Temperature-resistant high-thermal-conductivity cementing slurry system suitable for geothermal well and preparation method thereof

Abstract

The present application relates to geothermal resource development material technical field, specifically to the temperature-resistant high-thermal-conductivity cementing slurry system suitable for geothermal well and its preparation method, the temperature-resistant high-thermal-conductivity cementing slurry system suitable for geothermal well includes by weight percentage: 38.0wt. %~63.5wt. % G-grade oil well cement, 15.0wt. % siliceous material, 10wt. %~15wt. % serpentine, 10wt. %~30wt. % temperature-resistant thermal conductive material, 0.5wt. % high-temperature stabilizer, 1wt. %~1.5wt. % high-temperature dispersant, and the percentage of the total mass of the above raw materials 3wt. %~5wt. % high-temperature fluid loss additive, 1wt. %~3wt. % high-temperature retarder, 0.25wt. % defoaming agent.The present application has the characteristics of strong high-temperature resistance, high thermal conductivity, good toughness, micro-expansion and gas channeling prevention.

Description

Technical Field

[0001] This invention relates to the field of materials technology for geothermal resource development, specifically to a high-temperature resistant and thermally conductive cement slurry system suitable for geothermal wells and its preparation method. Background Technology

[0002] Geothermal energy, as a clean and pollution-free energy source, is receiving increasing attention, and clean, low-carbon energy is currently the main source of incremental energy supply. The vigorous development and utilization of geothermal resources is gaining popularity and is of great significance for reducing greenhouse gas emissions, alleviating energy shortages, and promoting the sustainable development of the national economy. Cementing is a crucial step in the geothermal well formation process, involving the injection of cementing materials between the geothermal well casing and the borehole wall to enhance heat exchange between the geothermal well heat exchanger and the rock and soil.

[0003] Chinese patent CN110590271A discloses a high thermal conductivity cement slurry for geothermal wells and its preparation method. The high thermal conductivity cement slurry comprises (by weight parts): cement, graphite powder and water, wherein, relative to 100 parts of cement, the graphite powder is 5-20 parts and the water is 44-50 parts.

[0004] Chinese patent CN109678420A discloses a cementing material for a mid-level geothermal well and a geothermal well. The cementing material includes cement, graphite powder, and surfactant.

[0005] Chinese patent CN111410480A discloses a mixed filler for heat transfer in buried pipe heat exchangers, with the following weight composition: cement 100; fresh water 45-58; sand 35-38; retarder 0.5-2; silica fume 4-6; fly ash 20; water-reducing agent 1; air-entraining agent 0.01-0.02; graphite 0.5-2; toughening fiber leak-proof agent 2-3.

[0006] Chinese patent CN114315256A discloses a high thermal conductivity and high heat insulation cement for geothermal wells and its preparation method. The high thermal conductivity and high temperature material includes water, G-grade high sulfate-resistant oil well cement, natural flake graphite, silicon carbide, and alumina. The weight ratio of water to G-grade high sulfate-resistant oil well cement is 0.42-0.60; the weight ratio of natural flake graphite to G-grade high sulfate-resistant oil well cement is 0.05-0.10; the weight ratio of silicon carbide and alumina to G-grade high sulfate-resistant oil well cement is 0.02-0.04; and the mass ratio of silicon carbide to alumina is 1:1-2.

[0007] Because well cementing operates in deep formations, it must not only meet requirements for high thermal conductivity but also ensure high temperature resistance, high compressive strength, short setting time, and good fluidity. Existing technologies primarily focus on high thermal conductivity, with limited consideration given to the cement's performance under high-temperature conditions. Therefore, providing a high-temperature resistant cementing material with high thermal conductivity and stable high-temperature performance is crucial for geothermal resource development. Summary of the Invention

[0008] The purpose of this invention is to provide a high-temperature resistant, high-thermal-conductivity cementing slurry system suitable for geothermal wells and its preparation method. This system exhibits good performance under high-temperature conditions and possesses characteristics of resistance to high-temperature strength degradation and high thermal conductivity.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A high-temperature resistant, high-thermal-conductivity cementing slurry system suitable for geothermal wells comprises the following raw materials by weight percentage:

