Screening of an Environmentally Friendly Corrosion Inhibitor for Mildly Acidic Geothermal Fluid Applications

Abstract

Successful utilisation of mildly acidic well fluids where the acidity is derived from sulfur species has been demonstrated through downhole pH adjustment. Limitations on this method of corrosion control have been encountered through high temperature precipitation of anhydrite requiring close balance of pH for minimisation of anhydrite and control of corrosion. This constraint has discouraged the use of NaOH for corrosion control in geothermal wells. An alternative scenario using corrosion inhibitors, with or without some intermediate pH adjustment has been proposed but has found resistance from users concerned with environmental impact of traditional oil and gas field inhibitors. This paper provides laboratory screening results for an environmentally friendly candidate corrosion inhibitor for acidic geothermal fluids. The candidate inhibitor was found to meet the requirements for inhibition in pH 3.5 brine but also did not adversely impact on the protective properties of H2S at higher pH values of 4.5 and 6.0. The results provide encouragement for use of this alternative solution for production of geothermal wells cased in carbon and low alloy steels that encounter mildly acidic fluids after completion.