Optimizing the Performance of Natural Gas Hydrate Inhibitors: Modifying the Alkyl Size in <i>N</i> -Alkyl Acrylamide

Natural gas remains one of the most critical energy sources worldwide. In deepwater gas hydrate formations, the use of hydrate inhibitors is essential during drilling operations to suppress secondary hydrate formation, maintain wellbore stability, and ensure uninterrupted fluid transport. However, the evolving challenges of drilling in shallow reservoirs under deepwater conditions have exposed the limitations of conventional hydrate drilling fluid systems, which are increasingly inadequate due to the suboptimal performance of traditional hydrate inhibitors. In this study, the commercial kinetic hydrate inhibitor poly(N-vinylcaprolactam) was modified via three approaches incorporating various alkyl groups, and the structures of the modified polymers were characterized using 1H NMR spectroscopy and FTIR spectroscopy. The performance was evaluated in 1 wt % inhibitor solutions prepared with deionized water, with pure deionized water as the control. Among the tested agents, P(NVCL-co-DMAA) exhibited the highest inhibition efficiency. It extended the hydrate formation time from 168 to 321 min and extended the hydrate formation temperature from 10.0 to 2.47 °C at a concentration of 1 wt %. Furthermore, molecular dynamics simulations were conducted to elucidate the inhibition mechanisms of the modified inhibitors. Radial distribution function analysis of methane molecules revealed that incorporating alkyl groups enhanced both the intensity and position of the distribution peaks between methane molecules. Notably, the inclusion of N,N-dimethylacrylamide allowed the modified inhibitor to outperform the conventional poly(N-vinylcaprolactam), reducing the adsorption energy between inhibitors and methane hydrate by 53.11%. Thus, the proposed alkyl modification method enhances the adsorption capacity on the surface of the hydrate. These findings offer valuable insights for designing more effective and efficient hydrate-formation inhibitors.