Thickening agent for hydrophobic association type fracturing fluid and preparation method of thickening agent

Abstract

The invention belongs to the technical field of oilfield chemistry, relates to a thickening agent for a high-temperature-resistant salt-resistant fracturing fluid and a preparation method of the thickening agent, and particularly relates to a thickening agent for a hydrophobic association type fracturing fluid and a preparation method of the thickening agent. The thickening agent for the hydrophobic association type fracturing fluid provided by the invention is prepared by polymerizing the following monomer raw materials: an amide monomer, a carboxylic group-containing monomer, a sulfonic acid monomer and a hydrophobic association monomer. According to the thickening agent for the hydrophobic association type fracturing fluid, a functional group and a hydrophobic group are introduced through molecular design, the thickening agent and an organic zirconium cross-linking agent construct a thermal stable cross-linked network, the temperature resistance and the shear resistance at 150-200 DEG C are higher than those required by a water-based fracturing technology (larger than 50 mPa.s), and the fracturing requirements of deep reservoirs are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry, and relates to a thickener for high-temperature and salt-resistant fracturing fluid and a preparation method thereof, and in particular to a thickener for hydrophobically associating fracturing fluid and a preparation method thereof. Background Art

[0002] As shallow oil and gas resources worldwide gradually deplete, the oil and gas industry is actively shifting toward the exploration and development of deep and ultra-deep oil and gas resources. However, this transition faces a significant challenge: deep oil and gas reservoirs are often exposed to extreme temperatures and pressures, placing even more stringent demands on the performance of fracturing fluids. Against this backdrop, polymer thickeners designed specifically for ultra-high-temperature environments have emerged as a key technology to address the challenges of deep oil and gas resource development.

[0003] Future research and development of fracturing fluid thickeners will focus on optimizing and innovating performance across multiple dimensions. Specifically, this will include reducing costs, improving dissolution efficiency, enhancing viscosity-increasing performance, optimizing high-temperature and salt tolerance, and exploring the development of environmentally friendly materials. In particular, the precise structure and functional group design of thickener molecules are crucial for enhancing their solubility and viscosity-increasing properties in fracturing fluids. Therefore, in-depth exploration of the molecular-level relationship between structure and performance will become a core focus of future thickener R&D, with the goal of developing an ideal fracturing fluid thickener that is both economical and efficient.

[0004] In the field of synthetic polymer thickeners, polyacrylamide and its derivatives have become the mainstream materials for fracturing fluid thickeners due to their unique molecular structure and excellent performance. By introducing functional groups such as hydration groups, rigid groups, and high-temperature resistant groups, these materials demonstrate significant advantages in high-temperature resistance and viscosity-increasing capabilities. Compared with natural polymers, synthetic polymers offer outstanding characteristics such as low water-insoluble matter content, significant viscosity-increasing effects, excellent gel-breaking properties, and manageable costs. More importantly, they can be tailored to the specific fracturing environment through the targeted design of their molecular structure, thereby developing highly customized fracturing fluid thickeners and significantly improving construction efficiency.

[0005] In order to meet the technical challenges in high temperature and high pressure environments, current research at home and abroad is focusing on the molecular design of polyacrylamide thickeners, improving viscosity-increasing performance, and enhancing temperature and salt resistance. Two major technical paths have been formed in the construction of fracturing fluid thickener systems:

[0006] The first is a hydrophobic association system based on dynamic physical cross-linking: by introducing a small amount of hydrophobic monomers into the hydrophilic polymer backbone, the physical association between the hydrophobic groups forms a reversible network structure to increase viscosity. This system has good shear thinning properties, but the association effect is easily shielded in high-salt environments, resulting in a significant drop in viscosity. Moreover, at ultra-high temperatures (>180°C), molecular thermal motion intensifies, the association points dissociate, and long-term thermal stability is challenged.

