Effect of Asphaltenes on the Kinetics of Methane Hydrate Formation and Dissociation in Oil-in-Water Dispersion Systems Containing Light Saturated and Aromatic Hydrocarbons

• Published in: Energy & fuels Vol. 35; no. 21; pp. 17410 - 17423
• Main Authors: Prasad, Siddhant Kumar, Nair, Vishnu Chandrasekharan, Sangwai, Jitendra S
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.11.2021
• Subjects: Fossil Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.1c02252

Proper understanding of the interaction of individual components of crude oil with hydrate formation and dissociation is essential to design an effective mitigation strategy for hydrate blockage, especially in offshore flowlines. In this study, various isothermal methane hydrate formation and dissociation kinetics experiments have been carried out in oil-in-water dispersion systems to understand the effect of liquid hydrocarbons (such as n-heptane and toluene) and asphaltenes with varying concentrations at 8 MPa and 275.15 K. To correlate the results obtained from the kinetics experiments, solubility tests and interfacial tension measurements have also been carried out. It was observed that aromatic hydrocarbons (e.g., toluene) in the system led to less dissolution of methane gas as compared to alkanes (e.g., n-heptane). This, along with the more developed oil–water interface due to the lower density difference with water, made the system more vulnerable to hydrate formation, and it displayed secondary hydrate induction. The presence of asphaltenes in the oil–water system showed higher gas consumption during hydrate formation at lower concentrations, possibly due to flocculated asphaltene molecules at the oil–water interface acting as nucleation sites for hydrate formation. As the concentration of asphaltene increases, the growth of hydrate crystals is found to be limited, as more asphaltene molecules tend to restrict the gas diffusion toward the water phase, controlling the growth kinetics during hydrate formation. The hydrate dissociation experiments suggest that the presence of flocculated asphaltenes in the system has delayed the dissociation of methane hydrate crystals for some time. The findings of this study will help gain an insight into the interaction of asphaltene, alkanes, and aromatics on the kinetics of methane hydrate formation and dissociation suitable for flow assurance applications.