Surfactant, its preparation method and imbibition agent

Abstract

The present disclosure provides a surfactant, a preparation method thereof, and a wicking agent. The surfactant includes the structures shown in formula (1) and formula (2). In formula (1), the connection point # connects a hydrogen atom and one or more of those in formula (2). Among them, at least one connection point # in formula (1) is connected to at least one connection point # in formula (2), n is a positive integer, and n ranges from 8 to 16. The surfactant has the characteristics of good dispersibility and small particle size, and can solve the problem of micelle aggregation of traditional surfactants and natural biological surfactants during use, and improve the oil recovery rate of small-pore oil reservoirs during the oil production process of low-permeability reservoirs.

Description

Technical Field

[0001] The present disclosure relates to a surfactant, a preparation method thereof, and a imbibition agent. Background Art

[0002] Low-permeability oilfields are characterized by low porosity and low permeability. The development prospect of low-permeability oilfields is very optimistic. However, the complexity of this type of reservoir determines its great development difficulty. In line with the development of technological innovation and environment-friendly strategies, nanotechnology and microbial enhanced oil recovery technology are expected to become new breakthrough points.

[0003] Biologically prepared nano-scale surfactants play an important role in low-permeability oil production, especially in improving oil recovery. However, traditional surfactants and biosurfactants are severely adsorbed in the reservoir, and surfactants are prone to form micelles during use, resulting in an increase in size and causing channel blockage, directly affecting the production efficiency. Therefore, how to further improve the development efficiency of low-permeability reservoirs is crucial. Summary of the Invention

[0004] The present invention discloses a surfactant, a preparation method thereof, and an imbibition agent. The surfactant has the characteristics of good dispersibility and small particle size. During use, the charge repulsion force between molecules can prevent the aggregation of polymer molecules, and can solve the problem of micelle aggregation of traditional surfactants and natural biosurfactants, and improve the oil recovery rate of small-pore oil reservoirs during the oil production process in low-permeability reservoirs.

[0005] In a first aspect, the present invention discloses a surfactant, which includes the structures shown in formula (1) and formula (2),

[0006] Formula (1)

[0007] Formula (2)

[0008] In formula (1), the connection point # connects a hydrogen atom and one or more of those in formula (2), wherein at least one connection point # in formula (1) is connected to at least one connection point # in formula (2), n is a positive integer, and n is 8 to 16.

[0009] In some alternative embodiments, the surfactant has the structure shown in formula (3):

[0010] Formula (3)

[0011] Wherein, n is a positive integer, and n is 8 to 16.

[0012] In some alternative embodiments, the surfactant is a nano-supramolecule. Among the surfactants, the number of particles with a particle size ranging from 10 nm to 30 nm accounts for more than 90% of the number of nano-supramolecules.

[0013] In some alternative embodiments, the interfacial tension between the surfactant and water is less than 0.1 mN / m, and the surface tension value between the surfactant and water is less than 20 mN / m.

[0014] In a second aspect, the present disclosure provides a method for preparing the surfactant of the first aspect. The method includes:

[0015] Formula (4)

[0016] Mix the compound shown in Formula (4) with cyclodextrin in an organic solution to obtain a mixed solution;

[0017] React the compound shown in Formula (4) in the mixed solution with cyclodextrin to prepare the surfactant.

[0018] In some alternative embodiments, the cyclodextrin is β-cyclodextrin, and the mass ratio of the compound shown in Formula (4) to cyclodextrin is (50 - 200):1.

[0019] In some alternative embodiments, reacting the compound shown in Formula (4) in the mixed solution with cyclodextrin to prepare the surfactant includes:

[0020] Stir the mixed solution at a rotation speed of 400 - 600 rpm at 20 - 30 °C to make the compound shown in Formula (4) in the mixed solution react with cyclodextrin.

[0021] In some alternative embodiments, the organic solution includes 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 4-dimethylaminopyridine and an organic solvent, and the mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to 4-dimethylaminopyridine is (2:1) to (10:1).

