A cement slurry system suitable for CO2 heat extraction geothermal wells and its preparation method

Abstract

The present invention discloses a cementing slurry system suitable for use in CO2-heating geothermal wells and its preparation method. The cementing slurry system comprises, by weight percentage, 42-63 wt.% of G-grade oil well cement, 1-2 wt.% of nano-boehmite, 20-25 wt.% of terrazzo waste, 20-25 wt.% of CO2-corrosion-resistant insulation material, and 1 wt.% of a dispersant. The present invention utilizes CO2-corrosion-resistant insulation material, combining inorganic and organic materials to synergistically enhance the material's CO2 corrosion resistance. It also utilizes an insulation matrix with high volcanic ash activity, low thermal conductivity, and excellent heat preservation effects. Nano-boehmite is used to promote and participate in the cement hydration reaction, and together with terrazzo, it reduces the calcium-silicon ratio, thereby improving the high-temperature strength and stability of the cement slurry system. The present invention also utilizes a variety of solid waste materials, resulting in environmentally friendly and low-cost materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal resource development, and in particular relates to a cement slurry system suitable for use in CO2 heat extraction geothermal wells and a preparation method thereof. Background Art

[0002] Geothermal energy is considered more environmentally friendly than fossil fuels due to its low cost, wide distribution, low pollution, and renewable nature. The current method for developing hot dry rock geothermal energy involves pumping cold water through surface injection wells as the heat-carrying fluid. Heat is extracted from the artificial heat reservoir and then withdrawn through production wells. The cooled water is then pumped back into an underground heat exchange system for recycling.

[0003] Combining geothermal development with CO2 resource utilization is a relatively new geothermal development technology. Hot dry rock was the first type of geothermal energy proposed to be exploited using supercritical CO2. Due to the non-polar nature of CO2 molecules, its chemical properties are relatively stable, giving it a greater advantage over cold water extraction. However, in a CO2-EGS environment, cement stone is subjected to high temperatures, high pressures, and a CO2-rich environment for a long time, placing stringent requirements on the cement stone. Furthermore, during the extraction of geothermal resources, there is a certain amount of heat loss. The thermal conductivity of the cement stone formed after the cement slurry solidifies is relatively high (approximately 1.0 W / (m·K)), resulting in significant heat loss along the way during hot water extraction and reinjection.

[0004] Existing technologies have taken into account the high-temperature strength degradation and thermal insulation of cement slurry systems, and corresponding research has been conducted, with some progress achieved. However, when developing hot dry rock geothermal resources using CO2-EGS, it is necessary not only to consider the stability of high-temperature strength, but also the heat loss during the mining process and the corrosion resistance of the wellbore.

[0005] Based on the above problems, it is particularly necessary to develop a cement slurry system with low thermal conductivity, stable high-temperature strength, good CO2 corrosion resistance and suitable for CO2 heating geothermal wells. Summary of the Invention

[0006] 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 a preparation method thereof, so as to at least solve some of the above technical problems.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A cement slurry system for a CO2 heat extraction geothermal well, comprising the following raw materials by weight percentage:

[0009] G-grade oil well cement: 42-63 wt.%;

[0010] Nanoboehmite: 1-2 wt.%;

[0011] Terrazzo waste: 20-30wt.%

[0012] CO2 corrosion resistant insulation material: 15-25wt.%;

[0013] Dispersant: 1wt.%;

[0014] And admixtures as percentage by weight of Grade G oil well cement:

[0015] High temperature fluid loss additive: 2-4wt.%;

[0016] High temperature retarder: 1-3wt.%;

[0017] Defoaming agent: 0.25wt.%;

[0018] The CO2 corrosion resistant thermal insulation material is obtained by mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in the weight ratio of (8-13):(1-2):(3-5):(3-5);

[0019] The heat-insulating matrix 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.

