A waterproof lock type thickening agent, a preparation method and application thereof

Abstract

This invention belongs to the field of petroleum industry chemicals technology, and discloses a waterproof and locking thickener, its preparation method and application. The method uses acrylamide and acrylic acid as the main monomers, and introduces polyoxyethylene ether and polymerizable cationic surfactant monomers as auxiliary monomers. The waterproof and locking thickener is prepared by quaternary copolymerization. By introducing polyoxyethylene ether and polymerizable cationic surfactant monomers into the polyacrylamide molecular chain, the thickener enables the rupture fluid to have both waterproof and locking functions, thereby reducing the step of adding water-locking inhibitors separately and improving the oil and gas production after fracturing.

Description

Technical Field

[0001] This invention belongs to the field of petroleum industry chemicals technology, and relates to a waterproof and lock-in thickener, its preparation method and application. Background Technology

[0002] Tight oil and gas reservoirs, as an important component of unconventional oil and gas resources, are characterized by low porosity, poor permeability, and narrow throats. Conventional extraction techniques are insufficient to achieve effective production, making hydraulic fracturing a core means of economically developing tight oil and gas reservoirs. The performance of the fracturing fluid directly determines the effectiveness of this stimulation, and thickeners, as key additives in the fracturing fluid system, play a crucial role in increasing the viscosity of the fracturing fluid to achieve the core functions of proppant transport and fracture creation.

[0003] However, conventional fracturing fluid thickeners currently face problems such as water-locking damage when applied to tight oil and gas reservoirs. The microscopic pore-throat structure of tight reservoirs is easily invaded by fracturing fluid filtrate, forming water phase retention. On the one hand, this blocks the oil and gas seepage channels, significantly reducing reservoir permeability; on the other hand, the retained water interacts with reservoir minerals and crude oil, easily triggering secondary damage such as clay hydration swelling and particle migration, further aggravating reservoir damage and making it difficult for the oil and gas well production capacity to reach expectations after fracturing.

[0004] Existing thickener products mostly focus on improving temperature and salt resistance, with insufficient targeted design for waterproofing and sealing functions. While some modified thickeners reduce hydrophilicity to some extent by introducing hydrophobic groups, the modification process is complex and costly. Furthermore, the solubility and viscosity-enhancing efficiency of modified thickeners in fracturing fluid systems decrease to varying degrees, making it difficult to balance workability and waterproofing / sealing effects. Meanwhile, commonly used water-based fracturing systems mainly consist of thickeners, crosslinking agents, breaker agents, and other additives. Surfactants, as important waterproofing / sealing additives, are usually added alone or in combination with other additives to achieve waterproofing and drainage effects. This results in complex liquid systems and cumbersome operations during construction, which is not conducive to on-site fracturing operations.

[0005] Therefore, there is an urgent need to develop a thickener with fewer limitations, strong core functions, and waterproof locking capabilities to simplify fracturing fluid systems, reduce construction steps, and increase the production of tight oil and gas wells. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a waterproof locking thickener, its preparation method, and its application, thereby solving the technical problems that existing fracturing fluid thickeners lack embedded waterproof locking function, require the addition of surfactants and additives, resulting in complex systems and cumbersome construction, and that modified thickeners often struggle to achieve both waterproof locking effect and good solubility and thickening properties.

[0007] This invention is achieved through the following technical solution: A method for preparing a waterproof, lock-in thickener includes the following steps: S1: Dissolve acrylic acid and polyoxyethylene ether in water and adjust the pH of the solution to 2-4; then add acrylamide and polymerizable cationic surfactant monomer in sequence, stir evenly, and obtain monomer solution; S2: When the temperature of the monomer solution drops below 7°C, nitrogen is bubbled into the solution to remove oxygen, and then an initiator is added to carry out the polymerization reaction. After the reaction is completed, polymer blocks are obtained. S3: The polymer block is crushed, granulated and dried to obtain the waterproof locking thickener.

