A micro-fracture self-repairing material for cement sheath and a preparation method and application thereof

Abstract

The present application relates to the technical field of oil and gas well cementing engineering, and particularly relates to a cementing cement microcrack self-repairing material, a preparation method and application thereof. The cementing cement microcrack self-repairing material is prepared by using an emulsion copolymerization method, and the raw material composition comprises the following components in parts by weight: deionized water 30 parts, monomer 3-12 parts, crosslinking agent 0.03-0.09 parts, initiator 0.06-0.3 parts, natural latex 3-20 parts, surfactant 1.5-3 parts, and filler 0.03-1.5 parts. The self-repairing material obtained by the present application has high liquid absorption rate in a weak acid solution, high swelling rate in the presence of carbon dioxide, and excellent mechanical properties. The self-repairing material can be added into a cementing fluid system, and is used in the environment of supercritical CO2 and CO2 formation water, two kinds of corrosive media in a water-wet environment, to seal the leakage channel of a wellbore and improve the sealing integrity of the wellbore.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas well cementing engineering, and particularly relates to a cementing cement stone microcrack self-repairing material, a preparation method and application thereof. BACKGROUND

[0002] Cement ring body integrity, interface sealing integrity and cement ring corrosion integrity are one of the key technologies to ensure the success of carbon dioxide geological utilization and storage. In the process of carbon dioxide storage, carbon dioxide dissolved in formation water will generate carbonic acid and decompose into carbonate, bicarbonate and hydrogen ions, making the formation water weakly acidic, which will seriously affect the performance of oil well cement stone. In addition, the injection of supercritical carbon dioxide, interface mud cake and the like can easily cause microannulus between the cement ring and the casing or the well wall, and carbon dioxide formation water channeling and carbon dioxide leakage problems can occur.

[0003] How to avoid carbon dioxide from escaping from the wellbore after storage is one of the key technologies that need to be studied at present. If a self-repairing material with a low particle size is added to the cementing fluid system, when microcracks or interface microannulus exist in the cement stone, the self-repairing material can expand in the presence of carbon dioxide formation water and carbon dioxide gas to seal the leakage channel, which is undoubtedly of great significance to the long-term storage of carbon dioxide. However, so far, no self-repairing material that can expand in the presence of carbon dioxide formation water and carbon dioxide gas has been found that can be applied to the cementing fluid. SUMMARY

[0004] The present application aims to develop a cementing cement stone microcrack self-repairing material, a preparation method and application thereof. The material has the functions of swelling in the presence of water and carbon dioxide gas under weak acid conditions, and the self-repairing material is applied to the cementing fluid system, which has the functions of swelling and self-repairing.

[0005] The cementing cement stone microcrack self-repairing material according to the present application comprises the following raw materials in parts by weight: deionized water 30 parts, monomer 3-12 parts, crosslinking agent 0.03-0.09 parts, initiator 0.06-0.3 parts, natural latex 3-20 parts, surfactant 1.5-3 parts, and filler 0.03-1.5 parts.

[0006] The monomer is acrylamide or diethylaminoethyl methacrylate or dimethylaminoethyl methacrylate, and preferably dimethylaminoethyl methacrylate.

[0007] The crosslinking agent is N, N-methylenebisacrylamide.

[0008] The initiator is ammonium persulfate or potassium persulfate.

[0009] The natural latex is from Taihua Rubber (General) Co., Ltd. The latex is a viscous milky white liquid flowing from rubber trees, has a pH of 10.50 at 25 DEG C, an ammonia content of 0.69%, a small amount of volatile fatty acids, magnesium and the like, and a solid content of 60%. The natural latex not only expands when meeting carbon dioxide, but also improves the tensile strength.

[0010] The surfactant is a non-ionic surfactant; the non-ionic surfactant is alkyl phenol polyoxyethylene ether or cocamide polyoxyethylene ether.

[0011] The filler is hydrophilic nano-silica produced by a sol-gel method.

[0012] The application further provides a preparation method of the self-repairing material for micro-cracks of a cement sheath, which is prepared by using an emulsion copolymerization method and includes the following steps:

[0013] (1) mixing deionized water, natural latex and a surfactant, and stirring uniformly to obtain solution I;

[0014] (2) mixing deionized water and a filler, and stirring uniformly to obtain solution II;

[0015] (3) mixing deionized water, an initiator, a monomer and a crosslinking agent, and stirring and dissolving to obtain solution III;

[0016] (4) adding solution I and solution II into solution III and stirring uniformly, under an oxygen-free condition, heating to 50-80 DEG C and standing for reaction, after the reaction is completed, processing the product into powder, namely the self-repairing material.