[0020] The present invention discloses a cement slurry system for geothermal wells suitable for CO2 heating, which has the characteristics of low thermal conductivity, good CO2 corrosion resistance, stable high-temperature strength, and good engineering application performance. Among them, nano-boehmite has a filling effect, a small size effect, and a surface effect, which promotes and participates in the cement hydration reaction, and increases the aluminum content in the hydration product. Terrazzo has a high silica content, which, together with the nano-boehmite, reduces the calcium-silicon ratio (Ca / Si), increases the silicon and aluminum content, and promotes the formation of CASH hydration products with better heat resistance, thereby improving the high-temperature strength stability of the cement slurry system. Under the synergistic effect of each component, the CO2 corrosion-resistant thermal insulation material can not only improve the high-temperature stability, early strength, toughness, and CO2 corrosion resistance of the cement system; it can also reduce filtration loss, reduce the thermal conductivity of the cement stone while meeting the construction performance requirements, improve the thermal insulation capacity of the cement stone, effectively reduce the heat loss during geothermal resource extraction, and improve the utilization rate of geothermal resources.

[0021] The thermal insulation matrix used in the present invention is made of hollow ceramic microspheres, waste rock wool board powder, opal powder, and modified polycarbonate. Its main components are SiO2 and Al2O3. When added to cement, it significantly reduces the calcium-silicon ratio (Ca / Si). This lowered Ca / Si ratio not only ensures the high-temperature strength of the cement paste and improves its heat resistance, but also reduces the formation of alkaline hydration products, inhibiting the formation of calcium carbonate. This, in turn, synergistically enhances the corrosion resistance of the cement paste with potassium aminotrimethylphosphonate and sodium monofluorophosphate. Among them, hollow ceramic microspheres are light, high in strength, high in volcanic ash activity, and have good thermal insulation effect. They have good bonding properties with other inorganic cementitious materials (waste rock wool board powder, protein rock powder and modified polycarbonate), and can promote the early hydration and strength development of geothermal cement. Due to its own low thermal conductivity, waste rock wool board powder has good thermal insulation performance. It can not only form a good three-dimensional network structure with the hydration products of cement, but also provide support for hollow ceramic microspheres, protein shale powder and modified polycarbonate. The main component of protein shale is SiO2, which has volcanic ash activity. The volcanic ash, with its numerous microporous structures, can be ground into a powder to further enhance its volcanic ash activity. This volcanic ash activity and microporous structure can be used not only as a filler to fill the gaps between hollow ceramic microspheres, waste rock wool boards, cement particles, and hydration products, but also as a thermal insulation and active material to enhance the performance of the cementing insulation. The modified polycarbonate exhibits excellent hydrophilicity and temperature resistance, forming a good bond with other matrix materials. It interacts with the network structure formed by the waste rock wool board powder to achieve toughening and brittleness reduction. Furthermore, it fully utilizes solid wastes such as lithium slag, molybdenum tailings, rare earth tailings, and waste rock wool boards, significantly reducing the environmental impact of solid waste, achieving a green, environmentally friendly, and low-cost approach.

[0022] In some embodiments of the present invention, a cement slurry system for a CO2-extracting geothermal well includes the following raw materials by weight percentage:

[0023] G-grade oil well cement: 50-60wt.%;

[0024] Nanoboehmite: 1-2 wt.%;

[0025] Terrazzo waste: 20-25wt.%

[0026] CO2 corrosion resistant insulation material: 20-25wt.%;

[0027] Dispersant: 1wt.%;

[0028] And admixtures as percentage by weight of Grade G oil well cement:

[0029] High temperature fluid loss additive: 2-3wt.%;

[0030] High temperature retarder: 2-3wt.%;

[0031] Defoaming agent: 0.25wt.%;

[0032] The CO2 corrosion resistant thermal insulation material is obtained by mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in the weight ratio of (8-13):(1-2):(3-5):(3-5);

[0033] The heat-insulating matrix 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.

[0034] Furthermore, the purity of the nano-boehmite is greater than 98 wt.%, and the particle size is 10 to 15 nm.

