Experimental Study on Aquathermolysis of Different Viscosity Heavy

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Experimental study on aquathermolysis of different viscosity heavy oil with superheated steam Shijun Huang, Meng Cao, and Linsong Cheng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00181 • Publication Date (Web): 02 Mar 2018 Downloaded from http://pubs.acs.org on March 5, 2018

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Experimental study on aquathermolysis of different viscosity heavy oil with superheated steam Shijun Huang, Meng Cao,* and Linsong Cheng College of Petroleum Engineering, China University of Petroleum (Beijing), 102249, Beijing, China ABSTRACT In this paper, a large number of experiments have been carried out to study the aquathermolysis of heavy oil of different viscosities with superheated steam. First, a high-temperature and high-pressure autoclave was independently designed to carry out an aquathermolysis reaction with superheated steam. Second, the viscosity of the heavy oil samples was measured before and after the aquathermolysis reaction by an MCR 302 rheometer. Finally, both the saturates, aromatics, resins and asphaltenes (SARA) content and the carbon number distribution of heavy oil samples before and after the aquathermolysis reaction were determined by chromatography. The experimental results show the following: (1) The higher the content of resins and asphaltenes, the longer is the reaction time for aquathermolysis equilibrium. (2) As for different viscosity oil samples, the starting temperature for aquathermolysis is different; however, the reaction temperature for aquathermolysis equilibrium is the same. (3) The cracking of resins is the main mechanism for the aquathermolysis of low viscosity heavy oil. The cracking of resins is also the dominant mechanism for the aquathermolysis of medium viscosity heavy oil, accompanied by the cracking of asphaltenes. The cracking of resins and asphaltenes is the primary mechanism for the aquathermolysis of high viscosity heavy oil. (4) The cracking of long-chain hydrocarbons into short-chain hydrocarbons is the main mechanism of aquathermolysis.

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Keywords: Aquathermolysis; Superheated steam; Viscosity; SARA; Carbon number distribution 1. Introduction Heavy oil has become a major study focus in the past decades because of the depletion of conventional light oil resources. 1 As we can see from Figure 1, heavy oil and bitumen are predicted to make up about 70% of the total remaining hydrocarbon resources. 2 Many processes have been developed to exploit heavy oil reservoirs, such as chemical recovery, thermal recovery, and microbial recovery.

3

Thermal recovery methods have been widely used and have proved to be

effective for the production of heavy crude oil. 4 In addition, steam injection into the formation has been adopted for decades to improve the recovery of heavy oil, mainly through the following three methods: cyclic steam stimulation5, steam-injection6-8, and steam-assisted gravity drainage. 9

15% 30%

Heavy oil Extra heavy oil 25%

Oil sands and bitumen Conventional oil

30%

Figure 1. Pie chart of total world oil reserves In addition to the fact that steam can reduce the viscosity of heavy oil, it has been observed that chemical reactions occur between steam and heavy oil. Hyne et al.

10

used the term

‘aquathermolysis’ to describe the chemical interaction of high-temperature and high-pressure water with the reactive components of heavy oil and tar sands bitumen to distinguish this process from the term ‘hydrothermolysis’, which has become associated with the interaction of hydrogen at elevated temperature and pressure. A few years later, by analyzing the compositions and gases of heavy oils


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from Canada, Clark11-18 found that under high-temperature and high-pressure conditions, desulfuration, denitrification, hydrogenization and water-gas-shift reactions could happen between steam and heavy oil. In recent years, more and more attention has been paid to the aquathermolysis of heavy oil. Fan et al.

19

have studied the composition changes of heavy oils. They found that the synergetic effects of

minerals and steam could increase the amount of saturated and aromatic hydrocarbons and decrease the amount of resins and asphaltenes in the heavy oils. Monin et al.

20

have studied the thermal

cracking of heavy-oil/mineral matrix systems at different temperatures and pressures. They indicated that chemical reactions between oil, possibly water, and the mineral matrix might result in dramatic changes in the composition of the heavy oil. Hamid Pahlavan et al.

21

pointed out that the

chemical reaction between oil and the matrix plays an important role in the steam-injection process. Zhao et al.

22

and Fan et al.

23

found that the viscosity of heavy oil from the Liaohe Oilfield

decreased significantly after aquathermolysis. The contents of heteroatoms, such as S, O, and N, were reduced. In addition, Fan24-29 indicated that minerals have a catalytic effect on the aquathermolysis of heavy oil during steam stimulation. Liu et al.

