Evaluation of the Toxicity of a Mixture of Geothermal and Fresh Groundwater in Case of Perforation of Well Casing

Abstract

Carbon steel casings of geothermal wells exploiting the Dogger aquifer in the Paris Basin are subject to corrosion due to the aggressivity of the geothermal fluid containing CI, HS-/H-S, and CO3/CO2. When localized this corrosion can lead to perforation of the casing thereby increasing the risk of contamination by geothermal fluids of the freshwater aquifers through which these geothermal casings pass. These aquifers are used as a drinking water resource in the Paris region. The evaluation of the toxicity of the Dogger fluid is based on the toxicity of the chemical species, the sulphate reducing bacteria (SRB) and the surfactant used for anticorrosion treatment. The maximum percentage of Dogger Fluid acceptable in freshwater aquifers was calculated for each chemical species concerned with the chemical composition of mixtures of these water standards). Species ere classified by decreasing toxicity taking into account their concentration in the geothermal fluid. The less tolerable species are Na, NH, CI, H2S, phenols and dissolved hydrocarbons. The more toxic species ar Be, Cd, Sb, Se, and V. Surfactants in the concentrations used do not represent a danger to human health and are degradable. This is also true for SRB but these bacteria can be active in the drinking water popes with as a consequence corrosion of these pipes and increase in iron and sulphide contents.