A slow-swellable polyacrylamide gel and a method for its preparation

Abstract

The present application provides a kind of slowly swelling polyacrylamide gel and its preparation method, the slowly swelling polyacrylamide gel is obtained by the polymerization of acrylamide monomer, stable crosslinking agent, unstable degradable crosslinking agent under the action of initiator, has the characteristics of stable at room temperature, but the swelling ratio gradually increases under high temperature or alkaline conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymers, and particularly relates to a slowly swelling polyacrylamide gel and a preparation method thereof. BACKGROUND

[0002] With the deepening of oil exploitation in China, major oilfields have entered the high water-cut stage, and the non-uniformity of oil layers has intensified, so the demand for water plugging and profile control gradually shifts to the deep part of the reservoir, which puts forward new technical performance requirements for water plugging and profile control agents.

[0003] Acrylamide polymers and cross-linked polyacrylamide gels are the most important high polymer water plugging and profile control agents. This is because polyacrylamide has strong hydrophilicity and almost no oil affinity, so the polyacrylamide water plugging agent has good selectivity for water and oil. The cross-linked network of the polyacrylamide gel swells and blocks the pore in water, but does not swell in oil, thereby selectively reducing the water phase permeability.

[0004] At present, most cross-linked polyacrylamide water plugging agents quickly swell during preparation or pumping, and the volume has even reached the maximum swelling multiple, so it is difficult to penetrate into the deep part of the reservoir, and the plugging efficiency is reduced. Controlling the swelling rate of the gel, i.e., using a slowly swelling polyacrylamide gel, so that the gel reaches the maximum swelling multiple in the deep part of the reservoir, is the best solution to improve the plugging efficiency.

[0005] The slow swelling of the polyacrylamide gel is generally achieved by coating method, hydrophobic monomer method, and double cross-linking method. The coating method uses chemical or physical methods to form a coating layer outside the gel, and the coating layer degrades or breaks down with the change of the external environment or the water absorption of the gel, thereby releasing the internal gel, which further swells by absorbing water. The coating method is complex, has poor repeatability, and is not suitable for industrial application due to the limited materials. The hydrophobic monomer method uses the hydrophobicity of the acrylate monomer to make the initial swelling multiple of the gel low, and the hydrophilicity is improved after hydrolysis, so the swelling multiple increases rapidly. However, the hydrophobic monomer generally has poor water solubility, and needs a surfactant for micellar solubilization to copolymerize with the hydrophilic monomer. At the same time, since the hydrophobic monomer does not have cross-linking ability, it is difficult to control the initial swelling multiple. The double cross-linking method uses stable cross-linking agents and unstable cross-linking agents to prepare the gel. The unstable cross-linking agent degrades at changes in temperature and pH value, so the cross-linking density decreases, thereby the swelling of the gel increases. For example, Yuan Cheng uses a quaternary ammonium salt type unstable cross-linking agent to prepare a slowly swelling gel, which realizes the adjustment of the swelling time within a certain range. However, the unstable cross-linking agent has poor stability and is easy to hydrolyze during preparation, so the controllability of the swelling rate is poor.

[0006] At present, the polyacrylamide gel suitable for deep water plugging and profile control is still an important factor limiting the deep development of oil resources, and a controllable slowly swelling polyacrylamide gel needs to be developed and researched. SUMMARY

[0007] The purpose of this invention is to provide a slow-swelling polyacrylamide gel and its preparation method.

[0008] This invention is achieved through the following technical solution:

[0009] A slow-swelling polyacrylamide gel is prepared by the following steps:

[0010] a) Under nitrogen protection, L-lysine triisocyanate was added to the reactor and heated to 50-100°C. Hydroxy acrylate was added dropwise under stirring and reacted for 60-150 min. Then, hydroxy acid was added dropwise and reacted for 60-150 min. After cooling, an unstable crosslinking agent was obtained.

[0011] b) Dissolve acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and a stable crosslinking agent in water, adjust the pH to 7-8, add an unstable crosslinking agent and PVA aqueous solution, purge with nitrogen for 15-30 min, add an initiator dropwise, heat to 40-70℃ to initiate polymerization and keep warm for 6-24 h to obtain a slowly swelling polyacrylamide gel.

