Low-density polyacrylamide dry powder particle, polyacrylamide suspension containing same, preparation method and application

Abstract

The invention discloses a low-density polyacrylamide dry powder particle, a polyacrylamide suspension containing the same, and a preparation method and application of the low-density polyacrylamide dry powder particle. The preparation method comprises the following steps: adding acrylamide and a comonomer into water to obtain a monomer solution; sequentially adding an emulsifier and an organic solvent dissolved with a pore-foaming agent into the monomer solution, uniformly dispersing the organic solvent dissolved with the pore-foaming agent into oil drops under the action of the emulsifier, and controlling the particle size of the oil drops to be 500nm-5mu m; and adding an initiator to carry out polymerization reaction in an inert atmosphere to obtain colloid, granulating, drying, crushing, and collecting particles with the particle size of less than or equal to 0.25 mm to obtain the low-density polyacrylamide dry powder particles. The polyacrylamide dry powder particles obtained by adopting the preparation method have lower density, the density is 1.1-1.3 g / mL, and when the polyacrylamide dry powder particles are used for preparing a polyacrylamide dry powder particle suspension, the addition amount of a suspending agent can be reduced, the overall viscosity of the suspension can be reduced, and the comprehensive performance of the suspension can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water-soluble polymer preparation, and more specifically to a low-density polyacrylamide dry powder particle, a polyacrylamide suspension containing the same, and a preparation method and application thereof. Background Art

[0002] With the large-scale exploitation of shale oil and shale gas, large-volume fracturing technology using slick water as fracturing fluid has been widely used because it can more effectively improve the permeability and conductivity of shale oil and gas layers. Drag reducers, as the core additives of the slick water fracturing fluid system, directly determine the performance and application effect of the slick water fracturing fluid system. At present, most high-performance drag reducers use acrylamide polymers. In slick water fracturing, in order to ensure the construction requirements of online preparation, there are extremely high requirements for the dissolution rate of drag reducers, and the general dissolution rate is less than 30 seconds. Therefore, emulsion polyacrylamide is the best choice, but emulsion polyacrylamide has some obvious disadvantages, such as low effective content, low molecular weight, low viscosity in high-mineralization water, etc., which cannot meet the use requirements in some occasions with extremely high construction requirements.

[0003] Dry powder polyacrylamide has ultra-high molecular weight and high viscosity that the emulsion type cannot achieve, which can effectively make up for the shortcomings of emulsion products. In order to ensure the convenience of online construction, it is necessary to disperse the dry powder particles of polyacrylamide into the oil phase to prepare a suspension. Chinese invention patent CN202210873789.6 describes an integrated thickener for fracturing and a preparation method thereof, wherein the thickener comprises the following components in weight percentage: 40-55% modified acrylamide polymer, 1-2% suspending agent, and 50-58% organic solvent. Chinese invention patent CN202110905455.8 describes a thickener suspension for fracturing fluid and a preparation method thereof, the method comprising: adding polyacrylamide powder, anti-adhesive agent and surfactant to a ball mill in sequence, and obtaining a mixed powder after ball milling; adding a first suspending agent, a second suspending agent, an anti-precipitation agent, and a structure regulator in the reactor in sequence and stirring and mixing to obtain a mixed solution; adding the mixed powder and the emulsifier in the mixed solution in sequence and stirring and mixing to obtain the thickener suspension. However, traditional polyacrylamide dry powder particles are obtained by aqueous solution polymerization. The specific steps are to dissolve acrylamide and comonomers in water, add initiators to polymerize and become colloids, granulate them into drying equipment for drying, and finally crush and screen. During the drying process, the colloid particles will quickly lose water and shrink, and finally become dense powder particles with a density of about 1.4g / mL, which is much larger than the density of the oil phase used to prepare the suspension (0.75-0.9g / mL). Due to the density difference between polyacrylamide dry powder particles and oil phase, in order to reduce the sedimentation and stratification speed of polyacrylamide, a large amount of suspending agent needs to be added to the oil phase to increase the viscosity of the system. On the one hand, the increase in viscosity has a negative impact on the later construction preparation, and on the other hand, the use of suspending agent also increases the residue content of the fracturing fluid. Summary of the invention

[0004] To solve the above problems, the first object of the present invention is to provide a method for preparing low-density polyacrylamide dry powder particles. The preparation method can successfully prepare polyacrylamide dry powder particles with a lower density, with a density between 1.1-1.3 g / mL. When the polyacrylamide dry powder particles are used to prepare a suspension, the amount of suspending agent can be greatly reduced, the viscosity of the suspension itself can be reduced, and the stability of the suspension can be maintained, thereby improving the comprehensive performance of the suspension.

