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Commonly used flow improvers in oilfields, such as ethylene-vinyl acetate copolymer (EVA), poly(octadecyl acrylate) (POA), and polymethylsilsesquioxane (PMSQ) are proven to be effective to enhance the flowability of crude oil. However, the addition of these flow improvers may change the stability of the emulsion and make the crude oil treatment process challenging. In this research, the impacts of different flow improvers on the interfacial properties of the emulsions containing asphaltenes are systematically investigated. The co-adsorption behaviors of the flow improvers and asphaltenes are analyzed through dynamic interfacial tension (DIFT). The rheological properties of the interfacial layer after the adsorption are explored via dilational viscoelasticity. Significant difference is observed in the structural properties of the interface adsorbed by different flow improvers, which is attributed to different interactions between the flow improvers and asphaltenes. To investigate these interactions, conductivity, asphaltenes precipitation, dynamic light scattering (DLS), and contact angle experiments are conducted systematically. Results show that EVA and POA can alter the interfacial properties by changing the asphaltene dispersion state. The interaction between EVA and asphaltenes is stronger than that between POA and asphaltenes due to the difference in molecular structures. Unlike EVA and POA, the change of interfacial property with the addition of PMSQ is attributed to the partial adsorption of asphaltenes on PMSQ.

Asphaltenes and solid particles are common compositions in crude oil emulsions. They can be anchored at the oil/water interface, exerting significant effects on the strength of an interfacial layer. In this study, the interactive effects of the asphaltenes and solid particles on the interfacial structure are investigated. First, the solid particles and asphaltenes are proven to perform different roles in stabilizing the emulsion by influencing the strength of the interfacial layer with the change in asphaltene concentration. Subsequently, the competitive coadsorption process of the asphaltenes and particles is examined by measuring the dynamic interfacial tension. The adsorption of particles could occupy the interfacial area, postponing the adsorption of asphaltenes. The crumpling ratio of the interfacial layer formed by the asphaltenes and solid particles indicates that the composite layer should be more flexible with a higher compressibility compared to that formed by only asphaltenes. It is observed by SEM that the binary layer possesses a composite structure with the particles as the framework and the asphaltenes as the filling. The interactive mechanism between the asphaltenes and particles should lie in the adsorption of the asphaltenes on the particles. Systematic experiments on the contact angle, adsorbed amount, and desorption percentage reveal that asphaltenes could adsorb on the surface of the particles, modifying the wettability. The change in asphaltene concentration will result in the varying wettability modification due to asphaltene adsorption on the particles, leading to the different adsorption abilities and barrier effects of the modified particles at the interface.

Summary Accurately predicting wax deposits in a crude pipeline through empirical formulas or numerical modeling is unreliable because of the incomplete mechanism and the time-dependent unsteady actual operating conditions. With the help of the data collected by the supervisory control and data acquisition system of pipelines, wax deposit prediction is made possible by developing the time-dependent data mining method. In this article, the data from a typical long-distance crude pipeline in China operating over a 4-year time period was investigated. The inlet temperature prediction was first conducted by developing the long short-term memory (LSTM)-recurrent neural networks (RNNs) model, during which the feature sequencing, overfitting problems, and optimal hyperparameters were fully considered. Because of the time sequence cell, the accuracy of the LSTM-RNN model, as well as the time consumption, is much better than the RNN model when dealing with a great deal of data over a long period of time. Taking the inlet temperature prediction results as input features, the prediction model of average wax deposit thickness was established based on the backpropagation (BP) neural network and optimized by the particle swarm optimization (PSO), chaos particle swarm optimization (CPSO), and adaptive chaos particle swarm optimization (ACPSO) algorithms. The conclusions and associated algorithm from this article help to determine the reasonable pigging circle of long-distance pipelines practically. It could also be applied to guide the wax deposit prediction in the wellbore or oil-gatheringpipes.

The precipitation of wax crystals in water-in-crude-oil emulsion impairs the safety and economy of multiphase transportation in oil fields. At present, there are different opinions on the precipita...

