Monitoring of saline fluids from geothermal plants: Special aspects of sampling, sample preservation and analysis

Abstract

Sampling and analysis of saline fluids requires experience and from time to time also an adaptation, optimisation or substitution of methods. Some hundreds of different saline fluids were sampled and analysed by the authors during the last decade. Based on examples some issues in order to find the actual composition of saline fluids are presented.
In detail, for determination of cations and elements inductively coupled plasma mass spectrometry (ICP-MS) is used. By this method both, major and minor, cations can be analysed. Based on the example of Ca analysis the matrix effect resulting in an overestimation of the concentration is demonstrated. In consequence, analysis with standard addition was performed. Another possibility is to substitute the method. In this case atomic absorption spectroscopy (AAS) can be the alternative method, for the determination of heavy metals a voltammetric method can be applied. A special method was used for analysis of sulphide: the polarography. Anions were analysed by ion chromatography based on standardised methods. Based on the examples of co-elution of fluoride with organic acids and thiosulfate with iodide it is shown that the fluid composition is complex and the procedure to analyse it can diverge from standardised methods. Radionuclide analysis in saline fluids using gamma ray spectrometry is complicated by the occurrence of radioactive disequilibria. A mathematical treatment of the analytical results is necessary to achieve correct concentrations for the date of sampling.