A method for preparing a high-temperature cement stone strength degradation inhibitor and its application

Abstract

This invention relates to the field of cementing materials technology, specifically disclosing a method for preparing a high-temperature cement stone strength degradation inhibitor and its application. The inhibitor is prepared using a two-step chemical modification method, based on a silane modifier, combined with active aluminum-containing materials, an activator, an alkaline modifier, and a solvent. Through steps such as silicate hydrolysis, surface grafting of the active aluminum-containing material, and secondary modification in an alkaline environment, a core-shell structured composite functional material is constructed. This material effectively inhibits cement stone strength degradation at temperatures of 180℃ and above, achieving a strength exceeding 40 MPa after 28 days of curing at 240℃. Furthermore, when added at a concentration of 10%, it affects the cement slurry thickening time by less than 65 minutes, while minimally interfering with the rheological properties of the cement slurry. It is suitable for high-temperature cementing operations in deep wells, ultra-deep wells, and thermal recovery wells. This invention combines high-temperature stability with construction friendliness, solving the technical challenges of shortening thickening time and increasing pumping risks associated with traditional aluminum-containing pozzolanic materials.

Description

Technical Field

[0001] This invention relates to the field of cementing materials technology, and in particular to a method for preparing a high-temperature cement stone strength degradation inhibitor and its application. Background Technology

[0002] As global oil and gas exploration and development continues to move towards deeper, ultra-deeper formations and high-temperature resources such as hot dry rocks and geothermal energy, cementing operations face increasingly demanding bottom-hole temperatures, with the highest circulating temperature reaching 230°C or even above 260°C. In such ultra-high temperature environments (usually >180°C), the core challenge for conventional silicate oil well cement stone is long-term strength degradation. The fundamental reason is that the main hydration product of cement—high calcium-silica ratio CSH gel—begins to transform into loosely structured, low-strength dicalcium silicate hydrate and other crystals after the temperature exceeds 110°C, leading to increased porosity and permeability of the cement stone, and severe deterioration of mechanical integrity and interlayer sealing performance.

[0003] Currently, the most common high-temperature resistance technology in the industry is to add silica fume (quartz sand, microsilica, etc.) to cement to adjust the calcium-silica ratio of the system and promote the formation of hydration products with better thermal stability, such as calcareous silica and calcareous hard silica. However, as pointed out by Chinese patent CN116410715A and other patents, relying solely on silica fume has limited effectiveness under ultra-high temperature conditions exceeding 180°C, and cement stone will still experience significant strength degradation after long-term curing. This is because calcareous silica transforms into calcareous hard silica over time, accompanied by an increase in porosity and permeability, ultimately leading to a loose cement stone structure. To address this challenge, the industry has successively developed various high-temperature reinforcing agents and anti-degradation materials. For example, Chinese patent CN116409954A uses a "crystal phase modification" reinforcing agent composed of sodium aluminate, calcium aluminate, metakaolin, etc., aiming to generate more stable phases such as ettringite and anorthite. Another Chinese patent CN118324433A prepares high-silica aluminum-based materials through a high-temperature melting method. Spherical glassy additives utilize their slow reaction characteristics to provide long-term strength support; Chinese patent CN112574730A also utilizes the synergistic effect of ultrafine active SiO2 and Al2O3 to generate a network structure of calcium aluminosilicate to enhance compactness. However, these existing technologies still have significant limitations: First, many reinforcing materials (such as metakaolin, nanomaterials, etc.) have large specific surface areas and high surface energy, and are prone to absorbing water and additives after being incorporated into cement slurry, leading to a sharp increase in slurry viscosity and deterioration of rheological properties, i.e., a severe "thickening" effect. This not only brings great difficulties to on-site mixing and pumping construction, but also limits its application in high-pressure well conditions that require high density and low water-cement ratio. Second, some materials (such as pyrophyllite, epidote, and other minerals used in Chinese patent CN119176694A) either have poor compatibility with additives in the system, or their own reactivity is difficult to control precisely, which may cause engineering problems such as abnormal thickening and poor settling stability.

