Cement slurry system suitable for CO2 heat extraction type geothermal well and preparation method thereof

Abstract

The present application relates to geothermal resource development technical field, specifically to the cementing slurry system suitable for CO2 heat extraction type geothermal well and its preparation method, the cementing slurry system includes 43wt. %~73wt. % low heat silicate cement, 10wt. %~15wt. % siliceous tailings, 5wt. %~10wt. % waste magnesium carbon brick, 10wt. %~30wt. % CO2 corrosion resistant high thermal conductivity material, 1.5wt. % dispersing agent, 0.5wt. % high temperature stabilizer, 2wt. %~4wt. % high temperature fluid loss additive of the total mass percentage of the above raw materials, 1wt. %~3wt. % high temperature retarder, 0.25wt. % defoaming agent, the present application has good system stability, low filtration loss, good additive adaptability, adjustable thickening time and other characteristics, in addition, it also has high thermal conductivity, CO2 corrosion resistance, gas channeling prevention and good high temperature toughness and other characteristics.

Description

Technical Field

[0001] This invention relates to the field of geothermal resource development technology, specifically to a cementing slurry system for CO2-extracting geothermal wells and its preparation method. Background Technology

[0002] With the rapid development of society and the economy, energy and environmental issues have received increasing attention. Green and environmentally friendly energy will occupy an increasingly important position in the field of energy research. Due to its renewability and wide geographical distribution, geothermal resources have become a key area of ​​research and development for renewable and clean energy worldwide. Currently, how to efficiently develop and utilize geothermal resources is one of the key issues facing the geothermal industry.

[0003] Geothermal wells, as tools for developing geothermal resources, are crucial to the effective utilization of geothermal energy. In actual geothermal cementing, high formation temperatures severely affect the performance of cement slurry and the quality of the cement sheath, making it difficult to meet cementing performance requirements. Traditional cementing cements, due to their low thermal conductivity, form the main thermal resistance in the heat exchange process, resulting in low heat exchange efficiency in geothermal wells. Existing research shows that increasing the thermal conductivity of the cement sheath can significantly improve the heat exchange efficiency of geothermal wells.

[0004] In addition, factors affecting geothermal extraction efficiency also include the heat extraction medium. Currently, the two commonly used heat extraction media are water and CO2. Utilizing supercritical CO2 to replace conventional water as the working medium for circulating geothermal energy or displacing underground hot water is a novel form of CO2 resource utilization. It is an effective means to achieve CO2 emission reduction and deep geothermal resource development, and is of great significance to both geothermal development and geological storage. However, when using supercritical CO2 for extraction, the cement sheath is subject to acid corrosion, leading to a decline in cement stone performance. To solve this problem, it is necessary to improve the corrosion resistance of the cement sheath.

[0005] Patent CN113800839A discloses a high thermal conductivity cementing material, its preparation method and application. The high thermal conductivity cementing material includes cement, silica powder, water-reducing agent, early strength agent and water, wherein the cement is 100 parts, silica powder is 15-30 parts, water-reducing agent is 0.4-0.6 parts, early strength agent is 0.2-0.3 parts and water is 70-80 parts.

[0006] Patent CN113372045A provides a low thermal resistance, low density composite cementing material for geothermal extraction and its preparation method. The solid phase material comprises 100 parts, water 75-85 parts, latex 0.4 parts, and defoamer 0.1 parts. The solid phase material, by weight, is made from the following raw materials: 2-10 parts mixed flake graphite, 0.2-0.8 parts graphite oxide, 0.2-0.6 parts hexagonal boron nitride, and poly… The raw materials consist of 0.2-0.8 parts acrylonitrile-based carbon fiber, 0.5 parts pitch-based carbon fiber, 9-15 parts quartz powder, 3-5 parts calcium carbonate whiskers, 6-9 parts silica fume, 7 parts fly ash, 4-6 parts blast furnace slag, 0.2 parts dispersant, 2 parts water loss reducer, 0.2 parts early strength agent, 0.5 parts lattice expansion agent, 2 parts crystal form stabilizer, and the balance being oil well cement. The total weight of the raw materials is 100 parts.