[0007] The second approach involves polymer gel systems based on strong chemical crosslinking. These systems utilize crosslinkers to form stable covalent or coordination bonds with specific functional groups on the polymer chains. While these systems offer relatively good high-temperature stability, they often suffer from issues such as slow dissolution, limited salt tolerance, difficulty breaking the gel, potential reservoir damage, and limited flexibility in rheological manipulation. In particular, crosslinking reactions can be inhibited or become unstable under conditions of high salinity.

[0008] In summary, existing PAM-based thickener technologies still face the following key technical bottlenecks when dealing with ultra-deep extreme environments:

[0009] Insufficient long-term stability at high temperature and high salt: Viscosity retention rate decreases significantly with increasing temperature and time. 2+ ,Mg 2+ ) environment, performance deteriorates faster;

[0010] It is difficult to achieve both viscosity-increasing performance and stability: increasing molecular weight or association / cross-linking density can enhance viscosity-increasing and initial stability, but this often leads to poor solubility, decreased shear resistance, or difficulty in breaking the gel;

[0011] Complexity of molecular structure design and performance balance: When introducing multiple functional monomers (hydration, rigidity, temperature resistance, salt resistance, and association) to improve comprehensive performance, the compatibility between monomers and the difficulty of controlling the polymerization process increase, and the functional groups may have mutual constraints.

[0012] Therefore, there is an urgent need to develop novel molecular design concepts and synthesis technologies for polymer thickeners, achieving better structural control at the molecular level to break through the performance limits of existing materials under ultra-high temperature, ultra-high salinity, and long-term stable service conditions, while also addressing multiple requirements such as solubility, rheology, gel breaking, environmental friendliness, and economic efficiency. This is not only a current research frontier in petroleum engineering, but also a core technological requirement for the economic and efficient development of deep and ultra-deep oil and gas resources. Summary of the Invention

[0013] In view of the defects of the prior art, the present invention provides a thickener for a hydrophobically associating fracturing fluid and a preparation method thereof.

[0014] Specifically, the hydrophobically associating fracturing fluid thickener provided by the present invention is prepared by polymerizing raw materials including the following monomers: amide monomers, carboxylic acid group-containing monomers, sulfonic acid monomers, and hydrophobically associating monomers.

[0015] In the above-mentioned hydrophobically associating fracturing fluid thickener, the molar ratio of the amide monomer, the carboxylic acid group-containing monomer, the sulfonic acid monomer, and the hydrophobically associating monomer is (80-85):(13-18):(3-8):(0.15-0.25).

[0016] In the above-mentioned hydrophobically associating fracturing fluid thickener, the amide monomer includes one or more of acrylamide and N,N-dimethylacrylamide.

[0017] In the above-mentioned hydrophobically associating fracturing fluid thickener, the carboxylic acid group-containing monomer includes one or more of acrylic acid, itaconic acid, and maleic anhydride.

[0018] In the above-mentioned hydrophobically associating fracturing fluid thickener, the sulfonic acid monomer includes one or more of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0019] The hydrophobically associating fracturing fluid thickener mentioned above, wherein the hydrophobically associating monomer includes one or more of octadecyldimethylallyl ammonium chloride and hexadecyldimethylallyl ammonium chloride.

[0020] The present invention provides a method for preparing a thickener for a hydrophobically associating fracturing fluid, comprising:

[0021] (1) dissolving an amide monomer, a carboxylic acid group-containing monomer, a sulfonic acid monomer, and a hydrophobically associating monomer in water according to a ratio to obtain a mixed solution;

[0022] (2) adding sodium formate and urea to the mixed solution, stirring, introducing inert gas nitrogen or argon, heating to 30-60° C., and adding an initiator to start the polymerization reaction;

[0023] (3) After the polymerization reaction is completed, the product is washed, dried, and crushed to obtain a thickener for high-temperature and salt-resistant fracturing fluid.

[0024] In the above-mentioned method for preparing a thickener for hydrophobically associating fracturing fluid, the total mass concentration of monomers in the mixed solution is 10-30%.

