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Effect of Different Clay Minerals on Heavy Oil Oxidation during Ignition Process Xiaocong Yu, Zhan Qu, Changbin Kan, and Xiaojiao Zhao Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 06 Oct 2017 Downloaded from http://pubs.acs.org on October 6, 2017
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Energy & Fuels
1
Effect of Different Clay Minerals on Heavy Oil
2
Oxidation during Ignition Process
3
Yu Xiaocong1,2, Qu Zhan1, Kan Changbin3*, Zhao Xiaojiao1
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(1. School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China;
5
2. Liaohe Oilfield Company Petrochina, Panjin 124010; China;
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3. School of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249,
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China)
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ABSTRACT: During the procedure of in-situ combustion (ISC) for heavy oil, the rate of heat
9
release at low temperature oxidation (LTO) stage directly affects the delay time and the effect of
10
ignition. This paper aimed at various clay minerals effects on heavy oil oxidation before ignition, at
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different reservoir temperatures and air/oil ratios, using a small batch reactor (SBR).
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Characterizations of the pressure, the reaction temperature, the post-test gases, the viscosity and the
13
asphalt content of heavy oil before and after oxidation were carried out. The results indicated that the
14
catalysis of clay minerals enhanced with the increase of temperature and air/oil ratio. At a rather
15
lower temperature (90 ℃), all three types of clay minerals did not obviously affect the temperature
16
increment or rising rate at LTO while they had a little effect on viscosity, but had great influence on
17
asphalt content, which increased greatly after the reaction. At a rather higher temperature (150 ℃),
18
clay minerals had great influence on the heat release. Montmorillonite had the best catalytic effect,
19
which was 4.28 times higher than blank sample in temperature rising rate under a higher air/oil
20
condition, while the viscosity of crude oil reduced, the concentration of asphalt slightly increased
21
after reaction. The results of this study provide new insight that the clay minerals in the reservoir or 1 ACS Paragon Plus Environment
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injecting a certain amount of clay minerals into the reservoir before ignition can accelerate the
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reaction rate and heat release rate, thus improve the ignition effect.
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KEYWORDS: clay; heavy oil; low temperature oxidation; catalysis; ignition; heat release speed
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1 INTRODUCTION
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With the increase of energy demand, more and more attention has been paid to the research of
6
unconventional energy resources1-3. Among those, high efficiency mining of heavy oil or natural
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bitumen has attracted much attention. The exploitation of heavy oil or natural bitumen requires heat
8
to assist. And in the thermal recovery methods, ISC is an attractive thermal recovery method which
9
could generate heat in-situ to change the mobility of crude oil in reservoir. Meantime, produces
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10
steam, flue gas and other displacement contents make crude oil much conveniently flow to
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production wells. ISC is known for its advantages such as its multiple displacement mechanisms，its
12
economical and attainable injection medium, and its wide range of application4,5. Furthermore many
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researchers have done a lot of research on the combustion stability, reaction rate and combustion
14
temperature of crude oil6,7. During ISC, the oxidation of crude oil could be divided into three major
15
stages8,9, known as LTO, thermal cracking (TC) and high temperature oxidation (HTO). At the initial
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stage of the formation of the combustion front, which is from LTO to ignition, the rate of heat release
17
of crude oil directly affects the rate and the result of ignition. As for heavy oil, the rate of heat release
18
of LTO stage is far less than that of HTO stage. Therefore, to improve the rate of heat release of
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crude oil will be of great importance during the ignition.
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The clay minerals in reservoir affect significantly while other operating parameters keep constant.