[0005] The second object of the present invention is to provide a low-density polyacrylamide dry powder particle prepared according to the preparation method as described above.

[0006] The third object of the present invention is to provide a polyacrylamide suspension comprising the low-density polyacrylamide dry powder particles as described above.

[0007] The fourth object of the present invention is to provide an application of the polyacrylamide suspension as described above in shale oil and shale gas production.

[0008] It should be noted that the total weight of monomers described in the present invention refers to the total weight of acrylamide and comonomers, and the total weight of raw materials described in the present invention refers to the total weight of all raw materials including acrylamide, comonomers, water, emulsifiers, porogens, organic solvents, initiators, and pH adjusters.

[0009] In order to achieve the above first object, the present invention adopts the following technical scheme:

[0010] The present invention discloses a method for preparing low-density polyacrylamide dry powder particles, comprising the following steps:

[0011] adding acrylamide and comonomer into water to obtain a monomer solution;

[0012] An emulsifier and an organic solvent containing a porogen are sequentially added to the monomer solution, and under the action of the emulsifier, the organic solvent containing the porogen is uniformly dispersed into oil droplets, and the particle size of the oil droplets is controlled to be 500 nm to 5 μm;

[0013] In an inert atmosphere, an initiator is added to carry out a polymerization reaction to obtain a colloid, and after granulation, drying and crushing, particles with a particle size of ≤0.25 mm are collected to obtain low-density polyacrylamide dry powder particles;

[0014] Wherein, the porogen is an azo compound.

[0015] In the art, azo compounds usually participate in the reaction as initiators. The present invention creatively changes the participation mode of azo compounds. The azo compounds are pre-dissolved in an organic solvent (oil phase). After the organic solvent is mixed with a monomer solution (water phase), the oil and water are separated to block the mixing of the azo compounds and the monomers, so that the azo compounds cannot function as initiators. At the same time, under the action of an emulsifier, the oil phase is uniformly dispersed in the water phase, and the oil phase is dispersed into oil droplets with a particle size of 500nm to 5μm by regulating the type and amount of the emulsifier. When the initiator is added to initiate the polymerization reaction, the system temperature is continuously increased, so that the oil droplets distributed in the water phase are heated, and the azo compounds are thermally decomposed (about 40°C) to generate nitrogen. The nitrogen remains in the colloid and occupies a certain space. In the later drying process, it can play a good pore-making role. Since there are many pores of 500nm to 5μm in the polyacrylamide dry powder particles prepared in this way, whether these pores are filled with air or residual organic solvent, the density of the polyacrylamide dry powder particles will be greatly reduced.

[0016] Further, the azo compound is selected from one or more of azobisisobutyronitrile, azobisisoheptylnitrile and azodicarbonamide; the azo compound is 0.01-2wt% of the mass of the organic solvent; illustratively, the azo compound can be 0.01wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 0.9wt%, 1wt%, 1.5wt%, 2wt% and the like of the mass of the organic solvent. Of course, those skilled in the art can also use other materials that can generate gas when heated to replace the azo compound, and similar effects can be achieved.

[0017] Further, when the synthesized polymer is an anionic copolymer, the comonomer is selected from one or more of nonionic monomers and anionic monomers;

[0018] The nonionic monomer is selected from other nonionic monomers except acrylamide, and the other nonionic monomers are selected from one or more of N-vinylpyrrolidone, 2-methylacrylamide, N,N-dimethylacrylamide and N-tert-butylacrylamide; the other nonionic monomers account for 0-5wt% of the total monomer amount; illustratively, the other nonionic monomers can account for 0wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% and the like of the total monomer amount.

