A self-healing agent for cement slurry in well cementing and its preparation method

Abstract

The present invention relates to the technical field of self-healing agents, and specifically, to a self-healing agent for cement slurry in well cementing and a preparation method thereof, which comprises the following components: 30-50 parts by weight of a modified polyethylene terephthalate-based polymer, 2-10 parts by weight of a metal oxide, 5-15 parts by weight of lithium silicate, 0.5-2 parts by weight of persulfate, 0.1-1 part by weight of Bacillus subtilis, and 1-5 parts by weight of calcium lactate. Isosorbide can react with the ester bonds in polyethylene terephthalate, thereby introducing more hydroxyl groups, and these hydroxyl groups can interact with the hydration products of cement or metal oxides and lithium silicate to promote the formation of new mineral phases at the cracks. The formation of this new mineral phase helps to fill and repair the cracks, realizing the self-healing of the cement slurry, and thus improving the long-term stability of the well cementing structure. Tetraethyl orthosilicate can act synergistically with other components such as the modified polyethylene terephthalate-based polymer to jointly promote the self-healing process of the cement stone.

Description

Technical Field

[0001] The present invention relates to the technical field of self-healing agents, and specifically, to a self-healing agent for cement slurry used in well cementing and a preparation method thereof. Background Art

[0002] In the field of oil and gas exploitation, well cementing operation is a key link to ensure the long-term stability of the wellbore, prevent the cross-flow of formation fluids, and protect the casing; as the core material for forming the cement sheath, the performance of the well cementing slurry directly affects the production life and safety of the entire oil and gas well; however, with the drastic changes in temperature and pressure during the exploitation of oil and gas wells, as well as the long-term erosion of formation fluids, the cement sheath is extremely prone to cracks; these cracks will not only cause the cross-leakage of formation fluids, reduce the exploitation efficiency of oil and gas wells, but also may lead to serious safety hazards, such as wellhead out-of-control, environmental pollution, etc.; traditional well cementing slurries cannot effectively repair themselves after cracks occur, and a large amount of manpower, material resources, and time are required for remedial measures such as secondary well cementing, which greatly increases the exploitation cost; as an emerging solution, self-healing technology aims to endow materials with the ability of self-repair, automatically seal micro-cracks through internal mechanisms, and restore the integrity and functionality of the structure.

[0003] Although some existing self-healing agents for well cementing slurries can improve the crack repair ability of the cement slurry to a certain extent, there are still many deficiencies; the repair effects of some self-healing agents are greatly affected by downhole environmental factors, and under extreme conditions such as high temperature, high pressure, and high salinity, the self-healing efficiency is significantly reduced; the repair products formed by some self-healing agents may gradually be damaged or dissolved under the long-term formation stress and fluid scouring, resulting in the recurrence of cracks and unable to achieve long-term and effective repair. In view of this, we propose a self-healing agent for well cementing slurry and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a self-healing agent for well cementing slurry and a preparation method thereof, so as to solve the problems proposed in the above background art that the repair effects of some self-healing agents are greatly affected by downhole environmental factors, and under extreme conditions such as high temperature, high pressure, and high salinity, the self-healing efficiency is significantly reduced; the repair products formed by some self-healing agents may gradually be damaged or dissolved under the long-term formation stress and fluid scouring, resulting in the recurrence of cracks and unable to achieve long-term and effective repair.

[0005] To achieve the above purpose, the present invention provides a self-healing agent for well cementing slurry, comprising the following components: 30-50 parts by weight of a modified polyethylene terephthalate-based polymer, 2-10 parts by weight of a metal oxide, 5-15 parts by weight of lithium silicate, 0.5-2 parts by weight of persulfate, 0.1-1 part by weight of Bacillus subtilis, and 1-5 parts by weight of calcium lactate;

[0006] The modified polyethylene terephthalate-based polymer is prepared by alcoholysis reaction of isosorbide with polyethylene terephthalate, and then mixing with tetraethyl orthosilicate and titanate.

[0007] Preferably, the preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0008] S1.1. Weigh the following components in parts by weight respectively: 50 - 80 parts by weight of polyethylene terephthalate, 10 - 30 parts by weight of isosorbide, 1 - 3 parts by weight of sodium hydroxide, 10 - 20 parts by weight of tetraethyl orthosilicate, 20 - 40 parts by weight of toluene, 5 - 15 parts by weight of titanate, and 0.1 - 0.5 parts by weight of acetic acid;

[0009] S1.2. Under nitrogen protection, mix polyethylene terephthalate with isosorbide, add sodium hydroxide with a concentration of 1 - 3%, slowly raise the temperature to 180 - 250 °C, and stir and react for 3 - 8 h at a speed of 300 - 600 r / min with a stirrer to obtain modified polyethylene terephthalate;

[0010] During the alcoholysis reaction, the ester bonds of polyethylene terephthalate (PET) will be broken and combined with isosorbide to form new ester bonds. This process introduces a large number of hydroxyl groups (-OH) into the product, significantly improving the hydrophilicity of the material and endowing it with stronger water absorption ability; this means that the modified PET can better adsorb and store water, thus providing advantages in various complex environments; in addition, these hydroxyl groups endow the material with higher chemical reactivity, creating favorable conditions for subsequent reactions with other functional components (such as siloxane, titanate, etc.). Through these subsequent reactions, a more complex and multifunctional network structure can be constructed, thereby enhancing the comprehensive performance of the material.

