Research on viscoelastic properties of water in waxy crude oil emulsion gels with the effect of droplet size and distribution

Li, Si; Huang, Qiyu; Wang, Lei; Fan, Kaifeng

doi:10.1002/cjce.22324

Cited by 21 publications

(5 citation statements)

References 19 publications

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“…When the temperature is further cooled to 28 °C (2.2 °C below the gelation temperature of the waxy crude oil), both the storage modulus and the yield stress turn to increase monotonically with increasing water content, as demonstrated in Figure , which is distinct from the results at their GTs. This monotonic increasing trend of the storage modulus and the yield stress agrees with previous studies, ,− ,, confirming the enhancement of gel structure by dispersed water droplets when the wax precipitates at the same temperature. However, when the crude oil emulsions just reach their gelation states, the wax-precipitating conditions are different, and the gel structures are composed of different amounts of wax crystals and water droplets.…”

Section: Results and Discussionsupporting

confidence: 91%

“…Existing research has revealed that the GT , or the gel point of a water-in-waxy crude oil emulsion is notably increased with the addition of dispersed water. However, all the present research focuses on the evolution of the rheological properties with different water cut at the same temperature, − while the differences of the structural characteristics among different water cut emulsions at their own GTs have not been investigated yet. Besides, the specific reason which causes a crude oil emulsion to gelatinize is also not clear.…”

Section: Introductionmentioning

confidence: 99%

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

Sun

Yang

et al. 2016

Energy Fuels

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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.

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Section: Results and Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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

Sun

Yang

et al. 2016

Energy Fuels

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“…During testing, the reference and sample were heated to 60 °C and then cooled to −20 °C at a rate of 5 °C/min. The relationship between heat flow and temperature was recorded to determine the WAT (Figure a). , The measured WATs in these experiment were all above 10 °C, which are higher than the hydrate formation temperature (<7 °C); hence, the solid wax crystals appeared prior to hydrate formation. The details of the measured WATs and the amount of precipitated wax at 3.5 °C are presented in Table S5 of the Supporting Information.…”

Section: Results and Discussionmentioning

confidence: 94%

Effect of Wax Crystals on Nucleation during Gas Hydrate Formation

et al. 2019

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Hydrate formation and wax deposition pose great flow assurance challenges to subsea oil pipes, especially when the two phenomena co-occur. Wax crystals can have a significant impact on hydrate nucleation and growth kinetics, but this phenomenon has not been studied in great detail. Here, the effect of wax crystals on hydrate nucleation was investigated using both molecular dynamics simulation methods and experiments conducted using a custom-designed high-pressure autoclave equipped with an on-line viscometer. Both the simulation and the experimental results demonstrated that the presence of wax crystals inhibits hydrate nucleation. The simulations showed that water droplets tend to approach and adsorb on wax crystals prior to nucleation, thus inhibiting the formation of hydrate cages. The experiments demonstrated that water cut and stirring rate play a significant role in determining the hydrate nucleation rate. In addition, adding more wax increased the viscosity of the emulsion, which limits mass transfer of gas to the oil−water interface.

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“…Table gives the compositions of the emulsions so prepared. Emulsion stability was checked by observing the samples at 22 °C (room temperature) for 48 h and after reheating at 50 °C for 2 h. If no macroscopic phase separation was observed during this time period, the emulsions were judged to be stable …”

Section: Methodsmentioning

confidence: 99%

“…Emulsion stability was checked by observing the samples at 22 °C (room temperature) for 48 h and after reheating at 50 °C for 2 h. If no macroscopic phase separation was observed during this time period, the emulsions were judged to be stable. 23 Larger batches of 40% water emulsions for flow loop experiments with the same compositions given in Table 1 were prepared within a reservoir contained within the flow loop itself. Once again, the emulsions were prepared at 50 °C; however, in this case, an overhead mixer was used (RW-20 Digital, IKA, 0−500 rpm) along with three built-in mixing baffles.…”

Section: Methodsmentioning

confidence: 99%

Effect of Emulsified Water on Gelled Pipeline Restart of Model Waxy Crude Oil Cold Flows

et al. 2019

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Recent work has shown the promise of cold flow technology for transporting waxy crude oils below their wax appearance temperatures. The thermal flux that results due to the difference between the temperature of the transported oil and the ambient is minimized in the implementation of cold flow, thus significantly lowering wax deposition on pipeline walls. Restarting pipelines carrying waxy oils under cold flow conditions is an important consideration. In previous work from our laboratory, we have shown that gelled pipeline restart pressures for water-free systems are significantly lower for pipelines shut down starting from pre-established cold flow conditions in comparison to pipeline shutdown starting from hot flow conditions. In this paper, we examine the applicability of this conclusion when varying amounts of emulsified water are present within the oil. We investigate model oils containing 7.0 wt % wax, with water cuts ranging from 0 to 60 wt %. Restart studies were conducted in a bench-scale, 0.4 in. diameter, 4 ft long flow loop. The pressure required to restart the gelled pipeline decreases with a decrease in the cold flow shutdown temperature and with an increase in the water content. Complementary rheological measurements show that the presence of water reduces the yield stress of model waxy crude oil gels.

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Research on viscoelastic properties of water in waxy crude oil emulsion gels with the effect of droplet size and distribution

Cited by 21 publications

References 19 publications

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

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

Effect of Wax Crystals on Nucleation during Gas Hydrate Formation

Effect of Emulsified Water on Gelled Pipeline Restart of Model Waxy Crude Oil Cold Flows

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