Quaternary polymer thickening agent, high-temperature-resistant fracturing fluid and preparation and application of quaternary polymer thickening agent and high-temperature-resistant fracturing fluid

Abstract

The invention relates to the technical field of oil and gas development, in particular to a quaternary polymer thickening agent, high-temperature-resistant fracturing fluid and preparation and application of the quaternary polymer thickening agent and the high-temperature-resistant fracturing fluid. The preparation method of the quaternary polymer thickening agent comprises the following steps: mixing acrylamide and N-vinyl caprolactam, and keeping an argon atmosphere to obtain a first reaction intermediate system; the preparation method comprises the following steps: adding acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid into deionized water, then adjusting the pH value to be neutral by using a saturated NaOH solution, and uniformly stirring to obtain a first mixed solution; dissolving 2, 2-azobis (isobutylamidine) dihydrochloride in deionized water, and uniformly stirring to obtain a second mixed solution; and adding the first mixed solution and the second mixed solution into the reaction intermediate system, uniformly stirring and mixing, and reacting for 8-12 hours to obtain the colloidal copolymer. And shearing, drying and crushing the copolymer to obtain the quaternary polymer thickening agent. The thickening agent disclosed by the invention is excellent in temperature resistance, and the viscosity of the corresponding fracturing fluid after shearing stability at 240 DEG C and 170 s <-1 > is 50 mPa.s or above.

Description

Technical Field

[0001] This application relates to the technical field of oil and gas development, specifically to a quaternary polymer thickener, a high-temperature fracturing fluid, and their preparation and application. Background Technology

[0002] With advancements in petroleum exploration technology, oil and gas resource development continues to expand into deeper areas, resulting in increasingly deeper drilling depths and higher reservoir temperatures. The number of abnormally high-temperature wells exceeding 4000 meters in depth and temperatures surpassing 180°C is growing. Currently, hydraulic fracturing remains the most effective technology for enhancing production in deep wells. Therefore, higher demands are placed on the temperature and shear resistance of fracturing fluid systems, requiring them to withstand temperatures above 180°C, and even maintain good fluidity and proppant carrying capacity at reservoir temperatures exceeding 200°C.

[0003] Thickeners are key components for fracturing fluids to maintain good fluidity and proppant carrying capacity. Currently, most thickeners in ultra-high temperature fracturing fluids are obtained by compounding carboxymethyl guar gum with polyacrylamide. However, due to the structure of guar gum itself, its temperature stability is very limited. The upper limit of the temperature resistance of guar gum fracturing fluid is only 177℃. At reservoir temperatures above 200℃, the fracturing fluid is prone to cross-linking bond breakage, which leads to poor stability and reduced viscosity. Summary of the Invention

[0004] This application aims to solve the problems of poor stability and reduced viscosity of fracturing fluids caused by the breakage of cross-linking bonds at high temperatures. The technical solution adopted in this application is as follows:

[0005] In a first aspect, this application relates to a quaternary polymer thickener, the structural formula of which is shown in formula (I):

[0006]

[0007] In equation (Ⅰ), x:y:z:w=(2~5):(1~4):(1~2):(0.2~0.6).

[0008] In a specific implementation, as an option, in formula (Ⅰ), x:y:z:w=(4~5):(3~4):(1.5~2):(0.5~0.6).

[0009] Secondly, this application also relates to a method for preparing the above-mentioned quaternary polymer thickener, comprising:

[0010] Acrylamide and N-vinylcaprolactam were mixed and kept under an argon atmosphere to obtain the first reaction intermediate system;

[0011] Acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were added to deionized water, and then the pH was adjusted to neutral with saturated NaOH solution. The mixture was stirred until homogeneous to obtain the first mixed solution.

[0012] Dissolve 2,2-azobisisobutylamidine dihydrochloride in deionized water and stir until homogeneous to obtain a second mixed solution;

[0013] The first mixed solution is added to the first reaction intermediate system and heated to 50-90°C to obtain the second reaction intermediate system;

[0014] The second mixed solution was added to the second intermediate reaction system, stirred and mixed evenly, and reacted for 8-12 hours to obtain a gel-like copolymer;

[0015] The copolymer is sheared, dried, and pulverized to obtain a quaternary polymer thickener.

[0016] In a specific embodiment, optionally, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylcaprolactam is (2-5):(1-4):(1-2):(0.2-0.6).

[0017] In a specific embodiment, optionally, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylcaprolactam is (4-5):(3-4):(1.5-2):(0.5-0.6).

