A polymer drag reducer and a method of making the same

Abstract

The application provides a polymer drag reducer and a preparation method thereof, and the preparation method comprises the following steps: modifying nano-silicon dioxide by using a silane coupling agent to obtain modified nano-silicon dioxide; dissolving the following raw materials in water to obtain an aqueous solution: 180-240 parts of acrylamide, 30-60 parts of an acrylic monomer, 10-30 parts of a salt-resistant monomer and 20-40 parts of a hydrophobic monomer; adding 5-15 parts of the modified nano-silicon dioxide into the aqueous solution, adjusting the pH value to weak alkalinity, and adding an initiator to initiate a polymerization reaction under a protective atmosphere, so that the polymer drag reducer is obtained. In the application, the surface of nano-SiO2 is modified by using a silane coupling agent, an unsaturated double bond is introduced into the surface of SiO2, a multi-arm polymer drag reducer is prepared, and finally, the drag reducer has the advantages of high molecular weight, good temperature resistance and salt resistance, strong shear resistance and excellent drag reduction performance.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a polymer drag reducer and its preparation method. Background Technology

[0002] Hydraulic fracturing often encounters reservoir conditions characterized by high temperature, high shear, and high salinity. Polyacrylamide or partially hydrolyzed polyacrylamide drag reducers degrade into smaller molecules under high shear rates; hydrolysis occurs at high temperatures; and the extended molecular chains tend to coil under high salinity conditions. All of these factors reduce drag reduction effectiveness or even eliminate drag reduction performance, rendering conventional polyacrylamide inadequate for such environmental requirements.

[0003] To address the aforementioned problems, the overall performance of polyacrylamide can be effectively improved by designing its molecular structure. Currently, introducing functional monomers with different groups is one of the most common modification methods. Rigid side groups or large side groups can effectively improve the thermal stability of polymer molecules; sulfonic acid groups, as strongly polar groups, have strong hydrophilicity and can increase the hydrodynamic radius of the polymer, improving its temperature and salt resistance; N-vinylpyrrolidone (NVP) has the function of inhibiting the hydrolysis of acrylamide groups, which can enhance the stability of the polymer.

[0004] CN110194816B discloses a salt-resistant drag-reducing polymer and its synthesis process. This technology improves the temperature and salt resistance of the drag-reducing agent by introducing AMPS monomers, and also has the advantages of simple production method, fast dissolution rate and high drag reduction rate. CN117866140A discloses a variable viscosity drag-reducing agent with temperature and salt resistance. The drag-reducing agent is composed of acrylamide, anionic monomer, hydrophobic monomer and zwitterionic monomer. The zwitterionic monomer promotes the extension of polymer chain in salt water environment, so that it has excellent temperature and salt resistance. The introduction of hydrophobic monomer enhances the viscosity-increasing performance of drag-reducing agent.

[0005] As geological conditions for reservoir stimulation become increasingly unfavorable, high temperature and high salinity will become the main targets for drag reduction agent technology research. Modifying the molecular structure of polymers solely with functional monomers is no longer sufficient to meet the requirements. Special molecular configurations can also effectively improve their temperature and salt resistance properties, such as comb-shaped polymers, block polymers, and network polymers. Summary of the Invention

[0006] To address the problems of existing polyacrylamide drag-reducing agents being prone to hydrolysis and thermal degradation at high temperatures, and having their molecular chains prone to coiling under high salt conditions, resulting in a significant decrease in drag-reducing effect, the present invention aims to provide a polymer drag-reducing agent and its preparation method.

[0007] To achieve the above objectives, the present invention provides a method for preparing a polymer drag-reducing agent, comprising:

[0008] S1: Modified nano-silica is obtained by modifying nano-silica with a silane coupling agent.

[0009] S2: Dissolve the following parts by weight of raw materials in water to obtain an aqueous solution: 180-240 parts of acrylamide, 30-60 parts of acrylic monomers, 10-30 parts of salt-resistant monomers, and 20-40 parts of hydrophobic monomers.

[0010] S3: Add 5-15 parts by weight of the modified nano-silica to the aqueous solution and stir thoroughly. Then adjust the pH value to weakly alkaline and add an initiator under a protective atmosphere to initiate the polymerization reaction, thereby obtaining the polymer drag reducer.

[0011] The polymer drag reducer prepared in this invention is a multi-arm polymer drag reducer with nano-SiO2 as the crosslinking center. This invention modifies the surface of nano-silica particles using a silane coupling agent to obtain silica containing unsaturated double bonds. Subsequently, it undergoes free radical polymerization with various functional monomers to prepare a polymer drag reducer with inorganic nanomaterials as the crosslinking center. Compared to linear polymer molecules, this drag reducer has a larger hydrodynamic volume, better elastic potential energy, and a more stable and long-lasting drag reduction effect. After the multiple hydroxyl groups on the surface of nano-SiO2 react with the silane coupling agent, they can connect multiple polymers containing unsaturated double bonds, forming a structure with SiO2 as the center and a surface covered with comb-like polymers. The presence of unsaturated bonds allows the polymers grafted onto the SiO2 surface to participate in copolymerization reactions as monomers. Furthermore, this invention introduces hydrophobic monomers, salt-resistant monomers, and modified nano-SiO2 during the synthesis of the polymer drag reducer to improve the temperature resistance, salt resistance, and shear resistance of the fracturing fluid, enabling it to cope with more complex and harsh reservoir conditions.

