Production method of salt-resistant drag reducer for oil well fracturing

Abstract

The invention relates to the technical field of drag reducer preparation, and in particular to a method for producing a salt-resistant drag reducer for oil well fracturing. S1.1, weighing the following raw materials in parts by weight: 27-32 parts by weight of a modified polymer, 0.6-1.1 parts by weight of a cross-linking agent, 0.1-0.3 parts by weight of an antioxidant, 2-6 parts by weight of an acetate buffer, 0.6-0.8 parts by weight of a surfactant, 0.02-0.04 parts by weight of a benzalkonium chloride biocide, and 0.2-0.4 parts by weight of a bentonite suspending agent; wherein, the modified The polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:2 to 4:10 to 13; S1.2, adding the above raw materials and continuously stirring to obtain a salt-resistant drag reducer; crotonic acid, acrylic acid phosphonate and acrylamide are used to prepare a modified polymer, and carboxyl and phosphonic acid groups are introduced into the polyacrylamide, thereby enhancing the water solubility of the polymer and, at the same time, improving the coordination ability of the modified polymer with the zirconium ions in the cross-linking agent, thereby improving the salt resistance and drag reduction effect of the modified polymer.

Description

Technical Field

[0001] The invention relates to the technical field of drag reducer preparation, in particular to a method for producing a salt-resistant drag reducer for oil well fracturing. Background Art

[0002] Oil well fracturing is a key technology in the process of oil and gas extraction. It aims to form cracks in oil and gas layers through hydraulic action, thereby improving the flow environment of oil and gas and increasing oil well production. In fracturing operations, the selection and performance of fracturing fluid are crucial. As an important component of fracturing fluid, the performance of salt-resistant drag reducer directly affects the effect and cost of fracturing operations. Salt-resistant drag reducer mainly reduces the friction resistance of fracturing fluid, improves pumping efficiency and reduces energy consumption. In addition, salt-resistant drag reducer also has good solubility and stability, and can quickly dissolve in fracturing fluid to form a uniform drag reduction system to ensure the smooth progress of fracturing operations.

[0003] Salt-resistant drag reducer is a chemical additive that can maintain high drag reduction performance in a high-salinity environment. In oil well fracturing operations, since formation water often contains high salt content, traditional drag reducers are prone to failure under high-salinity conditions, and their drag reduction effect is greatly reduced, resulting in a decrease in fracturing fluid delivery efficiency and increased operational difficulty and cost. In view of this, we propose a production method for salt-resistant drag reducer for oil well fracturing. Summary of the invention

[0004] The object of the present invention is to provide a method for producing a salt-resistant drag reducer for oil well fracturing, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides a method for producing a salt-resistant drag reducer for oil well fracturing. S1.1, weigh the following raw materials in parts by weight: 27-32 parts by weight of a modified polymer, 0.6-1.1 parts by weight of a cross-linking agent, 0.1-0.3 parts by weight of an antioxidant, 2-6 parts by weight of an acetate buffer, 0.6-0.8 parts by weight of a surfactant, 0.02-0.04 parts by weight of a benzalkonium chloride biocide, and 0.2-0.4 parts by weight of a bentonite suspending agent;

[0006] The modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:2 to 4:10 to 13;

[0007] S1.2. Add water to the reactor and heat it to 50-70°C, add the modified polymer while stirring for 30-50 minutes until the modified polymer is completely dissolved, then add the cross-linking agent and continue stirring for 40-50 minutes, then add the antioxidant and acetate buffer, adjust the pH value, continue stirring for 15-20 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, then add bentonite, stir for 30-40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0008] Preferably, in S1.1, the cross-linking agent is one or more combinations of zirconium acetate, zirconium oxychloride and tetrabutyl zirconate.

[0009] Preferably, in S1.1, the antioxidant is one or more combinations of 2,6-di-tert-butyl-4-methylphenol, ascorbic acid and tocopherol.