[0017] In the application, the product after material synthesis is in a colloidal state, and it is difficult to be crushed into micron-level particles by using a vacuum drying method. Therefore, the application further studies a method for processing the product into powder according to the properties of the product. The product can be processed into powder by using the following two methods:

[0018] Method one: the product is processed into powder by using a centrifugal spray dryer, wherein the feeding amount is 10% and the inlet temperature is 110 DEG C. The method must be mixed with deionized water to form a liquid to be able to be spray dried, and the powder amount prepared by a single test is small.

[0019] Method two: the product is dried and heated into a solid block, then is cut into small pieces, 20% of the mass of the solid is added as white carbon black for isolation, and the product is crushed into powder by using a liquid nitrogen crusher, the temperature is-80~-120 DEG C, preferably, the material is crushed twice by using the liquid nitrogen crusher, and the particle size is less than 70 mesh after crushing twice. In the process, the product is heated into a solid block and cut into large particles, and then cannot be directly crushed by using the liquid nitrogen crusher, otherwise, the large particles are easy to stick and block the equipment, and a certain mass of white carbon black must be added for isolation, and then the product is crushed by using the liquid nitrogen crusher.

[0020] The self-repairing material is further applied to the cementing fluid, and can be directly added to the cementing fluid as a component with expansion and self-repairing functions.

[0021] In the application, the initiator is decomposed into free radicals in deionized water and diffused into micelles or initiates polymerization in latex particles, and copolymerization of rubber molecules and monomers occurs in the graft copolymerization process. The core of the latex particles obtained at the end of the polymerization reaction is mainly composed of rubber molecules, and the outer layer is composed of products formed by graft polymerization and monomer polymerization. The dimethylaminoethyl methacrylate in the material determines the expansion ratio of the self-repairing material in weak acid, and the natural latex determines the expansion ratio of the self-repairing material in carbon dioxide. The working principle is that the dimethylaminoethyl methacrylate in the self-repairing material will undergo protonation reaction of tertiary amine group in low pH solution to produce expansion; in addition, the self-repairing material contains natural latex, and when carbon dioxide gas penetrates into the self-repairing material, the crosslinked network will change, thereby producing expansion.

[0022] In the material synthesis process, it is found that if the monomer is directly mixed with the latex, demulsification will occur quickly to generate large blocks of colloidal bodies. This is because the latex particles are negatively charged, and the dimethylaminoethyl methacrylate has the property of zwitterion, which easily causes the emulsion system to be unstable, leading to gelation. The use of surfactants can improve the stability of the latex and ensure the normal progress of the synthesis reaction. Fillers can change the physical properties of the synthesis product, improve the mechanical properties of the synthesis product, and reduce the cost.

[0023] The self-repairing material obtained by the application has high liquid absorption ratio in weak acid solution, high expansion ratio in carbon dioxide, and excellent mechanical properties.

[0024] Compared with the prior art, the application has the following advantages:

[0025] The application adopts specific raw materials and proportions, supplemented by the corresponding preparation method, realizes graft copolymerization of monomers and rubber molecules, and obtains a self-repairing material with high liquid absorption ratio in weak acid solution, high expansion ratio in carbon dioxide, and excellent mechanical properties, and the preparation process is safe and reliable.

[0026] (2) The self-repairing material can be directly applied to the cementing fluid system, and can be used in the supercritical CO2 and CO2 formation water two kinds of corrosive medium environments in the water wet environment, so as to seal the wellbore leakage channel and improve the sealing integrity of the wellbore. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The swelling ratio of the self-repairing material obtained from the examples and comparative examples in different pH solutions;

[0028] Figure 2 The swelling ratio of the self-repairing material obtained from the examples and comparative examples in carbon dioxide;

[0029] Figure 3 The tensile strength of the self-repairing material obtained from the examples and comparative examples. DETAILED DESCRIPTION

[0030] These embodiments are provided to make the purpose and technical solutions of the present application more thorough and complete. The examples are only for the purpose of explaining the present application, and the raw materials used are all commercially available.

[0031] Example 1

[0032] A micro-crack self-repairing material for well cementing, the raw material composition of which, in parts by weight, is: deionized water 30 g, acrylamide 5 g, N, N'-methylene bisacrylamide 0.03 g, ammonium persulfate 0.1 g, natural latex 5 g, alkylphenol polyoxyethylene ether 2 g, and nano-silicon dioxide 0.1 g.

