A geopolymer-based grout for sealing and abandoning shallow oil and gas wells

Abstract

The present application relates to a kind of geological polymer base slurry for sealing shallow oil and gas disposal well, it is prepared by dry mixing composite cementing material, alkali-activated solution and treatment agent slurry mixed;Dry mixing composite cementing material is made of mineral powder / fly ash mixture, wollastonite powder, sepiolite powder, silica fume, alkali-resistant glass fiber is uniformly mixed;Wollastonite powder is 2% to 6% of its mass, sepiolite powder is 0.5% to 1.5% of its mass, silica fume is 1% to 5% of its mass, alkali-resistant glass fiber is 0.1% to 0.3% of its mass, according to the mass of mineral powder / fly ash mixture;Treatment agent slurry is made of xanthan gum, polycarboxylic acid water reducing agent, polyether modified polysiloxane and water;The mass of water in the geological polymer base slurry is 45% to 50% of the mass of dry mixing composite cementing material.The present application is suitable for sealing shallow low-temperature environment oil and gas disposal well, has excellent sealing property, corrosion resistance and compressive strength, and low cost.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well sealing technology, specifically to a sealing material suitable for abandoned oil and gas wells in shallow and medium-depth formations, applicable to oil and gas extraction in both marine and onshore environments. Background Technology

[0002] As oil fields gradually enter the middle and late stages of development, the number of oil and gas wells requiring permanent sealing and decommissioning increases year by year. Well sealing is a crucial step in the environmentally friendly disposal of abandoned wells. The core process involves filling the wellbore with cementitious materials to isolate formation fluids, ensure wellbore stability, and protect the ecological environment. Conventional well sealing requires injecting cement slurry into the well to form multiple cement plugs at different locations, preventing oil, gas, and water from flowing upwards along the wellbore and achieving permanent sealing. However, using traditional Portland cement slurry for well sealing presents the following problems: (1) Traditional Portland cement slurry undergoes volume shrinkage during solidification, and once the cement plug inside the pipe shrinks, it forms micro-gaps, thus losing its function of sealing oil, gas, and water; (2) Cement plugs for sealing abandoned wells need to maintain mechanical and structural integrity over long geological periods. Usually, the formation contains corrosive fluids, and the mechanical and structural integrity of the cement plug inside the pipe faces severe challenges under long-term corrosion conditions; (3) Cement materials require high temperatures during construction to ensure the smooth progress of the curing process. However, for some shallow and medium-depth oil and gas wells, the low-temperature environment makes it difficult for traditional cement sealing materials to achieve the expected sealing effect, thereby increasing the risk of downhole operations. To solve the above problems, various additives such as expansion agents and corrosion inhibitors are usually added to Portland cement slurry. However, the addition of these additives significantly increases the price of the cement slurry system, resulting in higher costs for sealing abandoned wells. Furthermore, the expansion and long-term corrosion resistance of the cement slurry system still need further verification.