[0011] Grade G oil well cement: 38.0 wt.%~63.5 wt.%;

[0012] Siliceous material: 15.0 wt.%;

[0013] Serpentine: 10wt.%~15wt.%;

[0014] Temperature-resistant thermally conductive materials: 10 wt.% to 30 wt.%;

[0015] High temperature stabilizer: 0.5 wt.%;

[0016] High-temperature dispersant: 1 wt.% - 1.5 wt.%;

[0017] And additives accounting for a percentage of the total mass of the above raw materials:

[0018] High-temperature water loss reducing agent: 3wt.%~5wt.%;

[0019] High-temperature retarder: 1 wt.% to 3 wt.%;

[0020] Defoamer: 0.25 wt.%.

[0021] Furthermore, the siliceous material is a mixture of 200-mesh quartz sand, 800-mesh quartz sand, and 1200-mesh quartz sand in a mass ratio of 1:2:1, and the SiO2 content of the siliceous material is ≥95wt.%.

[0022] Furthermore, the serpentine rock has an MgO content ≥ 40.0 wt.%, an SiO2 content ≥ 40.0 wt.%, and an average particle size of 325 mesh.

[0023] Furthermore, the heat-resistant thermally conductive material is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of (8-12):(6-9):(2-3).

[0024] The high-temperature resistant and thermally conductive material of this invention, through the synergistic effect of its various raw materials, can significantly enhance the high-temperature resistance, high-temperature toughness, and thermal conductivity of well cement, ensuring the quality of the geothermal well itself while improving heat extraction efficiency and further promoting the development and utilization of geothermal resources.

[0025] Furthermore, the thermally conductive strengthening material is a mixture formed by mixing molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a mass ratio of 5:2:2:1 and then modifying the mixture.

[0026] The molybdenum disilicide has an effective material content of >99 wt.% and an average particle size of 15 μm; the tungsten diboride has an effective material content of >99 wt.% and an average particle size of 50 nm; the zirconium diboride has an effective material content of >99 wt.% and an average particle size of 50 nm; and the titanium diboride has an effective material content of >99 wt.% and an average particle size of 15 μm.

[0027] The heat-resistant and thermally conductive material of this invention is rationally designed. The raw materials, such as molybdenum disilicide, tungsten diboride, zirconium diboride, titanium diboride, and expanded graphite, inherently possess excellent thermal conductivity and strong temperature resistance. The thermally conductive reinforcing material reduces the gap between the reinforcing material and cement particles through small size and particle size distribution effects, increasing the density of the cement stone structure and mitigating the decrease in thermal conductivity caused by the presence of pores.

[0028] Furthermore, the reinforcing material is composed of graphite quartz schist, andalusite, and modified expanded graphite mixed in a mass ratio of 6:1:3; the average particle size of the polyetherimide after crushing and grinding is ≤45μm.

[0029] Furthermore, the graphite-quartz schist is flaky, with a graphite content of 15wt.%–20wt.%, a silica content of 50wt.%–60wt.%, and a mica content of 10wt.%–20wt.%; the average particle size of the graphite-quartz schist after crushing and grinding is ≤45μm; the andalusite has an Al2O3 content ≥50wt.%, a SiO2 content ≥40wt.%, and an average particle size ≤45μm; the modified expanded graphite is expanded graphite modified by low-temperature plasma, with an expansion volume of 600ml / g and an average particle size ≤74μm.

