Well cementation self-healing cement paste and preparation method thereof

Abstract

The invention relates to the technical field of oil and gas field development, in particular to well cementation self-healing cement paste and a preparation method thereof. The concrete is prepared from the following components in parts by weight: 4 to 6 parts of repairing agent, 41 to 53 parts of cement, 18 to 22 parts of silica fume, 0.1 to 0.5 part of basalt fiber, 1 to 5 parts of expanding agent, 0.3 to 0.9 part of fluid loss agent, 0.2 to 0.4 part of bentonite, 1.7 to 2.3 parts of naphthalene sulfonate formaldehyde condensate, 0.1 to 0.2 part of simethicone and 1 to 3 parts of retarder, wherein the repairing agent is formed by modifying ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxy silane according to the mass ratio of 1: (1-2): (0.1-0.3). According to the invention, ethyl cyanoacrylate is used for repairing micro cracks of cement, candelilla wax and nano silicon dioxide are used for carrying out microencapsulation to protect ethyl cyanoacrylate, and methoxy groups of 3-isocyanate propyl trimethoxy silane enhance the interface bonding force between microcapsules and a cement slurry system, so that the service life of a cement structure is effectively prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, in particular to a self-healing cement slurry for well cementing and a preparation method thereof. Background Art

[0002] Well cementing refers to the process of fixing the casing in the well wall through specific technological means, and using cement slurry and other materials to isolate oil, gas, water and other strata. The basic steps include bottom hole preparation, cement slurry calculation, cement slurry mixing, injection cementing, mud return and solidification, etc. The purpose is to ensure the smooth progress of drilling and the safety and efficiency of subsequent oil and gas production. It has wide application and significance in oil and gas well drilling and completion operations.

[0003] However, after the cement slurry solidifies in oil and gas wells, the long-term stress of the cement causes the cement to break and form microcracks. These microcracks are small and their specific locations cannot be determined. Therefore, conventional repair methods are time-consuming and labor-intensive, and have a low success rate. In view of this, we propose a self-healing cement slurry for cementing and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a self-healing cement slurry for cementing and a preparation method thereof, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides a self-healing cement slurry for cementing, comprising the following components: 4-6 parts by weight of a repair agent, 41-53 parts by weight of cement, 18-22 parts by weight of silica fume, 0.1-0.5 parts by weight of basalt fiber, 1-5 parts by weight of an expansion agent, 0.3-0.9 parts by weight of a fluid loss reducer, 0.2-0.4 parts by weight of bentonite, 1.7-2.3 parts by weight of a naphthalenesulfonate formaldehyde condensate, 0.1-0.2 parts by weight of dimethyl silicone oil, and 1-3 parts by weight of a retarder; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanatepropyltrimethoxysilane in a mass ratio of 1:1-2:0.1-0.3.

[0006] Preferably, the expansion agent is a CaO-MgO composite system with an expansion rate of 0.05%-0.2%.

[0007] Preferably, the fluid loss reducer is one of hydroxyethyl cellulose and polyacrylamide, and the retarder is one of calcium lignin sulfonate and tartaric acid.

[0008] Preferably, the preparation method of the repair agent is as follows: Under nitrogen protection, heat the candelilla wax at 60-70°C to melt, add the nano-silica powder under continuous stirring to ensure complete and uniform dispersion, and then drop 3-isocyanate propyltrimethoxysilane to obtain a wall material solution for use; Ethyl cyanoacrylate was mixed evenly with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise into the wall material solution, and stirring was continued for 30-50 minutes to obtain a repair agent.

[0009] Ethyl cyanoacrylate will initiate anionic polymerization reaction when it meets water. Once the polymerization reaction is initiated, the monomer molecules will quickly connect together to form long-chain polymers. As the polymerization reaction proceeds, ethyl cyanoacrylate gradually changes from liquid to solid, forming a tough polymer network that tightly binds the surface of the adherends together. Since ethyl cyanoacrylate has the characteristics of rapid response and strong adhesion, it becomes an effective crack repair agent. However, its sensitivity to moisture also affects its application in cementing self-healing cement slurry. Therefore, candelilla wax and nano-silica are mixed for microencapsulation. Since candelilla wax, as a natural material, has hydrophobic and barrier properties, wrapping the repair agent inside it can isolate moisture and effectively prevent ethyl cyanoacrylate from curing prematurely. Thereby ensuring the normal release and function of the ethyl cyanoacrylate repair agent. In order to further improve the protective effect of candelilla wax and its stability in the cement slurry system, 3-isocyanatepropyltrimethoxysilane is additionally added. The hydroxyl groups of candelilla wax and nano-silica are cross-linked with the isocyanate groups of 3-isocyanatepropyltrimethoxysilane, thereby improving the chemical stability, thermal stability, mechanical strength and barrier effect of candelilla wax. In the highly alkaline environment of cement slurry, the methoxy group of 3-isocyanatepropyltrimethoxysilane directly undergoes a condensation reaction with the hydroxyl groups on the surface of cement particles to generate stable Si-O-Si bonds, thereby enhancing the interfacial bonding between the microcapsules and the cement slurry system, without relying on hydrolysis to generate silanol groups, thereby improving compatibility.