[0025] In the above-mentioned method for preparing a thickener for hydrophobically associating fracturing fluid, the amount of sodium formate added is 0.1% to 0.5% of the total mass of the monomers; and the amount of urea added is 2% to 5% of the total mass of the monomers.

[0026] In the above-mentioned method for preparing a thickener for hydrophobically associating fracturing fluid, the inert gas is nitrogen or argon.

[0027] In the above-mentioned method for preparing a thickener for hydrophobically associating fracturing fluid, the heating temperature is 30-60°C.

[0028] In the above-mentioned method for preparing a thickener for hydrophobically associating fracturing fluid, the initiators are ammonium persulfate and sodium bisulfite.

[0029] The preparation method of the hydrophobically associating fracturing fluid thickener comprises the following steps: cutting the product and then soaking it in anhydrous ethanol for 2 to 4 hours.

[0030] The method for preparing the hydrophobically associating fracturing fluid thickener mentioned above has a molecular weight range of 1.5 to 2 million.

[0031] Compared with the prior art, the thickener for high temperature and salt resistant fracturing fluid of the present invention has the following beneficial effects:

[0032] (1) The hydrophobically associating fracturing fluid thickener of the present invention introduces functional groups and hydrophobic groups through molecular design, and constructs a thermally stable cross-linked network with an organic zirconium cross-linker. The heat resistance and shear resistance at 150-200°C are higher than the requirements of water-based fracturing technology (>50mPa·s), meeting the fracturing needs of deep oil reservoirs;

[0033] (2) The hydrophobically associating fracturing fluid thickener of the present invention has a high viscosity retention rate in high-mineralization formation water, overcoming the defects of conventional thickeners that are prone to phase separation or sudden viscosity drop in high-salt environments;

[0034] (3) The hydrophobically associating fracturing fluid thickener of the present invention has a simple preparation process, can effectively expand the scope of application, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other advantages and benefits will become apparent to those skilled in the art by reading the following detailed description of the preferred embodiment.The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present invention.

[0036] Figure 1 This is the infrared spectrum of the thickener for fracturing fluid prepared in Example 1.

[0037] Figure 2 This is a thermogravimetric curve of the thickener for fracturing fluid prepared in Example 1. DETAILED DESCRIPTION

[0038] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0039] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0040] The concept of the present invention is: based on monomers containing double bonds or monomers that can react with double bonds, through careful design and synthesis strategies, specific functional groups and hydrophobic monomers are introduced, which can significantly enhance the high temperature resistance and viscosity-increasing ability of the thickener for fracturing fluid. This type of copolymer thickener exhibits a series of advantages: its water-insoluble content is extremely low, ensuring the purity and stability of the fracturing fluid; its viscosity-increasing effect is significant, which can greatly increase the viscosity of the fracturing fluid, thereby improving its carrying and supporting capacity; its excellent gel-breaking performance can quickly degrade after the operation is completed, reducing damage to the formation; at the same time, its cost is controllable, providing economic feasibility for large-scale application. More importantly, the copolymer thickener for fracturing fluid is highly customizable. Through the directional design of the molecular structure, its functional group composition, chain segment length and distribution and other characteristics can be precisely adjusted to meet the special needs of different fracturing environments. This means that tailor-made thickeners for fracturing fluids can be developed for specific geological conditions, construction requirements, and fluid performance targets, ensuring efficient and safe fracturing operations under complex and changing construction conditions, significantly improving construction efficiency and oil and gas recovery rates.

[0041] Specifically, the hydrophobically associating fracturing fluid thickener provided by the present invention is prepared by polymerizing raw materials including the following monomers: amide monomers, carboxylic acid group-containing monomers, sulfonic acid monomers, and hydrophobically associating monomers.

