During operation of a geothermal plant, the temperature and pressure distributions in the reservoir rocks are modified, and the interaction between fluid and reservoir rock is affected. Thus, the chemical equilibrium in the geothermal system is changed during water production and the subsequent injection of the cooled water. As a result, some mineral phases become supersaturated and result in scaling processes, and a chemically modified geothermal fluid is injected into the reservoir, which may lead to fines migration.
Furthermore, the chemical composition of the formation water itself – combined with the modified fluid composition – may result in various fashions of corrosion, especially if iron-rich materials form part of the surface and downhole installations. Occasionally, operational challenges as consequence of improper design and dimensioning of the sub-surface facilities are observed in geothermal pants. These challenges normally relate to poor well completions and usually involves the design of the gravel packs, screens, casings and tubings.
From the PERFORM database, we have a good knowledge of the expected chemical composition of the geothermal waters at individual sites. Information about the chemical composition of the formation waters is useful in planning operations, so that risks of corrosion, scaling and clogging can be minimized.