Chemically bonded lost circulation additive, composite lost circulation additive comprising same, drilling fluid, and use thereof in drilling engineering

Abstract

The present invention provides a chemically bonded lost circulation additive, a composite lost circulation additive comprising same, a drilling fluid, and a use thereof in drilling engineering. The chemically bonded lost circulation additive comprises a core layer and an inorganic material coated on the outer surface of the core layer, wherein the material of the core layer has a structure as shown in formula (I). The lost circulation additive of the present application demonstrates a higher success rate of one blockage operation, better pressure-bearing capacity, better compatibility with a drilling fluid, stronger temperature resistance, stronger contamination resistance, and stronger salt tolerance.

Description

Chemical bonding plugging agent, composite plugging agent containing same, drilling fluid and its application in drilling engineering

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 22, 2023, with application number 202311791338.9 and invention name “Plugling agent and composite plugging agent containing same, drilling fluid and its application in drilling engineering”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention belongs to the technical field of oilfield chemical development, and more particularly relates to a chemical bonding plugging agent, a composite plugging agent containing the same, a drilling fluid and the application thereof in drilling engineering. Background Art

[0004] Drilling fluid loss is a global technical challenge in drilling projects. Currently, bridging plugging materials are the most commonly used plugging agents in the field. Bridging plugging materials include granular, flaky, and fibrous forms such as fruit shells, calcium carbonate, fibers, and mica. They rely on large particles to form bridges and small particles to fill and seal, preventing drilling fluid loss. However, relying solely on physical accumulation to seal the gaps has weak pressure-bearing capacity and a low success rate for one-time plugging. Summary of the Invention

[0005] In order to improve the above-mentioned problem, according to one aspect of the present invention, a chemical bonding plugging agent is provided, which comprises a core layer and an inorganic material coated on the outer surface of the core layer; the material of the core layer has a structure shown in Formula I:

[0006] In Formula I, express The number average molecular weight of the core layer material is 20,000 to 35,000. The values ​​of m and n are not particularly limited as long as they meet the number average molecular weight range of the core layer material. For example, m represents 10 to 14, and n represents 12 to 20.

[0007] First, the core layer material in the plugging agent of the present invention has a strong chemical bonding effect. During subsequent plugging applications, the inorganic material in the plugging agent is dispersed in the drilling fluid (either oil-based drilling fluid or water-based drilling fluid can be added to the drilling fluid. Due to the viscosity of the drilling fluid, it can be dispersed). This allows the core layer material to be exposed and in contact with each other. Under the high temperature (≥50°C) extrusion conditions of the formation, chemical bonding occurs to form an overall gel, which can more efficiently obtain a plugging layer with higher strength, better pressure bearing capacity, and better toughness. The principle of the above chemical bonding is as follows:

[0008] Based on this, the present invention not only significantly improves the success rate of leak plugging and optimizes the efficiency of leak plugging, overcoming the low initial plugging success rate of traditional bridging plugging agents that rely solely on physical accumulation; it also improves the pressure-bearing capacity of the plugging system, overcoming the drawback of traditional bridging plugging agents that rely solely on physical accumulation and result in weak pressure-bearing capacity. Furthermore, the leak plugging agent of the present invention also exhibits the following excellent properties: good high-temperature resistance, maintaining stable performance even in high-temperature downhole operations; good drilling fluid compatibility, with good compatibility with both water-based and oil-based drilling fluid systems, and better applicability; strong pollution resistance; and strong salt resistance.

[0009] Secondly, the core layer material in the plugging agent of the present invention is coated with an inorganic material, which effectively prevents the core layer material from sticking during storage and transportation, making storage and transportation more convenient. On-site construction can be directly prepared in the slurry mixing tank, eliminating the need for batch rod prying equipment. This simplifies construction, requires minimal equipment investment, is labor-intensive, and has low overall costs. This facilitates large-scale application and has promising prospects for industrial application. Furthermore, during subsequent plugging applications, the inorganic material can be dispersed in the drilling fluid, leaving the core layer material exposed and in contact with each other.

[0010] Furthermore, the weight ratio of the inorganic material to the core layer is 2 to 4:1; preferably, the weight ratio of the inorganic material to the core layer is 2 to 3:1. The inorganic material is selected from one or more of calcium carbonate, magnesium carbonate, bentonite, or talc. In an alternative embodiment, the core layer material and the inorganic material are mixed and stirred to form a physical coating (coating) of the inorganic material on the outer surface of the core layer.

