Cement-based self-healing material, and preparation method and application thereof

Abstract

The present application relates to a kind of cement-based self-repairing material and its preparation method and application, belong to oilfield cementing technical field.The preparation method of cement-based self-repairing material of the present application includes the following steps: mixture mainly by polymeric monomer, crosslinking agent, initiator and solvent is placed at polymerization temperature, make polymeric monomer, crosslinking agent carry out polymerization under the action of initiator;The polymeric monomer includes diacetone acrylamide and alkenyl quaternary ammonium salt, and the alkenyl quaternary ammonium salt contains more than two olefinic unsaturated double bond.The preparation method of cement-based self-repairing material of the present application, simple process, the cement-based self-repairing material prepared has good alkali resistance, hydrolysis resistance, has good stability in high-temperature alkaline environment of cement slurry, and under the action of calcium ion, will occur decrosslinking reaction, improve the water absorption of material, realize the water self-repairing of cement stone microcrack.

Description

TECHNICAL FIELD

[0001] The present application relates to a cement-based self-healing material and a preparation method and application thereof, and belongs to the technical field of oilfield cementing. BACKGROUND

[0002] Cementing operation is the process of injecting cement slurry into the annular space between the wellbore and the casing or between two continuous casing strings. The hardened cement stone can support the well wall and casing, seal the formation, prevent casing corrosion, control abnormal pore pressure, etc. Complete and durable interlayer isolation is the primary goal of cementing operation. However, the presence of filter cake during cementing of oil and gas wells, changes in downhole temperature and pressure, and cement volume shrinkage can cause microannulus between the two interfaces, forming a channel for downhole formation fluid migration. If the microannulus cannot be repaired in time, the interlayer isolation will fail, and then annular channeling will occur. Annular channeling will increase the opportunity for corrosive fluids in the formation to erode the casing, shorten the production life of the oil well, affect the safe, efficient and green production of oil and gas wells, and directly cause the decline of cementing quality and oil and gas well productivity, serious waste of oil and gas resources, and difficulty in later operations.

[0003] In recent years, a new technology of self-healing cement for solving the micro-cracks in the cement sheath of oil and gas wells has been developed, aiming to make the cement stone have self-repairing function to provide long-term interlayer isolation performance. Its greatest advantage is that it can improve the durability of the cement sheath without interrupting the normal production of oil and gas wells. The most important design idea of the self-healing technology of oil well cement is to add self-healing materials to the cement slurry, which are activated under certain conditions to generate new substances or provide internal extrusion stress to close the micro-cracks.

[0004] The responsive swelling self-healing technology is to pre-add self-healing materials (such as swellable rubber particles) which have a sensitive response to oil, gas, water and other substances penetrating into micro-cracks in the oil well cement slurry. When the cement sheath is damaged to produce micro-cracks, the pre-installed self-healing materials respond to the stimulus of the penetrating substances to produce swelling, thereby plugging the oil and gas migration channel. Its advantages are short response time and obvious effect. However, at present, the responsive swelling self-healing technology for water-swellable materials is not mature, and there is no industrialized product. The biggest difficulty of the water-swellable self-healing material is that the material will absorb the water in the cement slurry during the mixing process of the cement slurry, affecting the pumpability of the cement slurry. However, there have been a large number of research reports on cement-based self-healing materials. For example, Chinese patent document CN115448656A discloses a poly-Ca ion superabsorbent fiber cement-based self-healing material and a preparation method. The poly-Ca ion superabsorbent fiber cement-based self-healing material is composed of the following components in parts by mass: cement 500-1000 parts, water 230-460 parts, and poly-Ca ion superabsorbent fiber 2-6 parts. The poly-Ca ion superabsorbent fiber is a resin obtained by mixing and polymerizing acrylic acid and acrylate under the action of a crosslinking agent with a superabsorbent fiber. The obtained resin is hydrolyzed with alkali. The cement-based self-healing material has strong ability to adsorb calcium ions. After adsorbing a large amount of calcium ions, the high concentration of calcium ions accelerates the reaction with water and carbon dioxide in the air to generate calcium carbonate, thereby reinforcing the cracks and maintaining the integrity of the fiber, and achieving good self-healing effect in the cement-based material. The patent document uses poly-Ca ion superabsorbent fiber as the self-healing material, but the poly-Ca ion superabsorbent fiber is difficult to disperse uniformly in the cement slurry, and improper preparation process can result in poor self-healing effect, leading to unstable product performance. In addition, the preparation process of poly-Ca ion superabsorbent fiber is complex, resulting in high preparation cost, which is not conducive to large-scale industrialization. In addition, synthetic resin materials with good dispersibility in cement slurry can also be used, for example, Chinese patent document CN107759725B uses dimethylaminoethyl methacrylate and acryloyloxyethyl trimethylammonium chloride as pH-sensitive functional monomers to prepare a pH-sensitive water-absorbing resin suitable for oil well cement slurry. However, dimethylaminoethyl methacrylate and acryloyloxyethyl trimethylammonium chloride both contain ester groups, which can cause the ester groups in the synthesized resin to hydrolyze to carboxyl groups under high temperature and alkaline conditions in the cement slurry. The generated carboxyl groups can cause the resin to lose pH sensitivity, and at the same time, can cause the cement slurry to be super-retarded, so the pH-sensitive water-absorbing resin disclosed in the patent document cannot be used in high temperature and high alkaline environment. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a cement-based self-healing material, which can solve the problem of poor stability of the currently prepared synthetic resin cement-based self-healing material under high temperature and high alkaline conditions.

