A volume fracturing intelligent construction joint network thickening agent and a preparation method thereof

Abstract

The application discloses a volume fracturing intelligent construction fracture network thickening agent and a preparation method thereof, relates to the technical field of high-temperature oil and gas well fracturing fluid thickening agents, and the preparation method comprises the following steps: 1) synthesis of a biomimetic polymer skeleton; 2) grafting of a molecular shock absorber structure; and 3) modification of an intelligent switch group. The product is an intelligent biomimetic fracture network thickening agent, and through the synergistic effect of a biomimetic polymer skeleton, a dynamic disulfide bond molecular shock absorber and a crown ether intelligent switch group, specific response to potassium ions is realized. In K + The product can be quickly converted from a fluid state into an elastic gel state under triggering, and the sand carrying performance is significantly improved; the product has excellent high-temperature resistance and self-repairing capacity, and can be used for 10,000 s ‑1 The viscosity recovery rate after high-speed shearing is more than 78%, and the viscosity retention rate is kept high in long-term shearing. Meanwhile, the product has excellent gel breaking performance, and provides an intelligent controllable, efficient and stable fracture network construction solution for volume fracturing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature oil and gas well fracturing fluid thickening agent, and particularly relates to a volume fracturing intelligent fracture network building thickening agent and a preparation method thereof. BACKGROUND

[0002] The related art in the field is roughly as follows: in high-temperature oil and gas well fracturing operations, traditional polymer thickening agents face severe challenges. With the development of shale oil and gas to deep layers, the downhole temperature is generally higher than 150 DEG C, and in some blocks, it even reaches 200 DEG C. In this environment, the thermal motion of polymer molecular chains intensifies, resulting in a sharp decrease in viscosity, which seriously affects the sand carrying performance and fracture conductivity efficiency. In recent years, domestic and foreign researches mainly focus on the synthesis of temperature-resistant monomers and the modification of nano-composite materials, but neither of them can effectively solve the performance degradation problem under the synergistic action of high temperature and high shear.

[0003] At present, three technical routes are mainly used in the industry: ① acrylamide copolymer (such as AMPS copolymer), which improves the temperature resistance by introducing sulfonic acid groups, but the viscosity retention rate is less than 40% at 180 DEG C; ② hydrophobic associated polymer, which relies on physical crosslinking to maintain the structure, but has poor shear recovery; and ③ organic metal crosslinking system, which can improve the high-temperature performance, but has the problems of gel breaking difficulty and environmental risk.

[0004] The existing technologies generally have the following defects: ① molecular chain disentanglement under high-temperature conditions leads to viscosity collapse; ② irreversible structure damage under high shear rate; and ③ lack of self-adaptive adjustment ability to dynamic fractures, which requires manual adjustment of pumping parameters. SUMMARY

[0005] The present application relates to the technical field of high-temperature oil and gas well fracturing fluid thickening agent, and particularly relates to a volume fracturing intelligent fracture network building thickening agent and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the technical scheme is adopted as follows:

[0007] The present application first proposes a volume fracturing intelligent fracture network building thickening agent, which comprises the following steps:

[0008] S1, synthesis of a biomimetic polymer skeleton

[0009] 2,5-dihydroxyterephthalic acid, a number average molecular weight of 1000 g / mol polyoxypropylene triamine, and N-methyl pyrrolidone are sequentially added into three reaction kettles, mechanical stirring is started, and the solid is completely dissolved under nitrogen protection after stirring for 30 min to form a homogeneous solution;

[0010] N,N'-dicyclohexyl carbodiimide, 4-dimethylaminopyridine were added into the homogeneous solution, the temperature of oil bath was raised to 120-140℃, and the reaction was refluxed for 8h; after the reaction was completed, the heating was stopped, and the reaction solution was naturally cooled to below 40℃;

[0011] N,N'-dicyclohexyl carbodiimide (DCC) was used as a dehydrating agent, and 4-dimethylaminopyridine (DMAP) was used as a nucleophilic catalyst to assist the reaction of -COOH of 2,5-dihydroxyterephthalic acid and -NH2 of polyoxypropylenetriamine to form a "polyether-aromatic amide" prepolymer, and DCC was converted into white by-product N,N'-dicyclohexylurea, which was removed by filtration; in the prepolymer, the phenolic hydroxyl group (-OH) on the aromatic ring and the adjacent imino group (-NH-) of the amide bond underwent "intramolecular dehydration ring closure" at high temperature to form a benzoxazole heterocycle;

[0012] ;

[0013] The reaction solution was transferred out of the reaction kettle, filtered to remove the white N,N'-dicyclohexylurea by-product, and the filtrate was transferred into a rotary evaporator and concentrated at 60℃ water bath and -0.09MPa vacuum until a viscous crude biomimetic polymer product was obtained;

[0014] Benzoxazole is a rigid conjugated structure with extremely high chemical stability and can resist chain scission at high temperatures above 180℃, providing basic high-temperature resistance for the densification agent.