[0008] Preferably, the polyoxyethylene ether is one of methpropylene polyoxyethylene ether, isopentenyl polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and allyl polyoxyethylene ether.

[0009] Preferably, the polymerizable cationic surfactant monomer is methacryloyloxyethyl dimethyl dodecyl ammonium bromide.

[0010] Preferably, in the preparation method of the waterproof locking thickener according to claim 1, the monomer solution has a mass concentration of 40% to 42%.

[0011] Preferably, the ratio of acrylic acid, polyoxyethylene ether, acrylamide, polymerizable cationic surfactant monomer and initiator by weight is (11~17):(1~2):(15~22):(0.5~1):(0.05~0.1).

[0012] Preferably, the initiator includes at least one selected from potassium persulfate, ammonium persulfate, sodium bisulfite, ascorbic acid, azobisisobutyronitrile, and azobisisobutyramidine hydrochloride.

[0013] Preferably, in the preparation method of the waterproof locking thickener according to claim 1, the nitrogen deoxygenation time is 20-30 min.

[0014] Preferably, the polymerization reaction ends when the system temperature rises to 60-80°C.

[0015] A waterproof, lock-in thickener is prepared by the method described above.

[0016] The above-mentioned waterproof, lock-type thickener is used in the fracturing of tight oil and gas reservoirs.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing a waterproof and locking thickener. This method, through a unique quaternary copolymer molecular design, fundamentally solves the contradiction in existing technologies where additional additives are required, leading to system complexity and difficulty in balancing waterproof locking and thickening performance. This scheme polymerizes acrylic acid with polyoxyethylene ether (a nonionic surfactant monomer), acrylamide (the main thickening monomer), and polymerizable cationic surfactant monomers in the same reaction system. This design allows the resulting thickener molecular chain to simultaneously possess a thickening framework and surfactant groups: on the one hand, the polyacrylamide backbone ensures excellent water solubility and thickening / sand-carrying capacity; on the other hand, the introduced polyoxyethylene ether and cationic surfactant monomers act as "embedded" waterproof and locking functional units. After the fracturing fluid breaks down, these groups spontaneously migrate to the liquid-solid interface, significantly reducing the surface tension of water and altering the rock wettability (from hydrophilic to hydrophobic). Thus, without adding additional additives or changing the construction steps, the waterproof and locking function is achieved using the molecular's own structural characteristics, realizing "one agent, multiple functions." This simplifies the fracturing fluid system while ensuring good solubility and shear resistance.

[0018] Furthermore, the polyoxyethylene ether is one of methpropylene polyoxyethylene ether, isopentenyl polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and allyl polyoxyethylene ether, which specifies the specific type of polyether macromonomer. These monomers have good water solubility and polymerization activity. Introducing a long-chain polyether structure can effectively increase the steric hindrance of the molecule, which is not only beneficial to improving the temperature resistance of the polymer, but its hydrophilic-hydrophobic balance structure is also a key group for reducing surface tension and achieving waterproofing function.

[0019] Furthermore, the polymerizable cationic surfactant monomer is methacryloyloxyethyl dimethyl dodecyl ammonium bromide, which contains a long-chain alkyl group (hydrophobic group) and a quaternary ammonium salt cation (hydrophilic / adsorption group). The quaternary ammonium salt head is positively charged and can be strongly adsorbed on the negatively charged rock surface, while the long alkyl tails are arranged outward to form a hydrophobic layer, which effectively prevents the spread and retention of the aqueous phase in the pore throat, significantly reducing capillary resistance. This is the core chemical structure for achieving a "waterproof lock".

[0020] Furthermore, the monomer solution has a mass concentration of 40% to 42%, which falls within the range of high-concentration aqueous solution polymerization. Too low a concentration would make it difficult to increase the molecular weight of the product and would result in high energy consumption; too high a concentration would make heat dissipation difficult and could easily lead to "bursting polymerization." The specific window of 40% to 42% can balance the heat of reaction and chain growth efficiency, ensuring the production of high molecular weight, high-viscosity polymer blocks, while also guaranteeing the safety and controllability of the reaction process.

