Waxy Crude Oil Emulsion Research Articles

Research on Apparent Viscosity Variation of Water-in-Oil Waxy Crude Oil Emulsions Induced by a Magnetic Field

Research on Apparent Viscosity Variation of Water-in-Oil Waxy Crude Oil Emulsions Induced by a Magnetic Field

Effect of magnetic field on the apparent viscosity of water-in-oil waxy crude oil emulsion

The application of the magnetic field to reduce the apparent viscosity of water-in-oil waxy crude oil emulsions holds significant potential. A novel integrated magnetic processing apparatus was developed. The effects of magnetic treatment conditions on the viscosity of waxy crude oil and water-in-oil waxy crude oil emulsions with different water cuts were experimentally investigated. The viscosity reduction induced by the magnetic field was more pronounced for the emulsion with a higher water cut. The viscosity reduction degree of the emulsion first increased and then decreased with the increase in magnetic field intensity and magnetic treatment temperature. The viscosity reduction degree of the emulsion had a slight correlation with the magnetic treatment time and magnetic field frequency. Microscopic observation demonstrated that water droplet aggregation occurred in the magnetically treated emulsion compared to the untreated emulsion. Mechanism analysis shows that the oscillation of asphaltene molecules at the oil–water interface, the orientational arrangement of asphaltene molecules in crude oil, and the generation of monomeric water molecules induced by magnetic field contribute to the reduction in the apparent viscosity of waxy crude oil and the aggregation of water droplets. The viscosity of the emulsion is thus decreased. The research results provide a theoretical basis for the field application of viscosity reduction for water-in-oil waxy crude oil emulsion by magnetic treatment technology.

Study on microstructure evolution of waxy crude oil emulsions under dynamic cooling conditions.

A rheo-microscopy in situ synchronous measurement system was utilized to investigate the dynamic behavior of water droplets in W/O waxy crude oil emulsions subjected to dynamic cooling conditions, the microstructural evolution of water droplets aggregates can be categorized into three stages based on the various forms of wax crystals. The results show that under the joint action of wax crystals and water droplets, the water droplets aggregation trend and complexity in the system are negatively correlated with the changes of temperature and shear rate, and the water droplets movement behavior is positively correlated with the changes of temperature and shear rate. As the temperature decreases, the minimum edge distance of water droplets decreases by a maximum of 32.1%, the specific surface area (SA) decreases by a maximum of 12.0%, and the fractal dimension increases by a maximum of 11.7%. As the shear rate increases, the minimum edge distance of water droplets increases by up to 27.9%, the specific surface area (SA) increases by up to 10.1%, and the fractal dimension decreases by up to 8.5%. Additionally, an analysis is conducted on the collision aggregation behavior of water droplets in shear flow field based on population balance theory.

Effects of solvent composition and test temperature on the stability of water-in-model waxy crude oil emulsions

In this article, we investigated the influence of solvent composition and test temperature on the stability of the water-in-oil model emulsions through asphaltene dispersion stability, wax precipitation characteristics, rheology, interfacial film characteristics measurements of diluted model oil-simulated formation water, emulsion stability, microscopic observations, and molecular dynamics simulation. Specifically, we examined the stability of crude oil emulsions at 15° below and 30 above WAT using model oils containing 0.5 wt% asphaltenes and 10 wt% paraffin wax having varying solvent compositions. We observed that increasing the amount of liquid paraffin in the solvents led to smaller changes in the WAT, a reduction in the cumulative wax crystal at −20 °C, and a change in the form of wax crystals from fine particles to larger agglomerated wax crystals. However, the asphaltenes dispersion stability decreased along with it, rheology continued to improve. Meanwhile, we innovatively validated this experimental result using molecular dynamics simulations. Test temperature significantly affects emulsion stability. At 30 °C, increasing the percentage of liquid paraffin reduces interfacial tension, increases the dilatational modulus, and enhances the durability of the interfacial film. This contributes to form small droplets and increases emulsion stability. At 15 °C, increasing the liquid paraffin percentage promoted the development of a more structured wax crystals network, which significantly enhances emulsion stability by binding water droplets. Additionally, we observed that a wax crystal interfacial film could be developed from the wax crystals on the surface of emulsified drops, which improves the emulsion stability and interfacial film strength. Based on our findings, we innovatively present an influencing mechanism model of solvent composition on the synergistic stabilization of model oil emulsion using asphaltenes and paraffin wax.

