Early-strength compact anti-gas-channeling cement paste for well cementation and preparation method thereof

Abstract

The invention discloses early-strength compact anti-gas-channeling cement paste for well cementation and a preparation method thereof, and belongs to the technical field of well cementation materials. The early-strength compact anti-gas-channeling cement paste for well cementation comprises the following raw materials: 54-76 wt.% of superfine oil well cement; 5 to 10 wt.% of fly ash; 5 wt.% of silica fume; 5-10 wt.% of carbide slag; 5 to 12 wt.% of hollow glass beads; 3-6 wt.% of a composite early strength agent; 0.5 to 1.5 wt.% of a dispersant; and 0.5 to 1.5 wt.% of a fluid loss agent. The invention further discloses a preparation method of the early-strength compact anti-gas-channeling cement paste for well cementation. The early-strength compact anti-gas-channeling cement paste for well cementation shows excellent performance under a low-temperature condition, has the characteristics of rapid early strength increase, high final strength, short setting waiting time, compact set cement structure, outstanding anti-gas-channeling capability and the like, and is wide in density adjustment range and high in adaptability. The cement paste system disclosed by the invention can effectively meet multiple requirements on low-temperature adaptability, early strength and low-density performance in well cementation construction and subsequent mining processes in a low-temperature environment.

Description

Technical Field

[0001] The invention belongs to the technical field of cementing materials, and particularly relates to an early-strength, dense, and gas-channeling-proof cement slurry for cementing and a preparation method thereof. Background Art

[0002] During low-temperature cementing operations in coalbed methane formations and shallow surface cementing in deepwater layers, formation temperatures are generally low. Under these low-temperature conditions, conventional oil well cement slurry systems suffer from significant drawbacks, such as slow hydration reaction, slow early strength development, and high permeability of the hardened cement stone, making it difficult to meet the quality and timeliness requirements of cementing projects.

[0003] To address the challenges of low temperatures, the addition of early-strength agents is commonly used in existing technologies to shorten the setting time of cement slurry and improve its early strength. Existing early-strength agents for oil well cement primarily include inorganic salts, organic compounds, and nanomaterials. However, single-component early-strength agents often fail to fully meet the comprehensive requirements of cementing operations. They often suffer from issues such as excessive addition dosage, unsatisfactory early-strength effects, negative impacts on the flow properties (rheology) of the cement slurry, and insufficient gas channeling resistance.

[0004] For example, patent publication number CN 104194752 A discloses a low-temperature early strength agent for coalbed methane well cementing and a cement slurry containing the agent. The early strength agent is composed of the following ingredients: 1.5-2.5 parts by weight of calcium formate, 0.20-0.80 parts by weight of calcium sulfate, 0.30-1.0 parts by weight of aluminum sulfate, 0.20-1.0 parts by weight of sodium silicate, 0.20-0.80 parts by weight of sodium sulfate, 0.10-0.60 parts by weight of sodium aluminate, and 0.30-0.80 parts by weight of carbon nanotubes.

[0005] Another patent, CN 105462571 A, discloses a low-temperature cementing slurry system featuring low density, low-temperature early strength, and low fluid loss. Its thickening time and compressive strength meet the requirements of deepwater cementing field operations. The components and weight proportions of this low-temperature cement slurry system are as follows: 100 parts oil well cement, 62-175 parts oil well ultrafine cement, 7.3-23 parts nano-silica, 10-32 parts active calcium silicate, 15-50 parts hollow glass microspheres, 3.6-10 parts early strength agent, 3.2-8.6 parts fluid loss additive, 0.8-2.0 parts dispersant, and 120-195 parts water.

[0006] While existing technologies have alleviated the challenges of deepwater, low-temperature cementing to some extent, these cement slurry systems still have significant limitations. These include poor compatibility with admixtures, which severely impacts slurry workability; low early strength and poor channeling resistance; and the addition of early-strengthening agents, which increase slurry viscosity and deteriorate rheological properties. Therefore, addressing the challenges of cementing in low-temperature environments requires developing cement slurries that offer early strength, compactness, and channeling resistance, meeting the requirements of low-temperature cementing. Summary of the Invention

[0007] One of the purposes of the present invention is to provide an early-strength dense anti-gas channeling cement slurry for cementing, so as to solve the problems of low early strength, poor anti-gas channeling performance and poor rheological properties that are easily encountered in cement slurry systems in the prior art when used in low temperature environments.

