Anti-fatigue carbon dioxide corrosion resistant cement slurry for well cementation, preparation method and application thereof

Abstract

The application discloses an anti-fatigue carbon dioxide corrosion resistant cementing cement slurry and a preparation method and application thereof. The cementing cement slurry is composed of the following raw materials in parts by weight: oil well cement 90-100 parts, carbon dioxide modified slag powder 8-15 parts, stress buffer 5-12 parts, fiber toughening agent 0.4-0.8 parts, dispersing agent 0.5-3 parts, fluid loss reducer 1.5-2.5 parts, and water 40-50 parts. The stress buffer is a polymer microsphere with a core-shell structure, the inner core is a styrene-butadiene copolymer, and the outer shell is an epoxy resin grafting layer. The average particle size of the stress buffer is 20-50 microns. The cement formed after the cementing cement slurry is consolidated has excellent impact toughness, stress buffering capacity and carbon dioxide corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of cementing technology, specifically relating to a fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry, its preparation method, and its application. Background Technology

[0002] In my country, carbon dioxide capture, utilization and storage (CCUS) projects, especially in carbon dioxide flooding and carbon dioxide fracturing, cement sheaths have long faced severe service environment challenges. These challenges mainly come from two aspects: first, corrosion from high-concentration, high-pressure carbon dioxide; and second, the periodic alternating loads generated by wellbore pressure and temperature changes during production, as well as subsequent production enhancement operations (such as fracturing and acidizing).

[0003] First, under high-pressure conditions downhole, carbon dioxide dissolves in water to form carbonic acid, which reacts with calcium hydroxide, a cement hydration product, to form soluble calcium bicarbonate. This leads to a loose cement stone structure, decreased strength, and increased permeability. This corrosion process not only damages the sealing integrity of the cement annulus, potentially causing interlayer seal failure and annular pressurization, but also provides a pathway for corrosive fluids to migrate upwards, seriously threatening safe production and environmental protection. Current technologies often improve the corrosion resistance of cement stone by adding active materials such as silica fume and slag. However, while these materials improve corrosion resistance, they often have limited effect on improving the mechanical properties of the cement stone, particularly its toughness and impact resistance.

[0004] Secondly, traditional cementitious materials are inherently brittle, with low tensile strength and high elastic modulus. Under long-term alternating loads, microcracks easily form inside the cement sheath and continue to propagate, eventually leading to the formation of through cracks, i.e., fatigue failure. This fatigue damage significantly accelerates the intrusion of corrosive media such as carbon dioxide, forming a vicious cycle of "stress corrosion-fatigue damage," which greatly shortens the service life of oil and gas wells.

[0005] To alleviate the aforementioned problems, existing technologies typically employ the addition of fibers (such as basalt fibers and carbon fibers) or elastic particles (such as rubber powder) to improve the toughness of cement stone. However, while simple fiber toughening can improve impact resistance, it has a negative impact on strength. Conventional elastic particles may experience performance degradation under high temperature and pressure carbon dioxide conditions, failing to provide stable stress buffering during long-term service. Regarding carbon dioxide corrosion resistance, the literature "Methods to Enhance the Carbon Dioxide Corrosion Resistance of Oil Well Cement Stone" mentions improving the corrosion resistance of cement stone by incorporating latex and nano-liquid silica. The latex particles precipitate and connect to form a film on the surface of hydration products, hindering the penetration and diffusion of carbon dioxide and enhancing corrosion resistance. The nano-silicon in the nano-liquid silica reacts with calcium hydroxide, reducing the content of easily corroded calcium hydroxide and improving the cement stone's resistance to carbon dioxide corrosion. Patent CN114133172A utilizes the micropores within nano-silica cement stone to fill and plug pores, thereby improving the density and strength of the cement stone. Simultaneously, it can participate in the hydration reaction, increasing the Si / Ca ratio of the hydration products, thus improving the corrosion resistance of the hydration products. Therefore, improving corrosion resistance by adding nano-silica is the current mainstream research direction. However, nano-silica has a significant impact on the consistency of cement slurry, greatly increasing the difficulty of pumping cement slurry and placing high demands on on-site cementing operations.

