Experimental Investigation of the Rheological Properties of a Typical

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Experimental Investigation of the Rheological Properties of a Typical Waxy Crude Oil Treated with Supercritical CO2 and the Stability Change in Its Emulsion Guangyu Sun, Chuanxian Li, Shuang Yang, Fei Yang, and Yaqun Chen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04176 • Publication Date (Web): 13 May 2019 Downloaded from http://pubs.acs.org on May 14, 2019

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Experimental Investigation of the Rheological Properties of a Typical Waxy Crude Oil Treated with Supercritical CO2 and the Stability Change in Its Emulsion Guangyu Sun, Chuanxian Li,* Shuang Yang, Fei Yang, and Yaqun Chen College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China

ABSTRACT: 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. For probing 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 was 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 (WAT), and abnormal point, as well as the growth of the apparent viscosity and the yield stress. Due to the structural enhancement of the interface, as reflected by the dilational modulus increase in the interface, the

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stability of the scCO2-treated waxy crude oil emulsion is strengthened, and its demulsification efficiency is reduced after dosing with the same demulsifier. All these changes could unfavorably influence the safe transportation of the produced fluid in scCO2-flooding oil fields and the subsequent dewatering process.

1. Introduction In recent years, many of the world’s developing oil fields entered into the high water cut stage. However, due to the heterogeneity and low permeability of some reservoirs and the great difference in fluidity between the injection water and the crude oil, the displacement efficiency of water flooding is usually relatively low, leaving a good deal of residual reserves in these reservoirs. With this background, scCO2-EOR (supercritical CO2 enhanced oil recovery) is gradually finding its application as an effective flooding technology. Due to the low critical point of CO2, the miscible phase of crude oil and CO2 is easy to achieve in reservoirs, making scCO2 flooding an obviously superior technology when the gas supply is sufficient. Some of the advantages of the scCO2-EOR technology are stated as follows when compared with other EOR techniques. First, CO2 can readily dissolve in crude oil, markedly expanding its volume and greatly reducing its viscosity.1-4 Second, the miscible effect of scCO2 can reduce the crude oil/water interfacial tension (IFT), thus facilitating the emulsification and flow of the crude oil.5,6 Third, the strong extraction effect of scCO2 can gasify and move the light fractions (C5-C30) in the crude oil to the surface.7 Moreover, when the reservoir pressure drops, the scCO2-EOR can turn into solution gas drive and continue to displace oil.6,8 Based on the above advantages, the CO2 flooding technique has been widely applied in countries such as US, Canada, UK, Norway, Angola, etc. A CO2 flooding field test was first carried out in the SACROC Unit of the US in 1972, and the recovery ratios of the two blocks


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tested were increased by 10% and 7.5%.9 Subsequently, the scCO2-EOR programs were put into practice by Shell, Amoco, Texaco, Exxon, and other companies in succession. Until 2012, there were 112 scCO2 miscible flooding programs applied in the US in total, with an injection volume of 384 hundred million cubic meters and an oil production of 16.089 million tons per year. In China, Jiangsu Oilfield, Jilin Oilfield, Daqing Oilfield, Shengli Oilfield, and Changqing Oilfield have already conducted industrial tests. The application scales are being enlarged, and the injection techniques are being gradually improved. Meanwhile, carbon capture, utilization, and storage (CCUS) are gaining extensive attention. As a greenhouse gas, CO2 plays a crucial part in global warming. Currently, the scCO2-EOR program is widely considered a superior method for reducing carbon emissions and tackling global climate change.10 The high return of the oil production increase can offset the cost of CO2 storage, so the emission volume of CO2 can be reduced economically with the scCO2-EOR technology.11 However, some problems accompany the above advantages in scCO2 flooding. An important one is the precipitation and deposition of heavy components such as asphaltenes triggered by the interactions between scCO2 and crude oil, forming compact asphaltene aggregates.12-18 As we know, the equilibrium state of asphaltenes in crude oil may be upset as a result of changes in temperature and pressure or with the addition of chemicals, and the asphaltenes begin to precipitate. With increasing pressure the amount of dissolved CO2 in crude oil grows, leading to more precipitated asphaltenes, and the precipitated asphaltenes will flocculate.19 Further research reveals that the alkyl side-chain of the asphaltene molecules in the CO2-induced precipitate is shorter than that of the residual asphaltenes dispersed in crude oil.20 This indicates that the polarity of the CO2-induced precipitated asphaltenes is stronger than that of the dispersed ones.


