Experimental study of hydrate formation in oil–water systems using a high‐pressure visual autoclave

Abstract

To investigate the characteristics of hydrate formation in oil–water systems, a high‐pressure visual autoclave equipped with visual windows was used where a series of hydrate formation experiments were performed from natural gas + diesel oil + water systems at different water cuts (30 and 70%), rotation rates (100, 200, 300 r/min) and thermodynamic conditions (temperature, pressure). According to the temperature and pressure profiles in test experiments, the processes of hydrate formation under two kinds of experimental procedures were analyzed first. Then, based on the experimental phenomenon observed through the visual windows, hydrate morphologies and hydrate morphological evolvements throughout the experiments were mainly investigated. In experiments, the growth and annealing of hydrate films on the wall, the agglomeration and deposition of hydrate coated water droplets, flocculent‐like hydrate deposition with water trapped in and the Pickering effect of hydrates were identified. Simultaneously, based on the experimental data of thermodynamic parameters, the kinetics of hydrate formation was studied by calculating the variations of hydrate film area and gas consumption in different experiments. In addition, the influences of temperature, pressure, and rotation rate on hydrate morphologies, hydrate morphological evolvements, and hydrate formation kinetics were also focused on.

Investigation on Hydrate Growth at the Oil–Water Interface: In the Presence of Wax and Kinetic Hydrate Inhibitor

“…Natural gas hydrates (NGHs) are crystalline compounds composed of water and hydrocarbon gas molecules . NGHs are readily formed under the low-temperature and high-pressure conditions in oil and gas industry and could therefore pose a great threat to subsea flow assurance by agglomerating, jamming, bedding, and depositing in the transmission pipelines. − So far, NGHs in subsea flow assurance have been extensively investigated, and several hydrate prevention/management strategies have been proposed. − Except for NGHs, another big concern in subsea flow assurance is about wax. When the pipeline operating temperature falls below the wax appearance temperature (WAT), wax molecules dissolved in the crude oil will gradually precipitate and may deposit on the pipe wall, which may further lead to pipeline plugging.…”

Investigation on Hydrate Growth at Oil–Water Interface: In the Presence of Wax

“…Nevertheless, wax molecules still can move to the CP–water interface by Brownian motion and diffusion. Here, we supposed that, once there were sufficient wax molecules moved to the CP–water interface, the interfacial tension of the water droplet would decrease due to the change of the interfacial properties resulting from the existence of wax molecules. , In addition, during the hydrate growth process, the exothermic effect of hydrate formation would intensify the Brownian motion of wax molecules near the CP–water interface, which further increased the probability of the wax molecules moving to the interface. Under these circumstances, the interfacial tension of the water droplet would gradually decrease during hydrate growth.…”

“…In deepwater oil and gas transportation processes, natural gas hydrates can form easily in pipelines considering the suitable temperature and pressure conditions and therefore lead to pipeline plugging. − Up to now, hydrate prevention strategies have been widely investigated for deepwater flow assurance. − Recently, Wang et al ,, proposed a new strategy for hydrate management in deepwater well testing, which allows gas hydrate formation and deposition in the wellbore within a safe tolerance. According to their research, ,, the new strategy can save the usage of hydrate inhibitors beyond 50% and provide an important theoretical foundation for flow assurance in deepwater gas wells.…”

Investigation on Hydrate Growth at the Oil–Water Interface: In the Presence of Wax and Surfactant

“…Natural gas hydrates (NGHs) are solid compounds formed by water and natural gas molecules . In subsea oil and gas transportation processes, NGHs can form easily considering the high pipeline pressure and the low environmental temperature. − To date, NGHs have been widely studied for the prevention of pipeline plugging, and many different hydrate inhibition methods have been put forward. − In addition to NGHs, the precipitation and deposition of wax can also result in pipeline plugging . Due to the nature that both hydrate issues and wax issues normally appear under low-temperature conditions, hydrate and wax could exist simultaneously during subsea pipeline transportation processes and pose an even more serious threat to the oil industry. − Thus, investigations on hydrate issues under wax-containing conditions are badly needed.…”