Hydrophilic crosslinked polymers and methods of making and using the same

Abstract

The application relates to the field of oil field chemistry and discloses a hydrophilic crosslinked polymer and a preparation method and application thereof. The hydrophilic crosslinked polymer comprises structural unit A, structural unit B, structural unit C and structural unit D; the structural unit A has the structure shown in formula (1), the structural unit B has the structure shown in formula (2), the structural unit C has the structure shown in formula (3), and the structural unit D has the structure shown in formula (4); the hydrophilic crosslinked polymer microspheres have suitable particle sizes, can be expanded under the condition of temperature rise, and have low apparent viscosity under the premise of not affecting the expansion degree, heat resistance stability and particle size and the like; after the hydrophilic crosslinked polymer microspheres are added into a drilling fluid and an oil displacement system, the filtration loss of the drilling fluid can be reduced, the influence on the system viscosity is low, different shape formation fissures can be adapted to realize the plugging and strengthening effect on the formation.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemistry, specifically to a hydrophilic crosslinked polymer and its preparation method, and the application of the hydrophilic crosslinked polymer as a wellbore reinforcement material. Background Technology

[0002] Common methods for preparing polymer microspheres include suspension polymerization, emulsion polymerization, solution polymerization pulverization, and dispersion polymerization. Suspension polymerization produces products with a particle size range of 0.1-1 mm and a relatively wide particle size distribution. Emulsion polymerization can prepare nanoscale microspheres, but the emulsifiers in the product are difficult to remove completely, resulting in higher production costs. Solution polymerization pulverization uses free radical solution polymerization to obtain polymers, which are then dried, pulverized, and sieved to obtain granular polymers. This process is cumbersome, and the resulting products have large particle sizes and uneven distribution. Dispersion polymerization, depending on the type of dispersion medium, includes two main categories: aqueous dispersion polymerization and non-aqueous dispersion polymerization. Aqueous dispersion polymerization uses aqueous solutions as the dispersion medium and can obtain granular materials. It has advantages such as low energy consumption, environmental friendliness, and small product particle size, and has been widely used in recent years to prepare linear hydrophilic polymers.

[0003] CN108929404A discloses a method for preparing hydrophilic acrylamide-based crosslinked polymer microspheres, comprising the following steps: 1) adding methacryloyloxyethyltrimethylammonium chloride to distilled water, then adding 2,2-azo(2-methylpropylamidine) dihydrochloride and stirring until homogeneous, followed by nitrogen gas and water bath heating reaction; 2) removing the above reaction product, washing it three times with ethanol, then diluting it with acetone, and finally drying and pulverizing it in an oven; 3) adding ammonium sulfate to distilled water and stirring to dissolve it, obtaining an ammonium sulfate solution; 4) sequentially adding acrylamide, DMC, acrylic acid, 2,2-azo(2-methylpropylamidine) dihydrochloride, co-crosslinking agent, and dispersant to the ammonium sulfate solution in step 3) and dissolving them; 5) purging the above solution into a nitrogen gas water bath and heating reaction to obtain hydrophilic acrylamide-based crosslinked polymer microspheres. However, the above-mentioned hydrophilic acrylamide-based crosslinked polymer microspheres have a large particle size and high viscosity effect, making them unable to adapt to formation fractures of different shapes to achieve formation sealing and strengthening effects. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem in existing technologies where the large average particle size and high viscosity of hydrophilic cross-linked polymers prevent them from adapting to formation fractures of different shapes and achieving formation sealing and strengthening effects. This invention provides a hydrophilic cross-linked polymer, its preparation method, and its applications. The hydrophilic cross-linked polymer microspheres have a suitable particle size, can expand under heating conditions, and possess low apparent viscosity without affecting the degree of expansion, thermal stability, or particle size. When added to drilling fluids and oil displacement systems, it can reduce drilling fluid filtration loss and has minimal impact on system viscosity, enabling it to adapt to formation fractures of different shapes and achieve formation sealing and strengthening effects.

[0005] To achieve the above objectives, the first aspect of the present invention provides a hydrophilic crosslinked polymer, characterized in that the crosslinked polymer comprises structural unit A, structural unit B, structural unit C and structural unit D;

[0006] The structural unit A has the structure shown in equation (1), the structural unit B has the structure shown in equation (2), the structural unit C has the structure shown in equation (3), and the structural unit D has the structure shown in equation (4).

[0007]

[0008]

[0009] Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is C1-C2; m is an integer from 1 to 3.

[0010] A second aspect of the present invention provides a method for preparing a hydrophilic crosslinked polymer, characterized in that the method comprises the following steps:

[0011] S1. Prepare a polyethylene glycol aqueous solution;

[0012] S2. In the presence of an inert atmosphere, an initiator, a co-initiator, a crosslinking agent, and an optional hydrolysate, monomers A, B, C, and D are added to the polyethylene glycol aqueous solution to carry out a polymerization reaction, thereby obtaining the hydrophilic crosslinked polymer.

[0013] The monomer A has the structure shown in formula (6), the monomer B has the structure shown in formula (7), the monomer C has the structure shown in formula (8), and the monomer D has the structure shown in formula (9).

[0014]

[0015]

[0016] Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is C1-C2; m is an integer from 1 to 3.

[0017] A third aspect of the present invention provides a hydrophilic crosslinked polymer prepared by the above-described preparation method.

[0018] The fourth aspect of this invention provides the application of the above-mentioned hydrophilic crosslinked polymer as a wellbore reinforcing material.

