An ultrahigh thermal conductive cement paste, a preparation method and application thereof

Abstract

The application provides a super-high thermal conductivity cement slurry, a preparation method and application thereof, and relates to the technical field of well cementing. The super-high thermal conductivity cement slurry provided by the application comprises the following components in mass fraction: 100 parts of G-grade cement, 30-60 parts of water, 0.2-1.5 parts of a dispersing agent, 0.5-6 parts of a fluid loss additive, 0.1-5 parts of a defoaming agent, 0.1-10 parts of a retarder and 0.8-20 parts of a thermal conductivity material; the thermal conductivity material is a mixture of nano silicon, graphene and silane coupling agent surface modified graphite. The super-high thermal conductivity cement slurry provided by the application has super-high thermal conductivity, good stability and fluidity, high compressive strength of cement stone and meets the well cementing conditions of geothermal wells. The thermal conductivity coefficient of the super-high thermal conductivity cement slurry is 1.862-2.059 W / m·k, the cement slurry has good fluidity, the fluid loss is less than 50 mL, the 1.85g / cm 3 density of the cement slurry is greater than 22.8 MPa.

Description

Technical Field

[0001] This invention relates to the field of cementing technology, and in particular to an ultra-high thermal conductivity cement slurry, its preparation method, and its application. Background Technology

[0002] Geothermal energy is a green energy source, and its efficient extraction and utilization are of great significance in alleviating energy resource shortages. Currently, geothermal energy utilization in medium-deep strata is achieved through drilling and completion operations, with cementing being an indispensable part of the process. Cementing mainly involves injecting cement between the wellbore and the casing annulus, serving two purposes: supporting the casing and creating a reliable method for geothermal well heat extraction and utilization.

[0003] However, the thermal conductivity of cement slurry used for cementing is only 0.19 to 0.65 W / (m·K) after solidification, which is much smaller than that of rock (1.6 to 3.6 W / (m·K)). This results in a lower heat production rate for geothermal wells. Furthermore, the addition of ordinary thermal conductive materials to cement slurry will cause poor slurry stability, decreased strength, and reduced fluidity. Moreover, the thermal conductivity is still not high enough to meet the requirements of geothermal well cementing operations. For example, Zhang Hao et al. ("Factors Affecting the Thermal Conductivity of Cementing Materials for Geothermal Wells") added natural flake graphite, iron powder, and quartz to cement, achieving a thermal conductivity of 1.87 W / (m·K), but this reduced the cement's compressive strength. Guo Wen et al. ("Research on the Formulation of Cement Slurry System for 'Water-Conserving and Heat-Extracting' Geothermal Wells Based on the Mixed Weighted Method") studied geothermal well insulation cement, using natural flake graphite, silicon carbide, and alumina to improve the thermal conductivity of the cementing material. However, the higher the thermal conductivity, the more significant the decrease in cement compressive strength, failing to meet general strength requirements. These studies demonstrate that these methods merely involve theoretical research on the addition of thermally conductive materials to cement, without systematically studying the formulation of cement-based materials and additives. In particular, the impact of adding thermally conductive materials on cement slurry performance—reducing compressive strength and fluidity—means that the cement slurry's performance cannot meet the actual needs of well cementing. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an ultra-high thermal conductivity cement slurry, its preparation method, and its application. The ultra-high thermal conductivity cement slurry provided by this invention not only has ultra-high thermal conductivity but also good stability and fluidity, and the cement stone has high compressive strength, meeting the actual needs of geothermal well cementing.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides an ultra-high thermal conductivity cement slurry, comprising the following components in parts by weight: 100 parts of Grade G cement, 30-60 parts of water, 0.2-1.5 parts of dispersant, 0.5-6 parts of water loss reducing agent, 0.1-5 parts of defoamer, 0.1-10 parts of retarder, and 0.8-20 parts of thermally conductive material; wherein the thermally conductive material is a mixture of nano-silicon, graphene, and silane coupling agent surface-modified graphite, and the mass ratio of nano-silicon, graphene, and silane coupling agent surface-modified graphite in the thermally conductive material is 3:1:5.

[0007] Preferably, the method for preparing the silane coupling agent surface-modified graphite includes the following steps:

[0008] The silane coupling agent is dissolved in water to obtain a silane coupling agent solution;

[0009] Graphite and silane coupling agent solution were mixed and modified, and then dried to obtain silane coupling agent surface-modified graphite.