[0004] Therefore, developing a new type of multifunctional strength degradation inhibitor that can effectively suppress the long-term strength degradation of cement stone under ultra-high temperature conditions without adversely affecting the thickening performance of cement slurry has become the key to breaking through the bottleneck of ultra-high temperature cementing technology and ensuring the safety of deep earth engineering. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned defects in the prior art, especially the strength degradation problem of oil well cement stone in deep wells, ultra-deep wells and thermal recovery wells under long-term high temperature environment above 180°C, and at the same time overcomes the drawbacks of traditional aluminum-containing pozzolanic stabilizers that seriously shorten the cement slurry thickening time and increase the pumping risk.

[0006] This invention provides a high-temperature cement stone strength degradation inhibitor, which aims not only to efficiently maintain the strength stability of cement stone after high-temperature aging, but also to basically not interfere with the normal hydration process of cement paste, ensuring that its thickening performance meets the safe pumping requirements under complex deep well conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An innovative feature of a high-temperature cement stone strength degradation inhibitor is that the inhibitor is a composite functional material prepared by a two-step chemical modification method. The material first constructs an organic-inorganic hybrid interface on the surface of an active material through the hydrolysis and condensation of silicate esters. Then, the interface is reactivated and stabilized by the strong alkaline environment provided by alkaline oxides, ultimately forming a core-shell structure particle that can play a stabilizing and reinforcing role in the high-temperature phase transformation process of cement hydration.

[0009] Specifically, the inhibitor is prepared from the following raw materials through a specific process, with the proportions of each raw material based on 1 part by mass of the silicate ester modifier: silicate ester modifier: 1 part; aluminum-containing active material: 1-5 parts; activator: 0.05-0.1 parts; alkaline oxide modifier: 0.05-0.15 parts; anhydrous ethanol: 5-10 parts; deionized water: 8-14 parts.

[0010] The silicate ester modifier is one or any combination of tetraethyl orthosilicate, methyl orthosilicate, n-propyl orthosilicate, isopropyl orthosilicate, and octyl orthosilicate.

[0011] The active material is selected from one or any combination of boehmite, zeolite, montmorillonite, hydroxyapatite, metakaolin, etc.; its particle size is controlled at 200-600 mesh to ensure that it has good dispersibility and sufficient reaction specific surface area in cement paste.

[0012] The alkaline modifier is one or any combination of calcium oxide, magnesium oxide, calcium hydroxide, sodium hydroxide, and sodium silicate; it provides a critical alkaline environment in the final step, which may promote deeper chemical bonding between the silicate ester modified layer and the components in the cement paste.

[0013] The preparation method of the inhibitor mainly includes the following steps: (1) Pretreatment and hydrolysis of silicate materials: Under gentle heating and stirring, silicate modifiers are added dropwise to a mixed solvent of anhydrous ethanol and water to fully hydrolyze them; (2) Primary modification (construction of silicate layer): Active materials are added to the above hydrolysate, followed by the addition of an activator (such as ammonia water). The grafting and condensation reaction of silicates on the surface of the active material is completed at a specific temperature and time. After washing and drying, silicate modified active materials are obtained; (3) Secondary modification (alkaline pre-reaction): The above primary modification products are dispersed in an alkaline solution prepared by an alkaline modifier and a secondary reaction is carried out at a certain temperature. This process aims to strengthen the modified layer and further increase the inertness of the surface material; (4) Post-treatment: The reaction products are washed and soaked in ethanol to remove residues, and finally dried to obtain the strength decay inhibitor of the present invention.