[0011] In a preferred embodiment, the core layer material is granular with a particle size of 8-40 mesh (e.g., 8-10 mesh, 10-20 mesh, or 20-40 mesh); the inorganic material is granular with a particle size of 1800-2200 mesh (preferably 2000 mesh). The plugging agent material within this range is more easily absorbed into the leaking zone and exhibits good adaptability. Furthermore, it can be plugged while drilling or by slugging, which is simple to operate. It can then be stacked and bonded into a consolidated body, achieving high compressive strength.

[0012] Furthermore, the core layer material is obtained by polymerization and curing of polypropylene glycol, toluene diisocyanate and bis(2-hydroxyethyl) disulfide. The synthesis route is as follows:

[0013] Using polypropylene glycol, toluene diisocyanate and bis(2-hydroxyethyl) disulfide as raw materials for preparing the core layer material can further improve the tensile strength, elongation at break and chemical bonding efficiency of the plugging agent.

[0014] Furthermore, the core layer material is prepared by the following preparation method: at a temperature of 40 to 70° C., the polypropylene glycol and the toluene diisocyanate are first mixed and reacted for 10 to 40 minutes, and then the bis(2-hydroxyethyl) disulfide is added to the system and reacted for 10 to 40 minutes.

[0015] Furthermore, the curing temperature is 70-100° C. and the curing time is 5-16 hours.

[0016] In a preferred embodiment, the core layer material is prepared by the following method: polypropylene glycol and toluene diisocyanate are first mixed and stirred at a temperature of 40-50°C for 10-20 minutes, bis(2-hydroxyethyl) disulfide is then added to the system and polymerized for 15-25 minutes, and the polymerization product is cured at a temperature of 80-90°C for 6-12 hours to obtain the core layer material. The resulting plugging agent has superior high temperature resistance, salt resistance, and mechanical strength.

[0017] In order to improve the above problems, according to another aspect of the present invention, a composite plugging agent is provided, which includes a plugging agent A with a particle size of 10-20 mesh, a plugging agent B with a particle size of 20-40 mesh, and an optional plugging agent C with a particle size of 8-10 mesh; the plugging agent A, the plugging agent B and the plugging agent C are each independently selected from the aforementioned plugging agents; the weight ratio of the plugging agent A, the plugging agent B and the plugging agent C is 1-2:1:1-2.

[0018] It is explained here that the 10-20 mesh plugging agent A means that these particles can pass through the 10 mesh mesh but not the 20 mesh mesh; the 20-40 mesh plugging agent B means that these particles can pass through the 20 mesh mesh but not the 40 mesh; the 8-10 mesh plugging agent C means that these particles can pass through the 8 mesh mesh but not the 10 mesh.

[0019] Based on the aforementioned reasons, the plugging agent of the present invention offers a higher first-time plugging success rate, improved pressure bearing capacity, superior drilling fluid compatibility, enhanced temperature resistance, strong pollution resistance, and strong salt tolerance. The resulting composite plugging agent can achieve a "bridging-filling-bonding-sealing" effect in cracks, achieving superior leak prevention and sealing effectiveness.

[0020] Furthermore, the weight ratio of the plugging agent A, the plugging agent B and the plugging agent C is 1.5-2:1:1-1.5.

[0021] In order to improve the above-mentioned problem, according to another aspect of the present invention, a drilling fluid is provided, which includes the aforementioned plugging agent or the aforementioned composite plugging agent.

[0022] Based on the above reasons, the drilling fluid leakage prevention while drilling or plugging during drilling stop of the present invention can effectively solve the technical problems of fracture or pore leakage.

[0023] To address the aforementioned issues, another aspect of the present invention provides a plugging agent or composite plugging agent for use in drilling operations. Based on the aforementioned reasons, the plugging agent and composite plugging agent of the present invention can be widely used in drilling fluid leak prevention and plugging, for leak prevention while drilling or plugging during drilling stoppage, to address technical challenges related to leakage in fractures or pores. They can also be widely used to address wellbore instability in fractured formations, by chemically bonding and strengthening the wellbore. DETAILED DESCRIPTION

[0024] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0025] Source of raw materials:

[0026] Example 1

[0027] Add 50g of polypropylene glycol to a beaker, heat to 45°C, and begin stirring. Then, add 5g of toluene diisocyanate and stir for 15 minutes. Then, add 3g of bis(2-hydroxyethyl) disulfide and continue stirring for 20 minutes to obtain the product system. The product system is then placed in an 80°C oven for 6 hours, removed, and cooled to room temperature to obtain the desired product (number average molecular weight 32,000).