[0010] Preferably, in S1.1, the surfactant is one or more combinations of sodium dodecyl sulfate, polyoxyethylene alkyl ether and alkyl glycoside.

[0011] Preferably, in S1.2, acetate buffer is added to adjust the pH value to 4.5-5.5.

[0012] Preferably, the steps of preparing the modified polymer are specifically as follows:

[0013] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system under the protection of inert gas and keep it for a period of time, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 80-100°C for 3-5 hours to obtain a modified polymer.

[0014] The modified polymer is prepared from acrylamide, crotonic acid and acrylic acid phosphonate based on the principle of free radical copolymerization. Under the action of heating, the initiator decomposes to produce primary free radicals, which react with monomer molecules to form monomer free radicals. The monomer free radicals further react with other monomer molecules to form longer chain free radicals. When two chain free radicals meet, they can combine with each other to form a stable polymer chain. This process leads to the disappearance of free radicals and eventually forms a complete polymer chain. In this reaction, acrylamide is the main component, while crotonic acid and acrylic acid phosphonate are used as copolymers to introduce additional functionality. Since the carboxyl group has strong hydrophilicity, and the coordination ability of the phosphonic acid group with zirconium is stronger than that of the carboxyl group with zirconium ions, the introduction of the carboxyl group into the polyacrylamide helps to improve the solubility of the polymer in water, making it easier to form a stable solution, and facilitating on-site preparation and transportation. The phosphonic acid group is introduced into the polyacrylamide, and then a zirconium-based crosslinking agent is added. The zirconium in the zirconium-based crosslinking agent The ions can form stable coordination bonds with carboxyl and phosphonic acid groups. As zirconium ions form coordination bonds with functional groups on multiple polymer chains, a three-dimensional network structure is formed between the polymer chains. This three-dimensional network structure gives the modified polymer a higher viscosity and more stable physical properties. Even at high salt concentrations, the structure can remain intact, improving the salt resistance of the modified polymer in a high-salt environment. At the same time, the presence of the three-dimensional network structure can maintain the viscosity of the modified polymer at a higher shear rate, reducing the internal friction during fluid flow, thereby improving the drag reduction effect. In addition, the increased viscosity of the polymer solution helps to better carry the proppant (such as sand particles) into the formation fractures, increase its sand carrying capacity, and improve the conductivity of the fractures. Therefore, the high-viscosity and stable drag reducer achieves an increase in the pumping efficiency of the fracturing fluid and greatly reduces energy consumption. After the fracturing operation is completed, the drag reducer with good stability can also reduce problems in the backflow process, help to better recover the fracturing fluid, reduce environmental pollution, and improve resource utilization.

[0015] Preferably, the initiator is one or more combinations of dibenzoyl peroxide, ammonium persulfate and azobisisobutyronitrile.

[0016] Preferably, the added amount of the initiator is 0.8-3% of the total amount of monomers.

[0017] Preferably, the heating temperature of the reaction system is 60-90° C., and the reaction time is 12-15 h.

[0018] Preferably, the inert gas is nitrogen or argon.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In the production method of the salt-resistant drag reducer for oil well fracturing, crotonic acid and acrylic acid phosphonate are used to prepare a modified polymer through copolymerization with acrylamide, and carboxyl groups and phosphonic acid groups are introduced into the polyacrylamide, which, on the one hand, enhance the water solubility of the polymer, and on the other hand, improve the coordination ability of the modified polymer with the zirconium ion in the cross-linking agent to form a stable complex, thereby giving the modified polymer higher viscosity and more stable physical properties, thereby improving the salt resistance of the modified polymer in a high-salt environment, and the high viscosity characteristic also helps to reduce the internal friction during fluid flow, thereby improving the drag reduction effect. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] The production method of the salt-resistant drag reducer for oil well fracturing of the present invention:

