A plugging agent, its preparation method and application

Abstract

This application relates to a plugging agent, its preparation method, and its application, belonging to the field of petrochemical production technology. The raw material components of the plugging agent include: ultrafine cement, modified resin, tartaric acid-intercalated hydrotalcite, a fluid loss reducing agent, a dispersant, and a solvent. The diameter of the ultrafine cement is 0.1 μm to 1 μm; wherein, by weight, the ultrafine cement is 47 to 53 parts, the modified resin is 10 to 20 parts, the tartaric acid-intercalated hydrotalcite is 0.2 to 0.4 parts, the fluid loss reducing agent is 1.2 to 1.5 parts, the dispersant is 0.4 to 0.6 parts, and the solvent is 33 to 37 parts. The plugging agent provided by this application overcomes the problems of weak retention, poor bonding, and short shelf life of conventional plugging agents, thereby improving the plugging performance and thus improving the repair performance of casing damage.

Description

Technical Field

[0001] This application relates to the field of petrochemical production technology, and in particular to a plugging agent, its preparation method and application. Background Technology

[0002] Petroleum is hailed as the lifeblood of industry and is a strategic energy source that requires vigorous development. Rapid economic development has led to a rapid increase in petroleum consumption, and current oil production growth is insufficient to meet the increased demand. Therefore, improving oil recovery is imperative. In the later stages of oilfield development, as the duration of production increases, various geological factors and human operations cause different types and degrees of damage to the downhole casing. Oil and water wells may experience various casing damage phenomena such as casing bending, deformation, necking, perforation, and leakage, leading to formation water production or loss of the target layer, severely impacting production operations.

[0003] Various techniques exist for treating casing damage. Based on conventional isolation and production techniques, conventional chemical plugging techniques, and conventional casing patching techniques, new techniques have emerged, including LEP long-term isolation and production technology, high-strength chemical plugging technology, casing patching suspension repair technology, large-section composite plugging technology, and small-casing cementing repair technology. Currently, chemical plugging technology is highly flexible and widely used. With the development and improvement of chemical plugging technology, the variety of plugging materials is increasing. Cement plugging is the earliest and most widely used plugging technology for casing damage in oil and gas fields, possessing a simple preparation process, good stability, and strong retention and sealing capabilities. Furthermore, its micro-expansion properties can prevent shrinkage after cement solidification, thus avoiding water production in the later stages of plugging. However, the main problems with conventional chemical plugging agents include poor retention, poor bonding, and short shelf life. Moreover, when casing perforation and leakage occur, severe water production in the well is often present, and the water-rich environment of wells with casing damage is often unfavorable for subsequent casing damage repair using chemical plugging agents. Therefore, it is very important to explore a chemical sealant with strong retention, good bonding properties and long shelf life. Summary of the Invention

[0004] This application provides a sealing agent, its preparation method, and its application to solve the following technical problem: how to improve the sealing performance of the sealing agent.

[0005] In a first aspect, this application provides a sealing agent, the raw material components of which include: ultrafine cement, modified resin, and tartaric acid-intercalated hydrotalcite, wherein the diameter of the ultrafine cement is 0.1 μm to 1 μm; wherein, by weight,

[0006] The ultrafine cement is 47 to 53 parts, the modified resin is 10 to 20 parts, and the tartaric acid intercalated hydrotalcite is 0.2 to 0.4 parts.

[0007] Optionally, the tartaric acid intercalated hydrotalcite is 0.2 parts and the modified resin is 10 parts.

[0008] Optionally, the resin includes at least one of the following: urea-formaldehyde resin, phenolic resin, epoxy resin, unsaturated polyester resin, polyurethane resin, and silicone resin.

[0009] Optionally, the tartaric acid intercalated hydrotalcite is obtained from a magnesium aluminum hydrotalcite precursor via an ion exchange reaction.

[0010] Optionally, the raw materials of the sealing agent may also include: a water loss reducing agent, a dispersant, and a solvent.

[0011] Optionally, the water loss reducing agent comprises a polyvinyl alcohol complex; and / or,

[0012] The dispersant comprises at least one of the following: polycarboxylate, fatty alcohol polyoxyethylene ether; and / or,

[0013] The solvent includes water.

[0014] Optionally, by weight, the water loss reducing agent is 1.2 to 1.5 parts, the dispersant is 0.4 to 0.6 parts, and the solvent is 33 to 37 parts.

[0015] Optionally, the weight ratio of the solvent to the ultrafine cement is 0.7, the water loss reducing agent is 1.5 parts, and the dispersant is 0.4 parts.

[0016] Secondly, this application provides a method for preparing the sealing agent according to any one of the first aspects, the method comprising:

[0017] The ultrafine cement and solvent are mixed in the first step to obtain a first mixture.

[0018] The first mixture is mixed with tartaric acid intercalated hydrotalcite, a water loss reducing agent and a dispersant to obtain a second mixture.

[0019] The second mixture is mixed with the modified resin in a third mixture, and then the mixture obtained in the third mixture is cured to obtain a sealant.

[0020] Thirdly, this application provides an application of the plugging agent described in any embodiment of the first aspect in the repair of casing damage in oilfield oil and water wells.

[0021] The technical solutions provided in this application have the following advantages compared with the prior art:

