Preparation method of environment-friendly drag reducer for fracturing

Abstract

The invention relates to the technical field of oilfield exploitation, and discloses a preparation method of an environment-friendly drag reducer for fracturing. The environment-friendly drag reducer for fracturing is obtained by polymerizing acrylamide, acrylic acid, benzotriazole modified sulphobetaine and carbon nanotube modified Schiff base chitosan in water, washing and drying. A rigid heterocyclic structure of benzotriazole and an amide group can form a physical cross-linked network through hydrogen-bond interaction, so that the shear resistance of the drag reducer is improved; quaternary ammonium groups and sulfonic acid groups in sulphobetaine molecules improve the antibacterial performance of the drag reducer; the hydrophobicity of fluorenyl drives the drag reducer to form a hydrophobic association microcell in water, so that the shear resistance of the drag reducer is improved; the carbon nanotubes form an interpenetrating network in a polymer matrix, so that chain fracture under high shear is reduced; the positive charges of the quaternary phosphonium salt are more concentrated, so that the quaternary phosphonium salt is easier to adsorb and penetrate through cell membranes with negative charges of bacteria, and the antibacterial effect of the drag reducer is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield exploitation, and specifically to a preparation method of an environmentally friendly drag reducer for fracturing. Background Art

[0002] With the growth of the demand for unconventional oil and gas resources development, hydraulic fracturing technology has become a key means to improve reservoir permeability. In fracturing operations, as the core additive of the slickwater system, the drag reducer can effectively reduce the flow resistance of the fluid in the pipeline and fractures, improve the pumping efficiency of the fracturing fluid and reduce the construction energy consumption. At present, polyacrylamide and its modified derivatives are generally used as the main materials of the drag reducer at home and abroad. However, under high-shear reservoir conditions, the molecular chains are prone to breakage or conformational collapse, resulting in a sudden drop in viscosity and a decrease in the drag reduction rate. In addition, when the fracturing fluid stays in the formation for a long time, the growth of microorganisms such as sulfate-reducing bacteria and saprophytic bacteria will cause pipe corrosion, pore blockage and hydrogen sulfide pollution. Due to the lack of antibacterial function, traditional drag reducers are difficult to meet the long-term operation requirements. Therefore, there is an urgent need to develop a drag reducer for fracturing with strong shear resistance and good antibacterial effect. The literature "Synthesis and Performance Evaluation of High Salt-Resistant Drag Reducers" synthesized a high salt-resistant drag reducer using acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and hexadecyl acrylamide as monomers, a self-made oligomer as a dispersant, and a redox system as an initiator. It has a drag reduction rate of more than 76% under 10% calcium chloride conditions, but its antibacterial performance and shear resistance still need to be improved. Summary of the Invention

[0003] (1) Technical Problems to be Solved

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a preparation method of an environmentally friendly drag reducer for fracturing. The drag reducer prepared by the present invention has good antibacterial performance and shear resistance.

[0005] (2) Technical Solutions

[0006] To achieve the above object, the present invention provides the following technical solutions: A preparation method of an environmentally friendly drag reducer for fracturing, the preparation method comprising the following steps:

[0007] (1) Add 8-10 g of benzotriazole, 17-22 mL of formaldehyde solution, and 9-9.5 g of N-methyl-4-penten-1-amine to 80-100 mL of deionized water, stir and mix, heat up to 35-45 °C and react for 7-12 h. After the reaction is completed, add 20-28 mL of absolute ethanol after vacuum distillation, let it stand for precipitation, and vacuum dry the precipitate to obtain Intermediate 1;

[0008] (2) Add 3.2 - 5.4 g of 1,3 - propane sultone to 50 - 70 mL of acetone solvent, stir and dissolve at 30 - 34 °C. Dissolve 2 - 3.5 g of intermediate 1 in 25 - 35 mL of acetone, and add it dropwise to the 1,3 - propane sultone solution. After the dropwise addition, raise the temperature to the reaction temperature and react for 2 - 4 h. After the reaction is completed, filter and dry to obtain benzotriazole - modified sulfobetaine;

