The deep liquid composition was computed by a phase segregation model and the results showed that the composition was quite different for volatile components, while the change was insignificant for non-volatile components. Reykjanes well RN-32 was assumed to have a liquid enthalpy in order to compute the deep fluid composition at 250°C reservoir temperature.