21
Ranjbar studied the influence of crude oil oxidation from various clay amounts, and the result of the
22
experiments showed that increase the amount of clay could improve fuel deposition and decrease the
23
activation energy in combustion process10. The analysis was inferred to be caused by the high surface
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area and catalytic action of clay minerals. However, Ranjbar’s experiments primarily focus on the
25
concentration of clay minerals, but the experiments of the types of clay minerals were not studied. 2 ACS Paragon Plus Environment
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Vossoughi analyzed the results of sand, silica and kaolinite on crude oil oxidation by using DSC
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(differential scanning calorimeter) and TG (thermogravimetry)11. The experiments showed that the
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activation energy could be sharply decreased by adding kaolinite into crude oil. Kök applied
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TG-DTG (thermogravimetry/differential thermogravimetry) thermal analysis for various clay
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minerals on crude oil oxidation effects. Based on the results of the experiments, the input of clay
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minerals decreased the activation energy and reaction rate constant of crude oil reaction, increased
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the concentration of clay minerals, therefore the activation energy and reaction rate constant were
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further decreased. But the clay used in the experiments was not the main clay in the sandstone
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reservoir12. Pu applied DSC/TG/DTA (differential thermal analysis) thermal analysis methods for
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four clay minerals on crude oil oxidation kinetics. The results showed that clay minerals had the
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function of increasing the total enthalpy and reducing the activation energy, among which illite had
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the best catalytic effect13. Nassar applied three types of nanocrystalline metal oxides, NiO, Co3O4,
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Fe3O4, on asphalt oxidation under isothermal heating. The results showed that the activation energy
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was significantly decreased after the input of nanocrystalline metal oxides, and NiO had the optimum
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effect14. Rezaei studied the effect of different concentrations of nano-grade clay, silica and iron oxide
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on crude oil oxidation, and the experiments showed that the activation energy of LTO stage was
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slightly increased after the input of nano-grade clay and silica, however, the activation energy of
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HTO stage was sharply decreased. After the input of nano-grade iron oxide, the activation energy of
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both LTO and HTO stage was substantially decreased15. They also studied the effect of nanoparticles
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on surface tension of crude oil and found that the surface tension of crude oil increased slightly16.
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Akkutlu17 analyzed the effects of water soluble metal ions on improving combustion front. The
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results showed that the catalytic action of water soluble metal ions reduced the activation energy, and
23
increased the deposition of fuel to improve the specific surface area in order to modify the
24
combustion front. Çelebioğlu18 studied the catalytic action of three different metal salts, FeCl3, CuCl2
25
and MgCl2·6H2O, on light oil oxidation, according to the results of the experiments, the rate of 3 ACS Paragon Plus Environment
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CO2/CO in tail gas increased for the input of metal salts, and the rate of H/C reduced with the
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increase of experimental temperature. Burger and Sahuquet19 operated the experiment of 1.0% nickel
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oxides and 2000 ppm copper on the effects of the mixture of 24°API crude oil and sand with air. The
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results showed that the activation energy of LTO stage was reduced and the fuel deposition was
5
increased after the input of the catalyst, which also proved that, at an inferior temperature, a faster
6
reaction rate and heat release rate could be gained by adding catalyst.
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Previous studies have shown that reservoir clay could effectively increase the reaction rate of
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heavy oil for its high specific surface area and containing of various metal minerals. However, the
9
analyzing method primarily focus on the effects of catalyst on crude oil oxidation rate by using
10
thermal analyzer, and the contents of crude oil varied too much during the air flow due to a minor
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analyzing sample which could not completely simulate the condition of reservoir before ignition.
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Therefore, such method cannot analyze the change of the concentration of the samples20-23.
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In this paper, the effects of different types of clay minerals in sandstone reservoir on heavy oil
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LTO under various reaction temperatures and air/oil ratios were studied by operating lab experiments
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using a SBR, the pressure, the reaction temperature, the post-test gases, the viscosity and asphalt
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content of heavy oil before and after oxidation were analyzed, which could provide a reference of the
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influence degree of different clay minerals on heavy oil oxidation before ignition, and provide the
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basis for the design of parameters in ignition.
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2 EXPERIMENTAL SECTION
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2.1 Materials
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Oil sample: dehydrated and degassed heavy oil of in-situ combustion Du66 block in Liaohe Oil
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Field, the density of heavy oil at room temperature is 0.935 g/cm3, and its viscosity is 408.45 mPa⋅s
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when the stratum temperature is 65 ℃.
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Porous media: 10-60 mesh of glass beads and clay minerals (montmorillonite, kaolinite, and chlorite) were used to mimic reservoir porous media. Clay minerals were demarcated by using X-ray 4 ACS Paragon Plus Environment
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diffraction. As shown in Figure 1 and Table.
2 3
(a) Montmorillonite
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Figure 1. The three clay samples.