[0030] The thermally conductive reinforcing material of this invention is modified with a silane coupling agent (ethyl orthosilicate ethanol solution) to coat its surface with a layer of silica, thereby improving its hydrophilicity and participation in the hydration reaction. This enhances the bonding strength between the thermally conductive reinforcing material and the cement hydration products, and reduces porosity. The main components of the reinforcing material are SiO2, Al2O3, and graphite. This not only effectively reduces the Ca / Si ratio of the cementing cement, preventing the strength degradation of the cement stone under high-temperature conditions, but also utilizes the excellent thermal conductivity of graphite materials to further enhance the thermal conductivity of this invention through synergistic effects with the thermally conductive reinforcing material. In addition, the modified expanded graphite has a loose and porous worm-like structure, giving it a large surface area and flexibility. On the one hand, the large surface area provides a large number of crystallization points for the hydration products, promoting hydration. After modification, the increased hydrophilicity enhances the bonding strength between the modified graphite and the hydration products. On the other hand, its flexibility, in synergy with columnar andalusite and polyetherimide, disperses and interpenetrates the stress, reducing the brittleness of the cement stone and enhancing its flexibility.

[0031] Furthermore, the high-temperature stabilizer is a clay mineral; the high-temperature dispersant is an aldehyde-ketone condensate; the high-temperature water loss reducing agent is a 2-acrylamido-2-methylpropanesulfonic acid polymer; the high-temperature retarder is an AMPS polymer; and the defoamer is tributyl phosphate.

[0032] This invention also provides a method for preparing a high-temperature resistant and high-thermal-conductivity cement slurry system suitable for geothermal wells, comprising: Step 1, mixing G-grade oil well cement, siliceous materials, serpentine, high-temperature resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants according to their respective weight percentages to obtain powder; Step 2, weighing high-temperature dehydration reducer, high-temperature retarder and defoamer according to their respective weight percentages and mixing them with water to obtain a mixed liquid; Step 3, preparing cement slurry by mixing the powder and mixed liquid according to GB / T19139 standard, thereby obtaining the high-temperature resistant and high-thermal-conductivity cement slurry system suitable for geothermal wells.

[0033] Further, the preparation of the thermally conductive strengthening material includes: step a, mixing molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a ball mill at their respective mass ratios for 30 min to form mixture A; step b, placing mixture A in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirring and ultrasonically dispersing for 20 min, then placing it in a 60℃ constant temperature water bath and stirring, allowing it to react fully for 10 h; step c, centrifuging the product after the reaction at 1200 r / min for 5 min, washing it three times with anhydrous ethanol, and vacuum drying for 24 h to obtain the thermally conductive strengthening material.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The high-temperature resistant and thermally conductive cement slurry system for geothermal wells of the present invention has the characteristics of strong high temperature resistance, high thermal conductivity, good toughness, and micro-expansion to prevent gas channeling.

[0036] The high-temperature resistant and thermally conductive cementing slurry system for geothermal wells of this invention utilizes siliceous raw materials, serpentine, and high-temperature resistant and thermally conductive materials in synergy to reduce the Ca / Si ratio, prevent the cement stone strength degradation under high-temperature conditions, and improve the temperature resistance of the invention. The main component of serpentine, MgO, can participate in the cement hydration reaction and undergo volume expansion, effectively compensating for the volume shrinkage of the cement system caused by high temperatures and the use of ultrafine materials. This reduces the gap between the cement sheath and the formation, not only improving the bonding strength between the cement sheath and the formation and preventing gas channeling, but also enhancing the thermal conductivity of the cement stone. Through the synergy between the raw materials, this invention possesses excellent high-temperature resistance, high-temperature toughness, gas channeling prevention, and thermal conductivity. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] The following examples all demonstrate the preparation of cement slurry according to GB / T19139 standard, with a water-cement ratio of 0.44. The G-grade oil well cement was provided by Jiahua Special Cement Co., Ltd., the high-temperature retarder was an AMPS-type polymer, the high-temperature water loss reducer was a 2-acrylamido-2-methylpropanesulfonic acid-type polymer, and the high-temperature stabilizer was a clay mineral.

[0039] The siliceous material used in this embodiment of the invention is a mixture of 200-mesh quartz sand, 800-mesh quartz sand and 1200-mesh quartz sand in a mass ratio of 1:2:1, and the SiO2 content of the siliceous material is ≥95wt.%.

[0040] The serpentine rock used in this embodiment of the invention has an MgO content ≥40.0 wt.%, an SiO2 content ≥40.0 wt.%, and an average particle size of 325 mesh.

