Corrosion Behavior of 140 Grade Steel Casing Below Packer During Well Completion Process

Abstract

The corrosion behavior of TP140 steel was investigated based on the corrosion tests in such severe conditions as the live acid solution(15% HCl + 1.5% HF + 3% HAc + 5.1% inhibitor),spent acid and formation water containing CO2 corrosion with high pressure and high temperature.Also the electrochemical analysis was used to evaluate the corrosion resistance of TP140 in these environments. The results show that the uniform corrosion rate of TP140 in live acid solution,spent acid and formation water containing CO2 environment is 3.7490, 0.4361 and 0.5524 mm/a respectively. After spent acid corrosion, an incomplete Cu film is formed on the surface of the sample. The corrosion potential(-658 m V) of TP140 sample without removing the Cu film is higher than that(- 692 m V) of the sample with removed Cu film, which results in the corrosion drivingforce of the former is weaker than that of the latter. However, the self corrosion current density(3.1141 × 10- 5A/cm2) of the sample without removing the Cu film is significantly higher than that(1.0926×10- 5A/cm2) of the specimen with removed Cu film. Compared with the TP140 matrix of Fe, Cu is electropositive metal. So a typical large cathode-small anode structure because of incomplete Cu film is formed, which leads to serious local corrosion. The maximum depth of the corrosion pittings in these tests is up to 150 μm.