[0008] A second object of the present invention is to provide a method for preparing the cement slurry.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] In order to achieve the above-mentioned object, the present invention provides an early-strength, dense, and gas-channeling-proof cement slurry for well cementing, wherein the raw materials of the cement slurry include the following components in percentages: ultrafine oil well cement: 54-76 wt.%; fly ash: 5-10 wt.%; microsilica powder: 5 wt.%; carbide slag: 5-10 wt.%; hollow glass microspheres: 5-12 wt.%; composite early-strength agent: 3-6 wt.%; dispersant: 0.5-1.5 wt.%; and fluid loss additive: 0.5-1.5 wt.%.

[0011] In some embodiments of the present invention, the ultrafine oil well cement is obtained by ball milling G-grade oil well cement, and its specific surface area is greater than 550m 2 / kg;

[0012] Fly ash with a CaO content of less than 5wt.%, a SiO2 content of greater than 55wt.%, an Al2O3 content of greater than 30wt.%, and a particle size of less than 40μm;

[0013] The SiO2 content of the microsilica powder is greater than 96wt.%, and the particle size of the powder is less than 10μm;

[0014] The carbide slag has a specific surface area of ​​>500m 2 / kg, pH value is 12.5-13.2, preferably 12.8;

[0015] The hollow glass microspheres have a density of 0.58 g / cm 3 -0.62g / cm 3 , compressive strength 80MPa;

[0016] The dispersant is polynaphthalene sulfonate;

[0017] The fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) polymer;

[0018] The raw materials of the composite early strength agent are organic amine compounds, inorganic salts, polymer materials, modified nanomaterials and trace element additives, and the mass ratio thereof is 3:8:3:5:1;

[0019] The organic amine compound is a mixture of triisopropanolamine and N-aminoethylpiperazine, with a mass ratio of 2 to 4:1;

[0020] The inorganic salt is a mixture of aluminum nitrate and calcium sulfoaluminate, with a mass ratio of 1 to 3:1;

[0021] The polymer material is AMPS / AA / DMDAAC copolymer;

[0022] The trace element additive is a mixture of lithium borate, copper sulfate and ammonium molybdate in a mass ratio of 4 to 6:1 to 3:1.

[0023] The modified nanomaterial is a mixture of KH550-ZnO@CNTs and modified calcined kaolin in a mass ratio of 3:1 to 2;

[0024] In some embodiments of the present invention, the preparation method of KH550-ZnO@CNTs includes the following steps:

[0025] S1: placing multi-walled carbon nanotubes with a diameter of 20 to 30 nm in a plasma reactor protected by an inert gas, and treating at 280 to 320° C. for 1 to 3 hours to obtain hydroxylated activated carbon nanotubes; preferably, treating at 300° C. for 2 hours;

[0026] Then, the hydroxylated activated carbon nanotubes are immersed in a 1-4 mol / L nitric acid solution, refluxed at 80° C. for 2-6 hours, washed, and dried to obtain activated carbon nanotubes;

[0027] S2: Mixing 0.2-1.0 mol / L zinc nitrate ethanol solution and activated carbon nanotubes in a mass ratio of 15-60:1 and ultrasonically dispersing the mixture, heating the mixture to 50-70° C., adjusting the pH value of the reaction system to alkaline, preferably to 9; reacting the mixture for 2-8 hours, centrifuging the mixture, washing the mixture, and drying the mixture to obtain ZnO@CNTs composite powder;

[0028] S3: dissolving KH550 in an ethanol-water solution with a volume ratio of 4 to 6:1 to prepare a KH550 solution with a mass concentration of 5-10%, and adjusting the pH value to acidic; mixing the ZnO@CNTs composite powder obtained in S2 with the KH550 solution at a solid-liquid ratio of 1:5 to 20, stirring in a water bath at 50 to 70° C. for 4 to 8 hours, and simultaneously ultrasonically heating the reaction; centrifuging and drying to obtain the product KH550-ZnO@CNTs; preferably, in step S3, formic acid is added to adjust the pH value to 4 to 6.

