Preparation method of high-temperature-resistant and salt-resistant fly ash doped hydrogel

Abstract

The application provides a preparation method of high-temperature-resistant and salt-resistant fly ash doped hydrogel, and belongs to the technical field of oilfield water shutoff agents. The preparation method comprises the following steps: dissolving acrylamide in water to obtain a monomer solution; adding a crosslinking agent and an additive to the monomer solution, wherein the additive comprises carboxymethyl cellulose and fly ash, and stirring and dispersing to form a uniform mixed system; and adding an initiator to the mixed system to obtain a composite gel after reaction. In the mixed system, the mass ratio of carboxymethyl cellulose to fly ash is 1-5%:1-5%. The hydrogel prepared by the method can solve the problem of poor swelling of traditional polyacrylamide gel under the condition of strong alkali, high temperature and high salt.

Description

Technical Field

[0001] This invention belongs to the field of oilfield water shut-off agent technology, and specifically relates to a method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel. Background Technology

[0002] As oilfields enter the mid-to-late stages of development, the problem of high water cut becomes increasingly serious, generating a large amount of produced water each year, leading to increased oil-water separation costs and equipment corrosion. Hydrogels are one of the effective methods to solve the high water cut problem, among which pre-crosslinked hydrogels have attracted widespread attention due to their advantages such as strong controllability and minimal damage to the reservoir. However, traditional polyacrylamide pre-crosslinked hydrogels have poor swelling properties under high temperature and high salinity conditions, making it difficult to meet the requirements of complex reservoir environments.

[0003] In existing technologies, the stability of hydrogels can be improved by introducing natural polymers such as cellulose to form an interpenetrating network structure with polyacrylamide. However, under extreme conditions such as high temperature, high salinity, and strong alkali, the network structure is prone to dissociation due to the combined effects of factors such as intensified chain segment movement, osmotic pressure imbalance, and disruption of hydrogen bonding, leading to a decrease in the swelling performance of the hydrogel. Furthermore, existing research mainly focuses on performance optimization under single environmental factors. However, hydrogels often face more complex environmental conditions in practical applications. For example, in alkaline-surfactant-polymer (ASP) oil displacement processes, the reservoir environment typically exhibits complex characteristics, such as high salinity, high temperature, and increased alkalinity. Therefore, there is an urgent need to develop a hydrogel material with good resistance to high temperature and salt swelling under extremely alkaline conditions. Summary of the Invention

[0004] To address the problem of poor swelling properties of traditional polyacrylamide hydrogels under high temperature and high salt conditions, this invention provides a method for preparing and applying a high-temperature and salt-resistant fly ash-doped hydrogel. The addition of fly ash enhances the cross-linking network of the hydrogel through its porous structure and surface-active groups, thereby improving its thermal stability and salt resistance. This allows it to maintain excellent swelling properties even under high temperature and high salt conditions with strong alkalinity. Therefore, the prepared composite hydrogel can solve the problem of poor swelling properties of traditional polyacrylamide hydrogels under high temperature and high salt conditions.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel, the method comprising:

[0007] Acrylamide was dissolved in water to obtain a monomer solution;

[0008] A crosslinking agent and auxiliaries, including carboxymethyl cellulose and fly ash, are added to the monomer solution, and the mixture is stirred and dispersed to obtain a homogeneous mixed system.

[0009] An initiator was added to the mixture, and a composite gel was obtained after the reaction.

[0010] In the aforementioned mixed system, the mass ratio of carboxymethyl cellulose to fly ash is 1–5%:1–5%.

[0011] Furthermore, the acrylamide concentration in the monomer solution is 10–25% by mass.

[0012] Furthermore, the crosslinking agent includes N,N'-methylenebisacrylamide, wherein the concentration of N,N'-methylenebisacrylamide is 0.1%-3.0%.

[0013] Furthermore, a crosslinking agent and auxiliaries, including carboxymethyl cellulose and fly ash, are added to the monomer solution, and the mixture is stirred and dispersed to form a homogeneous mixture, specifically including:

[0014] Add crosslinking agent and additives, and stir for 45-90 minutes at a speed of 300-700 r / min and a water bath temperature of 40-70℃.

