Corrosion-resistant composite material for well cementing and method for preparing the same
By employing a multi-dimensional, multi-gradient anti-corrosion design, and utilizing the synergistic effects of materials such as nitric acid-pressurized lithium extraction slag, asbestos tailings, KH2PO4 microcapsules, and fluorapatite, the problem of the single anti-corrosion path in existing CO2 corrosion-resistant materials is solved, achieving efficient CO2 erosion inhibition and material performance improvement.
Patent Information
- Application Number
- CN202610957932.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-30
- Publication Date
- 2026-11-03
AI Technical Summary
Existing CO2 corrosion-resistant cementing materials have a single corrosion protection path and cannot effectively block the diffusion of molecular-level CO2, resulting in poor corrosion resistance.
A multi-component, multi-gradient anti-corrosion design is adopted, using lithium extraction slag under pressure with nitric acid, asbestos tailings and calcium sulfoaluminate as functional fillers, KH2PO4 microcapsules as self-responsive repair materials, and fluorapatite-supported lanthanum aminotrimethylphosphonate chelate and nanoporous silica-supported active magnesium oxide powder as corrosion-resistant reinforcing materials, forming a multi-component synergistic anti-CO2 corrosion mechanism.
It effectively inhibits CO2 erosion, significantly improves the compressive strength and permeability of cementing cement, reduces CO2 diffusion channels, enhances the corrosion resistance of materials, and reduces environmental pollution.
Smart Images
Figure CN123026397A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of cementing materials technology for oil and gas field development, specifically to an anti-corrosion composite material for cementing and its preparation method. Background Technology
[0002] Cement stone is prone to carbonation and decalcification in high-concentration CO2 (including supercritical CO2) environments. After CO2 enters the cement stone, it reacts with hydration products Ca(OH)2 and high-calcium-silicon ratio CSH gel to form calcium carbonate, which is further converted into soluble Ca(HCO3)2. This leads to increased porosity, reduced strength, and a significant increase in permeability of the cement stone, ultimately resulting in the loss of its interlayer sealing function and causing problems such as casing corrosion and storage leakage.
[0003] Existing CO2 corrosion-resistant cementing materials improve density and reduce permeability by adding anti-corrosion fillers or nanomaterials, or by using phosphate / phosphonate inhibitors. While these methods can partially improve the system's corrosion resistance, they still suffer from limited corrosion protection pathways and functions, only achieving micron-level pore sealing and failing to prevent molecular-level CO2 diffusion, resulting in poor corrosion resistance. Therefore, there is an urgent need to develop a novel, highly efficient CO2 corrosion-resistant composite material system with diverse synergistic mechanisms. Summary of the Invention
[0004] To overcome the aforementioned shortcomings of existing technologies, this invention proposes a high-efficiency and environmentally friendly corrosion-resistant composite material for cementing and its preparation method. This material adopts a "multi-element, multi-gradient corrosion protection" design concept to address the problem of a single corrosion protection path in existing technologies.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a corrosion-resistant composite material for cementing, comprising the following raw materials by weight percentage: Functional filler: 45-60%; Self-responsive repair material: 20-25%; Corrosion-resistant reinforcing materials: 20-30%; The functional filler is a mixture of lithium extraction slag under pressure with nitric acid, asbestos tailings, and calcium sulfoaluminate; The self-responsive repair material is KH2PO4 microcapsules; The corrosion-resistant reinforcing material is a mixture of fluorapatite-supported lanthanum aminotrimethylphosphonate chelate and nanoporous silica-supported active magnesium oxide powder.
[0006] Furthermore, the mass ratio of nitric acid pressure lithium extraction slag, asbestos tailings, and calcium sulfoaluminate in the functional filler is 6:2:1.
[0007] Furthermore, in the corrosion-resistant reinforcing material, the mass ratio of fluorapatite-supported lanthanum aminotrimethylphosphonate chelate to nanoporous silica-supported active magnesium oxide powder is 3:2.
[0008] Furthermore, the nitric acid pressure lithium extraction slag contains SiO2 content >70%, Al2O3 content >20%, and the median particle size of the nitric acid pressure lithium extraction slag is 1~20 μm; the asbestos tailings are heat-treated at 1200℃, in which SiO2 content >45%, MgO content >30%, and the median particle size of the asbestos tailings is 1~20 μm.
