Co-Evolution Law and Control Technology of Corrosion and Scaling in Water Injection Wells of a Middle East Carbonate Oilfield

Abstract

In order to compensate formation pressure and maintain oil production, a carbonate oilfield in the Middle East adopts water flood development. The injected water exhibits the feature of high salinity and high content of chloride, high content of H2S, and high content of scaling ion. As a result, severe corrosion perforation and plugging were encountered in less than two years, which seriously affects the normal water injection and production of the oilfield. This paper aims to find out the main controlling factors and co-evolution law of corrosion and scaling, and propose the prevention strategy. The composition of the scale samples is firstly analyzed by combustion method, XRD and atomic absorption spectrometry, and then the main controlling factors of corrosion and scaling are experimentally clarified. On this basis, immersion experiments at different times are further carried out to reveal the evolution of corrosion and scaling in injectors at different depths. The results show that temperature, salinity (mainly Cl-), total sulfur content, and sulfate reducing bacteria (SRB) are the main factors controlling corrosion and scaling, and there is a synergistic effect among them. Temperature and sulfide have a promoting effect on uniform corrosion and scaling, while the salinity in the range of 110g/L-180g/L has an inhibition effect, but has a promoting effect on localized corrosion under deposits; a small amount of SRB can still propagate rapidly under deposits, aggravating the localized corrosion. Along the wellbore profile from top to bottom, the uniform corrosion rate and scaling amount increase but the localized corrosion rate decreases, which indicates that the high risk of localized corrosion perforation in the middle and upper part of the wellbore, as compared to the lower part. It is consistent with the actual corrosion perforation law of water injection wells. The co-evolution mechanism of corrosion and scaling is a synergistic process of three factors: lower uniform corrosion rate under high salinity + sulfide-induced local corrosion initiation + SRB enrichment under deposits and acidification autocatalysis due to Cl- migration. Finally, corrosion and scale control measures were taken by deep desulfurization and adding corrosion inhibitor. This work provides useful practical experience for preventing corrosion and scale formation of high salinity injector in carbonate oilfield.