High-temperature-resistant oil well cement composite reinforcing agent and preparation method thereof

Abstract

The invention relates to the technical field of oil well treating agents, in particular to a high-temperature-resistant oil well cement composite reinforcing agent and a preparation method thereof. The high-temperature-resistant oil well cement composite reinforcing agent is prepared from the following materials in parts by weight: 40 to 50 parts of silane coupling agent modified zirconium silicate, 20 to 25 parts of red mud-based activated micro powder, 8 to 10 parts of fly ash, 10 to 12 parts of silane coupling agent modified microcapsules, 4 to 6 parts of magnesium borate whiskers, 2 to 3 parts of carbon nanotubes and 1 to 1.5 parts of halloysite. According to the high-temperature-resistant oil well cement composite reinforcing agent disclosed by the invention, the cement strength of the high-temperature-resistant oil well cement composite reinforcing agent in a high-temperature environment is improved, and the stability of the high-temperature-resistant oil well cement composite reinforcing agent in storage and use processes is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil well treatment agents, and in particular to a high-temperature resistant oil well cement composite reinforcing agent and a preparation method thereof. Background Art

[0002] Oil well cement plays a vital role in the oil and gas extraction process. It's primarily used in cementing operations, securing casing to the wellbore, isolating oil, gas, and water layers, preventing cross-flow between fluids in different formations, and protecting both the casing and the reservoir. As oil exploration and development expand into deeper formations and complex environments such as high temperature and high pressure, more stringent requirements are being placed on the performance of oil well cement, particularly its high-temperature resistance. As a key material for improving the high-temperature resistance of oil well cement, the development and application of high-temperature-resistant oil well cement composite enhancers are of great practical significance.

[0003] High-temperature-resistant oil-well cement composite enhancers are additives that significantly improve the performance of oil-well cement in high-temperature environments. They are typically composed of multiple functionally specific components that work synergistically to improve the cement's hydration process, microstructure, and physical and mechanical properties. Oil-well cement faces numerous challenges under high-temperature conditions, such as strength loss, increased permeability, and decreased volume stability. High-temperature-resistant oil-well cement composite enhancers can effectively alleviate these challenges by improving the cement's compressive strength, flexural strength, impermeability, and volume stability, ensuring cementing quality and extending the service life of the well.

[0004] An invention patent with publication number CN109111902A and IPC classification number C09K8 / 467 discloses a second interface enhancer for oil wells and a preparation method thereof. The second interface enhancer for oil wells comprises the following raw materials in parts by weight: 80-100 parts of fly ash, 100-150 parts of lithium magnesium silicate, 200-250 parts of ordinary Portland cement, 300-400 parts of quartz sand, 50-60 parts of red mud, 1-5 parts of silica fume, 0.5-1.0 part of a water reducer, and 50-80 parts of a reaction solution.

[0005] An invention patent with announcement number CN102031097B and IPC classification number C09K8 / 467 discloses a method for enhancing oil well cement slurry for petroleum and natural gas cementing. The main feature of the method is to add oil-absorbing swelling components such as oil-absorbing resin with a total solid mass of 0.1% to 3% and a particle size of 40 to 320 mesh to the oil well cement slurry and stir the mixture thoroughly. The oil-absorbing swelling components are capable of expanding in volume upon encountering and absorbing oil, thereby improving their ability to seal microcracks and microannular gaps and thereby reduce annular channeling.

[0006] An invention patent with publication number CN101063034A and IPC classification number C09K8 / 57 discloses a method for reinforcing oil well cement slurry with fine metal fibers. The method involves adding 0.5-5% of the weight of the solid phase mixture to the oil well cement slurry, with a diameter of 0.01mm-0.1mm and a length of 3mm-15mm, and thoroughly stirring the fibers to improve the cement slurry's self-plugging ability, thereby facilitating balanced cement injection and smooth pumping to the desired location.

[0007] Although some high-temperature resistant oil well cement composite enhancers currently on the market can improve the high-temperature resistance of cement to a certain extent, the enhancement effect is still difficult to meet the cementing needs of deep, high-temperature oil wells. In a high-temperature environment (such as exceeding 200°C), the strength of cement stone increases slowly, and even strength shrinkage occurs. This is mainly due to the limited ability of existing enhancers to improve the structure and properties of cement hydration products. They are unable to effectively inhibit the damage of high temperature to the microstructure of cement stone, resulting in increased porosity and reduced strength of cement stone. Some high-temperature resistant oil well cement composite enhancers exhibit poor stability during storage and use. During storage, certain components in the enhancer may undergo chemical reactions or physical changes, resulting in a decrease in its performance. Based on this, the present invention provides a high-temperature resistant oil well cement composite enhancer and a preparation method thereof. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-temperature resistant oil well cement composite strengthener and a preparation method thereof, which improves the cement strength of the high-temperature resistant oil well cement composite strengthener under high temperature (such as exceeding 200°C) environment and improves the stability of the high-temperature resistant oil well cement composite strengthener during storage and use.