In this paper, a novel ethylene-vinyl acetate copolymer (EVA)/amino-functionalized polymethylsilsesquioxane (PAMSQ) composite wax inhibitor (WI) was prepared through melt blending, and the rheological and wax depositing properties of the doped crude oil were studied. The EVA/PAMSQ composite can strongly crystallize with wax molecules and trigger the formation of compact wax flocs, which greatly improve the rheological properties of crude: compared to the pure EVA at the same dosage, the composite can further decrease the gel point and apparent viscosity (25 °C) by 14.6 °C and 92.0%, respectively. The wax deposition can also be inhibited by adding the composite: adding EVA inhibits the mass of the wax deposit at 24 h by 62.3%, and this number is suppressed by 77.9% after adding the EVA/PAMSQ composite, but the wax molecule diffusion is accelerated and the wax content in the wax deposit rises because of the improved crude oil rheological characteristics. Here, we develop the gel structure theory to consider the wax deposition process affected by the WI. Adding the WI contributes little to the wax precipitation temperature but decreases the gel structural strength of the oil a lot, and thus, the oil near the pipe wall can only form the wax deposit with a higher wax content to resist the pipe wall shearing. Therefore, the crude oil added EVA/PAMSQ composite possesses not only the lowest wax deposit rate and the highest aging rate but also the highest wax content in the wax deposit.

The amphiphilic dodecylbenzenesulfonic acid (DBSA) is usually added into wells as an asphaltene precipitation inhibitor. The interfacially active DBSA and asphaltenes will be both adsorbed at the o...

In the crude oil production, comb-like octadecyl acrylate (OA) polymers are usually added into the well as flow improver, causing the existence of OA polymers in the produced fluid. OA polymers and...

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.

As a kind of enhanced oil recovery technology, CO2 flooding is being employed more and more widely in oil fields. In CO2 flooding produced fluid, crude oil, water, and CO2 are transported simultane...

Paraffins cause many issues during the production and transportation of crude oils. To date, there is abundant research on the rheological properties of crude oils after paraffin crystallization an...

It is widely concerned that the adsorbed natural surface-active components at the interface between crude oil and produced water form a protective layer to prevent emulsion from instability. Asphaltenes and resins are considered to perform significant roles among these natural surface-active components in the crude oil. This study deals with the effect of the interactions between asphaltenes and resins on water/oil interfacial properties and emulsion stability. Firstly, the dynamic surface pressure of asphaltenes and resins are obtained with the shape analysis method of pendant droplet, respectively. A synergetic effect of asphaltenes and resins is confirmed by comparing the dynamic surface pressure of the binary system with that of the single system. The addition of resins enhances the interfacial affinity of asphaltenes at the beginning of the adsorption. Asphaltenes have stronger influence than resins in the long-term adsorption. Then, the dilational modulus is measured with the method of interfacial small-amplitude oscillation. The addition of resins reduces the dilational modulus, weakening the structural strength of interfacial layer. Conductivity experiments are carried out to determine the dispersed state of asphaltenes. Due to the synergetic effect of asphaltenes and resins, adding resins motivates the dispersal of asphaltenes, thus changing the turning point of conductivity to higher proportion of n-heptane. At last, emulsion stability experiments are performed to back up the synergetic effect occurred at the interface. The addition of resins increases the stability of emulsion at initial time. However, the emulsion stability is deteriorated when the resins are excessive. Similar to the adsorption phenomenon at the interface, resins have slighter impacts on emulsion stability in the long term. Asphaltenes still possess a dominated position in determining the emulsion stability.

Asphaltenes are natural pour point depressants, and the effect of asphaltene polarity on the low-temperature rheology of waxy oils has been well studied. In this paper, the influence of asphaltene ...

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.