[0010] Since ethyl cyanoacrylate monomer is more susceptible to polymerization, hydroquinone is added to prevent anionic polymerization and free radical polymerization; in order to improve the brittleness after curing, dioctyl phthalate is added to increase the impact strength of the cured layer.

[0011] Preferably, the nano silicon dioxide is 15-28% of the mass of candelilla wax.

[0012] Preferably, the hydroquinone accounts for 0.5-0.8% of the mass of ethyl cyanoacrylate.

[0013] Preferably, the dioctyl phthalate accounts for 11.2-13.5% of the mass of ethyl cyanoacrylate.

[0014] Preferably, the particle size distribution of the repair agent is 25-50 μm.

[0015] On the other hand, the present invention provides a method for preparing a self-healing cement slurry for cementing, which is used to prepare the self-healing cement slurry for cementing, comprising the following steps: Add cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent into a stirrer, premix for 5-10 minutes at room temperature at 100-200rpm, then add dimethyl silicone oil and retarder, calculate the required amount of water according to the water-cement ratio, add water and mix at 500-1000rpm for 10-15 minutes to obtain cementing self-healing cement slurry.

[0016] Preferably, the water-cement ratio is 0.38-0.45.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In the well cementing self-healing cement slurry and preparation method thereof, ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyltrimethoxysilane are used as main raw materials to prepare a repair agent, anionic polymerization reaction of ethyl cyanoacrylate is used to bond and repair micro cracks in cement, candelilla wax and nano-silicon dioxide are used to microencapsulate and protect ethyl cyanoacrylate to avoid premature curing and failure, and the methoxy group of 3-isocyanate propyltrimethoxysilane is used to enhance the interface bonding force between microcapsules and cement slurry system, improve compatibility, and further improve the chemical stability, thermal stability, mechanical strength and barrier effect of microcapsule wall materials, thereby effectively extending the service life of cement structures. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] A self-healing cement slurry for well cementing of the present invention comprises the following components: 4-6 parts by weight of a repair agent, 41-53 parts by weight of cement, 18-22 parts by weight of silica fume, 0.1-0.5 parts by weight of basalt fiber, 1-5 parts by weight of an expansion agent, 0.3-0.9 parts by weight of a fluid loss reducer, 0.2-0.4 parts by weight of bentonite, 1.7-2.3 parts by weight of a naphthalenesulfonate formaldehyde condensate, 0.1-0.2 parts by weight of dimethyl silicone oil and 1-3 parts by weight of a retarder; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxy silane in a mass ratio of 1:1-2:0.1-0.3; Preferably, the fluid loss reducer is hydroxyethyl cellulose and the retarder is calcium lignin sulfonate.