[0012] In this invention, the hydroxyacrylate is one or a combination of hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxyhexyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, and hydroxyhexyl methacrylate, preferably hydroxyethyl acrylate or hydroxyethyl methacrylate.

[0013] Preferably, the molar ratio of L-lysine triisocyanate to hydroxyacrylate is 1:2 to 2.2.

[0014] In this invention, the hydroxy acid is one or a combination of glycolic acid, 2-hydroxypropionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 3-hydroxypropanesulfonic acid, preferably 3-hydroxypropionic acid and 3-hydroxypropanesulfonic acid;

[0015] Preferably, the molar ratio of L-lysine triisocyanate to hydroxy acid is 1:0.8 to 1.

[0016] In this invention, the molar ratio of AM to AMPS is 1:0.1 to 0.5.

[0017] In this invention, the stable crosslinking agent is one or a combination of several of N,N-methylenebisacrylamide, N,N-propylenediacrylamide, N,N-tetramethylenediacrylamide, N,N-hexamethylenediacrylamide, and N,N-m-xylenediacrylamide, preferably N,N-methylenebisacrylamide;

[0018] Preferably, the mass ratio of the stable crosslinking agent to the acrylamide monomer (including AM and AMPS) is 0.1 to 1:1000.

[0019] In this invention, the mass ratio of the unstable crosslinking agent to the acrylamide monomer is 0.5 to 2:100.

[0020] In this invention, the mass ratio of PVA aqueous solution to acrylamide monomer is 1–5:5. Preferably, the PVA has a degree of polymerization of 500–1700, and the preferred concentration range is 5–20 wt%.

[0021] In this invention, the initiator is one or a combination of several of potassium persulfate, ammonium persulfate, azobisisobutyronitrile, azobisisobutyramidine hydrochloride, azodicyanovalerate, and azobisisopropylimidazoline, with potassium persulfate and azobisisobutyronitrile being preferred. The mass ratio of the initiator to the acrylamide monomer is 0.5–3:1000.

[0022] This invention introduces carboxylic acid or sulfonic acid, ester, and double bond structures into the crosslinking agent through a two-step reaction of isocyanate with hydroxyl groups. The carboxylic acid or sulfonic acid groups impart hydrophilicity, making the gel soluble in water and homopolymerizing with acrylamide, resulting in uniform crosslinking density. The double bonds provide crosslinking groups. The ester groups are relatively stable under normal conditions but hydrolyze under higher temperatures and alkaline conditions, causing a gradual decrease in the crosslinking density of the gel and an increase in swelling capacity. Simultaneously, the carboxylic acid groups obtained from hydrolysis further enhance the hydrophilicity of the gel, further improving its swelling capacity. Furthermore, the combined action of the unstable and stable crosslinking agents regulates the initial swelling ratio and can control the growth rate and final swelling ratio.

[0023] Compared with the prior art, the preparation method of the present invention has the following advantages: a slowly swelling gel can be prepared by copolymerizing an unstable crosslinking agent, a stable crosslinking agent, and an acryloyl monomer, and the swelling capacity and rate of the gel can be controlled, which is suitable for deep water shut-off and profile control in oil reservoirs. Detailed Implementation

[0024] The preparation method of the slow-swellable polyacrylamide gel of the present invention is further illustrated below with specific implementation examples. It should be understood that the embodiments given in this invention are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] Example 1:

[0026] a) Under nitrogen protection, 267g of L-lysine triisocyanate was added to the reactor, heated to 50°C, and 232g of hydroxyethyl acrylate was added dropwise with stirring for 150 min. Then, 140g of 3-hydroxypropanesulfonic acid was added dropwise for 120 min. After cooling, the unstable crosslinking agent I was obtained.

[0027] b) Dissolve 533g AM, 467g AMPS, and 0.5g N,N-methylenebisacrylamide in 1385g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 10g of unstable crosslinking agent I and 500g of 20% PVA aqueous solution (500 degree of polymerization). Purge with nitrogen for 30min. Add 0.5% potassium persulfate. Heat to 50℃ to initiate polymerization and keep warm for 24h to obtain gel 1.