[0009] Furthermore, the median particle size of the KH2PO4 microcapsules is 20–50 μm, and the capsule wall thickness is 1–5 μm.
[0010] Furthermore, the KH2PO4 microcapsules were prepared using a method comprising the following steps: (1) Dissolve KH2PO4 in deionized water to form a solution A with a KH2PO4 saturation of 0.9, and obtain core material grains after spray drying; (2) Mix diethylaminoethyl methacrylate monomer (30% by mass of core material grains) and methylenebisacrylamide crosslinking agent (1.2 mol% by molar amount of diethylaminoethyl methacrylate monomer) evenly to obtain monomer phase; Sodium dodecyl sulfate was dissolved in deionized water to prepare an aqueous solution with a sodium dodecyl sulfate mass fraction of 0.2-0.5%. Initiator K2S2O8, accounting for 0.6% of the mass of the above diethylaminoethyl methacrylate monomer, was added, stirred and dissolved, and the pH was adjusted to 7.0 to obtain the aqueous phase. Add KH2PO4 to the aqueous phase to achieve a KH2PO4 saturation of 0.8~0.9. The monomer phase was slowly added to the aqueous phase at a volume ratio of 9:1. The mixture was dispersed at 800-1000 rpm for 10 min to emulsify and obtain solution B. Then the stirring speed was reduced to 350-450 rpm. (3) Add core material grains to solution B, the mass ratio of solution B to core material grains is 12:1, stir evenly, and purge with nitrogen for 30 min to remove oxygen; heat to 65°C and maintain the temperature for 4 h for polymerization reaction. (4) After the polymerization reaction is completed, the reaction system is cooled to room temperature, the microcapsules are separated by filtration, washed once with an aqueous solution of KH2PO4 with a saturation of 0.8-0.9, washed once with ethanol, and then vacuum dried at 45°C until the water content is <2% to obtain dried microcapsules; (5) Dissolve KH550 silane coupling agent in ethanol to prepare an ethanol solution with a KH550 mass fraction of 1.0%, add dried microcapsules at a liquid-to-solid ratio of 10 mL / g, stir at room temperature for 40 min for pretreatment, filter and separate, and vacuum dry at 50°C for 2 h to obtain pretreated microcapsules. (6) Disperse the pretreated microcapsules in anhydrous ethanol, control the mass ratio of microcapsules to anhydrous ethanol to be 1:9, and disperse evenly under mechanical stirring at 300 rpm to obtain a microcapsule dispersion. (7) Add 20% of the dry weight of the microcapsules of tetraethyl orthosilicate and 35% of the dry weight of the microcapsules of deionized water to the microcapsule dispersion, adjust the pH to 9-10 with ammonia water, and stir at 300-500 rpm for 100 min at 30°C to hydrolyze and condense the tetraethyl orthosilicate to generate silica and coat the surface of the microcapsules; after the reaction is completed, filter and separate, wash twice with ethanol, and vacuum dry at 45°C to obtain KH2PO4 microcapsules with silica coating.
[0011] Furthermore, the fluorapatite-supported lanthanum aminotrimethylphosphonate chelate was prepared using a method comprising the following steps: Fluorapatite with a particle size of 120 nm was dispersed in deionized water to prepare a suspension A with a fluorapatite mass fraction of 8%. Add aminotrimethylphosphonic acid (35% of the mass of fluorapatite) to suspension A, adjust the pH to 5-6, and stir at room temperature for 30 min to form suspension B. Lanthanum nitrate hexahydrate, in an amount equal to that of aminotrimethylphosphonic acid, was added to suspension B. The mixture was heated to 60°C and stirred for 2 hours to form suspension C. The suspension C was filtered to separate the solid product; the solid product was washed three times with deionized water, and the washed solid product was vacuum dried at 80°C and then air-jet pulverized to 200 mesh to obtain the fluorapatite-supported lanthanum aminotrimethylphosphonic acid chelate.