[0014] The beneficial effects of the present invention: Compared with the prior art, the high-temperature cement stone strength degradation inhibitor provided by the present invention has the following significant advantages:

[0015] (1) The core of the inhibitor prepared by the present invention lies in the synergistic effect of step S4 (silicate modification) and step S6 (alkaline environment secondary modification) to construct a gradient composite shell on the surface of active aluminum-containing materials. First, step S4 uses an activator to catalyze the hydrolysis of silicate ester, and forms a primary organic-inorganic hybrid silicate layer on the surface of active aluminum-containing materials through chemical bonding, which plays a basic isolation role. More importantly, the alkaline oxides (such as calcium oxide and magnesium oxide) introduced in step S6 not only adjust the pH value of the system, but also participate in the reaction as a shell reaction material. In an alkaline environment, the active silanol groups on the surface react in situ with calcium / magnesium ions, transforming the primary silicate layer into a dense, hard and chemically inert calcium silicate or magnesium silicate inorganic shell. This composite shell structure overcomes the defect of the single silane modified layer being prone to premature hydrolysis and shedding in the high alkaline environment of cement slurry, and truly realizes the complete shielding of the active core at low temperature (pumping stage) and the directional release at high temperature (curing stage), which is an unexpected technical effect that cannot be achieved by a single modification technology.

[0016] (2) Since the inhibitor is mainly composed of surface-modified inorganic particles with stable chemical properties, it mainly plays a physical filling and specific interface role in cement slurry. It does not contain highly reactive ions or substances that would rapidly accelerate or delay cement hydration. Therefore, within the effective addition range, it has minimal impact on the thickening time of cement slurry, basically maintaining the initial rheological properties and construction safety window of the cement slurry, and greatly reducing the risk of safe pumping in long sealing sections of deep wells.

[0017] (3) The preparation method is mild and the parameters are controllable, making it easy to achieve large-scale production. The resulting product is compatible with existing oil well cement and admixture systems, can be directly dry-mixed into cement, is easy to use, and is suitable for high-temperature and high-pressure cementing operations under various harsh conditions.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments; Attached Figure Description

[0019] Figure 1 The thickening curve of the oil well cement slurry prepared using the anti-fading material of Comparative Example 1 of the present invention is shown.

[0020] Figure 2 Thickening curve of oil well cement slurry prepared using the anti-fading material of Comparative Example 2 of the present invention.

[0021] Figure 3 Thickening curve of oil well cement slurry prepared using the anti-fading material of Example 1 of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in the present invention should have the ordinary meaning understood by those skilled in the art. The features mentioned above or the features mentioned in the specific examples of the present invention can be combined arbitrarily. These specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0023] Sources of materials used in the embodiments of the present invention

[0024] The oil well cement used is Aksu Grade G high sulfur-resistant oil well cement;

[0025] The quartz sand used is cement quartz sand for cementing oil wells produced by China Petroleum Engineering Institute Technology Research Co., Ltd., with mesh sizes of 200 mesh and 600 mesh respectively;

[0026] The dispersants selected were DRS-1S and DRS-2S, cement dispersants for oil wells produced by China Petroleum Engineering Research Institute Co., Ltd.

[0027] The inorganic suspension stabilizer used is L58, an inorganic suspension stabilizer for cementing oil wells produced by the Technical Research Co., Ltd. of China Petroleum Engineering Institute.

[0028] The retarder used is DRH-3L, a cement retarder for oil wells produced by the Technical Research Company of China Petroleum Engineering Institute.

[0029] The fluid loss reducing agent selected is DRF-3L, a cement fluid loss reducing agent for oil wells produced by the Technical Research Co., Ltd. of China Petroleum Engineering Institute.

[0030] The suspending agent used is DRK-4L, a cement suspending agent for oil wells produced by the Technical Research Company of China Petroleum Engineering Institute.

[0031] Unless otherwise specified, the portions in this application are portions by weight.

[0032] Example 1: This example provides a high-temperature cement stone strength degradation inhibitor, prepared by modifying boehmite. The modifier is tetraethyl orthosilicate, the activator is ammonia, the alkaline modifier is calcium oxide, and the solvents are anhydrous ethanol and deionized water. The mass ratio of tetraethyl orthosilicate, boehmite, ammonia, anhydrous ethanol, deionized water, and calcium oxide is 1:1:0.05:5:8:0.05; wherein, the mesh size of the boehmite is 200 mesh; and the concentration of ammonia is 25%.