[0003] In the 1970s, French scientist Joseph Davidovits synthesized a novel cementitious material by activating metakaolin with alkali. At the 1976 International Union of Pure and Applied Chemistry (IUPAC) Macromolecular Conference, he proposed a unified name for this type of alkali-activated material: "polyaluminosilicate." This gel material is typically prepared using fly ash, metakaolin, and slag as main raw materials under alkaline activation conditions. It features low energy consumption, stable performance, high strength, high temperature resistance, and corrosion resistance, showing promise as a replacement for traditional Portland cement. Currently, it is widely used in civil engineering, building materials, environmental protection, non-ferrous casting, contaminated soil remediation, and soft soil solidification. However, directly applying such surface cementing formulations to oil and gas well sealing presents fundamental drawbacks: the environments of downhole temperature fluctuations (10-350℃), high pressure (10-100MPa), and complex formation fluids (containing H2S, CO2, and brine) differ greatly from the normal temperature, pressure, and weak corrosion conditions at the surface. This leads to problems such as uncontrolled thickening time, structural collapse at low or high temperatures, and insufficient corrosion resistance, making it unable to meet the requirements for cementing construction and long-term sealing. Existing geopolymer sealing systems are primarily developed and applied for high-temperature deep wells (≥100℃) (such as heavy oil thermal recovery wells and high-temperature gas wells). In high-temperature environments of 150℃-350℃, the alkali-activated reaction rate of geopolymers accelerates, forming a dense zeolite-like phase structure with a compressive strength of 55-100MPa and a permeability coefficient ≤1×10⁻⁶. -12 With a strength of m / s, its resistance to sulfate attack is 12 times that of silicate cement, effectively solving problems such as strength degradation and sealing failure of silicate cement in high-temperature deep wells. However, existing high-temperature geopolymer sealing systems cannot be directly applied to shallow and medium-low temperature environments. The main limitation is that the performance of geopolymers decreases significantly under low-temperature conditions: First, low temperatures greatly weaken the alkali-activated reactivity of cementitious materials, even causing the reaction to stop, with the 28-day compressive strength only 30%-40% of that in high-temperature scenarios, failing to meet the strength requirements (≥14MPa) for sealing shallow and medium-low wells; second, poor construction adaptability, with the slurry thickening time out of control at low temperatures, potentially exceeding 400 minutes due to slow reaction, affecting construction efficiency; and third, decreased structural density, with the porosity of geopolymers increasing to 18%-25% at low temperatures, significantly reducing impermeability and corrosion resistance, and increasing the permeability coefficient to 1×10⁻⁶. -10 With a speed of over m / s, it is on par with ordinary Portland cement, thus losing its core performance advantage. Summary of the Invention

[0004] The purpose of this invention is to provide a geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells. This geopolymer-based slurry is designed to address the problem that existing high-temperature geopolymer sealing systems cannot be directly applied to shallow and medium-depth low-temperature environments or are too costly.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: This geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells is prepared by mixing a dry-mixed composite cementitious material, an alkali-activated solution, and a treatment agent slurry; the dry-mixed composite cementitious material is composed of a mixture of mineral powder / fly ash, wollastonite powder, sepiolite powder, silica fume, and alkali-resistant glass fiber, wherein the mass of wollastonite powder is 2%-6% of the mass of the mineral powder / fly ash mixture, the mass of sepiolite powder is 0.5%-1.5% of the mass of the mineral powder / fly ash mixture, the mass of silica fume is 1%-5% of the mass of the mineral powder / fly ash mixture, and the mass of alkali-resistant glass fiber is [missing information - likely a percentage]. The total mass of water glass, sodium hydroxide, and sodium citrate in the alkaline activation solution is 14.2%-16.5% of the mass of the mineral powder / fly ash mixture; the treatment agent slurry is composed of xanthan gum, polycarboxylate superplasticizer, polyether-modified polysiloxane, and water, with xanthan gum accounting for 0.05%-0.15% of the mineral powder / fly ash mixture, polycarboxylate superplasticizer accounting for 0.2%-0.8% of the mineral powder / fly ash mixture, and polyether-modified polysiloxane accounting for 0.05%-0.1% of the mineral powder / fly ash mixture; the mass of water in the geopolymer-based slurry is 45%-50% of the mass of the dry-mixed composite cementitious material.

[0006] The specific preparation method of the geopolymer-based slurry used for sealing shallow and medium-depth abandoned oil and gas wells in the above scheme is as follows: the treatment agent slurry is placed in a mixing tank, the stirring device in the mixing tank is turned on, and then the prepared dry-mixed composite cementitious material is added to the mixing tank at a uniform speed. Stirring is continued for 15-30 minutes. At this time, a preparatory slurry that has not yet been activated is formed. Next, the alkaline activator solution is continuously injected into the preparatory slurry. After high-speed stirring, the geopolymer-based sealing slurry for sealing shallow and medium-depth abandoned oil and gas wells is obtained.

[0007] The above scheme consists of mineral powder and fly ash mixture, wherein the mineral powder mass percentage is 65%-75% and the fly ash mass percentage is 25%-35%.