[0022] The sealing agent provided in this application embodiment comprises the following raw material components: ultrafine cement, modified resin, and tartaric acid intercalated hydrotalcite. The diameter of the ultrafine cement is 0.1 μm to 1 μm. Specifically, by weight, the ultrafine cement is 47 to 53 parts, the modified resin is 10 to 20 parts, and the tartaric acid intercalated hydrotalcite is 0.2 to 0.4 parts. Ultrafine cement, with a diameter of 0.1μm to 1μm, can penetrate deeper into the micro-cracks of soil and rock, thereby improving the efficiency of consolidation and grouting. During the curing process, ultrafine cement effectively reduces cracks and pores in concrete and mortar, thus improving the overall density and durability of the material. Its high specific surface area and fine particles provide higher compressive and flexural strength after curing, offering high-strength support. Furthermore, the 47-53 parts ultrafine cement content balances the viscoelasticity and strength of the plugging agent. Modified resin, with its numerous functional groups, improves the adhesion of the plugging agent, allowing the ultrafine cement to better bond with the wellbore, forming a robust sealing layer. The modified resin fills the voids between cement particles, improving the chemical resistance and durability of the plugging agent, ensuring... To ensure the long-term stability of the repair effect, the modified resin, at 10-20 parts, provides the sealant with good bonding strength and durability. The tartaric acid-intercalated hydrotalcite has a layered structure, allowing tartaric acid to be intercalated between the layers. This structure effectively slows down the setting of cement, delaying the setting time of the ultrafine cement paste. Furthermore, the slowing effect can be adjusted by changing the interlayer anions. The tartaric acid-intercalated hydrotalcite, at 0.2-0.4 parts, allows for adjustment of the sealant's setting time to meet construction requirements. Therefore, the synergistic effect between ultrafine cement, modified resin, and tartaric acid-intercalated hydrotalcite results in an ultrafine cement sealant with strong retention, good bonding properties, and a long effective period, thus improving its sealant performance and consequently its repair performance for casing damage. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram illustrating the preparation principle of tartaric acid intercalated hydrotalcite provided in the embodiments of this application;

[0026] Figure 2A schematic flowchart illustrating a method for preparing a sealing agent according to an embodiment of this application;

[0027] Figure 3 XRD pattern of TA-LDHs retarder provided in the embodiments of this application;

[0028] Figure 4 Infrared spectrum of TA-LDHs retarder provided in the embodiments of this application;

[0029] Figure 5 SEM images of TA-LDHs retarder provided in the embodiments of this application; (A) - hydrotalcite precursor, (B) - hydrotalcite intercalation product;

[0030] Figure 6 An optimized dosage diagram of a leak-stopping agent and a dehydration-reducing agent is provided in an embodiment of this application.

[0031] Figure 7 An optimization diagram of the dosage of a plugging agent dispersant is provided in an embodiment of this application;

[0032] Figure 8 An optimization diagram of the density or flowability of a plugging agent and the dosage of TA-LDHs retarder is provided for embodiments of this application;

[0033] Figure 9 An optimization diagram of the compressive strength of a sealing agent and the dosage of TA-LDHs retarder is provided for an embodiment of this application.

[0034] Figure 10 An optimization diagram of the thickening properties (initial viscosity and thickening time) of a plugging agent and the dosage of TA-LDHs retarder provided for embodiments of this application;

[0035] Figure 11 An optimized graph showing the thickening properties (consistency, pressure, and temperature) and thickening time of a sealing agent provided in an embodiment of this application;

[0036] Figure 12 This is a schematic diagram of the sealing strength testing experimental device provided in the embodiments of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0039] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0041] In a first aspect, this application provides a sealing agent, the raw material components of which include: ultrafine cement, modified resin, and tartaric acid-intercalated hydrotalcite, wherein the diameter of the ultrafine cement is 0.1 μm to 1 μm; wherein, by weight,

[0042] The ultrafine cement is 47 to 53 parts, the modified resin is 10 to 20 parts, and the tartaric acid intercalated hydrotalcite is 0.2 to 0.4 parts.

[0043] In some embodiments, the tartaric acid-intercalated hydrotalcite is 0.2 parts and the modified resin is 10 parts.

[0044] In this embodiment, the ultrafine cement has a diameter of 0.1 μm to 1 μm, enabling it to penetrate deeper into the micro-cracks in soil and rock, thereby improving the efficiency of consolidation and grouting. During the curing process, the ultrafine cement effectively reduces cracks and pores in concrete and mortar, thus improving the overall density and durability of the material. Furthermore, the high specific surface area and fine particles of the ultrafine cement provide higher compressive and flexural strength after curing, offering high-strength support. The ultrafine cement content of 47 to 53 parts balances the viscoelasticity and strength of the plugging agent. The modified resin has numerous functional groups, improving the adhesion of the plugging agent and allowing the ultrafine cement to better bond with the well wall, forming a robust sealing layer. The modified resin fills the gaps between cement particles, improving the chemical resistance and durability of the plugging agent. This ensures the long-term stability of the repair effect, and the modified resin content of 10 to 20 parts gives the sealant good bonding strength and durability. The tartaric acid intercalated hydrotalcite (hereinafter also called retarder) has a layered structure, allowing tartaric acid to be intercalated between its layers. This structure has a good retarding effect on cement, delaying the setting time of ultrafine cement paste. Furthermore, by changing the interlayer anions, its retarding effect can be adjusted. The tartaric acid intercalated hydrotalcite content of 0.2 to 0.4 parts can adjust the setting time of the sealant to meet construction requirements. Therefore, the synergistic effect between ultrafine cement, modified resin, and tartaric acid intercalated hydrotalcite can form an ultrafine cement sealant with strong retention, good bonding properties, and long effective period, thereby improving the sealant's sealing performance and thus improving the repair performance of the casing damage. For example, the diameter of the ultrafine cement can be 0.1μm, 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, etc.; the ultrafine cement can be 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, etc.; the modified resin can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, etc.; and the tartaric acid-intercalated hydrotalcite can be 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, etc. In one embodiment, the tartaric acid-intercalated hydrotalcite can be 0.2 parts, and the modified resin can be 10 parts.

[0045] In some embodiments, the resin includes at least one of the following: urea-formaldehyde resin, phenolic resin, epoxy resin, unsaturated polyester resin, polyurethane resin, and silicone resin.