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Due to the intense shearing imposed by wellbores, choke valves and pumps, the emulsification of crude oil and water in produced fluid may occur in surface gathering pipelines from oil wells to processing stations.21 During multiphase pipeline transportation, whether the crude oil emulsion is stable or not may affect the flow pattern and the subsequent dewatering technology. The emulsion stability is highly dependent on the structure of the thin interfacial film that separates the droplets. Previous studies have confirmed that asphaltenes are the major constituents of the crude oil/water interfacial film.22,23 The interfacially active asphaltenes migrate to the oil/water interface from the bulk oil and tightly adsorb on it. The adsorption could facilitate the formation of an interfacial film with a cross-linked structure.24 Considering the above information, we can infer that the stability change in crude oil emulsions after scCO2 treatment is an inevitable result of the dispersed state change of asphaltenes. The stability of an emulsion can be characterized by the rheological properties of its droplet interface.25-27 Interfacial rheology includes interfacial shear rheology and interfacial dilational rheology. The shear viscoelastic properties of interfaces have been investigated extensively in earlier times. However, when the droplets collide with each other, the interfacial dilational viscoelasticity is considered a better indicator characterizing the interfacial structural strength.28,29 Many studies have agreed that the crude oil emulsion stability is positively correlated to the dilational viscoelasticity of the droplets.25-27,30-34 This is because the interfacial dilational viscoelasticity is capable of characterizing the interfacial structural strength quite well.25 Therefore, the effect of a scCO2 treatment on the emulsion stability can be reflected by the interfacial dilational viscoelasticity measurement. The effects of a scCO2 treatment on the rheology of a typical waxy crude oil, and then on its emulsion stability, were explored in this study. First, the composition changes in the waxy crude


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oil after the scCO2 treatment were examined, and then the effects of these changes on various rheological properties were analyzed. After that, the change in the macroscopical stability of the scCO2-treated crude oil emulsion was probed, and the mechanism behind the stability change was uncovered through the interfacial viscoelasticity test. Finally, the efficiency of a demulsifier on the scCO2-treated waxy crude oil emulsion was tested, aiming to assist the efficient oil-water separation of the scCO2-EOR produced fluid. 2. Experimental Section 2.1 Materials A wax-containing crude produced in the Changqing Oilfield in China was employed in the experiments. Some of the crude oil’s physical properties are displayed in Table 1. Clearly, the crude oil contains a high wax content and, accordingly, possesses a high pour point. Table 1. Some Physical Properties of the Waxy Crude Oil property

value

density at 20 °C (kg/m³)

847.6±0.1

wax content (wt %)

18.59±0.14

WAT (°C)

34.2±0.2

pour point with heat treatment at 50 °C (°C)

29.3±0.2

The CO2 was purchased from Tianyuan Gas Co., Ltd., China (purity > 99.8%). The brine water containing 0.05 mol/L sodium chloride (analytically pure) was used to prepare the emulsions. 2.2 scCO2 Treatment Method The scCO2 treatment was carried out in a homemade device (Figure 1). The device is capable of simulating the generalized reservoir conditions. The treatment procedures are introduced as follows. First, the CO2 in the gas cylinder was injected into the piston tank and the kettle to drive


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away the air in them. Then, the waxy crude oil was forced to interact with the CO2 at a mass ratio of 2.5:1 (crude oil: CO2) in the PVT reaction kettle for 8 h. The temperature and pressure in the kettle were maintained at 25.0±0.5 MPa and 80±1 °C, respectively, since these conditions are similar to the conditions in oil reservoirs. To simulate the pressure-drop from the reservoir to the wellhead, the pressure in the PVT kettle was then reduced to 2.5±0.1 MPa from 25.0±0.5 MPa after the interaction. The pressure was decreased by 0.5 MPa/min and was then maintained for another 30 min at this value. Ultimately, the pressure was lowered to the barometric pressure as a simulation of the process from the wellhead to the three-phase separator.

Figure 1. Schematic diagram of the scCO2-treatment device. 2.3 Composition and Rheology Determination of the Waxy Crude Oil Before and After the scCO2 Treatment (1) Composition determination. A gas chromatograph (3800GC, Varian Associates, Inc., US) was used to analyze the total hydrocarbons in the crude oil according to the Chinese standard SY/T 5779-2008 “Analytical method of hydrocarbons in petroleum and sediment by gas chromatography”. Because the crude oil was light crude, no dilution was needed before the


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sample was injected into the vaporizing chamber. After vaporization, the sample was carried to the capillary column with nitrogen gas to be separated. Next, the separated components were detected by the hydrogen flame ionization detector. The data were collected and processed by the chromatographic work station, and the spectrogram was obtained. The mass fraction of each hydrocarbon was calculated with the peak area normalization method. Each gas chromatography experiment was carried out in triplicate. The SARA contents (i.e., the saturates, the aromatics, the resins, and the asphaltenes) in the waxy crude oil were measured based on the ASTM standard D4124-09. A set of parallel experiments was conducted for the SARA determination. (2) Determination of WAT and precipitated wax content. The WAT of the waxy crude oil was obtained by the differential scanning calorimetry (DSC) method (DSC 821e, Mettler-Toledo Co., Switzerland). According to the heat release of the wax crystallization, the precipitated wax content was calculated. The amount of heat release caused by crystallization was the integral area between the baseline and the heat flow curve below the WAT. Since the enthalpy of paraffin crystallization could be taken as a constant, the precipitated wax content was achieved by dividing the heat release of the wax crystallization by the average enthalpy of paraffin crystallization. The DSC experiment was developed in duplicate. (3) Morphology observation of wax crystals and asphaltene particles. A polarizing microscope (BX51, Olympus Co., Japan) was used to observe the morphology of the precipitated wax crystals. The sample temperature was regulated by a heating stage. When the polarized light was projected on the crude oil sample, the area occupied by the amorphous substances blocked all the light, thus resulting in the all black of the visual field. In contrast, the area occupied by the wax crystals refracted the polarized light, thus leading to a bright vision. The microstructure of the wax crystals in each sample was photographed three times. The morphology of the asphaltene