[0022] In a third aspect, the present disclosure provides a imbibition agent for oil extraction. The imbibition agent includes the surfactant of the first aspect or the surfactant prepared by the preparation method of the second aspect and water. Among them, the mass content of the surfactant in the imbibition agent is 0.1% to 10%.

[0023] The technical solution of the embodiments of the present application has at least the following beneficial effects:

[0024] In the structure of the surfactant of the present application, a structure shown in formula (1) with a unique "hydrophobic inside and hydrophilic outside", that is, a cyclodextrin structure, is adopted, which can effectively encapsulate oil substances, thereby improving their solubility and stability in water; it is combined with the structure shown in formula (2) through chemical bonds. This material has a stable structure, good dispersibility and small particle size, and the charge repulsion force between the molecules of this surfactant can prevent the aggregation of polymer molecules, and can solve the problem of micelle aggregation of traditional surfactants and natural biological surfactants during use. During the crude oil recovery process in low-permeability reservoirs, this nano-scale surfactant can increase the fluidity of the mixture and enter the small-pore shale storing oil, improving the oil recovery rate of small-pore shale reservoirs.

[0025] Therefore, with the continuous development of the exploitation of nano-scale pore shale oil, the emergence and application of this surfactant have very important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required to be used in the embodiments of the present disclosure will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0027] Figure 1 A schematic diagram showing a microscopic model provided by some embodiments of the present disclosure.

[0028] In the drawings, the drawings are not necessarily drawn to actual scale. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Hereinafter, embodiments of the surfactant of the present disclosure, its preparation method and application are specifically disclosed with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0030] The "ranges" disclosed in the present disclosure are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are understood to be anticipated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all anticipated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present disclosure, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] If there is no special instruction, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0032] If there is no special instruction, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0033] If there is no special instruction, all steps of the present disclosure can be carried out sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0034] The present disclosure provides a surfactant, and the surfactant includes the structures shown in formula (1) and formula (2).

[0035] Formula (1)

[0036] Formula (2)

[0037] In formula (1), the connection # connects a hydrogen atom and one or more of formula (2), wherein at least one connection # in formula (1) is connected to at least one connection # in formula (2), n is a positive integer, and n is 8 to 16.

[0038] According to the embodiments of the present application, the surface hydroxyl groups of the structure shown in formula (1) in the surfactant have hydrophilic properties, and the internal alkyl or alkylene structure has lipophilic properties, which can effectively encapsulate oil substances, thereby improving their solubility and stability in water; the structure shown in formula (1) and the structure shown in formula (2) are combined by chemical bonds, and their particle sizes are uniform, having good dispersibility; the charge repulsion force between the molecules of the surfactant can solve the problem of micelle aggregation of traditional surfactants when the surfactant is used. During the crude oil recovery process in low-permeability reservoirs, the surfactant has strong wettability and can enter small pores during oil extraction, improving the recovery rate of oil stored in small pores.

[0039] In some alternative embodiments, the surfactant has the structure shown in formula (3):

[0040] Formula (3)

[0041] Wherein, n is a positive integer, and n is 8 to 16. Thus, the fluidity of the mixture is further improved, and it can better enter the small pores in small-pore oil extraction, further improving the recovery rate of oil stored in small pores.

[0042] n can be calculated as an average value.

[0043] In some alternative embodiments, the surfactant is a nano-supramolecule. Among the surfactants, the number of particles with a particle size of 10 nm to 30 nm accounts for more than 90% of the number of nano-supramolecules. Optionally, the number of particles with a particle size of 10 nm to 30 nm can account for 95% to 100% of the number of nano-supramolecules, and further optionally 96% to 98%. Thus, it is beneficial to enter the rocks of small pores in low-permeability reservoirs storing crude oil to achieve oil extraction.

[0044] The average particle size of the surfactant is 10 to 50 nm, and can be optionally 20 to 30 nm.

