Cementing material capable of being set and hardened in high-temperature environment and use method of cementing material

Abstract

The invention discloses a cementing material capable of being coagulated and hardened in a high-temperature environment and a use method thereof, and particularly relates to a cementing material capable of being coagulated and hardened at the environment temperature of 50-300 DEG C and keeping strength and a use method thereof. The cementing material is composed of magnesium oxide, magnesium hydroxide, a siliceous material, a stabilizer and a water-retaining agent, a proper amount of water is added during use, and aggregate and a water reducing agent are added according to needs. The cementing material disclosed by the invention can be used for well cementation, filling, supporting and the like in a high-temperature, high-pressure and high-humidity underground environment, keeps flowability and workability at a normal temperature, and can meet the flowability and workability for more than 6 hours by adjusting the composition of the cementing material so as to meet the requirements of long-distance conveying or pumping and pouring; and in an environment of 50-300 DEG C, the material is rapidly set and hardened to form strength, and long-term performance stability can be maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a cementitious material hardened and solidified in high-temperature environment and a use method, especially a cementitious material hardened and solidified in a high-temperature environment of 50-300℃ and a use method. BACKGROUND

[0002] In recent years, with the advance to deep underground, people have put forward higher requirements for cementitious materials applied to complex working conditions, such as underground oil and gas well construction, reinforcement and repair of geothermal wells, etc., which require cementitious materials to have good high-temperature stability, performance adjustment and control, etc. Generally, oil and gas wells or geothermal wells are located in underground layers hundreds or even thousands of meters deep, with harsh and complex environment, not only the temperature exceeds 150℃, but also the pressure reaches 70MPa, and in some cases the humidity is very high. The construction and reinforcement of oil and gas wells and the like located in these areas require special building materials. At present, the oil well cement used is prepared by adding various admixtures to portland cement. In order to meet the needs of actual engineering, the oil well cement is mixed with up to dozens of admixtures when used, including but not limited to accelerators, retarders, fluid loss additives, dispersants, plugging agents, lightening agents, etc. Although it can adapt to scenes with relatively low environmental temperature, at higher temperatures, the admixtures interact with each other, causing unstable and uncontrollable performance of the oil well cement, obvious performance degradation, and further problems such as pipe blockage and rapid setting during construction. In addition, when the content of sulfate in the underground layer is high, it will cause corrosion to the cement matrix, resulting in significant reduction in strength and failure in a short time. If the underground layer contains CO2, H2S and gas, etc., the cement matrix will also be corroded and fail. When the environmental temperature is higher than 200℃, the existing general oil well cement cannot meet the requirements. SUMMARY

[0003] Silicate cement is a cementitious material which is widely used at present. Cementitious material used in oil well and other underground engineering is still developed on the basis of silicate cement. Although the content of aluminum phase in oil well cement used at higher temperature is reduced to avoid the formation of more ettringite (AFt) which will decompose at 70℃ and above to cause a significant reduction in strength, the main hydration product of silicate cement, calcium silicate hydrate gel (C-S-H), will undergo a crystal phase transition at a temperature exceeding 140℃, resulting in a sharp decline in cement performance. Higher ambient temperature will also accelerate the hydration rate of cement, causing the hydration product to change, the crystallinity of the hydration product to increase, and the pore size of the cement stone to increase, resulting in a significant decline in strength. In particular, most additives will fail when the temperature exceeds 200℃, and existing oil well cement will not be able to be used. The high temperature and high pressure environment will also cause the existing oil well cement to produce a large shrinkage, thereby causing microcracks in the hardened cement slurry, affecting the cementing strength of the well wall and casing, causing annular channeling, and causing pollution and loss of oil and gas resources. In view of the above shortcomings of the existing oil well cement, the purpose of the present application is to provide a cementitious material mainly composed of magnesia material and siliceous material, which can fill the gap of cementitious material used in an environment with a temperature exceeding 200℃, and has the characteristics of stable high-temperature performance, corrosion resistance and carbonation resistance, and can adjust the setting time and the density of the hardened slurry to meet the requirements of different use environments. The cementitious material of the present application has excellent working performance, good high-temperature resistance and corrosion resistance at room temperature, and can be used in oil wells, geothermal wells and other high-temperature environments.

[0004] In a first aspect, the present application provides a cementitious material for setting and hardening in a high-temperature environment, which is composed of magnesia, magnesia hydroxide, siliceous material, stabilizer and water-retaining agent. Preferably, the mass of the magnesia hydroxide is less than or equal to 50% of the mass of the magnesia, the mass of the stabilizer is less than or equal to 3% of the total mass of the cementitious material, and the mass of the water-retaining agent is less than or equal to 2% of the total mass of the cementitious material. The ratio of the total mass of the magnesia hydroxide and the magnesia to the total mass of the silica in the siliceous material is 0.5-10.

[0005] Preferably, the magnesia is one of active magnesia, light-burned magnesia and heavy-burned magnesia, or a mixture of two or more thereof.

[0006] Preferably, when the magnesia is a mixture, the mass of the heavy-burned magnesia is greater than or equal to 40% of the total mass of the magnesia mixture.

[0007] Preferably, the maximum particle size of the magnesia is less than 80μm, and the mass fraction of MgO in the magnesia is ≥75%.

[0008] Preferably, the siliceous material is one or a mixture of several of quartz powder, fly ash, silica fume.

[0009] Preferably, when the siliceous material is a mixture, the mass of the quartz powder is greater than or equal to 30% of the total mass of the siliceous material mixture.

[0010] Preferably, the maximum particle size of the siliceous material is less than 80 microns; the mass fraction of SiO2 in the quartz powder and silica fume is greater than or equal to 85%, and the mass fraction of SiO2 in the fly ash is greater than or equal to 50%.

[0011] Preferably, the stabilizer is citric acid.

