Understanding environmental risks related to geothermal fluids

Abstract

The main objective of this thesis is to understand the environmental risks related to geothermal operations. The aim is to provide an integrated approach from both natural and social sciences and to perform this in three different country settings. These countries are Indonesia, Turkey and the Netherlands and they were selected because of their different geothermal system types. The integrated approach in this study results in a research process that requires a broad range of measurement and analysis techniques and a clear understanding of the natural and social disciplines. From the natural sciences approach this report studies the environmental risks through a geochemical characterization of the geothermal fluids, whereas the social sciences approach studies the risk perception on geothermal operations. The outline of the process followed is visualized in Figure 0.1. From the natural sciences approach, an extensive geochemical data set is used to characterize the geothermal fluids and their environmental risk. This contains approximately 750 sample measurements from three countries that were collected through partners and third parties. The samples are characterized with help of two ternary diagrams (Na-K-Mg and Cl-SO4-HCO3), their salinity (in TDS), pH and correlation coefficients between commonly occurring elements in fluids, such as Ca, Si and F. These fluid properties help to define the maturity, origin and characteristics of geothermal fluids at a broad range of locations in each of the three countries. Through this analysis we found a strong relation between the fluid classification and the sample type (well or spring) in Indonesia. Besides, a relative high influence of volcanic activity on the geochemistry was observed. The Turkish and Dutch samples are dominated by their geothermal system types that are respectively carbonatic and clastic sedimentary systems. The concentrations of nine toxic gases and elements dissolved in the geothermal fluids are analysed and compared to guideline values to determine the relative environmental risks in the three countries. The toxic gases are H2S, CO2 and CH4 and the toxic elements Al, As, Cd, F, Hg and Pb. Their effects on the environment differ but all of them affect the health of humans, flora and fauna when they contaminate groundwater or the atmosphere. From the risk analysis in the three countries it was found that the risk of excessive H2S pollution is highest in Indonesia, for CO2 in Turkey and for CH4 in the Netherlands. The contamination risk with toxic elements differs largely per element but often occurs in specific locations, for example with high volcanic impact. For the social sciences approach, a survey was distributed to measure how the public perceives the risks of geothermal energy. The population for this survey is people affiliated with the geothermal industry because of their prior knowledge on the subject. They are asked to indicate their (risk) perception through several statements and factors to which they indicate their level of agreement. The result indicates that the perceived risks were generally higher in countries with a higher risk, like Indonesia. However, there were several interesting exceptions to this rule in which the perceived risks were low whereas a relatively high environmental risk was identified, like for potential CH4 pollution in the Netherlands.