Polymer drag reducer suitable for water-based fracturing fluid

Abstract

The invention discloses a polymer drag reducer suitable for a water-based fracturing fluid, and belongs to the technical field of oil field fracturing. The drag reducer has a hyperbranched structure as shown in a formula I or a formula II, takes nano silicon dioxide as a branching core, and is grafted with a polyacrylamide chain and a hydrophobic functional monomer chain segment, and the preparation method comprises the following steps: firstly, dissolving acrylamide and a functional monomer in water, adjusting the pH value and removing oxygen, and then adding an initiator and a water reducer; adding a macromolecular initiator obtained by modifying nano silicon dioxide rich in hydroxyl on the surface, carrying out aqueous solution polymerization reaction, and finally hydrolyzing to obtain the product. The drag reducer disclosed by the invention has excellent shear resistance, temperature resistance and drag reduction performance, is particularly suitable for offshore large-displacement fracturing construction conditions, is low in cost and environment-friendly, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a polymer drag reducer suitable for water-based fracturing fluid, belonging to the technical field of oilfield fracturing. BACKGROUND

[0002] With the continuous development of oil and gas resources, the target reservoir gradually changes from conventional to unconventional, and the development difficulty increases, so that reservoir reconstruction is needed to achieve ideal oil and gas production. The slick water fracturing technology is one of the most important fracturing technologies for low-permeability oil and gas, tight sandstone oil and gas and shale gas resources. Due to the low overall viscosity of the slick water fracturing fluid system, in order to improve the carrying capacity of the proppant, the liquid injection speed needs to be increased during field operation, resulting in an increase in the pipe friction resistance.

[0003] As the core of the slick water fracturing system, the drag reducer plays a decisive role in the performance of the fracturing fluid and is a hot research topic at home and abroad. The addition of the drag reducer improves the rheological property of the slick water fracturing fluid system, which can effectively reduce the turbulent friction resistance generated by the fracturing fluid during flow, and meet the construction requirements of pressure reduction and injection increase. The traditional polymer drag reducer is prepared by inverse emulsion polymerization, and the long-chain hydrophobic monomer is introduced into the molecular chain to improve the flexibility of the molecular chain, and has good rheological property. The drag reduction performance of the polyacrylamide slick water drag reducer is greatly dependent on the macromolecular chain. In the high-temperature and high-salt reservoir environment, the amide bond of the conventional polyacrylamide molecule is easily broken into small molecules, which leads to a significant decrease in viscosity and affects or even loses the drag reduction effect. Especially, the large-volume injection of offshore fracturing fluid can easily cause the high-shear damage to the long-chain structure of the drag reducer, reducing the drag reduction rate; in addition, the development of the solid powder form can avoid the potential environmental risks of the emulsion drag reducer. With the continuous exploitation of oil and gas resources, special reservoirs have become the main battlefield of oil and gas development, and the traditional polyacrylamide drag reducer is increasingly difficult to meet the current exploitation requirements. SUMMARY

[0004] The purpose of the present application is to provide a powder-type high-shear-resistant hyperbranched polymer drag reducer suitable for water-based fracturing fluid, which has a hyperbranched structure, excellent shear resistance, is suitable for large-volume and high-speed injection conditions of offshore fracturing fluid, and has the advantages of low cost and environmental friendliness.

[0005] The polymer drag reducer suitable for water-based fracturing fluid provided by the present application has a structural formula as shown in formula I or formula II:

[0006] Formula I Formula II In the formula, represents nano silicon dioxide; In the formula, m is a number between 30,000 and 100,000, o is a number between 20,000 and 50,000, and p is a number between 1,000 and 5,000.

[0007] The application also provides a preparation method of the polymer drag reducer, comprising the following steps: After acrylamide and functional monomers are dissolved in water and the pH value is adjusted to 5-8, nitrogen is blown to remove oxygen, and then the initiator is added after temperature rising to perform the aqueous solution polymerization reaction, and then NaOH is added to perform hydrolysis to obtain the product. The structure of the functional monomer is shown in formula III or formula IV.

[0008] Formula III Formula IV In the formula, represents nano-silica; In the formula, m is a number between 3 and 10 ten-thousands, o is a number between 2 and 5 ten-thousands, and p is a number between 1 and 5 thousands.