[0023] S1.1, weigh the following raw materials in parts by weight: 27-32 parts by weight of modified polymer, 0.6-1.1 parts by weight of cross-linking agent, 0.1-0.3 parts by weight of antioxidant, 2-6 parts by weight of acetate buffer, 0.6-0.8 parts by weight of surfactant, 0.02-0.04 parts by weight of benzalkonium chloride biocide and 0.2-0.4 parts by weight of bentonite suspending agent;

[0024] The modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:2 to 4:10 to 13;

[0025] S1.2. Add water to the reactor and heat it to 50-70°C, add the modified polymer while stirring for 30-50 minutes until the modified polymer is completely dissolved, then add the cross-linking agent and continue stirring for 40-50 minutes, then add the antioxidant and acetate buffer, adjust the pH value to 4.5-5.5, continue stirring for 15-20 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, then add the bentonite, stir for 30-40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain the salt-resistant drag reducer.

[0026] The cross-linking agent is one or more combinations of zirconium acetate, zirconium oxychloride and tetrabutyl zirconate; the antioxidant is one or more combinations of 2,6-di-tert-butyl-4-methylphenol, ascorbic acid and tocopherol; the surfactant is one or more combinations of sodium dodecyl sulfate, polyoxyethylene alkyl ether and alkyl glycoside;

[0027] The cross-linking agent is zirconium acetate; the antioxidant is 2,6-di-tert-butyl-4-methylphenol; and the surfactant is sodium dodecyl sulfate.

[0028] Embodiment 1: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0029] S1.1. Weigh the following raw materials in parts by weight: 27 parts by weight of modified polymer, 0.6 parts by weight of zirconium acetate, 0.1 parts by weight of 2,6-di-tert-butyl-4-methylphenol, 2 parts by weight of acetate buffer, 0.6 parts by weight of sodium dodecyl sulfate, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0030] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0031] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0032] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0033] Embodiment 2: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0034] S1.1. Weigh the following raw materials in parts by weight: 30 parts by weight of modified polymer, 0.6 parts by weight of zirconium acetate, 0.1 parts by weight of 2,6-di-tert-butyl-4-methylphenol, 2 parts by weight of acetate buffer, 0.6 parts by weight of sodium dodecyl sulfate, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0035] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0036] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0037] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0038] Embodiment 3: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0039] S1.1. Weigh the following raw materials in parts by weight: 32 parts by weight of modified polymer, 0.6 parts by weight of zirconium acetate, 0.1 parts by weight of 2,6-di-tert-butyl-4-methylphenol, 2 parts by weight of acetate buffer, 0.6 parts by weight of sodium dodecyl sulfate, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0040] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0041] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0042] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0043] Embodiment 4: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0044] S1.1. Weigh the following raw materials in parts by weight: 32 parts by weight of modified polymer, 1.1 parts by weight of zirconium acetate, 0.3 parts by weight of 2,6-di-tert-butyl-4-methylphenol, 6 parts by weight of acetate buffer, 0.8 parts by weight of sodium dodecyl sulfate, 0.04 parts by weight of benzalkonium chloride biocide and 0.4 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0045] The initiator is dibenzoyl peroxide; the amount of the initiator added is 3% of the total amount of the monomer; the inert gas is nitrogen;

[0046] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0047] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0048] Embodiment 5: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0049] S1.1. Weigh the following raw materials in parts by weight: 32 parts by weight of modified polymer, 0.6 parts by weight of zirconium acetate, 0.1 parts by weight of 2,6-di-tert-butyl-4-methylphenol, 2 parts by weight of acetate buffer, 0.6 parts by weight of sodium dodecyl sulfate, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:2:10;

[0050] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0051] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0052] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0053] Embodiment 6: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0054] S1.1. Weigh the following raw materials in parts by weight: 32 parts by weight of modified polymer, 0.6 parts by weight of zirconium oxychloride, 0.1 parts by weight of ascorbic acid, 2 parts by weight of acetate buffer, 0.6 parts by weight of polyoxyethylene alkyl ether, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0055] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0056] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0057] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0058] Embodiment 7: A method for producing a salt-resistant drag reducer for oil well fracturing, comprising the following steps:

[0059] S1.1. Weigh the following raw materials in parts by weight: 32 parts by weight of modified polymer, 0.6 parts by weight of tetrabutyl zirconate, 0.1 parts by weight of tocopherol, 2 parts by weight of acetate buffer, 0.6 parts by weight of alkyl glycoside, 0.02 parts by weight of benzalkonium chloride biocide and 0.2 parts by weight of bentonite suspending agent; wherein the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphonate in a mass ratio of 7:4:13;

[0060] The initiator is dibenzoyl peroxide; the amount of the initiator added is 0.8% of the total amount of the monomer; the inert gas is nitrogen;

[0061] Dissolve acrylamide, crotonic acid and acrylic acid phosphonate in N,N-dimethylformamide, add initiator and stir evenly, heat the reaction system to 80°C and maintain for 12 hours under the protection of nitrogen, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 100°C for 5 hours to obtain a modified polymer.

[0062] S1.2. Add water to the reactor and raise the temperature to 70°C. Add the modified polymer while stirring for 30 minutes until the modified polymer is completely dissolved. Then add the cross-linking agent and continue stirring for 40 minutes. Then add the antioxidant and acetate buffer, adjust the pH value to 5, continue stirring for 15 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, add bentonite, stir for 40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

[0063] Comparative Example 1: The method of Example 3 was adopted to prepare a salt-resistant drag reducer using acrylamide, but crotonic acid and acrylic acid phosphonate were not added for modification.

[0064] Comparative Example 2: The method of Example 3 was adopted to prepare a modified polymer by introducing carboxyl groups of crotonic acid into polyacrylamide, but without introducing phosphonic acid groups of acrylic acid phosphonate.

[0065] Comparative Example 3: The method of Example 3 was adopted, and the amount of the modified polymer used was 10 parts by weight.

[0066] The present invention discloses a method for producing a salt-resistant drag reducer for oil well fracturing by using a modified polymer, wherein the performance index inspection items and inspection standards of the method for producing a salt-resistant drag reducer for oil well fracturing are as follows:

[0067] The drag reduction rate was measured and calculated according to the method specified in "SY / T 6376-2008 General Technical Conditions for Fracturing Fluids". The drag reduction rate of fracturing fluid drag reducers in 2wt% KCl solution was tested to characterize salt resistance. The drag reduction rate refers to the ratio of the friction resistance reduction of the fluid with added drag reducers to the original fluid without added drag reducers when flowing under the same conditions. The drag reduction rate reflects the ability of the drag reducer to reduce the flow resistance of the fluid. A higher drag reduction rate means that the fluid flows more smoothly in the pipeline and the transportation efficiency is higher. Salt resistance refers to the ability of the drag reducer to maintain its performance at different salt concentrations. In applications such as oil well fracturing, the fluid usually contains a high concentration of salt. Therefore, salt resistance is a key indicator for evaluating the performance of drag reducers. In a high-salinity environment, drag reducers with good salt resistance can maintain stable performance and ensure the flow efficiency of the fluid under complex geological conditions.

[0068] The above standards were used to test the production methods of the salt-resistant drag reducers for oil well fracturing prepared in the above Examples 1-7 and Comparative Examples 1-3, and the obtained data are shown in Table 1:

[0069] Table 1 Performance data of Examples 1-7 and Comparative Examples 1-3

[0070]

[0071] The above data fully show that compared with Comparative Examples 1-3, Examples 1-7 can fully show the effect of the modified polymer on the production method of the salt-resistant drag reducer for oil well fracturing in terms of drag reduction effect and salt resistance.

