29 March 2021

Geothermal water

More or less drinkable,
More or less young,
More or less hot,
More or less colored,
More or less mineralized,
More or less salty,
More or less sparkling,
More or less aggressive and tartarizing .
All it takes is to match it to the right container !

Plus ou moins potable,
Plus ou moins jeune, 
Plus ou moins chaude,
Plus ou moins colorée,
Plus ou moins minéralisée,
Plus ou moins salée,
Plus ou moins gazeuse,
Plus ou moins agressive et entartrice…
Le tout c’est qu’elle soit en équilibre avec le réservoir !

The water, from a marine or meteoric source, seeps into the rocks over time. It always tends towards a physico-chemical equilibrium with the rocks it crosses.

Henceforth, along its path, and depending on the pressure and temperature, the water will gradually change its composition, ‘loading’ itself with gas or mineral salts resulting from interactions with the rocks encountered.

Water can be naturally mineralized and gaseous. They have different compositions: CO2, Magnesium, Calcium, Potassium… according to the geological context of their source and their history.

Water that gradually becomes charged with gas is called a fluid. The gases most often found in the earth’s crust are Carbon Dioxide (CO2), Nitrogen (N2), Hydrogen Sulfide (H2S), Oxygen (O2), Hydrogen (H2), Methane (CH4), Helium (He), and Radon (Rn).

Water loaded with salts from a concentration of 50 g/L upwards is called brine. The most common salts found in the earth’s crust are Sodium Chloride (NaC1 or cooking salt), Potassium Chloride (KC1), Calcium Sulphate (CaSO4) and Ferrous Carbonate (FeCO3).

The higher the concentration of salts in water, the greater the risk of fouling and corrosion of materials (pipes, containers), in the same way that sea air corrodes metal objects in maritime environments. Deep geothermal brines are on average 5 to 10 times saltier than sea water.

Geothermal power plants are therefore adapted and built with materials specifically chosen to resist the specific corrosive agents in the water as well as and the solid particles it carries. Geothermal water can also be tinted or cloudy depending on its mineral and organic matter content. Finally, it may have a slight odour. In some volcanic regions (e.g. on the geothermal field of Bouillante in Guadeloupe), it smells like rotten eggs because of its H2S content, typical of volcanic activity.

Although it is generally not drinkable, geothermal water is not dangerous for humans. However it requires good practices for the operational maintenance of the installations, which allow the safe extraction of calories.

It does happen, very rarely, that water exploited for geothermal energy is drinkable, as is the case for the Albian aquifer in the Paris basin. In this case, it does not require specific treatments and does not present any particular challenges.

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