Method for enhancing electric field viscosity reduction effect and stability of waxy oil

Abstract

The application provides a method for enhancing the electric field viscosity reduction effect and stability of waxy oil. The method comprises the following steps: adding an additive to the waxy oil, wherein the additive is graphene and / or graphite, and the additive is added in an amount of 10-1000 ppm based on the mass of the waxy oil; and applying an electric field to the waxy oil added with the additive for viscosity reduction treatment. The technical scheme provided by the application can significantly improve the electric field viscosity reduction effect and stability of the waxy oil, and help improve the universality of the electric field modification method.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for enhancing the electric field viscosity reduction effect and stability of waxy oil, and belongs to the technical field of crude oil viscosity reduction. BACKGROUND

[0002] In recent years, the production and origin of waxy oil are rapidly increasing. For waxy oil, when the oil temperature decreases to the wax precipitation point, the wax molecules in the crude oil crystallize and precipitate, resulting in a sharp increase in the viscosity of the crude oil. As the temperature decreases, the crude oil gradually exhibits the characteristics of a non-Newtonian fluid, which makes the flowability of the crude oil poor. This brings a series of flow security problems to the pipeline transportation and storage process of waxy oil.

[0003] In the prior art, physical or chemical methods are usually used to improve the low-temperature flowability of crude oil. Electric field modification is a new method for modifying crude oil, which uses the negative current rheological effect of waxy oil to reduce viscosity. It is of great significance to explore and develop the electric field modification method of waxy oil to ensure the safe, efficient and energy-saving operation of the pipeline.

[0004] The viscosity of some waxy oil can be significantly reduced by applying a high-voltage electric field to it. Studies have shown that the viscosity reduction rate of some waxy oil can be as high as 60% or more when a high-voltage electric field is applied near the freezing point. Compared with traditional viscosity reduction methods, electric field viscosity reduction has the advantages of low cost, fast effect and no environmental pollution. The energy consumption required for electric field treatment is only 1% of the heating energy consumption required to achieve the same viscosity reduction effect. However, the electric field viscosity reduction effect of different waxy oils varies greatly. The electric field viscosity reduction effect of some waxy oils is weak or even non-existent.

[0005] Enhancing the electric field viscosity reduction effect and its stability, broadening the boundary conditions of the electric field viscosity reduction method, and providing corresponding theoretical guidance and technical support for the industrial application of the electric field modification technology of waxy oil are the current problems that need to be solved. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide a method for enhancing the electric field viscosity reduction effect and stability of waxy oil.

[0007] To achieve the above purpose, the present application provides a method for enhancing the electric field viscosity reduction effect and stability of waxy oil, which comprises the following steps:

[0008] An additive is added to the waxy oil, wherein the additive is graphene and / or graphite, and the addition amount of the additive is 10-1000 ppm based on the mass of the waxy oil;

[0009] An electric field is applied to the waxy oil with the additive to reduce the viscosity.

[0010] According to the specific embodiment of the present application, preferably, the graphene is graphene powder, and the particle size of the graphene powder is about 0.01-100 μm, more preferably 1-10 μm.

[0011] According to the specific embodiment of the present application, preferably, the graphite is graphite powder, and the particle size of the graphite powder is about 0.01-100 μm, more preferably 1-10 μm.

[0012] According to the specific embodiment of the present application, preferably, the addition amount of the graphene is 10 ppm-500 ppm.

[0013] According to the specific embodiment of the present application, the graphene powder and the graphite powder both have excellent electrical conductivity.

[0014] According to the specific embodiment of the present application, preferably, the intensity of the electric field is 0.2 kV / mm-5 kV / mm.

[0015] According to the specific embodiment of the present application, preferably, the time for the viscosity reduction treatment by applying the electric field is 1 min-60 min.