[0007] Patent CN114133172A discloses a carbon dioxide corrosion resistant cement slurry for well cementing and its preparation method. The CO2 corrosion resistant cement slurry is made of cement, nano-SiO2, UF cellulose fiber, fluid loss control agent, dispersant, and water. In 100 parts by weight of the cement, the content of each component is as follows: nano-SiO2 0.5-2.5%, UF cellulose fiber 0.1-0.5%, fluid loss control agent 0.6-0.8%, and dispersant 0.2-0.5%. The liquid-to-solid ratio of the CO2 corrosion resistant cement slurry is 0.44-0.50.

[0008] Patent CN109233766A discloses a high-temperature resistant, corrosion-resistant, low-density cementing fluid and its additive composition and application. The cementing fluid system comprises the following components in parts by weight: 50-85 parts silica powder, 30-57 parts fly ash, 53-105 parts zeolite, 18-65 parts hollow glass microspheres, 70-103 parts sodium silicate, 7-14 parts calcium hydroxide, 0.03-0.37 parts magnesium oxide, 0.05-0.6 parts drag reducer, 4.2-11.3 parts high-temperature fluid loss reducer, 0.06-1.6 parts high-temperature retarder, and 100 parts water.

[0009] For CO2-generating geothermal wells, extremely stringent requirements are placed on cementing slurry to improve their service life and heat extraction efficiency. The cementing slurry must not only possess high temperature resistance and high thermal conductivity, but also excellent corrosion resistance. However, the use of conventional cementing slurry currently suffers from low thermal efficiency, poor high-temperature resistance, and poor corrosion resistance, highlighting the urgent need to develop a cementing slurry system suitable for CO2-generating geothermal wells. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a cement slurry system suitable for CO2 heat extraction geothermal wells and its preparation method, so as to at least solve some of the above-mentioned technical problems.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] Cement slurry systems suitable for CO2-generating geothermal wells include the following raw materials by weight percentage:

[0013]

[0014]

[0015] And additives accounting for a percentage of the total mass of the above raw materials:

[0016] High-temperature water loss reducing agent 2wt.%~4wt.%;

[0017] High-temperature retarder 1wt.%~3wt.%;

[0018] Defoamer 0.25 wt.%.

[0019] The corrosion-resistant and high thermal conductivity cement slurry system for CO2-extracting geothermal wells of the present invention has many characteristics such as high temperature resistance, CO2 corrosion resistance, high thermal conductivity, gas channeling prevention, and good toughness through the mutual cooperation and interaction of its components. In addition, it also has the advantages of being green, environmentally friendly, and low cost.

[0020] Furthermore, the SiO2 content in the siliceous tailings is 65wt.% to 80wt.%, and the fineness of the siliceous tailings powder is ≥800 mesh; the siliceous tailings are one or more of copper tailings, iron tailings, and gold tailings.

[0021] Furthermore, the waste magnesia-carbon bricks are crushed and ground, with an MgO content ≥70%, a carbon content ≥20%, and an average particle size ≥1200 mesh.

[0022] The waste magnesia-carbon bricks of this invention can not only enhance the temperature resistance of the cementing slurry system, but also enhance the thermal conductivity together with the thermally conductive materials in the system.

[0023] Furthermore, the CO2 corrosion resistant high thermal conductivity material is composed of thermally conductive material, corrosion-resistant material and toughening material mixed in a mass ratio of (9-14):(4-8):(2-3).

[0024] The CO2 corrosion resistant and high thermal conductivity material of the present invention has properties such as high temperature resistance, toughening, gas channeling prevention, corrosion resistance and thermal conductivity.

[0025] Furthermore, the corrosion-resistant material is composed of nano-molybdenum trioxide, chlorite powder, and acidified serpentine powder mixed in a mass ratio of 2:1:1; the nano-molybdenum trioxide has a purity ≥99wt.% and an average particle size of 50-100nm; the chlorite powder contains SiO2 ≥55.0wt.%, Al2O3 ≥12wt.%, and MgO ≥9wt.%, with a purity ≥99wt.% and an average particle size of 800 mesh; the acidified serpentine powder contains MgO ≥40.0wt.%, SiO2 ≥40.0wt.%, and an average particle size of 325 mesh.

[0026] The acidified serpentine powder is prepared by the following steps: Step a, drying the serpentine powder at 120°C for 24 hours; Step b, acidifying the dried serpentine powder in a dilute sulfuric acid solution for 2 hours, wherein the dilute sulfuric acid is a mixture of water and 98% sulfuric acid at a volume ratio of 1:19; Step c, drying the acidified serpentine powder at 120°C for 2 hours after vacuum filtration to obtain the acidified serpentine powder.

