A high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent and a preparation method thereof

Abstract

The application relates to a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent and a preparation method thereof, relates to the technical field of oilfield chemistry and fine chemistry, and comprises the following steps: crosslinking and polymerizing non-ionic monomers and a crosslinking agent under the action of an initiator to form a first network structure, and utilizing a flexible polymer filled in the first network structure to form a second network structure. The flexible polymer is alkyl phenol polyoxyethylene ether. The flexible chain in the alkyl phenol polyoxyethylene ether structure still retains the function of a "sacrificial bond", can absorb the damage of high shear and high temperature to the rigid network structure, and enables the system to still have good resistance performance under the condition of no metal crosslinking. Meanwhile, due to the existence of benzene rings in the alkyl phenol polyoxyethylene ether structure, the pi-pi stacking effect can be increased on the basis, the intermolecular force is strengthened, and the resistance of the double-network structure is further improved. The double-network fracturing fluid thickening agent is simple in preparation, excellent in performance and high in practical value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield chemistry and fine chemistry, in particular to a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for oil and gas and the continuous improvement of oil and gas exploration and development level, low-porosity and low-permeability reservoirs have become the main target and technical research object of exploration and development. Hydraulic fracturing technology is an important technical measure for increasing production of oil and gas wells and injection of water injection wells. With the large-scale development of low-permeability oil and gas reservoirs in China, the performance research of fracturing fluid is becoming more and more important. The performance of fracturing fluid not only directly affects the success rate of fracturing operation, but also has a great influence on the fracturing effect. When developing low-permeability oil and gas fields by using fracturing technology, if sea water or oilfield produced water is used to prepare fracturing fluid, the cost can be greatly reduced, but sea water or oilfield produced water has high salinity, so it is urgent to develop a fracturing fluid system suitable for high salinity environment. Thickening agent is one of the most basic additives in fracturing fluid, and its thickening ability, thermal stability and shear stability are the main indicators for evaluating its quality, and are also one of the most important factors affecting the performance of fracturing fluid and the fracturing effect.

[0003] The inventor's prior patent CN109438618A discloses a temperature-resistant and salt-resistant double-network structure fracturing fluid thickening agent and a preparation method thereof. The temperature-resistant and salt-resistant double-network structure fracturing fluid thickening agent is formed by reacting a non-ionic monomer and a crosslinking agent to form a first network structure, and a salt-resistant monomer filled in the first network structure to form a second network structure. The fracturing fluid thickening agent exhibits excellent temperature-resistant and shear-resistant performance. Under the condition of 120℃, 170s -1 -1, the viscosity is reduced by about 50% compared with 10min, and finally stabilized at 200mPa·s. In CN112574735A, a functional polymer polyvinyl ester substance is used to replace the salt-resistant monomer, which effectively improves the temperature-resistant performance of the fracturing fluid thickening agent. In the past research, it is found that there is still great potential for the double-network structure fracturing fluid thickening agent, and it is imperative to continuously improve it to develop a new generation of products with more excellent performance. SUMMARY

[0004] The purpose of the present application is to provide a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent, which has a novel structure and excellent performance, and exhibits better salt-resistant and shear-resistant performance compared with the prior art.

[0005] Another object of the present application is to provide a preparation method of the high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent, which is simple and convenient to operate and can be used to quickly and efficiently prepare the high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent.

[0006] Embodiments of the present application are implemented as follows:

[0007] A high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent comprises a first network structure formed by cross-linking polymerization of non-ionic monomers and a cross-linking agent under the action of an initiator, and a second network structure composed of flexible polymers filled in the first network structure; wherein the non-ionic monomers are at least one of acrylamide and modified acrylamide, and the flexible polymers are alkyl phenol polyoxyethylene ether.

[0008] A preparation method of the double-network fracturing fluid thickening agent comprises the following steps:

[0009] The non-ionic monomers, the flexible polymers, and the cross-linking agent are mixed under an inert atmosphere to obtain a raw material mixture;

[0010] The raw material mixture is mixed with the initiator, and cross-linking polymerization reaction is carried out under an inert atmosphere.