[0006] The second object of the present application is to provide a cement-based self-repairing material, which can solve the problem that the synthetic resin cement-based self-repairing material cannot be used in high-temperature and high-alkaline environment.

[0007] The third object of the present application is to provide an application of the cement-based self-repairing material in well cementing, which can solve the problem that the synthetic resin cement-based self-repairing material used in the field of well cementing has poor alkali resistance.

[0008] To achieve the above object, the technical scheme adopted by the preparation method of the cement-based self-repairing material of the present application is as follows:

[0009] The preparation method of the cement-based self-repairing material comprises the following steps: placing a mixture mainly composed of polymerized monomers, a crosslinking agent, an initiator and a solvent at a polymerization temperature to make the polymerized monomers and the crosslinking agent undergo polymerization reaction under the action of the initiator; the polymerized monomers comprise diacetone acrylamide and an alkenyl quaternary ammonium salt, the alkenyl quaternary ammonium salt contains two or more alkenyl unsaturated double bonds, and the mass ratio of the diacetone acrylamide to the alkenyl quaternary ammonium salt is 1:(4-6); the crosslinking agent is N,N'-methylenebisacrylamide; and the mass of the crosslinking agent is 0.3%-0.7% of the mass of the polymerized monomers.

[0010] The preparation method of the cement-based self-repairing material of the present application has a simple process, and the prepared cement-based self-repairing material has good alkali resistance and hydrolysis resistance, good stability in a high-temperature and high-alkaline environment of cement slurry, and, under the action of calcium ions, will undergo de-crosslinking reaction to improve the water absorption multiple of the material and realize the water-induced self-repairing of cement stone micro-cracks. The alkenyl quaternary ammonium salt is a cationic monomer and a pH-sensitive functional monomer, which can reduce the water absorption multiple of the material in the alkaline environment of the cement slurry, reduce the influence on the performance of the cement slurry, and ensure the safety of well cementing construction; the diacetone acrylamide molecule contains a methyl group near the amide group, which provides steric hindrance effect and improves the alkali resistance and hydrolysis resistance of the material, thereby ensuring the stability of the material in the high-temperature and high-alkaline environment of the cement slurry. In addition, experimental results show that, when the diacetone acrylamide participates in the polymerization reaction, the ketone carbonyl group can undergo crosslinking reaction to reduce the water absorption multiple of the material, and when the prepared cement-based self-repairing material encounters a calcium ion environment, the ketone carbonyl group can undergo de-crosslinking reaction to further improve the water absorption multiple of the material, which is conducive to the water-induced expansion for repairing cement stone cracks or pores in the later period.

[0011] Preferably, the alkenyl quaternary ammonium salt is dimethyldiallylammonium chloride, diethyldiallylammonium chloride, methylethyldiallylammonium chloride, dimethyldiallylammonium bromide, diethyldiallylammonium bromide, or methylethyldiallylammonium bromide.