[0028] The target product was sheared and sieved into particles of different sizes, ranging from 8 to 10 mesh, 10 to 20 mesh, and 20 to 40 mesh. These particles were then uniformly stirred in 2000 mesh ultrafine calcium carbonate and then further sieved to obtain plugging agent C1 with a particle size of 8 to 10 mesh, plugging agent A1 with a particle size of 10 to 20 mesh, and plugging agent B1 with a particle size of 20 to 40 mesh. In plugging agent A1, the weight ratio of the inorganic material to the core layer was 2.2:1; in plugging agent B1, the weight ratio of the inorganic material to the core layer was 2.2:1; and in plugging agent C1, the weight ratio of the inorganic material to the core layer was 2.2:1.

[0029] Performance evaluation:

[0030] (1) Evaluation of drilling fluid compatibility

[0031] The plugging agents of different mesh sizes described in Example 1 were added to the drilling fluid base slurry. After rolling aging at 150°C for 16 hours, the drilling fluid rheology and fluid loss properties were tested. The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid system formulation and evaluation results are shown in Table 1.

[0032] Table 1

[0033] Note: The weight content of the plugging agent in Table 1 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C1 (8-10 mesh) means that the amount of plugging agent C1 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0034] Compatibility experiments show that the plugging agent of the present invention does not affect the rheology and filtration properties of the drilling fluid, has good compatibility, and can be directly added to the drilling fluid for plugging.

[0035] (2) Bonding strength evaluation

[0036] The product system in Example 1 was cast into a mold during the curing process to prepare a rectangular parallelepiped with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The mold was then cut in the middle with scissors, and the cut ends were spliced ​​together. The mold was placed in an 80°C oven for 6 hours and then placed on a universal testing machine to test the tensile strength. The tensile strength before and after shearing was compared, as shown in Table 2.

[0037] Table 2

[0038] Through the comparative experiment of bonding strength before and after shearing, it is concluded that the above-mentioned plugging agent of the present invention is sheared and then bonded, and the tensile strength after bonding is basically the same as that before shearing, and the bonding performance is good. The particles in the leaking layer will be tightly bonded together to achieve a plugging effect.

[0039] (3) Sealing pressure strength test

[0040] The plugging agents of different mesh sizes obtained in Example 1 were added to a drilling fluid base slurry. The compressive strength of the plugging was then tested using a crack sealing device (the temperature was set at 120°C, and the crack plugging process was performed in a compression state). The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid formulation and evaluation results are shown in Table 3.

[0041] Table 3

[0042] Note: The weight content of the plugging agent in Table 3 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C1 (8-10 mesh) means that the amount of plugging agent C1 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0043] The test results show that the plugging agent of the present invention can reach a pressure bearing strength of 8MPa at crack openings of 1mm and 3mm, but the traditional walnut shell plugging agent can only reach a pressure bearing strength of 2.5-3MPa. The plugging agent of the present invention has excellent pressure bearing effect.

[0044] Example 2

[0045] Add 60g of polypropylene glycol to a beaker, heat to 45°C, and begin stirring. Then, add 8g of toluene diisocyanate and stir for 15 minutes. Then, add 5g of bis(2-hydroxyethyl) disulfide and continue stirring for 20 minutes. Then, heat the mixture in a 90°C oven for 6 hours, remove it, and cool it to room temperature to obtain the desired product (number average molecular weight 30,000).

[0046] The target product was sheared and sieved into particles of different sizes between 8 and 10 meshes, 10 and 20 meshes, and 20 and 40 meshes, and stirred evenly in 2000 mesh ultrafine calcium carbonate, and then sieved to obtain plugging agent C2 with a particle size between 8 and 10 meshes, plugging agent A2 with a particle size between 10 and 20 meshes, and plugging agent B2 with a particle size between 20 and 40 meshes.

[0047] In plugging agent A2, the weight ratio of the inorganic material to the core layer is 2.5:1; in plugging agent B2, the weight ratio of the inorganic material to the core layer is 2.5:1; in plugging agent C2, the weight ratio of the inorganic material to the core layer is 2.5:1.

[0048] Performance evaluation:

[0049] (1) Evaluation of drilling fluid compatibility

[0050] The plugging agents of different mesh sizes described in Example 2 were added to the drilling fluid base slurry. After rolling aging at 150°C for 16 hours, the drilling fluid rheology and fluid loss properties were tested. The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid system formulation and evaluation results are shown in Table 4.

