A cementless geopolymer cementing material for CO2 flooding, its preparation method and application

Abstract

This invention belongs to the technical field of cementing materials for oil and gas wells. It discloses a cementless geopolymer cementing material for CO2 flooding, its preparation method, and its application. By mass, it comprises 50-70 parts of aluminosilicate precursor, 15-25 parts of alkali activator, 8-18 parts of modified filler, and 2-7 parts of rheology modifier. The aluminosilicate precursor is prepared by mixing metakaolin, fly ash, and slag. The alkali activator is a mixture of sodium silicate solution and sodium hydroxide. The modified filler is a compound of surface-grafted amino-containing nano-calcium carbonate and microsilica powder. The rheology modifier is a compound additive of fluid loss reducer, retarder, and dispersant. This invention significantly improves the long-term corrosion resistance and sealing stability of the cementing material through the synergistic effect of amino chemical carbon dioxide capture and the dense structure of microsilica powder. The cementless system has excellent environmental friendliness and can adapt to the cementing operation requirements of CO2 flooding oil and gas wells at different depths, possessing high industry application value.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas well cementing materials technology, and in particular to a cementless geopolymer cementing material for CO2 flooding, its preparation method and application. Background Technology

[0002] Cementing materials belong to the field of oil and gas field development and are core supporting materials for CO2 flooding to enhance oil and gas recovery and CO2 geological sequestration projects. Currently, my country's CO2 flooding industry has entered the stage of large-scale promotion. Oil and gas fields such as Changqing, Shengli, and Daqing have cumulatively built more than 10 million-ton-level CO2 flooding demonstration projects, covering well depths from shallow loose sandstone reservoirs of 1,000m to deep carbonate reservoirs of 8,000m. Cementing operations must simultaneously meet the requirements of construction rheological properties, early mechanical strength, and long-term interlayer isolation for more than 50 years. The core requirement is that the materials have the ability to withstand CO2 corrosion in environments with long-term pressure of 10-30MPa and temperature of 60-180℃.

[0003] Currently, the mainstream cementing material is the G-grade oil well cement modification system. Its core principle is to consume the calcium hydroxide generated during cement hydration by adding components such as silica fume, basalt fiber, and nano-silica, thereby reducing the overall alkalinity of the matrix and decreasing the probability of CO2 reacting with calcium hydroxide to form easily soluble calcium carbonate. This system has readily available raw materials and its construction process is fully compatible with existing cementing operations, and it has been widely used in cementing operations for various conventional oil and gas wells. However, this type of material cannot solve the inherent defect that the hydration products of the cement matrix are easily dissolved by acidic CO2 fluid. After curing for 90 days at 150℃ and 20MPa CO2, the strength retention rate is generally only about 70%, far below the minimum threshold of 80% required for CO2 flooding cementing. It cannot meet the long-term isolation requirements of deep CO2 flooding wells. At the same time, the carbon emissions from the production process of ordinary silicate cement are extremely high, which does not meet the green production requirements for oil and gas field development under the dual-carbon target.

[0004] The second type of existing technology that has been gradually promoted in recent years is ordinary geopolymer cementing material, which belongs to the cement-free system. The core principle is that the aluminosilicate precursor generates an amorphous three-dimensional aluminosilicate gel structure under the action of alkali. The matrix itself does not contain calcium hydroxide components that are easily dissolved by CO2, and its basic corrosion resistance is significantly better than that of conventional cement systems. It has been tested on a small scale in some shallow CO2 flooding wells. However, most existing ordinary geopolymer cementing materials use ordinary nano-calcium carbonate without functional modification as filler. CO2 can still penetrate through the micropores inside the matrix, dissolving the filler and forming interconnected channels, which leads to a rapid increase in matrix permeability and rapid failure of interlayer sealing capacity. At the same time, the rheological properties control methods of existing geopolymers are limited, and they generally have problems such as insufficient fluidity and excessive free fluid content. They cannot meet the cementing and pumping requirements of complex well types such as extended reach wells and horizontal wells. Under high pressure conditions with CO2 partial pressure exceeding 25MPa, the long-term sealing failure rate exceeds 40%, making it difficult to adapt to the long-term service requirements of large-scale CO2 geological storage.