[0008] In the above scheme, the fly ash contains SiO2 > 35%, Al2O3 > 15%, and CaO < 6%, and the sum of the contents of each component in the fly ash is 100%; the particle size is 800-900 mesh.

[0009] In the above scheme, the mineral powder contains SiO2 > 24%, Al2O3 > 16%, and CaO < 40%, and the sum of the contents of each component in the mineral powder is 100%; the particle size is 300-400 mesh, preferably S95 grade.

[0010] In the above scheme, the wollastonite powder is 1000-1500 mesh, the sepiolite powder is 200-300 mesh, and the silica fume is 100-300 nm; the alkali-resistant glass fiber is 12 mm in length and has an aspect ratio of 500-1000.

[0011] In the above scheme, the alkaline activation solution is an aqueous solution prepared from water glass, sodium hydroxide and sodium citrate. The total mass of water glass and sodium hydroxide is 14%-16% of the mass of the mineral powder / fly ash mixture, wherein the mass ratio of water glass to sodium hydroxide is 9:1, the modulus of water glass is 2 and the solid content is 36%-38%; the mass of sodium citrate is 0.2%-0.5% of the mineral powder / fly ash mixture.

[0012] The preparation method of the dry-mixed composite cementitious material in the above scheme is as follows: place mineral powder and fly ash in a high-efficiency dry powder mixer and mix for 15-30 minutes until the color is uniform. Then, under stirring, slowly add 2%-6% wollastonite powder, 0.5%-1.5% sepiolite powder and 1%-5% silica fume by weight of the mineral powder / fly ash mixture, and stir for 20-30 minutes. Finally, add 0.1%-0.3% alkali-resistant glass fiber by weight of the mineral powder / fly ash mixture, and continue stirring for 15-30 minutes until the fiber is fully dispersed to prepare the dry-mixed composite cementitious material.

[0013] The preparation method of the alkali activator solution in the above scheme is as follows: Calculate the mass of water glass and sodium hydroxide in the alkali activator solution according to 14%-16% of the mass of the mineral powder / fly ash mixture; calculate the mass of sodium citrate according to 0.2%-0.5% of the mass of the mineral powder / fly ash mixture; calculate the amount of water to prepare the alkali activator solution according to the alkali concentration of 35%-38%; dissolve sodium hydroxide in 1 / 3 of the water volume and stir until completely transparent; slowly add water glass and sodium citrate to the sodium hydroxide solution, add the remaining water, and continue stirring for 10-15 minutes to obtain the alkali activator solution. Seal the solution and let it stand for at least 24 hours to stabilize its performance.

[0014] The above-mentioned treatment agent slurry preparation method is as follows: Calculate the total water volume based on a water-to-solid ratio of 0.45-0.5. In a mixing container, add half of the total water volume minus the volume of the alkali solution. Under low-speed stirring, slowly add 0.05%-0.15% xanthan gum, 0.2%-0.8% polycarboxylate superplasticizer, and 0.05%-0.1% polyether-modified polysiloxane defoamer in sequence. Each component needs to be stirred for 5-15 minutes until it is uniformly dissolved before adding the next component. Add the remaining mixing water and stir for 5-15 minutes to finally obtain the treatment agent slurry. Beneficial effects

[0015] 1. This invention enables the sealing of abandoned oil and gas wells with depths up to 1500 meters in shallow to medium-depth formations. It utilizes a geopolymer-based sealing slurry system, which effectively solidifies at temperatures below 30°C and possesses excellent sealing properties, corrosion resistance, and compressive strength, making it particularly suitable for sealing shallow to medium-depth oil and gas wells. Compared to traditional methods for sealing abandoned oil and gas wells, this invention significantly reduces sealing costs and energy consumption. Compared to existing geopolymer materials, the geopolymer sealing material of this invention exhibits superior low-temperature curing characteristics, rapidly hardening at lower formation temperatures to meet sealing requirements, making it of significant application value in sealing shallow to medium-depth oil and gas wells.

[0016] 2. In this invention, silica fume provides a highly active silica supplement, optimizes the silica-alumina ratio, fills pores, and improves density.