[0016] According to the specific embodiment of the present application, preferably, the adding of the additive into the waxy oil comprises the following steps:

[0017] adding the graphene and / or the graphite into the waxy oil to obtain the waxy oil containing the graphene and / or the graphite;

[0018] heating the waxy oil containing the graphene and / or the graphite to a first predetermined temperature above the wax melting point of the waxy oil;

[0019] placing it in an ultrasonic water bath preheated to the same temperature (the first predetermined temperature) and performing ultrasonic oscillation for a first time to make the graphene and / or the graphite fully dispersed in the waxy oil system;

[0020] after the oscillation, placing the waxy oil containing the graphene and / or the graphite in a room temperature environment and standing for a second time to obtain the prepared waxy oil containing the graphene and / or the graphite.

[0021] According to the specific embodiment of the present application, preferably, the first predetermined temperature can be any temperature above the wax melting point.

[0022] According to the specific embodiment of the present application, preferably, the first time and the second time are both greater than 30 min.

[0023] According to the specific embodiment of the present application, the waxy oil treated by the present application is preferably the waxy oil after dehydration, and can reach the waxy oil meeting the long-distance transportation standard, i.e. the waxy oil with water content≤0.5%.

[0024] According to a specific embodiment of the present application, preferably, the wax content of the wax-containing oil is greater than or equal to 3wt%, more preferably 3wt%-25wt%.

[0025] According to a specific embodiment of the present application, preferably, the method comprises the following steps:

[0026] The prepared wax-containing oil containing graphene and / or graphite is heated to a first predetermined temperature (the first predetermined temperature is any temperature above the wax dissolution point of the wax-containing oil), and is kept in a rheometer at the same temperature for 20 minutes;

[0027] The temperature is lowered to a second predetermined temperature (the second predetermined temperature is any temperature within the wax precipitation point to the freezing point temperature range of the wax-containing oil) at a cooling rate of 0.2-2°C / min, and then kept for 20 minutes;

[0028] Then the wax-containing oil containing graphene and / or graphite is subjected to an electric field treatment of 0.2-5kV / mm for 1-60 minutes to complete the viscosity reduction treatment of the wax-containing oil.

[0029] The technical solution provided by the present application can significantly improve the electric field viscosity reduction effect and stability of the wax-containing oil, and help to improve the universality of the electric field modification technology. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a wax precipitation characteristic curve diagram of a simulation oil in a specific application example of the present application.

[0031] Figure 2 It is a wax dissolution characteristic curve diagram of a simulation oil in a specific application example of the present application.

[0032] Figure 3 It is a viscosity change diagram before and after electric field treatment in a specific application example of the present application.

[0033] Figure 4 It is the viscosity reduction effect of a wax-containing simulation oil containing only 200ppm graphene with the change of electric field intensity in a specific application example of the present application.

[0034] Figure 5 It is the viscosity reduction effect of a wax-containing simulation oil containing only 200ppm graphite with the change of electric field treatment time in a specific application example of the present application.

[0035] Figure 6 It is the viscosity reduction effect of a wax-containing simulation oil containing only 1000ppm graphite with the change of electric field treatment time in a specific application example of the present application.

[0036] Figure 7 It is a microscopic image of a wax-containing simulation oil containing graphene before and after electric field treatment in a specific application example of the present application.

[0037] Figure 8 A wax precipitation characteristic curve diagram of a certain typical waxy oil in the specific application example of the present application.

[0038] Figure 9 A wax dissolution characteristic curve diagram of a certain typical waxy oil in the specific application example of the present application.

[0039] Figure 10 A result graph of the change of the electric field viscosity reduction rate with the graphene concentration in the specific application example of the present application.

[0040] Figure 11 A result graph of the maintenance time of the viscosity reduction effect after the electric field is removed in the specific application example of the present application.

[0041] Figure 12 A result graph of the change of the electric field viscosity reduction rate with the electric field treatment temperature in the specific application example of the present application. DETAILED DESCRIPTION

[0042] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application are described in detail below, but cannot be understood as limiting the implementable scope of the present application.

[0043] Experimental content

[0044] 1. Comparison of different additives

[0045] Different additives with different properties were selected for comparison of the electric field viscosity reduction effect, wherein the different additives used and their properties are shown in Table 1.