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Table 1. The molecular formula and mineral content of the three clay samples
Clay type
(b)Kaolinite
Molecular formula
(Ca0.5,Na)0.67 (Al,Mg,Fe)4 montmorillonite (Si,Al)8O20(OH)4 nH2O）
6 7
kaolinite
Al4[Si4O10](OH)6
chlorite
(Mg,Fe2+,Fe3+) AlSi3O10(OH)8
Mineral composition type Content,% montmorillonite 56 kaolinite 4 quartz 32 calcite 5 rutile 2 anatase 1 kaolinite 78 quartz 17 gibbsite 5 chlorite 69 quartz 11 talc 10 illite 4 magnesite 6
(c)Chlorite
Catalytic element content Mn,% Fe,% Al,% total
5.55
1.37
8.86
15.78
0.09
0.81
22.51 23.41
9.31
2.13
8.27
19.71
2.2 Methods The experimental system contained
three parts: a high temperature and pressure system with
8
porous media, a data collect system and a pressurized gas pumping system, as shown in Figure 2.
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The reactor has a temperature tolerance of 800 ℃ and a pressure tolerance to 60 MPa. Its volume is
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430 ml. And the scheme is shown in Figure 3. The experimental parameters are shown in Table 2.
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1 2
1- data acquisition device; 2- PC; 3- pressure gauge; 4- gas analysis instrument; 5- electrothermal
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incubator; 6-reaction chamber; 7-intermediate container; 8- pressure gauge; 9- high pressure gas
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bottle; 10- supercharger; 11- air compressor; 12-air injection
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Figure 2. The scheme of experimental flow diagram.
6 7
Figure 3. The physical diagram of experimental device.
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For a standard experiment, 200 ml oil, certain clay minerals and 200 ml quartz sand (with a mesh
9
size of 10-60) were mixed evenly and loaded into the reactor. Afterwards, the reactor was placed in
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an electric constant temperature blower drying box and preheated for 24 hours at a given 6 ACS Paragon Plus Environment
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experimental temperature. Compressed air was then charged into the leaving rest space to the
2
required volume. The volume of injected air was calculated according to the air/oil ratio. Then
3
applying the gas equation of state, the pressure difference of the intermediate container was
4
calculated before and after the injection of the calculated air quantity. Of course, the intermediate
5
container must have enough gas storage before the experiment, and after injection of air, the pressure
6
of the intermediate container is still higher than the pressure of the reactor. The reactions may occur
7
spontaneously once the gas met the oil. There was no shaking or stirring of the reactor during the
8
experiment. The duration of one experiment lasted for 7 days. After the reaction, the reactor was
9
taken out of the box, and cooled to room temperature.
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For measurement, the temperature and pressure of the reactor system were measured continuously.
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After the reaction, effluent gas composition was measured for CO2, CO, O2, and light hydrocarbons
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(e.g., CH4). The viscosity and asphalt content of reacted oil was also analyzed. The viscosity of crude
13
oil before and after the oxidation was measured using BROOKFIELD DVRV-II rheometer. First, the
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pretreated crude oil was preheated at a constant temperature (65 ℃) for one hour. Then the viscosity
15
of the preheated oil was tested.
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The static condition of the SBR is close to that in the beginning of the ISC in a real reservoir,
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wherein air is injected at a very low rate for the first month, ensuring a long residence time for
18
contact between air and the residual oil. Also the advantage of using an isothermal SBR is that the
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reaction rate can be measured directly from the overall rate of pressure reduction. The ratio of O2
20
consumption can be analyzed from effluent gas. The viscosity ratio can also be calculated from the
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reacted oil.
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Table 2. The experimental parameters No 1 2 3 4
Temperature, ℃ 90
Content, % 0 10 10 10
Clay type Blank sample montmorillonite kaolinite chlorite
air/oil, Nm3/m3 26.38 26.38 26.38 26.38 7
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1
5 6 7 8 9 10 11 12 13 14 15 150 16 17 18 19 20 21 22 2.3 Calculations
0 10 10 10 0 10 10 10 15 15 15 0 10 10 10 15 15 15
Blank sample montmorillonite kaolinite chlorite Blank sample montmorillonite kaolinite chlorite montmorillonite kaolinite chlorite Blank sample montmorillonite kaolinite chlorite montmorillonite kaolinite chlorite
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68.83 68.83 68.21 64.82 26.38 26.38 26.38 26.38 26.38 26.38 26.38 68.83 68.83 68.21 64.82 64.82 68.83 68.21
2
(1) The method to calculate oxidation rate:
3
In this experiment, the crude oil was excessive while the oxygen was inadequate. Thus the
4
pressure drops primarily due to the consumption of oxygen in the experiment. During LTO stage,
5
oxygen was mainly expended, and the production of CO2 and CO was rather less. Therefore, the rate
6
of oxygen pressure drop was used to indicate the rate of reaction. The equation is:
υ=
7
∆ోమ ∆୲
≈
∆ ∆୲
(1)
8
Where υ is the oxidation rate, MPa/h; ∆Pమ is the oxygen pressure drop; ∆P is the system pressure
9
drop; and ∆t is the first five hours.
