Molecular dynamics simulation to explore the synergistic inhibition effect of kinetic and thermodynamic hydrate inhibitors

The combined injection of kinetic and thermodynamic hydrate inhibitors (KHIs and THIs) is considered as a promising method to prevent the blockage of oil and gas pipelines caused by the accidental formation of methane hydrate. To develop better strategies for enhancing inhibition effects, molecular dynamics simulation is employed to investigate the synergistic mechanism of a KHI and a THI (PVP-A and methanol, respectively). Our results show that the nucleation time is shortened from 22 ns to about 12 ns by 1.65 wt% PVP-A or 4.8 wt% methanol, exhibiting the promotion effect on hydrate formation under the simulated high subcooling conditions. However, the composite inhibitor composed of PVP-A and methanol with a total concentration of 4.8 wt% prolongs the nucleation time beyond 500 ns, showing amazing inhibition effect. The whole synergistic process of KHIs and THIs is mainly composed of three stages, i.e. gas adsorption, water arrangement destruction and steric hindrance stages, and the first one usually dominates the whole inhibition process. Adding THIs to the aqueous solution containing KHIs enhances the attraction to methane and weakens the driving force for hydrate formation. Therefore, the methane adsorption capacity of the hybrid inhibitors is suggested to be considered in the future development.