The Effect of Polymerization Degree of Hydrate Inhibitor on Hydrate Formation: Molecular Dynamics Simulations and Experiments

Natural methane hydrates are estimated to be the largest source of unexploited hydrocarbon fuel. However, there are many difficulties in drilling for natural gas hydrates production, among which inhibiting hydrate generation is an important issue. The conventional thermodynamic inhibitors have difficulties such as large dosages and are not environmentally friendly, while the widely used kinetic inhibitors also suffer from failure with high subcooling. Thus, it is urgent to develop new efficient hydrate inhibitors. Molecular design of hydrate inhibitor molecules using molecular simulations is one of the most common tools used. However, it is challenging to reproduce experimental-scale hydrate inhibitor fractions at the molecular scale. Thus, many studies have only investigated the effect of a minimal number of repeating units in an inhibitor on hydrate stability, leading to conclusions about the effects of various functional groups on hydrate stability. In contrast, a selection of the number of repeating units (polymerization degree, N) in the molecular structure of polymeric hydrate inhibitors has rarely been discussed. In this work, polymer PVP-N with different N was established based on NVP. The effect of a polymer molecular weight on hydrate formation was investigated. The results show that the different N in PVP has a significant effect on a diffusion coefficient of water molecules. A smaller N in PVP is more likely to inhibit hydrate formation during the phase of nucleation, but its effect is significantly weakened during the phase of formation. This study helps us to understand the effect of a polymer molecular weight on the performance of hydrate inhibitors and select an appropriate number of repeating units in molecular modeling, which dramatically reduces the difficulty of designing the molecular structures of hydrate inhibitors and other drilling fluid treatment agents, clarifies the mechanism of action of hydrate inhibitors and other drilling fluid treatment agents at the molecular scale, and is essential for developing high-performance drilling fluid treatment agents and promoting the commercial development of natural gas hydrates.