Acid-triggered hydrogel blocking agents and their preparation methods

Abstract

This invention discloses an acid-triggered hydrogel plugging agent and its preparation method, comprising polyacrylamide, carboxylated tannic acid, and slow-release iron, wherein the mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03-0.06:0.005-0.01. This invention solves the problems of existing gel plugging agents being unable to remain stable in acidic environments for extended periods and being difficult to inject.

Description

Technical Field

[0001] This invention belongs to the field of oil well plugging technology, specifically relating to acid-triggered hydrogel plugging agents and methods for preparing acid-triggered hydrogel plugging agents. Background Technology

[0002] CO2 flooding technology has become a research hotspot in recent years. CO2 gas has high fluidity and the effects of viscosity reduction, volume expansion, and reduced interfacial tension; therefore, compared with water flooding, gas flooding can better reduce residual oil saturation in pores. As a highly efficient and environmentally friendly block oil production and development method, CO2 flooding technology has a more significant recovery efficiency advantage than other oil displacement technologies, and is particularly suitable for the development of low-permeability reservoirs and the tapping of block oil production potential. However, CO2 flooding is also subject to many limiting factors. CO2 can escape into abandoned injection wellbores, and the failure of the CO2 injection wellbore integrity is the main cause of leakage. During gas flooding, CO2 not only escapes but also damages the wellbore. CO2 corrosion of oil well cement is one of the main factors affecting wellbore integrity. Under geological storage conditions, oil well cement is corroded by CO2, leading to structural damage and degradation of its sealing function. After being injected into the formation, CO2 dissolves in formation water, undergoing hydrolysis to form carbonic acid, causing formation corrosion. Therefore, CO2 containment treatment is necessary.

[0003] Existing plugging technologies mainly include foam plugging, solid particle plugging, and polymer gel plugging. Among them, gel plugging is the most widely used, but it cannot remain stable in acidic environments for extended periods and is not easy to inject. Summary of the Invention

[0004] The purpose of this invention is to provide an acid-triggered hydrogel plugging agent, which solves the problems that existing gel plugging agents cannot remain stable in acidic environments for a long time and are not easy to inject.

[0005] Another object of the present invention is to provide a method for preparing an acid-triggered hydrogel blocker.

[0006] The technical solution adopted in this invention is an acid-triggered hydrogel blocking agent composed of polyacrylamide, carboxylated tannic acid, and slow-release iron, wherein the mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03~0.06:0.005~0.01.

[0007] The invention is further characterized in that,

[0008] Slow-release iron is ferric citrate or EDTA-Fe.

[0009] The preparation method of carboxylated tannic acid is as follows:

[0010] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to a pH of 6.5 with anhydrous sodium carbonate at 0℃~5℃;

[0011] Step B: Neutralize an aqueous solution of chloroacetic acid with a mass concentration of 44%–60% to a pH of 6.5 with anhydrous sodium carbonate;

[0012] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, and then add a 30% sodium hydroxide aqueous solution dropwise to the reaction solution. Keep the reaction at this temperature and test the pH until the pH reaches 7, at which point the reaction is stopped to obtain carboxylated tannic acid.

[0013] The preparation method of polyacrylamide is as follows: octadecyl methacrylate hydrophobic monomer is added to an aqueous solution of sodium styrene sulfonate and stirred for 1 hour to form a microemulsion. Acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate are added to the microemulsion respectively, and after mixing evenly, NaOH solution is added. After the pH value is adjusted to 7, ammonium persulfate initiator is added to obtain polyacrylamide.

[0014] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0015] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate.

[0016] Another technical solution adopted in this invention is a method for preparing an acid-triggered hydrogel blocking agent, which is specifically implemented according to the following steps:

[0017] Step 1: Prepare carboxylated tannic acid;

[0018] Step 2: Prepare an aqueous solution of the sealing agent;

[0019] Step 3: Prepare acid-triggered hydrogel blocking agent.

[0020] The invention is further characterized in that,

[0021] The specific process of step 1 is as follows:

[0022] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to a pH of 6.5 with anhydrous sodium carbonate at 0℃~5℃;

[0023] Step B: Neutralize an aqueous solution of chloroacetic acid with a mass concentration of 44%–60% to a pH of 6.5 with anhydrous sodium carbonate;

[0024] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, and then add a 30% sodium hydroxide aqueous solution dropwise to the reaction solution. Keep the reaction at this temperature and test the pH until the pH reaches 7, at which point the reaction is stopped to obtain carboxylated tannic acid.

[0025] The specific process of step 2 is as follows: Add octadecyl methacrylate hydrophobic monomer to sodium styrene sulfonate aqueous solution and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix evenly. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and slow-release iron obtained in step 1 to polyacrylamide. Stir evenly with magnetic force and let stand for 2 hours to obtain the sealing agent aqueous solution.