[0041] The thermally conductive strengthening material used in this embodiment of the invention is a mixture formed by mixing molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a mass ratio of 5:2:2:1 and then modifying the mixture. The effective material content of molybdenum disilicide is >99 wt.%, and the average particle size is 15 μm; the effective material content of tungsten diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of zirconium diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of titanium diboride is >99 wt.%, and the average particle size is 15 μm.

[0042] The reinforcing material used in the embodiments of the present invention is a mixture of graphite quartz schist, andalusite, and modified expanded graphite in a mass ratio of 6:1:3; the average particle size of the polyetherimide used after crushing and grinding is ≤45μm.

[0043] The graphite quartz schist used in this embodiment of the invention is flaky, with a graphite content of 15wt.% to 20wt.%, a silica content of 50wt.% to 60wt.%, and a mica content of 10wt.% to 20wt.%. The average particle size of the graphite quartz schist after crushing and grinding is ≤45μm. The andalusite used has an Al2O3 content ≥50wt.%, a SiO2 content ≥40wt.%, and an average particle size ≤45μm. The modified expanded graphite used is expanded graphite modified by low-temperature plasma, with an expansion volume of 600ml / g and an average particle size ≤74μm.

[0044] The high-temperature stabilizer used in the embodiments of the present invention is a clay mineral; the high-temperature dispersant used is an aldehyde-ketone condensate; the high-temperature water loss reducing agent used is a 2-acrylamido-2-methylpropanesulfonic acid polymer; the high-temperature retarder used is an AMPS polymer; and the defoamer used is tributyl phosphate.

[0045] The preparation of the thermally conductive strengthening material used in this embodiment of the invention includes: step a, mixing molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a ball mill at their respective mass ratios for 30 min to form mixture A, thereby improving its surface roughness; step b, placing mixture A in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirring and ultrasonically dispersing for 20 min, then placing it in a 60℃ constant temperature water bath and stirring, allowing it to react fully for 10 h; step c, centrifuging the product after the reaction at 1200 r / min for 5 min, washing it three times with anhydrous ethanol, and vacuum drying for 24 h to obtain the thermally conductive strengthening material.

[0046] Example 1

[0047] As a preferred embodiment of the present invention, the specific composition of the high-temperature resistant and thermally conductive cementing slurry system suitable for geothermal wells used in this embodiment is shown in Table 1:

[0048] Table 1

[0049] Components Weight percentage (wt.%) Grade G oil well cement 38.0 Siliceous materials 15 Serpentine 15 High-temperature resistant thermal conductive materials 30 High temperature stabilizer 0.5 High temperature dispersant 1.5

[0050] In this embodiment, the heat-resistant thermally conductive material used is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of 8:9:3.

[0051] G-grade oil well cement, siliceous materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants were mixed evenly according to the weight percentages shown in Table 1 to obtain powder.

[0052] Weigh out 3 wt.% of the high-temperature water loss reducing agent, 1 wt.% of the high-temperature retarder and 0.5 wt.% of the defoamer, which account for the total mass of the above raw materials, and mix them with water to obtain a mixed liquid. The amount of water used is determined according to 0.44 water-cement ratio.

[0053] The powder and mixed liquid were prepared into cement slurry according to GB / T19139 standard, thus obtaining the high temperature resistant and high thermal conductivity cement slurry system 1# suitable for geothermal wells.

[0054] Example 2

[0055] As a preferred embodiment of the present invention, the specific composition of the high-temperature resistant and thermally conductive cementing slurry system suitable for geothermal wells used in this embodiment is shown in Table 2:

[0056] Components Weight percentage (wt.%) Grade G oil well cement 51.3 Siliceous materials 15 Serpentine 12 High-temperature resistant thermal conductive materials 20 High temperature stabilizer 0.5 High temperature dispersant 1.2

[0057] In this embodiment, the heat-resistant thermally conductive material used is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of 8:9:3.

[0058] G-grade oil well cement, siliceous materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants were mixed evenly according to the weight percentages shown in Table 2 to obtain powder.