[0028] Example 2:

[0029] a) Under nitrogen protection, 267g of L-lysine triisocyanate was added to the reactor, heated to 100°C, and 255g of hydroxyethyl acrylate was added dropwise with stirring for 60 min. Then, 126g of 3-hydroxypropanesulfonic acid was added dropwise for 60 min. After cooling, the unstable crosslinking agent II was obtained.

[0030] b) Dissolve 774g AM, 226g AMPS, and 1g N,N-methylenebisacrylamide in 1121g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 20g of unstable crosslinking agent II and 1000g of 5% PVA (degree of polymerization 1700) aqueous solution. Purge with nitrogen for 30min. Add 3g of azobisisobutyronitrile. Heat to 40℃ to initiate polymerization and keep warm for 6h to obtain gel 2.

[0031] Example 3:

[0032] a) Under nitrogen protection, 267g of L-lysine triisocyanate was added to the reactor, heated to 80°C, and 243g of hydroxyethyl acrylate was added dropwise with stirring for 150 min. Then, 86g of 3-hydroxypropionic acid was added dropwise for 150 min. After cooling, the unstable crosslinking agent III was obtained.

[0033] b) Dissolve 410g AM, 590g AMPS, and 0.1g N,N-methylenebisacrylamide in 1279g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 5g of unstable crosslinking agent III and 200g of 20% PVA (500 degree of polymerization) aqueous solution. Purge with nitrogen for 30min. Add 2g of potassium persulfate. Heat to 70℃ to initiate polymerization and keep warm for 12h to obtain gel 3.

[0034] Example 4:

[0035] a) Under nitrogen protection, 267g of L-lysine triisocyanate was added to the reactor, heated to 80°C, and 260g of hydroxyethyl methacrylate was added dropwise with stirring and reacted for 150min. Then, 90g of 3-hydroxypropionic acid was added dropwise and reacted for 150min. After cooling, the unstable crosslinking agent IV was obtained.

[0036] b) Dissolve 533g AM, 467g AMPS, and 0.5g N,N-methylenebisacrylamide in 1218g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 10g of unstable crosslinking agent IV and 500g of 10% PVA (700 degree of polymerization) aqueous solution. Purge with nitrogen for 30min. Add 2g of potassium persulfate. Heat to 50℃ to initiate polymerization and keep warm for 12h to obtain gel 4.

[0037] Example 5:

[0038] Dissolve 410g AM, 590g AMPS, and 0.1g N,N-methylenebisacrylamide in 1179g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 20g of unstable crosslinking agent III and 500g of 20% PVA (500 degree of polymerization) aqueous solution. Purge with nitrogen for 30min. Add 2g of potassium persulfate. Heat to 50℃ to initiate polymerization and keep warm for 12h to obtain gel 5.

[0039] Comparative Example 1:

[0040] 410g AM, 590g AMPS, and 0.1g N,N-methylenebisacrylamide were dissolved in 1179g of water. The pH was gradually adjusted to 7-8 by adding 10wt% sodium hydroxide aqueous solution. 3g of unstable crosslinking agent III and 500g of 20% PVA (500 degree of polymerization) aqueous solution were added. Nitrogen was purged for 30min. 2g of potassium persulfate was added. The mixture was heated to 50℃ to initiate polymerization and kept at that temperature for 12h to obtain comparative gel 1.

[0041] Comparative Example 2:

[0042] 410g AM, 590g AMPS, and 0.1g N,N-methylenebisacrylamide were dissolved in 1179g water. The pH was gradually adjusted to 7-8 by adding 10wt% sodium hydroxide aqueous solution. 25g of unstable crosslinking agent III and 500g of 20% PVA (degree of polymerization) aqueous solution were added. Nitrogen was purged for 30min. 2g of potassium persulfate was added. The mixture was heated to 50℃ to initiate polymerization and kept at that temperature for 12h to obtain comparative gel 2.