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(2) The method to calculate heat release rate of oxidation
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The increasing extent of temperature in this reaction is the difference between the highest
12
temperature Tmax and the starting temperature Ti. The heat release rate of oxidation is the temperature
13
increasing rate from the starting temperature to the highest temperature, and the calculating equation
14
is:
15
γ=
ౣ౮ ି ∆୲భ
(2)
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1
Where γ is the heat release rate of oxidation; Tmax is the highest temperature; Ti is the starting
2
temperature, and ∆tଵ is the time between the starting temperature and the highest temperature.
3
3 RESULTS AND DISCUSSION
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3.1 Effect on the oxidation reaction rate
5
Different clay minerals were tested under various temperatures and air/oil ratios. The reaction rate
6
was showed as pressure drop speed in the first five hours, the results of these experiments were
7
shown in Figure 4 and Figure 5. 1.05 montmorillonite 1
kaolinite chlorite
0.95
Pt/Pi
blank sample 0.9 0.85 0.8 0.75 0.7 0
20
40
8 9
60
80
100
Time, h
(a) The normalized pressure (Pt/Pi) versus time at 90 ℃ with low air/oil ratio 1.05 montmorillonite 1
kaolinite chlorite
0.95
blank sample 0.9 Pt/Pi
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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0.85 0.8 0.75 0.7 0
20
40
60
80
100
Time, h
10
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1
(b) The normalized pressure (Pt/Pi) versus time at 90 ℃ with high air/oil ratio 1.05 montmorillonite kaolinite 0.95
chlorite blank sample
Pt/Pi
0.85
0.75
0.65
0.55 0
20
40
2 3
60
80
100
Time, h
(c) The normalized pressure (Pt/Pi) versus time at 150 ℃ with low air/oil ratio 1.05 montmorillonite kaolinite chlorite
0.95
blank sample Pt/Pi
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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0.85
0.75
0.65 0
4
20
40
60
80
100
Time, h
5
(d) The normalized pressure (Pt/Pi) versus time at 150 ℃ with high air/oil ratio
6
Figure 4. Effect of different clay minerals on pressure change at 90 ℃ and 150 ℃ of heavy oil.
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0.90 low air/oil at 90 ℃ 0.80 0.70 Reaction rate, MPa/h
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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0.60
high air/oil at 90 ℃ low air/oil at 150 ℃ high air/oil at 150 ℃
0.50 0.40 0.30 0.20 0.10 0.00 blank
montmorillonite
kaolinite
chlorite
1 2 3
Figure 5. Effect of different clay minerals on oxidation rate at 90 ℃ and 150 ℃ of heavy oil. As shown in Figure 4 and Figure 5, the pressure drop speed under high air/oil ratio is larger than
4
that of low air/oil ratio under the two temperature conditions. That phenomenon is because low
5
temperature oxidation is an oxygenation reaction，and the positive direction of that is a pressure
6
reduce direction, so the improving of air/oil ratio is equal to the increase of reactive pressure.
7
Therefore, the oxygen partial pressure increased, and the rate of oxidation reaction also increased24.
8
However, with the increase of experiment temperature, the rate of oxidation reaction was also
9
increased, so the influence of air/oil ratio reduced at a higher temperature25. At 90 ℃, without clay
10
minerals, the rate of oxidation reaction was only about 0.1 MPa/h. After adding clay minerals, the
11
rate of oxidation reaction increased sharply. And the chlorite samples increased most, 5.9 times
12
higher at low air/oil ratio and 4.4 times higher at high air/oil ratio. That might be due to the catalytic
13
action of metals and the increase of specific surface area which enhanced the oxidation reaction rate.