[0035] Furthermore, the SiO2 content of the terrazzo waste is greater than 65wt.%, and the powder fineness is greater than 325 mesh.

[0036] Furthermore, the hollow ceramic microbeads have a particle size of 5 to 40 μm and a thermal conductivity of 0.09 to 0.11 W / (m·K).

[0037] Furthermore, the aluminum titanate is in powder form, and its particle size is ≥800 mesh.

[0038] Furthermore, the sodium monofluorophosphate is in powder form with a purity greater than 99% and a particle size greater than 325 meshes.

[0039] Furthermore, the potassium aminotri(methylenephosphonate) is a crystalline powder with a purity greater than 98% and a particle size greater than 160 mesh.

[0040] Preferably, the dispersant is an aldehyde-ketone condensate; the high-temperature fluid loss additive is a 2-acrylamido-2-methylpropanesulfonic acid polymer; the high-temperature retarder is an AMPS polymer; and the defoaming agent is tributyl phosphate.

[0041] The present invention combines the inorganic material sodium monofluorophosphate and the organic material potassium aminotrimethylphosphonate to synergistically enhance the CO2 corrosion resistance. The sodium monofluorophosphate reacts with the cement hydration product calcium hydroxide to form apatite, which coats the surface of the remaining hydration products to form a dense protective layer to prevent further CO2 intrusion; the potassium aminotrimethylphosphonate aqueous solution is weakly acidic and can react with the calcium hydroxide in the cement hydration product to form apatite. 2+ Chelation forms complexes, reduces the easily carbonized substances in the hydration products, inhibits and interferes with the formation and growth of calcium carbonate, and thus improves CO2 corrosion resistance; aluminum titanate has good heat resistance, and its microstructure has crystalline phases and pores, which give it low thermal conductivity and corrosion resistance. On the one hand, it can enhance temperature resistance, and on the other hand, it cooperates with the thermal insulation matrix to enhance thermal insulation performance.

[0042] The present invention also provides a method for preparing a cement slurry system for a CO2 heat extraction geothermal well, comprising the following steps:

[0043] Step 1: G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant are weighed and mixed uniformly in respective proportions to form a dry material;

[0044] Step 2: weigh the high-temperature fluid loss additive, high-temperature retarder and defoamer according to respective proportions and mix them evenly with water to form a liquid material;

[0045] Step 3: Mix and stir the dry material and the liquid material to obtain the cement slurry system for the CO2 heat extraction type geothermal well.

[0046] Furthermore, the hollow ceramic microspheres are prepared by a flame spraying method using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust as raw materials;

[0047] The waste rock wool board powder is prepared by drying the waste rock wool board or rock wool board waste, crushing it with a crusher, and then grinding it with an ultrafine grinder, and the average particle size is ≥325 mesh;

[0048] The protein shale powder is prepared by drying the protein shale in an oven and then grinding it in an ultrafine grinding mill. The average particle size is ≥1200 mesh and the SiO2 content is ≥90%.

[0049] The modified polycarbonate is prepared by melt blending waste rock wool board powder and polycarbonate in a mass ratio of 1:9, followed by blending, granulation, cooling, crushing, and then low-temperature plasma modification. The average particle size is ≥325 mesh.

[0050] In the hollow ceramic microbeads, the lithium slag is mainly composed of quartz phase, andalusite, corundum, and a small amount of glass phase, kaolinite and lithium carbonate; wherein the SiO2 content is greater than 60%, the Al2O3 content is greater than 20%, the Na2O content is 0.2-0.8%, and the K2O content is 0.1-4%; the purity of the zirconium silicide is greater than 99.9wt.%; 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.%; the main chemical components (SiO2, Fe2O3, Al2O3 and CaO, etc.) in the rare earth tailings account for greater than 82wt.%, wherein the SiO2 content is greater than 55wt.%, the Al2O3 content is greater than 14wt.%, and the CaF2 content is 0.25-0.30%; the sawdust is formed by crushing dry sawdust, and its average particle size is less than 20 mesh.