[0011] In the cementing operation, the modified polyethylene terephthalate can serve as an important water source, continuously providing the water required for the secondary hydration reaction of cement. This continuous water supply can extend the duration of the self-healing effect of the cement stone and provide more durable protection for the cementing structure; the long flexible chain segments of isosorbide are introduced into the modified polyethylene terephthalate after the alcoholysis reaction. These chain segments bring higher flexibility and stronger impact resistance to the material, greatly reducing the possibility of the material breaking due to brittleness and improving the overall reliability of the material.

[0012] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution; add modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 80 - 120 °C, and stir at a speed of 400 - 800 r / min for 30 - 60 min to obtain a mixture;

[0013] Tetraethyl orthosilicate hydrolyzes and polycondenses under specific conditions to form a silicone network structure. After mixing with modified polyethylene terephthalate, the formed silicone network can interact with the functional groups (such as hydroxyl groups) in the modified PET. This interaction constructs an organic-inorganic hybrid network structure at the molecular level, endowing the material with the flexibility of organic materials and the rigidity and stability of inorganic materials. In addition, the silicon dioxide-like products generated by the hydrolysis of tetraethyl orthosilicate can fill the voids between the molecular chains of the modified PET, making the material more dense, reducing the porosity, and significantly improving the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, this filling effect can also effectively prevent the penetration and diffusion of small molecules (such as gases or liquids), enhancing the barrier performance of the material. For the self-healing agent of the cement slurry for well cementing, this characteristic helps to reduce the crossflow of fluids such as oil and gas in the cement sheath.

[0014] When cracks appear in the material, the silicon dioxide-like products generated by the hydrolysis of tetraethyl orthosilicate can react with the active groups in the modified PET and the moisture in the environment to form new chemical bonds or physical bonds, thereby filling the cracks and achieving the self-healing function, ensuring the integrity and functionality of the material.

[0015] S1.4. Drop titanate into the mixture. After the dropping is completed, add acetic acid with a concentration of 98%, and at the same time continue to stir at a speed of 400 - 800 r / min for 10 - 15 min. After mixing evenly, raise the temperature to 120 - 150 °C and react for 1 - 3 h.

[0016] Titanate may react with the active groups (such as hydroxyl groups, silanol groups, etc.) in the modified polyethylene terephthalate or the hydrolysis products of tetraethyl orthosilicate to form chemical bonds with higher bond energy and stronger interaction force, thereby improving the strength and hardness of the material. This is crucial for the self-healing agent of the cement slurry for well cementing because higher strength and hardness can enable the cement stone to better withstand the formation pressure and resist the extrusion of the rock on the cement sheath, preventing the cement sheath from deforming and being damaged. Titanate may react with the acid to form stable compounds, forming a stable passivation film on the surface of the material to prevent acidic substances from further corroding the interior of the material and ensuring the structural integrity and performance stability of the material. Titanate can participate in the self-healing process of the material. When cracks appear in the material, the titanium element in the titanate can react with the substances in the environment to form new repair substances to fill the cracks, improving the self-healing ability and effect of the material.

[0017] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 50 - 80 °C and a vacuum degree of 0.08 - 0.1 MPa to obtain the modified polyethylene terephthalate-based polymer.

[0018] Preferably, in the step S1.2, the relative molecular mass of polyethylene terephthalate is 15,000 - 30,000.

[0019] Preferably, in the step S1.2, the rate of slow temperature rise is 20 - 30 °C / h.

[0020] Preferably, in the step S1.3, the concentration of tetraethyl orthosilicate solution is 30 - 70%.

[0021] Preferably, in the step S1.4, the titanate is any one of tetrabutyl titanate or tetraisopropyl titanate.

[0022] Preferably, in the step S1.4, the time for dropping the titanate is 20 - 40 min.

