Polyacrylamide gel, preparation method and application of polyacrylamide gel in water-based self-suspension fracturing propping agent

Abstract

The invention provides polyacrylamide gel, a preparation method and application of the polyacrylamide gel in a water-based self-suspension fracturing propping agent, and relates to the technical field of oil exploitation. The polyacrylamide gel disclosed by the invention is prepared from the following components in parts by weight: 40 to 50 parts of acrylamide, 20 to 30 parts of acrylic acid, 15 to 25 parts of 4-methacrylamide salicylic acid, 1.5 to 2 parts of diacraldehyde pentaerythritol, 0 to 4 parts of sodium carboxymethyl cellulose, 1 to 5 parts of carbamide, 5 to 15 parts of sodium hydroxide, 0.02 to 0.08 part of EDTA-2Na (Ethylene Diamine Tetraacetic Acid), 5 to 15 parts of cross-linking agent, 1 to 10 parts of initiator, 0.01 to 0.1 part of sodium formate and 40 to 65 parts of water. The polyacrylamide gel is prepared through a copolymerization method, the method is simple, and the obtained polyacrylamide gel is high in dissolution speed, good in drag reduction performance and excellent in salt resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of oil extraction, and particularly relates to a polyacrylamide gel, a preparation method thereof, and an application thereof in an aqueous self-suspending fracturing proppant. Background Art

[0002] Fracturing, as an important measure for increasing oil and gas production in oil and gas fields, has become the preferred measure and method for increasing production in low-permeability oil and gas fields and increasing reserves and production in tight shale oil and gas fields. During the oil extraction process, it is necessary to use a sand-carrying fluid to transport the proppant to the fracture to support the fracture. In order to improve the sand-carrying capacity of the sand-carrying fluid, various organic polymers are usually added to the sand-carrying fluid as thickeners to increase the viscosity of the sand-mixed fluid and achieve the purpose of suspending the proppant. In traditional fracturing processes, guar gum and the like are used as thickeners. However, it has been found that there are still many problems after being pumped into the ground, such as limited sand-carrying capacity, fast settlement speed, poor solubility and dispersion in water, abrasion of solid proppants, and damage to the fracturing fracture channel; in addition, after fracturing, due to the fact that some insoluble substances are not easily discharged and remain in the formation, it causes formation pollution and damage. Therefore, there are obvious problems in the fracturing system of traditional fracturing fluids and proppants.

[0003] Polyacrylamide is a common water-soluble polymer, and it has been widely used in oil extraction and drilling fracturing at present. However, the salt tolerance of polyacrylamide in practical applications is very limited, and the viscosity loss is obvious or even flocculation and precipitation occur under high salinity and high shear conditions. By increasing the associative groups, the mutual action between the associative groups helps to solve the above problems, but the associative action also causes the dissolution rate of polyacrylamide to decrease, and generally requires polyacrylamide to dissolve within 5 minutes and achieve a good thickening effect during the fracturing construction process, resulting in limited application of polyacrylamide gel.

[0004] Patent CN117209799A discloses a treatment method for accelerating the dissolution rate of polyacrylamide. By fully mixing and contacting the polyacrylamide powder with the treatment liquid, the treatment liquid adheres to the surface of the polyacrylamide powder to obtain polyacrylamide that can be quickly dissolved. The treatment liquid includes a penetrant, a co-solvent, an inorganic salt, and water, and the co-solvent includes acetamide, thiourea, and acetaldehyde; although this method can solve the problem of slow dissolution rate of polyacrylamide gel, it does not pay attention to problems such as the salt tolerance and mechanical shear stability of polyacrylamide gel. Patent CN105085801A discloses a fast-dissolving polyacrylamide and a preparation method thereof. By introducing hydrophilic groups containing carboxyl and sulfonic acid groups, the dissolution performance of the polymer is enhanced, but the dissolution time of this polyacrylamide gel at room temperature is about 10 minutes, and the fast solubility still needs to be improved. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a polyacrylamide gel, a preparation method thereof, and an application thereof in a water-based self-suspending fracturing proppant, which solves at least some of the problems existing in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: On the one hand, a polyacrylamide gel, comprising raw materials in the following parts by weight: 40-50 parts of acrylamide, 20-30 parts of acrylic acid, 15-25 parts of 4-methacrylamidosalicylic acid, 1.5-2 parts of diallyl aldehyde pentaerythritol, 0-4 parts of sodium carboxymethyl cellulose, 1-5 parts of urea, 5-15 parts of sodium hydroxide, 0.02-0.08 parts of EDTA-2Na, 5-15 parts of crosslinking agent, 1-10 parts of initiator, 0.01-0.1 parts of sodium formate, and 40-65 parts of water.

