Plugging agent, composite plugging agent containing plugging agent, drilling fluid and application of plugging agent in drilling engineering

Abstract

The invention provides a plugging agent, a composite plugging agent containing the plugging agent, a drilling fluid and application of the plugging agent in drilling engineering. The plugging agent comprises a core layer and an inorganic material coated on the outer surface of the core layer, and the material of the core layer has a structure as shown in a formula # imgabs0 #. The plugging agent disclosed by the invention is higher in one-time plugging success rate, better in pressure bearing capacity, better in drilling fluid compatibility, higher in temperature resistance, high in pollution resistance and high in salt resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of the development of oilfield chemicals, and more specifically, relates to a plugging agent, a composite plugging agent containing the same, a drilling fluid, and their applications in drilling engineering. Background Art

[0002] Drilling fluid loss is a worldwide technical problem in drilling engineering. Currently, bridging plugging materials are the most commonly used plugging agents on site. Bridging plugging materials include granular, flaky, and fibrous fruit shells, calcium carbonate, fibers, mica, etc. They rely on large particles to form a bridge and small particles to fill and seal to prevent drilling fluid loss. However, relying solely on physical action to stack and seal, the pressure-bearing capacity is weak, and the success rate of one-time plugging is low. Summary of the Invention

[0003] To improve the above problems, according to one aspect of the present invention, a plugging agent is provided, which includes a core layer and an inorganic material coated on the outer surface of the core layer; the material of the core layer has the structure shown in Formula I:

[0004]

[0005] In Formula I, represents The number-average molecular weight of the material of the core layer is 20,000 - 35,000. The values of m and n only need to satisfy the number-average molecular weight range of the material of the core layer, and there is no special limitation. For example, m represents 10 - 14, and n represents 12 - 20.

[0006] First of all, 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 (both oil-based drilling fluid and water-based drilling fluid are acceptable. When added to the drilling fluid, due to the viscosity of the drilling fluid, it can be dispersed), so that the core layer materials are exposed and come into contact with each other. Under the extrusion condition of high formation temperature (≥50°C), chemical bonding occurs to form an integral gel, and a plugging layer with higher strength, better pressure-bearing capacity, and better toughness can be obtained more efficiently. The principle of the above chemical bonding is as follows:

[0007]

[0008] Based on this, the present invention can not only greatly improve the success rate of plugging leaks and optimize the plugging efficiency, overcoming the problem of low success rate of primary plugging caused by the traditional bridging plugging agent relying only on physical accumulation; but also improve the pressure-bearing capacity of the plugging system, overcoming the drawback of weak pressure-bearing capacity caused by the traditional bridging plugging agent relying only on physical accumulation. At the same time, the above-mentioned plugging agent of the present invention also has the following excellent properties: good high-temperature resistance, still having stable properties during high-temperature downhole operations; good compatibility with drilling fluids, having good compatibility with both water-based and oil-based drilling fluid systems in the market, and better applicability; strong anti-pollution ability; and strong anti-salt ability.

[0009] Secondly, the outer surface of the core layer material in the plugging agent of the present invention is coated with an inorganic material, which effectively prevents the bonding of the core layer material during storage and transportation, making it more convenient for storage and transportation; during on-site construction, it can be directly prepared in a slurry mixing tank without the need for batch stirring equipment, with simple construction, less equipment investment required, low labor intensity, low comprehensive cost, and being convenient for large-scale popularization and application, and having a better industrial application prospect. Moreover, when the inorganic material is used in subsequent plugging applications, it can be dispersed in the drilling fluid to expose the core layer materials and make them contact each other.

[0010] Furthermore, the weight ratio of the inorganic material to the core layer is 2 - 3:1. The inorganic material is selected from one or more of calcium carbonate, magnesium carbonate, bentonite, or talcum powder. In an optional embodiment, the materials of the core layer and the inorganic material are mixed and stirred so that the inorganic material is coated (physically coated) on the outer surface of the core layer.