[0023] On the other hand, the present invention provides a preparation method of a self-healing agent for well cement slurry for preparing the above-mentioned self-healing agent for well cement slurry, which comprises the following steps:

[0024] S2.1: Weigh the following components in parts by weight respectively: 30 - 50 parts by weight of modified polyethylene terephthalate-based polymer, 2 - 10 parts by weight of metal oxide, 5 - 15 parts by weight of lithium silicate, 0.5 - 2 parts by weight of persulfate, 0.1 - 1 part by weight of Bacillus subtilis, and 1 - 5 parts by weight of calcium lactate;

[0025] S2.2: Uniformly mix the modified polyethylene terephthalate-based polymer, metal oxide, lithium silicate and persulfate, and stir with a stirrer at a speed of 100 - 200 rpm for 20 - 30 min to obtain a dry mixture;

[0026] S2.3: Slowly drop the activated Bacillus subtilis bacterial suspension into the dry mixture, and stir at a speed of 200 - 300 rpm for 5 - 10 min at the same time; add calcium lactate, and continue to stir at a speed of 200 - 300 rpm for 10 - 20 min to obtain a mixture;

[0027] Bacillus subtilis is resistant to high alkaline environments. The pH value of well cement slurry is usually between 11 - 12 in the initial stage, which belongs to a strong alkaline environment, and Bacillus subtilis can survive in this environment. Bacillus subtilis produces urease during metabolism to decompose urea into ammonia and carbonate ions, and the latter combines with Ca²⁺ in the environment to accelerate the precipitation process of calcium carbonate; calcium carbonate is a common filling material, which can fill the cracks and pores in the cement slurry to achieve the self-healing function, thereby improving the sealing performance and strength of the well cement slurry; in addition, calcium lactate can adjust the pH value of the mixture to a certain extent, create a suitable living environment for microorganisms such as Bacillus subtilis, ensure its normal metabolic activities, and is conducive to the self-healing agent to exert the best effect.

[0028] S2.4. Place the mixture in an oven and dry it at 40 - 60 °C for 1 - 2 days to obtain the self - healing agent for well - cementing slurry.

[0029] Preferably, in S2.2, the metal oxide is zinc oxide or magnesium oxide.

[0030] Preferably, in S2.3, the speed of slowly dripping the activated Bacillus subtilis suspension into the dry mixture is 1 - 5 mL / min.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. In the self - healing agent for well - cementing slurry and its preparation method, adding isosorbide can react with the ester bonds in polyethylene terephthalate, thereby introducing more hydroxyl groups. These hydroxyl groups can interact with the hydration products of cement or other additives (such as metal oxides, lithium silicate, etc.), promoting the formation of new mineral phases at the crack. The generation of this new mineral phase helps to fill and repair the cracks, realizing the self - healing of the cement slurry, and thus improving the long - term stability of the well - cementing structure.

[0033] 2. In the self - healing agent for well - cementing slurry and its preparation method, after adding tetraethyl orthosilicate, the silicon dioxide gel produced by its hydrolysis and polycondensation can form colloidal particles in the cracks; over time, these colloidal particles will gradually aggregate and solidify, thereby filling the cracks and realizing the self - healing of the cement stone; tetraethyl orthosilicate can synergistically act with other components such as modified polyethylene terephthalate - based polymers and metal oxides to jointly promote the self - healing process of the cement stone.

[0034] 3. In the self - healing agent for well - cementing slurry and its preparation method, after adding titanate, it can react with the components in the cement to generate substances with gelling properties, such as calcium titanate, etc. These substances can fill the pores and micro - cracks inside the cement stone, making the structure of the cement stone more dense, thereby improving the compressive strength and flexural strength of the cement stone. Specific Embodiments

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0036] The present invention provides a self-healing agent for cement slurry in well cementing, comprising the following components: 30-50 parts by weight of a modified polyethylene terephthalate-based polymer, 2-10 parts by weight of a metal oxide, 5-15 parts by weight of lithium silicate, 0.5-2 parts by weight of persulfate, 0.1-1 part by weight of Bacillus subtilis, and 1-5 parts by weight of calcium lactate;

[0037] The modified polyethylene terephthalate-based polymer is prepared by alcoholysis reaction of isosorbide with polyethylene terephthalate, and then mixing with tetraethyl orthosilicate and titanate.

[0038] The titanate is any one of tetrabutyl titanate or tetraisopropyl titanate, preferably tetrabutyl titanate.

[0039] The metal oxide is zinc oxide or magnesium oxide, preferably zinc oxide.

[0040] Activated Bacillus subtilis bacterial suspension: Using LB medium, shake-culturing at 37 °C at a speed of 150 rpm for 24 h to grow Bacillus subtilis to the logarithmic phase; after the culturing is completed, centrifuging the cultured bacterial liquid at a speed of 4000 rpm for 10 min to separate the bacterial cell precipitate; resuspending the bacterial cell precipitate with sterile normal saline to prepare a Bacillus subtilis bacterial suspension with a concentration of 10 7 CFU / mL for standby.

