Nucleation and Growth of Gas Hydrates in Emulsions of Water in Asphaltene-Containing Oils
Dongxu Zhang, Qiyu Huang, Rongbin Li, Huiyuan Li, Wei Wang, Haimin Zheng, Xiangrui Zhu, Xun Zhang
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.