[0072] Since the present invention adopts a modified polymer to prepare a production method of a salt-resistant drag reducer for oil well fracturing, the drag reduction effect and salt resistance of the production method of a salt-resistant drag reducer for oil well fracturing are effectively improved by the modified polymer, as follows:

[0073] It can be seen from Examples 1-3 that with the continuous increase in the content of the modified polymer, the drag reduction effect and salt resistance of the salt-resistant drag reducer for oil well fracturing gradually increase. This is because with the increase in the content of the modified polymer, the number of polymer molecules in the solution increases, and the interaction between the molecules also increases accordingly. When the polymer content increases, the number of crosslinking points between polymers and between polymers and zirconium-based crosslinkers will also increase. More crosslinking points mean a more stable three-dimensional network structure, which helps to improve the mechanical strength, temperature resistance and salt resistance of the polymer. In addition, the increase in the degree of crosslinking will increase the viscosity of the polymer solution, resulting in an increase in the internal friction of the fluid, thereby reducing the flow resistance of the fluid, which helps to improve the drag reduction effect of the drag reducer.

[0074] It can be seen from Examples 3 and 4 that with the continuous increase of other components in the salt-resistant drag reducer, the drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing have almost no obvious changes. This is because a sufficiently dense network structure has been formed between the polymer molecules, providing sufficient stability and viscosity, thereby achieving a significant improvement in salt resistance and drag reduction. Changes in other components within a certain range have limited effect on improving performance.

[0075] It can be seen from Examples 3 and 5 that with the change in the ratio of crotonic acid and acrylic acid phosphonate components in the modified polymer, the drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing decrease. This is because crotonic acid mainly plays a role in improving the water solubility of the modified polymer and secondly improves the stability of the modified polymer, and acrylic acid phosphonate mainly plays a coordination role to improve salt resistance and drag reduction effect. When the content of acrylic acid phosphonate decreases, the stability also decreases, and thus the salt resistance and drag reduction effect decrease slightly.

[0076] It can be seen from Examples 3, 6 and 7 that the drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing have almost no significant changes with the changes in the cross-linking agent, antioxidant and surfactant components. This is because the main function of the cross-linking agent is to form a more stable three-dimensional network structure between zirconium ions and polymers. Therefore, changing the cross-linking agent component but still containing zirconium elements will not affect the occurrence of cross-linking. The role of the antioxidant is to inhibit the oxidation reaction and extend the shelf life of the salt-resistant drag reducer. The role of the surfactant is to improve the fluidity of the liquid. Especially in a high-salt environment, the cross-linking agent, antioxidant and surfactant components are not the main reasons affecting the drag reduction and salt resistance effects of the salt-resistant drag reducer, so the drag reduction and salt resistance have almost no significant changes.

[0077] According to the above test experiments, the production method of the salt-resistant drag reducer for oil well fracturing prepared according to Example 3 has the best performance, so Example 3 is taken as the best example;

[0078] By comparing Example 3 with Comparative Examples 1-3, it can be seen that:

[0079] In Comparative Example 1, acrylamide was used to prepare a salt-resistant drag reducer, and crotonic acid and acrylic acid phosphonate were not added for modification. The drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing were poor. This is because the presence of functional groups such as carboxyl and phosphonic acid groups is crucial to improving the water solubility, salt resistance, thermal stability and cross-linking properties of the polymer. Without the introduction of additional functional groups such as carboxyl and phosphonic acid groups, the polymer and the zirconium-based cross-linking agent lacked a stable three-dimensional network structure, the polymer was not stable enough, and the viscosity was reduced. Therefore, the drag reduction effect and salt resistance performed poorly.

[0080] The modified polymer of Comparative Example 2 is prepared by introducing the carboxyl group of crotonic acid into polyacrylamide, but not introducing the phosphonic acid group of acrylic acid phosphonate. The drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing are poor. This is because the phosphonic acid group can more effectively complex metal ions, especially in a high-salinity environment, and the lack of the function of the phosphonic acid group limits the performance of the polymer in a high-salinity environment, so the drag reduction effect and salt resistance are poor.