[0009] (3) Add 5 - 5.5 g of 7 - bromo - 2 - formyl - 9,9 - dimethylfluorene to 60 - 90 mL of N,N - dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, add 4.2 - 4.6 g of allyldiphenylphosphine dropwise to it. After the dropwise addition, raise the temperature to 82 - 94 °C and react for 10 - 14 h. After the reaction is completed, perform vacuum distillation, wash with ether, filter and dry to obtain fluorenyl phosphonium salt;

[0010] (4) Dissolve 1.2 - 1.8 g of chitosan in 85 - 100 mL of acetic acid solution, add 6.7 - 7.4 g of fluorenyl phosphonium salt to it, and react at 30 - 35 °C for 14 - 18 h. After the reaction is completed, wash with absolute ethanol, centrifuge, and vacuum dry to obtain Schiff base chitosan;

[0011] (5) Add 1.8 - 2.4 g of acyl - chlorinated multi - walled carbon nanotubes to 70 - 80 mL of N,N - dimethylformamide solvent, ultrasonically disperse for 1.5 - 2.5 h, then add 2.6 - 3 g of Schiff base chitosan, ultrasonically disperse for 1 - 1.2 h. Under a nitrogen atmosphere, react at 98 - 105 °C for 15 - 20 h. After the reaction is completed, wash with deionized water and vacuum dry to obtain carbon nanotube - modified Schiff base chitosan;

[0012] During the above - mentioned reaction process, benzotriazole, formaldehyde, and N - methyl - 4 - penten - 1 - amine undergo a Mannich reaction to obtain intermediate 1 and introduce a tertiary amino group and an alkenyl group. The tertiary amino group in intermediate 1 and 1,3 - propane sultone undergo a nucleophilic ring - opening reaction to obtain benzotriazole - modified sulfobetaine. The bromine in 7 - bromo - 2 - formyl - 9,9 - dimethylfluorene and allyldiphenylphosphine undergo a phosphonium reaction to obtain fluorenyl phosphonium salt and introduce an aldehyde group and an alkenyl group. The amino group in chitosan and the aldehyde group in fluorenyl phosphonium salt undergo a Schiff base reaction to obtain Schiff base chitosan. The acyl - chloride group in acyl - chlorinated multi - walled carbon nanotubes and the hydroxyl group in Schiff base chitosan react to obtain carbon nanotube - modified Schiff base chitosan.

[0013] (6) Add 5.8 - 6.2 g of acrylamide, 1.7 - 2 g of acrylic acid, 0.4 - 0.8 g of benzotriazole - modified sulfobetaine, and 0.3 - 0.6 g of Schiff - base - modified chitosan with carbon nanotubes to 120 - 150 mL of deionized water. Stir and mix them. Add a sodium hydroxide solution with a mass fraction of 4.6% - 5% to adjust the pH value. Pass nitrogen for 25 - 35 min to remove oxygen. Then add 0.03 - 0.07 g of ammonium persulfate initiator and react at the reaction temperature for 3 - 6 h until a colloidal polymer is formed. Cut the colloid into granular form, wash it with absolute ethanol, and dry it under vacuum to obtain an environmentally friendly drag - reducing agent for fracturing.

[0014] Preferably, in the step (1), the mass fraction of the formaldehyde solution is 37% - 40%.

[0015] Preferably, in the step (2), the reaction temperature is 32 - 38 °C.

[0016] Preferably, in the step (3), the dropping time of allyldiphenylphosphine is controlled within 35 - 45 min.

[0017] Preferably, in the step (4), the mass fraction of the acetic acid solution is 1.2% - 1.6%.

[0018] Preferably, the preparation method of the acyl - chlorinated multi - wall carbon nanotubes in the step (5) is as follows: Add 2.5 - 3 g of carboxylated multi - wall carbon nanotubes, 65 - 85 mL of thionyl chloride, and 5 - 10 mL of N,N - dimethylformamide to a reactor. Stir and mix them, heat up to 60 - 70 °C, and reflux for 20 - 24 h. Rotate and evaporate to remove the unreacted thionyl chloride, wash with N,N - dimethylformamide, centrifuge and separate, and dry under vacuum to obtain acyl - chlorinated multi - wall carbon nanotubes.

[0019] Preferably, in the step (6), the pH value is 7.0 - 7.5.

[0020] Preferably, in the step (6), the reaction temperature is 52 - 60 °C.