[0015] The molar ratio of 2,5-dihydroxyterephthalic acid, polyoxypropylenetriamine, N,N'-dicyclohexyl carbodiimide and 4-dimethylaminopyridine is 1:1.1:2.2:0.01;

[0016] S2, grafting of a molecular shock absorber structure

[0017] The crude biomimetic polymer product was redissolved in N-methylpyrrolidone and transferred to another reaction kettle; 1,2-dithiopentane-3-valeric acid was dissolved in N-methylpyrrolidone and placed in a high-position dropping tank;

[0018] Under nitrogen protection, -COOH of 1,2-dithiopentane-3-valeric acid and free -NH2 of the polymer main chain underwent amidation reaction at 60℃ to form a "main chain-NH-CO-side chain (dithia ring)" structure;

[0019] ;

[0020] Under nitrogen protection and stirring, the solution was slowly added dropwise, and the dropwise time was controlled for 1h; after the addition was completed, the reaction was continued at 60℃ for 6h to complete the side chain grafting reaction, and a grafted polymer was obtained;

[0021] The disulfide bond (-S-S-) can reversibly cleave and recombine under stress, absorb energy, generate sulfur radicals, and then exchange or recombine with other disulfide bonds to achieve energy dissipation, similar to the shock absorption mechanism in living organisms. This dynamic covalent bond allows the polymer network to self-repair after damage and maintain viscosity stability.

[0022] The reaction system was kept at 60°C under nitrogen protection. The graphene quantum dot nanodispersion was slowly and uniformly added to the vigorously stirred grafted polymer through a constant-pressure dropping funnel within 2h. After the addition was completed, N,N'-dicyclohexyl carbodiimide and 4-dimethylaminopyridine were added to the system as condensation catalysts. The reaction temperature was raised to 85°C, and the system was refluxed under this condition for 6h to obtain the grafted composite polymer.

[0023] ;

[0024] The carboxyl groups of the carboxylated graphene quantum dots (GQDs) undergo amide reaction with the amino groups of the grafted polymer and are grafted onto the polymer.

[0025] The mass of the graphene quantum dots accounts for 0.3-0.7% of the dry mass of the grafted composite polymer. The addition amount of N,N'-dicyclohexyl carbodiimide is 2.5-3 times the mass of the carboxylated graphene quantum dots, and the addition amount of 4-dimethylaminopyridine is 0.2-0.3 times the mass of the carboxylated graphene quantum dots.

[0026] S3, modification of intelligent switch groups

[0027] The reaction system was kept at 60°C. (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid and tetrabutylammonium chloride were added to the grafted polymer or grafted composite polymer. The reaction temperature was raised to 80°C, and the system was reacted at this temperature for 4h to allow (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid to be connected to the end of the polymer through amide reaction.

[0028] ;

[0029] (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid is a functionalized crown ether derivative that is connected to the polymer chain through amide reaction. The cavity diameter of the cyclic structure of 18-crown-6 is about 2.6-3.2Å, which best matches the diameter of potassium ion (K + ) (about 2.66Å), so 18-crown-6 has the highest complexation constant and selectivity for K + . When the fracturing fluid enters the formation and encounters formation water containing K + , the crown ether groups grafted on the polymer will capture these ions. One K +The two or more crown ether macrocycles can be simultaneously captured by two or more crown ether groups, connecting two different crown ether groups; forming dynamic and reversible physical cross-linking points between polymer chains, significantly increasing the apparent viscosity of the solution.

[0030] After the crown ether complexation of the cation, the whole crown ether-ion complex carries positive electricity. These positively charged groups repel each other on the polymer chain, resulting in more stretched polymer chains, from the curled state to the more relaxed conformation. The combination of chain stretching and cross-linking network greatly increases the effective volume occupied by the polymer molecules in the solution, and the viscosity increases.

[0031] For fracturing fluid, it can more effectively suspend and transport proppants, ensuring that they are carried to the deep part of the fracture; high-viscosity liquid can produce wider cracks and more complex branch networks in the rock, thereby increasing the reservoir modification volume.

[0032] When the fracturing fluid is diluted and the ion concentration decreases, the complexation equilibrium is broken, the ions are dissociated from the crown ether cavity, the cross-linking points are disconnected, and the three-dimensional network is disintegrated, resulting in a decrease in viscosity.

