Structural Behaviors of Waxy Crude Oil Emulsion Gels

Abstract

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–Voigt 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.

Rheological and Thermal Behavior of Water-Waxy Crude Oil Emulsions and Model Oil Systems

“…1), suggested that the most strong influence is exercised by the shear stress applied during cooling. The aging time after cooling step, which accord to Sun et al (2014), favours a complete wax precipitation, also showed a minor impact, suggesting that 15 minutes is long enough for most wax precipitation. On the other hand, cooling rate, pointed in many studies as an important factor on yield stress of waxy oils (Venkatesan et.…”

Bingham’s model in the oil and gas industry

“…Water-in-crude oil emulsions generally undergo a solgel transition as temperature is decreased, especially for waxy oils (Hemmingsen et al 2005;Visintin et al 2008;Paso et al 2009;Maia Filho et al 2012;Haj-shafiei et al 2013;Barbato et al 2014;Sun et al 2014). The yield stress of these gelled emulsions may be very high (of the order of 1000 Pa), and an accurate and reproducible method for its measurement still lacks (Barbato et al 2014).…”

“…The yield stress of these gelled emulsions may be very high (of the order of 1000 Pa), and an accurate and reproducible method for its measurement still lacks (Barbato et al 2014). To the large number of difficulties already found in the determination of the rheological properties of waxy crude oils (Marchesini et al 2012), several other arise, due to many additional factors that influence the gel structure and hence the bulk rheology (Visintin et al 2008;Paso et al 2009;Maia Filho et al 2012;Sun et al 2014). Among these, we can mention the oil composition and molecular weight, drop size distribution, interfacial tension and rheology, salinity, and pH, just to name but a few.…”

Fabrication of a Cu2O/g‐C3N4/WS2 Triple‐Layer Photocathode for Photoelectrochemical Hydrogen Evolution

“…[8] The photocatalytic activity of g-C 3 N 4 can be further enhanced by combination with noble metals (Pd, Ag), [9] carbon spheres, [10] graphene or carbon nanotubes. [11] The metal-free g-C 3 N 4 is a typical n-type semiconductor, which possesses good electronic property as well as high thermal and chemical stability, making it an ideal material for the modification of Cu 2 O. [12] By combining Cu 2 O with g-C 3 N 4 , p-n heterojunction with intimate surface contact can also be formed to obtain highly active photocatalysts.…”