[0026] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0027] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0028] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03~0.06:0.005~0.01;

[0029] Slow-release iron is ferric citrate or EDTA-Fe.

[0030] The specific process of step 3 is as follows: add CO2 aqueous solution or acidic solution to the sealing agent aqueous solution obtained in step 2, control the pH value of the system to 1-6 by the amount added, let stand for 30 minutes, cross-link to form hydrogel, and obtain acid-triggered hydrogel sealing agent.

[0031] The beneficial effects of this invention are:

[0032] (1) The acid-triggered hydrogel blocking agent of the present invention can be in solution state under alkaline and neutral conditions, and under acidic conditions, the solution state forms gel to form a gel, which can be used as a CO2 discharging blocking agent;

[0033] (2) The acid-triggered hydrogel sealing agent of this invention is composed of polyacrylamide, carboxylated tannic acid, and slow-release iron. Under alkaline conditions, the hydrogen bonding effect of the carboxylated tannic acid on polyacrylamide is significantly weakened, as is the ionic bond effect of the slow-release iron on polyacrylamide, resulting in a solution state with good injectability. Under acidic conditions, the carboxylated tannic acid is converted into polyhydroxycarboxylated tannic acid, increasing the hydrogen bonding effect with polyacrylamide and enhancing the gelation force, thus making it more stable in acidic environments. Simultaneously, the complexing ability of the complexing agent with iron ions is weakened under acidic conditions, therefore the slow-release iron can accelerate the Fe... 3+ The release rate, and thus the gelation rate, are controlled. Attached Figure Description

[0034] Figure 1 This is a SEM image of the acid-triggered hydrogel blocker prepared in Example 5 of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0036] The acid-triggered hydrogel blocking agent of the present invention is composed of polyacrylamide, carboxylated tannic acid, and slow-release iron, wherein the mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03-0.06:0.005-0.01.

[0037] The acid-triggered hydrogel plugging agent of this invention is in solution state at pH=7-10 and forms a weak gel or gel state at pH=1-6, and can be used as a CO2 discharging plugging agent.

[0038] Slow-release iron is ferric citrate or EDTA-Fe.

[0039] Ferric citrate and EDTA-Fe exhibit weakened complexation ability towards iron ions under acidic conditions, thus accelerating the formation of Fe complexes. 3+ Release, enhancing gel strength.

[0040] The preparation method of carboxylated tannic acid is as follows:

[0041] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to a pH of 6.5 with anhydrous sodium carbonate at 0℃~5℃;

[0042] Step B: Neutralize an aqueous solution of chloroacetic acid with a mass concentration of 44%–60% to a pH of 6.5 with anhydrous sodium carbonate;

[0043] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, and then add a 30% sodium hydroxide aqueous solution dropwise to the reaction solution. Keep the reaction at this temperature and test the pH until the pH reaches 7, at which point the reaction is stopped to obtain carboxylated tannic acid.

[0044] Carboxylated tannic acid is chloroacetic acid-modified tannic acid. Carboxylated tannic acid can increase the water solubility of tannic acid and enhance hydrogen bonding.

[0045] The preparation method of polyacrylamide is as follows: octadecyl methacrylate hydrophobic monomer is added to an aqueous solution of sodium styrene sulfonate and stirred for 1 hour to form a microemulsion. Acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate are added to the microemulsion respectively, and after mixing evenly, NaOH solution is added. After the pH value is adjusted to 7, ammonium persulfate initiator is added to obtain polyacrylamide.

[0046] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0047] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate.

[0048] The polyacrylamide of this invention is a temperature- and salt-resistant hydrophobic associative polyacrylamide, composed of temperature- and salt-resistant functional monomers and long-chain hydrophobic monomers. The polymerization reaction is carried out at low temperatures in a dual redox initiation system using conventional ammonium persulfate initiator and carboxylated tannic acid and slow-release iron. The temperature-resistant monomer in the polymer is N-vinylpyrrolidone, which increases the temperature resistance of the hydrogel system; the salt-resistant monomer is sodium styrene sulfonate, which increases the salt resistance of the hydrogel system; and the long-chain hydrophobic monomer in the polymer is octadecyl methacrylate, which forms hydrophobic associative microdomains in aqueous solution, increasing the strength of the hydrogel system.

[0049] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0050] Step 1: Prepare carboxylated tannic acid;

[0051] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to a pH of 6.5 with anhydrous sodium carbonate at 0℃~5℃;

[0052] Step B: Neutralize an aqueous solution of chloroacetic acid with a mass concentration of 44%–60% to a pH of 6.5 with anhydrous sodium carbonate;

[0053] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0054] Step 2: Prepare an aqueous solution of the sealing agent;

[0055] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and slow-release iron obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the sealing agent.