[0005] Currently, existing cementing materials are not suitable for the long-term service requirements of deep CO2 flooding development. The industry urgently needs to develop a new type of cementing material with excellent CO2 corrosion resistance and long-term strength stability to solve the technical bottleneck of rapid strength decay and short sealing life of existing cement-based materials after corrosion, and ensure the long-term safe production of CO2 flooding oil and gas wells. Summary of the Invention

[0006] To address the shortcomings of existing oil and gas well cementing materials, such as poor CO2 corrosion resistance, rapid long-term strength decay, high brittleness, and low interfacial bonding strength, this invention provides a cementless geopolymer cementing material for CO2 flooding, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A cementless geopolymer cementing material for CO2 flooding comprises the following components by mass: 50-70 parts of aluminosilicate precursor, 15-25 parts of alkali activator, 8-18 parts of modified filler, and 2-7 parts of rheology modifier; wherein the aluminosilicate precursor is a powder obtained by mixing metakaolin, fly ash, and slag in a mass ratio of 1-3:2-4:3-5; and the alkali activator is a mixture system obtained by mixing sodium silicate solution with a modulus of 1.2-1.8 and solid sodium hydroxide in a mass ratio of 5-8:1. The modified filler is composed of nano-calcium carbonate with surface-grafted amino and microsilica powder in a mass ratio of 1:2~4. The rheology modifier is a compound additive obtained by mixing a fluid loss reducer, a retarder, and a dispersant in a mass ratio of 2~3:1~2:1. The cementing material has a compressive strength of not less than 14 MPa after 24 hours of curing, a permeability of less than 0.1 mD, and a compressive strength retention rate of not less than 90% after long-term curing in an environment with a CO2 partial pressure of 10~30 MPa and a temperature of 60~150℃. The interlayer sealing performance meets the requirements of API RP 65 standard.

[0008] Furthermore, the metakaolin in the aluminosilicate precursor is calcined at 700~850℃, has an active aluminum content of not less than 35wt%, uses Grade I fly ash, and has a specific surface area of ​​400~600m². 2 / kg.

[0009] Furthermore, the solid content of the alkali activator is 40-55 wt%, and the pH value of the solution is controlled at 12-14 during the preparation process.

[0010] Furthermore, the surface-grafted amino-containing nano-calcium carbonate has a particle size of 30-100 nm, the SiO2 content of the microsilica powder is not less than 92 wt%, and the specific surface area is 15-20 m². 2 / g.

[0011] Furthermore, the water loss reducing agent is an acrylamide copolymer, the retarder is hydroxyethylidene diphosphonic acid, and the dispersant is naphthalene sulfonate formaldehyde condensate.

[0012] Furthermore, the following steps are included: S1. Weigh the aluminosilicate precursor, modified filler, and rheology modifier according to the formula, place them in a constant speed stirrer and dry mix at a speed of 1000~1500r / min for 3~5min to obtain a uniform dry mix. S2. Weigh out sodium silicate solution and solid sodium hydroxide according to the ratio, mix and stir until completely dissolved to obtain an alkaline activator solution with the required modulus, and control the solution temperature at 20~30℃. S3. Add the alkaline activator solution to the dry mix and wet mix at a speed of 2000~3000 r / min for 8~12 min to obtain a homogeneous polymer slurry with a flowability greater than 22 cm and a free liquid content of less than 1.4 mL. S4. Inject the obtained geopolymer slurry into the mold or wellbore annulus required for cementing construction. Under pressure conditions of 0.1~120MPa, select the corresponding curing section according to the working conditions: S4-a curing temperature 40~100℃, suitable for shallow and medium-depth oil and gas wells; S4-b curing temperature 100~180℃, suitable for medium and deep oil and gas wells, and cure until completely solidified.

[0013] Furthermore, during the wet mixing process in step S3, the slurry density is controlled to be 1.8~2.2 g / cm³. 3 The density difference in settling stability does not exceed 0.03 g / cm³. 3 .

[0014] Furthermore, during the S4 step of the curing process, if used for on-site cementing operations, the thickening time of the slurry is 1-2 hours longer than the actual grouting time, and the thickening curve meets the requirements of API RP 10B-3 standard.

[0015] Furthermore, the geopolymer slurry prepared from the cementing material is used as a sealing material and injected into the casing and annulus of the CO2-driven oil and gas well. After solidification, it achieves interlayer sealing and casing support. It is suitable for cementing operations of CO2-driven oil and gas wells with a depth of 1000~10000m and a formation temperature of 40~180℃.