[0046] In the embodiments of this application, the resin can be one or more combinations of urea-formaldehyde resin, phenolic resin, epoxy resin, unsaturated polyester resin, polyurethane resin, and organosilicon resin. Through chemical modification, these resins can improve the mechanical properties and chemical stability of the modified resin in the sealing agent. The modified resin fills the voids between cement particles, improving the overall density and durability. Further, urea-formaldehyde resin can be selected, as it possesses advantages such as good adhesion, heat resistance, corrosion resistance, and high hardness. Exemplarily, the preparation method of modified urea-formaldehyde resin includes: weighing 40% urea and 60% formaldehyde by mass and dissolving them in a certain amount of deionized water to prepare a 200mL solution; weighing sodium hydroxide and sodium carbonate at a molar ratio of 4:1 and adding them to the deionized water to prepare an alkaline solution; adjusting the pH of the solution to 7.5-8.5; adding the solution to a reaction vessel; maintaining the reaction temperature at 80-90℃; and adding phenol as a modifier during the polycondensation reaction, with the amount being 10-20% of the urea content. The reaction is maintained for a certain time, usually 1 to 2 hours. After the reaction is complete, the obtained product is repeatedly rotary evaporated, washed, and filtered with anhydrous ethanol (to remove unreacted monomers), and then vacuum dried at 70°C for 24 hours to obtain modified urea-formaldehyde resin.

[0047] In some embodiments, the tartaric acid intercalated layered double hydroxide is obtained from a magnesium aluminum layered double hydroxide precursor via an ion exchange reaction. Figure 1 This is a schematic diagram illustrating the preparation principle of tartaric acid-intercalated hydrotalcite provided in the embodiments of this application; please refer to... Figure 1 .

[0048] In this embodiment, the preparation method of the magnesium aluminum hydrotalcite precursor includes: weighing magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in a Mg:Al molar ratio of 3:1 and adding them to deionized water to prepare a 200 mL mixed salt solution; weighing sodium hydroxide and sodium carbonate in a molar ratio of 4:1 and adding them to deionized water to prepare a 200 mL alkaline solution; simultaneously adding the prepared mixed salt solution and alkaline solution dropwise into a three-necked flask; maintaining the reaction temperature at 75°C; maintaining the dropping rate of the alkaline solution at one drop every two seconds; keeping the pH of the solution between 9 and 10; refluxing at 75°C for 5 hours; filtering and washing three times with water; and drying at 80°C for 15-25 hours to obtain the magnesium aluminum hydrotalcite precursor (Mg / Al-CO3-LDHs). The reaction equation is as follows:

[0049] Mg(NO3)2·6H2O+2Al(NO3)2·9H2→Mg6Al2(OH) 16 CO3·4H2O (1)

[0050] Tartaric acid dissolved in ethylene glycol solution was added to a three-necked flask. The pH was adjusted to approximately 4.5 with 0.1 mol / L NaOH solution. The precursor was then weighed into the three-necked flask at a molar ratio of 2:1 of tartaric acid to hydrotalcite precursor. The pH of the solution was measured, and the pH was maintained at 4.5 with 0.1 mol / L NaOH. After crystallization in an oil bath at 150°C for 5 hours, the solution was allowed to cool naturally, filtered, washed with deionized water until the pH of the filtrate was neutral, and the filter cake was vacuum dried at 80°C for 12 hours to obtain tartaric acid-intercalated hydrotalcite (Mg / Al-TA-LDHs), denoted as TA-LDHs.

[0051] In some embodiments, the raw materials of the plugging agent also include: a water loss reducing agent, a dispersant, and a solvent.

[0052] In some embodiments, the water loss reducing agent comprises a polyvinyl alcohol complex; and / or,

[0053] The dispersant comprises at least one of the following: polycarboxylate, fatty alcohol polyoxyethylene ether; and / or,

[0054] The solvent includes water.

[0055] In this embodiment, the raw materials of the plugging agent may further include: a water loss reducing agent, a dispersant, and a solvent. The water loss reducing agent can reduce water loss from the cement slurry during the consolidation process, maintaining the stability and fluidity of the slurry. The water loss reducing agent may include a polyvinyl alcohol composite. The polyvinyl alcohol composite can effectively reduce the water loss of the cement slurry because it can form a dense film on the surface of cement particles, effectively preventing water loss. The filter cake formed by the polyvinyl alcohol composite is denser, which helps improve the stability of the well wall. This polyvinyl alcohol composite is obtained by polymerizing polyvinyl alcohol with a crosslinking agent, which can be one or more combinations of borax, phosphoric acid, and glutaraldehyde.

[0056] An exemplary method for preparing polyvinyl alcohol composite (TSJ-1) includes: weighing a certain amount of deionized water and polyvinyl alcohol to prepare a 200 mL solution, stirring until PVA is completely dissolved, weighing hydrochloric acid at a molar ratio of 4:1 and adding it to the deionized water to prepare an acid solution, adjusting the pH of the solution to 5-6, adding the solution to a reaction vessel, maintaining the reaction temperature at 80℃, adding glutaraldehyde (1-10% of the mass of PVA), maintaining the reaction for a certain time from several hours to one day, and promoting the cross-linking reaction by stirring during the reaction. After the reaction is complete, the obtained product is repeatedly rotary evaporated with anhydrous ethanol, washed, filtered (to remove unreacted monomers), and then vacuum dried at 70℃ for 24 hours to obtain the polyvinyl alcohol-glutaraldehyde composite.

[0057] The dispersant (FSJ-1) can ensure that cement particles are uniformly dispersed in water, prevent agglomeration, and improve the fluidity and stability of the slurry. This dispersant can be one or more of polycarboxylate and fatty alcohol polyoxyethylene ether, which can significantly reduce the surface tension of water, allowing water to better wet cement particles and improve the dispersion effect.

[0058] An exemplary method for preparing a polycarboxylate dispersant includes: weighing 50% acrylic acid, 20% methacrylic acid, and 30% methyl acrylate by mass fraction and dissolving them in a certain amount of deionized water to prepare a 200 mL solution; weighing sodium hydroxide and sodium carbonate at a molar ratio of 4:1 and adding them to the deionized water to prepare an alkaline solution; adjusting the pH of the solution to 7-8; adding the solution to a reaction vessel; maintaining the reaction temperature at 80°C; adding 0.5-2% (total monomer mass ratio) of azobisisobutyramidine hydrochloride as an initiator; and maintaining the reaction for a certain time of 2-6 hours. After the reaction is complete, the obtained product is repeatedly rotary evaporated, washed, and filtered with anhydrous ethanol (to remove unreacted monomers); and then vacuum dried at 70°C for 24 hours to obtain the polycarboxylate dispersant.

