Inhibition performance and mechanisms of methane hydrate inhibitors in oil and gas pipelines

Abstract

During winter natural gas transportation, hydrate formation under low-temperature and high-pressure conditions frequently results in pipeline blockage and severe low assurance challenges. Although conventional thermodynamic hydrate inhibitors (THIs) are effective in shifting hydrate phase equilibrium, the application is constrained by high volumetric injection requirements and the associated operational costs, thereby driving research interest toward low-dosage hydrate inhibitors (LDHIs). This study integrates high-pressure pipeline flow simulations with molecular dynamics simulations to systematically evaluate the inhibition performance and elucidate the molecular-scale mechanisms of representative inhibitor classes in methane hydrates. Pipeline simulation results indicate that, at low additive concentrations: (1) the inhibition effectiveness of cations follows the order Al³⁺ > Fe²⁺ > Ca²⁺ > Na⁺, suggesting a strong dependence on ionic charge density; (2) at identical mass fraction, methanol exhibits greater thermodynamic inhibition performance than ethylene glycol. Notably, 5.0 wt% ethylene glycol accelerates hydrate formation kinetics, exhibiting an anomalous promotion effect. For kinetic inhibitors and their blends, the following observations were obtained: (3) PVP K30 exhibited optimal inhibition performance at 1.0 wt%, significantly extending the hydrate induction time; moreover, the combination of 1.0 wt% PVP K30 with 5.0 wt% methanol completely suppressed hydrate formation under the tested conditions while substantially reducing the required alcohol dosage; (4) molecular-scale analysis indicates that methanol and ethylene glycol primarily act by shifting the hydrate phase equilibrium and perturbing the hydrogen-bond network of water. In contrast, PVP K30 inhibits hydrate formation by disrupting hydrogen-bond structures and decreasing methane–water association through steric hindrance and interfacial adsorption. The blended system exhibits a clear synergistic effect between thermodynamic and kinetic inhibition, combining a phase equilibrium shift with delayed hydrate formation kinetics. This THI-focused investigation systematically clarifies the inhibition of mechanisms of representative additives and provides a scientific basis for selecting cost-effective LDHIs strategies for hydrate control in oil and gas pipelines, with direct relevance to mitigating hydrate blockage in field operations.