[0009] On the one hand, the present invention provides a high-temperature resistant oil well cement composite reinforcer, comprising the following materials in parts by weight: 40-50 parts of silane coupling agent modified zirconium silicate, 20-25 parts of red mud-based activated micropowder, 8-10 parts of fly ash, 10-12 parts of silane coupling agent modified microcapsules, 4-6 parts of magnesium borate whiskers, 2-3 parts of carbon nanotubes and 1-1.5 parts of halloysite.

[0010] Furthermore, the preparation method of the silane coupling agent modified zirconium silicate includes: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 25-35 minutes, adding silane coupling agent KH560, stirring and reacting at 55-65° C. for 3-5 hours, and centrifugally drying to obtain silane coupling agent modified zirconium silicate.

[0011] Furthermore, the usage ratio of the zirconium silicate powder, ethanol and silane coupling agent is 10 g: 200-300 mL: 0.3-0.4 g.

[0012] Furthermore, the red mud-based activated micropowder preparation method includes: washing the red mud with water to remove soluble salts, drying at 50-60°C for 10-12 hours, and then crushing it to less than 200 mesh; mixing the red mud with 4-6% dilute sulfuric acid with a solid-liquid ratio of 1g / 3-5mL, microwave heating at 110-120°C for 30-40 minutes, filtering, calcining at 750-850°C for 1-2 hours, and ball milling to less than 600 mesh to obtain the powder.

[0013] Furthermore, the preparation method of the silane coupling agent modified microcapsules includes: mixing the silane coupling agent KH-550 with ethanol and water, adjusting the pH to 4.5-5.5 with acetic acid, adding microcapsules, stirring at 55-65° C. for 1.5-2.5 hours, centrifuging, washing, and drying to obtain the microcapsules.

[0014] Furthermore, the usage ratio of the silane coupling agent, ethanol, water and microcapsules is 3-5 g: 60-100 mL: 6-10 mL: 15-20 g.

[0015] Furthermore, the preparation method of the microcapsules includes: melting and mixing solid paraffin and liquid paraffin to obtain an oil phase, mixing deionized water and sodium lauryl sulfate to obtain an aqueous phase, slowly pouring the oil phase into the aqueous phase, stirring and shearing, forming an O / W emulsion, dropping ethyl orthosilicate into the emulsion, and simultaneously dropping ammonia water to adjust the pH to 8.5-9.5, stirring at a temperature of 45-55° C. and 450-550 rpm for 2-3 hours, heating to 60-65° C. and continuing stirring for 50-60 minutes to promote condensation, and washing, drying, and sieving after centrifugal separation to obtain microcapsules with an average particle size of 60-100 μm.

[0016] Furthermore, the usage ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate and ethyl orthosilicate is (40-50) g: (40-50) g: (190-210) mL: (0.5-1.5) g: (18-22) g.

[0017] On the other hand, the present invention also provides a preparation method of a high-temperature resistant oil well cement composite reinforcer, which comprises the following steps: putting silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash into a high-speed mixer, dry mixing for 15-20 minutes at a speed of 1000-1200 rpm under nitrogen protection; adding silane coupling agent modified microcapsules and magnesium borate whiskers, injecting 2.8-3.6 parts of a polycarboxylate water-reducing agent aqueous solution with a mass concentration of 0.1%, ultrasonically dispersing at 40 kHz for 30 minutes, continuously adding carbon nanotubes pre-dispersed in 10-15 parts of ethylene glycol, homogenizing under a high pressure of 50 MPa, and adding the mixture together with halloysite into the system; continuously stirring for 2-3 hours at 300 rpm in a vacuum drying oven at 60°C, removing large particles through three-stage vibration screening of 400 mesh, 800 mesh and 1250 mesh, and air flow crushing to D50 = 8-12 μm in an environment with a relative humidity of ≤30%.