14
Transition metals have a better catalytic effect than other metals, and chlorite, in all three types of
15
clay minerals, has a highest concentration of transition metals, so it has a best catalytic effect. The
16
concentration of catalytic metal in kaolinite is the highest, and the content of that in montmorillonite
17
is the second place. To sum up, the effect order of three types clay minerals on heavy oil oxidation 11 ACS Paragon Plus Environment
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reaction is: chlorite > kaolinite > montmorillonite. When the experiment temperature was increased
2
to 150 ℃, the reaction rate of adding clay minerals is only about 0.2 MPa/h, which did not increase
3
much more than that of none clay minerals. However, montmorillonite is a 2:1 type layered silicate,
4
so that its stronger surface adsorption capability and adsorption capacity between the layers is
5
determined by its chemical structure, and the ion exchange capacity of montmorillonite is better than
6
that of kaolinite or chlorite, the activity of which increased with the temperature rise. So its the
7
catalytic action also improved. As a result, when the experiment temperature is 150 ℃, the effect
8
order of three clay minerals on oxidation reaction is: montmorillonite > chlorite > kaolinite. To sum
9
up, although the temperature is rather low at the initial stage of LTO, the existence of clay minerals
10
can increase the rate of LTO, improve the oxygen-consuming capacity of crude oil, and strengthen
11
the effectiveness of air input. When the tail gas reached the production well, there would be little
12
oxygen, so a safety production is promised.
13
As for the ISC of heavy oil, especially at the initial stage of ignition, the rate of LTO and the rate
14
of heat releasing directly affect the success of high-temperature ignition. The catalytic action of clay
15
minerals increased the rate of both reaction and heat releasing, however the quantity of released heat
16
cannot be represented by reaction rate. Hence, a contrastive analysis of temperature increment and
17
temperature rising rate on LTO of heavy oil by using various clay minerals needs to be operated.
18
3.2 Effect on the heat release rate of oxidation
19
The highest temperature and the time of reaching that temperature were tested in these
20
experiments, which could evaluate the effects of different clay minerals, under various temperature
21
and air/oil ratios, on temperature increment and temperature rising rate. The experimental results are
22
shown in Figure 6 and Figure 7.
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95
montmorillonite kaolinite chlorite blank
Temperature, ℃
94
93 91.9
92
91.7 91.4
91.5
91
90
89 0
2
4
6
8
1 2
10 Time, h
12
14
16
18
20
(a) The temperature rise at 90 ℃ with low air/oil ratio 95 montmorillonite kaolinite
93.7
94
chlorite
93.4
blank Temperature, ℃
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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93
93.0
92.7
92
91
90
89 0
3 4
5
10 Time, h
15
20
(b) The temperature rise at 90 ℃ with high air/oil ratio
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170 montmorillonite kaolinite 165
chlorite
Temperaturee, ℃
blank 160 155.0 155
152.7 152.2
152.1
150
145 0
5
10
15
20
Time, h
1 2
(c) The temperature rise at 150 ℃ with low air/oil ratio 170 montmorillonite
168.3
kaolinite 165
chlorite blank
Temperature, ℃
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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160 156.5 156.8 155.4
155
150
145 0
2
4
6
8
10
12
14
16
18
20
Time, h
3 4
(d) The temperature rise at 150 ℃ with high air/oil ratio
5
Figure 6. Effect of clay minerals on temperature change at 90 ℃ and 150 ℃ of heavy oil.
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0.8 low air/oil at 90 ℃ Temperature rising rate, ℃ /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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0.7
high air/oil at 90 ℃
0.6
low air/oil at 150 ℃
0.5
high air/oil at 150 ℃
0.4 0.3 0.2 0.1 0 blank
montmorillonite
kaolinite
chlorite
1 2
Figure 7. Effect of clay minerals on temperature rising rate at 90 ℃ and 150 ℃ of heavy oil.