[0042] Amide monomers form polymer chains through polymerization. Their molecular chains stretch in the solution and increase the internal friction between fluid molecules through interactions such as hydrogen bonds and van der Waals forces, providing an initial viscosity-increasing skeleton. Carboxylic acid-containing monomers provide sufficient -COOH groups to interact with the hydroxyl bridges of the cross-linking agent, cross-linking to form a gel. The rigid structure or large steric hindrance side groups of sulfonic acid monomers are introduced into the molecular chain to inhibit the thermal motion of the chain segments at high temperatures and delay thermal oxidative degradation. The hydrogen bonds of the amide groups are easily broken at high temperatures, but the long-chain alkyl groups of the hydrophobic associating monomers form reversible physical cross-linking points (such as "hydrophobic micro-domains") through van der Waals forces. These cross-linking points are more stable than hydrogen bonds at high temperatures, maintaining the network structure of the molecular chains and giving the solution high viscosity.

[0043] In a high salt environment, the electrolyte compresses the double layer and weakens the electrostatic repulsion. The strong anionic sulfonic acid group (-SO3 - ), has good tolerance to divalent cations and will not react with divalent cations to produce precipitation; secondly, the hydrophobic association effect is enhanced due to the "salting out effect" - salt ions destroy the ordered structure of water molecules, promote the hydrophobic aggregation of long-chain alkyl groups, form a denser physical network, and compensate for the viscosity loss caused by charge shielding.

[0044] This type of collaborative design breaks through the performance bottleneck of a single group, enabling the thickener to maintain excellent rheological properties in complex reservoir environments (such as high temperature and high salinity), and promotes the advancement of fracturing technology in unconventional oil and gas development.

[0045] In some preferred embodiments, the molar ratio of the amide monomer, the carboxylic acid group-containing monomer, the sulfonic acid monomer, and the hydrophobic associating monomer is (80-85):(13-18):(3-8):(0.15-0.25).

[0046] In practice, when the ratio of amide monomers is too high, the excess amide groups make the polymer chains overly hydrophilic, the formation of hydrophobic microdomains is insufficient, and the strength of the physical cross-linking network is reduced; when the ratio of amide monomers is too low, the proportion of hydrophobic monomers is relatively high, the dispersibility of the polymer in water becomes poor, and it is easy to form insoluble particles or gels. When the ratio of carboxylic acid monomers is too high, the salt sensitivity of the polymer is significantly enhanced, and it is easy to combine with calcium and magnesium ions to form precipitation; when the ratio of carboxylic acid monomers is too low, there are not enough carboxyl groups to participate in the cross-linking reaction, making it difficult to build a stable spatial network structure. When the ratio of sulfonic acid monomers is too high, the strong hydrophilicity will inhibit the formation of hydrophobic microdomains; when the ratio of sulfonic acid monomers is too low, the salt resistance and high-temperature stability are insufficient, making it difficult to effectively resist the attack of high-valent metal ions. When the ratio of hydrophobic associating monomers is too large, the excess hydrophobic monomers will form dense hydrophobic microdomains, causing the solution to undergo irreversible gelation at low concentrations; when the ratio of hydrophobic associating monomers is too small, the number of hydrophobic microdomains is small, the physical cross-linking points are sparse, and there is a lack of an effective dynamic cross-linking network. After shearing, the molecular chains are difficult to restore their original conformation, and the viscosity is reduced.

[0047] In the present invention, amide monomers are polymerized to form polymer chains, which extend in solution and increase internal friction between fluid molecules through interactions such as hydrogen bonding and van der Waals forces, providing an initial viscosity-enhancing framework. In some preferred embodiments, the amide monomers include one or more of acrylamide and N,N-dimethylacrylamide.

[0048] In the present invention, the carboxylic acid group-containing monomers can provide sufficient carboxyl groups to participate in the cross-linking reaction and construct a stable spatial network structure.

[0049] In some preferred embodiments, the carboxylic acid group-containing monomer includes one or more of acrylic acid, itaconic acid, and maleic anhydride.

[0050] In the present invention, the sulfonic acid monomers allow the molecular chains to fully stretch and thicken in the solution due to the strong ionization of the sulfonic acid groups, and the large steric groups and rigid groups they contain inhibit chain degradation at high temperatures. At the same time, the strong hydration effect of the sulfonate ions resists salt ion shielding, effectively hinders the curling of the molecular chains, increases the hydrodynamic volume of the polymer, and achieves temperature-resistant and salt-resistant viscosity enhancement.