[0029] In some embodiments of the present invention, the preparation method of modified calcined kaolin includes the following steps: calcining kaolin at 600-800°C for 1-4 hours for activation and depolymerization, adding it to a KH550 solution with a concentration of 5-10wt.% at a mass ratio of 1:10-20, and reacting it at 75-85°C for 2-6 hours under stirring conditions; centrifuging the solid, washing it, and drying it to obtain a modified product A; adding a saturated solution of Ca(OH)2 to the modified product A, heating the reaction, preferably at 60-70°C, to generate a nano-CSH core-shell structure, and drying it to obtain a modified calcined kaolin.

[0030] The KH550 solution used in the preparation of the modified calcined kaolin is prepared by dissolving KH550 in an ethanol-water solution with a volume ratio of 4 to 6:1.

[0031] Preferably, the solid-liquid ratio of the modified product A to the Ca(OH)2 saturated solution is 1g:10-20ml.

[0032] Preferably, the nano-CSH core-shell structure is generated and then spray-dried to obtain modified calcined kaolin.

[0033] In some embodiments of the present invention, KH550-ZnO@CNTs and modified calcined kaolin are pneumatically mixed in a mass ratio of 3:1-2 to obtain a modified nanomaterial.

[0034] The preparation method of nano-composite early strength agent for cementing cement specifically comprises the following steps:

[0035] Step 1. Dissolve the inorganic salt in deionized water (2-3 times its mass), and adjust the pH of the solution to acidic, preferably, 5.0-5.5; then add sodium citrate and ultrasonicate for 10-30 minutes to obtain a stable base solution A; the mass of sodium citrate is 0.6-1.0% of the mass of the inorganic salt solution;

[0036] Step 2. Add the polymer material to the stable base liquid A, stir, then add the modified nanomaterial, stir and simultaneously ultrasonicate, and spray-inject the organic amine compound to obtain base liquid B;

[0037] Preferably, the polymer material is added to the stable base liquid A, first stirred at 150-400 rpm for 2-10 minutes, then stirred at 600-1000 rpm for 2-10 minutes; after adding the modified nanomaterial, the mixture is stirred at 600-1000 rpm for 15-60 minutes, and ultrasonicated simultaneously;

[0038] Step 3: adding the trace element additive to the base liquid B and wet grinding to obtain a mixture A; preferably, wet grinding at a speed of 800-1000 rpm for 5-20 minutes to obtain a mixture A;

[0039] Step 4: Adding polycarboxylic acid drag reducer to mixture A, concentrating, and drying to obtain a nano-composite early strength agent; preferably, adding polycarboxylic acid drag reducer to mixture A, rotary evaporating the solvent, and then spray drying to obtain a nano-composite early strength agent.

[0040] The second aspect of the present invention discloses a method for preparing the above-mentioned early-strength, dense, and gas-proof cement slurry for well cementing, comprising the following steps: weighing materials according to a proportion, uniformly mixing fly ash, microsilica powder, carbide slag, hollow glass microspheres, a composite early-strength agent, a dispersant, a fluid loss additive, and ultrafine G-grade oil well cement to obtain a dry mix; adding water to prepare cement slurry, controlling the water-cement ratio to 0.55.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention is scientifically designed and ingeniously conceived. The early-strength, dense, and gas-channeling-resistant cement slurry for cementing exhibits excellent performance under low-temperature conditions, featuring rapid early strength growth, high ultimate strength, a short setting time, a dense cement stone structure, and outstanding gas-channeling resistance. Furthermore, it offers a wide density adjustment range and strong adaptability. The cement slurry system of the present invention effectively meets the multiple requirements for low-temperature adaptability, early strength, and low-density performance during cementing operations and subsequent mining operations in low-temperature environments.

[0043] In the cement slurry system of the present invention, carbide slag provides an alkaline environment on the one hand, promoting the dissolution of active silicon and aluminum ions in fly ash and reacting with them to form hydrated calcium silicate (aluminate), and together with the modified nanomaterials in the composite early strength agent, provides nucleation sites for cement hydration products, thereby promoting the occurrence of cement hydration reaction; on the other hand, it promotes the formation of trace element additives [CuMoO4] in the composite early strength agent. 2- Complex, filling the nanopores of CSH gel, improving cement density and early strength.