[0006] Therefore, there is an urgent need in the field for a cementing slurry system that can simultaneously achieve excellent resistance to carbon dioxide corrosion and superior fatigue resistance. This system should not only possess good cementing properties but also effectively inhibit the intrusion of carbon dioxide corrosion, exhibit excellent crack resistance and high-efficiency stress buffering capacity to cope with the chemical and mechanical coupling damage in complex downhole environments, ensuring the long-term sealing integrity of the cement sheath throughout the entire lifespan of the oil and gas well. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a fatigue-resistant and carbon dioxide corrosion-resistant cement slurry, its preparation method, and its application. The cement stone formed after the cement slurry solidifies exhibits excellent impact toughness, stress buffering capacity, and carbon dioxide corrosion resistance.

[0008] A fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry is composed of the following raw materials in parts by weight: 90-100 parts oil well cement, 8-15 parts carbon dioxide modified slag powder, 5-12 parts stress buffer, 0.4-0.8 parts fiber toughening agent, 0.5-3 parts dispersant, 1.5-2.5 parts fluid loss reducing agent, and 40-50 parts water.

[0009] The stress buffer is a polymer microsphere with a core-shell structure, the core being a styrene-butadiene copolymer and the outer shell being an epoxy resin graft layer, and the average particle size of the stress buffer is 20-50 μm.

[0010] Preferably, the stress buffer is prepared by the following method:

[0011] (S1) Epoxy resin, glycidyl methacrylate, aminosilane coupling agent, oil-soluble initiator, and stabilizer are mixed to obtain an oil phase mixture; emulsifier is added to water and stirred until dissolved to obtain an aqueous phase mixture; under shear conditions, the oil phase mixture is added to the aqueous phase mixture, shearing is continued for 2-5 minutes, and ultrasonic treatment is performed for 15-25 minutes to obtain a shell emulsion;

[0012] (S2) Under stirring, add deionized water to carboxylated styrene-butadiene latex to dilute to a solid content of 10-20%, adjust the pH value to 8-9, and heat to 75-80℃ under an inert atmosphere and stirring to obtain activated kernel seeds.

[0013] (S3) Maintain the temperature and inert atmosphere, and uniformly add the shell emulsion to the core seed. Control the amount of epoxy resin added per hour to be 15-25% of the solid component mass of the carboxylated styrene-butadiene latex. After the addition is completed, continue to keep warm and mature for 2.5-3.5 hours, cool, filter, and obtain a polymer microsphere emulsion with a core-shell structure.

[0014] (S4) Spray drying.

[0015] Preferably, the solid content of the carboxylated styrene-butadiene latex is 50-55 wt%.

[0016] Preferably, in step (S1), the mass ratio of epoxy resin, glycidyl methacrylate, aminosilane coupling agent, oil-soluble initiator, stabilizer, emulsifier, and water is (80-90):(10-15):(1-2):(0.5-2):(2-5):(2-8):(200-250).

[0017] Preferably, the mass ratio of the epoxy resin to the solid components in the carboxylated styrene-butadiene latex is 2:(3-3.5).

[0018] Preferably, the stabilizer is hexadecane or hexadecyl alcohol; the epoxy resin is bisphenol A type epoxy resin; the oil-soluble initiator is at least one of azobisisobutyronitrile, benzoyl peroxide, or dilauryl peroxide; and the emulsifier is a nonionic emulsifier.

[0019] Preferably, the carbon dioxide modified slag powder is prepared by the following method: water is added to the slag powder at a mass ratio of slag powder to water of 10:(2.5-4), the mixture is stirred and mixed evenly, transferred to a high-pressure reactor, and stirred and reacted for 3-5 hours under a CO2 atmosphere, 60-80℃, and 2.0-5.0MPa. After cooling to room temperature, the mixture is ground. The slag powder has an Al2O3 content ≥15wt% and a specific surface area ≥200m². 2 / g.

[0020] Preferably, the fiber toughening agent is a mixture of carbon nanotubes and basalt fibers in a mass ratio of 1:(15-20), wherein the carbon nanotubes have a diameter of 20-50 nm and a length of 10-30 μm; and the basalt fibers have a diameter of 8-15 μm and a length of 3-6 mm.

