Recently, several localized corrosion and cracking failures happened to API 5CT Grade C110 tubing in high-density formate completion fluid at high temperature, because of the leakage of CO2 and the mechanical damage on the tubing surface. In this paper, the hydrochemical simulation software is used to calculate the needed content of pH buffer. The corrosion behavior of C110 tubing was investigated with autoclave, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that 1 wt% Na2CO3 and 1 wt% NaHCO3 can maintain the pH of formate completion fluid mixed with 3 MPa (435 psi) CO2 up to 6.35, which means CO2 corrosion is restrained effectively. The simulated experiments show that the general corrosion rate of C110 tubing decreases from 0.45 mm/year to 0.24 mm/year, and the C110 tubing shows little localized corrosion and cracking susceptibility in the formate completion fluid when buffered with 1 wt% Na2CO3 and 1 wt% NaHCO3. The results of XRD and SEM indicate that the pH buffer is helpful to generate compact and protective FeCO3 corrosion product film.

Subject
Scanning electron microscopy, X-ray diffraction, Completion fluids, Modeling, Formates, Partial pressures, Acidity, Corrosion products, Tubing, Steel, Brines, Localized corrosion, Stress corrosion cracking
Keywords:
pH buffer, corrosion behavior, formate completion fluid, high temperature
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2019
Association for Materials Protection and Performance (AMPP)
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