Effects of waxes and asphaltenes on CO2 hydrate nucleation and decomposition in oil-dominated systems

Abstract

Hydrate formation is a major flow assurance issue for underwater multiphase pipelines. The heavy fractions in crude oil make it more complicated. However, the impact of a single fraction in oil on hydrate behaviors is still poorly understood. In response, this paper aims to investigate and compare the effects of waxes and asphaltenes on CO2 hydrate nucleation and decomposition, using a self-designed high-pressure autoclave. The results show that both waxes and asphaltenes retard hydrate nucleation, wherein asphaltenes have a more pronounced effect than waxes. Waxes mainly restrict gas diffusion in the bulk phase during hydrate nucleation. Asphaltenes are more effectively adsorbed on the surface of the water droplet and hydrate nucleus to retard the nucleation. In addition, the decomposition rate of hydrate particles is lowered when trapped in the wax gel-like structure, whereas it is enhanced by the increased hydrate surface area with asphaltenes. This work provides insights into the effects of crude oil components on the behaviors of hydrate, which can facilitate flow assurance applications in subsea multiphase pipelines.