Transmutable polymers, methods of making and using the same

Abstract

The application discloses a phase-changeable polymer and a preparation method and application thereof. The phase-changeable polymer contains structural unit A, structural unit B and hydrolysable cross-linking structural unit C, wherein the hydrolysable cross-linking structural unit C contains anhydride bonds and ester bonds; the phase-changeable polymer has obvious thermal weight loss characteristic peaks between 550-650 DEG C. The phase-changeable polymer can be prepared into a polymer oil displacement agent, which can realize the transformation from a gel particle dispersed phase to a solution continuous phase under reservoir conditions, and finally realize the slow-release and viscosity increase in a deep reservoir, so that the gel plugging and flow diversion line near a wellbore is adjusted, the solution viscosity is increased in a far wellbore to expand the swept volume, and the oil displacement efficiency is improved, thereby greatly improving the utilization rate of the polymer and the oil displacement efficiency and improving the oil recovery rate.

Description

Technical Field

[0001] This invention relates to the field of oilfield exploitation technology, specifically to phase change polymers, their preparation methods, and applications. Background Technology

[0002] As oilfields enter the high / ultra-high water-cut development stage, waterflooding becomes less effective. Due to long-term water injection erosion, the remaining oil in the oilfield exhibits characteristics of "high dispersion and local enrichment." The oil saturation in the near-wellbore zone is low, and the waterflooding effect extends from the near-wellbore zone in the early and mid-stages of development to deeper, more distant wells, eventually affecting the entire injection-production flow field. Achieving efficient tapping of the remaining oil and a significant increase in recovery rate is a pressing problem that needs to be solved for the sustainable development of old, high-water-cut oilfields both domestically and internationally.

[0003] Polymer flooding is one of the chemical flooding technologies that can significantly improve the recovery rate of old oilfields. The viscosity of the polymer solution is crucial for improving the water-oil mobility ratio, expanding the swept volume of the injected fluid, and substantially increasing the oil recovery rate, thus ensuring the economic benefits of polymer flooding development. Therefore, how to significantly reduce viscosity loss during polymer injection, achieve in-situ viscosity enhancement within the reservoir, improve the viscosity enhancement performance and mobility control capabilities of polymer-enhanced reservoirs at depth, and ultimately achieve the goal of significantly expanding the swept volume of waterflooding, is a key technical challenge that urgently needs to be solved in polymer flooding.

[0004] To address the challenges of poor temperature and salt resistance and significant viscosity loss in conventional polymers, domestic and international researchers have focused on improving polymer viscosity, reducing polymer dosage, and expanding the application range of polymer flooding by developing temperature- and salt-resistant polymers and controlling polymer viscosity loss during injection processes. Currently, the main approaches to improving the temperature and salt resistance of polymers are increasing their relative molecular mass and introducing functional monomers with special functional groups into the molecular chain. Simply increasing the relative molecular mass can improve the viscosity-enhancing properties, but higher molecular weight polymers are more susceptible to shear degradation, leading to viscosity loss and injection difficulties in lower permeability layers. Introducing functional monomers with special functional groups to improve temperature and salt resistance and increase viscosity, while significantly increasing the initial polymer viscosity, still cannot overcome the technical challenges of viscosity loss during injection and weak viscosity enhancement in deep reservoirs.

[0005] While various types of temperature- and salt-resistant polymers currently under development can improve viscosity-enhancing properties under reservoir conditions, delayed / extended viscosity-enhancing polymers can also improve viscosity retention during use to some extent, improve water-oil mobility, and expand the water-drive swept volume, thus broadening the reservoir range for polymer flooding applications. However, as oilfields enter the high water-cut development stage, long-term water injection scouring leads to the development of dominant seepage channels, exacerbating inter-layer, intra-layer, and planar contradictions, which can easily cause the displacement solution to surge and cross-flow. Therefore, simple continuous-phase viscosity-enhancing solutions are insufficient to overcome the "liquid absorption profile reversal" phenomenon caused by reservoir heterogeneity and polymer retention, which is not conducive to improving the utilization of crude oil in relatively low- and medium-permeability layers, has limited capacity to expand the swept volume, and cannot meet the demand for significantly improving oil recovery. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing technologies, such as weak displacement capacity, large shear viscosity loss, low effective viscosity underground, and limited ability to expand swept volume, which cannot meet the requirements for significantly improving oil recovery. This invention provides a phase change polymer, its preparation method, and its applications. The phase change polymer of this invention is initially dispersed as gel particles in brine. When injected into the formation, it exhibits certain shear resistance and simultaneously acts as a flow line regulator near the wellbore. As it migrates within the formation, under reservoir temperature conditions, the hydrolyzable cross-linked structure gradually hydrolyzes, achieving slow-release viscosity enhancement and maximizing the effective displacement viscosity. This results in expanding the swept volume in the far well section and achieving efficient oil displacement, significantly improving oil recovery.

[0007] To achieve the above objectives, the first aspect of the present invention provides a phase change polymer, the phase change polymer comprising structural unit A, structural unit B and hydrolyzable crosslinkable structural unit C, wherein structural unit A has the structure shown in formula (1), structural unit B has the structure shown in formula (2), and hydrolyzable crosslinkable structural unit C contains anhydride bonds and ester bonds.

[0008]

[0009] In this context, R1, R2, R3, R4, R5, and R6 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups; M is an alkali metal.

[0010] The phase change polymer exhibits a distinct thermogravimetric characteristic peak between 550-650℃.

[0011] A second aspect of the present invention provides a method for preparing a phase change polymer, the method comprising the following steps:

[0012] Under phase inversion controlled conditions, in the presence of an initiator and a phase inversion control agent, acrylamide monomers and acrylic monomers are subjected to solution polymerization in water to obtain a phase change polymer.

[0013] The phase inversion control agent includes anhydride compounds containing two or more carbon-carbon double bonds and acrylate compounds containing three or more carbon-carbon double bonds.

[0014] The third aspect of the present invention provides the application of the phase change polymer described in the first aspect or the phase change polymer prepared by the preparation method described in the second aspect in oil displacement.

[0015] A fourth aspect of the present invention provides a polymer flooding agent, the polymer flooding agent comprising a base liquid and a phase change polymer; wherein the phase change polymer is the phase change polymer described in the first aspect above or the phase change polymer prepared by the preparation method described in the second aspect above; the phase change polymer is dispersed in the base liquid in the form of gel particles and hydrolyzed under reservoir conditions to form a homogeneous solution.

[0016] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0017] The phase change polymer of this invention can be formulated into a polymer flooding agent. The initial state of the phase change polymer is a gel particle dispersion phase, which can reduce the chemical degradation of the polymer by divalent ions such as sulfur and iron in the injection water. When injected into the formation, the gel particle dispersion phase is dominant, which has strong shear resistance and a good ability to adjust the profile in near-wellbore high-permeability layers. Under reservoir conditions, it can realize the transformation from the gel particle dispersion phase to the solution continuous phase, and finally achieve slow-release viscosity enhancement in the deep reservoir, realizing oil displacement in distant wells. It achieves the dual effect of one agent and high-efficiency oil displacement, greatly improving the utilization rate of polymer and oil displacement efficiency, and improving crude oil recovery. Attached Figure Description

[0018] Figure 1 This is a gel particle dispersion phase formed by dispersing a phase change polymer in an aqueous sodium chloride solution according to one embodiment of the present invention.

[0019] Figure 2 yes Figure 1 The intermediate phase formed during the transformation of the gel particle dispersion phase into the continuous solution phase;

[0020] Figure 3 yes Figure 1 The continuous solution phase formed after the gel particle dispersion phase is completely dissolved;

[0021] Figure 4 This is the infrared spectrum of the phase change polymer obtained in Example 1 of the present invention;

[0022] Figure 5 This is the thermogravimetric curve of the phase change polymer obtained in Example 1 of the present invention;

[0023] Figure 6 The thermogravimetric curves of the polymer prepared in Comparative Example 1 are shown.

[0024] Figure 7 The thermogravimetric curves of the polymer obtained in Comparative Example 2 are shown.

[0025] Figure 8 The thermogravimetric curves of polyacrylamide (II) in Comparative Example 6 are shown.