[0012] In the above method for preparing polymer drag-reducing agents, preferably, in step S1, the modification treatment of the nano-silica includes the following steps:

[0013] Nano-silica, silane coupling agent, and ammonia water in a mass ratio of 15-20:1-2.1:0.8-1.5 are brought into full contact in an organic solvent to carry out a modification reaction, thereby obtaining the modified nano-silica.

[0014] Unmodified nano-SiO2 has a hydrophilic polar surface due to the presence of a large number of hydroxyl groups, making it prone to aggregation and difficult to disperse uniformly in high-viscosity polymer solutions. The modified nano-SiO2 of this invention is modified with a silane coupling agent, which reduces the number of hydroxyl groups on the SiO2 surface and increases the steric hindrance of SiO2 particles, thereby suppressing the tendency of nanoparticle self-aggregation.

[0015] This invention utilizes nano-SiO2, surface-modified with a silane coupling agent, to copolymerize with various functional monomers to prepare drag-reducing agents. The comb-like polymers on the SiO2 surface possess multiple polymerization sites, acting as crosslinking agents to prepare multi-arm copolymers with nano-SiO2 as the crosslinking center. The size, volume, and surface effects of nanoparticles can effectively improve material properties. Adding a certain proportion of nanomaterials to organic polymers prepares organic-inorganic nanocomposites. Utilizing the nucleation and crosslinking properties of nanomaterials, a synergistic effect is achieved with polymer molecules, effectively enhancing the overall performance of the polymer molecules.

[0016] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the silane coupling agent includes one or more combinations of 3-butenetriethoxysilane, 3-(isobutenoyloxy)propyltrimethoxysilane, and 3-(1,3-dimethylbutene)aminopropyltriethoxysilane.

[0017] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the organic solvent includes one or more of anhydrous ethanol, ethyl acetate, acetone, and toluene.

[0018] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the mass ratio of the organic solvent to the modified nano-silica is 5-7:15-20.

[0019] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the temperature of the modification reaction is 45-65℃ and the time is 18-32h.

[0020] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the modification treatment of the nano-silica further includes: separating the solid products from the reaction solution of the modification reaction, washing, purifying and drying them, thereby obtaining the modified nano-silica.

[0021] In the above-mentioned method for preparing polymer drag reducers, preferably, the acrylic monomers include one or more of acrylic acid, vinyl acrylic acid, acrylic anhydride acetate, N-isopropylacrylamide, and 2-ethylacrylic acid.

[0022] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the salt-resistant monomer includes one or more of N-phenylethyl-N-tetradecylmethylacrylamide, N,N-diethylacrylamide, methacryloyloxyethyltrimethylammonium chloride, and acryloyloxyethyltrimethylammonium chloride.

[0023] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the hydrophobic monomer includes one or more of octadecyl dimethylacryloyl ammonium chloride, 2-isopropyl-2-adamantyl methacrylate, octadecyl methacrylate, dodecyl methacrylate, and octadecyl acrylate.

[0024] In this invention, the presence of hydrophobic monomers provides hydrophobic association forces, which are weaker than chemical bonds but stronger than hydrogen bonds. The presence of these forces further strengthens the structural strength of the polymer network and significantly increases its viscoelasticity.

[0025] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, in step S2, the raw materials further include one or more of the following: molecular weight regulator, strength regulator, and toughening agent.

[0026] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, in step S2, the raw materials further include: 10-15 parts of molecular weight regulator, 45-60 parts of strength regulator, and 25-55 parts of toughening agent.

[0027] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the molecular weight regulator includes one or more of tetrachloromethane, dodecanethiol, butyl 3-mercaptopropionate, methylstyrene resin, and sodium salicylate.

[0028] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the strength modifier is one or a combination of two or more of isopropanol, pentafluoropentanol, α-methylstyrene, and isooctyl 3-mercaptopropionate.

[0029] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the toughening agent is one or a combination of two or more of sodium acetate, sodium sulfate, trichloroethane, and chlorobutane.

[0030] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, in step S3, after adding modified nano-silica, the stirring speed is 120-480 rpm, the time is 3-5 h, and the stirring temperature is 20-25℃.

[0031] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, in step S3, the pH value of the adjusted aqueous phase solution is 7.2-9.2.

[0032] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the pH adjuster used to adjust the pH value includes one or a combination of two or more of sodium hydroxide, ammonia, and sodium carbonate.