[0021] (III) Beneficial technical effects

[0022] In the present invention, an environmentally friendly drag - reducing agent for fracturing is obtained by polymerizing acrylamide, acrylic acid, benzotriazole - modified sulfobetaine, and Schiff - base - modified chitosan with carbon nanotubes in water, followed by washing and drying.

[0023] The rigid heterocyclic structure of benzotriazole in benzotriazole-modified sulfobetaine can form a physical cross-linked network with amide groups through hydrogen bonding. This interaction increases the binding force between molecular chains and reduces the slippage and breakage of chain segments under high shear force, thereby improving the shear resistance of the drag reducer. Sulfobetaine molecules contain both quaternary ammonium groups and sulfonic acid groups. The positively charged quaternary ammonium groups bind to bacterial cell membranes through electrostatic interaction, destroying membrane integrity and causing leakage of intracellular substances. Sulfonic acid groups can interfere with the activity of bacterial metabolic enzymes, block energy synthesis, inhibit bacterial reproduction, and improve the antibacterial properties of the drag reducer. In carbon nanotube-modified Schiff base chitosan, the fluorene group is composed of two benzene rings connected by The rigid planar structure formed by the five-membered ring connection and the hydrophobicity of the fluorene group drive it to form hydrophobic associated microdomains in water, enhancing the physical entanglement between molecular chains. These microdomains can temporarily dissociate and reassociate under high shear, improving the shear resistance of the drag reducer; the high aspect ratio and rigid structure of the carbon nanotubes form an interpenetrating network in the polymer matrix, limiting the slippage of the molecular chains and reducing chain breakage under high shear; chitosan chelates metal ions, interfering with the metabolic process of bacterial cells and exerting an antibacterial effect; the phosphorus atoms of quaternary phosphonium salts are larger in volume than the nitrogen atoms of quaternary ammonium salts and have a more concentrated positive charge, making them easier to adsorb and penetrate the negatively charged bacterial cell membrane, causing the membrane structure to disintegrate, thereby enhancing the antibacterial effect of the drag reducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the synthetic reaction formula for benzotriazole-modified sulfobetaine. DETAILED DESCRIPTION

[0025] Example 1

[0026] (1) To 80 mL of deionized water, 8 g of benzotriazole, 17 mL of a 37% formaldehyde solution, and 9 g of N-methyl-4-penten-1-amine were added, stirred, and heated to 35°C for 7 h. After the reaction, 20 mL of anhydrous ethanol was added after vacuum distillation, and the mixture was allowed to settle. The precipitate was vacuum dried to obtain intermediate 1;

[0027] (2) Add 3.2 g of 1,3-propane sultone to 50 mL of acetone solvent, stir and dissolve at 30°C, dissolve 2 g of intermediate 1 in 25 mL of acetone, and add it dropwise to the 1,3-propane sultone solution. After the addition is complete, heat to 32°C and react for 2 h. After the reaction is completed, filter and dry to obtain benzotriazole-modified sulfobetaine;

[0028] (3) Add 5 g of 7-bromo-2-formaldehyde-9,9-dimethylfluorene to 60 mL of N,N-dimethylformamide solvent and stir to dissolve. Under a nitrogen atmosphere, add 4.2 g of allyl diphenylphosphine dropwise thereto. The addition time is controlled within 35 min. After the addition is completed, the temperature is raised to 82 ° C. and the reaction is carried out for 10 h. After the reaction is completed, the mixture is evaporated under reduced pressure, washed with ether, filtered and dried to obtain a fluorenyl quaternary phosphonium salt.

[0029] (4) 1.2 g of chitosan was dissolved in 85 mL of 1.2% acetic acid solution, 6.7 g of fluorenyl quaternary phosphonium salt was added thereto, and the mixture was reacted at 30° C. for 14 h. After the reaction, the mixture was washed with anhydrous ethanol, centrifuged, and vacuum-dried to obtain Schiff base chitosan;

[0030] (5) Add 2.5 g of carboxylated multi-walled carbon nanotubes, 65 mL of thionyl chloride, and 5 mL of N,N-dimethylformamide to the reactor, stir and mix, heat to 60 ° C, reflux for 20 h, remove unreacted thionyl chloride by rotary evaporation, wash with N,N-dimethylformamide, centrifuge, and vacuum dry to obtain chlorinated multi-walled carbon nanotubes;

[0031] (6) 1.8 g of chlorinated multi-walled carbon nanotubes were added to 70 mL of N,N-dimethylformamide solvent and ultrasonically dispersed for 1.5 h. 2.6 g of Schiff base chitosan was then added and ultrasonically dispersed for 1 h. The mixture was reacted at 98 ° C for 15 h under a nitrogen atmosphere. After the reaction, the mixture was washed with deionized water and vacuum dried to obtain carbon nanotube-modified Schiff base chitosan.

