Evaluation of Corrosion Inhibitor Performance Under High Temperature / High Salinity Sweet Conditions

Abstract

CO2 corrosion is a vital problem in oil and gas production. The carbon steel pipe can suffer a long-term use economically under the CO2 corrosion environment by choosing an appropriate corrosion inhibitor. The performance of several corrosion inhibitors at elevated temperature & high salinity CO2 rich condition was evaluated for a field application. The performance of corrosion inhibitors was evaluated with an electrochemical measurement namely Liner Polarization Resistance (LPR) and weight loss coupons in autoclaves. LPR measures in-situ corrosion rate and it shows the inhibitor adhesion behavior on the metal surface. In the weight loss test, test coupons were mounted in a rotating cage and immersed in the test solution for a week. Test solution was synthetic brines with Total Dissolved Solids (TDS) 17%. The test solution was aerated with CO2 at ambient temperature and pressure before the corrosion test. It is well known that the inhibitor efficiency is encumbered with many variables, such as temperature, pressure, pH, flow speed and chemical composition of the production fluid. Salt content of formation water varies dependent on the location. Sometimes a production water analysis of a Middle East oil well shows more than 10% by weight. The inhibitors evaluated here had the temperature tolerance up to 100 °C and the same was the maximum test temperature. Some corrosion inhibitors performed better at low temperature than at high temperature. They showed poor inhibitor efficiency in case of pre-corrosion with high salinity at high temperature condition. This study also confirmed the validity of ILSS (Inhibitor Likelihood Success Score) introduced by Crossland et al. The score which was later acknowledged by HSE Office (UK) provided a useful information for inhibitor selection for pipelines in various field conditions. Several corrosion testing procedures were carried out to confirm the associated impact with/without pre-corrosion on the overall performance of the corrosion inhibitors. It seems that high salinity affects the inhibitor adhesion competing with corrosion product. The pre-corrosion test is an indispensable step for a qualification of corrosion inhibitors for a high salinity field.