Polymer viscosifier, its preparation method and high-temperature fracturing fluid and application

Abstract

This invention discloses a polymer thickener, its preparation method, high-temperature fracturing fluid, and its application, belonging to the field of oilfield chemical technology. The polymer thickener is polymerized from a monomer combination containing acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N-vinylpyrrolidone; in the monomer combination, the weight ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone is (5-30):(3-15):(0.1-2):(0.01-0.10); the polymerization uses a chain transfer agent and a co-solvent, wherein the chain transfer agent is a thiol and a formate; the co-solvent is an alcohol and / or a urea; and the viscosity-average molecular weight of the polymer thickener is 4 million to 8 million. The polymer thickener has characteristics such as low apparent viscosity and strong shear resistance, which is beneficial for its application in high-temperature fracturing fluids, etc.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology, and particularly relates to a polymer thickener, its preparation method, high-temperature fracturing fluid, and its application. Background Technology

[0002] my country possesses enormous potential for ultra-deep oil and gas resources. The Tarim Basin and Sichuan Basin, in particular, boast high abundance, large scale, and substantial overall reserves, making them the main battleground for exploring deep oil and gas resources at depths exceeding 10,000 meters. Deep / ultra-deep oil and gas resources represent a key area for future breakthroughs in my country's oil and gas exploration, development, and production enhancement. The stringent conditions faced by ultra-deep fracturing pose new challenges to fracturing fluids. Fracturing refers to a method of creating fractures in oil and gas reservoirs primarily through hydraulic action during oil or gas production. Thickeners, as key materials in fracturing fluids, mainly function to maintain the viscosity of the fracturing fluid system under operating conditions and to impart certain wellbore drag reduction and reservoir proppant carrying capacity. Conventional fracturing fluid thickeners are mostly natural plant gums, which are easily decomposed and destroyed under high-temperature conditions, leading to system instability and a rapid decrease in viscosity, making it difficult to meet the technical requirements of fracturing operations.

[0003] Synthetic polymer thickeners are generally polyacrylamide, which has high C-C bond energy, its molecular chains are not easily broken under high temperature conditions, and it has the characteristics of strong thickening ability, good gel breaking performance, and low residue. High-temperature fracturing fluids using polyacrylamide as a thickener are a key focus of research on ultra-high temperature reservoir fracturing both domestically and internationally. The preparation methods of polymer thickeners and the performance research of fracturing fluids are of great significance for improving the production and efficiency of oil and gas wells. For example, Chinese patent document CN 102146372 A discloses a reverse emulsion polymer thickener for fracturing fluids.

[0004] However, existing high-temperature fracturing fluid thickeners are generally polymerized from monomers containing N,N-dimethylacrylamide, resulting in high initial viscosity of the base fluid, making it difficult to pump and causing high pipeline friction. Therefore, controlling the swelling and thickening rate of the product to improve the system's temperature and shear resistance, increase sand addition strength, and thus enhance the deep oil and gas stimulation effect is one of the problems that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a polymer thickener, its preparation method, a high-temperature fracturing fluid, and its application. The polymer thickener provided by the present invention has the characteristics of low apparent viscosity and strong shear resistance, which is beneficial for its application in high-temperature fracturing fluids and the like.

[0006] To achieve the above objectives, the first aspect of the present invention provides a polymer thickener, which is polymerized from a monomer combination containing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone; wherein the weight ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone in the monomer combination is (5-30):(3-15):(0.1-2):(0.01-0.10); the polymerization employs a chain transfer agent and a co-solvent, wherein the chain transfer agent is a thiol and a formate; the co-solvent is an alcohol and / or a urea; and the viscosity-average molecular weight of the polymer thickener is 4 million to 8 million.

[0007] Preferably, in the monomer combination, the weight ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone is (10-20):(6-10):(0.5-1.5):(0.02-0.07).

[0008] Preferably, the chain transfer agent is sodium formate and dodecyl mercaptan, and / or the cosolvent is one or more of urea, ethanol and glycerol.

[0009] A second aspect of the present invention provides a method for preparing the aforementioned polymer thickener, comprising the following steps:

[0010] Acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinylpyrrolidone were used as monomers and mixed with water to obtain a mixture; an initiator, chain transfer agent and cosolvent were added to the mixture to carry out a polymerization reaction to obtain a polymer thickener.