[0051] In some preferred embodiments, the sulfonic acid monomer includes one or more of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0052] In the present invention, hydrophobic associating monomers are introduced with hydrophobic groups to form a reversible intermolecular association network in aqueous solution due to hydrophobic interaction, thereby increasing the fluid dynamics volume and intermolecular resistance, thereby achieving efficient viscosity increase.

[0053] In some preferred embodiments, the hydrophobically associating monomer includes one or more of octadecyldimethylallyl ammonium chloride and hexadecyldimethylallyl ammonium chloride.

[0054] On the other hand, the present invention also provides a method for preparing a thickener for high-temperature and salt-resistant fracturing fluid, comprising:

[0055] (1) dissolving an amide monomer, a carboxylic acid group-containing monomer, a sulfonic acid monomer, and a hydrophobically associating monomer in water according to a ratio to obtain a mixed solution with a concentration of 10 to 30%;

[0056] (2) adding sodium formate and urea to the mixed solution, stirring, introducing inert gas nitrogen or argon, heating to 30-60° C., and adding an initiator to start the polymerization reaction;

[0057] (3) After the polymerization reaction is completed, the product is washed, dried, and crushed to obtain a thickener for high-temperature and salt-resistant fracturing fluid.

[0058] The process flow for preparing the thickener for fracturing fluid of the present invention is simple, the application scope is expanded, and the application prospect is broad.

[0059] Sodium formate acts as a chain transfer agent by providing active hydrogen atoms to undergo chain transfer reactions with growing free radical chains, reducing free radical activity and terminating the growth of the original chain while initiating the formation of new chains, thereby regulating the molecular weight and distribution of the polymer and achieving effective control of the chain length of the polymerization product.

[0060] Urea can act as both a hydrogen bond donor and acceptor, competing for hydrogen bonding sites on the polymer chain and forming multiple hydrogen bonds with polar groups and water molecules on the polymer molecular chain. This weakens interactions between polymer molecules (such as hydrophobic association or hydrogen bond crosslinking) and reduces the aggregation and entanglement of molecular chains. Furthermore, the strong interaction between urea and water improves the solvation environment, making the polymer chains more flexible in water and thus increasing the solubility of the polymer. The amount of sodium formate added is 0.1% to 0.5% of the total monomer mass, and the amount of urea added is 2% to 5% of the total monomer mass.

[0061] In some preferred embodiments, the initiator is ammonium persulfate and sodium bisulfite in a mass ratio of (2-4): (1-2).

[0062] The amount of the initiator added is 0.1% to 0.25% of the total weight of the monomers.

[0063] In some preferred embodiments, the cleaning comprises: cutting the product into particles with a size of 3 to 5 mm, and then soaking the particles in anhydrous ethanol for 2 to 4 hours.

[0064] The molecular weight of the thickener for the high-temperature and salt-resistant polymer fracturing fluid prepared according to the method of the present invention is in the range of 1.5 to 2 million, thereby achieving rapid dissolution of the hydrophobic associating polymer.

[0065] Example

[0066] The present invention is further illustrated by way of examples below, but the invention is not limited to the scope of the examples. The experimental methods in the following examples where specific conditions are not specified were based on conventional methods and conditions. The raw materials used in the following examples were all commercially available.