[0011] The embodiments of the present application have the following beneficial effects:

[0012] The embodiments of the present application provide a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent and a preparation method thereof, which forms a first network structure by cross-linking polymerization of non-ionic monomers and a cross-linking agent under the action of an initiator, and forms a second network structure by filling flexible polymers in the first network structure. The non-ionic monomers are at least one of acrylamide and modified acrylamide, and the flexible polymers are alkyl phenol polyoxyethylene ether. The flexible segment in the structure of alkyl phenol polyoxyethylene ether still retains the function of a "sacrificial bond" and can absorb the damage of high shear and high temperature to the rigid network structure, so that the system can still have good resistance performance without metal cross-linking. At the same time, due to the presence of benzene rings in the structure of alkyl phenol polyoxyethylene ether, the π-π stacking effect can be increased on the basis of the original, and the intermolecular force can be strengthened, so that the resistance of the double-network structure is further improved. The double-network fracturing fluid thickening agent is simple to prepare, has excellent performance, and has good practical value. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0014] Figure 1 The results of the influence of monovalent potassium ions on the viscosity of the fracturing fluid thickening agent provided in Test Example 1 of the present application, wherein the ordinate represents viscosity (unit: mPa·s) and the abscissa represents salinity (unit: ×10 4 ppm);

[0015] Figure 2 The results of the influence of divalent calcium ions on the viscosity of the fracturing fluid thickening agent provided in Test Example 1 of the present application, wherein the ordinate represents viscosity (unit: mPa·s) and the abscissa represents salinity (unit: ×10 4 ppm). DETAILED DESCRIPTION

[0016] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by manufacturers are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by market purchase.

[0017] A high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent, a preparation method thereof, and an application thereof will be described in detail below.

[0018] A high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent includes a first network structure formed by cross-linking polymerization of non-ionic monomers and a cross-linking agent under the action of an initiator, and a second network structure composed of a flexible polymer filled in the first network structure; wherein the non-ionic monomer is at least one of acrylamide and modified acrylamide, and the flexible polymer is an alkyl phenol polyoxyethylene ether.

[0019] The flexible segment in the structure of the alkyl phenol polyoxyethylene ether still retains the function of a "sacrificial bond", which can absorb the damage of high shear and high temperature to the rigid network structure, so that the system can still have good tolerance performance without metal cross-linking. At the same time, due to the presence of benzene rings in the structure of the alkyl phenol polyoxyethylene ether, the π-π stacking effect can be increased on the basis of the original, and the intermolecular force is strengthened, so that the tolerance of the double-network structure is further improved.

[0020] Alternatively, the alkyl phenol polyoxyethylene ether includes at least one of nonyl phenol polyoxyethylene ether, octyl phenol polyoxyethylene ether, and dodecyl phenol polyoxyethylene ether. These alkyl phenol polyoxyethylene ethers are all mature products that can be directly obtained commercially, and the raw material sources are more extensive.

[0021] Further, the modified acrylamide includes N-aryl acrylamide. The N-aryl acrylamide is a product in which the N-H bond on the amino group of acrylamide is replaced by an aryl compound, including a phenyl group and a substituted phenyl group, which is a product in which the hydrogen on the benzene ring is replaced by an alkyl group, an alkoxy group, a hydroxyl group, an amino group, a nitro group, a halogen, or the like, and can be a monosubstituted product or a polysubstituted product. Alternatively, the modified acrylamide is at least one of N-phenyl acrylamide, N-(4-aminophenyl) acrylamide, N-(2-aminophenyl) acrylamide, 3-nitro-N-acrylaniline, N-(2-chlorophenyl) acrylamide, N-(4-chlorophenyl) acrylamide, and N-(p-tolyl) acrylamide, all of which are commercially available raw materials and are more widely available. By introducing a benzene ring into the modified acrylamide, a benzene ring can also exist in the first network structure, so that the flexible compound in the second network structure can also be subjected to π-π stacking, further strengthening the intermolecular force.

[0022] Further, as the content of the benzene ring increases, the viscosity of the entire system increases after the intermolecular force is strengthened, and during the crosslinking reaction, a mixture of acrylamide and modified acrylamide can be used as a non-ionic monomer to copolymerize to form the first network structure. The viscosity range of the entire system can be adjusted by adjusting the ratio between acrylamide and modified acrylamide.

[0023] Alternatively, the crosslinking agent is N,N'-methylenebisacrylamide. The crosslinking agent can form a covalent bridge between the polymer chains to form a network structure. The initiator is at least one of ammonium persulfate, potassium persulfate, and sodium percarbonate. The initiator is used to initiate the free radical reaction.

[0024] The embodiment of the present application also provides a preparation method of the double-network fracturing fluid thickener.

