Nucleation and Growth of Gas Hydrates in Emulsions of Water in Asphaltene-Containing Oils

Abstract

Asphaltenes in crude oils may affect hydrate formation in water–oil emulsions, complicating flow assurance and hydrate management in subsea oil–gas multiphase pipelines. In this study, the effects of asphaltenes on hydrate nucleation and growth in water-in-oil emulsions were investigated. It was found that the presence of asphaltenes inhibited hydrate nucleation. The inhibiting effect was enhanced with the increase in asphaltene content from 0 to 0.15 wt % and then was lowered with further increase in asphaltene content from 0.15 to 0.30 wt %. The asphaltenes were found to decrease the formed amount of hydrates. In addition, the effects of water cut, stirring rate, and reformation process on hydrate formation in asphaltene-containing emulsions were studied. The results showed that the nucleation rate of hydrates decreased with a reduction in water cut. The hydrate growth rate first increased and then decreased with decrease in the water cut, which could be attributed to the combined effects of gas concentration and water amount. Furthermore, both the nucleation rate and the growth rate of hydrates were observed to increase with an increase in the stirring rate, indicating the promoting effect of a high stirring rate on hydrate formation in asphaltene-containing emulsions. Finally, it was demonstrated that hydrates nucleated more easily during the reformation process. However, the growth rate during the reformation process was lower than that in the first formation. The results from this study have potential flow assurance applications when asphaltenes and hydrates coexist in the subsea pipelines.

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

“…Other factors such as the solubility state of heavy fractions play an important role in affecting hydrate formation. As the solubility of the heavier fraction in the oil phase decreases, it could promote the hydrate plugging tendency. ,, This happens due to the flocculated asphaltene molecules, which act as nucleation sites for hydrates. The addition of a surface-active agent lowers the interfacial tension between the hydrocarbon and water and enhances the contact between the two liquid phases.…”

“…38 Some studies have observed that a decrease in solubility of the heavier fraction in the oil could promote the hydrate plugging tendency. 40,43,44 Thus, the inhibition effect has also been observed to be lowered with an increase in asphaltene content. Crude oil is a complex mixture of hydrocarbons, which can be fractionated based on molecular weight and polarity.…”

“…Apart from hydrate inhibition in bulk, a promotion effect has also been observed at the interface due to increased methane diffusion through a gas–water interface . Some studies have observed that a decrease in solubility of the heavier fraction in the oil could promote the hydrate plugging tendency. ,, Thus, the inhibition effect has also been observed to be lowered with an increase in asphaltene content.…”

“…Asphaltene has been shown to increase hydrate induction and growth time in water−CO 2 −oil systems but does not avoid hydrate formation, typically working as a kinetic hydrate inhibitor (KHI). This happens due to the arrangement and solubility of asphaltenes at the interface or hindering of the guest−host interaction, 40 or both. 41 On the contrary, there are studies that have reported a decrease in the hydrate inhibition tendency with increased asphaltene content or even promotion.…”

Influence of Asphaltene Polarity on Hydrate Behaviors in Water-in-Oil Emulsions

“…This result was attributed to the hydrate particle diameter and the amount of formed hydrates. For the emulsions with the same water cut, the lower hydrate particle diameter would enlarge the surface area of the hydrate and further increase the dissociation rate. − …”