[0033] This reversibility enables the fracturing fluid to adapt to the formation environment. It automatically thickens in high-potassium formations and flows easily when it is returned, thereby reducing formation damage and improving the flowback rate.

[0034] The reaction solution is cooled to room temperature, and then poured into ice ether under vigorous stirring to precipitate, filtered, and the precipitated fibrous solid is collected and washed with deionized water and ethanol alternately; vacuum dried to obtain a yellowish to amber solid particle or powder of the intelligent biomimetic network thickening agent;

[0035] Among them, the mass of (+)- (18-crown-6) -2, 3, 11, 12-tetracarboxylic acid is 2.6-3.0% of the mass of the grafted polymer or grafted composite polymer; the mass of tetrabutylammonium chloride is 0.1-0.14% of the mass of the grafted polymer or grafted composite polymer;

[0036] S4, fracturing fluid preparation and application

[0037] The intelligent biomimetic network thickening agent is taken and added to a potassium chloride aqueous solution, stirred, and configured into a fracturing fluid, and a sodium hydroxide solution is used to adjust the pH value to 7.0±0.5;

[0038] Among them, the mass concentration of the intelligent biomimetic network thickening agent is 0.2-0.4%.

[0039] Preferably, in S1, the mass concentration of 2, 5-dihydroxyterephthalic acid and polyoxypropylene triamine in the homogeneous solution is 30-35%.

[0040] Preferably, in the S2, the concentration of the N-methylpyrrolidone solution of the biomimetic polymer is 1.2-1.4 mol / L.

[0041] Preferably, in the grafting composite polymer, the graphene quantum dot nanodispersion is obtained by ultrasonic dispersion of carboxylated graphene quantum dots in N-methylpyrrolidone.

[0042] Preferably, the nanodispersion is obtained by ultrasonic dispersion of carboxylated graphene quantum dots in N-methylpyrrolidone.

[0043] Preferably, in the S3, the mass of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid is 2.6-3.0% of the mass of the grafting polymer; the mass of tetrabutylammonium chloride is 0.1-0.14% of the mass of the grafting polymer.

[0044] Preferably, in the S4, the mass concentration of the aqueous potassium chloride solution is 5%; in the fracturing fluid, the mass concentration of the intelligent biomimetic network thickening agent is 0.2-0.4%.

[0045] The present application also proposes a volume fracturing intelligent construction network thickening agent prepared by the aforementioned preparation method, and the viscosity retention rate of the thickening agent without graphene quantum dots is 78% under high temperature conditions of 180℃, and the viscosity retention rate of the thickening agent with graphene quantum dots is increased to 85% at 200℃.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] 1. In the prior art, the polymer chain of the thickening agent is prone to hydrolysis, oxidative degradation or thermal scission in a high-temperature reservoir (usually higher than 150℃), resulting in a sharp decrease in viscosity and affecting the fracturing effect. In the step S1 of the present application, 2,5-dihydroxyterephthalic acid and polyoxypropylenetriamine are subjected to dehydration condensation to form a "polyether-aromatic amide" prepolymer, and then intramolecular dehydration ring closure generates a benzoxazole heterocycle. Benzoxazole is a rigid conjugated structure, and the conjugated system of its aromatic ring and heterocycle endows it with extremely high chemical stability and thermal stability. The conjugated electron cloud of the benzoxazole heterocycle is uniformly distributed, and the bond energy is high, which can effectively resist thermal vibration and free radical attack, and the chain is not prone to breakage at high temperatures above 180℃. In contrast, the carbon-carbon bond or ester bond of traditional polymers is prone to breakage at high temperatures.

[0048] 2. Existing viscosifiers usually undergo irreversible chain scission under high pressure shear (e.g. during fracturing), leading to permanent viscosity loss. In S2, 1,2-dithiopentane-3-valeric acid is grafted to the polymer backbone via amidation reaction, introducing disulfide bonds (-S-S-). Disulfide bonds can undergo reversible homolysis (generating sulfur radicals) under shear stress, and dissipate energy through recombination or exchange reactions, similar to shock-absorbing mechanisms in living organisms. This dynamic covalent bond allows the polymer network to self-repair after damage, restoring viscosity and thus maintaining long-term stability, improving the efficiency and service life of fracturing fluids.