[0033] The preparation method thereof is:

[0034] (1) In a beaker, add 10 g of deionized water and 5 g of natural latex, and add 2 g of alkylphenol polyoxyethylene ether, and stir uniformly with a magnetic stirrer to obtain solution I;

[0035] (2) In another beaker, add 10 g of deionized water and 0.1 g of nano-silicon dioxide, and stir uniformly with a magnetic stirrer to obtain solution II;

[0036] (3) In a reaction container, add 10 g of deionized water and 0.1 g of ammonium persulfate, and stir and dissolve with a magnetic stirrer, then add 5 g of acrylamide and 0.03 g of N, N'-methylene bisacrylamide, and stir uniformly to obtain solution III;

[0037] (4) Add solution I and solution II to solution III and stir uniformly, and after nitrogen deoxygenation, place in a 65°C water bath for 6 hours of static reaction. After the reaction is complete, heat the obtained product in a 100°C drying oven to form a solid block, then cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as a barrier, and then crush into granular form using a liquid nitrogen pulverizer under the condition of -100°C.

[0038] Example 2

[0039] A cement stone microcrack self-repairing material, raw material composition by weight parts: deionized water 30g, methacrylic acid diethylaminoethyl ester 5g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 5g, cocamide polyoxyethylene ether 2g, nanosilica 0.1g.

[0040] The preparation method is:

[0041] (1) add deionized water 10g and natural latex 5g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I;

[0042] (2) add deionized water 10g and 0.1g nanosilica in another beaker, and stir uniformly with a magnetic stirrer, to obtain solution II;

[0043] (3) add deionized water 10g and ammonium persulfate 0.1g in a reaction container, and stir and dissolve with a magnetic stirrer, then add methacrylic acid diethylaminoethyl ester 5g and N, N'-methylene bisacrylamide 0.03g, and stir uniformly, to obtain solution III;

[0044] (4) add solution I and solution II into solution III and stir uniformly, after nitrogen deoxygenation, in a 65℃ water bath, react for 6 hours. After the reaction is completed, the obtained product is heated into a solid block in a 100℃ drying oven, then cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as a separator, and then crush into granular shape under the condition of-100℃ using a liquid nitrogen pulverizer.

[0045] Example 3

[0046] A cement stone microcrack self-repairing material, raw material composition by weight parts: deionized water 30g, methacrylic acid dimethylaminoethyl ester 5g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 5g, cocamide polyoxyethylene ether 2g, nanosilica 0.1g.

[0047] The preparation method is:

[0048] (1) add deionized water 10g and natural latex 5g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I;

[0049] (2) add deionized water 10g and 0.1g nanosilica in another beaker, and stir uniformly with a magnetic stirrer, to obtain solution II;

[0050] (3) In the reaction vessel, add deionized water 10 g, ammonium persulfate 0.1 g, stir and dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 5 g, N, N'-methylene bisacrylamide 0.03 g, stir evenly, get solution III;

[0051] (4) Add solution I and solution II to solution III and stir evenly, deoxygenate with nitrogen, then react statically in a 65°C water bath for 6 hours. After the reaction is complete, the obtained product is heated into a solid block in a 100°C drying oven, then cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as a spacer, then crush into granular form using a liquid nitrogen pulverizer under the condition of -100°C.

[0052] Example 4

[0053] A well cementation cement stone microcrack self-repairing material, the raw material composition is, by weight: deionized water 30 g, dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, ammonium persulfate 0.2 g, natural latex 5 g, cocamide polyoxyethylene ether 2 g, nano silicon dioxide 0.3 g.

[0054] The preparation method is:

[0055] (1) In a beaker, add deionized water 10 g and natural latex 5 g, add 2 g of cocamide polyoxyethylene ether, stir evenly with a magnetic stirrer, get solution I;

[0056] (2) In another beaker, add deionized water 10 g and 0.3 g of nano silicon dioxide, stir evenly with a magnetic stirrer, get solution II.

[0057] (3) In the reaction vessel, add deionized water 10 g, ammonium persulfate 0.2 g, stir and dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, stir evenly, get solution III.

[0058] (4) Add solution I and solution II to solution III and stir evenly, deoxygenate with nitrogen, then react statically in a 65°C water bath for 6 hours. After the reaction is complete, the obtained product is heated into a solid block in a 100°C drying oven, then cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as a spacer, then crush into granular form using a liquid nitrogen pulverizer under the condition of -100°C.

