Objective In the H₂S/CO₂ coexistence system, corrosion of wellbore tubing will seriously affect the production safety of oil and gas wells, and the injection of efficient and targeted corrosion inhibitors into the wellbore is one of the most effective measures. In this paper, three corrosion inhibitors with good anti-corrosion effects against H₂S/CO₂ corrosion of wellbore materials are selected to simulate the corrosion behavior of P110S steel in the field.

Method   The corrosion evaluation of P110S steel was conducted using the weight loss method and surface morphology analysis. The polarization curves were analyzed through electrochemical testing. Additionally, molecular dynamics simulations were employed to calculate the adsorption energy and nucleophilic/electrophilic indices of the inhibitor molecules, along with analyzing the frontier orbital distribution.

Result  Mannich base-1 demonstrated the best performance in wellbore corrosion prevention, with an inhibition efficiency of up to 86.32%. Electrochemical testing results indicated that Mannich base-1 was a mixed type inhibitor mainly composed of anodes. Molecular dynamics simulation studies have found that all three inhibitor molecules could stably adsorb on the metal surface, among which Mannich base-1, containing a benzene ring and polar functional groups (O, N), adsorbs onto the Fe surface, with its long carbon chain aligning parallel to the Fe surface to form a stable adsorption configuration, which was consistent with the results obtained from the weight loss method.

Conclusion Mannich base-1 is the most optimal corrosion inhibitor for this field and can provide effective measures for the wellbore corrosion protection process.