[0018] The beneficial effects of the present invention are: This invention uses the silane coupling agent KH560 to surface-modify zirconium silicate, enhancing its interfacial adhesion to the cement matrix through chemical bonding. The ethoxy groups (-OC2H5) in the silane coupling agent molecules hydrolyze in an ethanol solution to form silanol groups (-Si-OH), which adsorb onto the zirconium silicate surface through hydrogen bonding. The cavitation effect generated by ultrasonic treatment exfoliates zirconium silicate aggregates, exposing more highly reactive surface sites and promoting condensation of silanol groups with hydroxyl groups (-Si-OH) on the zirconium silicate surface to form Si-O-Si covalent bonds. Organic functional groups (such as -NH2) grafted onto the modified zirconium silicate surface condense with hydroxyl groups of Ca(OH)2 during cement hydration, forming a stable chemically bonded network. This interfacial strengthening deflects microcrack propagation paths, significantly improving the fracture toughness of cement paste at high temperatures. The compressive strength of Comparative Example 1 decreased by 19.5% compared to Example 1, demonstrating the critical role of interfacial adhesion in high-temperature mechanical properties.

[0019] The present invention converts red mud into highly active micropowder through a dilute sulfuric acid acidification-calcination process, replacing traditional mineral admixtures. During the acid activation process, the aluminum and iron oxides in the red mud dissolve and recrystallize, forming nanoparticles with pozzolanic activity. The activated red mud micropowder participates in the pozzolanic reaction early in cement hydration, reacting with Ca(OH)2 to form CASH gel. This gel fills the pores of the cement paste, forming a dense three-dimensional network structure. The compressive strength of Comparative Example 3 decreased by 14.0% compared to Example 1, indicating that acid activation significantly stimulated the pozzolanic effect of the red mud and promoted the improvement of the density of the cement paste.

[0020] In the present invention, the microcapsules serve as temperature-responsive repair carriers, and their surface modification directly determines the storage stability and release efficiency. The silane coupling agent KH-550 forms a monomolecular layer on the surface of the microcapsules through a hydrolysis-condensation reaction. Under the action of thermal stress at 200°C, the phase change expansion of the paraffin core causes the shell to rupture, and the released repair substance penetrates through the microcracks and solidifies to form a self-repairing layer. This mechanism makes the compressive strength loss rate of Example 1 significantly lower than that of Comparative Example 8.

[0021] The silane coupling agent-modified zirconium silicate, red mud-based activated micropowder, and silane coupling agent-modified microcapsules of the present invention construct a high-temperature resistant reinforcement system through multi-scale synergistic action. The nanoscale interface transition zone of the modified zirconium silicate and the micron-scale volcanic ash product of the red mud-based activated micropowder form a gradient reinforcement structure. The temperature-responsive repair of the microcapsules and the crack bridging effect of the magnesium borate whisker-halloysite network structure form a dual anti-crack mechanism. During a 200°C thermal cycle, the pull-out effect of the whiskers consumes crack propagation energy, and the repair substance released by the microcapsules fills the microcracks. The two work together to reduce the compressive strength loss rate of Example 1 by 55.6% compared with Comparative Example 2.

[0022] The present invention constructs a toughening mechanism by combining temperature-responsive microcapsules with a whisker-halloysite three-dimensional network structure. Paraffin microcapsules modified with the silane coupling agent KH-550 can rupture under thermal stress, releasing repair substances to repair microcracks. The agglomeration rate of Comparative Example 5 was as high as 8.9%, indicating that the silane coupling agent inhibited microcapsule aggregation by reducing surface energy. Furthermore, magnesium borate whiskers and halloysite nanotubes form a three-dimensional network structure through hydrogen bonding and van der Waals forces, improving mechanical properties. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] It should be noted that red mud was purchased from Shandong Aluminum Company and ground to a specific surface area of ​​520m 2 / kg; the red mud is an industrial waste waste discharged when alumina is extracted from the aluminum industry; magnesium borate whiskers, purchased from Nanjing Chemical Reagent Co., Ltd., CAS No.: 13703-82-7; halloysite, purchased from Xi'an Mingchuangda Biotechnology Co., Ltd.; polycarboxylate water reducer, purchased from Shanghai Kaiyin Chemical, brand RHEOPLUS412; solid paraffin, CAS No.: 8002-74-2, item No. 327212, purchased from Merck; liquid paraffin, CAS No.: 8002-74-2, item No. 76234, purchased from Merck, and the remaining raw materials are also commercially available.

[0025] Example 1 This embodiment provides a high-temperature resistant oil well cement composite reinforcer, including the following materials in parts by weight: 45 parts of silane coupling agent-modified zirconium silicate, 22 parts of red mud-based activated micropowder, 9 parts of fly ash, 11 parts of silane coupling agent-modified microcapsules, 5 parts of magnesium borate whiskers, 2.5 parts of carbon nanotubes, and 1.2 parts of halloysite.