[0019] The anionic monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylallylsulfonic acid and vinylbenzenesulfonic acid; the anionic monomer accounts for 0-50wt% of the total monomer amount; illustratively, the anionic monomer can account for 0wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt% and the like of the total monomer amount.

[0020] The cationic monomer is selected from one or more of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, methyl allyl trimethyl ammonium chloride and dimethyl diallyl ammonium chloride; the cationic monomer accounts for 0-60wt% of the total monomer amount; illustratively, the cationic monomer can account for 0wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt% and the like of the total monomer amount, taking into account the problem of effective amount of some cationic monomers, for example, 80wt% acryloyloxyethyl trimethyl ammonium chloride, the effective amount of which is 80wt% of acryloyloxyethyl trimethyl ammonium chloride in the total weight, therefore, the proportion of the cationic monomer here is the proportion of the effective amount of the cationic monomer in the total monomer amount.

[0021] The acrylamide and comonomers account for 15-40wt% of the total weight of the raw materials; illustratively, the acrylamide and comonomers can account for 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% and the like of the total weight of the raw materials. If the calculation of the proportion also involves the effective amount of the cationic monomer, it is also calculated according to the same rules.

[0022] The present invention controls the particle size of the oil droplets containing the porogen by controlling the type and amount of the emulsifier, thereby affecting the pore size generated inside the obtained polyacrylamide dry powder particles and the dry powder density. If the oil droplet particle size is too large, the micropores will disappear after being crushed into particles below 0.25 mm. If micropores with smaller particle sizes are desired, a larger amount of emulsifier needs to be added, thereby affecting the comprehensive performance of the product.

[0023] Furthermore, the emulsifier is selected from one or more of nonionic emulsifiers, anionic emulsifiers and cationic emulsifiers;

[0024] The nonionic emulsifier is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene alkylamine and polyoxyethylene alkylamide;

[0025] The anionic emulsifier is selected from one or more of sodium alkyl sulfonate, sodium alkyl aryl sulfonate, sodium alkyl sulfate and secondary alkyl sodium sulfate;

[0026] The cationic emulsifier is selected from one or more of an amine salt emulsifier (such as dodecyl ammonium chloride) and / or a quaternary ammonium salt emulsifier (such as hexadecyl trimethyl ammonium bromide);

[0027] The emulsifier accounts for 0.4-5wt% of the total weight of the raw materials; illustratively, the emulsifier can account for 0.4wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt% and the like of the total weight of the raw materials.

[0028] Further, the initiator is selected from one or more of persulfate, hydrogen peroxide, tert-butyl hydroperoxide, bisulfite, sulfite, ferrous salt, thiosulfate, pyrosulfite, and tertiary amine compounds;

[0029] The initiator accounts for 0.001-0.1wt% of the total weight of the raw materials; illustratively, the initiator may account for 0.001wt%, 0.005wt%, 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt% and the like of the total weight of the raw materials.

[0030] Further, the organic solvent is selected from one or more of normal alkane solvents, isoalkane solvents, aromatic solvents, cycloalkane solvents, halogenated alkane solvents, ether solvents and lipid solvents;

[0031] The organic solvent accounts for 0.5-10wt% of the total weight of the raw material; illustratively, the organic solvent can account for 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt% and the like of the total weight of the raw material.

[0032] Furthermore, before the polymerization reaction, the pH value of the reaction system is controlled between 4-8, and the temperature of the reaction system is controlled to 0-15°C. The technician can selectively add various pH adjusters, such as sodium hydroxide, according to the pH value required by the reaction system before the polymerization reaction. Usually, the pH adjuster is added together with the emulsifier, organic solvent and other materials, and the pH value is fine-tuned before the reaction.

[0033] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0034] The present invention discloses a low-density polyacrylamide dry powder particle prepared by the preparation method as described above; the density of the polyacrylamide dry powder particle is 1.1-1.3 g / mL, the particle size is ≤0.25 mm, and the molecular weight is (600-2500)×10 4 Dalt.