[0021] Preferably, the dispersant is an acetone-formaldehyde condensate dispersant, and the water loss reducing agent is a polymer-based water loss reducing agent.

[0022] The method for preparing the fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry includes the following steps:

[0023] (1) Add fiber toughening agent and dispersant to water and sonicate for 10-20 min to obtain solution A;

[0024] (2) Mix solution A, oil well cement, carbon dioxide modified slag powder, stress buffer, and water loss reducer, stir evenly, and complete the preparation of cement slurry.

[0025] Preferably, the frequency of the ultrasonic treatment described in this invention is 20-40 kHz.

[0026] The application of the cement slurry described in this invention in carbon dioxide fracturing wells or carbon dioxide flooding and burial injection wells, wherein the bottom hole temperature of the carbon dioxide fracturing well or carbon dioxide flooding and burial injection well is ≤80℃ and the construction pressure is ≤20MPa.

[0027] In this invention, the core of the stress buffer has excellent elastic deformation capability, and the epoxy resin grafted layer of the outer shell can form a strong chemical bond with the cement hydration products, thereby forming an energy dissipation center inside the cement stone, effectively blunting the crack tip and buffering alternating stress.

[0028] The carbon dioxide modified slag powder forms stable calcium carbonate and aluminum phase products on its surface, which reduces its active sites for later reaction with CO2 downhole, while improving its early reaction activity in cement slurry, thus optimizing the early strength development and long-term corrosion resistance of the slurry.

[0029] The fiber toughening agent has an aspect ratio of ≥200:1, forming a "micro-nano" two-dimensional toughening network: carbon nanotubes can bridge nano- to micro-scale microcracks and hinder their propagation; basalt fibers bridge larger cracks and, through synergy with carbon nanotubes, significantly improve the fracture energy and impact resistance of the cement matrix.

[0030] Advantages of this invention:

[0031] 1. In this invention, the stress buffer can better combine with cement hydration products to achieve high stress elastic dissipation under high bonding conditions. On the one hand, it can suppress microcracks caused by the crystallization pressure when carbon dioxide invades and corrodes calcium carbonate, and work together with highly active slag powder to resist corrosion. On the other hand, it can absorb energy through stress buffering and work together with basalt fiber and carbon nanotube to construct a network structure to resist fatigue damage.

[0032] 2. This invention creatively introduces carbon dioxide modified slag powder. Through carbon dioxide modification treatment and high aluminum content optimization, it realizes the dual path of "dense filling" and "activation activation", reduces the porosity of cement stone, stabilizes the surface active points in advance, consumes the corrosion sensitive phase (free calcium hydroxide), generates stable acid-resistant products, and improves the carbon dioxide corrosion resistance of cement stone.

[0033] 3. Each component works synergistically to generate corrosion resistance and fatigue resistance by optimizing pore structure, buffering stress concentration, and preventing crack propagation, thus endowing the cement stone with excellent impact toughness, stress buffering capacity, and long-term carbon dioxide corrosion resistance after consolidation.

[0034] 4. The cement slurry significantly reduces the amount of nanomaterials required, greatly improves the homogeneity and pumpability of the slurry, and has good compatibility among its components, thus meeting the requirements of on-site cementing operations. Detailed Implementation

[0035] The following is a description of some of the raw materials used in this invention:

[0036] Emulsifier: Triton X-100, a nonionic emulsifier, purchased from Titan Technology Exploration Platform;

[0037] Carboxylated styrene-butadiene latex (XSBRL): Purchased from Jingjiang Tonggao Chemical Co., Ltd., solid content 50 wt%;

[0038] Epoxy resin: E51 bisphenol A type epoxy resin, purchased from Titan Technology Exploration Platform;

[0039] Slag powder: Purchased from Henan Borun Foundry Materials Co., Ltd., it is S95 grade high-activity slag powder with Al2O3 content of 16wt% and specific surface area of ​​412m² / g.

