A thermal insulation cement slurry system suitable for geothermal wells and its preparation method

Abstract

The present invention discloses an insulating cement slurry system suitable for geothermal wells and a preparation method thereof, which solves the problem of high thermal conductivity and poor thermal insulation performance of existing cement cementing. The insulating cement slurry of the present invention is composed of G-grade oil well cement, insulating material, lead-zinc tailings, silica fume, dispersant, high-temperature fluid loss additive, high-temperature retarder and defoamer, and the insulating material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, protein rock powder and modified polycarbonate. The present invention has the characteristics of low thermal conductivity, good thermal insulation effect, fast strength development, high compressive strength, good system stability and good toughness; it can not only effectively reduce heat loss in the process of geothermal resource exploitation and improve the utilization rate of geothermal resources, but also improve the temperature resistance and toughness of cement stone.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal resource development, and in particular relates to a thermal insulation cement slurry system suitable for geothermal wells and a preparation method thereof. Background Art

[0002] In recent years, the extensive development and utilization of fossil energy has led to increasingly severe resource and environmental problems, prompting a shift toward renewable and pollution-free energy sources. Geothermal resources, like other clean and renewable energy sources, are a purely green energy source. Their full development and utilization can effectively reduce environmental pollution and address climate change. The cement stone formed after the cement slurry solidifies has a relatively high thermal conductivity (approximately 1.0 W / (m·K)), lacking insulation properties and exhibiting poor thermal insulation performance. This results in significant heat loss during hot water extraction and reinjection, significantly wasting resources.

[0003] To address this issue, thermally insulating cement or low-thermal-conductivity materials can be added to the cement slurry to create an insulating cement. This material leverages its low thermal conductivity to address heat loss from geothermal resources. Therefore, developing a geothermal well cementing slurry system with low thermal conductivity, high compressive strength, and excellent toughness is crucial. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a thermal insulation cement slurry system suitable for geothermal wells and a preparation method thereof, so as to at least solve some of the above technical problems.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A thermal insulation cement slurry system suitable for geothermal wells is composed of the following raw materials in percentage by weight:

[0007] G-grade oil well cement: 56.5-81.5wt.%;

[0008] Thermal insulation material: 10-30wt.%;

[0009] Lead-zinc tailings: 5-10wt.%

[0010] Silica fume: 2wt.%;

[0011] Dispersant: 0.5-1.5wt.%;

[0012] And admixtures as percentage by weight of Grade G oil well cement:

[0013] High temperature fluid loss additive: 1-3wt.%;

[0014] High temperature retarder: 0.5~2wt.%;

[0015] Defoaming agent: 0.25wt.%;

[0016] The thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of (11-15):(1-3):(3-5):1;

[0017] The hollow ceramic microspheres are prepared from lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust by flame spraying. Preferably, the hollow ceramic microspheres have a particle size of 5 to 40 μm and a thermal conductivity of 0.09 to 0.11 W / (m·K).

[0018] The lithium slag is mainly composed of quartz phase, andalusite, corundum, and a small amount of glass phase, kaolinite and lithium carbonate; the SiO2 content is greater than 60wt.%, the Al2O3 content is greater than 20wt.%, the Na2O content is 0.2-0.8wt.%, and the K2O content is 0.1-4wt.%.

[0019] Wherein, the effective substance content of the zirconium silicide is greater than 99.9 wt.%.

[0020] The molybdenum tailings are mainly composed of diopside, albite and dolomite; wherein the SiO2 content is greater than 52wt.%, and the Al2O3 content is greater than 14wt.%.

[0021] Among them, the main chemical components (SiO2, Fe2O3, Al2O3 and CaO, etc.) in the rare earth tailings account for more than 82wt.%, of which SiO2 content is more than 55wt.%, Al2O3 content is more than 14wt.%, and CaF2 content is 0.25~0.30wt.%.

[0022] The sawdust is formed by crushing dry sawdust, and its average particle size is less than 20 meshes.

