A porous material for drilling wellbore insulation and its preparation method and application

Abstract

The present invention provides a porous material for wellbore insulation, and its preparation method and application, which belong to the field of oilfield chemical technology. The preparation method of the porous material of the present invention includes the following steps: fully mixing ceramsite powder and pore-forming agent; using colloidal solution as a binder, granulating, and then heat-treating to obtain porous ceramsite; fully dispersing porous ceramsite, anionic monomer, and cationic monomer in deionized water, adding an initiator, reacting, and then washing and drying to obtain the material. The porous material of the present invention uses natural ore and industrial waste as raw materials, and the raw materials are cheap and easy to obtain, with low cost and green environmental protection. The porous material of the present invention is applied to wellbore insulation to prevent the ceramsite from being screened out by the solid-liquid separation device, which is conducive to multiple recycling; the porous material has a large number of micron and nanometer pores inside, low thermal conductivity, and good thermal insulation effect; the surface of the porous material contains rich anionic and cationic groups, which can be adsorbed on the wellbore wall for effective and stable thermal insulation.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a porous material for thermal insulation of a drilling wellbore, a preparation method and an application thereof. Background Art

[0002] When drilling depths exceed 8,000 meters, wellbore temperatures reach over 200°C. High temperatures can lead to drilling fluid failure, damage to drill tools, and failure of logging-while-drilling equipment, making drilling extremely difficult. In more serious cases, serious accidents such as lost circulation, well collapse, and blowouts can occur, resulting in incalculable economic losses. Therefore, reducing wellbore temperatures is crucial for deep oil and gas development.

[0003] Wellbore temperature primarily comes from heat transfer from high-temperature strata. The high temperature of deep strata transfers heat to the wellbore wall, which in turn transfers it to the drilling fluid and drill pipe. Building an insulating layer on the wellbore wall can potentially reduce heat transfer from the strata into the wellbore, thereby lowering wellbore temperature. Porous ceramsite is a lightweight, porous material made from clay, shale, or industrial waste. It boasts advantages such as ease of processing, low cost, high strength, and low thermal conductivity, making it widely used in fields such as construction and horticulture. However, existing porous ceramsite is too large to be easily sieved out by solid-liquid separation equipment, making it difficult to recycle multiple times. Its thermal conductivity is too high, leaving its insulation effectiveness in need of improvement. Its surface properties prevent it from adsorbing onto wellbore rock for insulation, making modification difficult. For example, invention patent CN118495983A discloses a Yunnan laterite-based composite porous ceramsite and its preparation method. Through a simple process, ceramsite with high specific surface area, high porosity, and high strength, as well as nanopores, is produced. However, the ceramsite is very large, measuring 4.5-7 mm, and lacks surface modification, making it unsuitable for wellbore insulation. Patent CN114276084A discloses an insulating ceramsite wallboard, which describes the preparation of the modified ceramsite. The ceramsite surface is first activated with hexadecyltrimethylammonium bromide, allowing periclase powder to adsorb onto it. Finally, a silica layer is formed on the outside using ethyl orthosilicate. However, due to the size constraints and high thermal conductivity of the modified ceramsite, it cannot be used in wellbore insulation.

[0004] Therefore, the problem of drilling difficulties caused by ultra-high wellbore temperature has not been solved, and there is an urgent need to develop new technologies to reduce the wellbore temperature. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a porous material for drilling wellbore insulation, and its preparation method and application. The porous material of the present invention uses natural ores and industrial waste as raw materials. The raw materials are cheap and easy to obtain, low in cost, and environmentally friendly. The size of the porous material of the present invention can be reduced to below 100 μm. When used for wellbore insulation, it can prevent the ceramsite from being screened out by the solid-liquid separation device, which is conducive to multiple recycling; the porous material has a large number of micron and nano-scale pores inside, with low thermal conductivity and good thermal insulation effect; the surface of the porous material contains rich anion and cationic groups, which can be adsorbed on the wellbore wall for effective and stable thermal insulation.

[0006] The technical solutions of the present invention are as follows:

[0007] A porous material for thermal insulation of a drilling wellbore, wherein the porous material has a spherical structure, a thermal conductivity of 0.03 to 0.07 W / mk, a porosity of 80 to 95%, and a compressive strength of 1 to 3 MPa; the porous material has a multi-level cellular structure, a pore size of 0.01 to 20 μm; and the surface of the porous material has anionic and cationic groups.