[0046] Table 1. Additives and their properties

[0047] Additive Property Size Single-layer graphene powder Single-layer, two-dimensional honeycomb network structure, sheet, high electrical conductivity 1-10 μm Graphite powder Weakly conductive than graphite, sheet 1-10 μm Hexagonal boron nitride powder Insulating material, single-layer, same structure as graphene 1-10 μm Ferrosoferric oxide particles Magnetic particles, spherical 1-10 μm Nano-silicon dioxide particles Insulating material, spherical particles Nanometer order Cobalt naphthenate ionic solution Oil-soluble ionic solution Ionic

[0048] A waxy simulation oil containing only an additive was prepared, and a high-voltage electric field was applied to it for treatment, wherein the waxy simulation oil was prepared by combining paraffin, o-xylene and industrial white oil, the additive content was calculated based on the mass of the waxy simulation oil, and the additive content referred to the content of the pure additive. The related parameters of the prepared waxy simulation oil containing an additive are shown in Table 2:

[0049] Table 2. Composition table of waxy simulation oil containing an additive

[0050]

[0051] The test method is as follows:

[0052] Differential scanning calorimetry (DSC) was used to test the wax precipitation and dissolution characteristics of the oil sample, and the wax dissolution point, wax precipitation point and cumulative wax precipitation amount at each temperature were obtained, as shown in Figure 1 、 Figure 2 The wax dissolution point of the simulated oil was 40.76°C, the wax precipitation point was 33.15°C, and the wax content was 9.98wt%.

[0053] The temperature above the wax dissolution point (50°C) was selected as the sample loading temperature, i.e. the first predetermined temperature, and the temperature was reduced to 2°C above the freezing point at a rate of 0.5°C / min and held for 20 min. A high-voltage electric field with different electric field strengths (1-5 kV / mm) was applied to the oil sample at 2°C above the freezing point (28°C) for 90 s, and the equilibrium viscosity was tested 10 s -1 before and after the electric field treatment. The viscosity change of the oil sample before and after the electric field treatment is shown in Figure 3 .

[0054] The viscosity reduction rate was calculated as follows: the 10s -1 equilibrium viscosity before the electric field treatment was η0, the 10s -1 equilibrium viscosity after the electric field treatment was η E , and the viscosity reduction rate was:

[0055] Δη=(η0-η E ) / η0×100%.

[0056] Through testing, it was found that the wax-containing simulated oil containing only graphene had an electric field viscosity reduction effect under different electric field strengths (1-5 kV / mm) within 90 s of treatment, and the specific effect is shown in Figure 4 . Table 3 shows the viscosity of the simulated oil containing various additives before and after treatment with a 5 kV / mm high-voltage electric field for 90 s:

[0057] Table 3 shows the 10s -1 viscosity of the wax-containing simulated oil containing 200 ppm of additives before and after electric field treatment:

[0058]

[0059] From the above test results, it can be seen that for the wax-containing simulated oil system containing only graphene, the application of an electric field can produce an electric field viscosity reduction effect, and the viscosity reduction effect gradually increases with increasing electric field strength. When the electric field strength reaches 5 kV / mm, the 10s -1 equilibrium viscosity is reduced from 414.5 mPa·s to 81.6 mPa·s, with a viscosity reduction rate of 80.3%.

[0060] For the five simulated oils without electric field viscosity reduction effect, the electric field treatment time is extended to explore whether it has electric field viscosity reduction effect after sufficient time. According to the experimental results, it can be seen that: when the graphite with the same structure and similar properties is treated by 5kV / mm high voltage electric field for 30min, the viscosity reduction rate reaches 43.4%, as shown in Figure 5 .