[0027] The corrosion-resistant material of this invention is composed of nano-molybdenum trioxide, chlorite powder, and acidified serpentine powder. On the one hand, the high MgO content in chlorite powder and acidified serpentine powder causes volume expansion after participating in the hydration reaction, effectively compensating for the volume shrinkage of the cement system caused by high temperature and the use of ultrafine materials, reducing the gap between the cement sheath and the formation. This not only improves the bonding strength between the cement sheath and the formation and prevents gas channeling, but also enhances the thermal conductivity and corrosion resistance of the cement stone. On the other hand, chlorite powder and acidified serpentine powder can participate in and promote the hydration reaction, reducing the easily carbonized substances in the hydration products, and inhibiting and interfering with the formation and growth of calcium carbonate. In addition, the alkaline environment formed after the hydration of cement, chlorite powder, and serpentine powder promotes the reaction between nano-molybdenum trioxide and the hydration products, forming insoluble calcium molybdate that coats the surface of the hydration products, thereby preventing CO2 from reacting with the hydration products and improving corrosion resistance through a synergistic effect.

[0028] Furthermore, the thermally conductive material is composed of a thermally conductive strengthening material and a reinforcing material mixed at a mass ratio of 2:1; the reinforcing material is composed of graphite quartz schist, andalusite, and modified expanded graphite mixed at a mass ratio of 6:1:3; the graphite quartz schist is flaky, with a graphite content of 15wt.%–20wt.%, a SiO2 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 contains Al2O3 content ≥50wt.% and SiO2 content ≥40wt.%, and the average particle size of the andalusite is ≤45μm; the modified expanded graphite is expanded graphite modified by low-temperature plasma, and the average particle size of the modified expanded graphite is ≤74μm.

[0029] The modified expanded graphite of this invention has a loose, porous, worm-like structure with a large surface area and flexibility. Furthermore, its hydrophilicity is improved after modification: on the one hand, the large surface area provides numerous crystallization points for hydration products, promoting hydration; the improved hydrophilicity enhances its bonding with hydration products. On the other hand, its flexibility allows for relative stress dispersion, reducing the brittleness of cement stone and enhancing its toughness. Moreover, the excellent thermal conductivity of graphite materials can be combined with thermally conductive reinforcing materials to further enhance thermal conductivity.

[0030] Furthermore, the thermally conductive strengthening material is 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 the molybdenum disilicide is >99 wt.%, and the average particle size is 15 μm; the effective material content of the tungsten diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of the zirconium diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of the titanium diboride is >99 wt.%, and the average particle size is 15 μm.

[0031] The thermally conductive strengthening material is prepared by the following steps: Step A, molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride are mixed in a ball mill at a mass ratio of 5:2:2:1 for 30 min to form mixture A; Step B, mixture A is placed in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirred and ultrasonically dispersed for 20 min, and then placed in a 60℃ constant temperature water bath for stirring and reaction for 10 h; Step C, the product after the reaction is completed is centrifuged at 1200 r / min for 5 min, then washed three times with anhydrous ethanol, and vacuum dried for 24 h to obtain the thermally conductive strengthening material.

[0032] The thermally conductive material of this invention reduces the gap between itself and cement particles through small size effect and particle gradation effect, increases the density of cement stone structure, reduces the decrease in thermal conductivity of cement stone caused by the presence of pores, reduces cement stone permeability, and improves cement stone corrosion resistance. On the other hand, it enhances the bonding strength between itself and cement hydration products through modification, reduces pores, and enhances thermal conductivity.

[0033] Furthermore, the toughening material is made by melt blending polyetherimide and polybenzimidazole fiber at a mass ratio of 9:1, followed by granulation, cooling, pulverization, and then low-temperature plasma modification; the average particle size of the polyetherimide after crushing and grinding is ≤45μm; the effective substance content of the polybenzimidazole is >98%, and the average particle size is ≤45μm.