[0007] In a further embodiment, the mass ratio of acrylamide, acrylic acid, 4-methacrylamidosalicylic acid, and diallyl aldehyde pentaerythritol is (8-10):(4-6):(3-4):(0.3-0.4).

[0008] In this application, acrylamide and acrylic acid are used as monomers to copolymerize to prepare a polyacrylamide gel with a crosslinked network structure. By adding 4-methacrylamidosalicylic acid to the polyacrylamide gel, on the one hand, 4-methacrylamidosalicylic acid can undergo a free radical polymerization reaction to introduce hydrophilic groups, ensuring solubility in water, enabling the proppant to quickly suspend in water, reducing the friction resistance during the process of pumping the proppant into the formation, and having a good drag reduction effect; the introduced carboxyl groups, phenolic hydroxyl groups, etc. can react with acrylamide, crosslinking agent, etc. to a certain extent, increasing the crosslinking sites to a certain extent, improving the crosslinking density, and enhancing the strength of the gel. The increase in crosslinking density also limits the movement ability of the chain segments, making the gel more difficult to undergo irreversible deformation when subjected to shear force, improving the shear resistance, enabling it to quickly recover when sheared under the high-speed flow of formation fluid, and keeping the formation fluid at a certain viscosity, so that the proppant carried by it can enter deeper into the formation. As it contacts with oil and gas, the proppant continuously spreads in the fracture, effectively increasing the volume of the fracture, thereby better improving the formation conductivity; on the other hand, the introduction of hydroxyl groups, benzene rings, etc. enables the gel to form hydrogen bond physical crosslinks, forming a gel with a multiple network crosslinked structure, which helps to enhance the molecular chain rigidity and improve the strength and shear resistance of the gel.

[0009] Although the addition of 4-methacrylamidosalicylic acid helps to form a polyacrylamide gel with a multiple network structure and improve the strength, shear resistance, etc. of the gel, if the addition amount is too small, the synergistic effect is limited, and if the addition amount is excessive, the length of the gel molecular chain will increase, resulting in a decrease in the crosslinking degree, and thus a decrease in strength and shear resistance. In addition, the phenolic hydroxyl group in 4-methacrylamidosalicylic acid is easily oxidized, and under high-salt conditions, the salt ions compete with the hydroxyl group for hydration, which will cause the gel to shrink. Therefore, an excessive amount of 4-methacrylamidosalicylic acid will also affect the performance of the gel under high-salt conditions. To make up for the above defects, the present application introduces a certain amount of diallyl aldehyde acetal of pentaerythritol into the polyacrylamide gel, which can cooperate with 4-methacrylamidosalicylic acid to balance hydration, control the crosslinking degree, and avoid excessive hydrophobicization, thereby further improving the strength, salt tolerance, and shear resistance of the gel.

[0010] In a further embodiment, the crosslinking agent is a crosslinking agent containing a bisacrylamide group, including but not limited to N,N'-methylenebisacrylamide, N,N'-propylenediacrylamide, N,N'-tetramethylenediacrylamide, N,N'-hexamethylenediacrylamide, or N,N'-m-xylenediacrylamide, etc.

[0011] In a further embodiment, the initiator is selected from at least one of peroxide initiators and azo initiators.

[0012] Optionally, the peroxide initiator includes but not limited to benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, tert-butyl perbenzoate, tert-butyl perpivalate, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, potassium persulfate, sodium persulfate, ammonium persulfate, etc.

[0013] Optionally, the azo initiator includes but not limited to azodiisobutyronitrile, azodiisooctanenitrile, azodiisobutamidine hydrochloride, azodiisobimidazoline hydrochloride, etc.

[0014] In a further embodiment, the molecular weight of the polyacrylamide gel is less than 18 million, preferably 5 million - 18 million.

[0015] In a further embodiment, the degree of substitution DS of the sodium carboxymethylcellulose is 0.6 - 0.8, and the dosage of the sodium carboxymethylcellulose is preferably 5% - 8% of the mass of acrylamide.