[0059] Weigh out 4 wt.% of the high-temperature water loss reducing agent, 2 wt.% of the high-temperature retarder and 0.5 wt.% of the defoamer, which account for 4 wt.% of the total mass of the above raw materials, and mix them with water to obtain a mixed liquid. The amount of water used is determined according to 0.44 water-cement ratio.

[0060] The powder and mixed liquid were prepared into cement slurry according to GB / T19139 standard, thus obtaining the high-temperature resistant and thermally conductive cement slurry system 2# suitable for geothermal wells.

[0061] Example 3

[0062] As a preferred embodiment of the present invention, the specific composition of the high-temperature resistant and thermally conductive cementing slurry system suitable for geothermal wells used in this embodiment is shown in Table 3:

[0063] Table 3

[0064] Components Weight percentage (wt.%) Grade G oil well cement 63.5 Siliceous materials 15 Serpentine 10 High-temperature resistant thermal conductive materials 10 High temperature stabilizer 0.5 High temperature dispersant 1

[0065] In this embodiment, the heat-resistant thermally conductive material used is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of 8:9:3.

[0066] G-grade oil well cement, siliceous materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants were mixed evenly according to the weight percentages shown in Table 3 to obtain powder.

[0067] Weigh out 5 wt.% of the high-temperature water loss reducing agent, 3 wt.% of the high-temperature retarder and 0.5 wt.% of the defoamer, which account for the total mass of the above raw materials, and mix them with water to obtain a mixed liquid. The amount of water used is determined according to 0.44 water-cement ratio.

[0068] The powder and mixed liquid were prepared into cement slurry according to the GB / T19139 standard, thus obtaining the high-temperature resistant and thermally conductive cement slurry system 3# suitable for geothermal wells.

[0069] Example 4

[0070] As a preferred embodiment of the present invention, the specific composition of the high-temperature resistant and high-thermal-conductivity cement slurry system suitable for geothermal wells used in this embodiment is shown in Table 4:

[0071] Table 4

[0072] Components Weight percentage (wt.%) Grade G oil well cement 51.3 Siliceous materials 15 Serpentine 12 High-temperature resistant thermal conductive materials 20 High temperature stabilizer 0.5 High temperature dispersant 1.2

[0073] In this embodiment, the heat-resistant thermally conductive material used is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of 4:3:1.

[0074] G-grade oil well cement, siliceous materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants were mixed evenly according to the weight percentages shown in Table 4 to obtain powder.

[0075] Weigh out 4 wt.% of the high-temperature water loss reducing agent, 2 wt.% of the high-temperature retarder and 0.5 wt.% of the defoamer, which account for 4 wt.% of the total mass of the above raw materials, and mix them with water to obtain a mixed liquid. The amount of water used is determined according to 0.44 water-cement ratio.

[0076] The powder and mixed liquid were prepared into cement slurry according to GB / T19139 standard, thus obtaining the high-temperature resistant and thermally conductive cement slurry system 4# suitable for geothermal wells.

[0077] Example 5

[0078] As a preferred embodiment of the present invention, the specific composition of the high-temperature resistant and thermally conductive cementing slurry system suitable for geothermal wells used in this embodiment is shown in Table 5:

[0079] Table 5

[0080] Components Weight percentage (wt.%) Grade G oil well cement 51.3 Siliceous materials 15 Serpentine 12 High-temperature resistant thermal conductive materials 20 High temperature stabilizer 0.5 High temperature dispersant 1.2

[0081] In this embodiment, the heat-resistant thermally conductive material used is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of 6:3:1.

[0082] G-grade oil well cement, siliceous materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers and high-temperature dispersants were mixed evenly according to the weight percentages shown in Table 5 to obtain powder.

[0083] Weigh out 4 wt.% of the high-temperature water loss reducing agent, 2 wt.% of the high-temperature retarder and 0.5 wt.% of the defoamer, which account for 4 wt.% of the total mass of the above raw materials, and mix them with water to obtain a mixed liquid. The amount of water used is determined according to 0.44 water-cement ratio.

