Early-strength low-density fly ash multi-element multi-scale lost circulation cement slurry and preparation method thereof

Abstract

The application relates to the technical field of cement paste, and is an early-strength low-density fly ash multi-element multi-scale plugging cement paste and a preparation method thereof. The early-strength low-density fly ash multi-element multi-scale plugging cement paste raw material comprises G-grade oil well cement, fly ash, artificial glass microbeads, microsilica powder, a drag-reducing agent, a fluid loss reducer, a retarder, a defoaming agent, a reinforcing agent, water and a composite plugging agent. The early-strength low-density fly ash multi-element multi-scale plugging cement paste has a wide density range, a small density difference between upper and lower parts, good stability, high compressive strength, can significantly reduce the risk of collapse of a water-sensitive formation caused by immersion of filtrate, reduces damage to an oil and gas layer, can quickly form a solid plugging barrier, can meet the plugging operation requirements of low-pressure easy-leakage wells and malignant leakage wells, and improves plugging quality and efficiency.

Description

Technical Field

[0001] This invention relates to the field of cement slurry technology, specifically to an early-strength, low-density, multi-element, multi-scale leak-sealing cement slurry made from fly ash and its preparation method. Background Technology

[0002] Well leakage, a long-standing global drilling challenge, is prevalent in major oil and gas fields both domestically and internationally. It directly leads to the consumption of large quantities of drilling fluid and leak prevention / plugging materials, and can trigger secondary accidents such as stuck pipe, overflows, and blowouts, prolonging drilling cycles and, in severe cases, rendering the well unusable. Well leakage is one of the most common and complex operating conditions in oil drilling operations, posing a significant challenge to the normal implementation of oil and gas exploration and development drilling operations.

[0003] Most severe losses in formations are caused by fractures. These fractures that induce losses are specifically called "leakage-causing fractures." This type of severe loss mainly refers to encountering naturally occurring leakage-causing fractures (greater than 2mm to 5mm) or induced leakage-causing fractures, and sometimes large cavities. Currently, traditional integrated plugging agents are used in conventional pressurized well plugging, cement plugging of fractured losses, and oil-based mud drilling for leak prevention in low-pressure leak formations, achieving certain leak prevention and plugging effects in some blocks.

[0004] Low-density cement slurry made from fly ash is commonly used as a treatment for severe leakage in low-pressure wells due to its low cost. The principle is to seal the leakage channels by solidifying the cement slurry within them. However, in pores and large fractures, formation water or accumulating fluids are often present. Because the sealing cement is affected by the displacement and dilution of formation water or karst fluids, it is difficult to solidify near the well wall to form an effective sealing barrier, resulting in incomplete sealing of the leakage space. Adding sealing materials to fly ash cement slurry improves the sealing effect. However, due to a lack of in-depth research on the pressure characteristics, pore size, and physicochemical properties of the drilled formation, there is a lack of basis for implementing leakage prevention and sealing technologies.

[0005] Existing low-density fly ash-based cement slurry for sealing leaks still faces numerous technical challenges, such as: severe slurry settling, ineffective use of cementing materials, and failure to effectively seal and bond leakage channels; slow strength development of cement stone, resulting in cement particles not remaining in leakage channels and failing to provide a firm seal; and low strength of cement stone, making it difficult to improve the pressure resistance of the seal and leading to frequent re-leakage. Traditional sealing materials also have many defects, such as single flexible fibers tangling and clumping, single rigid fibers lacking flexibility, low density, hydrophobicity, and floating aggregation of rubber particles, resulting in poor bonding with cement slurry and other components; and low strength, high brittleness, and high density of mica and vermiculite, causing settling in the slurry and easy crushing during bridging and sealing. Plant-shell-based sealing agents have low density, are prone to stratification, have low strength, and are susceptible to high-temperature carbonization, limiting their application. Furthermore, the sealing material has a low degree of matching with the size of the pores and cracks, making it difficult to form a high-strength bridging and sealing barrier. For example, single-particle or double-particle polymer sealing materials form bridging in cracks and pores, allowing large cracks to be successfully filled by reducing the size of the bridging particles, thus achieving leakage sealing; however, for large cracks and pore-type malignant leaks, they cannot accumulate in the leakage channels or form bridging to form an effective blockage.

[0006] Existing sealing cement grouts still face many technical challenges, especially the poor sealing effect of low-density sealing cement grouts on severe leaks. Summary of the Invention

[0007] This invention provides an early-strength, low-density fly ash multi-element, multi-scale leak-sealing cement slurry and its preparation method, overcoming the shortcomings of the prior art and effectively solving the problem of poor sealing effect of existing leak-sealing cement slurries for severe leakage.