[0061] Increase the content of graphite, prepare a waxy simulated oil containing 1000ppm graphite, apply a high voltage electric field of 5kV / mm at 28℃ for different time, test the equilibrium viscosity at 10s -1 before and after electric field treatment. The change of electric field viscosity reduction effect with electric field treatment time is shown in Figure 6 . From the experimental results shown in Figure 6 , it can be found that the waxy simulated oil containing 1000ppm graphite treated by 5kV / mm high voltage electric field for 30min can also produce about 80% viscosity reduction effect. Compared with the waxy simulated oil containing graphene, if the same electric field viscosity reduction effect is wanted for the waxy simulated oil containing only graphite, higher electric field strength, longer electric field treatment time and more graphite addition are generally needed.

[0062] Based on the above results, there is a large conductivity difference between the additive and the wax crystal. Under the action of electric field, interface polarization occurs between the wax crystal particles and the additive, which makes the additive react with the wax crystal. By taking micrograph of wax crystal through polarizing microscope, the change of micro-morphology of wax crystal particles before and after electric field treatment is observed as shown in Figure 7 . From Figure 7 , it can be seen that: after electric field treatment, the graphene in the liquid oil accumulates on the surface of the wax crystal, which macroscopically shows that the viscosity of the oil sample decreases after electric field treatment.

[0063] Therefore, under the action of electric field, the additive which is easy to interface polarization with the wax crystal is a good material to strengthen the electric field viscosity reduction effect.

[0064] 2、Effect of adding graphene on electric field viscosity reduction effect and stability of waxy oil

[0065] The selected oil sample is a typical waxy oil, and its wax precipitation characteristics are shown in Figure 8 , and the wax dissolution characteristics curve is shown in Figure 9 , and its basic properties and test methods are shown in Table 4:

[0066] Table 4 Basic properties of a typical waxy oil

[0067] Parameter Value Test method 20 °C density (kg / m 3 )]]> 860.0 ISO 3675-1998 Congealing point (°C) 32 ASTM D5853-17 Gelation temperature (°C) 37.3 SAOS Wax precipitation point (°C) 46.16 DSC Wax dissolution point (°C) 65.86 DSC Wax content (wt%) 18.95 DSC Gum (wt%) 9.10 ASTM D4124-2018 Asphaltene (wt%) 0.70 ASTM D4124-09

[0068] (1) Different graphene concentrations and electric field treatment times

[0069] Treatment conditions: The waxy oil (including waxy oil added with graphene and waxy oil not added with graphene) was heated to 70°C (required to be higher than the wax dissolution point temperature of the oil sample) and placed in a rheometer, and kept at the same temperature for 20 min; then cooled to 2°C above the freezing point at a cooling rate of 0.5°C / min, and kept at the constant temperature for 20 min, and then subjected to a high-voltage electric field treatment of 3 kV / mm for different time.

[0070] Experimental results of viscosity reduction: Under the same electric field treatment conditions, the electric field viscosity reduction effect of the waxy oil added with graphene was obviously better than that of the waxy oil not added with graphene, and the electric field viscosity reduction effect gradually increased with the increase of the graphene concentration, as shown in Figure 10 The viscosity reduction rates of the waxy oil and the waxy oil added with 50, 100 and 200 ppm graphene were 58.1%, 64.7%, 68.5% and 78.4% respectively when the electric field treatment time reached 10 min. It can also be found from Figure 10 that the addition of graphene can shorten the electric field treatment time required to achieve the same viscosity reduction rate.

[0071] The influence of the addition of graphene on the stability of the viscosity reduction effect is shown in Figure 11 It can be seen from Figure 11 that after the addition of graphene, the electric field viscosity reduction effect is obviously improved, and the stability of the viscosity reduction effect of the waxy oil added with graphene is obviously better than that of the waxy oil not added with graphene after the electric field is removed. The stability of the electric field viscosity reduction effect of the waxy oil containing 200 ppm graphene is improved from 4 h to 12 h, greatly improving the viscosity recovery time after the electric field treatment. Similarly, with the increase of the graphene concentration, the stability of the viscosity reduction effect is also improved accordingly.

