Experimental Study on Corrosion of J55 Casing Steel and N80 Tubing Steel in High Pressure and High Temperature Solution Containing CO2 and NaCl

Abstract

The downhole casing and tubing in thermal recovery wells are the main channels for fluid flow. The corrosion for casing and tubing in high pressure (5 MPa) and high temperature (200 °C) (HPHT) fluid can cause string failure due to wall thinning, deformation, and fracture. In order to study the corrosion characteristics of J55 casing steel and N80 tubing steel in HPHT environment containing CO2 and NaCl, corrosion and corrosion inhibition experiments were carried out using a rotating autoclave at a pressure of 5 MPa and 50–200 °C environment. Morphologies and compositions of corrosion products were analyzed by SEM and XRD. HPHT corrosion process was discussed by Arrhenius equation and the transition state equation. Results showed that the corrosion rates of the two materials increased with CO2 partial pressure while increased initially and then decreased with increasing temperature. In CO2–NaCl solution, the saturate NaCl decreased the CO2 corrosion rates at low temperature (inhibition) and increased CO2 corrosion rates at high temperature. Meanwhile, SEM results showed that the surfaces of CO2 corrosion became more dense and uniform at high temperature. The increase of NaCl leaded to pitting and high concentration NaCl solution causes granular products to appear on the CO2 corrosion surface. The carbon steel corrosion rate is mainly controlled by kinetic parameters of activation; the activation parameters were increased by the increase in temperature and NaCl concentration. Oil-soluble imidazoline acts as a good inhibitor for corrosion of J55 and N80 in this work.