[0008] One of the technical solutions of this invention is achieved through the following measures: an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry, the raw materials comprising, by weight, 100 parts of G-grade oil well cement, 30 to 60 parts of fly ash, 0 to 50 parts of artificial glass microspheres, 6 to 45 parts of silica fume, 0.6 to 1.0 parts of drag reducer, 4 to 8 parts of water loss reducer, 0.3 to 1.5 parts of retarder, 0.4 to 0.6 parts of defoamer, 4 to 7 parts of reinforcing agent, 70 to 188 parts of water, and 3 to 6 parts of composite plugging agent.

[0009] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The above-mentioned composite sealant is obtained by mixing modified rubber, composite fiber and high-strength and tough resin-reinforced mica sealant in a mass ratio of (65 to 70): (5 to 8): (22 to 35).

[0010] The above-mentioned high-strength, high-toughness resin-reinforced mica sealing material is obtained by the following method: The first step involves stirring acrylic acid, polyoxyethylene ether, and methyl methacrylate in a mass ratio of 2:(0.5 to 1.5):(6 to 8) and allowing them to undergo a polymerization reaction to obtain a flexible block high-strength and tough resin. During polymerization, the reaction temperature is 180°C to 200°C and the reaction time is 1 to 2 hours. The second step involves adding mica sheets to the flexible block high-strength and high-toughness resin, stirring at a temperature of 180°C to 200°C until fully melted, and then injecting the mixture into a mold to obtain a prepolymer. The mass ratio of mica sheets to flexible block high-strength and high-toughness resin is (65 to 75): (25 to 35). The third step is to mold and cure the prepolymer at a temperature of 145℃ to 155℃ to obtain a prepolymer board with a thickness of 0.4mm to 0.6mm. The fourth step involves cooling and crushing the prepolymer board to obtain a high-strength, tough resin-reinforced mica sealing material with a particle size of 8mm to 15mm.

[0011] The modified rubber is obtained by the following method: rubber particles with a particle size of 0.2 mm to 4.0 mm are added to a sodium hydroxide solution with a mass concentration of 10% to 15% and soaked for 2 to 3 hours. Then, after filtration, washing, re-filtration and drying, the modified rubber is obtained.

[0012] The above-mentioned composite fiber is a mixture of glass fiber and flax fiber in a mass ratio of 4:(5 to 7), wherein the length of the glass fiber is 5 mm to 12 mm and the length of the flax fiber is 3 mm to 6 mm, and the mixing method is physical mixing.

[0013] The aforementioned reinforcing agent is one or more of an organic salt and an inorganic salt, wherein the organic salt is triethanolamine and the inorganic salt is one or more of sodium nitrite and sodium sulfate.

[0014] The above-mentioned reinforcing agent is a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:(3 to 5):(4 to 6).

[0015] The drag-reducing agents mentioned above are one or more of ketaldehyde condensates and polycarboxylic acids.

[0016] The aforementioned water loss reducing agent is one or more of polyvinyl alcohol and AMPS-type binary copolymer water loss reducing agents.

[0017] The aforementioned retarder is one or more of sodium citrate, sodium tartrate, sodium borate, sodium acetate, and sodium tripolyphosphate.

[0018] The above-mentioned early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry was obtained by the following method: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, artificial glass microspheres, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir at 4200rpm±200rpm for 1min to 2min to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength fly ash cement slurry. The fourth step is to add the required amount of composite sealing agent to the early-strength fly ash cement slurry and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength low-density fly ash multi-element multi-scale sealing cement slurry.

[0019] The second technical solution of the present invention is achieved through the following measures: a method for preparing a multi-element, multi-scale leak-stopping cement slurry made from early-strength, low-density fly ash, carried out according to the following method: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, artificial glass microspheres, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir at 4200rpm±200rpm for 1min to 2min to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength fly ash cement slurry. The fourth step is to add the required amount of composite sealing agent to the early-strength fly ash cement slurry and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength low-density fly ash multi-element multi-scale sealing cement slurry.

[0020] This invention provides an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a wide density range, small density difference between upper and lower layers, good stability, and high compressive strength. It can significantly reduce the risk of collapse caused by the filtrate soaking water-sensitive formations, reduce damage to oil and gas reservoirs, and quickly form a solid plugging barrier. It can meet the plugging requirements of low-pressure wells prone to leakage and wells with serious leakage, and improve the plugging quality and efficiency. Attached Figure Description

[0021] Figure 1 This is a simulated crack sealing effect diagram of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of the present invention. Detailed Implementation

[0022] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0023] The present invention will be further described below with reference to embodiments: Example 1: This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry contains the following raw materials by weight: 100 parts of G-grade oil well cement, 30 to 60 parts of fly ash, 0 to 50 parts of artificial glass microspheres, 6 to 45 parts of silica fume, 0.6 to 1.0 parts of drag reducer, 4 to 8 parts of water loss reducer, 0.3 to 1.5 parts of retarder, 0.4 to 0.6 parts of defoamer, 4 to 7 parts of reinforcing agent, 70 to 188 parts of water, and 3 to 6 parts of composite plugging agent.