[0023] The present invention is based on the principle of synergistic effect. The thermal insulation material is formed by mixing hollow ceramic microbeads, waste rock wool board powder, protein shale powder and modified polycarbonate in a certain proportion. The thermal insulation material has the characteristics of being green and environmentally friendly, having low thermal conductivity, good thermal insulation effect, high mechanical strength, high activity performance, good flexibility and low cost. The hollow ceramic microbeads are light in weight, high in strength, have high volcanic ash activity, good thermal insulation effect, and have good bonding properties with other inorganic cementitious materials. They can promote the early hydration and strength development of geothermal cement. The waste rock wool board powder has good thermal insulation properties due to its own low thermal conductivity. It can not only form a good three-dimensional network structure with the cement hydration product, but also provide support for the hollow ceramic microbeads, protein shale powder and modified polycarbonate. The protein shale is mainly composed of SiO2, which has volcanic ash activity and a large number of microporous structures. After being ground into powder, its volcanic ash activity can be further enhanced. The volcanic ash activity and microporous structure can be used not only as a filling material to fill the gaps between hollow ceramic microspheres, waste rock wool boards and cementing cement particles and hydration products, but also as a thermal insulation material and active material to enhance the performance of the thermal insulation material. The modified polycarbonate has good hydrophilicity and temperature resistance, can form good bonding with other matrix materials, and work together with the network structure formed by the waste rock wool board powder to achieve the effect of toughening and reducing brittleness. In addition, it makes full use of solid wastes such as lithium slag, molybdenum tailings, rare earth tailings and waste rock wool boards, which can greatly reduce the environmental pressure brought by solid waste, is green and environmentally friendly, and has low cost.

[0024] The hollow ceramic microspheres are prepared by using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust. A large amount of air is contained in the hollow ceramic microspheres, which can reduce the thermal conductivity of the thermal insulation material and improve the thermal insulation performance. At the same time, the hollow ceramic microspheres provide SiO2 and Al2O3 components necessary for ceramics. In addition, the lithium slag, molybdenum tailings and rare earth tailings are the main sources of alkali metal oxides (K2O and Na2O). The rare earth oxides in the rare earth tailings can serve as stabilizers and sintering aids, greatly improving the strength and toughness of the ceramic microspheres. As the firing temperature increases, the dolomite in the molybdenum tailings forms a diopside interlaced network structure, thereby improving the strength of the ceramic microspheres. The zirconium silicide further improves the density and strength of the ceramic microspheres. The sawdust generates a large amount of gas at high temperature, providing basic conditions for forming a hollow structure.

[0025] In some embodiments of the present invention, a thermal insulation cement slurry system suitable for geothermal wells is composed of the following raw materials in weight percentage:

[0026] G-grade oil well cement: 60-75wt.%;

[0027] Thermal insulation material: 15-25wt.%;

[0028] Lead-zinc tailings: 5-8wt.%

[0029] Silica fume: 2wt.%;

[0030] Dispersant: 1-1.5wt.%;

[0031] And admixtures as percentage by weight of Grade G oil well cement:

[0032] High temperature fluid loss additive: 1-2wt.%;

[0033] High temperature retarder: 1-2wt.%;

[0034] Defoaming agent: 0.25wt.%;

[0035] Preferably, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of (12-13): (2-3): 5: 1;

[0036] The hollow ceramic microbeads are prepared by using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust as raw materials and adopting a flame spraying method.

[0037] Furthermore, the SiO2 content of the lead-zinc tailings is greater than 60wt.%, and the particle size is greater than 325 mesh; the main chemical components of the lead-zinc tailings are SiO2, CaO, Fe2O3 and Al2O3, etc.

[0038] Furthermore, the SiO2 content of the silica fume is ≥90wt.% and the particle size is ≥800 mesh.

[0039] Furthermore, the dispersant is an aldehyde-ketone condensate.

[0040] Furthermore, the high-temperature fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid polymer.

[0041] Furthermore, the high-temperature retarder is an AMPS polymer.

[0042] Furthermore, the defoaming agent is tributyl phosphate.