Experimental Investigation on Viscosity Change of Waxy Crude Oil Emulsion with Magnetic Field

The rheological properties of emulsions are complex, leading to serious flow assurance issues that affect the economical and safe operation of pipelines. It has been reported that applying magnetic treatment technology can effectively improve the flowability of waxy crude oil. The study aims to investigate the influence of magnetic treatment on the viscosity of waxy crude oil emulsions. A dynamic electromagnetic treatment device was designed. The dynamic magnetic treatment experiments of waxy crude oil emulsion were carried out to explore the effects of magnetic field intensity and magnetic field frequency on the viscosity change of waxy crude oil emulsion. Research results show that with four different magnetic field frequencies, the viscosity of the emulsion decreases initially and then increases with the increase in magnetic field intensity. The variation law of emulsion viscosity with magnetic field intensity is related to the magnetic field frequency. When the magnetic field frequency is 100 Hz, the highest and lowest viscosity variation rates are 7.91% and -7.36%, respectively, which occur at the magnetic field strength of 110 mT and 30 mT, respectively. It is believed that applying a higher field strength electromagnetic field to the emulsion is beneficial for viscosity reduction. The research findings can provide guidance for the further study of the viscosity reduction of waxy crude oil emulsion magnetic treatment technology.

Rheo-optic in situ synchronous study on the gelation behaviour and mechanism of waxy crude oil emulsions

An improved rheo-optic in situ synchronous measurement system was employed to investigate the gelation behaviour and mechanism of waxy crude oil emulsions. By combining transmitted natural light and reflected polarized light microscopy, a multiangle composite light source was built to achieve the simultaneous observation of wax crystals and emulsified water droplets, as well as their dynamic aggregation process. Main outcomes on the microscopic mechanism were obtained by developed microscopic image processing method. It was found that the microstructure of W/O waxy crude oil emulsion has the evolution of “individual structure--homogeneous aggregate structure--heterogeneous coaggregate structure--floc structure” during the static cooling, which results in the four stages during gelation process. Different from previous studies, the aggregation of emulsified water droplets was found to be more significant and contributes to the formation and development of the wax crystals-emulsified water droplets coaggregate, which plays a decisive role in the further evolution of the gelled microstructure. Time series microscopic images show the dynamic aggregation of emulsified water droplets and wax crystals. Two different aggregation behaviours between wax crystals and water droplets were observed. That wax crystals can not only embed in gaps between adjacent water droplets and enhance the structure, but also surround the outside of the water droplets and continue to grow resulting in the interconnection of different coaggregates to form a larger floc structure. In addition, correlation between viscoelasticity and microstructure evolution of waxy crude oil emulsions of different water contents was discussed. With increasing water contents, the microstructure is changed from wax crystal flocculation structure as the main skeleton and the emulsified water droplets embedded in it, into the aggregation of emulsified water droplets occupying the main position. When the number of wax crystals and water droplets reaches a certain ratio, did wax crystals form coaggregates with emulsified water droplets, and the remaining wax crystals formed an overall flocculation structure, the viscoelasticity of the waxy crude oil emulsion is the highest. • Dynamic aggregation of wax crystals and emulsified water droplets was observed. • Two different aggregation behaviours between wax crystals and water droplets were found. • Aggregation of water droplets was found to be significant for the microstructure evolution. • New microscopic mechanism for gelation of W/O Waxy Crude Oil Emulsion was presented. • Correlation between viscoelastic and microstructure evolution was discussed. • Different ratios between wax crystals and water droplets lead to different viscoelasticity.

Experimental Study on the Effect of Wax Crystal-Water Droplet Aggregations on Wax Deposition of Water-in-Oil Emulsions

Wax deposition in waxy crude oil emulsions remains a flow assurance challenge in offshore production. Wax molecular diffusion driven by the positive temperature gradient from the liquid to the pipe wall has been widely studied and regarded as the primary wax deposition mechanism; however, a considerable wax deposit of emulsions at a zero-temperature difference was detected, in which condition molecular diffusion is not likely to occur, suggesting there were other mechanisms that contribute to wax deposition. In this work, the wax deposition mechanism of water-in-oil emulsions at a zero-temperature difference was explored by a cold finger apparatus regarding the role of wax crystals and water droplets on wax deposition. Through microscopy observation and component measurement of deposits, the wax deposition mechanism, namely, wax crystal-water droplet aggregation formation and adhesion behavior, was proposed. During wax deposition, wax crystals in the emulsion interacted with water droplets, organizing the basic structure of aggregation. The liquid oil phase was entrapped at the inner space of the aggregation and entrained by the wax crystal-water droplet structure to generate a wax deposit. The formation of wax crystal-water droplet aggregations depends on the experimental temperature, where a larger size of aggregations that formed at a lower temperature preferred to yield a thicker deposit under the same stirring speed, while for the same temperature operation conditions, the medium and low speed promoted the adhesion behavior of the aggregations to the cold finger resulting in an increase in deposits; however, the high stirring condition sloughed off the formed deposits, reducing the deposit mass. The findings denote that the presence of wax crystal-water droplet aggregations in emulsion should be considered when describing the wax deposition process at low temperatures.