[0026] The preparation method of the silane coupling agent modified zirconium silicate comprises: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 30 minutes, adding silane coupling agent KH560, stirring and reacting at 60°C for 4 hours, and centrifugally drying to obtain silane coupling agent modified zirconium silicate; the amount ratio of zirconium silicate powder, ethanol and silane coupling agent is 10 g: 250 mL: 0.35 g; The preparation method of the red mud-based activated micropowder includes: washing the red mud with water to remove soluble salts, drying it at 55°C for 11 hours, and then crushing it to less than 200 mesh; mixing the red mud with a 5% dilute sulfuric acid aqueous solution with a solid-liquid ratio of 1g / 4mL, heating it with a microwave at 115°C for 350 minutes, filtering it, calcining it at 800°C for 1.5 hours, and ball milling it to less than 600 mesh.

[0027] The preparation method of the silane coupling agent-modified microcapsules includes: Solid paraffin and liquid paraffin are melted and mixed to obtain an oil phase, deionized water and sodium lauryl sulfate are mixed to obtain an aqueous phase, the oil phase is slowly poured into the aqueous phase and stirred and sheared to form an O / W emulsion, ethyl orthosilicate is dropwise added to the emulsion, and ammonia water is simultaneously added dropwise to adjust the pH to 9, the mixture is stirred at 50° C. and 500 rpm for 2.5 hours, the temperature is raised to 62° C. and stirring is continued for 55 minutes to promote condensation, and the mixture is washed with deionized water after centrifugation, dried at 60° C. to constant weight, and sieved to obtain microcapsules with an average particle size of 80 μm; the amount ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate, and ethyl orthosilicate is 45 g:45 g:200 mL:1 g:20 g; Silane coupling agent KH-550 was mixed with ethanol and water, and the pH was adjusted to 55 with acetic acid. Microcapsules were added, and the mixture was stirred at 60°C for 2 hours. The mixture was centrifuged, washed, and dried to obtain the product. The ratio of the silane coupling agent, ethanol, water, and microcapsules was 4 g:80 mL:8 mL:17 g. The preparation method of the high-temperature resistant oil well cement composite reinforcer comprises the following steps: putting silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash into a high-speed mixer, and dry mixing them at a speed of 1100 rpm for 17 minutes under nitrogen protection; adding silane coupling agent modified microcapsules and magnesium borate whiskers, injecting 3.2 parts of a polycarboxylate water-reducing agent aqueous solution with a mass concentration of 0.1%, ultrasonically dispersing at 40 kHz for 30 minutes, continuously adding carbon nanotubes pre-dispersed in 12 parts of ethylene glycol, and adding the carbon nanotubes together with halloysite into the system after high-pressure homogenization at 50 MPa; continuously stirring at 300 rpm in a vacuum drying oven at 60°C for 2.5 hours, removing large particles through three-level vibration screening of 400 mesh, 800 mesh and 1250 mesh, and air flow pulverizing to D50=10 μm in an environment with a relative humidity of 30%.

[0028] Example 2 This embodiment provides a high-temperature resistant oil well cement composite reinforcer, including the following materials in parts by weight: 40 parts of silane coupling agent-modified zirconium silicate, 20 parts of red mud-based activated micropowder, 8 parts of fly ash, 10 parts of silane coupling agent-modified microcapsules, 4 parts of magnesium borate whiskers, 2 parts of carbon nanotubes, and 1 part of halloysite.

[0029] The preparation method of the silane coupling agent modified zirconium silicate comprises: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 25 minutes, adding silane coupling agent KH560, stirring and reacting at 55°C for 3 hours, and centrifugally drying to obtain silane coupling agent modified zirconium silicate; the amount ratio of zirconium silicate powder, ethanol and silane coupling agent is 10 g: 200 mL: 0.3 g; The preparation method of red mud-based activated micropowder includes: washing the red mud with water to remove soluble salts, drying it at 50°C for 10 hours, and then crushing it to less than 200 mesh; mixing the red mud with a 4% dilute sulfuric acid aqueous solution with a solid-liquid ratio of 1g / 3mL, heating it with a microwave at 110°C for 30 minutes, filtering it, calcining it at 750°C for 1 hour, and ball milling it to less than 600 mesh.