[0041] Example 1: A preparation method of a self-healing agent for cement slurry in well cementing, comprising the following steps:

[0042] S2.1. Weigh the following components by weight respectively: 40 parts by weight of a modified polyethylene terephthalate-based polymer, 6 parts by weight of zinc oxide, 10 parts by weight of lithium silicate, 1.2 parts by weight of persulfate, 0.5 part by weight of Bacillus subtilis, and 3 parts by weight of calcium lactate;

[0043] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry mixture;

[0044] S2.3. Dropwise add the activated Bacillus subtilis bacterial suspension to the dry mixture at a speed of 3 mL / min, and stir at a speed of 300 rpm for 10 min at the same time; add calcium lactate, and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0045] S2.4. Place the mixture in an oven and dry at 60 °C for 2 days to obtain a self-healing agent for cement slurry in well cementing.

[0046] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0047] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 13 parts by weight of isosorbide, 2 parts by weight of sodium hydroxide, 15 parts by weight of tetraethyl orthosilicate, 30 parts by weight of toluene, 10 parts by weight of tetrabutyl titanate, and 0.3 parts by weight of acetic acid;

[0048] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20,000 and isosorbide, add sodium hydroxide with a concentration of 2%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react for 6 h at a speed of 500 r / min with a stirrer to obtain modified polyethylene terephthalate;

[0049] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 50%; add modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir for 60 min at a speed of 600 r / min to obtain a mixture;

[0050] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0051] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 60 °C and a vacuum degree of 0.1 MPa to obtain a modified polyethylene terephthalate-based polymer.

[0052] Example 2: A preparation method of a self-healing agent for cement slurry for well cementing, comprising the following steps:

[0053] S2.1. Weigh the following components by weight: 40 parts by weight of modified polyethylene terephthalate-based polymer, 6 parts by weight of zinc oxide, 10 parts by weight of lithium silicate, 1.2 parts by weight of persulfate, 0.5 parts by weight of Bacillus subtilis, and 3 parts by weight of calcium lactate;

[0054] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir for 30 min at a speed of 200 rpm with a stirrer to obtain a dry mixture;

[0055] S2.3. Dropwise add an activated Bacillus subtilis bacterial suspension to the dry mixture at a speed of 3 mL / min, and stir at a speed of 300 rpm for 10 min; add calcium lactate, and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0056] S2.4. Place the mixture in an oven and dry it at 60 °C for 2 days to obtain the self-healing agent for the well cement slurry.

[0057] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0058] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 20 parts by weight of isosorbide, 2 parts by weight of sodium hydroxide, 15 parts by weight of tetraethyl orthosilicate, 30 parts by weight of toluene, 10 parts by weight of tetrabutyl titanate, and 0.3 parts by weight of acetic acid;

[0059] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20,000 and isosorbide, add sodium hydroxide with a concentration of 2%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react for 6 h at a speed of 500 r / min with a stirrer to obtain the modified polyethylene terephthalate;

[0060] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 50%; add the modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir for 60 min at a speed of 600 r / min to obtain a mixture;

[0061] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0062] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 60 °C and a vacuum degree of 0.1 MPa to obtain the modified polyethylene terephthalate-based polymer.

[0063] Example 3: A preparation method of a self-healing agent for well cement slurry, comprising the following steps:

[0064] S2.1. Weigh the following components by weight: 40 parts by weight of the modified polyethylene terephthalate-based polymer, 6 parts by weight of zinc oxide, 10 parts by weight of lithium silicate, 1.2 parts by weight of persulfate, 0.5 parts by weight of Bacillus subtilis, and 3 parts by weight of calcium lactate;

[0065] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry blend;

[0066] S2.3. Dropwise add the activated Bacillus subtilis suspension into the dry mixture at a rate of 3 mL / min, and stir at a speed of 300 rpm for 10 min; add calcium lactate, and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0067] S2.4. Place the mixture in an oven and dry it at 60 °C for 2 days to obtain the self-healing agent for well cement slurry.

[0068] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0069] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 26 parts by weight of isosorbide, 2 parts by weight of sodium hydroxide, 15 parts by weight of tetraethyl orthosilicate, 30 parts by weight of toluene, 10 parts by weight of tetrabutyl titanate, and 0.3 parts by weight of acetic acid;

[0070] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20,000 and isosorbide, add sodium hydroxide with a concentration of 2%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react at a speed of 500 r / min for 6 h to obtain the modified polyethylene terephthalate;

[0071] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 50%; add the modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir at a speed of 600 r / min for 60 min to obtain a mixture;

[0072] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0073] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 60 °C and a vacuum degree of 0.1 MPa to obtain the modified polyethylene terephthalate-based polymer.

[0074] Example 4: A preparation method of a self-healing agent for well cement slurry, comprising the following steps:

[0075] S2.1. Weigh the following components by weight: 40 parts by weight of the modified polyethylene terephthalate-based polymer, 6 parts by weight of zinc oxide, 10 parts by weight of lithium silicate, 1.2 parts by weight of persulfate, 0.5 parts by weight of Bacillus subtilis, and 3 parts by weight of calcium lactate;

[0076] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry blend;

[0077] S2.3. Dropwise add the activated Bacillus subtilis suspension into the dry blend at a rate of 3 mL / min while stirring at a speed of 300 rpm for 10 min; add calcium lactate and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0078] S2.4. Place the mixture in an oven and dry at 60 °C for 2 days to obtain a self-healing agent for well cement slurry.