3
As shown in Figure 6 and Figure 7, the temperature increment and rising rate of crude oil
4
oxidation reaction at high air/oil ratio are higher than that at low air/oil ratio, with the increase of
5
oxygen consumption, the temperature increment and rising rate also increased. The contact surface,
6
at LTO stage, was magnified due to a higher surface energy of clay minerals, so the temperature
7
increment and rising rate increased more under high air/oil ratio condition. For reaction temperature,
8
the temperature increment of heavy oil varied very small when the temperature was around 90 ℃,
9
under the conditions of clay either existing or not. However, the temperature rising rate had been
10
doubled under the influence of the catalysis of clay minerals. Additionally, the influence of the three
11
clay minerals on the temperature rise was very small. The activity of clay was increased and the
12
catalysis was strengthened when the temperature reached around 150 ℃, which can be seen from
13
Figure 7 obviously. But there is a limitation for temperature. Studies showed that clay minerals
14
would lose activity catalysis due to dehydration and dehydroxylation26-27. Montmorillonite had the
15
best effect among all three kinds of minerals in the experiments of the temperature increment and
16
rising rate on crude oil LTO, which was 2.61-3.88 times better than other clay minerals. Besides, it
17
was 4.28 times better than none clay sample at a high air/oil condition. That was because the
18
catalytic action of clay minerals was influenced by not only the types of catalytic metals, but also the 15 ACS Paragon Plus Environment
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1
amounts of B acid and L acid. The amounts of those two types of acids were influenced by the
2
adsorption capacity and the ion-exchanging capacity of clay28-30.Among the three types of clay
3
minerals, montmorillonite is a layered silicate 2:1 type. The internal surface area of montmorillonite
4
is 100-1000 times of other minerals while the external surface areas are equal. That indicates
5
montmorillonite has a remarkable surface adsorption capacity than other minerals. Besides, it also
6
has a stronger ion-exchanging capacity of 70-130 mmol/100g. Chlorite is a silicate 2:1+1 type, and it
7
has a strong layer inter-atomic forces and a small space in its crystal layer, so it could only provide a
8
surface adsorption. Besides its ion-exchanging capacity is rather weak, 10-40 mmol/100g. Kaolinite
9
is a layered silicate minerals 1:1 type without layer charge. The exchanging capacity of its cation is
10
only 3-15 mmol/100g, and is mostly located at edge surfaces of the crystals. That structure indicated
11
the adsorption and the ion-exchanging capacity of kaolinite are much weaker than those of
12
montmorillonite or chlorite.
13
The input of clay minerals improved the reaction rate, the temperature increment and the
14
temperature rising rate. But the viscosity and asphalt content of crude oil after oxidation directly
15
affects the mobility of crude oil, which influence the displacement results. Based on that, after the
16
oxidation, the viscosity and the asphalt content of crude oil were tested to compare the clay minerals
17
effects.
18
3.3 Effect on the viscosity of the heavy oil
19
After the crude oil LTO experiments were finished, tail gases were tested respectively. Then the
20
viscosity and the concentration of crude oil, after degassed, were tested. The results are shown in
21
Figure 8.
16 ACS Paragon Plus Environment
Page 17 of 26
50 low air/oil at 90 ℃ high air/oil at 90 ℃ 45
low air/oil at 150 ℃
Asphalt content, %
high air/oil at 150 ℃ 40
35
30
25
20 blank
montmorillonite
kaolinite
chlorite
1 2
(a) The asphalt content of heavy oil after LTO at 90 ℃ and 150 ℃
1000 low air/oil at 90 ℃ high air/oil at 90 ℃ 900
low air/oil at 150 ℃ high air/oil at 150 ℃
800 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
Energy & Fuels
700
600
500
400 blank
montmorillonite
kaolinite
chlorite
3 4
(b) The viscosity of heavy oil after LTO at 90 ℃ and 150 ℃
5
Figure 8. Effects of clay minerals on asphalt content and viscosity of heavy oil after LTO.
6
As shown in Figure 8 (a), after the input of clay minerals, the asphalt content of crude oil
7
increased, however a significant difference was not observed among the three clay minerals. From a
8
physical point of view, after adding clay minerals into crude oil, the asphalt was adsorbed or
17 ACS Paragon Plus Environment
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Page 18 of 26
1
deposited at the interlayer or the surface of clay minerals, which leaded to a magnified viscosity of
2
crude oil. From a chemical point of view, heavy oil LTO reaction are mainly adding oxygen reaction,
3
which turns crude oil to non-hydrocarbon and increases the asphalt contents of crude oil. Meantime,
4
partial light hydrocarbon was extracted to tail gas due to the extraction of the “imitating flue gases”
5
from reaction, which broke the collodial systems of crude oil, and led to a flocculation of partial
6
asphalt in the crude oil. As shown in Figure 8 (b), when the experiment temperature was around
7
90 ℃, at low air/oil ratio condition, only the viscosity of montmorillonite sample was reduced,
8
while at high air/oil ratio, the viscosity of both montmorillonite and chlorite samples were reduced.
9
Therefore, because of the catalytic action of clay, the rapid release of heat results in a small range of
10
cracking reactions, leading to a slight decrease in viscosity. While increased the temperature to
11
150 ℃, the viscosity of the oil was reduced than that at 90 ℃, which was around 30~100 mPa⋅s.
