Abstract
Many acidic geothermal wells with low-carbon steel casing materials benefit from the application of pH control chemicals such as NaOH. However, at high temperatures this can result in rapid scaling by anhydrite. In addition oxidation of iron in acid wells can lead to reductive deposition of heavy metals and in localized galvanic corrosion. Control of production fluid pH can require frequent adjustment of the NaOH addition. Corrosion inhibitors have been proposed as an alternative to pH adjustment in mildly acidic geothermal wells both for control of corrosion and scaling as well as for control of heavy metal deposition. In this study, a commercial corrosion inhibitor was used to quantify the level of corrosion mitigation of K55 casing material in simulated acidic geothermal electrolyte at different pH values and inhibitor concentrations. Results showed a decrease in corrosion rate as a function of increasing pH without inhibitor addition and a decrease in corrosion rate of over 90% with inhibitor addition at the lowest pH tested. The percentage decrease in corrosion rate was less at the higher pH values tested where the inhibitor free corrosion rates were lower and presumably controlled, in part, by iron sulfide/iron oxide formation.