[0012] Preferably, the water-retaining agent is one of cellulose ether, polyacrylamide or lignocellulose.

[0013] In a second aspect, the application also provides a method for using the cementitious material, the method comprising the following steps: In a normal temperature environment, first add water accounting for 20%-80% of the mass of the cementitious material powder to make a mixture with fluidity, and the fluidity or slump of the mixture is maintained for ≥2h; then the mixture is transported to a working scene with a temperature of 50℃-300℃ for pouring, and in the working scene, 10min

[0014] Compared with the prior art, the application has the following beneficial effects: 1. The high-temperature environment setting and hardening cementitious material provided by the application, compared with the silicate-based oil well cement system in the prior art, takes a magnesia-silica binary system as the core, optimizes the ratio of magnesium oxide, magnesium hydroxide and siliceous material (the ratio of the total mass of magnesium hydroxide and magnesium oxide to the total mass of silicon dioxide in the siliceous material is 0.5-10), and is supplemented with an appropriate amount of stabilizer (≤3%) and water-retaining agent (≤2%), which fundamentally solves the performance degradation problem of traditional calcium cementitious material in a high-temperature environment. The application avoids the adverse phase transition of the main hydration product C-S-H gel of portland cement above 140℃, the hydration product of magnesium silicate hydrate has excellent thermal stability and does not decompose below 400℃, and can be transformed into the thermodynamically more stable serpentine phase under high temperature and high pressure, thereby ensuring that the strength of the material does not decrease or even continuously increases in an extreme environment of 200-300℃.

[0015] 2、The present application is based on the low solubility characteristics of the magnesium system (pH value of components and hydration products <11, significantly lower than the pH value >12 of the traditional calcium system), which will not generate expansive products due to chemical reactions in high salinity groundwater, sulfate erosion, and CO2 / H2S acid gas environment. Due to the special microstructure of the hydration products, the aggressive media such as chloride ions and sulfate ions may enter in the form of ion exchange or intercalation, avoiding the volume expansion damage caused by the generation of ettringite or calcium carbonate in the traditional calcium system. In addition, the material system constructed by the present application has simple components (only 5 core components are needed), completely abandoning the technical defects of the existing oil well cement which needs to rely on dozens of additives, eliminating the uncontrollable risk of performance caused by the mutual interference between additives, and realizing the accurate control of the setting time (10-60 minutes adjustable) and the density of the hardened body.

[0016] 3、The present application has excellent workability (flowability retention time ≥2h, up to 10h) at room temperature, which fully meets the requirements of deep well long distance pumping construction; it can realize rapid strength development in 50-300℃ service environment, effectively prevent volume shrinkage and microcrack under high temperature and high pressure conditions, ensure the cementing integrity with the well wall and casing, and eliminate the risk of annular channeling. Especially important is that the material can fully utilize industrial waste slag as raw material source, filling the technical gap of cementing materials for superhigh temperature deep geothermal development and ultra-deep oil and gas well construction above 250℃, and providing key material support for major projects such as deep geothermal development and ultra-deep oil and gas well construction in China. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The X-ray diffraction pattern of the cementing material of embodiment 4 of the present application at different curing temperatures.

[0018] Figure 2 The infrared spectrum of the cementing material of embodiment 4 of the present application at different curing temperatures. DETAILED DESCRIPTION

[0019] The present application will be described in detail in the embodiments of the present application, and the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0020] Unless otherwise specified in specific cases, the numerical range listed in the present application includes the upper and lower limits, and all integers and fractions within the range, not limited to the specific values listed in the defined range.

[0021] I. A cementing material for setting and hardening in high temperature environment The cementing material comprises magnesium oxide, magnesium hydroxide, siliceous material, stabilizer and water-retaining agent; wherein, in the cementing material, the mass of magnesium hydroxide is less than or equal to 50% of the mass of magnesium oxide, the mass of the stabilizer is less than or equal to 3% of the total mass of the cementing material, and the mass of the water-retaining agent is less than or equal to 2% of the total mass of the cementing material; the ratio of the total mass of magnesium hydroxide and magnesium oxide to the total mass of silicon dioxide in the siliceous material is 0.5-10.

[0022] The present application is found in the study of existing Portland-based oil well cement that the hydration product (C-S-H gel) is prone to decomposition or phase transition in high temperature (above 200 DEG C) environment, resulting in a sharp decline in strength, and the prior art usually uses a variety of admixtures to solve this technical problem, but such compounding can cause synergistic interference to cause unstable performance, and is prone to swelling and cracking in the presence of sulfate, CO2, H2S and other corrosive media, and the shrinkage deformation under high temperature and high pressure can damage the cementing strength with the well wall and the casing. These problems have long restricted the application of materials in deep oil and gas wells, geothermal wells and other engineering projects, and the existing technology is difficult to fundamentally break through by improving components or adding admixtures. Therefore, the concept of the present application is to solve the above technical problems, abandon the improvement path of the traditional calcium cementing system, and turn to the construction of a new system with magnesium-silicon synergistic effect. First, the present application considers the thermodynamic stability of the hydration product, determines magnesium oxide and magnesium hydroxide as the magnesium core component by in-depth study of the magnesium-silicon hydration reaction mechanism, and quartz powder, fly ash and other silicon raw materials, and uses the hydration magnesium silicate (M-S-H) gel generated by the hydration of the two to provide the main strength source. Because the molecular structure of the gel is similar to that of the serpentine mineral, it naturally has high temperature stability, and this design is aimed at solving the core technical problem of high temperature failure of existing materials. Therefore, the present application designs a specific ratio of magnesium oxide and magnesium hydroxide (the mass of magnesium hydroxide is not more than 50% of the mass of magnesium oxide), accurately controls the proportion of heavy burned magnesium oxide in the system (not less than 40%), balances the hydration rate through the synergistic effect of the two magnesium components, and avoids the problem of too fast or too slow hydration of single magnesium oxide; the total mass ratio of magnesium and silicon is limited in the optimization interval of 0.5-10, which not only ensures the sufficient generation of M-S-H gel, but also avoids the performance imbalance caused by excessive single component; the functions of trace stabilizer (≤3%) and water retaining agent (≤2%) are coordinated, which not only simplifies the system complexity, but also avoids the adverse interference between the additives, which aims to solve the technical problem of synergistic failure of the admixture. In addition, in the selection and particle size distribution of raw materials, the proportion of heavy burned magnesium oxide in the magnesium oxide mixture is not less than 40%, the proportion of quartz powder in the silicon material is not less than 30%, and the maximum particle size of the two main materials is less than 80 microns, which lays a foundation for the hydration reaction and structure densification by optimizing the activity and particle packing density of the raw materials. At the same time, considering the resource utilization of industrial waste, the industrial waste of magnesium oxide, magnesium hydroxide and silicon dioxide is included in the scope of applicable raw materials, which takes into account the performance and environmental protection requirements.