[0032] (7) 5.8 g of acrylamide, 1.7 g of acrylic acid, 0.4 g of benzotriazole-modified sulfobetaine, and 0.3 g of carbon nanotube-modified Schiff base chitosan were added to 120 mL of deionized water, and the mixture was stirred. A 4.6% sodium hydroxide solution was added to adjust the pH value to 7.0, and nitrogen was introduced for 25 min to remove oxygen. 0.03 g of ammonium persulfate initiator was added thereto, and the mixture was reacted at 52 ° C for 3 h until a gel-like polymer was formed. The gel was cut into granules, washed with anhydrous ethanol, and vacuum-dried to obtain an environmentally friendly drag reducer for fracturing.

[0033] Example 2

[0034] (1) To 100 mL of deionized water, 10 g of benzotriazole, 22 mL of a 40% formaldehyde solution, and 9.5 g of N-methyl-4-penten-1-amine were added, stirred, and heated to 45°C for 12 h. After the reaction, 28 mL of anhydrous ethanol was added after vacuum distillation, and the precipitate was allowed to settle. The precipitate was vacuum dried to obtain intermediate 1;

[0035] (2) Add 5.4 g of 1,3 - propane sultone to 70 mL of acetone solvent, stir and dissolve at 34 °C. Dissolve 3.5 g of Intermediate 1 in 35 mL of acetone, and drop it into the 1,3 - propane sultone solution. After the dropping is complete, raise the temperature to 38 °C and react for 4 h. After the reaction is completed, filter and dry to obtain benzotriazole - modified sulfobetaine;

[0036] (3) Add 5.5 g of 7 - bromo - 2 - formyl - 9,9 - dimethylfluorene to 90 mL of N,N - dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, drop 4.6 g of allyldiphenylphosphine into it, and control the dropping time within 45 min. After the dropping is complete, raise the temperature to 94 °C and react for 14 h. After the reaction is completed, perform vacuum distillation, wash with ether, filter and dry to obtain fluorenyl quaternary phosphonium salt;

[0037] (4) Dissolve 1.8 g of chitosan in 100 mL of acetic acid solution with a mass fraction of 1.6%. Add 7.4 g of fluorenyl quaternary phosphonium salt to it, and react at 35 °C for 18 h. After the reaction is completed, wash with absolute ethanol, perform centrifugal separation, and vacuum dry to obtain Schiff - base chitosan;

[0038] (5) Add 3 g of carboxylated multi - walled carbon nanotubes, 85 mL of thionyl chloride, and 10 mL of N,N - dimethylformamide to the reactor, stir and mix, raise the temperature to 70 °C, and reflux for 24 h. Rotate and evaporate to remove the unreacted thionyl chloride, wash with N,N - dimethylformamide, perform centrifugal separation, and vacuum dry to obtain acyl - chlorinated multi - walled carbon nanotubes;

[0039] (6) Add 2.4 g of acyl - chlorinated multi - walled carbon nanotubes to 80 mL of N,N - dimethylformamide solvent, ultrasonically disperse for 2.5 h, then add 3 g of Schiff - base chitosan, ultrasonically disperse for 1.2 h, and react at 105 °C for 20 h under a nitrogen atmosphere. After the reaction is completed, wash with deionized water and vacuum dry to obtain carbon nanotube - modified Schiff - base chitosan;

[0040] (7) Add 6.2 g of acrylamide, 2 g of acrylic acid, 0.8 g of benzotriazole - modified sulfobetaine, and 0.6 g of carbon nanotube - modified Schiff - base chitosan to 150 mL of deionized water, stir and mix. Add a 5% sodium hydroxide solution to adjust the pH value to 7.5, pass nitrogen for 35 min to remove oxygen, add 0.07 g of ammonium persulfate initiator, and react at 60 °C for 6 h until it becomes a colloidal polymer. Cut the colloid into granular form, wash with absolute ethanol, and vacuum dry to obtain an environmentally friendly drag - reducing agent for fracturing.