[0072] (2) Different graphene concentrations and electric field treatment temperatures

[0073] Treatment conditions: The waxy oil (including waxy oil added with graphene and waxy oil not added with graphene) was heated to 70°C (required to be higher than the wax dissolution point temperature of the oil sample) and placed in a rheometer, and kept at the same temperature for 20 min; then cooled to 2°C above the freezing point at a cooling rate of 0.5°C / min, and kept at the constant temperature for 20 min, and then subjected to a high-voltage electric field treatment of 3 kV / mm for different time.

[0074] Treatment temperature: 7 temperatures of 34°C, 36°C, 38°C, 40°C, 42°C, 44°C and 46°C were selected between the freezing point and the wax precipitation point.

[0075] 10 s -1 balance viscosity and calculate the viscosity reduction rate, as shown in Figure 12

[0076] It can be seen from Figure 12 ​The experimental results of the viscosity reduction shown can see that: under the same electric field treatment conditions, the electric field viscosity reduction effect of the wax-containing oil added with graphene is obviously better than that of the wax-containing oil without graphene, and the electric field viscosity reduction effect gradually increases with the increase of the graphene concentration. When the graphene addition amount is 200 ppm, the electric field viscosity reduction rate at 34℃ increases from 58.6% to 79.4%, which increases by 20.8 percentage points.

[0077] Embodiment 1

[0078] The embodiment provides a method for enhancing the electric field viscosity reduction effect of a wax-containing oil, which comprises the following steps:

[0079] The paraffin, o-xylene and industrial white oil are mixed according to a mass ratio of 1:1:8 to obtain a wax-containing simulation oil;

[0080] The graphene is added into the wax-containing simulation oil to obtain a wax-containing simulation oil containing graphene; the addition amount of the graphene is 200 ppm based on the mass of the wax-containing simulation oil;

[0081] The wax-containing simulation oil containing graphene is heated to 50℃ and kept for 20 min;

[0082] The temperature is reduced to 28℃ at a reduction rate of 0.5℃ / min, and then kept for 20 min;

[0083] Then, the electric field treatment of 5kV / mm is applied to the wax-containing simulation oil containing graphene for 1.5 min, and the viscosity reduction treatment of the wax-containing simulation oil is completed.

[0084] The 10s -1 The equilibrium viscosity is reduced from 414.5 mPa·s to 81.6 mPa·s, and the viscosity reduction rate is as high as 80.3%.

[0085] Embodiment 2

[0086] The embodiment provides a method for enhancing the electric field viscosity reduction effect of a wax-containing oil, which comprises the following steps:

[0087] The paraffin, o-xylene and industrial white oil are mixed according to a mass ratio of 1:1:8 to obtain a wax-containing simulation oil;

[0088] The graphite powder is added into the wax-containing simulation oil to obtain a wax-containing simulation oil containing graphite; the addition amount of the graphite powder is 1000 ppm based on the mass of the wax-containing simulation oil;

[0089] The wax-containing simulation oil containing graphene is heated to 50℃ and kept for 20 min;

[0090] The temperature is reduced to 28℃ at a reduction rate of 0.5℃ / min, and then kept for 20 min;

[0091] Then the waxy simulation oil containing graphene is subjected to an electric field treatment of 5 kV / mm for 30 minutes to complete the viscosity reduction treatment of the waxy simulation oil.

[0092] The 10s -1 The equilibrium viscosity is reduced from 315.1 mPa s to 86.0 mPa s, and the viscosity reduction rate is as high as 72.7%.

[0093] Example 3

[0094] The embodiment provides a method for enhancing the electric field viscosity reduction effect of waxy oil, which comprises the following steps:

[0095] Graphene is added to the waxy oil to obtain waxy oil containing graphene; the addition amount of the graphene is 20 ppm, 50 ppm, 100 ppm and 200 ppm respectively based on the mass of the waxy crude oil;

[0096] The waxy crude oil containing graphene is heated to 70 DEG C and transferred into a 70 DEG C rheometer for constant temperature keeping for 20 min;

[0097] Then the temperature is reduced to 34 DEG C at a rate of 0.5 DEG C / min, and then kept for 20 min;

[0098] Then the waxy crude oil containing graphene is subjected to an electric field treatment of 3 kV / mm for 10 minutes to complete the viscosity reduction treatment of the waxy crude oil.

