Salt-resistant emulsion fracturing fluid thickening agent and preparation process thereof

Abstract

The application discloses a kind of anti-salt emulsion type fracturing fluid thickening agent and preparation process thereof, it is related to thickening agent technical field, including following component preparation: 2-methyl-N-[2-(2-oxo-1-imidazolidinyl)ethyl]-2-propenamide, 3-[N,N-dimethyl-[2-(2-methylprop-2-enyl oxy)ethyl]ammonium] propane-1-sulfonic acid inner salt, N-vinyl caprolactam, perfluoro octyl ethyl acrylate, crosslinking monomer, oil phase system, composite emulsifier, initiation system, nano reinforcing phase, chelating agent and deionized water.The anti-salt emulsion type fracturing fluid thickening agent can still maintain stable viscosity under high temperature and high salt conditions, and the preparation process is simple.

Description

Technical Field

[0001] This invention relates to the field of thickener technology, and in particular to a salt-resistant emulsion-type fracturing fluid thickener and its preparation process. Background Technology

[0002] In oil and gas field development, hydraulic fracturing technology is a key means to improve the recovery rate of low-permeability oil and gas reservoirs. As a core component of fracturing fluid, the performance of the fracturing fluid thickener directly affects the fracturing effect. However, existing thickeners generally suffer from performance degradation under high-temperature and high-salinity environments, limiting their application in complex oil and gas reservoirs.

[0003] Currently, thickeners for fracturing fluids are mainly prepared by polymerizing acrylamide with other monomers, such as sulfonic acid anionic monomers or quaternary ammonium salt cationic monomers. However, these fracturing fluid thickeners on the market have technical defects such as insufficient temperature resistance, and their salt resistance and shear resistance still need to be further improved, which hinders their development in the fields of petrochemicals and oilfield development.

[0004] To address the aforementioned issues, Chinese invention patent CN116622362B discloses a salt-resistant emulsion-type fracturing fluid thickener and its preparation process. The thickener is prepared from the following components by weight percentage: 25%-30% acrylamide, 2%-5% N-vinylpyrrolidone, 5%-8% 2-acrylamido-2-methylpropanesulfonic acid, 1-3% composite monomer, 25%-30% white oil, 1%-3% emulsifier, 0.1%-0.5% initiator, and the balance being water. The composite monomer includes one or more of alkyl methacrylate, alkyl acrylate, and N-alkyl-substituted acrylamide. This invention's thickener exhibits good temperature resistance and salt resistance, and is easy to use. In ultra-high temperature reservoir applications, the thickener demonstrates high salt resistance and stable apparent viscosity. The thickener exhibits good initial fluidity, making it easy to inject and allowing it to reach deep wells before exerting its effect, thus better realizing the thickener's function. However, it still has significant limitations in terms of resistance to ultra-high temperatures, resistance to ultra-high salt concentrations, long-term stability of emulsions, and adaptability to ultra-deep wells.

[0005] Therefore, developing a salt-resistant emulsion-type fracturing fluid thickener that can maintain stable viscosity under high temperature and high salt conditions and has a simple preparation process is of great practical significance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a salt-resistant emulsion-type fracturing fluid thickener that can maintain stable viscosity under high temperature and high salt conditions and has a simple preparation process, as well as its preparation process.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a salt-resistant emulsion-type fracturing fluid thickener, comprising the following components by weight percentage: 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide 20wt%-25wt%, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 8wt%-12wt%, N-vinylcaprolactam 3wt%-5wt%, perfluorooctyl ethyl acrylate 1wt%-2wt%, crosslinking monomer 0.1wt%-0.3wt%, oil phase system 25wt%-30wt%, composite emulsifier 2.5wt%-3.5wt%, initiator system 0.2wt%-0.4wt%, nano-reinforcing phase 0.5wt%-1wt%, chelating agent 0.03wt%-0.05wt%, with the balance being deionized water.

[0008] Preferably, the chelating agent is disodium ethylenediaminetetraacetate.

[0009] Preferably, the nano-reinforcing phase is cellulose nanocrystals.

[0010] Preferably, the cellulose nanocrystals have a length of 100-200 nm and a diameter of 10-20 nm.