[0067] Example 1

[0068] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0069] (1) Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and hexadecyldimethylallyl ammonium chloride in a molar ratio of 82:15:5:0.20 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 10 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0070] (2) After nitrogen was introduced for 20 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% by weight of ammonium persulfate and 0.1% by weight of sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0071] (3) Place the sealed beaker in a constant temperature water bath. After 2 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0072] (4) After the polymerization reaction is completed, the rubber block is taken out from the beaker, cut into pieces and granulated, cut into 3 mm particles, sieved and dried, soaked in anhydrous ethanol for 2 hours to remove unreacted monomers, and finally placed on a watch glass, dried in an oven for 5 hours, crushed with a grinder, and sieved with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0073] Figure 1 This is the infrared spectrum of the thickener used in fracturing fluid. 3344cm -1 The peak at 2978 cm corresponds to the stretching vibration absorption peak of NH of amide group; -1 and 2929cm -1 The peaks at 1650 cm represent the stretching vibration absorption peaks of methyl and methylene respectively; -1The peak at 1606 cm is the stretching vibration absorption peak of C=O; -1 It is the antisymmetric stretching vibration peak of -COO-; 1558cm -1 The peak at 1440 cm is the bending vibration absorption peak of the NH of the amide group; -1 and 1449cm -1 is the bending vibration absorption peak of CH, 1320cm -1 The characteristic peak at 1187cm indicates the presence of CN bond. -1 and 1037cm -1 The characteristic absorption peak of the sulfonic acid group is shown in Figure 2. By analyzing the spectrum, it can be confirmed that the molecular chain contains amide groups, carboxyl groups, sulfonic acid groups, and alkyl groups, which indicates that the hydrophobic group and functional group have been successfully introduced into the molecular chain.

[0074] Figure 2 The thermogravimetric analysis curve of the thickener for fracturing fluid is shown, which can be used to evaluate the thermal stability of the groups on the polymer macromolecular chain. According to the TGA (thermogravimetric analysis) curve, the weight loss process of the polymer can be divided into several stages. The first stage starts at 30°C and ends at 210°C. The weight loss in this stage is mainly due to the evaporation of water adsorbed between polymers. The decomposition temperature range of the second stage is approximately 210°C to 290°C. The weight loss in this stage is mainly due to the decomposition of the amide groups in the polymer. The weight loss in the third stage occurs between 287°C and 700°C, which is mainly due to the thermal decomposition of the polymer chain segments. These data show that at around 200°C, the polymer exhibits good thermal stability and can therefore be used under higher temperature conditions.

[0075] Example 2

[0076] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0077] (1) Acrylamide, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, and hexadecyldimethylallyl ammonium chloride in a molar ratio of 82:15:5:0.20 were added to a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 10 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0078] (2) After nitrogen was introduced for 30 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% by weight of ammonium persulfate and 0.1% by weight of sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0079] (3) Place the sealed beaker in a constant temperature water bath and react for 2 hours until the polymerization reaction is complete, obtaining a gel-like product. (4) After the polymerization reaction is complete, remove the gel block from the beaker, cut the gel block into pieces and granulate it into 4 mm particles, sieve and dry it, soak it in anhydrous ethanol for 3 hours to remove unreacted monomers, and finally place the gel particles on a watch glass, dry them in an oven for 6 hours, crush them with a grinder, and sieve them with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0080] Example 3

[0081] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0082] (1) Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and hexadecyldimethylallyl ammonium chloride in a molar ratio of 80:18:5:0.20 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 20 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0083] (2) After nitrogen was introduced for 30 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% by weight of ammonium persulfate and 0.1% by weight of sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0084] (3) Place the sealed beaker in a constant temperature water bath. After 4 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0085] (4) taking out the rubber block from the beaker, cutting the rubber block into pieces and granulating the pieces into 5 mm particles, sieving and drying the pieces, soaking them in anhydrous ethanol for 4 h to remove unreacted monomers, and finally placing the rubber particles on a watch glass, drying them in an oven for 6 h, crushing them with a grinder, and sieving them with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0086] Example 4

[0087] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0088] (1) Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and octadecyldimethylallyl ammonium chloride in a molar ratio of 82:15:5:0.20 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 20 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0089] (2) After nitrogen was introduced for 30 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% by weight of ammonium persulfate and 0.1% by weight of sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0090] (3) Place the sealed beaker in a constant temperature water bath. After 4 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0091] (4) After the polymerization reaction is completed, the rubber block is taken out from the beaker, cut into pieces and granulated, cut into 4 mm particles, sieved and dried, soaked in anhydrous ethanol for 3 hours to remove unreacted monomers, and finally placed on a watch glass, dried in an oven for 5 hours, crushed with a grinder, and sieved with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0092] Comparative Example 1