[0008] Preferably, according to the present invention, the porous material has a spherical structure, a thermal conductivity of 0.038 to 0.048 W / mk, a porosity of 82 to 88%, and a compressive strength of 1.2 to 2.3 MPa; the porous material has a multi-level cell structure with a pore size of 0.01 to 13 μm; and the surface of the porous material has anionic and cationic groups.

[0009] The method for preparing the porous material for drilling wellbore thermal insulation comprises the following steps:

[0010] (1) The ceramsite powder and the pore-forming agent are fully mixed to obtain a mixed powder; a colloidal solution is used as a binder to obtain ceramsite microspheres by granulation; and then porous ceramsite is obtained by heat treatment;

[0011] The ceramsite powder is one or a combination of two or more of clay, shale powder, fly ash, coal gangue or iron tailings; the pore-forming agent is a combination of micron particles and nanoparticles, the micron particles are polypropylene, polyethylene or polystyrene micron particles, and the nanoparticles are polypropylene, polyethylene or polystyrene nanoparticles; the colloidal solution is one or a combination of two or more of polyvinyl alcohol aqueous solution, polyacrylamide aqueous solution or polyethylene glycol aqueous solution;

[0012] (2) The porous ceramsite, anionic monomer, and cationic monomer are fully dispersed in deionized water, an initiator is added, and the mixture is reacted, and then washed and dried to obtain a porous material for drilling wellbore insulation;

[0013] The anionic monomer is one or a combination of two or more of 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonate, ethylenesulfonate, propylenesulfonate, acrylic acid, methacrylic acid or hydroxyethyl acrylic acid; the cationic monomer is one or a combination of two or more of dimethyldiallylammonium chloride, polyacrylammonium or polyquaternary ammonium salt; and the initiator is one or a combination of two or more of ammonium persulfate, sodium bisulfite or azobisisobutylimidazoline hydrochloride.

[0014] Preferably, according to the present invention, in step (1), the ceramsite powder is a combination of fly ash and coal gangue; wherein the mass ratio of fly ash to coal gangue is 1:0.5-1.

[0015] According to the preferred embodiment of the present invention, in step (1), the particle size of the ceramsite powder is 0.5-20 μm, preferably 5-12 μm.

[0016] Preferably, according to the present invention, in step (1), in the pore-forming agent, the particle size of the micron particles is 6-13 μm, and the particle size of the nanoparticles is 100-500 nm; the mass ratio of the micron particles to the nanoparticles is 2-4:1, preferably 3:1.

[0017] Preferably, according to the present invention, in step (1), the mass ratio of the ceramsite powder to the pore-forming agent is 3.75-5:1.

[0018] According to the present invention, preferably, in step (1), the mixing of the ceramsite powder and the pore-forming agent is carried out in a round pot granulator.

[0019] According to the preferred embodiment of the present invention, in step (1), the concentration of the colloidal solution is 0.1-0.8 wt%, preferably 0.5 wt%.

[0020] Preferably, according to the present invention, in step (1), the mass ratio of the mixed powder to the colloidal solution is 1:0.001-0.1.

[0021] Preferably, according to the present invention, in step (1), granulation is carried out in a round pot granulator; the mixed powder is rotated in the round pot granulator, and a colloidal solution is sprayed onto the surface of the mixed powder with a nano sprayer during the rotation process. Under the action of gravity and rotation, the mixed powder forms agglomerated micron balls, which are dried to obtain ceramsite microspheres; wherein, the rotation speed of the round pot granulator is 10 to 200 r / min, the rotation time is 2 to 10 min, and the spraying speed of the nano sprayer is 30 to 1000 ml / min.

[0022] Preferably, according to the present invention, in step (1), the heat treatment temperature is 1000-1500° C., the heat treatment time is 2-10 h, and the heat treatment atmosphere is air.

[0023] According to the preferred embodiment of the present invention, in step (2), the mass ratio of the porous ceramsite, the anionic monomer, the cationic monomer, the initiator and the deionized water is 1: (0.01-0.1): (0.005-0.1): (0.005-0.01): (0.5-3), preferably 1: 0.05: 0.05: 0.005: 1.

[0024] According to the preferred embodiment of the present invention, in step (2), the initiator is in the form of an initiator aqueous solution, and the concentration of the initiator aqueous solution is 0.5 to 5 wt%.

[0025] According to the preferred embodiment of the present invention, in step (2), the reaction temperature is 20-80°C, preferably 60-80°C, the reaction time is 6-12h, and the reaction is carried out in the absence of oxygen, under protective gas protection, and under stirring conditions; preferably, the protective gas is nitrogen or argon.