[0025] S1. The non-ionic monomer, the flexible polymer, and the crosslinking agent are mixed under an inert atmosphere to obtain a raw material mixture.

[0026] S2. The raw material mixture is mixed with the initiator, and a crosslinking polymerization reaction is carried out under an inert atmosphere.

[0027] Further, the inert atmosphere can be obtained by using nitrogen, helium, argon, or the like. The inert gas is directly introduced into the reaction container to remove oxygen.

[0028] Optionally, the concentration of the nonionic monomer in the dual-network fracturing fluid thickening agent is 2.5wt%-5wt%. When the concentration of the nonionic monomer is low, the degree of polymerization is low or even no polymerization occurs; when the concentration of the nonionic monomer is too high, the system forms a solid gel with poor fluidity. The inventors have found through tests that when the concentration is in the range of 2.5wt%-5wt%, the viscosity, fluidity, solubility and other comprehensive properties of the product are better.

[0029] Further, the mass ratio of the nonionic monomer, the flexible polymer, the crosslinking agent and the initiator is 1:(0.05-0.1):(0.0002-0.0005):(0.025-0.05). The crosslinking agent forms a network structure by crosslinking the linear polymer chain segments, and has a great influence on the viscosity of the system. When the amount of the crosslinking agent is too small, the network structure formed is sparse and unstable; when the amount of the crosslinking agent is too large, the network structure is tightly intertwined, resulting in loss of fluidity of the system and complete solidification. The flexible polymer is used to form a second network structure. When the amount of the flexible polymer is too small, the dual-network structure is difficult to form, resulting in poor stability of the dual-network structure and low viscosity; when the amount of the flexible polymer is too large, the density of the flexible network chain segments intertwined on the rigid structure is too high, resulting in that the molecular chains of the system cannot freely extend. Through condition screening, when the ratio is in the above range, the viscosity of the product formed is moderate, and the overall performance is better.

[0030] Optionally, the temperature for mixing the nonionic monomer, the flexible polymer and the crosslinking agent is 80-90℃, the mixing time is 1-3h, and after mixing is completed, the mixture is cooled to room temperature for use. Under this condition, the substances can be dissolved and mixed, so that the substances can be fully dispersed and mixed more uniformly.

[0031] Further, the crosslinking polymerization reaction is carried out at 30-50℃ for 20-30h. The free radical polymerization reaction is an exothermic reaction, and low temperature is conducive to obtaining high-viscosity polymers with high molecular weight, but the decomposition rate and conversion rate of the initiator are low, and low-viscosity polymers or even no polymerization occurs; when the temperature is too high, the free radical chain coupling termination of the initiator is accelerated, and the viscosity of the system is reduced. Under the above temperature and reaction time, the reaction effect is better.

[0032] The features and properties of the application are further described in detail below in combination with examples.

[0033] Example 1

[0034] This example provides a high-salt-resistant and shear-resistant dual-network fracturing fluid thickening agent, and a preparation method thereof is as follows:

[0035] S1. Add deionized water and nonylphenol polyoxyethylene ether into a reaction kettle in sequence, heat to 90℃, stir for 2h to dissolve, and then cool to room temperature; then add N-phenylacrylamide, stir for 5min, and then add N,N'-methylenebisacrylamide, stir for 5min, and then introduce nitrogen into the reaction kettle.

[0036] S2. Stop introducing nitrogen after 1h, add potassium persulfate, stir for 2min, heat to 30℃, and then continue to react for 30h under a nitrogen atmosphere to obtain the double-network fracturing fluid thickening agent.

[0037] The concentration of the N-phenylacrylamide is 2.5wt%, and the mass ratio of the N-phenylacrylamide, nonylphenol polyoxyethylene ether, N,N'-methylenebisacrylamide, and potassium persulfate is 1:0.05:0.0003:0.04.

[0038] Example 2

[0039] The present example provides a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent, and a preparation method thereof.

[0040] S1. Add deionized water and nonylphenol polyoxyethylene ether into a reaction kettle in sequence, heat to 90℃, stir for 2h to dissolve, and then cool to room temperature; then add N-phenylacrylamide, stir for 5min, and then add N,N'-methylenebisacrylamide, stir for 5min, and then introduce nitrogen into the reaction kettle.

[0041] S2. Stop introducing nitrogen after 1h, add potassium persulfate, stir for 2min, heat to 30℃, and then continue to react for 30h under a nitrogen atmosphere to obtain the double-network fracturing fluid thickening agent.