[0019] Through the above technical solutions, the hydrophilic crosslinked polymer, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0020] The hydrophilic crosslinked polymer of the present invention contains structural unit D. The introduction of structural unit D can cooperate with structural units A, B and C to further reduce the apparent viscosity of the hydrophilic crosslinked polymer and its viscosity effect when added to the drilling fluid system, while ensuring the thermal expansion performance and suitable particle size of the hydrophilic crosslinked polymer.

[0021] Furthermore, the hydrophilic cross-linked polymer of the present invention has a suitable average particle size. Preferably, the average particle size of the hydrophilic cross-linked polymer is 1-100 μm. It is temperature sensitive, and the average particle size of the polymer microspheres will expand tens of times when the temperature is increased. It can expand and gain deformability under heating conditions, and can enter and adapt to formation fractures of different shapes to achieve the sealing and strengthening effect on the formation. It can be used in formation profile control and water shut-off and drilling fluids. In oil production profile control and water shut-off, it can expand at formation temperature, thereby increasing the sealing strength. After being added to drilling fluid, it has no significant effect on the viscosity of the drilling fluid system. It can achieve sealing and strengthening of formation fractures or broken zones during drilling circulation and reduce drilling fluid leakage.

[0022] Furthermore, in the preparation method of the hydrophilic crosslinked polymer described in this invention, polyethylene glycol aqueous solution is used as the polymerization reaction medium, which facilitates the dissipation of polymerization heat. This method is particularly advantageous for preparing hydrophilic crosslinked polymer microspheres with suitable average particle size, capable of expansion under heating conditions, and low apparent viscosity. At the same time, the synthesis process is environmentally friendly. Attached Figure Description

[0023] Figure 1 This is a diagram showing the reverse bearing test results of the core after treatment with polymer microspheres prepared in Example 2 of this invention;

[0024] Figure 2 These are comparative photographs showing the well wall spalling situation of the polymer microspheres prepared in Example 2 of this invention before (A) and after (B);

[0025] Figure 3 Here are scanning electron microscope images of the polymer microspheres prepared in Example 2 of this invention;

[0026] Figure 4 This is a schematic diagram showing the particle size change of the polymer microspheres prepared in Example 2 of the present invention during heating and cooling.

[0027] Figure 5 The thermogravimetric analysis (TGA) curves of the polymer microspheres prepared in Example 2 of this invention are shown. Detailed Implementation

[0028] 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.

[0029] The first aspect of the present invention provides a hydrophilic crosslinked polymer, characterized in that the crosslinked polymer comprises structural unit A, structural unit B, structural unit C and structural unit D;

[0030] The structural unit A has the structure shown in equation (1), the structural unit B has the structure shown in equation (3), the structural unit C has the structure shown in equation (4), and the structural unit D has the structure shown in equation (5).

[0031]

[0032] Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is C1-C2; m is an integer from 1 to 3.

[0033] In this invention, the hydrophilic crosslinked polymer contains structural unit D. The introduction of structural unit D can cooperate with structural units A, B and C, and the microspheres formed by polymerization and crosslinking have better hydrophilicity. Under the premise of ensuring that the particle size and thermal expansion of the hydrophilic crosslinked polymer microspheres are not reduced, the apparent viscosity of the hydrophilic crosslinked polymer microspheres and their effect on the viscosity of drilling fluid are further reduced.

[0034] Furthermore, the hydrophilic cross-linked polymer microspheres provided by this invention have a flexible molecular weight and are temperature-sensitive, allowing them to expand and deform under heating conditions. They can enter and adapt to formation fractures of different shapes to achieve a sealing and strengthening effect on the formation. They can be used in formation profile control and water shut-off as well as in drilling fluids. In oil production profile control and water shut-off, they can expand at formation temperature, thereby increasing the sealing strength. When added to drilling fluid, they have no significant effect on the viscosity of the drilling fluid system. They can achieve sealing and strengthening of formation fractures or broken zones during drilling circulation, reducing drilling fluid leakage.

[0035] According to the present invention, in order to further improve the hydrophilicity of the hydrophilic crosslinked polymer, preferably, the structural unit A of the hydrophilic polymer further comprises the structural unit of the structure shown in formula (5):

[0036]

[0037] Where M is H, K or Na, preferably H, and R1 is as defined above.

[0038] In this invention, the structural unit of the structure shown in formula (5) is obtained by hydrolysis of the structural unit of a partial structure shown in formula (1).

[0039] In this invention, the content of the structural units of the structure shown in formula (5) is determined by infrared, chromatography, nuclear magnetic resonance and X-ray photoelectron spectroscopy methods.

[0040] In this invention, the hydrolysis reaction and the polymerization reaction are carried out simultaneously.

[0041] According to the present invention, the degree of hydrolysis of the hydrophilic crosslinked polymer is 0.1%-10%, preferably 0.1%-5%.

[0042] In this invention, the degree of hydrolysis is measured using the national standard GB / T 12005.6-1989.

[0043] According to the present invention, R1 and R2 are H, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 2; R4 and R5 are each independently methyl; R6 is benzyl or propenyl; R7 is H or methyl; R8 is H or CH3; R9 is H; R 10 and R 11 Each can be methyl or ethyl independently.

[0044] According to the present invention, based on the total weight of the hydrophilic crosslinked polymer, the content of structural unit A is 42-75 wt%, the content of structural unit B is 10-25 wt%, the content of structural unit C is 10-25 wt%, and the content of structural unit D is 2-10 wt%.