[0079] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0080] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 30 parts by weight of isosorbide, 2 parts by weight of sodium hydroxide, 15 parts by weight of tetraethyl orthosilicate, 30 parts by weight of toluene, 10 parts by weight of tetrabutyl titanate, and 0.3 parts by weight of acetic acid; 13 19.5 26 30

[0081] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20,000 and isosorbide, add sodium hydroxide with a concentration of 2%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react at a speed of 500 r / min with a stirrer for 6 h to obtain modified polyethylene terephthalate;

[0082] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 50%; add the modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir at a speed of 600 r / min for 60 min to obtain a mixture;

[0083] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98% while continuing to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0084] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 60 °C and a vacuum degree of 0.1 MPa to obtain a modified polyethylene terephthalate-based polymer.

[0085] Example 5: A preparation method of a self-healing agent for well cement slurry, comprising the following steps:

[0086] S2.1. Weigh the following components in parts by weight respectively: 30 parts by weight of modified polyethylene terephthalate-based polymer, 2 parts by weight of zinc oxide, 5 parts by weight of lithium silicate, 0.5 part by weight of persulfate, 0.1 part by weight of Bacillus subtilis, and 1 part by weight of calcium lactate;

[0087] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry blend;

[0088] S2.3. Dropwise add the activated Bacillus subtilis bacterial suspension to the dry blend at a speed of 3 mL / min, and stir at a speed of 300 rpm for 10 min; add calcium lactate and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0089] S2.4. Place the mixture in an oven and dry it at 60 °C for 2 days to obtain a self-healing agent for well cement slurry.

[0090] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0091] S1.1. Weigh the following components in parts by weight respectively: 65 parts by weight of polyethylene terephthalate, 26 parts by weight of isosorbide, 1 part by weight of sodium hydroxide, 10 parts by weight of tetraethyl orthosilicate, 20 parts by weight of toluene, 5 parts by weight of tetrabutyl titanate, and 0.1 part by weight of acetic acid;

[0092] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20000 and isosorbide, add sodium hydroxide with a concentration of 1%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react with a stirrer at a speed of 500 r / min for 6 h to obtain modified polyethylene terephthalate;

[0093] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 30%; add the modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir at a speed of 600 r / min for 60 min to obtain a mixture;

[0094] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0095] S1.5. After the reaction is completed, the reaction system is subjected to rotary evaporation at 60 °C under a vacuum of 0.1 MPa to obtain a modified polyethylene terephthalate-based polymer.

[0096] Example 6: A preparation method of a self-healing agent for cement slurry for well cementing, comprising the following steps:

[0097] S2.1. Weigh the following components by weight: 40 parts by weight of a modified polyethylene terephthalate-based polymer, 2 parts by weight of zinc oxide, 5 parts by weight of lithium silicate, 0.5 parts by weight of persulfate, 0.1 parts by weight of Bacillus subtilis, and 1 part by weight of calcium lactate;

[0098] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry mixture;

[0099] S2.3. Dropwise add an activated Bacillus subtilis suspension to the dry mixture at a rate of 3 mL / min, and stir at a speed of 300 rpm for 10 min; add calcium lactate, and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture;

[0100] S2.4. Place the mixture in an oven and dry it at 60 °C for 2 days to obtain a self-healing agent for cement slurry for well cementing.

[0101] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0102] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 26 parts by weight of isosorbide, 1 part by weight of sodium hydroxide, 10 parts by weight of tetraethyl orthosilicate, 20 parts by weight of toluene, 5 parts by weight of tetrabutyl titanate, and 0.1 parts by weight of acetic acid;

[0103] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20000 and isosorbide, add sodium hydroxide with a concentration of 1%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react with a stirrer at a speed of 500 r / min for 6 h to obtain a modified polyethylene terephthalate;

[0104] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 30%; add the modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir at a speed of 600 r / min for 60 min to obtain a mixture;

[0105] S1.4. Drop tetrabutyl titanate into the mixture over a period of 40 min. After the addition is complete, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min. After thorough mixing, raise the temperature to 150 °C and react for 3 h.

[0106] S1.5. After the reaction is completed, subject the reaction system to rotary evaporation at 60 °C under a vacuum of 0.1 MPa to obtain the modified polyethylene terephthalate-based polymer.

[0107] Example 7: A method for preparing a self-healing agent for well cement slurry, comprising the following steps:

[0108] S2.1. Weigh the following components by weight: 50 parts by weight of modified polyethylene terephthalate-based polymer, 2 parts by weight of zinc oxide, 5 parts by weight of lithium silicate, 0.5 parts by weight of persulfate, 0.1 parts by weight of Bacillus subtilis, and 1 part by weight of calcium lactate.