[0020] Embodiment 1: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 6 parts by weight of repair agent, 53 parts by weight of cement, 22 parts by weight of silica fume, 0.5 parts by weight of basalt fiber, 5 parts by weight of CaO-MgO composite system, 0.9 parts by weight of hydroxyethyl cellulose, 0.4 parts by weight of bentonite, 2.3 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.2 parts by weight of dimethyl silicone oil and 3 parts by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:1:0.1; nano silicon dioxide accounts for 20% of the mass of candelilla wax; hydroquinone accounts for 0.8% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 13.5% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 30 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0021] Embodiment 2: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 6 parts by weight of repair agent, 53 parts by weight of cement, 22 parts by weight of silica fume, 0.5 parts by weight of basalt fiber, 5 parts by weight of CaO-MgO composite system, 0.9 parts by weight of hydroxyethyl cellulose, 0.4 parts by weight of bentonite, 2.3 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.2 parts by weight of dimethyl silicone oil and 3 parts by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:1.5:0.2; nano-silica accounts for 20% of the mass of candelilla wax; hydroquinone accounts for 0.8% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 13.5% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 30 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0022] Embodiment 3: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 6 parts by weight of repair agent, 53 parts by weight of cement, 22 parts by weight of silica fume, 0.5 parts by weight of basalt fiber, 5 parts by weight of CaO-MgO composite system, 0.9 parts by weight of hydroxyethyl cellulose, 0.4 parts by weight of bentonite, 2.3 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.2 parts by weight of dimethyl silicone oil and 3 parts by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:2:0.3; nano-silica accounts for 20% of the mass of candelilla wax; hydroquinone accounts for 0.8% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 13.5% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 30 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0023] Embodiment 4: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 6 parts by weight of repair agent, 41 parts by weight of cement, 18 parts by weight of silica fume, 0.1 parts by weight of basalt fiber, 1 part by weight of CaO-MgO composite system, 0.3 parts by weight of hydroxyethyl cellulose, 0.2 parts by weight of bentonite, 1.7 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.1 parts by weight of dimethyl silicone oil and 1 part by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:2:0.3; nano-silica accounts for 15% of the mass of candelilla wax; hydroquinone accounts for 0.5% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 11.2% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 25 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0024] Embodiment 5: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 4 parts by weight of repair agent, 53 parts by weight of cement, 22 parts by weight of silica fume, 0.5 parts by weight of basalt fiber, 5 parts by weight of CaO-MgO composite system, 0.9 parts by weight of hydroxyethyl cellulose, 0.4 parts by weight of bentonite, 2.3 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.2 parts by weight of dimethyl silicone oil and 3 parts by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:2:0.3; nano-silica accounts for 20% of the mass of candelilla wax; hydroquinone accounts for 0.8% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 13.5% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 30 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0025] Example 6: A method for preparing a self-healing cement slurry for cementing, comprising the following steps: Prepare components: 5 parts by weight of repair agent, 53 parts by weight of cement, 22 parts by weight of silica fume, 0.5 parts by weight of basalt fiber, 5 parts by weight of CaO-MgO composite system, 0.9 parts by weight of hydroxyethyl cellulose, 0.4 parts by weight of bentonite, 2.3 parts by weight of naphthalenesulfonate formaldehyde condensate, 0.2 parts by weight of dimethyl silicone oil and 3 parts by weight of calcium lignin sulfonate; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanate propyl trimethoxysilane in a mass ratio of 1:2:0.3; nano-silica accounts for 20% of the mass of candelilla wax; hydroquinone accounts for 0.8% of the mass of ethyl cyanoacrylate; dioctyl phthalate accounts for 13.5% of the mass of ethyl cyanoacrylate; Under nitrogen protection, the candelilla wax was heated and melted at 60°C, and nano-silica powder was added under continuous stirring to ensure complete and uniform dispersion, and then 3-isocyanatepropyltrimethoxysilane was added dropwise to obtain a wall material solution for use; ethyl cyanoacrylate was mixed with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise to the wall material solution, and the stirring was continued for 30 minutes to obtain a repair agent with a particle size distribution of 30 μm; Cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent were added to a stirrer and premixed at room temperature and 100 rpm for 5 minutes. Then dimethyl silicone oil and retarder were added. The required amount of water was calculated based on the water-cement ratio of 0.41. Water was added and mixed at 1000 rpm for 10 minutes to obtain cementing self-healing cement slurry.

[0026] Comparative Example 1: The method of Example 3 was adopted without adding a repairing agent.

[0027] Comparative Example 2: The method of Example 3 was adopted, and ethyl cyanoacrylate and candelilla wax were directly used without modifying ethyl cyanoacrylate and candelilla wax by 3-isocyanatepropyltrimethoxysilane.

[0028] The present invention adopts a self-healing cement slurry for well cementing prepared by using a repairing agent, wherein the performance index inspection items and inspection standards of the cement slurry are as follows: The compressive strength of cement paste under standard curing conditions was tested to observe whether the self-healing component affects the initial strength and long-term strength development. Standard size specimens (50 mm × 50 mm × 50 mm cubes) were prepared and cured for 7 days under standard curing conditions (20 °C ± 2 °C, relative humidity 95%). A universal material testing machine was used for compression testing, and the loading rate was kept constant at (0.5 ± 0.05) MPa / s. The maximum load at failure was recorded and the compressive strength F was calculated. c =F max / A, where F c is the compressive strength (MPa), F max is the maximum bearing capacity (N), A is the pressure-bearing area of ​​the specimen (m²), and then a spherical indenter with a diameter of 2 mm is used to apply an initial load of 200 N to simulate the compressive strength recovery rate after 7 days of self-healing at 50°C when the specimen is subjected to local stress concentration; The permeability test is used to evaluate the permeability characteristics of cement paste and determine whether the self-healing component can effectively reduce the permeability and improve the sealing. A cylindrical sample with a diameter of 50 mm and a height of 100 mm, which has been cured for 7 days, is installed on the permeameter. Nitrogen is used as the permeation gas and a pressure of 20 MPa is applied for 1 hour. The amount of fluid passing through the specimen and the corresponding pressure difference are recorded. The permeability coefficient k=Q⋅L / A⋅ΔP⋅t is calculated according to Darcy's law, where Q is the amount of fluid passing through the specimen (m³), L is the specimen length (m), A is the specimen cross-sectional area (m²), ΔP is the pressure difference (Pa), and t is the time (s). The self-healing rate is calculated as (permeability coefficient before self-healing - permeability coefficient after self-healing) / permeability coefficient before self-healing × 100%. The self-healing rates of the specimens before and after the addition of the self-healing component are compared to evaluate their effect on reducing permeability.