30

carried out a field test on

super-heavy oil aquathermolysis production in the Liaohe oilfield. They found that the total carbon number and aromatic carbon number of crude oil decreased significantly. Jia et al.

31

showed that

appreciable amounts of H2S and CO2 could be generated as a result of the aquathermolysis through laboratory studies and pilot project tests. Catalysts and water have been adopted for the thermal cracking of heavy oil to lower the reaction temperature after Hyne’s pioneering work, and the process was named catalytic aquathermolysis. After more than 30 years of research, many types of catalysts have been used. These catalysts can be


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classified into three groups: (1) inorganic solid particles, such as metal oxides, metal sulfides, and mineral particles; (2) water-soluble metal salts, including iron salts, vanadium, and nickel salts; and (3) oil-soluble metal compounds, such as molybdenum oleate. Kök

32

identified three reaction

regions in a crude oil and lithology mixture, known as fuel deposition, high temperature oxidation and low temperature oxidation. Chen et al.

33

showed that the synthesized amphiphilic metallic

chelate-aromatic sulfonic iron was more efficient than other catalysts they had synthesized previously. Yi et al.

34

dramatically. Luo et al.

indicated that catalysts helped to increase the amount of H2 and CO 35

found that a higher dispersion of the catalyst improved the ability to

prevent excessive cracking of heavy oil. Zhao et al.

36

showed that an oil-soluble cobalt- and

nickel-based catalyst could significantly reduce the viscosity of heavy oil. Jeon et al.

37

indicated

that a CoMo bimetallic catalyst could improve the potential of asphaltene and sulfur conversion. Chao et al.

38

found that an aromatic sulfonic copper catalyst could remove some heteroatoms in

heavy oil molecules, such as S, O and N. Wang et al.

39

studied the aquathermolysis of heavy crude oil with amphiphilic nickel and iron

catalysts. They found that both catalysts caused changes in the molecular structures in heavy oil, which is beneficial to the breakage of C-S bonds in asphlatenes and resins. Muraza et al. 40 reviewed the progress made and the fundamental issues related to catalysts development. Munawar et al.

41

studied the effect of hematite nanoparticles on aquathemolysis. They found that thiophene conversion increased with reaction time, as well as with temperature and catalyst concentration, but decreased with thiophene/water ratio and particle size. Iskandar et al. 42 found that a nanocatalyst in an aquathermolysis reaction could effectively reduce the viscosity of heavy oil. Cao et al. 43 studied catalytic aquathermolysis with an amphiphilic cobalt catalyst and found that the synthesized


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catalyst showed active interfacial behavior, decreasing the surface tension and interfacial tension between heavy oil and the liquid phase. Wen et al. 44 studied the activity of H4SiW12O40 on viscosity reduction by vis-breaking, involving the hydrocracking of heavier hydrocarbon fractions in the feed. Chen et al. 45 showed that the viscosities of a range of extra-heavy oils could be reduced by up to 90% using K3PMo12O40 with nano-Keggin structure at 280 °C. Maity et al.

46

indicated that acid sites

would enhance the activity of most oxide catalysts during aquathermolysis. Williams et al.

47

showed that the hydration of a range of molybdenum oxide loadings over Al2O3 effectively improve its acidic properties. It has been reported that superheated steam huff and puff process is adopted for the thermal recovery of heavy oils and tar sands, such as Orinoco heavy oil, Athabasca tar sands and Utah tar sands.

48, 49

Li et al.

50

proposed that aquathermolysis of heavy oil occurs in the oil layer when

superheated steam is injected. Song et al. 51 presented a new aquathermolysis study of conventional heavy oil in superheated steam. He found that the reaction will reach equilibrium after a certain period of time and will not be sensitive to reaction time. Katritzky et al.

52

proposed that water

participates as a catalyst, reactant, and solvent in reactions of organic compounds with superheated water. In addition, transformations of organic compounds in superheated water help removing sulfur and nitrogen from heavy oil. Zhou et al.