[0043] The present invention also provides a method for preparing a thermal insulation cement slurry system suitable for geothermal wells, which is applied to the thermal insulation cement slurry system suitable for geothermal wells and comprises the following steps:

[0044] Step 1, weighing and uniformly mixing Grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume and dispersant in respective proportions to obtain a mixture;

[0045] Step 2: weighing a high-temperature fluid loss additive, a high-temperature retarder, and a defoamer according to respective proportions and uniformly mixing them with water to obtain a mixed solution;

[0046] Step 3: Mix and stir the mixture and the mixed liquid according to GB / T19139 standard to obtain the thermal insulation cement slurry system.

[0047] Furthermore, the preparation method of the hollow ceramic microspheres includes:

[0048] Step A, drying the lithium slag and calcining it at high temperature for h to obtain activated lithium slag; preferably, the calcination temperature is 680-700° C. and the calcination time is 1-1.5 h;

[0049] Step B, mixing activated lithium slag, zirconium silicide, molybdenum tailings, and rare earth tailings in a mass ratio of (60-74):(13-15):(10-20):(1-5), wet-milling for 1 hour, and then drying to form a mixture A; preferably, the mass ratio of activated lithium slag, zirconium silicide, molybdenum tailings, and rare earth tailings is 68:15:15:2, the wet-milling time is 0.5-2 hours, and the milling medium is anhydrous ethanol;

[0050] Step C, uniformly mixing mixture A and sawdust in a mass ratio of (90-95):(5-10) to form mixture B, using a flame spray gun to spray mixture B, and cooling and solidifying to obtain a sprayed product; preferably, the mass ratio of mixture A to sawdust is 95:10;

[0051] Step D, collecting the sprayed product and vacuum drying it to obtain the hollow ceramic microspheres; preferably, the drying temperature is 70-85° C. and the drying time is 6-7 hours;

[0052] Preferably, in step C, the powder feeding gas of mixture B is oxygen, the powder feeding rate is 15 g / s, the gas introduced into the flame spray gun is oxygen-acetylene, the oxygen pressure is 0.6 MPa, the acetylene pressure is 0.15 MPa, the jet flame temperature is 2600°C, and the quenching distance is 500 mm; distilled water is used as the cooling medium, and the melt-sprayed product is sprayed into distilled water for rapid cooling and solidification.

[0053] The preparation method of the waste rock wool board powder is as follows: after drying the waste rock wool board or rock wool board waste, the waste rock wool board or rock wool board waste is coarsely crushed by a crusher and then ground by an ultrafine grinder to obtain the waste rock wool board powder, wherein the particle size of the waste rock wool board powder is ≥325 mesh;

[0054] The protein shale powder is prepared by drying the protein shale in an oven and then grinding the protein shale in an ultrafine grinding mill to obtain the protein shale powder, wherein the protein shale powder has a particle size of ≥1200 mesh, a microporous structure, and a main component of amorphous active silicon dioxide with a SiO2 content of ≥90wt.%;

[0055] The preparation method of the modified polycarbonate comprises the following steps: melt-blending waste rock wool board powder and polycarbonate in a mass ratio of 1:9, subjecting the mixture to blending, granulation, cooling, and crushing, and then subjecting the mixture to low-temperature plasma modification to form the modified polycarbonate, wherein the average particle size of the modified polycarbonate is ≥325 mesh.

[0056] The present invention adopts a flame spraying method to form hollow ceramic microspheres, which has a simple process flow, convenient equipment operation and low energy consumption.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. The thermal insulation cement slurry system suitable for geothermal wells provided by the present invention has the characteristics of low thermal conductivity, good thermal insulation effect, rapid strength development, high compressive strength, good system stability and good toughness. It can not only effectively reduce heat loss during geothermal resource extraction and improve geothermal resource utilization, but also improve the temperature resistance and toughness of cement stone.