[0015] Furthermore, the initiator comprises potassium persulfate, wherein the concentration of potassium persulfate is 0.1%-1%.

[0016] Furthermore, the step of adding an initiator to the mixture and obtaining a composite gel after the reaction specifically includes:

[0017] Add the initiator and react for 45-90 minutes at a rotation speed of 300-700 r / min and a water bath temperature of 40-70℃, with nitrogen gas introduced throughout the process to purge air.

[0018] Based on the same inventive concept, the present invention provides a high-temperature and salt-resistant fly ash-doped hydrogel, which is prepared by the above-mentioned preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel.

[0019] Based on the same inventive concept, this invention also provides the application of the above-mentioned high-temperature and salt-resistant fly ash-doped hydrogel in water plugging.

[0020] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0021] 1. The fly ash-doped hydrogel prepared by this invention exhibits excellent high-temperature and salt swelling ratio (158.9 g / g) at pH 12.0. -1 This solves the problem of poor high-temperature and salt resistance swelling of traditional polyacrylamide hydrogels, thereby improving product performance.

[0022] 2. The fly ash-doped hydrogel prepared by this invention exhibits excellent water-blocking performance, with a blocking efficiency of up to 93.3%, which is significantly better than the blocking efficiency of 66.7% of polyacrylamide hydrogel.

[0023] 3. The raw materials used in the preparation method of this invention are readily available and inexpensive. Furthermore, the use of waste fly ash as an additive enables the reuse of industrial waste, aligning with the goals of a circular economy and demonstrating significant environmental benefits. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 It is a high-temperature and salt-resistant fly ash-doped hydrogel with a swelling ratio in different salt solutions.

[0026] Figure 2 It is a high-temperature and salt-resistant fly ash-doped hydrogel whose swelling ratio is measured at different pH values.

[0027] Figure 3 It is a high-temperature and salt-resistant fly ash-doped hydrogel with swelling ratio at different temperatures (pH=6.0).

[0028] Figure 4 It is a high-temperature and salt-resistant fly ash-doped hydrogel with swelling ratio at different temperatures (pH=12.0).

[0029] Figure 5 It is a high-temperature and salt-resistant fly ash-doped hydrogel with swelling ratios at different NaCl concentrations (pH=6.0).

[0030] Figure 6 It is a high-temperature and salt-resistant fly ash-doped hydrogel with swelling ratios at different NaCl concentrations (pH=12.0).

[0031] Figure 7 It is a high-temperature and salt-resistant fly ash-doped hydrogel with swelling ratios at different particle sizes.

[0032] Figure 8 It is the swelling ratio of a high-temperature and salt-resistant fly ash-doped hydrogel at pH=6.0 and pH=12.0 (8.0% NaCl solution, 120℃, particle size ≤0.125mm). Detailed Implementation

[0033] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0034] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] The following will describe in detail the preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to the present application, with reference to the embodiments and experimental data.

[0037] All raw materials used in the embodiments of this invention are commercially available. Acrylamide, N,N'-methylenebisacrylamide, hydrochloric acid, sodium hydroxide, sodium chloride, calcium chloride, and potassium persulfate were all provided by Chengdu Kelong Chemical Co., Ltd.; carboxymethyl cellulose was provided by Chengdu Huaxia Chemical Reagent Co., Ltd.; and fly ash was provided by Hebei Shijiazhuang Huaneng Shang'an Power Plant.

[0038] Example 1

[0039] This embodiment describes a method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel, comprising the following steps:

[0040] (1) Weigh 20.0g of acrylamide and dissolve it in 100mL of distilled water. Place it in a water bath stirrer and stir for 10min to completely dissolve it, and then obtain a monomer solution.

[0041] (2) Add 0.3g of crosslinking agent N,N'-methylenebisacrylamide to the monomer solution and continue stirring for 30min to mix evenly. Then weigh 0.5g of carboxymethyl cellulose and 0.5g of fly ash and stir for 60min at 500r / min and 50℃ in a water bath to obtain a uniform mixed system.