[0042] The concentration of the N-phenylacrylamide is 2.5wt%, and the mass ratio of the N-phenylacrylamide, nonylphenol polyoxyethylene ether, N,N'-methylenebisacrylamide, and potassium persulfate is 1:0.05:0.0003:0.04.

[0043] Example 3

[0044] The present example provides a high-salt-resistant and shear-resistant double-network fracturing fluid thickening agent, and a preparation method thereof.

[0045] S1. Add deionized water and nonylphenol polyoxyethylene ether into a reaction kettle in sequence, heat to 90℃, stir for 2h to dissolve, and then cool to room temperature; then add N-phenylacrylamide, stir for 5min, and then add N,N'-methylenebisacrylamide, stir for 5min, and then introduce nitrogen into the reaction kettle.

[0046] S2. After 1 hour, stop the nitrogen gas supply, add ammonium persulfate and stir for 2 minutes, raise the temperature to 50°C, and continue the reaction for 20 hours under a nitrogen atmosphere to obtain the dual-network fracturing fluid thickener.

[0047] The concentration of N-(4-aminophenyl)acrylamide is 5 wt%, and the mass ratio of N-(4-aminophenyl)acrylamide, octylphenol polyoxyethylene ether, N,N'-methylenebisacrylamide, and ammonium persulfate is 1:0.1:0.0003:0.05.

[0048] Example 4

[0049] This embodiment provides a highly salt-resistant and shear-resistant dual-network fracturing fluid thickener, the preparation method of which is as follows:

[0050] S1. Add deionized water and octylphenol polyoxyethylene ether to the reactor in sequence, heat to 80°C, stir for 1 hour to dissolve, and then cool to room temperature; then add N-(2-chlorophenyl)acrylamide, stir for 5 minutes, then add N,N'-methylenebisacrylamide, stir to dissolve for 5 minutes, and then introduce nitrogen gas into the reactor.

[0051] S2. After 1 hour, stop the nitrogen flow, add ammonium persulfate and stir for 2 minutes, raise the temperature to 40°C, and continue the reaction under nitrogen atmosphere for 24 hours to obtain the dual-network fracturing fluid thickener.

[0052] The concentration of N-(2-chlorophenyl)acrylamide is 4 wt%, and the mass ratio of N-(2-chlorophenyl)acrylamide, octylphenol polyoxyethylene ether, N,N'-methylenebisacrylamide, and ammonium persulfate is 1:0.05:0.0002:0.025.

[0053] Example 5

[0054] This embodiment provides a highly salt-resistant and shear-resistant dual-network fracturing fluid thickener, the preparation method of which is as follows:

[0055] S1. Add deionized water and dodecylphenol polyoxyethylene ether to the reactor in sequence, heat to 85°C, stir for 1 hour to dissolve, and then cool to room temperature; then add acrylamide and N-phenylacrylamide, stir for 5 minutes, then add N,N'-methylenebisacrylamide, stir to dissolve for 5 minutes, and then introduce nitrogen gas into the reactor.

[0056] S2. After 1 hour, stop the nitrogen flow, add ammonium persulfate and stir for 2 minutes, raise the temperature to 40°C, and continue the reaction under nitrogen atmosphere for 24 hours to obtain the dual-network fracturing fluid thickener.

[0057] The concentration of acrylamide is 2 wt%, N-phenylacrylamide is 1.5 wt%, and the mass ratio of nonionic monomer, dodecylphenol polyoxyethylene ether, N,N'-methylenebisacrylamide, and ammonium persulfate is 1:0.06:0.0005:0.03.

[0058] Comparative Example 1

[0059] This comparative example provides a dual-network fracturing fluid thickener, the preparation method of which is basically the same as that of Example 1, except that dodecylphenol polyoxyethylene ether is replaced with an equal amount of isotridecyl alcohol polyoxyethylene ether.

[0060] Comparative Example 2

[0061] This comparative example provides a dual-network fracturing fluid thickener, the preparation method of which is basically the same as that of Example 1, except that dodecylphenol polyoxyethylene ether is replaced with an equal amount of polyvinyl alcohol formate.

[0062] Comparative Example 3

[0063] This comparative example provides a fracturing fluid thickener, the preparation method of which is basically the same as that of Example 1, except that dodecylphenol polyoxyethylene ether is not added.