[0026] According to the present invention, preferably, in step (2), washing is performed using deionized water.

[0027] The porous material for thermal insulation of drilling wells is used as a thermal insulation material for thermal insulation of ultra-deep drilling wells.

[0028] Preferably, according to the present invention, the ultra-deep layer is a layer with a depth greater than or equal to 8000m.

[0029] The technical features and beneficial effects of the present invention are as follows:

[0030] (1) The present invention uses natural ores and industrial waste as raw materials. The raw materials are cheap and readily available, which can significantly reduce the preparation cost, is environmentally friendly, and realizes the resource utilization of waste. The preparation method of the present invention is simple, easy to implement, and suitable for industrial production.

[0031] (2) The present invention uses ultrafine powdered ceramsite as raw material, micron and nano-graded polymer particles as pore-forming agents, and colloidal solution as a binder. Through rotary granulation and nano-spraying assistance, combined with heat treatment, porous ceramsite with a multi-level cellular structure is prepared, which can achieve ultrafine particle size and a large number of micron and nano-scale pores. The method of the present invention enables the size of the porous material of the present invention to be reduced to below 100 μm. When used for wellbore insulation, it can prevent the ceramsite from being screened out by the solid-liquid separation device, facilitating multiple recycling. The porous material has a large number of micron and nano-scale pores inside, has high porosity, low thermal conductivity, good thermal insulation effect, and high strength.

[0032] (3) The present invention modifies the porous ceramsite into anions and cations so that it can adsorb onto the well wall surface with any charge, thereby achieving stable and effective heat insulation. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0034] Meanwhile, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0035] Example 1

[0036] A method for preparing a porous material for thermal insulation of a drilling wellbore comprises the following steps:

[0037] (1) Fly ash, coal gangue, polypropylene micron particles, and polystyrene nanoparticles are fully stirred and mixed in a round pot granulator to form a mixed powder. The mass ratio of fly ash, coal gangue, polypropylene micron particles, and polystyrene nanoparticles is 1:1:0.3:0.1, the particle size of fly ash is 6-12 μm, the particle size of coal gangue is 5-12 μm, the particle size of polypropylene micron particles is 6-13 μm, and the particle size of polystyrene nanoparticles is 100-500 nm.

[0038] (2) The mixed powder in step (1) is rotated in a round pot granulator. During the rotation, a 0.5 wt% polyvinyl alcohol aqueous solution (Mw is 9000-10000) is sprayed onto the surface of the mixed powder using a nano sprayer. Under the action of gravity and rotation, the powder forms agglomerated microspheres, which are then dried to obtain ceramsite microspheres. The rotation speed of the round pot granulator is 50 r / min, the rotation time is 3 min, and the spraying speed of the nano sprayer is 80 ml / min. The mass ratio of the mixed powder to the polyvinyl alcohol aqueous solution is 1:0.05.

[0039] (3) heat-treating the ceramsite microspheres in step (2) in a muffle furnace to obtain porous ceramsite, wherein the heat treatment temperature is 1300° C., the heat treatment time is 3 h, and the heat treatment atmosphere is air;

[0040] (4) The porous ceramsite, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride and deionized water in step (3) are placed in a three-necked flask, oxygen is removed under a nitrogen atmosphere, and then a 3 wt% aqueous solution of ammonium persulfate is added and stirred at 70° C. for 8 hours. After the reaction is completed, the reaction product is washed with deionized water and then dried to obtain a porous material for drilling wellbore insulation. The mass ratio of the porous ceramsite, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, deionized water and ammonium persulfate is 1:0.05:0.05:1:0.005.

[0041] The porous ceramsite prepared in this embodiment has a particle size of 60-80 μm; the thermal conductivity of the porous material is 0.045 W / m·k, the porosity is 85%, the compressive strength is 2.2 MPa, it has a multi-level cellular structure, a pore size of 0.01-13 μm, and has both anions and cations on the surface.

[0042] Example 2

[0043] A method for preparing a porous material for thermal insulation of a drilling wellbore is as described in Example 1, except that the mass ratio of fly ash, coal gangue, polypropylene micron particles, and polystyrene nanoparticles added in step (1) is 1:0.8:0.3:0.1. The other steps and conditions are the same as those in Example 1.

