Nanocomposite hydrogel for repairing microcracks in cement ring, self-repairing cement and preparation method thereof

Abstract

A nanocomposite hydrogel for repairing microcracks in cement ring, self-healing cement and preparation method, which relate to the technical field of functional materials, solve the problem of poor plugging effect of existing cementing means, and can be applied to the oil and gas well completion construction process in the field of petrochemical industry. Preparation method of hydrogel: slowly add a certain amount of nanomaterial into deionized water, stir to obtain a uniform mixture; add at least two monomers of anionic monomers, functional monomers that produce anions after hydrolysis, and functional monomers that produce cationic groups after hydrolysis in the presence of acidic gases to the mixture, and then add a cross-linking agent and an initiator, and react to obtain a nanocomposite hydrogel. Preparation of self-healing cement: dry the nanocomposite hydrogel for repairing microcracks in cement ring, crush it into gel powder, add it to cement slurry, stir to obtain a uniform mixture; dry the mixture to obtain self-healing cement.

Description

Technical Field

[0001] The invention relates to the technical field of functional materials, and in particular to a nano-composite hydrogel for repairing micro-cracks in a cement ring, a self-repairing cement and a preparation method thereof. Background Art

[0002] Today, climate change has become a common problem faced by mankind. With the further increase in global greenhouse gas emissions represented by carbon dioxide, it has posed a huge threat to the ecosystem. Therefore, how to effectively solve the problem of carbon dioxide emissions has aroused widespread concern. Among them, carbon dioxide capture, utilization and storage (CCUS) has become one of the indispensable key technologies. Using CCUS technology to store CO2 in underground formations is an effective measure to reduce carbon emissions. However, in the process of oil and gas development, due to the inherent brittleness of cement materials, microcracks will inevitably form when internal stress and external loads are applied. Over time, the integrity of the interlayer is gradually destroyed, resulting in CO2 leakage. In addition, the annular air channeling formed not only makes it impossible for subsequent drilling operations to proceed normally, but in severe cases, it will also result in the scrapping of the entire well. Therefore, CCUS technology puts higher requirements on cementing quality.

[0003] In addition, associated petroleum gases such as H2S and CO2 that appear during coalbed methane extraction and mine construction have always been considered by-products of oil and gas extraction. Their presence will accelerate cement erosion, pose a great threat to underground operations, and endanger construction safety.

[0004] At present, there are two main cementing methods. One is to improve the toughness of cement by chemical modification or physical filler based on the inherent properties of cement itself, but this method can only guarantee the integrity of cement stone in the early stage. Once microcracks appear in cement stone during actual production and use, it will no longer be effectively sealed. The second is to add repair agents that can respond to the external environment to the oil well cement slurry, such as adding conventional water-absorbing polymers, but this material lacks good response characteristics to natural gas and cannot achieve directional self-repair of cracks. At the same time, the large amount of small molecule salts in the underground have serious damage to the mechanical properties and response characteristics of the material, affecting the sealing effect. Summary of the invention

[0005] In order to solve the problem of poor plugging effect of existing cementing means, the present invention proposes a nano-composite hydrogel for repairing micro-cracks in cement ring, self-healing cement and a preparation method.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a nanocomposite hydrogel for repairing microcracks in a cement ring comprises the following steps:

[0008] S1. Slowly add a certain amount of nanomaterial into deionized water and stir to obtain a uniform mixture;

[0009] S2, adding at least two monomers of anionic monomers, functional monomers that generate anions after hydrolysis, and functional monomers that generate cationic groups after hydrolysis in the presence of acidic gas to the mixture of step S1, and then adding a crosslinking agent and an initiator, and obtaining a nanocomposite hydrogel after reaction.