[0024] In this invention, the density of the artificial glass microspheres used as raw material is 0.50 g / cm³. 3 Up to 0.60 g / cm 3 The pressure resistance ranges from 60 MPa to 70 MPa. It has a uniform particle size distribution, strong anti-crushing ability, and high compressive strength. The raw material fly ash has high activity, with a fineness (45µm square hole sieve residue) ≤8%, a total mass fraction of silicon dioxide (SiO2), aluminum oxide (Al2O3) and ferric oxide (Fe2O3) ≥85%, and a strength activity index ≥80%.

[0025] Example 2: As an optimization of the above example, the composite sealant raw materials include modified rubber, composite fiber and high-strength toughness resin-reinforced mica sealant material in a mass ratio of (65 to 70): (5 to 8): (22 to 35).

[0026] Example 3: As an optimization of the above examples, a high-strength, tough resin-reinforced mica plugging material is obtained by the following method: The first step involves stirring acrylic acid, polyoxyethylene ether, and methyl methacrylate in a mass ratio of 2:(0.5 to 1.5):(6 to 8) and allowing them to undergo a polymerization reaction to obtain a flexible block high-strength and tough resin. During polymerization, the reaction temperature is 180°C to 200°C and the reaction time is 1 to 2 hours. The second step involves adding mica sheets to the flexible block high-strength and high-toughness resin, stirring at a temperature of 180°C to 200°C until fully melted, and then injecting the mixture into a mold to obtain a prepolymer. The mass ratio of mica sheets to flexible block high-strength and high-toughness resin is (65 to 75): (25 to 35). The third step is to mold and cure the prepolymer at a temperature of 145℃ to 155℃ to obtain a prepolymer board with a thickness of 0.4mm to 0.6mm. The fourth step involves cooling and crushing the prepolymer board to obtain a high-strength, tough resin-reinforced mica sealing material with a particle size of 8mm to 15mm.

[0027] Example 4: As an optimization of the above examples, the modified rubber is obtained by the following method: rubber particles with a particle size of 0.2 mm to 4.0 mm are added to a sodium hydroxide solution with a mass concentration of 10% to 15% and soaked for 2 to 3 hours. Then, after filtration, washing, re-filtration and drying, the modified rubber is obtained.

[0028] Example 5: As an optimization of the above example, the composite fiber is a mixture of glass fiber and flax fiber in a mass ratio of 4:(5 to 7), wherein the length of the glass fiber is 5 mm to 12 mm, the length of the flax fiber is 3 mm to 6 mm, and the mixing method is physical mixing.

[0029] Example 6: As an optimization of the above examples, the reinforcing agent is one or more of an organic salt and an inorganic salt, wherein the organic salt is triethanolamine and the inorganic salt is one or more of sodium nitrite and sodium sulfate.

[0030] Example 7: As an optimization of the above example, the reinforcing agent is a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:(3 to 5):(4 to 6).

[0031] Example 8: As an optimization of the above examples, the drag-reducing agent is one or more of a ketaldehyde condensate and a polycarboxylic acid, preferably, the ketaldehyde condensate is the ketaldehyde condensate USZ.

[0032] Example 9: As an optimization of the above example, the water loss reducing agent is one or more of polyvinyl alcohol and AMPS-based binary copolymer water loss reducing agents. Preferably, the water loss reducing agent is AMPS-based binary copolymer water loss reducing agent G33S.

[0033] Example 10: As an optimization of the above example, the retarder is one or more of sodium citrate, sodium tartrate, sodium borate, sodium acetate and sodium tripolyphosphate. The retarder used is retarder BXR-200L, which is a mixture of sodium tripolyphosphate and boric acid.