[0044] The composite early-strength agent of the present invention contains no chloride ions, which helps ensure the safety of cementing operations and protects oil and gas well casing. Adding it to cement slurry does not cause thickening and significantly shortens the waiting time for oil and gas well cementing under low-temperature conditions. Furthermore, while improving the early strength of oil well cement, it also optimizes the pore structure within the cement paste, making it more dense and effectively reducing the probability of gas channeling.

[0045] The composite early strength agent of the present invention has excellent low-temperature early strength effect under the synergistic effect of various components, which is beneficial to shortening the cementing waiting time of shallow oil and gas wells, improving the density of cement paste, and reducing the risk of gas channeling. The organic amine compound and lithium borate destroy the hydrogen bond network of water molecules, enhance the reactivity of water molecules, and reduce the cement hydration energy barrier; the borate ions released by lithium borate react with the Ca released by cement hydration. 2+ Forming a stable calcium borate complex, filling capillary pores, reducing porosity, and improving cement paste density; it can also reduce liquid phase Ca 2+ Concentrations can disrupt the C3S hydration equilibrium, accelerating calcium silicate dissolution and CSH gel nucleation, thereby improving the early strength of cement. The modified nanomaterials provide heterogeneous nucleation sites, inducing rapid, low-temperature formation of CSH gel. Furthermore, the modified calcined kaolin provides active silicon and aluminum ions to generate additional hydration products. The nano-CSH in the core-shell structure shares crystal structure similarities with cement hydration products, lowering the C3S hydration nucleation barrier and accelerating the hydration process. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] The raw materials of the composite early strength agent described in the embodiment of the present invention are: organic amine compound, inorganic salt, polymer material, modified nanomaterial and trace element additive, and the mass ratio thereof is 3:8:3:5:1.

[0048] The organic amine compound is a mixture of triisopropanolamine and N-aminoethylpiperazine in a mass ratio of 3:1; the inorganic salt is a mixture of aluminum nitrate and calcium sulfoaluminate in a mass ratio of 2:1; the polymer material is an AMPS / AA / DMDAAC copolymer; the trace element additive is a mixture of lithium borate, copper sulfate, and ammonium molybdate in a mass ratio of 5:2:1; and the modified nanomaterial is a mixture of KH550-ZnO@CNTs and modified calcined kaolin in a mass ratio of 3:1.

[0049] The preparation method of the modified nanomaterial comprises the following steps:

[0050] S1: Multi-walled carbon nanotubes with a diameter of 20-30 nm were placed in an argon-protected plasma reactor and treated at 300°C for 2 hours to obtain hydroxylated activated carbon nanotubes; the activated carbon nanotubes were immersed in a 3 mol / L nitric acid solution, refluxed at 80°C for 4 hours, washed with deionized water until neutral, and dried in a vacuum drying oven at 60°C;

[0051] S2: A 0.5 mol / L zinc nitrate ethanol solution and activated carbon nanotubes were mixed at a mass ratio of 30:1 and ultrasonically dispersed for 1 hour; the mixture was then heated to 60°C and ammonia was added dropwise under constant stirring to adjust the pH to 9. The mixture was reacted for 4 hours and then centrifuged. The mixture was washed three times with anhydrous ethanol and dried in a vacuum at 80°C to obtain ZnO@CNTs composite powder;

[0052] S3: KH550 was dissolved in an ethanol-water solution with a volume ratio of 5:1 to prepare a 10% KH550 ethanol-water solution, formic acid was added to adjust the pH to 5, and magnetic stirring was performed for 1.5 hours; the ZnO@CNTs composite powder obtained in S2 was mixed with the KH550 solution at a solid-liquid ratio of 1:10, stirred in a 60°C water bath for 6 hours, and ultrasonicated simultaneously; after the reaction, the mixture was centrifuged and dried in a vacuum at 60°C to obtain the product KH550-ZnO@CNTs;