[0011] In a preferred embodiment, the material of the core layer is granular, with a particle size of 8 - 40 mesh (for example, it can be 8 - 10 mesh, 10 - 20 mesh, 20 - 40 mesh); the inorganic material is granular, with a particle size of 1800 - 2200 mesh (preferably a particle size of 2000 mesh). When the plugging agent material is within the above range, it is easier to enter the leakage layer, has good self-adaptability; and can be used for plugging while drilling or in slugging, with simple operation, and can be stacked and bonded into a consolidated body subsequently to achieve a relatively high pressure-bearing strength.

[0012] Furthermore, the material of the core layer is obtained by polymerization and curing of polypropylene glycol, toluene diisocyanate. The synthesis route is as follows:

[0013]

[0014] Using polypropylene glycol, toluene diisocyanate, and bis(2-hydroxyethyl) disulfide as the 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.

[0015] In a preferred embodiment, the material of the core layer is prepared by the following preparation method: under the temperature condition of 40-50°C, first mix and stir polypropylene glycol and toluene diisocyanate for 10-20 min, then add bis(2-hydroxyethyl) disulfide to the system for polymerization reaction for 15-25 min, and cure the polymerization reaction product at 80-90°C for 6-12 h to obtain the material of the core layer. The plugging agent obtained thereby has more excellent high-temperature resistance, salt resistance and mechanical strength properties.

[0016] 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 foregoing plugging agents; 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.

[0017] It should be noted here that the plugging agent A with a particle size of 10-20 mesh means that these particles can pass through the mesh of 10 mesh but cannot pass through the mesh of 20 mesh; the plugging agent B with a particle size of 20-40 mesh means that these particles can pass through the mesh of 20 mesh but cannot pass through the mesh of 40 mesh; the plugging agent C with a particle size of 8-10 mesh means that these particles can pass through the mesh of 8 mesh but cannot pass through the mesh of 10 mesh.

[0018] For the reasons described above, the plugging agent of the present invention has a higher primary plugging success rate, better pressure-bearing capacity, better compatibility with drilling fluid, stronger high-temperature resistance, strong anti-pollution performance and strong salt resistance. The composite plugging agent obtained by compounding can achieve the functions of "bridging - filling - bonding - plugging" in the cracks, and the plugging and leakage prevention effects are better.

[0019] To improve the above problems, according to another aspect of the present invention, a drilling fluid is provided, which includes the foregoing plugging agent or the foregoing composite plugging agent.

[0020] For the reasons described above, the drilling fluid of the present invention can prevent leakage while drilling or plug leakage while stopping drilling, and can effectively solve the technical problems of fractured or porous leakage.

[0021] To improve the above problems, according to another aspect of the present invention, an application of the foregoing plugging agent or the foregoing composite plugging agent in drilling engineering is provided. For the reasons described above, the plugging agent and the composite plugging agent of the present invention can be widely used in the field of drilling fluid leakage prevention and plugging, prevent leakage while drilling or plug leakage while stopping drilling, and solve the technical problems of fractured or porous leakage; they can also be widely used to solve the problem of wellbore instability in broken formations and carry out wellbore wall solidification operations through chemical bonding. Specific Embodiments

[0022] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0023] Raw material source:

[0024] Polypropylene glycol CAS No.: 25322-69-4 Toluene diisocyanate CAS No.: 26471-62-5 Bis(2-hydroxyethyl) disulfide CAS No.: 1892-29-1 Calcium carbonate (2000 mesh, 800 mesh) Zhengzhou Dongfang Auxiliary Co., Ltd. Bentonite slurry Zhengzhou Dongfang Auxiliary Co., Ltd. Xanthan gum Zhengzhou Dongfang Auxiliary Co., Ltd. Low-viscosity sodium carboxymethyl cellulose Zhengzhou Dongfang Auxiliary Co., Ltd. Walnut shell (10 - 20, 20 - 40 mesh) Zhengzhou Dongfang Auxiliary Co., Ltd.

[0025] Example 1

[0026] Add 50 g of polypropylene glycol to a beaker, heat to 45 °C and start stirring, then add 5 g of toluene diisocyanate, and stir for 15 min. Then add 3 g of bis(2-hydroxyethyl) disulfide, and continue stirring for 20 min to obtain a product system. Then place the above product system in an oven at 80 °C and heat for 6 h. After taking it out and cooling to room temperature, the target product (number average molecular weight is 32,000) is obtained.