[0010] Preferably, the mass concentration of the silane coupling agent solution is 0.5-2.5%; and the mass of the silane coupling agent is 0.02-5% of the mass of graphite.

[0011] Preferably, the dispersant comprises one or more of lignin sulfonate, polynaphthalene sulfonate, polystyrene sulfonate, and acetone condensate.

[0012] Preferably, the water loss reducing agent includes one or more of hydroxyethyl cellulose, acrylamide-sodium acrylate copolymer, and N,N-dimethylacrylamide-AMPS copolymer.

[0013] Preferably, the defoamer includes one or more of tributyl phosphate, mineral oil, and THIX-299 silicone polyether.

[0014] Preferably, the retarder comprises one or more of hydroxyethylidene diphosphonic acid, sodium chloride, sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer.

[0015] Preferably, the retarder is a mixture of sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer, wherein the mass ratio of sodium tripolyphosphate to sodium borate in the mixture is 2:1, and the mass ratio of the sum of the masses of sodium tripolyphosphate and sodium borate to the mass of AMPS-itaconic acid copolymer is 1:3.

[0016] This invention provides a method for preparing the ultra-high thermal conductivity cement slurry described in the above technical solution, comprising the following steps:

[0017] Grade G cement, thermally conductive material, dispersant and water loss reducing agent are first mixed to obtain a first mixture;

[0018] Water, defoamer, and retarder are mixed a second time to obtain a second mixture;

[0019] The first mixture and the second mixture are mixed in a third mixture to obtain the ultra-high thermal conductivity cement slurry.

[0020] This invention provides the application of the ultra-high thermal conductivity cement slurry described in the above technical solutions or the ultra-high thermal conductivity cement slurry prepared by the preparation method described in the above technical solutions in geothermal well cementing.

[0021] This invention provides an ultra-high thermal conductivity cement slurry, comprising the following components in parts by weight: 100 parts of Grade G cement, 30-60 parts of water, 0.2-1.5 parts of dispersant, 0.5-6 parts of water loss reducing agent, 0.1-5 parts of defoamer, 0.1-10 parts of retarder, and 0.8-20 parts of thermally conductive material; the thermally conductive material is a mixture of nano-silicon, graphene, and silane coupling agent surface-modified graphite, wherein the mass ratio of nano-silicon, graphene, and silane coupling agent surface-modified graphite in the thermally conductive material is 3:1:5. Compared with the prior art, the beneficial effects of this invention are as follows:

[0022] This invention combines nano-silicon, graphene, and silane coupling agent-modified graphite in a certain proportion as a thermally conductive material and adds it to cement, which can significantly improve the thermal conductivity of cement slurry under low dosage conditions.

[0023] Silane coupling agent surface-modified graphite has good water dispersibility and low surface energy, can be uniformly dispersed in slurry water, and is easily wetted by cement macromolecules, which improves the dispersion and adhesion of thermally conductive materials, improves their fluidity with cement, and improves their bonding strength and thermal conductivity with cement.

[0024] A thermally conductive material is prepared by compounding nano-silicon, graphene, and silane coupling agent-modified graphite in a certain proportion. It has good compatibility with cement slurry and can be mixed with cement slurry in any proportion without affecting the safe thickening time and rheological properties of cement slurry. Moreover, this thermally conductive material has a filling effect, which can effectively fill the capillary pores and gel pores in cement, greatly reducing the porosity and making the cement structure more compact, thereby enhancing toughness and improving the compressive strength of cement stone.

[0025] This invention combines the above-mentioned thermally conductive material with dispersant, fluid loss reducer, defoamer and retarder in a specific ratio. The entire cement slurry system has good compatibility, high strength, good stability and thermal conductivity, and can significantly improve cementing quality.

[0026] Furthermore, this invention uses a mixture of sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer as a retarder. Sodium tripolyphosphate and sodium borate are mixed at a mass ratio of 2:1 as a medium- and low-temperature inorganic phosphate retarder, and are compounded with AMPS-itaconic acid copolymer high-temperature retarder at a ratio of 1:3. This results in good retarding effect of cement slurry under both low and high temperature conditions, significantly improving the temperature resistance and adjustability of thickening time of cement slurry.