[0059] 2. The thermal insulation material provided by the present invention has good activity, and promotes the hydration process and strength development of cementing cement under the synergistic effect of silica fume, reducing the use of early strength agents and reinforcing agents in the system and reducing costs; the lead-zinc tailings with high silica content improves the temperature resistance of the cement slurry system and ensures the strength stability of the cement slurry under high temperature environment. DETAILED DESCRIPTION

[0060] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0061] The preparation method of the waste rock wool board powder in the embodiment of the present invention is: after the waste rock wool board or rock wool board waste is dried, it is coarsely crushed by a crusher and then ground by an ultrafine grinder to obtain the waste rock wool board powder.

[0062] The preparation method of the protein shale powder in the embodiment of the present invention is: placing the protein shale in an oven for drying, and then placing it in an ultrafine grinding mill to grind it to obtain the protein shale powder.

[0063] The preparation method of the modified polycarbonate in the embodiment of the present invention is as follows: waste rock wool board powder and polycarbonate are melt-blended in a mass ratio of 1:9, granulated, cooled, crushed, and then modified by low-temperature plasma to form the modified polycarbonate.

[0064] The hollow ceramic microbeads in the embodiments of the present invention are produced using a flame spraying method using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings, and sawdust as raw materials. The lithium slag primarily consists of quartz, andalusite, and corundum, with minor amounts of glass, kaolinite, and lithium carbonate. The slag contains >60 wt.%, >20 wt.%, and >20 wt.% Al2O3. The Na2O content is 0.2-0.8 wt.%, and the K2O content is 0.1-4 wt.%.

[0065] The effective substance content of zirconium silicide is greater than 99.9 wt.%.

[0066] Molybdenum tailings are mainly composed of diopside, albite and dolomite; the SiO2 content is greater than 52wt.%, and the Al2O3 content is greater than 14wt.%.

[0067] The main chemical components (SiO2, Fe2O3, Al2O3 and CaO, etc.) in rare earth tailings account for >82wt.%, of which SiO2 content is >55wt.%, Al2O3 content is >14wt.%, and CaF2 content is 0.25~0.30wt.%.

[0068] The hollow ceramic microspheres in the embodiment of the present invention are prepared by the following method:

[0069] Step A, drying the lithium slag in an oven, and then calcining the slag in a muffle furnace at 700° C. for 1.5 hours to obtain activated lithium slag;

[0070] Step B, grinding activated lithium slag, zirconium silicide, molybdenum tailings, and rare earth tailings in a wet ball mill at a mass ratio of 60:15:20:5 for 1 hour using anhydrous ethanol as the liquid medium; and drying the mixture after ball milling to form a mixture A;

[0071] Step C, mixing mixture A and sawdust in a mass ratio of 95:5 to form mixture B, using a flame spray gun to spray the mixture B, and spraying the sprayed product into distilled water as a cooling medium for rapid cooling and solidification; wherein the powder feeding gas of mixture B is oxygen and the powder feeding rate is 15g / s; the gas introduced into the flame spray gun is oxygen-acetylene, the oxygen pressure is 0.6MPa, the acetylene pressure is 0.12MPa, the spray flame temperature is 2600°C, and the quenching distance is 500mm;

[0072] Step D: collecting the sprayed product and vacuum drying it to obtain the hollow ceramic microspheres; preferably, the drying temperature is 70-85° C. and the drying time is 6-7 hours.

[0073] The hollow ceramic microbeads in the embodiment of the present invention have a particle size of 5 to 40 μm and a thermal conductivity of 0.09 to 0.11 W / (m·K).

[0074] The cement slurries in the following examples were prepared according to GB / T19139 standard, wherein Grade G oil well cement was provided by Jiahua Special Cement Co., Ltd., and the high-temperature retarder and high-temperature fluid loss additive were provided by Sichuan Xuran Hongchen New Materials Co., Ltd. Unless otherwise specified in the examples, all percentages are by weight.

[0075] Example 1

[0076] As a preferred embodiment of the present invention, the specific composition of an insulating cement slurry system suitable for geothermal wells disclosed in this embodiment is shown in Table 1, and the admixtures, calculated as a percentage by weight of G-grade oil well cement (with G-grade oil well cement as 100 wt.%), are: 2 wt.% high-temperature fluid loss additive, 0.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0077] Table 1

[0078] Components Weight percentage (wt.%) G-grade oil well cement 56.5 Insulation materials 30 Lead-zinc tailings 10 silica fume 2 dispersants 1.5

[0079] In this embodiment, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of 11:3:5:1.