[0021] Furthermore, based on parts by weight, the ratio of acrylic acid, polyoxyethylene ether, acrylamide, polymerizable cationic surfactant monomer, and initiator is (11~17):(1~2):(15~22):(0.5~1):(0.05~0.1). This ratio precisely controls the proportion of hydrophilic (AM, AA) and hydrophobic / surfactant (polyether, cationic monomer) groups. Too much hydrophobic monomer will result in poor thickening or ineffective thickening; too little will lead to insufficient water-locking effect. This ratio range ensures that the product has sufficient viscosity while reducing liquid residue to below 57.6%.

[0022] Furthermore, the initiator includes at least one of potassium persulfate, ammonium persulfate, sodium bisulfite, ascorbic acid, azobisisobutyronitrile, and azobisisobutyramidine hydrochloride. This scheme requires the temperature to be lowered to below 7°C, therefore a system suitable for low-temperature initiation is needed. These initiators are all water-soluble or oil-soluble, capable of effectively generating free radicals to initiate polymerization at low temperatures. Furthermore, by using them in combination (such as in a redox system), the initiation temperature can be further reduced, ensuring the reaction conversion rate.

[0023] Furthermore, the nitrogen purging time for deoxygenation is 20-30 minutes, as oxygen is an inhibitor of free radical polymerization. Sufficient deoxygenation (20-30 minutes) can completely remove dissolved oxygen from the aqueous solution, avoid induction period and free radical quenching, ensure a smooth start of the polymerization reaction and obtain high molecular weight polymers, reduce residual monomers, and improve product purity.

[0024] Furthermore, during the polymerization reaction, the reaction ends when the system temperature rises to 60-80℃. Utilizing the exothermic nature of polymerization, setting the temperature at 60-80℃ as the end of the reaction signifies that the monomer conversion rate has reached a high level. This control method is simple and intuitive, requiring no complex online monitoring equipment, facilitating process control in industrial production, and ensuring batch-to-batch product stability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The results are the temperature resistance and shear strength test results of the thickeners prepared in Examples 1-3 of this invention; Figure 2 The images show the droplet state of the thickener prepared in Examples 1-3 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0027] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0029] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0030] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0031] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0032] This invention provides a method for preparing a waterproof, locking thickener, comprising the following steps: S1: Dissolve acrylic acid (AA) and polyoxyethylene ether in water and adjust the pH of the solution to 2-4; then add acrylamide (AM) and polymerizable cationic surfactant monomer in sequence, stir evenly to obtain monomer solution; The polyoxyethylene ether is one of methpropylene polyoxyethylene ether (HPEG), isopentenyl alcohol polyoxyethylene ether (TPEG), fatty alcohol polyoxyethylene ether (AEO), and allyl polyoxyethylene ether (APEG).