[0012] Preferably, the initiator comprises a main initiator and an auxiliary initiator. The main initiator functions to initiate the polymerization reaction of the polymerization monomer and the crosslinking agent at the polymerization temperature, and the auxiliary initiator functions to improve the initiation effect of the initiator, reduce the amount of the initiator, and ensure that the polymerization reaction can be carried out completely.

[0013] Preferably, the main initiator is a persulfate salt, and the auxiliary initiator is a tertiary amine compound.

[0014] The amount of the initiator affects the ease of the polymerization reaction, the speed of the polymerization reaction, and the molecular weight and distribution of the polymerization product. In consideration of the time of the polymerization reaction and the molecular weight of the polymerization product, preferably, the mass of the main initiator is 0.4% to 0.8% of the mass of the polymerization monomer. Preferably, the mass of the auxiliary initiator is 15% to 30% of the mass of the initiator.

[0015] When selecting the solvent, in order to ensure that the components in the mixture can be mixed uniformly, the selected solvent needs to be able to dissolve the polymerization monomer, the crosslinking agent, and the initiator. In order to reduce costs and make the production process green and environmentally friendly, preferably, the solvent is water.

[0016] The amount of the solvent affects the concentration of the polymerization monomer and the crosslinking agent, and thus affects the ease of the polymerization reaction and the time of the polymerization reaction. In order to save time and avoid the adverse effects of too fast reaction, preferably, the mass of the polymerization monomer is 5% to 13.5% of the mass of the solvent. For example, the mass of the polymerization monomer is 5.9% to 13.3% of the mass of the solvent.

[0017] When the solvent is water, in order to ensure that the initiator can be uniformly dispersed in the solvent, and thus better initiate the polymerization reaction and make the distribution of the groups in the reaction product more uniform, preferably, the main initiator is a water-soluble persulfate salt, and the auxiliary initiator is a water-soluble tertiary amine compound. For example, the water-soluble persulfate salt is selected from one or any combination of ammonium persulfate, sodium persulfate, and potassium persulfate. For example, the water-soluble tertiary amine compound is tetramethylethylenediamine and / or tetramethylpropylenediamine.

[0018] The polymerization temperature can be selected according to the type of the initiator. In actual operation, the matching relationship between the initiator and the polymerization temperature in the prior art can be referred to. When the main initiator is a persulfate salt and the auxiliary initiator is a tertiary amine compound, preferably, the polymerization temperature is room temperature. Carrying out the polymerization reaction at room temperature can reduce production costs.

[0019] In order to ensure that the polymerization monomer and the crosslinking agent can be fully polymerized, preferably, the time of the polymerization reaction is not less than 7h.

[0020] Preferably, the mixture is prepared by a method comprising the following steps: adding the polymerization monomer and the crosslinking agent into a solvent, mixing uniformly, then adding the initiator, mixing uniformly again, to obtain the mixture.

[0021] After the polymerization reaction is completed, the product of the polymerization reaction is dispersed in the solvent, which can be used directly or after drying and then used, and after drying, the product can be crushed to form a powder product with a suitable particle size according to the specific use environment. In order to facilitate transportation, weighing and storage, preferably, the preparation method of the cement-based self-healing material further comprises the following steps: drying and crushing the system after the polymerization reaction.

[0022] The particle size after crushing can be determined according to the specific use environment. Generally, the particle size of the cement-based self-healing material is in the range of 150-270 μm. If the particle size of the cement-based self-healing material is too large, it is not conducive to uniform dispersion in the cement slurry. If the particle size of the cement-based self-healing material is too small, the surface area is large, which is easy to absorb moisture in the air, and is not conducive to storage. Preferably, the particle size of the cement-based self-healing material is not greater than 300 μm. For example, the particle size of the cement-based self-healing material is 150-300 μm.

[0023] The technical scheme adopted by the cement-based self-healing material of the present application is:

[0024] A cement-based self-healing material prepared by the preparation method of the cement-based self-healing material described above.

[0025] The cement-based self-healing material of the present application has good alkali resistance and hydrolysis resistance, good stability in a high-temperature alkali environment of the cement slurry, and under the action of calcium ions, it will undergo a de-crosslinking reaction to improve the water absorption multiple of the material and realize the water-induced self-repair of the micro-cracks of the cement stone.