[0023] The design idea after implementation, the present application found not only solve the problem of strength decay of traditional materials in the environment above 200 ℃, more in the implementation process showed beyond the expected technical effect: hydration of hydrated magnesium silicate gel generated in 400 ℃ below the structure is stable, and in high temperature and high pressure conditions spontaneously to the thermodynamic more stable serpentine phase transition, realize the continuous growth of strength, completely break through the existing material highest use temperature difficult to exceed 200 ℃ limit; At the same time, the system pH value naturally maintained in the weak alkaline range below 10, fundamentally inhibit the corrosion reaction path of sulfate, chloride and acid gas, so that the material in the complex corrosion environment shows far beyond the design of long-term stability. Especially key is that the system only needs five kinds of core components to realize the accurate control of setting time (10-60 minutes adjustable), the persistent retention of fluidity (≥2 hours at room temperature) and the comprehensive performance of high temperature strength rapid development, completely abandon the traditional oil well cement relying on dozens of admixtures, the unity of its simplified formula and excellent performance, fully embodies the deep level of synergistic mechanism between material components and the precise control level of high temperature phase transition behavior. And after further implementation, the present application also found that the corrosion resistance performance realizes the qualitative improvement, M-S-H gel has chemical inertia to corrosion ions such as chloride and sulfate, and the product generated by the reaction of unreacted magnesium component with corrosion ions has no obvious expansion, but can fill the pores of the system, improve the density, form the synergistic effect of corrosion resistance and densification, completely solve the expansion and cracking problem of calcium system, suitable for more extensive corrosion environment; The volume stability and cementing strength are significantly better than expected. Originally only concerned about the strength retention at high temperature, it is found in practical application that the system has no obvious shrinkage deformation in high temperature and high humidity environment, effectively avoiding the generation of microcracks in hardened paste, and the cementing strength with wellbore and casing is greatly improved, which fundamentally blocks the risk of annular channeling, which benefits from the synergistic effect of three-dimensional network structure of M-S-H gel and particle size distribution optimization; The low alkalinity characteristic not only avoids the influence of high pH value on the underground ecological environment, but also significantly improves the compatibility of the material with natural fibers and other reinforcing components, expanding the application scenarios; The system adaptability far exceeds the expectation, by adjusting the magnesium silicon ratio, raw material type and functional additive amount, without adding other admixtures, it can meet the engineering requirements under different depth and temperature and pressure conditions, from shallow geothermal well to complex conditions of deep oil and gas well, showing strong performance adjustability and scene compatibility.

[0024] In some embodiments of the present application, the magnesium oxide is one or a mixture of several of active magnesium oxide, light-burned magnesium oxide and heavy-burned magnesium oxide. These magnesium oxides, used alone or in combination, can achieve the technical effects described in the present application. Magnesium oxides with different degrees of calcination have different hydration kinetics and temperature responsiveness. The dense crystal structure of heavy-burned magnesium oxide formed by high-temperature calcination exhibits slow and continuous hydration characteristics in an ultra-high temperature environment (200-300°C), effectively avoiding the risk of flash setting; light-burned magnesium oxide has a developed mesoporous structure and high surface energy, and is highly active with siliceous materials in a medium temperature range (100-200°C), capable of quickly forming a strength skeleton; active magnesium oxide provides a basic hydration driving force at room temperature due to its rich surface defects and high reactivity. By precisely controlling the ratio of magnesium oxides with different degrees of calcination, the setting time can be accurately controlled in the entire temperature range from room temperature to 300°C, which can maintain workability for several hours or even more than ten hours at room temperature to meet the long-distance pumping requirements, and can achieve rapid setting and hardening and rapid development of strength in a high-temperature environment, perfectly matching the different requirements of the construction window period in deep engineering under different temperature gradients at different depths.