[0026] Figure 9 These are the viscosity curves of the phase change polymers obtained in Examples 1-3 of this invention as a function of time.

[0027] Figure 10 These are curves showing the change of elastic modulus over time of the phase change polymers obtained in Examples 1-3 of this invention.

[0028] Figure 11 These are comparison diagrams showing the shear resistance of the polymers obtained in Examples 1-3 and Comparative Examples 1-3 and 6. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the 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.

[0030] The first aspect of the present invention provides a phase change polymer, the phase change polymer comprising structural unit A, structural unit B and hydrolyzable crosslinkable structural unit C, wherein structural unit A has the structure shown in formula (1), structural unit B has the structure shown in formula (2), and hydrolyzable crosslinkable structural unit C contains anhydride bonds and ester bonds;

[0031]

[0032] In this context, R1, R2, R3, R4, R5, and R6 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups; M is an alkali metal.

[0033] The phase change polymer exhibits a distinct thermogravimetric characteristic peak between 550-650℃.

[0034] In some embodiments, R1, R2, R3, R4, R5 and R6 are each preferably hydrogen or C1-C6 straight-chain or branched alkyl groups, more preferably hydrogen or C1-C4 straight-chain or branched alkyl groups; and even more preferably hydrogen, methyl or ethyl.

[0035] In a particularly preferred embodiment of the present invention, R1, R2 and R3 in formula (1) are all hydrogen, and the structure shown in formula (1) can be a structural unit derived from acrylamide monomer; R4, R5 and R6 in formula (2) are all hydrogen, and the structure shown in formula (2) can be a structural unit derived from acrylic acid monomer.

[0036] According to the present invention, examples of the alkali metal may be any one of Li, Na and K.

[0037] According to the present invention, the test method for the characteristic peak of thermogravimetric analysis is as follows: using a thermogravimetric analyzer, under a nitrogen atmosphere, the instrument's heating rate is 20℃ / min, and the temperature range is 25-800℃, the thermogravimetric curve of the phase change polymer dry powder at 25-800℃ is plotted.

[0038] According to some embodiments of the present invention, the integral area of ​​the thermogravimetric characteristic peak of the phase change polymer between 550-650°C accounts for 10-20% of the integral area of ​​the thermogravimetric characteristic peak between 25-800°C, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, and any value in any range of any two sets of values, preferably 12-19%, more preferably 15-19%.

[0039] According to the present invention, the method for measuring the integral area of ​​the characteristic peak of thermogravimetric analysis is as follows: A certain mass of a phase change polymer sample is placed in a thermogravimetric balance, and an thermogravimetric analyzer (TGA-Q500, TA) is used to conduct the experiment under the following conditions: the temperature is increased at a rate of 10℃ / min in an air atmosphere at a rate of 60mL / min, and the test temperature range is 25-800℃. The thermogravimetric curve of the phase change polymer sample is obtained. Based on the shape and height of the peak, the integral area of ​​the characteristic peak of thermogravimetric analysis of the sample within a specific temperature range can be directly calculated using the built-in software.

[0040] The thermogravimetric curves obtained using the above testing methods show that the phase change polymer of this invention exhibits a distinct thermogravimetric characteristic peak between 550-650℃. This is likely due to the presence of weakly cross-linked phase inversion groups in the phase change polymer. The integral area of ​​the thermogravimetric characteristic peak between 550-650℃ accounts for 10-20% of the integral area of ​​the thermogravimetric characteristic peak between 25-800℃. This indicates that the weakly cross-linked phase inversion groups of this phase change polymer enable a slow release of viscosity, ultimately achieving a higher viscosity.

[0041] The reason why this invention can achieve slow viscosity release is that the hydrolyzable crosslinkable structural unit C, containing anhydride and ester bonds, temporarily "binds" the water-soluble polymer together through controllable weak crosslinking technology. This allows for a controllable transition from the dispersed gel particle phase to the continuous solution phase, resulting in a lower initial viscosity of the polymer, which reaches a higher viscosity after complete release. This achieves a dual-effect and highly efficient oil displacement. The phase change polymer has strong resistance to degradation and a high elastic modulus, acting as a deformable particle-based displacement agent in the near-wellbore zone. Under changes in formation conditions and weak crosslinking, the phase change polymer gradually hydrolyzes and releases a viscosity-enhancing polymer, achieving slow-release viscosity enhancement in the deep reservoir and improving oil recovery.

[0042] According to some embodiments of the present invention, the phase change polymer is dispersed in an aqueous sodium chloride solution with a sodium chloride concentration of 10000 mg / L to form a dispersion with a phase change polymer gel particle concentration of 2500 mg / L; at 75°C, the initial elastic modulus of the dispersion is not less than 15 Pa; the viscosity of the dispersion after standing for 2 hours is not greater than 20 mPa·s, and the elastic modulus is not less than 10 Pa; the viscosity of the homogeneous solution formed after the dispersion is completely dissolved is not less than 100 mPa·s, and the elastic modulus is not greater than 1 Pa; the time for the dispersion to completely dissolve is not less than 24 hours.

[0043] According to the present invention, the phase change polymer is dispersed in an aqueous sodium chloride solution to form a dispersion in which the phase change polymer gel particles are the dispersed phase. The dispersion is gradually hydrolyzed over time at 75°C, slowly releasing viscosity and ultimately achieving sustained-release viscosity enhancement.

[0044] According to the present invention, viscosity and elastic modulus are measured by an Anton Paar rheometer MCR301.

[0045] According to the present invention, the method for testing viscosity and elastic modulus includes the following steps:

[0046] (1) After dispersing the dry powder of the phase change polymer of the present invention (particle size D50 is 500 μm) into an aqueous solution of sodium chloride with a sodium chloride concentration of 10000 mg / L, the phase change polymer will be dispersed in the aqueous solution of sodium chloride in the form of gel particles to form a dispersion with a phase change polymer concentration of 2500 mg / L.

[0047] (2) Dispense the dispersion into 10-20 ampoules, connect a vacuum device, evacuate for 2 hours, and then flame seal; take out one ampoule, and first use the flat plate mode of the Anton Paar MCR301 rheometer with a spacing of 0.2 mm to test the initial elastic modulus of the dispersion at room temperature; filter the phase change polymer dispersion through an 80-mesh filter to remove particles, and use the coaxial cylinder mode of the rheometer to test the initial viscosity of the filtrate at 75°C;

[0048] (3) Place the remaining ampoules in a 75°C oven. After 2 hours, take out one ampoule and test the elastic modulus of the dispersion and the viscosity of the filtrate using the same method as in step (2).

[0049] (4) Take out one ampoule at regular intervals and observe whether the dispersion still contains insoluble particles until the dispersion is a transparent liquid. When the dispersion is a transparent liquid, use the same method as in step (2) to test the elastic modulus of the transparent liquid and the viscosity of the filtrate with an Anton Paar MCR301 rheometer. When the difference between the two viscosities is no more than 5 mPa·s, it is defined as the phase change polymer has been completely dissolved and completely converted.

[0050] In step (4) of this invention, the time interval for taking out the ampoule is flexibly determined according to the situation of insoluble particles in the dispersion. If the content of insoluble particles is large, the time interval can be appropriately extended. For example, one ampoule is taken out for observation every 10-20 hours. If the content of insoluble particles is small, the time interval can be appropriately shortened. For example, one ampoule is taken out for observation every 3-5 hours.

[0051] In this invention, a phase-change polymer is dispersed in an aqueous sodium chloride solution to form a dispersion containing phase-change polymer gel particles. Over time, the gel particle dispersion gradually transforms into a continuous solution phase. The specific transformation process is as follows: Figures 1-3 As shown, Figure 1 The present invention is a gel particle dispersion phase formed by dispersing the phase change polymer in an aqueous sodium chloride solution; Figure 2 yes Figure 1 The intermediate phase formed during the transformation of the gel particle dispersion phase into the continuous solution phase; Figure 3 yes Figure 1 The solution is a continuous phase formed after the gel particle dispersion phase is completely dissolved. Therefore, the initial state of the dispersion in this invention is a dispersion containing a phase-change polymer gel particle dispersion phase. Over time, the gel particle dispersion phase gradually transforms into a continuous phase, and the completely dissolved transparent liquid is a homogeneous solution.