[0059] The preparation method of fatty alcohol polyoxyethylene ether dispersant includes: weighing a certain amount of deionized water and lauryl alcohol to prepare a 200 mL solution; weighing sodium hydroxide and sodium carbonate in a molar ratio of 4:1 and adding them to the deionized water to prepare an alkaline solution; adjusting the pH of the solution to 7-8; slowly adding ethylene oxide (10% of the mass of lauryl alcohol); adding the solution to a reaction vessel; maintaining the reaction temperature at 130℃; and maintaining the reaction for a certain time of 1 to 3 hours. After the reaction is complete, the obtained product is repeatedly rotary evaporated with anhydrous ethanol, washed, and filtered (to remove unreacted monomers); and then vacuum dried at 70℃ for 24 hours to obtain the fatty alcohol polyoxyethylene ether dispersant.

[0060] The solvent can be water. When ultrafine cement comes into contact with water, the hydration reaction is accelerated, producing calcium silicate hydrate (CSH) gel and other hydration products. These products are the main source of the strength of hardened cement paste.

[0061] In some embodiments, the water loss reducing agent is 1.2 to 1.5 parts by weight, the dispersant is 0.4 to 0.6 parts by weight, and the solvent is 33 to 37 parts by weight.

[0062] In some embodiments, the weight ratio of the solvent to the ultrafine cement is 0.7, the water loss reducing agent is 1.5 parts, and the dispersant is 0.4 parts.

[0063] In the embodiments of this application, the water loss reducing agent can be 1.2 to 1.5 parts, thereby maintaining the stability of the sealing agent during the injection process and reducing water loss; the dispersant can be 0.4 to 0.6 parts, thereby giving the sealing agent good flowability and stability; the solvent can be 33 to 37 parts, thereby giving the sealing agent appropriate flowability and setting properties. For example, the above-mentioned water loss reducing agent can be 1.2, 1.3, 1.4, 1.5 parts, etc.; the above-mentioned dispersant can be 0.4, 0.45, 0.5, 0.55, 0.6 parts, etc.; the above-mentioned solvent can be 33, 34, 35, 36, 37 parts, etc. Further, the weight ratio of solvent to ultrafine cement can be 0.7, the water loss reducing agent can be 1.5 parts, and the dispersant can be 0.4 parts.

[0064] In summary, ultrafine cement, due to its small particle size, can better penetrate into cracks and pores, thus improving retention. The fineness of ultrafine cement ensures that the plugging agent can penetrate deep into tiny cracks to form an effective seal. The addition of a fluid loss reducer can reduce water loss of the plugging agent during injection, maintain the stability of the slurry, and maintain good fluidity and retention during injection. The dispersant can prevent the agglomeration of ultrafine cement particles, maintain the uniformity and fluidity of the slurry, and good dispersibility ensures that the plugging agent can be evenly distributed on the damaged area, improving the bonding quality. Tartaric acid intercalated hydrotalcite extends the setting time of the plugging agent, providing more time for construction. An appropriate setting time ensures that the plugging agent can fully bond at the predetermined location, forming a solid sealing structure. The addition of modified resin can improve the bonding strength and durability of the plugging agent, enhance the adhesion between the plugging agent and the wellbore material, improve the long-term stability of the sealing structure, thereby improving the plugging performance of the plugging agent and, consequently, its repair performance for casing damage.

[0065] Secondly, this application provides a method for preparing the sealing agent according to any one of the first aspects. Figure 2 A schematic flowchart illustrating a method for preparing a sealing agent according to an embodiment of this application; please refer to [link / reference]. Figure 2 The method includes:

[0066] S1. The ultrafine cement and solvent are mixed in a first mixing process to obtain a first mixture.

[0067] S2. The first mixture is mixed with tartaric acid intercalated hydrotalcite, a water loss reducing agent and a dispersant to obtain a second mixture.

[0068] S3. The second mixture is mixed with the modified resin in a third mixing process, and then the mixture obtained in the third mixing process is cured to obtain a sealing agent. The stirring speed of the third mixing process can be 1200 r / min, and the curing time can be 7 days to 30 days.

[0069] The preparation method of this sealing agent is based on the above-mentioned sealing agent. The specific raw material composition of the sealing agent can be referred to the above embodiments. Since the preparation method of this sealing agent adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0070] Thirdly, this application provides an application of the plugging agent described in any embodiment of the first aspect in the repair of casing damage in oilfield oil and water wells.

[0071] The application of this plugging agent in the repair of casing damage in oil and water wells in oilfields is based on the above-mentioned plugging agent. The specific raw material composition of the plugging agent can be referred to in the above embodiments. Since the plugging agent adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0072] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0073] Example 1

[0074] A sealing agent, by mass fraction, comprises the following raw materials: ultrafine cement (0.1μm~1μm): 50%, modified urea-formaldehyde resin: 15%, tartaric acid intercalated hydrotalcite: 0.2%, polyvinyl alcohol composite (polyvinyl alcohol-glutaraldehyde composite): 1.2%, polycarboxylate: 0.4%, and water: 33.2%.

[0075] Example 2

[0076] A sealing agent, by mass fraction, comprises the following raw materials: ultrafine cement (0.1μm~1μm): 47%, modified urea-formaldehyde resin: 15.5%, tartaric acid intercalated hydrotalcite: 0.4%, polyvinyl alcohol composite (polyvinyl alcohol-glutaraldehyde composite): 1.5%, fatty alcohol polyoxyethylene ether: 0.6%, and water: 35%.

[0077] Example 3

[0078] A sealing agent, by mass fraction, comprises the following raw materials: ultrafine cement (0.1μm~1μm): 53%, modified urea-formaldehyde resin: 10%, tartaric acid intercalated hydrotalcite: 0.3%, polyvinyl alcohol composite (polyvinyl alcohol-glutaraldehyde composite): 1.3%, fatty alcohol polyoxyethylene ether: 0.5%, and water: 34.9%.