[0025] In some embodiments of the present application, when the magnesium oxide is a mixture and the mixture contains heavy-burned magnesium oxide, the mass of the heavy-burned magnesium oxide is greater than or equal to 40% of the total mass of the magnesium oxide mixture, calculated as a percentage by mass. The reason for limiting the proportion of heavy-burned magnesium oxide is that the complete crystal lattice structure formed during the high-temperature calcination process of heavy-burned magnesium oxide has low surface energy and high lattice energy, and is not easy to distort in a 200-300°C environment, providing a stable nucleation substrate for hydrated magnesium silicate gel and effectively inhibiting the structural collapse caused by high-temperature phase transition. Microstructure analysis shows that under a curing condition of 150-300°C, the hydrated product in a system with a heavy-burned magnesium oxide proportion ≥40% maintains structural integrity and gradually transforms into a more thermodynamically stable serpentine phase as the temperature increases. The technical effect is that this proportion design significantly improves the long-term strength stability of the material in an ultra-high temperature environment, and still maintains a high mechanical strength at 300°C, and the strength decay rate is significantly reduced after multiple temperature cycles, fundamentally solving the problems of interface debonding and strength collapse caused by thermal stress in traditional cementitious materials in deep well high temperature environments. Therefore, when the magnesium oxide is a mixture, the mass of the heavy-burned magnesium oxide can be selected from 40% to 95%, 50% to 95%, 50% to 90% of the total mass of the magnesium oxide mixture, and can also be 40%, 50%, 60%, 70%, 80%, 90%, 95%, etc., as well as all ranges and sub-ranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0026] In some embodiments of the present application, the maximum particle size of the magnesium oxide is less than 80 μm, and the mass fraction of MgO in the magnesium oxide is ≥75% by mass. The optimization of particle size distribution promotes the uniformity of the hydration reaction, and the high-purity component eliminates the interference of impurities. Small particle size ensures the temporal and spatial consistency of the release rate of magnesium ions, avoiding micro-cracks caused by local supersaturation; high purity reduces the influence of impurities such as CaO and Fe2O3 on the formation of magnesium silicate gel network structure. Microscopic morphology observation shows that the hydration rate of magnesium oxide in this parameter range is moderate, and the gel pore structure is more optimized. Under high temperature and high pressure conditions, the slurry flowability loss rate is significantly reduced, the working performance retention time is greatly extended; the mechanical strength of the hardened body in extreme environment is significantly improved, and the strength dispersion is obviously reduced; at the same time, it shows excellent long-term stability in corrosive medium, providing material guarantee for reliable sealing of deep engineering. Therefore, the average particle size of magnesium oxide can be selected from 1-75 μm, 1-50 μm, 1-20 μm, and can also be 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, etc., as well as all ranges and sub-ranges between the above-mentioned values; the mass fraction of MgO in the magnesium oxide can be selected from 75%-99%, 75%-95%, 80%-95%, 85%-95%, and can also be 75%, 80%, 85%, 90%, 95%, etc., as well as all ranges and sub-ranges between the above-mentioned values; it should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0027] In some embodiments of the present application, the siliceous material is one or a mixture of several of quartz powder, fly ash, silica fume. Different forms of SiO2 have complementary effects in terms of reactivity, particle packing and high temperature stability. Quartz powder provides a stable crystalline SiO2 skeleton, and its crystal structure remains intact at high temperatures, providing long-term stability to the system; silica fume, with its nanoscale particle size and high activity, quickly participates in the reaction and fills the micropores in the early hydration stage, significantly improving early strength and density; the glassy component in fly ash is gradually activated at high temperatures to form secondary hydration products, optimizing the microstructure and achieving resource utilization of industrial waste slag. By reasonably matching different siliceous materials, the strength development can be precisely controlled in a wide temperature range. The silica fume-based system has rapid early strength development, suitable for rapid consolidation requirements; the quartz powder-based system has excellent long-term stability, suitable for long-term service in ultra-deep wells; the introduction of fly ash significantly reduces the material cost while ensuring performance, achieving the unity of performance and economy.

[0028] In some embodiments of the present application, when the siliceous material is a mixture, the mass of the quartz powder is greater than or equal to 30% of the total mass of the siliceous material mixture, calculated as a percentage by mass. The high-temperature phase transition stability of quartz crystals plays a regulatory role in the thermal expansion behavior of the overall system. Quartz maintains a stable alpha-quartz structure below 300°C, and its low thermal expansion coefficient effectively buffers the accumulation of internal stress caused by temperature changes, preventing the cracking and structural damage of hydration products during the high-temperature phase transition process. Thermal analysis results show that the mass loss rate of the system with a quartz powder content of ≥30% is significantly reduced in a high-temperature environment, and the structural integrity is better maintained. This proportion design significantly improves the durability of the material in a temperature alternating environment, and after multiple high-temperature-normal temperature cycles, the strength retention rate and interfacial bonding performance are significantly better than those of systems without or with low content of quartz powder, successfully solving the problem of annular sealing failure caused by temperature fluctuations in deep engineering, and providing key material support for the long-term integrity of ultra-deep oil and gas wells. Therefore, the mass of the quartz powder is selected from 30% to 90%, 45% to 85%, 50% to 80%, 60% to 80%, calculated as a percentage by mass, and can also be 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, etc., as well as all ranges and sub-ranges between the above-mentioned values; it should be understood that in the implementation scheme, any of the above-mentioned ranges can be combined with any other range.