[0059] Example 5

[0060] A cement stone microcrack self-repairing material, raw material composition by weight parts: deionized water 30g, dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.09g, ammonium persulfate 0.1g, natural latex 5g, cocamide polyoxyethylene ether 2g, nanosilica 0.3g.

[0061] The preparation method is:

[0062] (1) add deionized water 10g and natural latex 5g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I;

[0063] (2) add deionized water 10g and 0.5g nanosilica in another beaker, and stir uniformly with a magnetic stirrer, to obtain solution II.

[0064] (3) add deionized water 10g, ammonium persulfate 0.1g in a reaction container and stir to dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.09g, and stir uniformly, to obtain solution III.

[0065] (4) add solution I and solution II into solution III and stir uniformly, after nitrogen deoxygenation, in a 65℃ water bath, static reaction for 8 hours. After the reaction is completed, the obtained product is heated into a solid block in a 100℃ drying oven, then cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as isolation, and then crush into granular shape under the condition of-100℃ using a liquid nitrogen pulverizer.

[0066] Example 6

[0067] A cement stone microcrack self-repairing material, raw material composition by weight parts: deionized water 30g, dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 10g, cocamide polyoxyethylene ether 2g, nanosilica 0.1g.

[0068] The preparation method is:

[0069] (1) add deionized water 10g and natural latex 10g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I;

[0070] (2) add deionized water 10g and 0.1g nanosilica in another beaker, and stir uniformly with a magnetic stirrer, to obtain solution II.

[0071] (3) In the reaction vessel, add deionized water 10 g, ammonium persulfate 0.1 g, stir to dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, stir to uniform, get solution III.

[0072] (4) Add solution I and solution II to solution III and stir to uniform, after nitrogen deoxidation, in 65℃ water bath pot, static reaction 8 hours. After reaction, the obtained product is heated to solid block in 100℃ drying oven, then cut into small pieces, add white carbon black 20% of solid material mass as isolation, then crush to granular under -100℃ condition by using liquid nitrogen crusher.

[0073] Example 7

[0074] A kind of cement stone microcrack self-repairing material of well cementing, raw material composition is as follows by weight parts: deionized water 30 g, dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, ammonium persulfate 0.1 g, natural latex 20 g, cocamide polyoxyethylene ether 2 g, nano silicon dioxide 0.1 g.

[0075] Its preparation method is as follows:

[0076] (1) In a beaker, add deionized water 10 g and natural latex 20 g, add 2 g cocamide polyoxyethylene ether, stir to uniform with a magnetic stirrer, get solution I;

[0077] (2) In another beaker, add deionized water 10 g and 0.1 g nano silicon dioxide, stir to uniform with a magnetic stirrer, get solution II.

[0078] (3) In the reaction vessel, add deionized water 10 g, ammonium persulfate 0.1 g, stir to dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, stir to uniform, get solution III.

[0079] (4) Add solution I and solution II to solution III and stir to uniform, after nitrogen deoxidation, in 65℃ water bath pot, static reaction 6 hours. After reaction, the obtained product is heated to solid block in 100℃ drying oven, then cut into small pieces, add white carbon black 20% of solid material mass as isolation, then crush to granular under -100℃ condition by using liquid nitrogen crusher.

[0080] Comparative Example 1

[0081] A cement stone micro-crack self-repairing material, raw material composition in weight parts: deionized water 30g, N-(3-dimethylamino propyl) methacrylamide 5g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 5g, cocamide polyoxyethylene ether 2g, nano-silicon dioxide 0.1g.

[0082] The preparation method is:

[0083] (1) add deionized water 10g and natural latex 5g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I;

[0084] (2) add deionized water 10g and 0.1g nano-silicon dioxide in another beaker, stir uniformly with a magnetic stirrer, to obtain solution II;

[0085] (3) add deionized water 10g and ammonium persulfate 0.1g in a reaction container, stir and dissolve with a magnetic stirrer, then add N-(3-dimethylamino propyl) methacrylamide 5g and N, N'-methylene bisacrylamide 0.03g, stir uniformly, to obtain solution III;

[0086] (4) add solution I and solution II into solution III and stir uniformly, after nitrogen deoxygenation, stand in a 65℃ water bath for 6 hours. After the reaction is completed, heat the obtained product in a 100℃ drying oven into a solid block, cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as isolation, then crush into granular shape under the condition of-100℃ by using a liquid nitrogen pulverizer.

