Corrosion by HCI in Dry Steam Wells Controlled using Potassium Carbonate without Destroying Superheat

Abstract

An increasing amount of the dry geothermal steam produced in Sonoma and Lake Counties, California contains sufficient hydrogen chloride (HCl) to severely corrode well casing and surface piping. Sodium hydroxide is injected into the surface piping to neutralize HCl, but requires that enough water be injected with it to desuperheat the steam and provide sufficient liquid to keep the reaction products in solution. Sodium hydroxide and water cannot be injected downhole for this purpose because localized cooling of the casing might induce condensation of acidic and highly corrosive salt solutions. Also, the concentrated caustic employed is itself corrosive and hazardous. Potassium carbonate is much less hazardous than caustic, but equally effective in neutralizing HCl. Excellent corrosion control has been demonstrated in field trials using potassium carbonate.1 Because potassium carbonate and the potassium salts produced are highly soluble up to high levels of superheat, only a small amount of carrier water needs to be added, and the steam remains superheated with no risk of inducing localized corrosion.