[0011] Preferably, the total weight ratio of monomers in the mixture is 15-35 wt%, more preferably 18-30 wt%, and even more preferably 20-28 wt%.

[0012] Preferably, the initiator is a combination of at least two of ammonium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride. Further, the initiator is preferably ammonium persulfate and sodium bisulfite (in a 1:1 mass ratio), or ammonium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride, in a weight ratio of 1:1:2; preferably, the total amount of the initiator is 0.03-0.10 wt% of the total amount of the monomer combination.

[0013] Preferably, the polymerization reaction temperature is 20-70℃, for example, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, or any value within the range of any two of the above values, preferably 35-45℃; the polymerization reaction time is 4-36h, for example, 4h, 8h, 12h, 16h, 20h, 24h, 28h, 30h, 36h, or any value within the range of any two of the above values, preferably 20-24h. After the polymerization reaction is completed, a colloid is obtained, which can be cut into small pieces and dried to obtain a polymer thickener powder.

[0014] A third aspect of the present invention provides a high-temperature fracturing fluid, comprising a thickener, a crosslinking agent, a temperature stabilizer, and water, wherein the thickener is the polymer thickener described above.

[0015] Preferably, the total weight of the high-temperature fracturing fluid is 100%, the content of the thickener is 0.5-1.5 wt%, the content of the crosslinking agent is 0.8-1.2 wt%, the content of the temperature stabilizer is preferably 0.3-1.5 wt%, and water is the balance (which can be 95.0-99.1 wt%).

[0016] More preferably, the total weight of the high-temperature fracturing fluid is 100%, the content of the thickener is 0.8-1.5 wt%, the content of the crosslinking agent is 0.8-1.2 wt%, the content of the temperature stabilizer is 0.5-1.2 wt%, and water is the balance (which can be 96.1-97.9 wt%).

[0017] Preferably, the crosslinking agent is a metal crosslinking agent, more preferably an organozirconium crosslinking agent, which can be one or more of zirconium oxychloride, zirconium nitrate, zirconium sulfate, zirconium lactate, zirconium triethanolamine, and zirconium glycerol.

[0018] Preferably, the temperature stabilizer is at least one selected from sodium thiosulfate, sodium sulfite, thiourea, and triethanolamine.

[0019] The fourth aspect of the present invention provides the application of the high-temperature fracturing fluid as described above in the pressure stimulation of high-temperature wells, wherein the temperature of the high-temperature well is above 200°C, and more specifically 200-260°C.

[0020] Compared with existing technologies, the polymer thickener provided by this invention is composed of monomers containing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone, and is polymerized by solution polymerization using a chain transfer agent and a co-solvent. This invention utilizes the aqueous solution polymerization reaction of quaternary monomers under certain conditions to form a polymer thickener, which has advantages such as high temperature resistance, low viscosity at high dosages for easy pumping, good viscoelasticity, and strong proppant carrying capacity. It can improve the temperature and shear resistance of high-temperature fracturing fluid systems, meet the requirements for large-scale proppant addition in high-temperature and high-pressure reservoirs, and has good application prospects.

[0021] The high-temperature fracturing fluid of this invention is composed of the aforementioned polymer thickener, crosslinking agent, temperature stabilizer, and water; it can be applied in pressure stimulation of high-temperature wells. In some embodiments, the high-temperature fracturing fluid is subjected to a temperature of 260°C for 170 seconds. -1 After continuous shearing for 90 minutes, the viscosity is greater than 100 mPa·s. Attached Figure Description

[0022] Figure 1 The diagram shows the state of the polymer thickener base liquid prepared in Examples 1 to 4 and Comparative Example 1 of this invention.

[0023] Figure 2 The graph shows the test results of the high-temperature shear resistance of the high-temperature fracturing fluid composed of the polymer thickener prepared in Example 1 of this invention.

[0024] Figure 3 The graph shows the test results of the high-temperature shear resistance of the high-temperature fracturing fluid composed of the polymer thickener prepared in Example 2 of this invention.