[0056] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0057] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0058] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03~0.06:0.005~0.01;

[0059] Slow-release iron is ferric citrate or EDTA-Fe;

[0060] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0061] Add an aqueous solution of CO2 or an acidic solution to the sealing agent aqueous solution obtained in step 2. Control the pH value of the system to 1-6 by the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent.

[0062] Example 1

[0063] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0064] Step 1: Prepare carboxylated tannic acid;

[0065] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to pH 6.5 with anhydrous sodium carbonate at 0°C;

[0066] Step B: Neutralize the 44% (w / w) aqueous solution of chloroacetic acid with anhydrous sodium carbonate to a pH of 6.5;

[0067] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0068] Step 2: Prepare an aqueous solution of the sealing agent;

[0069] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and ferric citrate obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the sealing agent.

[0070] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0071] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0072] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03:0.005;

[0073] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0074] Add an aqueous solution of CO2 or an acidic solution to the sealing agent aqueous solution obtained in step 2. Control the pH value of the system to 1 by the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent.

[0075] Example 2

[0076] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0077] Step 1: Prepare carboxylated tannic acid;

[0078] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to pH 6.5 with anhydrous sodium carbonate at 2°C;

[0079] Step B: Neutralize the 48% aqueous chloroacetic acid solution with anhydrous sodium carbonate to a pH of 6.5;

[0080] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0081] Step 2: Prepare an aqueous solution of the sealing agent;

[0082] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and ferric citrate obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the sealing agent.

[0083] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0084] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0085] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.04:0.006;

[0086] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0087] Add an aqueous CO2 solution or an acidic solution to the sealing agent aqueous solution obtained in step 2. Control the pH value of the system to 3 by the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent.

[0088] Example 3

[0089] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0090] Step 1: Prepare carboxylated tannic acid;

[0091] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to pH 6.5 with anhydrous sodium carbonate at 3°C;

[0092] Step B: Neutralize the 50% aqueous solution of chloroacetic acid with anhydrous sodium carbonate to a pH of 6.5;

[0093] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0094] Step 2: Prepare an aqueous solution of the sealing agent;

[0095] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and ferric citrate obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the sealing agent.

[0096] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0097] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0098] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.05:0.007;

[0099] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0100] Add an aqueous solution of CO2 or an acidic solution to the sealing agent aqueous solution obtained in step 2. Control the pH value of the system to 4 by the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent.

[0101] Example 4

[0102] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0103] Step 1: Prepare carboxylated tannic acid;

[0104] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to pH 6.5 with anhydrous sodium carbonate at 4°C;

[0105] Step B: Neutralize the 55% aqueous solution of chloroacetic acid with anhydrous sodium carbonate to a pH of 6.5;

[0106] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0107] Step 2: Prepare an aqueous solution of the sealing agent;

[0108] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and EDTA-Fe obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the blocking agent.

[0109] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0110] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0111] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.06:0.009;

[0112] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0113] Add an aqueous solution of CO2 or an acidic solution to the sealing agent aqueous solution obtained in step 2. Control the pH value of the system to 5 by the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent.

[0114] Example 5

[0115] The preparation method of the acid-triggered hydrogel blocking agent of the present invention is carried out according to the following steps:

[0116] Step 1: Prepare carboxylated tannic acid;

[0117] Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid to pH 6.5 with anhydrous sodium carbonate at 5°C;

[0118] Step B: Neutralize the 60% aqueous solution of chloroacetic acid with anhydrous sodium carbonate to a pH of 6.5;

[0119] Step C: Add the chloroacetic acid aqueous solution neutralized in Step 2 to the tannic acid aqueous solution neutralized in Step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid.

[0120] Step 2: Prepare an aqueous solution of the sealing agent;

[0121] Add octadecyl methacrylate hydrophobic monomer to an aqueous solution of sodium styrene sulfonate and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix well. Add NaOH solution and adjust the pH to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and EDTA-Fe obtained in step 1 to the polyacrylamide. Stir magnetically until uniform and let stand for 2 hours to obtain an aqueous solution of the blocking agent.

[0122] The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.5.

[0123] The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate;

[0124] The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.06:0.01;

[0125] Step 3: Prepare acid-triggered hydrogel blocking agent;

[0126] Add an aqueous CO2 solution or an acidic solution to the sealing agent aqueous solution obtained in step 2, controlling the pH of the system to 6 by adjusting the amount added. Let it stand for 30 minutes to crosslink and form a hydrogel, thus obtaining an acid-triggered hydrogel sealing agent. Figure 1 As shown.

[0127] The acid-triggered hydrogel blockers obtained in Examples 1 to 5 were tested for tensile strength, gel strength E, and elongation ε. The test results are shown in Table 1.

[0128] Table 1 Performance of Acid-Triggered Hydrogel Blocking Agents in Examples 1-5

[0129]

[0130] As can be seen from Table 1, the gels prepared in Examples 1 to 5 of the present invention have good mechanical properties under acidic conditions.