53

studied the effect of superheated steam on

aquathermolysis of heavy oil at different temperatures condition. The results indicated that the physical properties of heavy oil sample changed significantly after reacting with superheated steam. Most studies tend to focus on aquathermolysis between heavy oil and steam/minerals/catalysts, but little work has been done to study aquathermolysis with superheated steam. Moreover, the


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previous studies of aquathermolysis mainly focus on super-heavy oil. The reaction of low-/medium-visicosity heavy oil with superheated steam has not been deeply studied. Therefore, in this paper, a series of experiments has been carried out to study aquathermolysis between heavy oil and superheated steam. The novelty of this paper lies in three aspects: (1) a new high-temperature and high-pressure autoclave is independently designed, where the superheated status of steam could be maintained; (2) the reaction time and the reaction temperature for equilibrium are identified for different viscosity heavy oil; and (3) the aquathermolysis reaction of low/medium/high viscosity heavy oil are systematically and deeply studied. 2. Experimental section 2.1. Experimental system The experimental system mainly includes the following three devices: an autoclave, an Anton Paar rheometer, and a gas chromatography. Aquathermolysis of heavy oil with superheated steam was conducted in a high-temperature and high-pressure autoclave, as shown in Figure 2. The Kettle body and kettle cover are made of stainless steel, with good corrosion resistance. The autoclave is equipped with a pressure gauge, a safety valve and a sampling port. The maximum operating temperature and pressure are 350 °C and 40 MPa, respectively. The reaction temperature is controlled by the instrument through electric heating. The internal volume of the reactor is changed by adjusting the plunger so that the internal pressure of the kettle body is lower than the saturation pressure, and thus the superheated steam is provided. The viscosity of the oil samples was measured by a MCR 302 rheometer, as shown in Figure 3, equipped with a ball bearing motor to automatically lift the measuring head to accurately set the measuring gap.


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Figure 2. Physical picture of autoclave

Figure 3. Physical picture of Anton Paar rheometer

Figure 4. Physical picture of gas chromatography As shown in Figure 4, a gas chromatography can be used for measuring both the SARA content and the carbon number distribution of heavy oil before and after aquathermolysis reaction. The SARA are separated by the liquid-solid adsorption chromatography method, and then the SARA content can be measured. The main basis of this method is that the interaction between the sample


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molecules and the surface of the adsorbent and the flowing liquid is different so that the different components are separated. The separation process is shown as follows: The asphaltenes in the sample are precipitated with n-heptane and adsorbed on a neutral alumina adsorbent; saturates are rinsed by petroleum ether; aromatics are rinsed by benzene; resins are rinsed by benzene and ether. In order to make the result of the SARA measurement more convincing, the measuring process is repeated three times. In addition, the carbon number is measured by gas chromatography simulated distillation method. This method uses a non-polar column with a certain degree of resolution to determine the retention time of known n-alkane mixture components under linear temperature-programmed conditions. 2.2. Experimental process The heavy oil and distilled water are put into an autoclave, and the system is heated to a fixed temperature. After the aquathermolysis reaction, viscosity is measured by MCR 302 rheometer, and both SARA content and carbon number distribution are measured by gas chromatography. The process is shown as below: (1) Prepare for oil samples and distilled water. (2) Check the sealing of experimental device. (3) Put 100g heavy oil and 30g distilled water into high-temperature and high-pressure autoclave, then seal the autoclave. (4) Turn on the autoclave and preheat to the desired temperature. (5) After reaction, put the oil into the water thermostat system. (6) Measure the viscosity by MCR 302 rheometer. (7) Measure both the SARA content and the carbon number distribution by chromatography.


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2.3. Experimental scheme In this experiment, four oil samples were selected to carry out aquathermolysis experiments of different viscosity heavy oil and study the difference of aquathermolysis reactions between different viscosity heavy oil and superheated steam. The #1 heavy oil sample was selected from Kenkyak Oilfield. The #2, #3 and #4 heavy oil samples were selected from different blocks of Liaohe Oilfield. The basic physical properties of the four heavy oil samples are presented in Table 1. Table 1. The Physical Properties of Oil Samples SARA

Oil samples

Viscosity (mPa·s)

Saturates (%)

Aromatics (%)

Resins (%)

Asphaltenes (%)