[0033] The preparation method of the above-mentioned high-temperature cement stone strength degradation inhibitor includes the following steps:

[0034] S1 was prepared by mixing 5 parts of anhydrous ethanol with 2 parts of deionized water at a water bath temperature of 30℃ and a stirring speed of 200r / min.

[0035] S2 adds 1 part of tetraethyl orthosilicate to the mixed solvent prepared in S1 at a rate of 1 drop per second until the mixture is completely added; thus, mixed solution 1 is obtained.

[0036] S3 adds 1 part of boehmite to the mixed solution 1 prepared by S2 within 20s, mixes for 20s, and obtains mixed solution 2;

[0037] S4 adds 0.05 parts of ammonia water dropwise to the mixed solution 2 prepared by S3 at a rate of 1 drop per second. After the addition is complete, the mixture is reacted at a constant temperature of 30°C for 2 hours with a stirring speed of 200 r / min. After the reaction is stopped, the mixture is vacuum filtered, washed with anhydrous ethanol until the filtrate is clear to remove unreacted substances, and then dried at 60°C to obtain the modified boehmite precursor.

[0038] S5. Add calcium oxide (0.05 times the mass of tetraethyl orthosilicate) to deionized water (6 times the mass of tetraethyl orthosilicate) to allow it to react and disperse fully, thus preparing an alkaline solution.

[0039] S6. The modified boehmite precursor obtained in step S4 is added to the alkaline solution prepared in step S5, and the reaction is carried out for 4 hours under the conditions of 30°C water bath and 200r / min stirring.

[0040] S7 Wash the material from step S6 with deionized water five times, filter it, soak it in anhydrous ethanol for 12 hours, and finally dry it at 60°C to obtain the high-temperature cement stone strength degradation inhibitor.

[0041] Example 2: This example provides a high-temperature cement stone strength degradation inhibitor, prepared by zeolite modification. The modifier is methyl orthosilicate, the activator is sodium hydroxide solution, the alkaline modifier is magnesium oxide, and the solvents are anhydrous ethanol and deionized water. The mass ratio of methyl orthosilicate, zeolite, sodium hydroxide solution, anhydrous ethanol, deionized water, and magnesium oxide is 1:5:0.1:10:14:0.15; wherein, the zeolite has a mesh size of 600; and the sodium hydroxide solution has a concentration of 5%.

[0042] The preparation method of the above-mentioned high-temperature cement stone strength degradation inhibitor includes the following steps:

[0043] S1 was prepared by mixing 10 parts of anhydrous ethanol with 8 parts of deionized water at a water bath temperature of 60℃ and a stirring speed of 400r / min.

[0044] S2 adds 1 part of methyl orthosilicate to the mixed solvent prepared in S1 at a rate of 2 drops per second until the solution is completely added; thus obtaining mixed solution 1.

[0045] S3 adds 5 parts of zeolite to the mixed solution 1 prepared by S2 within 20s, mixes for 20s, and obtains mixed solution 2.

[0046] S4 adds 0.1 parts of sodium hydroxide solution to mixed solution 2 prepared in S3 at a rate of 2 drops per second. After the addition is complete, the mixture is reacted at a constant temperature of 60°C for 6 hours with a stirring speed of 400 r / min. After the reaction is stopped, the mixture is vacuum filtered, washed with anhydrous ethanol until the filtrate is clear to remove unreacted substances, and then dried at 60°C to obtain the modified zeolite precursor.

[0047] S5. Add magnesium oxide, which is 0.15 times the mass of methyl orthosilicate, to deionized water, which is 6 times the mass of methyl orthosilicate, to allow it to react and disperse fully, and prepare an alkaline solution.

[0048] S6. The modified zeolite precursor obtained in step S4 is added to the alkaline solution prepared in step S5, and the reaction is carried out for 12 hours under the conditions of 60°C water bath and 400r / min stirring.

[0049] S7 Wash the material from step S6 with deionized water five times, filter it, soak it in anhydrous ethanol for 12 hours, and finally dry it at 60°C to obtain the high-temperature cement stone strength degradation inhibitor.