[0011] Preferably, the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of (1-3):2:(0.8-1.2).

[0012] Preferably, the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:(0.8-1.2).

[0013] Preferably, the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:(1-2):(0.8-1.2).

[0014] Preferably, the crosslinking monomer is polyethylene glycol diacrylate.

[0015] Preferably, the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0016] Another objective of this invention is to provide a preparation process for the salt-resistant emulsion-type fracturing fluid thickener, comprising the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 28-32 min, bubbling with CO2 for deoxygenation for 20-30 min, adjusting the pH to 6.5-7.0 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 3500-4200 r / min, continuing shearing for 9-11 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 48-52℃, reacting for 2 h; then raising the temperature to 68-72℃ and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 38-42℃ and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0017] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0018] (1) The preparation process of the salt-resistant emulsion fracturing fluid thickener disclosed in this invention has a short process, low energy consumption, low equipment dependence, high preparation efficiency and high finished product qualification rate, and is suitable for continuous large-scale production. It has high promotion and application value.

[0019] (2) The salt-resistant emulsion-type fracturing fluid thickener disclosed in this invention is made of the following components in weight percentage: 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide 20wt%-25wt%, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 8wt%-12wt%, N-vinylcaprolactam 3wt%-5wt%, perfluorooctyl ethyl acrylate 1wt%-2wt%, crosslinking monomer 0.1wt%-0.3wt%, oil phase system 25wt%-30wt%, composite emulsifier 2.5wt%-3.5wt%, initiator system 0.2wt%-0.4wt%, nano-reinforcing phase 0.5wt%-1wt%, chelating agent 0.03wt%-0.05wt%, and the balance being deionized water. Through the synergistic effect of the various components, the prepared salt-resistant emulsion-type fracturing fluid thickener can maintain a stable viscosity even under high temperature and high salt conditions.

[0020] (3) The salt-resistant emulsion-type fracturing fluid thickener disclosed in this invention, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, under high salt environment, its positive and negative charge groups are induced by salt ions to promote polymer chain extension, enhance the interaction with water molecules, and maintain thickening ability; the imidazole ring of 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide has strong polarity and charge stability, which can reduce the interference of salt ions on the polymer backbone; disodium ethylenediaminetetraacetate chelates metal ions in water, avoiding their destruction of polymer structure, and further weakening the negative impact of salt ions. The above synergistic effect enables the thickener to maintain excellent thickening performance under high salt conditions, solving the key pain point of traditional thickeners "viscosity reduction upon contact with salt". The N-vinylcaprolactam cyclic structure forms stable hydrogen bonds at high temperatures, enhancing the interaction between polymer chains and resisting thermal deformation. The crosslinked chain length of polyethylene glycol diacrylate, with a number-average molecular weight of 575, is moderate, ensuring the strength of the network structure while avoiding brittleness caused by excessive crosslinking, and maintaining viscoelasticity at high temperatures. Cellulose nanocrystals form hydrogen bonds with polymer chains through their high specific surface area, acting as a "nanoskeleton" to enhance the mechanical strength of the system and reduce structural damage under shear. The oil phase, a blend of white oil, isododecane, and PAO10, has strong antioxidant properties and is not easily decomposed at high temperatures, providing a stable medium for the emulsion.

[0021] (4) The salt-resistant emulsion-type fracturing fluid thickener disclosed in this invention is a compound of Span80 and Tween80 at a ratio of 1:(0.8-1.2), with an HLB value suitable for the oil phase system, forming a tight interfacial film to inhibit droplet aggregation; ultrasonic pretreatment ensures component homogeneity, and nanocellulose is added under shear at 3500-4200 r / min to avoid its aggregation and further stabilize the emulsion structure; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite at a mass ratio of (1-3):2:(0.8-1.2), which, combined with the redox mechanism, improves the monomer conversion rate and reduces emulsion degradation caused by residual monomers. The final emulsion has good stability, solving the problem of "short storage period and easy demulsification during construction" of traditional emulsions.

