Structural Behaviors of Waxy Crude Oil Emulsion Gels

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• 作者：Guangyu Sun ; Jinjun Zhang ; Hongying Li
• 刊名：Energy & Fuels
• 出版年：2014
• 出版时间：June 19, 2014
• 年：2014
• 卷：28
• 期：6
• 页码：3718-3729
• 全文大小：703K
• 年卷期：v.28,no.6(June 19, 2014)
• ISSN：1520-5029

文摘

At low ambient temperatures in offshore environments, the water-in-oil emulsions of waxy crude oil develop a combined structure of wax crystals and water droplets, resulting in gelling and other complicated flow problems which may severely challenge flow assurance of the multiphase production and transportation system. In this study, the viscoelastic and yield behaviors of waxy crude emulsion gels were investigated, and analyses were then made by investigating the roles of wax particles and water droplets. Small amplitude oscillatory measurements were first carried out to study the effects of dispersed water on the structure and its evolution with time elapsing. Then, creep and recovery tests were conducted within the linear viscoelastic region to further investigate the viscoelastic behaviors of the emulsion gels. Further, the influence of dispersed water on the yield behaviors was studied by stress sweep measurements, and the effects of temperature, i.e., the precipitated wax, on the yield stress and yield strain were investigated by shear-rate-controlled loading measurements. The emulsion was found to become more elastic with the increase of the water cut, exhibiting phenomena such as the loss angle decreasing, storage modulus growing-up, the emulsion gelling at higher temperature, and strain recoverability increasing. The creep and recovery behavior may well be described by a mechanical analogy model with one Maxwell model and two Kelvin鈥揤oigt models associated in series. Compared to the brittle structure of the gelled waxy crude oil as was reported in previous studies, the emulsion gels become more ductile with the increase of the water cut. The yield stresses of both the crude oil and the emulsion gels increase monotonically with the increase of the precipitated wax, and the yield strain of the emulsions with few precipitated wax particles increases with decreasing temperature, which is contrary to the waxy crude oil and the emulsions with low water cut, and interestingly the yield strain of emulsions may show both of these opposite trends, first increasing and then decreasing with the continuous decrease of temperature. All structural behavior differences between the emulsions and the waxy crude oil may be attributed to the roles that the dispersed water droplets may play and the interactions of the wax particles and the water droplets.