A high-temperature-resistant and strong-bonding plugging cement system for oil and water wells, a preparation method and application thereof

Abstract

The application relates to the technical field of well repairing processes, and discloses a high-temperature-resistant and strong-cementing leak-stopping cement system for oil-water wells as well as a preparation method and application thereof. The leak-stopping cement system is composed of a solid component and a liquid component; the solid component contains cement, active alumina, superfine high-purity silica sand, fiber toughening material, graphene oxide and mud cake modifier; the liquid component contains water and additives; the mud cake modifier is composed of sodium metasilicate salt, silicate mineral micro powder and organic resin; the additives include at least one of a retarder, a suspending agent, a dispersant, a fluid loss additive and a defoaming agent; and the fiber toughening material is a calcium carbonate whisker with a needle-like or fibrous structure. The high-temperature-resistant and strong-cementing leak-stopping cement system of the application still has high strength at high temperature, has strong cementing capacity, ensures the stability and reliability of well repairing operations, and is particularly suitable for casing leak-stopping operations of thick oil wells and high-temperature wells.

Description

Technical Field

[0001] This invention relates to the field of well workover technology, specifically to a high-temperature resistant, strongly cemented plugging cement system for oil and water wells, its preparation method, and its application. Background Technology

[0002] In the later stages of Shengli Oilfield's development, as the water cut increased year by year and the number of old wells grew, the problem of downhole casing damage became increasingly serious, becoming one of the key factors affecting oil and gas production and the company's economic benefits. During long-term oil and gas extraction, the casing is subjected to the combined effects of high temperature and pressure, corrosion, mechanical stress, and geological stress, resulting in damage, deformation, and even breakage. This not only restricts the stability of oilfield production but also seriously threatens wellbore safety and operational efficiency. Therefore, developing a long-term, high-temperature-resistant, and strongly cemented cement plugging system suitable for complex well conditions has become an urgent need to ensure the stable development of Shengli Oilfield and improve its economic benefits.

[0003] Casing damage is a particularly prominent issue in older wells. Traditional repair methods, such as casing windowing and sidetracking, and casing removal and replacement, while effective in certain complex well conditions, are complex, costly, and unsuitable for large-scale implementation. Cement plugging and well repair technology, however, has demonstrated significant practical value in the repair of older wells in oilfields due to its simple process, short construction period, and low cost. By drilling and installing cement plugs at the damaged casing, not only can the wellbore sealing performance be effectively restored, but the service life of oil and water wells can also be significantly extended.

[0004] While existing cement plugging technologies are relatively mature, their durability and bonding strength often fail to meet long-term use requirements under high temperature and pressure. Invention patent CN111315706A describes a high-density micro-fine cement system for high-pressure cementing operations, employing a combination of micro-fine cement and manganese tetroxide to effectively fill micro-cracks and achieve sealing in high-pressure areas. However, this technology is primarily suitable for high-density plugging of micro-cracks. Due to its high density and poor fluidity, it is unsuitable for repairing larger cracks and casing damage in cement plugging processes, and it struggles to meet the strength and long-term durability requirements under complex well conditions.

[0005] Invention patent CN112479635A proposes a high-temperature resistant, large-temperature-difference elastic-toughness cement slurry system, aiming to solve the problem of cement sheath failure during cementing in ultra-deep, high-temperature oil and gas wells. This system improves the mechanical properties of the cement stone under high temperature and large temperature difference environments, particularly the overall sealing performance and compressive strength of the cement sheath, through the application of elastic materials and toughening agents. However, this system overemphasizes toughness under large temperature differences and lacks optimal adaptability to conventional cement plugging operations, making it difficult to meet the wide applicability requirements of materials in actual cement plugging processes.

[0006] Invention patent CN114685125B proposes a high-temperature resistant cement slurry system for heavy oil thermal recovery wells, specifically designed for the high-temperature environment of steam-driven and steam injection processes. It can maintain high compressive strength and durability at temperatures up to 320°C. This system improves the strength and high-temperature resistance of the cement slurry through a combination of high-temperature reinforcing agents, microsilica, and lattice expansion agents, making it particularly suitable for thermal recovery operations in heavy oil wells. While this system focuses on long-term durability and compressive strength under high-temperature conditions, cement plugging processes typically require higher fluidity and rapid sealing capabilities to repair casing damage and form a stable plugging layer. Therefore, this cement system cannot meet the specific needs of cement plugging operations.