[0045] In this invention, when the content of each structural unit in the hydrophilic crosslinked polymer meets the above-mentioned limitations, the obtained hydrophilic crosslinked polymer is a microsphere with a small average particle size and controllable particle size.

[0046] In this invention, the content of each structural unit in the polymer is measured using infrared, chromatography, nuclear magnetic resonance and X-ray photoelectron spectroscopy instruments.

[0047] Furthermore, based on the total weight of the hydrophilic crosslinked polymer, the content of structural unit A is 50-70 wt%, the content of structural unit B is 15-25 wt%, the content of structural unit C is 15-25 wt%, and the content of structural unit D is 3-9 wt%.

[0048] In this invention, based on the total weight of the hydrophilic crosslinked polymer, the content of the structural unit in structural unit A, which has the structure shown in formula (5), is 0.25-7 wt%, preferably 0.25-3.5 wt%.

[0049] According to the present invention, the degree of crosslinking of the hydrophilic crosslinked polymer is 20%-80%, preferably 25%-75%.

[0050] In this invention, the degree of crosslinking of hydrophilic crosslinked polymers is tested using the equilibrium swelling method.

[0051] According to the present invention, the hydrophilic crosslinking polymer is a random copolymer.

[0052] In this invention, nuclear magnetic resonance (NMR) was used to test the hydrophilic crosslinked polymer, which showed that the hydrophilic crosslinked polymer was a random copolymer.

[0053] According to the present invention, the hydrophilic crosslinked polymer has an expansion factor of 5-45, preferably 10-35, relative to the initial particle size, at 80°C in the presence of water.

[0054] In this invention, the initial particle size refers to the particle size of the hydrophilic crosslinked copolymer at room temperature (20-30°C).

[0055] In this invention, the expansion ratio refers to the ratio of the particle size of the hydrophilic cross-linked polymer after it has fully absorbed water at 80°C to the initial particle size (the particle size before absorbing water). The particle size of the hydrophilic cross-linked polymer is measured using a laser particle size analyzer such as the Malvern Mastersizer 2000.

[0056] In this invention, the swelling process of the hydrophilic crosslinked polymer is a water absorption and swelling process.

[0057] According to the present invention, the apparent viscosity of the hydrophilic crosslinked polymer at 25°C is 5-25 mPa·s, preferably 10-35 mPa·s.

[0058] In this invention, a rotational viscometer is used to test the apparent viscosity of the hydrophilic crosslinked polymer.

[0059] According to the present invention, the particle size of the hydrophilic crosslinked polymer is 0.5-150 μm, preferably 2-80 μm.

[0060] In this invention, a laser particle size analyzer is used to test the average particle size of the hydrophilic cross-linked polymer microspheres.

[0061] A second aspect of the present invention provides a method for preparing a hydrophilic crosslinked polymer, characterized in that the method comprises the following steps:

[0062] S1. Prepare a polyethylene glycol aqueous solution;

[0063] S2. In the presence of an inert atmosphere, an initiator, a co-initiator, a crosslinking agent, and an optional hydrolysate, monomers A, B, C, and D are added to the polyethylene glycol aqueous solution to carry out a polymerization reaction, thereby obtaining the hydrophilic crosslinked polymer.

[0064] The monomer A has the structure shown in formula (6), the monomer B has the structure shown in formula (7), the monomer C has the structure shown in formula (8), and the monomer D has the structure shown in formula (9).

[0065]

[0066]

[0067] Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is C1-C2; m is an integer from 1 to 3.

[0068] In this invention, monomer D is copolymerized with monomers A, B, and C to introduce them into the polymer molecular chain, which further reduces the impact of hydrophilic cross-linked polymer microspheres on the viscosity of drilling fluids and oil displacement systems. Simultaneously, by adjusting the amount of each monomer added to meet the aforementioned range, hydrophilic cross-linked polymer microspheres with small average particle size and suitable particle size can be obtained.

[0069] According to the present invention, R1 and R2 are H, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4 and R5 are each independently methyl; R6 is benzyl or propenyl; R7 is H or methyl; R8 is H or CH3; R9 is H; R 10 and R 11 Each can be methyl or ethyl independently.

[0070] In a preferred embodiment of the present invention, monomer A is acrylamide; monomer B is at least one of dimethyl diallyl ammonium chloride, methacryloyloxyethyl dimethyl benzyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxyethyl dimethyl benzyl ammonium chloride, and acryloyloxyethyl trimethyl ammonium chloride; monomer C is at least one of methacrylic acid, acrylic acid, and butenoic acid; and monomer D is at least one of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

[0071] According to the present invention, in step S1, the mass concentration of the polyethylene glycol aqueous solution is 5-50 wt%, preferably 10-30 wt%.

[0072] According to the present invention, the weight-average molecular weight of the polyethylene glycol is 16,000-24,000, preferably 18,000-22,000.

[0073] According to the present invention, in step S2, relative to the total weight of the polyethylene glycol aqueous solution, the amount of monomer A is 10-30 wt%; the amount of monomer B is 4-15 wt%; the amount of monomer C is 4-15 wt%; and the amount of monomer D is 2-5 wt%.

[0074] More preferably, relative to the total weight of the polyethylene glycol aqueous solution, the amount of monomer A is 10-28 wt%; the amount of monomer B is 5-15 wt%; the amount of monomer C is 5-15 wt%; and the amount of monomer D is 2-4 wt%.