[0035] In order to achieve the third object, the present invention adopts the following technical solutions:

[0036] The present invention discloses a polyacrylamide suspension as described above, wherein the polyacrylamide suspension comprises the following raw material components in the following mass percentages:

[0037] Polyacrylamide dry powder particles 20-55wt%;

[0038] Suspending agent 0.2-5wt%;

[0039] The rest is organic solvent.

[0040] Furthermore, the polyacrylamide suspension includes 0.2-2 wt % of a suspending agent.

[0041] Furthermore, the polyacrylamide suspension comprises 30-50 wt % of polyacrylamide dry powder particles.

[0042] In order to achieve the fourth objective, the present invention adopts the following technical solutions:

[0043] The present invention discloses an application of the polyacrylamide suspension as described above in the exploitation of shale oil and shale gas.

[0044] The beneficial effects of the present invention are as follows:

[0045] The present invention discloses a method for preparing low-density polyacrylamide dry powder particles. By adjusting the addition state of azo compounds so that they are heated inside a polymerization system to generate a large amount of nitrogen, pores of 500nm to 5μm are formed inside the obtained polyacrylamide dry powder particles, thereby achieving the purpose of reducing the density of the polyacrylamide dry powder particles. The density of the polyacrylamide dry powder particles is between 1.1-1.3g / mL after testing.

[0046] The low-density polyacrylamide dry powder particles prepared are used in the preparation of polyacrylamide suspensions, which can significantly reduce the amount of suspending agent introduced, reduce the viscosity of the suspension itself, improve the workability, and at the same time maintain the stability of the suspension and improve the comprehensive performance of the suspension. DETAILED DESCRIPTION

[0047] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0048] Example 1

[0049] Add 7020 kg of water into a batching kettle with a volume of 10 cubic meters, and add 2000 kg of acrylamide, 50 kg of N-vinyl pyrrolidone, and 500 kg of acrylic acid in sequence under stirring to obtain a monomer solution;

[0050] 277kg of sodium hydroxide, 50kg of emulsifier AEO-9 and 1kg of azodicarbonamide (dissolved in 800kg of No. 3 white oil) were added to the monomer solution in sequence, the pH of the reaction system was controlled to 7.0, the temperature was lowered to 3°C, and the mixture was transferred to the reactor. The nitrogen was passed and the emulsifier was turned on for stirring. After stirring for 30 minutes, 100g of ammonium persulfate (dissolved in 1000g of water) and 800g of sodium bisulfite (dissolved in 4000g of water) were added in sequence. During the reaction, the system naturally heated up and gradually thickened. The nitrogen and emulsification stirring were continued for 5 minutes and then stopped. The reactor was sealed and allowed to react for about 3 hours to the highest temperature, and the temperature was kept for 2 hours. After the reaction, a colloid was obtained. The colloid material in the reactor was extruded and granulated, and transported to the drying equipment for drying. After drying, it was crushed and sieved, and the particles with a particle size of ≤0.25mm were collected and packaged. It was determined that the density of the obtained polyacrylamide dry powder particles was 1.15g / mL. Molecular weight 2100×10 4 Dalt.

[0051] Example 2

[0052] Add 6866 kg of water into a batching kettle with a volume of 10 cubic meters, and add 1900 kg of acrylamide, 500 kg of acrylic acid and 300 kg of 2-acrylamido-2-methylpropanesulfonic acid in sequence under stirring to obtain a monomer solution;

[0053] To the monomer solution, 335 kg of sodium hydroxide, 60 kg of emulsifier PEG600-MO, 8 kg of sodium lauryl polyoxyethylene ether sulfate and 0.3 kg of azobisisobutyronitrile (dissolved in 50 kg of n-octane) were added in sequence, the pH of the reaction system was controlled to 8.0, the temperature was lowered to 10°C, the mixture was transferred to a reactor, nitrogen was passed through and the emulsifier was turned on for stirring, and after stirring for 30 min, 500 g of hydrogen peroxide (dissolved in 3000 g of water) and 100 g of ferrous sulfate heptahydrate (dissolved in 1000 g of water) were added in sequence. During the reaction, the system naturally heated up and gradually thickened. The nitrogen passing and emulsification stirring were continued for 5 min and then stopped. The reactor was sealed and allowed to react for about 4 h to the highest temperature, and the mixture was kept warm for 2 h. After the reaction, a colloid was obtained. The colloid material in the reactor was extruded and granulated, and transported to a drying device for drying. After drying, the mixture was crushed and sieved, and particles with a particle size of ≤0.25 mm were collected and packaged. The obtained polyacrylamide dry powder particle density was measured to be 1.25 g / mL. The molecular weight was 2500×10 4 Dalt.

