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

Abstract

Asphaltenes\nin crude oils may affect hydrate formation in water–oil\nemulsions, complicating flow assurance and hydrate management in subsea\noil–gas multiphase pipelines. In this study, the effects of\nasphaltenes on hydrate nucleation and growth in water-in-oil emulsions\nwere investigated. It was found that the presence of asphaltenes inhibited\nhydrate nucleation. The inhibiting effect was enhanced with the increase\nin asphaltene content from 0 to 0.15 wt % and then was lowered with\nfurther increase in asphaltene content from 0.15 to 0.30 wt %. The\nasphaltenes were found to decrease the formed amount of hydrates.\nIn addition, the effects of water cut, stirring rate, and reformation\nprocess on hydrate formation in asphaltene-containing emulsions were\nstudied. The results showed that the nucleation rate of hydrates decreased\nwith a reduction in water cut. The hydrate growth rate first increased\nand then decreased with decrease in the water cut, which could be\nattributed to the combined effects of gas concentration and water\namount. Furthermore, both the nucleation rate and the growth rate\nof hydrates were observed to increase with an increase in the stirring\nrate, indicating the promoting effect of a high stirring rate on hydrate\nformation in asphaltene-containing emulsions. Finally, it was demonstrated\nthat hydrates nucleated more easily during the reformation process.\nHowever, the growth rate during the reformation process was lower\nthan that in the first formation. The results from this study have\npotential flow assurance applications when asphaltenes and hydrates\ncoexist in the subsea pipelines.