[0027] Shear the target product and screen it into particles with different particle sizes between 8 - 10 mesh, 10 - 20 mesh, and 20 - 40 mesh, and stir them evenly in 2000-mesh ultrafine calcium carbonate respectively. Then continue screening to obtain plugging agent C1 with a particle size between 8 - 10 mesh, plugging agent A1 with a particle size between 10 - 20 mesh, and plugging agent B1 with a particle size between 20 - 40 mesh. In plugging agent A1, the weight ratio of inorganic material to the core layer is 2.2:1; in plugging agent B1, the weight ratio of inorganic material to the core layer is 2.2:1; in plugging agent C1, the weight ratio of inorganic material to the core layer is 2.2:1.

[0028] Performance evaluation:

[0029] (I) Evaluation of drilling fluid compatibility

[0030] Add plugging agents with different mesh numbers in Example 1 to the drilling fluid base slurry respectively. After rolling and aging at 150 °C for 16 h, test the rheology and filtration performance of the drilling fluid. Among them, the formula of the drilling fluid base slurry is: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The formula and evaluation results of the drilling fluid system are shown in Table 1.

[0031] Table 1

[0032]

[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, 2 wt% plugging agent C1 (8 - 10 mesh) means that the dosage of plugging agent C1 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0034] Through the compatibility experiment, it is found that the plugging agent of the present invention does not affect the rheology and filtration loss of the drilling fluid, has good compatibility, and can be directly added to the drilling fluid for plugging use.

[0035] (2) Adhesion strength evaluation

[0036] During the curing process of the product system in Example 1, it was poured into a mold to prepare a cuboid with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. Then, it was cut in half with scissors, and the cut parts were spliced together and placed in an oven at 80 °C for 6 h. Then, it was placed on a universal testing machine to test the tensile strength, and the tensile strength before and after cutting was compared, as shown in Table 2.

[0037] Table 2

[0038] Status Tensile strength / kPa Before shearing 754.2 After shearing 750.6

[0039] Through the comparison experiment of the adhesion strength before and after cutting, it is found that after the plugging agent of the present invention is cut and then bonded, the tensile strength after bonding is basically the same as that before cutting, and the bonding performance is good. The particles in the leakage layer will be tightly bonded together to achieve the plugging effect.

[0040] (3) Plugging pressure-bearing strength test

[0041] The plugging agents with different mesh numbers obtained in Example 1 were added to the drilling fluid base slurry, and then the plugging pressure-bearing strength was tested using a crack plugging device (the temperature was set at 120 °C, and the crack was in a squeezed state during the experimental process). Among them, the formula of the drilling fluid base slurry 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 formula and evaluation results are shown in Table 3.

[0042] Table 3

[0043]

[0044] 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, 2 wt% plugging agent C1 (8 - 10 mesh) means that the dosage of plugging agent C1 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0045] From the test results, it can be seen that the plugging agent of the present invention can reach a pressure-bearing strength of 8 MPa at crack openings of 1 mm and 3 mm, while the traditional walnut shell plugging agent can only reach a pressure-bearing strength of 2.5 - 3 MPa. The plugging agent of the present invention has excellent pressure-bearing effect.

[0046] Example 2

[0047] Add 60 g of polypropylene glycol to a beaker, heat it to 45 °C and start stirring, then add 8 g of toluene diisocyanate and stir for 15 min. Then add 5 g of bis(2-hydroxyethyl) disulfide and continue stirring for 20 min. Then place the above mixture in an oven at 90 °C and heat for 6 h. After taking it out and cooling to room temperature, the target product (number-average molecular weight is 30,000) is obtained.

[0048] Shear the target product and screen it into particles with different particle sizes between 8 - 10 mesh, 10 - 20 mesh, and 20 - 40 mesh, and stir them evenly in 2000-mesh ultrafine calcium carbonate respectively. Then continue screening to obtain plugging agent C2 with a particle size between 8 - 10 mesh, plugging agent A2 with a particle size between 10 - 20 mesh, and plugging agent B2 with a particle size between 20 - 40 mesh.