[0029] In some embodiments of the present application, the maximum particle size of the siliceous material is less than 80 pm; the mass fraction of SiO2 in the quartz powder and silica fume is greater than or equal to 85% by mass percentage, which refers to the total mass fraction of SiO2 in the quartz powder and silica fume; and the mass fraction of SiO2 in the fly ash is greater than or equal to 50%. The close packing is achieved by optimizing the particle size distribution, and the high-purity SiO2 ensures the stoichiometric accuracy of the hydration reaction. The small particle size of the siliceous material provides sufficient reaction interface to accelerate the magnesium-silicon hydration reaction, and the high SiO2 content avoids the interference of components such as Al2O3 and CaO on the formation path of magnesium silicate hydrate gel, ensuring the purity and stability of the hydration product. Microstructure characterization shows that the hydration product under this combination of parameters has a dense layered structure, and the micro-pore distribution is more uniform and reasonable. The strength development rate of the material is significantly improved at high temperature, and the required strength threshold can be reached at an early stage; it can still maintain a high residual strength under extreme high temperature (above 300°C) conditions; and it also shows excellent long-term stability in corrosive environments such as sulfate and chloride ions, fully verifying its structural reliability in deep extreme environments. Therefore, the average particle size of the siliceous material is selected from 0.1-80 pm, 0.5-50 pm, 0.5-30 pm, 0.5-20 pm, which can be 0.1 pm, 0.5 pm, 1.0 pm, 5 pm, 10 pm, 15 pm, 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, and all ranges and sub-ranges between the above-mentioned values; at the same time, the mass fraction of SiO2 in the quartz powder and silica fume can be selected from 85%-99%, 90%-98%, 92%-98% by mass percentage, which can also be 85%, 90%, 95%, 99%, and all ranges and sub-ranges between the above-mentioned values; the mass fraction of SiO2 in the fly ash can be 50%, 60%, 70%, 80%, 90%, 95%, and all ranges and sub-ranges between the above-mentioned values; it should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0030] In some embodiments of the present application, the stabilizer is citric acid. The citric acid molecules can form a complex with Mg2+ and Ca2+ ions, thereby preventing the aggregation of Mg2+ and Ca2+ ions and the formation of MgO and CaO crystals, and ensuring the stability of the magnesium-silicon hydration product. 2+The citric acid can form a stable six-membered ring complex with magnesium ions, effectively delaying the supersaturation precipitation process of Mg(OH)2, and its molecular structure is adsorbed on the surface of the hydration product, inhibiting the disordered crystal growth and promoting the formation of a more dense and uniform gel structure. The setting time is precisely controlled in a wide temperature range (50-300℃), and the setting window period is stably in the ideal range of 10-60 minutes, which is much better than the setting out-of-control phenomenon of traditional cementitious materials at high temperatures; at the same time, the internal structure of the hardened body is more uniform and dense, the porosity is significantly reduced, and the impermeability and mechanical strength are simultaneously improved, providing reliable construction controllability and long-term service guarantee for high-temperature grouting engineering.

[0031] In some embodiments of the present application, the water-retaining agent is one of cellulose ether, polyacrylamide or lignocellulose. Cellulose ether forms a hydrogen bond network through the rich hydroxyl groups on the molecular chain, effectively locking free water molecules; polyacrylamide forms a three-dimensional gel network by winding the long chain of high molecules, preventing water migration; lignocellulose uses the capillary force generated by its porous fiber structure to adsorb and retain water. High-temperature water loss tests show that the water retention capacity of the system containing the water-retaining agent is significantly better than that of the system without the water-retaining agent at 300℃. In the process of ultra-high temperature grouting, the water loss rate of the slurry is greatly reduced, effectively preventing the generation of early plastic shrinkage cracks; at the same time, sufficient water ensures the full progress of the hydration reaction, making the material strength development more uniform and complete; the microstructure of the hardened body is more dense, and the dispersion of the mechanical properties is significantly reduced, providing a key guarantee for the quality consistency of large-scale application in deep engineering, significantly improving the safety and reliability of engineering service II. A method of using a cementitious material Under normal temperature environment, first add water accounting for 20%-80% of the mass of the cementitious material powder to make a mixture with fluidity, so that the fluidity or slump time of the mixture is ≥2h; then transport it to a working scene with a temperature of 50℃-300℃ for pouring, in which the setting time is 10min

[0032] The method of using the cementitious material described in the present application has high engineering adaptability and formulation flexibility. In the specific implementation process, first, 20%-80% of the water of the mass of the cementitious material powder is added to the cementitious material powder at room temperature to form a basic slurry. The basic slurry itself has the fluidity to meet the construction requirements and the flowability retention ability of at least 2 hours, and can be completely transported to a high-temperature use environment of 50-300°C through pumping and other means, and realize precise setting control and subsequent strength development in the environment for 10-60 minutes. The addition of aggregate (such as standard sand) and water reducing agent is an optional item, and whether to add depends on the individual needs of the specific project for the density, economy or special working performance of the hardened body: when the slurry density needs to be adjusted or the cost needs to be reduced, aggregate can be selectively added; when the fluidity needs to be further optimized or the water consumption needs to be reduced, water reducing agent can be selectively added. Core experimental data shows that even without adding any aggregate and water reducing agent, the cementitious material system described in the present application can still maintain excellent controllability of setting time, rapid strength development ability and long-term thermal stability in a super-high temperature environment (up to 300°C), and the basic technical effect is completely determined by the chemical composition and hydration mechanism of the cementitious material itself. Aggregate and water reducing agent are only auxiliary means for performance adjustment, and are not necessary technical features for achieving the technical effect of the present application.

[0033] III. Examples and Comparative Examples (1) The test methods and provisions are as follows: 1. The test environment includes normal temperature curing (22 ± 2°C), autoclave curing (50 ± 5°C, 150 ± 5°C and 250 ± 5°C, corresponding pressures are 1.08 atm, 1.42 atm and 1.76 atm), and high temperature (300 ± 5°C) after the slurry hardens.

[0034] 2. The setting time test was conducted using a Vicat apparatus in accordance with GB / T 1346-2024 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". For the cementitious material of this invention, the above standard test was performed exactly as described above when the curing temperature was 22°C at room temperature. When the curing temperature exceeds 50℃, refer to the above standards and GB / T 10238-2015 "Oil Well Cement". Place the sample in a cylindrical mold with an inner diameter of 20mm and a height of 40mm, and then place the whole sample in a well-sealed, high-temperature resistant plastic container with a small amount of moisture at the bottom. Then cure at the corresponding temperature. When the curing temperature is 50℃, remove one container during the test, open the container and take out the sample. Use the penetration test. Test every 5 minutes for the first 20 minutes, and every 10 minutes thereafter, until the slurry sets. When the curing temperature is 150℃ and 250℃, prepare 8 containers for each sample. Take out one container for each test, place the container under a fan to cool it for 2 minutes, then depressurize it, open the container and take out the sample. Use the penetration test. Test every 5 minutes for the first 20 minutes, and every 10 minutes thereafter. If it has not set after 1 hour, stop testing. The setting time is recorded as greater than 1 hour.