[0049] 3. Viscosity adjustment of traditional viscosifiers relies on pH or simple ionic strength changes, with single and irreversible responsiveness. The crown ether group in this invention provides a reversible "smart switch" that can automatically optimize viscosity according to the ion environment downhole, adapting to complex formation conditions and improving fracture network construction accuracy. (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid is connected to the end of the polymer via amidation reaction, introducing crown ether groups. Crown ether can selectively complex potassium ions (from potassium chloride in fracturing fluid), adjusting viscosity by changing the electrostatic interaction and conformation between polymer chains. Under high pressure or high temperature conditions, crown ether-ion complexation can enhance network structure and improve viscosity; under normal conditions, it maintains low viscosity for easy pumping.

[0050] 4. In existing technologies, the addition of inorganic nanomaterials (such as silica or clay) often has poor dispersion and weak interfacial bonding, resulting in limited reinforcement effect. The GQDs in this invention are covalently grafted, achieving uniform dispersion and strong interfacial bonding, increasing the viscosity retention rate of the viscosifier to 85% at 200°C. Carboxylated graphene quantum dots (GQDs) are grafted to the polymer via amidation reaction, forming a nanocomposite structure. The high specific surface area and rigid lamellar structure of GQDs can act as physical crosslinking points, enhancing the rigidity and thermal conductivity of the polymer network, dispersing stress and inhibiting chain segment movement, thereby improving viscosity retention at high temperatures.

[0051] In summary, this invention starts from molecular design, introduces rigid heterocycles, dynamic covalent bonds, intelligent crown ethers and nanometer quantum dots, solving the core problems of existing viscosifiers, such as viscosity instability, easy degradation and single function under high temperature and high shear environment. Compared with existing technologies, it has made significant progress, especially suitable for volume fracturing operations in deep, high-temperature reservoirs. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 NMR hydrogen spectrum of the biomimetic polymer produced by the invention. DETAILED DESCRIPTION

[0053] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0054] The purity and manufacturers of each drug used in the experiment are shown in Table 1:

[0055] Table 1. Raw drug information

[0056]

[0057] Example 1:

[0058] A preparation method of a volume fracturing intelligent construction network thickening agent, comprising the following steps:

[0059] S1, synthesis of a biomimetic polymer skeleton

[0060] 2,5-dihydroxy terephthalic acid, polyoxypropylene triamine, and N-methyl pyrrolidone were sequentially added to a three-necked reaction kettle, mechanical stirring was started, and the reaction was stirred for 30 min under nitrogen protection until the solids were completely dissolved to form a homogeneous solution;

[0061] N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine were added to the homogeneous solution, the temperature of the oil bath was increased to 120-140 DEG C, and the reaction was refluxed for 8 h; after the reaction was completed, the heating was stopped, and the reaction liquid was naturally cooled to below 40 DEG C;

[0062] The reaction liquid was transferred out of the reaction kettle, filtered, and the white N,N'-dicyclohexyl urea by-product was removed, and the filtrate was transferred into a rotary evaporator, concentrated under a 60 DEG C water bath and a vacuum of-0.09 MPa, until a viscous biomimetic polymer crude product was obtained;

[0063] Part of the biomimetic polymer crude product was separated and purified, dissolved with dimethyl sulfoxide, and subjected to nuclear magnetic resonance hydrogen spectrum detection, and the obtained results are shown in Table 2: Figure 1

[0064] 1 HNMR analysis showed that the aromatic peak at 7.0-7.5 ppm confirmed the formation of benzoxazole heterocycle; the strong peak at 1.0-1.5 ppm corresponded to the methyl hydrogen of the polyoxypropylene chain, and the peak at 3.0-4.0 ppm was the methylene / hydrogen of the polyoxypropylene chain, which proved that the polyoxypropylene main chain was reserved; the peak near 8.0 ppm was the -NH- hydrogen of the heterocycle or amide bond, indicating that the amidation and ring closure reaction was completed; the peak at about 2.0 ppm was the residual amino hydrogen, which left active sites for subsequent grafting. The solvent interference was small, the spectrum matched the target skeleton structure, and the biomimetic polymer skeleton was successfully synthesized in the S1 step.

[0065] S2, grafting of a molecular shock absorber structure ​

[0066] The crude product of the biomimetic polymer was redissolved in N-methylpyrrolidone and transferred to another reaction kettle; 1,2-dithiopentane-3-pentanoic acid was dissolved in N-methylpyrrolidone and placed in a high-position dropping tank;

[0067] The solution was slowly added dropwise under nitrogen protection and stirring, and the dropwise time was controlled to be 1 h; after the dropwise addition was completed, the reaction was continued at 60°C for 6 h to completely complete the side chain grafting reaction, and a grafted polymer was obtained;

[0068] S3, modification of the intelligent switch group

[0069] The reaction system was kept at 60°C, and (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid and tetrabutylammonium chloride were added to the grafted polymer, the reaction temperature was increased to 80°C, and the reaction was carried out at this temperature for 4 h to link (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to the end of the polymer through an amidation reaction;