[0007] Invention patent CN117659971B describes a high-temperature resistant cement slurry system for cementing hot dry rock, exhibiting excellent high-temperature stability and compressive strength, suitable for cementing operations under extreme high-temperature conditions. This cement slurry system enhances its high-temperature resistance and elasticity by combining raw materials such as nano-silica emulsion and iron ore powder with glass fiber-modified whisker agents and flake talc modifiers. The system formulation emphasizes compressive strength at high temperatures; however, the cementitious properties and durability of the cement paste were not investigated.

[0008] From a production practice perspective, the performance of materials faces particular challenges in the application of sealing systems, especially in high-temperature environments. Existing technologies have some shortcomings in addressing the strength degradation and insufficient bonding strength caused by high-temperature environments: 1. Intensity degradation in high-temperature environments (1) Crystallization of CSH gel At room temperature, CSH (calcium silicate hydrate gel) formed during cement hydration is an amorphous material with good strength. However, at high temperatures, CSH gel recrystallizes to form calcium silicate, a material with a more porous crystal structure and lower strength than CSH gel.

[0009] (2) Transformation of shale into hard silicate As the curing time increases, especially under high-temperature conditions, the siliceous calcium stone will continue to transform into hard siliceous calcium stone. The crystal structure of hard siliceous calcium stone is more porous, which further leads to a decrease in the strength of the cement stone.

[0010] (3) Internal shrinkage and formation of microcracks The transformation of hydration products is accompanied by changes in the internal pore structure, leading to shrinkage within the cement paste. Prolonged high-temperature curing exacerbates this shrinkage, causing the formation and propagation of internal microcracks, ultimately resulting in a significant decrease in strength.

[0011] 2. Weak bonding strength (1) Weakness of the transition zone between the first and second interfaces The interface transition zone between the cement sheath and the casing (interface one) or the formation (interface two) is a relatively weak area in the cement paste. Under high temperature and chemical action, the transition zone may become even weaker, affecting the overall bonding performance.

[0012] (2) Chemically unstable at high temperatures Under high temperature conditions, some minerals in cement stone may decompose or recrystallize, affecting its chemical stability and thus reducing the bonding strength.

[0013] In conclusion, developing a cement-based leak-sealing system with excellent durability and strong bonding properties under high-temperature environments is of paramount importance. This system must not only possess high compressive and tensile strength but also maintain stable structural properties under long-term high-temperature and high-pressure conditions to ensure the long-term sealing capability of the cement-based leak-sealing material. Summary of the Invention

[0014] To overcome the problems of strength degradation and poor bonding performance of existing plugging cement systems under long-term high-temperature environments, this invention provides a high-temperature resistant, strongly bonding plugging cement system for oil and water wells, its preparation method, and its application. The technical solution is as follows: A high-temperature resistant and strongly cemented plugging cement system for oil and water wells, comprising solid and liquid components; the solid components and their respective mass percentages are: cement 40%–60%, activated alumina 1%–3%, ultrafine high-purity silica sand 30%–50%, fiber toughening material 3%–8%, graphene oxide 0.03%–0.1%, and mud cake modifier 0.5%–1.5%; the liquid components and their respective mass percentages are: water 70%–90%, and oil well cement additives 10%–30%; the mass ratio of the solid to liquid components is (1:0.3) to (1:0.6).

[0015] Furthermore, the sludge cake modifier is composed of sodium metasilicate, silicate mineral powder, and organic resin.

[0016] Furthermore, the oil well cement additive includes at least one of the following: retarder, suspending agent, dispersant, fluid loss reducer, and defoamer.

[0017] Furthermore, the cement includes Grade G oil well cement.

[0018] Furthermore, the fiber toughening material comprises calcium carbonate whiskers having a needle-like or fibrous structure.

[0019] Furthermore, the purity of the graphene oxide is greater than 99.5%.

[0020] Furthermore, the graphene oxide has a thickness of 4–20 nm and a micro-flake size of 5–10 μm.

[0021] Furthermore, the number of graphene oxide layers is less than 20.

[0022] The preparation method of the high-temperature resistant and strongly cemented plugging cement system for oil and water wells described above includes the following steps: (1) Cement, activated alumina, ultrafine high-purity silica sand, fiber toughening material, graphene oxide and mud cake modifier are mixed according to the mass ratio to obtain solid components; (2) Mix water and oil well cement additives according to the mass ratio to obtain a liquid component; (3) The solid component obtained in step (1) and the liquid component obtained in step (2) are mixed according to the mass ratio to obtain a high-temperature resistant and strongly bonded sealing system.