[0010] Preferably, the nanomaterial is graphene oxide, carbon nanotubes, montmorillonite, kaolinite, diatomaceous earth or laponite;

[0011] The anionic monomer is acrylic acid, methacrylic acid, dimethacrylic acid, vinyl sulfonic acid, methyl vinyl sulfonic acid, sodium styrene sulfonate, alkyl olefinic acid or AMPS;

[0012] The functional monomers that generate anions after hydrolysis are acrylamide, dimethylacrylamide, acrylonitrile, acrylates or methacrylates, etc.;

[0013] The functional monomer that is hydrolyzed in the presence of acidic gas to generate a cationic group is dialkylaminoalkyl methacrylate, dialkylaminoalkyl acrylate or N-vinyl alkylamide.

[0014] Preferably, the crosslinking agent is N,N′-methylenebisacrylamide, and the initiator is ammonium persulfate, V-50, VA-044 or a photoinitiator.

[0015] Preferably, the mass ratio of the anionic monomer, the functional monomer that generates anions after hydrolysis, and the functional monomer that generates cationic groups after hydrolysis in the presence of acidic gas is 1-8:1-4:0-4;

[0016] The amount of the nano material is 1% to 30% of the total mass of the anion monomer, the functional monomer that generates anions after hydrolysis, and the functional monomer that generates cationic groups after hydrolysis in the presence of acidic gas.

[0017] Preferably, the reaction in step S2 is carried out at a temperature of 30° C. to 60° C. or under ultraviolet irradiation, and the reaction time is 4 h to 24 h.

[0018] A nano composite hydrogel for repairing micro cracks in cement ring is prepared by the above preparation method.

[0019] A self-repairing cement comprises the cement ring microcrack repairing nanocomposite hydrogel as described above.

[0020] A method for preparing the self-healing cement as described above comprises the following steps:

[0021] Step 1: drying the cement ring micro-crack repair nanocomposite hydrogel, crushing it into gel powder, adding it into cement slurry, and stirring to obtain a uniform mixture;

[0022] Step 2: Dry the mixture to obtain self-healing cement.

[0023] Preferably, in step 1, the mass of the gel powder is less than 5% of the mass of cement, and the water-cement ratio of the cement slurry is 0.40-0.70.

[0024] Preferably, the drying temperature is 50°C to 80°C.

[0025] Compared with the prior art, the specific beneficial effects of the present invention are:

[0026] 1. The nanocomposite hydrogel provided by the present invention can realize its own amphoteric polyelectrolyte structure design under the external stimulation of cement curing and underground geological conditions (alkaline environment of cement slurry - induction of underground acidic gas), and some functional groups can generate anionic groups (negative charge) through hydrolysis or neutralization, and the gelling particles in the microcracks of cement stone further react when contacting the underground acidic gas to generate cationic groups. The reverse polyelectrolyte effect can be used to improve the salt resistance of the material, ensure the swelling performance and mechanical properties of the gelling material, and improve the plugging and repair effect;

[0027] 2. The monomers for preparing the nanocomposite hydrogel provided by the present invention can be selected from functional units containing acrylonitrile and N-vinyl alkylamide. When the above functional units are selected at the same time, the five-membered cyclic amidine group produced by high-temperature hydrolysis can further improve the thermal stability, mechanical properties and salt resistance of the gelling material;

[0028] 3. The preparation method provided by the present invention has a simple process and the reaction raw materials are easily available; the self-healing cement prepared by the present invention can be triggered to self-repair by toxic acidic gases such as H2S and CO2 generated during mine exploitation and construction, and can adapt to the complex underground application environment of oil extraction. It not only provides a solution to the CO2 emission problem, but also has important significance for ensuring cementing safety and improving completion quality.

[0029] The present invention can be applied to the oil and gas well completion construction process in the petrochemical field to improve the wellbore integrity and achieve the blocking and sealing of toxic acidic gases in the underground mineral mining process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the infrared spectrum of the hydrogel prepared in Example 1;

[0031] Figure 2 is the infrared spectrum of the hydrogel after hydrolysis in CO2 in Example 1;

[0032] Figure 3 is an infrared spectrum of the hydrogel after hydrolysis in an alkaline solution in Example 1;

[0033] Figure 4 Schematic diagram of the test results of the mechanical properties of the hydrogels in Examples 1 to 4;

[0034] Figure 5 This is a schematic diagram of the sealing pressure test instrument; DETAILED DESCRIPTION

[0035] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as a limitation to the present invention.