[0041] Example 3

[0042] (1) Add 9 g of benzotriazole, 19.5 mL of formaldehyde solution with a mass fraction of 38.5%, and 9.2 g of N-methyl-4-penten-1-amine to 90 mL of deionized water. Stir and mix, then heat up to 40 °C and react for 9.5 h. After the reaction is completed, add 24 mL of absolute ethanol after vacuum distillation, let it stand for precipitation, and vacuum dry the precipitate to obtain Intermediate 1;

[0043] (2) Add 4.3 g of 1,3-propane sultone to 60 mL of acetone solvent, stir and dissolve at 32 °C. Dissolve 2.8 g of Intermediate 1 in 30 mL of acetone, and drop it into the 1,3-propane sultone solution. After dropping, heat up to 35 °C and react for 3 h. After the reaction is completed, filter and dry to obtain benzotriazole-modified sulfobetaine;

[0044] (3) Add 5.2 g of 7-bromo-2-formyl-9,9-dimethylfluorene to 75 mL of N,N-dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, drop 4.4 g of allyldiphenylphosphine into it, and control the dropping time within 40 min. After dropping, heat up to 88 °C and react for 12 h. After the reaction is completed, perform vacuum distillation, wash with ether, filter and dry to obtain fluorenyl quaternary phosphonium salt;

[0045] (4) Dissolve 1.5 g of chitosan in 92 mL of acetic acid solution with a mass fraction of 1.4%, add 7.1 g of fluorenyl quaternary phosphonium salt to it, and react at 32 °C for 16 h. After the reaction is completed, wash with absolute ethanol, centrifuge, and vacuum dry to obtain Schiff base chitosan;

[0046] (5) Add 2.8 g of carboxylated multi-walled carbon nanotubes, 75 mL of thionyl chloride, and 7.5 mL of N,N-dimethylformamide to the reactor, stir and mix, heat up to 65 °C, reflux and react for 22 h. Rotate and evaporate to remove the unreacted thionyl chloride, wash with N,N-dimethylformamide, centrifuge, and vacuum dry to obtain acyl chloride multi-walled carbon nanotubes;

[0047] (6) Add 2.1 g of acyl chloride multi-walled carbon nanotubes to 75 mL of N,N-dimethylformamide solvent, ultrasonically disperse for 2 h, then add 2.8 g of Schiff base chitosan, ultrasonically disperse for 1.1 h, and react at 102 °C for 17.5 h under a nitrogen atmosphere. After the reaction is completed, wash with deionized water and vacuum dry to obtain carbon nanotube-modified Schiff base chitosan;

[0048] (7) Add 6 g of acrylamide, 1.9 g of acrylic acid, 0.6 g of benzotriazole modified sulfobetaine, and 0.4 g of Schiff base chitosan modified by carbon nanotubes to 135 mL of deionized water, stir and mix. Add a sodium hydroxide solution with a mass fraction of 4.8% to adjust the pH value to 7.2. Pass nitrogen for 30 min to remove oxygen. Add 0.05 g of ammonium persulfate initiator thereto, and react at 56 °C for 4.5 h until a colloidal polymer is obtained. Cut the colloid into granules, wash with absolute ethanol, and dry in vacuum to obtain an environmentally friendly drag reducer for fracturing.

[0049] Example 4

[0050] (1) Add 8 g of benzotriazole, 17 mL of formaldehyde solution with a mass fraction of 37%, and 9 g of N-methyl-4-penten-1-amine to 80 mL of deionized water, stir and mix. Heat up to 35 °C and react for 7 h. After the reaction is completed, add 20 mL of absolute ethanol after vacuum distillation, let it stand for precipitation, and dry the precipitate in vacuum to obtain Intermediate 1.

[0051] (2) Add 3.2 g of 1,3-propane sultone to 50 mL of acetone solvent, stir and dissolve at 30 °C. Dissolve 2 g of Intermediate 1 in 25 mL of acetone, and drop it into the 1,3-propane sultone solution. After dropping, heat up to 32 °C and react for 2 h. After the reaction is completed, filter and dry to obtain benzotriazole modified sulfobetaine.