[0070] The reaction solution was cooled to room temperature, and was poured into ice ether under vigorous stirring to precipitate, was filtered, and the precipitated fibrous solid was collected and washed with deionized water and ethanol alternately; vacuum drying was performed to obtain a yellowish to amber solid particle or powder of the intelligent biomimetic network gelling agent;

[0071] S4, preparation and application of the fracturing fluid

[0072] The intelligent biomimetic network gelling agent was taken and added to a potassium chloride aqueous solution, was stirred, and was configured into a fracturing fluid, and a sodium hydroxide solution was used to adjust the pH value to 7.0±0.5.

[0073] In the S1, the number average molecular weight of the polyoxypropylene triamine was 1000 g / mol; the molar ratio of 2,5-dihydroxyterephthalic acid, polyoxypropylene triamine, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine was 1:1.1:2.2:0.01; and the mass concentration of 2,5-dihydroxyterephthalic acid and polyoxypropylene triamine in the homogeneous solution was 30%.

[0074] In the S2, the concentration of the N-methylpyrrolidone solution of the biomimetic polymer was 1.4 mol / L, and the mass of 1,2-dithiopentane-3-pentanoic acid was 4% of the mass of the biomimetic polymer.

[0075] In the S3, the mass of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was 3.0% of the mass of the grafted polymer; and the mass of tetrabutylammonium chloride was 0.1% of the mass of the grafted polymer.

[0076] In the S4, the mass concentration of the potassium chloride aqueous solution was 5%; and in the fracturing fluid, the mass concentration of the intelligent biomimetic network gelling agent was 0.4%.

[0077] Example 2

[0078] The experimental scheme is the same as that in Example 1, but in S1, the number average molecular weight of the polyoxypropylene triamine is 1000; the molar ratio of 2,5-dihydroxyterephthalic acid, polyoxypropylene triamine, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine is 1:1.1:2.2:0.01; the mass concentration of 2,5-dihydroxyterephthalic acid and polyoxypropylene triamine in the homogeneous solution is 32.5%.

[0079] In S2, the concentration of the N-methylpyrrolidone solution of the biomimetic polymer is 1.3 mol / L, and the mass of 1,2-dithiopentane-3-valeric acid is 4.5% of the mass of the biomimetic polymer.

[0080] In S3, the mass of (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid is 2.8% of the mass of the grafted polymer; the mass of tetrabutylammonium chloride is 0.12% of the mass of the grafted polymer.

[0081] In S4, the mass concentration of the potassium chloride aqueous solution is 5%; in the fracturing fluid, the mass concentration of the intelligent biomimetic network thickening agent is 0.3%.

[0082] Example 3

[0083] The experimental scheme is the same as that in Example 1, but in S1, the number average molecular weight of the polyoxypropylene triamine is 1000; the molar ratio of 2,5-dihydroxyterephthalic acid, polyoxypropylene triamine, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine is 1:1.1:2.2:0.01; the mass concentration of 2,5-dihydroxyterephthalic acid and polyoxypropylene triamine in the homogeneous solution is 35%.

[0084] In S2, the concentration of the N-methylpyrrolidone solution of the biomimetic polymer is 1.2 mol / L, and the mass of 1,2-dithiopentane-3-valeric acid is 5% of the mass of the biomimetic polymer.

[0085] In S3, the mass of (+)- (18-crown-6)-2,3,11,12-tetracarboxylic acid is 2.6% of the mass of the grafted polymer; the mass of tetrabutylammonium chloride is 0.14% of the mass of the grafted polymer.

[0086] In S4, the mass concentration of the potassium chloride aqueous solution is 5%; in the fracturing fluid, the mass concentration of the intelligent biomimetic network thickening agent is 0.2%.

[0087] Example 4

[0088] The experimental scheme is the same as that in Example 2, but the grafted polymer uses graphene quantum dots as a nano-enhanced phase, and the specific implementation process includes the following steps:

[0089] The reaction system is kept at 60℃ and under nitrogen protection, the nanodispersion is slowly and uniformly added to the grafting polymer under vigorous stirring through a constant pressure dropping funnel within 2h, after the addition is completed, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine are added to the system as condensation catalysts; the reaction temperature is raised to 85℃, and the grafting composite polymer is obtained under the condition of refluxing reaction for 6h; the subsequent use method of the grafting composite polymer is the same as that of the grafting polymer.