#1

260

63.37

25.00

10.98

0.65

#2

700

53.31

19.92

24.46

2.31

#3 #4

4000 12000

27.38 30.54

27.79 25.15

42.54 41.08

2.27 3.23

The experimental scheme mainly includes the following four categories: time sensitivity experiment, temperature sensitivity experiment, SARA measurement, and carbon number measurement. When the reaction temperature was 240 °C, the superheated steam in the autoclave produced a higher superheat degree, and hydrothermal cracking reaction occurred at this temperature.30 Therefore, the temperature was set to 240 °C during the time sensitivity experiment. Set reaction times were 0 h, 12 h, 24 h, 36 h and 48 h. A time sensitivity experiment provided the foundation to study the degree of aquathermolysis reaction between heavy oil and superheated steam and the change of heavy oil viscosity. The reaction time was set to 36 h during the temperature sensitivity experiment. Set reaction temperatures were 160 °C, 200 °C, 240 °C and 300 °C. After reaction, the viscosity was measured by rheometer, which helped to analyze the effect of temperature on the degree of aquathermolysis reaction. Based on the time sensitivity experiment


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and temperature sensitivity experiment, both the SARA content and carbon number of heavy oil samples can be obtained by gas chromatography. 3. Results and discussion 3.1. Effect of reaction time Aquathermolysis of heavy oil samples was conducted at 240 ºC for different periods of reaction time (0, 12, 24, 36 and 48 h). Figure 5 shows the effect of reaction time on a high viscosity oil sample. Figure 6 shows the effect of reaction time on a low viscosity oil sample. After reaction, the viscosity of the oil samples reduced significantly, and then the oil viscosity reduction became very slight. As we can see from Figure 7, the reaction times for the aquathermolysis equilibrium of different viscosity oil samples are different. As for high viscosity heavy oil, the reaction would reach its equilibrium after 30 h, and the final viscosity-reducing ratio would achieve 60%. In addition, for low viscosity heavy oil, the reaction would reach its equilibrium after 15 h, and the final viscosity-reducing ratio would achieve 48%. Therefore, the higher the viscosity of heavy oil, the greater the reaction time for equilibrium is, which is related closely to SARA content. Because the resin content and asphaletenes content is higher, the heavy oil needs more reaction time for aquathermolysis equilibrium.


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14000

Oil viscosity (mPa·s)

12000 High viscosity

10000 8000 6000 4000 2000 0 0

10

20 30 Reaction time (h)

40

50

Figure 5. Effect of reaction time on viscosity of high viscosity oil sample 800 700

Oil viscosity (mPa·s)

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

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Low viscosity

600 500 400 300 200 100 0 0

10

20 30 Reaction time (h)

40

Figure 6. Effect of reaction time on viscosity of low viscosity oil sample

Figure 7. Effect of reaction time on viscosity-reducing ratio


50

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3.2. Effect of reaction temperature In order to study the effect of reaction temperature on the aquathermolysis of heavy oil samples, experiments were conducted on high viscosity oil samples and low viscosity oil samples at different temperatures (160, 200, 240, and 300 ºC). The reaction time was kept constant at 36 h to eliminate its influence. Figures 8 and 9 show the viscosity of oil samples after reaction. As we can see, at the beginning of reaction, the viscosity reduced very slowly. As the reaction temperature increased, the viscosity of the oil samples reduced significantly, and then the oil viscosity changed very slightly.

Figure 8. Effect of reaction temperature on viscosity of high viscosity oil sample

Figure 9. Effect of reaction temperature on viscosity of low viscosity oil sample


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Figure 10. Effect of reaction temperature on viscosity-reducing ratio Figure 10 shows the effect of reaction temperature on the viscosity-reducing ratio for different viscosity oil samples. As for high viscosity heavy oil, as the reaction temperature was raised from 25 to 160 ºC, the viscosity changed very slightly. However, when the reaction temperature was raised to 240 ºC, the viscosity of the oil sample reduced sharply, which means an aquathermolysis reaction happened. As the reaction temperature increased, the viscosity of oil sample experienced little change, which indicates the aquathermolysis reaction reached equilibrium. In addition, as for low viscosity heavy oil, as the reaction temperature was raised to from 25 to 200 ºC, the viscosity changed very slightly. Nevertheless, when the reaction temperature was increased to 240 ºC, the viscosity of the oil sample reduced dramatically, which means an aquathermolysis reaction occurred. As the reaction temperature increased, the viscosity of oil sample experienced little change, which indicates the aquathermolysis reaction reached equilibrium. Therefore, compared with the low viscosity oil sample, the starting temperature of high viscosity heavy oil is lower. It is because the high viscosity oil sample contains more asphaltenes, which are very sensitive to the temperature and are easily accompanied with cracking with the increase of temperature. However, the reaction temperature for equilibrium is the same.