[0022] (5) The salt-resistant emulsion-type fracturing fluid thickener disclosed in this invention uses a fluorinated monomer (perfluorooctyl ethyl acrylate) to reduce surface energy and improve anti-fouling properties (such as adsorption of formation impurities) and water resistance; a segmented temperature-controlled polymerization process (low-temperature initiation-medium-temperature polymerization-low-temperature crosslinking) ensures a uniform polymer structure and avoids excessive or insufficient local crosslinking, making the thickening performance more stable; the biocompatibility of cellulose nanocrystals improves environmental friendliness and meets the needs of green mining. This thickener can be widely used in fracturing operations of complex reservoirs such as conventional oil and gas reservoirs, high-salt and high-temperature oil and gas reservoirs, and shale gas, solving the limitation of existing products that "meet single performance standards but have poor overall adaptability". Detailed Implementation

[0023] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0024] Example 1

[0025] A salt-resistant emulsion-type fracturing fluid thickener comprises the following components in weight percentage: 20wt% 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide, 8wt% 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, 3wt% N-vinylcaprolactam, 1wt% perfluorooctyl ethyl acrylate, 0.1wt% crosslinking monomer, 25wt% oil phase system, 2.5wt% composite emulsifier, 0.2wt% initiator system, 0.5wt% nano-reinforcing phase, 0.03wt% chelating agent, and the balance being deionized water.

[0026] The chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the length of the cellulose nanocrystals is 100-200 nm and the diameter is 10-20 nm; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of 1:2:0.8; the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:0.8; the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:1:0.8; the crosslinking monomer is polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0027] A preparation process for the salt-resistant emulsion-type fracturing fluid thickener includes the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 28 min, bubbling with CO2 for 20 min to remove oxygen, adjusting the pH to 6.5 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 3500 r / min, continuing shearing for 9 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 48°C, reacting for 2 h; then raising the temperature to 68°C and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 38°C and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0028] Example 2

[0029] A salt-resistant emulsion-type fracturing fluid thickener comprises the following components in weight percentage: 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide 21wt%, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 9wt%, N-vinylcaprolactam 3.5wt%, perfluorooctyl ethyl acrylate 1.2wt%, crosslinking monomer 0.15wt%, oil phase system 26wt%, composite emulsifier 2.7wt%, initiator system 0.25wt%, nano-reinforcing phase 0.6wt%, chelating agent 0.035wt%, and the balance being deionized water.

[0030] The chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the length of the cellulose nanocrystals is 100-200 nm and the diameter is 10-20 nm; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of 1.5:2:0.9; the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:0.9; the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:1.3:0.9; the crosslinking monomer is polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0031] A preparation process for the salt-resistant emulsion-type fracturing fluid thickener includes the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 29 min, bubbling with CO2 for 23 min to remove oxygen, adjusting the pH to 6.6 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 3600 r / min, continuing shearing for 9.5 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 49°C, reacting for 2 h; then raising the temperature to 69°C and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 39°C and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0032] Example 3

[0033] A salt-resistant emulsion-type fracturing fluid thickener comprises the following components in weight percentage: 23wt% 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide, 10wt% 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, 4wt% N-vinylcaprolactam, 1.5wt% perfluorooctyl ethyl acrylate, 0.2wt% crosslinking monomer, 28wt% oil phase system, 3wt% composite emulsifier, 0.3wt% initiator system, 0.8wt% nano-reinforcing phase, 0.04wt% chelating agent, and the balance being deionized water.

[0034] The chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the length of the cellulose nanocrystals is 100-200 nm and the diameter is 10-20 nm; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of 2:2:1; the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:1; the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:1.5:1; the crosslinking monomer is polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0035] A preparation process for the salt-resistant emulsion-type fracturing fluid thickener includes the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 30 min, bubbling with CO2 for 25 min to remove oxygen, adjusting the pH to 6.7 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 3800 r / min, continuing shearing for 10 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 50°C and reacting for 2 h; then raising the temperature to 70°C and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 40°C and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0036] Example 4

[0037] A salt-resistant emulsion-type fracturing fluid thickener comprises the following components in weight percentage: 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide 24wt%, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 11wt%, N-vinylcaprolactam 4.5wt%, perfluorooctyl ethyl acrylate 1.8wt%, crosslinking monomer 0.25wt%, oil phase system 29wt%, composite emulsifier 3.3wt%, initiator system 0.35wt%, nano-reinforcing phase 0.9wt%, chelating agent 0.045wt%, and the balance being deionized water.