[0033] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, in step S3, the initiation temperature of the polymerization reaction is 10-20°C and the reaction time is 3-6 hours.

[0034] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, during the polymerization reaction, the reaction temperature is controlled to increase at a rate of 0.1-0.4℃ / min.

[0035] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the initiator includes one or a combination of two or more of ammonium persulfate, potassium persulfate, sodium bisulfite, ferrous ammonium sulfate, and tert-butyl hydroperoxide.

[0036] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the mass ratio of the initiator to the modified nano-silica is 0.002-0.01:15-20.

[0037] In the above-mentioned method for preparing polymer drag-reducing agents, preferably, the protective gas includes one or a combination of two or more of nitrogen, helium, and argon.

[0038] In the above-mentioned method for preparing the polymer drag-reducing agent, preferably, the method further includes: washing, drying, pulverizing, and sieving the product of the polymerization reaction to obtain the polymer drag-reducing agent. More preferably, the detergent used for washing is anhydrous ethanol.

[0039] The present invention also provides a polymer drag-reducing agent, which is prepared by the above-described method for preparing polymer drag-reducing agents.

[0040] The technical solution provided by this invention has the following advantages:

[0041] (1) This invention combines inorganic nanomaterials and organic polymers, two materials with different properties, through grafting, copolymerization, and other methods to successfully prepare an organic-inorganic composite material. This material combines the rigidity and thermal stability of inorganic nanomaterials with the toughness of organic polymers. Utilizing the synergistic effect of nanoparticles and polymers, the drag-reducing agent can maintain the integrity of its molecular structure in high-mineralization brine. The multi-arm branched structure also helps prevent the drag-reducing agent from precipitating or agglomerating in high-mineralization brine systems, improving the dispersion stability of the drag-reducing agent in brine. The addition of rigid nanoparticles allows the polymer molecular chains to recover rapidly after shearing, significantly improving shear resistance. The introduction of inorganic nanoparticles achieves the goal of enhancing the comprehensive performance of polymer materials.

[0042] (2) In this invention, a silane coupling agent is used to modify the surface of nano-SiO2, introducing unsaturated double bonds into the surface of SiO2. The modified nano-SiO2 can participate in the copolymerization reaction as a monomer. Since the surface of SiO2 contains multiple polymerization sites, it can be used as a crosslinking center to react with monomers such as acrylamide, acrylic acid, and temperature and salt resistant monomers to prepare multi-arm polymer drag-reducing agents. The drag-reducing agent finally formed by this invention has excellent comprehensive performance, mainly manifested in high molecular weight, good temperature and salt resistance, strong shear resistance, and excellent drag reduction performance. Detailed Implementation

[0043] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0044] This invention provides a method for preparing a polymer drag-reducing agent, comprising the following steps:

[0045] (1) Disperse nano-SiO2 in an organic solvent in an ultrasonic cleaner, and add silane coupling agent and ammonia water in sequence; the present invention does not have special requirements for the source of the nano-SiO2, which is commercially available high-purity spherical nano-SiO2 with a particle size of 150nm.

[0046] (2) Under a nitrogen atmosphere, the reaction was carried out at 50°C for 24 hours. Excess solvent was removed by vacuum distillation. The modified SiO2 was separated by centrifugation and washed with anhydrous ethanol and centrifuged again. The above steps were repeated several times to purify the product. Finally, the pure nano-SiO2 was dried in an oven at 50°C for 24 hours to obtain modified nano-SiO2. The present invention does not specify the conditions for vacuum distillation, separation, purification and drying. Conventional methods and conditions can be used.

[0047] (3) Acrylamide, acrylic monomers, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, molecular weight regulator, strength regulator, toughening agent and deionized water are mixed in a certain mass ratio to obtain an aqueous solution;

[0048] (4) Add modified nano-SiO2 and stir thoroughly; adjust the pH of the entire system to a weakly alkaline pH.

[0049] (5) Under a nitrogen atmosphere, an initiator is added to initiate the polymerization reaction; the product after the reaction is washed, dried, pulverized, and sieved with anhydrous ethanol to finally obtain the polymer drag-reducing agent. This invention does not specify the conditions for washing, drying, pulverizing, and sieving; conventional methods and conditions are sufficient.

[0050] In this invention, the modification reaction route of nano-SiO2 is as follows:

[0051]

[0052] The synthetic route of the polymer drag-reducing agent of the present invention is as follows:

[0053]

[0054]

[0055] The polymer drag-reducing agent obtained by this invention has the general structural formula shown in Formula I:

[0056]

[0057] Where x is an acrylic monomer, m, n, p, y, and z are the monomer molar ratios, and m+n+p+y+z=1.