[0054] Example 3

[0055] 5536 kg of water was added to a batching kettle with a volume of 10 cubic meters, and 1600 kg of acrylamide and 2800 kg of 80 wt% acryloyloxyethyl trimethyl ammonium chloride were added in sequence under stirring to obtain a monomer solution; 80 kg of emulsifier hexadecyl trimethyl ammonium bromide and 0.6 kg of azobisisoheptanenitrile (dissolved in 200 kg of xylene) were added to the monomer solution in sequence, the pH of the reaction system was controlled to 4.0, the temperature was lowered to 2°C, the mixture was transferred to a reactor, nitrogen was passed through, and the emulsifier was turned on for stirring. After stirring for 30 minutes, the mixture was stirred for 30 minutes. 50g of tert-butyl hydroperoxide (dissolved in 1000g of water) and 300g of sodium thiosulfate (dissolved in 3000g of water) were added in sequence. During the reaction, the system naturally heated up and gradually thickened. Nitrogen was continued to be passed and emulsified and stirred for 5 minutes before stopping. The reactor was sealed and allowed to react for about 2.5 hours until the highest temperature was reached. The temperature was kept for 2 hours. After the reaction, a colloid was obtained. The colloid material in the reactor was extruded and granulated, and transported to a drying device for drying. After drying, it was crushed and sieved, and particles with a particle size of ≤0.25mm were collected and packaged. The obtained polyacrylamide dry powder particle density was measured to be 1.2g / mL. The molecular weight was 1200×10 4 Dalt.

[0056] Example 4

[0057] 6866 kg of water was added to a batching kettle with a volume of 10 cubic meters, and 1800 kg of acrylamide, 1200 kg of 80 wt% methacryloyloxyethyl trimethyl ammonium chloride and 800 kg of 60 wt% dimethyl diallyl ammonium chloride were added in sequence under stirring to obtain a monomer solution; 90 kg of emulsifier lauryl alcohol polyoxyethylene ether-23, 100 kg of dodecyl trimethyl ammonium chloride and 0.8 kg of azodicarbonamide (dissolved in 500 kg of ethanol) were added in sequence to the monomer solution; 5 white oil), control the pH of the reaction system to 4.5, cool to 4°C, transfer to the reactor, pass nitrogen and open the emulsifier to stir, stir for 30 minutes, add 20g of tert-butyl hydroperoxide (dissolved in 1000g water), 80g of sodium persulfate (dissolved in 1000g water) and 500g of sodium pyrosulfite (dissolved in 2000g water) in turn, the system naturally heats up and gradually thickens during the reaction, continue passing nitrogen and emulsifying stirring for 5 minutes and then stop, seal the reactor and let it stand for about 4 hours to the highest temperature, continue to keep warm for 2 hours, and obtain colloid after the reaction is completed. The colloid material in the reactor is extruded and granulated, and transported to the drying equipment for drying. After drying, it is crushed and sieved, and the particles with a particle size of ≤0.25mm are collected and packaged. It has been determined that the density of the obtained polyacrylamide dry powder particles is 1.18g / mL. The molecular weight is 600×10 4 Dalt.

[0058] Example 5

[0059] In order to better illustrate the advantages of the low-density polyacrylamide dry powder particles prepared by the present invention in preparing suspensions, three suspension samples were prepared according to the formula in Table 1, and the viscosity and stability of the suspensions prepared using commercially available high-density polyacrylamide dry powder particles of a certain brand No. 2520 as raw materials and the polyacrylamide dry powder particles prepared by the present invention as raw materials under the same stability were compared. The results are shown in Table 1.