[0012] Furthermore, the nanoporous silica-supported active magnesium oxide powder is prepared using a method comprising the following steps: Mesoporous silica with a pore size of 25 nm was dispersed in anhydrous ethanol, and the mass ratio of mesoporous silica to anhydrous ethanol was controlled at 1:9 to obtain a mesoporous silica dispersion. Add 30% by mass of active magnesium oxide to the mesoporous silica dispersion to obtain a mixture with a particle size of active magnesium oxide <20 nm. The mixture was ultrasonically dispersed for 30 min to uniformly disperse and load the active magnesium oxide onto the pores and surface of the mesoporous silica, thus obtaining a loaded suspension. The loaded suspension was rotary evaporated to remove the anhydrous ethanol solvent, resulting in a loaded solid powder. The solid powder was dried in an inert atmosphere at 120°C to obtain nanoporous silica-supported active magnesium oxide powder.
[0013] A second aspect of this invention provides a method for preparing a corrosion-resistant composite material for cementing, comprising the following steps: Step 1: Weigh the functional filler, self-responsive repair material, and corrosion-resistant reinforcing material according to their respective weight percentages; Step 2: First, add each component of the functional filler to the dry powder mixer and mix them evenly at 400 rpm for 10 minutes. Step 3: Add self-responsive repair material and corrosion-resistant reinforcing material, and continue stirring for 5 minutes until evenly mixed to obtain corrosion-resistant composite material for well cementing.
[0014] Furthermore, the functional fillers are pretreated before use: the lithium extraction slag from nitric acid pressure and the asbestos tailings are crushed to a median particle size of 1~20 μm, and the asbestos tailings are preheated at 1200℃.
[0015] The anti-corrosion composite material for cementing of this invention has the following mechanism of multi-component synergistic resistance to CO2 corrosion.
[0016] The nitric acid-pressurized lithium extraction slag and asbestos tailings in the functional filler are rich in active silica-alumina components (SiO2, Al2O3), which can undergo a secondary hydration reaction with the cement hydration product Ca(OH)2 to generate CSH gel with a low calcium-to-silicon ratio. This reduces the free Ca in the cement stone. 2+ The concentration of calcium sulfoaluminate is reduced, decreasing the substances that react with CO2. On the other hand, it refines the pore structure, cutting off the rapid diffusion channels of CO2. Simultaneously, the early hydration of calcium sulfoaluminate forms ettringite, further increasing the matrix density and buying time for subsequent chemical defense.
[0017] When CO2 breaches the physical barrier and the outer shell of the self-responsive repair material (KH2PO4 microcapsules), causing a drop in local pH, the polymer inner shell of the KH2PO4 microcapsules responds. This shell is polymerized from diethylaminoethyl methacrylate, and its side chains contain tertiary amines. Under the normal alkaline environment of cement stone (pH≈12~13), the polymer is in a contracted and compacted state; when the pH drops to the acidic range, the tertiary amines protonate, the polymer chains change from a hydrophobic state to a hydrophilic state, the shell swells, permeability increases, and may even rupture, thereby promoting the slow release of KH2PO4. The released KH2PO4 rapidly reacts with the active magnesium oxide supported on nanoporous silica in the corrosion-resistant reinforcing material and the active MgO released from asbestos tailings in the functional filler, generating in situ MgKPO4·6H2O with low solubility and micro-expansion characteristics in the presence of water. This phase is chemically stable in a CO2 environment and can actively deposit at the bottlenecks of pores and microcracks to form a dense blocking network, which essentially blocks the further diffusion of CO2.
[0018] Corrosion-resistant reinforcing materials further leverage multi-scale synergistic effects: Fluoroapatite itself has extremely strong acid resistance and can serve as an inert anti-corrosion skeleton to maintain the structural integrity of cement stone; the loaded aminotrimethylphosphonic acid can chelate the Ca produced during cement hydration. 2+ This reduces the content of reactants that can be corroded by CO2; chelated lanthanum ions (La 3+ It can interact with invading CO3 2- or HCO3 - A deposition reaction occurs, generating in-situ insoluble lanthanum carbonate (La2(CO3)3), further blocking ion migration channels. In the presence of water, the active magnesium oxide supported on nanoporous silica can react with intruding CO2 to form micro-expandable magnesium carbonate (MgCO3), compensating for cement stone shrinkage. Simultaneously, it can react with KH2PO4 released from the self-responsive repair material to form MgKPO4·6H2O, creating a synergistic enhancement. Furthermore, the mesoporous silica can participate in the secondary hydration of cement, refining the hydration product grains and reducing matrix porosity.