[0090] The nanodispersion is obtained by ultrasonic dispersion of the carboxylated graphene quantum dots in N-methyl pyrrolidone; the mass of the carboxylated graphene quantum dots accounts for 0.5% of the mass of the final intended polymer solid;

[0091] The addition amount of N,N'-dicyclohexyl carbodiimide is 2.75 times the mass of the carboxylated graphene quantum dots, and the addition amount of 4-dimethylamino pyridine is 0.25 times the mass of the carboxylated graphene quantum dots.

[0092] Also designed are:

[0093] Example 5: The same as the formulation and experimental method of Example 2, but instead of using (+) - (18-crown-6) -2, 3, 11, 12-tetracarboxylic acid, a carboxylated p-tert-butyl calix[4]arene of the same molar amount is used;

[0094] Example 6: The same as the formulation and experimental method of Example 2, but instead of using 1, 2-dithiopentane-3-pentanoic acid, a di(dithiocarbonyl) tetrathiafulvalene of a molar amount of 1 / 2 is used;

[0095] Comparative Example 1: The same as the formulation and experimental method of Example 2, but in the S1, the temperature of the refluxing reaction is controlled at 100℃;

[0096] Comparative Example 2: The same as the formulation and experimental method of Example 2, but in the S1, the temperature of the refluxing reaction is controlled at 160℃;

[0097] Comparative Example 3: The same as the formulation and experimental method of Example 2, but in the S1, the number average molecular weight of the polyoxypropylene triamine is 400g / mol;

[0098] Comparative Example 4: The same as the formulation and experimental method of Example 2, but in the S1, the number average molecular weight of the polyoxypropylene triamine is 3000g / mol.

[0099] For each example and comparative example, the specific solubility and dissolution rate, rheological property test, sand suspension performance, gel breaking performance and other performance detection are carried out according to SY / T 6376 "General Technical Conditions for Fracturing Fluid" and SY / T 5107 "Performance Evaluation Method of Water-based Fracturing Fluid", and the corresponding results are shown in the following table:

[0100] Table 2. Performance test data of each fracturing fluid

[0101]

[0102] The temperature rising curve was set to test the viscosity retention rate of Example 2 at different temperatures;

[0103]

[0104] Designing Comparative Example 5 to verify the ionic responsiveness of the application;

[0105] Comparative Example 5: The same as the formulation and experimental method of Example 2, but the thickening agent was prepared into a fracturing fluid in a NaCl aqueous solution of the same mass concentration;

[0106] The fracturing fluid was subjected to 10000 s -1 of shear rate using a rheometer or a high-speed stirrer for a period of time, so that its viscosity decreased significantly. Then, it was quickly returned to low shear conditions, and the recovery of viscosity over time was monitored to verify the self-repairing ability of the application;

[0107] Self-repairing ability verification experiment: using a Hake rheometer, a "ladder change shear rate" program was used to simulate the high-speed shear (equivalent to the end of the fracture) and low-speed shear (inside the fracture) process that the fracturing fluid experiences in the pipeline.

[0108] Initial stage: measure the initial viscosity (η0) at a low shear rate (1 s -1 ).

[0109] High-speed shear stage: instantaneously increase the shear rate to 10000 s -1 and maintain for 60 seconds to simulate the extreme shear that the fracturing fluid experiences in the perforation and near-wellbore zone, and record the viscosity at this time (η1).

[0110] Recovery stage: quickly reduce the shear rate back to 1 s -1 , continuously monitor the recovery of viscosity over time (180 seconds), and record the final recovered viscosity (η2).

[0111] Recovery rate = (η2-η1) / (η0-η1) x 100%

[0112]

[0113] On the rheometer, by alternately changing the ion concentration in the solution of Comparative Example 5, injecting KCl concentrate in the middle of the test, and monitoring the real-time changes of storage modulus and loss modulus online, the intelligent response rheology of the application was verified;

[0114] Smart response rheological verification experiment: dynamic oscillation test using a rheometer equipped with an online titration tool;

[0115] Initial state: load the fracturing fluid of Comparative Example 5 into the measurement unit, apply a fixed frequency of 1 Hz and a strain of 0.5% (within the linear viscoelastic region), and continuously monitor the storage modulus (G', representing elasticity) and loss modulus (G", representing viscosity).

[0116] Smart response trigger: at 100 seconds into the test, a small amount of high-concentration KCl concentrate is quickly injected through the titration system, causing the K + Concentration instantaneously reaches a level comparable to a 5% KCl solution.

[0117] Continuous monitoring: continue to monitor the changes in G' and G" over time until the modulus values stabilize again.