[0027] Therefore, the ultra-high thermal conductivity cement slurry provided by this invention not only possesses ultra-high thermal conductivity but also exhibits good stability and fluidity, and high compressive strength of the cement stone, meeting the cementing requirements for geothermal wells. Example results show that the ultra-high thermal conductivity cement slurry provided by this invention has a thermal conductivity of 1.862–2.059 W / m·K, good fluidity, a water loss of less than 50 mL, and a water loss of 1.85 g / cm³. 3 The density of the cement paste has a compressive strength greater than 22.8 MPa after 24 hours. Detailed Implementation

[0028] This invention provides an ultra-high thermal conductivity cement slurry, comprising the following components in parts by weight: 100 parts of Grade G cement, 30-60 parts of water, 0.2-1.5 parts of dispersant, 0.5-6 parts of water loss reducing agent, 0.1-5 parts of defoamer, 0.1-10 parts of retarder, and 0.8-20 parts of thermally conductive material; wherein the thermally conductive material is a mixture of nano-silicon, graphene, and silane coupling agent surface-modified graphite, and the mass ratio of nano-silicon, graphene, and silane coupling agent surface-modified graphite in the thermally conductive material is 3:1:5.

[0029] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known to those skilled in the art.

[0030] By mass, the ultra-high thermal conductivity cement slurry provided by the present invention comprises 100 parts of Grade G cement, wherein the Grade G cement is beneficial to the cementing effect.

[0031] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention comprises 0.8–20 parts of thermally conductive material, preferably 1–15 parts, more preferably 3–10 parts, and even more preferably 5–7 parts. In this invention, the thermally conductive material is a mixture of nano-silicon, graphene, and silane coupling agent surface-modified graphite. In this invention, the preparation method of the silane coupling agent surface-modified graphite preferably includes the following steps:

[0032] The silane coupling agent is dissolved in water to obtain a silane coupling agent solution;

[0033] Graphite and silane coupling agent solution are mixed and modified to obtain silane coupling agent surface-modified graphite.

[0034] In this invention, the silane coupling agent is preferably one or more of vinylsilane, methacryloxysilane, 3-triethoxysilyl-1-propylamine, vinyltriethoxysilane, butadienetriethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane, more preferably a mixture of vinylsilane and 3-triethoxysilyl-1-propylamine in a mass ratio of 3:2; the mass concentration of the silane coupling agent solution is preferably 0.5-2.5%, more preferably 0.5-1%. In this invention, the graphite preferably includes one or more of natural flake graphite, amorphous graphite, and artificial graphite, and the particle size of the graphite is preferably 1-90 μm. In this invention, the graphite is preferably added in the form of a graphite dispersion, which is preferably obtained by ultrasonically dispersing graphite in water; this invention does not have particular requirements on the concentration of the graphite dispersion, and it is preferable to wash the graphite multiple times with ethanol and deionized water before ultrasonic dispersion. In this invention, the mass of the silane coupling agent is preferably 0.02-5% of the graphite mass, more preferably 3.5-4.5%. In this invention, the modification temperature is preferably 25-60°C, and the modification time is preferably 12-24 hours. The modification is preferably carried out under stirring conditions. After modification, the resulting modified liquid is preferably cooled to room temperature and then filtered. The solid product is then dried to obtain silane coupling agent-modified graphite. The drying temperature is preferably 70-118°C, and the drying time is preferably 15 minutes to 24 hours, specifically based on drying to constant weight. This invention modifies the surface of graphite with a silane coupling agent, enabling the graphite to have good water dispersibility and low surface energy, allowing it to be uniformly dispersed in slurry water and easily wetted by cement macromolecules. This improves the dispersion and adhesion of the thermally conductive material, enhancing its fluidity with cement while increasing its bonding strength with cement.

[0035] In this invention, the graphene is preferably one or more of single-layer graphene, double-layer graphene, and few-layer graphene.

[0036] In this invention, the nano-silicon preferably includes silicon dioxide and / or crystalline silicon, and the particle size of the nano-silicon is preferably 1 to 20 nm.

[0037] This invention incorporates a compound of nano-silicon, graphene, and silane coupling agent-modified graphite in a specific ratio into cement as a thermally conductive material. This significantly improves the thermal conductivity of cement slurry even with low dosage. Furthermore, this thermally conductive material exhibits good compatibility with cement slurry, allowing for mixing in any proportion without significantly affecting the safe thickening time and rheological properties of the slurry. Moreover, this thermally conductive material has a filling effect, effectively filling the capillary pores and gel pores in cement, greatly reducing porosity, resulting in a more compact cement structure, enhanced toughness, and improved compressive strength of cement paste.

[0038] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention comprises 30-60 parts water, preferably 40-50 parts. In this invention, the water is preferably fresh water.

