Isotopic evidence for a magmatic contribution to fluids of the geothermal systems of Larderello, Italy, and The Geysers, California

Acid chloride corrosion of geothermal well casings, production piping and power plant equipment has resulted in costly corrosion damage, frequent curtailments of power plants and the permanent shut-in of wells in certain areas of The Geysers. Techniques have been developed to mitigate these corrosion problems, allowing continued production of steam from high chloride wells with minimal impact on production and power generation facilities.The optimization of water and caustic steam scrubbing, steam/liquid separation and process fluid chemistry has led to effective and reliable corrosion mitigation systems currently in routine use at The Geysers. When properly operated, these systems can yield steam purities equal to or greater than those encountered in areas of The Geysers where chloride corrosion is not a problem. Developments in corrosion monitoring techniques, steam sampling and analytical methodologies for trace impurities, and computer modeling of the fluid chemistry has been instrumental in the success of this technology.

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Current techniques in acid-chloride corrosion control and monitoring at The Geysers

Geochemical constraints on supercritical fluids in geothermal systems

Earthquake-induced variations in the composition of the water in the geothermal reservoir at Vulcano Island, Italy

A simple method to compute hydrogen chloride abatement in geothermal power plants

Chloride (Cl) concentrations of 10-120 ppm{sub w} have been measured in superheated steam produced by wells at The Geysers, a vapor-dominated geothermal field in northern California. Corrosion of the well casing and steam-gathering system has been recognized in some parts of The Geysers, and is apparently related to the presence of Cl. Cl in the steam is in a volatile form, generated with the steam at reservoir temperatures, and probably travels to the wellhead as HCl gas. Published experimental data for partial pressures of HCl in steam over aqueous HCl solutions and for dissociation constants of HCl were used to calculate distribution coefficients for HCl. Reservoir liquid Cl concentrations capable of generating steam with the observed Cl concentrations were then calculated as a function of pH and temperatures from 250 to 350o C. Equilibrium mineral/liquid reactions with the K-mica and K-feldspar assemblage found in the wells limit the reservoir liquid pH values at various Cl concentrations to about 5 to 6 (near neutral at 250 to 350o C). Within this pH range, liquid at 250o C could not produce steam containing the high Cl concentrations observed. However, liquid at higher temperatures (300 to 350o C) with chloride concentrations greater than more » 10,000 ppm{sub w} could generate steam with 10 to over 200 ppm{sub w} Cl. There is a positive correlation between pH and the chloride concentrations required to generate a given Cl concentration in steam. The concentration of Cl in superheated steam constrains not only the reservoir liquid composition, but the temperature at which the steam last equilibrated with liquid. « less

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A.H. Truesdell

Papers

Hydrogen chloride in superheated steam and chloride in deep brine at The Geysers geothermal field, California