[0009] The initiator is obtained by reacting the surface-hydroxyl-rich nano-silica with ACVA-Cl shown in formula V.

[0010] Formula V.

[0011] Preferably, the surface-hydroxyl-rich nano-silica is prepared by the following method: S1, treating the nano-silica with a mixture of hydrogen peroxide, ammonia water and distilled water at 50-70℃ for 30-60min, and then washing with the hydrogen peroxide; S2, treating the nano-silica with a mixture of the hydrogen peroxide, hydrochloric acid and the distilled water at 50-70℃ for 30-60min, and then washing with the hydrogen peroxide; The surface-hydroxyl-rich nano-silica is reacted with ACVA-Cl shown in formula V in the presence of triethylamine.

[0012] Preferably, the preparation method of the monomer shown in formula III comprises the following steps: The acetone solution of 2-(dimethylamino)ethyl methacrylate is added dropwise with the acetone solution of bromo-n-octadecane, after the dropwise addition is completed, the temperature is raised to 55-60℃, and then the stirring reaction is performed for 10-20 hours to obtain the product.

[0013] Preferably, the preparation method of the monomer shown in formula IV comprises the following steps: The acetone solution of 2-(dimethylamino)ethyl methacrylate is added dropwise with the acetone solution of 1,3-propane sulfonic acid lactone, after the dropwise addition is completed, the temperature is raised to 55-60℃, and then the stirring reaction is performed for 10-20 hours to obtain the product.

[0014] In the preparation method, the water-soluble polymerization reaction is carried out after being heated to 70-75℃. The temperature of the water-soluble polymerization reaction is 70-75 o C, and the time is 4-12h.

[0015] In the preparation method, the mass ratio of the acrylamide to the functional monomer is 100:1-2. The mass ratio of the acrylamide to the initiator is 100:0.1-0.3.

[0016] The present application uses acrylamide (AM), hydrophobic functional monomer methyl methacryloyloxy ethyl octadecyl dimethyl ammonium bromide (C18AM) or betaine monomer methyl methacryloyloxy ethyl (dimethyl ammonium) propanesulfonic acid (BTAM) as raw materials, uses nano-silica with a hydroxyl end group as a hyperbranched parent nucleus, and synthesizes a branched hyperbranched polyacrylamide containing a hydrophobic functional group by macromolecular radical initiation copolymerization, which has good drag reduction performance.

[0017] Compared with the prior art, the present application has good temperature resistance and shear stability, is suitable for offshore fracturing fluid large discharge and high speed injection conditions, and has the advantages of low cost and environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 HNMR nuclear magnetic chart of the quaternary ammonium salt monomer C18AM monomer.

[0019] Figure 2 HNMR nuclear magnetic chart of the betaine monomer BTAM monomer.

[0020] Figure 3 The viscosity of HPAM in 3K mineralized water is affected by the reaction time. DETAILED DESCRIPTION

[0021] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0022] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0023] Example 1, preparation of initiator Nano-SiO2-ACVA

[0024] The synthesis route of the initiator Nano-SiO2-ACVA is shown above.

[0025] 1. Synthesis of ACVA-Cl Azodicynovaleric acid (ACVA) 1 eq was added to 1:5 (g / V) dichloromethane, 0o C When the white solid was completely dissolved, 30 mL of dichloromethane was added, and the reaction was stirred at room temperature for 6 hours. o C The dichloromethane and excess thionyl chloride were removed by distillation under reduced pressure to obtain a large amount of white solid ACVA-Cl crude product. The crude product was dissolved in 1:5 (g / V) dichloromethane, and the insoluble matter was removed by filtration. The solution was distilled under reduced pressure to remove dichloromethane to obtain 0.86 eq of ACVA-Cl.

[0026] 2. Surface activation of Nano-SiO2 First, Nano-SiO2 was treated with a 30% hydrogen peroxide: 28-30% ammonia water: distilled water solution at a volume ratio of 1:1:5 (V / V) at 60°C for 40 minutes, washed with 10 mL of 30% hydrogen peroxide, and then treated with an acidic solution of 30% hydrogen peroxide: hydrochloric acid: distilled water at a volume ratio of 1:1:5 (V / V) at 60°C for 40 minutes. The Nano-SiO2 was washed again with 10 mL of 30% hydrogen peroxide, and then cleaned with dichloromethane and ethanol, respectively. Finally, the Nano-SiO2-OH was dried in a vacuum oven at 150°C to obtain Nano-SiO2-OH with a surface rich in hydroxyl (OH) groups.