[0075] The amount of the initiator relative to the total weight of the monomers is 0.1-5 wt%, preferably 0.1-4 wt%; the amount of the co-initiator is 0.1-5 wt%, preferably 0.1-4 wt%; the amount of the crosslinking agent is 0.0001-0.4 wt%, preferably 0.001-0.2 wt%; and the amount of the hydrolysate is 0-2 wt%, preferably 0.1-1.5 wt%.

[0076] According to the present invention, the initiator is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0077] According to the present invention, the co-initiator is selected from at least one of sodium bisulfite, ammonium bisulfite, and potassium bisulfite.

[0078] According to the present invention, the crosslinking agent is N,N'-methylenebisacrylamide.

[0079] According to the present invention, the hydrolyzing agent is selected from at least one of NaOH, Na2CO3 and KOH.

[0080] According to the present invention, the polymerization reaction is carried out in the presence of a dispersant.

[0081] According to the present invention, the dispersant is selected from polymethacryloyloxyethyltrimethylammonium chloride and / or sodium chloride.

[0082] In this invention, the polymethacryloyloxyethyltrimethylammonium chloride has a weight-average molecular weight of 100,000 to 300,000, preferably 120,000 to 250,000.

[0083] According to the present invention, the amount of the dispersant is 2-10 wt%, preferably 3-9 wt%, relative to the total weight of the monomers.

[0084] According to the present invention, the conditions for the polymerization reaction include: polymerization temperature of 45-75°C, preferably 45-65°C; polymerization time of 2-8 hours, preferably 3-7 hours.

[0085] In this invention, the inert atmosphere can be a conventional atmosphere in the art that can provide an inert environment, such as nitrogen.

[0086] A third aspect of the present invention provides a hydrophilic crosslinked polymer prepared by the above-described preparation method.

[0087] The fourth aspect of this invention provides the application of the above-mentioned hydrophilic crosslinked polymer as a wellbore reinforcing material.

[0088] The present invention will be described in detail below through embodiments. In the following embodiments,

[0089] The initial particle size of the hydrophilic cross-linked polymer microspheres and the particle size after swelling equilibrium in water at 80°C were tested using a Malvern Mastersizer 2000.

[0090] The degree of crosslinking of hydrophilic crosslinked polymers was tested using the equilibrium swelling method;

[0091] The thermogravimetric analysis (TGA) of the hydrophilic crosslinked polymer was performed using a Mettler Toledo thermogravimetric analyzer.

[0092] The apparent viscosity of the hydrophilic crosslinked polymer was tested using a six-speed rotational viscometer from Qingdao Haitongda Special Instrument Co., Ltd.

[0093] The degree of hydrolysis of the hydrophilic crosslinked polymer was determined according to the national standard GB / T 12005.6-1989.

[0094] The water loss was tested using a ZNS-type mud water loss meter from Qingdao Brothers Petroleum Machinery Factory.

[0095] The sand bed plugging performance was tested using the FA-type non-permeable drilling fluid filtration tester from Qingdao Haitongda Special Instrument Co., Ltd.

[0096] The reverse bearing capacity test was conducted using a multi-functional automatic core displacement device from Jiangsu Huaan Scientific Research Co., Ltd.

[0097] Monomer E has the following structure:

[0098]

[0099] All raw materials used in the examples and comparative examples are commercially available products.

[0100] Example 1

[0101] Step 1: Take 13 parts of polyethylene glycol (weight average molecular weight of 18000) and add it to 55 parts of distilled water. Stir thoroughly to dissolve and obtain a polyethylene glycol solution.

[0102] Step 2: Add 13 parts acrylamide, 5 parts acryloyloxyethyltrimethylammonium chloride, 5 parts methacrylic acid, 2 parts ethyl dimethylaminoacrylate, 0.8 parts initiator, 0.8 parts co-initiator, 1.5 parts dispersant, 0.05 parts crosslinking agent, and 0.5 parts hydrolysant to the polyethylene glycol solution from Step 1 in sequence and dissolve thoroughly. The initiator is 0.8 parts potassium persulfate, the co-initiator is 0.8 parts ammonium bisulfite, the dispersant is 1.5 parts polymethacryloyloxyethyltrimethylammonium chloride (weight average molecular weight of 200,000), the crosslinking agent is 0.05 parts N,N-methylenebisacrylamide, and the hydrolysant is 0.5 parts NaOH.

[0103] Step 3: The solution obtained in Step 2 is heated to 45°C in a water bath and reacted for 7 hours to obtain hydrophilic cross-linked polymer microspheres.

[0104] Tests showed that, based on the total weight of the polymer, the content of structural unit A provided by acrylamide was 70 wt%, of which the content of structural unit A of the structure shown in formula (5) was 0.25 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride was 13 wt%, the content of structural unit C provided by acrylic acid was 12 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate was 5 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0105] Example 2

[0106] Step 1: Take 15 parts of polyethylene glycol (weight average molecular weight of 20,000) and add it to 60 parts of distilled water. Stir thoroughly to dissolve and obtain a polyethylene glycol solution.

[0107] Step 2: Add 14 parts of acrylamide, 5.5 parts of methacryloyloxyethyltrimethylammonium chloride, 5.5 parts of acrylic acid, 2.5 parts of dimethylaminoethyl methacrylate, 1 part of initiator, 1 part of co-initiator, 2 parts of dispersant, 0.01 parts of crosslinking agent, and 0.5 parts of hydrolysate to the polyethylene glycol solution from Step 1 and dissolve them thoroughly. The initiator is 1 part of ammonium persulfate, the co-initiator is 1 part of sodium bisulfite, the dispersant is 2 parts of polymethacryloyloxyethyltrimethylammonium chloride (weight average molecular weight of 150,000), the crosslinking agent is 0.001 parts of N,N-methylenebisacrylamide, and the hydrolysate is Na2CO3.