[0051] The present invention uses lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust to make hollow ceramic microspheres. The hollow ceramic microspheres have a large amount of air inside, which can reduce the thermal conductivity of the insulation material and improve the thermal insulation performance. At the same time, the components of SiO2 and Al2O3 required for ceramics are provided. In addition, 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 be used 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 phase interlaced network structure, which improves the strength of the ceramic microspheres. Zirconium silicide further improves the density and strength of the ceramic microspheres. Sawdust produces a large amount of gas at high temperature, providing basic conditions for forming a hollow structure. The present invention uses a flame spray gun melt spraying method to form hollow ceramic microspheres, which has a simple process flow, convenient equipment operation and low energy consumption.

[0052] Preferably, the preparation method of the hollow ceramic microspheres comprises:

[0053] Step A, drying and calcining the lithium slag at high temperature to obtain activated lithium slag;

[0054] Step B, weighing 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 drying to form a mixture A; preferably, the wet ball milling mass ratio of activated lithium slag, zirconium silicide, molybdenum tailings and rare earth tailings is 75:10:10:5;

[0055] Step C, weighing a mixture A and sawdust in a mass ratio of (90-95):(5-10), uniformly mixing them to form a mixture B, using a flame spray gun to spray the mixture B, and cooling and solidifying to obtain a sprayed product; the mass ratio of the mixture A to the sawdust is preferably 90:10;

[0056] 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.

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

[0058] This invention utilizes CO2 corrosion-resistant insulation materials, combining inorganic and organic materials to synergistically enhance the material's CO2 corrosion resistance. It also utilizes an insulation matrix with high volcanic ash activity, low thermal conductivity, and excellent thermal insulation. Nanoboehmite is used to promote and participate in cement hydration reactions, and together with terrazzo, it reduces the calcium-silicon ratio, improving the high-temperature strength and stability of the cement slurry system. This invention also utilizes a variety of solid waste materials, making it environmentally friendly and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The weight loss curves of the cement slurry systems prepared in Examples 1 to 5 of the present invention and Comparative Example 1 after 28 days of corrosion are shown. 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 accompanying drawings of 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0061] The nano-boehmite in the embodiment of the present invention has a purity greater than 98 wt.% and a particle size of 10 to 15 nm.

[0062] The SiO2 content of the terrazzo waste in the embodiment of the present invention is greater than 65wt.%, and the powder fineness is greater than 325 mesh.

[0063] The aluminum titanate described in the embodiment of the present invention is in powder form, and its particle size is ≥800 mesh.

[0064] The sodium monofluorophosphate described in the embodiment of the present invention is in powder form with a purity of >99% and a particle size of >325 mesh.

[0065] The potassium aminotri(methylenephosphonate) in the embodiment of the present invention is a crystalline powder with a purity of >98% and a particle size of >160 mesh.

[0066] The thermal insulation matrix in the embodiment of the present invention 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.

[0067] The particle size of the hollow ceramic microbeads is 5 to 40 μm, and the thermal conductivity is 0.09 to 0.11 W / (m·K).

[0068] The preparation method of hollow ceramic microspheres comprises:

[0069] Step A, drying the lithium slag in an oven at 60° C. for 8 h, and then calcining the slag in a muffle furnace at 700° C. for 1.5 h to obtain activated lithium slag;

[0070] Step B, placing 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 and grinding for 1 hour, using anhydrous ethanol as the liquid medium, a ball milling liquid-to-solid ratio of 2:1, a ball milling speed of 30 r / min, and a ball milling time of 2 hours; and drying in an oven at 60° C. for 2 hours 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: Collect the melt-sprayed product and dry it in a vacuum at 80° C. and 0.07 MPa for 6 h to obtain the hollow ceramic microspheres.