[0025] Figure 4 The figure shows the test results of the high-temperature shear resistance of the fracturing fluid composed of the polymer thickener prepared in Comparative Example 2 of this invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] This invention provides a polymer thickener, which is polymerized from a monomer combination containing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone; wherein the weight ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid and N-vinylpyrrolidone in the monomer combination is (5-30):(3-15):(0.1-2):(0.01-0.10); the polymerization employs a chain transfer agent and a co-solvent, wherein the chain transfer agent is a thiol and a formate; the co-solvent is an alcohol and / or a urea; and the viscosity-average molecular weight of the polymer thickener is 4 million to 8 million.

[0028] Furthermore, the present invention provides a method for preparing the polymer thickener, comprising the following steps: using acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone as monomers, mixing with water to obtain a mixture; adding an initiator, a chain transfer agent and a cosolvent to the mixture, and carrying out a polymerization reaction to obtain the polymer thickener.

[0029] The polymer thickener provided by this invention has the characteristics of simple synthesis, low apparent viscosity and strong shear resistance, which is beneficial for its application in high-temperature fracturing fluids and the like.

[0030] The polymer thickener described in this embodiment of the invention is formed by solution polymerization in an aqueous solution using a combination of monomers containing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone, as well as an initiator, chain transfer agent, and cosolvent.

[0031] In the polymer thickener and its preparation according to the present invention, the weight ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone in the monomer combination can be (5-30):(3-15):(0.1-2):(0.01-0.1); preferably (10-20):(6-10):(0.5-1.5):(0.02-0.07). Acrylamide monomers constitute a large proportion, combined with small amounts of acrylic acid and N-vinylpyrrolidone (NVP) monomers. In some preferred embodiments, the mass ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone is 15:8:1:0.05, or 14:9:1:0.06.

[0032] Furthermore, the monomers in the mixture account for 15-35 wt% of the total weight, more preferably 18-30 wt%, and even more preferably 20-28 wt%.

[0033] The preparation method of the polymer thickener described in the embodiments of the present invention may include: adding a combination of monomers containing acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinylpyrrolidone to water and mixing them according to the above mass ratio to obtain a mixture; adding an initiator, a chain transfer agent and a cosolvent to the mixture to carry out a copolymerization reaction to obtain a colloidal polymer thickener.

[0034] In the preparation method described in this embodiment of the invention, the polymerization reaction is carried out in the presence of an initiator. The initiator is preferably a combination of at least two of ammonium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (AIBA). Combining multiple initiators is beneficial for improving the performance of the polymerized product. More preferably, the total amount of the initiator is 0.03-0.10 wt% of the total amount of the monomer combination.

[0035] In a preferred embodiment, the weight ratio of ammonium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride as initiators is 1:1:2. In another preferred embodiment, the weight ratio of ammonium persulfate and sodium bisulfite as initiators is 1:1. The embodiments of the present invention utilize compound initiators and introduce chain transfer agents to control the polymerization reaction rate, and introduce co-solvents to control the swelling and tackification rate of the product, etc.

[0036] The chain transfer agent is a thiol or formate, which can regulate the molecular weight of the polymer. Preferably, the chain transfer agent is two of sodium formate, 2-mercaptoethanol, and dodecyl mercaptan, and includes at least sodium formate; the chain transfer agent is further composed of sodium formate and dodecyl mercaptan. In some embodiments, the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio of 9:1 to 2).

[0037] Meanwhile, the co-solvent is an alcohol and / or a urea compound. The alcohol, such as ethanol or isopropanol, enhances the solubility of the monomer, facilitating the aqueous polymerization reaction and the application of its products. Preferably, the co-solvent is any one or more of urea, ethanol, and glycerol. In some embodiments, the co-solvent is urea and ethanol (the mass ratio of the two can be 1:1 to 2).

[0038] In a preferred embodiment, the polymerization temperature is 20-70°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, or any value within the range of any two of the above values, preferably 35-45°C; the polymerization time is 4-36 hours, for example, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 30 hours, 36 hours, or any value within the range of any two of the above values, preferably 20-24 hours.

[0039] In the preparation method described in this embodiment of the invention, the polymerization reaction is carried out in the presence of water (which may be distilled water or deionized water) as a solvent. In the reaction system, the mass concentration of the polymerizable monomer is preferably 20-28 wt%; this is a preferred proportion of the monomer weight to the total weight, where the total weight refers to the sum of the masses of all substances, including monomer, initiator, co-solvent, chain transfer agent, and water.