[0053] S4: The calcined kaolin powder, which was activated and depolymerized after calcination at 700°C for 2 hours, was added to the KH550 ethanol hydrolysis solution prepared in S3 at a solid-to-liquid ratio of 1:15; stirring was continued at 80°C for 4 hours. After the reaction, the solid was centrifuged and separated, and washed three times with ethanol to remove unreacted materials. The modified product A was obtained after vacuum drying at 50°C. A saturated solution of Ca(OH)2 was added to the modified product A, and the reaction was carried out at 70°C for 5 hours to generate a nano-CSH core-shell structure. The modified calcined kaolin was obtained after spray drying; the solid-to-liquid ratio of the modified product A to the saturated solution of Ca(OH)2 was 1g:15ml;

[0054] S5: KH550-ZnO@CNTs and modified calcined kaolin were pneumatically mixed in a mass ratio of 3:1 to obtain modified nanomaterials.

[0055] The preparation method of composite early strength agent is as follows:

[0056] Step 1. Dissolve and mix inorganic salts and deionized water in a 3:7 mass ratio in a 40°C water bath. Add 5% ammonia water dropwise while stirring at 800 rpm to adjust the pH to 5.0-5.5. Add 0.8 wt.% sodium citrate and ultrasonicate for 20 min to obtain a stable base solution A.

[0057] Step 2. Add AMPS / AA / DMDAAC copolymer to base liquid A, stir at 300 rpm for 5 minutes, then at 800 rpm for 5 minutes; add modified nanomaterial, stir at 800 rpm for 30 minutes, and simultaneously sonicate; spray inject organic amine compound at a rate of 2 ml / min to obtain base liquid B;

[0058] Step 3. Add the trace element additive to the base liquid B and wet grind at 900 rpm for 10 min to obtain a mixture A;

[0059] Step 4: Transfer mixture A to a rotary evaporator, add 0.15% polycarboxylic acid drag reducer, control the solid content to ≥40wt%, spray dry, pass through a nitrogen circulation system, control the inlet air temperature to 160°C and the outlet air temperature to 80°C, and obtain a composite early strength agent.

[0060] Example 1

[0061] As a preferred embodiment of the present invention, the early-strength dense anti-gas channeling cement slurry for cementing used in this embodiment is specifically composed of: 54wt.% ultrafine oil well cement, 10wt.% fly ash, 5wt.% microsilica powder, 10wt.% calcium carbide slag, 12wt.% hollow glass microspheres, 6wt.% composite early strength agent, 1.5wt.% dispersant, and 1.5wt.% fluid loss additive.

[0062] Among them, ultrafine oil well cement is obtained by ball milling G grade oil well cement, and its specific surface area is more than 550m 2 / kg;

[0063] The fly ash has a CaO content of less than 5wt.%, a SiO2 content of more than 55wt.%, an Al2O3 content of more than 30wt.%, and a particle size of less than 40μm;

[0064] The SiO2 content in the microsilica powder is greater than 96wt.%, and the particle size is less than 10μm;

[0065] Carbide slag has a specific surface area of ​​>500m 2 / kg, pH value is 12.8;

[0066] The density of hollow glass microspheres is 0.58g / cm 3 -0.62g / cm 3 , compressive strength 80MPa;

[0067] The dispersant is polynaphthalenesulfonate;

[0068] The fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) polymer.

[0069] Weigh the materials according to the above proportions and evenly mix fly ash, microsilica fume, carbide slag, hollow glass microspheres, composite early strength agent, dispersant, fluid loss additive, and ultrafine Grade G oil well cement to produce a dry mix. Prepare the cement slurry according to GB / T-19139 with a water-cement ratio of 0.55 to obtain early strength, dense, and gas channeling prevention cement slurry #1 for well cementing.

[0070] Example 2

[0071] As a preferred embodiment of the present invention, the early-strength dense anti-gas channeling cement slurry for cementing used in this embodiment is specifically composed of: 65wt.% ultrafine oil well cement, 8wt.% fly ash, 5wt.% microsilica powder, 8wt.% calcium carbide slag, 8wt.% hollow glass microspheres, 4wt.% composite early strength agent, 1wt.% dispersant, and 1wt.% fluid loss additive.