[0039] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention includes 0.2 to 1.5 parts of dispersant, preferably 0.6 to 1 part. In this invention, the dispersant preferably includes one or more of lignin sulfonate, polynaphthalene sulfonate, polystyrene sulfonate, and acetone condensate. The lignin sulfonate is preferably calcium lignin sulfonate, the polynaphthalene sulfonate is preferably sodium polynaphthalene sulfonate, and the polystyrene sulfonate is preferably sodium polystyrene sulfonate. In embodiments of this invention, the dispersant is preferably a mixture of calcium lignin sulfonate and sodium polystyrene sulfonate, and the mass ratio of calcium lignin sulfonate to sodium polystyrene sulfonate is preferably 3:1.

[0040] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention includes 0.5 to 6 parts, preferably 1 to 2 parts, of a water loss reducing agent. In this invention, the water loss reducing agent preferably includes one or more of hydroxyethyl cellulose, acrylamide-sodium acrylate copolymer, and N,N-dimethylacrylamide-AMPS copolymer, more preferably a mixture of hydroxyethyl cellulose and N,N-dimethylacrylamide-AMPS copolymer, wherein the mass ratio of hydroxyethyl cellulose to N,N-dimethylacrylamide-AMPS copolymer is preferably 2:1.

[0041] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention includes 0.1 to 5 parts of defoamer, preferably 0.4 to 1.5 parts. In this invention, the defoamer preferably includes one or more of tributyl phosphate, mineral oil, and THIX-299 silicone polyether, more preferably a mixture of tributyl phosphate and THIX-299 silicone polyether, wherein the mass ratio of tributyl phosphate to THIX-299 silicone polyether is preferably 4:1.

[0042] Based on the mass fraction of Grade G cement, the ultra-high thermal conductivity cement slurry provided by this invention includes 0.1 to 10 parts of a retarder, preferably 0.5 to 5 parts. In this invention, the retarder preferably includes one or more of hydroxyethylidene diphosphonic acid, sodium chloride, sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer, more preferably a mixture of sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer. The mass ratio of sodium tripolyphosphate to sodium borate in the mixture is preferably 2:1, and the mass ratio of the sum of the masses of sodium tripolyphosphate and sodium borate to the mass of AMPS-itaconic acid copolymer is preferably 1:3. This invention adds dispersants, water loss reducers, retarders, and defoamers to the cement slurry with specific components and contents, resulting in good interactions between the components and the cement and thermally conductive materials.

[0043] The ultra-high thermal conductivity cement slurry provided by this invention not only possesses ultra-high thermal conductivity (1.862~2.059W / m·k), but also exhibits good stability and fluidity, and high compressive strength of the cement stone (1.85g / cm). 3 The cement slurry with a density greater than 22.8 MPa after 24 hours meets the cementing conditions for geothermal wells.

[0044] This invention provides a method for preparing the ultra-high thermal conductivity cement slurry described in the above technical solution, comprising the following steps:

[0045] Grade G cement, thermally conductive material, dispersant and water loss reducing agent are first mixed to obtain a first mixture;

[0046] Water, defoamer, and retarder are mixed a second time to obtain a second mixture;

[0047] The first mixture and the second mixture are mixed in a third mixture to obtain the ultra-high thermal conductivity cement slurry.

[0048] The present invention does not have any special requirements for the first, second and third mixing methods, as long as the components are mixed evenly.

[0049] This invention provides the application of the ultra-high thermal conductivity cement slurry described in the above technical solutions or the ultra-high thermal conductivity cement slurry prepared by the preparation methods described in the above technical solutions in geothermal well cementing. This invention does not impose any special requirements on the method of application; methods well known to those skilled in the art can be used.

[0050] The following detailed description of the ultra-high thermal conductivity cement slurry, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0051] In each embodiment, the preparation method of silane coupling agent surface-modified graphite is as follows:

[0052] Dissolve 2.5g of silane coupling agent (the silane coupling agent is a mixture of vinylsilane and 3-triethoxysilyl-1-propylamine in a mass ratio of 3:2) in water to prepare a silane coupling agent solution with a mass concentration of 0.5%.

[0053] The surface of 60g of graphite was washed repeatedly with ethanol and deionized water. Then, the graphite was added to water and ultrasonically dispersed to obtain a stable graphite dispersion. A 0.5% (w / w) silane coupling agent solution was added to the graphite dispersion and stirred at 60°C for 12h. After cooling to room temperature, the mixture was separated by vacuum filtration. The filtered product was placed in a vacuum oven and dried at 70°C for 24h to obtain silane coupling agent surface-modified graphite.