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particles in the samples with/without scCO2 treatment was photographed under direct light. In addition, the droplet size distribution in the crude oil emulsions was also acquired with the microscope. Nano Measurer software (Fudan University, China) was used to calculate the size of the droplets in the micrographs. To ensure the statistical magnitude and reduce the uncertainty, two samples from each crude oil emulsion were photographed under the microscope. For each sample, six micrographs were taken by moving the visual field. As a result, the average droplet size was obtained by calculating the size of the droplets in the twelve microscopic images. (4) Pour point test. The measurement of the pour point was based on the ASTM standard D5853-11. The pour point tests of the wax crude oils with and without scCO2 treatment were conducted after pretreatment with different heating temperatures. Each pour point was tested three times. The test results are presented in Table 2. Table 2. Pour point of the waxy crude oils with/without scCO2 treatment heat-treatment temperature (oC)

pour point without scCO2 treatment (oC)

pour point after scCO2 treatment (oC)

80±1

21.7±0.1

22.8±0.2

70±1

23.1±0.2

24.2±0.2

60±1

26.8±0.1

28.0±0.3

50±1

29.3±0.2

31.1±0.2

As shown in Table 2, the pour points both with and without scCO2 treatment present a descending tendency with the increasing heat-treatment temperature. The pour point is reduced markedly after the 70 °C heat-treatment, indicating a good heat-treatment effect at this temperature. Therefore, 70 °C was chosen as the unified heat-treatment temperature in the following rheological studies. In the meantime, we can see a slight increase in the pour point after the scCO2 treatment.


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(5) Measurement of the viscosity-temperature curve. The rheological tests, including the viscosity-temperature test and the yield stress test, were performed with a rheometer (AR-G2, TA Instruments, US). The coaxial cylinder was chosen as the measuring system. The viscositytemperature curve was measured by following the steps below. First, the waxy crude oil (with or without scCO2 treatment) was heated at 70 °C in a water bath for 30 min, and the coaxial cylinder measuring system was also set to 70 °C at the same time. The waxy crude oil was then transferred to the measuring system after the heat treatment. The different shear rates (50 s-1, 100 s-1, 200 s-1, 350 s-1, 500 s-1) were loaded to the sample for 10 min each to ensure the achievement of viscosity equilibrium. The temperature was then cooled at 0.5 °C/min. Every 5 °C, the viscosity was measured once by loading the shear rates until the temperature reached the WAT. At the temperatures below the WAT and above the pour point, the apparent viscosity was also tested in the same way, but the sample was replaced by a new one after each test. The new sample was pretreated at 70 °C and cooled to the test temperature at 0.5 °C/min before the shear rates were loaded. (6) Measurement of the yield stress. The heat treatment and cooling procedures were the same as those of the viscosity test. When the temperature was cooled to and below the pour point, the sample was maintained in the cylinder for 20 min. Then, the shear stress was loaded in a linearly increasing way (5 Pa/min) to determine the yield point. When the stress was increased to a certain value, the shear strain rose sharply, indicating the yielding of the gel structure. The viscosity and yield stress measurements were conducted in duplicate. 2.4 Preparation and Stability Test Methods of the Water-in-Waxy Crude Oil Emulsion (1) Emulsion preparation. The emulsions with the total volume of 60 mL were prepared in a 200 mL beaker. The volume fraction of the brine was controlled at 30%. The brine was poured


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into the beaker after the addition of the crude oil. Then, the oil-brine mixture was placed into a 50 °C water bath and kept for 20 min. Subsequently, the emulsification of the mixture was accomplished by a digital stirrer (RW20, IKA group, Germany). The emulsifying condition was stirring at 1000 rpm for 600 s. (2) Determining the emulsion stability with the electric conductivity method. The prepared water-in-oil (W/O) emulsion was isothermally transferred to a glass tube. The temperature was maintained by placing the tube in a water bath. Then, a platinum black electrode (DDS-307, INESA Scientific Instrument Co., Ltd., China) was put in the top half of the emulsion (Figure 2). The variation in the conductivity was then recorded with time by the conductivity meter.

Figure 2. Schematic of measuring the emulsion stability by the electric conductivity method at (a) a shorter time and (b) a longer time. When instability happens in the W/O emulsion, the dispersed water droplets will coalesce and fall towards the bottom due to density differences (Figure 2b). As a result, the water content in the upper layer will gradually decrease, resulting in a continuous reduction of the electric conductivity. Considering this result, we defined a term, the reduction ratio of specific conductivity  r , as exhibited in eq 1.