[0064] Experimental Example 1

[0065] This experiment used the fracturing fluid thickeners provided in Examples 1, 2, and 5, as well as Comparative Examples 1-3, diluted with monovalent potassium ion brine to a nonionic monomer concentration of 0.84 wt%. The viscosity of each sample was then tested under different salinity conditions. The test results are as follows: Figure 1 As shown.

[0066] Depend on Figure 1 It can be seen that Comparative Example 1 and Comparative Example 2, which use flexible polymers without benzene rings to form the second network structure, have similar viscosities. Within the range of potassium ion salinity of 0–300,000 ppm, the viscosity fluctuates mainly within the range of 52–58 mPa·s, indicating that potassium ions have little impact on them. However, within the range of 300,000–450,000 ppm, the viscosity of both fracturing fluid thickeners shows a significant decrease. This indicates that as the dual network structure adsorbs more potassium ions, the adsorption amount gradually exceeds its upper limit, and the dual network structure collapses to some extent.

[0067] In contrast, the alkyl phenol polyoxyethylene ether used in the embodiment 1 of the present application can enhance the intermolecular force through the π-π stacking effect. The enhancement of the intermolecular force, on the one hand, shows that the initial viscosity of the embodiment 1 is higher under the same non-ionic monomer concentration, reaching 62.1 mPa·s, and on the other hand, the upper limit of the embodiment 1 is higher, and the viscosity does not show a significant downward trend until the potassium ion salinity reaches 400,000 ppm.

[0068] The embodiment 2 introduces a benzene ring structure into the structure of the non-ionic monomer on the basis of the embodiment 1, and the intermolecular force is stronger. The initial viscosity reaches 72.3 mPa·s, and the viscosity does not show a significant downward trend even when the potassium ion salinity reaches 450,000 ppm.

[0069] The embodiment 5 uses two non-ionic monomers to copolymerize to form a first network structure. It can be seen that the initial viscosity is between the embodiment 1 and the embodiment 2, and also has better salt resistance. It shows that the viscosity can be adjusted by adjusting the content of the benzene ring in the non-ionic monomer.

[0070] The comparative example 3 provides a single network fracturing fluid thickener without a flexible polymer. The viscosity of the single network fracturing fluid thickener shows a downward trend as a whole in the salinity range of 0-450,000 ppm, from the initial 38.0 mPa·s to 20.5 mPa·s, and the salt resistance is poor.

[0071] Test example 2

[0072] In this test example, the fracturing fluid thickeners provided by the embodiments 1, 2, 5, and the comparative examples 1-3 are diluted with a divalent calcium ion brine to a non-ionic monomer concentration of 0.84 wt%, and then the viscosity of each sample is tested under different salinity conditions. The test results are shown in Figure 2 .

[0073] From Figure 2 it can be seen that the viscosity change caused by the divalent calcium ion has many similarities with the monovalent potassium ion. The viscosity of the fracturing fluid thickeners provided by the comparative examples 1-2 also shows a significant downward trend when the salinity reaches 300,000 ppm. The embodiments of the present application successfully increase the salt resistance upper limit of the fracturing fluid thickener to more than 450,000 ppm by introducing the π-π stacking effect.

[0074] Unlike the test example 1, the viscosity of the fracturing fluid thickener with a double network structure increases sharply by about 40-50% compared with the initial viscosity when the calcium ion salinity is 100,000 ppm. With the continuous growth of the salinity, the viscosity falls back to a value close to the initial viscosity. However, this phenomenon does not occur in the fracturing fluid thickener with a single network structure (comparative example 3).

[0075] Test Example 3

[0076] In this test example, the fracturing fluid thickening agents provided in Examples 1, 2, 5, and Comparative Examples 1-3 were used to prepare fracturing fluid samples at 25°C, 170 s -1 The viscosity after shearing for 5 min was taken as the initial viscosity, and the viscosity after continuous shearing for 120 min at 160°C was taken as the final viscosity. The viscosity retention rate was calculated as the ratio of the final viscosity to the initial viscosity. The comparison results are shown in Table 1.

[0077] Table 1, Comparison results of viscosity retention rate

[0078] Initial viscosity / mPa s Final viscosity / mPa s Viscosity retention Example 1 212 153 72.2% Example 2 224 165 73.7% Example 5 246 186 75.6% Comparative Example 1 175 125 71.4% Comparative Example 2 190 132 69.5% Comparative Example 3 138 31 22.5%

[0079] As can be seen from Table 1, due to the influence of π-π stacking, the intermolecular forces of the examples are enhanced, so the initial viscosities of Examples 1, 2, and 5 are significantly higher than those of the comparative examples, and the viscosity increases with the increase of the amount of benzene rings introduced.

