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

Abstract

The invention provides a preparation method of high-temperature-resistant and salt-resistant fly ash doped hydrogel, and belongs to the technical field of oil field water shutoff agents.The preparation method comprises the steps that acrylamide is dissolved in water, and a monomer solution is obtained; a cross-linking agent and an auxiliary agent are added into the monomer solution, the auxiliary agent comprises carboxymethyl cellulose and fly ash, and the mixture is stirred and dispersed to form a uniform mixed system; adding an initiator into the mixed system, and reacting to obtain composite gel; wherein in the mixed system, the mass ratio of the carboxymethyl cellulose to the fly ash is (1-5%): (1-5%). The hydrogel prepared by the method can solve the problem of poor swelling property of the traditional polyacrylamide gel under the conditions of strong base, high temperature and high salt.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield water plugging agents, and particularly relates to a preparation method of a fly ash-doped hydrogel with high temperature and salt resistance. Background Art

[0002] As the oilfield enters the middle and late stages of development, the problem of high water cut becomes increasingly serious. A large amount of produced water is generated every year, leading to an increase in the cost of oil-water separation and equipment corrosion. Hydrogel is one of the effective methods to solve the problem of high water cut. Among them, pre-crosslinked hydrogel has received extensive attention due to its strong controllability and small damage to the reservoir. However, traditional polyacrylamide pre-crosslinked hydrogels have poor swelling properties under high temperature and high salt conditions and are difficult to meet the requirements of complex reservoir environments.

[0003] In the prior art, 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 salt, and strong alkali, due to the combined effects of factors such as increased movement of gel network segments, osmotic pressure imbalance, and disruption of hydrogen bond interactions, the network structure is prone to dissociation, resulting in a decrease in the swelling performance of the hydrogel. In addition, existing research mainly focuses on the performance optimization under a single environmental factor. However, hydrogels often face more complex environmental conditions in practical applications. For example, during the alkaline-surfactant-polymer (ASP) flooding process, the reservoir environment usually 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 swelling performance against high temperature and salt under extremely alkaline conditions. Summary of the Invention

[0004] In order to solve the problem of poor swelling properties of traditional polyacrylamide hydrogels under high temperature and high salt conditions, the present invention provides a preparation method and application of a fly ash-doped hydrogel with high temperature and salt resistance. Due to the addition of fly ash, the crosslinked network of the hydrogel is enhanced through its porous structure and surface active groups, while its thermal stability and salt resistance are improved, enabling it to maintain excellent swelling properties in a high temperature and high salt environment under strong alkali conditions. 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] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a preparation method of a fly ash-doped hydrogel with high temperature and salt resistance, and the preparation method includes:

[0007] Dissolve acrylamide in water to obtain a monomer solution;

[0008] Add a crosslinking agent and an auxiliary agent to the monomer solution. The auxiliary agent includes carboxymethyl cellulose and fly ash, and stir and disperse to obtain a uniform mixed system;

[0009] An initiator is added to the said mixed system, and a composite gel is obtained after the reaction;

[0010] Among them, in the said mixed system, the mass ratio of carboxymethyl cellulose to fly ash is 1–5%: 1–5%.

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

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

[0013] Furthermore, a crosslinking agent and an auxiliary agent are added to the said monomer solution. The auxiliary agent includes carboxymethyl cellulose and fly ash, and a uniform mixed system is formed by stirring and dispersing, specifically including:

[0014] The crosslinking agent and the auxiliary agent are added, and stirring is carried out at a rotation speed of 300 - 700 r / min and a water bath temperature of 40 - 70 °C for 45 - 90 min.

[0015] Furthermore, the said initiator includes potassium persulfate, and the concentration of potassium persulfate is 0.1% - 1%.

[0016] Furthermore, adding the said initiator to the said mixed system, and a composite gel is obtained after the reaction, specifically including:

[0017] The initiator is added, and the reaction is carried out at a rotation speed of 300 - 700 r / min and a water bath temperature of 40 - 70 °C for 45 - 90 min, and nitrogen is introduced throughout the process to remove air.

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

[0019] Based on the same inventive concept, the present invention also provides the application of the fly ash-doped hydrogel with high temperature and salt resistance as described above in water shutoff.

[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 the present invention has an excellent high temperature and salt resistance swelling ratio under the condition of pH = 12.0, which is 158.9 g / g -1 , solving the problem of poor high temperature and salt resistance swelling property of traditional polyacrylamide hydrogels, thereby improving the performance of the product.