[0017] 3. In this invention, sepiolite powder is a fibrous clay mineral that provides micro-reinforcement and thickening effects. It forms a "micro-nano-macro" multi-scale reinforcement effect with alkali-resistant glass fiber.

[0018] 4. In this invention, wollastonite powder and sepiolite powder improve the body temperature reactivity of fly ash / mineral powder.

[0019] 5. The alkali-resistant glass fiber of this invention plays a toughening role. Utilizing its excellent mechanical properties and unique chemical corrosion resistance, it compensates for the brittleness and shrinkage defects of the matrix through physical bridging, crack control and load transfer, thereby preparing a gel-cured body with high strength, high toughness and excellent durability. Detailed Implementation Example 1

[0020] This geopolymer-based slurry, used for sealing shallow and medium-depth abandoned oil and gas wells, is prepared by mixing dry-mixed composite cementitious materials, alkaline activation solutions, and treatment agents, as detailed below:

[0021] Preparation of dry-mixed composite cementitious material: Weigh 500g of mineral powder and 269g of fly ash into a high-efficiency dry powder mixer, stir and mix for 15-30 minutes until the color is uniform. The mixing ratio is: mineral powder 65% and fly ash 35%. Then, while stirring, slowly add 46.14g of wollastonite powder, 11.54g of sepiolite powder and 38.45g of silica fume in sequence, and stir and mix for 20-30 minutes. Finally, add 0.78g of alkali-resistant glass fiber, and continue to stir and mix for 15-30 minutes until the fiber is fully dispersed. The dry-mixed composite cementitious material can be prepared in the end.

[0022] Preparation of the alkaline activator solution: The water-to-solid ratio is 0.5, and the total amount of water used is calculated to be 433 mL. Weigh 12.30 g of sodium hydroxide and dissolve it in 120 mL of water, stirring until completely transparent; slowly add 110.74 g of water glass to the above solution, continue stirring for 10-15 min, seal and let it stand for 24 h.

[0023] Preparation of the treatment agent slurry: In a mixing container, add 100 mL of water. While stirring at low speed, slowly add 1.55 g of sodium citrate, 0.41 g of xanthan gum, 1.64 g of polycarboxylate superplasticizer (PCE), and 0.39 g of polyether-modified polysiloxane defoamer (GPE type). Each treatment agent should be stirred for 5-15 minutes until uniformly dissolved before adding the next. Add the remaining mixing water to bring the total water volume to 433 mL, and stir for 5-15 minutes to obtain a slurry containing PCE, xanthan gum, and the defoamer treatment agent.

[0024] Take a certain amount of the above-prepared treatment agent slurry and place it in a mixing tank. Turn on the stirring device, and then add the above-prepared dry-mixed composite cementitious material into the mixing tank at a uniform speed. Continue stirring for 15-30 minutes. At this time, a preparatory slurry with good fluidity that has not yet been activated is formed. Continuously inject the alkali activator solution into the preparatory slurry and stir at high speed (about 12000 r / min) to obtain a geopolymer-based sealing slurry for sealing shallow abandoned oil and gas wells.

[0025] The slurry was poured into a 25×50mm cylindrical mold and cured in a water bath at 20℃ for 2 days and 7 days. The cured body was then removed and subjected to compressive strength and permeability tests. The thickening time was measured using a high-temperature, high-pressure thickening instrument. Its corrosion resistance was determined using a 28-day acid corrosion test. The interfacial bonding strength was determined using an interfacial bonding test. The test results are shown in Table 1.

[0026] Table 1. Basic physical properties of the geopolymer-based sealing slurry of this invention.

[0027] Example 2

[0028] This geopolymer-based slurry, used for sealing shallow and medium-depth abandoned oil and gas wells, is prepared by mixing dry-mixed composite cementitious materials, alkaline activation solutions, and treatment agents, as detailed below:

[0029] Preparation of dry-mixed composite cementitious material: Weigh 577g of mineral powder and 192g of fly ash into a high-efficiency dry powder mixer, stir and mix for 15-30 minutes until the color is uniform. The mixing ratio is: mineral powder 75%, fly ash 25%. Then, while stirring, slowly add 15.38g of wollastonite powder, 3.85g of sepiolite powder and 7.69g of silica fume in sequence, and stir and mix for 20-30 minutes. Finally, add 2.31g of alkali-resistant glass fiber, and continue to stir and mix for 15-30 minutes until the fiber is fully dispersed. The dry-mixed composite cementitious material can be prepared in the end.