[0035] 3. The flowability test shall be conducted in accordance with the jumping table method in GB / T 2419-2020 "Determination of Flowability of Cement Mortar". The timing shall be started when the slurry is stirred. The first test shall be conducted after the stirring is completed. Then the flowability shall be tested and recorded at 1 hour and 6 hours respectively.

[0036] 4. The sulfate attack resistance test was conducted according to GB / T 749-2008 "Test Method for Sulfate Attack Resistance of Cement", using both the immersion method and the wet-dry cycle method. The molded specimens were cured in an environment of 22 ± 2℃ and 75% relative humidity for 28 days (including 6 hours of curing at 50℃ during this period), and then immersed in a 5% sodium sulfate solution. The water was changed every month. The compressive strength was tested before immersion, after 28 days, and after 56 days. For the wet-dry cycle method, the specimens were cured in the same environment for 7 days, then immersed in a 5% sodium sulfate + magnesium sulfate composite solution for 16 hours, and then dried at 40℃ for 8 hours, marking one cycle. The compressive strength was tested before the wet-dry cycle, after 25 wet-dry cycles, and after 50 wet-dry cycles.

[0037] 5. The compressive strength test shall be conducted in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar" and using a universal testing machine.

[0038] 6. The density of the hardened sample was tested using the vacuum water retention method.

[0039] 7. The curing temperature is 150℃ and 250℃, and a certain temperature rising time is needed, which is counted as 50% of the age.

[0040] (2) Examples and Comparative Examples Example 1: The powder is weighed according to the mass ratio of heavy burned magnesium oxide: magnesium hydroxide: quartz powder = 9: 1: 3, and 0.05% of polyacrylamide and 0.10% of citric acid are added to the powder, and 0.15% of polycarboxylic acid water reducing agent is added and mixed fully, then 23% of water of the mass of the powder material is added and stirred for 5 minutes to fully mix the water and the powder material to prepare a homogeneous slurry. The flow spread of the slurry is tested, and the setting time of the slurry is tested under the conditions of normal temperature, 50℃, 150℃ and 250℃ respectively. While testing the workability, the slurry is poured into a test mold and placed in the same environment for curing, and the compressive strength is tested after 3 hours, 1 day and 7 days of curing.

[0041] Example 2: The powder is weighed according to the mass ratio of heavy burned magnesium oxide: light burned magnesium oxide: quartz powder: fly ash = 18: 2: 2: 1, and 0.05% of lignocellulose and 0.25% of citric acid are added to the powder, and mixed fully, then 29% of water of the mass of the powder material is added and stirred for 5 minutes to fully mix the water and the powder material to prepare a homogeneous slurry. The flow spread of the slurry is tested, and the setting time of the slurry is tested under the conditions of normal temperature, 50℃, 150℃ and 250℃ respectively. While testing the workability, the slurry is poured into a test mold and placed in the same environment for curing, and the compressive strength is tested after 3 hours, 1 day and 7 days of curing.

[0042] Example 3: The powder is weighed according to the mass ratio of heavy burned magnesium oxide: light burned magnesium oxide: quartz powder: silica ash = 5: 5: 2: 1, and 0.05% of polyacrylamide and 0.50% of citric acid are added to the powder, and mixed fully, then 32% of water of the mass of the powder material is added and stirred for 5 minutes to fully mix the water and the powder material to prepare a homogeneous slurry. The flow spread of the slurry is tested, and the setting time of the slurry is tested under the conditions of normal temperature, 50℃, 150℃ and 250℃ respectively. While testing the workability, the slurry is poured into a test mold and placed in the same environment for autoclave curing, and the compressive strength is tested after 3 hours, 1 day and 7 days of curing.

[0043] Example 4: The powders are weighed according to the mass ratio of light-burned magnesium oxide: silica ash: fly ash = 10:1:2, and 0.75% of citric acid is added to the powders, which are then mixed thoroughly, and 38% of water by mass of the powders is added and stirred for 5 minutes to mix the water and the powders thoroughly to prepare a homogeneous slurry. The flow spread of the slurry is tested, and the setting time of the slurry is tested at room temperature, 50°C, 150°C, and 250°C, respectively. While the working performance is being tested, the slurry is cast into a mold and placed in the same environment for autoclave curing, and the compressive strength at the corresponding ages of 3 hours, 1 day, and 7 days is tested. The slurry is prepared according to the above-mentioned ratio and method, cast into a mold, and placed in a 50°C environment for autoclave curing for 3 days, and after the mold is removed, the test block is placed in a 300°C environment for 6 hours, and the compressive strength is tested.

[0044] Example 5: The powders are weighed according to the mass ratio of light-burned magnesium oxide: active magnesium oxide: magnesium hydroxide: silica ash = 6:3:1:3, and 1.00% of citric acid and 0.30% of polycarboxylic acid water reducer by mass of the powders are added, which are then mixed thoroughly, and 40% of water by mass of the powders is added and stirred for 5 minutes to mix the water and the powders thoroughly to prepare a homogeneous slurry. The flow spread of the slurry is tested, and the setting time of the slurry is tested at room temperature, 50°C, 150°C, and 250°C, respectively. While the working performance is being tested, the slurry is cast into a mold and placed in the same environment for autoclave curing, and the compressive strength at the corresponding ages of 3 hours, 1 day, and 7 days is tested.

[0045] Example 6: The powders are weighed according to the mass ratio of heavy-burned magnesium oxide: light-burned magnesium oxide: magnesium hydroxide: silica ash = 6:3:1:3, and 0.25% of citric acid, 0.05% of polyacrylamide, and 0.80% of a naphthalene-based water reducer by mass of the powders are added, and 3 times the mass of the powders of standard sand is added, which are then mixed thoroughly, and 35% of water by mass of the powders is added and stirred for 5 minutes. The flow spread of the mortar is tested, and the setting time of the mortar is tested at room temperature, 50°C, 150°C, and 250°C, respectively. While the working performance is being tested, the slurry is cast into a mold and placed in the same environment for autoclave curing, and the compressive strength at the corresponding ages of 3 hours, 1 day, and 7 days is tested.