12
That was, at a higher temperature, the catalytic action of clay minerals was strengthened, promoting
13
the cracking reaction, which caused a partial crude oil splitting and the viscosity reduction.
14
Montmorillonite has the strongest catalytic action of all three types of minerals. Viscosity of the
15
sample with that reduced mostly. Chlorite took the second place for a rather smaller splitting due to a
16
rather lower temperature increase. The viscosity reduced finitely in the chlorite sample and the
17
kaolinite sample.
18
According to above experiments, clay minerals play a positive role in reaction speed and heat
19
release on heavy oil in LTO reaction at a rather higher temperature and higher air/oil ratio. The
20
decrease of its viscosity (65 ℃) after degassing is around 7%-10%, which is more beneficial to
21
improve the displacement efficiency in in-situ combustion.
22
3.4 The tail gas analysis
23 24
The tail gas of experiments 1-12, 16-19 were analyzed and the results were shown in Table 3. Table 3. Analysis of the tail gas No Gas component content, %
Consumption ratio of 18
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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
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 16 17 18 19
Combustible gas 1.8 2.0 2.0 2.5 1.8 2.0 2.0 2.5 3.7 4.5 4.0 4.0 3.7 4.0 3.5 3.5
O2
CO2 CO
H2 S N2
4 2.2 2.3 2.1 7.4 5.8 7 6 0.7 0.3 0.6 0.5 0 0 0 0
1.15 1.46 1.3 1.39 1.69 1.89 1.7 1.88 2.14 3.03 2.43 2.64 4.62 4.89 4.69 4.78
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.24 0.28 0.26 0.27 0.27 0.32 0.27 0.3 0.45 0.393 0.329 0.333 0.58 0.484 0.405 0.436
92.81 94.06 94.14 93.74 88.84 89.99 89.03 89.32 93.01 91.78 92.64 92.53 91.10 90.63 91.41 91.28
O2 , % 80.86 89.47 88.99 89.95 64.59 72.25 66.51 71.29 96.52 98.56 97.13 97.61 100.00 100.00 100.00 100.00
1
According to Table 3, after addition of clay minerals, the concentration of flammable gas was
2
increased. The use ratio of O2 was improved, and the production of CO2 and CO was magnified.
3
Those were mainly due to the catalytic action of clay minerals, which improved the rate of low
4
temperature oxidation reaction and accelerated the cracking reaction. However when the temperature
5
was rather low (90 ℃), with the increase of air/oil ratio which led to a limited temperature rising
6
rate, the consumption ratio of O2 reduced due to overmuch O2 which could not be consumed timely
7
(No 5-8). After the temperature was raised to around 150 ℃, the reaction rate and heat release rate
8
of LTO was increased significantly, so the use ratio of O2 reached 100% (No 16-19). Besides, the
9
production of CO2 increased 1.5 times than that at a lower air/oil ratio. According to the experimental
10
results, when the initial temperature of the reservoir is low, the air injection rate is not suitable if too
11
high, otherwise it will cause the potential danger to the production well because of the surplus
12
oxygen. When the reservoir temperature reached a higher level (>150 ℃), the air injection rate can
13
increase to a high level, which can improve the ignition effect and shorten the ignition time in the
14
ignition period. When the ignition is finished, the amount of air required for combustion should be
15
gradually reduced. 19 ACS Paragon Plus Environment
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1
Page 20 of 26
3.5 Effect of different clay concentration on LTO At 150 ℃, catalytic oxidation experiments of various clay concentrations were operated, and the
2 3
results are shown in Table 4 and Table 5.