[0060] Table 1 Comparison of suspending agent dosage and viscosity under the same stability of suspension

[0061]

[0062] It can be seen that the low-density polyacrylamide dry powder particles of the present invention can significantly reduce the apparent viscosity of the suspension while achieving the same suspension stability in the preparation of the suspension, thereby improving the application performance of on-site injection.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing low-density polyacrylamide dry powder particles, It is characterized in that The steps include: adding acrylamide and comonomer into water to obtain a monomer solution; An emulsifier and an organic solvent containing a porogen are sequentially added to the monomer solution, and under the action of the emulsifier, the organic solvent containing the porogen is uniformly dispersed into oil droplets, and the particle size of the oil droplets is controlled to be 500 nm to 5 μm; In an inert atmosphere, an initiator is added to carry out a polymerization reaction to obtain a colloid, and after granulation, drying and crushing, particles with a particle size of ≤0.25 mm are collected to obtain low-density polyacrylamide dry powder particles; Wherein, the porogen is an azo compound.

2. The preparation method according to claim 1, It is characterized in that The azo compound is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile and azodicarbonamide; The azo compound is 0.01-2 wt % of the mass of the organic solvent.

3. The preparation method according to claim 1, It is characterized in that The comonomer is selected from one or more of nonionic monomers, anionic monomers and cationic monomers; The nonionic monomer is selected from one or more of N-vinylpyrrolidone, 2-methylacrylamide, N,N-dimethylacrylamide and N-tert-butylacrylamide; the nonionic monomer accounts for 0-5wt% of the total monomer amount; The anionic monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylallylsulfonic acid and vinylbenzenesulfonic acid; the anionic monomer accounts for 0-50wt% of the total monomer amount; The cationic monomer is selected from one or more of acryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, methyl allyl trimethyl ammonium chloride and dimethyl diallyl ammonium chloride; the cationic monomer accounts for 0-60wt% of the total monomer amount; The acrylamide and comonomers account for 15-40 wt% of the total weight of the raw materials.

4. The preparation method according to claim 1, It is characterized in that The emulsifier is selected from one or more of nonionic emulsifiers, anionic emulsifiers and cationic emulsifiers; The nonionic emulsifier is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene alkylamine and polyoxyethylene alkylamide; The anionic emulsifier is selected from one or more of sodium alkyl sulfonate, sodium alkyl aryl sulfonate, sodium alkyl sulfate and secondary alkyl sodium sulfate; The cationic emulsifier is selected from one or more of amine salt emulsifiers and / or quaternary ammonium salt emulsifiers; The emulsifier accounts for 0.4-5wt% of the total weight of the raw materials.

5. The preparation method according to claim 1, It is characterized in that The initiator is selected from one or more of persulfate, hydrogen peroxide, tert-butyl hydroperoxide, bisulfite, sulfite, ferrous salt, thiosulfate, pyrosulfite, and tertiary amine compounds; The initiator accounts for 0.001-0.1 wt% of the total weight of the raw materials.

6. The preparation method according to claim 1, It is characterized in that The organic solvent is selected from one or more of normal alkane solvents, isoalkane solvents, aromatic solvents, cycloalkane solvents, halogenated alkane solvents, ether solvents and lipid solvents; The organic solvent accounts for 0.5-10 wt% of the total weight of the raw materials.

7. The preparation method according to claim 1, It is characterized in that Before the polymerization reaction, the pH value of the reaction system is controlled between 4-8, and the temperature of the reaction system is controlled to 0-15°C.

8. A low-density polyacrylamide dry powder particle, It is characterized in that Prepared by the preparation method according to any one of claims 1 to 7; The density of the polyacrylamide dry powder particles is 1.1-1.3 g / mL, the particle size is ≤0.25 mm, and the molecular weight is (600-2500)×10 4 Dalt.

9. A polyacrylamide suspension, It is characterized in that The polyacrylamide suspension comprises the following raw material components in mass percentage: 20-55wt% of the polyacrylamide dry powder particles as claimed in claim 8; Suspending agent 0.2-5wt%; The rest is organic solvent.

10. Use of the polyacrylamide suspension as claimed in claim 9 in shale oil and shale gas exploitation.

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