The Application of Mechanical-Chemical Corrosion Theory in Downhole Tubing CO₂Corrosion Research

Abstract

Indoor simulating experiment is a main method for oil field CO 2 corrosion research. Experimental parameters are very important for an accurate simulation. Based on the mechanical-chemical corrosion theory, the external load may be possible to accelerate the corrosion rate. However, the influence of N 2 pressure on CO 2 corrosion during the simulating experiment is negligible. Because the coupon stress induced by additional N 2 pressure is very low, therefore, the N 2 adding procedure can be cancelled and a more safety working space for researchers will be created. However, it does not mean that mechanical-chemical corrosion influence can be ignored. For downhole tubing, the hoop stress generated from the formation compress or liquid column internal pressure is remarkable; stress effect on corrosion has to be taken into consideration. When pit cavity especially occurred on the internal tubing surface, the stress concentration effect will induce a much higher local stress. Mechanical-chemical corrosion will become significant and more study should be performed on this topic.

Investigation of Stress Concentration and Casing Strength Degradation Caused by Corrosion Pits

“…In practice, double or multiple corrosion pits are common to be observed in oil and gas transportation casing, tubing, or pipeline (as shown Figure 1), and high stress could accelerate corrosion kinetics [9]. Therefore, the stress concentration enhanced by the double pits needs to be considered.…”

Corrosion problems in the oil country tubular goods and their mitigation – a review

“…Besides, according to the theory of mechanical-chemical corrosion (Gutman, 1998), the total pressure may have an effect on CO 2 corrosion because the external pressure will influence the metal's corrosion process and accelerate corrosion rate (Liu et al, 2009). But in an experiment and simulation, the influence of N 2 pressure on CO 2 corrosion is negligible when the stress is not very high (less than 50 MPa) (Zhu et al, 2015).…”

Numerical simulation of the double pits stress concentration in a curved casing inner surface

“…[3][4][5] Additionally, the corrosion process is also related to the structure mechanical stress, which could accelerate the corrosion rate in some circumstance. 6 Thus, the stress level on the casing, especially the stress level around the corrosion pits needs to be evaluated properly. Stress concentration is a stress increasing phenomenon in which geometric shapes change dramatically.…”