Kinetic Hydrate Inhibitors─Which is Best, Block or Statistical Copolymers?

Abstract

Kinetic hydrate inhibitors (KHIs) have been used for nearly 30 years to prevent gas hydrate formation in oil and gas production flow lines. The main component in KHI formulations is one or more water-soluble polymers. Copolymers are often used, to improve either the performance or compatibility issues such as high temperature or brine composition. Industrially, copolymers are mostly obtained by conventional radical polymerization, giving statistical copolymers. Some work has been previously reported on block copolymers as KHIs but it is still not clear if this type of polymer structure gives any significant advantages. Here we report the controlled synthesis of well-defined statistical and block copolymers containing the most commercially common vinyl amide monomers used in KHIs, that is, N-vinyl caprolactam, N-vinylpyrrolidone, and N-isopropylacrylamide. The polymerization control enabled a good structural comparison of the KHI performance of block versus statistical copolymers. KHI experiments were conducted under high pressure in steel rocking cells with a natural gas mixture. Most tests were without but sometimes with a liquid hydrocarbon phase. In summary, we did not observe a significant performance improvement for the block copolymers compared to that of the equivalent statistical copolymers.