[0049] In plugging agent A2, the weight ratio of inorganic material to the core layer is 2.5:1; in plugging agent B2, the weight ratio of inorganic material to the core layer is 2.5:1; in plugging agent C2, the weight ratio of inorganic material to the core layer is 2.5:1.

[0050] Performance evaluation:

[0051] (1) Evaluation of the compatibility with drilling fluid

[0052] Add plugging agents with different mesh numbers in Example 2 to the drilling fluid base slurry respectively. After rolling and aging at 150 °C for 16 h, test the rheological properties and filtration properties of the drilling fluid. Among them, the formula of the drilling fluid base slurry is: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The formula of the drilling fluid system and the evaluation results are shown in Table 4.

[0053] Table 4

[0054]

[0055] 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, 2 wt% plugging agent C2 (8 - 10 mesh) means that the dosage of plugging agent C2 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0056] Through the compatibility experiment, it is concluded that the plugging agent does not affect the rheological properties and filtration properties of the drilling fluid, and the compatibility is good, and it can be directly added to the drilling fluid for plugging.

[0057] (2) Evaluation of the bonding strength

[0058] The product system in Example 2 was poured into a mold during the curing process to form a cuboid with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. Then, it was cut in half with scissors, and the cut surfaces were joined together. It was left standing in an oven at 90 °C for 6 h, and then the tensile strength was tested on a universal testing machine. The tensile strength before and after cutting was compared, as shown in Table 5.

[0059] Table 5

[0060] Status Tensile strength / kPa Before shearing 810.0 After shearing 806.8

[0061] Through the comparison experiment of the bonding strength before and after cutting, it was found that after the plugging agent was cut and then bonded, the tensile strength after bonding was basically the same as that before cutting, and the bonding performance was good. The particles in the leakage layer would be tightly bonded together to achieve the plugging effect.

[0062] (III) Plugging pressure-bearing strength test

[0063] The plugging agents with different mesh numbers obtained in Example 2 were added to the drilling fluid base slurry, and then the plugging pressure-bearing strength was tested using a fracture plugging device (temperature set at 120 °C, and the fracture was in a squeezed state during the experimental process). Among them, the formula of the drilling fluid base slurry 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 formula and evaluation results are shown in Table 6.

[0064] Table 6

[0065]

[0066]

[0067] 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, 2 wt% plugging agent C2 (8 - 10 mesh) means that the dosage of plugging agent C2 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0068] From the test results, it can be seen that the above plugging agent of the present invention can form a pressure-bearing strength of 8 MPa at crack openings of 1 and 3 mm, while the traditional walnut shell plugging agent can only reach a pressure of 2.5 - 3 MPa. The pressure-bearing effect of the plugging agent is excellent.

[0069] Example 3

[0070] 62 g of polypropylene glycol was added to a beaker, heated to 45 °C and stirred. Then, 8.2 g of toluene diisocyanate was added and stirred for 15 min. Then, 5.2 g of bis(2-hydroxyethyl) disulfide was added and stirring was continued for 20 min. Then, the above mixture was placed in an oven at 90 °C and heated for 6 h. After taking it out and cooling to room temperature, the target product (number average molecular weight of 33000) was obtained.

[0071] The target product is sheared and screened into particles with different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh, and then uniformly stirred in 2000-mesh ultrafine calcium carbonate, and then continue to be screened to obtain plugging agent C3 with a particle size between 8 and 10 mesh, plugging agent A3 with a particle size between 10 and 20 mesh, and plugging agent B3 with a particle size between 20 and 40 mesh.

[0072] In plugging agent A3, the weight ratio of inorganic material to core layer is 2.5:1; in plugging agent B3, the weight ratio of inorganic material to core layer is 2.5:1; in plugging agent C3, the weight ratio of inorganic material to core layer is 2.5:1.

[0073] Performance evaluation:

[0074] (1) Evaluation of drilling fluid compatibility

[0075] The plugging agents with different mesh numbers in Example 3 are respectively added to the drilling fluid base slurry, and after rolling and aging at 150 °C for 16 h, the rheological properties and filtration properties of the drilling fluid are tested. Among them, the formula of the drilling fluid base slurry is: 4 wt% bentonite slurry + 0.2 wt% xanthan gum + 0.2 wt% low-viscosity sodium carboxymethyl cellulose + 95.6 wt% water. The formula and evaluation results of the drilling fluid system are shown in Table 7.