[0131] In the polymerization reaction using a conventional ammonium persulfate initiator and a dual redox initiation system of carboxylated tannic acid and slow-release iron, the ratio of carboxylated tannic acid to slow-release iron varies. With the gradual increase of acidity, the two enhance the hydrogen bonding and ionic bonding of the hydrophobic associating polymer, respectively, resulting in increased gel strength.

[0132] As can be seen from Examples 1-5, under acidic conditions, different proportions of chloroacetic acid have a significant impact on gel strength. The higher the proportion of chloroacetic acid, the more carboxyl groups in the polymer increase, the more crosslinking points increase, the stronger the hydrogen bonding effect of carboxylated tannic acid on hydrophobic associating polymers, and the stronger the gel strength.

[0133] As can be seen from Examples 1-5, the proportion of complexed iron can improve gel strength. Increasing the Fe content... 3+ Concentration and control of Fe 3+ The release rate is accelerated under acidic conditions because the complexing agent's ability to complex with iron ions is weakened. 3+ The release rate, and thus the gelation rate, are controlled.

[0134] In summary, the sealing gel material of the present invention has good acid responsiveness, can effectively control gelation time, and enhance gel strength.

Claims

1. An acid-triggered hydrogel blocking agent, characterized in that, It is composed of polyacrylamide, carboxylated tannic acid, and slow-release iron, wherein the mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03~0.06:0.005~0.01; The slow-release iron is ferric citrate or EDTA-Fe; The method for preparing the carboxylated tannic acid is as follows: Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid with anhydrous sodium carbonate to a pH of 6.5 at 0℃~5℃; Step B: Neutralize the chloroacetic acid aqueous solution with a mass concentration of 44%~60% with anhydrous sodium carbonate to a pH of 6.5; Step C: Add the chloroacetic acid aqueous solution neutralized in step 2 to the tannic acid aqueous solution neutralized in step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid. The preparation method of the polyacrylamide is as follows: octadecyl methacrylate hydrophobic monomer is added to an aqueous solution of sodium styrene sulfonate, and the mixture is stirred for 1 hour to form a microemulsion. Acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate are added to the microemulsion, and after mixing evenly, NaOH solution is added. After the pH value is adjusted to 7, ammonium persulfate initiator is added to obtain polyacrylamide. The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.

5. The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate.

2. A method for preparing an acid-triggered hydrogel blocking agent, characterized in that, The specific steps are as follows: Step 1: Prepare carboxylated tannic acid; The specific process of step 1 is as follows: Step A: Neutralize a 15% (w / w) aqueous solution of tannic acid with anhydrous sodium carbonate to a pH of 6.5 at 0℃~5℃; Step B: Neutralize the chloroacetic acid aqueous solution with a mass concentration of 44%~60% with anhydrous sodium carbonate to a pH of 6.5; Step C: Add the chloroacetic acid aqueous solution neutralized in step 2 to the tannic acid aqueous solution neutralized in step 1, heat to 60°C, add 30% sodium hydroxide aqueous solution dropwise to the reaction solution, keep the reaction at the temperature, test the pH until the pH reaches 7 and stop the reaction to obtain carboxylated tannic acid. Step 2: Prepare an aqueous solution of the sealing agent; The specific process of step 2 is as follows: Add octadecyl methacrylate hydrophobic monomer to sodium styrene sulfonate aqueous solution and stir for 1 hour to form a microemulsion. Add acrylamide, N-vinylpyrrolidone and sodium styrene sulfonate to the microemulsion and mix evenly. Add NaOH solution and adjust the pH value to 7. Add ammonium persulfate initiator to obtain polyacrylamide. Add carboxylated tannic acid and slow-release iron obtained in step 1 to polyacrylamide. Stir evenly with magnetic force and let stand for 2 hours to obtain the sealing agent aqueous solution. The mass ratio of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, sodium styrene sulfonate, and water is 0.5:5:20:5:5:64.

5. The initiator ammonium persulfate accounts for 1% of the sum of the solute in the sodium styrene sulfonate aqueous solution, the solute in the octadecyl methacrylate hydrophobic monomer, acrylamide, N-vinylpyrrolidone, and sodium styrene sulfonate; The mass ratio of polyacrylamide, carboxylated tannic acid, and slow-release iron is 10:0.03~0.06:0.005~0.01; The slow-release iron is ferric citrate or EDTA-Fe; Step 3: Prepare acid-triggered hydrogel blocking agent; The specific process of step 3 is as follows: add CO2 aqueous solution or acidic solution to the sealing agent aqueous solution obtained in step 2, control the pH value of the system to 1~6 by adding amount, let stand for 30 min, cross-link to form hydrogel, and obtain acid triggered hydrogel sealing agent.

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