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 r   0   t  /  0

(1)

where  0 refers to the conductivity of the W/O emulsion at t=0, μs·cm-1;  t refers to the conductivity at any time t, μs·cm-1. Theoretically, the value of  r will increase from 0 to 1 with the gradual reduction of the electric conductivity as time passes. Therefore, a lower value of  r at the same time indicates a smaller variation in the droplet size distribution, i.e., a higher stability of the emulsion. The conductivity test was conducted in duplicate. (3) Interfacial property measurement. The kinetic processes of the interfacial properties were acquired via a drop tensiometer (TRACKER H, Teclis Scientific, France). The crude oil was loaded into the U-shape needle to form oil drops. The brine was contained in the thermostatic cell as the external phase. The dynamic IFT was obtained by analyzing the drop shape. The dilatational modulus was calculated by oscillating the drop sinusoidally. The oscillation amplitude was set to be 6.667% of the drop volume, and the frequency was 0.2 Hz. All the interfacial experiments were repeated three times. (4) Testing the demulsification characteristics of the emulsion. The dodecyl polyoxyethylene polyoxypropylene ether (C12H25O(EO)5(PO)4) (Henkel China) with a purity higher than 99% was used as the demulsifier. The oil-water separation rate after the addition of the demulsifier was determined by a bottle test. First, the prepared crude oil emulsion was transferred into a colorimetric tube, and the demulsifier with the concentration of 100 ppm was added into the emulsion. The colorimetric tube was then kept at 50 °C by placing it in a thermostatic water bath, and the time was recorded simultaneously. The separated water volume was inspected versus time, and the separated water ratio was calculated according to eq 2. fv 

V1 100% V2

(2)


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where V1 is the separated water volume, mL; V2 is the total water volume dispersed in the crude oil emulsion at the initial moment, mL. According to this equation, the smaller f v is over the same time, the more stable the emulsion is. The bottle test was conducted in duplicate. 3. Results and Discussion 3.1 Composition Change of the Waxy Crude Oil After the scCO2 Treatment The SARA contents in the waxy crude oils before and after the scCO2 treatment are presented in Table 3. As is observed in the table, the saturates account for the largest proportion in the waxy crude oils. In contrast, the contents of both resins and asphaltenes are relatively low. When compared with the waxy crude oil without the scCO2 treatment, the sample after treatment contains more aromatics, resins and asphaltenes but less saturates. The mass ratio of resins plus asphaltenes clearly increased after the scCO2 treatment. Table 3. SARA contents in the waxy crude oils before/after scCO2 treatment saturates

aromatics

resins

asphaltenes

(saturates+aromatics)/

(wt %)

(wt %)

(wt %)

(wt %)

(resins+asphaltenes)

without treatment

72.86±0.17

18.40±0.09

8.02±0.11

0.72±0.04

10.44

after scCO2 treatment

70.25±0.21

19.89±0.13

8.85±0.07

1.01±0.06

9.14

sample

Next, the carbon number distributions (CNDs) of the hydrocarbons in the waxy crude oils before and after the scCO2 treatment were measured, and Figure 3 exhibits the results. The mass fraction of C9 is the highest in the crude oils both with and without scCO2 treatment. On the whole, the content of the hydrocarbons shows a decreasing trend with an increasing carbon number above C9. After the scCO2 treatment, part of the hydrocarbons below C19 are extracted from the crude oil, leading to the content reduction in light hydrocarbons and liquid paraffins,


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and the corresponding increase in the content of paraffin wax and microcrystalline wax. The reason behind this phenomenon is that scCO2 and the waxy crude oil are miscible under the experimental conditions. In the miscible system, the CO2-CO2 molecular clusters may be dispersed into the organic liquid molecules. The dispersion forces between the light hydrocarbon molecules and the carbon dioxide molecules are stronger than the cohesive forces among the carbon dioxide molecules themselves. As a result, the light hydrocarbons are wrapped by the CO2-CO2 molecular clusters.35 Once the pressure is lowered, the light hydrocarbons in the crude oil will be carried away with the escape of CO2; therefore, the content of the smaller carbonnumber hydrocarbons declines.

Figure 3. CNDs of the hydrocarbons in the waxy crude oils with/without scCO2 treatment. 3.2 Variation in the Rheological Properties and Wax Precipitation Characteristics of the Waxy Crude Oil Induced by the scCO2 Treatment (1) Viscosity/apparent viscosity. The viscosity evolution of the waxy crude oils before and after the scCO2 treatment with temperature was determined after the 70 °C heat-treatment, and the viscosity-temperature relationship of the untreated oil is displayed in Figure 4 as an example. The abnormal point of the crude oil without the scCO2 treatment is approximately 27 °C. That is, the untreated crude oil becomes a non-Newtonian fluid below this temperature. Likewise, the


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abnormal point after the scCO2 treatment is also obtained according to the viscosity/apparent viscosity-temperature curves, and it changes to 31 °C which is 4 °C higher than that without the scCO2 treatment. From the comparison between the viscosity/apparent viscosity-temperature curves in Figure 5, we can see that there is a clear increase in the apparent viscosity after the scCO2 treatment in the non-Newtonian temperature range. This is quite different from the CO2dissolved situation for crude oil. According to the previous studies1-3 and our study4, the dissolution of CO2 at high pressures is capable of significantly reducing the viscosity of crude oil.

Figure 4. Viscosity/apparent viscosity vs. temperature for the untreated waxy crude oil.

Figure 5. Comparison of the viscosity/apparent viscosity-temperature curves with and without scCO2 treatment at 50 s-1.


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(2) Yield stress. The yield characteristics of the waxy crude oils with and without scCO2 treatment were measured at their pour point temperatures and below. The determination of the yield point is demonstrated in Figure S1 (Supporting Information), and the yield stress values are demonstrated in Figure 6. Apparently, the scCO2-treated waxy crude oil possesses a larger yield stress than the untreated oil, manifesting the strengthening of the gel structure after the scCO2 treatment.