[0026] The technical scheme adopted by the cement-based self-healing material of the present application is:

[0027] A cement-based self-healing material prepared by the preparation method of the cement-based self-healing material described above.

[0028] When the cement-based self-healing material of the present application is used in well cementing, the cement-based self-healing material has good alkali resistance and hydrolysis resistance, good stability in a high-temperature alkali environment of the cement slurry, and under the action of calcium ions, it will undergo a de-crosslinking reaction to improve the water absorption multiple and realize the water-induced self-repair of the micro-cracks of the cement stone. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure shows the change curve of the water absorption multiple of the cement-based self-healing material prepared in Example 1 of the present application in water and cement slurry filtrate with time.

[0030] Figure 2 The water absorption ratio of the cement-based self-repairing material prepared in Embodiment 2 tested in water and cement paste filtrate as a function of time;

[0031] Figure 3 The water absorption ratio of the cement-based self-repairing material prepared in Embodiment 3 tested in water and cement paste filtrate as a function of time;

[0032] Figure 4 The water absorption ratio of the cement-based self-repairing material prepared in Embodiment 4 tested in water and cement paste filtrate as a function of time;

[0033] Figure 5 The results of the initial water absorption ratio and the secondary water absorption ratio of the cement-based self-repairing material prepared in Embodiment 2 measured in different initial testing media. DETAILED DESCRIPTION

[0034] The technical solutions of the present application are further described below in conjunction with the detailed description. It should be noted that the purpose of the present embodiment is to further illustrate the present application, and is not a limitation on the protection scope of the present application.

[0035] Firstly, the preparation method of the cement-based self-repairing material of the present application is as follows:

[0036] Embodiment 1

[0037] The preparation method of the cement-based self-repairing material of the present embodiment specifically comprises the following steps:

[0038] 23.0g of distilled water, 3.00g of diacetone acrylamide, 12.00g of dimethyl diallyl ammonium chloride, and 0.065g of N,N-methylene bisacrylamide were sequentially added into a flask, and then nitrogen was introduced into the flask under stirring. After the diacetone acrylamide and the N,N-methylene bisacrylamide were completely dissolved, 0.060g of ammonium persulfate and 0.018g of tetramethyl ethylenediamine were added into the flask. After stirring for 2min, the stirring was stopped, and the mixture in the flask was left to stand at room temperature for 7h to allow the mixture in the flask to undergo a polymerization reaction. After the reaction was completed, the mixture in the flask was taken out and dried at 85℃ for 2d. Then, the dried solid was crushed to obtain a cement-based self-repairing material (with a particle size of 150-300μm).

[0039] Embodiment 2

[0040] The preparation method of the cement-based self-repairing material of the present embodiment specifically comprises the following steps:

[0041] Into a flask, 25.0 g of distilled water, 2.5 g of diacetone acrylamide, 12.5 g of dimethyldiallylammonium chloride, 0.045 g of N,N-methylenebisacrylamide were sequentially added, and then nitrogen was introduced into the flask under stirring. After the diacetone acrylamide and the N,N-methylenebisacrylamide were completely dissolved, 0.075 g of ammonium persulfate and 0.020 g of tetramethylethylenediamine were added to the flask. After stirring for 2 min, the stirring was stopped, and the mixture in the flask was left to stand at room temperature for 7 h to allow the mixture in the flask to undergo a polymerization reaction. After the reaction was completed, the mixture in the flask was taken out and dried at 85℃ for 2 d. The dried solid was pulverized to obtain a cement-based self-repairing material (particle size: 150-300 μm).

[0042] Example 3

[0043] The method for preparing the cement-based self-repairing material of the present example specifically includes the following steps:

[0044] Into a flask, 37.5 g of distilled water, 2.14 g of diacetone acrylamide, 12.86 g of dimethyldiallylammonium chloride, 0.078 g of N,N-methylenebisacrylamide were sequentially added, and then nitrogen was introduced into the flask under stirring. After the diacetone acrylamide and the N,N-methylenebisacrylamide were completely dissolved, 0.120 g of ammonium persulfate and 0.018 g of tetramethylethylenediamine were added to the flask. After stirring for 2 min, the stirring was stopped, and the mixture in the flask was left to stand at room temperature for 7 h to allow the mixture in the flask to undergo a polymerization reaction. After the reaction was completed, the mixture in the flask was taken out and dried at 85℃ for 2 d. The dried solid was pulverized to obtain a cement-based self-repairing material (particle size: 150-300 μm).