[0058] According to some preferred embodiments, in step (1): the organic solvent is one or a combination of two or more of anhydrous ethanol, ethyl acetate, acetone, and toluene; the silane coupling agent is one or a combination of two or more of 3-butenetriethoxysilane, 3-(isobutenoyloxy)propyltrimethoxysilane, and 3-(1,3-dimethylbutene)aminopropyltriethoxysilane; the amounts of each substance, by weight, are: 5-7 parts of organic solvent (e.g., 5 parts, 6 parts, 7 parts), and silane... Alkane coupling agent 1.1-2.1 parts (e.g. 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2.0 parts, 2.1 parts), ammonia water 0.8-1.5 parts (e.g. 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts), nano SiO2 15-20 parts (e.g. 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts).

[0059] According to some preferred embodiments, in step (3), the acrylic monomer is one or a combination of two or more of acrylic acid, vinyl acrylic acid, acrylic anhydride acetate, N-isopropylacrylamide, and 2-ethylacrylic acid; the molecular weight regulator is one or a combination of two or more of tetrachloromethane, dodecanethiol, butyl 3-mercaptopropionate, methylstyrene resin, and sodium salicylate; the strength regulator is one or a combination of two or more of isopropanol, pentafluoropentanol, α-methylstyrene, and isooctyl 3-mercaptopropionate; and the toughening agent is one or a combination of two or more of sodium acetate, sodium sulfate, trichloroethane, and chlorobutane.

[0060] According to some preferred embodiments, in step (3), the amounts of each substance, by weight, are: 180-240 parts of acrylamide (e.g., 180, 190, 200, 210, 220, 230, or 240 parts), 30-60 parts of acrylic monomers (e.g., 30, 35, 40, 45, 50, 55, or 60 parts), and 15-25 parts of N-phenylethyl-N-tetradecylmethylacrylamide (e.g., 15, 1...). 6 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts or 25 parts), 20-40 parts (e.g., 20 parts, 25 parts, 30 parts, 35 parts or 40 parts) of octadecyl dimethacryloyl ammonium chloride, 10-15 parts (e.g., 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts) of molecular weight regulator, 45-60 parts (e.g., 45 parts, 50 parts, 55 parts or 60 parts) of strength regulator, modified nano-SiO2 5-15 parts (e.g., 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 parts), 0.002-0.010 parts of initiator (e.g., 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005, 0.0055 or 0.006 parts), 25-55 parts of toughening agent (e.g., 25, 30, 35, 40, 45, 50, 55 or 60 parts), 469-610 parts of water (e.g., 469, 470, 475, 485, 505, 525, 545, 565, 585, 605 or 610 parts).

[0061] According to some preferred embodiments, in step (4), the stirring speed is 120-480 rpm (e.g., 120 rpm, 200 rpm, 280 rpm, 360 rpm, 440 rpm, 360 rpm, 400 rpm, 440 rpm or 480 rpm); the stirring time is 3-5 h (e.g., 3 h, 3.5 h, 4 h, 4.5 h or 5 h); and the stirring temperature is 20-30 °C (20 °C, 22 °C, 24 °C, 26 °C, 28 °C or 30 °C).

[0062] According to some preferred embodiments, in step (4), the pH of the aqueous mixture is adjusted to 7.2-9.2 (e.g., 7.2, 7.6, 8.0, 8.4 or 9.2) using a pH adjuster, wherein the pH adjuster is one or a combination of two or more of sodium hydroxide, ammonia, and sodium carbonate.

[0063] According to some preferred embodiments, in step (5), the initiator is one or a combination of two or more of ammonium persulfate, potassium persulfate, sodium bisulfite, ferrous ammonium sulfate, and tert-butyl hydroperoxide; the initiation temperature of the polymerization reaction is 10-20°C (e.g., 10°C, 15°C, or 20°C); the polymerization reaction time is 3-6 h (e.g., 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, or 6 h); during the polymerization reaction, the reaction temperature increases at a rate of 0.1-0.4°C / min (e.g., 0.1°C / min, 0.2°C / min, 0.3°C / min, or 0.4°C / min).

[0064] The present invention will now be described in detail with reference to specific embodiments.

[0065] Example 1: Preparation of Modified Nano-SiO2

[0066] This embodiment provides a modified nano-SiO2, the preparation method of which is as follows:

[0067] Formula (by weight):

[0068] 17 parts nano SiO2, 1.5 parts 3-(1,3-dimethylbutene)aminopropyltriethoxysilane, 5 parts anhydrous ethanol, and 1.2 parts ammonia.

[0069] Preparation method:

[0070] S1: Nano-SiO2 is dispersed in anhydrous ethanol in an ultrasonic cleaner, and then 3-(1,3-dimethylbutene)aminopropyltriethoxysilane and ammonia are added successively.

[0071] S2: Under a nitrogen atmosphere, react at 50°C for 24 hours. Remove excess solvent by vacuum distillation. Separate the modified SiO2 using a centrifuge, wash with anhydrous ethanol, and centrifuge again. Repeat the above steps multiple times to purify the product. Finally, dry the pure nano-SiO2 in an oven at 50°C for 24 hours to obtain modified nano-SiO2.