Figure 6. Yield stresses of the waxy crude oils with/without scCO2 treatment at their pour point temperatures and below. (3) Wax precipitation characteristics. To explore the function mechanism of the scCO2 treatment behind the above low-temperature rheological properties, the wax precipitation characteristics were further tested and analyzed. The WAT can be determined with the heat flow curves (one example presented in Figure 7a). The untreated waxy crude oil has the WAT of 34.2±0.2 °C, and the cumulative content of the precipitated wax with decreasing temperature is demonstrated in Figure 7b. The total wax precipitation content from the WAT to -20 °C is 18.59±0.30 wt %. In contrast, the WAT of the waxy crude oil after the scCO2 treatment rises to 36.3±0.1 °C, and the cumulative wax precipitation content from the WAT to -20 °C changes to


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19.09±0.32 wt %. Thus, it can be easily seen that both the WAT and the wax precipitation content are increased after the waxy crude oil is treated by scCO2.

Figure 7. Heat flow curves (a) and cumulative contents of precipitated wax (b) of the untreated/treated waxy crude oils with decreasing temperature. The crystal morphology of the precipitated wax was then observed at 20 °C and 10 °C, and the microscopic images are displayed in Figure 8. All the white spots in Figure 8 are wax crystals. By comparing the images, we can see that the wax crystal particle size decreases due to the scCO2 treatment. The morphology of the wax particles is further analyzed by the ImageJ software (NIH, US), and the average results of three repeated tests are presented in Table 4. The average size of the wax particles evidently decreases after the waxy crude oil is treated by scCO2 at the same temperature, while the number of the wax particles increases. This implies that there are more crystal nuclei in the scCO2-treated crude oil than in the untreated crude oil because CO2 can lead to the precipitation of asphaltenes and microcrystalline paraffins. The precipitated small particles can play the role of nuclei. The morphology of the asphaltene particles with and without the scCO2 treatment is displayed in Figure S2 (Supporting Information). It is obvious that both the size and the amount of the asphaltene particles are larger after the scCO2 treatment. This


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result is a clear indication that the asphaltenes can truly be precipitated by CO2. As a result, more crystals are formed through crystallization on these nuclei. Additionally, it has been proven above that the scCO2 treatment results in the viscosity increase in the crude oil. The higher viscosity can hinder the migration of paraffin molecules to the precipitated crystals, thereby hindering the growth of the crystals. Eventually, the crystal size of the precipitated wax after scCO2 treatment decreases but the amount becomes larger. The larger-in-amount and smaller-insize wax crystals mean a larger interface between the wax crystals and the liquid oil. Therefore, more liquid oil can be trapped by the wax crystal structure, thus worsening the rheological properties. In summary, the scCO2 treatment results in the worsening of the crude oil’s rheological properties, such as increases in the abnormal point, the pour point, the WAT, the apparent viscosity, the yield stress, etc. The reason for the worsening lies in the composition change in the crude oil. The scCO2 extracts the light hydrocarbons in the crude oil,7 leading to a decreased amount of saturates and an increased amount of heavy components such as resins, asphaltenes, and hydrocarbons with carbon numbers above 24. Therefore, the waxy crude oil becomes “heavier” in fact after the scCO2 treatment.


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(a)

(b)

(c) (a)

(d) (a)

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Figure 8. Microstructure of the wax crystals with/without scCO2 treatment: (a) untreated, 20 °C; (b) treated, 20 °C; (c) untreated, 10 °C; (d) treated, 10 °C. Table 4. Statistical results of the wax crystal particles in the microscopic images at 20 °C sample without treatment after scCO2 treatment

average wax

proportion of the average area occupied by

particle numbers

each wax particle to the overall area (%)

4802±314

(2.02±0.13)×10-3

14401±1077

(5.61±0.42)×10-4

3.3 Emulsion Stability of the scCO2-Treated Waxy Crude Oil (1) Macroscopic stability. After emulsification, the conductivity change with time was recorded in real time for the upper-layer emulsion. The reduction ratio of the specific


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conductivity  r was then calculated according to eq 1, and its evolution with time is shown in Figure 9. As is displayed in the figure, the  r of the emulsion formed by the untreated crude oil increases rapidly with time and reaches an equilibrium after approximately 18 min of quiescence. In contrast, for the emulsion formed by the scCO2-treated crude oil,  r grows slower under the same condition, and its value stays below that without treatment during the whole test. This difference proves that the scCO2 treatment imposed on the waxy crude oil makes the emulsion a more stable system. This result is also quite different from the situation when CO2 is dissolved in the crude oil emulsion, in which the emulsion stability is evidently weakened with the increasing amount of dissolved CO2.36

Figure 9. Evolution of the reduction ratio of specific conductivity with time for the emulsions formed by the untreated and scCO2-treated waxy crude oils at 50 °C.

Further, the microstructures of the just-prepared crude oil emulsions were observed with the microscope, and the micrographs are displayed in Figure 10. It is shown that no significant difference in the droplet size exists between the untreated and scCO2-treated crude oil emulsions.