[0040] Carbon nanotubes: purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with a diameter of 20-50nm and a length of 10-30μm;

[0041] Basalt fiber: purchased from Zhejiang Shijin Basalt Fiber Co., Ltd., with a diameter of 8-15um and a length of 3-6mm;

[0042] Dispersant: Acetone-formaldehyde condensate dispersant USZ purchased from Weihui Chemical.

[0043] Water loss control agent: GD-3 polymer-based water loss control agent purchased from Weihui Chemical.

[0044] All other materials are commercially available standard products.

[0045] Example 1: A fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry, composed of the following raw materials in parts by weight: 95 parts of G-grade oil well cement, 10 parts of carbon dioxide modified slag powder, 8 parts of stress buffer, 0.6 parts of fiber toughening agent, 1.5 parts of dispersant, 2.0 parts of fluid loss reducing agent, and 45 parts of water.

[0046] The fiber toughening agent is a mixture of carbon nanotubes and basalt fibers in a mass ratio of 1:15.

[0047] The carbon dioxide modified slag powder is prepared by the following method: water is slowly and evenly added to the slag powder at a mass ratio of 10:3, and stirred to form a moist but non-dispersible loose granular material. The material is then transferred to a high-pressure reactor, and CO2 is introduced to replace the air. The reaction is carried out under a CO2 atmosphere, at 70°C and 3.0 MPa for 4 hours, with a stirring speed of 200 rpm. After cooling to room temperature, the material is ground and passed through a 200-mesh sieve to obtain the carbon dioxide modified slag powder.

[0048] The stress buffer is a polymer microsphere with a core-shell structure, the core being a styrene-butadiene copolymer and the outer shell being an epoxy resin graft layer. The stress buffer has an average particle size of 20 μm and is prepared by the following method:

[0049] (S1) Mix 8.5g of E51 bisphenol A epoxy resin, 1.0g of glycidyl methacrylate, 0.2g of aminosilane coupling agent KH550, 0.1g of oil-soluble initiator azobisisobutyronitrile, and 0.3g of hexadecane as a co-stabilizer to obtain an oil phase mixture; add 0.5g of nonionic emulsifier Triton X-100 to 22.0g of water and stir until dissolved to obtain an aqueous phase mixture; under high-speed shearing at 8000rpm, slowly add the oil phase mixture to the aqueous phase mixture, continue shearing for 3min, and sonicate at an ultrasonic frequency of 20kHz for 20min to obtain a shell emulsion that is milky white, uniform, delicate, and stable.

[0050] (S2) Take 25.5g of carboxylated styrene-butadiene latex and place it in the reactor. Turn on the stirring and add 102g of deionized water to dilute it to a solid content of 10%. Add 5wt% ammonia water to adjust the pH value to 8. Purge the air with nitrogen. Under the conditions of nitrogen and stirring, raise the temperature to 80℃ to obtain activated kernel layer seeds.

[0051] (S3) Maintain the temperature and nitrogen atmosphere, and use a constant pressure injection pump to uniformly add shell emulsion to the core seed, control the dropping rate, and add epoxy resin at 15% of the solid component mass of the carboxylated styrene-butadiene latex per hour. After the addition is completed, continue to keep warm and mature for 3 hours. After naturally cooling to room temperature, filter with a 300-mesh filter cloth. The filtrate is the polymer microsphere emulsion with core-shell structure.

[0052] (S4) Spray drying was carried out under the conditions of atomization pressure of 3.0 bar, nozzle orifice diameter of 2 mm, inlet temperature of 160℃, outlet temperature of 60℃, and feed rate of 350 mL / min to obtain powdered polymer microspheres.

[0053] The preparation method of the fatigue-resistant and carbon dioxide corrosion-resistant cement slurry is as follows:

[0054] (1) Add fiber toughening agent and dispersant to water and sonicate at an ultrasonic frequency of 20 kHz for 15 min to obtain solution A;

[0055] (2) Mix solution A, oil well cement, carbon dioxide modified slag powder, stress buffer, and water loss reducer, stir evenly, and complete the preparation of cement slurry.