[0052] (3) Add 5.5 g of 7-bromo-2-formyl-9,9-dimethylfluorene to 90 mL of N,N-dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, drop 4.6 g of allyldiphenylphosphine into it, and control the dropping time within 45 min. After dropping, heat up to 94 °C and react for 14 h. After the reaction is completed, perform vacuum distillation, wash with ether, filter and dry to obtain fluorenyl quaternary phosphonium salt.

[0053] (4) Dissolve 1.8 g of chitosan in 100 mL of acetic acid solution with a mass fraction of 1.6%, add 7.4 g of fluorenyl quaternary phosphonium salt thereto, and react at 35 °C for 18 h. After the reaction is completed, wash with absolute ethanol, perform centrifugal separation, and dry in vacuum to obtain Schiff base chitosan.

[0054] (5) Add 2.8 g of carboxylated multi-walled carbon nanotubes, 75 mL of thionyl chloride, and 7.5 mL of N,N-dimethylformamide to the reactor, stir and mix. Heat up to 65 °C and reflux for 22 h. Rotate and evaporate to remove the unreacted thionyl chloride, wash with N,N-dimethylformamide, perform centrifugal separation, and dry in vacuum to obtain acyl chloride multi-walled carbon nanotubes.

[0055] (6) Add 2.1 g of acyl chloride multi-walled carbon nanotubes to 75 mL of N,N-dimethylformamide solvent, ultrasonically disperse for 2 h, then add 2.8 g of Schiff base chitosan, ultrasonically disperse for 1.1 h, under a nitrogen atmosphere, react at 102 °C for 17.5 h. After the reaction, wash with deionized water and vacuum dry to obtain carbon nanotube modified Schiff base chitosan;

[0056] (7) Add 6 g of acrylamide, 1.9 g of acrylic acid, 0.6 g of benzotriazole modified sulfobetaine, and 0.4 g of carbon nanotube modified Schiff base chitosan to 135 mL of deionized water, stir and mix, add a sodium hydroxide solution with a mass fraction of 4.8% to adjust the pH value to 7.2, pass nitrogen for 30 min to remove oxygen, add 0.05 g of ammonium persulfate initiator thereto, react at 56 °C for 4.5 h until it becomes a colloidal polymer, cut the colloid into granules, wash with absolute ethanol, and vacuum dry to obtain an environmentally friendly drag reducer for fracturing.

[0057] Example 5

[0058] (1) Add 9 g of benzotriazole, 19.5 mL of formaldehyde solution with a mass fraction of 38.5%, and 9.2 g of N-methyl-4-penten-1-amine to 90 mL of deionized water, stir and mix, heat up to 40 °C and react for 9.5 h. After the reaction, carry out vacuum distillation and then add 24 mL of absolute ethanol, let it stand for precipitation, and vacuum dry the precipitate to obtain Intermediate 1;

[0059] (2) Add 4.3 g of 1,3-propane sultone to 60 mL of acetone solvent, stir and dissolve at 32 °C, dissolve 2.8 g of Intermediate 1 in 30 mL of acetone, and drop it into the 1,3-propane sultone solution. After dropping, heat up to 35 °C and react for 3 h. After the reaction, filter and dry to obtain benzotriazole modified sulfobetaine;

[0060] (3) Add 5 g of 7-bromo-2-formyl-9,9-dimethylfluorene to 60 mL of N,N-dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, dropwise add 4.2 g of allyldiphenylphosphine thereto, control the dropping time within 35 min. After dropping, heat up to 82 °C and react for 10 h. After the reaction, carry out vacuum distillation, wash with ether, filter and dry to obtain fluorenyl quaternary phosphonium salt;

[0061] (4) Dissolve 1.2 g of chitosan in 85 mL of acetic acid solution with a mass fraction of 1.2%, add 6.7 g of fluorenyl quaternary phosphonium salt thereto, and react at 30 °C for 14 h. After the reaction, wash with absolute ethanol, carry out centrifugal separation, and vacuum dry to obtain Schiff base chitosan;