For the pipeline transportation of waxy crude oil, pour point depressants (PPDs) have been developed and used to improve its flowability at low temperature. As supercritical CO2 (scCO2) flooding becomes a common technique to improve oilfield recovery, how the sensitivity of PPD changes due to the degassed crude oil treated by CO2 should be studied. In this work, the effect of scCO2 extraction on the performance of EVA in improving the flowability of Changqing degassed crude oil is investigated by means of a self-developed scCO2 treating equipment, SARA/HTGC analysis, SEM analysis, pour point test, rheological measurement, asphaltene precipitation test, particle size analysis, DSC test, and microscopic observation. The results show that without EVA addition, scCO2 extraction aggravates the flowability of the crude oil at low temperature. The scCO2 extraction extracts light components from asphaltene aggregates causing asphaltenes to precipitate, which inhibits the asphaltenes on playing a role as the natur...

In this article, poly(aminopropyl/methyl)silsesquioxane (PAMSQ) microspheres with different polarities were first synthesized and characterized. The polarity of the PAMSQ microspheres is progressively enhanced by increasing the aminopropyl molar ratios (1–25 mol%). Then, the effect of PAMSQ microspheres with different polarities on the flowability of the model waxy oils with/without asphaltenes was studied through rheological tests, DSC analyses, microstructure observation and asphaltenes precipitating measurement. The results indicated the PAMSQ microspheres alone could spacially hinder the interactions among the precipitated paraffin crystals, thus slightly improving the flowability of the model waxy oil without asphaltenes (MO-1). The improving ability of PAMSQ microspheres deteriorates with the polarity increasing, and the MO-1 shows the best flowability after adding 200 ppm PAMSQ-1 microsphere (with the aminopropyl molar ratio at 1 mol%). To our surprise, adding PAMSQ microspheres can significantly improve the flow behavior of the model waxy oil with 0.75 wt% asphaltenes (MO-2). Based on the asphaltenes precipitation data, the PAMSQ microspheres could adsorb asphaltenes to form the PAMSQ/asphaltene composite particles in MO-2. The composite particles can play a role of the heterogeneous nucleation templates for paraffin molecules and facilitate the formation of larger and more compact wax floccules, thus enhancing the flowability of MO-2 at low temperatures. The flow improving ability of the PAMSQ microspheres for MO-2 increases with increasing the polarity of the microspheres due to the increased interactions between the microspheres and asphaltenes. The MO-2 exhibits the best flowability after adding 200 ppm PAMSQ-3 microsphere (with aminopropyl molar ratio at 15 mol%). When the polarity of the microspheres is too strong (PMASQ-4 microsphere), however, the microspheres cannot dispersed in waxy oil stably, thus inhibiting the interactions between the microspheres and asphaltenes and deteriorating the flow improving ability of the microspheres for MO-2.

With the continuous exploitation of heavy oil resources, the stability of heavy oil emulsions and further its demulsification technology are receiving more and more attention. One of the most important elements that affect the stability of heavy oil emulsion is asphaltenes. Under this background, the effect of the aggregation state of asphaltenes on the structure-related properties of the model oil/brine water interface is investigated in this study, and further the relation between the structural properties of the interface and the macroscopic stability of the emulsion is studied. It is observed through the dynamic light scattering experiment that there is an abrupt increase in the particle size of the asphaltene aggregates at the concentration of 100 ppm, indicating the enhancement of the aggregation degree above this concentration. The higher level of aggregation changes the adsorption kinetics of the asphaltenes at the interface, causing a slower descending rate of the diffusion coefficient. Meanwhile...

The influence of thermal treatment temperature on the flowability and wax deposition characteristics of Changqing waxy crude oil was researched in detail through pour point/rheological tests, a cylindrical Couette wax deposition experimental device, DSC analyses, asphaltenes stability tests, and microscopic observations. It is found that the flowability of the crude oil can be greatly improved through increasing the thermal treatment temperature. Meanwhile, the wax deposition rate of the crude oil can be outstandingly inhibited with the increase of thermal treatment temperature from 50 to 70 °C. Moreover, the flow regime can also influence the wax deposition characteristics. Under cold flow regime (22 °C/12 °C), the structure of formed wax deposits is homogeneous while the aging of the wax deposits is not obvious. Under hot flow regime (30 °C/20 °C), the aging of the wax deposits is obvious, but a heterogeneous two-layer structure exists in the formed wax deposits at the thermal treatment temperatures 50 ...