[0019] Through the synergistic effect of the above-mentioned multi-component and multi-gradient composite materials, the composite material of the present invention achieves effective inhibition of CO2 erosion.
[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a multi-scale synergistic mechanism to resist CO2 corrosion, overcoming the limitations of traditional single-material corrosion resistance and giving it excellent CO2 corrosion resistance. The preparation process is simple and cost-controllable. Using solid waste as the main raw material significantly reduces environmental pollution and lowers material costs.
[0021] 2. This invention uses nitric acid-pressurized lithium extraction slag, asbestos tailings, and calcium sulfoaluminate as functional fillers. The nitric acid-pressurized lithium extraction slag and asbestos tailings, as active silica-alumina components, undergo a secondary hydration reaction with cement hydration products, reducing the system's calcium content. 2+ Concentration inhibits CO2 reactivity; calcium sulfoaluminate provides the early structural framework for the system. The combined effect of these three factors increases matrix density and reduces the penetration path of corrosive media.
[0022] 3. The self-responsive repair material and corrosion-resistant reinforcing material provided by this invention form a secondary dense phase MgKPO4·6H2O through a synergistic reinforcement mechanism, fundamentally hindering CO2 diffusion and blocking carbonization. When the pH of the carbonized region decreases, the self-responsive repair material slowly releases KH2PO4, which reacts with the active magnesium oxide supported on nanoporous silica and the active MgO contained in asbestos tailings in the functional filler, jointly promoting the in-situ generation of MgKPO4·6H2O. This product is stable and insoluble in water in a CO2 environment, self-growing in pores and microcracks, rapidly blocking channels and crack tips, forming a dense network, and significantly reducing matrix permeability.
[0023] 4. The corrosion-resistant reinforcing material provided by this invention improves the mechanical properties and corrosion resistance of the matrix through a multi-scale synergistic reinforcement mechanism. Fluoroapatite itself has a much higher acid resistance than conventional filler materials and can serve as an inert anti-corrosion skeleton; the loaded aminotrimethylphosphonic acid can chelate the Ca produced during cement hydration. 2+ This reduces the content of reactants that can be corroded by CO2; chelated lanthanum ions can react in situ with carbonate ions to form insoluble lanthanum carbonate, blocking pore channels. Mesoporous silica can participate in the secondary hydration of cement, refining the grains of hydration products and reducing the porosity of the matrix; on the other hand, the supported active magnesium oxide can react with intruding CO2 to form micro-expandable magnesium carbonate, and can also react with KH2PO4 released from the self-responsive repair material to form MgKPO4·6H2O, compensating for cement stone shrinkage, while simultaneously blocking corrosion channels in situ, effectively preventing the penetration of CO2 and acidic media from the formation. Attached Figure Description
[0024] Figure 1 The thermogravimetric analysis curves of Examples 1-3 and cement paste after 28 days of corrosion in the same CO2 corrosive environment are shown. Detailed Implementation
[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0026] In this embodiment of the invention, the functional filler used is a mixture of nitric acid pressure lithium extraction slag, asbestos tailings, and calcium sulfoaluminate in a mass ratio of 6:2:1. The nitric acid pressure lithium extraction slag has a SiO2 content >70%, an Al2O3 content >20%, and a median particle size of 1~20 μm; the asbestos tailings are heat-treated at 1200℃, with a SiO2 content >45%, an MgO content >30%, and a median particle size of 1~20 μm; the calcium sulfoaluminate is a commercially available product with an effective content >90% and a median particle size of 5-10 μm.
[0027] In this embodiment of the invention, the self-responsive repair material used is KH2PO4 microcapsules. The median particle size of the KH2PO4 microcapsules is 20~50 μm, and the capsule wall thickness is 1~5 μm.