[0016] Furthermore, after the geopolymer slurry is injected into the annulus, the replacement operation complies with the construction specifications of GB / T 19139, and the interface bonding strength after curing is not less than 2.0 MPa.

[0017] The present invention has the following beneficial effects: This invention employs a modified filler composed of nano-calcium carbonate with surface-grafted amino groups and microsilica powder. The amino groups can actively capture CO2 that invades the solidified body and generate stable carbonate products. At the same time, the active silicon component in the microsilica powder can further combine with the mineralization reaction products to form a dense low-calcium-to-silica gel phase, which significantly reduces the diffusion rate of CO2. This effectively solves the defects of existing ordinary cement-based cementing materials, such as decalcification of hydration products and significant strength reduction after long-term CO2 erosion, and ensures the structural stability of the solidified body during long-term service.

[0018] This invention uses a cementless geopolymer as the matrix phase. By adjusting the composition ratio of the aluminosilicate precursor and the modulus parameters of the alkali activator, the three-dimensional network aluminosilicate gel generated after curing does not contain high-calcium hydration products that are susceptible to CO2 corrosion. Its overall toughness is much higher than that of conventional modified corrosion-resistant cement systems. At the same time, the performance requirements of the slurry under different working conditions can be adjusted by the ratio of rheology modifiers. After curing, it has excellent interfacial bonding performance with casing and formation, effectively solving the defects of existing modified corrosion-resistant cement systems such as high brittleness, insufficient interfacial bonding strength, and substandard long-term service performance under high temperature and high pressure CO2 environment, and avoiding the hidden danger of interlayer flow during service.

[0019] The cementing material of this invention can adapt to the cementing operation requirements of different well depths and temperature ranges. It is suitable for shallow and medium-depth CO2-driven oil and gas wells, as well as deep and ultra-deep CO2-driven oil and gas wells, and can meet the long-term isolation requirements. The raw materials are widely available, and the construction process is compatible with existing conventional cementing operation technology. No additional modifications are required to the on-site construction equipment. It has good promotion and application value in various CO2-driven oil and gas reservoirs. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing cementless geopolymer cementing material for CO2 flooding proposed in this invention; Figure 2 The bar chart shows the retention rate of compressive strength after 90 days of CO2 corrosion for different groups proposed in this invention. Figure 3This is a line graph showing the 90-day strength retention rate under different CO2 partial pressures proposed in this invention. Figure 4 This is a radar chart comparing the core performance proposed in this invention. Detailed Implementation

[0021] The following will refer to the appendices in the embodiments of the present invention. Figure 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Reaction Mechanism and Coupling Agent Selection Explanation The reaction pathway of surface-grafted amino groups with CO2 is as follows: Step 1: The amino group reacts with CO2 to form carbamate. 2R-NH2 + CO2 → R-NHCOO - +R-NH3 + In the second step, the carbamate ions further react with calcium ions in the system to form calcium carbonate precipitate, while simultaneously regenerating the amino groups. R-NHCOO - +Ca 2+ +H₂O→CaCO₃↓+R-NH₂+H + This invention employs a dual synergistic mechanism of amino chemical defense and microsilica physical densification: amino groups grafted onto the surface of nano-calcium carbonate actively capture CO2 that invades the solidified body. After the above two-step reaction, dense calcium carbonate precipitate is generated in situ to fill the micropores inside the matrix. At the same time, the amino groups can cyclically participate in the capture reaction to achieve long-term CO2 blocking. The active SiO2 in the microsilica powder participates in the polymerization reaction, crosslinking with the silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra in the system to form a denser NASH or CASH gel structure, filling the original pores of the matrix, blocking the CO2 diffusion channels, and providing active sites for the mineralization reaction after the amino group captures CO2.

[0023] The synergistic effect is quantitatively extrapolated as follows: When an equal amount of grafted amino-based nano-calcium carbonate is added alone, the CO2 capture efficiency is about 60% and the long-term strength retention rate is about 78%; when an equal amount of microsilica powder is added alone, the porosity decreases by about 25% and the long-term strength retention rate is about 72%; the theoretically expected combined strength retention rate after the two are combined is about 82%, and the actual strength retention rate of this invention can reach more than 90%. The additional synergistic effect comes from the synergistic effect of the calcium carbonate generated by amino mineralization and the cross-linking of microsilica powder to form a dense gel.