[0080] Similarly, due to the enhancement of intermolecular forces, the fracturing fluid thickening agents provided in the examples exhibit stronger high-temperature shear resistance, and the viscosity retention rate can reach more than 72.2%, and the viscosity retention rate further increases with the increase of the amount of benzene rings introduced, and the highest reaches 75.6%.

[0081] Comparative Example 1 and Comparative Example 2 use flexible polymers without benzene rings. The initial viscosity of Comparative Example 1 is reduced to 175 mPa·s, and the viscosity retention rate is reduced to 71.4%. The initial viscosity of Comparative Example 2 is reduced to 190 mPa·s, and the viscosity retention rate is reduced to 69.5%. Although both still have certain high-temperature shear resistance, their initial viscosities and viscosity retention rates cannot reach the level of the examples. In addition, the high-temperature shear resistance of the single-network system of Comparative Example 3 is completely incomparable with the double-network, and the viscosity retention rate is only 22.5%. Again, it is confirmed that the fracturing fluid thickening agent with double-network structure is significantly better than the single-network system.

[0082] In summary, the embodiment of the present application provides a high salt-resistant and shear-resistant double network fracturing fluid thickening agent and a preparation method thereof, which forms a first network structure by cross-linking and polymerization of non-ionic monomers and cross-linking agents under the action of an initiator, and utilizes a flexible polymer filled in the first network structure to form a second network structure. The non-ionic monomer is at least one of acrylamide and modified acrylamide, and the flexible polymer is an alkylphenol polyoxyethylene ether. The flexible segment in the structure of the alkylphenol polyoxyethylene ether still retains the function of a "sacrificial bond", can absorb the damage of high shear and high temperature to the rigid network structure, and enables the system to still have good tolerance performance without metal cross-linking. At the same time, due to the presence of benzene rings in the structure of the alkylphenol polyoxyethylene ether, the π-π stacking effect can be increased on the basis, the intermolecular force is strengthened, and the tolerance of the double network structure is further improved. The double network fracturing fluid thickening agent is simple to prepare, has excellent performance, and has better practical value.

[0083] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A highly salt-resistant and shear-resistant dual-network fracturing fluid thickener, characterized in that, The dual-network fracturing fluid thickener comprises a first network structure formed by crosslinking polymerization of a nonionic monomer and a crosslinking agent under the action of an initiator, and a second network structure composed of a flexible polymer filled in the first network structure; wherein the nonionic monomer is at least one of acrylamide and modified acrylamide, and the flexible polymer is alkylphenol polyoxyethylene ether; in the dual-network fracturing fluid thickener, the concentration of the nonionic monomer is 2.5wt%~5wt%; the mass ratio of the nonionic monomer to the flexible polymer is 1:(0.05~0.1).

2. The dual-network fracturing fluid thickener according to claim 1, characterized in that, The alkylphenol polyoxyethylene ether includes at least one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, and dodecylphenol polyoxyethylene ether.

3. The dual-network fracturing fluid thickener according to claim 1, characterized in that, The modified acrylamide includes N-arylacrylamide.

4. The dual-network fracturing fluid thickener according to claim 1, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide.

5. The dual-network fracturing fluid thickener according to claim 1, characterized in that, The initiator is at least one of ammonium persulfate, potassium persulfate, and sodium percarbonate.

6. A method for preparing a dual-network fracturing fluid thickener as described in any one of claims 1 to 5, characterized in that, include: The nonionic monomer, the flexible polymer, and the crosslinking agent are mixed under an inert atmosphere to obtain a raw material mixture; the raw material mixture is then mixed with the initiator, and a crosslinking polymerization reaction is carried out under an inert atmosphere.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the nonionic monomer, the crosslinking agent, and the initiator is 1:(0.0002~0.0005):(0.025~0.05).

8. The preparation method according to claim 7, characterized in that, The nonionic monomer, the flexible polymer, and the crosslinking agent are mixed at a temperature of 80-90°C for 1-3 hours, and then cooled to room temperature before use.

9. The preparation method according to claim 8, characterized in that, The crosslinking polymerization reaction is carried out at 30~50℃ for 20~30h.

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