[0023] Based on the above description, a high-temperature resistant and strongly bonded plugging cement system for oil and water wells is applied to the plugging operations of casing leakage and external leakage in heavy oil wells and high-temperature wells.

[0024] The basic principle behind the leak-sealing cement system of this invention, which achieves high-temperature resistance and strong bonding, is as follows: 1. Activated alumina enhances the stability of calcareous silica. The addition of activated alumina significantly improves the temperature resistance of cement paste because it can enter the CSH gel and react with calcareous silica to form Al-calcareous silica. This structure effectively inhibits the transformation of calcareous silica to calcareous silica under high-temperature conditions, thus maintaining the stability of the cement paste at high temperatures. By suppressing this phase transformation process, the system can maintain higher strength and stability under extreme high-temperature environments, especially maintaining strong bonding and long-lasting temperature resistance at 260℃.

[0025] 2. Graphene oxide and fiber-reinforced toughening materials improve the toughness of cement stone. This invention significantly improves the toughness and crack resistance of cement paste by incorporating graphene oxide and fiber-reinforcing materials. Graphene oxide, due to its unique two-dimensional sheet structure, effectively prevents crack propagation and fills microscopic pores, thereby enhancing the overall structural stability of the cement matrix. The fiber-reinforcing materials further improve the crack resistance and durability of the cement paste by dispersing external stress and absorbing impact and deformation. The synergistic effect of these two materials enables the cement paste to exhibit excellent crack resistance and toughening effects under high temperature and high pressure environments, ensuring its mechanical and bonding properties during long-term use.

[0026] 3. Mud cake modifier improves interfacial bonding performance. The addition of a mud cake modifier significantly enhances the interfacial bonding ability between the cement paste and the formation. This modifier, composed of sodium metasilicate, silicate mineral powder, and organic resin, effectively improves the density and permeability of the mud cake, enhancing the adhesion between the cement paste and the formation. By improving the quality of the interface, this system can improve wellbore sealing performance, reduce cement paste debonding or failure caused by formation fractures or wellbore inhomogeneity, thereby improving the long-term safety and reliability of well workover operations.

[0027] Compared with the prior art, the present invention has the following main advantages: 1. The high-temperature resistant, strongly cemented plugging cement system of this invention enhances the high-temperature resistance of the cement stone by adding activated alumina, preventing structural instability at high temperatures and ensuring its strength is maintained under extreme conditions. The addition of graphene oxide and fiber toughening materials significantly enhances the toughness and crack resistance of the cement stone, effectively improving its compressive strength and durability. Simultaneously, the use of a mud cake modifier enhances the interfacial bonding ability between the cement stone and the formation, ensuring the stability and reliability of well workover operations.

[0028] 2. The high-temperature resistant, strong-bonding, leak-sealing cement system of the present invention was tested for its physical and mechanical properties at 2 days, 30 days, 60 days, and 90 days under curing conditions of 200℃ and 150MPa. Compared with conventional systems, the leak-sealing cement system of the present invention has significantly more stable performance, and the strength of the sample at 90 days of age showed a significant increase.

[0029] 3. The high-temperature resistant, strong-bonding plugging cement system of the present invention can not only solve the problem of cement stone strength degradation in ultra-high temperature environments, but also improve well repair quality and increase the reliability and safety of the wellbore.

[0030] 4. The high-temperature resistant, strongly bonded plugging cement system of this invention is particularly suitable for long-term plugging operations of casing leakage and external leakage in heavy oil wells and high-temperature wells. Activated alumina enhances the high-temperature resistance of the cement stone, ensuring that structural stability and strength do not decrease under extreme high-temperature environments, making it suitable for handling the high-temperature conditions commonly encountered in heavy oil wells. Graphene oxide and fiber toughening materials significantly enhance the toughness and crack resistance of the cement stone, ensuring that it is not prone to cracking or falling off under high pressure, making it suitable for plugging operations. The mud cake modifier improves the interfacial adhesion between the cement stone and the formation, further enhancing the long-term sealing effect, effectively preventing wellbore leakage, and ensuring the long-term safety and stability of the operation. Attached Figure Description

[0031] Figure 1 The present invention provides a flowchart for the preparation of a high-temperature resistant, strongly adhesive leak-sealing cement system. Detailed Implementation

[0032] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] Most additives are polymers, which can be solid or liquid. Their specific properties are mainly determined by various slurry characteristics such as density, rheology, thickening, and water loss, and usually need to be adjusted according to the actual engineering application conditions. Additives can be obtained commercially.

