The main difficulties in applying technologies based on hydrate formation are the slow hydrate formation rate, low storage capacity, severe formation conditions and environmentally devastating promoters. Nano-sized graphene oxide has special microstructure features such as its functional groups and a large specific surface area, which can lead to high heat and mass transfer efficiency, large gas dissolution, fast nucleation and formation rate. In this work, CO₂ hydrate formation with and without graphene oxide nanoparticles was investigated. Herein, the promoting mechanism and effects of graphene oxide concentrations in different initial pressures ranging from 3 to 5 MPa at 279 K on CO₂ hydrate formation process were studied experimentally. The experimental results showed that graphene oxide can shorten the induction time by 53–74.3% and increase the gas consumption up to 5.1–15.9% under different system pressures. Based on the results, the optimum concentration was ascertained as 50 ppm under which condition, the induction time and the reaction time were the shortest while the pressure drop and the gas consumption reached the maximum.

The formation and accumulation of hydrates in high pressure oil and gas pipelines bring great risks to field development and deep-water transportation. In this paper, a high pressure flow loop equipped with visual window was used to study the growth process of hydrates in a pipe flow system and slurry flow characteristics. Deionized water, industrial white oil and CO₂ were selected as the experiment medium. A series of experiments with different initial pressures (2.5–3 MPa), liquid loads (7–9 L), flow rates (25–35 kg min⁻¹) and water cuts (60–100%) were designed and carried out. Specifically, hydrate formation and slurry flow characteristics in two different systems, pure water and oil–water emulsion system, were compared. Both of the systems experienced an induction stage, slurry flow stage and followed by a plugging stage. Although hydrate growth gradually ceased in the slurry flow stage, plugging still occurred due to the continuous agglomeration of hydrates. Visual observation showed that there were obvious stratification of the oil–water emulsion systems at the later time of slurry flow stage, which directly resulted in pipe blockage. The hydrate induction time of the flow systems gradually decreased with the increasing initial pressure, initial flow rate and water content. And the induction time tended to decrease first and then slowly increase with the increasing liquid loading. For emulsion systems, the apparent viscosity and friction coefficient of the hydrate slurry increased with the increasing water content, indicating that there were higher plugging risks compared to the pure water systems. Moreover, the results of sensitivity analysis showed that the water content was the main factor affecting the hydrate induction time, followed by the influence of liquid carrying capacity and flow rate, and the initial pressure had the least influence on the induction time. Conclusions obtained in this paper can provide some reference not only for the prevention and management of hydrates in pipelines, but also for the application of CO₂ hydrate as a refrigerant.