[0033] The polymerizable cationic surfactant monomer is methacryloyloxyethyl dimethyl dodecyl ammonium bromide (DMAEMA-Q). S2: When the temperature of the monomer solution drops below 7°C, nitrogen is bubbled into the solution to remove oxygen, and then an initiator is added to carry out the polymerization reaction. After the reaction is completed, polymer blocks are obtained. Specifically, the monomer solution can be bottled and refrigerated. When the solution temperature drops below 7°C, the solution is transferred to a reactor and N2 is introduced to remove O2 from the solution. Then, an initiator is added dropwise to initiate the polymerization reaction. When the solution becomes viscous, the N2 supply is stopped, the reactor is sealed, and placed in an insulated jacket. The temperature change of the system is recorded every 0.5 hours until the temperature rises to 60~80°C, at which point the reaction is considered complete. The nitrogen deoxygenation time is 20-30 minutes; The proportions of acrylic acid, polyoxyethylene ether, acrylamide, polymerizable cationic surfactant monomer and initiator, by weight, are (11~17):(1~2):(15~22):(0.5~1):(0.05~0.1). The monomer solution has a mass concentration of 40% to 42%, which refers to the percentage of the monomer's mass relative to the total mass of the system. Specifically, it represents the percentage of the total mass of acrylic acid, polyoxyethylene ether, acrylamide, and polymerizable cationic surfactant monomers relative to the total mass of acrylic acid, polyoxyethylene ether, acrylamide, polymerizable cationic surfactant monomers, initiator, and water. In other words, the monomer accounts for 40% to 42% of the total mass of the reaction system. The initiator includes at least one of potassium persulfate, ammonium persulfate (APS), sodium bisulfite, ascorbic acid (VC), azobisisobutyronitrile, and azobisisobutyramidine hydrochloride (V-50); S3: The polymer block is crushed, dried and granulated to obtain the waterproof locking thickener.

[0034] The drying temperature is 70~90℃ and the time is 4~6 hours.

[0035] In addition, this invention also discloses a waterproof locking thickener prepared by the above method, wherein the structural formula of the waterproof locking thickener is:

[0036] Where n is 60,000 to 100,000, x is 200 to 1,500, y is 2,000 to 10,000, and z is 2,000 to 10,000.

[0037] This invention introduces the surfactant monomer polyoxyethylene ether and the polymerizable cationic surfactant monomer methacryloyloxyethyl dimethyl dodecyl ammonium bromide into the molecular chain of polyacrylamide. The polyether segments and quaternary ammonium salt released after gel breaking significantly reduce the surface tension of water. The positively charged quaternary ammonium salt at the head adsorbs onto the rock, while the long alkyl chain at the tail is hydrophobic, reducing capillary resistance and seepage resistance, improving the interaction force at the liquid-solid interface or liquid-gas interface, and inhibiting the water-locking effect in tight oil and gas reservoirs. The viscosity of this thickener can still reach 70 mPa·s under high temperature shear conditions, and it also has excellent friction reduction and sand-carrying capacity.

[0038] This invention has a simple configuration and excellent overall performance, operating at 90℃ for 170 seconds. -1 After 60 minutes of shearing at the specified shear rate, the gel viscosity can still reach over 70 mPa·s, demonstrating strong water-locking ability. It can reduce liquid residue to 57.6% under the same conditions, minimizing damage to the underlying layer. This invention proposes a water-locking thickener for fracturing tight oil and gas reservoirs, prepared via quaternary copolymerization using acrylamide (AM) and acrylic acid (AA) as the main monomers, and polymerizable nonionic polyether surfactants and polymerizable cationic surfactant monomers as auxiliary monomers. This gives the polyacrylamide thickener a water-locking function.

[0039] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0040] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0041] Example 1 A waterproof, lock-in thickener is prepared from the following components in parts by weight: 22 parts acrylamide, 17 parts acrylic acid, 1 part allyl polyoxyethylene ether, 0.6 parts methacryloyloxyethyl dimethyl dodecyl ammonium bromide, 59.4 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); wherein the monomer accounts for 40.6% of the total mass of the reaction system, where the monomer refers to the total mass of acrylamide, acrylic acid, allyl polyoxyethylene ether, and methacryloyloxyethyl dimethyl dodecyl ammonium bromide accounting for 40.6% of the total mass of acrylamide, acrylic acid, allyl polyoxyethylene ether, methacryloyloxyethyl dimethyl dodecyl ammonium bromide, and deionized water.