[0072] Among them, ultrafine oil well cement is obtained by ball milling G grade oil well cement, and its specific surface area is greater than 550m 2 / kg;

[0073] The fly ash has a CaO content of less than 5 wt.%, a SiO2 content of greater than 55 wt.%, an Al2O3 content of greater than 30 wt.%, and a particle size of less than 40 μm;

[0074] The SiO2 content in the microsilica powder is greater than 96wt.%, and the particle size is less than 10μm;

[0075] Carbide slag has a specific surface area of ​​>500m 2 / kg, pH value is 12.8;

[0076] The density of hollow glass microspheres is 0.58g / cm 3 -0.62g / cm 3 , compressive strength 80MPa.

[0077] The dispersant is polynaphthalenesulfonate;

[0078] The fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) polymer;

[0079] Weigh the materials according to the above proportions and evenly mix fly ash, microsilica fume, carbide slag, hollow glass microspheres, composite early strength agent, dispersant, fluid loss additive, and ultrafine Grade G oil well cement to obtain a dry mix. Prepare the cement slurry according to GB / T-19139 with a water-cement ratio of 0.55 to obtain early strength, dense, and gas channeling-proof cement slurry No. 2 for well cementing.

[0080] Example 3

[0081] As a preferred embodiment of the present invention, the early-strength dense anti-gas channeling cement slurry for cementing used in this embodiment is specifically composed of: 76wt.% ultrafine oil well cement, 5wt.% fly ash, 5wt.% microsilica powder, 5wt.% calcium carbide slag, 5wt.% hollow glass microspheres, 3wt.% composite early strength agent, 0.5wt.% dispersant, and 0.5wt.% fluid loss additive.

[0082] Ultrafine oil well cement is obtained by ball milling G grade oil well cement, and its specific surface area is greater than 550m 2 / kg;

[0083] The fly ash has a CaO content of less than 5wt.%, a SiO2 content of more than 55wt.%, an Al2O3 content of more than 30wt.%, and a particle size of less than 40μm;

[0084] The SiO2 content in the microsilica powder is greater than 96wt.%, and the particle size is less than 10μm;

[0085] Carbide slag has a specific surface area of ​​>500m 2 / kg, pH value is 12.8;

[0086] The density of hollow glass microspheres is 0.58g / cm 3 -0.62g / cm 3 , compressive strength 80MPa;

[0087] The dispersant is polynaphthalenesulfonate;

[0088] The fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) polymer;

[0089] Weigh the materials according to the above proportions and evenly mix fly ash, microsilica fume, carbide slag, hollow glass microspheres, composite early strength agent, dispersant, fluid loss additive, and ultrafine Grade G oil well cement to create a dry mix. Prepare cement slurry according to GB / T-19139 with a water-cement ratio of 0.55 to obtain early strength, dense, and gas channeling-proof cement slurry #3 for well cementing.

[0090] Comparative Example 1

[0091] Compared with Example 3, this comparative example does not contain carbide slag, and ultrafine oil well cement is used to replace the carbide slag. Other conditions are the same.

[0092] Comparative Example 2

[0093] Compared with Example 3, this comparative example does not contain a composite early strength agent, and other conditions are the same.

[0094] Comparative Example 3

[0095] Compared with Example 3, this comparative example uses a commercially available early strength agent, and the other conditions are the same.

[0096] Test Example 1

[0097] The engineering properties of the cement slurries prepared in Examples 1 to 3 and Comparative Examples 1 to 3, such as water loss, fluidity, anti-channeling coefficient, and thickening time, were tested with reference to the oil well cement test method in accordance with GB / T 19139. Furthermore, the cement was cured at 15° C. for 72 h in accordance with the standard GB / T 19139. The relative permeability of the cement paste samples was tested, as shown in Table 1.