[0087] Comparative example 2

[0088] A cement stone micro-crack self-repairing material, raw material composition in weight parts: deionized water 20g, dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 5g, cocamide polyoxyethylene ether 2g.

[0089] The preparation method is:

[0090] (1) add deionized water 10g and natural latex 5g in a beaker, add 2g cocamide polyoxyethylene ether and stir uniformly with a magnetic stirrer, to obtain solution I.

[0091] (2) add deionized water 10g and ammonium persulfate 0.1g in a reaction container, stir and dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10g and N, N'-methylene bisacrylamide 0.03g, stir uniformly, to obtain solution II.

[0092] (3) Solution I is added to solution II and stirred uniformly, and after oxygen removal by nitrogen, the reaction is allowed to stand in a 65°C water bath for 6 hours. After the reaction is completed, the obtained product is heated into a solid block in a 100°C drying oven, cut into small pieces, and then isolated by adding white carbon black accounting for 20% of the mass of the solid material. Then, the product is crushed into granules using a liquid nitrogen pulverizer under the condition of -100°C.

[0093] Comparative Example 3

[0094] A cement sheath micro-fracture self-repairing material, the raw material composition of which is as follows in terms of weight parts: deionized water 20 g, dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, ammonium persulfate 0.1 g, butadiene-styrene rubber latex 5 g, and cocamide polyoxyethylene ether 2 g.

[0095] The preparation method is as follows:

[0096] (1) In a beaker, 10 g of deionized water and 5 g of butadiene-styrene rubber latex are added, and 2 g of cocamide polyoxyethylene ether is added and stirred uniformly using a magnetic stirrer to obtain solution I.

[0097] (2) In a reaction container, 10 g of deionized water and 0.1 g of ammonium persulfate are added and stirred and dissolved using a magnetic stirrer, and then 10 g of dimethylaminoethyl methacrylate and 0.03 g of N, N'-methylene bisacrylamide are added and stirred uniformly to obtain solution II.

[0098] (3) Solution I is added to solution II and stirred uniformly, and after oxygen removal by nitrogen, the reaction is allowed to stand in a 65°C water bath for 6 hours. After the reaction is completed, the obtained product is heated into a solid block in a 100°C drying oven, cut into small pieces, and then isolated by adding white carbon black accounting for 20% of the mass of the solid material. Then, the product is crushed into granules using a liquid nitrogen pulverizer under the condition of -100°C.

[0099] Comparative Example 4

[0100] A cement sheath micro-fracture self-repairing material, the raw material composition of which is as follows in terms of weight parts: deionized water 20 g, dimethylaminoethyl methacrylate 10 g, N, N'-methylene bisacrylamide 0.03 g, ammonium persulfate 0.1 g, butadiene-styrene rubber latex 5 g, and cocamide polyoxyethylene ether 2 g.

[0101] The preparation method is as follows:

[0102] (1) In a beaker, 10 g of deionized water and 5 g of butadiene-styrene rubber latex are added, and 2 g of cocamide polyoxyethylene ether is added and stirred uniformly using a magnetic stirrer to obtain solution I.

[0103] (2) In the reaction vessel, add deionized water 10 g, ammonium persulfate 0.1 g, stir to dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10 g, N, N'- methylene bisacrylamide 0.03 g, stir to uniform, get solution II.

[0104] (3) Add solution I to solution II and stir to uniform, after nitrogen deoxidation, in 65°C water bath, static reaction for 6 hours, there is still part of white emulsion in the beaker. After the reaction is completed, the obtained product is heated to solid block in 100°C drying oven, then cut into small pieces, add white carbon black 20% of the mass of solid material as isolation, then crush into granular shape with liquid nitrogen pulverizer under -100°C condition.

[0105] Experimental example

[0106] The method for measuring the liquid absorption ratio of the self-repairing material is as follows:

[0107] Considering the application environment of the self-repairing material, the test temperature of the liquid absorption ratio of the material is set to 70°C. The test steps are as follows: adjust the pH of the to-be-tested liquid with glacial acetic acid and sodium hydroxide respectively; wet a 500-mesh nylon bag with the to-be-tested liquid; weigh a certain mass (m0) of sample particles into the nylon bag, and weigh the total mass (m1) of the nylon bag and the sample; pour the to-be-tested liquid into the container, and put the nylon bag and the sample into it; take out the nylon bag after soaking for 3 days, absorb the water in the nylon bag with a napkin, and then weigh the total mass (m2) of the nylon bag and the sample. The liquid absorption expansion ratio of the self-repairing material is Q=(m2-m1) / m0, and the test results are shown in Table 1. Figure 1