[0034] This invention modifies polyetherimide by adding polybenzimidazole fibers, which possess strong toughness and good compatibility, effectively improving its toughness, temperature resistance, and hydrophilicity. On one hand, the polybenzimidazole fibers act as heterogeneous nucleation agents, enhancing the toughness and temperature resistance of the polyetherimide; on the other hand, polar groups such as ether bonds, imidazole bonds, and amide bonds increase interfacial compatibility with cement hydration products, improving bonding strength. Furthermore, the toughening material and modified expanded graphite work synergistically, dispersing and interpenetrating to form a toughening framework, further enhancing the material's toughness.

[0035] Furthermore, the dispersant is an aldehyde-ketone condensate; the high-temperature stabilizer is a clay mineral; 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.

[0036] This invention also provides a method for preparing a cement slurry system suitable for CO2-generating geothermal wells, comprising: Step 1, mixing low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant and high-temperature stabilizer in proportion to form a dry powder; Step 2, weighing high-temperature dehydration reducer, high-temperature retarder and defoamer in proportion and mixing with water to obtain a mixed liquid; Step 3, preparing cement slurry by mixing the dry powder and mixed liquid according to GB / T19139 standard, thereby obtaining the cement slurry system suitable for CO2-generating geothermal wells.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The cement slurry system for CO2-generating geothermal wells of the present invention has the characteristics of good system stability, low filtration loss, good adaptability to admixtures, and adjustable thickening time; in addition, it also has the characteristics of high thermal conductivity, resistance to CO2 corrosion, prevention of gas channeling, and good high-temperature toughness.

[0039] On the one hand, this invention can improve the extraction and heat extraction efficiency of geothermal resources and reduce the corrosive damage to cement stone caused by CO2 when using CO2 as the heat extraction medium; on the other hand, it can enhance the temperature resistance, strength and toughness of geothermal wells in high-temperature environments, thereby ensuring the cementing quality and service life of geothermal wells.

[0040] This invention reduces the calcium-silica ratio of the cement slurry system by using low-heat silicate cement, siliceous tailings, and CO2-resistant, high-thermal-conductivity materials, thereby improving the system's temperature resistance and preventing the cement stone's strength from declining under high-temperature conditions. The addition of waste magnesia-carbon bricks reduces the environmental pressure from solid waste, resulting in a green, environmentally friendly, and low-cost material. Attached Figure Description

[0041] Figure 1 The weight loss curves of cement slurry system 1 to 6# after 28 days of corrosion are shown. Detailed Implementation

[0042] 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.

[0043] The following examples all demonstrate the preparation of cement slurry according to GB / T19139 standard, with a water-cement ratio of 0.44.

[0044] The siliceous tailings used in this embodiment of the invention have a SiO2 content of 65wt.% to 80wt.% and a powder fineness of ≥800 mesh; the siliceous tailings are one or more of copper tailings, iron tailings, and gold tailings.

[0045] The waste magnesia-carbon bricks used in this embodiment of the invention are produced by crushing and grinding, with an MgO content ≥70%, a carbon content ≥20%, and an average particle size ≥1200 mesh.

[0046] The corrosion-resistant material used in this embodiment of the invention is a mixture of nano-molybdenum trioxide, chlorite powder, and acidified serpentine powder in a mass ratio of 2:1:1. The nano-molybdenum trioxide has a purity ≥99wt.% and an average particle size of 50-100nm. The chlorite powder contains ≥55.0wt.% SiO2, ≥12wt.% Al2O3, and ≥9wt.% MgO, and has a purity ≥99wt.% and an average particle size of 800 mesh. The acidified serpentine powder contains ≥40.0wt.% MgO and ≥40.0wt.% SiO2, and has an average particle size of 325 mesh.

[0047] The acidified serpentine powder used in this embodiment of the invention is prepared by the following steps: Step a, drying the serpentine powder at 120°C for 24 hours; Step b, acidifying the dried serpentine powder in a dilute sulfuric acid solution for 2 hours, wherein the dilute sulfuric acid is a mixture of water and 98% sulfuric acid at a volume ratio of 1:19; Step c, drying the acidified serpentine powder at 120°C for 2 hours after vacuum filtration to obtain the acidified serpentine powder.