[0030] Preparation of the alkaline activator solution: The water-to-solid ratio is 0.45, and the total amount of water used is calculated to be 400 mL. Weigh 10.77 g of sodium hydroxide and dissolve it in 120 mL of water, stirring until completely transparent; slowly add 96.89 g of water glass to the above solution, continue stirring for 10-15 min, seal and let it stand for 24 h.

[0031] Preparation of the treatment agent slurry: In a mixing container, add 100 mL of water. While stirring at low speed, slowly add 3.83 g of sodium citrate, 1.15 g of xanthan gum, 6.14 g of polycarboxylate superplasticizer (PCE), and 0.77 g of polyether-modified polysiloxane defoamer (GPE type). Each treatment agent should be stirred for 5-15 minutes until uniformly dissolved before adding the next. Add the remaining mixing water to bring the total volume to 400 mL, and stir for 5-15 minutes to obtain a slurry containing PCE, xanthan gum, and the defoamer treatment agent.

[0032] Take a certain amount of the above-prepared treatment agent slurry and place it in a mixing tank. Turn on the stirring device, and then add the above-prepared dry-mixed composite cementitious material into the mixing tank at a uniform speed. Continue stirring for 15-30 minutes. At this time, a preparatory slurry with good fluidity that has not yet been activated is formed. Continuously inject the alkali activator solution into the preparatory slurry and stir at high speed (about 12000 r / min) to obtain a geopolymer-based sealing slurry for sealing shallow abandoned oil and gas wells.

[0033] The slurry was poured into a 25×50mm cylindrical mold and cured in a water bath at 20℃ for 2 days and 7 days. The cured body was then removed and subjected to compressive strength and permeability tests. The thickening time was measured using a high-temperature and high-pressure thickening instrument. The corrosion resistance was measured using a 28-day acid corrosion test. The interfacial bonding strength was measured using an interfacial bonding test. The test results are shown in Table 2.

[0034] Table 2. Basic physical properties of the geopolymer-based well sealing slurry of this invention.

[0035] Example 3

[0036] This geopolymer-based slurry, used for sealing shallow and medium-depth abandoned oil and gas wells, is prepared by mixing dry-mixed composite cementitious materials, alkaline activation solutions, and treatment agents, as detailed below:

[0037] Preparation of dry-mixed composite cementitious material: Weigh 538g of mineral powder and 231g of fly ash into a high-efficiency dry powder mixer, stir and mix for 15-30 minutes until the color is uniform. The mixing ratio is: 70% mineral powder and 30% fly ash. Then, while stirring, slowly add 30.76g of wollastonite powder, 7.69g of sepiolite powder and 23.00g of silica fume in sequence, and stir and mix for 20-30 minutes. Finally, add 1.54g of alkali-resistant glass fiber, and continue to stir and mix for 15-30 minutes until the fiber is fully dispersed. The dry-mixed composite cementitious material can be prepared in the end.

[0038] Preparation of the alkaline activator solution: The water-to-solid ratio is 0.45, and the total amount of water used is calculated to be 375 mL. Weigh 11.54 g of sodium hydroxide and dissolve it in 120 mL of water, stirring until completely transparent; slowly add 103.82 g of water glass to the above solution, continue stirring for 10-15 min, seal and let it stand for 24 h.

[0039] Preparation of the treatment agent slurry: In a mixing container, add 100 mL of water. While stirring at low speed, slowly add 2.31 g of sodium citrate, 0.77 g of xanthan gum, 3.85 g of polycarboxylate superplasticizer (PCE), and 0.54 g of polyether-modified polysiloxane defoamer (GPE type). Each treatment agent should be stirred for 5-15 minutes until uniformly dissolved before adding the next. The final product is a slurry containing PCE, xanthan gum, and defoamer.