[0079] Example 4

[0080] A sealing agent, by mass fraction, comprises the following raw materials: ultrafine cement (0.1μm~1μm): 47.8%, modified urea-formaldehyde resin: 17%, tartaric acid intercalated hydrotalcite: 0.3%, polyvinyl alcohol composite (polyvinyl alcohol-glutaraldehyde composite): 1.4%, polycarboxylate 0.5%, and water 33%.

[0081] The preparation method of the sealing agent in Examples 1-4 includes: S11, mixing ultrafine cement with a solvent to obtain a first mixture; S21, mixing the first mixture with tartaric acid-intercalated hydrotalcite, a water loss reducing agent, and a dispersant to obtain a second mixture; S31, mixing the second mixture with a modified resin, and then curing the mixture obtained from the third mixture to obtain the sealing agent. The stirring speed of the third mixture can be 1200 r / min, and the curing time can be 30 days.

[0082] Thickening performance test: The thickening time of the plugging agents in Examples 1-4 was tested according to the test methods in GB / T 19139-2012 "Test Methods for Oil Well Cement". The plugging agents in Examples 1-4 were placed on the drive plate inside the autoclave. After the slurry cup rotation speed stabilized, hydrocarbon oil was added and a potentiometer was placed in place. After the autoclave was filled with hydrocarbon oil, the thickening apparatus was sealed, and the experiment began. The time required from the start of heating (120℃) and pressurization (80MPa) until the consistency reached 100 Bc, and the consistency of the cement slurry at the end of the experiment were recorded. Please refer to Table 1 for the thickening performance test results.

[0083] Table 1 Thickening performance test results

[0084] Thickening time (min) Example 1 192 Example 2 183 Example 3 195 Example 4 176

[0085] As shown in Table 1, the retarder in the plugging agent has excellent dispersibility and stability, and can be uniformly dispersed in the cement slurry, effectively extending the thickening time of the cement slurry. The plugging agents in Examples 1 to 4 can achieve precise control of the thickening time of the cement slurry, meet the cementing requirements under different well depths and geological conditions, and meet the requirements of construction operations.

[0086] Compressive strength test: The compressive strength of the plugging agents in Examples 1-4 was tested according to the test methods in GB / T 19139-2012 "Test Methods for Cement in Oil Wells". The prepared plugging agent was poured into a 5×5×5cm... 3The sample was placed in a cubic model and then cured in a high-temperature, high-pressure curing autoclave. The curing time was set to 48 hours, the curing temperature to 120°C, and the pressure to 6.9 MPa. When the curing time exceeded the experimental time, the sample was demolded, and the compressive strength was evaluated using a pressure test method. Please refer to Table 2 for the compressive strength test results.

[0087] Table 2 Compressive strength test results

[0088] Compressive strength (MPa) Example 1 35 Example 2 37 Example 3 39 Example 4 36

[0089] As shown in Table 2, the compressive strength of the cementing and plugging agents in the embodiments is all higher than 35 MPa, which ensures that the plugging agent has sufficient pressure bearing capacity, can effectively support the well wall, prevent the well wall from collapsing due to formation pressure, and improve the stability of the wellbore.

[0090] The following tests were performed on the tartaric acid intercalated hydrotalcite retarder provided in this application:

[0091] (1) X-ray diffraction test

[0092] The hydrotalcite precursor and hydrotalcite intercalation product prepared in the embodiments of this application were tested using a DX-2700 X-ray diffractometer. The dried sample was ground into powder, then pressed into a pellet for phase analysis to determine the crystallinity of the hydrotalcite precursor and whether the ion exchange reaction was successful. During the test, the scanning range was 3° to 60°, and the step size was 0.02° / s. Figure 3 XRD patterns of TA-LDHs retarders provided in the embodiments of this application; please refer to Figure 3 The results indicate that the XRD test results of the magnesium aluminum layered double hydroxide (TLD) precursor prepared by the co-precipitation method have a stable baseline. The characteristic diffraction peaks at the (003), (006), (009), and (110) crystal planes of TLD have high intensity and sharp peak shapes, without any impurity peaks, proving that the prepared magnesium aluminum layered double hydroxide precursor has high crystallinity, obvious layered structure, and regular structure. Observation of the XRD test results of the intercalation product shows that, compared with the TLD precursor, the (003) crystal plane diffraction peak and the overall structure have shifted to lower angles, and the peak shapes are complete. According to the Bragg equation, the ion exchange reaction is successful. The diffraction angle 2θ corresponding to the diffraction peak of the (003) crystal plane of the hydrotalcite precursor is 11.68°, and the diffraction angle 2θ corresponding to the diffraction peak of the (003) crystal plane of the intercalated product is 7.48°. The interlayer spacing of the hydrotalcite precursor can be calculated to be 0.76 nm and that of the intercalated product is 1.18 nm by Bragg equation. The increase in interlayer spacing indicates that the ionic reaction proceeded successfully and that the tartaric acid intercalation of hydrotalcite was successful.

[0093] (2) Infrared spectroscopy test

[0094] The changes in chemical bonds following the ion exchange reaction between tartaric acid and the hydrotalcite precursor were determined using a WQF520 Fourier transform infrared absorption spectrometer. A 1% KBr solution was used to prepare the sample pellets, and the prepared sample pellets were then subjected to infrared spectroscopy scanning at a range of 4000 cm⁻¹. -1 ~400cm -1 . Figure 4 Infrared spectra of TA-LDHs retarder provided in the embodiments of this application; please refer to Figure 4 This indicates that in the Mg / Al-CO3-LDH infrared spectral band, 3500 cm⁻¹ -1 The relatively broad absorption peaks on the left and right are the OH vibration bands of physically adsorbed water or water of crystallization and the stretching vibration absorption peaks of M-OH; 1360 cm⁻¹ -1 The area near the symmetric vibrational absorption peak of the carbonate ion; at 750 cm⁻¹ -1 The Mg-O-Al stretching vibration peaks of the hydrotalcite lamellae appeared on both sides, at 680 cm⁻¹. -1 The appearance of a Mg-OH-Al bending vibration peak at 1360 cm⁻¹ indicates the successful preparation of the magnesium aluminum layered double hydroxide precursor via coprecipitation. Observation of the Mg / Al-TA-LDH infrared spectral bands reveals a peak at 1360 cm⁻¹. -1 CO3 at the location -2 The absorption peak disappears at 1600 cm⁻¹. -1 and 1400cm -1 Antisymmetric and symmetric absorption peaks of carboxylate ions appear nearby, at 1000 cm⁻¹. -1 An absorption peak for in-plane bending vibration of OH was observed at 2900 cm⁻¹. -1 The presence of stretching vibration peaks of CH bonds indicates that an ion exchange reaction occurred between the hydrotalcite precursor and tartaric acid, and that tartaric acid successfully inserted into the interlayer of the hydrotalcite precursor and interacted with the hydrotalcite layers through ionic bonds.