[0048] The thermally conductive material used in this embodiment of the invention is a mixture of thermally conductive reinforcing material and reinforcing material at a mass ratio of 2:1; the reinforcing material is a mixture of graphite quartz schist, andalusite, and modified expanded graphite at a mass ratio of 6:1:3; the graphite quartz schist is flaky, with a graphite content of 15wt.% to 20wt.%, a SiO2 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 contains Al2O3 content ≥50wt.% and SiO2 content ≥40wt.%, and the average particle size of the andalusite is ≤45μm; the modified expanded graphite is expanded graphite modified by low-temperature plasma, and the average particle size of the modified expanded graphite is ≤74μm.

[0049] The thermally conductive strengthening material used in this embodiment of the invention is 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 the molybdenum disilicide is >99 wt.%, and the average particle size is 15 μm. The effective material content of the tungsten diboride is >99 wt.%, and the average particle size is 50 nm. The effective material content of the zirconium diboride is >99 wt.%, and the average particle size is 50 nm. The effective material content of the titanium diboride is >99 wt.%, and the average particle size is 15 μm.

[0050] The thermally conductive strengthening material used in this embodiment of the invention is prepared by the following steps: Step A, molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride are mixed in a ball mill at a mass ratio of 5:2:2:1 for 30 min to form mixture A; Step B, mixture A is placed in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirred and ultrasonically dispersed for 20 min, and then placed in a 60°C constant temperature water bath for stirring and reaction for 10 h; Step C, the product after the reaction is completed is centrifuged at 1200 r / min for 5 min, then washed three times with anhydrous ethanol, and vacuum dried for 24 h to obtain the thermally conductive strengthening material.

[0051] The toughening material used in this embodiment of the invention is made by melt blending polyetherimide and polybenzimidazole fiber in a mass ratio of 9:1, followed by granulation, cooling, pulverization, and then low-temperature plasma modification. The average particle size of the polyetherimide after crushing and grinding is ≤45μm. The effective substance content of the polybenzimidazole is >98%, and the average particle size is ≤45μm.

[0052] The dispersant used in the embodiments of the present invention is an aldehyde-ketone condensate; the high-temperature stabilizer used is a clay mineral; 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.

[0053] Example 1

[0054] As a preferred embodiment of the present invention, the specific composition of the cement slurry system for CO2 heat extraction geothermal wells used in this embodiment is shown in Table 1:

[0055] Table 1

[0056] Components Weight percentage (wt.%) Low-heat silicate cement 43 Siliceous tailings 15 Waste magnesia-carbon bricks 10 <![CDATA[CO2 corrosion-resistant high thermal conductivity material]]> 30 dispersant 1.5 High temperature stabilizer 0.5

[0057] In this embodiment, the CO2 corrosion resistant and high thermal conductivity material used is a mixture of thermally conductive material, corrosion-resistant material and toughening material in a mass ratio of 9:8:3.

[0058] Low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer are mixed evenly according to the weight percentages shown in Table 1 to obtain powder. 4 wt.% high-temperature water loss reducer, 3 wt.% high-temperature retarder, and 0.25 wt.% defoamer, accounting for a percentage of the total mass of the above raw materials, are weighed according to their respective proportions and mixed with water (the amount of water added is determined with a water-cement ratio of 0.44) to obtain a mixed liquid. According to GB / T19139 standard, the dry materials and the mixed liquid are mixed and stirred to obtain cementing slurry system #1.

[0059] Example 2

[0060] As a preferred embodiment of the present invention, the specific composition of the cement slurry system for CO2 heat extraction geothermal wells used in this embodiment is shown in Table 2:

[0061] Table 2

[0062] Components Weight percentage (wt.%) Low-heat silicate cement 57 Siliceous tailings 13 Waste magnesia-carbon bricks 8 <![CDATA[CO2 corrosion-resistant and highly heat-conductive material]]> 20 dispersant 1.5 High temperature stabilizer 0.5

[0063] In this embodiment, the CO2 corrosion resistant and high thermal conductivity material used is a mixture of thermally conductive material, corrosion-resistant material and toughening material in a mass ratio of 9:8:3.

[0064] Low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer are mixed evenly according to the weight percentages shown in Table 2 to obtain powder. 4 wt.% high-temperature water loss reducer, 3 wt.% high-temperature retarder, and 0.25 wt.% defoamer, accounting for a percentage of the total mass of the above raw materials, are weighed according to their respective proportions and mixed with water (the amount of water added is determined with a water-cement ratio of 0.44) to obtain a mixed liquid. According to GB / T19139 standard, the dry materials and the mixed liquid are mixed and stirred to obtain cementing slurry system #2.

