Green corrosion inhibitors for drilling operation: New derivatives of fatty acid-based inhibitors in drilling fluids for 1018 carbon steel in CO2-saturated KCl environments

Corrosion of the oilfield drilling equipment can considerably affect its drilling effectiveness, service life, and operation safety as well as the surrounding environment. In this study, inhibition effects of three eco-friendly fatty acid-based inhibitors, Polyethylene glycol-2 oleamide (PEG-2 oleamide), Glycerol myristate (GM) and Glycerol linoleate (GL), in emulsion-based drilling fluids against corrosion of carbon steel were investigated. The inhibitors were characterized by Fourier transform infrared (FT-IR) spectroscopy and CHNS–O analysis. Effects of the inhibitors on corrosion of the steel were evaluated by means of electrochemical measurements of open circuit potential (OCP) and potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectrophotometer (XPS) were employed to study morphology and the chemical composition of surface layer adsorbed on the metal surface. The study demonstrates remarkable performance of the green inhibitors especially PEG-2 oleamide, which shows an inhibition efficiency of 99.7%. The high inhibition capability results from a formed protective layer that blocks corrosive ions to attack the steel surface. First-principles calculations and molecular dynamics simulation were performed, which reveal chemical bonding between the inhibitors and iron surface, and stronger intermolecular attraction in the adsorbed film of, e.g., PEG-2 oleamide, which renders the PEG-2 oleamide–induced film particularly durable.