[0040] The preparation method of the polymer thickener described in this embodiment of the invention is as follows: the water bath temperature is set to 20-70℃, the monomer, chain transfer agent and co-solvent are added to the solvent, and the pH value of the mixture is adjusted to between 8.0 and 9.0 with a pH adjuster, mainly to optimize the polymerization reaction conditions and make the reaction effect better; the pH adjuster can be sodium hydroxide.

[0041] After nitrogen purging to remove oxygen, an initiator is added, and nitrogen purging to remove oxygen is continued. The mixed solution after nitrogen purging and oxygen removal is placed in a water bath, kept at a constant temperature, stirred evenly, and then stirring is stopped. The reaction continues for 20-24 hours to obtain a polymer thickener colloid. The colloid is cut into small pieces, dried at 60-80℃, and a polymer thickener powder product is obtained, which belongs to a nonionic polyacrylamide derivative.

[0042] In this invention, the polymer thickener has a molecular structure comprising amide groups, carboxylic acid groups, sulfonic acid groups, etc.; its viscosity-average molecular weight is 4 million to 8 million, preferably 5 million to 8 million, and more preferably 6 million to 7 million. Here, the viscosity-average molecular weight of the polymer thickener is determined according to GB 17514-08 Method for Determining the Molecular Weight of Polyacrylamide in Water Treatment Agents.

[0043] In this embodiment of the invention, a base liquid can be prepared by mixing 1.0% polymer thickener with water. The base liquid has a smooth surface, low viscosity (viscosity at room temperature ≤150 mPa.s), and good elasticity.

[0044] This invention provides a high-temperature fracturing fluid containing a thickener, a crosslinking agent, a temperature stabilizer, and water. The thickener is either the polymer thickener described above or a polymer thickener prepared according to the method described above. This high-temperature fracturing fluid is also called a high-temperature resistant or heat-resistant fracturing fluid and can be used under harsh conditions.

[0045] In a preferred embodiment, with a total weight of 100 wt% for the high-temperature fracturing fluid, the content of the polymer thickener is 0.3-2.0 wt%, the content of the crosslinking agent is 0.3-1.5 wt%, the content of the temperature stabilizer is 0.3-1.5 wt%, and the water content is 95.0-99.1 wt%. More preferably, with a total weight of 100 wt% for the high-temperature fracturing fluid, the content of the polymer thickener is 0.8-1.5 wt%, the content of the crosslinking agent is 0.8-1.2 wt%, the content of the temperature stabilizer is 0.5-1.2 wt%, and the water content is 96.1-97.9 wt%.

[0046] In the high-temperature fracturing fluid of the present invention, the crosslinking agent is preferably a metal crosslinking agent; further, the metal crosslinking agent is an organozirconium crosslinking agent. Even further, the organozirconium crosslinking agent can be selected from one or more of zirconium oxychloride, zirconium nitrate, zirconium sulfate, zirconium lactate, zirconium triethanolamine, and zirconium glycerol. In a preferred embodiment of the present invention, the crosslinking time is controlled by the matching crosslinking agent, further reducing pipeline friction, which is beneficial to improving the system's temperature and shear resistance and increasing the strength of sand addition.

[0047] In the high-temperature fracturing fluid of the present invention, the temperature stabilizer is selected from at least one of sodium thiosulfate, sodium sulfite, thiourea, and triethanolamine.

[0048] The high-temperature fracturing fluid is composed of the aforementioned polymer thickener, crosslinking agent, temperature stabilizer, and water; for example, the high-temperature fracturing fluid is subjected to fracturing at 260°C for 170 seconds. -1 After 90 minutes of continuous shearing, the viscosity exceeds 100 mPa·s. The high-temperature fracturing fluid system exhibits good temperature and shear resistance, meeting the requirements for large-scale propulsion in high-temperature and high-pressure reservoirs, and shows promising application prospects.

[0049] Furthermore, this invention also provides the application of the aforementioned high-temperature fracturing fluid in pressure stimulation of high-temperature wells. Preferably, the temperature of the high-temperature well is 200-260°C.

[0050] The following examples further illustrate the polymer thickener, its preparation method, and the high-temperature fracturing fluid and their applications according to the present invention. The examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples. Unless otherwise specified, the experimental methods in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples are commercially available.