In CO2 flooding, the dissolution of CO2 in produced fluid may change the stability of crude oil emulsion, thereby affecting the design/operation of the gathering pipeline and oil–water separation. The purpose of this study is to investigate the stability change of crude oil emulsion and its mechanisms after the dissolution of CO2. The stability of the CO2-dissolved crude oil emulsions is determined with a self-made apparatus. The mechanisms of the stability change are uncovered from interfacial properties and bulk viscosity. It is found that the stability of the crude oil emulsions is visibly reduced with an increasing dissolved quantity of CO2. This is partly attributed to the fact that dissolved-state CO2 can lessen the interfacial dilational modulus and increase the loss angle markedly, thus lowering the structural strength and elasticity of the interface. Meanwhile, the dissolution of CO2 in crude oil can reduce its viscosity, resulting in easier collision of droplets. In view of these experimental re...

Recently, studies on the use of polymer nanomaterial composites as pour-point depressants (PPD) have drawn much attention, but the crystallization properties and improved rheological performance of waxy crude oils using nanoclay-based composite PPDs have rarely been reported. In this paper, montmorillonite (Mnt) was first organically modified using octadecyltrimethylammonium chloride (C21H46NCl, or stearyltrimethylammonium chloride) in aqueous solution. Then, the organically modified Mnt (OMnt) material was dispersed into a polyoctadecylacrylate (POA) matrix to prepare a POA/OMnt composite PPD by melt blending. The composition, structure, and morphology of Mnt, OMnt, and the POA/OMnt composite PPDs were investigated. The results showed that the OMnt and POA were compatible and that the OMnt was exfoliated into several sheets in the POA matrix. Subsequently, the isothermal crystallization kinetics of the POA/OMnt composite PPDs showed that small amounts of OMnt had a dramatic impact on POA chain motion during crystallization and facilitated POA crystallization. After it was added to a waxy crude oil, the POA/OMnt composite PPDs produced better rheological properties and performance than identical concentrations of the neat POA. The POA/OMnt composite PPDs can act as wax nucleation sites for wax molecule precipitation and result in larger and more compact wax crystal flocs, which adversely affect the formation of a wax crystal network and, thus, favor the improvement of waxy crude oil rheology.

The effect of the drag reducer, which is a kind of effective chemical additive for the pipelines, is closely related to its dissolution dispersity in the oil product. In this paper, the effects of ...

In the previous work, we have reported that small dosages of the polymethylsilsesquioxane (PMSQ) microsphere can effectively improve the performance of the EVA pour point depressant (PPD) and the amount of EVA PPD adsorbed on the microsphere evidently influences the efficiency of the EVA/PMSQ composite particle. To further promote the adsorption of EVA on the microsphere and enhance the efficiency of the composite particle, here, the amino-functionalized PMSQ microspheres with different amino molar ratios (PAMSQ) are first synthesized and characterized. The flow behavior, exothermic crystallization and microstructure of the waxy crude oil undoped/doped with EVA, EVA/PMSQ and EVA/PAMSQ are systemically investigated. Results show that 50 ppm EVA PPD can greatly improve the flow behavior of the oil and small dosages (2.5 ppm) of PMSQ microsphere can significantly improve the performance of the EVA PPD. After the amino-functionalization, the flow improving efficiency of EVA/PAMSQ is further enhanced: the gelation point, G′, G″, apparent viscosity and yield stress of the oil sample decrease to a lower value. The best performance is found at adding 50 ppm EVA + 2.5 ppm PAMSQ-2 (with amino molar ratios at 15%). Compared to EVA/PMSQ, the EVA/PAMSQ exhibits a stronger nucleation effect to increase the WAT of the oil sample slightly, and outstandingly modifies the morphology of the precipitated wax crystals into larger and more compact flocs. The amino-functionalization facilitates more EVA PPDs adsorbing and concentrating on the PAMSQ microsphere, causing the formation of the EVA/PAMSQ composite particles. The composite particles provide stronger nucleation effect for the wax precipitation, resulting in larger and more compact wax microstructures and then further improving the flow behavior of the oil. The rheological improving performance of EVA/PAMSQ for the waxy crude oil increases with the increase of amino molar ratio and the efficiency of EVA/PAMSQ-2 reaches the best. When the amino molar ratio is too high (PMASQ-3), the PAMSQ-3 microsphere is unstable in oil phase and aggregates into large particle flocs, which inhibits the EVA adsorption on the PAMSQ-3 microsphere and then weakens the rheological improving efficiency of the EVA/PAMSQ-3 composite particle.