[0073] The waste rock wool board powder is prepared by drying the waste rock wool board or waste rock wool board, crushing the waste rock wool board or waste rock wool board with a crusher, and then grinding the waste rock wool board with an ultrafine grinder to obtain the waste rock wool board powder;

[0074] The average particle size of waste rock wool board powder is ≥325 mesh;

[0075] The preparation method of the protein shale powder comprises the following steps: drying the protein shale in an oven, and then grinding the protein shale in an ultrafine grinding mill to obtain the protein shale powder; the average particle size of the protein shale powder is ≥1200 mesh, and the SiO2 content is ≥90wt.%;

[0076] 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; the average particle size of the modified polycarbonate is ≥325 mesh.

[0077] Example 1

[0078] As a preferred embodiment of the present invention, the specific composition of a cement slurry system for a CO2 heat extraction geothermal well disclosed in this embodiment is shown in Table 1, as well as the admixtures, calculated as a percentage by weight of Grade G oil well cement (with Grade G oil well cement as 100 wt.%): 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0079] Table 1

[0080] Components Weight percentage (wt.%) G-grade oil well cement 42 Nanoboehmite 2 Terrazzo waste 30 <![CDATA[CO2 corrosion resistant thermal insulation material]]> 25 Dispersant (aldehyde ketone condensation product) 1

[0081] In this embodiment, the CO2 corrosion-resistant thermal insulation material is obtained by fully mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in a weight ratio of 8:2:5:5.

[0082] In this embodiment:

[0083] Mixing G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant in a weight percentage (wt.%) of 42:2:30:25:1 to form a dry material;

[0084] 2.5 wt.% of high-temperature fluid loss additive, 1.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed evenly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to form a liquid material;

[0085] According to GB / T19139 standard, dry materials and liquid materials were mixed and stirred to obtain cementing slurry system #1.

[0086] Example 2

[0087] As a preferred embodiment of the present invention, the specific composition of a cement slurry system for a CO2 heat extraction geothermal well disclosed in this embodiment is shown in Table 2, and the admixtures, calculated as a percentage by weight of Grade G oil well cement (with Grade G oil well cement as 100 wt.%), are: 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0088] Table 2

[0089] Components Weight percentage (wt.%) G-grade oil well cement 52.5 Nanoboehmite 1.5 Terrazzo waste 25 <![CDATA[CO2 corrosion resistant thermal insulation material]]> 20 Dispersant (aldehyde ketone condensation product) 1

[0090] In this embodiment, the CO2 corrosion-resistant thermal insulation material is obtained by fully mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in a weight ratio of 8:2:5:5.

[0091] In this embodiment:

[0092] Mixing G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant in a weight percentage (wt.%) of 52.5:1.5:25:20:1 to form a dry material;

[0093] 2.5 wt.% of high-temperature fluid loss additive, 1.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed evenly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to form a liquid material;

[0094] According to GB / T19139 standard, dry materials and liquid materials were mixed and stirred to obtain cementing slurry system #2.

[0095] Example 3

[0096] As a preferred embodiment of the present invention, the specific composition of a cement slurry system for a CO2 heat extraction geothermal well cementing system disclosed in this embodiment is shown in Table 3, and the admixtures, calculated as a percentage by weight of Grade G oil well cement (G oil well cement is 100 wt.%), are: 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0097] Table 3

[0098]

[0099]

[0100] In this embodiment, the CO2 corrosion-resistant thermal insulation material is obtained by fully mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in a weight ratio of 8:2:5:5.

[0101] In this embodiment:

[0102] Mixing G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant in a weight percentage (wt.%) of 63:1:20:15:1 to form a dry material;

[0103] 2.5 wt.% of high-temperature fluid loss additive, 1.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed evenly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to form a liquid material;

[0104] According to GB / T19139 standard, dry materials and liquid materials were mixed and stirred to obtain cementing slurry system #3.

