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In the transportation of carbon dioxide through pipelines, the formation of hydrates presents a significant challenge, potentially obstructing the pipeline flow and compromising operational safety. One of the effective hydrate inhibition strategies to mitigate economic losses is adding poly(N-vinylcaprolactam) (PVCap). This study aims to investigate the effect of PVCap on hydrate inhibition performance using a high-pressure visualization stirring reactor to conduct experiments on CO2hydrate generation characteristics. Employing microscopic equipment, the study assesses PVCap’s influence on various parameters including the induction time of hydrate generation, gas consumption rate, and adhesion between hydrate particles. The experimental results indicate that PVCap can effectively inhibit the generation of carbon dioxide hydrate compared to a pure water system. The inhibition effect of PVCap on hydrate increases within the concentration range of 0–1.5 wt %. However, this effect diminishes at higher concentrations (2 wt %), attributed to PVCap’s adsorption onto the cage structure of hydrates. Consequently, the increased adsorption interferes with mass transfer at the gas–water interface. In addition, PVCap influences the surface roughness of hydrate particles, reducing particle adhesion within the 0–1.5 wt % concentration range but exacerbating at higher concentrations (2 wt %). This investigation sheds light on PVCap’s role in hydrate inhibition, crucial for ensuring the secure flow of hydrates in pipeline operations.

During the operation of deep-sea pipelines, the accumulation and deposition of hydrates are important reasons for pipeline blockage. The current main measure to solve the hydrate plugging problem is the addition of low-dose inhibitors (LDHIs), but it is not yet known whether the precipitation of wax crystals will affect their effectiveness. Therefore, in this study, the hydrate cohesive force within the wax-free/wax-containing system was directly measured by using a micromechanical force device (MMF) and the reasons for the change in cohesive force were analyzed from a morphological point of view. The results showed that glycine was effective in reducing the cohesion between hydrate particles in both wax-free/wax-containing systems and still exerted the effect of antiagglomeration agent (AA) at very low concentrations (as low as 0.10 wt %). Moreover, the optimum concentration of glycine was 0.50 wt %. At this concentration, the cohesive force decreased from 8.54 to 7.07 mN/m in the wax-free system, a decrease of about 17.2%, while the cohesive force decreased from 5.94 to 2.15 mN/m in the wax-containing system, a decrease of about 63.8%. By observation of the morphology of the hydrate particles, the presence of glycine was found to reduce the volume of the liquid bridge by changing the surface roughness and wettability of the particles, thereby reducing the cohesive force. And when wax was contained in the system, the wax further reduced the wettability by adsorbing on the surface of the hydrate particles. However, under certain AA conditions, the increase in wax concentration (from 0.1 to 0.3 wt %) resulted in the free water inside the hydrate being more likely to form liquid bridges with the surrounding particles, thus weakening the effect of AA. This work analyzes the effect on cohesive force in the simultaneous presence of LDHIs and wax from a morphological point of view, which is beneficial in providing more insights into securing safe hydrate flow management.

Precipitation of wax crystals and hydrate formation during deep-sea multiphase pipeline transportation would limit pipeline transportation flow and even trigger accidents. It is necessary to study the hydrate formation behavior in the wax-containing system. This paper utilized a mixture of number 60 Kunlun paraffin wax and number 2 industrial white oil to simulate the wax-containing system, and the CO2hydrate was formed in the wax-containing system. The morphology of CO2hydrate formation was captured by the microscope and the charge-coupled device imaging system. In this study, the influences of the wax crystal concentrations on the induction time and cumulative gas consumption of hydrate formation were investigated, and the effects of wax crystal precipitation on the CO2hydrate nucleation mechanism were discussed. The experimental results indicated that, for the wax crystal concentrations of 1.50 and 2.50 wt %, the induction time of CO2hydrate formation in the wax-containing system was reduced by 29.23 and 69.23% compared to that in the pure water system, respectively. However, for the wax crystal concentration of 0.50 wt %, the induction time of CO2hydrate formation in the wax-containing system was increased by 130.77% compared to that in the pure water system. The reason for this was that the precipitation of wax crystals at high concentrations increased the chance of heterogeneous nucleation and the probability of heterogeneous nucleation increased with the increase of wax crystal concentrations. However, for the wax crystals at low concentrations, it not only lowered the chance of cross nucleation but also increased the mass transfer resistance for gas diffusion, thereby resulting in the increase of the induction time of hydrate formation. It was also found that, with the increase of the wax crystal concentrations, the cumulative gas consumption during hydrate formation decreased gradually. When the wax crystal concentration increased to 2.50 wt %, the cumulative gas consumption was reduced by 32.96% compared to that of the pure water system. The experimental results obtained in this study were helpful for understanding the kinetic characteristics of hydrate formation in the wax-containing system, which is meaningful for the pipeline flow assurance, safety, and economic security of pipeline transportation as well as the development of carbon capture and storage.