F22, a low alloy steel, has become widely used in oil field production systems. However, current scale inhibitor technologies on the market often cause severe corrosion on F22, particularly at high temperature conditions. Therefore, F22 compatible scale inhibitors are in demand in the oil and gas industry. A F22 compatible scale inhibitor is required to be only mildly corrosive on F22, with a general corrosion rate of ≤ 4 mpy and no pitting corrosion, while maintaining high scale inhibition efficiency with a low minimum inhibitor concentration (MIC). A wide range of scale inhibitor products were evaluated for F22 corrosion rates in inhibitor compatibility testing and scale inhibition in dynamic tube-blocking (DTB) testing. The test temperature was as high as 240 °F (116 °C), and the test brine had positive saturation indices for calcium carbonate (CaCO3) and iron carbonate (FeCO3) scales. Based on the performance of both F22 compatibility and scale inhibition, the best blend was selected for further evaluation, i.e., subsea certification. Finally, the developed product has met all the requirements of a F22 compatible scale inhibitor, and has gone through a successful field trial, and it is ready for larger scale applications.
F22 is a low alloy steel that typically contains 12% Carbon, 2.25% Chromium, and 1.0% Molybdenum1. This steel has been widely used in oil production systems, especially in well head design and construction. As a low alloy steel, F22 can be corroded by oilfield chemicals under certain circumstances. For example, it was observed in the Gulf of Mexico that typical scale inhibitor chemistries caused severe corrosion on F22.
Scale inhibitors are referring to the class of chemicals that can prevent or retard scale formation. Typical scales in the oil field include carbonate scales (e.g., calcium carbonate, iron carbonate), sulfate scales (e.g., barium sulfate, calcium sulfate), sulfide scales (e.g., iron sulfide, lead sulfide), and halite2. Scales often form due to temperature and pressure changes during oil and gas production from reservoir to surface, or due to co-mingling of incompatible fluid3. Chemical scale inhibition is an economical and commonly used method for scale control. There are several different types of scale inhibitors, including phosphonate, phosphate ester, sulfonate polymer, polyacrylic acid, polymaleic acid, and more2. Different types of scale inhibitors show different corrosion risk on F224. For the same type of scale inhibitor chemistry, scale inhibitor product with low pH is typically more corrosive than scale inhibitor product with neutral pH4.