[0051] Example 1

[0052] The polymer thickener composition and preparation raw materials are as follows (by weight): 21 parts monomer, 0.02 parts chain transfer agent, 0.02 parts co-solvent, 2.9 parts pH adjuster, 0.06 parts initiator, and 76 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio 9:1); the co-solvent is urea and ethanol (mass ratio 1:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (mass ratio 1:1:2); and the solvent is distilled water.

[0053] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer, chain transfer agent, and co-solvent to the solvent, and adjust the pH of the mixture to between 8.0 and 9.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for another 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0054] Example 2

[0055] The polymer thickener composition and preparation raw materials are as follows (by weight): 25 parts monomer, 0.02 parts chain transfer agent, 0.02 parts co-solvent, 3.4 parts pH adjuster, 0.06 parts initiator, and 71.5 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio 9:1); the co-solvent is urea and ethanol (mass ratio 1:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (mass ratio 1:1:2); and the solvent is distilled water.

[0056] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer, chain transfer agent, and co-solvent to the solvent, and adjust the pH of the mixture to between 8.0 and 9.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for another 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0057] Example 3

[0058] The polymer thickener composition and preparation raw materials are as follows (by weight): 25 parts monomer, 0.02 parts chain transfer agent, 0.02 parts co-solvent, 3.4 parts pH adjuster, 0.06 parts initiator, and 71.5 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio 9:1); the co-solvent is urea and ethanol (mass ratio 1:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate and sodium bisulfite (mass ratio 1:1); and the solvent is distilled water.

[0059] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer, chain transfer agent, and co-solvent to the solvent, and adjust the pH of the mixture to between 8.0 and 9.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for another 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0060] Example 4

[0061] The polymer thickener composition and preparation raw materials are as follows (by weight): 25 parts monomer, 0.02 parts chain transfer agent, 0.02 parts co-solvent, 3.1 parts pH adjuster, 0.06 parts initiator, and 71.8 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio 9:1); the co-solvent is urea and ethanol (mass ratio 1:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (mass ratio 1:1:2); and the solvent is distilled water.

[0062] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer, chain transfer agent, and co-solvent to the solvent, and adjust the pH of the mixture to between 7.0 and 8.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for another 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0063] Comparative Example 1

[0064] The polymer thickener composition and preparation raw materials are as follows (by weight): 25 parts monomer, 0.02 parts chain transfer agent, 0.02 parts co-solvent, 3.4 parts pH adjuster, 0.06 parts initiator, and 71.5 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is dodecyl mercaptan; the co-solvent is urea and ethanol (mass ratio 1:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (mass ratio 1:1:2); and the solvent is distilled water.

[0065] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer, chain transfer agent, and co-solvent to the solvent, and adjust the pH of the mixture to between 8.0 and 9.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for another 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0066] Comparative Example 2

[0067] The raw materials for preparing the polymer thickener are as follows (by weight): 25 parts monomer, 0.02 parts chain transfer agent, 3.6 parts pH adjuster, 0.06 parts initiator, and 71.32 parts solvent. The monomer is acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone (mass ratio 15:8:1:0.05); the chain transfer agent is sodium formate and dodecyl mercaptan (mass ratio 9:1); the pH adjuster is sodium hydroxide; the initiator is potassium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride (mass ratio 1:1:2); and the solvent is distilled water.

[0068] The preparation method of the polymer thickener is as follows: Set the water bath temperature to 40℃, add the monomer and chain transfer agent to the solvent, and adjust the pH of the mixture to between 8.0 and 9.0 using a pH adjuster. After purging with nitrogen for 20 minutes to remove oxygen, add the initiator and continue purging with nitrogen for 30 minutes. Place the nitrogen-purged mixture in a water bath, maintain a constant temperature of 40℃ and a rotation speed of 100 r / min, stir until homogeneous, then stop stirring and continue the reaction for 20 hours to obtain a polymer thickener colloid. Cut the colloid into small pieces, dry at 70℃, and obtain the polymer thickener powder.

[0069] Performance testing

[0070] (1) Swelling rate test:

[0071] Using the polymer thickeners prepared in Examples 1-4, Comparative Examples 1 and 2 (Comparative Example 1 did not contain sodium formate, and Comparative Example 2 did not contain urea or ethanol), a base solution of 1.0% polymer thickener and water was prepared. The dissolution and viscosity test results are shown in the table below. The state of some product base solutions is shown in the table below. Figure 1 As shown; observe the product's melting state, whether it has elasticity, and test the swelling time.