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In addition, the statistical result manifests that the average droplet size of the untreated crude oil emulsion is 62.29±3.17 μm, while the value changes to 56.39±2.62 μm for the emulsion formed by the scCO2-treated crude oil. This means the droplets become slightly smaller under the same shearing condition. As is known, the emulsion with smaller dispersed droplets usually possesses a higher stability.37 In addition, it can also be seen from the two micrographs that more interfacial active substances such as asphaltenes adsorb at the droplet surface after the scCO2 treatment, making the surface look thicker and darker in the micrograph.

(a)

(b)

Figure 10. Micrographs of the emulsions formed by the untreated and scCO2-treated waxy crude oils at 50 °C.

(2) IFT and dilational viscoelasticity. The IFT between the waxy crude oil and the brine at different temperatures was tested. As is demonstrated in Figure 11, the dynamic IFT gradually declines with time, indicating the ability of reducing the IFT by the continuous adsorption of asphaltenes. According to Langevin and Argillier, the adsorption time of asphaltenes is rather long, of the order of 1000 s,38 which is in line with the results of this study. Moreover, it is shown that the IFTs of both the untreated and treated crude oil are reduced with increasing temperature. Similar trends can also be found in previous studies.39-41 Compared with the


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untreated waxy crude oil, the scCO2-treated one has a larger IFT at the same temperature, and the gap becomes larger and larger with decreasing temperature. As mentioned in the Introduction, the alkyl side-chain of the precipitated asphaltene molecules induced by the CO2 treatment is shorter than that of the residual asphaltenes dispersed in crude oil,20 indicating that the polarity of the CO2-induced precipitated asphaltenes is stronger than that of the dispersed ones. As a result, the remaining asphaltene molecules which can adsorb at the interface become weaker in their interfacial activity, so the IFT of the scCO2-treated waxy crude oil becomes larger.

Figure 11. Variation in the IFT between the brine and the waxy crude oil with time at different temperatures before/after scCO2 treatment.

However, many research studies have shown that emulsion stability is not necessarily correlated to IFT.7,28,40,42,43 The decrease in IFT does not ensure a high-stability emulsion. In contrast, there exists a positive correlation between the stability and the dilational viscoelasticity of the interface.26,29,32-34 The interfacial dilatational modulus can represent the structural strength of an interface. The changes in the interfacial dilatational moduli with time are drawn in Figure 12 based on the test results. It is shown in the figure that the dilatational modulus gradually


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increases with time, which also indicates the continuous adsorption of asphaltenes. Consequently, the interfacial structure is strengthened by the dynamic adsorption process. Like the IFT, the interfacial dilatational moduli of both the untreated and treated crude oil are also reduced with increasing temperature. After scCO2 treatment, the waxy crude oil and the brine can form a stronger interfacial film with an evidently higher dilatational modulus, thus resulting in a more stable emulsion which has already been proved in Figure 9. The reason for the strengthened interfacial film lies in the fact that the light components in the waxy crude oil had been extracted and taken away by the scCO2 before the interfacial experiment. The extraction results in the increase in the content of the active substances such as asphaltenes. Consequently, the adsorption quantity is increased at the interface, and accordingly, the interfacial structure is strengthened.

Figure 12. Variation in the interfacial dilational modulus between the waxy crude oil and the brine with time at different temperatures before/after scCO2 treatment.

3.4 Susceptibility of the Crude Oil Emulsion to the Demulsifier after scCO2 Treatment To evaluate the susceptibility of the untreated and scCO2-treated crude oil emulsions to a


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demulsifier, the emulsions were dosed with the same concentration of dodecyl polyoxyethylene polyoxypropylene ether. The separated water volume in 60 min was recorded by a bottle test, and the water separation ratio was calculated and illustrated in Figure 13. According to the curves in the figure, the untreated crude oil emulsion is almost completely dewatered after the demulsifier is added for 20 min, while approximately 15% of the brine in the scCO2-treated waxy crude oil emulsion still stays emulsified in the 60 min test. This phenomenon declares the fact again that the waxy crude oil emulsion becomes more stable and more difficult to demulsify if the crude oil is treated by scCO2.

Figure 13. Variation in the water separation ratio with time after the addition of the demulsifier to the emulsions formed by the untreated and scCO2-treated waxy crude oils.

4. Conclusion After the waxy crude oil is treated by scCO2, its physical and rheological properties are evidently changed, and the macroscopic stability of its W/O emulsion is affected, as well. Compared with the waxy crude oil without the scCO2 treatment, the treated one contains fewer light hydrocarbons (below C23) and more heavy hydrocarbons (above C24), and the proportions


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of resins and asphaltenes are increased. These composition changes result in the growth of the yield stress and the viscosity and the increase in the WAT, the abnormal point and the pour point. In short, the crude oil’s flowability is worsened. The scCO2 treatment to the crude oil enhances its emulsion stability. After adding the same concentration of demulsifier, the scCO2-treated crude oil emulsion becomes more difficult to dewater. Further, the interfacial dilational viscoelasticity tests prove that the interfacial structure is strengthened due to the scCO2 treatment, which accounts for the enhancement of the emulsion stability.