[0095] (3) Scanning electron microscopy test

[0096] The prepared hydrotalcite precursor and the intercalated TA-LDHs samples were sputtered with gold and then subjected to scanning electron microscopy (SEM) analysis. Figure 5 SEM images of TA-LDHs retarder provided in the embodiments of this application; (A) - hydrotalcite precursor, (B) - hydrotalcite intercalation product; please refer to Figure 5As can be seen from the SEM image, the microstructure of the prepared hydrotalcite precursor did not change significantly compared to the sample after the ion exchange reaction. In contrast, the TA-LDHs sample exhibited a more pronounced lamellar structure, with the lamellars stacked sequentially to form relatively large lamellar structures. While the hydrotalcite precursor also had a lamellar structure with clear boundaries, the lamellars varied in size and were randomly stacked, with some layers encapsulating each other, and some structures appearing as small spherical masses. It can be inferred that the exchange of tartrate and carbonate ions made the arrangement of the hydrotalcite lamellars more orderly.

[0097] To investigate the optimal water-cement ratio (the weight ratio of solvent to ultrafine cement).

[0098] The optimal water-cement ratio for the ultrafine cement plugging system was screened based on the water separation rate, fluidity, density, and setting time at 80℃. For the water separation rate determination, 100 mL of cement slurry (first study system: water and ultrafine cement) was taken, and the amount of water separation was observed over 2 hours. The setting time was determined at 80℃, following the method specified in GB / T 1346-2019. Please refer to Table 3 for the effect of different water-cement ratios on the basic properties of ultrafine cement slurry.

[0099] Table 3 shows the experimental results: a higher water-cement ratio, lower cement content, lower cement slurry density, and more pronounced water separation. The water separation capacity of the cement slurry affects the diffusion range and pressure of the slurry during grouting; excessive water separation can negatively impact the grouting effect. When the water-cement ratio is less than 1.0, the amount of water separation is relatively small. The ultrafine cement slurry prepared at this ratio exhibits strong stability, high fluidity, and good flowability, meeting the requirements of on-site construction. The water-cement ratio of the ultrafine cement slurry also significantly affects its setting time. When the water-cement ratio is between 0.5 and 0.8, an increased water-cement ratio delays the initial setting time and prolongs the overall setting time. When the water-cement ratio is greater than 0.8, the ultrafine cement slurry becomes unstable due to the excessive water-cement ratio, causing some cement particles to settle and resulting in uneven concentration. Consequently, the initial setting time is advanced, and the overall setting time is shortened. Therefore, a water-cement ratio of 0.7 is selected as the water-cement ratio for the ultrafine cement plugging system.

[0100] Table 3. Effects of different water-cement ratios on the basic properties of ultrafine cement paste

[0101] water-cement ratio 0.5 0.6 0.7 0.8 0.9 1.0 Water separation volume / mL 0 0 0 0 0 1 Flowability / cm 18.5 24.0 27.0 28.0 29.0 30.0 <![CDATA[Density / g·cm -3 > 1.82 1.74 1.68 1.56 1.40 1.35 Initial setting time / min 102 110 123 152 145 135 Final setting time / min 125 140 165 189 183 173

[0102] Optimization of water loss reducing agent dosage

[0103] This application uses JSJ-1 (polyvinyl alcohol-glutaraldehyde complex, hereinafter the same) as a water loss reducing agent. JSJ-1, a water-soluble polymer chain bundle aggregate, reduces the permeability of the cement slurry filter cake and introduces various functional groups into the polymer to enhance its high-temperature and salt resistance. The optimal dosage of the water loss reducing agent was screened by studying its effect on the filtration loss of the cement slurry. A high-temperature, high-pressure filtration tester was used to measure the liquid phase filtration loss of the cement slurry at 80°C for 30 minutes. Detailed procedures are described in GB / T19139—2012, the test method for oil well cement, specifically the static filtration loss test for cement. The second research system consisted of: ultrafine cement + water loss reducing agent + 0.4% retarder + 0.2% dispersant (polycarboxylate, hereinafter the same) + water, with a water-cement ratio of 0.7. Only the amount of water loss reducing agent was varied. Figure 6 An optimization diagram of the dosage of a leak-stopping agent and a dehydration-reducing agent is provided for embodiments of this application; please refer to [link / reference]. Figure 6 The results indicate that the filtration loss of ultrafine cement slurry decreases with increasing dosage of the water loss reducing agent. When the dosage of the water loss reducing agent is less than 1.5%, the effect on reducing filtration loss of the cement slurry is significant. Especially when the dosage of the water loss reducing agent is in the range of 0.5% to 1.2%, the filtration loss of the ultrafine cement slurry can be reduced substantially. When the dosage of the water loss reducing agent is greater than 1.5%, the filtration loss is less than 50 mL, and increasing the dosage of the water loss reducing agent does not significantly improve the filtration loss further. Considering all factors, 1.5% is selected as the dosage of the water loss reducing agent for the ultrafine cement slurry plugging system.