[0018] In a specific embodiment, optionally, the molar ratio of acrylamide, N-vinylcaprolactam and 2,2-azobisisobutylamidine dihydrochloride is (2-5):(0.2-0.6):(0.05-0.16).

[0019] Thirdly, this application also relates to the application of the aforementioned quaternary polymer thickener in fracturing fluids.

[0020] Fourthly, this application also relates to a high-temperature resistant fracturing fluid, which includes the aforementioned quaternary polymer thickener.

[0021] In a specific embodiment, optionally, the high-temperature fracturing fluid comprises the following components in parts by weight: 0.5 to 1.5 parts of the quaternary polymer thickener, 0.03 to 0.09 parts of nano-crosslinking agent, 0.03 to 0.08 parts of breaker, and the balance being water.

[0022] In a specific embodiment, optionally, the nano-crosslinking agent is prepared by the following method:

[0023] Citric acid and zirconium oxychloride were dissolved in deionized water and stirred to obtain a mixed solution;

[0024] An organic amine is added to the mixed solution, and the reaction is carried out at a reaction temperature of 60–90°C for 4–6 hours to obtain a nano-crosslinking agent.

[0025] In a specific embodiment, optionally, the molar ratio of citric acid, zirconium oxychloride, and organic amine is 1:1:(1-5).

[0026] In a specific embodiment, optionally, the organic amine includes any one or more of diethylenetriamine, triisopropanolamine, and triethanolamine.

[0027] Fifthly, this application also relates to the application of the aforementioned high-temperature fracturing fluid in oil and gas development.

[0028] In summary, the advantages of this application over the prior art include:

[0029] This application provides a quaternary polymer thickener and further uses it to formulate a high-temperature resistant fracturing fluid. Compared to current natural polymers that are mainly linked by acetal bonds (glycosidic bonds) on the main chain and have a temperature limit of only 177°C, the quaternary polymer thickeners in Examples 1-7 of this application have a thermogravimetric decomposition temperature between 242 and 263°C, exhibiting good temperature resistance. After the quaternary polymer thickener and nano-crosslinking agent are compounded to form a fracturing fluid, the fracturing fluid exhibits good temperature resistance at 240°C for 170 seconds. -1 After shear stabilization, the viscosity is above 50 mPa·s, indicating good temperature and shear resistance.

[0030] Furthermore, the quaternary polymer thickener in this embodiment requires 3-6 minutes to release over 90% of its viscosity when prepared with water, and the base liquid viscosity is 63-172 mPa·s. It exhibits rapid dissolution and dispersion, moderate viscosity, and ease of preparation and pumping. After crosslinking of the base liquid, the crosslinking time is between 4-8.5 minutes, demonstrating delayed crosslinking properties to meet the needs of different well depths. The crosslinked liquid viscosity is between 600-2000 mPa·s, exhibiting good suspension stability for high-sand-ratio, large-particle-size proppants, with minimal sedimentation within 1 hour.

[0031] Furthermore, the addition of a breaker to the crosslinking solution enables rapid gel breaking at 240℃, with the viscosity of the gelling solution remaining stable at 3 mPa·s. The residue content of the gelling solution is only 5–13 mg / L, and the core damage rate is 8.6–9.7%, resulting in low reservoir damage after gel breaking. Additionally, the surface tension of the gelling solution is <28 mN / m, and the interfacial tension is <2 mN / m, facilitating flowback. Detailed Implementation

[0032] Chinese patent CN111944510A discloses a thickener for cleaning fracturing fluid. The thickener comprises the following raw materials: modified carboxymethyl guar gum, an acrylamide / acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid ternary polymer, an inorganic metal salt, an alcohol, and water. The fracturing fluid gel prepared with this thickener can achieve a viscosity of up to 320 mPa·s, but its temperature tolerance is only around 180°C.

[0033] Chinese patent CN111574989A discloses a multi-hydroxyl thickener and a high-temperature resistant alcohol-based fracturing fluid system. The multi-hydroxyl thickener is formed by copolymerizing three monomers—acrylamide, N-vinylpyrrolidone, and N-acrylamidopropyl-N,N,N-dimethylhydroxyethylammonium chloride—in an aqueous solution. The alcohol-based fracturing fluid system, by introducing the multi-hydroxyl thickener, exhibits high temperature resistance and shear strength, but its temperature resistance only reaches 160℃.

[0034] In summary, the inventors discovered that the temperature resistance limit of current thickeners is typically below 200℃, causing fracturing fluids to exhibit poor stability and low viscosity at temperatures above 200℃. To promote oil and gas development in deep and ultra-deep wells, it is urgent to improve the temperature resistance of thickeners.