[0034] Regarding the dosage of components, all component parts in the examples are by mass, and all percentages are by mass percentage; the ratios between components are by mass ratios. This will not be elaborated further below.

[0035] The mass ratio of solid to liquid components can be 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, or 1:0.6. In the solid components, the cement content can be 40%, 45%, 50%, 55%, or 60%; the activated alumina content can be 1%, 1.5%, 2%, 2.5%, or 3%; the ultrafine high-purity silica sand content can be 30%, 35%, 40%, 45%, or 50%; the fiber toughening material content can be 3%, 4%, 5%, 6%, 7%, or 8%; and the mud cake modifier content can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%.

[0036] The cement used in this embodiment is Grade G oil well cement, whose chemical composition mainly contains 65.13% CaO, 18.45% SiO2, and 2.99% Al2O3; the ultrafine high-purity silica sand used has a SiO2 content greater than 97% and a particle size D50 of 6.7–10 μm, which can be 6.7 μm, 7 μm, 8 μm, 9 μm, or 10 μm; the activated alumina used is a porous, highly adsorbent alumina material with a particle size D50 of 5 μm and a specific surface area of ​​220 m² / g; the graphene oxide used has a purity greater than 99%. 0.5%, thickness 4-20 nm, flake size 5-10 μm, number of layers less than 20; the toughening fiber material used is a calcium carbonate whisker with a needle-like or fibrous structure, with an average length of 20 μm and an aspect ratio of 15:1; the mud cake modifier used is composed of sodium metasilicate (promoting the formation of silicate hardening material inside the mud cake), silicate mineral micro powder (helping to form a network structure inside the mud cake), and organic resin (filling the voids inside the mud cake) in a ratio of 3:7:1, wherein the particle size D50 of the silicate mineral micro powder is 0.46 μm. Example 1

[0037] The high-temperature resistant, strongly bonded leak-sealing cement system consists of solid and liquid components, with a mass ratio of 1:0.44 between the solid and liquid components. The solid component contains 58.8% Grade G oil well cement and 41.2% ultrafine high-purity silica sand (D50=6.7μm).

[0038] The liquid component contains 75.3% water, 4.9% suspending agent, 6.6% dispersant, 5.4% retarder, 7.2% water loss reducing agent and 0.6% defoamer.

[0039] The preparation process is as follows: (1) Cement and ultrafine high-purity silica sand are mixed according to the proportion to obtain solid components; (2) Mix water and additives (including suspending agents, dispersants, retarders, water loss reducers and defoamers) according to the specified ratio to obtain a liquid component; (3) Add the liquid component obtained in step (2) into the mold, and then add the solid component obtained in step (1) into the liquid component at a stirring speed of 4000 rpm. After the addition is complete, stir at a speed of 12000 rpm for 35 seconds. Example 2

[0040] The high-temperature resistant, strong-bonding, leak-sealing cement system consists of solid and liquid components, with a weight ratio of 1:0.43 between the solid and liquid components. The solid component contains 52.4% Grade G oil well cement, 36.6% ultrafine high-purity silica sand (D50=6.7μm), 8% fiber toughening material, and 3% activated alumina. The liquid component contains 75.3% water, 4.9% suspending agent, 6.6% dispersant, 5.4% retarder, 7.2% water loss reducing agent and 0.6% defoamer.

[0041] The preparation process is as follows: (1) Cement, ultrafine high-purity silica sand, fiber toughening material and activated alumina are mixed according to the proportion to obtain solid components; (2) Mix water and additives (including suspending agents, dispersants, retarders, water loss reducers and defoamers) according to the specified ratio to obtain a liquid component; (3) Add the liquid component obtained in step (2) into the mold, and then add the solid component obtained in step (1) into the liquid component at a stirring speed of 4000 rpm. After the addition is complete, stir at a speed of 12000 rpm for 35 seconds. Example 3

[0042] The high-temperature resistant, strong-bonding, leak-sealing cement system consists of solid and liquid components, with a weight ratio of 1:0.44 between the solid and liquid components. The solid component contains 51.4% Grade G oil well cement, 36% ultrafine high-purity silica sand (D50=6.7μm), 8% fiber toughening material, 3% activated alumina, 1.5% mud cake modifier, and 0.1% graphene oxide. The liquid component contains 74.8% water, 4.9% suspending agent, 6.8% dispersant, 5.5% retarder, 7.4% water loss reducing agent and 0.6% defoamer.