[0108] The method for evaluating the expansion ratio of the self-repairing material when encountering carbon dioxide gas is as follows:

[0109] After drying, the self-repairing material is cut into small pieces, the mass M1 of the sample is weighed, the length, width and height of the sample are measured with a vernier caliper, and the volume V1 is calculated. Then, the sample is fixed in the middle container, and the middle container is vacuumized. The middle container is provided with a pressure gauge, 5 MPa of CO2 gas is introduced into the middle container, the sample is taken out after 1 day, and the mass M2 of the sample is weighed again. The mass expansion ratio P of the sample is (M2-M1) / M1. However, it is found that the mass of the samples of the examples and the comparative examples does not change basically after the introduction of carbon dioxide. In addition, the sample expanded by the introduction of carbon dioxide is placed below the liquid level of a graduated cylinder containing a certain amount of deionized water, and the change of the liquid level is observed, so as to calculate the volume expansion ratio of the self-repairing material when encountering carbon dioxide gas. The test results are shown in Table 2. Figure 2

[0110] The method for testing the mechanical properties of the self-repairing material is as follows:

[0111] ​​After the self-repairing material is dried, it is cut into a rectangular sample of 30 mm x 3 mm x 5 mm. The mechanical property of the self-repairing material sample is tested by using a ZQ990 tension machine, the maximum range of the testing machine is 2 kN, the tensile rate is set to 50 mm / min, the experimental environment temperature is room temperature, 3 samples are tested in each group, and the test results are averaged. The stress (σ) is calculated by dividing the test tension value (F) by the initial cross-sectional area (S0), σ = F / S0. The test results are shown in Table 1. Figure 3

[0112] It can be found from Examples 1-3, 7 and Comparative Examples 1-4 that the type and amount of monomer and latex have a greater influence on the liquid absorption ratio of the self-repairing material in the weak acid solution. It can be seen from Examples 3-5 and Comparative Example 2 that the amount of crosslinking agent, initiator and filler has a certain influence on the swelling ratio and tensile strength of the self-repairing material when encountering carbon dioxide. Figure 2 Figure 3 It can be seen that the amount of natural latex is the main factor affecting the swelling ratio and tensile strength of the self-repairing material when encountering carbon dioxide. It can be found from Examples 3-5 and Comparative Example 2 that the amount of crosslinking agent, initiator and filler has a certain influence on the swelling ratio and tensile strength of the self-repairing material when encountering carbon dioxide. In Example 7, the amount of natural latex is 20 g, the amount of dimethylaminoethyl methacrylate is 10 g, and the amount of nano-silicon dioxide is 0.1 g, and the self-repairing material obtained has a higher liquid absorption ratio in the weak acid solution, the swelling ratio when encountering carbon dioxide can reach more than 35 times, and the tensile strength can reach 0.7 MPa.

[0113] The embodiments of the present application are exemplary descriptions and are not limited to the disclosed content. Modifications and changes made by those skilled in the art without departing from the technical solutions of the present application are still within the protection scope of the present application.​​

Claims

1. A cement stone microfracture self-repairing material for use in cementing fluids, characterized in that, The raw material composition is: deionized water 30g, dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.03g, ammonium persulfate 0.1g, natural latex 20g, cocamide polyoxyethylene ether 2g, nano-silicon dioxide 0.1g, by weight; The preparation method is: (1) in a beaker, add deionized water 10g and natural latex 20g, add 2g cocamide polyoxyethylene ether, stir uniformly with a magnetic stirrer, to obtain solution I; (2) in another beaker, add deionized water 10g and 0.1g nano-silicon dioxide, stir uniformly with a magnetic stirrer, to obtain solution II; (3) in a reaction container, add deionized water 10g, ammonium persulfate 0.1g, stir and dissolve with a magnetic stirrer, then add dimethylaminoethyl methacrylate 10g, N, N'-methylene bisacrylamide 0.03g, stir uniformly, to obtain solution III; (4) add solution I and solution II to solution III and stir uniformly, after nitrogen deoxygenation, in a 65℃ water bath, static reaction for 6 hours; After the reaction is completed, the obtained product is heated into a solid block in a 100℃ drying oven, cut into small pieces, add white carbon black accounting for 20% of the mass of the solid material as a separator, then crush into granular shape under the condition of-100℃ using a liquid nitrogen pulverizer.

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