[0024] The present invention selects aminosilane as a coupling agent for the following reasons: Although epoxy groups can react with CO2, their reaction rate and conversion rate are lower than those of amino groups, and the reaction product is a cyclic carbonate, which cannot undergo further mineralization reaction to fill the pores; alkyl silanes can only improve the interfacial compatibility between the filler and the matrix, but do not have the function of capturing CO2; fluorinated coupling agents are too expensive and will inhibit the alkaline-induced crosslinking activity of geopolymers; after grafting, the amino groups on the surface of aminosilane are weakly basic, which can undergo rapid mineralization reaction with acidic CO2. At the same time, the amino groups can form hydrogen bonds with the silanol groups in the geopolymer system, further improving the interfacial bonding force, resulting in the best overall performance and cost-effectiveness.

[0025] All basic raw materials used in this embodiment meet the technical requirements: metakaolin calcination temperature 700~850℃, active aluminum content ≥35wt%; fly ash is grade I fly ash; slag specific surface area 400~600m² 2 / kg; alkali activator solid content 40~55wt%, pH 12~14; microsilica powder SiO2 content ≥92wt%, specific surface area 15~20m² 2 / g; the water loss reducing agent is an acrylamide copolymer, the retarder is hydroxyethylidene diphosphonic acid, and the dispersant is naphthalene sulfonate formaldehyde condensate.

[0026] This interfacial bonding strength test adopted the interlayer sealing strength test method specified in API RP 65. The high pressure differential gas channeling evaluation index of this method is highly compatible with the long-term sealing performance evaluation requirements of CO2 flooded oil and gas wells. The test results can directly reflect the interfacial sealing ability of the material in the CO2 flooding scenario.

[0027] Cementing Material Preparation Examples Example 1 Weigh out 50 parts by mass of aluminosilicate precursor, wherein the mass ratio of metakaolin, fly ash and slag is 1:4:5; 25 parts by mass of alkali activator, wherein the mass ratio of sodium silicate solution with modulus 1.2 to solid sodium hydroxide is 5:1; 8 parts by mass of modified filler, wherein the mass ratio of nano-calcium carbonate with surface-grafted aminos to microsilica powder is 1:2; and 7 parts by mass of rheology modifier, wherein the mass ratio of water loss reducer, retarder and dispersant is 2:2:1.

[0028] The preparation steps are as follows: S1. The aluminosilicate precursor, modified filler, and rheology modifier are placed in a constant speed stirrer and dry-mixed at 1000 r / min for 5 min to obtain a dry mixture. S2 Weigh out sodium silicate solution and solid sodium hydroxide according to the ratio, mix and stir until completely dissolved to obtain alkali activator solution, and control the solution temperature at 20℃; S3 adds the alkali activator solution to the dry mix and wet mixes at 2000 r / min for 12 min to obtain a slurry with a density of 1.8 g / cm³.3 The density difference in sedimentation stability is 0.02 g / cm³. 3 The geopolymer slurry has a fluidity of 23 cm and a free liquid content of 1.2 mL. S4 injects the slurry into the mold and cures it at 0.1 MPa and 60°C until it is fully solidified.

[0029] This embodiment is applicable to cementing operations in shallow and medium-depth CO2-driven oil and gas wells. The slurry thickening time is 1 hour longer than the actual grouting time, which meets the requirements of API RP 10B-3 standard.

[0030] Example 2 Weigh out 70 parts by mass of aluminosilicate precursor, in which the mass ratio of metakaolin, fly ash and slag is 3:2:3; 15 parts by mass of alkali activator, in which the mass ratio of sodium silicate solution with modulus 1.8 to solid sodium hydroxide is 8:1; 18 parts by mass of modified filler, in which the mass ratio of nano-calcium carbonate with surface-grafted aminos to microsilica powder is 1:4; and 2 parts by mass of rheology modifier, in which the mass ratio of water loss reducer, retarder and dispersant is 3:1:1.

[0031] The preparation steps are as follows: S1. The aluminosilicate precursor, modified filler, and rheology modifier are placed in a constant speed stirrer and dry-mixed at 1500 r / min for 3 min to obtain a dry mixture. S2 Weigh out sodium silicate solution and solid sodium hydroxide according to the ratio, mix and stir until completely dissolved to obtain alkali activator solution, and control the solution temperature at 30℃; S3 adds the alkali activator solution to the dry mix and wet mixes at 3000 r / min for 8 min to obtain a slurry with a density of 2.2 g / cm³. 3 The density difference in sedimentation stability is 0.025 g / cm³. 3 The geopolymer slurry had a flowability of 22.5 cm and a free liquid content of 1.3 mL. S4 injects the slurry into the mold and cures it at 120MPa and 180℃ until it is fully solidified.