[0045] Example 4

[0046] The method for preparing the cement-based self-repairing material of the present example specifically includes the following steps:

[0047] Into a flask, 25 g of distilled water, 2.14 g of diacetone acrylamide, 12.86 g of dimethyldiallylammonium chloride, 0.105 g of N,N-methylenebisacrylamide were sequentially added, and then nitrogen was introduced into the flask under stirring. After the diacetone acrylamide and the N,N-methylenebisacrylamide were completely dissolved, 0.090 g of ammonium persulfate and 0.016 g of tetramethylethylenediamine were added to the flask. After stirring for 2 min, the stirring was stopped, and the mixture in the flask was left to stand at room temperature for 7 h to allow the mixture in the flask to undergo a polymerization reaction. After the reaction was completed, the mixture in the flask was taken out and dried at 85℃ for 2 d. The dried solid was pulverized to obtain a cement-based self-repairing material (particle size: 150-300 μm).

[0048] Comparative Example 1

[0049] The preparation method of the cement-based self-healing material of the present comparative example is different from the preparation method of the cement-based self-healing material of Example 2 only in that, in the preparation method of the cement-based self-healing material of the present comparative example, the diacetone acrylamide is replaced by 2-acrylamido-2-methylpropanesulfonic acid.

[0050] Comparative Example 2

[0051] The preparation method of the cement-based self-healing material of the present comparative example is different from the preparation method of the cement-based self-healing material of Example 2 only in that, in the preparation method of the cement-based self-healing material of the present comparative example, the diacetone acrylamide is replaced by 2-acrylamido-2-methylpropanesulfonic acid.

[0052] Comparative Example 3

[0053] The preparation method of the cement-based self-healing material of the present comparative example is different from the preparation method of the cement-based self-healing material of Example 2 only in that, in the preparation method of the cement-based self-healing material of the present comparative example, the dimethyldiallylammonium chloride is replaced by allyltrimethylammonium chloride.

[0054] Comparative Example 4

[0055] The preparation method of the cement-based self-healing material of the present comparative example is different from the preparation method of the cement-based self-healing material of Example 2 only in that, in the preparation method of the cement-based self-healing material of the present comparative example, the dimethyldiallylammonium chloride is replaced by methacrylamidotrimethylammonium chloride.

[0056] Second, the specific implementation of the cement-based self-healing material of the present application is as follows:

[0057] The cement-based self-healing material of the present embodiment is prepared by the preparation method of any one of the cement-based self-healing materials of Examples 1-4, which is not described here again.

[0058] Third, the specific implementation of the application of the cement-based self-healing material of the present application in well cementing of oil and gas wells is as follows:

[0059] The cement-based self-healing material prepared by the preparation method of any one of the cement-based self-healing materials of Examples 1-4 can be used as an oil well cement additive or an oil well cement slurry additive in the cement slurry used for well cementing of oil and gas wells.

[0060] Experimental Example 1

[0061] To evaluate the water absorption of the cement-based self-healing materials prepared in Examples 1-4 and Comparative Examples 1-4 in different acid and alkaline environments, the cement-based self-healing material (mass W1) was put into a white nylon bag (the white nylon bag has multiple pores, and the pore size is smaller than the particle size of the cement-based self-healing material), and then the white nylon bag containing the cement-based self-healing material (total mass W2) was put into distilled water, cement paste filtrate, calcium chloride solution (0.012 mol / L) or sodium hydroxide solution (pH = 13), respectively. The nylon bag was taken out every certain period of time, the surface water was absorbed with water absorption paper, the total mass of the nylon bag and the cement-based self-healing material after absorbing liquid was weighed and recorded as W3, and the water absorption multiple of the cement-based self-healing material was calculated. The calculation formula is: water absorption multiple (g / g) = (W3-W2) / W1. With the extension of the test time, the water absorption multiple of the cement-based self-healing material remained unchanged and reached a maximum value. At this time, the water absorption of the cement-based self-healing material reached saturation. The maximum value of the water absorption multiple of different cement-based self-healing materials obtained by the test is shown in Table 1. The test results also show that the water absorption of different cement-based self-healing materials in distilled water, cement paste filtrate, calcium chloride solution (0.012 mol / L) or sodium hydroxide solution (pH = 13) reaches saturation state at a test time of 180 min. In this experimental example, the particle size of the cement-based self-healing materials prepared in Examples 1-4 and Comparative Examples 1-4 used in the test is the same.