[0027] 3. Synthesis of Nano-SiO2-ACVA 5 g of Nano-SiO2-OH was dispersed in 100 mL of dichloromethane containing 20 g of ACVA-Cl, and 0 o C 10 mL of triethylamine was added dropwise, and after stirring for 2 hours, the solid was filtered. The solid powder was washed with dichloromethane (3 times * 50 mL), and then dried to obtain Nano-SiO2-ACVA.

[0028] Example 2, synthesis of functional monomer 1. Design and synthesis of quaternary ammonium salt monomer C18AM

[0029] The synthesis equation of the quaternary ammonium salt functional monomer C18AM is shown above. The molecular structure contains positive and negative charges, which can improve the salt resistance of the polymerization. Moreover, the molecular structure contains a long hydrophobic alkyl chain, which produces hydrophobic association in aqueous solution, increasing the viscosity of the polymer aqueous solution.

[0030] The specific synthesis steps are as follows: 5.0 mL of monomer 2-(dimethylamino)ethyl methacrylate, 40.0 mL of acetone, and 10 mL of a solution of 9.9 g of brominated n-octadecane in acetone were added dropwise. After the addition was complete, the temperature was raised to 55 oC, stirring for 10 hours, the system produced a large amount of white solid, after cooling and filtering, the crude product was repeatedly washed with 100 mL of acetone to remove unreacted monomer and bromo-n-octadecane, and finally the white solid was dried under vacuum to obtain the product.

[0031] HNMR characterization of product C18AM is shown as Figure 1 HNMR chart shows that the structure of the obtained product is the same as the molecular design structure, and the product has high purity.

[0032] 2. Design and synthesis of betaine monomer BTAM

[0033] The synthesis equation of betaine functional monomer BTAM is shown above, which contains positive and negative charges in the molecular structure, and can improve the salt resistance of polymerization. The specific synthesis steps are as follows: 5.0 mL of monomer 2- (dimethylamino) ethyl methacrylate, 25.0 mL of acetone, and 10 mL of acetone solution containing 2.6 mL of 1, 3-propane sulfonic acid lactone were added. After the dropwise addition was completed, the temperature was raised to 55 o C, stirring for 10 hours, the system produced a large amount of white solid, after cooling and filtering, the crude product was repeatedly washed with 20 mL of acetone to remove unreacted monomer and sulfonic acid lactone, and finally the white solid BTAM was dried under vacuum to obtain the product.

[0034] HNMR characterization of product BTAM is shown as Figure 2 HNMR chart shows that the structure of the obtained product is the same as the molecular design structure, and the product has high purity.

[0035] Example 3, synthesis of Nano-SiO2@HPAM The synthesis route of polymer Nano-SiO2@HPAM-PC18AM is shown as follows:

[0036] The synthesis route of polymer Nano-SiO2@HPAM-PBTAM is shown as follows:

[0037] 1. Polymerization process After adding acrylamide monomer AM, functional monomer (C18AM or BTAM), and H2O into a three-necked flask in turn, stirring to dissolve completely, testing the pH value of aqueous solution, adjusting the pH value to 7-8 with NaOH or HCl aqueous solution, then removing oxygen in water with N2, raising the temperature to 40 o C, adding catalyst Nano-SiO2-ACVA and stirring uniformly, keeping the temperature at 70-75 oThe reaction between C and C proceeds for a period of time. Then, NaOH is added, and the mixture is hydrolyzed at a certain temperature. After drying, the product is dispersed into a white powder.

[0038] Table 1. Usage of each raw material

[0039] 2. Effect of reaction time on copolymer viscosity Add AM (100.0g), functional monomer, and H2O to a three-necked flask in sequence, stir until completely dissolved, then purge with N2 to remove oxygen from the water, and heat to 65°C. o C. Add initiator Nano-SiO2-ACVA (0.10g) and maintain the temperature at 70-73°C. o The reactions between C and C are carried out at different times during polymerization. Then NaOH is added at 120°C. o Hydrolyze under C and dry.