[0032] This embodiment is applicable to cementing operations in deep CO2-driven oil and gas wells. The slurry thickening time is 2 hours longer than the actual grouting time, which meets the requirements of API RP 10B-3 standard.

[0033] Example 3 Weigh out 60 parts by mass of aluminosilicate precursor, wherein the mass ratio of metakaolin, fly ash and slag is 2:3:4; 20 parts by mass of alkali activator, wherein the mass ratio of sodium silicate solution with modulus 1.5 to solid sodium hydroxide is 6.5:1; 13 parts by mass of modified filler, wherein the mass ratio of nano-calcium carbonate with surface-grafted aminos to microsilica powder is 1:3; and 4.5 parts by mass of rheology modifier, wherein the mass ratio of water loss reducer, retarder and dispersant is 2.5:1.5:1.

[0034] The preparation steps are as follows: S1. The aluminosilicate precursor, modified filler, and rheology modifier are placed in a constant speed stirrer and dry-mixed at 1200 r / min for 4 min to obtain a dry mixture. S2 Weigh out sodium silicate solution and solid sodium hydroxide according to the ratio, mix and stir until completely dissolved to obtain alkali activator solution, and control the solution temperature at 25℃; S3 adds the alkali activator solution to the dry mix and wet mixes at 2500 r / min for 10 min to obtain a slurry with a density of 2.0 g / cm³. 3 The density difference in sedimentation stability is 0.022 g / cm³. 3 The geopolymer slurry has a fluidity of 24 cm and a free liquid content of 1.1 mL. S4 injects the slurry into the mold and cures it at 60MPa and 100℃ until it is fully solidified.

[0035] This embodiment is applicable to cementing operations in medium-deep CO2-driven oil and gas wells. The slurry thickening time is 1.5 hours longer than the actual grouting time, which meets the requirements of API RP 10B-3 standard.

[0036] Example 4 100g of nano-calcium carbonate with a particle size of 30-100nm was weighed and placed in 1000mL of anhydrous ethanol. The nano-calcium carbonate was ultrasonically dispersed for 30min to obtain a 10% (w / w) nano-calcium carbonate suspension. The pH of the system was adjusted to 9-10 with ammonia. The temperature was raised to 60℃, and 5g of γ-aminopropyltriethoxysilane was added dropwise. The mixture was stirred at a constant temperature for 4h. The pH of the system was monitored in real time during the reaction. Ammonia was added to maintain the pH at 9-10. After the reaction, the conductivity of the supernatant was measured. Once the conductivity stabilized and remained unchanged, it was confirmed that there was no free coupling agent residue.

[0037] The solid product was then centrifuged, washed three times with anhydrous ethanol to remove unreacted coupling agent, dried in a vacuum oven at 80°C for 12 hours, ground, and passed through a 200-mesh sieve to obtain amino-grafted nano-calcium carbonate. Fourier transform infrared spectroscopy was performed on the product prepared in this example, and a wavelength of 2930 cm⁻¹ was observed. -1 2850cm -1 The characteristic peak of the methylene stretching vibration at 1560 cm⁻¹, and the peak at 1560 cm⁻¹.-1 The characteristic peak of amino bending vibration at the point proves that the amino group has been successfully grafted onto the surface of nano-calcium carbonate via covalent bonds.

[0038] Comparative Example Blank group: Only aluminosilicate precursor, alkali activator, and rheology modifier are retained, without adding any modified filler, and the proportions of the remaining components are the same as in Example 1.

[0039] Unmodified CaCO3 group: The modified filler is composed of ungrafted amino-containing nano-calcium carbonate and microsilica powder in a 1:3 ratio, and the remaining component ratios are the same as in Example 1. Unmodified nano-calcium carbonate will undergo a dissolution reaction under long-term CO2 corrosion to generate soluble calcium bicarbonate, resulting in a significant increase in the porosity of the solidified body and performance degradation.