[0035] The present application will be described in detail below through specific embodiments and comparative examples:

[0036] Example 1

[0037] This embodiment discloses a quaternary polymer thickener, the structural formula of which is shown in formula (Ⅰ):

[0038]

[0039] In equation (Ⅰ), x:y:z:w=2:1:1:0.2.

[0040] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0041] (1) Weigh 2 mmol acrylamide and 0.2 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0042] (2) Weigh 1 mmol of acrylic acid and 1 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 8 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.05 mmol of 2,2-azobisisobutylamidine dihydrochloride in 4 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0043] (3) Add the first mixed solution to the three-necked flask in (1) and heat it to 50°C. Then add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 8 hours to obtain a gel-like copolymer.

[0044] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0045] During fracturing, the viscosity of the thickener alone is insufficient to effectively carry proppant. A crosslinking agent is also needed to increase the viscosity of the fracturing fluid, thereby improving its proppant-carrying capacity. In the development of unconventional reservoirs, higher demands are placed on the temperature and pressure resistance of the crosslinking agent. Currently used inorganic boron crosslinking agents have two drawbacks: First, borate crosslinking agents require high polymer concentrations to maintain high viscosity, leading to substantial residue buildup and high treatment costs. Second, borate crosslinking agents only exhibit certain thermal stability at high pH values, easily causing soil alkalization and damaging the soil geology.

[0046] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 0.5 parts of the quaternary polymer thickener, 0.03 parts of nano crosslinking agent, 0.03 parts of breaker and 99.44 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0047] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent in this embodiment includes:

[0048] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0049] (2) 0.1 mol of diethylenetriamine was added to the above reaction system and reacted at a reaction temperature of 90°C for 4 h to obtain a nano crosslinking agent.

[0050] Example 2

[0051] The difference between this embodiment and Embodiment 1 is that in the structural formula of the quaternary polymer thickener, x:y:z:w = 3:2:1:0.4.

[0052] In this embodiment, the preparation method of the quaternary polymer thickener includes:

[0053] (1) Weigh 3 mmol acrylamide and 0.4 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0054] (2) Weigh 2 mmol of acrylic acid and 1 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 16 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.11 mmol of 2,2-azobisisobutylamidine dihydrochloride in 10 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0055] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 60°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 10 hours to obtain a gel-like copolymer.

[0056] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0057] This embodiment provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 0.6 parts of the quaternary polymer thickener, 0.04 parts of nano crosslinking agent, 0.04 parts of breaker, and 99.32 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0058] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0059] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0060] (2) 0.3 mol of triethanolamine was added to the above reaction system and reacted at a reaction temperature of 80°C for 5 h to obtain a nano crosslinking agent.

[0061] Example 3

[0062] The difference between this embodiment and Embodiment 1 is that in the quaternary polymer thickener structure of this embodiment, x:y:z:w = 4:3:1.5:0.5.

[0063] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0064] (1) Weigh 4 mmol acrylamide and 0.5 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0065] (2) Weigh 3 mmol of acrylic acid and 1.5 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 10 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.16 mmol of 2,2-azobisisobutylamidine dihydrochloride in 6 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0066] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 70°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 12 hours to obtain a gel-like copolymer.

[0067] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0068] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 0.8 parts of the quaternary polymer thickener, 0.05 parts of nano crosslinking agent, 0.05 parts of breaker, and 99.1 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0069] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0070] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0071] (2) 0.5 mol of triisopropanolamine was added to the above reaction system and reacted at a reaction temperature of 70°C for 6 h to obtain the nano crosslinking agent.

[0072] Example 4

[0073] The difference between this embodiment and Embodiment 1 is that in the quaternary polymer thickener structure of this embodiment, x:y:z:w = 5:4:2:0.6.

[0074] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0075] (1) Weigh 5 mmol acrylamide and 0.6 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0076] (2) Weigh 4 mmol of acrylic acid and 2 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 20 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.13 mmol of 2,2-azobisisobutylamidine dihydrochloride in 15 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0077] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 80°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 8 hours to obtain a gel-like copolymer.

[0078] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0079] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 1 part of the quaternary polymer thickener, 0.06 parts of nano crosslinking agent, 0.06 parts of breaker and 98.88 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0080] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0081] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0082] (2) 0.1 mol of diethylenetriamine was added to the above reaction system and reacted at a reaction temperature of 90°C for 4 h to obtain a nano crosslinking agent.

[0083] Example 5

[0084] The difference between this embodiment and Embodiment 1 is that in the quaternary polymer thickener structure of this embodiment, x:y:z:w = 4:2.5:1:0.3.