[0042] (3) Add 0.1g of potassium persulfate initiator to the mixed system, and react for 60min at a speed of 500r / min and a water bath temperature of 70℃. Nitrogen gas is introduced throughout the reaction to remove oxygen from the system. After the reaction is completed, a composite hydrogel is obtained.

[0043] Comparative Example 1

[0044] The only difference between Comparative Example 1 and Example 1 is that carboxymethyl cellulose and fly ash were not added; the other operating steps were the same as in Example 1.

[0045] Example 2

[0046] This embodiment tests the performance of the products prepared in Example 1 and Comparative Example 1.

[0047] 1. The salt swelling resistance of Example 1 and Comparative Example 1 under different concentrations of sodium chloride and calcium chloride solutions was tested. The test method was as follows: Example 1 and Comparative Example 1 were immersed in salt solutions of different concentrations (NaCl (0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 8.0%), CaCl2 (0.5%, 1.0%, 2.0%, 3.0%)) at 25°C for at least 8 hours to ensure that the hydrogel reached a constant weight. The test results are as follows. Figure 1 As shown.

[0048] from Figure 1 It can be seen that the salt-tolerance swelling ratio of Example 1 in the same salt solution is higher than that of Comparative Example 1, and the swelling ratio in NaCl solution is higher than that in CaCl2 solution at the same percentage content. In NaCl solution, when the concentration increases from 0.5% to 8.0%, the swelling ratio of Example 1 increases from 13.9 g / L. -1 Reduced to 11.5 gg -1 Meanwhile, the control group 1 was 9.5 gg. -1 Reduced to 6.1 gg -1 In CaCl2 solution, as the concentration increased from 0.5% to 3.0%, the swelling ratio in Example 1 increased from 12.1 g / L. -1 Reduced to 11.6 gg -1 Comparative Example 1 from 7.4 gg -1 Reduced to 6.5 gg -1 Because fly ash and carboxymethyl cellulose are introduced, and the surface of fly ash is rich in ion exchange sites, it can react with Na+ in salt solutions. + and Ca 2+ An ion exchange process occurs. This ion exchange process increases the ion concentration inside the hydrogel, further enhancing the salt swelling resistance of the interpenetrating network hydrogel formed by carboxymethyl cellulose and polyacrylamide.

[0049] 2. The swelling ratios of Example 1 and Comparative Example 1 under different pH conditions were tested. The test method was as follows: the pH of the aqueous solution was adjusted to 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0 using 0.1M HCl and NaOH solutions, respectively. Then, Example 1 and Comparative Example 1 were immersed in aqueous solutions at different pH values ​​(2.0-12.0) for at least 8 hours to ensure that the hydrogel reached a constant weight. The test results are as follows. Figure 2 As shown.

[0050] from Figure 2 It can be seen that as the pH value increases from 2.0 to 12.0, the swelling ratio in Example 1 generally shows an upward trend. At pH = 6.0, the swelling ratio reaches its maximum under acidic conditions, at 40.4 g / L. -1 At pH 12.0, the swelling ratio reaches its maximum under alkaline conditions, at 64.9 g / L. -1 Furthermore, the swelling ratio of Example 1 under different pH conditions was always higher than that of Comparative Example 1.

[0051] 3. The swelling ratios of Example 1 and Comparative Example 1 in solutions at different temperatures (pH = 6.0 and pH = 12.0) were tested. The test method was as follows: the pH of the aqueous solutions was adjusted to 6.0 and 12.0 respectively using 0.1M HCl and NaOH solutions. Then, Example 1 and Comparative Example 1 were placed in solutions at pH 6.0 and 12.0, respectively, and the oven temperatures were adjusted to 25, 40, 60, 80, and 120°C. Under these conditions, swelling was allowed for at least 8 hours to ensure that the hydrogel reached a constant weight. The test results are as follows. Figure 3 and Figure 4 As shown.