[0080] In this embodiment:

[0081] Mixing grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume, and dispersant in a weight ratio of 56.5:30:10:2:1.5 to obtain a mixture;

[0082] 2 wt.% of high-temperature fluid loss additive, 0.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed uniformly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to obtain a mixed solution;

[0083] The mixture and the mixed liquid were mixed and stirred according to GB / T19139 standard to obtain thermal insulation cement slurry system #1.

[0084] Example 2

[0085] As a preferred embodiment of the present invention, the specific composition of an insulating cement slurry system suitable for geothermal wells disclosed in this embodiment is shown in Table 2, and the admixtures, calculated as a percentage by weight of G-grade oil well cement (with G-grade oil well cement as 100 wt.%), are: 2 wt.% high-temperature fluid loss additive, 0.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0086] Table 2

[0087] Components Weight percentage (wt.%) G-grade oil well cement 68.5 Insulation materials 20 Lead-zinc tailings 8 silica fume 2 dispersants 1.5

[0088] In this embodiment, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of 11:3:5:1.

[0089] In this embodiment:

[0090] Mixing grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume, and dispersant in a weight ratio of 68.5:20:8:2:1.5 to obtain a mixture;

[0091] 2 wt.% of high-temperature fluid loss additive, 0.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed uniformly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to obtain a mixed solution;

[0092] The mixture and the mixed liquid were mixed and stirred according to GB / T19139 standard to obtain thermal insulation cement slurry system #2.

[0093] Example 3

[0094] As a preferred embodiment of the present invention, the specific composition of an insulating cement slurry system suitable for geothermal wells disclosed in this embodiment is shown in Table 3, and the admixtures, calculated as a percentage by weight of G-grade oil well cement (with G-grade oil well cement as 100 wt.%), are: 2 wt.% high-temperature fluid loss additive, 0.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0095] Table 3

[0096] Components Weight percentage (wt.%) G-grade oil well cement 81.5 Insulation materials 10 Lead-zinc tailings 5 silica fume 2 dispersants 1.5

[0097] In this embodiment, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of 11:3:5:1.

[0098] In this embodiment:

[0099] Mixing grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume, and a dispersant in a weight ratio of 81.5:10:5:2:1.5 to obtain a mixture;

[0100] 2 wt.% of high-temperature fluid loss additive, 0.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed uniformly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to obtain a mixed solution;

[0101] The mixture and the mixed liquid were mixed and stirred according to GB / T19139 standard to obtain thermal insulation cement slurry system #3.

[0102] Example 4

[0103] As a preferred embodiment of the present invention, the specific composition of an insulating cement slurry system suitable for geothermal wells disclosed in this embodiment is shown in Table 4, and the admixtures, calculated as a percentage by weight of G-grade oil well cement (with G-grade oil well cement as 100 wt.%), are: 2 wt.% high-temperature fluid loss additive, 0.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0104] Table 4

[0105]

[0106]

[0107] In this embodiment, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of 13:2:5:1.

[0108] In this embodiment:

[0109] Mixing grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume, and dispersant in a weight ratio of 68.5:20:8:2:1.5 to obtain a mixture;

[0110] 2 wt.% of high-temperature fluid loss additive, 0.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed uniformly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to obtain a mixed solution;

[0111] The mixture and the mixed liquid were mixed and stirred according to GB / T19139 standard to obtain thermal insulation cement slurry system #4.

[0112] Example 5

[0113] As a preferred embodiment of the present invention, the specific composition of an insulating cement slurry system suitable for geothermal wells disclosed in this embodiment is shown in Table 5, and the admixtures, calculated as a percentage by weight of G-grade oil well cement (G-grade oil well cement is 100 wt.%), are: 2 wt.% high-temperature fluid loss additive, 0.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0114] Table 5

[0115] Components Weight percentage (wt.%) G-grade oil well cement 68.5 Insulation materials 20 Lead-zinc tailings 8 silica fume 2 dispersants 1.5

[0116] In this embodiment, the thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, opal powder and modified polycarbonate in a weight ratio of 15:1:3:1.