Effect of EVA wax inhibitor on the W/O emulsion stabilized by asphaltenes and paraffin wax

Ethylene-vinyl acetate copolymer (EVA) is a typical wax inhibitor. It is plausible the EVA could influence the stability of waxy crude oil emulsion because it was influencing both the dispersion state of asphaltenes and the wax precipitation properties. In this paper, the number after the EVA represents the VA content, and the more VA content means the stronger polarity of EVA. Based on the physical characteristics of model crude oil, the emulsion stability, and interfacial properties, the influence of EVA polarity (from EVA 10 to EVA 40) on the stability of model waxy crude oil emulsions (the oil/water volume ratio is fixed at 7:3) containing both asphaltenes and paraffin wax was systematically studied at two different temperatures (30 ℃ and 15 ℃). The results demonstrated that the increment of EVA polarity can not only greatly improve the dispersion state of asphaltenes, but also significantly improve the flowability of model crude oil by changing the morphology of wax crystals. The competitive adsorption of EVA to the interfacial film can be facilitated by the increased polarity of EVA, thus decreasing the asphaltene mass ratio in the interfacial film and then causing the decrease of the interfacial tension and the dilational modulus. The test temperature impacted the stability of the W/O emulsion. At the temperature of 30 ℃ which was higher than the wax appearance temperature (WAT), the interfacial modulus was the main factor affecting the emulsion stability and then increasing EVA polarity caused the emulsion stability to decrease. At the temperature of 15 ℃ below the WAT, due to the formation of large amount of wax crystal particles, the low-temperature flowability of the oil sample was greatly aggravated, which can improve the emulsion stability—increasing the EVA polarity greatly improved the oil rheology, thus leading to a decrease in the emulsion stability. In addition, the size of wax crystals formed in the emulsion was much smaller than those formed in the oil phase, but the amount became larger. We speculated that the emulsified water droplets could serve as wax nucleators, promoting the formation of wax crystal layers around the droplets, which will also favor the emulsion stability at 15 ℃.

Effects of paraffin wax content and test temperature on the stability of water-in-model waxy crude oil emulsions

Waxy crude oil is important fossil energy containing both paraffin wax and some asphaltene. The interactions between paraffin wax and asphaltene not only affect the crude oil rheology, but also the stability of crude oil emulsion. To further understand the influences of paraffin waxes on the W/O emulsion stability, in the course of this work, the effects of paraffin wax content and test temperature on the stability of W/O emulsions (with fixed asphaltene concentration of 0.5 wt%) were investigated grounded on the physical property tests of the oils, macroscopic stability measurement of the emulsions, microscopic observation of the emulsions and oil-water interfacial properties test. The results indicated that increasing the paraffin content enhances the WAT of the oils but weakens the asphaltene stability in the oil phase thus leading to the aggregation of asphaltene into a bigger size. The rheology of the model waxy oils deteriorates greatly with increasing the content of paraffin wax. The emulsion stability is outstandingly affected by the test temperature. At 30 °C (much more than the WAT), increasing the paraffin wax content benefits the asphaltene adsorption at the oil-water interface, which then reduces the interfacial tension but increases the strength of the asphaltene film formed at the interface, this facilitates the formation of smaller water droplets and improves the stability of the emulsion to some extent. At a test temperature of 15 °C (well below the WAT), increasing the content of paraffin wax also facilitates the formation of a stronger network structure of wax crystals, which dramatically improves the emulsion stability by immobilizing water droplets in the network. Meanwhile, the water droplets in the emulsion containing 15 wt% paraffin wax have the smallest size and largest number, and can efficiently act as the wax crystal nucleators thus dramatically changing the precipitated wax crystals into very small particles and facilitating the development of a wax crystal film around the droplets. This film also helps to improve the stabilization of the emulsion.