[0104] Dispersant dosage optimization

[0105] The third research system consisted of ultrafine cement, 1.5% water loss reducer JSJ-1, 0.4% retarder TA-LDHs, dispersant FSJ-1, and water, with a water-cement ratio of 0.7. In this application, FSJ-1 was selected as the dispersant for the ultrafine cement sealing system. The optimal dosage of the dispersant was determined by studying the effect of different dosages on the fluidity of the ultrafine cement slurry. Figure 7 An optimization diagram of the dosage of a plugging agent dispersant is provided for an embodiment of this application; please refer to [link / reference]. Figure 7 This indicates that the dispersant carries a negative charge opposite to that of the cement particles, thus enabling it to adsorb onto the cement particles and neutralize the attractive forces between them. In contrast, hydrated CaSiO3 carries the same positive charge as the cement particles, therefore repelling them. Under the influence of the charge, the cement particles separate. However, excessive dispersion can damage the cement microstructure, leading to particle sedimentation or an increase in free water. Analysis of the experimental results shows that when the dispersant dosage exceeds 0.4%, the change in the fluidity of the ultrafine cement slurry is relatively small. Considering all factors, 0.4% is selected as the optimal dosage of dispersant for the ultrafine cement plugging system.

[0106] Optimization of TA-LDHs retarder dosage

[0107] The fourth research system consisted of ultrafine cement, 1.5% water loss reducer JSJ-1, retarder TA-LDHs, 0.4% dispersant FSJ-1, and water, with a water-cement ratio of 0.7. This application's embodiments investigated the effects of retarders on cement fluidity, density, rheology, thickening time, and compressive strength to comprehensively screen for the optimal retarder dosage. Figure 8 An optimization diagram of the density or flowability of a plugging agent versus the dosage of TA-LDHs retarder is provided for embodiments of this application; please refer to [link to relevant documentation]. Figure 8 Based on the effects of retarder dosage on the flow properties of ultrafine cement slurry shown in Table 4, it can be seen that the addition of retarder has little effect on the flowability and density of ultrafine cement slurry. When the retarder dosage increases to 0.2%, the flowability of ultrafine cement slurry increases slightly. Hydrotalcite is a nanomaterial with a layered structure and good dispersibility, which can improve the flowability of ultrafine cement slurry. The calculation results in Table 4 show that the addition of retarder increases the rheological index of cement slurry, decreases the consistency coefficient, enhances the flowability and dispersibility of cement slurry, and improves the overall stability of ultrafine cement slurry.

[0108] Figure 9 An optimization diagram of the compressive strength of a sealing agent and the dosage of TA-LDHs retarder is provided for embodiments of this application; please refer to [link / reference]. Figure 9 The results show that, under the same 1-day curing time, the early strength of cement paste initially decreased slightly with the addition of retarder, then increased. When the dosage reached 0.3%, the early strength showed a slight decreasing trend again. In comparison, under 3-day and 7-day curing times, the compressive strength of cement paste generally showed a trend of first increasing and then decreasing, but the pressure value was always higher than or equal to the initial value without retarder. At a dosage of 0.1%, the inhibitory effect of tartaric acid in TA-LDHs retarder on the cement hydration reaction was dominant, resulting in a weakening of early strength. After a period of time, this inhibitory effect weakened, and cement particles came into direct contact with water, accelerating the hydration reaction. The hydration products formed a hardened structure through interweaving, so it had little impact on the later strength of cement paste, with a maximum compressive strength of 29 MPa.

[0109] Figure 10 An optimization graph showing the thickening performance of a sealing agent and the addition of TA-LDHs retarder is provided for embodiments of this application; the horizontal axis represents the change in retarder addition, the blue vertical axis represents the change in the initial consistency of the cement paste (corresponding to the blue curve), and the red vertical axis represents the change in thickening time (corresponding to the red curve). Figure 11This is an optimization graph showing the thickening performance of a sealing agent and the dosage of TA-LDHs retarder, provided in an embodiment of this application. The horizontal axis represents the change in thickening time, the black vertical axis represents the change in temperature (corresponding to the black curve), the red vertical axis represents the change in pressure (corresponding to the red curve), and the blue vertical axis represents the consistency (corresponding to the blue curve). This graph can record the time it takes for the consistency to reach 100 Bc, i.e., the thickening time. Please refer to [link to relevant documentation]. Figures 10-11 It can be seen that the addition of TA-LDHs retarder significantly prolongs the thickening time of the ultrafine cement sealing system. As the TA-LDHs retarder dosage increased from 0 to 0.4%, the thickening time of the cement slurry system increased from 158 min to 387 min. This shows that TA-LDHs retarder has a good retarding effect on ultrafine cement slurry with a relatively small dosage, and the thickening time shows a linear relationship with the increase of retarder dosage. The thickening curve with a retarder dosage of 0.2% is stable, without phenomena such as "core encapsulation," "stepping," or "flash setting," and has a short overall transition time with a clear right-angle characteristic. In conclusion, the recommended TA-LDHs retarder dosage is 0.2%.

[0110] Table 4. Effect of retarder dosage on the flow properties of ultrafine cement paste

[0111] Retarder dosage / % Φ300 Φ200 Φ100 n <![CDATA[K / Pa·S n ]]> 0 88 61 50 0.514 1.823 0.1 96 69 52 0.557 1.521 0.15 98 62 51 0.593 1.240 0.2 94 58 47 0.630 0.945 0.3 95 60 46 0.659 0.797 0.4 92 56 44 0.670 0.720

[0112] Resin dosage optimization

[0113] The fifth research system consists of ultrafine cement, 1.5% water loss reducer JSJ-1, 0.2% retarder TA-LDHs, 0.4% dispersant FSJ-1, modified urea-formaldehyde resin, and water, with a water-cement ratio of 0.7.

[0114] Table 5. Compressive strength test results of resins with different dosages

[0115] resin wt% Compressive strength (MPa) 10 35 30 37 50 38 70 33 90 36

[0116] This application's embodiments investigate the effect of resin dosage on the compressive strength of cement. Please refer to Table 5 for the compressive strength test results of different resin dosages. Cement is cheaper than resin, so the resin dosage should be minimized while meeting performance requirements. With a resin dosage of 10%, the compressive strength of the coupled system is 35 MPa; with a resin dosage of 90%, the compressive strength is 36 MPa. Further increasing the resin dosage initially increases the compressive strength of the coupled cement system, then decreases, with minimal overall fluctuation. Considering economy and practicality, a resin dosage of 10% is selected.