[0034] Example 11: As an optimization of the above examples, the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry was obtained according to the following method: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, artificial glass microspheres, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir at 4200rpm±200rpm for 1min to 2min to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength fly ash cement slurry. The fourth step is to add the required amount of composite sealing agent to the early-strength fly ash cement slurry and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength low-density fly ash multi-element multi-scale sealing cement slurry.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the technical specifications of the early-strength, low-density fly ash multi-element, multi-scale leak-stopping cement slurry of this invention are: ① Density range 1.20 g / cm³ 3 Up to 1.75 g / cm 3 ② API water loss < 50 mL; ③ 8-hour early compressive strength > 2.5 MPa; ④ Stability density difference ≤ 0.02 g / cm³ 3 ⑤ The pressure-bearing capacity for sealing 2mm cracks is >2.7MPa; Secondly, this invention, a multi-element, multi-scale leak-stopping cement slurry made from early-strength, low-density fly ash, breaks through the density limitations of traditional fly ash cement slurries. Through indoor experiments, artificial glass microspheres and microsilica flakes were introduced, with the actual density of the artificial glass microspheres being 0.50 g / cm³. 3 Up to 0.60 g / cm 3 It has a pressure resistance of up to 70MPa, and the density fluctuation of the cement paste is less than or equal to 0.03g / cm³ under conditions of 120℃ and 70MPa. 3 Fly ash exhibits high activity, with a fineness (residue on a 45µm square-hole sieve) ≤8%, a total mass fraction of silica (SiO2), alumina (Al2O3), and ferric oxide (Fe2O3) ≥85%, and a strength activity index ≥80%. This solves the pressure resistance problem of existing low-density fly ash cement slurry. Adding it to cement slurry significantly reduces its density and maintains a low liquid-to-solid ratio, which is beneficial for the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention to maintain good comprehensive performance under high temperature and high pressure conditions. Third, the composite plugging agent synthesized in this invention is obtained by mixing modified rubber, composite fibers, and high-strength, tough resin-reinforced mica plugging material. This overcomes the limitations of single plugging materials, such as difficulty in matching the size of the borehole, difficulty in bridging leakage channels, and weak sealing barriers. It achieves a synergistic effect of modified rubber, composite fibers, and high-strength, tough resin-reinforced mica plugging material, effectively solving the problems of "not being able to squeeze in, not being able to stop, and not being able to seal firmly." Specifically, the composite fibers are uniformly dispersed in the cement slurry and enter the borehole under pressure differential. Through random interweaving and bridging, they form a dense, three-dimensional network structure, preventing drilling fluid leakage and improving the strength of the sealing barrier. Fourth, the high-strength, high-toughness resin-reinforced mica sealing material synthesized in this invention solves the problems of low strength, high brittleness, and breakage of flaky mica flakes. This high-strength, high-toughness resin-reinforced mica sealing material has good compatibility with cement slurry and strong bridging ability. Under pressure, it tumbles and embeds itself into the pore wall, enhancing the interfacial strength. Furthermore, it rapidly bridges at the throat, providing a barrier for the following particles. It works synergistically with modified rubber and composite fibers to form a high-strength shielding wall. Indoor experimental results show that it can effectively seal a 1mm crack leakage layer under 5MPa pressure, has a relatively low density, and good suspension stability. Fifth, the modified rubber synthesized in this invention effectively solves the problems of hydrophobic rubber particles, agglomeration, difficulty in effective bridging and filling of single rubber particles, and loose bonding with cement slurry and formation surfaces by surface modification treatment of multi-size rubber particles. Under pressure differential, small-size rubber particles are embedded and blocked in micropores and microcracks; large-size rubber particles are squeezed into larger pores and have self-adaptive deformation ability, effectively bridging and forming a solid integrated sealing layer with fly ash cement slurry. Sixth, in this invention, the composite fiber is composed of glass fiber and flax fiber in a certain proportion, wherein the mass ratio of glass fiber to flax fiber is 4:6, the length of glass fiber is about 5mm to 12mm, and the length of flax fiber is about 3mm to 6mm. This achieves an optimized design of rigid and flexible fibers, as well as long and short fibers, and constructs a three-dimensional network structure for leak sealing. This effectively solves the problem of insufficient rigidity and tangling of flexible fibers in existing sealing cement slurry, improves the impact resistance of cement stone, and further enhances the leak prevention and sealing effect. Seventh, the reinforcing agent synthesized in this invention is obtained by compounding organic and inorganic salts. It can activate the hydration activity of fly ash, accelerate the hydration rate, and further improve the early compressive strength of fly ash cement stone, which is beneficial to improving the success rate of one-time sealing. Eighth, this invention adjusts the proportion of microsilica powder, which enhances the suspension stability of the early-strength low-density fly ash multi-element multi-scale plugging cement slurry system, enhances the thixotropic ability of the early-strength low-density fly ash multi-element multi-scale plugging cement slurry, improves the retention capacity of pores and cracks, and improves the compressive strength of cement stone by filling the pores between cement particles, thereby further enhancing the sealing quality.

[0036] In summary, for wells with large-sized pores and severe leakage, the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention effectively solves the problems of mismatched size between existing plugging materials and pores, difficulty in bridging, retention, filling, and forming solid plugs, and inability to firmly seal pores. Its preparation method is simple and quick, with strong on-site operability and practicality. It exhibits significant plugging effect for severe leakage, effectively reducing the cost of existing plugging materials, saving time in plugging operations, and forming a highly efficient and synergistic plugging process. In the composite plugging agent of this invention, the high-strength, tough resin-reinforced mica plugging material has high strength in its flaky mica and strong rigid skeleton throat-sealing ability. The composite fibers, with their varying lengths and rigidity, adapt to the modified rubber for plugging and bridging, further enhancing the slurry's resistance to water dilution in the leakage layer. This enables rapid bridging and sealing in the leakage layer, allowing the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention to effectively fill bridging pores and solidify, forming a robust sealing barrier.