[0043] The preparation process is as follows: (1) Cement, ultrafine high-purity silica sand, fiber toughening material, activated alumina, mud cake modifier and graphene oxide are mixed in proportion to obtain solid components; (2) Mix water and additives (including suspending agents, dispersants, retarders, water loss reducers and defoamers) according to the specified ratio to obtain a liquid component; (3) Add the liquid component obtained in step (2) into the mold, and then add the solid component obtained in step (1) into the liquid component at a stirring speed of 4000 rpm. After the addition is complete, stir at a speed of 12000 rpm for 35 seconds.

[0044] Comparative Example 1 The method described in Example 1 is implemented, except that the composition of the solid components is different. In this case, the content of ultrafine high-purity silica sand in the solid components is reduced, the content of cement is 71.4%, and the content of ultrafine high-purity silica sand is 28.6%.

[0045] Comparative Example 2 The method described in Example 2 is implemented, except that the composition of the solid components is different. The content of activated alumina in the solid components is reduced, the cement content is 52.8%, the ultrafine high-purity silica sand content is 37.2%, the fiber toughening material content is 8%, and the activated alumina content is 2%.

[0046] Comparative Example 3 The method described in Example 2 is implemented, except that the composition of the solid components is different. The content of activated alumina in the solid components is reduced, the cement content is 53.4%, the content of ultrafine high-purity silica sand is 37.6%, the content of fiber toughening material is 8%, and the content of activated alumina is 1%.

[0047] Comparative Example 4 The method described in Example 3 is implemented, except that the composition of the solid components is different. The solid components contain a reduced content of sludge cake modifier, a cement content of 51.6%, an ultrafine high-purity silica sand content of 36.3%, a fiber toughening material content of 8%, an active alumina content of 3%, a sludge cake modifier content of 1%, and a graphene oxide content of 0.1%.

[0048] Comparative Example 5 The method described in Example 3 is implemented, except that the composition of the solid components is different. The solid components contain a reduced content of sludge cake modifier, a cement content of 51.9%, an ultrafine high-purity silica sand content of 36.5%, a fiber toughening material content of 8%, an active alumina content of 3%, a sludge cake modifier content of 0.5%, and a graphene oxide content of 0.1%.

[0049] Comparative Example 6 The method described in Example 3 is implemented, except that the composition of the solid component is different. In this example, the solid component does not contain graphene oxide, and the cement content is 51.5%, the ultrafine high-purity silica sand content is 36%, the fiber toughening material content is 8%, the active alumina content is 3%, and the sludge cake modifier is 1.5%.

[0050] Test Example 1 The thickening time of the cement system in Example 1 was tested at 240℃ and 120 MPa. The system was designed to thicken under high temperature and high pressure for more than 5 hours. The heating time of the formula during curing was about 2 hours. It was designed to remain in a fluid state after reaching the target temperature and pressure, thus meeting the conditions for high temperature and high pressure molding.

[0051] Test Example 2 The cement systems of Examples 1-3 and Comparative Examples 1-6 were cured in situ at 260℃ and 150 MPa for 2 days, 30 days, 60 days and 90 days respectively, and the compressive strength of each system was tested.

[0052] Test Example 3 The cement systems of Examples 1-3 and Comparative Examples 1-6 were subjected to in-situ curing at 260℃ and 150 MPa for 2 days, 30 days, 60 days, and 90 days, respectively, and the gas permeability of each system was tested.

[0053] Test Example 4 The cement systems of Examples 1-3 and Comparative Examples 1-6 were subjected to in-situ curing at 260℃ and 150 MPa for 2 days, 30 days, 60 days and 90 days respectively, and the hydration products of each system were detected by XRD.

[0054] Please refer to Table 1 for the above test results.