[0016] When the degree of substitution (DS) of sodium carboxymethyl cellulose is too low, its solubility is poor. When the DS is too high, there will be too many crosslinking sites provided, resulting in excessive crosslinking degree of the gel, which will affect the solubility, strength and shear resistance of the gel, and the weak gel formed by simply crosslinking sodium carboxymethyl cellulose has poor proppant-carrying performance and shear resistance. Therefore, in this application, sodium carboxymethyl cellulose with a DS of 0.6 - 0.8 is selected to cooperate with other components. On the one hand, it can increase the crosslinking degree to a certain extent and enhance the strength and shear resistance of the gel; on the other hand, it can also reduce the salting-out effect of the gel under high-salt or high-mineralization conditions and improve the stability of the gel under high-salt and high-mineralization conditions. In addition, the applicant found that the addition amount of sodium carboxymethyl cellulose needs to be limited within the range of 5% - 8% of the mass of acrylamide. Excessive addition easily leads to excessive crosslinking degree of the gel, which will not only not improve the performance of the gel, but also reduce the strength and shear resistance of the gel.

[0017] On the other hand, the above-mentioned method for preparing polyacrylamide gel is characterized by including the following steps: (1) Mix sodium hydroxide, urea, EDTA-2Na, acrylic acid and water to obtain solution I; (2) Dissolve acrylamide in water, add 4-methacrylamidosalicylic acid, dipropylene aldehyde pentaerythritol and crosslinking agent and mix evenly to obtain solution II; mix solution II and solution I to obtain a reaction solution; (3) Add an initiator to the reaction solution, the reaction temperature is not lower than 70 °C, and the time is 3 - 5 h; finally add sodium formate to stop the reaction to obtain polyacrylamide gel.

[0018] In a further embodiment, the reaction temperature is preferably 70 - 80 °C; the time is 3 - 5 h.

[0019] In a further embodiment, the solution II also includes sodium carboxymethyl cellulose.

[0020] In a further embodiment, it also includes drying the polyacrylamide gel to a moisture content ≤ 10% to make polyacrylamide gel dry powder.

[0021] On the other hand, the above-mentioned polyacrylamide gel is used in the preparation of water-based self-suspending fracturing proppants.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The polyacrylamide gel of the present invention is prepared by a copolymerization method, and its dissolution time is within 300 s, with a fast dissolution speed and excellent shear resistance. The proppants prepared by using this polyacrylamide gel have good drag reduction effect, so that the proppants can be quickly suspended in water and can carry the proppants deeper into the formation, and the purpose that the proppants can fully fill the fracturing cracks during the fracturing process can be achieved.

[0023] 2. The polyacrylamide gel of the present invention forms a gel with a multiple network cross-linked structure by adding 4-methacrylamidosalicylic acid, which improves the cross-linking density, enhances the strength of the gel, improves the shear resistance, and enables the proppant to enter deeper into the formation. When a certain amount of dipropionaldehyde pentaerythritol acetal is added to the polyacrylamide gel, it synergistically acts with 4-methacrylamidosalicylic acid to balance hydration, control the degree of cross-linking, and avoid excessive hydrophobicity, thereby further enhancing the strength, salt tolerance, and shear resistance of the gel.

[0024] 3. The polyacrylamide gel of the present invention, by adding sodium carboxymethyl cellulose with a certain degree of substitution, can not only increase the degree of cross-linking to a certain extent, enhance the strength and shear resistance of the gel, but also reduce the salting-out effect of the gel under high-salt or high salinity conditions, and improve the stability of the gel under high-salt and high salinity conditions.

[0025] 4. The polyacrylamide gel of the present invention can be used as a fracturing proppant. Its unique molecular structure on the surface makes the fracturing proppant have good lubricity, greatly reducing the frictional resistance during its migration, effectively reducing the loss of the proppant and the loss of the proppant to the pipe string and injection equipment. Description of the Drawings

[0026] Figure 1 It is a physical picture of the polyacrylamide gel obtained in Example 6 of this application; Figure 2 It is an infrared spectrum diagram of the polyacrylamide gel obtained in Example 6 of this application. Detailed Embodiments

[0027] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary illustration of the scope claimed by the present invention. Those skilled in the art can make various changes and modifications to the invention according to the disclosed content, and it should also fall within the scope claimed by the present invention.

