Experimental Investigation on the Gelation Process and Gel Structure of Water-in-Waxy Crude Oil Emulsion

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• 作者：Guangyu SunChuanxian Li ; Fei Yang ; Bo YaoZuoqu Xiao
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：31
• 期：1
• 页码：271-278
• 全文大小：486K
• ISSN：1520-5029

文摘

The W/O emulsion formed by waxy crude oil tends to gelatinize under low-temperature gathering conditions, which may harm the flow assurance of multiphase transportation. This study mainly focused on the wax-precipitating gelation process of crude oil emulsions, and the structural differences of the emulsions with different water fractions at their gelation temperatures (GTs). First, the changes of wax appearance temperature (WAT) and precipitated wax amount at GT with variable water cut were investigated by DSC. Then, the specific structural properties of these different water cut emulsions at their own GTs were investigated by viscoelastic, yielding behavior, and structural breakdown experiments. On these bases, the gelation mechanism of a waxy crude oil emulsion was deduced. The WAT of a waxy crude oil emulsion was found to rise, evidently with the addition of dispersed water, verifying that water droplets provide necessary nucleation sites for paraffins and thus make them more prone to precipitate. When temperature was cooled down to their respective GTs, the accumulative precipitated wax amount within the emulsions was obviously reduced with increasing water cut. The combination of this phenomenon and further microscopic experiments proved the difference in gelation mechanism. These rheological tests manifested that both storage modulus and yield stress reached their minimum values at about 30% water cut when all emulsions were kept at their respective GTs, while the flow behavior index and the structural breakdown rate came to their maxima at the same water cut. These results are different from what have been known about the rheological properties at the same temperature below the gel point, demonstrating that the structural strength of the emulsion with about 30% water cut is the weakest at the GT. A conclusion could be finally deduced from the above research that, with the dispersed water increasing, the gelation mechanism of a waxy crude oil emulsion is changed, from a spanned wax crystal network structure which traps separated water droplets to an interlinking droplet flocs structure whose interface is adsorbed by a small amount of wax crystals.