[0030] The preparation method of the silane coupling agent-modified microcapsules includes: Solid paraffin and liquid paraffin are melted and mixed to obtain an oil phase, deionized water and sodium lauryl sulfate are mixed to obtain an aqueous phase, the oil phase is slowly poured into the aqueous phase and stirred and sheared to form an O / W emulsion, ethyl orthosilicate is dropwise added to the emulsion, and ammonia water is simultaneously added dropwise to adjust the pH to 8.5, the mixture is stirred at 45°C and 450rpm for 2h, the temperature is raised to 60°C and stirring is continued for 50min to promote condensation, and the mixture is washed with deionized water after centrifugation, dried at 60°C to constant weight, and sieved to obtain microcapsules with an average particle size of 60 μm; the amount ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate, and ethyl orthosilicate is 40g:40g:190mL:0.5g:18g; Silane coupling agent KH-550 was mixed with ethanol and water, and the pH was adjusted to 4.5 with acetic acid. Microcapsules were added and stirred at 55°C for 1.5 hours. The mixture was centrifuged, washed, and dried to obtain the product. The ratio of the silane coupling agent, ethanol, water, and microcapsules was 3 g:60 mL:6 mL:15 g. The preparation method of the high-temperature resistant oil well cement composite reinforcer comprises the following steps: putting silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash into a high-speed mixer, and dry mixing them at a speed of 1000 rpm for 15 minutes under nitrogen protection; adding microcapsules modified with silane coupling agent and magnesium borate whiskers, injecting 2.8 parts of a polycarboxylate water-reducing agent aqueous solution with a mass concentration of 0.1%, ultrasonically dispersing at 40 kHz for 30 minutes, continuously adding carbon nanotubes pre-dispersed in 10 parts of ethylene glycol, homogenizing under a high pressure of 50 MPa, and adding the carbon nanotubes together with halloysite into the system; continuously stirring at 300 rpm in a vacuum drying oven at 60°C for 2 hours, removing large particles through three-level vibration screening of 400 mesh, 800 mesh and 1250 mesh, and air flow pulverizing to a D50 of 10 μm in an environment with a relative humidity of 30%.

[0031] Example 3 This embodiment provides a high-temperature resistant oil well cement composite reinforcer, including the following materials in parts by weight: 50 parts of silane coupling agent-modified zirconium silicate, 25 parts of red mud-based activated micropowder, 10 parts of fly ash, 12 parts of silane coupling agent-modified microcapsules, 6 parts of magnesium borate whiskers, 3 parts of carbon nanotubes, and 1.5 parts of halloysite.

[0032] The preparation method of the silane coupling agent-modified zirconium silicate comprises: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 35 minutes, adding silane coupling agent KH560, stirring and reacting at 65°C for 5 hours, and centrifugally drying to obtain silane coupling agent-modified zirconium silicate; the amount ratio of zirconium silicate powder, ethanol and silane coupling agent is 10 g:300 mL:0.4 g; Among them, the preparation method of the red mud-based activated micropowder includes: washing the red mud with water to remove soluble salts, drying it at 60°C for 12 hours, and then crushing it to less than 200 mesh; mixing the red mud with a dilute sulfuric acid aqueous solution with a mass concentration of 6% at a solid-liquid ratio of 1g / 5mL, heating it with a microwave at 120°C for 40 minutes, filtering it, calcining it at 850°C for 2 hours, and ball milling it to less than 600 mesh.

[0033] The preparation method of the silane coupling agent-modified microcapsules includes: Solid paraffin and liquid paraffin are melted and mixed to obtain an oil phase, deionized water and sodium lauryl sulfate are mixed to obtain an aqueous phase, the oil phase is slowly poured into the aqueous phase and stirred and sheared to form an O / W emulsion, ethyl orthosilicate is dropwise added to the emulsion, and ammonia water is added dropwise to adjust the pH to 9.5, and the mixture is stirred at 55° C. and 550 rpm for 3 h, then heated to 65° C. and stirred for 60 min to promote condensation, and washed with deionized water after centrifugation, dried at 60° C. to constant weight, and sieved to obtain microcapsules with an average particle size of 100 μm; the amount ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate, and ethyl orthosilicate is 50 g:50 g:210 mL:1.5 g:22 g; Silane coupling agent KH-550 was mixed with ethanol and water, and the pH was adjusted to 5.5 with acetic acid. Microcapsules were added, and the mixture was stirred at 65°C for 2.5 hours. The mixture was centrifuged, washed, and dried to obtain the product. The ratio of the silane coupling agent, ethanol, water, and microcapsules was 5 g:100 mL:10 mL:20 g. The preparation method of the high-temperature resistant oil well cement composite reinforcer comprises the following steps: putting silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash into a high-speed mixer, and dry mixing them at a speed of 1200 rpm for 20 minutes under nitrogen protection; adding microcapsules modified with silane coupling agent and magnesium borate whiskers, injecting 3.6 parts of a polycarboxylate water-reducing agent aqueous solution with a mass concentration of 0.1%, ultrasonically dispersing at 40 kHz for 30 minutes, continuously adding carbon nanotubes pre-dispersed in 15 parts of ethylene glycol, and adding the carbon nanotubes together with halloysite into the system after high-pressure homogenization at 50 MPa; continuously stirring at 300 rpm in a vacuum drying oven at 60°C for 3 hours, removing large particles through three-level vibration screening of 400 mesh, 800 mesh and 1250 mesh, and air flow pulverizing to D50=10 μm in an environment with a relative humidity of 30%.