[0052] The phase change polymer of this invention is dispersed in an aqueous sodium chloride solution to form a dispersion containing a phase change polymer gel particle dispersion phase. The initial elastic modulus of the dispersion is not less than 15 Pa, and the viscosity of the transparent liquid (i.e., homogeneous solution) after complete dissolution is not less than 100 mPa·s, with a complete dissolution time of not less than 24 hours. Under reservoir conditions, the transformation from the gel particle dispersion phase to the continuous solution phase can be achieved. The gel particle dispersion phase strongly protects the polymer polymer against degradation and acts as a deformable particle displacement agent in the near-wellbore zone, ultimately achieving slow-release viscosity enhancement in the deep reservoir, thus achieving a dual-effect and highly efficient oil displacement. Therefore, the phase change polymer of this invention has a certain sealing strength near the wellbore and viscosity-enhancing and oil displacement performance in the far well.

[0053] According to some embodiments of the present invention, the molar ratio of the hydrolyzable crosslinkable structural unit C to the structural unit A is not greater than 0.1:100, for example, 0.1:100, 0.09:100, 0.08:100, 0.07:100, 0.06:100, 0.05:100, 0.04:100, 0.03:100, 0.02:100, 0.01:100, and any value within the range of any two sets of values, preferably 0.01-0.08:100, more preferably 0.02-0.05:100.

[0054] According to a preferred embodiment of the present invention, the molar ratio of structural unit A to structural unit B and the hydrolyzable crosslinkable structural unit C is 100:5-40:0.01-0.08, for example, 100:5:0.01, 100:10:0.02, 100:15:0.03, 100:20:0.04, 100:25:0.05, 100:30:0.06, 100:35:0.07. The values ​​are 100:40:0.08, 100:40:0.01, 100:35:0.02, 100:30:0.03, 100:25:0.04, 100:20:0.05, 100:15:0.06, 100:10:0.07, 100:5:0.08, and any value within the range of any two sets of values, preferably 100:10-25:0.02-0.05.

[0055] According to some embodiments of the present invention, the molar ratio of anhydride bonds to ester bonds in the hydrolyzable crosslinkable structural unit C is 0.2-2:1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, and any value within the range of any two values, preferably 0.5-1.5:1.

[0056] According to some embodiments of the present invention, the anhydride bonds in the hydrolyzable crosslinkable structural unit C are derived from anhydride compounds containing two or more carbon-carbon double bonds, preferably from acrylic anhydride and / or methacrylic anhydride.

[0057] According to some embodiments of the present invention, the ester bonds in the hydrolyzable crosslinkable structural unit C are derived from acrylate compounds containing three or more carbon-carbon double bonds; preferably from one or more of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, and tripentaerythritol octaacrylate.

[0058] The hydrolyzable crosslinkable structural unit C of the present invention contains anhydride bonds and ester bonds, resulting in a high degree of polymerization and numerous crosslinking points. This allows for control of the thickening properties of the polymer solution system after phase change and the strength of the phase-changeable polymer particles before phase change. The two work together to control the phase change time and phase change properties of the polymer.

[0059] According to some embodiments of the present invention, the phase change polymer further comprises a structural unit D, the structural unit D being selected from at least one of the structures shown in formula (3), formula (4), and formula (5);

[0060]

[0061] Among them, R7, R8, R9, R 10 R 11 R 12 R 13 R 14 R 15 R 16 R 17 and R 18 Each is independently hydrogen or a C1-C10 straight-chain or branched alkyl group;

[0062] X1 is a C1-C10 straight-chain or branched alkylene group;

[0063] M1 and M2 are each independently hydrogen or an alkali metal.

[0064] In this invention, examples of the C1-C10 straight-chain or branched alkyl groups can be, for example, any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, n-hexyl, isohexyl, n-heptyl, isoheptyl, 2-methylhexyl, 2-ethylhexyl, 1-methylheptyl, 2-methylheptyl, n-octyl, isooctyl, n-nonyl, isononyl, and 3,5,5-trimethylhexyl.

[0065] In this invention, examples of the C1-C10 straight-chain or branched alkylene groups may be, for example, any one of methylene, 1,2-ethylene, n-propylene, isopropylene, n-butylene, isobutylene, n-pentylene, isopentylene, n-hexylene, isohexylene, n-heptylene, isoheptylene, 2-methylhexylene, 2-ethylhexylene, 1-methylheptylene, 2-methylheptylene, n-octylene, isooctylene, and n-nonylene.

[0066] In this invention, R 15 It can be located at any position on the benzene ring in formula (4), that is, it can be located at the ortho or meta position of the sulfonyl group.

[0067] In some implementations, R7, R8, R9, and R in equation (3) 10 and R 11 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl, or ethyl.

[0068] In some embodiments, X in formula (3) is preferably a straight-chain or branched alkylene group of C1-C6, more preferably a straight-chain or branched alkylene group of C1-C3, and even more preferably methylene or 1,2-ethylene.

[0069] In some embodiments, M1 in formula (3) is preferably hydrogen or sodium, more preferably hydrogen.

[0070] In a particularly preferred embodiment of the present invention, R7, R8, and R9 in formula (3) are all hydrogen, and R 10 and R 11 All are methyl groups, X is methylene, and M1 is hydrogen. In this case, the monomer with the structure shown in formula (3) is 2-acrylamido-2-methylpropanesulfonic acid (AMPS) monomer.

[0071] In some implementations, R in equation (4) 12 R 13 R 14 and R 15 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6, more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl or ethyl.

[0072] In some embodiments, M2 in formula (4) is preferably hydrogen or sodium, more preferably sodium.

[0073] In a particularly preferred embodiment of the invention, R in formula (4) 12 R 13 R 14 and R 15Both are hydrogen, and M2 is sodium. In this case, the monomer with the structure shown in formula (4) is sodium styrene sulfonate monomer.

[0074] In some implementations, R in equation (5) 16 R 17 and R 18 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl, or ethyl.

[0075] In a particularly preferred embodiment of the invention, R in formula (5) 16 R 17 and R 18 Both are hydrogen, and at this time, the monomer with the structure shown in formula (5) is an N-vinyl-2-pyrrolidone monomer.

[0076] According to some embodiments of the present invention, the molar ratio of the structural unit A to the structural unit D is 100:0-10, for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, and any value within the range of any two values, preferably 100:3-8.

[0077] According to some embodiments of the present invention, the phase transition temperature of the phase change polymer is 55-85°C, preferably 60-80°C.

[0078] The phase change polymer of the present invention can transform from a gel particle dispersed phase to a continuous solution phase in a sodium chloride aqueous solution at a certain temperature, which is 55-85°C, preferably 60-80°C. The possible reason for this phase transformation is that at this temperature, the cross-linking bonds of the network structure in the phase change polymer break, changing from a bulk structure to a linear structure.

[0079] According to some embodiments of the present invention, the viscosity-average molecular weight of the phase change polymer is 25 million to 35 million, preferably 30 million to 35 million.

[0080] Unless otherwise specified, the unit of viscosity-average molecular weight in this invention is g / mol.

[0081] Viscosity-average molecular weight: The intrinsic viscosity of the polymer measured by an Ubbelohde viscometer, and then calculated using the following formula:

[0082]

[0083] In the formula, M η [η] is the viscosity-average molecular weight, g / mol; [η] is the intrinsic viscosity, mL / g.

[0084] According to some embodiments of the present invention, the content of the network structure of the phase change polymer is 30-80 wt%, preferably 30-60 wt%.

[0085] This invention characterizes the chemical crosslinking network structure of phase change polymers using the content of network structure components. The method for testing the content of network structure components is as follows:

[0086] 1.1 Accurately weigh 0.5 g ± 0.0001 g of the phase change polymer sample, denoted as m. 10 .

[0087] 1.2 Accurately weigh the beaker and record the mass as m. 11 Weigh a certain amount of standard prepared salt water into a 1000mL beaker, turn on the constant speed stirrer and slowly add the sample along the vortex wall for 30s at (300±20)r / min, and then stir at (300±20)r / min for 15min~30min until the particles are evenly dispersed.

[0088] 1.3 Add water to the beaker to a total of 1000 mL.

[0089] 1.4 To prevent dissolved air foam from carrying particles, gently stir with a glass rod every 10 minutes, repeating 3 times.