[0105] Example 4

[0106] As a preferred embodiment of the present invention, the specific composition of a cement slurry system for a CO2 heat extraction geothermal well cementing system disclosed in this embodiment is shown in Table 4, and the admixtures, calculated as a percentage by weight of Grade G oil well cement (G oil well cement is 100 wt.%), are: 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0107] Table 4

[0108] Components Weight percentage (wt.%) G-grade oil well cement 52.5 Nanoboehmite 1.5 Terrazzo waste 25 <![CDATA[CO2 corrosion resistant thermal insulation material]]> 20 Dispersant (aldehyde ketone condensation product) 1

[0109] In this embodiment, the CO2 corrosion-resistant thermal insulation material is obtained by fully mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in a weight ratio of 13:2:5:5.

[0110] In this embodiment:

[0111] Mixing G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant in a weight percentage (wt.%) of 52.5:1.5:25:20:1 to form a dry material;

[0112] 2.5 wt.% of high-temperature fluid loss additive, 1.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed evenly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to form a liquid material;

[0113] According to GB / T19139 standard, dry materials and liquid materials were mixed and stirred to obtain cementing slurry system #4.

[0114] Example 5

[0115] As a preferred embodiment of the present invention, the specific composition of a cement slurry system for a CO2 heat extraction geothermal well cementing system disclosed in this embodiment is shown in Table 5, and the admixtures, calculated as a percentage by weight of Grade G oil well cement (G oil well cement is 100 wt.%), are: 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0116] Table 5

[0117] Components Weight percentage (wt.%) G-grade oil well cement 52.5 Nanoboehmite 1.5 Terrazzo waste 25 <![CDATA[CO2 corrosion-resistant thermal insulation material]]> 20 Dispersant (aldehyde ketone condensation product) 1

[0118] In this embodiment, the CO2 corrosion-resistant thermal insulation material is obtained by fully mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in a weight ratio of 13:1:3:3.

[0119] In this embodiment:

[0120] Mixing G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant in a weight percentage (wt.%) of 52.5:1.5:25:20:1 to form a dry material;

[0121] 2.5 wt.% of high-temperature fluid loss additive, 1.5 wt.% of high-temperature retarder and 0.25 wt.% of defoamer in weight percentage of G-grade oil well cement are mixed evenly with water (the amount of water added is determined based on a water-cement ratio of 0.5) to form a liquid material;

[0122] According to GB / T19139 standard, dry materials and liquid materials were mixed and stirred to obtain cementing slurry system #5.

[0123] Comparative Example 1

[0124] The comparative cement slurry system provided in Comparative Example 1 has a specific composition as shown in Table 6, and the admixtures, calculated as a percentage by weight of Grade G oil well cement (Grade G oil well cement is 100 wt.%), are: 2.5 wt.% high-temperature fluid loss additive, 1.5 wt.% high-temperature retarder, and 0.25 wt.% defoamer.

[0125] Table 6

[0126] Components Weight ratio (%) G-grade oil well cement 79 silica sand 20 dispersants 1

[0127] In Comparative Example 1, the SiO2 content of the silica sand is ≥95wt.%, and the powder fineness is ≥800 mesh.

[0128] In Comparative Example 1, Grade G oil well cement, silica sand, a dispersant, and water were uniformly mixed in a weight percentage (wt.%) of 79:20:1 (the amount of water added was determined based on a water-cement ratio of 0.5), and then 2.5 wt.% of a high-temperature fluid loss additive, 1.5 wt.% of a high-temperature retarder, and 0.25 wt.% of a defoamer were added (based on 100 wt.% of the Grade G oil well cement) to obtain a comparative cement slurry system.

[0129] The above-mentioned G-grade oil well cement is provided by Jiahua Special Cement Co., Ltd., and the high-temperature retarder, high-temperature fluid loss additive and defoaming agent are provided by Sichuan Xuran Hongchen New Materials Co., Ltd. The high-temperature retarder is an AMPS polymer, the high-temperature fluid loss additive is a 2-acrylamido-2-methylpropanesulfonic acid polymer, and the defoaming agent is tributyl phosphate.