[0045] The particle size detection of this nano-supramolecule surfactant can be measured using a dynamic light scattering instrument (DLS).

[0046] In some alternative embodiments, the contact angle between the surfactant and oil is 9.8° to 10.2°, and can be optionally 10° to 10.1°.

[0047] The contact angle refers to the angle formed by a liquid on the surface of a solid, which reflects the wetting degree of the liquid on the solid. A small contact angle indicates that the liquid is more likely to wet the solid surface.

[0048] When the contact angle is within the above range, it indicates that the solution containing the surfactant is more likely to spread on the rock surface, improve the wettability of the rock, reduce the interfacial tension, promote the uniform penetration of the surfactant solution into the oil layer, strip and disperse the oil droplets, form emulsions or foams, increase the flow channels of the oil, and thus improve the oil displacement efficiency.

[0049] In addition, when the contact angle between the surfactant and the oil is within the above range, it can reduce the flow resistance of the surfactant in the porous medium, reduce the injection pressure, increase the swept volume of the displacing fluid, cover more unexploited oil areas, and improve the recovery rate.

[0050] In some alternative embodiments, the interfacial tension between the surfactant and water is less than 0.1 mN / m, and the surface tension value between the surfactant and water is less than 20 mN / m. Optionally, the interfacial tension between the surfactant and water is 0.06 ± 0.01 mN / m, and the surface tension value between the surfactant and water is 18.8 ± 0.2 mN / m.

[0051] The interfacial tension means that the surfactant can better reduce the interfacial tension between oil and water. A low interfacial tension may make it easier for water to penetrate into the oil layer.

[0052] When the interfacial tension between the surfactant and water and the surface tension value between the surfactant and water are within the above range, it can weaken the binding of capillary force to the oil droplets, make the oil easier to be displaced from the rock pores, improve the oil displacement efficiency, reduce the injection resistance, cover more unexploited oil areas, and improve the recovery rate.

[0053] In a second aspect, the present disclosure provides a preparation method of the surfactant in the first aspect, and the method includes: Step 100 to Step 200.

[0054] Formula (4)

[0055] In Step 100, the compound shown in Formula (4) is mixed with cyclodextrin in an organic solution to obtain a mixed solution.

[0056] In this step, the cyclodextrin can be α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, and its surface has hydroxyl groups, which can undergo an esterification reaction with the compound shown in Formula (4).

[0057] The compound shown in formula (4) and cyclodextrin can be mixed in an organic solution. The organic solution can be a mixed solution containing 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) and 4-dimethylaminopyridine (DMAP), a mixed solution containing N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine (DCC / DMAP solution system), and a mixed solution containing N,N'-diisopropylcarbodiimide and 4-dimethylaminopyridine (DIC / DMAP solution system).

[0058] The organic solvent in the organic solution can be ethanol, N,N-dimethylformamide, dimethyl sulfoxide, etc.

[0059] In some alternative embodiments, the cyclodextrin is β-cyclodextrin, and the mass ratio of the compound shown in formula (4) to cyclodextrin is (50-200):1, optionally (60-150):1, and further optionally (80-120):1.

[0060] Step 200: React the compound shown in formula (4) in the mixture with cyclodextrin to obtain a surfactant.

[0061] In this step, the compound shown in formula (4) is from the metabolite of a microorganism.

[0062] In some alternative embodiments, in step 200, reacting the compound shown in formula (4) in the mixture with cyclodextrin to obtain a surfactant includes:

[0063] Stir the mixture at 20-30°C at a rotation speed of 400-600 rpm to react the compound shown in formula (4) in the mixture with cyclodextrin.

[0064] Optionally, the temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, etc. Optionally, the rotation speed of stirring can be 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm, 450 rpm, 460 rpm, 470 rpm, 480 rpm, 490 rpm, 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm, 600 rpm, etc.

