Removing Iron Sulfide Scale: A Novel Approach

Abstract

Abstract Iron sulfide is a common scale-formation in sour-gas wells that restricts tubular diameter, reducing well productivity. Compared to other scales, iron sulfide has unique risks associated with chemical removal. For example, due to the corrosiveness of hydrochloric acid (the most common chemical agent for both sulfide and carbonate scale removal), damage to the completion metallurgy at elevated temperature limits its applicability. Another main concern related to the use of acid for iron sulfide removal is the rapid generation of H2S byproduct and the risks associated with production of this toxic gas to the surface. Owing to H2S toxicity and the resultant elevated corrosion risk, new chemical solutions are needed for high-temperature FeS scale dissolution with low H2S generation. This study describes the development and characterization of a powerful noncorrosive solution for iron sulfide removal based on a chelating agent. Testing shows the fluid dissolution capacity under varied temperatures, scale-surface area, treatment fluid volume, and exposure time. Tests are also included showing the comparative benefits in dissolution capacity compared to other commercially used products such as diethylenetriaminepentaacetic acid (DTPA) and Tetrakis (hydroxymethyl) phosphonium sulfate (THPS). Finally, the mild-pH of the new chemical solution provides significantly lower corrosion rate. This work describes an altogether new family of chemicals for sulfide scale, providing high dissolution capacity, low corrosion rates, and limited generation of toxic H2S.