Study on the prediction method of thixotropy of water-in-oil waxy crude oil emulsions

The thixotropy of water-in-waxy crude emulsion is the basic data used for flow safety studies of oil-water mixed pipelines. This work studied the shearing rate of a water-in-waxy crude oil emulsion under constant shear stress loading conditions. A relative shear rate was defined. A prediction method was developed to estimate the thixotropy of a waxy crude oil emulsion under constant shear stress loading conditions. The method only requires the thixotropy data of 3 water content emulsions and dehydrated crude oil, it can estimate the thixotropic characteristics of the oil-water-waxy crude oil emulsion of any volume of water content.

Effects of Asphaltene Concentration and Test Temperature on the Stability of Water-in-Model Waxy Crude Oil Emulsions.

In oil fields, the formation of water-in-waxy crude oil emulsion is inevitable. The dissolved/crystallized state wax can interact with asphaltenes and then greatly affect the emulsion stability. However, studies on this aspect are still insufficient. In this work, the effects of the test temperature (30 °C well above the wax appearance temperature (WAT) and 15 °C well below the WAT) and asphaltene concentration (0∼1.5 wt %) on the stability of the water-in-model waxy crude oil emulsions containing 10 wt % wax were systematically investigated. When the model crude oils contain no wax, the flowability of the oils is good and the asphaltene concentration has little influence on the oil rheology. Increasing the asphaltene concentration facilitates the adsorption of asphaltenes to the oil–water interface, thus reducing the interfacial tension and water droplet size while enhancing the interfacial dilatational modulus. The stability of the emulsions improves with the increase in the asphaltene concentration, but the emulsions are still unstable. When the model crude oils contain 10 wt % wax, the WAT slightly decreases from the initial 25 to 24 °C after the addition of asphaltenes. The oil rheology is greatly improved by the addition of 0.05 wt % asphaltenes. With the further increase of the asphaltene concentration, the improved rheological ability of the asphaltenes deteriorates rapidly. At the asphaltene concentration of 1.5 wt %, the oil rheology is dramatically aggravated. The stability of the emulsion containing 10 wt % wax is mainly controlled by two aspects: on the one hand, the dissolved-state wax (30 °C) could facilitate the adsorption of asphaltenes to the interface, further reduce the interfacial tension and the water droplet size, and enhance the interfacial dilatational modulus; on the other hand, the wax crystals precipitated in the oil phase (15 °C) can form a stronger network structure at relatively high asphaltene concentrations (0.5∼1.5 wt %) and then immobilize the water droplets. The above two aspects greatly improve the sedimentation and coalescence stabilities of the emulsions at 15 °C. In addition, we did not find persuasive evidence showing that the wax could crystallize around the water droplets and strengthen the oil–water interfacial films.

Study on the thixotropy and structural recovery characteristics of waxy crude oil emulsion

Waxy crude oil emulsion has thixotropic properties at the temperature near gel point, which is a macro-mechanical characterization of the structure failure and recovery of waxy crude oil emulsion. In this paper, the thixotropic behaviors of waxy crude oil emulsion near gel point were studied using hysteresis loop formed by stress linear increase and decrease, as well as the structural recovery characteristics. The influence of the loading conditions and water content on the thixotropy of waxy crude oil emulsion were analyzed with hysteresis loop area. The concept of “structural recovery” was introduced to study the degree of structural recovery after different stewing, and influencing factors were taken into account. Results have shown that for waxy crude oil emulsion, the failure to fully restore of the structure after lysis is the cause of the formation of hysteresis loop, and the loading conditions will not affect the strength of thixotropy and the degree of structural recovery. Additionally, the dispersed phase droplets weaken the thixotropy and structure recovery characteristics of waxy crude oil emulsion, and the greater the water content, the weaker the thixotropy. The findings can help to better understand the safe and economic operation of waxy crude oil-water pipeline transportation.