[0028] In this application, 4-methacrylamidosalicylic acid (CAS No. 50512-48-6) was purchased from Shanghai Youhe Biotechnology Co., Ltd., and dipropionaldehyde pentaerythritol acetal (CAS No. 78-19-3) was purchased from Suzhou Qihang Biotechnology Co., Ltd. Other chemical reagents were obtained through conventional commercial channels without special instructions.

[0029] In this application, the polyacrylamide gel is prepared by the following method: Add urea, EDTA-2Na, acrylic acid, acrylamide, acrylic acid, 4-methacrylamidosalicylic acid, dipropenal acetal pentaerythritol, and cross-linking agent into water, adjust the pH with sodium hydroxide, then add the initiator for reaction, and finally add sodium formate to stop the reaction to obtain the polyacrylamide gel. Among them, the addition order of the raw materials urea, EDTA-2Na, acrylic acid, acrylamide, acrylic acid, 4-methacrylamidosalicylic acid, and dipropenal acetal pentaerythritol has no prior limitation. In the following specific examples, the preparation method of the polyacrylamide gel is as follows: (1) Mix sodium hydroxide, urea, EDTA-2Na, acrylic acid with water to obtain Solution I; (2) Dissolve acrylamide in water, add 4-methacrylamidosalicylic acid, dipropenal acetal pentaerythritol, and cross-linking agent and mix evenly to obtain Solution II. Mix Solution II with Solution I to obtain the reaction solution; (3) Add the initiator to the reaction solution, react at 70-80 °C for 3-5 h, and finally add sodium formate to stop the reaction to obtain the polyacrylamide gel. When sodium carboxymethylcellulose is included in the polyacrylamide gel, sodium carboxymethylcellulose is added in any step of step (2). For example, it can be added before acrylamide or added to water together, or added together with 4-methacrylamidosalicylic acid, dipropenal acetal pentaerythritol, and cross-linking agent, or added finally, and the polyacrylamide gel can be successfully prepared. Although the above preparation steps list the specific addition order of the raw materials, the preparation order of Solution I and Solution II in steps (1) and (2) can be changed. The cross-linking agent is usually added before the initiator, but adding it simultaneously with the initiator or adding the initiator first and then adding the cross-linking agent has no effect on the preparation of the polyacrylamide gel, and it does not constitute a limitation to the application. It can be understood that changing the addition order of one or several of these raw materials can still exhibit the advantages described above, and a polyacrylamide gel with a fast dissolution rate, high drag reduction, good salt tolerance, and good mechanical shear stability can be obtained. Those skilled in the art can easily change the addition order of these raw materials without creative labor.

[0030] The present invention will be further described below by way of specific examples. All chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified.

[0031] Example 1 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 5 parts of sodium hydroxide, 1 part of urea, 0.02 part of EDTA-2Na, 20 parts of acrylic acid with 10 parts of water to obtain Solution I; (2) Dissolve 40 parts of acrylamide in 30 parts of water, add 15 parts of 4-methacrylamidosalicylic acid and 5 parts of N,N-tetramethylenediacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 1 part of tert-butyl hydroperoxide to the reaction solution, react at 70 °C for 3 h, and finally add 0.01 part of sodium formate to stop the reaction to obtain a polyacrylamide gel.

[0032] Example 2 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 8 parts of sodium hydroxide, 3 parts of urea, 0.05 part of EDTA-2Na, 25 parts of acrylic acid and 15 parts of water to obtain Solution I; (2) Dissolve 45 parts of acrylamide in 45 parts of water, add 20 parts of 4-methacrylamidosalicylic acid and 10 parts of N,N-methylenebisacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 8 parts of tert-butyl hydroperoxide to the reaction solution, react at 80 °C for 3 h, and finally add 0.05 part of sodium formate to stop the reaction to obtain a polyacrylamide gel.

[0033] Example 3 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 15 parts of sodium hydroxide, 5 parts of urea, 0.08 part of EDTA-2Na, 30 parts of acrylic acid and 20 parts of water to obtain Solution I with a mass concentration of 50%; (2) Dissolve 50 parts of acrylamide in 45 parts of water, add 25 parts of 4-methacrylamidosalicylic acid and 15 parts of methylenebisacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 10 parts of tert-butyl hydroperoxide to the reaction solution, react at 80 °C for 5 h, and finally add 0.1 part of sodium formate to stop the reaction to obtain a polyacrylamide gel.

[0034] Example 4 The difference from Example 2 is that the addition amount of 4-methacrylamidosalicylic acid is 25 parts, that is, the mass ratio of acrylamide, acrylic acid and 4-methacrylamidosalicylic acid is 9:5:5.