[0028] KH2PO4 microcapsules were prepared using a method comprising the following steps: (1) KH2PO4 is dissolved in deionized water to form a solution A with a KH2PO4 saturation of 0.9. After spray drying (inlet 180℃ / outlet 80℃), the core material grains are obtained. (2) Mix diethylaminoethyl methacrylate monomer (30% by mass of core material grains) and methylenebisacrylamide crosslinking agent (1.2 mol% by molar amount of diethylaminoethyl methacrylate monomer) evenly to obtain monomer phase; Sodium dodecyl sulfate was dissolved in deionized water to prepare an aqueous solution with a sodium dodecyl sulfate mass fraction of 0.2-0.5%. Initiator K2S2O8, accounting for 0.6% of the mass of the above diethylaminoethyl methacrylate monomer, was added, stirred and dissolved, and the pH was adjusted to 7.0 to obtain the aqueous phase. Add KH2PO4 to the aqueous phase to achieve a KH2PO4 saturation of 0.8~0.9. The monomer phase was slowly added to the aqueous phase at a volume ratio of 9:1. The mixture was dispersed at 800-1000 rpm for 10 min to emulsify and obtain solution B. Then the stirring speed was reduced to 350-450 rpm. (3) Add core material grains to solution B, the mass ratio of solution B to core material grains is 12:1, stir evenly, and purge with nitrogen for 30 min to remove oxygen; heat to 65°C and maintain the temperature for 4 h for polymerization reaction. (4) After the polymerization reaction is completed, the reaction system is cooled to room temperature, the microcapsules are separated by filtration, washed once with an aqueous solution of KH2PO4 with a saturation of 0.8-0.9, washed once with ethanol, and then vacuum dried at 45°C until the water content is <2% to obtain dried microcapsules; (5) Dissolve KH550 silane coupling agent in ethanol to prepare an ethanol solution with a KH550 mass fraction of 1.0%, add dried microcapsules at a liquid-to-solid ratio of 10 mL / g, stir at room temperature for 40 min for pretreatment, filter and separate, and vacuum dry at 50°C for 2 h to obtain pretreated microcapsules. (6) Disperse the pretreated microcapsules in anhydrous ethanol, control the mass ratio of microcapsules to anhydrous ethanol to be 1:9, and disperse evenly under mechanical stirring at 300 rpm to obtain a microcapsule dispersion. (7) Add 20% of the dry weight of the microcapsules of tetraethyl orthosilicate and 35% of the dry weight of the microcapsules of deionized water to the microcapsule dispersion, adjust the pH to 9-10 with ammonia water, and stir at 300-500 rpm for 100 min at 30°C to hydrolyze and condense the tetraethyl orthosilicate to generate silica and coat the surface of the microcapsules; after the reaction is completed, filter and separate, wash twice with ethanol, and vacuum dry at 45°C to obtain KH2PO4 microcapsules with silica coating.
[0029] In this embodiment of the invention, the corrosion-resistant reinforcing material used is a mixture of fluorapatite-supported lanthanum aminotrimethylphosphonate chelate and nanoporous silica-supported active magnesium oxide powder in a mass ratio of 3:2.
[0030] The fluorapatite-supported lanthanum aminotrimethylphosphonate chelate was prepared using a method comprising the following steps: Fluorapatite with a particle size of 120 nm was dispersed in deionized water to prepare a suspension A with a fluorapatite mass fraction of 8%. Add aminotrimethylphosphonic acid (35% of the mass of fluorapatite) to suspension A, adjust the pH to 5-6, and stir at room temperature for 30 min to form suspension B. Lanthanum nitrate hexahydrate, in an amount equal to that of aminotrimethylphosphonic acid, was added to suspension B. The mixture was heated to 60°C and stirred for 2 hours to form suspension C. The suspension C was filtered to separate the solid product; the solid product was washed three times with deionized water, and the washed solid product was vacuum dried at 80°C and then air-jet pulverized to 200 mesh to obtain the fluorapatite-supported lanthanum aminotrimethylphosphonic acid chelate.