[0062] Table 1 Maximum value of water absorption multiple of different cement-based self-healing materials and time for the water absorption of the cement-based self-healing material to reach saturation

[0063]

[0064]

[0065] As can be seen from Table 1, the maximum value of the water absorption multiple of the cement-based self-healing materials prepared in Examples 1-4 and Comparative Examples 1-2 tested in water is much greater than the maximum value of the water absorption multiple tested in cement paste filtrate, calcium chloride solution (0.012 mol / L) or sodium hydroxide solution (pH = 13), which is conducive to the increase in the volume of the water absorption and expansion in the later stage to repair the cracks or pores of the cement stone (after the self-healing material expands in the cement paste system, it occupies a certain volume. When cracks or pores appear after the cement paste is solidified, the self-healing material expands when it comes into contact with water. Only when the water absorption multiple of the self-healing material in water is much greater than the water absorption multiple in the cement paste filtrate, can the self-healing material better repair the cracks or pores). However, the maximum value of the water absorption multiple of the cement-based self-healing material prepared in Comparative Examples 3-4 tested in water is close to the maximum value of the water absorption multiple tested in cement paste filtrate, calcium chloride solution (0.012 mol / L) or sodium hydroxide solution (pH = 13), indicating that the cement-based self-healing material prepared in Comparative Examples 3-4 cannot better play a role in repairing the cracks or pores of the cement stone.

[0066] In addition, the water absorption ratio of the cement-based self-healing materials prepared in Examples 1-4 was plotted against time when tested in water and cement paste filtrate at different times, and the results are shown in FIG. 2. Figures 1-4 Figures 1-4 It can be seen from FIG. 2 that the water absorption ratio of the cement-based self-healing materials prepared in Examples 1-4 gradually increased with time and reached a saturated state at 180 min; all four materials had pH sensitivity, and the water absorption ratio in the cement paste filtrate was less than that in water.

[0067] Experimental Example 2

[0068] To test whether the cement-based self-healing materials prepared in Examples 1-4 and Comparative Examples 1-4 had the function of calcium ion-enhanced water absorption, the cement-based self-healing materials prepared in Examples 1-4 and Comparative Examples 1-4 were first placed in cement paste filtrate, calcium chloride solution (0.012 mol / L), or sodium hydroxide solution (pH = 13) at a temperature of 90°C, and the maximum water absorption ratio of each cement-based self-healing material at 90°C was determined. Then each cement-based self-healing material was taken out and placed in distilled water at a temperature of 90°C to continue the determination of the water absorption ratio, and the maximum water absorption ratio of each cement-based self-healing material in distilled water was recorded. The maximum water absorption ratio of each cement-based self-healing material obtained by first testing in the initial test medium at 90°C was defined as the initial water absorption ratio, and the maximum water absorption ratio obtained by testing in distilled water at a temperature of 90°C was defined as the secondary water absorption ratio. The initial test medium was cement paste filtrate, calcium chloride solution (0.012 mol / L), or sodium hydroxide solution (pH = 13). The results of the initial water absorption ratio and the secondary water absorption ratio of each cement-based self-healing material tested in different initial test media are shown in Table 2.

[0069] Table 2 Initial water absorption ratio and secondary water absorption ratio of each cement-based self-healing material

[0070]

[0071]