[0040] Take a certain amount of the above-prepared treatment agent slurry and place it in a mixing tank. Turn on the stirring device, and then add the above-prepared dry-mixed composite cementitious material into the mixing tank at a uniform speed. Continue stirring for 15-30 minutes. At this time, a preparatory slurry with good fluidity that has not yet been activated is formed. Continuously inject the alkali activator solution into the preparatory slurry and stir at high speed (about 12000 r / min) to obtain a geopolymer-based sealing slurry for sealing shallow abandoned oil and gas wells.

[0041] The slurry was poured into a 25×50mm cylindrical mold and cured in a water bath at 30℃ for 2 and 7 days. The cured body was then removed and subjected to compressive strength and permeability tests. The thickening time was measured using a high-temperature and high-pressure thickening instrument. The corrosion resistance was measured using a 28-day acid corrosion test. The interfacial bonding strength was measured using an interfacial bonding test. The test results are shown in Table 3.

[0042] Table 3. Basic physical properties of the geopolymer-based sealing slurry of this invention.

[0043] Comparative Example 1

[0044] The cost of the geopolymer-based well sealing system of this invention was compared with that of Grade G oil well cement slurry, with a formulation density of 1.88 g / cm³. 3 Volume is 1m 3 The calculations were performed based on the slurry, with the average value of the added proportions used in the calculations. The results are shown in Table 4.

[0045] Table 4. Cost Comparison Analysis of the Well Sealing System of the Present Invention and On-site Oil Well Cement

[0046]

[0047] As can be seen from Table 4, to prepare 1m 3 For well sealing slurry of the same density, the cost per cubic meter of the well sealing system of the present invention is approximately RMB 1,240, while the cost per cubic meter of traditional G-grade oil well cement is approximately RMB 2,750. The geopolymer-based well sealing slurry of the present invention reduces the cost of well sealing materials by approximately 54.9%, which is a significant cost reduction. Comparative Example 2

[0048] Cement slurry samples were taken from the oilfield for performance testing. The cement slurry formula was: Grade G oil well cement + 6% quick-setting early-strength agent (DS-132) + 0.5% drag reducer (GD-1) + 0.05% defoamer + water, with a water-cement ratio of 0.45. The test results are shown in Table 5.

[0049] Table 5 Basic physical properties of cement paste

[0050]

[0051] Comparative Example 2 shows that the sealing system provided by the present invention has higher compressive strength, sealing performance and acid corrosion resistance than the cement slurry system used in oilfields, and can meet the requirements of on-site construction.

[0052] This invention can rapidly harden at lower formation temperatures to meet well sealing requirements, while reducing well sealing costs.

Claims

1. A geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells, characterized in that: This geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells is prepared by mixing a dry-mixed composite cementitious material, an alkali-activated solution, and a treatment agent slurry. The dry-mixed composite cementitious material is composed of a mixture of mineral powder / fly ash, wollastonite powder, sepiolite powder, silica fume, and alkali-resistant glass fiber. The mass percentages of wollastonite powder, sepiolite powder, silica fume, and alkali-resistant glass fiber are 2%-6% of the mineral powder / fly ash mixture, 0.5%-1.5%, 1%-5%, and 0.1%-0.3%, respectively. The total mass of water glass, sodium hydroxide, and sodium citrate in the alkaline activation solution is 14.2%-16.5% of the mass of the mineral powder / fly ash mixture; the treatment agent slurry is composed of xanthan gum, polycarboxylate superplasticizer, polyether-modified polysiloxane, and water, with xanthan gum accounting for 0.05%-0.15% of the mineral powder / fly ash mixture, polycarboxylate superplasticizer accounting for 0.2%-0.8% of the mineral powder / fly ash mixture, and polyether-modified polysiloxane accounting for 0.05%-0.1% of the mineral powder / fly ash mixture; the mass of water in the geopolymer-based slurry is 45%-50% of the mass of the dry-mixed composite cementitious material.

2. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 1, characterized in that: The preparation method of the geopolymer-based slurry is as follows: the treatment agent slurry is placed in a mixing tank, the stirring device in the mixing tank is turned on, and then the prepared dry-mixed composite cementitious material is added to the mixing tank at a uniform speed. The stirring is continued for 15-30 minutes. At this time, a preparatory slurry that has not yet been activated is formed. Next, the alkaline activator solution is continuously injected into the preparatory slurry. After high-speed stirring, a geopolymer-based sealing slurry for sealing shallow abandoned oil and gas wells is obtained.

3. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 2, characterized in that: The mineral powder / fly ash mixture is composed of mineral powder and fly ash, wherein the mineral powder accounts for 65%-75% by mass and the fly ash accounts for 25%-35% by mass.

4. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 3, characterized in that: The fly ash contains SiO2 > 35%, Al2O3 > 15%, and CaO < 6%, with the sum of the contents of each component in the fly ash being 100%; the particle size is 800-900 mesh.

5. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 4, characterized in that: The mineral powder contains SiO2 > 24%, Al2O3 > 16%, and CaO < 40%, with the sum of the contents of each component in the mineral powder being 100%; the particle size is 300-400 mesh, and the grade is S95.

6. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 5, characterized in that: The wollastonite powder is 1000-1500 mesh, the sepiolite powder is 200-300 mesh, and the silica fume is 100-300 nm; the alkali-resistant glass fiber is 12 mm in length and has an aspect ratio of 500-1000.

7. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 6, characterized in that: The alkaline activation solution is an aqueous solution prepared from water glass, sodium hydroxide and sodium citrate. The total mass of water glass and sodium hydroxide is 14%-16% of the mass of the mineral powder / fly ash mixture, wherein the mass ratio of water glass to sodium hydroxide is 9:1, the modulus of water glass is 2 and the solid content is 36%-38%; the mass of sodium citrate is 0.2%-0.5% of the mineral powder / fly ash mixture.

8. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 7, characterized in that: The preparation method of the dry-mixed composite cementitious material is as follows: mineral powder and fly ash are placed in a high-efficiency dry powder mixer and mixed for 15-30 minutes until the color is uniform. Then, under stirring, 2%-6% of wollastonite powder, 0.5%-1.5% of sepiolite powder and 1%-5% of silica fume are added slowly according to the mass of the mineral powder / fly ash mixture, and stirred for 20-30 minutes. Finally, 0.1%-0.3% of alkali-resistant glass fiber is added according to the mass of the mineral powder / fly ash mixture, and stirring is continued for 15-30 minutes until the fiber is fully dispersed to prepare the dry-mixed composite cementitious material.

9. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 8, characterized in that: The method for preparing the alkali activator solution is as follows: Calculate the mass of water glass and sodium hydroxide in the alkali activator solution based on 14%-16% of the mass of the mineral powder / fly ash mixture; calculate the mass of sodium citrate based on 0.2%-0.5% of the mass of the mineral powder / fly ash mixture; calculate the amount of water needed to prepare the alkali activator solution based on an alkali concentration of 35%-38%; dissolve sodium hydroxide in 1 / 3 of the water volume and stir until completely transparent; slowly add water glass and sodium citrate to the sodium hydroxide solution, add the remaining water, and continue stirring for 10-15 minutes to obtain the alkali activator solution. Seal the solution and allow it to mature and stand for at least 24 hours to stabilize its properties.

10. The geopolymer-based slurry for sealing shallow and medium-depth abandoned oil and gas wells according to claim 9, characterized in that: The method for preparing the treatment agent slurry is as follows: Calculate the total water volume based on a water-to-solid ratio of 0.45-0.

5. In a mixing container, add half the total water volume minus the volume of the alkali solution. Under low-speed stirring, slowly add 0.05%-0.15% xanthan gum, 0.2%-0.8% polycarboxylate superplasticizer, and 0.05%-0.1% polyether-modified polysiloxane defoamer in sequence. Each component must be stirred for 5-15 minutes until uniformly dissolved before adding the next component. Add the remaining mixing water and stir for 5-15 minutes to finally obtain the treatment agent slurry.

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