[0031] Nanoporous silica-supported active magnesium oxide powder is prepared by a method including the following steps: Mesoporous silica with a pore size of 25 nm was dispersed in anhydrous ethanol, and the mass ratio of mesoporous silica to anhydrous ethanol was controlled at 1:9 to obtain a mesoporous silica dispersion. Add 30% by mass of active magnesium oxide to the mesoporous silica dispersion to obtain a mixture with a particle size of active magnesium oxide <20 nm. The mixture was ultrasonically dispersed for 30 min to uniformly disperse and load the active magnesium oxide onto the pores and surface of the mesoporous silica, thus obtaining a loaded suspension. The loaded suspension was rotary evaporated to remove the anhydrous ethanol solvent, resulting in a loaded solid powder. The solid powder was dried in an inert atmosphere at 120°C to obtain nanoporous silica-supported active magnesium oxide powder.
[0032] In this embodiment of the invention, the preparation method of the corrosion-resistant composite material for cementing is as follows: Weigh out the functional filler, self-responsive repair material, and corrosion-resistant reinforcement material according to their respective weight percentages; First, add each component of the functional filler to a dry powder mixer and mix them evenly at 400 rpm for 10 minutes. Add self-responsive repair material and corrosion-resistant reinforcing material, continue stirring for 5 minutes until evenly mixed, and the corrosion-resistant composite material for cementing is obtained.
[0033] Example 1, as a preferred embodiment of the present invention, provides a corrosion-resistant composite material for cementing, the composition of which is as follows: Functional filler: 45%; Self-responsive repair materials: 25%; Corrosion-resistant reinforcing material: 30%.
[0034] Example 2, as a preferred embodiment of the present invention, provides a corrosion-resistant composite material for cementing, the composition of which is as follows: Functional filler: 52%; Self-responsive repair materials: 23%; Corrosion-resistant reinforcing material: 25%.
[0035] Example 3, as a preferred embodiment of the present invention, provides a corrosion-resistant composite material for cementing, the composition of which is as follows: Functional filler: 60%; Self-responsive repair materials: 20%; Corrosion-resistant reinforcing material: 20%.
[0036] Comparative Example 1 differs from Example 1 in that it does not contain self-responsive repair material, while all other conditions are the same.
[0037] Comparative Example 2 differs from Example 1 in that it does not contain corrosion-resistant reinforcing materials, while all other conditions are the same.
[0038] Comparative Example 3 differs from Example 1 in that it does not contain functional fillers, while all other conditions are the same.
[0039] For the test example, according to GB / T 19139-2012 standard, the cement slurries of Examples 1-3 and Comparative Examples 1-3 were prepared respectively, with a water-cement ratio of 0.50. Simultaneously, pure Grade G oil well cement slurry was prepared as a blank control, with a water-cement ratio of 0.50. Wherein: Examples 1-3: The composite material of each example was added to Grade G oil well cement at a dosage of 8% of the dry weight of cement to prepare cement slurry. Comparative Examples 1-3: The composite materials of each comparative example were added to Grade G oil well cement at a dosage of 8% of the dry weight of cement to prepare cement slurry. Blank control: pure G-grade oil well cement (i.e., cement paste), water-cement ratio 0.50, without any added composite materials.
[0040] All the cement pastes prepared above were cured and then placed in a CO2 corrosion reactor. The carbonization temperature was 90℃, the total pressure was 10 MPa, the CO2 partial pressure was 5 MPa, and the carbonization period was 7 days and 28 days. The test results of compressive strength, strength retention rate, and permeability are shown in Table 1.
[0041] Table 1. Mechanical properties and permeability test results of cement stone samples
[0042] Table 1 shows that the compressive strength of cement paste (blank control) decreased significantly with prolonged corrosion time, with a loss of 28.7%, while the permeability increased significantly. The cement samples from Examples 1-3 were significantly superior to cement paste in both compressive strength and permeability. With prolonged corrosion time, the compressive strength of the samples from Examples 1-3 only decreased slightly (decay rate <8%), and the permeability was lowest at 28 days. Based on the combined data of compressive strength and permeability, this invention effectively improves the compressive strength of cement stone and reduces its permeability through a multi-mechanism synergy, significantly enhancing the cement stone's resistance to CO2 erosion and exhibiting excellent corrosion resistance. Furthermore, all components are indispensable.