[0034] Example 4 This embodiment provides a high-temperature resistant oil well cement composite reinforcer, including the following materials in parts by weight: 40 parts of silane coupling agent-modified zirconium silicate, 25 parts of red mud-based activated micropowder, 8 parts of fly ash, 12 parts of silane coupling agent-modified microcapsules, 4 parts of magnesium borate whiskers, 3 parts of carbon nanotubes, and 1 part of halloysite.

[0035] The preparation method of the silane coupling agent modified zirconium silicate comprises: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 35 minutes, adding silane coupling agent KH560, stirring and reacting at 55°C for 5 hours, and centrifugally drying to obtain silane coupling agent modified zirconium silicate; the amount ratio of zirconium silicate powder, ethanol and silane coupling agent is 10 g: 200 mL: 0.4 g; The preparation method of red mud-based activated micropowder includes: washing the red mud with water to remove soluble salts, drying it at 50°C for 12 hours, and then crushing it to less than 200 mesh; mixing the red mud with a 5% dilute sulfuric acid aqueous solution with a solid-liquid ratio of 1g / 3mL, heating it with a microwave at 120°C for 30 minutes, filtering it, calcining it at 850°C for 1 hour, and ball milling it to less than 600 mesh.

[0036] The preparation method of the silane coupling agent-modified microcapsules includes: Solid paraffin and liquid paraffin are melted and mixed to obtain an oil phase, deionized water and sodium lauryl sulfate are mixed to obtain an aqueous phase, the oil phase is slowly poured into the aqueous phase and stirred and sheared to form an O / W emulsion, ethyl orthosilicate is dropwise added to the emulsion, and ammonia water is simultaneously added dropwise to adjust the pH to 9.5, the mixture is stirred at 45°C and 550 rpm for 2 hours, the temperature is raised to 65°C and stirring is continued for 50 minutes to promote condensation, and the mixture is washed with deionized water after centrifugation, dried at 60°C to constant weight, and sieved to obtain microcapsules with an average particle size of 100 μm; the amount ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate, and ethyl orthosilicate is 40 g:50 g:190 mL:1.5 g:18 g; Silane coupling agent KH-550 was mixed with ethanol and water, and the pH was adjusted to 5.5 with acetic acid. Microcapsules were added, and the mixture was stirred at 55°C for 2.5 hours. The mixture was centrifuged, washed, and dried to obtain the product. The ratio of the silane coupling agent, ethanol, water, and microcapsules was 3 g:100 mL:6 mL:20 g. The preparation method of the high-temperature resistant oil well cement composite reinforcer comprises the following steps: putting silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash into a high-speed mixer, and dry-mixing them at a speed of 1000 rpm for 20 minutes under nitrogen protection; adding microcapsules modified with silane coupling agent and magnesium borate whiskers, injecting 2.8 parts of a polycarboxylate water-reducing agent aqueous solution with a mass concentration of 0.1%, ultrasonically dispersing at 40 kHz for 30 minutes, continuously adding carbon nanotubes pre-dispersed in 15 parts of ethylene glycol, homogenizing under a high pressure of 50 MPa, and adding the carbon nanotubes together with halloysite into the system; continuously stirring at 300 rpm in a vacuum drying oven at 60°C for 2 hours, removing large particles through three-stage vibration screening of 400 mesh, 800 mesh and 1250 mesh, and air flow pulverizing the mixture to a D50 of 10 μm in an environment with a relative humidity of 30%.