[0037] Example 12: This composite sealant is obtained by physically mixing modified rubber, composite fibers, and high-strength, tough resin-reinforced mica sealant in a mass ratio of 65:5:30 at room temperature. High-strength, tough resin-reinforced mica sealing material is obtained by the following method: The first step is to mix acrylic acid, polyoxyethylene ether and methyl methacrylate in a mass ratio of 2:1:7 evenly, and put them into a reaction vessel while stirring and heating. The temperature of the reaction vessel is controlled at 180℃ to 200℃. After the polymerization reaction is fully completed for 1 to 2 hours, it is stopped to obtain a flexible block high strength toughness resin. The second step involves adding mica sheets to the flexible block high-strength and high-toughness resin, stirring and heating simultaneously to fully melt the flexible block high-strength and high-toughness resin at a temperature of 180°C to 200°C. After stirring evenly, the mixture is poured into a mold to obtain a prepolymer. The mass ratio of mica sheets to flexible block high-strength and high-toughness resin is 65:35. The third step is to place the prepolymer into a hot press machine and mold it at a temperature of 150℃ to obtain a prepolymer board with a thickness of 0.4mm. The fourth step is to cool the prepolymer board to room temperature, and after crushing and sieving, obtain a high-strength and tough resin-reinforced mica sealing material with a thickness of 0.4 mm and a particle size of 8 mm to 15 mm.

[0038] Modified rubber is obtained by the following method: Rubber particles with a particle size of 0.2 mm to 4.0 mm were soaked in a 12% sodium hydroxide solution. After filtration, the particles were washed twice with water, filtered again, and dried in an oven at 105°C for 12 hours to obtain modified rubber.

[0039] Composite fibers are obtained by the following method: Composite fibers are obtained by physically mixing glass fibers with a length of 12 mm and flax fibers with a length of 5 mm at a mass ratio of 4:6.

[0040] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry comprises, by weight, 100 parts of Grade G oil well cement, 30 parts of fly ash, 6 parts of silica fume, 0.6 parts of drag reducer (ketone-aldehyde condensate USZ), 4 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.5 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 4 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 70 parts of water, and 4 parts of composite plugging agent. It is obtained according to the following method: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir for 2 minutes at a speed of 4200rpm±200rpm to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and then stir at high speed for 35 seconds at a speed of 4000rpm±200rpm to obtain early-strength fly ash cement slurry. The fourth step involves adding the required amount of composite sealing agent to the early-strength fly ash cement slurry and stirring at a high speed of 4000 rpm ± 200 rpm for 35 seconds to obtain an early-strength, low-density fly ash multi-element, multi-scale sealing cement slurry with a density of 1.75 g / cm³. 3 .

[0041] Example 13: The composite sealant is prepared using the same method as in Example 12 of this invention.

[0042] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry comprises, by weight, 100 parts of Grade G oil well cement, 35 parts of fly ash, 10 parts of silica fume, 0.8 parts of drag reducer (ketone-aldehyde condensate USZ), 4 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.5 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 4 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 108 parts of water, and 4 parts of composite plugging agent. The remaining steps are identical, yielding an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a density of 1.60 g / cm³. 3 .

[0043] Example 14: The difference between this composite sealant and Example 12 of the present invention is that the third step, "Putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.4 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.4 mm and a particle size of 8 mm to 15 mm," is modified to "The third step, putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.5 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.5 mm and a particle size of 8 mm to 15 mm," while the remaining steps are the same.

[0044] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry differs from Example 12 of this invention in that, by weight, the raw materials include 100 parts of Grade G oil well cement, 40 parts of fly ash, 15 parts of silica fume, 0.5 parts of drag reducer (ketone-aldehyde condensate USZ), 6 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.3 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 4 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 150 parts of water, and 4 parts of composite plugging agent. The remaining steps are the same, resulting in an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a density of 1.50 g / cm³. 3 .

[0045] Example 15: The difference between this composite sealant and Example 12 of the present invention is that the third step, "Putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.4 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.4 mm and a particle size of 8 mm to 15 mm," is modified to "The third step, putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.5 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.5 mm and a particle size of 8 mm to 15 mm," while the remaining steps are the same.

[0046] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry differs from Example 12 of this invention in that, by weight, the raw materials include 100 parts of Grade G oil well cement, 50 parts of fly ash, 15 parts of artificial glass microspheres, 30 parts of silica fume, 0.4 parts of drag reducer (ketone-aldehyde condensate USZ), 8 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.2 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 5 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 180 parts of water, and 4 parts of composite plugging agent. The remaining steps are the same, resulting in an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a density of 1.40 g / cm³. 3 .

[0047] Example 16: The difference between this composite sealant and Example 12 of the present invention is that the third step, "Putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.4 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.4 mm and a particle size of 8 mm to 15 mm," is modified to "The third step, putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.6 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.6 mm and a particle size of 8 mm to 15 mm," while the remaining steps are the same.

[0048] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry differs from Example 12 of this invention in that, by weight, the raw materials include 100 parts of G-grade oil well cement, 55 parts of fly ash, 37 parts of artificial glass microspheres, 30 parts of silica fume, 0.2 parts of drag reducer (ketone-aldehyde condensate USZ), 8 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.1 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 5 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 185 parts of water, and 4 parts of composite plugging agent. The remaining steps are the same, resulting in an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a density of 1.30 g / cm³. 3 .