[0090] 1.5 Change the water after approximately 2 hours of sedimentation. During the pouring of the solution, constantly monitor the interface between the network structure and the aqueous solution.

[0091] 1.6 Repeat steps 1.4 and 1.5 three times.

[0092] 1.7 Take the precipitate below the interface and wash it with anhydrous ethanol to obtain a white insoluble substance. Repeat the washing with anhydrous ethanol twice, let it stand for a while, transfer the insoluble substance to a beaker, and place it in a constant temperature drying oven to dry to constant weight at 110°C.

[0093] 1.8 Remove the beaker containing the insoluble matter, place it in a desiccator, cool for 30 minutes, and weigh it to an accuracy of 0.0001 g, recording it as m. 12 .

[0094] 1.9 The content N of network structure is calculated using the following formula:

[0095]

[0096] In the formula:

[0097] N—Network structure content, %;

[0098] m 12 —This represents the mass of the sample after washing and settling, in grams;

[0099] m11 —Beaker mass, g;

[0100] m 10 —Initial sample mass, g.

[0101] A second aspect of the present invention provides a method for preparing a phase change polymer, the method comprising the following steps:

[0102] Under phase inversion controlled conditions, in the presence of an initiator and a phase inversion control agent, acrylamide monomers and acrylic monomers are subjected to solution polymerization in water to obtain a phase change polymer.

[0103] The phase inversion control agent includes anhydride compounds containing two or more carbon-carbon double bonds and acrylate compounds containing three or more carbon-carbon double bonds.

[0104] The phase inversion control agent of the present invention comprises both anhydride compounds containing two or more carbon-carbon double bonds and acrylate compounds containing three or more carbon-carbon double bonds. The anhydride compounds have similar activity to acrylamide monomers and can increase the degree of polymerization in the polymerization reaction, thereby controlling the thickening properties of the polymer solution system after phase inversion. The acrylate compounds have multiple crosslinking points, thereby controlling the strength of the phase-changeable polymer gel particles before phase inversion. The two work together to control the phase inversion time and phase inversion properties of the polymer.

[0105] The preparation method of the present invention forms a hydrolyzable cross-linked structure by adding a phase inversion control agent, which temporarily "binds" the water-soluble polymer together. Under certain conditions, it can realize the transformation from the dispersed phase of gel particles to the continuous phase of solution. During this process, the thickening polymer is gradually hydrolyzed and released, which has the effect of slow-release thickening.

[0106] The initiator used in this invention is a free radical initiator, which is selected from one or more of organic peroxide initiators, azo initiators, and redox initiators.

[0107] Preferably, the organic peroxide initiator is selected from one or more of benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0108] Preferably, the azo initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisobutyramidoline hydrochloride.

[0109] Preferably, the redox initiator is selected from one or more of the following groups: ammonium persulfate and sodium bisulfite, potassium persulfate and sodium bisulfite, hydrogen peroxide and tartaric acid, hydrogen peroxide and sodium formaldehyde sulfoxylate, ammonium persulfate and ferrous sulfate, hydrogen peroxide and ferrous sulfate, and benzoyl peroxide and N,N-diethylaniline.

[0110] According to some embodiments of the present invention, the molar ratio of the anhydride compound to the acrylate compound is 2-6:1, for example, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, and any value within the range of any two values, preferably 3-5:1.

[0111] According to some embodiments of the present invention, the acid anhydride compound is selected from acrylic anhydride and / or methacrylic anhydride.

[0112] According to some embodiments of the present invention, the acrylate compound is selected from one or more of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, and tripentaerythritol octaacrylate.

[0113] According to some embodiments of the present invention, the amount of the phase inversion control agent added is not greater than 0.1 mol% of the acrylamide monomer, for example, 0.09 mol%, 0.08 mol%, 0.07 mol%, 0.06 mol%, 0.05 mol%, 0.04 mol%, 0.03 mol%, 0.02 mol%, 0.01 mol%, and any value within the range of any two sets of values, preferably 0.01-0.08 mol%, more preferably 0.02-0.05 mol%.

[0114] According to a preferred embodiment of the present invention, the molar ratio of the acrylamide monomer, the acrylic monomer, and the phase inversion control agent is 100:5-40:0.01-0.08, for example, 100:5:0.01, 100:10:0.02, 100:15:0.03, 100:20:0.04, 100:25:0.05, 100:30:0.06, 100:35:0.07, 1 The values ​​are 00:40:0.08, 100:40:0.01, 100:35:0.02, 100:30:0.03, 100:25:0.04, 100:20:0.05, 100:15:0.06, 100:10:0.07, 100:5:0.08, and any value within the range of any two sets of values, preferably 100:10-25:0.02-0.05.

[0115] According to this invention, the main function of the phase inversion control agent is to transform the linear molecular chains of the polymer into a three-dimensional network structure through crosslinking points. At the aforementioned molar ratio, the resulting phase-change polymer exhibits better sustained-release thickening effect. If too much phase inversion control agent is added, the number of crosslinking points increases, and at reservoir temperatures, the crosslinking bonds are not easily broken, preventing the network structure from completely transforming into a linear structure for thickening. If too little phase inversion control agent is added, there are too few crosslinking points, making it impossible to form a complete network structure, resulting in rapid thickening of the polymer in the initial dispersion stage, failing to achieve the purpose of slow release underground.

[0116] According to some embodiments of the present invention, the acrylamide monomer is selected from at least one of the monomers with the structure shown in formula (I);

[0117]

[0118] R1, R2 and R3 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups.

[0119] In some embodiments, R1, R2 and R3 in formula (I) are each preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl or ethyl.

[0120] In a particularly preferred embodiment of the present invention, R1, R2 and R3 in formula (I) are all hydrogen, and the monomer with the structure shown in formula (I) is an acrylamide monomer.

[0121] In some embodiments, the acrylic monomer is selected from at least one of the monomers with the structure shown in formula (II);

[0122]

[0123] R4, R5 and R6 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups.

[0124] In some embodiments, R4, R5 and R6 in formula (II) are each preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl or ethyl.

[0125] In a particularly preferred embodiment of the present invention, R4, R5 and R6 in formula (II) are all hydrogen, and in this case, the monomer of the structure shown in formula (II) is an acrylic acid monomer.

[0126] In some embodiments, the monomers of the solution polymerization reaction further include temperature- and salt-resistant monomers, which are selected from at least one of the monomers with the structure shown in formula (III), the monomers with the structure shown in formula (IV), and the monomers with the structure shown in formula (V).

[0127]

[0128] Among them, R7, R8, R9, R 10 R 11 R 12 R 13 R 14 R 15 R 16 R 17 and R 18 Each is independently hydrogen or a C1-C10 straight-chain or branched alkyl group;

[0129] X1 is a C1-C10 straight-chain or branched alkylene group;

[0130] M1 and M2 are each independently hydrogen or an alkali metal.

[0131] In this invention, the examples of straight-chain or branched alkyl groups of C1-C10 and the examples of straight-chain or branched alkylene groups of C1-C10 are the same as in the first aspect, as detailed in the description of the first aspect, and will not be repeated here.

[0132] In this invention, R 15 It can be located at any position on the benzene ring in formula (IV), that is, it can be located at the ortho or meta position of the sulfonyl group.

[0133] In some implementations, R7, R8, R9, and R in formula (III) 10 and R 11 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl, or ethyl.

[0134] In some embodiments, X in formula (III) is preferably a straight-chain or branched alkylene group of C1-C6, more preferably a straight-chain or branched alkylene group of C1-C3, and even more preferably methylene or 1,2-ethylene.

[0135] In some embodiments, M1 in formula (III) is preferably hydrogen or sodium, more preferably hydrogen.

[0136] In a particularly preferred embodiment of the present invention, R7, R8, and R9 in formula (III) are all hydrogen, R 10 and R 11All are methyl groups, X is methylene, and M1 is hydrogen. In this case, the monomer with the structure shown in formula (III) is 2-acrylamido-2-methylpropanesulfonic acid (AMPS) monomer.

[0137] In some implementations, R in formula (IV) 12 R 13 R 14 and R 15 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6, more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl or ethyl.

[0138] In some embodiments, M2 in formula (IV) is preferably hydrogen or sodium, more preferably sodium.