[0072] Example 2

[0073] This embodiment provides a polymer drag-reducing agent, the preparation method of which is as follows:

[0074] Formula (by weight):

[0075] 200 parts acrylamide, 45 parts acrylic acid, 22 parts N-phenylethyl-N-tetradecylmethylacrylamide, 34 parts octadecyldimethylacryloylammonium chloride, 12 parts dodecanethiol, 50 parts isopropanol, 13 parts modified nano-SiO2 of Example 1, 0.005 parts ammonium persulfate, 0.002 parts sodium bisulfite, 32 parts sodium acetate, and 521.8 parts deionized water.

[0076] Preparation method:

[0077] S1: Acrylamide, acrylic acid, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, dodecyl mercaptan, isopropanol, sodium acetate and deionized water are mixed in a certain mass ratio to obtain an aqueous solution;

[0078] S2: Add modified nano-SiO2 particles and stir at 280 rpm for 3 hours at 25°C;

[0079] S3: Use sodium hydroxide solution to adjust the pH of the entire system to a weakly alkaline pH of 8.4;

[0080] S4: Under a nitrogen atmosphere, ammonium persulfate and sodium bisulfite were added, and the polymerization reaction was started at 15°C. The reaction temperature was increased at 0.2°C / min. After 4 hours of reaction, the product was washed with anhydrous ethanol, dried, pulverized, and sieved to obtain the polymer drag reducer.

[0081] Example 3

[0082] This embodiment provides a polymer drag-reducing agent, the preparation method of which is as follows:

[0083] Formula (by weight):

[0084] 211 parts acrylamide, 41 parts vinyl acrylic acid, 18 parts N-phenylethyl-N-tetradecylmethylacrylamide, 29 parts octadecyldimethylacryloylammonium chloride, 11 parts tetrachloromethane, 50 parts pentafluoropentanol, 12 parts modified nano-SiO2 of Example 1, 0.005 parts potassium persulfate, 0.002 parts ferrous ammonium sulfate, 28 parts sodium sulfate, and 546.4 parts deionized water.

[0085] Preparation method:

[0086] S1: Acrylamide, vinyl acrylic acid, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, tetrachloromethane, pentafluoropentanol, sodium sulfate and deionized water are mixed in a certain mass ratio to obtain an aqueous solution;

[0087] S2: Add modified nano-SiO2 particles and stir at 320 rpm for 4 hours at 25°C;

[0088] S3: Use sodium hydroxide solution to adjust the pH of the entire system to a weakly alkaline pH of 8;

[0089] S4: Under a nitrogen atmosphere, an initiator is added to initiate the polymerization reaction. The polymerization reaction begins at 15°C, and the reaction temperature increases at a rate of 0.3°C / min. After 3.5 hours of reaction, the product is washed with anhydrous ethanol, dried, pulverized, and sieved to obtain the polymer drag reducer.

[0090] Example 4

[0091] This embodiment provides a polymer drag-reducing agent, the preparation method of which is as follows:

[0092] Formula (by weight):

[0093] 190 parts acrylamide, 37 parts acetic acid acrylic anhydride, 18 parts N-phenylethyl-N-tetradecylmethylacrylamide, 35 parts octadecyldimethylacryloylammonium chloride, 14 parts 3-mercaptopropionic acid butyl ester, 48 parts α-methylstyrene, 8 parts modified nano-SiO2 of Example 1, 0.005 parts potassium persulfate, 0.002 parts tert-butyl hydrogen peroxide, 47 parts trichloroethane and 512.8 parts deionized water.

[0094] Preparation method:

[0095] S1: Acrylamide, acrylic anhydride acetate, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, butyl 3-mercaptopropionate, α-methylstyrene, trichloroethane and deionized water are mixed in a certain mass ratio to obtain an aqueous solution.

[0096] S2: Add modified nano-SiO2 particles and stir at 360 rpm for 3.5 h at 30 °C;

[0097] S3: Use ammonia solution to adjust the pH of the entire system to a weakly alkaline pH of 7.6;

[0098] S4: Under a nitrogen atmosphere, an initiator is added to initiate the polymerization reaction. The polymerization reaction begins at 20°C, and the reaction temperature increases at a rate of 0.4°C / min. After 3 hours of reaction, the product is washed, dried, pulverized, and sieved with anhydrous ethanol to obtain the polymer drag reducer.

[0099] Example 5

[0100] This embodiment provides a polymer drag-reducing agent, the preparation method of which is as follows:

[0101] Formula (by weight):

[0102] 208 parts acrylamide, 51 parts acetic acid acrylic anhydride, 21 parts N-phenylethyl-N-tetradecylmethylacrylamide, 37 parts octadecyldimethylacryloylammonium chloride, 11 parts methylstyrene resin, 54 parts isooctyl 3-mercaptopropionate, 11 parts modified nano-SiO2 of Example 1, 0.005 parts ammonium persulfate, 0.002 parts tert-butyl hydrogen peroxide, 29 parts chlorobutane, and 487.6 parts deionized water.