[0055] Table 1. Summary of test results for the cement systems of the examples and comparative examples

[0056] Based on the test results in Table 1, a brief analysis is as follows: A comparison of Examples 1, 2, and 3 shows that Example 1, with its higher oil well cement content, exhibits excellent early compressive strength (41.92 MPa), making it suitable for applications requiring rapid achievement of high strength. However, due to its relatively simple composition, consisting only of oil well cement and ultrafine high-purity silica sand, it suffers from rapid strength decay at 90 days (26.7%) and high liquid permeability (0.066 mD), indicating insufficient impermeability. In contrast, Examples 2 and 3 have more refined formulations, including fiber-reinforced materials and activated alumina. Although their early compressive strength is slightly lower than Example 1, their strength decay is slower, and their 90-day compressive strength exceeds that of Example 1. In particular, Example 3 achieves a 90-day compressive strength of 34.59 MPa. Furthermore, Examples 2 and 3 exhibit lower liquid permeability (0.007 mD and 0.006 mD, respectively), demonstrating better impermeability and making them suitable for applications requiring high long-term strength and impermeability.

[0057] The results of the comparative examples differ significantly from those of the corresponding embodiments: Compared with Example 1, Comparative Example 1 had a lower content of ultrafine high-purity silica sand in its solid component, resulting in lower early and 90-day compressive strength than Example 1 (31.19 MPa and 25.53 MPa, respectively), showing a significant decrease in strength and insufficient durability.

[0058] Compared with Example 2, Comparative Examples 2 and 3 reduced the content of active alumina in the solid components, resulting in faster strength degradation. The degradation rates after 90 days were 20.1% and 17.9%, respectively, which were significantly higher than those of Example 2 (0.8%), indicating that active alumina played an important role in maintaining long-term strength.

[0059] Compared with Example 3, the reduction in the content of mud cake modifier in the solid component of Comparative Examples 4 and 5 led to a decrease in compressive strength. The compressive strength of Comparative Example 4 at 90 days was 32.81 MPa, and that of Comparative Example 5 was 33.28 MPa, both slightly lower than that of Example 3, indicating that the mud cake modifier has a certain influence on the strength of the material.

[0060] Compared with Example 3, Comparative Example 6 removed graphene oxide from the solid component, resulting in a slight decrease in compressive strength. The 90-day compressive strength was 33.89 MPa, and the liquid permeability increased significantly (from 0.006 mD to 0.037 mD), demonstrating that graphene oxide can improve the stability and impermeability of cement stone.

[0061] In summary, Example 1 is suitable for quickly achieving high strength, while the formulations of Examples 2 and 3 are more reasonable and can better maintain long-term strength and impermeability. Adjustments to the proportions indicate that some key components (such as activated alumina, sludge modifier, and graphene oxide) play an important role in improving the strength, durability, and impermeability of the cement system.

Claims

1. A high-temperature resistant, strongly bonded plugging cement system for oil and water wells, characterized in that, The plugging cement system consists of solid components and liquid components; the solid components and their respective mass percentages are as follows: cement 40%–60%, activated alumina 1%–3%, ultrafine high-purity silica sand 30%–50%, fiber toughening material 3%–8%, graphene oxide 0.03%–0.1%, and mud cake modifier 0.5%–1.5%; the liquid components and their respective mass percentages are as follows: water 70%–90%, and oil well cement additive 10%–30%; the mass ratio of the solid components to the liquid components is (1:0.3) to (1:0.6).

2. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The mud cake modifier is composed of sodium metasilicate, silicate mineral powder, and organic resin.

3. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The oil well cement additive includes at least one of the following: retarder, suspending agent, dispersant, fluid loss reducer, and defoamer.

4. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The cement includes Grade G oil well cement.

5. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The fiber-reinforced material comprises calcium carbonate whiskers having a needle-like or fibrous structure.

6. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The purity of the graphene oxide is greater than 99.5%.

7. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The graphene oxide has a thickness of 4–20 nm and a micro-flake size of 5–10 μm.

8. The high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to claim 1, characterized in that, The number of graphene oxide layers is less than 20.

9. A method for preparing a high-temperature resistant, strongly cemented plugging cement system for oil and water wells according to any one of claims 1-8, comprising the following steps: (1) Cement, activated alumina, ultrafine high-purity silica sand, fiber toughening material, graphene oxide and mud cake modifier are mixed according to the mass ratio to obtain solid components; (2) Mix water and oil well cement additives according to the mass ratio to obtain a liquid component; (3) The solid component obtained in step (1) and the liquid component obtained in step (2) are mixed according to the mass ratio to obtain a high-temperature resistant and strongly bonded sealing system.

10. The application of a high-temperature resistant, strongly bonded plugging cement system for oil and water wells according to any one of claims 1-8 in the plugging operation of casing leakage and external leakage in heavy oil wells and high-temperature wells.

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