[0043] Comparative Example 3:

[0044] Dissolve 410g AM, 590g AMPS, and 0.1g N,N-methylenebisacrylamide in 1179g of water. Gradually add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7-8. Add 500g of 20% PVA (500 degree of polymerization) aqueous solution and purge with nitrogen for 30min. Add 2g of potassium persulfate, heat to 50℃ to initiate polymerization, and keep warm for 12h to obtain comparative gel 3.

[0045] The swelling ratio test results of the above 8 groups of gels at different times are shown in Table 1 below.

[0046] Table 1. Results of swelling ratio tests for Examples 1-5 and the comparative examples.

[0047]

[0048]

[0049] Swelling ratio test method: Weigh a certain mass of gel block and immerse it in the solution. After a period of time, remove the liquid adhering to the surface with filter paper and weigh the mass again. Calculate the swelling ratio according to the formula: Swelling ratio = (mass - initial mass × solid content) / (initial mass × solid content).

[0050] Examples 1-5 show that by adjusting the dosage of stable and unstable crosslinking agents, the time to reach the final swelling ratio can be achieved within 1 to 3 weeks. The unstable crosslinking agent slightly improves the swelling capacity after hydrolysis. Comparative Example 1 shows that an excessively low dosage of unstable crosslinking agent results in an excessively fast swelling rate. Comparative Example 2 shows that an excessively high dosage of unstable crosslinking agent results in an excessively slow swelling rate, requiring at least 5 weeks to reach the final swelling ratio. Comparative Example 3 shows that without the addition of the agent, the swelling reaches the final ratio rapidly, lacking a slow swelling capacity. The swelling reaches the final ratio during ground operations, which is not conducive to deep penetration into the pores.

Claims

1. A method for preparing a slowly swelling polyacrylamide gel, comprising: a) L-lysine triisocyanate was added to a reactor, heated, and hydroxy acrylate was slowly added to react. Then, hydroxy acid was slowly added to react, and the mixture was cooled to obtain an unstable crosslinking agent. b) Acrylamide AM, 2-acrylamide-2-methylpropanesulfonic acid AMPS, and a stable crosslinking agent are dissolved in water, the pH is adjusted to 7-8, an unstable crosslinking agent and PVA aqueous solution are added, and an initiator is added dropwise to initiate polymerization, thereby obtaining a slowly swellable polyacrylamide gel; wherein, the molar ratio of AM to AMPS is 1:0.1-0.5, the mass ratio of the stable crosslinking agent to the acrylamide monomer is 0.1-1:1000, the mass ratio of the unstable crosslinking agent to the acrylamide monomer is 0.5-2:100, and the acrylamide monomer is the sum of AM and AMPS.

2. The method according to claim 1, wherein, The hydroxyacrylate is one or more of hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxyhexyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, and hydroxyhexyl methacrylate.

3. The method according to claim 1 or 2, wherein, The molar ratio of L-lysine triisocyanate to hydroxyacrylate is 1:2 to 2.

2.

4. The method according to claim 1, wherein, The hydroxy acid is one or more of glycolic acid, 2-hydroxypropionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, and 3-hydroxypropanesulfonic acid.

5. The method according to claim 1 or 4, wherein, The molar ratio of L-lysine triisocyanate to hydroxy acid is 1:0.8-1.

6. The method according to claim 1, wherein, The stable crosslinking agent is one or more of N,N-methylenebisacrylamide, N,N-propylenediacrylamide, N,N-tetramethylenediacrylamide, N,N-hexamethylenediacrylamide, and N,N-m-xylenediacrylamide.

7. The method according to claim 1, wherein, The mass ratio of PVA aqueous solution to acrylamide monomer is 1–5:5; the degree of polymerization of PVA is 500–1700; and the concentration of PVA aqueous solution is 5–20 wt%.

8. The method according to claim 1, wherein, The initiator is one or more of potassium persulfate, ammonium persulfate, azobisisobutyronitrile, azobisisobutylamidine hydrochloride, azobiscyanopentanoic acid, and azobisisopropylimidazoline.

9. The method according to claim 8, wherein, The mass ratio of initiator to acrylamide monomer is 0.5–3:1000.

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