[0049] Example 17: The difference between this composite sealant and Example 12 of the present invention is that the third step, "Putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.4 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.4 mm and a particle size of 8 mm to 15 mm," is modified to "The third step, putting the prepolymer into a hot press and molding it at 150°C to obtain a prepolymer board with a thickness of 0.6 mm; the fourth step, cooling the prepolymer board to room temperature, and after crushing and sieving, obtaining a high-strength and tough resin-reinforced mica sealant material with a thickness of 0.6 mm and a particle size of 8 mm to 15 mm," while the remaining steps are the same.

[0050] This early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry differs from Example 12 of this invention in that, by weight, the raw materials include 100 parts of Grade G oil well cement, 55 parts of fly ash, 45 parts of artificial glass microspheres, 45 parts of silica fume, 0.8 parts of drag reducer (ketone-aldehyde condensate USZ), 8 parts of water loss reducer (AMPS-type binary copolymer water loss reducer G33S), 0.1 parts of retarder (retarder BXR-200L), 0.5 parts of defoamer (defoamer G603), 5 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite, and sodium sulfate in a mass ratio of 1:4:5), 188 parts of water, and 4 parts of composite plugging agent. The remaining steps are the same, resulting in an early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry with a density of 1.20 g / cm³. 3 .

[0051] Example 18: The composite sealant is prepared using the same method as in Example 12 of this invention.

[0052] The difference between this early-strength, low-density fly ash multi-element, multi-scale sealing cement grout and Example 12 of the present invention is that the raw material "4 parts of composite sealing agent" is changed to "5 parts of composite sealing agent", while the other steps are the same.

[0053] Example 19: The composite sealant is prepared using the same method as in Example 12 of this invention.

[0054] The difference between this early-strength, low-density fly ash multi-element, multi-scale sealing cement grout and Example 12 of this invention is that the raw material "4 parts of composite sealing agent" is changed to "6 parts of composite sealing agent", while the other steps are the same.

[0055] Comparative Example 1: The composite sealant is prepared using the same method as in Example 12 of this invention.

[0056] The difference between this sealing cement grout and Example 12 of the present invention is that no composite sealing agent is added to the raw materials, but the other steps are the same.

[0057] Example 20: The composite sealant is prepared using the same method as in Example 15 of this invention.

[0058] The difference between this early-strength, low-density fly ash multi-element, multi-scale sealing cement grout and Example 15 of the present invention is that the raw material "4 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:4:5)" is modified to "5 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:4:5)". All other steps are the same.

[0059] Example 21: The composite sealant is prepared using the same method as in Example 15 of this invention.

[0060] The difference between this early-strength, low-density fly ash multi-element, multi-scale sealing cement grout and Example 15 of the present invention is that the raw material "4 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:4:5)" is modified to "6 parts of reinforcing agent (a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:4:5)". All other steps are the same.

[0061] Comparative Example 2: The composite sealant is prepared using the same method as in Example 15 of this invention.

[0062] The difference between this early-strength, low-density fly ash multi-element, multi-scale plugging cement grout and Example 15 of this invention is that no reinforcing agent is added to the raw materials (triethanolamine, sodium nitrite, and sodium sulfate are mixed in a mass ratio of 1:4:5), while the other steps are the same.

[0063] Experimental Example 1: To investigate the pressure-bearing capacity of the early-strength low-density fly ash multi-element multi-scale sealing cement slurry of the present invention, prepared using composite sealing agents with different addition amounts as raw materials, for sealing large-size cracks.

[0064] Experimental Method: Referring to the water loss test method in standard GB / T 19139-2012 "Test Methods for Cement in Oil Wells", the filter screen was replaced with a slotted plate simulating formation fractures with widths of 1mm, 2mm, and 3mm. The pressure resistance of the early-strength low-density fly ash multi-element multi-scale plugging cement slurry (with different amounts of composite plugging agent) prepared in Examples 12, 18, and 19 of this invention and the plugging cement slurry prepared in Comparative Example 1 (without composite plugging agent) to seal large-size fractures was tested. The pressure started from 0, and the pressure when all the early-strength low-density fly ash multi-element multi-scale plugging cement slurry of this invention was lost was recorded as the sealing pressure.

[0065] Experimental Results: Table 1 shows the pressure-bearing capacity of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention for sealing large-size fractures. As can be seen from Table 1, for wells with severe leakage, the amount of composite plugging agent added significantly affects the pressure-bearing capacity. For fractures in the same formation, a larger amount of composite plugging agent results in a relatively higher concentration of bridging particles within the fracture, leading to stronger pressure-bearing capacity. Compared with the plugging cement slurry prepared in Comparative Example 1 (without composite plugging agent), the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention improves the pressure-bearing capacity of sealing 1mm fractures by 190% to 250%; 2mm fractures by 200% to 256%; and 3mm fractures by 6.6 to 7.0 times. This indicates that the modified rubber, composite fiber, and high-strength, tough resin-reinforced mica sealing material in the composite sealing agent have a synergistic effect, resulting in a high degree of compatibility between the early-strength, low-density fly ash multi-element, multi-scale sealing cement slurry of this invention and large-size cracks. The sealing quality is improved through the composite fiber three-dimensional network, the sheet-like high-strength, tough resin-reinforced mica sealing material bridging, and the filling of modified rubber elastic particles.