[0103] Preparation method:

[0104] S1: Acrylamide, acrylic anhydride acetate, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, methylstyrene resin, isooctyl 3-mercaptopropionate, chlorobutane and deionized water are mixed in a certain mass ratio to obtain an aqueous solution.

[0105] S2: Add modified nano-SiO2 particles and stir at 480 rpm for 5 h at 28℃;

[0106] S3: Use ammonia solution to adjust the pH of the entire system to a weakly alkaline pH of 7.8;

[0107] S4: Under a nitrogen atmosphere, an initiator is added to initiate the polymerization reaction. The polymerization reaction begins at 18°C, and the reaction temperature increases at a rate of 0.2°C / min. After 4.5 hours of reaction, the product is washed with anhydrous ethanol, dried, pulverized, and sieved to obtain the polymer drag reducer.

[0108] Example 6

[0109] This embodiment provides a polymer drag-reducing agent, the preparation method of which is as follows:

[0110] Formula (by weight):

[0111] 230 parts acrylamide, 38 parts 2-ethylacrylic acid, 25 parts N-phenylethyl-N-tetradecylmethylacrylamide, 41 parts octadecyldimethylacryloylammonium chloride, 13.5 parts sodium salicylate, 49 parts isopropanol, 11 parts modified nano-SiO2 of Example 1, 0.005 parts ammonium persulfate, 0.002 parts sodium bisulfite, 48 parts sodium acetate, and 566.7 parts deionized water.

[0112] Preparation method:

[0113] S1: Acrylamide, 2-ethylacrylic acid, N-phenylethyl-N-tetradecylmethylacrylamide, octadecyldimethylacryloylammonium chloride, sodium salicylate, isopropanol, chlorobutane and deionized water are mixed in a certain mass ratio to obtain an aqueous solution;

[0114] S2: Add modified nano-SiO2 particles and stir at 480 rpm for 5 h at 28℃;

[0115] S3: Use ammonia solution to adjust the pH of the entire system to a weakly alkaline pH of 7.8;

[0116] S4: Under a nitrogen atmosphere, an initiator is added to initiate the polymerization reaction. The polymerization reaction begins at 20°C, and the reaction temperature increases at a rate of 0.1°C / min. After 6 hours of reaction, the product is washed, dried, pulverized, and sieved with anhydrous ethanol to obtain the polymer drag reducer.

[0117] Comparative Example 1

[0118] This comparative example provides a polymer drag reducer, which is prepared in the same way as in Example 2, except that no modified nano-SiO2 was added in Comparative Example 1.

[0119] The drag-reducing agent prepared in this comparative example is a quaternary copolymer with a linear molecular structure.

[0120] Comparative Example 2

[0121] This comparative example provides a polymer drag reducer, which is prepared in the same way as in Example 2, except that no strength modifier is added in Comparative Example 2.

[0122] The polymer prepared in this comparative example has a lower apparent viscosity and poorer viscoelastic properties.

[0123] Comparative Example 3

[0124] This comparative example provides a polymer drag-reducing agent, which is prepared in the same way as in Example 2, except that no toughening agent is added in Comparative Example 3.

[0125] The polymer prepared in this comparative example has poor elasticity, which is not conducive to reducing drag and carrying sand in fracturing fluid.

[0126] Comparative Example 4

[0127] This comparative example provides a polymer drag reducer, which is prepared in the same way as in Example 2, except that in Comparative Example 4, zirconium lactate crosslinking agent is used instead of modified nano-SiO2.

[0128] The polymer prepared in this comparative example does not possess the special star-shaped multi-arm structure.

[0129] Comparative Example 5

[0130] This comparative example provides a polymer drag reducer, which is prepared in the same way as in Example 2, except that in Comparative Example 5, zirconium citrate crosslinking agent is used instead of modified nano-SiO2.

[0131] The polymer prepared in this comparative example does not possess the special star-shaped multi-arm structure.

[0132] Comparative Example 6

[0133] This comparative example provides a polymer drag reducer, which is prepared in the same way as in Example 2, except that in Comparative Example 6, unmodified nano-SiO2 is used instead of modified nano-SiO2.

[0134] This comparative example uses unmodified nano-SiO2 to prepare polymer drag reducers. Since no unsaturated double bonds are introduced on the surface of SiO2, it cannot be used as a functional monomer to copolymerize with other monomers, and the prepared polymer does not have a special structure.

[0135] Performance testing

[0136] The polymer drag-reducing agents of the above examples and comparative examples were evaluated for their performance. Their apparent viscosity and drag reduction rate in brine with a salinity of 80,000 were tested. The experimental results are shown in Table 1.