[0037] Comparative Example 1 In Comparative Example 1, the zirconium silicate was not modified with a silane coupling agent, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0038] Comparative Example 2 In Comparative Example 2, no silane coupling agent-modified zirconium silicate was added, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0039] Comparative Example 3 In Comparative Example 3, the red mud-based activated micropowder was not subjected to acid activation treatment. Instead, the red mud was directly washed with water to remove soluble salts, dried at 55° C. for 11 h, and then crushed to less than 600 mesh. The rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0040] Comparative Example 4 In Comparative Example 4, no red mud-based activated micropowder was added, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0041] Comparative Example 5 The microcapsules in Comparative Example 5 were not modified with a silane coupling agent, and the rest were the same as in Example 1, and the preparation steps were the same as in Example 1.

[0042] Comparative Example 6 In Comparative Example 6, liquid paraffin was replaced with soybean oil, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0043] Comparative Example 7 In Comparative Example 7, the microcapsules modified with the silane coupling agent were replaced with solid paraffin of equal mass, and the rest were the same as in Example 1, and the preparation steps were the same as in Example 1.

[0044] Comparative Example 8 In Comparative Example 8, no silane coupling agent-modified microcapsules were added, and the rest of the process was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0045] Test Example: The following tests were performed on the enhancers prepared in Examples 1-4 and Comparative Examples 1-8: Compressive strength: A concrete slurry was prepared by uniformly mixing 140 parts of coarse aggregate (purchased from Zhuzhou Aggregate New Materials Co., Ltd., 5-10 mm) with 8 parts of water, adding 40 parts of PO42.5 Portland cement (purchased from Anhui Conch Cement Co., Ltd.), 5 parts of a reinforcing agent, and 6 parts of water. The mixture was stirred at 200 rpm for 5 minutes to obtain a concrete slurry. The mixture was cured in an autoclave at 200°C / 21 MPa for 7 days. The compressive strength test of the prepared concrete was performed in accordance with GB / T50081-2019. Thermal cycle stability test: The concrete specimens were subjected to 30 cycles from 200°C to 50°C, with a single cycle time of 2 hours, and the compressive strength loss rate after the cycle was measured; Storage stability test: The enhancer sample was sealed and stored in an environment of 40°C and RH 75%. The agglomeration rate of the enhancer was tested after 60 days. Corrosion resistance coefficient: refer to GB / T50082-2019 to conduct sulfate corrosion resistance test on the prepared concrete; Water permeability test: Test in accordance with CJJ / T135-2009; The results are shown in Table 1 below.

[0046] Table 1: Performance Test Compressive strength (MPa, 7d) Compressive strength loss rate (%) Agglomeration rate (%) (residue after 400 mesh sieve) Corrosion resistance coefficient Permeability coefficient (mm / s) Example 1 36.4 8.4 1.1 0.98 3.2 Example 2 35.8 9.1 1.6 0.96 3.0 Example 3 36.1 8.7 1.4 0.97 3.0 Example 4 35.6 9.2 1.8 0.96 2.8 Comparative Example 1 29.3 15.2 4.7 0.91 2.6 Comparative Example 2 26.8 18.9 5.3 0.88 2.5 Comparative Example 3 31.5 12.7 3.2 0.93 2.7 Comparative Example 4 28.1 17.5 6.1 0.85 2.4 Comparative Example 5 32.7 14.3 8.9 0.95 2.8 Comparative Example 6 33.2 11.6 2.9 0.94 2.7 Comparative Example 7 30.8 16.8 3.7 0.90 2.6 Comparative Example 8 28.9 19.4 4.5 0.89 2.5 Combined with the above content, it can be seen that the 7-day compressive strength of Examples 1-4 is significantly higher than that of all comparative examples. Among them, the strength of Comparative Example 1 is reduced by 19.5% compared with that of Example 1, indicating that the silane coupling agent modification effectively improves the mechanical properties at high temperature by enhancing the interfacial bonding between zirconium silicate and the cement matrix. The strength of Comparative Example 4 is reduced by 22.8% compared with that of Example 1, indicating that the acid activation treatment of red mud significantly stimulates its activity and enhances its density. The compressive strength loss rate of Example 1 is only 8.4%, which is much lower than that of Comparative Example 1 and Comparative Example 8. Magnesium borate whiskers and halloysite form a three-dimensional network structure, which inhibits the expansion of microcracks in a 200°C thermal cycle and improves thermal shock resistance. The microcapsules release repair substances in response to temperature to repair thermal stress damage.