[0065] Example 3

[0066] As a preferred embodiment of the present invention, the specific composition of the cement slurry system for CO2 heat extraction geothermal wells used in this embodiment is shown in Table 3:

[0067] Table 3

[0068]

[0069]

[0070] In this embodiment, the CO2 corrosion resistant and high thermal conductivity material used is a mixture of thermally conductive material, corrosion-resistant material and toughening material in a mass ratio of 9:8:3.

[0071] Low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer are mixed evenly according to the weight percentages shown in Table 3 to obtain powder. 4 wt.% high-temperature water loss reducer, 3 wt.% high-temperature retarder, and 0.25 wt.% defoamer, accounting for 1% of the total mass of the above raw materials, are weighed according to their respective proportions and mixed with water (the amount of water added is determined with a water-cement ratio of 0.44) to obtain a mixed liquid. According to GB / T19139 standard, the dry materials and the mixed liquid are mixed and stirred to obtain cementing slurry system #3.

[0072] Example 4

[0073] As a preferred embodiment of the present invention, the specific composition of the cement slurry system for CO2 heat extraction geothermal wells used in this embodiment is shown in Table 4:

[0074] Table 4

[0075] Components Weight percentage (wt.%) Low-heat silicate cement 57 Siliceous tailings 13 Waste magnesia-carbon bricks 8 <![CDATA[CO2 corrosion-resistant high thermal conductivity material]]> 20 dispersant 1.5 High temperature stabilizer 0.5

[0076] In this embodiment, the CO2 corrosion resistant and high thermal conductivity material used is a mixture of thermally conductive material, corrosion-resistant material and toughening material in a mass ratio of 6:3:1.

[0077] Low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer are mixed evenly according to the weight percentages shown in Table 4 to obtain powder. 3 wt.% high-temperature water loss reducer, 2 wt.% high-temperature retarder, and 0.25 wt.% defoamer, accounting for a percentage of the total mass of the above raw materials, are weighed according to their respective proportions and mixed with water (the amount of water added is determined with a water-cement ratio of 0.44) to obtain a mixed liquid. According to GB / T19139 standard, the dry materials and the mixed liquid are mixed and stirred to obtain cementing slurry system #4.

[0078] Example 5

[0079] As a preferred embodiment of the present invention, the specific composition of the cement slurry system for CO2 heat extraction geothermal wells used in this embodiment is shown in Table 5:

[0080] Table 5

[0081] Components Weight percentage (wt.%) Low-heat silicate cement 57 Siliceous tailings 13 Waste magnesia-carbon bricks 8 <![CDATA[CO2 corrosion-resistant and highly heat-conductive material]]> 20 dispersant 1.5 High temperature stabilizer 0.5

[0082] In this embodiment, the CO2 corrosion resistant and high thermal conductivity material used is a mixture of thermally conductive material, corrosion-resistant material and toughening material in a mass ratio of 7:2:1.

[0083] Low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer are mixed evenly according to the weight percentages shown in Table 5 to obtain powder. 2 wt.% high-temperature water loss reducer, 1 wt.% high-temperature retarder, and 0.25 wt.% defoamer, accounting for a percentage of the total mass of the above raw materials, are weighed according to their respective proportions and mixed with water (the amount of water added is determined with a water-cement ratio of 0.44) to obtain a mixed liquid. According to GB / T19139 standard, the dry materials and the mixed liquid are mixed and stirred to obtain cementing slurry system #5.

[0084] Comparative Example 1

[0085] This comparative example is based on 73 wt.% low-heat silicate cement + 25 wt.% silica sand + 1.5% dispersant + 0.5% high-temperature stabilizer, and 2 wt.% high-temperature water loss reducer, 1 wt.% high-temperature retarder and 0.25 wt.% defoamer, accounting for a percentage of the total mass of the above raw materials. The cement slurry was prepared according to GB / T19139 standard with a water-cement ratio of 0.44, resulting in cementing slurry system #6.

[0086] The engineering performance of the cementing slurry systems obtained in Examples 1-5 and Comparative Example 1 was tested in accordance with GB / T19139 Oil Well Cement Test Method. The test results are shown in Table 6.