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3.3. Change in SARA The SARA analysis and viscosity measurement of heavy oil samples were carried out before and after reaction, and the experimental results are shown in Table 2 and Table 3, respectively. The results show that after reacting with superheated steam, the saturates content and aromatics content of heavy oil increase, which indicates that cracking happened between the condensed nucleus compound and the heterocyclic compound. In addition, the resins content and asphaltenes content of heavy oil decrease, which shows that heavy components are cleaved to light components. Therefore, the viscosity of heavy oil samples after aquathermolysis is reduced due to these two main reasons, as shown in Table 3. Table 2. Components Content Before and After Aquathermolysis Oil samples

SARA Saturates %

Aromatics %

Resins %

Asphaltenes %

#1

Before After

63.37 66.18

25.00 25.10

10.98 8.39

0.65 0.45

#2

Before

53.31

19.92

24.46

2.31

After

58.76

23.03

16.26

1.95

#3

Before After

27.38 34.94

27.79 29.96

42.54 33.05

2.27 2.04

#4

Before After

30.54 40.67

25.15 27.43

41.08 29.04

3.23 2.86

Table 3. Viscosity Before and After Aquathermolysis Oil samples

Before mPa·s

After mPa·s

Change value mPa·s

Change rate %

#1

260

187

73

28.08

#2 #3 #4

700 4000 12000

348 2350 4801

352 1650 7199

50.29 41.25 59.99

As we can see from Figures 11 and 12, the content of saturates and aromatics has great influence on the viscosity of low viscosity heavy oil (260, 700 mPa·s). The higher the content of saturates and aromatics, the lower the viscosity of heavy oil samples is. However, the content of resins and


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asphaltenes has great influence on the viscosity of high viscosity heavy oil (4000, 12000 mPa·s). In addition, the content of asphaltenes is greater than the content of resins in high viscosity heavy oil, which indicates that the influence of asphaltenes on viscosity is greater than that of resins. 105

Components content (%)

90 75

Saturates

60

Aromatics

45

Resins

30 Asphaltenes 15 0 260

700 4000 Viscosity (mPa·s)

12000

Figure 11. The content of SARA before aquathermolysis reaction 105 90 Components content (%)

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75

Saturates

60

Aromatics

45

Resins

30 Asphaltenes 15 0 260

700 4000 Viscosity (mPa·s)

12000

Figure 12. The content of SARA after aquathermolysis reaction Figure 13 (a) shows the SARA change of #1 oil sample before and after an aquathermolysis reaction. Both an increase in the content of saturates and a decrease in the content of resins are observed for the #1 oil sample. In addition, the content of aromatics and asphaltenes changes little. These phenomena can be explained by the cracking of resins into saturates. For the #2 oil sample, as shown in Figure 13 (b), an increase in the content of saturates and armatics and a significant decrease in the content of resins are observed. For the #3 oil sample, as shown in Figure 13 (c), the 15 ACS Paragon Plus Environment

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saturates content increases noticeably and aromatics content increase slightly. However, resins content decreases significantly and asphaltenes content changes slightly. This phenomenon shows that for medium viscosity heavy oil, the cracking of resins into saturates is the main way of aquathermolysis reaction, accompanied with the cracking of asphaltenes. For the #4 oil sample, as shown in Figure 14 (d), the asphaltenes content changes more obviously as compared with the #3 oil sample. It shows that the cracking of asphaltenes also plays an important role in aquathermolysis reaction. Component content (%)

150 After reaction

120

a

Before reaction

90 60 30 0 Saturates

Aromatics

Resins

Asphaltenes

Component content (%)

120 After reaction

90

b

Before reaction 60 30 0 Saturates

80

Component content (%)

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

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Aromatics

Resins

Asphaltenes

After reaction Before reaction

c


Aromatics

Resins

Asphaltenes


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80 Component content (%)