[0029] According to the above standards, the self-healing cement slurries prepared in the above Examples 1-6 and Comparative Examples 1-2 were tested, and the obtained data are shown in Table 1: Table 1 Performance data of Examples 1-6 and Comparative Examples 1-2

[0030] The above data fully demonstrate that compared with Comparative Examples 1-2, Examples 1-6 can fully demonstrate the effect of the repair agent on the self-healing performance of the cementing self-healing cement slurry.

[0031] Since the present invention uses a repairing agent to prepare the cementing self-healing cement slurry, the performance of the cementing self-healing cement slurry is effectively improved by the repairing agent, as follows: It can be seen from Examples 1-3 that as the proportion of the repair agent component continues to increase, the self-healing performance of the cementing self-healing cement slurry is significantly improved. Since ethyl cyanoacrylate is a fast-curing adhesive, it can quickly polymerize and cure when exposed to moisture to form a strong polymer film, which helps to seal cracks. Candelilla wax helps protect the repair agent from premature curing. 3-isocyanatepropyltrimethoxysilane can enhance the adhesion between the repair agent and the cement matrix and promote better interfacial bonding. When the repair agent containing these ingredients is introduced into the cement slurry, the repair agent will react after contacting water on the crack surface to generate a filler with higher strength and durability, thereby effectively filling the cracks and restoring some mechanical properties.

[0032] It can be seen from Examples 3 and 4 that with the continuous change of the content of other components, the self-healing performance of the cementing self-healing cement slurry does not change significantly, indicating that small changes in other components within a certain range are not sufficient to significantly affect the self-healing effect of the cementing self-healing cement slurry.

[0033] It can be seen from Examples 3, 5 and 6 that as the content of the repair agent continues to change, the self-healing properties of the cementing self-healing cement slurry continues to change. As the content of the repair agent increases, the amount of the repair agent distributed in the cement matrix increases, which means that when cracks or damage occur, more repair materials can participate in the repair process, thereby improving the overall self-healing efficiency and effect. In addition, the introduction of microcapsules into the cement slurry will additionally increase the porosity inside the cement matrix, thereby weakening its overall density and causing a decrease in compressive strength. Therefore, as the content of the repair agent increases, the compressive strength of the cement slurry decreases instead.

[0034] According to the above test experiments, the self-healing cement slurry prepared according to Example 3 has the best performance, so Example 3 is taken as the best example; By comparing Example 3 with Comparative Examples 1-2, it can be seen that: In Comparative Example 1, no repair agent was added, and the self-healing effect of the cementing self-healing cement slurry was poor. The absence of the addition of the repair agent means that the cement matrix itself lacks components that can actively respond to cracks and repair them. Once cracks appear, the cement matrix can only rely on its own hydration products and tiny particles to try to fill the cracks, but this is usually not enough to completely close the cracks or restore the original strength. The repair process is inefficient, which significantly affects the overall mechanical properties of the material.

[0035] In Comparative Example 2, ethyl cyanoacrylate and candelilla wax are directly used, and ethyl cyanoacrylate and candelilla wax are not modified by 3-isocyanatepropyltrimethoxysilane. The self-healing effect of the cementing self-healing cement slurry is worse. Due to the lack of effective chemical bonding of 3-isocyanatepropyltrimethoxysilane, the compatibility and adhesion between the microcapsules and the cement matrix are weak, the interfacial adhesion is insufficient, and stress concentration points are easily formed. The stress concentrated areas are more prone to damage, thereby reducing the bearing capacity and service life of the entire structure. Therefore, the self-healing effect of the cementing self-healing cement slurry is poor.