[0085] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0086] (1) Weigh 4 mmol acrylamide and 0.3 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0087] (2) Weigh 2.5 mmol of acrylic acid and 1 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 10 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.12 mmol of 2,2-azobisisobutylamidine dihydrochloride in 4 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0088] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 90°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 9 hours to obtain a gel-like copolymer.

[0089] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0090] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 1.2 parts of the quaternary polymer thickener, 0.07 parts of nano crosslinking agent, 0.07 parts of breaker and 98.66 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0091] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0092] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0093] (2) 0.4 mol of triethanolamine was added to the above reaction system and reacted at a reaction temperature of 75°C for 6 h to obtain the nano crosslinking agent.

[0094] Example 6

[0095] The difference between this embodiment and Embodiment 1 is that in the quaternary polymer thickener structure of this embodiment, x:y:z:w = 2.5:1.5:1.5:0.6.

[0096] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0097] (1) Weigh 2.5 mmol acrylamide and 0.6 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0098] (2) Weigh 1.5 mmol of acrylic acid and 1.5 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 16 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.14 mmol of 2,2-azobisisobutylamidine dihydrochloride in 8 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0099] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 85°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 11 hours to obtain a gel-like copolymer.

[0100] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0101] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 1.4 parts of the quaternary polymer thickener, 0.08 parts of nano crosslinking agent, 0.08 parts of breaker and 98.44 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0102] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0103] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0104] (2) 0.3 mol of triisopropanolamine was added to the above reaction system and reacted at a reaction temperature of 85°C for 6 h to obtain the nano crosslinking agent.

[0105] Example 7

[0106] The difference between this embodiment and Embodiment 1 is that in the quaternary polymer thickener structure of this embodiment, x:y:z:w = 4:1:2:0.6.

[0107] The preparation method of the quaternary polymer thickener in this embodiment includes:

[0108] (1) Weigh 4 mmol acrylamide and 0.6 mmol N-vinylcaprolactam, transfer them to a three-necked flask, and evacuate the flask three times to maintain an argon atmosphere.

[0109] (2) Weigh 1 mmol of acrylic acid and 2 mmol of 2-acrylamido-2-methylpropanesulfonic acid and add them to 20 ml of deionized water. Then adjust the pH to neutral with saturated NaOH solution and stir until homogeneous to obtain the first mixed solution. Dissolve 0.15 mmol of 2,2-azobisisobutylamidine dihydrochloride in 10 ml of deionized water and stir until homogeneous to obtain the second mixed solution.

[0110] (3) Add the first mixed solution to the three-necked flask in (1) and heat to 90°C. Continue to add the second mixed solution dropwise to the three-necked flask in (1), stir and mix evenly, and keep warm to carry out the polymerization reaction for 2 hours to obtain a gel-like copolymer.

[0111] (4) The copolymer obtained in (3) is sheared, dried and crushed to obtain a quaternary polymer thickener.

[0112] This embodiment further provides a high-temperature resistant fracturing fluid. The preparation method of the high-temperature resistant fracturing fluid includes: stirring and mixing 1.5 parts of the quaternary polymer thickener, 0.09 parts of nano crosslinking agent, 0.08 parts of breaker and 98.33 parts of water evenly to obtain the high-temperature resistant fracturing fluid.

[0113] It should be noted that ammonium persulfate is used as the depolymerizing agent in this embodiment. The preparation method of the nano-crosslinking agent includes:

[0114] (1) Dissolve 0.1 mol of citric acid with a purity of 99.5% and 0.1 mol of zirconium oxychloride in 200 ml of deionized water and stir thoroughly until completely dissolved;

[0115] (2) 0.1 mol of triisopropanolamine was added to the above reaction system and reacted at a reaction temperature of 90°C for 4 h to obtain the nano crosslinking agent.

[0116] The high-temperature fracturing fluids in Examples 1-7 were evaluated for their main performance according to the industry standard SY / T5107-2016 "Performance Evaluation Method for Water-based Fracturing Fluids". The evaluation results are shown in Table 1.

[0117] Table 1. Performance Evaluation of High-Temperature Fracturing Fluids in Examples 1-7

[0118]

[0119]

[0120] As shown in Table 1, for the fracturing fluids in Examples 1-7, the time required for viscosity release of over 90% when using water for preparation is 3-5 minutes. The viscosity of the base fluid is between 63 and 172 mPa·s, indicating rapid dissolution and dispersion, moderate viscosity, and ease of preparation and pumping. After adding the crosslinking agent, the crosslinking time of the base fluid is 4-8.5 minutes, exhibiting delayed crosslinking properties, which can meet the needs of different well depths. Furthermore, the viscosity of the crosslinked fluid is between 600 and 2000 mPa·s, which is beneficial to the suspension stability of high-sand-ratio, large-particle-size proppant, with virtually no settling within 1 hour.