Here, we reported that by adjusting the stirring speed, condensation pH value, precursor concentration and reaction temperature, the morphologies of the polymethylsilsesquioxane (PMSQ) microsphere could be well controlled through the two-step sol-gel synthesis. Because of the specific structural property and strong hydrophobicity, the obtained PMSQ microsphere dispersed well in the ethylene-vinyl acetate copolymer (EVA) matrix to form EVA/PMSQ hybrid. Subsequently, the thermal properties of both EVA and EVA/PMSQ hybrid were investigated through the TGA and DSC tests. The presence of PMSQ microsphere generates a significant delay in the thermal degradation processes of EVA, thus improving the thermal stability of EVA. The PMSQ microsphere also obviously increases the onset crystallization temperature and the crystallization rate of EVA, meaning that adding PMSQ microsphere enhances the crystallization ability of EVA. Finally, by applying rheological tests and microscopic observation, EVA/PMSQ hybrid was found to further improve the flow behavior of Qinghai waxy crude oil than the neat EVA did. The EVA/PMSQ hybrid can act as heterogeneous nucleation templates of wax crystals, and favor the formation of wax crystal flocs with increased size and compactness, thus inhibiting the continuous wax crystal network structure and further improving the flow behavior of the waxy crude oil.

In part 1 (10.1021/acs.energyfuels.7b03657), the synergistic effect of ethylene–vinyl acetate copolymer (EVA) pour point depressant (PPD) and rensin-stabilized asphaltenes on improving the flowability of synthetic waxy oil has been verified. This paper is a continuous work studying the effect of the asphaltene content (0.01–3 wt %) on the synergistic effect between EVA PPD and resin-stabilized asphaltenes. The results showed that, in the absence of EVA and with the increase of the asphaltene content, the precipitated wax crystals of the waxy oil tend to grow gradually from initial big needle-like to smaller and more regular (spherical-like) particles with a larger amount; therefore, adding aphaltenes can only decrease the apparent viscosity of waxy oil at the temperature range slightly lower than the wax precipitation temperature (WPT) (the precipitated wax crystal amount is low), and the temperature range is broadened by increasing the asphaltene content. When the temperature is decreased far below the W...

In this paper, the effect of POA PPD together with resin-stabilized asphaltenes on the flow behavior of model waxy oils was investigated through rheological test, DSC, microscopic observation and a...

With the gradual popularization and application of CO2 flooding technology in oilfields, the physical properties of produced fluid, including the stability of the emulsion formed by crude oil and produced water, may be changed, consequently influencing the surface gathering and dewatering processes. In order to investigate the stability changes of heavy oil emulsions and their mechanisms after supercritical CO2 (scCO2) flooding, a device that could simulate the scCO2 treatment condition in the oil reservoir was first designed and used to pretreat the heavy oil. Then, the effects of scCO2 treatment on the stability of heavy oil emulsion were investigated by means of a bottle test and microscopic observation. The results revealed that the stability of the emulsion formed by scCO2-treated degassed heavy oil was improved. The reason for the stability improvement was then deeply explored from two aspects, i.e., the bulk viscosity and the structural strength of the water–oil interface. On the one hand, it was f...