4
Table 4. The experimental conditions of different clay concentrations on LTO
No
5
air/oil
Clay type
Clay content, %
10 montmorillonite 13 11 low kaolinite 14 12 Chlorite 15 17 montmorillonite 20 18 high kaolinite 21 19 Chlorite 22 Table 5. Influence of clay with different concentrations on LTO
10 15 10 15 10 15 10 15 10 15 10 15
Gas component content, % Temperature increment, ℃
Temperatu re rising rate, ℃/s
Combustible gas
10
3.8
0.127
5
13
5
0.143
6.7
11
2.1
0.053
2.2
14
2.6
0.074
2.6
12
2.5
0.115
2.7
15
2.8
0.138
2.8
17
18.6
0.744
18.3
0
20
19.5
0.765
19.5
0
18
6
0.192
6.5
0
21
6.8
0.227
6.8
0
No
O2 0. 3 0. 1 0. 6 0. 4 0. 5 0. 3
CO
CO
2
3.0 3 3.2 2 2.4 3 2.8 5 2.6 4 3.1 1 4.8 9 4.9 9 4.6 9 4.8
0.39 3 0.40 5 0.32 9 0.44 3 0.33 3 0.46 2 0.48 4 0.49 6 0.40 5 0.43
Consumpti on ratio of O2 , %
Asphal t Viscosit conten y, mPa·s t, %
98.56
545.75
31.02
99.52
542.37
31.93
97.13
608.86
31.56
98.09
584
31.88
97.61
554.88
31.23
98.56
574.57
31.86
100
681.87
37.64
100
679.79
37.79
100
700.28
38.12
100
697.16
38.5 20
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Energy & Fuels
6 4.7 8
1
2 0.43 19 6.8 0.285 6.8 0 100 694.21 38.04 6 0.48 22 8.2 0.315 8.2 0 4.9 100 684.47 38.36 2 Based on Table 4 and Table 5, increase the air/oil (comparison No 10-15 and No 17-22), the
2
temperature increment, rising rate, and the consumption ratio of O2 all increased. Meanwhile, the
3
viscosity and asphalt content also increased, which may be due to an oxygenated reaction at low
4
temperature and the Van der Waals force of the heavy oil molecules increment for adding clay
5
minerals31. While increase the concentration of clay (from 10% to 15%), the temperature increment,
6
rising rate, and the concentration of CO2 and CO on crude oil at LTO stage all increased.
7
Montmorillonite had the best catalytic effect of all three clay minerals. Its temperature increment at
8
high air/oil ratio was almost 3 times larger than other clay minerals. The concentration of the asphalt
9
in crude oil slightly increased after adding clay minerals, but its viscosity briefly reduced. Thus it can
10
be seen, at LTO stage, when the temperature reached a rather higher level, reservoir with certain
11
amount of clay minerals could have a significant higher reactive rate. If the clay concentration is too
12
high, it will affect the porosity and permeability of the reservoir, and have little effect on the
13
exothermic growth of oxidation reaction, which is of little significance.
14
4 CONCLUSION
15
(1) Clay improves the reaction rate, accelerates heat release rate and magnifies the rate of oxygen
16
consumption on crude oil at LTO stage. Meantime, due to the catalytic action of clay of proceeding
17
fuel deposition, after the oxidation, the concentration of asphalt in crude oil increased as a side effect.
18
The catalytic activity of all three type clay minerals increased on crude oil LTO with the rising of
19
temperature and increase of air/oil ratio.
20
(2) At a rather lower temperature, the catalytic activity of clay is rather lower, and the increase of
21
temperature rising rate and reaction rate is not obvious, but chlorite has the best catalytic effect. At a
22
rather higher temperature, the catalytic activity of clay magnified, and the catalytic cracking reaction 21 ACS Paragon Plus Environment
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Page 22 of 26
1
was strengthened. Thus the reaction rate and heat release rate of LTO were increased significantly.
2
Montmorillonite has the best catalytic result, which is 3.39 times higher than the sample with no clay
3
in temperature increment, and 4.28 times higher than the sample with no clay in temperature rising
4
rate. At higher temperature, clay minerals also contribute to the viscosity reduction for its catalytic
5
during LTO.
6
(3) As the concentration of clay minerals increased, the temperature increment, the temperature
7
rising rate, and the concentration of CO2 and CO also increased on crude oil LTO stage.
8
Montmorillonite has the best catalytic effect among all three types of clay minerals. At the highest
9
air/oil ratio, the temperature increment of that is almost 3 times larger than other clay minerals. The
10
concentration of asphalt in crude oil was slightly increased while the concentration of clay minerals
11
increased, however the viscosity of all decreased.
12
This study provides new insight that the clay minerals in the reservoir or injection of a certain
13
amount of clay minerals into the reservoir can improve the ignition effect. Furthermore, the influence
14
of clay minerals on the parameters in the ignition process can be studied, especially the ignition
15
temperature, ignition delay time, temperature increment and pressure increment. It can provide
16
important information for ignition technology design.
17
ACKNOWLEDGMENT
18
The authors acknowledge the financial support of National Demonstration Project of Major
19
Scientific & Technological Research (No.2011ZX03008) in 12th Five-Year of China. This research
20
belongs to the pilot test of development technology in in-situ combustion.
21
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