[0062] (5) Add 3 g of carboxylated multi-walled carbon nanotubes, 85 mL of thionyl chloride, and 10 mL of N,N-dimethylformamide to the reactor, stir and mix, heat up to 70 °C, reflux for 24 h, rotary evaporate to remove unreacted thionyl chloride, wash with N,N-dimethylformamide, centrifuge and separate, and dry in vacuum to obtain acyl chloride multi-walled carbon nanotubes;

[0063] (6) Add 2.4 g of acyl chloride multi-walled carbon nanotubes to 80 mL of N,N-dimethylformamide solvent, ultrasonically disperse for 2.5 h, then add 3 g of Schiff base chitosan, ultrasonically disperse for 1.2 h, and react at 105 °C for 20 h under a nitrogen atmosphere. After the reaction, wash with deionized water and dry in vacuum to obtain carbon nanotube modified Schiff base chitosan;

[0064] (7) Add 6.2 g of acrylamide, 2 g of acrylic acid, 0.8 g of benzotriazole modified sulfobetaine, and 0.6 g of carbon nanotube modified Schiff base chitosan to 150 mL of deionized water, stir and mix, add a 5% sodium hydroxide solution to adjust the pH value to 7.5, pass nitrogen for 35 min to remove oxygen, add 0.07 g of ammonium persulfate initiator, and react at 60 °C for 6 h until a gel-like polymer is formed. Cut the gel into granules, wash with anhydrous ethanol, and dry in vacuum to obtain an environmentally friendly drag reducer for fracturing.

[0065] Comparative Example 1

[0066] Compared with Example 5, the difference in this comparative example is that benzotriazole modified sulfobetaine is not contained in step (7).

[0067] Comparative Example 2

[0068] Compared with Example 5, the difference in this comparative example is that carbon nanotube modified Schiff base chitosan is not contained in step (7).

[0069] Use distilled water to prepare drag reducer solutions with a concentration of 500 mg / L for the drag reducers in Examples 1-5 and Comparative Examples 1-2, and then use an SLSY type pipeline friction meter to measure the drag reduction performance of the drag reducer solutions. Select a test pipeline with a diameter of 10 mm × 2.5 m, an experimental flow rate of 30 L / min, and an experimental temperature of 25 °C. The test results are shown in Table 1.

[0070] Table 1: Drag reduction performance test.

[0071] Project Drag reduction rate (%) Example 1 90.2 Example 2 91.4 Example 3 90.8 Example 4 91.5 Example 5 90.7 Comparative Example 1 83.2 Comparative Example 2 79.6

[0072] As can be seen from Table 1, compared with the drag reducers in Comparative Examples 1-2, the drag reducers in Examples 1-5 of the present invention have a drag reduction rate of more than 90% and have a good drag reduction effect.

[0073] The antibacterial properties of the drag reducers in Examples 1-5 and Comparative Examples 1-2 were tested in accordance with SY / T0532-1993, "Bacterial Analysis Methods for Oilfield Injection Water - Extinction Dilution Method." The drag reducers were tested at a concentration of 500 mg / L, a temperature of 25°C, and an 8-hour contact time. The test results are shown in Table 2.

[0074] Table 2: Antibacterial performance test.

[0075]

[0076]

[0077] As can be seen from Table 2, the drag reducers of Examples 1-5 of the present invention have an antibacterial rate of more than 98% compared with the drag reducers of Comparative Examples 1-2, and have better drag reduction effects.

[0078] The drag reducers in Examples 1-5 and Comparative Examples 1-2 were prepared into 500 mg / L drag reducer solutions using distilled water, and the apparent viscosities of the drag reducer solutions at different shear times were measured using a DSR-1 dynamic shear rheometer. The shear rate was 180 s -1 The experimental temperature is 25°C. The test results are shown in Table 3.

[0079] Table 3: Shear resistance test.

[0080]

[0081] As shown in Table 3, the drag reducers of Examples 1-5 of the present invention are better than those of Comparative Examples 1-2 in 180s. -1 Under the conditions of shear rate, it still maintains a high viscosity value after a certain shear time and has good shear resistance.

[0082] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, numerous modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention.