[0036] In summary, the performance and stability of the repair agent were significantly improved by encapsulating ethyl cyanoacrylate in candelilla wax and nano-silica and modifying it with 3-isocyanatepropyltrimethoxysilane; First, ethyl cyanoacrylate can quickly polymerize to form a tough polymer network when it comes into contact with water, and it has strong adhesion and good repair effect. However, it is extremely sensitive to moisture in the environment and is easy to solidify prematurely during storage or construction, which affects its stability and release effect in cement slurry. Therefore, candelilla wax and nano-silica are mixed for microencapsulation, and the repair agent is wrapped inside it, which can isolate moisture and effectively prevent ethyl cyanoacrylate from solidifying prematurely. When microcracks are generated in the cement matrix due to stress, the mechanical stress at the cracks causes the microcapsule wall material to rupture, releasing ethyl cyanoacrylate in the core material; at the same time, the moisture that penetrates into the cracks contacts ethyl cyanoacrylate, triggering its anionic polymerization reaction, quickly forming a polymer network, repairing the cracks, and avoiding premature polymerization of ethyl cyanoacrylate. At the same time, the addition of nano-silica not only enhances the mechanical strength of the microcapsules, but also provides more active hydroxyl sites, promoting subsequent chemical modifications; Secondly, in order to further improve the protective effect of candelilla wax and its stability in the cement slurry system, 3-isocyanate propyl trimethoxy silane was introduced to enhance the chemical stability, thermal stability and mechanical strength of the microcapsules, and significantly enhance the interfacial bonding between the microcapsules and the cement slurry system, thereby improving the compatibility. Finally, through this microencapsulation strategy, not only the problem of ethyl cyanoacrylate's sensitivity to moisture was solved, but the storage stability of the repair agent was also significantly enhanced, thereby effectively extending the service life of the cement structure.

[0037] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A self-healing cement slurry for cementing, characterized in that: The invention comprises the following components: 4-6 parts by weight of a repairing agent, 41-53 parts by weight of cement, 18-22 parts by weight of silica fume, 0.1-0.5 parts by weight of basalt fiber, 1-5 parts by weight of an expansion agent, 0.3-0.9 parts by weight of a fluid loss reducer, 0.2-0.4 parts by weight of bentonite, 1.7-2.3 parts by weight of a naphthalenesulfonate formaldehyde condensate, 0.1-0.2 parts by weight of dimethyl silicone oil and 1-3 parts by weight of a retarder; The repair agent is modified from ethyl cyanoacrylate, candelilla wax and 3-isocyanatepropyltrimethoxysilane in a mass ratio of 1:1-2:0.1-0.

3.

2. The self-healing cement slurry for cementing according to claim 1, characterized in that: The expansion agent is a CaO-MgO composite system, and the expansion rate is 0.05%-0.2%.

3. The self-healing cement slurry for cementing according to claim 1, characterized in that: The fluid loss reducer is one of hydroxyethyl cellulose and polyacrylamide, and the retarder is one of calcium lignin sulfonate and tartaric acid.

4. The self-healing cement slurry for cementing according to claim 1, characterized in that: The preparation method of the repair agent is as follows: Under nitrogen protection, heat the candelilla wax at 60-70°C to melt, add the nano-silica powder under continuous stirring to ensure complete and uniform dispersion, and then drop 3-isocyanate propyltrimethoxysilane to obtain a wall material solution for use; Ethyl cyanoacrylate was mixed evenly with hydroquinone and dioctyl phthalate to obtain a core material solution, and the core material solution was added dropwise into the wall material solution, and stirring was continued for 30-50 minutes to obtain a repair agent.

5. The self-healing cement slurry for cementing according to claim 4, characterized in that: The nano silicon dioxide is 15-28% of the mass of the candelilla wax.

6. The self-healing cement slurry for cementing according to claim 4, characterized in that: The hydroquinone accounts for 0.5-0.8% of the mass of ethyl cyanoacrylate.

7. The self-healing cement slurry for cementing according to claim 4, characterized in that: The dioctyl phthalate accounts for 11.2-13.5% of the mass of ethyl cyanoacrylate.

8. The self-healing cement slurry for cementing according to claim 4, characterized in that: The particle size distribution of the repair agent is 25-50 μm.

9. A method for preparing a self-healing cement slurry for cementing, used for preparing the self-healing cement slurry for cementing as claimed in any one of claims 1 to 8, characterized in that: The steps include: Add cement, silica fume, basalt fiber, expansion agent, fluid loss reducer, bentonite, naphthalenesulfonate formaldehyde condensate and repair agent into a stirrer, premix for 5-10 minutes at room temperature at 100-200rpm, then add dimethyl silicone oil and retarder, calculate the required amount of water according to the water-cement ratio, add water and mix at 500-1000rpm for 10-15 minutes to obtain cementing self-healing cement slurry.

10. The method for preparing the self-healing cement slurry for cementing according to claim 9, characterized in that: The water-cement ratio is 0.38-0.45.

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