[0052] Depend on Figure 3 and Figure 4 It can be seen that the gel's swelling ratio under alkaline conditions (pH 12.0) is consistently greater than that under acidic conditions (pH 6.0). In Example 1, the highest swelling ratio at 120°C under pH 12.0 conditions was 170.5 g / g. -1 The swelling ratio is 50.5 gg higher than at pH 6.0. -1 The swelling ratio was 124.7 gg higher than that of Comparative Example 1 under the same conditions. -1 The reason is that under alkaline high-temperature conditions (pH 12.0, 120℃), the high temperature promotes the hydrolysis of the -CONH2 groups in the hydrogel to generate -COO. - This increases the osmotic pressure inside the hydrogel, thereby promoting its swelling ratio. Furthermore, fly ash is rich in chemically stable inorganic components (SiO2 and Al2O3). The silicon-oxygen tetrahedra in SiO2 and the aluminum-oxygen octahedra in Al2O3 form a robust three-dimensional network structure by sharing oxygen atoms, which further enhances the temperature resistance of the gel.

[0053] 4. The swelling ratios of Example 1 and Comparative Example 1 in NaCl solutions of different concentrations (0.5%, 1.0%, 2.0%, 3.0%, 5.0%, and 8.0%) were tested. The test method was as follows: the pH of the NaCl solution was adjusted to 6.0 and 12.0 respectively using 0.1M HCl and NaOH solutions. The soaking time was no less than 8 hours at 25°C to ensure the hydrogel reached a constant weight. The test results are as follows. Figure 5 and Figure 6 As shown.

[0054] from Figure 5 and Figure 6 It can be seen that the salt-resistant swelling ratio of the gel is consistently greater under alkaline conditions (pH 12.0) than under acidic conditions (pH 6.0). In Example 1, the highest salt-resistant (8% NaCl) swelling ratio was 53.2 g / L at pH 12.0. -1 The swelling ratio is 21.0 gg, which is higher than that at pH 6.0. -1 The swelling ratio is 11.5 gg, which is higher than that at pH 7.0. -1 It also has a higher swelling ratio than Comparative Example 1 (18.4 gg) under the same conditions. -1 The reason is that under strongly alkaline conditions, a large amount of OH- in the solution... - Ions diffuse into the three-dimensional network structure of the hydrogel and react chemically with the surface components of fly ash particles to generate Al(OH)4. - [SiO(OH)3] - and [SiO2(OH)2] 2- These are isohydrated anions. They attract sodium ions through electrostatic interactions, reducing the sodium ion concentration in the solution, thereby lowering the external osmotic pressure, stabilizing the internal structure of the hydrogel, and enhancing its swelling capacity in high-salt environments.

[0055] 5. The swelling ratios of Example 1 and Comparative Example 1 at different particle sizes were tested. The test method was as follows: The dried sample of Example 1 was pulverized into particles and sieved through 40-mesh (0.177-0.425 mm), 80-mesh (0.125-0.177 mm), and 120-mesh (≤0.125 mm) sieves to obtain particles within a specific particle size range. After soaking for at least 8 hours, the hydrogel reached swelling equilibrium. The test results are as follows. Figure 7 As shown.

[0056] from Figure 7 It can be seen that as the particle size decreases, the swelling ratio of Example 1 gradually increases. When the particle size decreases from 0.425 mm to 0.125 mm, the equilibrium swelling ratio of Example 1 decreases from 28.9 g / cm³. -1 Increased to 38.3 gg -1 This indicates that reducing particle size helps improve the water absorption capacity of the hydrogel.

[0057] 6. The swelling ratio of Example 1 and Comparative Example 1 under optimized conditions was tested. The test method was as follows: the pH of the salt solution was adjusted to 6.0 and 12.0 respectively using 0.1M HCl and NaOH solutions. Samples with a particle size ≤0.125mm were immersed in the solution at pH 6.0 or 12.0, 120℃, and 8.0% NaCl for at least 8 hours until swelling equilibrium was reached. The test results are as follows. Figure 8 As shown.

[0058] from Figure 8 It can be seen that, after optimization (120℃, 8.0% NaCl, particle size ≤0.125mm), Example 1 exhibits a higher swelling ratio than Comparative Example 1 under the same pH conditions. At pH 12.0, the swelling ratio of Example 1 is 158.9g. -1 The swelling ratio was significantly higher than that of Comparative Example 1 (39.8 gg). -1 Under different pH conditions, the swelling ratio of Example 1 at pH 12.0 after optimization (120℃, 8.0% NaCl, particle size ≤0.125mm) was 158.9 gg. -1 The swelling ratio above pH 6.0 is 108.6 gg. -1 This demonstrates that Example 1 exhibits excellent temperature and salt swelling resistance under strongly alkaline conditions.