Both polymeric pour point depressants (PPDs) and asphaltenes can improve the flowability of waxy oils. However, the effect of polymeric PPDs together with asphaltenes on the flowability of waxy oils is not clear. In this paper, the synergistic effect of ethylene–vinyl acetate (EVA) PPD (100 ppm) and resin-stabilized asphaltenes (0.75 wt %) on the flow behavior of model waxy oils (10–20 wt % wax content) was investigated through rheological tests, DSC analysis, microscopic observation, and asphaltenes precipitation tests. The results showed that the asphaltenes disperse well in the xylene/mineral oil solvent as small aggregates (around 550 nm) with the aid of resins. The EVA or asphaltenes alone moderately improve the flow behavior of waxy oils by changing the wax crystals’ morphology from long and needlelike to a large, radial pattern or fine particles, respectively. The wax precipitation temperatures (WPTs) of waxy oils are also slightly decreased by adding EVA or asphaltenes, meaning that the cocrystall...

In real crude-oil pipelines, the formed wax deposits could be heterogeneous along the radial or axial directions. However, studies on this aspect are scarce. In this paper, the effect of the polyoctadecyl acrylate (POA) wax inhibitor on the wax deposition of 10 wt % model waxy oil was investigated with the aid of an in-house wax deposition device, differential scanning calorimetry test, high-temperature gas chromatography–Fourier transform infrared analysis, and microscopic observation. The results showed that adding POA in the model waxy oil greatly modifies the morphology of precipitated wax crystals, thus greatly changing the wax deposition behavior of the oil. For oil sample 1 (without POA), the precipitated wax crystals (needle-like) more easily form porous network structures, causing the formation of a thick and porous wax deposit with relatively low WAT, wax conten,t and critical carbon number (CCN). With the increase of POA concentration (oil samples 2–5), the precipitated wax crystals become more...

This study is specifically concerned with the effect and mechanism of asphaltenes and wax inhibitors on the wax deposition characteristics of model waxy oil. According to the rheological and wax deposition test, the pure model waxy oil has a pour point higher than the pipe wall temperature, and the formed wax deposit exhibits the slowest aging rate and homogeneous wax deposit structure. Based on the DSC and rheological experiments, the solubility of wax crystals is hardly influenced by asphaltenes or wax inhibitors, but the decrease of oil viscosity and the weakened low-temperature gel structure induced by asphaltenes and wax inhibitors would increase the wax molecular diffusion coefficient and wax content in the wax deposit, which ultimately leads to a thinner and harder wax deposit. Moreover, based on the molecular dynamic simulation, the EVA molecules can be adsorbed on the asphaltene surface thus forming EVA-asphaltene composite particles, which can change the crystallization habit of wax molecules and the wax crystal micromorphology, thereby dramatically improving the crude oil rheology at low temperatures and inhibiting wax deposition. This work provides a comprehensive understanding of the wax deposition mechanism induced by asphaltenes and wax inhibitors, which helps to the well or pipeline operation safety and efficiency.

Research shows that the wax crystals precipitated in crude oil emulsions can not only form a three-dimensional network, but also be adsorbed at the oil-water interface, which prevents the coalescence of water droplets and thus enhances the stability of the water-in-oil (W/O) emulsions. A deeper exploration on the crystallization behavior of wax crystals at the interface and the specific roles of wax crystals and droplets played during the network formation process in the W/O model oil emulsions was conducted in this study through interfacial experiments, microscopic observation and rheological measurement. The results show that the emulsifier can promote the crystallization of paraffin wax at the interface if the wax molecules are able to co-crystallize with the emulsifier. It helps to form an elastic interfacial film, preventing the water droplet coalescence. The droplets covered with wax crystals can participate in the network forming process and play a leading role. It is further discovered that the crystals formed by the binding of the wax molecules and the emulsifier molecules become spherical and not prone to overlap with each other. By contrast, no crystallization of paraffin wax will take place on the surface of droplets when there is no co-crystallization effect between the paraffin wax and the emulsifier. Under this circumstance, the wax crystals are slender and needle-like, and are easily overlapped with each other. As a result, the wax crystals play a dominant role in the network forming process.