[0117] Maintenance time and sealing test

[0118] The raw materials for the sealant include: cement + 1.5% water loss reducer JSJ-1 + 0.2% retarder TA-LDHs + 0.4% dispersant FSJ-1 + 10% modified urea-formaldehyde resin + water, with a water-cement ratio of 0.7.

[0119] a. The effect of mineralization on the sealing performance of ultrafine cement plugging systems

[0120] Figure 12 This is a schematic diagram of the sealing strength testing apparatus provided in the embodiments of this application; please refer to... Figure 12 The effects of different mineralization levels on the sealing performance of the ultrafine cement plugging system were analyzed, and Table 6 shows the influence of these levels on the sealing performance. It can be seen that with increasing mineralization, the pressure gradient breakthrough and plugging rate of the ultrafine cement plugging system fluctuate within a small range, with minimal changes. This indicates that mineralization has little impact on the sealing performance of the ultrafine cement plugging system, and it exhibits good salt resistance. Furthermore, at a mineralization level of 65680 mg·L⁻¹, the system showed good performance. -1 At that time, the ultrafine cement plugging system could still maintain a pressure gradient exceeding 90.5 MPa·m. -1 The blocking rate is above 99%.

[0121] Table 6. Effects of different mineralization on the sealing performance of ultrafine cement plugging system

[0122]

[0123]

[0124] b. Effects of different curing times on the sealing performance of ultrafine cement plugging systems

[0125] Please refer to Table 7 for the effect of different curing times on the sealing performance of the ultrafine cement plugging system. This shows that the plugging rate and breakthrough pressure gradient of the ultrafine cement plugging system increase with increasing curing time. Furthermore, after a certain curing period, the plugging system exhibits a high plugging rate and breakthrough pressure gradient, at which point the plugging performance of the plugging agent changes little with increasing days. When the curing time is 30 days, the breakthrough pressure gradient of the plugging agent reaches its maximum value of 92.03 MPa·m. -1 The blocking rate also reached its maximum value of 99.37%.

[0126] Table 7. Effects of different curing times on the sealing performance of ultrafine cement plugging system

[0127]

[0128] c. Effect of different injection volumes on the sealing performance of ultrafine cement plugging systems

[0129] Please refer to Table 8 for the effect of different injection volumes on the sealing performance of the ultrafine cement plugging system. It can be seen that the plugging rate and breakthrough pressure gradient of the plugging agent system gradually increase with the increase of its injection volume; when the injection volume reaches 0.8 PV, the plugging effect of the plugging agent is better, with a plugging rate of over 90% and a breakthrough pressure gradient greater than 70 MPa·m. -1 When the injection volume is 1 PV, the breakthrough pressure gradient increases to 91.70 MPa·m. -1 The blocking rate has risen to 99.12%.

[0130] Table 8. Effects of different injection volumes on the sealing performance of the ultrafine cement plugging system

[0131]

[0132]

[0133] One or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0134] (1) Using ultrafine cement as the main body, compared with ordinary oil well cement, it has the characteristics of smaller particle size, better rheological properties, and easier entry into the formation. When ultrafine cement slurry enters the formation and solidifies, it will reduce the effective porosity and average pore size of the plugging section, thereby reducing its permeability, so as to achieve the purpose of water blocking, channeling prevention, and leakage prevention.

[0135] (2) Tartaric acid intercalated hydrotalcite retarder has a good retarding effect on cement, which can solve the problem that the thickening time of ultrafine cement is too short when used on site, making it easier to hydrate and causing tight construction time.

[0136] (3) The ultrafine cement and the urea-formaldehyde resin system are coupled to achieve the effect of increasing each other's strength.

[0137] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A lost circulation material, characterized in that, The raw material components of the sealing agent include: ultrafine cement, modified resin, and tartaric acid-intercalated hydrotalcite, wherein the diameter of the ultrafine cement is 0.1 μm to 1 μm; wherein, by weight, The ultrafine cement is 47 to 53 parts, the modified resin is 10 to 20 parts, and the tartaric acid intercalated hydrotalcite is 0.2 to 0.4 parts.

2. The lost circulation material of claim 1, wherein, The tartaric acid-intercalated hydrotalcite is 0.2 parts, and the modified resin is 10 parts.

3. The lost circulation material of claim 1, wherein, The resin includes at least one of the following: urea-formaldehyde resin, phenolic resin, epoxy resin, unsaturated polyester resin, polyurethane resin, and silicone resin.

4. The lost circulation material of claim 1, wherein, The tartaric acid intercalated hydrotalcite is obtained from magnesium aluminum hydrotalcite precursors through an ion exchange reaction.

5. The sealing agent according to claim 1, characterized in that, The raw materials for the sealing agent also include: a water loss reducing agent, a dispersant, and a solvent.

6. The lost circulation material of claim 5, wherein, The water loss reducing agent includes a polyvinyl alcohol complex; and / or, The dispersant comprises at least one of the following: polycarboxylate, fatty alcohol polyoxyethylene ether; and / or, The solvent includes water.

7. The sealing agent according to claim 5, characterized in that, By weight, the water loss reducing agent is 1.2 to 1.5 parts, the dispersant is 0.4 to 0.6 parts, and the solvent is 33 to 37 parts.

8. The lost circulation material of claim 7, wherein, The weight ratio of the solvent to the ultrafine cement is 0.7, the water loss reducing agent is 1.5 parts, and the dispersant is 0.4 parts.

9. A method for preparing the sealing agent according to any one of claims 1 to 8, characterized in that, The method includes: The ultrafine cement and solvent are mixed in the first step to obtain a first mixture. The first mixture is mixed with tartaric acid intercalated hydrotalcite, a water loss reducing agent and a dispersant to obtain a second mixture. The second mixture is mixed with the modified resin in a third mixture, and then the mixture obtained in the third mixture is cured to obtain a sealant.

10. The application of the plugging agent according to any one of claims 1 to 8 in the repair of casing damage in oil and water wells in oilfields.

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