[0118]

[0119] The self-repairing ability of the thickening agent and the smart response rheology are derived from the multi-scale synergistic effect of "dynamic bond reversible action", "host-guest interaction", "rigid skeleton support", and "nanometer enhancement synergy" in the molecular structure. Data analysis:

[0120] The core of self-repairing is the reversible breaking-recombination of dynamic covalent bonds (disulfide bonds), combined with the "crown ether-K + Host-guest crosslinking network reconstruction, when the fracturing fluid is subjected to 10000 s -1 High-speed shearing, the physical entanglement between polymer chains is broken, and the reversible breaking of the disulfide bond (-S-S-) of 1,2-dithiopentane-3-valerate grafting occurs, consuming external force to protect the main chain, resulting in a sudden drop in system viscosity from the initial η0 (420 mPa・s) to η1 (55 mPa・s), and the molecular chains are in a dispersed state of "unentanglement and broken bonds".

[0121] Low shear rate stage, the broken -S-S- bonds are recombined through mechanisms such as nucleophilic substitution of sulfur atoms and free radical exchange under low shear, allowing the dispersed molecular chains to reconnect; K + Accurate matching with the cavity (diameter about 2.6 Å) of (+) - (18-crown-6) -2,3,11,12-tetracarboxylic acid, forming a stable 1:1 host-guest inclusion complex. Multiple polymer chains are quickly aggregated into a three-dimensional network through the bridging action of "crown ether-K + The final viscosity of Example 2 is restored to η2 (380 mPa・s), with a recovery rate of 92.50%.

[0122] The ionic radius of Na + is about 0.95 Å, and Comparative Example 5 uses an aqueous NaCl solution, and 18-crown-6 has a strong complexing ability for Na+ The inclusion constant of K + cannot effectively form a "crown ether-metal ion" crosslinking network; if the disulfide bond is absent, the molecular chain is difficult to recombine after breaking, resulting in η1 of only 40 mPa・s after shearing and η2 of only 90 mPa・s after recovery, and a recovery rate of only 29.40%.

[0123] The intelligent response is derived from the "on-off" regulation of the polymer network by the host-guest interaction of crown ether-metal ion; in the initial state, the inclusion of K + is extremely weak, and the polymer chains are only maintained by weak physical entanglement, showing that the loss modulus G" (3 Pa) > the storage modulus G' (1.5 Pa), the system is in a "fluid state" (viscosity is dominant), and it is convenient for pumping construction. After the injection of KCl, the concentration of K + suddenly rises, and the crown ether rapidly forms a stable host-guest inclusion compound with K + . At 110 s, multiple polymer chains are bridged by "crown ether-K + -crown ether", and are aggregated from a "dispersed state" into a "network state", the elasticity is rapidly enhanced, showing that G' (5 Pa) > G" (4.5 Pa), the system is converted into a "gel state" (elasticity is dominant), and it is beneficial for sand carrying and fracture creation. At 150 s-300 s, more K + participates in the inclusion, the network continues to densify, G' increases from 15 Pa to 35 Pa, G" increases from 8 Pa to 12 Pa, G' is always greater than G", the gel state is stable, and it is proved that the response of the crown ether to K + has the characteristics of "rapid triggering and continuous enhancement".

[0124] In addition to the dynamic disulfide bond and the crown ether host-guest, the auxiliary role of other structures on the performance cannot be ignored: the benzoxazole heterocycle synthesized by S1 is a conjugated rigid structure, which provides the basis for the polymer to resist high temperature and degradation, and provides stable "skeletal support" for the dynamic bond and the host-guest interaction; the graphene quantum dots are combined with the polymer main chain through covalent bonds, which on the one hand "anchors" the main chain and inhibits excessive slipping during shearing; on the other hand, the large specific surface area provides additional physical crosslinking points, which cooperatively improves the self-repairing efficiency and response speed; if the disulfide bond is replaced by a tetrathiafulvalene (embodiment 6, containing more dynamic-S-S- bonds), the self-repairing sites are more abundant; if the crown ether is replaced by a calixarene (embodiment 5, a multidentate macrocycle), more ion types can be responded, and the applicability of intelligent regulation is further expanded.