[0130] The slurry engineering properties of the comparative cement slurry system and the cementing cement slurry systems #1 to #5 prepared in Examples 1 to 5 were tested at 150°C with reference to the GB / T19139 oil well cement test method. The results are shown in Table 7.

[0131] Table 7

[0132]

[0133]

[0134] According to the experimental data in Table 7, the water loss of cement slurry systems #1 to #5 configured in Examples 1 to 5 is less than 40 ml, which is better than the comparative cement slurry system. In addition, their fluidity and free liquid meet the construction requirements, the slurry has good stability, the thickening time is controllable, and various engineering performances are good.

[0135] Cement pastes from cementing slurry systems #1 to #5 and the control slurry system were placed in a high-temperature, high-pressure corrosion reactor in a high-temperature, high-pressure, vapor-containing supercritical CO₂ environment. The curing temperature was 180°C, the CO₂ pressure was 5 MPa, the total pressure was 10 MPa, and the partial pressure of N₂ was 7 and 28 days, respectively. Compressive strength was tested using a NYSQ-2017 pressure testing machine. Permeability measurements were also conducted on each slurry sample according to the SY / T 6466-2000 standard, "Evaluation Method for High-Temperature Performance of Oil Well Cement," and thermal conductivity was tested using a DRE-2C thermal conductivity tester using the transient plane heat source method. The test results are shown in Table 8.

[0136] Table 8

[0137]

[0138]

[0139] According to the experimental data in Table 8, after a certain corrosion age, the comparative cement slurry system without the addition of nano-boehmite, terrazzo waste, and CO2 corrosion-resistant insulation material has low compressive strength and severe decay, while the cementing cement slurry systems #1 to #5 configured in Examples 1 to 5 have high compressive strength and do not show decay. The compressive strength has increased slightly, indicating that the cementing cement slurry system for CO2 heating geothermal wells of the present invention has good resistance to high-temperature strength decay. The cement slurry permeability in Comparative Example 1 increased significantly, while the cement slurry permeability in Examples 1 to 5 increased slightly, but overall it was much smaller than the cement slurry system in Comparative Example 1. Compared with Comparative Example 1, the thermal conductivity of Examples 1 to 5 decreased significantly, and the thermal conductivity was less than 0.420 (W / m·k). The thermal insulation effect is good, which can reduce heat loss during geothermal resource extraction.

[0140] The cement pastes from the aforementioned cementing slurry systems #1 to #5 and the comparative cement slurry system were placed in a high-temperature, high-pressure corrosion reactor. The cement pastes were exposed to a high-temperature, high-pressure, and vapor-containing supercritical CO2 environment. The curing temperature was 180°C, the CO2 pressure was 5 MPa, the total pressure was 10 MPa, and the N2 partial pressure was 28 days. The cured products from each cementing slurry system were analyzed by thermogravimetric analysis. Figure 1 shown.

[0141] Since the corrosion product of cement is calcium carbonate, and the decomposition temperature range of calcium carbonate is 600-770℃, thermogravimetric analysis is used to measure the weight loss of cement stone in this temperature range to characterize the corrosion of cement stone under given conditions. The greater the weight loss of the sample in the above range, the more susceptible the sample is to corrosion, and vice versa, the more corrosion-resistant the sample is.

[0142] Figure 1The weight loss curves for the 28-day corrosion period for the comparative cement slurry system and cementing slurries #1 to #5 are shown. Thermogravimetric testing of the samples was performed on a thermal analyzer manufactured by Mettle Toledo, Inc., at a heating rate of 10°C / min under nitrogen atmosphere.

[0143] pass Figure 1 It can be seen that within the temperature range of 600-770°C, the weight loss TG (%) of the cementing cement slurry systems #1-#5 in Examples 1-5 are all less than that of the comparative cement slurry system, that is, the corrosion resistance of the cementing cement slurry systems #1-#5 is much greater than that of the comparative cement slurry system, indicating that the cementing cement slurry system suitable for CO2 heating type geothermal wells of the present invention has excellent corrosion resistance.