[0108] Step 3: The solution obtained in Step 2 is heated to 50°C in a water bath and reacted for 6 hours to obtain hydrophilic cross-linked polymer microspheres.

[0109] Based on the total weight of the polymer, the content of structural unit A provided by acrylamide is 55 wt%, of which the content of structural unit A of the structure shown in formula (5) is 1.1 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride is 21 wt%, the content of structural unit C provided by acrylic acid is 21 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate is 3 wt%.

[0110] The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0111] Scanning electron microscope image of the polymer microspheres as follows Figure 3 As shown, by Figure 3 It can be seen that the prepared product consists of spherical particles with a relatively uniform particle size distribution; the schematic diagram of the particle size change of the polymer microspheres during heating and cooling is shown below. Figure 4 As shown, by Figure 4 It can be seen that the particle diameter of the hydrophilic cross-linked polymer microspheres changes repeatedly under heating and cooling conditions; the thermogravimetric analysis (TGA) curve of the polymer microspheres is shown below. Figure 5 As shown, Figure 5 The results show that before 100℃, a small amount of adsorbed water evaporates, with a weight loss rate of 4.11 wt%. When the temperature is raised to 262.5℃, the polymer begins to show significant weight loss, indicating that small molecules begin to be released from the polymer. The weight loss rate reaches its maximum at around 349.9℃. After the temperature rises to 409.1℃, the mass no longer changes significantly. This demonstrates that the polymer microspheres provided by this invention have excellent thermal stability, and their structure is not significantly damaged at a high temperature of 260℃.

[0112] Example 3

[0113] Step 1: Take 17 parts of polyethylene glycol (weight average molecular weight of 22000) and add it to 65 parts of distilled water. Stir thoroughly to dissolve and obtain a polyethylene glycol solution.

[0114] Step 2: In sequence, add 15 parts acrylamide, 6 parts methacryloyloxyethyl dimethyl benzyl ammonium chloride, 6 parts butenoic acid, 3 parts diethylaminoethyl methacrylate, 1.2 parts initiator, 1.2 parts co-initiator, 2.5 parts dispersant, 0.2 parts crosslinking agent, and 0.8 parts hydrolysant to the polyethylene glycol solution from Step 1 and dissolve them thoroughly. The initiator is 1.2 parts sodium persulfate, the co-initiator is 1.2 parts potassium bisulfite, the dispersant is 2.5 parts polymethacryloyloxyethyl trimethyl ammonium chloride (weight average molecular weight 280,000), the crosslinking agent is 0.2 parts N,N-methylenebisacrylamide, and the hydrolysant is 0.8 parts KOH.

[0115] Step 3: The solution obtained in Step 2 is heated to 60°C in a water bath and reacted for 4 hours to obtain hydrophilic cross-linked polymer microspheres.

[0116] Based on the total weight of the polymer, the content of structural unit A provided by acrylamide is 60 wt%, of which the content of structural unit A of the structure shown in formula (2) is 3.4 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride is 18 wt%, the content of structural unit C provided by acrylic acid is 18 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate is 4 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0117] Example 4

[0118] Step 1: Take 17 parts of polyethylene glycol (weight average molecular weight of 20,000) and add it to 65 parts of distilled water. Stir thoroughly to dissolve and obtain a polyethylene glycol solution.

[0119] Step 2: In sequence, add 15 parts acrylamide, 6 parts dimethyl diallyl ammonium chloride, 6 parts butenoic acid, 3 parts diethylaminoethyl methacrylate, 1.2 parts initiator, 1.2 parts co-initiator, 2.5 parts dispersant, 0.01 parts crosslinking agent, and 1.4 parts hydrolysant to the polyethylene glycol solution from Step 1 and dissolve them thoroughly. The initiator is 1.2 parts sodium persulfate, the co-initiator is 1.2 parts potassium bisulfite, the dispersant is 2.5 parts polymethacryloyloxyethyltrimethylammonium chloride (weight average molecular weight of 120,000), the crosslinking agent is 0.01 parts N,N-methylenebisacrylamide, and the hydrolysant is 1.4 parts NaOH.

[0120] Step 3: The solution obtained in Step 2 was heated to 65°C in a water bath for 3 hours to obtain hydrophilic crosslinked polymer microspheres. Based on the total weight of the polymer, the content of structural unit A provided by acrylamide was 50 wt%, of which the content of structural unit A of the structure shown in formula (2) was 2.5 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride was 21 wt%, the content of structural unit C provided by acrylic acid was 20 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate was 9 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0121] Example 5

[0122] Step 1: Take 17 parts of polyethylene glycol (weight average molecular weight of 20,000) and add it to 65 parts of distilled water. Stir thoroughly to dissolve and obtain a polyethylene glycol solution.

[0123] Step 2: In sequence, add 15 parts acrylamide, 6 parts acryloyloxyethyl dimethyl benzyl ammonium chloride, 6 parts butenoic acid, 3 parts dimethylaminoethyl methacrylate, 1.2 parts initiator, 1.2 parts co-initiator, 2.5 parts dispersant, 0.002 parts crosslinking agent, and 1.2 parts hydrolysant to the polyethylene glycol solution from Step 1 and dissolve them thoroughly. The initiator is 1.2 parts sodium persulfate, the co-initiator is 1.2 parts potassium bisulfite, the dispersant is 2.5 parts polymethacryloyloxyethyl trimethyl ammonium chloride (weight average molecular weight 240,000), the crosslinking agent is 0.002 parts N,N-methylenebisacrylamide, and the hydrolysant is 1.2 parts KOH.