[0022] 2. The fly ash-doped hydrogel prepared by the present invention exhibits excellent water plugging performance, with a plugging efficiency as high as 93.3%, significantly superior to the 66.7% plugging efficiency of polyacrylamide hydrogel.

[0023] 3. In the preparation method of the present invention, the raw materials are easily available and the cost is low. By using waste fly ash as an auxiliary agent, the reuse of industrial waste residues is realized, meeting the goal of circular economy and having significant environmental protection benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

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

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

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

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

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

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

[0031] Figure 7 It is the swelling ratio of a high-temperature and salt-resistant fly ash-doped hydrogel with 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 °C, particle size ≤ 0.125 mm). DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be specifically described below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention, rather than to limit the present invention.

[0034] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention pertains. In case of any contradiction, this specification shall prevail.

[0035] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0036] The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel of the present application will be described in detail below in conjunction with examples and experimental data.

[0037] All raw materials in the embodiments of the present invention can be obtained through commercial channels. Among them, acrylamide, N,N'-methylenebisacrylamide, hydrochloric acid, sodium hydroxide, sodium chloride, calcium chloride, and potassium persulfate are provided by Chengdu Kelong Chemical Co., Ltd.; carboxymethyl cellulose is provided by Chengdu Huaxia Chemical Reagent Co., Ltd.; fly ash is provided by Huaneng Shang'an Power Plant in Shijiazhuang, Hebei.

[0038] Example 1

[0039] The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel in this example includes the following steps:

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

[0041] (2) Add 0.3 g of N,N'-methylenebisacrylamide as a crosslinking agent to the monomer solution, continue stirring for 30 min to make it evenly mixed, then weigh 0.5 g of carboxymethyl cellulose and 0.5 g of fly ash respectively, and stir at a rotation speed of 500 r / min and a water bath temperature of 50 °C for 60 min to obtain a uniformly mixed system.

[0042] (3) Add 0.1 g of potassium persulfate as an initiator to the mixed system, react at a rotation speed of 500 r / min and a water bath temperature of 70 °C for 60 min, then introduce nitrogen throughout the process to remove oxygen in the reaction system. After the reaction is completed, a composite hydrogel is obtained.

[0043] Comparative Example 1

[0044] The difference between Comparative Example 1 and Example 1 is only that carboxymethyl cellulose and fly ash are not added, and the remaining operation steps are the same as those in Example 1.

[0045] Example 2

[0046] In this example, the products obtained in Example 1 and Comparative Example 1 were subjected to performance testing.

[0047] 1. The salt tolerance swelling of Example 1 and Comparative Example 1 in sodium chloride and calcium chloride solutions with different concentrations was tested. The test method was as follows: Example 1 and Comparative Example 1 were immersed in salt solutions with 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 h to ensure that the hydrogel reached a constant weight. The test results are as Figure 1 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 of Example 1 in the NaCl solution at the same percentage content is higher than that in the CaCl2 solution. In the NaCl solution, when the concentration increased from 0.5% to 8.0%, the swelling ratio of Example 1 decreased from 13.9 g / g -1 to 11.5 g / g -1 , while that of Comparative Example 1 decreased from 9.5 g / g -1 to 6.1 g / g -1 ; in the CaCl2 solution, when the concentration increased from 0.5% to 3.0%, the swelling ratio of Example 1 decreased from 12.1 g / g -1 to 11.6 g / g -1 , and that of Comparative Example 1 decreased from 7.4 g / g -1 to 6.5 g / g -1 . Due to the introduction of fly ash and carboxymethyl cellulose, and the surface of fly ash is rich in a large number of ion exchange sites, which can exchange with Na + and Ca 2+ in the salt solution. This ion exchange process increases the ion concentration inside the hydrogel and further enhances the salt tolerance swelling ability of the interpenetrating network hydrogel formed by carboxymethyl cellulose and polyacrylamide.

[0049] 2. The swelling ratios of Example 1 and Comparative Example 1 at different pH values 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 0.1 M HCl and NaOH solutions respectively, and then Example 1 and Comparative Example 1 were immersed in aqueous solutions with different pH values (2.0 - 12.0) for at least 8 h to ensure that the hydrogel reached a constant weight. The test results are as Figure 2 shown.

[0050] From Figure 2 it can be seen that when the pH value increases from 2.0 to 12.0, the swelling ratio of Example 1 generally shows an upward trend. When pH = 6.0, the swelling ratio reaches the maximum under acidic conditions, which is 40.4 g / g -1 , and when pH = 12.0, the swelling ratio reaches the maximum under alkaline conditions, which is 64.9 g / g -1 , and the swelling ratio of Example 1 under different pH conditions is always higher than that of Comparative Example 1.