[0059] 7. The blocking capabilities of Example 1 and Comparative Example 1 were tested. The experimental steps are as follows:

[0060] (1) Fill the sandbag with 80-100 mesh quartz sand, and add 2 mL min. -1 The sandbag was saturated by injecting 8.0% NaCl solution at a flow rate of 100%. After the outlet flow rate stabilized, the outlet flow rate and pressure were recorded, and the initial permeability k0 of the sandbag was calculated.

[0061] (2) After injecting 0.5PV of gel suspension with a concentration of 0.2% into the sandbag, seal the sandbag and heat it at 120°C for 48 hours to form a hydrogel.

[0062] (3) After the hydrogel forms, it is again injected at 2 mL / min. -1 An 8.0% NaCl solution was injected at a flow rate of [value missing], and the permeability k1 of the sandbag after the hydrogel injection was calculated after the pressure difference stabilized.

[0063] The formula for calculating penetration rate is as follows:

[0064]

[0065] Where k is the permeability, in mD, and q is the flow rate, in mL / min. -1 μ is the viscosity of the fluid at the experimental temperature, in mPa·s. L is the length of the sandbag, in cm. A is the cross-sectional area of ​​the sandbag, in cm². 2 P1 and P2 are the pressures at the sandbag inlet and outlet, respectively, in MPa.

[0066] The formula for calculating the blocking rate is as follows:

[0067]

[0068] φ represents the plugging rate. k0 represents the fluid permeability before plugging, and k1 represents the fluid permeability after plugging, both in mD.

[0069] The formula for calculating the residual drag factor is as follows:

[0070]

[0071] RRF stands for Residual Resistance Factor. k0 is the fluid permeability before plugging, and k1 is the fluid permeability after plugging, in mD.

[0072] The sealing performance test results of the gel water-blocking agents obtained in Example 1 and Comparative Example 1 are shown in Table 1:

[0073] Table 1. Blocking efficiency of hydrogel solutions

[0074]

[0075] As shown in Table 1, Comparative Example 1 had an initial permeability of 1500.0 mD, which decreased to 500.0 mD after injection, with a plugging rate of 66.7% and a residual resistance factor of 3.0, indicating that it had some plugging capability but limited capacity. Example 1, on the other hand, had an initial permeability of 1800.0 mD, which decreased to 120.0 mD after injection, with a plugging rate as high as 93.3% and a residual resistance factor of 15.0, significantly better than Comparative Example 1.

[0076] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel, characterized in that, Includes the following steps: Acrylamide is dissolved in water to prepare a monomer solution with a mass concentration of 10% to 25%. A crosslinking agent and an auxiliary agent are added to the monomer solution, and the mixture is stirred and dispersed to form a uniform mixed system. The auxiliary agent includes carboxymethyl cellulose and fly ash, and the mass fraction of both in the mixed system is 1% to 5%. The crosslinking agent includes N,N′-methylenebisacrylamide, and its concentration in the mixed system is 0.1% to 3.0%. An initiator is added to the mixed system, and a composite gel is obtained after reaction.

2. The method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 1, characterized in that, Add a crosslinking agent and auxiliaries, including carboxymethyl cellulose and fly ash, to the monomer solution, and stir and disperse to form a homogeneous mixture, specifically including: Add crosslinking agent and additives, and stir for 45-90 minutes at a speed of 300-700 r / min and a water bath temperature of 40-70 ℃.

3. The method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 1, characterized in that, The initiator includes potassium persulfate, wherein the concentration of potassium persulfate is 0.1% - 1%.

4. The method for preparing a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 3, characterized in that, Adding an initiator to the mixture to obtain a composite gel specifically includes: Add the initiator and react for 45-90 minutes at a rotation speed of 300-700 r / min and a water bath temperature of 40-70℃, with nitrogen gas introduced throughout the process to purge air.

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