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

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After reaction

d

Before reaction


Aromatics

Resins

Asphaltenes

Figure 13. Component content comparison between different oil samples before and after reaction (a) 260 (b) 700 (c) 4000 (d) 12000 mPa·s As we can see from Figure 14, an increase of saturates and aromatics and a decrease of resins and asphaltenes are both observed. In addition, the content of resins and saturates changes most obviously. Therefore, the cracking of resins into saturates is the main reason for the decrease of viscosity. Figure 15 shows the changing ratio of SARA of four oil samples. Because the asphaltenes content of #1 oil sample (260 mPa·s) is so small, its changing ratio is not taken into consideration. As we can see from Figure 15, the changing ratio of resins among four oil samples is most obvious, which shows a significant decrease of resins content in aquathermolysis reaction. On the other hand, an increase of saturates and aromatics content indicates that aquathermolysis reaction can reduce effectively viscosity of heavy oil with superheated steam. In addition, the changing ratio of asphaltenes is approximately 15%. Because the molecular weight of asphaltene is biggest among SARA, the decrease of asphaltenes content plays a dramatic role in heavy oil viscosity. Although the changing ratio of asphaltenes is less than that of resins, decrement of 15% has significant impact on viscosity.


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Change of SARA content (%)

40

12000 mPa·s

20

4000 mPa·s 0 Saturates

Aromatics

Resins

Asphaltenes

700 mPa·s 260 mPa·s

-20

-40

Figure 14. SARA content change of different viscosity heavy oil samples 80

Changing ratio of SARA content (%)

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

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40

12000 mPa·s 4000 mPa·s

0 Saturates

Aromatics

Resins

Asphaltenes 700 mPa·s

-40

260 mPa·s

-80

-120

Figure 15. SARA content changing ratio of different viscosity heavy oil samples 3.4. Change of carbon number In order to study the aquathermolysis reaction with superheated steam, carbon number distribution is measured for the #3 oil sample (4000 mPa·s) and #4 oil sample (12000 mPa·s) as shown in Table 4 and Table 5, respectively. As we can see from Table 4 and Table 5, the components of crude oil are obviously changed. In addition, the content of high carbon number hydrocarbons is lower, and the content of light hydrocarbons is higher.


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Table 4. Components Content Change of #3 Oil Sample Before and After Aquathermolysis Alkane C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C20 C22

wt (%) Before

After

0 0 0 0 0.4 0.4 1.2 2 3 2.3 2.7 3 2.5 2.5 3 2.5 3.5 3.3 4.7 4.5

0 0 0 0 2 3 3 4 3.6 4 4.5 4.5 4 5.5 6 5.3 4.6 5.5 4 4.1

Alkane C24 C26 C28 C30 C32 C34 C36 C38 C40 C42 C44 C46 C48 C50 C52 C54 C56 C58 C60 C62

wt (%) Before

After

4 4.5 4 5 4.5 3 2.2 2.4 2.2 1.6 1.6 1.4 1.6 1.6 1.4 1.5 1.5 1 1 1.8

3.3 3 3 3.6 3 2 2 1.5 1.2 0.5 0.8 0.5 1 0 0.4 0.8 1 0.8 0.3 0.5

Alkane C64 C66 C68 C70 C72 C74 C76 C78 C80 C82 C84 C86 C88 C90 C92 C94 C96 C98 C100 C102

wt (%) Before

After

1 0.6 0.6 0.8 0.7 0.5 0.6 0.6 0.5 0.8 0.5 0.5 0.5 0.6 0.4 0.6 0.4 0.5 0 0

0.4 0.2 0 0.5 0 0.3 0.5 0 0.5 0.5 0.2 0 0 0 0 0 0.1 0 0 0

Table 5. Components Content Change of #4 Oil Sample Before and After Aquathermolysis Alkane C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16

wt (%) Before

After

0 0 0 0 0 0 0 0.5 1 1 1 1 0.5 1.6 1 0.9

0 0 0 0 0 1.5 3 4 4.5 4.8 3 4.3 3.2 4.5 5.4 3.5

Alkane C24 C26 C28 C30 C32 C34 C36 C38 C40 C42 C44 C46 C48 C50 C52 C54

wt (%) Before

After

2.6 2.7 3 4 5.5 2.9 2.6 3 3 2.4 2.6 2 3 3 3.5 3

4.3 2.2 3.4 2.2 3 2.5 2.2 1.2 1.4 1.7 1.5 1.2 1.4 2 1 2


Alkane C64 C66 C68 C70 C72 C74 C76 C78 C80 C82 C84 C86 C88 C90 C92 C94

wt (%) Before

After

1.8 1.7 1.5 1.5 1.6 1.4 1.5 1.5 1.5 1.5 1.2 1.6 1.4 1.5 1.3 1.3

1.2 0.7 1 0.8 0.2 0 0 0.3 1 0.5 0 0.4 0.6 0 0.2 0

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

C17 C18 C20 C22

1 1.5 2 2.7

3.8 4 4 3

C56 C58 C60 C62

2.5 2.2 2.3 2

0.7 1.1 1 0.4

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C96 C98 C100 C102

1.2 1.5 0.5 0

0.2 0 0 0

Figure 16. Carbon number distribution of #3 oil sample before and after aquathermolysis

