Corrosion mitigation is critical for successful managed pressure drilling (MPD), underbalanced drilling (UBD), and air drilling operations. During these operations, large volumes of gas are injected to lower the hydrostatic pressure in the annulus. Most often the injected gas contains some oxygen and the gas is circulated in combination with some quantity of drilling fluid or liquid. Due to the oxygen content and aqueous environment, corrosion potential during MPD/UBD/air drilling operations is high.

Without a proper corrosion mitigation program during these operations, corrosion can lead to the catastrophic failure of drillstring components with corrosion rates 15 times or higher than the industry-acceptable rate of <2 lb/ft2/yr. These high corrosion rates can lead to numerous operational problems resulting in higher well costs and/or formation damage.

This paper discusses how to properly design, implement, and monitor a successful corrosion program to mitigate corrosion during MPD/UBD/air drilling operations. Furthermore, it highlights a process that utilizes membrane technology as a mechanical means of reducing oxygen concentration in the gaseous media in combination with chemical corrosion inhibitors to alter the drilling fluid environment. By using this process, the corrosion rates can be controlled to satisfactory levels during these operations.

Other areas of discussion include membrane technology, drilling fluid chemistry in terms of corrosion control, and the types of corrosion that occur during a MPD/UBD/air drilling operation. Laboratory data will be presented demonstrating the development and limits of the various corrosion control chemistries. And finally, the operational considerations of an effective corrosion control program with case histories will be presented.

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