[0066] Experimental Example 2: The compressive strength of the early-strength low-density fly ash multi-element multi-scale plugging cement slurry of the present invention, prepared with different amounts of reinforcing agents as raw materials, was investigated.

[0067] Experimental methods: The early compressive strength of the early-strength low-density fly ash multi-element multi-scale plugging cement slurry (with different amounts of reinforcing agent) prepared in Examples 15, 20 and 21 of this invention and the plugging cement slurry prepared in Comparative Example 2 (without reinforcing agent) were tested at 60°C according to the methods specified in standard GB / T19139-2012 "Test Methods for Cement in Oil Wells".

[0068] Experimental results: The early compressive strength of the early-strength low-density fly ash multi-element multi-scale plugging cement grout of the present invention at 60℃ is shown in Table 2. As can be seen from Table 2, with the increase of the amount of reinforcing agent, the early strength of the early-strength low-density fly ash multi-element multi-scale plugging cement grout of the present invention after adding the reinforcing agent is 80% to 140% higher than that of Comparative Example 2 (without reinforcing agent), and the early strength of the early-strength low-density fly ash multi-element multi-scale plugging cement grout after adding the reinforcing agent is 50% to 70% higher than that of Comparative Example 2 (without reinforcing agent), thus establishing a solid barrier for high-quality plugging.

[0069] Experimental Example 3: To investigate the sealing effect of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of the present invention.

[0070] Experimental method: The early-strength low-density fly ash multi-element multi-scale plugging cement slurry prepared in Examples 12 to 17 of this invention was subjected to a plugging pressure test. The test was conducted according to the water loss test method in standard GB / T 19139-2012 "Test Methods for Cement in Oil Wells". The filter screen was replaced with a slotted plate with a width of 2 mm and 3 mm to simulate formation fractures. The pressure started from 0 and the pressure when all the cement slurry was lost was recorded as the plugging pressure.

[0071] Experimental results: The early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention has the following simulated crack sealing effect: Figure 1 As shown, from Figure 1 It can be seen that the higher the density of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention, the stronger its filling and bonding ability, and the stronger its sealing and pressure-bearing capacity. The sealing capacity of the same cement slurry for cracks decreases with increasing crack width, but the decrease is not significant. This is because different cracks require matching particle sizes for the bridging particles; the larger the crack size, the higher the required concentration and particle size of the bridging particles, resulting in a more significant sealing effect. It exhibits good sealing and pressure-bearing capacity for 2mm and 3mm cracks, with a maximum pressure-bearing capacity of up to 4.8MPa for 2mm cracks. The plugging slurry system is stable and can effectively solve the problem of sealing low-pressure, easily leaking wells. Therefore, the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention has a good sealing effect.

[0072] Experimental Example 3: To investigate the comprehensive performance of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of the present invention.

[0073] Experimental method: The early-strength low-density fly ash multi-element multi-scale plugging cement slurry prepared in Examples 12 to 17 of this invention was comprehensively evaluated. The performance included stability density difference, water loss, 24h compressive strength, 8h compressive strength and 70MPa compressive density. The experimental temperature was 60℃.

[0074] Experimental Results: The comprehensive performance of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention is shown in Table 3. Table 3 shows that the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention has a wide density range, API water loss <50mL, with an average of 34mL. It can significantly reduce the risk of collapse caused by leaching of water-sensitive formations by the filtrate, while also reducing damage to oil and gas reservoirs. Furthermore, the density difference between the upper and lower layers of the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention is ≤0.02g / cm³. 3 It exhibits good stability; the average compressive strength over 24 hours and the early compressive strength over 8 hours reach 5.3 MPa, enabling it to quickly form a robust sealing barrier, demonstrating excellent overall performance.

[0075] In summary, the early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry of this invention has a wide density range, small density difference between upper and lower layers, good stability, and high compressive strength. It can significantly reduce the risk of collapse caused by the filtrate soaking water-sensitive formations, reduce damage to oil and gas reservoirs, and quickly form a solid plugging barrier. It can meet the plugging requirements of low-pressure wells prone to leakage and wells with serious leakage, and improve the plugging quality and efficiency.

[0076] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A high-strength, low-density, multi-element, multi-scale leak-sealing cement slurry made from fly ash, characterized in that... The raw materials, by weight, include 100 parts of Grade G oil well cement, 30 to 60 parts of fly ash, 0 to 50 parts of artificial glass microspheres, 6 to 45 parts of silica fume, 0.6 to 1.0 parts of drag reducer, 4 to 8 parts of water loss reducer, 0.3 to 1.5 parts of retarder, 0.4 to 0.6 parts of defoamer, 4 to 7 parts of reinforcing agent, 70 to 188 parts of water, and 3 to 6 parts of composite plugging agent.