It has been reported that the oil dispersible polymethylsilsesquioxane (PMSQ) microsphere can effectively improve the flow behavior of the waxy crude oil through the spacial hindrance effect. Because of the complex composition of the crude oil, in this work, model waxy oil is used to further investigate the effects and mechanisms of PMSQ microspheres on influencing the rheology of the waxy oil. The effects of PMSQ microspheres with sizes from 200 nm to 10 μm on the formation and breakage of the waxy oil gel are first studied based on the rheological measurements. Results show that adding PMSQ microsphere effectively inhibits the formation of the waxy oil gel and weakens the gel structure of the waxy oil formed at 20 °C under static cooling condition. The gelation point, the G ′, G ″ value at 20 °C/25 °C and the yield stress at 20 °C of the doped waxy oil are found to first decrease and then increase with the increase of the PMSQ microsphere size, and the PMSQ-3 (2 μm) has the best improving performance. Under static isothermal condition, the formation of waxy oil gel is delayed after adding the PMSQ microsphere. However, under dynamic cooling condition, adding PMSQ microsphere slightly increases the losing flow point and apparent viscosity of the waxy oil. DSC results show that PMSQ microsphere can act as the heterogeneous nucleation sites favoring slight increase of the WAT but have no apparent influence on the precipitated wax crystals’ amount of the waxy oil at each temperature. Associated with the microstructure observation, the mechanism of the PMSQ microsphere influencing the formation and breakage of waxy oil gel is deduced. Under static cooling condition and static isothermal condition, PMSQ microsphere occupies a certain space in oil phase and impedes the interactions of the precipitated wax crystals around the microsphere through spacial hindrance effect, thus effectively inhibiting the formation of wax crystal network under static cooling and weakening the strength of the formed waxy oil gel. Under dynamic cooling condition, the interactions among the precipitated wax crystals are greatly weakened by shearing, the PMSQ microsphere cannot further weaken the interactions among the precipitated wax crystals, but act as a dispersed phase in the waxy oil to increase the concentration of the dispersed phases (wax crystals and PMSQ) at each temperature, resulting in the slightly higher losing flow point and apparent viscosity for the doped waxy oil.

In a previous work, the addition of the polymethylsilsesquioxane (PMSQ) microsphere (50–400 ppm) can improve the flow behavior of waxy crude oil through the spacial hindrance effect. However, the flow improving efficiency of the neat PMSQ microsphere is not as good as the traditional polymeric pour point depressants (PPDs). In this paper, the effect of the ethylene-vinyl acetate copolymer (EVA2806) PPD together with the PMSQ microsphere (with the size around 2 µm) on the flow behavior of a typical waxy crude oil was investigated. The results show that adding 50 ppm EVA PPD can greatly improve the flow behavior of the oil. The neat PMSQ microsphere cannot improve the flow behavior of the oil at small dosages (≤10 ppm), but can significantly improve the performance of the EVA PPD. The gelation point, G′, G″, transient apparent viscosity and yield stress of the oil decrease further after adding both 50 ppm EVA and a small amount of the PMSQ microsphere (≤10 ppm). The best flow improving efficiency is found at 50 ppm EVA + 2.5 ppm PMSQ. The addition of the PMSQ microsphere has little influence on the WAT and precipitated wax crystal amount of the oil doped with EVA, but outstandingly changes the morphology of the precipitated wax crystals into larger and more compact flocs. The adsorption tests show that the EVA molecules can adsorb and concentrate on the PMSQ microsphere, thus causing the formation of the EVA/PMSQ composite particles. The composite particles can act as nucleation templates for the wax precipitation, resulting in larger and more compact wax microstructures and then further improving the flow behavior of the oil. The PMSQ microsphere dosage and the amount of EVA PPD adsorbed on the microsphere obviously influence the performance of the composite particle with the best performance at 50 ppm EVA + 2.5 ppm PMSQ. The findings mentioned above provide a new way to improve the performance of polymeric PPDs efficiently.