[0044] The porous ceramsite prepared in this embodiment has a particle size of 60-80 μm; the thermal conductivity of the porous material is 0.041 W / m·k, the porosity is 86%, the compressive strength is 1.6 MPa, it has a multi-level cellular structure, a pore size of 0.01-13 μm, and has both anions and cations on the surface.

[0045] Example 3

[0046] A method for preparing a porous material for thermal insulation of a drilling wellbore is as described in Example 1, except that the mass ratio of fly ash, coal gangue, polypropylene micron particles, and polystyrene nanoparticles added in step (1) is 1:0.5:0.3:0.1. The other steps and conditions are the same as those in Example 1.

[0047] The porous ceramsite prepared in this embodiment has a particle size of 60~80μm; the thermal conductivity of the porous material is 0.038W / m·k, the porosity is 88%, the compressive strength is 1.3MPa, it has a multi-level cell structure, a pore size of 0.01~13μm, and has both anions and cations on the surface.

[0048] Example 4

[0049] A method for preparing a porous material for thermal insulation of a drilling wellbore is as described in Example 1, except that in step (2), the rotation time of the rotary granulation is 5 minutes, and the other steps and conditions are the same as in Example 1.

[0050] The porous ceramsite prepared in this embodiment has a particle size of 70~90μm; the thermal conductivity of the porous material is 0.040W / m·k, the porosity is 87%, the compressive strength is 1.2MPa, it has a multi-level cell structure, a pore size of 0.01~13μm, and has both anions and cations on the surface.

[0051] Example 5

[0052] A method for preparing a porous material for thermal insulation of a drilling wellbore is as described in Example 1, except that in step (4), the mass ratio of porous ceramsite, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallylammonium chloride, deionized water, and ammonium persulfate is 1:0.01:0.005:1:0.005. The other steps and conditions are the same as in Example 1.

[0053] The porous ceramsite prepared in this embodiment has a particle size of 60~80μm; the thermal conductivity of the porous material is 0.044W / m·k, the porosity is 86%, the compressive strength is 2.0MPa, it has a multi-level cell structure, a pore size of 0.01~13μm, and has both anions and cations on the surface.

[0054] Example 6

[0055] A method for preparing a porous material for thermal insulation of a drilling wellbore is as described in Example 1, except that in step (4), the mass ratio of porous ceramsite, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallylammonium chloride, deionized water, and ammonium persulfate is 1:0.1:0.1:1:0.005. The other steps and conditions are the same as those in Example 1.

[0056] The porous ceramsite prepared in this embodiment has a particle size of 60~80μm; the thermal conductivity of the porous material is 0.048W / m·k, the porosity is 82%, the compressive strength is 2.3MPa, it has a multi-level cell structure, a pore size of 0.01~13μm, and has both anions and cations on the surface.

[0057] Comparative Example 1

[0058] A method for preparing a porous material is as described in Example 1, except that the mass ratio of fly ash, coal gangue, polypropylene microparticles, and polystyrene nanoparticles added in step (1) is 1:0.1:0.3:0.1. The other steps and conditions are the same as those in Example 1.

[0059] The particle size of the porous ceramsite prepared in this comparative example is 60~80μm; the thermal conductivity of the porous material is 0.027W / m·k, the porosity is 94%, it has a multi-level cellular structure, the pore size is 0.01~13μm, and the surface has both anions and cations; due to the low addition amount of coal gangue, the reinforcing phase cannot be evenly infiltrated into the skeleton structure of the porous ceramsite material, resulting in a sharp decrease in compressive strength to only 0.5MPa.

[0060] Comparative Example 2

[0061] A method for preparing a porous material is as described in Example 1, except that the mass ratio of fly ash, coal gangue, polypropylene microparticles, and polystyrene nanoparticles added in step (1) is 1:2:0.3:0.1. The other steps and conditions are the same as those in Example 1.

[0062] The porous ceramsite prepared in this comparative example has a particle size of 60~80μm; the thermal conductivity of the porous material is 0.087W / m·k, the porosity is 64%, it has a multi-level cellular structure, the pore size is 0.5~10μm, and the surface has both anions and cations; due to the excessive addition of coal gangue, a large amount of reinforcing phase penetrates into the skeleton structure of the porous ceramsite material, resulting in a decrease in porosity and pore size, and an increase in compressive strength to 5MPa.

[0063] Comparative Example 3

[0064] A method for preparing a porous material is as described in Example 1, except that the mass fraction of the polyvinyl alcohol aqueous solution sprayed in step (2) is 1 wt%. The other steps and conditions are the same as those in Example 1.

