Steel corrosion inhibition by calcium nitrate in halide-enriched completion fluid environments

Abstract

Calcium nitrate (Ca(NO 3) 2) has been suggested to inhibit steel corrosion. However, the effectiveness of corrosion inhibition offered by calcium nitrate in highly halide-enriched environments, for example, completion fluids, is not well known. To better understand this, the inhibition of corrosion of API P110 steel by Ca(NO 3) 2 was studied using vertical scanning interferometry in solutions consisting of 10 mass % calcium chloride (CaCl 2) or 10 mass % calcium bromide (CaBr 2), for example, to simulate the contact of completion fluids with the steel sheath in downhole (oil and gas) applications. The evolution of the surface topography resulting from the initiation and growth of corrosion pits, and general corrosion was examined from the nano-scale to micron-scale using vertical scanning interferometry. Special focus was paid to quantify surface evolution in the presence of Ca(NO 3) 2. The results indicate that, at low concentrations (≈1 mass %), Ca(NO 3) 2 successfully inhibited steel corrosion in the presence of both CaCl 2 and CaBr 2. Statistical analysis of surface topography data reveals that such inhibition results from suppression of corrosion at fast corroding pitting sites. However, at higher concentrations, calcium nitrate's effectiveness as a corrosion inhibitor is far less substantial. These results provide a means to rationalize surface topography evolution against the electrochemical origin of corrosion inhibition by NO 3 − species, and provide guidance regarding the kinetics, and susceptibility to degradation of the steel sheath during exposure to halide-enriched completion fluids.

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