[0109] S2.2. Uniformly mix the modified polyethylene terephthalate-based polymer, zinc oxide, lithium silicate, and persulfate, and stir with a stirrer at a speed of 200 rpm for 30 min to obtain a dry blend.

[0110] S2.3. Drop the activated Bacillus subtilis suspension into the dry blend at a rate of 3 mL / min, while stirring at a speed of 300 rpm for 10 min; add calcium lactate and continue to stir at a speed of 300 rpm for 20 min to obtain a mixture.

[0111] S2.4. Place the mixture in an oven and dry at 60 °C for 2 days to obtain the self-healing agent for well cement slurry.

[0112] The preparation method of the modified polyethylene terephthalate-based polymer is as follows:

[0113] S1.1. Weigh the following components by weight: 65 parts by weight of polyethylene terephthalate, 26 parts by weight of isosorbide, 1 part by weight of sodium hydroxide, 10 parts by weight of tetraethyl orthosilicate, 20 parts by weight of toluene, 5 parts by weight of tetrabutyl titanate, and 0.1 part by weight of acetic acid.

[0114] S1.2. Under nitrogen protection, mix polyethylene terephthalate with a relative molecular mass of 20,000 and isosorbide, add sodium hydroxide with a concentration of 1%, raise the temperature to 220 °C at a rate of 25 °C / h, and stir and react with a stirrer at a speed of 500 rpm for 6 h to obtain modified polyethylene terephthalate.

[0115] S1.3. Dissolve tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution with a concentration of 30%; add modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lower the temperature to 120 °C, and stir at a speed of 600 r / min for 60 min to obtain a mixture;

[0116] S1.4. Dropwise add tetrabutyl titanate to the mixture, and the dropping time is 40 min; after the dropping is completed, add acetic acid with a concentration of 98%, and continue to stir at a speed of 800 r / min for 15 min; after mixing evenly, raise the temperature to 150 °C and react for 3 h;

[0117] S1.5. After the reaction is completed, perform rotary evaporation on the reaction system at 60 °C and a vacuum degree of 0.1 MPa to obtain a modified polyethylene terephthalate-based polymer. Comparative Example 1

[0118] Adopt the method of Example 3, without using the modified polyethylene terephthalate-based polymer, and directly use polyethylene terephthalate to prepare polyethylene terephthalate. Comparative Example 2

[0119] Adopt the method of Example 3. In the preparation method of the modified polyethylene terephthalate-based polymer, remove tetraethyl orthosilicate. Comparative Example 3

[0120] Adopt the method of Example 3. In the preparation method of the modified polyethylene terephthalate-based polymer, remove titanate.

[0121] The self-healing agent for well cement slurry prepared by the present invention through a modified polyethylene terephthalate-based polymer, wherein the performance index inspection items and inspection standards of the self-healing agent for well cement slurry are as follows:

[0122] According to the GB / T 50082-2009 standard, prepare a cement stone specimen with standard dimensions (100×100×400 mm), use a cutting tool to create a crack with a width of 0.5 mm and a length of 100 mm on the specimen; completely immerse the specimen with the crack in the self-healing agent, take it out after 28 days to observe the width, and calculate the crack healing rate through the formula; a high crack healing rate indicates that the self-healing agent can effectively seal the crack, reduce the infiltration of moisture, gas and other harmful substances, thereby improving the integrity and durability of the structure.

[0123] According to the GB / T 50082-2009 standard, prepare cement paste specimens of standard size (100×100×400 mm), and use cutting tools to create cracks with a width of 0.5 mm and a length of 100 mm on the specimens; use a professional permeability tester (such as a constant-pressure head permeameter) for measurement, and calculate the permeability recovery rate through a formula; a high permeability recovery rate means that the self-healed cement paste has regained good sealing performance, preventing fluid leakage and reducing the risk of environmental pollution.

[0124] Through the above standards, the self-healing agents for well cement slurries prepared in Examples 1-7 and Comparative Examples 1-3 were tested, and the obtained data are shown in Table 1:

[0125] Table 1 Performance data of self-healing agents for well cement slurries in Examples 1-7 and Comparative Examples 1-3;

[0126]

[0127] It can be seen from Examples 1-4 that when the mass ratio of isosorbide to polyethylene terephthalate in the modified polyethylene terephthalate-based polymer gradually increases, the crack healing rate and permeability recovery rate of the self-healing agent for well cement slurries gradually increase. However, when the mass ratio of isosorbide to polyethylene terephthalate reaches a certain value, the crack healing rate and permeability recovery rate of the self-healing agent for well cement slurries gradually decrease. Thus, it can be known that with the increase of the mass ratio of isosorbide, both the crack healing rate and permeability recovery rate of the self-healing agent for well cement slurries are improved, but excessive increase may reduce the crack healing rate and permeability recovery rate of the self-healing agent for well cement slurries;