[0047] In addition, the agglomeration rate of Example 1 is only 1.1%, while the agglomeration rate of Comparative Example 5 is as high as 8.9%. This is because the silane coupling agent can modify the surface of the microcapsules, reduce their surface energy, and prevent moisture absorption and agglomeration. The corrosion resistance coefficient of Example 1 is 0.98, which is much higher than that of Comparative Example 4. This is because the aluminum and iron oxides in the red mud activated micropowder react with sulfate to form a dense layer, which inhibits the penetration of corrosive ions.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A high temperature resistant oil well cement composite enhancer, characterized in that: The invention comprises the following materials in parts by weight: 40-50 parts of silane coupling agent modified zirconium silicate, 20-25 parts of red mud-based activated micropowder, 8-10 parts of fly ash, 10-12 parts of silane coupling agent modified microcapsules, 4-6 parts of magnesium borate whiskers, 2-3 parts of carbon nanotubes and 1-1.5 parts of halloysite.

2. The high temperature resistant oil well cement composite reinforcing agent according to claim 1, characterized in that: The preparation method of the silane coupling agent modified zirconium silicate comprises: dispersing zirconium silicate powder in ethanol, ultrasonically treating for 25-35 minutes, adding silane coupling agent KH560, stirring and reacting at 55-65° C. for 3-5 hours, and centrifugally drying to obtain the silane coupling agent modified zirconium silicate.

3. The high temperature resistant oil well cement composite reinforcing agent according to claim 2, characterized in that: The usage ratio of the zirconium silicate powder, ethanol and silane coupling agent is 10 g: 200-300 mL: 0.3-0.4 g.

4. The high temperature resistant oil well cement composite reinforcing agent according to claim 1, characterized in that: The red mud-based activated micropowder preparation method comprises: washing the red mud with water to remove soluble salts, drying at 50-60°C for 10-12 hours, and then crushing the red mud to less than 200 mesh; mixing the red mud with 4-6% dilute sulfuric acid at a solid-liquid ratio of 1g / 3-5mL, heating the red mud with microwaves at 110-120°C for reaction for 30-40 minutes, filtering, calcining at 750-850°C for 1-2 hours, and ball milling the red mud to less than 600 mesh.

5. The high temperature resistant oil well cement composite reinforcing agent according to claim 1, characterized in that: The preparation method of the silane coupling agent modified microcapsules comprises: mixing silane coupling agent KH-550 with ethanol and water, adjusting the pH to 4.5-5.5 with acetic acid, adding microcapsules, stirring at 55-65° C. for 1.5-2.5 hours, centrifuging, washing, and drying to obtain the microcapsules.

6. The high temperature resistant oil well cement composite reinforcing agent according to claim 5, characterized in that: The usage ratio of the silane coupling agent, ethanol, water and microcapsules is 3-5 g: 60-100 mL: 6-10 mL: 15-20 g.

7. The high temperature resistant oil well cement composite reinforcing agent according to claim 5, characterized in that: The preparation method of the microcapsules comprises: melting and mixing solid paraffin and liquid paraffin to obtain an oil phase, mixing deionized water and sodium lauryl sulfate to obtain an aqueous phase, slowly pouring the oil phase into the aqueous phase, stirring and shearing, forming an O / W emulsion, dropwise adding ethyl orthosilicate into the emulsion, and simultaneously dropwise adding ammonia water to adjust the pH to 8.5-9.5, stirring at a temperature of 45-55° C. and 450-550 rpm for 2-3 hours, heating to 60-65° C. and continuing stirring for 50-60 minutes to promote condensation, and washing, drying, and sieving after centrifugal separation to obtain microcapsules with an average particle size of 60-100 μm.

8. The high temperature resistant oil well cement composite reinforcing agent according to claim 7, characterized in that: The usage ratio of the solid paraffin, liquid paraffin, deionized water, sodium lauryl sulfate and ethyl orthosilicate is (40-50) g: (40-50) g: (190-210) mL: (0.5-1.5) g: (18-22) g.

9. The high temperature resistant oil well cement composite reinforcing agent according to claim 7, characterized in that: The stirring and shearing speed is 9000-11000 rpm, and the time is 10-15 minutes.

10. A method for preparing a high temperature resistant oil well cement composite reinforcing agent according to any one of claims 1 to 9, characterized in that the steps include: Silane coupling agent modified zirconium silicate, red mud-based activated micropowder and fly ash are put into a high-speed mixer for mixing; silane coupling agent modified microcapsules and magnesium borate whiskers are added, and a polycarboxylate water-reducing agent aqueous solution is added for ultrasonic dispersion, and carbon nanotubes are pre-dispersed in an ethylene glycol solution, and after high-pressure homogenization, they are added together with halloysite into the system; large particles are removed through three-level vibration screening of 400 mesh, 800 mesh and 1250 mesh, and the product is obtained after air flow crushing to D50=8-12 μm in an environment with relative humidity ≤30%.