[0065] These reaction conditions can promote the reaction of the compound shown in formula (4) with cyclodextrin, cause more of the compound shown in formula (4) to react with the surface hydroxyl groups in cyclodextrin, and improve the comprehensive performance of the surfactant.

[0066] In some alternative embodiments, in step 200, the stirring time can be 8 - 12 h.

[0067] In some alternative embodiments, in step 200, the organic solution includes 1 - ethyl-(3 - dimethylaminopropyl)carbodiimide hydrochloride and 4 - dimethylaminopyridine and an organic solvent. The mass ratio of 1 - ethyl-(3 - dimethylaminopropyl)carbodiimide hydrochloride to 4 - dimethylaminopyridine is (2:1) to (10:1), and can be optionally 5:1, 6:1, 7:1, 8:1, 9:1, etc. This solution is beneficial to the esterification reaction of the compound shown in formula (4) with cyclodextrin, and on the basis of considering the reaction efficiency, further improves the comprehensive performance of the surfactant.

[0068] In a third aspect, the present disclosure provides a wicking agent for oil extraction. The wicking agent includes the surfactant of the first aspect or the surfactant prepared by the preparation method of the second aspect and water. Among them, the mass content of the surfactant in the wicking agent is 0.1% to 10%. The surfactant in this wicking agent can enter the small pores in the oil reservoir, can make the oil easier to be displaced from the rock pores, improve the oil displacement efficiency, and further reduce the injection resistance, can cover more unexploited oil areas, and further improve the recovery rate.

[0069] Embodiment

[0070] The following examples more specifically describe the content disclosed in the present disclosure. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0071] Example 1 Preparation of surfactant

[0072] Synthesis with reference to Wang M, Yu H, Li X, et al.. Metabolic Engineering, 2020,62:235 - 248. Three kinds of compounds shown in formula (4) are prepared, where n is 10, 13, 14 respectively, and the raw materials of the compounds shown in formula (4) are obtained from microbial fermentation metabolites.

[0073] Formula (4),

[0074] Among them, n is 10, 13, 14.

[0075] The three compounds prepared above shown in formula (4) were respectively dissolved in an EDCI / DMAP mixed solution with a volume of 80 mL with β-cyclodextrin at a mass ratio of 60:1, 75:1, and 80:1. The EDCI / DMAP mixed solution was prepared by mixing 1.8 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) and 0.9 g of 4-dimethylaminopyridine (DMAP) and adding ethanol as a solvent; the compound shown in formula (4) and β-cyclodextrin were stirred and reacted at 25 °C at 500 rpm for 12 h. Among them, the molecular weight of β-cyclodextrin was 1134.984, and the excess unreacted substances were removed through an ultrafiltration centrifugal tube with a cut-off molecular weight of 2 kDa to obtain the surfactant shown in formula (3). Through liquid chromatography and mass spectrometry tests, and calculation using the formula, the final yield of the surfactant was calculated: (total amount of cyclodextrin added - remaining amount of unreacted cyclodextrin) / total amount of cyclodextrin added; the final yields of the surfactant shown in formula (3) were 62.4%, 71.8%, and 73.2% respectively.

[0076] Performance Test

[0077] (1) Particle size test of surfactant

[0078] Take 10 mg of the surfactant sample prepared in Example 1 (n = 14), and dilute it with ultrapure water to an aqueous solution with a mass fraction of 0.1% to ensure that the sample concentration is within the detection range of the instrument. It was measured using a dynamic light scattering instrument (DLS). According to the sample characteristics, the detection parameters were set, the detection temperature was set at 25 °C, and the scattering angle was 90°. The filtered sample was added to the sample cell to ensure that the height of the sample solution in the sample cell was about 2 / 3 of the total height of the cell body, and each sample was collected for 30 s. The CONTIN method was used for data analysis to obtain the results in Table 1.

[0079] Table 1

[0080]

[0081] As shown in Table 1, the particle size of the surfactant was mainly 10 - 30 nm.