[0040] Physical mixing group: Unmodified nano-calcium carbonate, aminosilane, and microsilica powder were directly physically mixed as modified fillers without grafting reaction. The proportions of the remaining components were the same as in Example 1. The aminosilane was not covalently grafted with the nano-calcium carbonate, resulting in uneven dispersion and an inability to form a continuous and effective amino functional layer on the surface of the nano-calcium carbonate. This significantly reduced CO2 capture efficiency, allowing it to exert only a small amount of interfacial modification effect.

[0041] The control group of this invention: surface-grafted amino nano-calcium carbonate prepared in Example 4 was compounded with microsilica powder at a ratio of 1:3 as a modified filler, and the remaining component ratios were the same as in Example 1.

[0042] Performance testing and data comparison All sample performance tests were conducted using standard methods: 24-hour compressive strength was tested according to API RP 10B-3, permeability was tested according to GB / T 29172, long-term corrosion performance was tested after curing in a high-pressure reactor at a CO2 partial pressure of 20MPa and a temperature of 120℃ for 90 days to determine the strength retention rate, and interfacial bonding strength was tested according to API RP 65.

[0043] Table 1 Component Parameter Table of Examples The three embodiments cover all component parameter endpoints defined by the technical requirements, verifying that the technical solution of the present invention is applicable across the entire parameter range.

[0044] Table 2 Performance Comparison of Examples and Comparative Examples The performance of all three embodiments was superior to that of the comparative examples. The 24-hour compressive strength of the unmodified CaCO3 group was slightly higher than that of the control group, due to the early filling effect of nano-calcium carbonate. However, the strength retention rate after 90 days of corrosion was only 52.0%, far lower than the 62.3% of the control group, verifying the defect of unmodified calcium carbonate being dissolved by CO2, leading to performance degradation. The strength retention rate of the control group of this invention reached 92.1%, far exceeding the theoretical superposition value of 82% for the individual effects of amino groups and microsilica powder, exceeding the theoretical value by about 10 percentage points. This verifies that the dual synergistic mechanism brings significant technical effects and effectively solves the defects of existing cementing materials, such as poor corrosion resistance, rapid strength decay, and low interfacial bonding strength.

[0045] refer to Figure 2 This figure visually reflects the differences in long-term CO2 corrosion resistance among different modification schemes. The strength retention rate of the unmodified CaCO3 group was lower than that of the blank group, verifying the defect of unmodified nano-calcium carbonate being dissolved by CO2, resulting in performance degradation. The performance of the physical mixing group was only slightly better than that of the blank group, indicating that the ungrafted aminosilane could not form a stable functional layer, and the long-term CO2 capture effect was lacking. The strength retention rates of the control group of this invention and Example 2 were both much higher than the industry benchmark of 80%, and exceeded the theoretical superimposed strength retention rate (82%) of amino and microsilica powder alone by about 10 percentage points, proving that the scheme of this invention can effectively solve the problem of insufficient long-term corrosion resistance of existing cementing materials.

[0046] refer to Figure 3 This figure reflects the corrosion resistance stability of different schemes under different CO2 partial pressure conditions. The strength retention rate of the physical mixture group decreases rapidly with increasing CO2 partial pressure, falling below the industry benchmark of 80% after the partial pressure exceeds 20 MPa, which cannot meet the requirements for use in medium-deep high-pressure CO2 flooding wells. The strength retention rates of the control group and Example 2 of this invention are stable at over 90% across the entire partial pressure range of 10-30 MPa, with fluctuations not exceeding 5%. This indicates that the amino capture and microsilica powder compaction synergistic system of this invention can function stably over a wide pressure range, adapting to the cementing needs of various CO2 flooding oil and gas wells with depths of 1000-10000m and large differences in CO2 partial pressure, and possesses excellent adaptability to operating conditions.

[0047] refer to Figure 4This figure comprehensively showcases the multi-dimensional performance of different schemes. The blank group's indicators are all at a low level, failing to meet the basic requirements of CO2 flooding cementing; the physical hybrid group only shows a slight improvement in early strength, with significant shortcomings in permeability and long-term corrosion resistance, failing to achieve long-term effective isolation; the control group of this invention performs best in all four core indicators, especially with permeability far lower than the other two groups, indicating superior compaction, and long-term strength retention rate close to the maximum value, proving its outstanding corrosion resistance. The interface cementing strength also meets the API RP 65 standard requirements, simultaneously meeting the multi-dimensional requirements of early strength, long-term isolation, and interface sealing in cementing operations, adapting to the working conditions of complex CO2 flooding oil and gas wells.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cementless geopolymer cementing material for CO2 flooding, characterized in that, The product comprises the following components by mass: 50-70 parts of aluminosilicate precursor, 15-25 parts of alkali activator, 8-18 parts of modified filler, and 2-7 parts of rheology modifier. The aluminosilicate precursor is a powder obtained by mixing metakaolin, fly ash, and slag in a mass ratio of 1-3:2-4:3-5. The alkali activator is a mixed system obtained by mixing sodium silicate solution with a modulus of 1.2-1.8 and solid sodium hydroxide in a mass ratio of 5-8:

1. The modified filler is a compound of nano-calcium carbonate with surface-grafted amino groups and microsilica powder in a mass ratio of 1:2-4. The rheology modifier is a compound additive obtained by mixing a water loss reducer, a retarder, and a dispersant in a mass ratio of 2-3:1-2:

1.

2. The cementless geopolymer cementing material for CO2 flooding according to claim 1, characterized in that, The metakaolin in the aluminosilicate precursor is calcined at 700-850℃, has an active aluminum content of not less than 35wt%, uses Grade I fly ash, and has a specific surface area of ​​400-600 m². 2 / kg.

3. The cementless geopolymer cementing material for CO2 flooding according to claim 1, characterized in that, The solid content of the alkali activator is 40-55 wt%, and the pH value of the solution is controlled at 12-14 during the preparation process.

4. The cementless geopolymer cementing material for CO2 flooding according to claim 1, characterized in that, The surface-grafted amino-containing nano-calcium carbonate has a particle size of 30-100 nm, the SiO2 content of the microsilica powder is not less than 92 wt%, and the specific surface area is 15-20 m². 2 / g.

5. The cementless geopolymer cementing material for CO2 flooding according to claim 1, characterized in that, The water loss reducing agent is an acrylamide copolymer, the retarder is hydroxyethylidene diphosphonic acid, and the dispersant is naphthalene sulfonate formaldehyde condensate.

6. A method for preparing a cementless polymer cementing material for CO2 flooding, used to prepare the cementless polymer cementing material for CO2 flooding as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Weigh the aluminosilicate precursor, modified filler, and rheology modifier according to the formula, place them in a constant speed stirrer and dry mix at a speed of 1000~1500r / min for 3~5min to obtain a uniform dry mix. S2. Weigh out sodium silicate solution and solid sodium hydroxide according to the ratio, mix and stir until completely dissolved to obtain an alkaline activator solution with the required modulus, and control the solution temperature at 20~30℃. S3. Add the alkali activator solution to the dry mix and wet mix at a speed of 2000~3000 r / min for 8~12 min to obtain a homogeneous polymer slurry with a flowability greater than 22 cm and a free liquid content of less than 1.4 mL. S4. Inject the obtained geopolymer slurry into the mold or wellbore annulus required for cementing construction. Under pressure conditions of 0.1~120MPa, select the corresponding curing section according to the working conditions: S4-a curing temperature 40~100℃, suitable for shallow and medium-depth oil and gas wells; S4-b curing temperature 100~180℃, suitable for medium-deep and deep oil and gas wells, and cure until fully solidified.

7. The preparation method according to claim 6, characterized in that, During the wet mixing process in step S3, the slurry density is controlled to be 1.8~2.2 g / cm³. 3 The density difference in settling stability does not exceed 0.03 g / cm³. 3 .

8. The preparation method according to claim 6, characterized in that, During the S4 step of the curing process, if used for on-site cementing operations, the thickening time of the slurry is 1-2 hours longer than the actual grouting time, and the thickening curve meets the requirements of API RP 10B-3 standard.

9. An application of a cementless polymer cementing material for CO2 flooding, used for applying the cementless polymer cementing material for CO2 flooding as described in claims 1 to 5, characterized in that, The geopolymer slurry prepared from the cementing material is used as a sealing material and injected into the casing and annulus of the formation in CO2-driven oil and gas wells. After solidification, it achieves interlayer sealing and casing support. It is suitable for cementing operations in CO2-driven oil and gas wells with a depth of 1000~10000m and a formation temperature of 40~180℃.

10. The application according to claim 9, characterized in that, After the geopolymer slurry is injected into the annulus, the replacement operation shall comply with the construction specifications of GB / T 19139, and the interface bonding strength after curing shall not be less than 2.0 MPa.

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