[0051] 3. Test the swelling ratios of Example 1 and Comparative Example 1 in solutions at different temperatures (pH = 6.0 and pH = 12.0). The test method is as follows: Use 0.1 M HCl and NaOH solutions to adjust the pH of the aqueous solution to 6.0 and 12.0 respectively, and then place Example 1 and Comparative Example 1 in solutions with pH 6.0 and 12.0. Adjust the oven temperature to 25, 40, 60, 80, and 120 °C respectively. Under these conditions, swell for at least 8 h to ensure that the hydrogel reaches a constant weight. The test results are as Figure 3 and Figure 4 shown.

[0052] From Figure 3 and Figure 4 it can be seen that the temperature-resistant swelling ratio of the gel is always greater under alkaline conditions (pH 12.0) than under acidic conditions (pH 6.0). The highest temperature-resistant (120 °C) swelling ratio of Example 1 under pH 12.0 conditions is 170.5 g / g -1 , which is higher than the swelling ratio of 50.5 g / g at pH 6.0 -1 , and higher than the swelling ratio of 124.7 g / g of Comparative Example 1 under the same conditions -1 . The reason is that under the conditions of high temperature in alkaline (pH 12.0, 120 °C), high temperature promotes the hydrolysis of -CONH2 groups in the hydrogel to generate -COO - , which increases the osmotic pressure inside the hydrogel, thereby promoting its swelling ratio. And fly ash is rich in chemically stable inorganic components (SiO2 and Al2O3). The silicon-oxygen tetrahedron in SiO2 and the aluminum-oxygen octahedron in Al2O3 form a strong three-dimensional network structure by sharing oxygen atoms, further enhancing the temperature resistance of the gel.

[0053] 4. Test the swelling ratios of Example 1 and Comparative Example 1 in NaCl solutions with different concentrations (0.5%, 1.0%, 2.0%, 3.0%, 5.0%, and 8.0%). The test method is as follows: Use 0.1 M HCl and NaOH solutions to adjust the pH of the NaCl solution to 6.0 and 12.0 respectively. Under the condition of 25 °C, the soaking time is not less than 8 h to ensure that the hydrogel reaches a constant weight. The test results are as Figure 5 and Figure 6 shown.

[0054] From Figure 5 and Figure 6 it can be seen that the salt tolerance swelling ratio of the gel is always greater under alkaline conditions (pH 12.0) than under acidic conditions (pH 6.0). The highest swelling ratio of Example 1 under salt tolerance (8% NaCl) at pH 12.0 is 53.2 g / g -1 , which is higher than the swelling ratio of 21.0 g / g at pH 6.0 -1 , higher than the swelling ratio of 11.5 g / g at pH 7.0 -1 , and also higher than the swelling ratio of 18.4 g / g of Comparative Example 1 under the same conditions -1 . The reason is that under strongly alkaline conditions, a large number of OH - ions diffuse into the three-dimensional network structure of the hydrogel and chemically react with the surface components of fly ash particles to form Al(OH)4 - , [SiO(OH)3] - and [SiO2(OH)2] 2- and other hydrated anions. These anions attract sodium ions through electrostatic interaction, reduce the sodium ion concentration in the solution, thereby reducing the external osmotic pressure, stabilizing the internal structure of the hydrogel, and enhancing its swelling ability in a high-salt environment.

[0055] 5. Test the swelling ratios of Example 1 and Comparative Example 1 at different particle sizes. The test method is as follows: After drying, Example 1 is crushed into particles and screened 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 h, the hydrogel reaches swelling equilibrium. The test results are as Figure 7 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 increases from 28.9 g / g -1 to 38.3 g / g -1 , indicating that the decrease in particle size helps to improve the water absorption capacity of the hydrogel.

[0057] 6. Test the swelling ratios of Example 1 and Comparative Example 1 after optimization. The test method is as follows: Use 0.1 M HCl and NaOH solutions to adjust the pH of the salt solution to 6.0 and 12.0 respectively. Under the conditions of pH 6.0 or 12.0, 120 °C, and 8.0% NaCl, soak the samples with a particle size ≤0.125 mm in the solution. After soaking for at least 8 h, it reaches swelling equilibrium. The test results are as Figure 8 shown.

