In the recent years, application of ionic liquids in flow assurance has been enhanced due their potential as viable candidates for chemical mitigation of gas hydrates. Such clathrate compounds, in which gas molecules are trapped in hydrogen bonded caged formed by water molecules, comprise a major part of flow issues in pipeline conditions of low temperatures and higher pressures. Their formation can cause plugging, thereby disrupting the normal oil and gas flow. One flow assurance strategy consists in injecting different chemicals acting as gas hydrate inhibitors (GHIs). Ionic liquids have a strong potential for this application. Therefore, challenges, issues and current trends on their use as GHIs have been discussed in detail. Contrary to usual GHIs, Ionic liquids can act both as on thermodynamic (THI) and kinetic (KHI) hydrate inhibitors (as well as anti-agglomerates). . This dual functionality of ionic liquids is advantageous for gas hydrate mitigation. In preceding open literature, the studies on the applications of dual functional behavior of ionic liquids for mixed gases are found to be limited. The discussion on mixed gas hydrates behavior is novel and the factors influencing are highlighted. It is found that imidazolium based ionic liquids have been studied frequently in THI and KHI applications for pure CO2 and CH4 hydrates as their performance is better. While in the case of mixed gas hydrates, only quaternary ammonium salts have been studied yet. They showed better performance in terms of THI and KHI. Furthermore, the prospects of the use of ionic liquids in gas hydrate inhibition applications in flow assurance are also considered.

This paper presents an experimental and modeling studies on the thermodynamic inhibition effects of the mixture of monoethlyene glycol (MEG) and glycine (Gly) on the carbon dioxide hydrate phase boundary condition. The monoethlyene glycol and glycine (1:1) mixture inhibition effects were investigated at concentrations of 5, 10, and 15 wt.% and pressure ranges from 2.0–4.0 MPa. The effects of the proposed mixture on the carbon dioxide hydrate phase boundary were evaluated by measuring the dissociation temperature of carbon dioxide hydrate using a T-cycle method. The synergistic effect was evaluated based on comparison with pure MEG and Gly data. The results show that 15 wt.% of MEG and Gly mixture displays the highest inhibition effect compared to the 5 and 10 wt.% mixtures, respectively. However, the synergistic effect is higher at 10 wt.%. Dickens' model was also adopted to predict the phase equilibrium data of CO2 hydrates in the presence of the mixture. The modified model successfully predicted the data within a maximum error of ± 0.52 K.

In this study, series of non-ionic surfactants from Span and Tween are evaluated for their ability to affect the viscosity profile of cyclopentane hydrate slurry. The surfactants; Span 20, Span 40, Span 80, Tween 20, Tween 40 and Tween 80 were selected and tested to provide different hydrophilic–hydrophobic balance values and allow evaluation their solubility impact on hydrate formation and growth time. The study was performed by using a HAAKE ViscotesterTM 500 at 2 °C and a surfactant concentration ranging from 0.1 wt%–1 wt%. The solubility characteristic of the non-ionic surfactants changed the hydrate slurry in different ways with surfactants type and varying concentration. The rheological measurement suggested that oil-soluble Span surfactants was generally inhibitive to hydrate formation by extending the hydrate induction time. However, an opposite effect was observed for the Tween surfactants. On the other hand, both Span and Tween demonstrated promoting effect to accelerate hydrate growth time of cyclopentane hydrate formation. The average hydrate crystallization growth time of the blank sample was reduced by 86% and 68% by Tween and Span surfactants at 1 wt%, respectively. The findings in this study are useful to understand the rheological behavior of surfactants in hydrate slurry.

This paper presents the macroscopic observation of catastrophic gas hydrate growth during a shut-in, cold start-up and flowing conditions, simulating a natural gas transmission line operation. All experiments are conducted with a fixed simulated natural gas composition to form structure II gas hydrate with 11 K subcooling in the isochoric rocking cells. In order to simulate inhibited test systems, a formulated copolymer of vinylpyrolidone and vinylcaprolactam (PVP/PVCap) is included in some of the cells studied. Detailed macroscopic images and interpretation of pressure (P) and temperature (T) data are used to present our findings. It is found that production profiles such as different shut-in time and the mechanism of mass transfer of water from the bulk water phase to gas hydrate phase influence the gas hydrate growth in distinctive ways. Moreover, the capillary force in the gas hydrate structure may provide a greater driving force to promote gas hydrate growth than the diffusion rate of gases into the bulk water phase under shut-in and cold-start up conditions. Additionally, the number of critical nuclei formed during the initial stage of gas hydrate growth may influence the type of bulk gas hydrate present in the system at a later stage, i.e., finely dispersed hydrates or a slush type of gas hydrate.