[0050] Example 3: This example provides a high-temperature cement stone strength degradation inhibitor, prepared by modifying montmorillonite. The modifier is n-propyl orthosilicate, the activator is sodium silicate solution, the alkaline modifier is calcium hydroxide, and the solvents are anhydrous ethanol and deionized water. The mass ratio of n-propyl orthosilicate, montmorillonite, sodium silicate solution, anhydrous ethanol, deionized water, and calcium hydroxide is 1:2:0.08:8:8:0.1; wherein, the montmorillonite has a mesh size of 325; and the sodium silicate solution has a concentration of 45%.

[0051] The preparation method of the above-mentioned high-temperature cement stone strength degradation inhibitor includes the following steps:

[0052] S1 was prepared by mixing 8 parts of anhydrous ethanol with 2 parts of deionized water at a water bath temperature of 40℃ and a stirring speed of 300r / min.

[0053] S2 adds 1 part of n-propyl orthosilicate dropwise to the mixed solvent prepared in S1 at a rate of 1 drop per second until the solution is completely added; thus obtaining mixed solution 1.

[0054] S3 adds 2 parts of montmorillonite to the mixed solution 1 prepared by S2 within 20s, mixes for 20s, and obtains mixed solution 2;

[0055] S4 adds 0.08 parts of sodium silicate solution to mixed solution 2 prepared in S3 at a dropping rate of 1 drop per second. After the addition is complete, the mixture is reacted at a constant temperature of 60°C for 4 hours with a stirring speed of 300 r / min. After the reaction is stopped, the mixture is vacuum filtered, washed with anhydrous ethanol until the filtrate is clear to remove unreacted substances, and then dried at 60°C to obtain the modified montmorillonite precursor.

[0056] S5. Add calcium hydroxide (0.1 times the mass of n-propyl orthosilicate) to deionized water (6 times the mass of n-propyl orthosilicate) to allow it to react and disperse fully, thus preparing an alkaline solution.

[0057] S6. The modified montmorillonite precursor obtained in step S4 is added to the alkaline solution prepared in step S5, and the reaction is carried out for 8 hours under the conditions of 60°C water bath and 300r / min stirring.

[0058] S7 Wash the material from step S6 with deionized water five times, filter it, soak it in anhydrous ethanol for 12 hours, and finally dry it at 60°C to obtain the high-temperature cement stone strength degradation inhibitor.

[0059] Example 4: This Example 4 provides a high-temperature cement stone strength degradation inhibitor, which differs from Example 1 only in that: the high-temperature cement stone strength degradation inhibitor of Example 4 is prepared by modifying hydroxyapatite, the modifier is isopropyl orthosilicate, the activator is ammonia, the alkaline modifier is magnesium hydroxide, anhydrous ethanol and deionized water; the mass ratio of isopropyl orthosilicate, hydroxyapatite, ammonia, anhydrous ethanol, deionized water and magnesium hydroxide is 1:2:0.1:8:2:0.1; the remaining steps are the same as in Example 1.

[0060] Example 5: This Example 5 provides a high-temperature cement stone strength degradation inhibitor, which differs from Example 1 only in that: the high-temperature cement stone strength degradation inhibitor of Example 5 is prepared by modifying metakaolin, the modifier is octyl orthosilicate, the activator is ammonia, the alkaline modifier is calcium oxide, anhydrous ethanol and deionized water; the mass ratio of octyl orthosilicate, metakaolin, ammonia, anhydrous ethanol, deionized water and calcium oxide is 1:2:0.1:8:2:0.1; the remaining steps are the same as in Example 1.

[0061] Comparative Example 1: This Comparative Example 1 provides a high-temperature cement stone strength degradation inhibitor: 200 mesh quartz sand.

[0062] Comparative Example 2: This Comparative Example 2 provides a high-temperature cement stone strength degradation inhibitor: boehmite (mesh size 325 mesh).

[0063] Comparative Example 3: This Comparative Example 3 provides a high-temperature cement stone strength degradation inhibitor: zeolite (mesh size 325 mesh).