[0058] From Figure 8 It can be seen that after Example 1 was optimized under the conditions (120 °C, 8.0% NaCl, particle size ≤ 0.125 mm), the swelling ratio under the same pH conditions was higher than that of Comparative Example 1. At pH 12.0, the swelling ratio of Example 1 was 158.9 g / g -1 , significantly higher than the swelling ratio of 39.8 g / g in Comparative Example 1 -1 . Under different pH conditions, after Example 1 was optimized under the conditions (120 °C, 8.0% NaCl, particle size ≤ 0.125 mm), the swelling ratio at pH 12.0 was 158.9 g / g -1 higher than the swelling ratio of 108.6 g / g at pH 6.0 -1 , indicating that Example 1 has excellent temperature and salt tolerance swelling ratio under strong alkaline conditions.

[0059] 7. The plugging ability of Example 1 and Comparative Example 1 was tested, and the experimental steps were as follows:

[0060] (1) Fill the sand pack with quartz sand of 80 - 100 mesh, and inject 8.0% NaCl solution at a flow rate of 2 mL / min -1 to saturate the sand pack. After the outlet flow rate is stable, record the outlet flow rate and pressure, and calculate the initial permeability k0 of the sand pack.

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

[0062] (3) After the hydrogel is formed, inject 8.0% NaCl solution again at a flow rate of 2 mL / min -1 . After the pressure difference is stable, calculate the permeability k1 of the sand pack after injecting the hydrogel.

[0063] The calculation formula for permeability is as follows:

[0064]

[0065] where k is the permeability, with the unit of mD. q is the flow rate, with the unit of mL / min -1 . μ is the viscosity of the fluid under the experimental temperature conditions, with the unit of mPa·s. L is the length of the sand bag, with the unit of cm. A is the cross-sectional area of the sand bag, with the unit of cm 2 . P1 and P2 are the pressures at the inlet and outlet of the sand bag respectively, with the unit of MPa.

[0066] The calculation formula for the plugging rate is as follows:

[0067]

[0068] φ is the plugging rate. k0 is the fluid permeability before plugging, and k1 is the fluid permeability after plugging, with the unit of mD.

[0069] The calculation formula for the residual resistance factor is as follows

[0070]

[0071] RRF is the residual resistance factor. k0 is the fluid permeability before plugging, and k1 is the fluid permeability after plugging, with the unit of mD.

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

[0073] Table 1 Blocking efficiency of the hydrogel solution

[0074]

[0075] As can be seen from Table 1, in Comparative Example 1, the initial permeability was 1500.0 mD, and after injection, the permeability decreased to 500.0 mD, the plugging rate was 66.7%, and the residual resistance factor was 3.0, indicating that it had a certain plugging ability but the plugging ability was limited. While in Example 1, the initial permeability was 1800.0 mD, and after injection, the permeability decreased to 120.0 mD, the plugging rate was as high as 93.3%, and the residual resistance factor was 15.0, significantly superior to Comparative Example 1.

[0076] Finally, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0077] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of a fly ash-doped hydrogel with high temperature and salt resistance, characterized in that , The hydrogel doped with fly ash has excellent high-temperature resistance and salt-resistant swelling properties under strong alkaline conditions.

2. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 1, characterized in that, The preparation method includes: Dissolve acrylamide in water to obtain a monomer solution; Add a crosslinking agent and an auxiliary agent to the monomer solution. The auxiliary agent includes carboxymethyl cellulose and fly ash, and stir and disperse to form a uniform mixed system; Add an initiator to the mixed system, and obtain a composite gel after reaction; Among them, in the mixed system, the mass ratio of carboxymethyl cellulose to fly ash is 1–5%: 1–5%.

3. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 2, characterized in that, In the monomer solution, the acrylamide concentration is 10–25% by mass concentration.

4. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 2, characterized in that, The crosslinking agent includes N,N'-methylenebisacrylamide, and the concentration of N,N'-methylenebisacrylamide is 0.1%-3.0%.

5. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 4, wherein Add a crosslinking agent and an auxiliary agent to the monomer solution. The auxiliary agent includes carboxymethyl cellulose and fly ash, and stir and disperse to form a uniform mixed system, specifically including: Add a crosslinking agent and additives, and stir at a rotational speed of 300 - 700 r / min under a water bath condition of 40 - 70 O °C for 45 - 90 min.

6. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 2, characterized in that, The initiator includes potassium persulfate, and the concentration of potassium persulfate is 0.1%-1%.

7. The preparation method of a high-temperature and salt-resistant fly ash-doped hydrogel according to claim 6, characterized in that, Add an initiator to the mixed system to obtain a composite gel, specifically including: Add an initiator and react for 45 - 90 min under the conditions of a rotation speed of 300 - 700 r / min and a water bath temperature of 40 - 70 O °C while introducing nitrogen throughout the process to exclude air.

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