[0076] Table 7

[0077]

[0078]

[0079] 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, 2 wt% plugging agent C3 (8 - 10 mesh) means that the dosage of plugging agent C3 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0080] Through the compatibility experiment, it is found that the plugging agent does not affect the rheological properties and filtration properties of the drilling fluid, and has good compatibility, and can be directly added to the drilling fluid for plugging.

[0081] (2) Evaluation of bonding strength

[0082] The product system in Example 3 is poured into a mold during the curing process to form a cuboid with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. Then it is cut in half with scissors, and the cut surfaces are spliced together, placed in an oven at 90 °C for 6 h, and then the tensile strength is tested on a universal testing machine. The tensile strength before and after cutting is compared, as shown in Table 8.

[0083] Table 8

[0084] Status Tensile strength / kPa Before shearing 805.0 After shearing 801.2

[0085] Through the shear bond strength comparison experiment before and after shearing, it is obtained that after the plugging agent is sheared and then bonded, the tensile strength after bonding is basically the same as that before shearing, and the bonding performance is good. In the leakage layer, the particles will be tightly bonded together to achieve the plugging effect.

[0086] (3) Sealing pressure-bearing strength test

[0087] The plugging agents with different mesh numbers obtained in Example 2 were added to the drilling fluid base slurry, and then the sealing pressure-bearing strength was tested using a fracture sealing device (the temperature was set at 120 °C, and the fracture was in a squeezed state during the experimental process). Among them, the formula of the drilling fluid base slurry 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 formula and evaluation results are shown in Table 9.

[0088] Table 9

[0089]

[0090] 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, 2 wt% plugging agent C3 (8 - 10 mesh) means that the dosage of plugging agent C3 (8 - 10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[0091] From the test results, it can be seen that the above plugging agent of the present invention can form a pressure-bearing strength of 8 MPa at crack openings of 1 and 3 mm, while the traditional walnut shell plugging agent is only 2.5 - 3 MPa, and the pressure-bearing effect of the plugging agent is excellent.

[0092] Comparative Example 1

[0093] 50 g of polypropylene glycol was added to a beaker, heated to 45 °C and stirred, then 5 g of toluene diisocyanate was added and stirred for 15 min. Then 3 g of adipic dihydrazide was added and stirred for another 20 min to obtain a product system. Then the above product system was placed in an oven at 80 °C and heated for 6 h. After taking it out and cooling to room temperature, the target product was obtained. The target product was sheared and screened into particles with different particle sizes between 8 - 10 mesh, 10 - 20 mesh, and 20 - 40 mesh, and were respectively stirred evenly in 2000-mesh ultrafine calcium carbonate, and then screened again 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.

[0094] 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.

[0095] The product system in Comparative Example 1 was poured into a mold during the curing process to prepare a cuboid with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. Then, it was cut in half with scissors, and the cut parts were spliced together and placed in an oven at 80 °C for 6 h. Then, it was 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 this application reached 750.6 kPa.

[0096] The plugging agent in Comparative Example 1 was added to the drilling fluid base slurry, and then the plugging pressure-bearing strength was tested using a fracture plugging device. The formula was as follows: drilling fluid base slurry + 2 wt% plugging agent D (8 - 10 mesh) + 1 wt% plugging agent E (10 - 20 mesh) + 2 wt% plugging agent F (20 - 40 mesh) + 3 wt% ultrafine calcium carbonate (800 mesh). The pressure-bearing pressure at a crack opening of 3 mm was only 3.5 MPa, which was quite different from the pressure-bearing capacity of 8 MPa of the plugging agent in Example 1 of this application. Although the acylhydrazone bond also has an adhesive effect, this material cannot achieve adhesion at a temperature ≥ 60 °C. This is because as the temperature rises, the copolymer molecular chain curls and embeds the acylhydrazone bond, and it is difficult for the acylhydrazone bond at the cut to undergo dynamic exchange, so adhesion cannot be achieved. Moreover, the plugging agent in Comparative Example 1 is not resistant to high temperature compared with the aforementioned plugging agent in this application, and it cannot achieve an adhesive effect in deep well leakage layers.