[0046] Example 7: The powders were weighed according to the mass ratio of light-burned magnesium oxide: magnesium hydroxide: silica ash = 7:3:3, plus 0.10% of lignin and 1.5% of citric acid based on the mass of the powders, mixed thoroughly, then 65% of water based on the mass of the powders was added and stirred for 5 minutes to make a homogeneous slurry. The flow spread of the slurry was tested, and the setting time of the slurry was tested at room temperature, 50°C, 150°C, and 250°C, respectively. At the same time, the workability of the slurry was tested, and the slurry was cast into a mold and placed in the same environment for autoclave curing. The compressive strength was tested after 3 hours, 1 day, and 7 days of curing.

[0047] Comparative Example 1:

[0048] Commercially available G-grade oil well cement was mixed with 0.3% dispersant, 0.2% defoaming agent, and 0.3% suspending agent according to the proportions recommended in the oil well cement guide, and 44% water based on the mass of the cement was added and stirred thoroughly to prepare a cement slurry. The flow spread of the slurry was tested, and the setting time of the slurry was tested at room temperature, 50°C, 150°C, and 250°C, respectively. At the same time, the workability of the slurry was tested, and the slurry was cast into a mold and placed in the same environment for curing. The compressive strength was tested after 3 hours, 1 day, and 7 days of curing. The slurry was prepared according to the above proportions and method, cast into a mold, and placed in a 50°C environment for autoclave curing for 3 days. After demolding, the test block was placed in a 300°C environment for 6 hours, then removed and tested for compressive strength.

[0049] Table 1 Performance of Examples and Comparative Examples Note: - not tested or not testable. Table 2 Sulfate Resistance Performance of Examples and Comparative Examples From the test results of the examples and comparative examples, it can be seen that: 1) The setting time realizes temperature-responsive precise regulation, and the construction adaptability far exceeds that of traditional materials. Compared with Comparative Example 1 (commercially available G-grade oil well cement), the setting time regulation characteristics of the cementing material of the present application show the advantages of quality: first, the normal temperature (22°C) construction window period is significantly prolonged: the setting time of Example 1 and Example 2 both exceeds 600 minutes (10 hours), and Example 3 reaches 535 minutes, and the flow spread of Example 1 and Example 2 after 6 hours of stirring still maintains 230 mm, which is basically the same as the initial fluidity (240 mm, 235 mm). However, the normal temperature setting time of Comparative Example 1 is only 180 minutes, and the flow spread is reduced to 185 mm after 1 hour, and it completely loses fluidity after 6 hours, which cannot meet the long-distance pumping or complex working condition pouring requirements. This proves that the cementing material described in the present application can realize normal temperature retarding and flow, and solves the technical problems of fast setting and low construction fault tolerance of traditional cement at normal temperature. Second, the setting rate is precisely controllable at high temperature: at 50°C, the setting time of Example 5 is only 30 minutes, and the setting time of Example 4 is 50 minutes, which can quickly harden and form; at 150°C, the setting time of Example 4 and Example 7 is 20 minutes and 30 minutes respectively, which not only guarantees the operation time, but also quickly forms early strength; at 250°C, the setting time of Example 6 is only 10 minutes, and the setting time of Example 1 is 40 minutes, which adapts to the rapid sealing requirement under high temperature and high pressure. Looking back at Comparative Example 1, the setting time at 50°C is 100 minutes, and the hardening is slow; at 150°C, it is only 5 minutes, which is easy to solidify and block the pipe; at 250°C, it has completely lost construction performance and cannot be tested, showing the defects of fast setting at normal temperature and uncontrollable setting at high temperature. This also shows from the side that the temperature response characteristics of the high-temperature accelerating and fast hardening of the present application cannot be realized by the traditional material through the compounding of external additives.

[0050] 2) High-temperature mechanical properties are stable and excellent, breaking through the temperature use limit of traditional materials. This is the most core advantage of the present application, which forms an absolute difference compared with the high-temperature performance of Comparative Example 1: first, the high-temperature strength retention capability above 200°C: under the curing condition of 250°C, the 7-day compressive strength of Example 1 is 29.1 MPa, and the 3-hour strength of Example 6 is as high as 37.7 MPa; while the 3-hour strength of Comparative Example 1 at 250°C is only 1.0 MPa, and the 7-day strength is still 1.0 MPa, basically losing the load-bearing and sealing functions. Secondly, the service capability at 300°C extreme high temperature: after curing at 300°C for 6 hours, the 3-hour compressive strength of Example 4 is 38.1 MPa, and the 1-day strength is maintained at 34.5 MPa; the 1-day strength of Example 6 at 300°C is 30.5 MPa; while the strength of Comparative Example 1 at 300°C environment is always ≤1.0 MPa, completely fails. Combined with microscopic analysis, it can be known that the core hydration product M-S-H gel of the present application does not decompose at 150°C-300°C, but rather converts into more stable serpentine phase; while the C-S-H gel of Comparative Example 1 undergoes crystal phase transition and structure collapse above 200°C. This proves that the present application successfully breaks through the temperature use limit of 200°C of traditional cementitious materials, and solves the core problem that the prior art cannot adapt to extreme high-temperature working conditions below 300°C.