[0128] Isosorbide contains multiple hydroxyl (-OH) functional groups and has high reactivity. When the mass ratio of isosorbide to polyethylene terephthalate increases, the content of hydroxyl groups in the system relatively increases, which can undergo complexation reactions with calcium ions in the cement hydration products to generate more substances with gelling properties. These substances can fill the cracks, thereby increasing the crack healing rate and permeability recovery rate; in addition, the addition of isosorbide can improve the flexibility and adhesiveness of the polymer, enabling it to better adapt to the deformation and expansion of the cracks; at the same time, its adhesion performance with the cement paste is also enhanced, enabling the self-healing agent to adhere more firmly to the crack surface, effectively preventing fluid penetration, and thus increasing the permeability recovery rate; moreover, the improvement of flexibility helps the self-healing agent to form a continuous healing layer in the cracks, improving the crack healing effect.

[0129] Furthermore, through the comparison of Examples 5-7, it can be seen that: when other components remain unchanged, only when the proportion of the modified polyethylene terephthalate-based polymer gradually increases, the crack healing rate and permeability recovery rate of the well cement slurry self-healing agent gradually increase. Thus, it can be known that the modified polyethylene terephthalate-based polymer has significant flexibility and viscosity. When its proportion increases, it can better flow into the cracks of the cement stone to form effective filling. This filling not only directly reduces the width and length of the cracks, thereby increasing the crack healing rate; as the proportion of the modified polyethylene terephthalate-based polymer increases, after filling the cracks, it can reduce the permeability of the cracks and prevent fluid from permeating through the cracks, thereby increasing the permeability recovery rate; the modified polyethylene terephthalate-based polymer can play a role similar to a toughening agent in the cement slurry, helping to improve the microstructure of the cement stone and making it more dense. This dense structure can not only increase the strength of the cement stone but also reduce the generation and expansion of cracks, thereby increasing the crack healing rate and permeability recovery rate; in addition, the modified polyethylene terephthalate-based polymer can also provide more material and energy support for the self-healing reaction, enabling the self-healing reaction to proceed continuously. After cracks appear, this continuous self-healing reaction can continuously fill and repair the cracks, thereby increasing the crack healing rate and permeability recovery rate.

[0130] Comparing Example 3 with Comparative Example 1, it can be seen that when directly using polyethylene terephthalate to prepare polyethylene terephthalate without using the modified polyethylene terephthalate-based polymer, the crack healing rate and permeability recovery rate of the well cement slurry self-healing agent are significantly reduced.

[0131] Taking Example 3 as the optimal example and combining it with Comparative Example 2, it can be known that in the preparation method of the modified polyethylene terephthalate-based polymer, when tetraethyl orthosilicate is removed, the crack healing rate and permeability recovery rate of the well cement slurry self-healing agent are significantly reduced;

[0132] Tetraethyl orthosilicate is an important silicon source. Through hydrolysis and polycondensation reactions, it generates silicides such as silicon dioxide. These silicides can react with components such as calcium and aluminum in the cement slurry to form gelling minerals such as calcium silicate and calcium aluminate, thereby increasing the crack healing rate and permeability recovery rate. When tetraethyl orthosilicate is removed, due to the lack of silicon source, the generation of gelling minerals is reduced, which in turn affects the filling and healing effects of cracks, resulting in a significant decrease in the crack healing rate and permeability recovery rate. During the reaction process, tetraethyl orthosilicate forms a three-dimensional network structure, which can enhance the mechanical properties and stability of the modified polyethylene terephthalate-based polymer. At the same time, it can also intertwine with the hydration products in the cement stone to form a denser structure, thereby improving the impermeability and crack healing ability of the cement stone. However, when tetraethyl orthosilicate is removed, the formation of the three-dimensional network structure is hindered, the performance of the modified polyethylene terephthalate-based polymer deteriorates, and the strengthening effect on the cement stone weakens, resulting in a decrease in the crack healing rate and permeability recovery rate.

[0133] Example 3 is taken as the optimal example. Combining with Comparative Example 3, it can be seen that in the preparation method of the modified polyethylene terephthalate-based polymer, when the titanate is removed, the crack healing rate and permeability recovery rate of the well cement slurry self-healing agent are significantly reduced.

[0134] Titanate can significantly promote the polymerization reaction, increase the growth rate and crosslinking degree of molecular chains, thereby endowing the polymer with better structure and performance. However, when the titanate is removed, the polymerization reaction rate decreases significantly, resulting in an uneven molecular weight distribution of the polymer and a decrease in the crosslinking degree of molecular chains, which in turn weakens the mechanical properties and self-healing ability of the polymer, ultimately affecting the crack healing rate and permeability recovery rate. At the same time, titanate can also improve the interfacial bonding force between the modified polyethylene terephthalate-based polymer and the cement stone. It forms a transition layer between the two, enhancing the bonding tightness of the two. However, when the titanate is removed, the interfacial bonding force weakens, resulting in easy debonding between the self-healing agent and the cement stone, thereby reducing the filling and repair effects of the self-healing agent on cracks and further reducing the crack healing rate and permeability recovery rate.