[0124] Step 3: The solution obtained in Step 2 was heated to 60°C in a water bath for 5 hours to obtain hydrophilic crosslinked polymer microspheres. Based on the total weight of the polymer, the content of structural unit A provided by acrylamide was 65 wt%, of which the content of structural unit A of the structure shown in formula (2) was 0.8 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride was 14 wt%, the content of structural unit C provided by acrylic acid was 14 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate was 7 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0125] Example 6

[0126] Hydrophilic crosslinked polymer microspheres were prepared according to the method of Example 1, except that azodihydrochloride was used as the initiator instead of ammonium persulfate and sodium bisulfite. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0127] Example 7

[0128] Hydrophilic crosslinked polymer microspheres were prepared according to the method of Example 1, except that the amount of each monomer was different from that in Example 1. Specifically, the amount of acrylamide was 11 parts, the amount of acryloyloxyethyltrimethylammonium chloride was 5 parts, the amount of methacrylic acid was 5 parts, and the amount of dimethylaminoacrylate was 5 parts.

[0129] Tests showed that, based on the total weight of the polymer, the content of structural unit A provided by acrylamide was 72 wt%, of which the content of structural unit A of the structure shown in formula (5) was 3.8 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride was 9 wt%, the content of structural unit C provided by acrylic acid was 9 wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate was 10 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0130] Example 8

[0131] Hydrophilic crosslinked polymer microspheres were prepared according to the method of Example 1, except that the amount of each monomer was different from that in Example 1. Specifically, the amount of acrylamide was 20 parts, the amount of acryloyloxyethyltrimethylammonium chloride was 3 parts, the amount of methacrylic acid was 3 parts, and the amount of dimethylaminoacrylate was 0.5 parts.

[0132] According to the test, the content of structural unit A provided by acrylamide is 81wt% based on the total weight of the polymer, of which the content of structural unit A of the structure shown in formula (5) is 2.5wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride is 9wt%, the content of structural unit C provided by acrylic acid is 8.5wt%, and the content of structural unit D provided by dimethylaminoethyl methacrylate is 1.5wt%.

[0133] The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0134] Comparative Example 1

[0135] Hydrophilic acrylamide-based crosslinked polymer microspheres were prepared according to CN108929404A. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0136] Comparative Example 2

[0137] Hydrophilic cross-linked polymer microspheres were prepared according to the method of Example 1, except that they did not contain dimethylaminoethyl acrylate.

[0138] Based on the total weight of the polymer, the content of structural unit A provided by acrylamide was 72 wt%, of which the content of structural unit A of the structure shown in formula (5) was 0.6 wt%, the content of structural unit B provided by methacryloyloxyethyltrimethylammonium chloride was 14 wt%, and the content of structural unit C provided by acrylic acid was 14 wt%. The particle size, weight-average molecular weight, apparent viscosity, degree of crosslinking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0139] Comparative Example 3

[0140] Hydrophilic cross-linked polymer microspheres were prepared according to the method of Example 1, except that monomer E was used instead of monomer D. The particle size, weight-average molecular weight, apparent viscosity, degree of cross-linking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0141] Comparative Example 4

[0142] Hydrophilic cross-linked polymer microspheres were prepared according to the method of Example 1, except that an aqueous solution of ammonium sulfate was used instead of an aqueous solution of polyethylene glycol. The particle size, weight-average molecular weight, apparent viscosity, degree of cross-linking, and degree of hydrolysis of the polymer microspheres are shown in Table 1.

[0143] Table 1. Results of polymer microsphere particle size testing

[0144]

[0145] As shown in Table 1, the hydrophilic cross-linked polymer microspheres prepared by the method of this invention can expand at 80°C in the presence of water, and the particle size after expansion is at least 7.5 times that before expansion, while the apparent viscosity is significantly reduced. When these hydrophilic cross-linked polymer microspheres are added to water-based drilling fluid, they expand and increase in volume under heating conditions. During the drilling fluid circulation process, under the pressure of the fluid column, they enter and adapt to formation fractures of different shapes, achieving the functions of sealing, bridging, and strengthening the formation, transforming the formation from a fractured, low-strength state into a unified structure.

[0146] Test Example 1

[0147] The hydrophilic cross-linked polymer microspheres were added to a density of 1.93 g / cm³ according to the dosages shown in Table 3. 3 The effect of hydrophilic cross-linked polymer microspheres on the plugging performance of a high-density drilling fluid (water-based drilling fluid system: 2 wt% bentonite slurry + 3 wt% sulfomethylphenol resin + 1 wt% bitumen + barite and water) was tested. The test results are shown in Table 2. Figure 1 As shown.

[0148] Table 2. Effects of polymer microspheres on drilling fluid properties

[0149]

[0150]

[0151] Note: Aging conditions are 120℃ for 16 hours.

[0152] As shown in Table 2, the hydrophilic cross-linked polymer microspheres of this invention can be used as a carrier in drilling fluid without significantly affecting its performance. As shown in Table 2, when the polymer microspheres are added at concentrations of 20 g / L and 30 g / L, they exhibit a certain reduction in filtration loss in the drilling fluid, but no significant thickening effect. The polymer microspheres have a density of 1.93 g / cm³. 3 It has little impact on the performance of the drilling fluid in the field. It has a certain viscosity-reducing effect at low dosages, and the increase in apparent viscosity of drilling fluid is less than 7% when the dosage is 30g / L.