[0087] Table 6

[0088]

[0089] Based on the experimental data in Table 6, it can be concluded that the cement slurry prepared in Examples 1-5 has a water loss of <40ml, and its fluidity and free fluid meet the construction requirements. The thickening time is adjustable, and all engineering performances are good. It also exhibits good compatibility with admixtures and is superior to the cement slurry prepared in Comparative Example 1. The SPN value of the cement slurry prepared in Examples 1-5 is less than 1.7, which is much lower than the SPN value of Comparative Example 1, indicating that the cement slurry system of the present invention possesses excellent anti-gas channeling performance.

[0090] The cement slurry obtained in Examples 1-5 and Comparative Example 1 was poured into molds to form cement stone samples, which were then placed in a high-temperature and high-pressure corrosion reactor for curing. The curing temperature was 180℃, the CO2 pressure was 5MPa, the total pressure was 10MPa, and the N2 partial pressure was 7d and 28d respectively. 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 property tests were performed. The cement stone mechanical testing standard was based on GB / T50266-2013 "Standard for Testing Methods of Engineering Rock Mass," and the experimental equipment used was an RTR-1000 triaxial rock mechanics tester. The permeability of the cement stone samples from Examples 1-5 and Comparative Example 1 was measured according to standard SY / T6466-2000 "Evaluation Method for High-Temperature Resistance Performance of Oil Well Cement Stone." The thermal conductivity of the cement stone was tested using a DRE-2C thermal conductivity meter with the transient plane heat source method. The test results are shown in Table 7.

[0091] Table 7

[0092]

[0093]

[0094] As shown in Table 7, after a certain corrosion period, the cement stones of cement slurry systems 1# to 5# exhibit a 7-day compressive strength greater than 45 MPa and a 28-day compressive strength greater than or equal to 48 MPa, demonstrating significantly greater strength development than cement stones of cement slurry system 6#. Furthermore, unlike cement slurry system 6#, the compressive strength of cement slurry systems 1# to 5# does not show any decline, indicating good high-temperature resistance of this invention. The 28-day permeability of cement slurry systems 1# to 5# is slightly higher than the 7-day permeability, but still less than 0.03 mD, with an elastic modulus ≤ 7.5 GPa and a thermal conductivity > 1.3 W / (m·K), all of which are far superior to those of cement slurry system 6#.

[0095] Thermogravimetric analysis was performed on the solidified products of the cement slurry systems in Examples 1-5 and Comparative Example 1. Figure 1 These are the weight loss curves of cement slurry systems #1 to #6 after 28 days of corrosion. Thermogravimetric analysis of the samples was conducted on a thermal analysis instrument manufactured by Mettle Toledo, with a heating rate of 10℃ / min and nitrogen protection.

[0096] pass Figure 1 The experimental results show that the corrosion resistance of the solidified products of cement slurry system 1# to 5# is much greater than that of the solidified product of cement slurry system 6#, indicating that the present invention has excellent corrosion resistance.

[0097] In summary, this invention possesses excellent engineering performance due to the synergistic effect of its component materials, and features high temperature resistance, good toughness, high thermal conductivity, good gas channeling prevention, and good corrosion resistance. This invention has significant engineering and scientific value in improving the thermal energy utilization efficiency of geothermal drilling and extraction, the service life of geothermal wells, and the cementing quality.