[0038] The chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the length of the cellulose nanocrystals is 100-200 nm and the diameter is 10-20 nm; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of 2.5:2:1.1; the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:1.1; the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:1.8:1.1; the crosslinking monomer is polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0039] A preparation process for the salt-resistant emulsion-type fracturing fluid thickener includes the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 31 min, bubbling with CO2 for 28 min to remove oxygen, adjusting the pH to 6.9 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 4100 r / min, continuing shearing for 10.5 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 51°C and reacting for 2 h; then raising the temperature to 71°C and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 41°C and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0040] Example 5

[0041] A salt-resistant emulsion-type fracturing fluid thickener comprises the following components in weight percentage: 25wt% 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide, 12wt% 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, 5wt% N-vinylcaprolactam, 2wt% perfluorooctyl ethyl acrylate, 0.3wt% crosslinking monomer, 30wt% oil phase system, 3.5wt% composite emulsifier, 0.4wt% initiator system, 1wt% nano-reinforcing phase, 0.05wt% chelating agent, and the balance being deionized water.

[0042] The chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the length of the cellulose nanocrystals is 100-200 nm and the diameter is 10-20 nm; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of 3:2:1.2; the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:1.2; the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:2:1.2; the crosslinking monomer is polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 575.

[0043] A preparation process for the salt-resistant emulsion-type fracturing fluid thickener includes the following steps: mixing all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically dispersing for 32 min, bubbling with CO2 for 30 min to remove oxygen, adjusting the pH to 7.0 to form a homogeneous emulsion; adding the nano-reinforcing phase under shear at 4200 r / min, continuing shearing for 11 min, then transferring the emulsion to a high-pressure reactor, purging with nitrogen three times, and then performing three-stage temperature-controlled polymerization: first, adding 60% of the total mass of the initiation system at 52℃ and reacting for 2 h; then raising the temperature to 72℃ and adding the remaining 40% of the initiation system, reacting for 3 h; finally, lowering the temperature to 42℃ and adding polyethylene glycol diacrylate, maintaining the temperature for 1 h to obtain a crosslinked emulsion.

[0044] Comparative Example 1

[0045] This example provides a salt-resistant emulsion-type fracturing fluid thickener and its preparation process, which is basically the same as in Example 1. The difference is that an equal amount of acrylamide is used instead of 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide, and perfluorooctyl ethyl acrylate is not added.

[0046] Comparative Example 2

[0047] This example provides a salt-resistant emulsion-type fracturing fluid thickener and its preparation process, which is basically the same as in Example 1. The difference is that an equal amount of 2-acrylamido-2-methylpropanesulfonic acid is used instead of the 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, and no nano-reinforcing phase is added.

[0048] Structural Characterization: Taking Example 1 as an example, 10g of the emulsion sample was dried in a vacuum freeze dryer (-50℃, 0.01MPa) for 48h to remove the oil phase and moisture, obtaining polymer powder. The powder was mixed with KBr at a mass ratio of 1:100, ground in an agate mortar until the particle size was <2μm, and compressed into tablets (pressure 10MPa, holding pressure for 30s) to form transparent sheets. Following GB / T 6040-2019, a Nicolet iS50 spectrometer was used with a scanning range of 4000-400cm². -1 4cm resolution -1 A total of 64 scans were performed, and air interference was deducted from the background scan.

[0049] The result shows: 1670cm -1 Amide II bands appear at 1620 cm (C=O stretching). -1 The appearance of the C=N stretching vibration peak of the imidazole ring at 1190 cm⁻¹ confirms the successful polymerization of 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide; -1 (S=O asymmetric stretching) and 1040cm -1 The peak intensity ratio of (S=O symmetric stretching) is 1.8:1, indicating that the sulfonic acid group of the inner salt of 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid is fully preserved; 1230 cm⁻¹ -1 The presence of the CF characteristic peak at 1640 cm⁻¹ indicates successful polymerization of perfluorooctyl ethyl acrylate; -1 The presence of a C=O stretching vibration peak in the lactam ring indicates successful polymerization of N-vinylcaprolactam; 1100 cm⁻¹ -1 The presence of a stretching vibration peak of the ether bond (COC) indicates that polyethylene glycol diacrylate has been successfully polymerized.