[0072] According to Table 1, the polymer thickeners prepared in Examples 1 and 2 reached their final viscosity in 15 minutes, the polymer thickener prepared in Example 3 reached its final viscosity in 1 hour, and the polymer thickener prepared in Example 4 reached its final viscosity in 2 hours. This indicates that azobisisobutyramidine hydrochloride and pH value affect the swelling performance of the product to some extent. Compared to Example 2, Comparative Example 1, which did not add the chain transfer agent sodium formate, produced a polymer thickener that reached its final viscosity in 2 hours and had a longer swelling time. Comparative Example 2, which did not add the co-solvent urea and ethanol, produced a polymer thickener that reached its final viscosity in 30 minutes and had a slightly longer swelling time.

[0073] Table 1. Swelling test results of the examples and comparative examples.

[0074]

[0075] Note: The data in parentheses is the viscosity initiation rate, which is the current viscosity / final viscosity × 100%.

[0076] like Figure 1 As shown, Figure 1 From left to right, the polymer thickener base liquids prepared in Examples 1-4 and Comparative Example 1 are shown. It can be seen that the base liquids prepared in Examples 1 and 2 have the smoothest surfaces; the base liquids have a room temperature viscosity ≤150 mPa·s, exhibiting low viscosity and good elasticity.

[0077] Based on the viscosity measured by the Brookfield viscometer, the molecular weight was estimated to be 4 million to 8 million. The viscosity-average molecular weights of the samples in Examples 1-4 were 5.8 million, 6.6 million, 7.3 million, and 7.9 million, respectively.

[0078] It should be noted that the dissolution and swelling performance is the result of the combined effects of monomer type ratio, chain transfer agent, and cosolvent, mainly reflecting the control of polymer molecular weight by several factors and the introduction of hydrophilic groups. In on-site construction, the shorter the dissolution and swelling time of the thickener, the more conducive it is to rapid solution preparation and improved construction efficiency; at the same time, it reduces the need for large-capacity storage equipment, lowering equipment investment and operating costs. Generally, a dissolution and swelling time of ≤30 min is required. Therefore, high-temperature rheological performance tests were only conducted on Examples 1 and 2 and Comparative Example 2, where the dissolution and swelling time was ≤30 min.

[0079] (2) High-temperature rheological performance test:

[0080] Preparation of base solution: Measure 1000 mL of tap water and pour it into the Wu Yin mixer. Adjust the speed of the Wu Yin mixer until the liquid vortex can be seen at the top of the central shaft of the mixer blade. Then, measure and add 10 g of the polymer thickener prepared in Example 1, Example 2 and Comparative Example 2, and 10 mL of temperature stabilizer (self-made, 3 parts by weight of ethanol from Henan Jiuheng Biotechnology Co., Ltd., 27 parts by weight of sodium thiosulfate from Jinan Runmeite Chemical Technology Co., Ltd., and 70 parts by weight of water). After the thickener dissolves and becomes viscous, use a syringe to draw 10 mL of temperature stabilizer and add it to the solution. Stop stirring after 3 minutes to obtain the base solution.

[0081] Take 100 mL of the above base liquid and add 1.0 mL of crosslinking agent (self-made, patent number ZL 201811561548.8 Example 2) to each. After stirring evenly, different high-temperature fracturing fluids are obtained.

[0082] The high-temperature and shear resistance properties of the above-mentioned variable viscosity fracturing fluid were tested using an RS6000 high-temperature and high-pressure rheometer. The heating rate was controlled at 3.0℃ / min ± 0.2℃ / min, the experimental temperature was 260℃, and the shear rate was 170s. -1 The shearing time was 90 minutes. Test results: at 260℃, 170 seconds... -1 After shearing for 90 min, the rheological viscosities of the systems corresponding to the thickeners prepared in Examples 1 and 2 were 65 mPa·s and 151 mPa·s, respectively, at 260 °C and 170 s. -1 After shearing for 50 min, the rheological viscosity of the system corresponding to the thickener prepared in Comparative Example 2 was 50 mPa·s. The test results are as follows: Figures 2-4 As shown, Examples 1 and 2 can both meet the viscosity requirement of ≥50 mPa·s in the industry standard SY / T7627—2021 "Technical Requirements for Water-based Fracturing Fluids". It can also be seen that the polymer thickener prepared in Example 2 has better performance.