[0056] Example 2: A fatigue-resistant and carbon dioxide corrosion-resistant cement slurry for cementing wells, composed of the following raw materials in parts by weight: 90 parts of Grade G oil well cement, 8 parts of carbon dioxide modified slag powder, 12 parts of stress buffer, 0.4 parts of fiber toughening agent, 0.5 parts of dispersant, 1.5 parts of fluid loss reducing agent, and 40 parts of water; the rest is the same as in Example 1.

[0057] Example 3: A fatigue-resistant and carbon dioxide corrosion-resistant cement slurry for cementing wells, composed of the following raw materials in parts by weight: 100 parts of Grade G oil well cement, 15 parts of carbon dioxide modified slag powder, 5 parts of stress buffer, 0.8 parts of fiber toughening agent, 3 parts of dispersant, 2.5 parts of fluid loss reducing agent, and 50 parts of water; the rest is the same as in Example 1.

[0058] Example 4: A fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry, composed of the following raw materials in parts by weight: 95 parts of G-grade oil well cement, 10 parts of carbon dioxide modified slag powder, 8 parts of stress buffer, 0.6 parts of fiber toughening agent, 1.5 parts of dispersant, 2.0 parts of fluid loss reducing agent, and 45 parts of water.

[0059] The fiber toughening agent is a mixture of carbon nanotubes and basalt fibers in a mass ratio of 1:18.

[0060] The carbon dioxide modified slag powder was prepared by the following method: water was slowly and evenly added to the slag powder at a mass ratio of 10:2.5, and stirred to form a moist but non-dispersible loose granular material. The material was then transferred to a high-pressure reactor, and CO2 was introduced to replace the air. The reaction was carried out under a CO2 atmosphere, at 60°C and 5.0 MPa for 3 hours, with a stirring speed of 200 rpm. After cooling to room temperature, the material was ground and passed through a 200-mesh sieve to obtain the carbon dioxide modified slag powder.

[0061] The stress buffer is a polymer microsphere with a core-shell structure, the core being a styrene-butadiene copolymer and the outer shell being an epoxy resin graft layer. The stress buffer has an average particle size of 38 μm and is prepared by the following method:

[0062] (S1) Mix 8.0g of E51 bisphenol A epoxy resin, 1.0g of glycidyl methacrylate, 0.1g of aminosilane coupling agent KH550, 0.05g of oil-soluble initiator benzoyl peroxide, and 0.2g of hexadecane as a co-stabilizer to obtain an oil phase mixture; add 0.2g of nonionic emulsifier Triton X-100 to 20.0g of water and stir until dissolved to obtain an aqueous phase mixture; under high-speed shearing at 8000rpm, slowly add the oil phase mixture to the aqueous phase mixture, continue shearing for 2min, and sonicate at an ultrasonic frequency of 30kHz for 15min to obtain a shell emulsion that is milky white, uniform, delicate, and stable;

[0063] (S2) Take 28g of carboxylated styrene-butadiene latex and place it in the reactor. Turn on the stirring and add 59.5g of deionized water to dilute it to a solid content of 16%. Add 5wt% ammonia water to adjust the pH value to 9. Purge the air with nitrogen. Under the conditions of nitrogen and stirring, raise the temperature to 75℃ to obtain activated kernel seeds.

[0064] (S3) Maintain the temperature and nitrogen atmosphere, and use a constant pressure injection pump to uniformly add shell emulsion to the core seed, control the dropping rate, and add epoxy resin at 20% of the solid component mass of the carboxylated styrene-butadiene latex per hour. After the addition is completed, continue to keep warm and mature for 2.5 hours. After naturally cooling to room temperature, filter with a 300-mesh filter cloth. The filtrate is the polymer microsphere emulsion with core-shell structure.

[0065] (S4) Spray drying was carried out under the conditions of atomization pressure of 2.0 bar, nozzle orifice diameter of 2 mm, inlet temperature of 160℃, outlet temperature of 60℃, and feed rate of 450 mL / min to obtain powdered polymer microspheres.