Claims

1. A preparation method of an environmentally friendly drag reducer for fracturing, characterized in that, The preparation method comprises the following steps: (1) Add 8 - 10 g of benzotriazole, 17 - 22 mL of formaldehyde solution, and 9 - 9.5 g of N - methyl - 4 - penten - 1 - amine to 80 - 100 mL of deionized water, stir and mix, heat up to 35 - 45 °C and react for 7 - 12 h. After the reaction is completed, add 20 - 28 mL of absolute ethanol after vacuum distillation, let it stand for precipitation, and vacuum - dry the precipitate to obtain Intermediate 1; (2) Add 3.2 - 5.4 g of 1,3 - propane sultone to 50 - 70 mL of acetone solvent, stir and dissolve at 30 - 34 °C. Dissolve 2 - 3.5 g of Intermediate 1 in 25 - 35 mL of acetone, and drop - add it into the 1,3 - propane sultone solution. After the dropping is completed, heat up to the reaction temperature and react for 2 - 4 h. After the reaction is completed, filter and dry to obtain benzotriazole - modified sulfobetaine; (3) Add 5 - 5.5 g of 7 - bromo - 2 - formyl - 9,9 - dimethylfluorene to 60 - 90 mL of N,N - dimethylformamide solvent, stir and dissolve. Under a nitrogen atmosphere, drop - add 4.2 - 4.6 g of allyldiphenylphosphine into it. After the dropping is completed, heat up to 82 - 94 °C and react for 10 - 14 h. After the reaction is completed, carry out vacuum distillation, wash with ether, filter and dry to obtain fluorene - based quaternary phosphonium salt; (4) Dissolve 1.2 - 1.8 g of chitosan in 85 - 100 mL of acetic acid solution, add 6.7 - 7.4 g of fluorene - based quaternary phosphonium salt to it, and react at 30 - 35 °C for 14 - 18 h. After the reaction is completed, wash with absolute ethanol, carry out centrifugal separation, and vacuum - dry to obtain Schiff - base chitosan; (5) Add 1.8 - 2.4 g of acyl - chlorinated multi - walled carbon nanotubes to 70 - 80 mL of N,N - dimethylformamide solvent, ultrasonically disperse for 1.5 - 2.5 h, then add 2.6 - 3 g of Schiff - base chitosan, ultrasonically disperse for 1 - 1.2 h. Under a nitrogen atmosphere, react at 98 - 105 °C for 15 - 20 h. After the reaction is completed, wash with deionized water and vacuum - dry to obtain carbon - nanotube - modified Schiff - base chitosan; (6) Add 5.8 - 6.2 g of acrylamide, 1.7 - 2 g of acrylic acid, 0.4 - 0.8 g of benzotriazole - modified sulfobetaine, and 0.3 - 0.6 g of carbon - nanotube - modified Schiff - base chitosan to 120 - 150 mL of deionized water, stir and mix. Add a sodium hydroxide solution with a mass fraction of 4.6% - 5% to adjust the pH value, introduce nitrogen for 25 - 35 min to remove oxygen, add 0.03 - 0.07 g of ammonium persulfate initiator, and react at the reaction temperature for 3 - 6 h until a gel - like polymer is formed. Cut the gel into granular form, wash with absolute ethanol, and vacuum - dry to obtain an environmentally friendly drag - reducer for fracturing; 2. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, wherein In the step (1), the mass fraction of the formaldehyde solution is 37% - 40%.

3. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that In the step (2), the reaction temperature is 32 - 38 °C.

4. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that, In the step (3), the dropping time of allyldiphenylphosphine is controlled within 35 - 45 min.

5. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that, In the step (4), the mass fraction of the acetic acid solution is 1.2% - 1.6%.

6. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that In the step (5), the preparation method of the acyl chlorinated multi-walled carbon nanotubes is as follows: Add 2.5 - 3 g of carboxylated multi-walled carbon nanotubes, 65 - 85 mL of thionyl chloride, and 5 - 10 mL of N,N-dimethylformamide into a reactor, stir and mix, heat up to 60 - 70 °C, reflux for 20 - 24 h, rotary evaporate to remove the unreacted thionyl chloride, wash with N,N-dimethylformamide, centrifuge and separate, and dry under vacuum to obtain the acyl chlorinated multi-walled carbon nanotubes.

7. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that, In the step (6), the pH value is 7.0 - 7.

5.

8. The preparation method of the environmentally friendly drag reducer for fracturing according to claim 1, characterized in that, In the step (6), the reaction temperature is 52 - 60 °C.

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