[0084] The powder and mixed liquid were prepared into cement slurry according to the GB / T19139 standard, thus obtaining the high-temperature resistant and thermally conductive cement slurry system 5# suitable for geothermal wells.

[0085] Comparative Example 1

[0086] Based on the formula of 68.5 wt.% Grade G oil well cement + 30 wt.% silica material + 0.5 wt.% high temperature stabilizer + 1 wt.% high temperature dispersant, and 4 wt.% high temperature water loss reducer and 2 wt.% high temperature retarder accounting for 4 wt.% of the total mass of the above raw materials, cement slurry was prepared according to GB / T19139 standard with a water-cement ratio of 0.44, resulting in cementing slurry system 6#.

[0087] The engineering performance of cement slurry obtained in Examples 1-5 and Comparative Example 1 was tested according to GB / T19139 Oil Well Cement Test Method. The test results are shown in Table 6.

[0088] Table 6

[0089]

[0090]

[0091] Based on the experimental data in Table 6, it can be concluded that the cement slurry prepared in Examples 1 to 5 has a water loss of ≤35ml, and the fluidity and free fluid meet the construction requirements. The slurry has good stability, controllable thickening time, and good adaptability to additives, which is conducive to improving the safety of high-temperature cementing operations. The anti-gas channeling SPN value is <1.2, which has good anti-gas channeling performance and can achieve effective isolation.

[0092] The cementing slurries obtained in Examples 1-5 and Comparative Example 1 were tested at 180°C. The compressive strength was tested using an NYSQ-2017 pressure testing machine. Core samples were taken from the cured cement stone, and then triaxial mechanical properties were tested. The mechanical testing standard for cement stone was based on GB / T50266-2013 "Standard for Test Methods of Engineering Rock Mass". The equipment used in the experiment was an RTR-1000 triaxial rock mechanics tester. The thermal conductivity of the cementing slurry was tested using a DRE-2C thermal conductivity meter employing the transient plane heat source method. The test results are shown in Table 7.

[0093] Table 7

[0094]

[0095] Based on the experimental data in Table 7, it can be concluded that the cement slurry systems of Examples 1-5 have a 2-day compressive strength > 40 MPa, a 7-day compressive strength > 44 MPa, a 2-day elastic modulus ≤ 8.6 GPa, and a thermal conductivity ≥ 2.0 W / (m·K). Compared with the cement slurry system obtained in Comparative Example 1, the compressive strength, temperature resistance, toughness, and thermal conductivity of the high-temperature resistant and thermally conductive cement slurry system of the present invention are all enhanced. This indicates that the present invention possesses excellent high-temperature resistance, high-temperature toughness, and thermal conductivity, which can meet the engineering performance requirements under harsh geothermal extraction environments, improve the quality of geothermal wells, thereby improving the efficiency of geothermal resource extraction and saving resources.

[0096] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A high-temperature resistant, high-thermal-conductivity cementing slurry system suitable for geothermal wells, characterized in that, Including the following raw materials by weight percentage: Grade G oil well cement: 38.0 wt.%~63.5 wt.%; Silica material: 15.0 wt.%; Serpentine: 10wt.%~15wt.%; Temperature-resistant thermally conductive material: 10wt.%~30wt.%; High temperature stabilizer: 0.5 wt.%; High-temperature dispersant: 1 wt.% - 1.5 wt.%; And additives accounting for a percentage of the total mass of the above raw materials: High-temperature water loss reducing agent: 3wt.%~5wt.%; High-temperature retarder: 1wt.%~3wt.%; Defoamer: 0.25 wt.%; The serpentine rock contains ≥40.0 wt.% MgO and ≥40.0 wt.% SiO2. The heat-resistant thermally conductive material is a mixture obtained by mixing thermally conductive reinforcing material, reinforcing material and polyetherimide in a mass ratio of (8-12): (6-9): (2-3); The thermally conductive strengthening material is a mixture of molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a mass ratio of 5:2:2:1, which is then modified. The thermally conductive strengthening material is modified with tetraethyl orthosilicate ethanol solution, and the surface of the thermally conductive strengthening material is coated with a layer of silicon dioxide. The reinforcing material is composed of graphite quartz schist, andalusite, and modified expanded graphite in a mass ratio of 6:1:3; the modified expanded graphite is expanded graphite modified by low-temperature plasma.