[0035] Example 5 The difference from Example 2 is that the addition amount of 4-methacrylamidosalicylic acid is 10 parts, that is, the mass ratio of acrylamide, acrylic acid and 4-methacrylamidosalicylic acid is 9:5:2.

[0036] Example 6 The difference from Example 2 is that it further includes 1.5 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.3. The picture of the obtained polyacrylamide gel is as Figure 1 shown, and it is tested using a Nicolet 6700 infrared spectrometer in the United States, and the result is as Figure 2 shown. It can be seen that the characteristic peak of amide I band (C=O stretching vibration) is at 1672 cm -1 , the characteristic peak of amide II band (N-H bending vibration) is at 1565 cm -1 . In addition, the stretching vibration absorption peak of C-O-C in dipropenal acetal pentaerythritol is at 1048 cm -1 , and the characteristic peak of the benzene ring skeleton in 4-methacrylamidosalicylic acid appears at 1585 cm -1 , which indicates that the polyacrylamide gel is successfully prepared.

[0037] Example 7 The difference from Example 2 is that it further includes 2 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.4.

[0038] Example 8 The difference from Example 2 is that it further includes 3 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.6.

[0039] Example 9 The difference from Example 7 is that the dipropenal acetal pentaerythritol in step (2) is replaced with an equal amount of dipropenylamine.

[0040] Example 10 The difference from Example 2 is that solution II in step (2) further includes 3.6 parts of sodium carboxymethylcellulose (degree of substitution 0.6), and sodium carboxymethylcellulose is added after acrylamide.

[0041] Example 11 The difference from Example 7 is that solution II in step (2) further includes 2.25 parts of sodium carboxymethylcellulose (degree of substitution 0.8), and sodium carboxymethylcellulose is added simultaneously with acrylamide.

[0042] Example 12 The difference from Example 11 is that the degree of substitution of sodium carboxymethylcellulose is 0.5.

[0043] Example 13 The difference from Example 11 is that the degree of substitution of sodium carboxymethyl cellulose is 1.0.

[0044] Comparative Example 1 The difference from Example 2 is that 4-methylacrylamidosalicylic acid in step (2) is replaced with an equal amount of acrylic acid.

[0045] Comparative Example 2 The difference from Example 2 is that 4-methylacrylamidosalicylic acid in step (2) is replaced with an equal amount of 2-acrylamido-2-methylpropanesulfonic acid.

[0046] Test Example Test the molecular weight, dissolution time in water, shear resistance, and drag reduction rates in fresh water and salt water of the polyacrylamide gels prepared in the above examples and comparative examples; among them, the drag reduction rate is tested according to the technical indicators of SY / T 5107-2016, using a JZLI-type drag reduction rate tester. The polyacrylamide gels are added to fresh water at 0.05% (volume percentage) and to salt water (8% sodium chloride and 2% calcium chloride in seawater) at 0.25% (volume percentage) respectively.

[0047] Table 1 shows the test results of molecular weight, dissolution time in water, and drag reduction rate. As shown in the table, the molecular weight of the preferred polyacrylamide gel of the present invention is between 5 million and 18 million, the dissolution time is less than 300 s, the drag reduction rate in fresh water reaches more than 73%, and the drag reduction rate in seawater is more than 62%. The drag reduction effect is good and it has a certain salt resistance. It can also be seen that compared with Comparative Example 1, the drag reduction rate of the polyacrylamide gels obtained in Examples 1-3 in fresh water is significantly improved, that is, the addition of 4-methylacrylamidosalicylic acid helps to improve the drag reduction effect of the polyacrylamide gel; in addition, the drag reduction rate of Examples 1 and 2 in seawater is slightly improved compared with Comparative Example 1, while the drag reduction rate of Example 3 decreases. This shows that although the addition of 4-methylacrylamidosalicylic acid can improve the drag reduction effect of the gel, adding too much will lead to a decrease in salt resistance. Compared with Example 2, in Examples 6 / 7 / 10 / 11, diallyl aldehyde acetalized pentaerythritol and / or sodium carboxymethyl cellulose are added, and their drag reduction rates in seawater are significantly improved. It can be seen that adding diallyl aldehyde acetalized pentaerythritol or sodium carboxymethyl cellulose to the gel helps to make up for the defect of the decrease in salt resistance caused by the addition of 4-methylacrylamidosalicylic acid.