[0137] Experimental methods:

[0138] 1. Preparation of saline solution: The 80,000 ppm saline solution used in this experiment is prepared from sodium chloride, magnesium chloride, calcium chloride and deionized water. The concentration of sodium chloride is 40,000 ppm, the concentration of magnesium chloride is 20,000 ppm and the concentration of calcium chloride is 20,000 ppm.

[0139] 2. Apparent viscosity: Weigh 2.00g of drag-reducing agent sample and dissolve it in 500.00g of the above-mentioned 80,000 salinity brine. Use a high-speed stirrer to stir at 1500rpm for 3min. Use a six-speed viscometer to test its apparent viscosity in mPa·s.

[0140] 3. Drag Reduction Rate: The drag reduction rate of the drag-reducing agent sample in brine with a salinity of 80,000 was tested using a circulating pipeline friction test system. The mass fraction of the drag-reducing agent sample was 0.1%, and the test cycle time was 60 minutes. Before the experiment, the experimental pipeline was thoroughly cleaned with tap water, and the pressure difference of the tap water was measured. After adding a certain amount of test sample, the pressure difference of the sample solution was measured again. The pressure difference and flow rate values ​​at different flow velocities were recorded. After each flow rate adjustment, three values ​​were read after the readings stabilized, and the average value was taken as the final result. All experiments were conducted under turbulent conditions. After the test, when it was necessary to replace the sample, the testing device was thoroughly cleaned to minimize residual material. Unless otherwise specified, all tests were conducted in a 0.008m pipeline at room temperature (approximately 25°C). The drag reduction rate calculation formula is:

[0141] DR=(△P1-△P2) / △P1×100;

[0142] △P1 is the frictional pressure difference when brine flows through the pipeline, in Pascals (Pa);

[0143] △P2 is the frictional pressure difference when the salt solution with added drag-reducing agent flows through the pipeline, in Pascals (Pa);

[0144] DR represents the drag reduction rate of the drag-reducing agent, expressed as a percentage.

[0145] Table 1. Test results of drag reduction performance of drag-reducing agents

[0146] Drag reducing agent Apparent viscosity Initial drag reduction Drag reduction at 60 min Example 2 52 mPa-s 76.21％ 74.28％ Example 3 48 mPa-s 72.83％ 70.54％ Example 4 47 mPa-s 74.41％ 71.28％ Example 5 50 mPa-s 72.59％ 70.37％ Example 6 44 mPa-s 69.21％ 66.72％ Comparative Example 1 47 mPa-s 57.39％ 54.84％ Comparative Example 2 43 mPa-s 62.81％ 59.71％ Comparative Example 3 5 mPa-s 63.29％ 60.24％ Comparative Example 4 49 mPa-s 67.45％ 63.34％ Comparative Example 5 51 mPa-s 65.39％ 62.73％ Comparative Example 6 43 mPa-s 66.28％ 65.56％

[0147] As shown in Table 1, the multi-arm polymer drag reducer centered on nano-SiO2 prepared in this invention exhibits good apparent viscosity, maintains high viscoelasticity, excellent shear resistance, excellent salt resistance, and good drag reduction performance in 80,000% salinity brine. After 60 minutes of cycling in a drag reduction tester, it still maintains a high drag reduction rate, and the drag reduction rate does not decrease with long-term cyclic shearing. This indicates that its long-term shear resistance and salt resistance in high-salinity brine are excellent, effectively maintaining structural stability, with a high drag reduction rate retention rate and excellent long-term drag reduction effect.

[0148] As shown in Comparative Example 1, the present invention uses modified nano-SiO2 as a functional monomer to copolymerize with acrylamide, acrylic acid, and hydrophobic and salt-resistant monomers to prepare a copolymer with a special structure. The copolymer uses nano-silica particles as the central skeleton, and the branches composed of other monomers are connected with silica to form a star-shaped molecular structure. Compared with the linear molecule without nano-silica (Comparative Example 1), its molecular structure is more stable in high-mineralized salt water, and its drag reduction performance is better.

[0149] Comparative Examples 2 and 3 show that strength modifiers and toughening agents can effectively improve the overall performance of polymer drag reducers. Comparative Examples 4 and 5 show that, without adding modified nano-SiO2, the performance of polymer drag reducers can also be improved by introducing different types of organic zirconium crosslinking agents (zirconium citrate and zirconium lactate). However, in practical applications, the crosslinking ratio, temperature, pH value, and shear rate of the crosslinking agent will directly affect the crosslinking effect, and its application conditions are relatively limited. At the same time, the high production cost also limits its large-scale use.