[0043] The calcium carbonate formed during CO2 corrosion of cement stone undergoes thermal decomposition within the 600-750℃ temperature range. Therefore, the CO2 corrosion resistance of cement stone can be evaluated by measuring the weight loss rate within this temperature range using thermogravimetric analysis: the lower the weight loss rate, the stronger the corrosion resistance.
[0044] Figure 1 The thermogravimetric analysis (TGA) curves of Examples 1-3 and cement paste after 28 days of corrosion in the same CO2 corrosive environment are shown. The thermal analysis was conducted on a Mettler Toledo thermal analysis instrument at a heating rate of 10°C / min under nitrogen protection.
[0045] from Figure 1 It can be seen that the weight loss rate (mass loss change value) of the samples in Examples 1-3 in the calcium carbonate thermal decomposition range is significantly lower than that of cement paste, indicating that the CO2 corrosion resistance of the cement system of the present invention is significantly better than that of cement paste.
[0046] 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 corrosion-resistant composite material for cementing wells, characterized in that, Includes the following raw materials by weight percentage: Functional filler: 45-60%; Self-responsive repair material: 20-25%; Corrosion-resistant reinforcing materials: 20-30%; The functional filler is a mixture of lithium extraction slag under pressure with nitric acid, asbestos tailings, and calcium sulfoaluminate; The self-responsive repair material is KH2PO4 microcapsules; The corrosion-resistant reinforcing material is a mixture of fluorapatite-supported lanthanum aminotrimethylphosphonate chelate and nanoporous silica-supported active magnesium oxide powder.
2. The anti-corrosion composite material for cementing according to claim 1, characterized in that, The mass ratio of nitric acid pressure lithium extraction slag, asbestos tailings and calcium sulfoaluminate in the functional packing is 6:2:
1.
3. The anti-corrosion composite material for cementing according to claim 1, characterized in that, In the corrosion-resistant reinforced material, the mass ratio of fluorapatite-supported lanthanum aminotrimethylphosphonate chelate to nanoporous silica-supported active magnesium oxide powder is 3:
2.
4. The anti-corrosion composite material for cementing according to claim 1, characterized in that, The lithium extraction slag produced by nitric acid pressure extraction has a SiO2 content of >70%, an Al2O3 content of >20%, and a median particle size of 1~20 μm; the asbestos tailings, after heat treatment at 1200℃, have a SiO2 content of >45%, an MgO content of >30%, and a median particle size of 1~20 μm.
5. The anti-corrosion composite material for cementing according to claim 1, characterized in that, The median particle size of KH2PO4 microcapsules is 20~50μm, and the capsule wall thickness is 1~5μm.
6. The anti-corrosion composite material for cementing according to claim 1, characterized in that, KH2PO4 microcapsules were prepared using a method comprising the following steps: (1) Dissolve KH2PO4 in deionized water to form a solution A with a KH2PO4 saturation of 0.9, and obtain core material grains after spray drying; (2) Mix diethylaminoethyl methacrylate monomer (30% by mass of core material grains) and methylenebisacrylamide crosslinking agent (1.2 mol% by molar amount of diethylaminoethyl methacrylate monomer) evenly to obtain monomer phase; Sodium dodecyl sulfate was dissolved in deionized water to prepare an aqueous solution with a sodium dodecyl sulfate mass fraction of 0.2-0.5%. Initiator K2S2O8, accounting for 0.6% of the mass of the above diethylaminoethyl methacrylate monomer, was added, stirred and dissolved, and the pH was adjusted to 7.0 to obtain the aqueous phase. Add KH2PO4 to the aqueous phase to achieve a KH2PO4 saturation of 0.8~0.