[0093] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0094] (1) Acrylamide, acrylic acid, and hexadecyldimethylallyl ammonium chloride in a molar ratio of 82:15:0.2 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 20 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0095] (2) After nitrogen was introduced for 40 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% of the total weight of the monomers in ammonium persulfate and 0.1% of the total weight of the monomers in sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0096] (3) Place the sealed beaker in a constant temperature water bath. After 4 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0097] (4) taking out the rubber block from the beaker, cutting the rubber block into pieces and granulating them into 4 mm particles, sieving and drying them, soaking them in anhydrous ethanol for 3 hours to remove unreacted monomers, and finally placing the rubber particles on a watch glass, drying them in an oven for 8 hours, crushing them with a grinder, and sieving them with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0098] Comparative Example 2

[0099] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0100] (1) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and octadecyldimethylallyl ammonium chloride in a molar ratio of 82:5:0.2 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 20 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0101] (2) After nitrogen was introduced for 40 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% of the total weight of the monomers in ammonium persulfate and 0.1% of the total weight of the monomers in sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0102] (3) Place the sealed beaker in a constant temperature water bath. After 4 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0103] (4) taking out the rubber block from the beaker, cutting the rubber block into pieces and granulating them into 4 mm particles, sieving and drying them, soaking them in anhydrous ethanol for 3 hours to remove unreacted monomers, and finally placing the rubber particles on a watch glass, drying them in an oven for 8 hours, crushing them with a grinder, and sieving them with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0104] Comparative Example 3

[0105] A method for preparing a thickener for a hydrophobically associating fracturing fluid comprises the following steps:

[0106] (1) Acrylamide, acrylic acid, and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 82:15:5 were placed in a 500 ml beaker, and a certain amount of distilled water was added to prepare a mixed solution with a monomer concentration of 20 wt%; sodium formate (0.25% of the total weight of the monomers) and urea (2% of the total weight of the monomers) were added, the mixture was thoroughly mixed, stirred evenly, and placed in a constant temperature water bath.

[0107] (2) After nitrogen was introduced for 40 minutes to fully expel the dissolved air in the solution, when the temperature of the mixed solution reached the initiation temperature of 40°C, a redox system initiator consisting of 0.1% of the total weight of the monomers in ammonium persulfate and 0.1% of the total weight of the monomers in sodium bisulfite was added to initiate polymerization. The inert gas was continued to be introduced until the solution became viscous, and the beaker mouth was sealed with plastic wrap.

[0108] (3) Place the sealed beaker in a constant temperature water bath. After 4 hours of reaction, the polymerization reaction is completed and a gel-like product is obtained.

[0109] (4) taking out the rubber block from the beaker, cutting the rubber block into pieces and granulating them into 4 mm particles, sieving and drying them, soaking them in anhydrous ethanol for 3 hours to remove unreacted monomers, and finally placing the rubber particles on a watch glass, drying them in an oven for 8 hours, crushing them with a grinder, and sieving them with a 200-mesh sieve to obtain the high-temperature resistant and salt-resistant polymer fracturing fluid thickener.

[0110] The thickeners prepared in Examples 1-4 and Comparative Examples 1-3 were prepared using the following method: 495 g of fresh water or highly mineralized water required for fracturing fluid preparation was weighed and transferred to the high-stirring cup of a digitally controlled high-speed agitator at a speed of 3000 r / min ± 90 r / min. 5 g of the fracturing fluid thickener polymer powder synthesized in Example 1 was added. After stirring for 2 minutes, the speed was adjusted to 1000 r / min ± 30 r / min, and stirring was stopped after 3 minutes. The liquid was transferred to a beaker and placed in a constant temperature water bath at 25°C ± 1°C for 4 hours to obtain a 1% fracturing fluid thickener polymer solution. The highly mineralized water was prepared by adding 26.423 g of NaCl, 0.695 g of KCl, 4.999 g of Na2SO4, 0.286 g of NaHCO3, 1.662 g of CaCl2, and 12.69 g of MgCl2·H2O to 1 L of distilled water.