[0042] The specific preparation process is as follows: (1) According to the above dosage, first add acrylic acid and allyl polyoxyethylene ether to an appropriate amount of deionized water, adjust the pH value to 2~4, then add acrylamide and methacryloyloxyethyl dimethyl dodecyl ammonium bromide, and add deionized water to the target monomer concentration (40.6wt%), stir until homogeneous, and obtain monomer solution; (2) When the solution temperature drops below 7°C, transfer the solution to the reactor and introduce N2 to remove O2 from the solution. After N2 is introduced for 30 minutes, add the initiator to initiate the reaction. Stop introducing N2 when the solution becomes viscous. Seal the reactor and place it in an insulation jacket. Record the temperature change of the system every 0.5 hours until the temperature rises to 60~80°C, at which point the reaction is considered to be over.

[0043] (3) After cooling, take out the rubber block, cut it into pieces, dry it at 70°C for 6 hours, crush and granulate it to obtain a waterproof lock-type thickener for fracturing tight oil and gas reservoirs.

[0044] Example 2 A waterproof, lock-in thickener is prepared from the following components in parts by weight: 22 parts acrylamide, 17 parts acrylic acid, 1.4 parts allyl polyoxyethylene ether, 0.6 parts methacryloyloxyethyl dimethyl dodecyl ammonium bromide, 59 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); wherein the monomer accounts for 40% of the total mass percentage of the reaction system. The specific preparation process is as follows: (1) According to the above dosage, first add acrylic acid and allyl polyoxyethylene ether to an appropriate amount of deionized water, adjust the pH value to 2~4, then add acrylamide and methacryloyloxyethyl dimethyl dodecyl ammonium bromide, and add deionized water to the target monomer concentration, stir until homogeneous, and obtain monomer solution. (2) When the solution temperature drops below 7°C, transfer the solution to the reactor and introduce N2 to remove O2 from the solution. After N2 is introduced for 30 minutes, add the initiator to initiate the reaction. Stop introducing N2 when the solution becomes viscous. Seal the reactor and place it in an insulation jacket. Record the temperature change of the system every 0.5 hours until the temperature rises to 60~80°C, at which point the reaction is considered to be over.

[0045] (3) After cooling, remove the rubber block, cut it into pieces, and dry it at 70~90℃ for 4~6 hours. After crushing and granulating, a waterproof lock-type thickener for fracturing tight oil and gas reservoirs is obtained.

[0046] Example 3 A waterproof, lock-in thickener is prepared from the following components by weight: 22 parts acrylamide, 17 parts acrylic acid, 1.4 parts allyl polyoxyethylene ether, 0.8 parts methacryloyloxyethyl dimethyl dodecyl ammonium bromide, 58.8 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); wherein the monomer accounts for 41.2% of the total mass percentage of the reaction system. The specific preparation process is as follows: (1) According to the above dosage, first add acrylic acid and allyl polyoxyethylene ether to an appropriate amount of deionized water, adjust the pH value to 2~4, then add acrylamide and methacryloyloxyethyl dimethyl dodecyl ammonium bromide, and add deionized water to the target monomer concentration, stir until homogeneous, and obtain monomer solution. (2) When the solution temperature drops below 7°C, transfer the solution to the reactor and introduce N2 to remove O2 from the solution. After N2 is introduced for 30 minutes, add the initiator to initiate the reaction. Stop introducing N2 when the solution becomes viscous. Seal the reactor and place it in an insulation jacket. Record the temperature change of the system every 0.5 hours until the temperature rises to 60~80°C, at which point the reaction is considered to be over.

[0047] (3) After cooling, remove the rubber block, cut it into pieces, and dry it at 70~90℃ for 4~6 hours. After crushing and granulating, a waterproof lock-type thickener for fracturing tight oil and gas reservoirs is obtained.

[0048] Comparative Example 1 The difference between this embodiment and Embodiment 1 is as follows: It is prepared from the following components by weight: 22 parts acrylamide, 17 parts acrylic acid, 59.4 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); that is, allyl polyoxyethylene ether and methacryloyloxyethyl dimethyl dodecyl ammonium bromide are not added to the components.