[0048] Table 1

[0049] The shear resistance is tested according to the technical indicators of SY / T 5107-2016. During the test, the polyacrylamide gel is prepared into a solution with a mass fraction of 1%, and the shear rate is 170 s -1, at a temperature of 25 °C, the apparent viscosity of the test solution at different shear times was measured to evaluate its shear resistance. Table 2 shows the test results of shear resistance. As shown in the table, the 1% solution of polyacrylamide gel prepared in Examples 1 / 2 / 3 / 6 / 7 / 10 / 11 of the present invention has an apparent viscosity in the range of 410 - 470 mPa·s at a shear rate of 170 s -1 and the viscosity range is 165 - 200 mPa·s after 12 h of long-term shear, showing good shear resistance and compensating for the defect of poor shear stability of the existing polyacrylamide gel.

[0050] Comparing with Examples 2 / 3 / 4 / 5 and Comparative Examples 1 / 2, it can be seen that although the addition of 4-methylacrylamidosalicylic acid can enhance the shear resistance of the gel, if the addition amount is too small, the enhancement effect is limited, and if the addition amount is too large, the shear resistance will also decrease.

[0051] Comparing with Examples 2 / 6 / 7 / 8 / 9, it can be seen that introducing a certain amount of dipropionaldehyde pentaerythritol into the polyacrylamide gel helps to improve the shear resistance of the gel.

[0052] Comparing with 2 / 10 / 11 / 12 / 13, it can be seen that although introducing sodium carboxymethylcellulose into the polyacrylamide gel helps to improve the shear resistance of the gel, it is affected by the degree of substitution of sodium carboxymethylcellulose. Only by adding sodium carboxymethylcellulose with a degree of substitution DS in the range of 0.6 - 0.8 can the shear resistance of the gel be improved.

[0053] Table 2

[0054] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A polyacrylamide gel, characterized in that: Contains the following raw materials in parts by weight: 40-50 parts of acrylamide, 20-30 parts of acrylic acid, 15-25 parts of 4-methacrylamidosalicylic acid, 1.5-2 parts of diacryl pentaerythritol acetal, 0-4 parts of sodium carboxymethyl cellulose, 1-5 parts of carbonamide, 5-15 parts of sodium hydroxide, 0.02-0.08 parts of EDTA-2Na, 5-15 parts of crosslinking agent, 1-10 parts of initiator, 0.01-0.1 parts of sodium formate, and 40-65 parts of water; The cross-linking agent is a cross-linking agent containing a bisacrylamide group; The initiator is selected from at least one of a peroxide initiator and an azo initiator.

2. The polyacrylamide gel according to claim 1, characterized in that The mass ratio of acrylamide, acrylic acid, 4-methacrylamidosalicylic acid and diacryl pentaerythritol is (8-10):(4-6):(3-4):(0.3-0.4).

3. The polyacrylamide gel according to claim 1, characterized in that: The molecular weight of the polyacrylamide gel is less than 18 million.

4. The polyacrylamide gel according to claim 1, characterized in that The degree of substitution DS of the sodium carboxymethyl cellulose is 0.6-0.

8.

5. The polyacrylamide gel according to claim 4, characterized in that The dosage of the sodium carboxymethyl cellulose is 5%-8% of the mass of acrylamide.

6. The method for preparing the polyacrylamide gel according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) mixing sodium hydroxide, carbonamide, EDTA-2Na, acrylic acid and water to obtain solution I; (2) dissolving acrylamide in water, adding 4-methylacrylamidosalicylic acid, diacrylamide pentaerythritol acetal, and a crosslinking agent, and mixing well to obtain a solution II, and mixing the solution II with the solution I to obtain a reaction solution; (3) Adding an initiator to the reaction solution to carry out a reaction at a temperature not lower than 70°C for 3-5 hours; finally, adding sodium formate to stop the reaction and obtain polyacrylamide gel.

7. The preparation method according to claim 6, characterized in that: The solution II also includes sodium carboxymethyl cellulose.

8. The preparation method according to claim 6, characterized in that: The method also includes drying the polyacrylamide gel to a water content of ≤10% to prepare polyacrylamide gel dry powder.

9. Use of the polyacrylamide gel according to any one of claims 1 to 5 or the polyacrylamide gel prepared by the preparation method according to any one of claims 6 to 8 in preparing a water-based self-suspending fracturing proppant.

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