[0082] (2) Zeta potential detection method of surfactant

[0083] Take 10 mg of the surfactant prepared in Example 1 (n = 14), dilute it with ultrapure water to a 0.1% aqueous solution, mix the diluted sample thoroughly to ensure uniform dispersion of the particles, inject the diluted sample into the sample cell of a Zeta potential analyzer for measurement. The results show that the Zeta potential of the 0.1% surfactant is -35 mV. According to the general standard of Zeta potential, when the absolute value of the Zeta potential is greater than 30 mV, the surfactant has good stable dispersibility and can solve the problem of traditional micelle aggregation.

[0084] (3)Measurement of the surface tension of the surfactant

[0085] Respectively, prepare aqueous sample solutions with a mass concentration of 0.1% of the surfactant (n = 14) prepared in Example 1 and the compound sample of formula (4) prepared in Example 1 using distilled water.

[0086] The instrument used for testing is a QBZY-2 type automatic surface tension meter. Based on the platinum plate method (Wilhelmy Plate method) technology, the surface tension is measured (measurement range 0 - 400 N / m), and the indoor temperature is 25 ± 2 °C.

[0087] The specific steps are as follows: When the instrument starts testing, first measure the surface tension of pure water, which is about 72 mN / m. Then, measure the surface tension of the above two sample solutions with a mass concentration of 0.1% using the same method. Perform three parallel tests and take the average value, which is recorded as the final surface tension value of the sample aqueous solution at this concentration.

[0088] The surface tension value of the surfactant is 18.8 ± 0.2 mN / m, and the surface tension value of the compound sample of formula (4) is 29.8 ± 0.5 mN / m. This shows that compared with the compound sample of formula (4), the surface tension of the surfactant in this application is lower, and the surfactant in this application exhibits stronger surface activity.

[0089] (4)Measurement of the interfacial tension of the surfactant

[0090] Respectively, prepare aqueous sample solutions with a mass concentration of 0.1% of the surfactant (n = 14) prepared in Example 1 and the compound sample of formula (4) prepared in Example 1 using distilled water.

[0091] Use a TX500C type rotating drop interfacial tension meter for measurement. The density of the internal phase crude oil in the test system is 0.84 g / cm 3 , set the instrument temperature to 25 °C, the rotating drop speed during testing is 5000 rpm, record the interfacial tension value of the rotating drop every 30 min, and test until the interfacial tension value is stable.

[0092] The interfacial tension of the surfactant is 0.06 ± 0.01 mN / m, and the interfacial tension of the compound shown in formula (4) prepared in Example 1 is 3.34 ± 0.05 mN / m. It shows that compared with the compound sample shown in formula (4), the surface tension value of the surfactant of the present application is lower, and the surfactant of the present application exhibits stronger surface activity.

[0093] (5) Measurement of the contact angle of the surfactant

[0094] Place a clean glass slide in the aged oil, which is prepared from crude oil and kerosene according to a mass ratio of 2:5, and the viscosity of the aged oil is about 180 mPa·s. Seal the bottle mouth and age it at 60 °C for more than one month for measuring the contact angle of the surfactant to evaluate its wettability. Respectively, prepare aqueous solutions of the surfactant (n = 14) prepared in Example 1 and the compound sample shown in formula (4) prepared in Example 1 with distilled water at a mass concentration of 0.1%. Before the experiment, treat the excess crude oil on the surface of the aged glass slide, soak it in the above two aqueous solution samples for 10 min, and then dry the glass slide.

[0095] Measure by the sessile drop method using a SCI6000E contact angle measuring instrument. During the test, the volume of the water droplet is 2 μL, and the contact angle of the stable state of the droplet is obtained by using the built-in camera of the instrument combined with the angle measurement software. To ensure the accuracy and reliability of the obtained experimental test results, at least three groups of contact angles are measured for each sample, and the average value of multiple groups of data is taken as the contact angle value of the surfactant.