[0065] The porous ceramsite prepared in this comparative example has a particle size of 200-1000 μm; the thermal conductivity of the porous material is 0.065 W / m·k, the porosity is 73%, the compressive strength is 3 MPa, it has a multi-level cellular structure, the pore size is 0.1-50 μm, and the surface carries both anions and cations; due to the increase in the mass fraction of the polyvinyl alcohol colloidal solution, the viscosity of the nucleated particles increases during rotary granulation, and a large amount of free material is adsorbed, resulting in an increase in the size and pore size of the porous ceramsite material and an increase in the thermal conductivity.

[0066] Comparative Example 4

[0067] A method for preparing a porous material is as described in Example 1, except that step (4) is not performed and the porous ceramsite is not modified.

[0068] The porous ceramsite prepared in this comparative example has a particle size of 60-80 μm; the thermal conductivity of the porous material is 0.043 W / m·k, the porosity is 87%, the compressive strength is 2.1 MPa, it has a multi-level cellular structure, a pore size of 0.01-13 μm, and no anions or cations on the surface.

[0069] The particle size of the porous ceramsite in Examples 1-6 and Comparative Examples 1-4, the thermal conductivity, porosity, compressive strength and pore size indicators of the porous materials are shown in Table 1.

[0070] Table 1 Particle size, thermal conductivity, porosity, strength and pore size of porous materials

[0071]

[0072] As shown in Table 1, as the amount of gangue decreased in the examples, the total mass percentage of the mixed powder also decreased, and the mass percentage of the pore-forming agent increased. This resulted in an increase in the porosity of the porous ceramsite, a decrease in thermal conductivity, and a decrease in strength. However, it had little effect on the particle size and pore size of the porous ceramsite. As the rotation time increased, the size of the ceramsite also increased. This is because new powder was continuously added to the ceramsite during the continuous rotation process, causing it to grow larger, but this had little effect on performance. In Comparative Example 1, excessively reducing the mass of gangue resulted in an increase in the porosity and a decrease in thermal conductivity of the prepared porous ceramsite, but a significant decrease in strength. In Comparative Example 2, excessively increasing the mass of gangue resulted in a decrease in the porosity and an increase in thermal conductivity of the prepared porous ceramsite, but a sharp increase in strength. In Comparative Example 3, increasing the concentration of the colloidal solution resulted in an increase in the solution viscosity. Spraying the colloidal solution onto the mixed powder resulted in large clumps of powder forming balls, resulting in an increase in size, density, and strength. In Comparative Example 4, the porous ceramsite was not modified, the porosity of the porous ceramsite was slightly increased, and the thermal conductivity was increased.

[0073] Test Example 1

[0074] Research on thermal insulation properties of porous materials

[0075] (1) Prepare base slurry, whose components are water, bentonite and anhydrous sodium carbonate, with a mass ratio of 100:2:1;

[0076] (2) The porous material prepared in Examples 1-3 was dispersed into the base slurry prepared in step (1) to form a mud cake by filtration. The mass ratios of the base slurry to the porous material were 1:0.005, 1:0.01, and 1:0.03, respectively.

[0077] (3) Place the mud cake from step (2) on a heating table and heat it at a constant temperature of 200°C for 30 minutes. Observe the surface temperature of the mud cake with an infrared camera.

[0078] The thermal insulation effects of pure mud cake without porous materials and mud cake with porous materials of different mass ratios are shown in Table 2

[0079] Table 2 Mud cake insulation effect

[0080]

[0081] Table 2 shows that the addition of porous material produces a mud cake with excellent thermal insulation properties. Furthermore, as the amount of porous material added increases and the thermal conductivity of the porous material decreases, the temperature difference between the upper and lower parts of the mud cake increases. This is primarily because the porous material is evenly distributed within the mud cake, and its matrix structure is more complex than that of a solid material, increasing the heat conduction path and thus achieving a greater temperature difference.