[0144] 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 cement slurry system for geothermal wells suitable for CO2 heating, characterized in that: The present invention comprises the following raw materials in percentage by weight: G-grade oil well cement: 42-63 wt.%; Nanoboehmite: 1-2 wt.%; Terrazzo waste: 20-30wt.% CO2 corrosion resistant insulation material: 15-25wt.%; Dispersant: 1wt.%; And admixtures as percentage by weight of Grade G oil well cement: High temperature fluid loss additive: 2-4wt.%; High temperature retarder: 1-3wt.%; Defoaming agent: 0.25wt.%; The CO2 corrosion resistant thermal insulation material is obtained by mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in parts by weight (8-13):(1-2):(3-5):(3-5); The thermal insulation matrix is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, protein shale powder and modified polycarbonate in a weight ratio of 11:3:5:

1.

2. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1, characterized in that: The present invention comprises the following raw materials in percentage by weight: G-grade oil well cement: 50-60wt.%; Nanoboehmite: 1-2 wt.%; Terrazzo waste: 20-25wt.% CO2 corrosion resistant insulation material: 20-25wt.%; Dispersant: 1wt.%; And admixtures as percentage by weight of Grade G oil well cement: High temperature fluid loss additive: 2-3wt.%; High temperature retarder: 2-3wt.%; Defoaming agent: 0.25wt.%; The CO2 corrosion resistant thermal insulation material is obtained by mixing a thermal insulation matrix, aluminum titanate, sodium monofluorophosphate and potassium aminotri(methylenephosphonate) in parts by weight (8-13):(1-2):(3-5):(3-5); The thermal insulation matrix is obtained by mixing hollow ceramic microspheres, waste rock wool board powder, protein shale powder and modified polycarbonate in a weight ratio of 11:3:5:

1.

3. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The purity of the nano-boehmite is greater than 98 wt.%, and the particle size is 10-15 nm.

4. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The SiO2 content of the terrazzo waste is greater than 65%.

5. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The hollow ceramic microbeads have a particle size of 5 to 40 μm and a thermal conductivity coefficient of 0.09 to 0.11 W / (m·K).

6. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The aluminum titanate is in powder form, and its particle size is ≥800 mesh.

7. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The sodium monofluorophosphate is in powder form with a purity greater than 99 wt.% and a particle size greater than 325 meshes.

8. A cement slurry system for a CO2 heat extraction geothermal well according to claim 1 or 2, characterized in that: The potassium aminotri(methylenephosphonate) is a crystalline powder with a purity greater than 98 wt.% and a particle size greater than 160 meshes.

9. The method for preparing a cement slurry system for a CO2 heat extraction geothermal well according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: G-grade oil well cement, nano-boehmite, terrazzo waste, CO2 corrosion-resistant insulation material, and dispersant are weighed and mixed uniformly according to respective proportions to form a dry material; Step 2: weigh the high-temperature fluid loss additive, high-temperature retarder and defoamer according to respective proportions and mix them evenly with water to form a liquid material; Step 3: Mix and stir the dry material and the liquid material to obtain the cement slurry system for the CO2 heat extraction type geothermal well.

10. The method for preparing a cement slurry system for a CO2 heat extraction geothermal well according to claim 9, characterized in that: The hollow ceramic microspheres are prepared by using lithium slag, zirconium silicide, molybdenum tailings, rare earth tailings and sawdust as raw materials and adopting flame spraying method. The waste rock wool board powder is prepared by drying the waste rock wool board or rock wool board waste, crushing it with a crusher, and then grinding it with an ultra-fine grinder; The protein shale powder is prepared by drying the protein shale in an oven and then grinding it in an ultrafine grinding mill. The modified polycarbonate is prepared by melt blending waste rock wool board powder and polycarbonate in a mass ratio of 1:9, followed by blending, granulation, cooling, and crushing, and then undergoing low-temperature plasma modification.

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