[0125] The above merely describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacements or changes to the technical solutions and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a volume-fracturing intelligent building fracture network gelling agent, characterized in that, The method comprises the following steps: S1, synthesis of a biomimetic polymer skeleton A three-necked reaction kettle is sequentially added with 2,5-dihydroxyterephthalic acid, polyoxypropylene triamine with a number average molecular weight of 1000 g / mol, N-methyl pyrrolidone, and mechanical stirring is started. After 30 min of stirring under nitrogen protection until the solids are completely dissolved, a homogeneous solution is formed; N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine are added to the homogeneous solution, and the temperature of the oil bath is raised to 120-140 DEG C. The reaction is refluxed for 8 h. After the reaction is completed, heating is stopped, and the reaction liquid is naturally cooled to below 40 DEG C; The reaction liquid is transferred out of the reaction kettle, filtered to remove the white N,N'-dicyclohexyl urea by-product, and the filtrate is transferred into a rotary evaporator. Concentration is carried out under a 60 DEG C water bath and -0.09 MPa vacuum until a viscous biomimetic polymer crude product is obtained; The molar ratio of 2,5-dihydroxyterephthalic acid, polyoxypropylene triamine, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine is 1:1.1:2.2:0.01; S2, grafting of a molecular shock absorber structure The biomimetic polymer crude product is redissolved in N-methyl pyrrolidone and transferred into another reaction kettle. 1,2-dithiopentane-3-pentanoic acid is dissolved in N-methyl pyrrolidone and placed in a high-position dropping funnel; The mass of 1,2-dithiopentane-3-pentanoic acid is 4-5% of the mass of the biomimetic polymer; Under nitrogen protection and stirring, the solution is slowly added dropwise, and the dropwise addition time is controlled to be 1 h. After the dropwise addition is completed, the reaction is continued at 60 DEG C for 6 h to completely complete the side chain grafting reaction, and a grafted polymer is obtained; The reaction system is kept at 60 DEG C and under nitrogen protection, and the graphene quantum dot nanodispersion is slowly and uniformly added dropwise into the grafted polymer under vigorous stirring through a constant-pressure dropping funnel within 2 h. After the dropwise addition is completed, N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine are added to the system as condensation catalysts. The reaction temperature is raised to 85 DEG C, and the reaction is refluxed under this condition for 6 h to obtain a grafted composite polymer; The mass of the graphene quantum dots is 0.3-0.7% of the dry mass of the grafted composite polymer. The addition amount of N,N'-dicyclohexyl carbodiimide is 2.5-3 times the mass of the carboxylated graphene quantum dots, and the addition amount of 4-dimethylamino pyridine is 0.2-0.3 times the mass of the carboxylated graphene quantum dots; S3, modification of an intelligent switch group The reaction system is kept at 60 DEG C, and (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid and tetrabutylammonium chloride are added to the grafted polymer or grafted composite polymer. The reaction temperature is raised to 80 DEG C, and the (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid is connected to the end of the polymer through an amidation reaction under this temperature for 4 h; The reaction liquid is cooled to room temperature, and is poured into ice ether under vigorous stirring to precipitate, filtered, and the precipitated fibrous solid is washed with deionized water and ethanol alternately. Vacuum drying is performed to obtain a light yellow to amber solid particle or powder of the intelligent biomimetic network thickening agent; The mass of (+)- (18-crown-6) -2, 3, 11, 12-tetracarboxylic acid is 2.6-3.0% of the mass of the grafted polymer or grafted composite polymer; the mass of tetrabutylammonium chloride is 0.1-0.14% of the mass of the grafted polymer or grafted composite polymer. S4, fracturing fluid preparation and application The intelligent bionic network stitching thickening agent is taken into a potassium chloride aqueous solution, stirred, configured into a fracturing fluid, and a sodium hydroxide solution is used to adjust the pH value to 7.0±0.

5. The mass concentration of the intelligent bionic network stitching thickening agent is 0.2-0.4%.

2. The method of claim 1, wherein the volume-fracturing intelligent construction of the fracture network gel is prepared by the following steps: 1) mixing the components of the gel to obtain a mixture; 2) heating the mixture to obtain a gel; and 3) cooling the gel to obtain the volume-fracturing intelligent construction of the fracture network gel. In the S1, the mass concentration of 2, 5-dihydroxyterephthalic acid and polyoxypropylene triamine in the homogeneous solution is 30-35%.

3. The method for preparing a volumetric fracturing intelligent construction fracture network thickener according to claim 1, characterized in that: In the S2, the concentration of the N-methylpyrrolidone solution of the bionic polymer is 1.2-1.4 mol / L.

4. The method of claim 1, wherein the method further comprises: In the grafted composite polymer, the graphene quantum dot nanodispersion is obtained by ultrasonic dispersion of carboxylated graphene quantum dots in N-methylpyrrolidone, and the solid content is 1-3%. ​ 5. The method of claim 1, wherein the method further comprises: In the S4, the mass concentration of the potassium chloride aqueous solution is 5%. ​ 6. A volume fracturing intelligent construction network stitching thickening agent prepared by the preparation method of any one of claims 1-5.

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