[0051] 3) The mechanical strength develops rapidly and evenly, taking into account early load-bearing and long-term stability. Compared with the uneven characteristics of Comparative Example 1 that the normal temperature performance is acceptable and the high-temperature performance is completely failed, the strength development of the present application presents a synergistic advantage in the whole temperature range: first, the early strength rapidly increases at medium and high temperatures: after curing at 150°C for 3 hours, the strength of Example 4 is 20.2 MPa, and the strength of Example 6 is 16.3 MPa, far exceeding the strength of Comparative Example 1 which is 2.7 MPa; after curing at 250°C for 3 hours, the strength of Example 6 is 37.7 MPa, while the strength of Comparative Example 1 is only 1.0 MPa, and the examples can meet the needs of rapid sealing and early load-bearing under high-temperature working conditions. Secondly, the long-term strength is stable and does not decline: after curing at 150°C for 7 days, the strength of Example 2 is 33.7 MPa, the strength of Example 3 is 35.2 MPa, and the strength of Comparative Example 1 is only 3.2 MPa; after curing at 250°C for 7 days, the strength of Example 1 is 29.1 MPa, and Comparative Example 1 has completely failed. Furthermore, the normal temperature strength steadily increases: the 1-day strength of Example 3 at normal temperature is 17.1 MPa, and the 7-day strength is 28.5 MPa, the 1-day strength of Example 4 at normal temperature is 18.7 MPa, although the early (3-hour) strength at normal temperature is lower than that of Comparative Example 1 (1.0 MPa vs 1.0 MPa), but it completely adapts to the strength development rhythm of normal temperature construction, and does not have the defect of the cliff-like drop of high-temperature strength of Comparative Example 1.

[0052] 4) Multi-scenario adaptability, density and temperature zone coverage ability far exceed traditional materials. Compared with the application limitation of Comparative Example 1, the present application shows a wide range of working condition adaptability: first, temperature zone coverage range: Example 1 adapts to extreme high temperature above 250℃, Examples 2 and 3 adapt to 150℃-250℃, Examples 4, 6 and 7 adapt to below 150℃, and Example 5 adapts to 50℃, forming a full temperature zone coverage of 50℃-300℃. It is also due to the different working conditions targeted by different examples that not all examples are tested in Table 1. Comparative Example 1 can only be used at room temperature-150℃ at low strength, and is completely ineffective above 250℃. Second, density adjustability: the density of the cementing material of the present application ranges from 1.45 to 2.45 g / cm3, which can be optimized by particle size distribution to adapt to the needs of lightweight sealing or high-density anti-channeling; and the density of Comparative Example 1 is fixed at 2.14 g / cm3, which cannot meet the density requirements of diversified working conditions.

[0053] 5) Since there is overlap in the use of some examples, Examples 1, 3 and 4 are selected as representatives for testing in terms of resistance to sulfate attack. The use of these three examples covers the full temperature range of below 150℃, 150-250 and above 250. As can be analyzed from Table 2, the salt corrosion resistance of the examples is excellent, and can avoid performance degradation caused by aggressive media. The present application shows excellent corrosion resistance, whether under immersion or dry-wet cycle conditions, the strength does not decrease and even increases. It meets different working conditions, has the potential to serve for a longer time and has better durability. In contrast, traditional materials have poor salt corrosion resistance and need additional measures or methods to improve. Comparative Example 1 can react with calcium hydroxide in the system to generate ettringite due to the entry of aggressive media into the matrix, resulting in expansion stress and cracks in the matrix, and even performance degradation, especially under dry-wet cycle conditions, the damage is more obvious.

[0054] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those of ordinary skill in the art should understand that modifications or equivalent replacements to the technical solutions of the present application without departing from the spirit and scope of the technical solutions should be covered within the scope of the claims of the present application.

Claims

1. A cementitious material that sets and hardens in a high temperature environment, characterized in that, The cementing material is composed of magnesium oxide, magnesium hydroxide, siliceous material, stabilizer and water-retaining agent. In the cementing material, the mass of magnesium hydroxide is less than or equal to 50% of the mass of magnesium oxide, the mass of the stabilizer is less than or equal to 3% of the total mass of the cementing material, and the mass of the water-retaining agent is less than or equal to 2% of the total mass of the cementing material, according to the mass percentage; the ratio of the total mass of magnesium hydroxide and magnesium oxide to the total mass of silicon dioxide in the siliceous material is 0.5-10.

2. Cementitious material according to claim 1, characterized in that The magnesium oxide is one of active magnesium oxide, light-burned magnesium oxide and heavy-burned magnesium oxide or a mixture of several thereof.

3. Cementitious material according to claim 2, characterized in that When the magnesium oxide is a mixture, the mass of heavy-burned magnesium oxide is greater than or equal to 40% of the total mass of the magnesium oxide mixture, according to the mass percentage.

4. Cementitious material according to claim 3, characterized in that The maximum particle size of the magnesium oxide is less than 80 μm, and the mass fraction of MgO in the magnesium oxide is ≥75%, according to the mass percentage.

5. The cementitious material of claim 1, wherein, The siliceous material is one of quartz powder, fly ash and silica fume or a mixture of several thereof.

6. Cementitious material according to claim 5, characterized in that When the siliceous material is a mixture, the mass of quartz powder is greater than or equal to 30% of the total mass of the siliceous material mixture, according to the mass percentage.

7. Cementitious material according to claim 6, characterized in that The maximum particle size of the siliceous material is less than 80 μm; the mass fraction of SiO2 in quartz powder and silica fume is greater than or equal to 85%, and the mass fraction of SiO2 in fly ash is greater than or equal to 50%, according to the mass percentage.

8. The cementitious material of claim 1, wherein, The stabilizer is citric acid.

9. The cementitious material of claim 1, wherein, The water-retaining agent is one of cellulose ether, polyacrylamide or lignocellulose.

10. A method of use of a cementitious material, characterised in that, The use method of the cementing material according to any one of claims 1-9 is as follows: At normal temperature, first add water accounting for 20%-80% of the mass of the cementing material powder to prepare a mixture with fluidity, so that the fluidity or slump of the mixture is maintained for ≥2 h; then deliver the mixture to a working scene with a temperature of 50-300 ℃ for pouring, in which the setting time is 10-60 min, and finally hardened to form strength.

Images