[0150] As shown in Comparative Example 6, compared with surface-modified nano-SiO2, conventional nano-SiO2, although not participating in the copolymerization reaction as a monomer and unable to form a special structure centered on SiO2, contains a large number of hydroxyl groups on its surface that can form hydrogen bonds with the amide groups on the polymer molecular chain, thereby improving the strength of the polymer molecular structure. In addition, hydroxyl groups, as hydrophilic groups, can also inhibit polymer hydrolysis, and the introduction of rigid particles can also improve the overall storage modulus of the system. Therefore, unmodified nano-SiO2 can improve the performance of polymer molecules to a certain extent. Its thickening and drag-reducing properties under high salinity conditions are stronger than those of Comparative Example 1 without SiO2, but weaker than those of the example with modified nano-SiO2.

Claims

1. A method for preparing a polymer drag-reducing agent, comprising: S1: Modified nano-silica is obtained by modifying nano-silica with a silane coupling agent. S2: Dissolve the following parts by weight of raw materials in water to obtain an aqueous solution: 180-240 parts of acrylamide, 30-60 parts of acrylic monomers, 10-30 parts of salt-resistant monomers, and 20-40 parts of hydrophobic monomers. S3: Add 5-15 parts by weight of the modified nano-silica to the aqueous solution and stir thoroughly. Then adjust the pH value to weakly alkaline and add an initiator under a protective atmosphere to initiate the polymerization reaction, thereby obtaining the polymer drag reducer.

2. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, In S1, the modification treatment of the nano-silica includes the following steps: Nano-silica, silane coupling agent, and ammonia water in a mass ratio of 15-20:1-2.1:0.8-1.5 are brought into full contact in an organic solvent to carry out a modification reaction, thereby obtaining the modified nano-silica.

3. The method for preparing the polymer drag-reducing agent according to claim 2, wherein, The silane coupling agent includes one or more combinations of 3-butenetriethoxysilane, 3-(isobutenoyloxy)propyltrimethoxysilane, and 3-(1,3-dimethylbutene)aminopropyltriethoxysilane.

4. The method for preparing the polymer drag-reducing agent according to claim 2, wherein, The organic solvent includes one or more of anhydrous ethanol, ethyl acetate, acetone, and toluene; And / or, the mass ratio of the organic solvent to the modified nano-silica is 5-7:15-20.

5. The method for preparing the polymer drag-reducing agent according to claim 2, wherein, The modification reaction is carried out at a temperature of 45-65℃ for a time of 18-32 hours. And / or, the modification treatment of the nano-silica further includes: separating the solid products from the reaction solution of the modification reaction, washing, purifying and drying them, thereby obtaining the modified nano-silica.

6. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, The acrylic monomers include one or more of acrylic acid, vinyl acrylic acid, acrylic anhydride acetate, N-isopropylacrylamide, and 2-ethylacrylic acid.

7. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, The salt-resistant monomer includes one or more of N-phenylethyl-N-tetradecylmethylacrylamide, N,N-diethylacrylamide, methacryloyloxyethyltrimethylammonium chloride, and acryloyloxyethyltrimethylammonium chloride.

8. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, The hydrophobic monomer includes one or more of the following: octadecyl dimethylacryloyl ammonium chloride, 2-isopropyl-2-adamantyl methacrylate, octadecyl methacrylate, dodecyl methacrylate, and octadecyl acrylate.

9. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, In S2, the raw material further includes one or more of the following: molecular weight regulator, strength regulator, and toughening agent; And / or, in S2, the raw materials further include: 10-15 parts of molecular weight regulator, 45-60 parts of strength regulator, and 25-55 parts of toughening agent.

10. The method for preparing the polymer drag-reducing agent according to claim 9, wherein, The molecular weight regulator includes one or more of tetrachloromethane, dodecanethiol, butyl 3-mercaptopropionate, methylstyrene resin, and sodium salicylate. And / or, the strength modifier is one or a combination of two or more of isopropanol, pentafluoropentanol, α-methylstyrene, and isooctyl 3-mercaptopropionate; And / or, the toughening agent is one or a combination of two or more of sodium acetate, sodium sulfate, trichloroethane, and chlorobutane.

11. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, In S3, the pH value of the adjusted aqueous solution is 7.2-9.2; And / or, the pH adjusters used include one or more of sodium hydroxide, ammonia, and sodium carbonate; And / or, in S3, after adding modified nano-silica, the stirring speed is 120-480 rpm, the time is 3-5 h, and the stirring temperature is 20-25℃.

12. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, In S3, the polymerization reaction is initiated at a temperature of 10-20°C and the reaction time is 3-6 hours. And / or, during the polymerization reaction, the reaction temperature is controlled to increase at a rate of 0.1-0.4℃ / min.

13. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, The initiator includes one or more of ammonium persulfate, potassium persulfate, sodium bisulfite, ferrous ammonium sulfate, and tert-butyl hydroperoxide.

14. The method for preparing the polymer drag-reducing agent according to claim 1, wherein, The mass ratio of the initiator to the modified nano-silica is 0.002-0.01:15-20.

15. A polymer drag-reducing agent, which is prepared by the method of any one of claims 1-14.

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