[0135] 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. The above embodiments and descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A self-healing agent for cementing slurry, characterized in that: The invention comprises the following components: 30-50 parts by weight of a modified polyethylene terephthalate-based polymer, 2-10 parts by weight of a metal oxide, 5-15 parts by weight of a lithium silicate, 0.5-2 parts by weight of a persulfate, 0.1-1 parts by weight of Bacillus subtilis and 1-5 parts by weight of calcium lactate; The modified polyethylene terephthalate-based polymer is prepared by alcoholysis of isosorbide and polyethylene terephthalate, followed by mixing with tetraethyl orthosilicate and titanate; The preparation method of the modified polyethylene terephthalate-based polymer is as follows: S1.1, respectively weigh the following components in parts by weight: 50-80 parts by weight of polyethylene terephthalate, 10-30 parts by weight of isosorbide, 1-3 parts by weight of sodium hydroxide, 10-20 parts by weight of tetraethyl orthosilicate, 20-40 parts by weight of toluene, 5-15 parts by weight of titanate, and 0.1-0.5 parts by weight of acetic acid; S1.2, under nitrogen protection, polyethylene terephthalate and isosorbide are mixed, sodium hydroxide with a concentration of 1-3% is added, the temperature is slowly raised to 180-250°C, and agitated at a speed of 300-600 r / min for 3-8 hours to obtain modified polyethylene terephthalate; S1.3, dissolving tetraethyl orthosilicate in toluene to obtain a tetraethyl orthosilicate solution; adding modified polyethylene terephthalate to the tetraethyl orthosilicate solution, lowering the temperature to 80-120° C., and stirring at a speed of 400-800 r / min for 30-60 min to obtain a mixture; S1.4, add titanate to the mixture, add 98% acetic acid after the addition, and continue stirring at 400-800r / min for 10-15min; after mixing evenly, raise the temperature to 120-150℃ and react for 1-3h; S1.

5. After the reaction is completed, the reaction system is subjected to rotary evaporation at 50-80°C and a vacuum degree of 0.08-0.1 MPa to obtain a modified polyethylene terephthalate-based polymer.

2. The self-healing agent for cementing slurry according to claim 1, characterized in that: In the above S1.2, the relative molecular mass of polyethylene terephthalate is 15000-30000.

3. The self-healing agent for cementing slurry according to claim 1, characterized in that: In the step S1.2, the temperature is slowly increased at a rate of 20-30°C / h.

4. The self-healing agent for cementing slurry according to claim 1, characterized in that: In S1.3, the concentration of the ethyl orthosilicate solution is 30-70%.

5. The self-healing agent for cementing slurry according to claim 1, characterized in that: In the above S1.4, the titanate is any one of tetrabutoxy titanate or tetraisopropoxy titanate.

6. The self-healing agent for cementing slurry according to claim 1, characterized in that: In the step S1.4, the time for adding titanate dropwise is 20-40 min.

7. A method for preparing a cementing slurry self-healing agent, used for preparing the cementing slurry self-healing agent as claimed in any one of claims 1 to 6, characterized in that: The preparation method of the cementing slurry self-healing agent is as follows: S2.

1. Weigh the following components in parts by weight respectively: 30-50 parts by weight of modified polyethylene terephthalate-based polymer, 2-10 parts by weight of metal oxide, 5-15 parts by weight of lithium silicate, 0.5-2 parts by weight of persulfate, 0.1-1 parts by weight of Bacillus subtilis and 1-5 parts by weight of calcium lactate; S2.2, uniformly mixing the modified polyethylene terephthalate-based polymer, the metal oxide, the lithium silicate and the persulfate, stirring with a stirrer at a speed of 100-200 rpm for 20-30 min to obtain a dry blend; S2.3, slowly drop the activated Bacillus subtilis suspension into the dry mix, and stir at a speed of 200-300 rpm for 5-10 min; add calcium lactate, and continue stirring at a speed of 200-300 rpm for 10-20 min to obtain a mixture; S2.

4. Place the mixture in an oven and dry it at 40-60°C for 1-2 days to obtain a cementing slurry self-healing agent.

8. The method for preparing the self-healing agent for cementing slurry according to claim 7, characterized in that: In the above-mentioned S2.2, the metal oxide is zinc oxide or magnesium oxide.

9. The method for preparing the self-healing agent for cementing slurry according to claim 7, characterized in that: In S2.3, the activated Bacillus subtilis suspension is slowly added to the dry mix at a rate of 1-5 mL / min.

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