[0117] In this embodiment:

[0118] Mixing grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume, and dispersant in a weight ratio of 68.5:20:8:2:1.5 to obtain a mixture;

[0119] 2 wt.% of high-temperature fluid loss additive, 0.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed uniformly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to obtain a mixed solution;

[0120] The mixture and the mixed liquid were mixed and stirred according to GB / T19139 standard to obtain thermal insulation cement slurry system #5.

[0121] Comparative Example 1

[0122] A comparative cement slurry system was obtained by preparing a cement slurry with 100% G-grade oil well cement + 2% high-temperature fluid loss additive + 0.5% high-temperature retarder at a water-cement ratio of 0.5 in accordance with GB / T19139 standard.

[0123] Test example

[0124] The slurry engineering properties of the comparative example cement slurry system and the thermal insulation cement slurry systems #1 to #5 prepared in Examples 1 to 5 were tested at 120°C with reference to the GB / T19139 oil well cement test method. The results are shown in Table 6.

[0125] Table 6

[0126]

[0127] According to the experimental data in Table 6, the thermal insulation cement slurry systems #1 to #5 configured in Examples 1 to 5 have a water loss of less than 30 ml, good slurry stability, and adjustable thickening time, which meet the construction requirements.

[0128] The thermal insulation cement slurry systems #1-#5 prepared in Examples 1-5 and the comparative cementing cement slurry system of Comparative Example 1 were cured at 150°C and then subjected to performance testing. Compressive strength was tested using a NYSQ-2017 pressure testing machine; the elastic modulus of the cement paste was measured using a triaxial stress testing machine; and the thermal conductivity of the cement paste was tested using a DRE-2C thermal conductivity tester using the transient plane heat source method. The test results are shown in Table 7 below.

[0129] Table 7

[0130]

[0131] The experimental data in Table 7 show that the 24-hour compressive strength of the cement slurry systems in Examples 1-5 all exceeded 13 MPa, demonstrating rapid strength development and excellent heat resistance. This ensures that the high-temperature strength of the cement slurry remains stable, and the thermal conductivity is significantly lower than that of the comparative example. These test results demonstrate that the insulating cement slurry system prepared by the present invention exhibits low thermal conductivity and excellent insulation performance, effectively mitigating heat loss and reducing resource waste during geothermal resource development. It also exhibits high early strength and steadily increasing high-temperature strength, contributing to safe construction.

[0132] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are intended to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or refinements made to the main design concept and spirit of the present invention that have no substantive significance, provided that the technical problems they solve are still consistent with those of the present invention, should be included in 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 should also be included in the patent protection scope of the present invention.

Claims

1. A thermal insulation cement slurry system suitable for geothermal wells, characterized in that: The following raw materials are included in weight percentage: Grade G oil well cement: 56.5~81.5wt.%; Insulation material: 10~30wt.%; Lead-zinc tailings: 5~10wt.% Silica fume: 2wt.%; Dispersant: 0.5~1.5wt.%; And admixtures as percentage by weight of Grade G oil well cement: High temperature fluid loss additive: 1~3wt.%; High temperature retarder: 0.5~2wt.%; Defoaming agent: 0.25wt.%; The thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, protein shale powder and modified polycarbonate in a weight ratio of (11-15):(1-3):(3-5):1; The hollow ceramic microspheres are prepared using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust as raw materials by flame spraying. The hollow ceramic microspheres have a particle size of 5 to 40 μm and a thermal conductivity of 0.09 to 0.11 W / (m·K). The preparation method of the modified polycarbonate comprises the following steps: melt-blending waste rock wool board powder and polycarbonate in a mass ratio of (1-2):(9-10), subjecting the mixture to blending, granulation, cooling, and crushing, and then subjecting the mixture to low-temperature plasma modification to form the modified polycarbonate.

2. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1, characterized in that: The following raw materials are included in weight percentage: Grade G oil well cement: 60~75wt.%; Insulation material: 15~25wt.%; Lead-zinc tailings: 5~8wt.% Silica fume: 2wt.%; Dispersant: 1~1.5wt.%; And admixtures as percentage by weight of Grade G oil well cement: High temperature fluid loss additive: 1~2wt.%; High temperature retarder: 1~2wt.%; Defoaming agent: 0.25wt.%; The thermal insulation material is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, protein shale powder and modified polycarbonate in a weight ratio of (12-13): (2-3): 5: 1; The hollow ceramic microbeads are prepared by using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust as raw materials and adopting a flame spraying method.

3. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The SiO2 content of the lead-zinc tailings is greater than 60wt.%, and the particle size is greater than 325 mesh.

4. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The SiO2 content of the silica fume is ≥90 wt.%, and the particle size is ≥800 mesh.

5. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The dispersant is an aldehyde-ketone condensate.

6. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The high-temperature fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid polymer.

7. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The high temperature retarder is an AMPS polymer.

8. The thermal insulation cement slurry system suitable for geothermal wells according to claim 1 or 2, characterized in that: The defoaming agent is tributyl phosphate.

9. A method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1, weighing and uniformly mixing Grade G oil well cement, thermal insulation material, lead-zinc tailings, silica fume and dispersant in respective proportions to obtain a mixture; Step 2: weighing a high-temperature fluid loss additive, a high-temperature retarder, and a defoamer according to respective proportions and uniformly mixing them with water to obtain a mixed solution; Step 3: Mix and stir the mixture and the mixed liquid to obtain the thermal insulation cement slurry system.

10. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 9, characterized in that: The preparation method of the hollow ceramic microspheres comprises: Step A, drying the lithium slag and calcining it at high temperature to obtain activated lithium slag; Step B, mixing activated lithium slag, zirconium silicide, molybdenum tailings, and rare earth tailings in a mass ratio of (60-74):(13-15):(10-20):(1-5), wet ball milling, and then drying to form a mixture A; Step C, uniformly mixing the mixture A and sawdust in a mass ratio of (90-95):(5-10) to form a mixture B, using a flame spray gun to spray the mixture B, and cooling and solidifying to obtain a sprayed product; Step D, collecting the sprayed product and vacuum drying it to obtain the hollow ceramic microspheres; The preparation method of the waste rock wool board powder is as follows: after drying the waste rock wool board or rock wool board waste, the waste rock wool board or rock wool board waste is coarsely crushed by a crusher and then ground by an ultrafine grinder to obtain the waste rock wool board powder; The preparation method of the protein shale powder comprises: placing the protein shale in an oven for drying, and then placing the protein shale in an ultrafine grinding mill for grinding to obtain the protein shale powder; The preparation method of the modified polycarbonate comprises the following steps: melt-blending waste rock wool board powder and polycarbonate in a mass ratio of (1-2):(9-10), subjecting the mixture to blending, granulation, cooling, and crushing, and then subjecting the mixture to low-temperature plasma modification to form the modified polycarbonate.

11. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 10, characterized in that: In the step A, the calcination temperature is 680-700° C., and the calcination time is 1-1.5 hours.

12. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 10, characterized in that: In the step B, the mass ratio of activated lithium slag, zirconium silicide, molybdenum tailings, and rare earth tailings is 68:15:15:2, the wet ball milling time is 0.5-2 hours, and the ball milling medium is anhydrous ethanol.

13. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 10, characterized in that: In the step C, the mass ratio of the mixture A to the sawdust is 95:

10.

14. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 10, characterized in that: In the step D, the drying temperature is 70-85° C. and the drying time is 6-7 hours.

15. The method for preparing a thermal insulation cement slurry system suitable for geothermal wells according to claim 10, characterized in that: In the preparation method of the modified polycarbonate, the mass ratio of the waste rock wool board powder to the polycarbonate is 1:9.

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