[0139] In a particularly preferred embodiment of the invention, R in formula (IV) 12 R 13 R 14 and R 15 Both are hydrogen, and M2 is sodium. In this case, the monomer with the structure shown in formula (IV) is sodium styrene sulfonate.

[0140] In some implementations, R in equation (V) 16 R 17 and R 18 Each of the components is preferably hydrogen or a straight-chain or branched alkyl group of C1-C6; more preferably hydrogen or a straight-chain or branched alkyl group of C1-C4; and even more preferably hydrogen, methyl, or ethyl.

[0141] In a particularly preferred embodiment of the invention, R in formula (V) 16 R 17 and R 18 All are hydrogen, and in this case, the monomer with the structure shown in formula (V) is an N-vinyl-2-pyrrolidone monomer.

[0142] In some embodiments, the molar ratio of the acrylamide monomer to the temperature- and salt-resistant monomer is 100:0-10, for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, and any value within any range of any two values, preferably 100:3-8.

[0143] According to some embodiments of the present invention, the solution polymerization conditions include: adjusting the pH value to 6-9 under inert gas protection, reacting at 2-10°C for at least 2 hours, preferably reacting at 3-9°C for 3-10 hours.

[0144] In this invention, an alkaline substance is added to adjust the pH value. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium bicarbonate (baking soda), or lithium hydroxide (LiOH) is added to adjust the pH value to 6-9.

[0145] According to a particularly preferred embodiment of the present invention, the method for preparing a phase change polymer specifically includes the following steps:

[0146] Acrylamide monomer, acrylic acid monomer, phase inversion control agent, and optional temperature- and salt-resistant monomer are dissolved in an appropriate amount of water. The phase inversion control agent is selected from a compound system of acid anhydride and acrylate compounds. The pH is adjusted to 6-9, and inert gas or nitrogen is introduced into the water for at least 20 minutes to obtain a mixture. Under low temperature conditions, a free radical initiator is rapidly added to the obtained mixture, and inert gas or nitrogen is introduced for at least 5 minutes. The mixture is sealed, and after reacting for at least 2 hours, a phase change polymer block is obtained. The obtained phase change polymer block is taken out and crushed using a pulverizer to obtain polymer granules. After drying, the granules are granulated to obtain a phase change polymer dry powder.

[0147] The present invention also provides a phase change polymer prepared by the preparation method described in the second aspect above.

[0148] The third aspect of the present invention provides the application of the phase change polymer described in the first aspect or the phase change polymer prepared by the preparation method described in the second aspect in oil displacement.

[0149] The phase change polymer of the present invention can transform from a gel particle dispersed phase to a continuous solution phase at a specific temperature. The reason for the phase change is that at a specific temperature, the cross-linking bonds in the network structure will break, transforming from a bulk structure into a linear structure.

[0150] The method of this invention yields a phase change polymer with a three-dimensional network structure, which can release and transform into a linear polymer at a certain temperature to achieve thickening, while also exhibiting good temperature resistance and strong crosslinking ability. The phase change polymer of this invention can be used alone as a polymer flooding agent, or it can be compounded with surfactants for use in polymer flooding agents.

[0151] A fourth aspect of the present invention provides a polymer flooding agent, the polymer flooding agent comprising a base liquid and a phase change polymer; wherein the phase change polymer is the phase change polymer described in the first aspect above or the phase change polymer prepared by the preparation method described in the second aspect above; the phase change polymer is dispersed in the base liquid in the form of gel particles and hydrolyzed under reservoir conditions to form a homogeneous solution.

[0152] According to the present invention, the phase change polymer is initially dispersed in the base liquid in the form of gel particles, that is, the initial stage of the polymer flooding agent is a gel particle dispersion. Preferably, the dry powder of the phase change polymer is dispersed in the base liquid in situ before injection to form a dispersion containing the phase change polymer gel particle dispersion phase. During the injection of the polymer flooding agent into the formation, it is gradually hydrolyzed under reservoir conditions. The flooding agent gradually transforms from the gel particle dispersion phase to the continuous solution phase, and is slowly released and thickened in the deep reservoir, eventually forming a homogeneous solution.

[0153] According to the present invention, the base liquid refers to water injected into the mine or a homogeneous solution containing oil displacement additives.

[0154] According to some embodiments of the present invention, the content of the phase change polymer in the polymer displacement agent is 0.15-0.3 wt%.

[0155] According to the present invention, reservoir conditions mainly refer to reservoir temperature, which is 55-85℃, preferably 60-80℃.

[0156] This invention employs a controllable weak crosslinking technique to temporarily "bind" water-soluble polymers together. Initially, the polymer is a gel particle dispersion. After injection into the formation, the "bound" water-soluble polymer is gradually hydrolyzed and released under reservoir conditions. This water-soluble polymer is also a viscosity-enhancing polymer, which can slowly release gradient viscosity enhancement in the deep reservoir. Simultaneously, the gel particle dispersion phase gradually transforms into a continuous solution phase, thereby achieving phase transformation. The rate of phase transformation is controlled by adjusting the degree of unsaturated grafting modification of the amide groups in the viscosity-enhancing polymer, thus achieving controllable phase transformation. This results in gel-induced flow line adjustment in the near-wellbore section, and solution viscosity enhancement in the far-wellbore section to expand the swept volume and achieve efficient oil displacement.

[0157] This invention allows for the acquisition of phase change polymers with different release times by controlling different degrees of crosslinking, thereby enabling the selection of phase change polymers with appropriate release times based on different oil reservoirs.

[0158] The present invention will be described in detail below through preparation examples and embodiments, but the scope of protection of the present invention is not limited to the following description.

[0159] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0160] Example 1

[0161] A method for preparing a phase change polymer, comprising the following steps:

[0162] (1) Dissolve acrylamide monomer, acrylic acid monomer, 2-acrylamido-2-methylpropanesulfonic acid monomer and phase inversion control agent in an appropriate amount of water, add NaOH to adjust the pH to 7, and purge the water with nitrogen for 30 minutes to obtain a mixed solution; wherein, the molar ratio of acrylamide monomer, acrylic acid monomer and 2-acrylamido-2-methylpropanesulfonic acid monomer is 100:25:5, the phase inversion control agent is acrylic anhydride, tripentaerythritol octaacrylate and trimethylolpropane trimethacrylate (the molar ratio of the three is 6:1:1), and the molar ratio of acrylamide monomer to phase inversion control agent is 100:0.05;

[0163] (2) Under low temperature conditions, the mixture obtained in step (1) is rapidly added to azobisisobutyronitrile, nitrogen is continuously introduced for 10 minutes, the container is sealed, and the solution polymerization reaction is carried out at 10°C for 5 hours to obtain a phase change polymer block.

[0164] (3) Take out the phase change polymer block obtained in step (2), crush the block with a pulverizer to obtain polymer granules, dry and granulate to obtain phase change polymer dry powder.

[0165] The infrared spectrum of the phase change polymer obtained in Example 1 is as follows: Figure 4 As shown, from Figure 4 As can be seen, at a wavenumber of 3424 cm⁻¹ -1 1684cm -1 1454cm -1 and 1314cm -1 The characteristic absorption peak corresponding to the amide group is located at a wavenumber of 1548 cm⁻¹. -1 1399cm -1 The characteristic absorption peak corresponding to the carboxylic acid group is 1179 cm⁻¹. -1 The characteristic absorption peak at this location is for sulfonic acid groups; therefore, the phase change polymer prepared in this example contains amide groups, carboxylic acid groups, and sulfonate groups. The wavenumber is 1848 cm⁻¹. -1 The position is the antisymmetric peak of the acid anhydride C=O, 1037 cm⁻¹. -1 The CO stretching peak of acid anhydrides is 1775 cm⁻¹. -1 This is the C=O stretching peak of the ester, at 1179 cm⁻¹. -1 The CO stretching peak of the ester indicates that the phase inversion control agent has been successfully introduced into the polymer.

[0166] Thermogravimetric curves were plotted based on the aforementioned method for testing thermogravimetric characteristic peaks. The thermogravimetric curve of the phase change polymer obtained in Example 1 is shown below. Figure 5 As shown, from Figure 5The thermogravimetric curves show that the phase change polymer prepared in Example 1 has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 18.8% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0167] The content of the network structure of the phase change polymer prepared in Example 1 was 56.0 wt% obtained by washing and sedimentation.