[0153] Test Example 2

[0154] River sand with a particle size of 40-70 mesh was used to prepare the sand bed. After adding river sand to the required height in the pressure pipe, appropriate vibration was performed to ensure that the sand bed had a reasonable degree of compaction. Well slurry with or without polymer microspheres was added to the sand bed. Under a pressure of 1 MPa, the immersion depth of the fluid was recorded at regular intervals. The difference in immersion depth of the drilling fluid was used to characterize the repair and strengthening performance of the polymer microspheres. The results are shown in Table 3.

[0155] Table 3. Blocking and Enhancement Performance of Polymer Microspheres

[0156]

[0157]

[0158] As shown in Table 3, the immersion depth of the drilling fluid was significantly reduced after the addition of polymer microspheres: after 30 minutes of pressurization, the leakage of the drilling fluid containing polymer microspheres decreased from 0.4 cm in the blank drilling fluid to 0.1 cm, indicating that the polymer microspheres have good repair and strengthening effects. The plugging ability of the drilling fluid containing polymer microspheres after hot rolling at 120℃ for 16 hours did not change significantly compared with that at room temperature, indicating that the prepared polymer microspheres have good temperature resistance.

[0159] Test Example 3

[0160] The polymer microsphere product provided in Example 2 was introduced into the core in the forward direction at a flow rate of 2 ml / min. After 4 min, an 8 wt% KCl solution was introduced in the reverse direction at a rate of 5 ml / min. The change in inlet pressure was observed. The magnitude of the inlet pressure reflects the reverse pressure bearing capacity of the core treated with polymer microspheres. The results are shown in […]. Figure 1 .

[0161] Depend on Figure 1 As shown, the reverse pressure of the core treated with polymer microspheres can reach more than 6 MPa, and there is no liquid seepage at the outlet end, which further indicates that the polymer microspheres have a good sealing and strengthening effect.

[0162] Test Example 4

[0163] In a field test at the Jiangsha 211-2HF (1850m) well section, the addition of 2 parts by weight of the polymer microspheres provided in Example 2 significantly reduced wellbore spalling and significantly reduced the size of the spalled pieces. This indicates that the polymer microspheres have a good wellbore repair and strengthening effect. The results are shown in [Figure 1]. Figure 2 (Figure A shows rock cuttings without the hydrophilic cross-linked polymer microspheres of the present invention, and Figure B shows rock cuttings after using the hydrophilic cross-linked polymer microspheres of the present invention). From Figure 2 As can be seen from B, the rock cuttings particle size significantly decreased after the addition of the hydrophilic cross-linked polymer microspheres of the present invention, indicating that the polymer microspheres have a strengthening and repairing effect on the well wall.

[0164] The embodiments of the present invention have been described in detail above with reference to the examples. However, the present invention is not limited to the above embodiments. For those skilled in the art, after learning the contents described in the present invention, several equivalent changes and substitutions can be made without departing from the principle of the present invention. These equivalent changes and substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A hydrophilic crosslinked polymer, characterized in that, The crosslinked polymer comprises structural unit A, structural unit B, structural unit C, and structural unit D; Based on the total weight of the hydrophilic crosslinked polymer, the content of structural unit A is 42-75 wt%, the content of structural unit B is 10-25 wt%, the content of structural unit C is 10-25 wt%, and the content of structural unit D is 2-10 wt%. The degree of crosslinking of the hydrophilic crosslinked polymer is 20%-80%; The degree of hydrolysis of the hydrophilic crosslinked polymer is 0.1%-10%; Structural unit A is provided by monomer A, structural unit B is provided by monomer B, structural unit C is provided by monomer C, and structural unit D is provided by monomer D; The preparation method of the hydrophilic crosslinked polymer includes the following steps: S1. Prepare a polyethylene glycol aqueous solution; S2. In the presence of an inert atmosphere, an initiator, a co-initiator, a crosslinking agent, and a hydrolyzing agent, monomers A, B, C, and D are added to the polyethylene glycol aqueous solution to carry out a polymerization reaction, thereby obtaining the hydrophilic crosslinked polymer. The monomer A has the structure shown in formula (6), the monomer B has the structure shown in formula (7), the monomer C has the structure shown in formula (8), and the monomer D has the structure shown in formula (9). Equation (6); Equation (7); Equation (8); Equation (9); Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is independently C1-C2; m is an integer from 1 to 3; In step S1, the mass concentration of the polyethylene glycol aqueous solution is 10-30 wt%. The weight-average molecular weight of the polyethylene glycol is 16,000-24,000; The hydrolyzing agent is selected from at least one of NaOH, Na2CO3 and KOH; The polymerization reaction is carried out in the presence of a dispersant, which is polymethacryloyloxyethyltrimethylammonium chloride.

2. The hydrophilic crosslinked polymer according to claim 1, wherein, R1 and R2 are H, and R3 is a C1-C2 alkylene group or... n is an integer from 1 to 2; R4 and R5 are each independently methyl; R6 is benzyl or propenyl; R7 is H or methyl; R8 is H or CH3; R9 is H; R 10 and R 11 Each can be methyl or ethyl independently.

3. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, Based on the total weight of the hydrophilic crosslinked polymer, the content of structural unit A is 50-70 wt%, the content of structural unit B is 15-25 wt%, the content of structural unit C is 15-25 wt%, and the content of structural unit D is 3-9 wt%.

4. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, The degree of crosslinking of the hydrophilic crosslinked polymer is 25%-75%.

5. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, The hydrophilic crosslinked polymer is a random copolymer.

6. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, The hydrophilic crosslinked polymer expands by 5-45 relative to its initial particle size in the presence of water at 80°C.

7. The hydrophilic crosslinked polymer according to claim 6, wherein, The hydrophilic crosslinked polymer expands by 10⁻³⁵ relative to its initial particle size in the presence of water at 80°C.

8. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, The apparent viscosity of the hydrophilic crosslinked polymer at 25°C is 5-25 mPa·s.

9. The hydrophilic crosslinked polymer according to claim 8, wherein, The apparent viscosity of the hydrophilic crosslinked polymer at 25°C is 10-20 mPa·s.

10. The hydrophilic crosslinked polymer according to claim 1, wherein, The degree of hydrolysis of the hydrophilic crosslinked polymer is 0.1%-5%.

11. The hydrophilic crosslinked polymer according to claim 1 or 2, wherein, The hydrophilic crosslinked polymer has a particle size of 0.5-150 μm.

12. The hydrophilic crosslinked polymer according to claim 11, wherein, The hydrophilic crosslinked polymer has a particle size of 2-80 μm.

13. A method for preparing the hydrophilic crosslinked polymer according to any one of claims 1-12, characterized in that, The method includes the following steps: S1. Prepare a polyethylene glycol aqueous solution; S2. In the presence of an inert atmosphere, an initiator, a co-initiator, a crosslinking agent, and a hydrolyzing agent, monomers A, B, C, and D are added to the polyethylene glycol aqueous solution to carry out a polymerization reaction, thereby obtaining the hydrophilic crosslinked polymer. The monomer A has the structure shown in formula (6), the monomer B has the structure shown in formula (7), the monomer C has the structure shown in formula (8), and the monomer D has the structure shown in formula (9). Equation (6); Equation (7); Equation (8); Equation (9); Wherein, R1 is H or CH3, R2 is H or CH3, and R3 is a C1-C2 alkylene group or n is an integer from 1 to 3; R4, R5, and R6 are each independently a C1-C7 alkyl, alkenyl, or aryl group; R7 is H or a C1-C2 alkyl group; R8 is H or CH3; R9 is H or CH3; R 10 and R 11 Each is an alkyl group that is independently C1-C2; m is an integer from 1 to 3; In step S1, the mass concentration of the polyethylene glycol aqueous solution is 10-30 wt%. The weight-average molecular weight of the polyethylene glycol is 16,000-24,000; The hydrolyzing agent is selected from at least one of NaOH, Na2CO3 and KOH; The polymerization reaction is carried out in the presence of a dispersant, which is polymethacryloyloxyethyltrimethylammonium chloride.

14. The preparation method according to claim 13, wherein, R1 and R2 are H, and R3 is a C1-C2 methylene group or n is an integer from 1 to 2; R4 and R5 are each independently methyl; R6 is benzyl or propenyl; R7 is H or methyl; R8 is H or CH3; R9 is H; R 10 and R 11 Each can be methyl or ethyl independently.

15. The preparation method according to claim 13 or 14, wherein, In step S1, the mass concentration of the polyethylene glycol aqueous solution is 15-30 wt%. And / or, the weight-average molecular weight of the polyethylene glycol is 18,000-22,000.

16. The preparation method according to claim 13 or 14, wherein, In step S2, relative to the total weight of the polyethylene glycol aqueous solution, the amount of monomer A is 10-30 wt%; the amount of monomer B is 4-15 wt%; the amount of monomer C is 4-15 wt%; and the amount of monomer D is 2-5 wt%.

17. The preparation method according to claim 16, wherein, Relative to the total weight of the polyethylene glycol aqueous solution, the amount of monomer A is 10-28 wt%; the amount of monomer B is 5-15 wt%; the amount of monomer C is 5-15 wt%; and the amount of monomer D is 2-4 wt%. The amount of the initiator relative to the total weight of the monomer is 0.1-5 wt%; the amount of the co-initiator is 0.1-5 wt%; the amount of the crosslinking agent is 0.0001-0.4 wt%; and the amount of the hydrolysant is 0-2 wt%, not 0.

18. The preparation method according to claim 17, wherein, The amount of the initiator relative to the total weight of the monomer is 0.1-4 wt%; the amount of the co-initiator is 0.1-4 wt%; the amount of the crosslinking agent is 0.001-0.2 wt%; and the amount of the hydrolysant is 0.1-1.5 wt%.

19. The preparation method according to claim 13 or 14, wherein, The crosslinking agent is N,N'-methylenebisacrylamide.

20. The preparation method according to claim 19, wherein, The polymethacryloyloxyethyltrimethylammonium chloride has a weight-average molecular weight of 100,000 to 300,000. And / or, the amount of the dispersant is 2-10 wt% relative to the total weight of the monomers.

21. The preparation method according to claim 20, wherein, The weight-average molecular weight of the polymethacryloyloxyethyltrimethylammonium chloride is 120,000-280,000. And / or, the amount of the dispersant is 3-9 wt% relative to the total weight of the monomers.

22. The preparation method according to claim 13 or 14, wherein, The conditions for the polymerization reaction include: polymerization temperature of 45-75℃; polymerization time of 2-8 hours.

23. The preparation method according to claim 22, wherein, The conditions for the polymerization reaction include: polymerization temperature of 45-65℃; polymerization time of 3-7 hours.

24. The use of the hydrophilic crosslinked polymer according to any one of claims 1-12 as a wellbore reinforcement material.

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