[0036] Example 1.

[0037] 0.4 g of montmorillonite was added to 16 g of deionized water and stirred for 30 min to obtain a uniform mixture. Then, 2.6 g of monomers acrylamide, 0.6 g of acrylonitrile, 0.8 g of N-vinyl formamide and 0.01 g of N,N′-methylenebisacrylamide were added. After ultrasonic treatment for 10 min, a uniform pre-solution was obtained. Finally, under nitrogen protection, 0.01 g of initiator VA-044 was added. The obtained pre-solution was transferred to a manual mold made of two glass plates and silicone rubber with a syringe, and reacted at 50 °C for 24 h to obtain a nanocomposite hydrogel.

[0038] Example 2.

[0039] In the preparation process of this embodiment, no montmorillonite is added, and the rest is the same as that of embodiment 1.

[0040] Example 3.

[0041] The amount of montmorillonite added during the preparation process of this example is 0.2 g, and the rest is the same as that of Example 1.

[0042] Example 4.

[0043] The amount of montmorillonite added during the preparation process of this embodiment is 0.6 g, and the rest is the same as that of Example 1.

[0044] Example 5.

[0045] 1000 g of cement was mixed with 440 g of water to obtain cement slurry, and then 50 g of the dry powder of the hydrogel obtained in Example 1 was added to the cement slurry. After stirring with a mixer, the mixed cement slurry was poured into a mold, cured at 70° C., and taken out after 24 hours to obtain cement stone.

[0046] Example 6.

[0047] The amount of dry powder of the hydrogel added in this example is 0 g, and the rest is the same as that in Example 5.

[0048] Example 7.

[0049] The amount of dry powder of the hydrogel added in this example is 10 g, and the rest is the same as that in Example 5.

[0050] Example 8.

[0051] The amount of dry powder of the hydrogel added in this example is 30 g, and the rest is the same as that in Example 5.

[0052] Example 9.

[0053] 0.4 g of diatomaceous earth was added to 16 g of deionized water and stirred for 30 min to obtain a uniform mixture. Then, 2.8 g of monomer acrylamide, 1.2 g of dimethylaminoethyl methacrylate and 0.01 g of N,N′-methylenebisacrylamide were added. After ultrasonic treatment for 10 min, a uniform pre-solution was obtained. Finally, under nitrogen protection, 0.01 g of initiator VA-044 was added. The obtained pre-solution was transferred to a manual mold made of two glass plates and silicone rubber with a syringe, and reacted at 50°C for 24 h to obtain a nanocomposite hydrogel.

[0054] 1000 g of cement was mixed with 440 g of water to obtain cement slurry, and then 50 g of dry powder of nanocomposite hydrogel was added to the cement slurry. After stirring with a mixer, the mixed cement slurry was poured into a mold, cured at 70° C., and taken out after 24 hours to obtain cement stone.

[0055] Example 10.

[0056] 0.6 g of carbon nanotubes were added to 16 g of deionized water, and stirred for 20 min to obtain a uniform mixture. Then, 1.8 g of acrylonitrile, 0.9 g of sodium styrene sulfonate, 1.3 g of N-methyl-N-vinyl acetamide and 0.01 g of N,N′-methylenebisacrylamide were added. After ultrasonic treatment for 10 min, a uniform pre-solution was obtained. Finally, 0.01 g of initiator V-50 was added under nitrogen protection. The obtained pre-solution was transferred to a manual mold made of two glass plates and silicone rubber with a syringe, and reacted at 50 ° C for 24 h to obtain a nanocomposite hydrogel.