[0168] The viscosity-average molecular weight of the phase change polymer prepared in Example 1 is 34.8 million.

[0169] Example 2

[0170] A method for preparing a phase change polymer, comprising the following steps:

[0171] (1) Dissolve acrylamide monomer, acrylic acid monomer, sodium styrene sulfonate monomer and phase inversion control agent in an appropriate amount of water, add KOH to adjust the pH to 8, and purge the water with nitrogen for 40 minutes to obtain a mixed solution; wherein, the molar ratio of acrylamide monomer, acrylic acid monomer and sodium styrene sulfonate monomer is 100:20:5, the phase inversion control agent is acrylic anhydride, tripentaerythritol octaacrylate and ethoxylated trimethylolpropane triacrylate (the molar ratio of the three is 6:1:1), and the molar ratio of acrylamide monomer to phase inversion control agent is 100:0.03;

[0172] (2) Under low temperature conditions, benzoyl peroxide is rapidly added to the mixture obtained in step (1), nitrogen gas is continuously introduced for 8 minutes, the container is sealed, and solution polymerization reaction is carried out at 5°C for 3 hours to obtain a phase change polymer block.

[0173] (3) Take out the phase change polymer block obtained in step (2), crush the block with a pulverizer to obtain polymer granules, dry and granulate to obtain phase change polymer dry powder.

[0174] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 17.4% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0175] The content of the network structure of the phase change polymer prepared in this example was 52.8 wt% obtained by washing and sedimentation.

[0176] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 34.2 million.

[0177] Example 3

[0178] A method for preparing a phase change polymer, comprising the following steps:

[0179] (1) Dissolve acrylamide monomer, acrylic acid monomer, N-vinyl-2-pyrrolidone monomer and phase inversion control agent in an appropriate amount of water, add LiOH to adjust the pH to 9, and purge the water with nitrogen for 20 minutes to obtain a mixed solution; wherein, the molar ratio of acrylamide monomer, acrylic acid monomer and N-vinyl-2-pyrrolidone monomer is 100:15:3, the phase inversion control agent is acrylic anhydride and ethoxylated trimethylolpropane triacrylate (the molar ratio of the two is 4:1), and the molar ratio of acrylamide monomer to phase inversion control agent is 100:0.02;

[0180] (2) Under low temperature conditions, ammonium persulfate and sodium bisulfite are rapidly added to the mixture obtained in step (1), nitrogen gas is continuously introduced for 5 minutes, the container is sealed, and solution polymerization reaction is carried out at 2°C for 2 hours to obtain phase change polymer blocks.

[0181] (3) Take out the phase change polymer block obtained in step (2), crush the block with a pulverizer to obtain polymer granules, dry and granulate to obtain phase change polymer dry powder.

[0182] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.6% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0183] The content of the network structure of the phase change polymer prepared in this example was 37.2 wt% obtained by washing and sedimentation.

[0184] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 32.8 million.

[0185] Example 4

[0186] The phase change polymer was prepared according to the method of Example 1, except that in step (1), the phase inversion control agent was methacrylic anhydride, tripentaerythritol octaacrylate and trimethylolpropane trimethacrylate (the molar ratio of the three was 6:1:1), and the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.05; the remaining steps were the same as in Example 1.

[0187] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integrated area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 18.2% of the integrated area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0188] The content of the network structure of the phase change polymer prepared in this example was 55.2 wt% obtained by washing and sedimentation.

[0189] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 33.4 million.

[0190] Example 5

[0191] The phase change polymer was prepared according to the method of Example 2, except that in step (1), the phase inversion control agent was acrylic anhydride, tripentaerythritol octaacrylate and ethoxylated trimethylolpropane triacrylate (the molar ratio of the three was 6:1:1), and the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.04; the remaining steps were the same as in Example 2.

[0192] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integrated area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 17.9% of the integrated area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0193] The content of the network structure of the phase change polymer prepared in this example was 53.6 wt% obtained by washing and sedimentation.

[0194] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 34.6 million.

[0195] Example 6

[0196] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and trimethylolpropane trimethacrylate (molar ratio of the two was 4:1); the remaining steps were the same as in Example 3.

[0197] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 14.3% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0198] The content of the network structure of the phase change polymer prepared in this example was 42.1 wt% obtained by washing and sedimentation.

[0199] The phase change polymer prepared in this embodiment has a viscosity-average molecular weight of 33 million.

[0200] Example 7

[0201] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and tripentaerythritol octaacrylate (molar ratio of the two was 4:1); the remaining steps were the same as in Example 3.

[0202] Thermogravimetric curves were plotted based on the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 15.2% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0203] The content of the network structure of the phase change polymer prepared in this example was 45.1 wt% obtained by washing and sedimentation.

[0204] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 33.5 million.

[0205] Example 8

[0206] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was methacrylic anhydride and ethoxylated trimethylolpropane trimethacrylate (molar ratio of the two was 4:1); the remaining steps were the same as in Example 3.

[0207] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.9% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0208] The content of the network structure of the phase change polymer prepared in this example was 38.6 wt% obtained by washing and sedimentation.

[0209] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 32.2 million.

[0210] Example 9

[0211] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (the molar ratio of the two was 5:1); the remaining steps were the same as in Example 3.

[0212] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.3% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0213] The content of the network structure of the phase change polymer prepared in this example was 36.3 wt% obtained by washing and sedimentation.

[0214] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 33.2 million.

[0215] Example 10

[0216] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (the molar ratio of the two was 3:1); the remaining steps were the same as in Example 3.

[0217] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.8% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0218] The content of the network structure of the phase change polymer prepared in this example was 39.2 wt% obtained by washing and sedimentation.

[0219] The phase change polymer prepared in this embodiment has a viscosity-average molecular weight of 32 million.

[0220] Example 11

[0221] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (the molar ratio of the two was 2:1); the remaining steps were the same as in Example 3.

[0222] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 14.0% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0223] The content of the network structure of the phase change polymer prepared in this example was 41.8 wt% obtained by washing and sedimentation.

[0224] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 31.3 million.

[0225] Example 12

[0226] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (the molar ratio of the two was 6:1); the remaining steps were the same as in Example 3.

[0227] Thermogravimetric curves were plotted based on the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.0% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0228] The content of the network structure of the phase change polymer prepared in this example was 33.5 wt% obtained by washing and sedimentation.

[0229] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 32.7 million.

[0230] Example 13

[0231] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.04; the remaining steps were the same as in Example 3.

[0232] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integrated area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 15.5% of the integrated area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0233] The content of the network structure of the phase change polymer prepared in this example was 45.3 wt% obtained by washing and sedimentation.

[0234] The phase change polymer prepared in this embodiment has a viscosity-average molecular weight of 34 million.

[0235] Example 14

[0236] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (molar ratio of the two was 6:1), and the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.05; the remaining steps were the same as in Example 3.

[0237] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 16.2% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0238] The content of the network structure of the phase change polymer prepared in this example was 47.8 wt% obtained by washing and sedimentation.

[0239] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 34.5 million.

[0240] Example 15

[0241] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the phase inversion control agent was acrylic anhydride and ethoxylated trimethylolpropane triacrylate (molar ratio of the two was 6:1), and the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.08; the remaining steps were the same as in Example 3.

[0242] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 16.8% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0243] The content of the network structure of the phase change polymer prepared in this example was 51.5 wt% obtained by washing and sedimentation.

[0244] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 30.6 million.

[0245] Example 16

[0246] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the molar ratio of acrylamide monomer, acrylic acid monomer and N-vinyl-2-pyrrolidone monomer was 100:5:10; the remaining steps were the same as in Example 3.

[0247] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.8% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0248] The content of the network structure of the phase change polymer prepared in this example was 37.8 wt% obtained by washing and sedimentation.

[0249] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 28.9 million.

[0250] Example 17

[0251] The phase change polymer was prepared according to the method of Example 3, except that in step (1), the molar ratio of acrylamide monomer, acrylic acid monomer and N-vinyl-2-pyrrolidone monomer was 100:40:2; the remaining steps were the same as in Example 3.