Corresponding Author *E-mail: [email protected] ACKNOWLEDGMENTS We would like to thank the National Natural Science Foundation of China (51704315) and the Fundamental Research Funds for the Central Universities (18CX02004A) for the financial support. References (1) Li, H. Z.; Zheng, S. X.; Yang, D. Y. Enhanced swelling effect and viscosity reduction of solvent(s)/CO2/heavy-oil systems. SPE J. 2013, 18(4), 695−707. (2) Badamchi-Zadeh, A.; Yarranton, H. W.; Maini, B. B.; Satyro, M. A. Phase behaviour and physical property measurements for VAPEX solvents: Part II. Propane, carbon dioxide and Athabasca bitumen. J. Can. Pet. Technol. 2009, 48(3), 57−65.


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(3) Behzadfar, E.; Hatzikiriakos, S. G. Rheology of bitumen: Effects of temperature, pressure, CO2 concentration and shear rate. Fuel 2014, 116, 578–587. (4) Sun, G.; Li, C.; Wei, G.; Yang, F. Characterization of the viscosity reducing efficiency of CO2 on heavy oil by a newly developed pressurized stirring-viscometric apparatus. J. Petrol. Sci. Eng. 2017, 156, 299–306. (5) Mahdavi, E.; Zebarjad, F. S.; Taghikhani, V.; Ayatollahi, S. Effects of paraffinic group on interfacial tension behavior of CO2–asphaltenic crude oil systems. J. Chem. Eng. Data 2014, 59(8), 2563-2569. (6) Wang, X.; Gu, Y. Oil recovery and permeability reduction of a tight sandstone reservoir in immiscible and miscible CO2 flooding processes. Ind. Eng. Chem. Res. 2011, 50(4), 2388−2399. (7) Wang, X.; Zhang, S.; Gu, Y. Four important onset pressures for mutual interactions between each of three crude oils and CO2. J. Chem. Eng. Data 2010, 55(10), 4390–4398. (8) Farajzadeh, R.; Andrianov, A.; Zitha, P. Investigation of immiscible and miscible foam for enhancing oil recovery. Ind. Eng. Chem. Res. 2009, 49(4), 1910−1919. (9) Merchant, D. Enhanced oil recovery–the history of CO2 conventional wag injection techniques developed from lab in the 1950’s to 2017. Carbon Management Technology Conference; Houston, USA, July 17–20, 2017. (10) Hu, R.; Crawshaw, J. P.; Trusler, J. M.; Boek, E. S. Rheology of diluted heavy crude oil saturated with carbon dioxide. Energy Fuels 2014, 29(5), 2785−2789. (11) Lv, G.; Li, Q.; Wang, S.; Li, X. Key techniques of reservoir engineering and injection– production process for CO2 flooding in China's SINOPEC Shengli Oilfield. J. CO2 Util. 2015, 11, 31–40.


25

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 29

(12) Zanganeh, P.; Ayatollahi, S.; Alamdari, A.; Zolghadr, A.; Dashti, H.; Kord, S. Asphaltene deposition during CO2 injection and pressure depletion: A visual study. Energy Fuels 2012, 26(2), 1412−1419. (13) Escrochi, M.; Mehranbod, N.; Ayatollahi, S. The gas−oil interfacial behavior during gas injection into an asphaltenic oil reservoir. J. Chem. Eng. Data 2013, 58(9), 2513−2526. (14) Jafari Behbahani, T.; Ghotbi, C.; Taghikhani, V.; Shahrabadi, A. Investigation on asphaltene deposition mechanisms during CO2 flooding processes in porous media: A novel experimental study and a modified model based on multilayer theory for asphaltene adsorption. Energy Fuels 2012, 26(8), 5080−5091. (15) Hemmati-Sarapardeh, A.; Ayatollahi, S.; Ghazanfari, M. H.; Masihi, M. Experimental determination of interfacial tension and miscibility of the CO2−crude oil system; temperature, pressure, and composition effects. J. Chem. Eng. Data 2014, 59(1), 61−69. (16) Gabrienko, A. A.; Martyanov, O. N.; Kazarian, S. G. Behavior of asphaltenes in crude oil at high-pressure CO2 conditions: In situ attenuated total reflection–fourier transform infrared spectroscopic imaging study. Energy Fuels 2016, 30(6), 4750−4757. (17) Ju, B.; Fan, T.; Jiang, Z. Modeling asphaltene precipitation and flow behavior in the processes of CO2 flood for enhanced oil recovery. J. Petrol. Sci. Eng. 2013, 109, 144–154. (18) Loureiro, T. S.; Palermo, L. C. M.; Spinelli, L. S. Influence of precipitation conditions (nheptane or carbon dioxide gas) on the performance of asphaltene stabilizers. J. Petrol. Sci. Eng. 2015, 127, 109−114. (19) Lu, T.; Li, Z.; Fan, W.; Zhang, X.; Lv, Q. Nanoparticles for inhibition of asphaltenes deposition during CO2 flooding. Ind. Eng. Chem. Res. 2016, 55(23), 6723−6733.