[0111] Apparent viscosity was measured using a 12-speed rotary viscometer: 350 mL of fracturing fluid thickener polymer solution of varying concentrations was measured using a graduated cylinder and transferred to a rotary viscosity measuring cup. The apparent viscosity was measured using the rotary viscometer at a rotational speed of 100 r / min. The test results are shown in Table 1. These results demonstrate that the fracturing fluid thickeners prepared in Examples 1-4 are suitable for use in both freshwater and saltwater formulations and exhibit excellent salt tolerance.

[0112] Table 1

[0113]

[0114] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art will appreciate that these embodiments are intended only to illustrate the present invention and are not to be construed as limiting the scope of the present invention. It should be noted that any equivalent variations and substitutions to these embodiments are to be considered encompassed within the scope of the claims of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A thickener for a hydrophobically associating fracturing fluid, characterized in that: The polymer is prepared by polymerizing raw materials including the following monomers: amide monomers, carboxylic acid group-containing monomers, sulfonic acid monomers and hydrophobic associating monomers.

2. The hydrophobically associating fracturing fluid thickener according to claim 1, characterized in that: The molar ratio of the amide monomer, the carboxylic acid group-containing monomer, the sulfonic acid monomer, and the hydrophobic associating monomer is (80-85):(13-18):(3-8):(0.15-0.25).

3. The thickener for hydrophobically associating fracturing fluid according to claim 1, characterized in that: The amide monomers include one or more of acrylamide and N,N-dimethylacrylamide.

4. The hydrophobically associating fracturing fluid thickener according to claim 1, characterized in that: The carboxylic acid group-containing monomer includes one or more of acrylic acid, itaconic acid, and maleic anhydride.

5. The hydrophobically associating fracturing fluid thickener according to claim 1, characterized in that: The sulfonic acid monomers include one or more of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

6. The thickener for hydrophobically associating fracturing fluid according to claim 1, characterized in that: The hydrophobically associating monomers include one or more of octadecyldimethylallyl ammonium chloride and hexadecyldimethylallyl ammonium chloride.

7. The method for preparing a hydrophobically associating fracturing fluid thickener according to any one of claims 1 to 6, characterized in that: include: (1) dissolving an amide monomer, a carboxylic acid group-containing monomer, a sulfonic acid monomer, and a hydrophobically associating monomer in water according to a ratio to obtain a mixed solution; (2) adding sodium formate and urea to the mixed solution, stirring, introducing inert gas nitrogen or argon, heating to 30-60° C., and adding an initiator to start the polymerization reaction; (3) After the polymerization reaction is completed, the product is washed, dried, and crushed to obtain a thickener for high-temperature and salt-resistant fracturing fluid.

8. The preparation method according to claim 7, characterized in that The total mass concentration of monomers in the mixed solution is 10-30%.

9. The preparation method according to claim 7, characterized in that The amount of sodium formate added is 0.1% to 0.5% of the total mass of the monomers; the amount of urea added is 2% to 5% of the total mass of the monomers.

10. The preparation method according to claim 7, characterized in that The inert gas is nitrogen or argon.

11. The preparation method according to claim 7, characterized in that The heating temperature is 30-60°C.

12. The preparation method according to claim 7, characterized in that The initiators are ammonium persulfate and sodium bisulfite.

13. The preparation method according to claim 7, characterized in that The cleaning comprises: cutting the product and then soaking it in anhydrous ethanol for 2 to 4 hours.

14. A thickener for a hydrophobically associating fracturing fluid, characterized in that: The method is obtained by the preparation method according to any one of claims 7 to 13.

15. The hydrophobically associating fracturing fluid thickener according to claim 14, characterized in that: The molecular weight of the hydrophobically associating fracturing fluid thickener is in the range of 1.5 to 2 million.

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