[0098] Table 1

[0099]

[0100] From the experimental data in Table 1, it can be seen that the density of the cement slurries prepared in Examples 1-3 ranges from 1.40 to 1.60 g / cm 3 The water loss and fluidity of the slurry can well meet the construction requirements. The SPN value of cement slurry is less than 2.0, indicating that the slurry has good anti-channeling properties and reduces the risk of channeling. The permeability of cement stone is less than 0.62×10 -3 mD, indicating that the cement paste has low permeability and dense structure. Compared with Example 3, the cement slurries of Comparative Examples 1-3 have prolonged thickening time, greatly reduced anti-channeling ability of the slurry, and increased cement paste permeability.

[0101] Test Example 2

[0102] The compressive strength of the cement slurry systems prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was tested at different temperatures according to the GB / T 19139 oil well cement test method. The results are shown in Table 2.

[0103] Table 2

[0104]

[0105] The data in Table 2 show that the cement slurries prepared in Examples 1-3 exhibited a compressive strength greater than 3.5 MPa after 24 hours of curing at 10°C, meeting the early strength requirements for cement slurries in low-temperature regions, effectively shortening drilling cycles and improving operational efficiency. Compared to Example 3, the compressive strength of the cement pastes prepared in Comparative Examples 1-3 was significantly lower.

[0106] From the above cases, it can be seen that the early-strength dense anti-gas channeling cement slurry for cementing formed by adopting the technical solution of the present invention has good construction performance, a wide density adaptability range, rapid strength development, good anti-channeling performance, and the formed cement stone has low permeability and a dense structure. It can effectively solve the problems of slow strength development, poor construction performance, and poor anti-channeling performance of low-temperature and low-density cement slurry in the existing technology.

[0107] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. An early-strength, dense, and gas-proof cement slurry for cementing, characterized in that: The raw materials include the following components in percentages: ultrafine oil well cement: 54-76wt.%; fly ash: 5-10wt.%; microsilica fume: 5wt.%; carbide slag: 5-10wt.%; hollow glass microspheres: 5-12wt.%; composite early strength agent: 3-6wt.%; Dispersant: 0.5-1.5wt.%; fluid loss additive: 0.5-1.5wt.%.

2. The early-strength, dense, and gas-channeling-proof cement slurry for cementing according to claim 1, characterized in that: The ultrafine oil well cement is obtained by ball milling G-grade oil well cement, and its specific surface area is greater than 550m 2 / kg; The fly ash has a CaO content of less than 5 wt.%, a SiO2 content of greater than 55 wt.%, an Al2O3 content of greater than 30 wt.%, and a particle size of less than 40 μm; The SiO2 content of the microsilica powder is greater than 96wt.%, and the particle size of the powder is less than 10μm; The carbide slag has a specific surface area of ​​>500m 2 / kg, pH value is 12.5-13.2; The hollow glass microspheres have a density of 0.58 g / cm 3 -0.62g / cm 3 , compressive strength 80MPa; The dispersant is polynaphthalene sulfonate; The fluid loss additive is a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) polymer.

3. The early-strength, dense, and gas-channeling-proof cement slurry for cementing according to claim 2, characterized in that: The raw materials of the composite early strength agent are organic amine compounds, inorganic salts, polymer materials, modified nanomaterials and trace element additives, and the mass ratio thereof is 3:8:3:5:1; The organic amine compound is a mixture of triisopropanolamine and N-aminoethylpiperazine, with a mass ratio of 2 to 4:1; The inorganic salt is a mixture of aluminum nitrate and calcium sulfoaluminate, with a mass ratio of 1 to 3:1; The polymer material is AMPS / AA / DMDAAC copolymer; The trace element additive is a mixture of lithium borate, copper sulfate, and ammonium molybdate in a mass ratio of 4 to 6:1 to 3:1; The modified nanomaterial is a mixture of KH550-ZnO@CNTs and modified calcined kaolin in a mass ratio of 3:1 to 2.