2. The early-strength, low-density fly ash multi-element, multi-scale leak-sealing cement slurry according to claim 1, characterized in that... The composite sealant is obtained by mixing modified rubber, composite fiber and high-strength toughness resin-reinforced mica sealant in a mass ratio of 65 to 70: 5 to 8: 22 to 35.

3. The early-strength, low-density fly ash multi-element, multi-scale leak-sealing cement slurry according to claim 2, characterized in that... High-strength, tough resin-reinforced mica sealing material is obtained by the following method: The first step involves stirring acrylic acid, polyoxyethylene ether, and methyl methacrylate in a mass ratio of 2:0.5 to 1.5:6 to 8 and allowing them to undergo a polymerization reaction to obtain a flexible block high-strength and tough resin. During polymerization, the reaction temperature is 180°C to 200°C and the reaction time is 1 to 2 hours. The second step involves adding mica sheets to the flexible block high-strength and high-toughness resin, stirring at a temperature of 180°C to 200°C until fully melted, and then injecting the mixture into a mold to obtain a prepolymer. The mass ratio of mica sheets to flexible block high-strength and high-toughness resin is 65 to 75: 25 to 35. The third step is to mold and cure the prepolymer at a temperature of 145℃ to 155℃ to obtain a prepolymer board with a thickness of 0.4mm to 0.6mm. The fourth step involves cooling and crushing the prepolymer board to obtain a high-strength, tough resin-reinforced mica sealing material with a particle size of 8mm to 15mm.

4. The early-strength, low-density fly ash multi-element, multi-scale leak-sealing cement slurry according to claim 2 or 3, characterized in that... Modified rubber is obtained by the following method: rubber particles with a particle size of 0.2 mm to 4.0 mm are added to a sodium hydroxide solution with a mass concentration of 10% to 15% and soaked for 2 to 3 hours. Then, after filtration, washing, re-filtration and drying, modified rubber is obtained.

5. The early-strength, low-density fly ash multi-element, multi-scale leak-sealing cement slurry according to claim 2, 3, or 4, characterized in that... The composite fiber is a mixture of glass fiber and flax fiber in a mass ratio of 4:5 to 7, wherein the length of the glass fiber is 5 mm to 12 mm and the length of the flax fiber is 3 mm to 6 mm, and the mixing method is physical mixing.

6. The early-strength, low-density, multi-element, multi-scale leak-stopping cement slurry made from fly ash according to any one of claims 1 to 5, characterized in that... The reinforcing agent is one or more of an organic salt and an inorganic salt, wherein the organic salt is triethanolamine and the inorganic salt is one or more of sodium nitrite and sodium sulfate.

7. The early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry according to any one of claims 1 to 6, characterized in that... The reinforcing agent is a mixture of triethanolamine, sodium nitrite and sodium sulfate in a mass ratio of 1:3 to 5:4 to 6.

8. The early-strength, low-density, multi-element, multi-scale leak-stopping cement slurry made from fly ash according to any one of claims 1 to 7, characterized in that... The drag-reducing agent is one or more of ketaldehyde condensates and polycarboxylic acids; or / and the water loss reducing agent is one or more of polyvinyl alcohol and AMPS-type binary copolymer water loss reducing agents; or / and the retarder is one or more of sodium citrate, sodium tartrate, sodium borate, sodium acetate and sodium tripolyphosphate.

9. The early-strength, low-density, multi-element, multi-scale leak-stopping cement slurry made from fly ash according to any one of claims 1 to 8, characterized in that... Obtained using the following method: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, artificial glass microspheres, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir at 4200rpm±200rpm for 1min to 2min to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength fly ash cement slurry. The fourth step is to add the required amount of composite sealing agent to the early-strength fly ash cement slurry and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength low-density fly ash multi-element multi-scale sealing cement slurry.

10. A method for preparing early-strength, low-density fly ash multi-element, multi-scale plugging cement slurry according to any one of claims 1 to 8, characterized in that... Perform it as follows: The first step is to thoroughly mix and stir the required amounts of Grade G oil well cement, artificial glass microspheres, fly ash, and silica fume to obtain a mixed ash sample. The second step is to add the required amount of drag reducer, water loss reducer, retarder, enhancer and defoamer to the required amount of water, and stir at 4200rpm±200rpm for 1min to 2min to obtain the slurry. The third step is to mix the mixed ash sample with the slurry, and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength fly ash cement slurry. The fourth step is to add the required amount of composite sealing agent to the early-strength fly ash cement slurry and stir at high speed for 35 to 45 seconds at a speed of 4000 rpm ± 200 rpm to obtain early-strength low-density fly ash multi-element multi-scale sealing cement slurry.

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