[0081] In comparative example 3, the dosage of the modified polymer is 10 parts by weight, and the drag reduction and salt resistance of the salt-resistant drag reducer for oil well fracturing are poor. This is because at a lower polymer content, the number of polymer molecules is small, the intermolecular interaction is insufficient, the formed network structure is not dense enough, the polymer has poor stability, low viscosity, and the internal friction of the fluid is small, so the drag reduction effect and salt resistance are relatively weak.

[0082] In summary, the modified polymer is prepared by copolymerization of crotonic acid and acrylic acid phosphonate with acrylamide, carboxyl groups and phosphonic acid groups are introduced into polyacrylamide, the hydrophilicity of the carboxyl groups is utilized to increase the water solubility of the polymer, and the coordination ability of the phosphonic acid groups and carboxyl groups with the zirconium-based cross-linking agent is utilized to improve the stability and viscosity of the polymer, thereby giving the salt-resistant drag reducer excellent salt resistance and drag reduction effect.

[0083] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for producing a salt-resistant drag reducer for oil well fracturing, characterized in that: S1.1, weigh the following raw materials in parts by weight: 27-32 parts by weight of modified polymer, 0.6-1.1 parts by weight of cross-linking agent, 0.1-0.3 parts by weight of antioxidant, 2-6 parts by weight of acetate buffer, 0.6-0.8 parts by weight of surfactant, 0.02-0.04 parts by weight of benzalkonium chloride biocide and 0.2-0.4 parts by weight of bentonite suspending agent; Wherein, the modified polymer is prepared by copolymerization of acrylamide, crotonic acid and acrylic acid phosphate in a mass ratio of 7:2 to 4:10 to 13; in said S1.1, the crosslinking agent is one or more combinations of zirconium acetate, zirconium oxychloride and tetrabutyl zirconate; S1.

2. Add water to the reactor and heat it to 50-70°C, add the modified polymer while stirring for 30-50 minutes until the modified polymer is completely dissolved, then add the cross-linking agent and continue stirring for 40-50 minutes, then add the antioxidant and acetate buffer, adjust the pH value, continue stirring for 15-20 minutes, then add the surfactant and benzalkonium chloride to ensure complete dispersion, then add bentonite, stir for 30-40 minutes, filter to remove the undissolved particles, cool to room temperature, and obtain a salt-resistant drag reducer.

2. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 1, characterized in that: In S1.1, the antioxidant is one or more combinations of 2,6-di-tert-butyl-4-methylphenol, ascorbic acid and tocopherol.

3. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 1, characterized in that: In the above S1.1, the surfactant is one or more combinations of sodium dodecyl sulfate, polyoxyethylene alkyl ether and alkyl glycoside.

4. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 1, characterized in that: In the S1.2, acetate buffer is added to adjust the pH value to 4.5-5.

5.

5. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 1, characterized in that: The steps of preparing the modified polymer are specifically as follows: Dissolve acrylamide, crotonic acid and acrylic acid phosphate in N,N-dimethylformamide, add an initiator and stir evenly, heat the reaction system under the protection of inert gas and keep it for a period of time, stop heating after the reaction is completed, cool to room temperature, filter, wash with water, and then place in an oven at 80-100°C for 3-5h to obtain a modified polymer; The heating temperature of the reaction system is 60-90° C., and the reaction time is 12-15 hours.

6. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 5, characterized in that: The initiator is one or more combinations of dibenzoyl peroxide, ammonium persulfate and azobisisobutyronitrile.

7. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 5, characterized in that: The added amount of the initiator is 0.8-3% of the total amount of monomers.

8. The method for producing a salt-resistant drag reducer for oil well fracturing according to claim 5, characterized in that: The inert gas is nitrogen or argon.

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