[0051] Table 4

[0052] Note: The weight content of the plugging agent in Table 4 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C2 (8-10 mesh) means that the amount of plugging agent C2 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0053] Through compatibility experiments, it was found that the plugging agent does not affect the rheology and filtration properties of the drilling fluid, has good compatibility, and can be directly added to the drilling fluid for plugging.

[0054] (2) Bonding strength evaluation

[0055] The product system in Example 2 was cast into a mold during the curing process to prepare a rectangular parallelepiped with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The mold was then cut in the middle with scissors, and the cut ends were spliced ​​together. The mold was placed in a 90°C oven for 6 hours and then placed on a universal testing machine to test the tensile strength. The tensile strength before and after shearing was compared, as shown in Table 5.

[0056] Table 5

[0057] Through the comparative experiment of bonding strength before and after shearing, it was found that after the plugging agent was sheared and then bonded, the tensile strength after bonding was basically the same as before shearing, and the bonding performance was good. The particles in the leaking layer would be tightly bonded together to achieve the plugging effect.

[0058] (3) Sealing pressure strength test

[0059] The plugging agents of different mesh sizes obtained in Example 2 were added to the drilling fluid base slurry. The plugging compressive strength was then tested using a crack sealing device (the temperature was set at 120°C, and the crack plugging process was performed in a compression state). The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid formulation and evaluation results are shown in Table 6.

[0060] Table 6

[0061] Note: The weight content of the plugging agent in Table 6 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C2 (8-10 mesh) means that the amount of plugging agent C2 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0062] The test results show that the plugging agent of the present invention can form a pressure bearing strength of 8MPa at crack openings of 1 and 3mm, but the traditional walnut shell plugging agent only has a pressure of 2.5-3MPa. The plugging agent has excellent pressure bearing effect.

[0063] Example 3

[0064] Add 62g of polypropylene glycol to a beaker, heat to 45°C, and begin stirring. Then, add 8.2g of toluene diisocyanate and stir for 15 minutes. Then, add 5.2g of bis(2-hydroxyethyl) disulfide and continue stirring for 20 minutes. Then, heat the mixture in a 90°C oven for 6 hours, remove it, and cool it to room temperature to obtain the desired product (number average molecular weight 33,000).

[0065] The target product was sheared and sieved into particles of different sizes between 8 and 10 meshes, 10 and 20 meshes, and 20 and 40 meshes, and stirred evenly in 2000 mesh ultrafine calcium carbonate, and then sieved to obtain plugging agent C3 with a particle size between 8 and 10 meshes, plugging agent A3 with a particle size between 10 and 20 meshes, and plugging agent B3 with a particle size between 20 and 40 meshes.

[0066] In plugging agent A3, the weight ratio of the inorganic material to the core layer is 2.5:1; in plugging agent B3, the weight ratio of the inorganic material to the core layer is 2.5:1; in plugging agent C3, the weight ratio of the inorganic material to the core layer is 2.5:1.

[0067] Performance evaluation:

[0068] (1) Evaluation of drilling fluid compatibility

[0069] The plugging agents of different mesh sizes described in Example 3 were added to the drilling fluid base slurry. After rolling aging at 150°C for 16 hours, the drilling fluid rheology and fluid loss properties were tested. The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid system formulation and evaluation results are shown in Table 7.

[0070] Table 7

[0071] Note: The weight content of the plugging agent in Table 7 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C3 (8-10 mesh) means that the amount of plugging agent C3 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0072] Through compatibility experiments, it was found that the plugging agent does not affect the rheology and filtration properties of the drilling fluid, has good compatibility, and can be directly added to the drilling fluid for plugging.

[0073] (2) Bonding strength evaluation

[0074] The product system in Example 3 was cast into a mold during the curing process to prepare a rectangular parallelepiped with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. It was then cut in the middle with scissors, and the cut ends were spliced ​​together. The mold was placed in a 90°C oven for 6 hours and then placed on a universal testing machine to test the tensile strength. The tensile strength before and after shearing was compared, as shown in Table 8.

[0075] Table 8

[0076] Through the comparative experiment of bonding strength before and after shearing, it was found that after the plugging agent was sheared and then bonded, the tensile strength after bonding was basically the same as before shearing, and the bonding performance was good. The particles in the leaking layer would be tightly bonded together to achieve the plugging effect.