[0057] 1000 g of cement was mixed with 440 g of water to obtain cement slurry, and then 50 g of dry powder of nanocomposite hydrogel was added to the cement slurry. After stirring with a mixer, the mixed cement slurry was poured into a mold, cured at 70° C., and taken out after 24 hours to obtain cement stone.

[0058] Example 11.

[0059] 0.2 g of graphene oxide was added to 16 g of deionized water and stirred for 30 min to obtain a uniform mixture, followed by the addition of 1.2 g of dimethylacrylamide, 0.3 g of ethyl acrylate, 1.5 g of 2-(tert-butylamino)ethyl methacrylate and 0.01 g of N,N′-methylenebisacrylamide, and ultrasonication for 10 min to obtain a uniform pre-solution. Finally, 0.01 g of initiator V-50 was added under nitrogen protection, and the obtained pre-solution was transferred to a manual mold made of two glass plates and silicone rubber with a syringe, and reacted at 50°C for 24 h to obtain a nanocomposite hydrogel.

[0060] 1000 g of cement was mixed with 440 g of water to obtain cement slurry, and then 50 g of dry powder of nanocomposite hydrogel was added to the cement slurry. After stirring with a mixer, the mixed cement slurry was poured into a mold, cured at 70° C., and taken out after 24 hours to obtain cement stone.

[0061] Effect example 1.

[0062] The chemical structure changes of the hydrogel in different application environments were characterized. The hydrogel in Example 1 was placed in acidic gas CO2 and alkaline solution (simulating cement environment) for hydrolysis for 10 hours, dried and crushed, and then analyzed by infrared spectroscopy. The infrared spectra of the original hydrogel in Example 1, the hydrogel after hydrolysis in CO2, and the hydrogel after hydrolysis in alkaline solution are shown in Figure 1. Figures 1 to 3 As shown in the figure, it can be clearly observed that compared with the original hydrogel, under alkaline conditions, AM in the hydrogel network is hydrolyzed to produce carboxyl groups; under CO2 conditions, AN and NVF in the hydrogel network are hydrolyzed to produce vinylamine and amidine groups with primary amine groups.

[0063] Effect example 2.

[0064] The hydrogels obtained in Examples 1 to 4 were made into dumbbell-shaped specimens and subjected to mechanical property tests using a tensile machine. The test results are as follows: Figure 4 As shown, the results show that the mechanical properties of the obtained nanocomposite hydrogels are enhanced with the increase of montmorillonite content.

[0065] Effect example 3.

[0066] The healing performance of the cement stone obtained in Example 5 was tested. The intact cement stone was artificially fractured to create cracks, and then cured under CO2 gas with a relative humidity of 80% for 10 h, 30 h, and 60 h, respectively. The cracks on the surface of the samples before and after curing were observed under a microscope. By comparison, it can be found that the width of the initial cracks is about 50 μm. The cracks of the cement stone cured in the CO2 environment can all heal themselves. After 3 days of self-repair, the cracks of the cement stone are almost completely filled with the expanded hydrogel, and the hydrogel cracks become thinner and unclear.

[0067] Put the cement stone before and after curing into the testing instrument to test the sealing pressure. See the schematic diagram of the testing instrument for details. Figure 5 As shown in Table 1, as the pressure gradually increases from 0Pa, gas is continuously pumped into the test instrument. When the gas begins to flow out of the cracks and the pressure gauge indicates a return to 0Pa, the maximum sealing pressure is recorded as the breakthrough pressure. The test results are shown in Table 1. It can be seen that the breakthrough pressure of the cement stone before curing is 0MPa, while the gas penetration pressure of the cement stone after curing can reach 3.2MPa, that is, as the curing time increases, the breakthrough pressure of the cement stone increases.

[0068] Table 1

[0069] Maintenance time 0h 10h 30h 60h Breakthrough pressure 0.1MPa 1.1μm 2.6MPa 3.2MPa

[0070] Effect example 4.