[0050] The emulsion before the addition of polyethylene glycol diacrylate in Example 1 was dried in a vacuum freeze dryer (-50°C, 0.01 MPa) for 48 hours to remove the oil phase and moisture, obtaining a polymer powder. The weight-average molecular weight (Mb) of the prepolymer before crosslinking was determined using a Waters 1515 gel permeation chromatograph. w ) = 1.7 × 10 6 Number average molecular weight (M n ) = 1.4 × 10 6 PDI=1.21.

[0051] Performance characterization: At room temperature, 1 wt% of the thickener from the examples was added to a 200 g / L NaCl solution, and the apparent viscosity of the solution was tested; the thickeners from each example were subjected to a shear rate of 170 s⁻¹ at 180 °C. -1 Under the condition of continuous shearing for 2 hours, the apparent viscosity of the solution was tested; the thickeners of each case were left to stand at 60°C for 3 months to observe whether stratification occurred.

[0052] Table 1. Performance Characterization Results of Salt-Resistant Emulsion-Type Fracturing Fluid Thickener

[0053]

[0054] As can be seen from Table 1, the salt-resistant emulsion-type fracturing fluid thickeners involved in the embodiments of the present invention have more stable viscosity than the comparative product under high temperature and high salt conditions; the combined use of 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide, perfluorooctyl ethyl acrylate, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and nano-reinforcing phase is beneficial to improving the above-mentioned performance.

[0055] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A salt-resistant emulsion-type fracturing fluid thickener, characterized in that, It comprises the following components by weight percentage: 2-methyl-N-[2-(2-oxo-1-imidazolyl)ethyl]-2-acrylamide 20wt%-25wt%, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 8wt%-12wt%, N-vinylcaprolactam 3wt%-5wt%, perfluorooctyl ethyl acrylate 1wt%-2wt%, crosslinking monomer 0.1wt%-0.3wt%, oil phase system 25wt%-30wt%, complex emulsifier 2.5wt%-3.5wt%, initiator The composition consists of 0.2wt%-0.4wt% of a nano-reinforcing phase, 0.5wt%-1wt% of a chelating agent, and the balance being deionized water; the chelating agent is disodium ethylenediaminetetraacetate; the nano-reinforcing phase is cellulose nanocrystals; the initiation system is a mixture of potassium persulfate, azobisisobutyronitrile, and sodium bisulfite in a mass ratio of (1-3):2:(0.8-1.2); the composite emulsifier is a mixture of Span80 and Tween80 in a mass ratio of 1:(0.8-1.2); the oil phase system is a mixture of white oil No. 3, isododecane IP1620, and DowSyn PAO10 in a mass ratio of 1:(1-2):(0.8-1.2); and the crosslinking monomer is polyethylene glycol diacrylate.

2. The salt-resistant emulsion-type fracturing fluid thickener according to claim 1, characterized in that, The cellulose nanocrystals have a length of 100-200 nm and a diameter of 10-20 nm.

3. The salt-resistant emulsion-type fracturing fluid thickener according to claim 1, characterized in that, The number-average molecular weight of the polyethylene glycol diacrylate is 575.

4. A preparation process for a salt-resistant emulsion-type fracturing fluid thickener according to any one of claims 1-3, characterized in that, The process includes the following steps: Mix all components except the nano-reinforcing phase, the initiation system, and the crosslinking monomer, ultrasonically disperse for 28-32 min, bubble CO2 through the mixture for 20-30 min to remove oxygen, adjust the pH to 6.5-7.0 to form a homogeneous emulsion; add the nano-reinforcing phase under shear at 3500-4200 r / min, continue shearing for 9-11 min, then transfer the emulsion to a high-pressure reactor, purge with nitrogen three times, and polymerize in three stages under controlled temperature. First, add 60% of the total mass of the initiation system at 48-52℃ and react for 2 h; then raise the temperature to 68-72℃ and add the remaining 40% of the initiation system, react for 3 h; finally, lower the temperature to 38-42℃ and add polyethylene glycol diacrylate, maintain the temperature for 1 h, and obtain a crosslinked emulsion.

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