[0096] The contact angle between the surfactant and the aged oil is 10 ± 0.2 °, and the contact angle between the compound shown in formula (4) prepared in Example 1 and the aged oil is 25 ± 0.3 °. It shows that compared with the compound sample shown in formula (4), the contact angle of the surfactant of the present application is reduced to 10 ± 0.2 °, showing more excellent wetting reversal performance.

[0097] (6) Detection of the high-temperature resistance performance of the surfactant

[0098] Prepare a working solution with a mass concentration of 0.1% of the surfactant sample (n = 14) prepared in Example 1 with distilled water, seal the bottle mouth, place it in an oven at 121 °C for heat preservation for 2 h, and then measure the surface tension value of this aqueous solution at 25 ± 2 °C. The specific test steps refer to the above test method.

[0099] The surface tension value of the surfactant after high-temperature treatment is 19.2 ± 0.5 mN / m, which is similar to the surface tension value of 18.8 ± 0.2 mN / m of the surfactant without high-temperature treatment. This result indicates that the surfactant can work stably at a temperature of 120 °C.

[0100] (7) Detection of the salt tolerance performance of the surfactant

[0101] The prepared surfactant samples (n = 14) and the compound shown in formula (4) of the unmodified cyclodextrin in Example 1 were respectively prepared into working solutions with a mass concentration of 0.1% using mineralized water. The mass concentrations of CaCl 2 , MgCl 2 in the mineralized water were 2 g / L respectively, and the mass concentration of NaCl was 6 g / L. The surface tension value of the aqueous solution was measured at 25 ± 2 °C. The specific measurement steps refer to the above.

[0102] Test results: The surface tension value of the surfactant in Example 1 of this application was as low as 25.2 ± 0.4 mN / m, and the salinity was ≥ 1 × 10 5 mg / L. The surface tension value of the compound shown in formula (4) at the same concentration was 29.4 ± 0.6 mN / m.

[0103] This result indicates that, compared with the compound shown in formula (4), the surfactant in Example 1 of this application has enhanced high-salt resistance performance.

[0104] (8) Detection of the capillary self-aspiration height of the surfactant

[0105] Preparation of the oil-wet capillary: The capillary (inner diameter 0.35 mm) was successively ultrasonically treated with carbon tetrachloride and benzene:acetone:ethanol = 7:1.5:1.5 (volume ratio) for 30 min to remove surface organic substances; then it was successively ultrasonically treated with dilute hydrochloric acid solution (1:10) and hydrofluoric acid solution (10%) for 30 min to roughen and activate the capillary surface; finally, it was ultrasonically cleaned with deionized water to remove the residual acid until pH > 6.5 and dried at 105 °C;

[0106] Preparation of the aged oil: The aged oil was prepared from crude oil:aviation kerosene:bitumen in a mass ratio of 2:5:3; the treated capillary was completely immersed in the aged oil and aged for 2 - 4 weeks at 60 °C to obtain the treated capillary;

[0107] The treated capillary was infiltrated with kerosene for 2 min to clean the asphalt deposited on the inner and outer walls of the capillary so as not to affect the observation; the kerosene outside the tube was blown dry with nitrogen and placed in a closed environment at 60 °C for drying to obtain the oil-wet capillary, which was stored for later use.

[0108] Test sample preparation: Prepare surfactants (n = 10, 13, 14) obtained in Example 1 and the compound shown in formula (4) at a concentration of 1 g / L respectively, and add carmine indicator to each. Keep the solution temperature at 25 ± 0.2 °C. Pour the solution to be tested into a cuvette up to the top boundary, and place a scale upright against the rear wall behind. Vertically place the treated oil-wet capillary into the cuvette, use a glass slide to keep the inclination angle of all test capillaries consistent, read and record the height difference between the liquid level in the capillary and the height of the cuvette, and record the liquid level height when the capillary is immersed in the liquid surface for 10 min respectively.