[0082] The above is only a specific embodiment of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial modification of the present invention using this concept shall be deemed an infringement of the scope of protection of the present invention. However, any simple modification, equivalent change, and modification of the above embodiment made in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a porous material for thermal insulation of a drilling wellbore, comprising the steps of: (1) The ceramsite powder and the pore-forming agent are fully mixed to obtain a mixed powder; a colloidal solution is used as a binder to obtain ceramsite microspheres by granulation; and then porous ceramsite is obtained by heat treatment; The ceramsite powder is one or a combination of two or more of clay, shale powder, fly ash, coal gangue or iron tailings; the pore-forming agent is a combination of micron particles and nanoparticles, the micron particles are polypropylene, polyethylene or polystyrene micron particles, and the nanoparticles are polypropylene, polyethylene or polystyrene nanoparticles; the colloidal solution is one or a combination of two or more of polyvinyl alcohol aqueous solution, polyacrylamide aqueous solution or polyethylene glycol aqueous solution; The particle size of the ceramsite powder is 0.5-20 μm; the particle size of the micron particles in the pore-forming agent is 6-13 μm, and the particle size of the nanoparticles is 100-500 nm; the mass ratio of the micron particles to the nanoparticles is 2-4:1; the mass ratio of the ceramsite powder to the pore-forming agent is 3.75-5:1; the concentration of the colloidal solution is 0.1-0.8 wt%; and the mass ratio of the mixed powder to the colloidal solution is 1:0.001-0.1; (2) The porous ceramsite, anionic monomer, and cationic monomer are fully dispersed in deionized water, an initiator is added, and the mixture is reacted, and then washed and dried to obtain a porous material for drilling wellbore insulation; The anionic monomer is one or a combination of two or more of 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonate, ethylenesulfonate, propylenesulfonate, acrylic acid, methacrylic acid or hydroxyethylacrylic acid; the cationic monomer is one or a combination of two or more of dimethyldiallylammonium chloride, polyacrylammonium or polyquaternary ammonium salt; the initiator is one or a combination of two or more of ammonium persulfate, sodium bisulfite or azobisisobutylimidazoline hydrochloride; The mass ratio of porous ceramsite, anionic monomer, cationic monomer, initiator and deionized water is 1: (0.01-0.1): (0.005-0.1): (0.005-0.01): (0.5-3).

2. The method for preparing the porous material for drilling wellbore thermal insulation according to claim 1, characterized in that: In step (1), the ceramsite powder is a combination of fly ash and coal gangue; wherein the mass ratio of fly ash to coal gangue is 1:0.5-1.

3. The method for preparing the porous material for drilling wellbore thermal insulation according to claim 1, characterized in that: In step (1), the mixing of ceramsite powder and pore-forming agent is carried out in a round pot granulator.

4. The method for preparing the porous material for drilling wellbore thermal insulation according to claim 1, characterized in that: In step (1), one or more of the following conditions are included: i. Granulation is carried out in a round pot granulator; the mixed powder rotates in the round pot granulator, and a colloidal solution is sprayed onto the surface of the mixed powder using a nano sprayer during the rotation process. Under the action of gravity and rotation, the mixed powder forms agglomerated micron balls, which are then dried to obtain ceramsite microspheres; wherein, the rotation speed of the round pot granulator is 10 to 200 r / min, the rotation time is 2 to 10 minutes, and the spraying speed of the nano sprayer is 30 to 1000 ml / min; ii. The heat treatment temperature is 1000-1500°C, the heat treatment time is 2-10 hours, and the heat treatment atmosphere is air.

5. The method for preparing the porous material for drilling wellbore thermal insulation according to claim 1, characterized in that: In step (2), one or more of the following conditions are included: i. The initiator is in the form of an initiator aqueous solution with a concentration of 0.5 to 5 wt%; ii. The reaction temperature is 20-80°C, the reaction time is 6-12h, and the reaction is carried out in the absence of oxygen, under protective gas protection, and with stirring.

6. The porous material for thermal insulation of a drilling wellbore obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The porous material has a spherical structure, a thermal conductivity of 0.03 to 0.07 W / mk, a porosity of 80 to 95%, and a compressive strength of 1 to 3 MPa; the porous material has a multi-level cellular structure with a pore size of 0.01 to 20 μm; and the surface of the porous material has anionic and cationic groups.

7. The porous material for drilling wellbore thermal insulation according to claim 6, characterized in that: The porous material has a spherical structure, a thermal conductivity of 0.038 to 0.048 W / mk, a porosity of 82 to 88%, and a compressive strength of 1.2 to 2.3 MPa; the porous material has a multi-level cellular structure with a pore size of 0.01 to 13 μm; and the surface of the porous material has anionic and cationic groups.

8. Use of the porous material for thermal insulation of a drilling wellbore obtained by the preparation method according to any one of claims 1 to 5, characterized in that: Used as thermal insulation material for ultra-deep drilling wellbore insulation.

9. The use of the porous material for thermal insulation of a drilling well according to claim 8, characterized in that: Ultra-deep layers are layers with a depth greater than or equal to 8000m.

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