Interfacial Tension Prediction of Readily-Mixed Waxy Crude Oil Emulsion at Pour Point Temperature

In the industry, stubborn emulsion still constitutes up to 20% of the total emulsion volume. The existing remediation strategies for emulsion treatment rely heavily on the study of heavy crude oil emulsion. However, minimal information is available on integrating interfacial rheology with emulsion stability on waxy crude oil emulsion. The proposed research provides a study to the development of integration between interfacial rheology and emulsion stability so that it can be a quick assessment but an accurate method to measure emulsion stability. The primary objectives of the research are to provide an extensional study to the design development of a comprehensive interfacial rheology protocol for the assessment of emulsion stability by developing a method of testing and monitoring the interfacial rheology and to investigate the demulsification ability of the waxy crude oil emulsion subjected to microbial treatment. The novelty of this study is to use the newly developed measurement protocol via interfacial rheology to predict emulsion stability. Application of the microbes on waxy crude oil to breakdown the water-in-oil emulsion using a rheometer will also be explored. The treatment is targeted to disintegrate the interfacial layer within the emulsion leading to better oil recovery. Rheological properties of the emulsion will be monitored upon the microbial injection to analyze the effects of the treatment on the rheology of emulsion. The outcomes from this research is that the newly developed protocol will predict emulsion stability that could resolve the stubborn emulsion issues via the developed interfacial rheology protocol, which could be time-saving and increases the production efficiency. This research paper is a study to develop a correlation on surface tension and interfacial tension between crude oil, water and a readily-mixed emulsion.

Investigation on gelation nucleation kinetics of waxy crude oil emulsions by their thermal behavior

Waxy crude oil emulsions exhibit gelation behavior, with nucleation observed within a certain temperature range. A kinetic model was developed and validated based on the thermal parameters obtained from differential scanning calorimetry cooling thermograms, and the nucleation rates of various water-in-waxy crude oil emulsions were determined in the temperature range in which gelation occurs. Although temperature had a dominant effect on the gelation and nucleation behavior of waxy crude oil emulsions, the nucleation rate also increased as the water volume fraction in the emulsion increased. Emulsified water droplets with smaller radii can be completely covered by wax particles, inducing a greater nucleation rate. Subjecting the emulsions to a greater shearing strength also increased the nucleation rate. This study provided new insights into the nucleation processes that occur during the formation of waxy crude oil emulsion gels and, in particular, the role of the emulsification properties.

Experimental Investigation of the Rheological Properties of a Typical Waxy Crude Oil Treated with Supercritical CO2 and the Stability Change in Its Emulsion

The application of supercritical CO₂ (scCO₂)-flooding technology is increasing worldwide. After a waxy crude oil is treated with scCO₂, its composition and rheological properties are changed and the stability of its emulsion is accordingly altered as well, thus affecting the dewatering process in gathering stations. To probe the specific changes occurring in waxy crude oil and its emulsion after scCO₂ flooding, a scCO₂ treatment device was first designed to simulate the reservoir conditions. Next, the composition changes in the waxy crude oil caused by the scCO₂ treatment were studied, and the changes in the rheological properties, such as the pour point, viscosity, yield stress, and wax precipitation characteristics, caused by the composition variation were analyzed. Then, the stability of the degassed crude oil emulsion and the corresponding interfacial properties were examined. Finally, the demulsification characteristics of the emulsion under the action of a demulsifier were tested. The results reveal a content increase in the heavy components, such as asphaltenes, resins, and high-carbon-number hydrocarbons, in the waxy crude oil as a result of the scCO₂ extraction of the light components. This results in increases in the pour point, wax appearance temperature, and abnormal point as well as the growth of the apparent viscosity and yield stress. As a result of the structural enhancement of the interface, as reflected by the dilational modulus increase in the interface, the stability of the scCO₂-treated waxy crude oil emulsion is strengthened and its demulsification efficiency is reduced after dosing with the same demulsifier. All of these changes could unfavorably influence the safe transportation of the produced fluid in scCO₂-flooding oil fields and the subsequent dewatering process.

The Influence of the Microstructure of W/O Emulsion of Waxy Crude Oil on Its Rheology

In this article, the viscosity-temperature characteristics of W/O waxy crude oil emulsion under different microstructures were studied, and the characteristics of the microstructure were described by the analysis of the dispersed phase parameters including the average particle size, the degree of dispersion, and the nonuniformity of average particle size. On this basis, we discuss the effects of temperature, shear rate and the microstructure on the apparent viscosity of Daqing crude oil emulsion. The results showed that with the increasing of stirring speed, the number of droplets and the degree of dispersion phase dispersion increased, average droplet size and nonuniformity of average particle size reduced; the average particle size of the dispersed phase decreased by 0.5 μm, and the abnormal point increased by about 1°C. For emulsions with the same microstructure, as the temperature or shear rate rising, the rate and percentage of the reduction in apparent viscosity decreased. At the same temperature or shear rate, the reduction rate in apparent viscosity increases with the average particle size of dispersed phase decreases, in contrast to the percentage of reduction in apparent viscosity, which revealed a definitive correlation between average particle size of dispersed phase and the apparent viscosity in the non-Newtonian fluid that from 34°;C to 48°;C; the absolute value of Pearson’s correlation coefficient was above 0.8, which was highly negatively correlated; as the temperature rose, the absolute value of Pearson’s correlation coefficient decreased from 0.839 to 0.216.