[0049] Comparative Example 2 The difference between this embodiment and Embodiment 1 is as follows: It is prepared from the following components by weight: 22 parts acrylamide, 17 parts acrylic acid, 0.6 parts methacryloyloxyethyl dimethyl dodecyl ammonium bromide, 59.4 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); that is, no allyl polyoxyethylene ether is added to the components.

[0050] Comparative Example 3 The difference between this embodiment and Embodiment 1 is as follows: It is prepared from the following components by weight: 22 parts acrylamide, 17 parts acrylic acid, 1 part allyl polyoxyethylene ether, 59.4 parts deionized water, and 0.05 parts initiator (APS:VC:V-50); that is, no methacryloyloxyethyl dimethyl dodecyl ammonium bromide is added to the components.

[0051] In addition, the properties of the product obtained by this invention are characterized by the following test experiments: The apparent viscosity of the solution was determined using an HTD-ST digital display six-speed rotational viscometer. The surface tension of the solution after the thickener breaks down was experimentally determined using a DCAT21 interfacial tensiometer at a temperature of 25℃. The performance evaluation of waterproof locking was carried out using a self-absorption test (spontaneous seepage method): artificial rock cores with similar pore permeability were immersed in gel-breaking liquids with different thickeners, and the change of spontaneous water absorption over time was measured. The hydrophilicity and water-locking tendency of the rock cores were judged by the water absorption and rate. The inhibition effect was reflected by reducing the water absorption or slowing down the water absorption rate.

[0052] Experimental instruments and methods Viscosity measurement: The viscosity of the liquid was measured using an HTD-ST digital display six-speed rotary viscometer at a speed of 100 rpm.

[0053] pH value: Measured using pH test paper.

[0054] Thickening time: Start timing with a stopwatch from the moment the thickener is added to the test liquid until it is fully swollen.

[0055] Suspended sediment stability: Take 70g of a solution containing a certain concentration of thickener, add 30g of ceramsite (40 / 70 mesh), stir evenly, and observe the sedimentation of the ceramsite at room temperature. Calculate the ratio of the decrease in the height of the ceramsite accumulation surface to the total liquid height after 30 minutes. The smaller the ratio, the better the suspension stability.

[0056] Degradation and gel breaking properties: Take 100 mL of a solution with a certain concentration of thickener, add 0.04% APS, stir well, and let stand at 80℃ for 4 hours. After cooling to room temperature, use an Ubbelohde viscometer to test the kinematic viscosity of the solution, which is the degradation performance.

[0057] Residue content: After the liquid is broken up, it is filtered through a filter membrane with a specific pore size (e.g., 0.45 μm), the insoluble matter is collected, dried, weighed, and the residue content is calculated.

[0058] Surface tension: The surface tension of the solution after gel breaking was measured using a DCAT21 interfacial tensiometer at a temperature of 25℃.

[0059] Temperature and shear resistance: Using a Thermo Fisher HAAKE Mars40 rheometer, at 90℃ for 170 seconds... -1 After shearing for 1 hour at (shear rate), the temperature resistance and shear strength of the thickener were tested.

[0060] Waterproof lock performance evaluation: (1) The DSA optical droplet morphology analysis system designed and manufactured by Kruss GmbH, Germany, was used. The equilibrium contact angle of the artificial rock core after immersion in the gel breaking solution of different cases for 24 hours was determined by the "lying drop method". (2) Artificial rock cores with similar porosity and permeability were selected and immersed in the thickener solution after gel breaking. After centrifugation at 10000r / min, the percentage content of the residual liquid after centrifugation was determined.

[0061] The viscosity, thickening time, and suspension stability test results of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 of this invention are shown in Table 1. As can be seen from Table 1, compared with the comparative examples, the viscosity and suspension stability of the thickeners were improved with the increase of the content of allyl polyoxyethylene ether and methacryloyloxyethyl dimethyl dodecyl ammonium bromide in the examples.