2. The high-temperature resistant and high-thermal-conductivity cementing slurry system for geothermal wells according to claim 1, characterized in that, The siliceous material is a mixture of 200-mesh quartz sand, 800-mesh quartz sand and 1200-mesh quartz sand in a mass ratio of 1:2:1, and the SiO2 content of the siliceous material is ≥95wt.%.

3. The high-temperature resistant and high-thermal-conductivity cement slurry system for geothermal wells according to claim 1, characterized in that, The serpentine has an average grain size of 325 mesh.

4. The high-temperature resistant and high-thermal-conductivity cement slurry system for geothermal wells according to claim 1, characterized in that, The molybdenum disilicide has an effective material content of >99 wt.% and an average particle size of 15 μm; the tungsten diboride has an effective material content of >99 wt.% and an average particle size of 50 nm; the zirconium diboride has an effective material content of >99 wt.% and an average particle size of 50 nm; and the titanium diboride has an effective material content of >99 wt.% and an average particle size of 15 μm.

5. The high-temperature resistant and high-thermal-conductivity cementing slurry system for geothermal wells according to claim 1, characterized in that, The average particle size of the polyetherimide after crushing and grinding is ≤45μm.

6. The high-temperature resistant and high-thermal-conductivity cement slurry system for geothermal wells according to claim 5, characterized in that, The graphite-quartz schist is flaky, with a graphite content of 15wt.%~20wt.%, a silica content of 50wt.%~60wt.%, and a mica content of 10wt.%~20wt.%. The average particle size of the graphite-quartz schist after crushing and grinding is ≤45μm. The andalusite has an Al2O3 content ≥50wt.%, a SiO2 content ≥40wt.%, and an average particle size ≤45μm. The modified expanded graphite has an expansion volume of 600ml / g and an average particle size ≤74μm.

7. The high-temperature resistant and high-thermal-conductivity cementing slurry system for geothermal wells according to claim 1, characterized in that, The high-temperature stabilizer is a clay mineral; the high-temperature dispersant is an aldehyde-ketone condensate; the high-temperature water loss reducing agent is a 2-acrylamido-2-methylpropanesulfonic acid polymer; the high-temperature retarder is an AMPS polymer; and the defoamer is tributyl phosphate.

8. The method for preparing a high-temperature resistant, high-thermal-conductivity cementing slurry system suitable for geothermal wells according to any one of claims 1 to 7, characterized in that, include: Step 1: Mix G-grade oil well cement, silica materials, serpentine, heat-resistant and thermally conductive materials, high-temperature stabilizers, and high-temperature dispersants according to their respective weight percentages to obtain a powder. Step 2: Weigh out the high-temperature water loss reducer, high-temperature retarder, and defoamer according to their respective weight percentages and mix them with water to obtain a mixed liquid. Step 3: Prepare cement slurry by mixing the powder and mixed liquid according to GB / T19139 standard, thus obtaining the heat-resistant and thermally conductive cement slurry system suitable for geothermal wells.

9. The method for preparing a high-temperature resistant, high-thermal-conductivity cementing slurry system suitable for geothermal wells according to claim 8, characterized in that, The preparation of the thermally conductive strengthening material includes: step a, mixing molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride in a ball mill at their respective mass ratios for 30 min to form mixture A; step b, placing mixture A in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirring and ultrasonically dispersing for 20 min, then placing it in a 60℃ constant temperature water bath and stirring, allowing it to react fully for 10 h; step c, centrifuging the product after the reaction at 1200 r / min for 5 min, washing it repeatedly with anhydrous ethanol 3 times, and vacuum drying for 24 h to obtain the thermally conductive strengthening material.

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