The Role of Shearing Energy and Interfacial Gibbs Free Energy in the Emulsification Mechanism of Waxy Crude Oil

Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process particularly, both in terms of transportation energy consumption and separation efficiency. To deal with the production and operational problems which are related to crude oil emulsions, especially to ensure the separation and transportation of crude oil-water systems, it is necessary to better understand the emulsification mechanism of crude oil under different conditions from the aspects of bulk and interfacial properties. The concept of shearing energy was introduced in this study to reveal the driving force for emulsification. The relationship between shearing stress in the flow field and interfacial tension (IFT) was established, and the correlation between shearing energy and interfacial Gibbs free energy was developed. The potential of the developed correlation model was validated using the experimental and field data on emulsification behavior. It was also shown how droplet deformation could be predicted from a random deformation degree and orientation angle. The results indicated that shearing energy as the energy produced by shearing stress working in the flow field is the driving force activating the emulsification behavior. The deformation degree and orientation angle of dispersed phase droplet are associated with the interfacial properties, rheological properties and the experienced turbulence degree. The correlation between shearing stress and IFT can be quantified if droplet deformation degree vs. droplet orientation angle data is available. When the water cut is close to the inversion point of waxy crude oil emulsion, the interfacial Gibbs free energy change decreased and the shearing energy increased. This feature is also presented in the special regions where the suddenly changed flow field can be formed. Hence, the shearing energy is an effective form that can show the contribution of kinetic energy for the oil-water mixtures to interfacial Gibbs free energy in emulsification process, and the emulsification mechanism of waxy crude oil-water emulsions was further explained from the theoretical level.

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

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. Whe...

Start-up flow behavior of pipelines transporting waxy crude oil emulsion

Water-in-waxy crude oil emulsion tends to gelatinize under shutdown conditions when the atmospheric temperature or sea water temperature is lower than its pour point, threatening pipeline restart safety. Based on previous researches about the complex rheological properties of waxy crude oil emulsion gel, elasto-viscoplastic thixotropic models were first compared with each other according to experimental results, and the model proposed by Teng was screened out to be the most accurate one that could describe the whole response after shear loading. Then the effects of rheological changes on pipeline start-up flow after the formation of emulsion gel were computed numerically with the help of this thixotropic model. It was found out through a case study of a 50km long pipeline that the time for the flow to start and from start state to steady state at terminal of the pipeline transporting 30% water cut emulsion gel increases by 5.8 times and 2.1 times respectively when compared with the time for original crude oil. Meanwhile, the steady flow rate after start-up decreases dramatically by 85.9%. The pipeline transporting waxy crude oil could be restarted successfully at the pressure of 1.0MPa, while it need to be pressurized to 5.0MPa to resume flow when its 60% water cut emulsion gel is formed. All these results indicate that the emulsification of waxy crude oil makes pipeline restart more difficult, and the lengthening of the pipeline magnifies the influence of the emulsification. Therefore, the possibility of wax precipitation in crude oil emulsion and further the structural characteristics of the formed emulsion gel have to be taken into consideration during multiphase pipeline shutdown.

Study on Viscoelastic Behaviors of Waxy Crude Water-in-Oil Emulsion

Emulsion of waxy crude oil is one of the common states in the subsea pipeline. At low temperatures in offshore environment, waxy crude oils with water could form the crude oil emulsion gel of oil-in-water emulsion. Thus, the waxy crude oil emulsion viscoelastic behavior for deep sea transportation and restarting pipeline safety is particularly important. By means of MASIII HAAKE rheometer which is produced by German company, waxy crude oil emulsion viscoelastic behavior is explored at different volumetric water contents and different shear stresses. By analyzing the rate of change of shear rate in the initial stage, the influence rules of viscoelastic properties were summarized, with the change of volumetric water content and the applied shear stress and based on the experimental results, the law of emulsion is explained from the micro level. It is proposed that brittle fracture exists between wax crystals, and flexible fracture was found in the interaction between water droplets and wax crystals.