[0066] 2. The preparation method of the fatigue-resistant and carbon dioxide corrosion-resistant cement slurry is as follows:

[0067] (1) Add fiber toughening agent and dispersant to water and sonicate at an ultrasonic frequency of 30 kHz for 10 min to obtain solution A;

[0068] (2) Mix solution A, oil well cement, carbon dioxide modified slag powder, stress buffer, and water loss reducer, stir evenly, and complete the preparation of cement slurry.

[0069] Example 5: A fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry, composed of the following raw materials in parts by weight: 95 parts of G-grade oil well cement, 10 parts of carbon dioxide modified slag powder, 8 parts of stress buffer, 0.6 parts of fiber toughening agent, 1.5 parts of dispersant, 2.0 parts of fluid loss reducing agent, and 45 parts of water.

[0070] The fiber toughening agent is a mixture of carbon nanotubes and basalt fibers in a mass ratio of 1:20.

[0071] The carbon dioxide modified slag powder is prepared by the following method: water is slowly and evenly added to the slag powder at a mass ratio of 10:4, and stirred to form a moist but non-dispersible loose granular material. The material is then transferred to a high-pressure reactor, and CO2 is introduced to replace the air. The reaction is carried out under a CO2 atmosphere, at 80°C and 2.0 MPa for 5 hours, with a stirring speed of 200 rpm. After cooling to room temperature, the material is ground and passed through a 200-mesh sieve to obtain the carbon dioxide modified slag powder.

[0072] The stress buffer is a polymer microsphere with a core-shell structure, the core being a styrene-butadiene copolymer and the outer shell being an epoxy resin graft layer. The stress buffer has an average particle size of 50 μm and is prepared by the following method:

[0073] (S1) 9.0g of E51 bisphenol A epoxy resin, 1.5g of glycidyl methacrylate, 0.2g of aminosilane coupling agent KH550, 0.2g of oil-soluble initiator dilauryl peroxide, and 0.5g of hexadecyl alcohol co-stabilizer were mixed to obtain an oil phase mixture; 0.8g of nonionic emulsifier Triton X-100 was added to 25.0g of water and stirred until dissolved to obtain an aqueous phase mixture; under high-speed shearing at 8000rpm, the oil phase mixture was slowly added to the aqueous phase mixture, sheared for 5min, and ultrasonically treated at 40kHz for 25min to obtain a shell emulsion that is milky white, uniform, delicate, and stable.

[0074] (S2) Take 28.8g of carboxylated styrene-butadiene latex and place it in the reactor. Turn on the stirring and add 43.2g of deionized water to dilute it to a solid content of 20%. Add 5wt% ammonia water to adjust the pH value to 9. Purge the air with nitrogen. Under the conditions of nitrogen and stirring, raise the temperature to 80℃ to obtain activated kernel seeds.

[0075] (S3) Maintain the temperature and nitrogen atmosphere, and use a constant pressure injection pump to uniformly add shell emulsion to the core seed, control the dropping rate, and add epoxy resin at a rate of 25% of the solid component mass of the carboxylated styrene-butadiene latex per hour. After the addition is completed, continue to keep warm and mature for 3.5 hours. After naturally cooling to room temperature, filter with a 300-mesh filter cloth. The filtrate is the polymer microsphere emulsion with a core-shell structure.

[0076] (S4) Spray drying was carried out under the conditions of atomization pressure of 1.0 bar, nozzle orifice diameter of 2 mm, inlet temperature of 160℃, outlet temperature of 60℃, and feed rate of 550 mL / min to obtain powdered polymer microspheres.

[0077] The preparation method of the fatigue-resistant and carbon dioxide corrosion-resistant cement slurry is as follows:

[0078] (1) Add fiber toughening agent and dispersant to water and sonicate at an ultrasonic frequency of 40 kHz for 20 min to obtain solution A;

[0079] (2) Mix solution A, oil well cement, carbon dioxide modified slag powder, stress buffer, and water loss reducer, stir evenly, and complete the preparation of cement slurry.

[0080] Comparative Example 1: No carbon dioxide modified slag powder, stress buffer and fiber toughening agent were added, and everything else was the same as in Example 1.

[0081] Comparative Example 2: No carbon dioxide-modified slag powder was added; all other aspects were the same as in Example 1.