9. The monomer phase was slowly added to the aqueous phase at a volume ratio of 9:
1. The mixture was dispersed at 800-1000 rpm for 10 minutes to emulsify and obtain solution B. Then the stirring speed was reduced to 350-450 rpm. (3) Add core material grains to solution B, the mass ratio of solution B to core material grains is 12:1, stir evenly, and purge with nitrogen for 30 min to remove oxygen; heat to 65°C and maintain the temperature for 4 h for polymerization reaction. (4) After the polymerization reaction is completed, the reaction system is cooled to room temperature, the microcapsules are separated by filtration, washed once with an aqueous solution of KH2PO4 with a saturation of 0.8-0.9, washed once with ethanol, and then vacuum dried at 45°C until the water content is <2% to obtain dried microcapsules; (5) Dissolve KH550 silane coupling agent in ethanol to prepare an ethanol solution with a KH550 mass fraction of 1.0%, add dried microcapsules at a liquid-to-solid ratio of 10 mL / g, stir at room temperature for 40 min for pretreatment, filter and separate, and vacuum dry at 50°C for 2 h to obtain pretreated microcapsules. (6) Disperse the pretreated microcapsules in anhydrous ethanol, control the mass ratio of microcapsules to anhydrous ethanol to be 1:9, and disperse evenly under mechanical stirring at 300 rpm to obtain a microcapsule dispersion. (7) Add 20% of the dry weight of the microcapsules of tetraethyl orthosilicate and 35% of the dry weight of the microcapsules of deionized water to the microcapsule dispersion, adjust the pH to 9-10 with ammonia water, and stir at 300-500 rpm for 100 min at 30°C to hydrolyze and condense the tetraethyl orthosilicate to generate silica and coat the surface of the microcapsules; after the reaction is completed, filter and separate, wash twice with ethanol, and vacuum dry at 45°C to obtain KH2PO4 microcapsules with silica coating.
7. The anti-corrosion composite material for cementing according to claim 1, characterized in that, The fluorapatite-supported lanthanum aminotrimethylphosphonate chelate was prepared by a method comprising the following steps: Fluorapatite with a particle size of 120 nm was dispersed in deionized water to prepare a suspension A with a fluorapatite mass fraction of 8%. Add aminotrimethylphosphonic acid (35% of the mass of fluorapatite) to suspension A, adjust the pH to 5-6, and stir at room temperature for 30 minutes to form suspension B. Lanthanum nitrate hexahydrate, in an amount equal to that of aminotrimethylphosphonic acid, was added to suspension B. The mixture was heated to 60°C and stirred for 2 hours to form suspension C. The suspension C was filtered to separate the solid product; the solid product was washed three times with deionized water, and the washed solid product was vacuum dried at 80°C and then air-jet pulverized to 200 mesh to obtain the fluorapatite-supported lanthanum aminotrimethylphosphonic acid chelate.
8. The anti-corrosion composite material for cementing according to claim 1, characterized in that, Nanoporous silica-supported active magnesium oxide powder is prepared by a method including the following steps: Mesoporous silica with a pore size of 25 nm was dispersed in anhydrous ethanol, and the mass ratio of mesoporous silica to anhydrous ethanol was controlled at 1:9 to obtain a mesoporous silica dispersion. Add 30% by mass of active magnesium oxide to the mesoporous silica dispersion to obtain a mixture with a particle size of active magnesium oxide <20 nm. The mixture was ultrasonically dispersed for 30 min to uniformly disperse and load the active magnesium oxide onto the pores and surface of the mesoporous silica, thus obtaining a loaded suspension. The loaded suspension was rotary evaporated to remove the anhydrous ethanol solvent, resulting in a loaded solid powder. The solid powder was dried in an inert atmosphere at 120°C to obtain nanoporous silica-supported active magnesium oxide powder.
9. A method for preparing a corrosion-resistant composite material for cementing as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Weigh the functional filler, self-responsive repair material, and corrosion-resistant reinforcing material according to their respective weight percentages; Step 2: First, add each component of the functional filler to the dry powder mixer and mix them evenly at 400 rpm for 10 minutes. Step 3: Add self-responsive repair material and corrosion-resistant reinforcing material, and continue stirring for 5 minutes until evenly mixed to obtain corrosion-resistant composite material for well cementing.
10. The preparation method according to claim 9, characterized in that, The functional fillers are pretreated before use: the lithium extraction slag from nitric acid pressure and the asbestos tailings are crushed to a median particle size of 1~20 μm, and the asbestos tailings are preheated at 1200℃.