[0072] The results of the initial water absorption ratio and the secondary water absorption ratio of the cement-based self-healing material prepared in Example 2 measured in different initial test media were plotted, and the results are shown in FIG. 3 (CSF in FIG. 3 represents cement paste filtrate, CaCl2 represents calcium chloride solution, and NaOH represents sodium hydroxide solution). From Table 2 and FIG. 3, it can be seen that the cement-based self-healing material prepared in Example 2 had the function of calcium ion-enhanced water absorption, and the secondary water absorption ratio in distilled water was greater than the initial water absorption ratio in the initial test medium. Figure 5 Figure 5 Figure 5 ​​​It can be seen that the initial water absorption of the cement-based self-healing material prepared in Example 2 in the cement slurry filtrate, calcium chloride solution (0.012 mol / L) or sodium hydroxide solution (pH = 13) is not much different, in the range of 11-13 g / g; the secondary water absorption obtained in the subsequent test in the cement slurry filtrate, calcium chloride solution (0.012 mol / L) is greatly increased, much higher than the maximum water absorption (25.18 g / g) obtained by the cement-based self-healing material alone in water; and the secondary water absorption obtained in the subsequent test in the sodium hydroxide solution (pH = 13) changes little. It shows that the cement-based self-healing material prepared in Example 2 has the effect of calcium ion strengthening water absorption, and the cement-based self-healing material will undergo a de-crosslinking reaction after encountering calcium ions, which can improve the water absorption of the material in water and enhance the self-healing ability of the material. According to the test results in Table 2, it can be seen that the cement-based self-healing materials prepared in Examples 1, 3-4 also have the effect of calcium ion strengthening water absorption. In addition, the cement-based self-healing materials prepared in Comparative Examples 1-2 do not have the effect of calcium ion strengthening water absorption, and the secondary water absorption is much smaller than the maximum water absorption obtained by the cement-based self-healing material alone in water; at the same time, although the cement-based self-healing materials prepared in Comparative Examples 3-4 also have the effect of calcium ion strengthening water absorption, the water absorption in the cement slurry filtrate is too high, which is not conducive to practical application, and the secondary water absorption and the initial water absorption are not much different, which is not conducive to the repair of cracks or pores in the cement stone by water absorption and swelling in the later stage.

Claims

1. A method for preparing a cement-based self-healing material, characterized in that, The method comprises the following steps: The mixture mainly composed of polymerization monomer, crosslinking agent, initiator and solvent is placed at a polymerization temperature, so that the polymerization monomer and the crosslinking agent are polymerized under the action of the initiator; the polymerization monomer is composed of diacetone acrylamide and an alkenyl quaternary ammonium salt containing two or more than two ethylenic unsaturated double bonds, and the mass ratio of the diacetone acrylamide to the alkenyl quaternary ammonium salt is 1: (4-6); the crosslinking agent is N, N'-methylene bisacrylamide; and the mass of the crosslinking agent is 0.3%-0.7% of the mass of the polymerization monomer.

2. The method for preparing a cement-based self-healing material according to claim 1, wherein, The alkenyl quaternary ammonium salt is dimethyldiallylammonium chloride, diethyldiallylammonium chloride, methylethyldiallylammonium chloride, dimethyldiallylammonium bromide, diethyldiallylammonium bromide or methylethyldiallylammonium bromide.

3. The method of claim 1, wherein the cement-based self-healing material is prepared by mixing the cement-based self-healing material with water in a ratio of 1 : 0.5 to 1 : 1.

5. The initiator comprises a main initiator and an auxiliary initiator; the main initiator is a persulfate salt, and the auxiliary initiator is a tertiary amine compound.

4. The method for preparing a cement-based self-healing material according to claim 3, wherein The mass of the main initiator is 0.4%-0.8% of the mass of the polymerization monomer; and the mass of the auxiliary initiator is 15%-30% of the mass of the initiator.

5. The method of claim 1, wherein the cement-based self-healing material is prepared by mixing the cement, the microcapsules, and the catalyst. The solvent is water.

6. The method for preparing a cement-based self-healing material according to any one of claims 1 to 5, wherein The mass of the polymerization monomer is 5%-13.5% of the mass of the solvent.

7. The method for preparing a cement-based self-healing material according to claim 3 or 4, wherein The main initiator is selected from one or any combination of ammonium persulfate, sodium persulfate and potassium persulfate, and the auxiliary initiator is tetramethylethylenediamine and / or tetramethylpropylenediamine.

8. The method for preparing a cement-based self-healing material according to any one of claims 1 to 5, wherein The polymerization time is not less than 7h. 9.A cement-based self-healing material prepared by the preparation method of the cement-based self-healing material according to any one of claims 1-8. 10.Use of a cement-based self-healing material prepared by the preparation method of the cement-based self-healing material according to any one of claims 1-8 in well cementation of an oil and gas well.

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