[0071] The cement pastes obtained in Examples 5-8 were subjected to a healing performance test, and the results of the healing performance test are shown in Table 2. It can be seen that as the hydrogel content in the cement paste increases, the healing ability of the cement paste cracks increases.

[0072] Table 2

[0073] Mixing ratio 0％ 1％ 3％ 5％ Width before healing 55μm 53μm 58μm 51μm Width after healing 50μm 26μm 18μm 4μm Healing efficiency 9％ 51％ 69％ 92％

[0074] Effect example 5.

[0075] The healing performance test of the cement paste obtained in Example 5 was carried out. Cracks were formed by artificial fracturing and the cement paste was placed in H2S gas with a relative humidity of 80% for 60 hours. The test results are shown in Table 3.

[0076] Effect Example 6.

[0077] The healing performance of the cement pastes obtained in Examples 9 to 11 was tested respectively. The intact cement pastes were artificially fractured to produce cracks, and then placed in a CO2 gas with a relative humidity of 80% for curing for 60 hours. The test results are shown in Table 3.

[0078] Table 3

[0079]

[0080] Obviously, the above embodiments are only preferred examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A self-repairing cement, characterized in that: Contains nanocomposite hydrogel for repairing microcracks in cement sheath; The cement ring microcrack repair nanocomposite hydrogel is prepared by the following method: S1. Slowly add a certain amount of nanomaterial into deionized water and stir to obtain a uniform mixture; S2, adding anionic monomers, functional monomers that generate anions after hydrolysis, and functional monomers that generate cationic groups after hydrolysis in the presence of acidic gas to the mixture in step S1, and then adding a crosslinking agent and an initiator, and obtaining a nanocomposite hydrogel after reaction; The functional monomer that generates anions after hydrolysis is acrylonitrile; The functional monomer that is hydrolyzed by acidic gas to generate cationic groups is N-vinyl alkylamide; The mass usage ratio of the anionic monomer, the functional monomer that generates anions after hydrolysis and the functional monomer that generates cationic groups after hydrolysis in the presence of acidic gas is 1-8:1-4:0-4, wherein the usage of the functional monomer that generates cationic groups after hydrolysis in the presence of acidic gas is not 0.

2. The self-repairing cement according to claim 1, characterized in that: The nanomaterial is graphene oxide, carbon nanotubes, montmorillonite, kaolinite, diatomaceous earth or laponite; The anionic monomer is acrylic acid, methacrylic acid, vinyl sulfonic acid, methyl vinyl sulfonic acid, sodium styrene sulfonate, alkyl acrylate or AMPS.

3. The self-repairing cement according to claim 1, characterized in that: The crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate, V-50, VA-044 or a photoinitiator.

4. The self-repairing cement according to claim 1, characterized in that: The amount of the nano material used is 1%-30% of the total mass of the anion monomer, the functional monomer that generates anions after hydrolysis, and the functional monomer that generates cationic groups after hydrolysis in the presence of acidic gas.

5. The self-repairing cement according to claim 1, characterized in that: The reaction in step S2 is carried out at a temperature of 30° C. to 60° C. or under ultraviolet irradiation, and the reaction time is 4 h to 24 h.

6. A method for preparing the self-healing cement according to any one of claims 1 to 5, characterized in that: The steps include: Step 1, mixing cement and water to obtain cement slurry, drying the cement ring micro-crack repair nanocomposite hydrogel, crushing it into gel powder, adding it to the cement slurry, and stirring to obtain a uniform mixture; Step 2: Dry the mixture to obtain self-healing cement.

7. The method for preparing the self-repairing cement according to claim 6, characterized in that: In step 1, the mass of the gel powder is less than 5% of the mass of cement, and the water-cement ratio of the cement slurry is 0.40-0.

70.

8. The method for preparing the self-repairing cement according to claim 6, characterized in that: The temperature of the drying process is 50°C-80°C.

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