[0054] Example 1

[0055] Weigh each component according to the following mass ratio:

[0056] The formula comprises 100% grade cement + 40% fresh water + 0.6% dispersant + 1.8% water loss reducing agent + 0.4% defoamer + 0.5% retarder + 1% thermally conductive material. The dispersant is a mixture of calcium lignosulfonate and sodium polystyrene sulfonate in a 3:1 mass ratio; the water loss reducing agent is a mixture of hydroxyethyl cellulose and N,N-dimethylacrylamide-AMPS copolymer in a 2:1 mass ratio; the defoamer is a mixture of tributyl phosphate and THIX-299 silicone polyether in a 4:1 mass ratio; the retarder is a mixture of sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer, wherein the mass ratio of sodium tripolyphosphate to sodium borate in the mixture is 2:1, and the mass ratio of the sum of the masses of sodium tripolyphosphate and sodium borate to the mass of AMPS-itaconic acid copolymer is 1:3; and the thermally conductive material is a mixture of silane coupling agent surface-modified graphite, nano-silicon, and graphene in a 5:3:1 mass ratio.

[0057] The solid materials (cement, thermally conductive materials, dispersant and water loss reducer) are premixed evenly and set aside. Then, the liquid materials (fresh water, defoamer and retarder) are mixed evenly and added to the premixed solid materials. The mixture is stirred evenly to obtain ultra-high thermal conductivity cement slurry.

[0058] Example 2

[0059] Weigh each component according to the following mass ratio:

[0060] 100% Grade G cement + 40% fresh water + 0.6% dispersant + 1.8% water loss reducer + 0.4% defoamer + 0.5% retarder + 3% thermally conductive material, wherein the dispersant, water loss reducer, defoamer, retarder and thermally conductive material are the same as in Example 1.

[0061] The solid materials (cement, thermally conductive materials, dispersant and water loss reducer) are premixed evenly and set aside. Then, the liquid materials (fresh water, defoamer and retarder) are mixed evenly and added to the premixed solid materials. The mixture is stirred evenly to obtain ultra-high thermal conductivity cement slurry.

[0062] Example 3

[0063] Weigh each component according to the following mass ratio:

[0064] The mixture consists of 100% Grade G cement, 40% fresh water, 0.6% dispersant, 1.8% water loss reducer, 0.4% defoamer, 0.5% retarder, and 5% thermally conductive material, wherein the dispersant, water loss reducer, defoamer, retarder, and thermally conductive material are the same as in Example 1.

[0065] The solid materials (cement, thermally conductive materials, dispersant and water loss reducer) are premixed evenly and set aside. Then, the liquid materials (fresh water, defoamer and retarder) are mixed evenly and added to the premixed solid materials. The mixture is stirred evenly to obtain ultra-high thermal conductivity cement slurry.

[0066] Example 4

[0067] Weigh each component according to the following mass ratio:

[0068] The mixture consists of 100% Grade G cement, 40% fresh water, 0.6% dispersant, 1.8% water loss reducer, 0.4% defoamer, 0.5% retarder, and 7% thermally conductive material, wherein the dispersant, water loss reducer, defoamer, retarder, and thermally conductive material are the same as in Example 1.

[0069] The solid materials (cement, thermally conductive materials, dispersant and water loss reducer) are premixed evenly and set aside. Then, the liquid materials (fresh water, defoamer and retarder) are mixed evenly and added to the premixed solid materials. The mixture is stirred evenly to obtain ultra-high thermal conductivity cement slurry.

[0070] Comparative Example 1

[0071] The thermally conductive material is omitted, and the rest is the same as in Example 1.

[0072] The properties of cement slurry and the mechanical properties of cement stone prepared in Comparative Example 1 and Examples 1-4 were tested (in accordance with national standards GB 10238-2005 "Oil Well Cement" and GB / T 19139-2012 "Test Methods for Oil Well Cement"). The results are shown in Tables 1 and 2.

[0073] Table 1 Thermal conductivity of cement slurry

[0074] Example Thermal conductive material addition percentage Thermal conductivity (W / m·K) Comparative Example 1 0 1.298 Example 1 1 1.862 Example 2 3 1.926 Example 3 5 1.972 Example 4 7 2.059

[0075] As can be seen from Table 1, the thermal conductivity of cement slurry improves with the increase of thermal conductive material content. When the thermal conductive material content is 7%, the thermal conductivity of cement slurry is 2.059 W / m·K, which is 59% higher than that of cement slurry without thermal conductive material.