[0062] In addition, the results of the debonding performance and surface tension test of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in Table 2. As can be seen from Table 2, the addition of functional monomers has little effect on the debonding performance of the thickener, but greatly improves the surface tension of the debonding liquid, effectively alleviates the capillary pressure effect, and thus significantly reduces water lock damage.

[0063] Meanwhile, the present invention evaluates the water-locking performance of the prepared thickener. The test results of the percentage of residual liquid after centrifugation in the artificial rock core are shown in Table 3. Table 3 shows that, compared to the comparative example, the percentage of residual liquid in the artificial rock core of the thickener in the example is 31.1% lower. The test results of the water-locking performance of the artificial rock core are shown in Table 4. Table 4 shows that, compared to formation water, conventional fracturing fluid base fluid, and 0.3% drainage aid + conventional fracturing fluid, the residual liquid content in the artificial rock core of the example is lower, indicating that the thickener solution in the example is more easily discharged from the rock core, thereby reducing the risk of water lock.

[0064] Table 1. Performance test results of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0065] Table 2. Results of the thickener breaking performance and surface tension of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0066] Table 3. Percentage of residual liquid after centrifugation in artificial rock cores of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0067] Table 4. Results of the test on the waterproofing and locking performance of the thickeners prepared in Examples 1-3 of this invention in artificial rock cores.

[0068] In addition, the test results of the temperature resistance and shear strength of the thickeners prepared in Examples 1-3 of this invention are shown in the figure. Figure 1 ,Depend on Figure 1 It can be seen that Examples 1-3 were performed at 90℃ for 170 seconds. -1 After shearing at the shear rate for 60 minutes, the viscosity of the thickener can still reach 70 mPa·s, demonstrating excellent high-temperature resistance and shear resistance.

[0069] The state of the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 after soaking the rock slabs in the gelling solution for 24 hours is shown in the figure. Figure 2 ,Depend on Figure 2 It can be seen that the contact angle of the droplets after the rock slab was soaked in the thickener breaking liquid of the embodiment is greater than that of the comparative example. This indicates that the thickener breaking liquid of the embodiment reduces the wettability of the rock and soil surface, making it difficult for water to spread on the hole wall and tending to gather into water droplets or water flow. This water is easier to flow and return.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a waterproof, lock-in thickener, characterized in that, Includes the following steps: S1: Dissolve acrylic acid and polyoxyethylene ether in water and adjust the pH of the solution to 2-4; then add acrylamide and polymerizable cationic surfactant monomer in sequence, stir evenly, and obtain monomer solution; S2: When the temperature of the monomer solution drops below 7°C, nitrogen is bubbled into the solution to remove oxygen, and then an initiator is added to carry out the polymerization reaction. After the reaction is completed, polymer blocks are obtained. S3: The polymer block is crushed, granulated and dried to obtain the waterproof locking thickener.

2. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The polyoxyethylene ether is one of methpropylene polyoxyethylene ether, isopentenyl alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and allyl polyoxyethylene ether.

3. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The polymerizable cationic surfactant monomer is methacryloyloxyethyl dimethyl dodecyl ammonium bromide.

4. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The monomer solution has a mass concentration of 40% to 42%.

5. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The proportions of acrylic acid, polyoxyethylene ether, acrylamide, polymerizable cationic surfactant monomer and initiator, based on parts by weight, are (11~17):(1~2):(15~22):(0.5~1):(0.05~0.1).

6. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The initiator includes at least one of potassium persulfate, ammonium persulfate, sodium bisulfite, ascorbic acid, azobisisobutyronitrile, and azobisisobutyramidine hydrochloride.

7. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, The nitrogen deoxygenation time is 20-30 minutes.

8. The method for preparing a waterproof, type-locking thickener according to claim 1, characterized in that, When a polymerization reaction is carried out, the reaction ends when the system temperature rises to 60~80℃.

9. A waterproof, lock-in thickener, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the waterproof, lock-type thickener as described in claim 9 in the fracturing of tight oil and gas reservoirs.

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