[0099] Before and after the electric field treatment, the viscosity reduction rates of the waxy simulation oil without graphene (i.e. the oil sample without adding graphene) and the waxy simulation oil with the addition amount of graphene being 50 ppm, 100 ppm and 200 ppm respectively reach 58.1%, 64.7%, 68.5% and 78.4% respectively, as shown in Figure 10 .

[0100] Example 4

[0101] The embodiment provides a method for enhancing the stability of the electric field viscosity reduction effect of waxy oil, which comprises the following steps:

[0102] Graphene is added to the waxy crude oil to obtain waxy crude oil containing graphene; the addition amount of the graphene is 50 ppm, 100 ppm and 200 ppm respectively based on the mass of the waxy crude oil;

[0103] The waxy oil containing graphene is heated to 70 DEG C and transferred into a 70 DEG C rheometer for constant temperature keeping for 20 min;

[0104] Then the temperature is reduced to 34 DEG C at a rate of 0.5 DEG C / min, and then kept for 20 min;

[0105] The waxy simulated oil containing graphene was then subjected to an electric field treatment of 2 kV / mm for 10 minutes to complete the viscosity reduction treatment of the waxy oil.

[0106] After the addition of 200 ppm of graphene, the maintenance time of the electric field viscosity reduction effect of the waxy oil was increased from 4 h to 12 h, greatly improving the recovery time of the viscosity after electric field treatment, as shown in Figure 11 .

Claims

1. A method for enhancing the viscosity-reducing effect and stability of waxy oil under an electric field, comprising the following steps: Additives that enhance the viscosity-reducing effect of electric field are added to waxy oil, wherein the additives are graphene and / or graphite, and the amount of additives added is 10ppm-1000ppm based on the mass of the waxy oil. Applying an electric field to waxy oils containing additives to reduce viscosity; Adding additives to waxy oils to enhance the viscosity-reducing effect of the electric field includes the following steps: Adding graphene and / or graphite to a waxy oil yields a waxy oil containing graphene and / or graphite. The waxy oil containing graphene and / or graphite is heated to a first predetermined temperature above the melting point temperature of the waxy oil. Place it in an ultrasonic water bath that has been preheated to the same temperature and perform ultrasonic oscillation for the first time to ensure that graphene and / or graphite are fully dispersed in the wax-containing oil system. After the shaking is complete, place the waxy oil containing graphene and / or graphite in a room temperature environment and let it stand for a second time to obtain the prepared waxy oil containing graphene and / or graphite. The prepared waxy oil containing graphene and / or graphite is heated to a first predetermined temperature above the melting point temperature of the waxy oil, and then placed in a rheometer and kept at the same temperature for 20 minutes. Cool the oil at a rate of 0.2-2°C / min to a second predetermined temperature between the wax precipitation point and the freezing point, and then hold the temperature for 20 minutes. When the additive is graphene or a combination of graphene and graphite, the waxy oil containing the additive is subjected to an electric field of 0.2-5 kV / mm for 1-60 minutes to complete the viscosity reduction treatment of the waxy oil; when the additive is graphite, the waxy oil containing the additive is subjected to an electric field of 0.2-5 kV / mm for 30-60 minutes to complete the viscosity reduction treatment of the waxy oil.

2. The method according to claim 1, wherein, The graphene is graphene powder with a particle size of 0.01-100 μm.

3. The method according to claim 2, wherein, The amount of graphene added is 10ppm-500ppm.

4. The method according to claim 1, wherein, The graphite is graphite powder with a particle size of 0.01-100 μm.

5. The method according to claim 1, wherein, Both the first and second time periods are greater than 30 minutes.

6. The method according to claim 1, wherein, The water content of the waxy oil is ≤0.5%.

7. The method according to claim 1, wherein, The wax content of the waxy oil is greater than or equal to 3 wt%.

8. The method according to claim 7, wherein, The wax content of the waxy oil is 3 wt%-25 wt%.

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