Effective Corrosion Inhibitor Formulation for Carbon Steel in Downhole Sweet Gas Wells

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Corrosion of the internal surfaces of pipelines is one of the serious issues facing the oil and gas industry. Produced oil and gas always contain some water mixed with brines and contain varying amounts of carbon dioxide (sweet gas), hydrogen sulfide (sour gas) and organic acids1. All of these can affect the integrity of the low-carbon steel pipes used in the construction of downhole gas wells. CO2 gas, along with the high salt content of production water, causes serious corrosion on the internal walls of corrosion resistance alloys (CRAs) and steel pipelines used in downhole gas wells.

Product Number: 51323-19009-SG

Author: Ime Bassey Obot, Ahmad A. Sorour, Tao Chen, Qiwei Wang

Publication Date: 2023

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Corrosion of the internal surfaces of pipelines is one of the serious corrosion issues facing the oil and gas industry. Produced oil and gas always contain water mixed with brines and varying amounts of carbon dioxide (sweet gas), hydrogen sulfide (sour gas) and organic acids. All of these can affect the integrity of the low-carbon steel pipes. Corrosion Inhibitors have become one of the best practical methods to mitigate internal corrosion damage, especially in downhole gas wells. In the present study, we developed a corrosion inhibitor formulation, abbreviated NAM-4 based on cost effective chemistries for use in downhole sweet gas wells. The corrosion inhibition performance of NAM-4 for C1018 carbon steel in CO2 saturated 3.5% NaCl brine was investigated. The efficiency of the inhibitor formulation was investigated at different inhibitor concentrations (25, 50, 75, 100, 125 ppm), test duration (6-72 h), and temperatures (30-80oC) using linear polarization resistance (LPR) and potentiodynamic polarization (PDP) measurements. The post-immersion surface characterization of the exposed C1018 carbon steel with and without NAM-4 was carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The excellent corrosion inhibition efficiency (> 97 %) was obtained at a very low concentration of 50 ppm, indicating the ability of NAM-4 to significantly protect the carbon steel against sweet (carbon dioxide) corrosion. The significance of this study is the possibility of replacing conventional toxic corrosion inhibitor formulations with cost effective ones for use in oilfield applications.