Figure 17. Carbon number distribution of #4 oil sample before and after aquathermolysis As we can see from Figures 16 and 17, C20 is determined for the critical carbon number. After aquathermolysis reaction, the alkane content increases when the carbon number is higher than C20,


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and the alkane content decreases when the carbon number is lower than C20. The carbon number distribution results indicate that the heavy oil could react with superheated steam, and the quality of heavy oil is upgraded. In addition, the decrease of high carbon number hydrocarbons indicates that the main reason for this is the cracking of long-chain hydrocarbons into short-chain hydrocarbons. Moreover, as we can see from carbon number distribution before aquathermolysis reaction, the higher the viscosity of heavy oil samples, the higher the percentage of high carbon number hydrocarbons is. Therefore, after aquathermolysis reaction, the degree of cracking of long-chain hydrocarbons into short-chain hydrocarbons increases significantly, and thus the decrease of heavy oil viscosity is more obvious. 3.5. Guidance for oil fields In this paper, a series of experiments and research have been done to study aquathermolysis between heavy oil and superheated steam, including reaction time, reaction temperature, SARA content and carbon number. The laboratory experiments can be used as guidance for an oil field and provide an optimization of parameters for an oil field. Some significant guidelines lie in three aspects: (1) Because proper reaction time is needed for entirely cracking of heavy oil, the reaction time between heavy oil and superheated steam should be set to the time of reaction equilibrium. (2) The reaction temperature should reach the temperature of reaction equilibrium. (3) Because it not only changes the structure of heavy oil but also significantly reduces the viscosity of heavy oil, the aquathermolysis technique with superheated steam can be applied to the development of the Liaohe Oilfield. 4. Conclusions In this paper, a series of experiments has been conducted to study aquathermolysis between


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

different viscosity heavy oil and superheated steam. The experimental results are analyzed in detail. The main meaningful findings are listed below. (1) The reaction time for aquathermolysis equilibrium increases with increasing resins and asphaltenes content. After reaction equilibrium has been achieved, aquathermolysis is not sensitive to reaction time. (2) Compared with low viscosity heavy oil, the starting temperature for aquathermolysis of high viscosity heavy oil is lower. However, reaction temperature for aquathermolysis equilibrium is the same. (3) The SARA content has a strong influence on aquathermolysis. For low viscosity heavy oil, the cracking of resins is the main mechanism of aquathermolysis. For medium viscosity heavy oil, the cracking of resins is the dominant mechanism of aquathermolysis, accompanied by the cracking of asphaltenes. For high viscosity heavy oil, the cracking of resins and asphaltenes is the primary mechanism of aquathermolysis. (4) After an aquathermolysis reaction, the content of high carbon number hydrocarbons is lower, and the content of light hydrocarbons is higher, which indicates that the cracking of long-chain hydrocarbons into short-chain hydrocarbons is the main mechanism of aquathermolysis. Author Information Corresponding Author *E-mail: [email protected] ORCID Meng Cao: 0000-0002-4860-0852 Author Contributions


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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. Acknowledgements The authors acknowledge the project named Mechanism and Characterization of Exploitation with Complex Solvent-Superheated Steam, which is provided by the National Natural Science Fund of China (NO. U1762102). Abbreviations SARA: saturates, aromatics, resins and asphaltenes References (1) Khalil, M.; Lee, R. L.; Liu, N. Hematite nanoparticles in aquathermolysis: A desulfurization study of thiophene Fuel 2015, 145, 214-220. (2) Alboudwarej. Highlighting heavy oil Oilfield Review 2006, 18, 34-53. (3) Sheikholeslami, M.; Rokni H.B. Nanofluid two phase model analysis in existence of induced magnetic field Int. J. Heat Mass Transfer 2017, 107, 288-299. (4) Sheikholeslami, M.; Hayat, T.; Alsaedi, A.; Abelman, S. Numerical analysis of EHD nanofluid force convective heat transfer considering electric field dependent viscosity Int. J. Heat Mass

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Experimental Study on Aquathermolysis of Different Viscosity Heavy

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