[0040] A polymer solution with a concentration of 1750 mg / L was prepared using 9K mineralized water. The viscosity of the solution was tested, and the results are as follows: Figure 3 As shown.

[0041] from Figure 3 As can be seen, the viscosity of the polymer aqueous solution reached near equilibrium after 4.5 hours of polymerization, indicating that the polymerization reaction had reached its maximum value. Therefore, the polymerization reaction time should be controlled to be no less than 4.5 hours. In subsequent polymerization reactions, a polymerization reaction time of 5.5 hours was selected.

[0042] The hyperbranched polyacrylamide with branched hydrophobic functional groups synthesized in this invention exhibits excellent drag reduction performance. The drag reduction performance was evaluated using the method described in Section 7.8 of SY / T 7627-2021 "Technical Requirements for Water-Based Fracturing Fluids". Experimental results show that the maximum drag reduction rates of this hyperbranched polyacrylamide solution reached 57.1%, 70.3%, 74.6%, and 74.1% at concentrations of 0.05%, 0.08%, 0.12%, and 0.15%, respectively. The drag reduction performance reached its peak (74.6%) at a concentration of 0.12%, demonstrating its application potential as a highly efficient drag reducer.

Claims

1. A polymer drag reducer suitable for water-based fracturing fluids, having the structural formula shown in Formula I or Formula II: Formula I Formula II In the formula, This indicates nano-silica; In the formula, m is a number between 30,000 and 100,000, o is a number between 20,000 and 50,000, and p is a number between 3,000 and 10,000.

2. The method for preparing the polymer drag-reducing agent according to claim 1, comprising the following steps: Acrylamide and functional monomers are dissolved in water, the pH is adjusted to 5-8, nitrogen is purged to remove oxygen, the temperature is raised, an initiator is added, and an aqueous solution polymerization reaction is carried out. After the reaction is completed, NaOH is added for hydrolysis to obtain the product. The structure of the functional unit is shown in Formula III or Formula IV: Formula III Formula IV In the formula, This indicates nano-silica; In the formula, m is a number between 30,000 and 100,000, o is a number between 20,000 and 50,000, and p is a number between 1,000 and 5,000.

3. The preparation method according to claim 2, characterized in that: The initiator is obtained by reacting nano-silica with hydroxyl-rich surfaces with ACVA-Cl as shown in Formula V; Formula V.

4. The preparation method according to claim 3, characterized in that: The hydroxyl-rich nano-silica was prepared according to the following method: S1. Treat nano-silica with a mixture of hydrogen peroxide, ammonia and distilled water at 50-70℃ for 30-60 min, and then wash with the hydrogen peroxide. S2. Treat the nano-silica with a mixture of hydrogen peroxide, hydrochloric acid and distilled water at 50-70°C for 30-60 minutes, and then wash with hydrogen peroxide. The nano-silica with hydroxyl-rich surface reacts with ACVA-Cl as shown in Formula V in the presence of triethylamine.

5. The preparation method according to any one of claims 2-4, characterized in that: The preparation method of the monomer shown in Formula III includes the following steps: Add an acetone solution of bromo-n-octadecane dropwise to an acetone solution of 2-(dimethylamino)ethyl methacrylate. After the addition is complete, heat to 55-60℃ and stir the reaction for 10-20 hours to obtain the final product.

6. The preparation method according to any one of claims 2-4, characterized in that: The preparation method of the monomer shown in Formula IV includes the following steps: Add an acetone solution of 1,3-propanesulfonate lactone dropwise to an acetone solution of 2-(dimethylamino)ethyl methacrylate. After the addition is complete, heat to 55-60℃ and stir the reaction for 10-20 hours to obtain the product.

7. The preparation method according to any one of claims 2-6, characterized in that: The aqueous solution polymerization reaction is carried out after the temperature is raised to 70-75℃; The temperature of the aqueous solution polymerization reaction is 70-75°C. o C, the time is 4-12 hours.

8. The preparation method according to any one of claims 2-7, characterized in that: The mass ratio of the acrylamide to the functional monomer is 100:1-2; The mass ratio of acrylamide to the initiator is 100:0.1-0.

3.

9. The application of the polymer drag reducer of claim 1 in oil and gas development.

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