[0121] Furthermore, the thermogravimetric decomposition temperature of the quaternary polymer thickeners in Examples 1-7 is all above 240°C, and at 240°C for 170 seconds... -1 After stabilization, the viscosity is above 50 mPa·s, exhibiting good temperature and shear resistance. With the addition of a breaker, the fracturing fluid can rapidly break down at 240℃, with a breaker viscosity of 3 mPa·s, a residue content between 5 and 13 mg / L, and a core damage rate between 8.6% and 9.7%. Breakdown causes minimal damage to the reservoir, and the surface tension of the breaker is <28 mN / m, with an interfacial tension <2 mN / m, facilitating flowback.

[0122] Furthermore, as shown in Table 1, the fracturing fluids in Examples 3 and 4, at 240°C and 170s... -1 The viscosity after shear stabilization reaches over 120 mPa·s. This indicates that when the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylcaprolactam in the thickener is (4-5):(3-4):(1.5-2):(0.5-0.6), the corresponding fracturing fluid viscosity retention rate is further superior to other embodiments.

[0123] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," just as "comprising" is interpreted as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A quaternary polymer thickener, characterized in that, The structural formula of the quaternary polymer thickener is shown in Formula (Ⅰ): In equation (Ⅰ), x:y:z:w=(2~5):(1~4):(1~2):(0.2~0.6).

2. The quaternary polymer thickener according to claim 1, characterized in that, In equation (Ⅰ), x:y:z:w=(4~5):(3~4):(1.5~2):(0.5~0.6).

3. A method for preparing the quaternary polymer thickener according to claim 1 or 2, characterized in that, include: Acrylamide and N-vinylcaprolactam were mixed and kept under an argon atmosphere to obtain the first reaction intermediate system; Acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid were added to deionized water, and then the pH was adjusted to neutral with saturated NaOH solution. The mixture was stirred until homogeneous to obtain the first mixed solution. Dissolve 2,2-azobisisobutylamidine dihydrochloride in deionized water and stir until homogeneous to obtain a second mixed solution; The first mixed solution is added to the first reaction intermediate system and heated to 50-90°C to obtain the second reaction intermediate system; The second mixed solution was added to the second intermediate reaction system, stirred and mixed evenly, and reacted for 8-12 hours to obtain a gel-like copolymer; The copolymer is sheared, dried, and pulverized to obtain a quaternary polymer thickener.

4. The method for using a quaternary polymer thickener according to claim 3, characterized in that, The molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylcaprolactam is (2-5):(1-4):(1-2):(0.2-0.6).

5. The method for using a quaternary polymer thickener according to claim 3, characterized in that, The molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylcaprolactam is (4-5):(3-4):(1.5-2):(0.5-0.6).

6. The method for using a quaternary polymer thickener according to claim 3 or 4, characterized in that, The molar ratio of acrylamide, N-vinylcaprolactam and 2,2-azobisisobutylamidine dihydrochloride is (2-5):(0.2-0.6):(0.05-0.16).

7. The application of the quaternary polymer thickener according to claim 1 or 2 in fracturing fluid.

8. A high-temperature resistant fracturing fluid, characterized in that, Includes the quaternary polymer thickener as described in claim 1 or 2.

9. The high-temperature fracturing fluid according to claim 8, characterized in that, The components include the following parts by mass: 0.5 to 1.5 parts of the quaternary polymer thickener, 0.03 to 0.09 parts of the nano-crosslinking agent, 0.03 to 0.08 parts of the depolymerizer, and the balance being water.

10. The high-temperature fracturing fluid according to claim 9, characterized in that, The nano-crosslinking agent is prepared using the following method: Citric acid and zirconium oxychloride were dissolved in deionized water and stirred to obtain a mixed solution; An organic amine is added to the mixed solution, and the reaction is carried out at a reaction temperature of 60–90°C for 4–6 hours to obtain a nano-crosslinking agent.

11. The high-temperature fracturing fluid according to claim 10, characterized in that, The molar ratio of citric acid, zirconium oxychloride, and organic amine is 1:1:(1-5).

12. The high-temperature fracturing fluid according to claim 10, characterized in that, The organic amines include any one or more of diethylenetriamine, triisopropanolamine, and triethanolamine.

13. The application of the high-temperature fracturing fluid according to claims 8 to 12 in oil and gas development.

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