[0097] Comparative Example 2

[0098] 50 g of polypropylene glycol was added to a beaker, heated to 45 °C and stirring was started. Then, 5 g of toluene diisocyanate was added and stirred for 15 min. Then, 3 g of 2,2'-dithiobenzoic acid was added and stirring was continued for 20 min. Then, the above mixture was placed in an oven at 80 °C and heated for 6 h. After taking it out and cooling to room temperature, the target product was obtained.

[0099] The target product was sheared and screened into particles with different particle sizes between 8 - 10 mesh, 10 - 20 mesh, and 20 - 40 mesh, and were respectively stirred evenly in 2000-mesh ultrafine calcium carbonate, and then screened continuously to obtain plugging agent M with a particle size between 8 - 10 mesh, plugging agent J with a particle size between 10 - 20 mesh, and plugging agent K with a particle size between 20 - 40 mesh.

[0100] 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.

[0101] The product system in Comparative Example 2 was poured into a mold during the curing process to prepare a cuboid with a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. Then, it was cut in half with scissors, and the cut parts were spliced together. It was left standing in an oven at 80 °C for 6 h, and then the tensile strength was tested on a universal testing machine. The tensile strength after cutting and splicing was only 40.4 kPa, while the tensile strength of the plugging agent in Example 1 of this application reached 750.6 kPa.

[0102] The plugging agent in Comparative Example 2 was added to the drilling fluid base slurry, and then the plugging pressure-bearing strength was tested using a crack plugging device. The formula was as follows: drilling fluid base slurry + 2 wt% plugging agent M (8 - 10 mesh) + 1 wt% plugging agent K (10 - 20 mesh) + 2 wt% plugging agent J (20 - 40 mesh) + 3 wt% ultrafine calcium carbonate (800 mesh). The pressure-bearing pressure at a crack opening of 3 mm was only 2.5 MPa, which was quite different from the pressure-bearing capacity of 8 MPa of the plugging agent in Example 1 of this application. The degree of combination of aromatic and polyurethane was relatively low.

Claims

1. A plugging agent, characterized in that, It includes a core layer and an inorganic material coated on the outer surface of the core layer; the material of the core layer has the structure shown in Formula I: In the formula (I), means the numerical 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 plugging agent according to claim 1, characterized in that, The material of the core layer is obtained by polymerization and curing of polypropylene glycol, toluene diisocyanate and bis(2-hydroxyethyl) disulfide.

3. The plugging agent according to claim 2, wherein, The polymerization includes: under the temperature condition of 40-50 °C, first mixing and reacting the polypropylene glycol and the toluene diisocyanate for 10-20 min, and then adding the bis(2-hydroxyethyl) disulfide to the system and reacting for 15-25 min; The temperature of the curing is 80-90 °C and the time is 6-12 h.

4. The plugging agent according to claim 1, wherein The inorganic material is selected from one or more of calcium carbonate, magnesium carbonate, bentonite and talc powder.

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

1.

6. The plugging agent according to claim 1, wherein, The material of the core layer is granular, and the particle size is 8-40 mesh.

7. The plugging agent according to claim 1, characterized in that, The inorganic material is granular, and the particle size is 1800-2200 mesh.

8. A composite plugging agent, characterized in that, It includes a plugging agent A with a particle size between 10-20 mesh, a plugging agent B with a particle size between 20-40 mesh, and optionally a plugging agent C with a particle size between 8-10 mesh; The plugging agent A, the plugging agent B and the plugging agent C are each independently selected from the plugging agents described in any one of claims 1 to 7; 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.

9. A drilling fluid, characterized in that, It includes the plugging agent described in any one of claims 1 to 7, or the composite plugging agent described in claim 8.

10. The application of the plugging agent described in any one of claims 1 to 7, the composite plugging agent described in claim 8, and the drilling fluid described in claim 9 in the drilling engineering.

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