[0077] (3) Sealing pressure strength test

[0078] The plugging agents of different mesh sizes obtained in Example 2 were added to the drilling fluid base slurry. The compressive strength of the plugging was then tested using a crack sealing device (the temperature was set at 120°C, and the crack plugging process was performed in a compression state). The drilling fluid base slurry formulation was: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The drilling fluid formulation and evaluation results are shown in Table 9.

[0079] Table 9

[0080] Note: The weight content of the plugging agent in Table 8 refers to the weight ratio of the material to the drilling fluid base slurry. For example, 2wt% of plugging agent C3 (8-10 mesh) means that the amount of plugging agent C3 (8-10 mesh) used is 2wt% of the drilling fluid base slurry.

[0081] The test results show that the plugging agent of the present invention can form a pressure bearing strength of 8MPa at crack openings of 1 and 3mm, but the traditional walnut shell plugging agent only has a pressure of 2.5-3MPa. The plugging agent has excellent pressure bearing effect.

[0082] Comparative Example 1

[0083] Add 50g of polypropylene glycol to a beaker, heat to 45°C and begin stirring. Then add 5g of toluene diisocyanate and stir for 15 minutes. Then add 3g of adipic acid dihydrazide and continue stirring for 20 minutes to obtain the product system. The above product system is then placed in an 80°C oven and heated for 6 hours. After cooling to room temperature, the target product is obtained. The target product is sheared and sieved into particles of different sizes between 8-10 mesh, 10-20 mesh, and 20-40 mesh. Each of these is stirred evenly in 2000 mesh ultrafine calcium carbonate and then further sieved to obtain plugging agent D with a particle size between 8-10 mesh, plugging agent E with a particle size between 10-20 mesh, and plugging agent F with a particle size between 20-40 mesh.

[0084] In plugging agent A, the weight ratio of the inorganic material to the core layer is 1:1; in plugging agent B, the weight ratio of the inorganic material to the core layer is 1:1; in plugging agent C, the weight ratio of the inorganic material to the core layer is 1:1.

[0085] The product system in Comparative Example 1 was cast into a mold during the curing process to prepare a rectangular parallelepiped with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. It was then cut in the middle with scissors, and the cut ends were spliced ​​together. The mixture was placed in an 80°C oven for 6 hours, and then placed on a universal testing machine to test the tensile strength. The tensile strength after cutting and splicing was only 25.2 kPa, while the tensile strength of the plugging agent in Example 1 of the present application reached 750.6 kPa.

[0086] The plugging agent in the comparative example 1 is added to the drilling fluid base slurry, and then the crack plugging device is utilized to test the plugging pressure bearing strength. The formula is as follows: drilling fluid base slurry+2wt% plugging agent D (8~10 orders)+1wt% plugging agent E (10~20 orders)+2wt% plugging agent F (20~40 orders)+3wt% superfine calcium carbonate (800 orders), which is only a pressure bearing strength of 3.5MPa at 3mm crack aperture, differs greatly from the pressure bearing capacity 8MPa of the plugging agent of the present application embodiment 1. Although the acylhydrazone bond also has a bonding effect, this material can not realize bonding under temperature ≥60 ℃ of conditions, because the temperature rises and the copolymer molecular chain curls and embeds the acylhydrazone bond, and the acylhydrazone bond at the incision is difficult to dynamically exchange, so it is impossible to realize bonding. And the plugging agent in the comparative example 1 is not resistant to high temperatures compared with the aforementioned plugging agent of the application, and can't realize bonding in the deep well leaking layer.

[0087] Comparative Example 2

[0088] Add 50g of polypropylene glycol to a beaker, heat to 45°C, and begin stirring. Then, add 5g of toluene diisocyanate and stir for 15 minutes. Then, add 3g of 2,2'-dithiodibenzoic acid and continue stirring for 20 minutes. The mixture is then placed in an 80°C oven for 6 hours, removed, and cooled to room temperature to obtain the desired product.

[0089] The target product is sheared and sieved into particles of different sizes between 8 and 10 meshes, 10 and 20 meshes, and 20 and 40 meshes, and is respectively stirred evenly in 2000 mesh ultrafine calcium carbonate, and then further sieved to obtain a plugging agent M with a particle size between 8 and 10 meshes, a plugging agent J with a particle size between 10 and 20 meshes, and a plugging agent K with a particle size between 20 and 40 meshes.