[0064] Comparative Example 4: This Comparative Example 4 provides a high-temperature cement stone strength degradation inhibitor: montmorillonite (mesh size 325 mesh).

[0065] Comparative Example 5: This Comparative Example 5 provides a high-temperature cement stone strength degradation inhibitor: hydroxyapatite (mesh size 325 mesh).

[0066] Comparative Example 6: This Comparative Example 6 provides a high-temperature cement stone strength degradation inhibitor: metakaolin (mesh size 325 mesh).

[0067] Comparative Example 7: This Comparative Example 7 provides a high-temperature cement stone strength degradation inhibitor, which differs from Example 3 only in that: the high-temperature cement stone strength degradation inhibitor of Comparative Example 7 is prepared by modifying montmorillonite, the modifier is n-propyl orthosilicate, the activator is sodium silicate solution, and the solvent is anhydrous ethanol and deionized water; the mass ratio of n-propyl orthosilicate, montmorillonite, sodium silicate solution, anhydrous ethanol and deionized water is 1:2:0.08:8:2; the remaining steps are the same as in Example 3.

[0068] Slurry performance testing

[0069] The high-temperature cement stone strength degradation inhibitors prepared in Examples 1-5 and Comparative Examples 1-7 were applied to oil well cement. The basic formula of the oil well cement slurry was: Aksu G-grade oil well cement + 30% quartz sand (200 mesh) + 20% quartz sand (600 mesh) + 10% strength degradation inhibitor + 2% L58 + 1.2% DRS-1S + 1% DRS-2S + 3% DRK-4L + 5% DRF-3L + 5% retarder DRH-3L + 55% water. Except for cement, other materials were added based on the weight of Aksu G-grade oil well cement, and the liquid-solid ratio was 0.44. The thickening time, fluidity and other properties of the prepared oil well cement slurry were measured at 200℃. The test results are shown in Table 1. The thickening properties of the oil well cement slurry prepared in Examples 1 and Comparative Example 1 at different temperatures are shown in Table 2.

[0070] Table 1. Thickening time and fluidity of oil well cement slurry formulations prepared with different strength degradation inhibitors at 200℃.

[0071] ;

[0072] Table 2. Thickening time of oil well cement slurry prepared in Example 1 and Comparative Example 1 at different temperatures.

[0073] ;

[0074] Table 1 shows the effects of different strength degradation inhibitors on the thickening time and fluidity of oil well cement slurry under simulated downhole conditions of 200℃ / 130MPa. Comparative Example 1 uses quartz sand, a strength degradation inhibitor currently considered to have the least impact on thickening time in the industry. Comparative Example 1 has a thickening time of 465 min and a fluidity of 24 cm. The thickening times of Examples 1-5 range from 398 to 420 min, and the fluidities range from 22.5 to 23.5 cm, with differences from Comparative Example 1 of 45 to 65 min and 0.5 to 1.5 cm, respectively. Figure 1 and Figure 3 Thickening curve analysis shows that the thickening curve of the strength decay inhibitor is similar to that of quartz sand, with a smooth and straight consistency curve that remains at a low level of 10-15 Bc. The right-angle inflection point appears at approximately 7 hours (420 minutes). Compared to... Figure 1 (465 minutes), only slightly shortened, completely within the safe construction range; this indicates that although the core of the strength degradation inhibitor of the present invention is a highly active aluminum material, after modification, its rheological performance and thickening characteristics in cement slurry are very close to those of quartz sand; while the thickening time and fluidity of Comparative Examples 2-5 are 164~284 min and 21~23.5 cm, respectively; among them, the thickening time of Comparative Example 6 (unmodified metakaolin) is as short as 164 min, while that of Example 5 (modified metakaolin) is increased to 412 min; comparison Figure 2 and Figure 3 It can be seen that the thickening time of the unmodified boehmite in Comparative Example 2 was only 183 min, and it was accompanied by "bulging" phenomenon. The thickening time of the modified boehmite in Example 1 recovered to 420 min, which was more than twice as long, and the slurry state was good (no core or bulging). This shows that the unmodified active material reacts too quickly, which seriously threatens the construction safety. The strength decay inhibitor prepared after modification can maintain the slurry fluidity at about 23 cm without thickening phenomenon. Compared with Comparative Example 7, the silicate modification of Comparative Example 7 extended the thickening time of the strength decay inhibitor by 53 min and increased the slurry fluidity, eliminating the core phenomenon of the slurry. However, compared with Example 3, the thickening time of Comparative Example 7 was shortened by 97 min, which is still difficult to meet the requirements of high temperature cementing construction. In summary, the surface modification technology of the present invention effectively passivates the early reaction activity of the active material, eliminates its negative impact on the rheological properties and thickening time of cement slurry, and ensures the safety and pumpability of deep well cementing construction while ensuring the strength in the later stage of high temperature.