[0109] Test results: The capillary spontaneous imbibition heights of the surfactants (n = 10, 13, 14) obtained in Example 1 are 23 mm, 26 mm, and 28 mm in sequence. The capillary spontaneous imbibition height of the compound shown in formula (4) is 13 mm, which is 10 mm, 13 mm, and 15 mm higher than that of the surfactants obtained in Example 1, indicating a better imbibition effect.

[0110] (9) Application of surfactant nano-new molecules as imbibition agents in low-permeability oilfield exploitation

[0111] Respectively prepare sample aqueous solutions with a mass concentration of 0.1% of the surfactants (n = 10, 13, 14) prepared in Example 1 and the compound sample shown in formula (4) obtained in Example 1 with distilled water.

[0112] Permeability detection of surfactants in low-permeability oilfield exploitation:

[0113] 1. Take natural cores from low-permeability oilfields. The air permeability of the cores is (10 - 50) × 10 -3 μm 2 Dry them in an oven at 60 °C for later use.

[0114] 2. Place the cores in the displacement process, set appropriate pressures, and saturate the cores with filtered kerosene and KCl brine respectively at a fixed flow rate under the condition of 60 °C.

[0115] 3. Place the cores back into the process. Wait until the flow pressure of the cores is stable and unchanged, and record the inlet pressure of the cores.

[0116] 4. Conduct reverse water lock treatment with filtered KCl brine and wait for the equilibrium and stable treatment.

[0117] 5. Repeat the above steps (3) and (4), and calculate the permeability value k 1 ;

[0118] 6. Flow the aqueous solutions of the surfactants prepared in Example 1 (n = 10, 13, 14) and the compound sample solution shown in formula (4) in reverse at a fixed flow rate respectively. After reaching equilibrium and stability, flow kerosene at a forward flow rate until the core flow pressure remains stable and unchanged. Record the core inlet pressure and calculate the permeability value k. 2 ;

[0119] Calculation method for the permeability improvement rate of the core:

[0120]

[0121] Table 2 Test results of the permeability improvement rate of the imbibition agent

[0122]

[0123] As shown in Table 2, the permeability improvement rate of the surfactant is more than 25%, and the permeability improvement rate of the compound shown in formula (4) is 13% - 15%. Therefore, compared with the compound shown in formula (4), the permeability improvement rate of the surfactant in Example 1 is increased. Thus, the permeability is increased by about 12%, which can significantly improve the oilfield exploitation effect and resource utilization rate.

[0124] (10) Microscopic displacement experiment evaluation of the surfactant

[0125] Respectively prepare the surfactant prepared in Example 1 (n = 10, 13, 14) and the compound sample shown in formula (4) prepared in Example 1 into sample aqueous solutions with a mass concentration of 0.1% using distilled water.

[0126] Figure 1 The schematic diagram of the microscopic model provided by some embodiments of the present disclosure is shown. Specifically, the microscopic model is a commercially available glass sheet with a size of 4 cm × 4 cm and a thickness of 3 mm. The microscopic model with the above-mentioned pores is obtained through etching treatment by a lithography machine. There are multiple pores in the microscopic model. The pores in the microscopic model can allow particles with a specific particle size to pass through. The particle size of the particles is 40 mm. The pore volume of the microscopic model is 27 μL, the porosity is 42.5%, and the pore diameter is 20 - 100 μm.

[0127] Refer to the reference Journal of Petroleum Science and Engineering 210 (2022)110084 to prepare the microscopic displacement model. Inject saturated simulated oil into the microscopic displacement model. The saturated simulated oil is prepared by mixing crude oil and kerosene in a mass ratio of 3:5. The viscosity of the saturated simulated oil is about 180 mPa·s. The oil is aged in a constant temperature oven at 90°C for 24 h to obtain the aged microscopic displacement model.