[0252] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 12.2% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0253] The content of the network structure of the phase change polymer prepared in this example was 35.6 wt% obtained by washing and sedimentation.

[0254] The phase change polymer prepared in this embodiment has a viscosity-average molecular weight of 27.5 million.

[0255] Example 18

[0256] The polymer was prepared according to the method of Example 3, except that in step (1), the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.1; the remaining steps were the same as in Example 1.

[0257] Thermogravimetric curves were plotted according to the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the phase change polymer prepared in this embodiment has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks between 550-650℃ accounts for 19.6% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0258] The content of the network structure of the phase change polymer prepared in this example was 58.3 wt% obtained by washing and sedimentation.

[0259] The viscosity-average molecular weight of the phase change polymer prepared in this embodiment is 26.3 million.

[0260] Comparative Example 1

[0261] The polymer was prepared according to the method of Example 3, except that no phase inversion control agent was added in step (1). That is, in step (1): acrylamide monomer, acrylic acid monomer and N-vinyl-2-pyrrolidone monomer were dissolved in an appropriate amount of water, the pH was adjusted to 9, and nitrogen gas was introduced into the water for 20 minutes to obtain a mixture; the remaining steps were the same as in Example 3.

[0262] The thermogravimetric curve of the polymer obtained in the comparative example is as follows: Figure 6 As shown, from Figure 6 As can be seen, the polymer obtained in this comparative example does not exhibit obvious thermogravimetric characteristic peaks between 550-650℃.

[0263] Comparative Example 2

[0264] The phase change polymer was prepared according to the method of Example 3, except that in step (1), only acrylic anhydride was added as a phase inversion control agent, wherein the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.02; the remaining steps were the same as in Example 3.

[0265] The thermogravimetric curve of the polymer obtained in the comparative example is as follows: Figure 7 As shown, from Figure 7 As can be seen, the polymer obtained in this comparative example does not have obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks accounts for 6.5% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0266] Comparative Example 3

[0267] The phase change polymer was prepared according to the method of Example 3, except that in step (1), only ethoxylated trimethylolpropane triacrylate was added as a phase inversion control agent, wherein the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.02; the remaining steps were the same as in Example 3.

[0268] Thermogravimetric curves were plotted based on the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the polymer prepared in this comparative example has obvious thermogravimetric characteristic peaks between 550-650℃, and the integrated area of ​​the thermogravimetric characteristic peaks accounts for 21.6% of the integrated area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0269] Comparative Example 4

[0270] The phase change polymer was prepared according to the method of Example 1, except that in step (1), only tripentaerythritol octaacrylate and trimethylolpropane trimethacrylate were added as phase inversion control agents, wherein the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.05; the remaining steps were the same as in Example 1.

[0271] Thermogravimetric curves were plotted based on the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the polymer prepared in this comparative example has obvious thermogravimetric characteristic peaks between 550-650℃, and the integral area of ​​the thermogravimetric characteristic peaks accounts for 25.6% of the integral area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0272] Comparative Example 5

[0273] The phase change polymer was prepared according to the method of Example 2, except that in step (1), only tripentaerythritol octaacrylate and ethoxylated trimethylolpropane triacrylate were added as phase inversion control; wherein, the molar ratio of acrylamide monomer to phase inversion control agent was 100:0.03; the remaining steps were the same as in Example 2.

[0274] Thermogravimetric curves were plotted based on the aforementioned test method for thermogravimetric characteristic peaks. It can be seen from the thermogravimetric curves that the polymer prepared in this comparative example has obvious thermogravimetric characteristic peaks between 550-650℃, and the integrated area of ​​the thermogravimetric characteristic peaks accounts for 23.2% of the integrated area of ​​the thermogravimetric characteristic peaks between 25-800℃.

[0275] Comparative Example 6

[0276] Dongying Baomo Environmental Engineering Co., Ltd. produces oil displacement polyacrylamide (II) (standard Q / SHCG0159—2021).

[0277] The thermogravimetric curve of polyacrylamide (II) is as follows: Figure 8 As shown, from Figure 8 As can be seen, polyacrylamide (II) does not have obvious thermal weight loss characteristic peaks between 550-650℃.

[0278] Test case

[0279] 2500 mg of the phase change polymer powder obtained in Examples 1-18 and the polymer powder obtained in Comparative Examples 1-6 were accurately weighed and dissolved in 1 L of sodium chloride solution (sodium chloride concentration of 10000 mg / L). The mixture was stirred thoroughly for 2 h. The initial elastic modulus was tested at 25 °C using a flat rotor (PP50) of a rheometer (MCR301, Anton Paar), and the initial aqueous phase viscosity was tested at 75 °C using a coaxial cylindrical rotor (CC27) of the rheometer. If the polymer was not completely dissolved, it was dispensed into multiple ampoules, vacuum-sealed, flame-sealed, and placed in a 75 °C oven. The ampoules were taken out at regular intervals to observe whether the particles had dissolved. One ampoule was taken out for each sample, and its elastic modulus and aqueous phase viscosity were tested. The time when the particles disappeared was the time of complete dissolution. The corresponding data and results are shown in Table 1.

[0280] Table 1. Polymer phase change properties

[0281]

[0282]

[0283] As shown in Table 1, the phase change polymers prepared in Examples 1-18 have high initial elastic modulus and can transform from a discontinuous gel particle dispersion phase to a continuous solution phase within 1-15 days. After transformation, they exhibit high viscosity, thus achieving strong plugging near the wellbore and strong oil displacement far from the wellbore. Comparative Examples 1 and 6 polymers dissolve quickly and do not possess formation phase change capability. Comparative Examples 2-5 polymers exhibit certain phase change performance, but with only anhydride-based phase change control agents added, their initial elastic modulus is low, resulting in weak plugging strength. Conversely, with only ester-based phase change control agents added, they exhibit high elastic modulus, and their viscosity after release is relatively lower than that of the examples. Therefore, both anhydride-based and acrylate-based phase change control agents must be present simultaneously.

[0284] Through Table 1 and Figure 5-8 It can be seen that the phase change polymers obtained in the embodiments of the present invention have obvious thermal weight loss characteristic peaks and a complete dissolution time of 1-15 days, while polymers without thermal weight loss characteristic peaks have a complete dissolution time of less than 15 hours.

[0285] Figure 9 and Figure 10 The figures show the viscosity and elastic modulus of the phase change polymers prepared in Examples 1-3 of this invention as a function of time. As can be seen from the figures, the viscosity gradually increases with time, while the elastic modulus gradually decreases with time. Different viscosity release times can be adjusted as needed.

[0286] Application examples

[0287] The phase change polymer powders obtained in Examples 1-3 and the polymer powders obtained in Comparative Examples 1, 2, 3, and 6 were dispersed in 1000 mL of sodium chloride solution (sodium chloride concentration 10000 mg / L) to form a dispersion with a polymer concentration of 2500 mg / L. The dispersion was stirred for 2 hours, and then sheared for 30 seconds using a Wu Yin stirrer. For polymers that were not completely dissolved before shearing, they were deoxygenated after shearing and placed in an oven to allow complete release. The viscosity of the polymer that was completely released without shearing was compared to that of the polymer to obtain the polymer shear viscosity retention rate. The results are as follows: Figure 11 As shown. (Through) Figure 11 The results show that, in Examples 1-3 of this invention, the polymers initially formed as gel particles exhibited good shear resistance and high viscosity retention rates after release, all exceeding 80%. In contrast, Comparative Examples 1 and 6, after dispersion, completely dissolved into linear polymers, whose molecular chains were easily sheared, resulting in poor shear resistance and shear viscosity retention rates of around 50%. Although Comparative Examples 2 and 3 possessed certain shear resistance, Comparative Example 2 used only acrylic anhydride as a phase inversion control agent, resulting in weak crosslinking strength and lower shear resistance than Example 3. Comparative Example 3 used only acrylate as a phase inversion control agent, resulting in high crosslinking strength and strong shear resistance, but this affected the molecular weight of the synthesized polymer, thus affecting its viscosity.