[0082] Comparative Example 3: No stress buffer was added; otherwise, it was the same as Example 1.

[0083] Comparative Example 4: No fiber toughening agent was added; otherwise, it was the same as Example 1.

[0084] Comparative Example 5: Slag powder was used instead of carbon dioxide modified slag powder, that is, the slag powder was not modified in any way, and everything else was the same as in Example 1.

[0085] Performance testing:

[0086] 1. Routine performance testing

[0087] Referring to the test methods in "Test Methods for Cement in Oil Wells" (Standard No.: GB / T 19139-2012), equipment such as a double-cylinder pressurized thickener and a high-temperature and high-pressure water loss meter were used to test the thickening time, fluidity, and water loss of the cement slurry. The results are shown in Table 1.

[0088] Table 1. Conventional performance tests of cement grout

[0089] ,

[0090] As shown in Table 1, the addition of modified high-activity slag powder, stress buffer, and fiber toughening agent has little impact on the overall performance of cement slurry and can meet the requirements of on-site construction.

[0091] 2. Fatigue and corrosion resistance test

[0092] Cement slurry was poured into a mold and cured at 80℃ and 20MPa for 24 hours. After demolding, samples were prepared for fatigue and corrosion resistance tests. The specific process is as follows:

[0093] (1) Prepare cylindrical cement stone samples with a diameter of 2.5 cm and a height of 5 cm. Use a multi-functional pressure testing machine to simulate fracturing and production injection. Apply longitudinal cyclic stress to the upper and lower bottom surfaces of the cylindrical sample. The applied stress is 10 MPa, the number of cycles is 10, and the duration of each cycle is 10 minutes. After loading, test the remaining compressive strength of the cement stone and compare it with the original compressive strength. Calculate the strength retention rate after cyclic loading. The results are shown in Table 2.

[0094] (2) The cement stone test block was placed in simulated formation water at 80℃ and 20 MPa CO2 pressure for 30 days to conduct a high temperature and high pressure corrosion test. The corrosion depth and compressive strength of the test block after corrosion were tested, and the strength decay rate after corrosion was calculated. The results are shown in Table 2.

[0095] Wherein, the strength retention rate after cyclic loading = (remaining compressive strength after loading / original compressive strength) × 100%; the strength degradation rate after corrosion = [(original compressive strength - compressive strength after corrosion) / original compressive strength] × 100%;

[0096] Table 2 Results of fatigue and corrosion resistance tests on cement stone

[0097] ,

[0098] As shown in Table 2, the cement stone prepared in the embodiments of the present invention exhibits excellent fatigue resistance and carbon dioxide corrosion resistance.

[0099] (1) After repeated cyclic loading fatigue damage of cement stone, the present invention exhibits excellent fatigue resistance, which is due to the stress buffer (core-shell microspheres) effectively absorbing and dispersing stress and inhibiting the initiation of microcracks; at the same time, the fiber toughening agent plays a bridging and crack-preventing role, preventing crack propagation. The synergistic effect of the two greatly improves the fatigue life of cement stone.

[0100] (2) In terms of corrosion resistance, the strength degradation rate after corrosion was less than 11%, and the corrosion depth was less than or equal to 1.0 mm, which was significantly better than the comparative example. This is attributed to the modified high-activity slag powder, which refined the pore structure of cement stone through secondary hydration, blocked the corrosion channels, and chemically consumed calcium hydroxide to generate a more stable low-calcium-silicon ratio CSH gel. At the same time, the stress buffer can inhibit the microcracks caused by the crystallization pressure when carbon dioxide invades and corrodes calcium carbonate, thus synergistically improving the corrosion resistance with the modified high-activity slag powder. Meanwhile, the fiber toughening agent fills the tiny, nanoscale pores, increasing the difficulty of carbon dioxide intrusion.

[0101] In summary, the cement slurry system provided by this invention successfully solves the problem of balancing corrosion resistance and fatigue resistance in the prior art, and is particularly suitable for cementing operations under harsh well conditions with carbon dioxide corrosion risk and alternating loads.