[0128] A microscopic displacement experiment device was built, including an aged microscopic displacement model, a water injection system, and an image acquisition system. Among them, the water injection system consists of a constant-speed and constant-pressure pump, a micro-syringe, and a model support. The image acquisition system includes a microscope, a camera, and a computer. The injection pressure was measured by an electronic pressure gauge (0 - 50 kPa, Senex, USA). The parameters of the constant-flow pump were set for water flooding. During this period, the water injection rate was 50 μL / min, and the displacement time was 10 min. Then, the surfactant aqueous solution (mass concentration of 0.1%) and the compound sample solution shown in formula (4) were used for displacement respectively. The injection rate was 25 μL / min, and the displacement time was 30 min. After the set time ended, the displacement device was left standing for 12 h. Then, the surfactant aqueous solution (mass concentration of 0.1%) and the compound sample solution shown in formula (4) were used for displacement respectively for another 15 min at a rate of 120 μL / min. After the experiment ended, the saturation of the corresponding given phase was calculated using the MATLAB program.

[0129] Calculation of recovery factor: After the original image was sharpened, the water, gas, oil, and glass phases were distinguished by the given pixel intensity thresholds. Then, according to the proportion of the area of the given phase in the total pore area, the saturation of the given phase was calculated using the MATLAB program. Recovery factor = (1 - saturation) × 100%.

[0130] Test results: The recovery factor after microscopic displacement of the surfactant prepared in Example 1 was more than 50%, and the recovery factor after microscopic displacement of the compound shown in formula (4) without modified cyclodextrin was about 30%. Compared with the recovery factor after microscopic displacement of the compound shown in formula (4), the recovery factors of the surfactant prepared in Example 1 were increased by about 18% (n = 10), 22% (n = 13), and 20% (n = 14) respectively, and the oil film stripping effect was improved.

[0131] It should be noted that the present disclosure is not limited to the above embodiments. The above embodiments are only examples. Embodiments having the same composition and the same function and effect as the technical idea within the scope of the technical solution of the present disclosure are all included in the technical scope of the present disclosure. In addition, within the scope not departing from the gist of the present disclosure, various modifications that can be thought of by those skilled in the art to the embodiments and other ways constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A surfactant, characterized in that The surfactant has a structure shown in formula (3): Formula (3) Wherein, n is a positive integer, and n is 8 to 16.

2. The surfactant according to claim 1, characterized in that The surfactant is a nano-supramolecular, and among the surfactant, the number of particles with a diameter of 10 nm to 30 nm accounts for more than 90% of the number of the nano-supramolecular.

3. The surfactant according to claim 1, characterized in that The interfacial tension between the surfactant and water is less than 0.1 mN / m, and the surface tension between the surfactant and water is less than 20 mN / m.

4. A method for preparing a surfactant according to any one of claims 1 to 3, characterized in that: The method comprises: Mixing the compound represented by formula (4) and cyclodextrin in an organic solution to obtain a mixed solution; Formula (4) The compound represented by formula (4) in the mixed solution is reacted with cyclodextrin to obtain the surfactant.

5. The preparation method according to claim 4, characterized in that: The cyclodextrin is β-cyclodextrin, and the mass ratio of the compound represented by formula (4) to cyclodextrin is (50-200):

1.

6. The preparation method according to claim 4, characterized in that: The step of reacting the compound represented by formula (4) in the mixed solution with cyclodextrin to obtain the surfactant comprises: The mixed solution is stirred at 20-30° C. and at a rotation speed of 400-600 rpm to allow the compound represented by formula (4) in the mixed solution to react with cyclodextrin.

7. The preparation method according to claim 4, characterized in that: The organic solution comprises 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 4-dimethylaminopyridine and an organic solvent, and the mass ratio of the 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to the 4-dimethylaminopyridine is (2:1) to (10:1).

8. An imbibing agent for oil production, characterized in that: The imbibing agent comprises the surfactant described in any one of claims 1 to 3 or the surfactant prepared by the preparation method described in any one of claims 4 to 7 and water, wherein the mass content of the surfactant in the imbibing agent is 0.1% to 10%.

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