[0075] The thickening times of Example 1 (modified boehmite of the present invention) and Comparative Example 1 (quartz sand) at 150℃ and 180℃ are shown in Table 2. At 150℃, the difference in thickening time between Example 1 and Comparative Example 1 is only about 34 min; at 180℃, the difference in thickening time between Example 1 and Comparative Example 1 is only about 32 min. This shows that the modified strength decay inhibitor can effectively meet the safe construction time requirements for cementing operations at 150~200℃.

[0076] Compressive strength test

[0077] The strength degradation inhibitor prepared in Example 1 was applied to oil well cement. The basic formula of the oil well cement slurry was: Aksu G-grade oil well cement + 30% quartz sand (200 mesh) + 20% quartz sand (600) + 10% strength degradation inhibitor + 2% L58 + 1.2% DRS-1S + 1% DRS-2S + 3% DRK-4L + 5% DRF-3L + 5% retarder DRH-3L + 55% water. Except for cement, other materials were added based on the weight of Aksu G-grade oil well cement, and the liquid-solid ratio was 0.44. The compressive strength of the prepared oil well cement slurry was measured at 240℃, and the results are shown in Table 3.

[0078] Table 3 Compressive strength of oil well cement stone at different curing times

[0079] ;

[0080] Table 4. Compressive strength of oil well cement stone in Example 1 and Comparative Example 1, cured at different temperatures for different times.

[0081] ;