[0083] Compared with CN 102146372 A "Reverse Emulsion Polymer Thickener for Fracturing Fluid and its Preparation Method", the polymer thickener prepared in the embodiments of this invention uses an aqueous solution polymerization process that is simpler than emulsion polymerization. Furthermore, this invention, by introducing a specific chain transfer agent and adding the co-solvents urea and ethanol, can form a strong hydrogen bond network with water molecules, increasing the system polarity, optimizing monomer dispersion, avoiding gelation caused by excessive crosslinking, ensuring reaction uniformity, and significantly improving the density and temperature and shear resistance of the polymer thickener network.

[0084] In summary, the embodiments of the present invention provide a polymer thickener and its preparation method, which has the advantages of fast swelling speed, good elasticity, low viscosity of base fluid (≤150mPa·s), easy pumping, and crosslinking fracturing fluid composed of a crosslinking agent with a temperature resistance of up to 260℃, thus meeting the technical requirements of deep oil and gas fracturing construction.

[0085] The preferred embodiments of the present invention disclosed above are merely for illustrating the present invention, and the present invention is not limited thereto. Those skilled in the art will understand that, within the scope of the present invention's concept, modifications can be made to the technical solutions of the present invention, or some technical features can be combined in any other way. Such modifications or combinations do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the various embodiments of the present invention, and should be considered as the content disclosed in the present invention, all of which fall within the protection scope of the present invention.

Claims

1. A polymer thickener, characterized in that, It is polymerized from a monomer combination containing acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinylpyrrolidone; wherein the weight ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid and N-vinylpyrrolidone in the monomer combination is (5-30):(3-15):(0.1-2):(0.01-0.10); The polymerization employs a chain transfer agent and a co-solvent, wherein the chain transfer agent is a thiol or a formate; and the co-solvent is an alcohol and / or a urea. The viscosity-average molecular weight of the polymer thickener is 4 million to 8 million.

2. The polymer thickener according to claim 1, characterized in that, In the monomer combination, the weight ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone is (10-20):(6-10):(0.5-1.5):(0.02-0.07).

3. The polymer thickener according to claim 1, characterized in that, The chain transfer agent is sodium formate and dodecyl mercaptan, and / or the cosolvent is one or more of urea, ethanol and glycerol.

4. The method for preparing the polymer thickener according to any one of claims 1-3, characterized in that, Includes the following steps: A mixture was prepared by mixing acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinylpyrrolidone with water to obtain a solution. An initiator, a chain transfer agent, and a cosolvent are added to the mixture to carry out a polymerization reaction, thereby obtaining a polymer thickener.

5. The preparation method according to claim 4, characterized in that, The total weight ratio of monomers in the mixture is 15-35 wt%.

6. The preparation method according to claim 4, characterized in that, The initiator is at least two combinations of ammonium persulfate, sodium bisulfite, and azobisisobutyramidine hydrochloride.

7. The preparation method according to claim 4, characterized in that, The polymerization reaction is carried out at a temperature of 20-70℃ for 4-36 hours. After the polymerization reaction is completed, a colloid is obtained. The colloid is then cut into pieces and dried to obtain a polymer thickener powder.

8. A high-temperature fracturing fluid, characterized in that, It includes a thickener, a crosslinking agent, a temperature stabilizer, and water, wherein the thickener is a polymer thickener as described in any one of claims 1-3.

9. The high-temperature fracturing fluid according to claim 8, characterized in that, With the total weight of the high-temperature fracturing fluid as 100%, the content of the thickener is 0.5-1.5 wt%; and the content of the crosslinking agent is 0.8-1.2 wt%. The crosslinking agent is preferably a metal crosslinking agent, more preferably an organozirconium crosslinking agent, and can be one or more of zirconium oxychloride, zirconium nitrate, zirconium sulfate, zirconium lactate, zirconium triethanolamine, and zirconium glycerol; the temperature stabilizer is preferably at least one of sodium thiosulfate, sodium sulfite, thiourea, and triethanolamine.

10. The application of the high-temperature fracturing fluid as described in claim 8 or 9 in the pressure stimulation of high-temperature wells, wherein the temperature of the high-temperature well is above 200°C.

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