[0288] The phase change polymer (PCP) powders obtained in Examples 1-18 and Comparative Examples 1-6 were used as polymer flooding agents in a dual-tube oil displacement process for a long core (1m). The polymer concentration was 2500 mg / L. At 75°C, water flooding was first performed at an injection rate of 0.5 mL / min until the produced fluid water cut was greater than 98%. Then, a 0.6 PV polymer slug was injected, followed by water flooding until the produced fluid water cut reached 100%, at which point the experiment was terminated. It should be noted that because the PCP takes a long time to completely dissolve, if the polymer is directly water flooded after injection, the PCP may not completely dissolve and be released, potentially resulting in an unsatisfactory oil displacement effect. Therefore, after the polymer slug was injected, both ends of the core were sealed until the polymer was completely dissolved before subsequent water flooding. The corresponding data and results are shown in Table 2.

[0289] Table 2 Comparison of Dual-Pipe Oil Displacement Effects

[0290]

[0291]

[0292] In Table 2, enhanced oil recovery refers to the increased oil recovery rate based on water drive.

[0293] As can be seen from the results in Table 2, the phase change polymer of the present invention has better plugging properties and the ability to adjust the split flow rate compared with the polymer of the comparative example, thus achieving a higher recovery rate.

[0294] As can be seen from the above, the phase change polymer of this invention has strong shear resistance and excellent ability to adjust the profile of near-well high-permeability layers. Under reservoir conditions, it can realize the transformation from the dispersed phase of gel particles to the continuous phase of solution, and finally achieve slow-release viscosity enhancement in the deep reservoir, realizing oil displacement in distant wells, achieving the purpose of dual effect of one agent and high-efficiency oil displacement, greatly improving the utilization rate of polymer and oil displacement efficiency, and improving crude oil recovery rate.

[0295] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A phase change polymer, characterized in that, The phase change polymer contains structural unit A, structural unit B and hydrolyzable crosslinkable structural unit C. Structural unit A has the structure shown in formula (1), structural unit B has the structure shown in formula (2), and hydrolyzable crosslinkable structural unit C contains anhydride bonds and ester bonds. In this context, R1, R2, R3, R4, R5, and R6 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups; M is an alkali metal. The phase change polymer exhibits a distinct thermogravimetric characteristic peak between 550-650℃.

2. The phase change polymer according to claim 1, wherein, The integral area of ​​the thermogravimetric characteristic peak of the phase change polymer between 550-650℃ accounts for 10-20% of the integral area of ​​the thermogravimetric characteristic peak between 25-800℃. And / or, the phase change polymer is dispersed in an aqueous sodium chloride solution with a sodium chloride concentration of 10000 mg / L to form a dispersion with a phase change polymer gel particle concentration of 2500 mg / L; at 75°C, the initial elastic modulus of the dispersion is not less than 15 Pa; the viscosity of the dispersion after standing for 2 hours is not greater than 20 mPa·s, and the elastic modulus is not less than 10 Pa; the viscosity of the homogeneous solution formed after the dispersion is completely dissolved is not less than 100 mPa·s, and the elastic modulus is not greater than 1 Pa; the time for the dispersion to completely dissolve is not less than 24 hours.

3. The phase change polymer according to claim 1 or 2, wherein, The molar ratio of the hydrolyzable crosslinkable structural unit C to the structural unit A is not greater than 0.1:

100.

4. The phase change polymer according to any one of claims 1-3, wherein, The molar ratio of structural unit A to structural unit B and the hydrolyzable crosslinkable structural unit C is 100:5-40:0.01-0.08, preferably 100:10-25:0.02-0.

05.

5. The phase change polymer according to any one of claims 1-4, wherein, The molar ratio of anhydride bonds to ester bonds in the hydrolyzable crosslinkable structural unit C is 0.2-2:

1.

6. The phase change polymer according to any one of claims 1-5, wherein, The anhydride bonds in the hydrolyzable crosslinkable structural unit C are derived from anhydride compounds containing two or more carbon-carbon double bonds, preferably from acrylic anhydride and / or methacrylic anhydride.

7. The phase change polymer according to any one of claims 1-6, wherein, The ester bonds in the hydrolyzable crosslinkable structural unit C are derived from acrylate compounds containing three or more carbon-carbon double bonds; preferably from one or more of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, and tripentaerythritol octaacrylate.

8. The phase change polymer according to any one of claims 1-7, wherein, The phase change polymer further contains a structural unit D, which is selected from at least one of the structures shown in formula (3), formula (4), and formula (5). Among them, R7, R8, R9, R 10 R 11 R 12 R 13 R 14 R 15 R 16 R 17 and R 18 Each is independently hydrogen or a C1-C10 straight-chain or branched alkyl group; X1 is a C1-C10 straight-chain or branched alkylene group; M1 and M2 are each independently hydrogen or alkali metal; Preferably, the molar ratio of structural unit A to structural unit D is 100:0-10, and more preferably 100:3-8.

9. The phase change polymer according to any one of claims 1-8, wherein, The phase transition temperature of the phase change polymer is 55-85℃, preferably 60-80℃.

10. The phase change polymer according to any one of claims 1-9, wherein, The viscosity-average molecular weight of the phase change polymer is 25 million to 35 million, preferably 30 million to 35 million. And / or, the content of the network structure of the phase change polymer is 30-80 wt%, preferably 30-60 wt%.

11. A method for preparing a phase change polymer, characterized in that, The preparation method includes the following steps: Under solution polymerization conditions, in the presence of an initiator and a phase inversion control agent, acrylamide monomers and acrylic monomers are subjected to solution polymerization in water to obtain a phase change polymer. The phase inversion control agent includes anhydride compounds containing two or more carbon-carbon double bonds and acrylate compounds containing three or more carbon-carbon double bonds.

12. The preparation method according to claim 11, wherein, The molar ratio of the acid anhydride compound to the acrylate compound is 2-6:

1.

13. The preparation method according to claim 11 or 12, wherein, The acid anhydride compounds are selected from acrylic anhydride and / or methacrylic anhydride; And / or, the acrylate compound is selected from one or more of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, and tripentaerythritol octaacrylate.

14. The preparation method according to any one of claims 11-13, wherein, The amount of the phase inversion control agent added shall not exceed 0.1 mol% of the acrylamide monomer; Preferably, the molar ratio of the acrylamide monomer, the acrylic monomer and the phase inversion control agent is 100:5-40:0.01-0.08, and more preferably 100:10-25:0.02-0.

05.

15. The preparation method according to any one of claims 11-14, wherein, The acrylamide monomer is selected from at least one of the monomers with the structure shown in formula (I); R1, R2 and R3 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups; And / or, the acrylic monomer is selected from at least one of the monomers with the structure shown in formula (II); R4, R5 and R6 are each independently hydrogen or C1-C10 straight-chain or branched alkyl groups.

16. The preparation method according to any one of claims 11-15, wherein, The monomers used in the solution polymerization reaction also include temperature- and salt-resistant monomers, which are selected from at least one of the monomers with the structure shown in formula (III), the monomers with the structure shown in formula (IV), and the monomers with the structure shown in formula (V). Among them, R7, R8, R9, R 10 R 11 R 12 R 13 R 14 R 15 R 16 R 17 and R 18 Each is independently hydrogen or a C1-C10 straight-chain or branched alkyl group; X1 is a C1-C10 straight-chain or branched alkylene group; M1 and M2 are each independently hydrogen or alkali metals; Preferably, the molar ratio of the acrylamide monomer to the temperature- and salt-resistant monomer is 100:0-10, and more preferably 100:3-8.

17. The preparation method according to any one of claims 11-16, wherein, The solution polymerization conditions include: adjusting the pH to 6-9 under inert gas protection and reacting at 2-10°C for at least 2 hours.

18. The use of the phase change polymer according to any one of claims 1-10 or the phase change polymer prepared by the preparation method according to any one of claims 11-17 in oil displacement.

19. A polymer-based oil displacement agent, characterized in that, The polymer flooding agent comprises a base liquid and a phase change polymer, wherein the phase change polymer is the phase change polymer according to any one of claims 1-10 or the phase change polymer prepared by the preparation method according to any one of claims 11-17; the phase change polymer is dispersed in the base liquid in the form of gel particles and hydrolyzed under reservoir conditions to form a homogeneous solution.

20. The polymer oil displacement agent according to claim 19, wherein, In the polymer displacement agent, the content of the phase change polymer is 0.15-0.3 wt%.

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