Claims

1. A fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry, characterized in that: It is composed of the following raw materials in parts by weight: 90-100 parts oil well cement, 8-15 parts carbon dioxide modified slag powder, 5-12 parts stress buffer, 0.4-0.8 parts fiber toughening agent, 0.5-3 parts dispersant, 1.5-2.5 parts water loss reducer, and 40-50 parts water. The stress buffer is a polymer microsphere with a core-shell structure, the core being a styrene-butadiene copolymer and the outer shell being an epoxy resin graft layer, and the average particle size of the stress buffer is 20-50 μm. The stress buffer is prepared by the following method: (S1) Epoxy resin, glycidyl methacrylate, aminosilane coupling agent, oil-soluble initiator, and stabilizer are mixed to obtain an oil phase mixture; emulsifier is added to water and stirred until dissolved to obtain an aqueous phase mixture; under shear conditions, the oil phase mixture is added to the aqueous phase mixture, shearing is continued for 2-5 minutes, and ultrasonic treatment is performed for 15-25 minutes to obtain a shell emulsion; (S2) Under stirring, add deionized water to carboxylated styrene-butadiene latex to dilute to a solid content of 10-20%, adjust the pH value to 8-9, and heat to 75-80℃ under an inert atmosphere and stirring to obtain activated kernel seeds. (S3) Maintain the temperature and inert atmosphere, and uniformly add the shell emulsion to the core seed. Control the amount of epoxy resin added per hour to be 15-25% of the solid component mass of the carboxylated styrene-butadiene latex. After the addition is completed, continue to keep warm and mature for 2.5-3.5 hours, cool, filter, and obtain a polymer microsphere emulsion with a core-shell structure. (S4) Spray drying.

2. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: In step (S1), the mass ratio of epoxy resin, glycidyl methacrylate, aminosilane coupling agent, oil-soluble initiator, stabilizer, emulsifier and water is (80-90):(10-15):(1-2):(0.5-2):(2-5):(2-8):(200-250).

3. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: The mass ratio of the epoxy resin to the solid components in the carboxylated styrene-butadiene latex is 2:(3-3.5).

4. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: The stabilizer is hexadecane or hexadecyl alcohol; the epoxy resin is bisphenol A type epoxy resin; the oil-soluble initiator is at least one of azobisisobutyronitrile, benzoyl peroxide, or dilauryl peroxide; and the emulsifier is a nonionic emulsifier.

5. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: The carbon dioxide modified slag powder is prepared by the following method: water is added to the slag powder at a mass ratio of slag powder to water of 10:(2.5-4), the mixture is stirred and mixed evenly, transferred to a high-pressure reactor, and stirred and reacted for 3-5 hours under a CO2 atmosphere, 60-80℃, and 2.0-5.0MPa. After cooling to room temperature, it is ground. The slag powder has an Al2O3 content ≥15wt% and a specific surface area ≥200m². 2 / g.

6. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: The fiber toughening agent is a mixture of carbon nanotubes and basalt fibers in a mass ratio of 1:(15-20), wherein the carbon nanotubes have a diameter of 20-50 nm and a length of 10-30 μm; and the basalt fibers have a diameter of 8-15 μm and a length of 3-6 mm.

7. The fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry according to claim 1, characterized in that: The dispersant is an acetone-formaldehyde condensate dispersant, and the water loss reducing agent is a polymer water loss reducing agent.

8. The method for preparing the fatigue-resistant and carbon dioxide corrosion-resistant cement slurry according to claim 1, characterized in that: Includes the following steps: (1) Add fiber toughening agent and dispersant to water and sonicate for 10-20 min to obtain solution A; (2) Mix solution A, oil well cement, carbon dioxide modified slag powder, stress buffer, and water loss reducer, stir evenly, and complete the preparation of cement slurry.

9. The application of the fatigue-resistant and carbon dioxide corrosion-resistant cementing slurry of claim 1 in carbon dioxide fracturing wells or carbon dioxide flooding and burial injection wells, characterized in that: The bottom hole temperature of the carbon dioxide fracturing well or the carbon dioxide flooding and burial injection well shall be ≤80℃ and the construction pressure shall be ≤20MPa.