[0076] Table 2. Cement slurry fluidity and strength data (density ρ is in g / cm³). 3 )

[0077]

[0078] Note: Δρ is the density difference between the upper and lower parts of the cement slurry after it has stood for 2 hours.

[0079] Table 2 shows that, compared with cement slurry without thermally conductive material, cement slurry with added thermally conductive material exhibits better overall rheological properties, indicating good compatibility between the additives and the thermally conductive material. In particular, the zero density difference between the upper and lower layers indicates uniform distribution of the solid and liquid phases in the system, resulting in good slurry stability and improved cementing quality. When the thermally conductive material content is 5%, the compressive strength of the cement slurry reaches 24.8 MPa, and the thickening time generally shows a shorter trend, but the thickening time is controllable. Therefore, cement stone with added thermally conductive material not only has high thermal conductivity but also high compressive strength (1.85 g / cm³). 3 The high-density, high-thermal-conductivity cement slurry has a compressive strength greater than 22.8 MPa after 24 hours and a low water loss (less than 50 mL), meeting the requirements for cementing.

[0080] As can be seen from the above embodiments, the ultra-high thermal conductivity cement slurry provided by the present invention not only has ultra-high thermal conductivity, but also good stability and fluidity, and the cement stone has high compressive strength, which meets the actual needs of geothermal well cementing.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cement slurry with ultra-high thermal conductivity, characterized in that, It is composed of the following components in parts by weight: 100 parts of Grade G cement, 30-60 parts of water, 0.2-1.5 parts of dispersant, 0.5-6 parts of water loss reducing agent, 0.1-5 parts of defoamer, 0.1-10 parts of retarder, and 0.8-10 parts of thermally conductive material; the thermally conductive material is a mixture of nano-silicon, graphene, and silane coupling agent surface-modified graphite, wherein the mass ratio of nano-silicon, graphene, and silane coupling agent surface-modified graphite in the thermally conductive material is 3:1:5; the retarder is a mixture of sodium tripolyphosphate, sodium borate, and AMPS-itaconic acid copolymer, wherein the mass ratio of sodium tripolyphosphate to sodium borate in the mixture is 2:1, and the mass ratio of the sum of the masses of sodium tripolyphosphate and sodium borate to the mass of AMPS-itaconic acid copolymer is 1:

3.

2. The ultra-high thermal conductivity cement slurry according to claim 1, characterized in that, The preparation method of the silane coupling agent surface-modified graphite includes the following steps: The silane coupling agent is dissolved in water to obtain a silane coupling agent solution; Graphite and silane coupling agent solution were mixed and modified, and then dried to obtain silane coupling agent surface-modified graphite.

3. The ultra-high thermal conductivity cement slurry according to claim 2, characterized in that, The mass concentration of the silane coupling agent solution is 0.5-2.5%; the mass of the silane coupling agent is 0.02-5% of the mass of graphite.

4. The ultra-high thermal conductivity cement slurry according to claim 1, characterized in that, The dispersant includes one or more of lignin sulfonate, polynaphthalene sulfonate, polystyrene sulfonate, and acetone condensate.

5. The ultra-high thermal conductivity cement slurry according to claim 1, characterized in that, The water loss reducing agent includes one or more of hydroxyethyl cellulose, acrylamide-sodium acrylate copolymer, and N,N-dimethylacrylamide-AMPS copolymer.

6. The ultra-high thermal conductivity cement slurry according to claim 1, characterized in that, The defoamer includes one or more of tributyl phosphate, mineral oil, and THIX-299 silicone polyether.

7. The method for preparing ultra-high thermal conductivity cement slurry according to any one of claims 1 to 6, characterized in that, Includes the following steps: Grade G cement, thermally conductive material, dispersant and water loss reducing agent are first mixed to obtain a first mixture; Water, defoamer, and retarder are mixed a second time to obtain a second mixture; The first mixture and the second mixture are mixed in a third mixture to obtain the ultra-high thermal conductivity cement slurry.

8. The application of the ultra-high thermal conductivity cement slurry according to any one of claims 1 to 6 or the ultra-high thermal conductivity cement slurry prepared by the preparation method according to claim 7 in geothermal well cementing.

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