[0090] In plugging agent M, the weight ratio of the inorganic material to the core layer is 1:1; in plugging agent J, the weight ratio of the inorganic material to the core layer is 1:1; in plugging agent K, the weight ratio of the inorganic material to the core layer is 1:1.

[0091] The product system in Comparative Example 2 was cast into a mold during the curing process to prepare a rectangular parallelepiped with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. It was then cut in the middle with scissors, and the cut ends were spliced ​​together. The mixture was placed in an 80°C oven for 6 hours, and then placed on a universal testing machine to test the tensile strength. The tensile strength after shearing and splicing was only 40.4 kPa, while the tensile strength of the plugging agent in Example 1 of the present application reached 750.6 kPa.

[0092] The plugging agent in Comparative Example 2 was added to the drilling fluid base slurry, and then the plugging pressure strength was tested using a crack plugging device. The formula is as follows: drilling fluid base slurry + 2wt% plugging agent M (8-10 mesh) + 1wt% plugging agent K (10-20 mesh) + 2wt% plugging agent J (20-40 mesh) + 3wt% ultrafine calcium carbonate (800 mesh). The pressure bearing capacity of the plugging agent in Example 1 of this application was only 2.5MPa at a 3mm crack opening, which is significantly different from the 8MPa pressure bearing capacity of the plugging agent in Example 1 of this application. The degree of bonding between aromatics and polyurethane is low.

Claims

1. A chemical bonding plugging agent, wherein: It comprises a core layer and an inorganic material coated on the outer surface of the core layer; the material of the core layer has a structure shown in Formula I: In the formula I, express The values ​​of m and n satisfy that the number average molecular weight of the material of the core layer is 20,000 to 35,000.

2. The chemical bonding plugging agent according to claim 1, wherein: The material of the core layer is obtained by polymerization and curing of polypropylene glycol, toluene diisocyanate and bis(2-hydroxyethyl) disulfide.

3. The chemical bonding plugging agent according to claim 2, wherein: The polymerization comprises: firstly mixing the polypropylene glycol and the toluene diisocyanate for reaction for 10 to 40 minutes at a temperature of 40 to 70° C., and then adding the bis(2-hydroxyethyl) disulfide into the system for reaction for 10 to 40 minutes.

4. The chemical bonding plugging agent according to claim 2, wherein: The polymerization comprises: firstly mixing the polypropylene glycol and the toluene diisocyanate for reaction for 10 to 20 minutes at a temperature of 40 to 50° C., and then adding the bis(2-hydroxyethyl) disulfide into the system for reaction for 15 to 25 minutes.

5. The chemical bonding plugging agent according to claim 2, wherein: The curing temperature is 70-100° C. and the curing time is 5-16 hours.

6. The chemical bonding plugging agent according to claim 2, wherein: The curing temperature is 80-90° C. and the curing time is 6-12 hours.

7. The chemical bonding plugging agent according to claim 1, wherein: The inorganic material is selected from one or a combination of two or more of calcium carbonate, magnesium carbonate, bentonite and talc.

8. The chemical bonding plugging agent according to claim 1, wherein: The weight ratio of the inorganic material to the core layer is 2 to 4:

1.

9. The chemical bonding plugging agent according to claim 1, wherein: The weight ratio of the inorganic material to the core layer is 2 to 3:

1.

10. The chemical bonding plugging agent according to claim 1, wherein: The material of the core layer is granular, and the particle size is 8-40 meshes.

11. The chemical bonding plugging agent according to claim 1, wherein: The inorganic material is in a granular form with a particle size of 1800 to 2200 meshes.

12. A composite plugging agent, wherein: It includes a plugging agent A with a particle size between 10 and 20 meshes, a plugging agent B with a particle size between 20 and 40 meshes, and optionally a plugging agent C with a particle size between 8 and 10 meshes; The plugging agent A, the plugging agent B and the plugging agent C are each independently selected from the chemical bonding plugging agent according to any one of claims 1 to 11; The weight ratio of the plugging agent A, the plugging agent B and the plugging agent C is 1-2:1:1-2.

13. The composite plugging agent according to claim 12, wherein: The weight ratio of the plugging agent A, the plugging agent B and the plugging agent C is 1.5-2:1:1-1.

5.

14. A drilling fluid, wherein: It comprises the chemical bonding plugging agent according to any one of claims 1 to 11, or the composite plugging agent according to claim 12 or 13.

15. Use of the chemical bonding plugging agent according to any one of claims 1 to 11, the composite plugging agent according to claim 12 or 13, or the drilling fluid according to claim 14 in drilling engineering.

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