4. The early-strength, dense, and gas-channeling-proof cement slurry for cementing according to claim 3, characterized in that: The preparation method of KH550-ZnO@CNTs includes the following steps: S1: placing multi-walled carbon nanotubes with a diameter of 20 to 30 nm in a plasma reactor protected by an inert gas, and treating at 280 to 320° C. for 1 to 3 hours to obtain hydroxylated activated carbon nanotubes; preferably, treating at 300° C. for 2 hours; Then, the hydroxylated activated carbon nanotubes are immersed in a 1-4 mol / L nitric acid solution, refluxed at 80° C. for 2-6 hours, washed, and dried to obtain activated carbon nanotubes; S2: Mixing 0.2-1.0 mol / L zinc nitrate ethanol solution and activated carbon nanotubes in a mass ratio of 15-60:1 and ultrasonically dispersing the mixture, heating the mixture to 50-70° C., adjusting the pH value of the reaction system to alkaline, preferably to 9; reacting the mixture for 2-8 hours, centrifuging the mixture, washing the mixture, and drying the mixture to obtain ZnO@CNTs composite powder; S3: dissolving KH550 in an ethanol-water solution with a volume ratio of 4 to 6:1 to prepare a KH550 solution with a mass concentration of 5-10%, and adjusting the pH value to acidic; mixing the ZnO@CNTs composite powder obtained in S2 with the KH550 solution at a solid-liquid ratio of 1:5 to 20, stirring in a water bath at 50 to 70° C. for 4 to 8 hours, and simultaneously ultrasonically heating the reaction; centrifuging and drying to obtain the product KH550-ZnO@CNTs; preferably, in step S3, formic acid is added to adjust the pH value to 4 to 6.

5. The early-strength, dense, and gas-channeling-proof cement slurry for cementing according to claim 3, characterized in that: The preparation method of modified calcined kaolin comprises the following steps: calcining kaolin at 600-800°C for 1-4 hours for activation and depolymerization, adding the kaolin to a 5-10 wt.% KH550 solution at a mass ratio of 1:10-20, and reacting at 75-85°C for 2-6 hours under stirring; separating the solid by centrifugation, washing, and drying to obtain a modified product A; Adding a saturated solution of Ca(OH)2 to the modified product A, heating the reaction, preferably at 60-70°C, to generate a nano-CSH core-shell structure, and drying to obtain a modified calcined kaolin; Preferably, the KH550 solution used in the preparation of the modified calcined kaolin is prepared by dissolving KH550 in an ethanol-water solution with a volume ratio of 4 to 6:1; Preferably, the solid-liquid ratio of the modified product A to the Ca(OH)2 saturated solution is 1 g:10-20 ml; Preferably, the nano-CSH core-shell structure is generated and then spray-dried to obtain modified calcined kaolin.

6. The early-strength, dense, and gas-channeling-proof cement slurry for cementing according to claim 3, characterized in that: The preparation method of the composite early strength agent comprises the following steps: Step 1. Dissolve the inorganic salt in deionized water (2-3 times its mass), and adjust the pH of the solution to acidic, preferably, 5.0-5.5; then add sodium citrate and ultrasonicate for 10-30 minutes to obtain a stable base solution A; the mass of sodium citrate is 0.6-1.0% of the mass of the inorganic salt solution; Step 2. Add the polymer material to the stable base liquid A, stir, then add the modified nanomaterial, stir and simultaneously ultrasonicate, and spray-inject the organic amine compound to obtain base liquid B; Preferably, the polymer material is added to the stable base liquid A, first stirred at 150-400 rpm for 2-10 minutes, then stirred at 600-1000 rpm for 2-10 minutes; after adding the modified nanomaterial, the mixture is stirred at 600-1000 rpm for 15-60 minutes, and ultrasonicated simultaneously; Step 3: adding the trace element additive to the base liquid B and wet grinding to obtain a mixture A; preferably, wet grinding at a speed of 800-1000 rpm for 5-20 minutes to obtain a mixture A; Step 4: Adding polycarboxylic acid drag reducer to mixture A, concentrating, and drying to obtain a nano-composite early strength agent; preferably, adding polycarboxylic acid drag reducer to mixture A, rotary evaporating the solvent, and then spray drying to obtain a nano-composite early strength agent.

7. The method for preparing the early-strength, dense, and gas channeling-proof cement slurry for cementing according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: weighing materials according to a proportion, uniformly mixing fly ash, microsilica powder, carbide slag, hollow glass microspheres, a composite early strength agent, a dispersant, a fluid loss additive and ultrafine G-grade oil well cement to obtain a dry mix; and adding water to prepare cement slurry, controlling the water-cement ratio to be 0.55.

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