[0082] As shown in Table 3, Comparative Example 1, which uses conventional silica sand (silica powder), has a 2-day strength of 24.84 MPa. However, as the curing time is extended to 7 days, the strength drops sharply to 17.58 MPa, and further declines to 13.11 MPa after 28 days, a decrease of nearly 50%. This is consistent with its thickening curve ( Figure 1 While the results were good, the inability to maintain the strength in the later stages presented a stark contrast, confirming that a single silicon source cannot suppress the high-temperature strength degradation of oil well cement stone at 240℃. Comparing Examples 1-5 with Comparative Examples 2-7, both maintained stable high-temperature strength from 2 to 28 days, with long-term strength exceeding 40 MPa after 28 days, significantly higher than Comparative Example 1. This demonstrates that the strength degradation inhibitor of this invention can successfully release its internal active aluminum source under high-temperature and high-alkali conditions, participating in hydration reactions to generate stable high-temperature stable phases such as siliceous calcium silicate or calcium aluminum feldspar. The modification treatment did not sacrifice the material's later-stage chemical activity. As shown in Table 4, at 180℃, the strength of Comparative Example 1 began to decline significantly to 18.20 MPa after 28 days, showing signs of degradation, while the strength of the concrete examples... Example 1 maintains the high-temperature strength of the oil well cement stone at 39.8 MPa. When the temperature rises to 210℃, the strength degradation of Comparative Example 1 intensifies, decreasing to 16.10 MPa after 28 days, while Example 1 enhances the high-temperature strength of the oil well cement stone to 41.8 MPa. Combining the 240℃ data in Table 3, this invention is applicable to deep wells, ultra-deep wells, and hot dry rock cementing at temperatures above 180℃, especially 200~260℃. In summary, this invention, by constructing a "silicate-alkaline oxide" double-layer modified coating structure, achieves the phased release of the active material's "inertization during construction" and "activation during service," thereby ensuring both the thickening performance of the oil well cement slurry and the high-temperature strength of the oil well cement stone, demonstrating outstanding engineering application value.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-temperature cement stone strength degradation inhibitor, characterized in that, The inhibitor is a core-shell structured particle, wherein the core is an aluminum-containing active material, and the shell is a silicate ester hydrolysis condensate and an alkaline inorganic substance, wherein the alkaline inorganic substance is calcium silicate or magnesium silicate; the inhibitor is prepared from the following raw materials through specific steps: based on the silicate ester modifier, its composition is as follows: Silicate ester modifier: 1 part; Aluminum-containing active material: 1-5 parts; Activator: 0.05~0.1 parts; Alkaline modifier: 0.05~0.15 parts; Anhydrous ethanol: 5-10 parts; Deionized water: 8-14 parts; The silicate ester modifier is one or any combination of tetraethyl orthosilicate, methyl orthosilicate, n-propyl orthosilicate, isopropyl orthosilicate, and octyl orthosilicate. The aluminum-containing active material is selected from one or any combination of boehmite, zeolite, montmorillonite, hydroxyapatite, and metakaolin. The alkaline modifier is selected from one or any combination of calcium oxide, magnesium oxide, calcium hydroxide, and magnesium hydroxide. The preparation steps include: S1. Preparation of silicate ester pretreatment solution: Mix anhydrous ethanol (5-10 times the mass of silicate ester modifier) ​​with deionized water (2-8 times the mass of deionized water) and prepare a dispersion solvent by stirring at 200-400 r / min in a water bath at 30-60℃. S2. Hydrolysis of silicate esters: Add the silicate ester modifier dropwise to the dispersion solvent in step S1 at a rate of 1 to 2 drops per second. After the addition is complete, continue stirring to ensure complete hydrolysis. S3. Dispersion of active material: Add aluminum-containing active material, which accounts for 1 to 5 times the mass of silicate ester modifier, to the mixture obtained in step S2 within 20 seconds, and mix and stir for 20 seconds; S4. Silicate modification reaction: Add activator at a rate of 1-2 drops per second, which is 0.05-0.1 times the mass of silicate modifier. After the addition is complete, react at a constant temperature of 30-60℃ and 200-400 r / min for 2-6 hours. After the reaction is completed, vacuum filter the product, wash the product with anhydrous ethanol until the filtrate is clear, and dry it at 60℃ to obtain the silicate modified active material precursor. S5. Preparation of alkaline modification solution: Add 0.05 to 0.15 times the mass of the silicate ester modifier to 6 times the mass of the silicate ester modifier in deionized water, allow it to react and disperse fully, and prepare an alkaline solution; S6. Secondary modification in an alkaline environment: The silicate ester modified active material precursor obtained in step S4 is added to the alkaline solution prepared in step S5, and the reaction is carried out for 4 to 12 hours under the conditions of 30~60℃ water bath and 200~400 r / min stirring, so that the silicate layer on the surface is converted into calcium silicate or magnesium silicate inorganic shell. S7. Post-processing: Wash the material obtained from the reaction in step S6 with deionized water 5 times, filter it, soak it in anhydrous ethanol for 12 hours, and finally dry it at 60°C to obtain the high-temperature cement stone strength degradation inhibitor.

2. The high-temperature cement stone strength degradation inhibitor according to claim 1, characterized in that: The particle size of the active material is 200-600 mesh.

3. The high-temperature cement stone strength degradation inhibitor according to claim 1, characterized in that: The activator is one of the following: 25% ammonia solution, 5% sodium hydroxide solution, or 45% sodium silicate solution.

4. The application of a high-temperature cement stone strength degradation inhibitor as described in any one of claims 1 to 3, characterized in that: It is used in oil well cement slurry that can withstand temperatures of 180℃ and above, and its addition amount is 5~20% of the dry ash mass of the oil well cement.

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