[0098] 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 cementing slurry system suitable for CO2-generating geothermal wells, characterized in that, Including the following raw materials by weight percentage: Low-heat silicate cement 43wt.%~73wt.%; Siliceous tailings 10wt.%~15wt.%; Waste magnesia-carbon bricks: 5 wt.%~10 wt.%; CO2 corrosion resistant, high thermal conductivity material 10wt.%~30wt.%; Dispersant 1.5 wt.%; High temperature stabilizer 0.5 wt.%; And additives accounting for a percentage of the total mass of the above raw materials: High-temperature water loss reducing agent 2wt.%~4wt.%; High-temperature retarder 1wt.%~3wt.%; Defoamer 0.25 wt.%; The CO2 corrosion resistant and high thermal conductivity material is composed of thermally conductive material, corrosion-resistant material and toughening material mixed in a mass ratio of (9~14):(4~8):(2~3); The corrosion-resistant material is composed of nano-molybdenum trioxide, chlorite powder, and acidified serpentine powder mixed in a mass ratio of 2:1:1; the nano-molybdenum trioxide has a purity ≥99wt.% and an average particle size of 50~100nm; the chlorite powder has a SiO2 content ≥55.0wt.%, an Al2O3 content ≥12wt.%, and an MgO content ≥9wt.%, and a purity ≥99wt.% and an average particle size of 800 mesh; the acidified serpentine powder has an MgO content ≥40.0wt.%, a SiO2 content ≥40.0wt.%, and an average particle size of 325 mesh. The thermally conductive material is composed of a thermally conductive strengthening material and a reinforcing material mixed at a mass ratio of 2:1; the reinforcing material is composed of graphite quartz schist, andalusite, and modified expanded graphite mixed at a mass ratio of 6:1:3; the graphite quartz schist is flaky, with a graphite content of 15wt.%~20wt.%, a SiO2 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 contains an Al2O3 content ≥50wt.%, a SiO2 content ≥40wt.%, and an average particle size of ≤45μm; the modified expanded graphite is expanded graphite modified by low-temperature plasma, and the average particle size of the modified expanded graphite is ≤74μm. The thermally conductive strengthening material is 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 the molybdenum disilicide is >99 wt.%, and the average particle size is 15 μm; the effective material content of the tungsten diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of the zirconium diboride is >99 wt.%, and the average particle size is 50 nm; the effective material content of the titanium diboride is >99 wt.%, and the average particle size is 15 μm. The thermally conductive strengthening material is prepared by the following steps: Step A, molybdenum disilicide, tungsten diboride, zirconium diboride, and titanium diboride are mixed in a ball mill at a mass ratio of 5:2:2:1 for 30 min to form mixture A; Step B, mixture A is placed in a 6 wt.% tetraethyl orthosilicate ethanol solution, mechanically stirred and ultrasonically dispersed for 20 min, and then placed in a 60℃ constant temperature water bath for stirring and reaction for 10 h; Step C, the product after the reaction is completed is centrifuged at 1200 r / min for 5 min, washed three times with anhydrous ethanol, and vacuum dried for 24 h to obtain the thermally conductive strengthening material. The toughening material is made by melt blending polyetherimide and polybenzimidazole fiber at a mass ratio of 9:1, followed by granulation, cooling, pulverization, and then low-temperature plasma modification. The average particle size of the polyetherimide after crushing and grinding is ≤45μm. The effective substance content of the polybenzimidazole is >98%, and the average particle size is ≤45μm.

2. The cementing slurry system for CO2-generating geothermal wells according to claim 1, characterized in that, The siliceous tailings contain 65wt.%~80wt.% SiO2 and have a fineness of ≥800 mesh; the siliceous tailings are one or more of copper tailings, iron tailings, and gold tailings.

3. The cementing slurry system for CO2-generating geothermal wells according to claim 1, characterized in that, The waste magnesia-carbon bricks are produced by crushing and grinding, with an MgO content ≥70%, a carbon content ≥20%, and an average particle size ≥1200 mesh.

4. The cementing slurry system for CO2-generating geothermal wells according to claim 1, characterized in that, The acidified serpentine powder is prepared by the following steps: Step a, drying the serpentine powder at 120°C for 24 hours; Step b, acidifying the dried serpentine powder in a dilute sulfuric acid solution for 2 hours, wherein the dilute sulfuric acid is a mixture of water and 98% sulfuric acid at a volume ratio of 1:19; Step c, drying the acidified serpentine powder at 120°C for 2 hours after vacuum filtration to obtain the acidified serpentine powder.

5. The cementing slurry system for CO2-generating geothermal wells according to claim 1, characterized in that, The dispersant is an aldehyde-ketone condensate; the high-temperature stabilizer is a clay mineral; 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.

6. The method for preparing a cementing slurry system suitable for CO2-generating geothermal wells according to any one of claims 1 to 5, characterized in that, include: Step 1: Mix low-heat silicate cement, siliceous tailings, waste magnesia-carbon bricks, CO2-resistant high thermal conductivity material, dispersant, and high-temperature stabilizer in proportion to form a dry powder; Step 2: Weigh high-temperature water loss reducer, high-temperature retarder, and defoamer in proportion and mix with water to obtain a mixed liquid; Step 3: Prepare cement slurry by mixing the dry powder and mixed liquid according to GB / T19139 standard, thus obtaining the cement slurry system suitable for CO2 heat recovery geothermal wells.

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