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Energy & Fuels

(20) Deo, M.; Parra, M. Characterization of carbon-dioxide-induced asphaltene precipitation. Energy Fuels 2011, 26(5), 2672−2679. (21) Sun, G.; Zhang, J.; Li, H. Structural behaviors of waxy crude oil emulsion gels. Energy Fuels 2014, 28(6), 3718–3729. (22) He, L.; Lin, F.; Li, X.; Sui, H.; Xu, Z. Interfacial sciences in unconventional petroleum production: From fundamentals to applications. Chem. Soc. Rev. 2015, 44(15), 5446–5494. (23) Liu, J.; Zhao, Y.; Ren, S. Molecular dynamics simulation of self-aggregation of asphaltenes at an oil/water interface: Formation and destruction of the asphaltene protective film. Energy Fuels 2015, 29(2), 1233–1242. (24) Tchoukov, P.; Yang, F.; Xu, Z.; Dabros, T.; Czarnecki, J.; Sjöblom, J. Role of asphaltenes in stabilizing thin liquid emulsion films. Langmuir 2014, 30(11), 3024–3033. (25) Nguyen, D.; Balsamo, V.; Phan, J. Effect of diluents and asphaltenes on interfacial properties and steam-assisted gravity drainage emulsion stability: Interfacial rheology and wettability. Energy Fuels 2013, 28(3), 1641–1651. (26) Yarranton, H. W.; Sztukowski, D. M.; Urrutia, P. Effect of interfacial rheology on model emulsion coalescence: I. Interfacial rheology. J. Colloid Interf. Sci. 2007, 310(1), 246–252. (27) Alvarez, G.; Poteau, S.; Argillier, J. F.; Langevin, D.; Salager, J. L. Heavy oil−water interfacial properties and emulsion stability: Influence of dilution. Energy Fuels 2009, 23(1), 294–299. (28) Wang, Y.; Zhang, L.; Sun, T.; Zhao, S.; Yu, J. A study of interfacial dilational properties of two different structure demulsifiers at oil–water interfaces. J. Colloid Interf. Sci. 2004, 270(1), 163–170.


27

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 29

(29) Rane, J. P.; Pauchard, V.; Couzis, A.; Banerjee, S. Interfacial rheology of asphaltenes at oil– water interfaces and interpretation of the equation of state. Langmuir 2013, 29(15), 4750–4759. (30) Quintero, C. G.; Noïk, C.; Dalmazzone, C.; Grossiord, J. L. Formation kinetics and viscoelastic properties of water/crude oil interfacial films. Oil Gas Sci. Technol. 2009, 64(5), 607–616. (31) Varadaraj, R.; Brons C. Molecular origins of crude oil interfacial activity. Part 4: Oil–water interface elasticity and crude oil asphaltene films. Energy Fuels 2012, 26(12), 7164–7169. (32) Kilpatrick, P. K. Water-in-crude oil emulsion stabilization: Review and unanswered questions. Energy Fuels 2012, 26(7), 4017–4026. (33) Qiao, P.; Harbottle, D.; Tchoukov, P.; Masliyah, J.; Sjöblom, J.; Liu, Q.; Xu, Z. Fractionation of asphaltenes in understanding their role in petroleum emulsion stability and fouling. Energy Fuels 2017, 31(4), 3330–3337. (34) Verruto, V. J.; Le, R. K.; Kilpatrick, P. K. Adsorption and molecular rearrangement of amphoteric species at oil−water interfaces. J. Phys. Chem. B 2009, 113(42), 13788–13799. (35) Dufour, J.; Calles, J. A.; Marugán, J.; Giménez-Aguirre, R.; Peña, J. L.; Merino-García, D. Influence of hydrocarbon distribution in crude oil and residues on asphaltene stability. Energy Fuels 2010, 24(4), 2281–2286. (36) Sun, G.; Liu, D.; Li, C.; Yang, D.; Wei, G.; Yang, F.; Yao, B. Effects of dissolved CO2 on the crude oil/water interfacial viscoelasticity and the macroscopic stability of water-in-crude oil emulsion. Energy Fuels 2018, 32(9), 9330–9339. (37) Moradi, M.; Alvarado, V.; Huzurbazar, S. Effect of salinity on water-in-crude oil emulsion: Evaluation through drop-size distribution proxy. Energy Fuels 2010, 25(1), 260–268.


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(38) Langevin, D.; Argillier, J. F. Interfacial behavior of asphaltenes. Adv. Colloid Interfac. 2016, 233, 83–93. (39) Zeppieri, S.; Rodríguez, J.; López de Ramos, A. L. Interfacial tension of alkane+water systems. J. Chem. Eng. Data 2001, 46(5), 1086–1088. (40) Wang, D.; Lin, M.; Dong, Z.; Li, L.; Jin, S.; Pan, D.; Yang, Z. Mechanism of high stability of water-in-oil emulsions at high temperature. Energy Fuels 2016, 30(3), 1947–1957. (41) Moeini, F.; Hemmati-Sarapardeh, A.; Ghazanfari, M. H.; Masihi, M.; Ayatollahi, S. Toward mechanistic understanding of heavy crude oil/brine interfacial tension: The roles of salinity, temperature and pressure. Fluid Phase Equilibr. 2014, 375, 191–200. (42) Nour, A. H.; Abu Hassan, M. A.; Yunus, R. M. Characterization and demulsification of water-in-crude oil emulsions. J. Appl. Sci. 2007, 7, 1437–1441. (43) Angle, C. W.; Hua, Y. Dilational interfacial rheology for increasingly deasphalted bitumens and n-C5 asphaltenes in toluene/NaHCO3 solution. Energy Fuels 2012, 26(10), 6228–6239.


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Experimental Investigation of the Rheological Properties of a Typical

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