Formation and Evolution of the Corrosion Scales on Super 13Cr Stainless Steel in a Formate Completion Fluid With Aggressive Substances

Xiaoqi Yue,Zhihao Qu,Zhile Yang,Luyao Huang,Yong Hua,Lei Zhang

doi:10.3389/fmats.2021.802136

Abstract

The formation and evolution of the corrosion scales on the super 13Cr stainless steel (SS) surface after exposure in a formate completion fluid with the presence of various aggressive substances was investigated. The results indicate that the formation of Fe3O4 covered the surface of super 13Cr SS as the inner layer accompanied with outer scattered FeS. The corrosion rate was below 0.07 mm/year after 120 h of exposure in the formate fluid at 180°C under N2 environments; the presence of aggressive substances such as sulfide and CO2 in the formate fluid promoted the proceeding of anodic dissolution in the early period, and the ingress of CO2 progressively increased the general corrosion rate to 1.7 mm/year. For CO2-containing conditions, the formation of FeCr2O4 and Cr(OH)3 was detected in the inner corrosion product layers, and the precipitation of “sheet”-shaped iron carbonate (FeCO3) was detected as the outer layer. The accumulation rate of corrosion products increases by two orders of magnitude with the ingress of CO2, corresponding to thicker corrosion products, but the dissolution rate is still three orders of magnitude higher than when CO2 was absent.

Highlights

The exploitation and production of ultra-deep reservoirs for future energy supply have been highlighted as a practical strategy to achieve the effective application of fossil energy
It can be seen that the corrosion rate of S13Cr stainless steel (SS) was high (21.94 mm/year) when CO2 was introduced into the formate fluid, in comparison with the value of 1.177 mm/year under the N2 condition
The average mass loss tended to increase with time prolonged; the slope of the increasing curve decreased with time, which indicates the corrosion rates of S13Cr SS decreased with immersion time, showing a sharply reduction from 5 to 48 h

Summary

Introduction

The exploitation and production of ultra-deep reservoirs for future energy supply have been highlighted as a practical strategy to achieve the effective application of fossil energy. Due to the high pressure (115–140 MPa), high temperature (170°C–190°C), and complex corrosive medium, the corrosion issues of highly dense brine-based completion fluids on tubing and casing materials in ultra-deep high-temperature wells have become a research hot spot in the course of oil and gas exploitation (Yue et al, 2020a; Li et al, 2020; Zhao et al, 2020). Formate brines with filtrate viscosity and low-water activities are more potential to be a safe option for the deep wells (the average depth >6,000 m), and the operating temperature can be over 150°C (Howard and others, 1995; Bungert et al, 2000). Among formate brines, KCOOH solution has been widely used as the alternative option for such arduous conditions based on its large solubility and low corrosivity (Leth-Olsen, 2004)

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Discussion

Conclusion