A high-toughness micro-expansion cement slurry suitable for high-temperature cementing, a preparation method and application thereof

Abstract

The application provides a high-temperature well cementing high-toughness micro-expansion cement slurry, which comprises the following raw materials in parts by weight: G-grade oil well cement 60-90 parts by weight, active material 20-40 parts by weight, high-performance toughening agent 3-12 parts by weight, nano oxide 3-10 parts by weight, expansion agent 0.5-5 parts by weight, chemical activator 3-5 parts by weight, high-temperature fluid loss additive 1-3 parts by weight, high-temperature retarder 0.5-3 parts by weight, dispersing agent 0.1-1 parts by weight, and defoaming agent 0.2-1 parts by weight. By adding the active material, the high-performance toughening agent, the nano oxide and the expansion agent, the high-temperature resistance, the toughness of the cement slurry and the cementing quality of the cement sheath are improved; the four components jointly improve the high-temperature resistance, the toughness and the cementing performance of the surrounding rock interface of the cement; and by being used in cooperation with other components, the cement slurry has the advantages of good stability, small fluid loss and good rheological property, is suitable for well cementing of underground gas storage, can improve the well cementing quality of the formation sealing section, and guarantees the cement sheath sealing integrity under frequent injection and production.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field cementing technology, specifically to a high-toughness micro-expansion cement slurry suitable for high-temperature cementing, its preparation method, and its application. Background Technology

[0002] Cement used for well cementing is silicate cement, which has disadvantages such as low tensile strength, poor impact strength, and susceptibility to brittle cracking. When the assembly is subjected to external forces, the cement sheath is likely to be the first to crack and fail. Therefore, in order to enhance the sealing integrity of the cement sheath and ensure the safe and efficient production of injection and production wells, it is necessary to develop a high-temperature resistant, high-toughness, micro-expansion cement slurry system.

[0003] CN117228979A discloses a high-temperature resistant, low-density cement slurry system. The system uses cement, high-temperature retarder, high-temperature fluid loss reducer, hollow microspheres, reinforcing materials, laterite nickel slag, and high-temperature resistant elastic materials as additives to prepare low-density cement slurry according to GB / T19139 standard, which balances the formation sealing section with low pressure coefficient.

[0004] CN110937857A discloses a high-temperature resistant and anti-channeling emulsion-based toughening cement slurry and its preparation method. The high-temperature resistant and anti-channeling emulsion-based toughening cement slurry comprises the following components by weight: 100 parts of low-heat-of-hydration cement, 3-20 parts of high-temperature resistant organic anti-channeling emulsion, 3-15 parts of high-temperature resistant inorganic anti-channeling emulsion, 0.5-5 parts of high-temperature resistant toughening material, 20-90 parts of high-temperature strength stabilizing material, 1-10 parts of high-temperature expanding agent, 1-12 parts of high-temperature water loss reducing agent, 0.1-10 parts of high-temperature retarder, 0.5-3 parts of defoamer, 0-300 parts of density adjusting material, and 35-200 parts of water.

[0005] CN112830700A discloses a high-temperature strength stabilizer for oil well cement and a cement slurry for cementing, as well as their preparation method. The high-temperature strength stabilizer, by mass percentage, consists of 73%–75% reinforcing agent, 22%–24% crystalline phase stabilizing component, and 2%–4% pH adjuster. The reinforcing agent includes crystalline silica and can undergo a hydration reaction with silicate cement at temperatures above 200°C to generate needle-like hard calcium silicate and fibrous calcium silicate crystals. The crystalline phase stabilizing component is prepared from alumina and sepiolite in a mass ratio of 3.0–4.0:0.8–1.2 and can participate in the hydration reaction of the cement slurry at temperatures above 200°C to generate fibrous aluminized calcium silicate crystals. The pH adjuster is solid sodium silicate with a modulus of 1–2. This invention can effectively prevent the later-stage strength decay of cement sheaths, improve the compactness of cement stone, and meet the cementing requirements of ultra-deep and ultra-high temperature wells.

[0006] Although the addition of certain toughness and high-temperature resistant materials to the cement slurry has improved the performance of cement stone toughness and high-temperature strength degradation, the interfacial bonding performance between the cement sheath and the rock formation is poor when high-temperature resistance and toughness are met. This makes it difficult to guarantee the cementing quality of the formation sealing section, which plays an important role in the integrity of the wellbore during the operation of the gas storage facility. Summary of the Invention

[0007] To address the technical problems of poor interfacial bonding performance between cement sheath and surrounding rock, poor impact resistance of cement, and susceptibility to brittle cracking in existing technologies, this application provides a high-toughness micro-expansion cement slurry suitable for high-temperature cementing, its preparation method, and its application. This cement slurry has characteristics such as high temperature resistance, high toughness, and strong bonding, which can meet the cementing quality requirements of gas storage facilities and the sealing integrity of cement sheaths throughout the entire life cycle of injection and production, ensuring the safe and efficient operation of gas storage facilities.

[0008] A high-toughness micro-expansion cement slurry suitable for high-temperature cementing, comprising the following raw materials in parts by weight: 60-90 parts by weight of G-grade oil well cement, 20-40 parts by weight of active material, 3-12 parts by weight of high-performance toughening agent, 3-10 parts by weight of nano-oxide, 0.5-5 parts by weight of expansion agent, 3-5 parts by weight of chemical activator, 1-3 parts by weight of high-temperature fluid loss reducing agent, 0.5-3 parts by weight of high-temperature retarder, 0.1-1 parts by weight of dispersant, and 0.2-1 parts by weight of defoamer;

[0009] Preferably, the cement slurry comprises the following raw materials in parts by weight: 6580 parts by weight of Grade G oil well cement, 2535 parts by weight of active material, 48 parts by weight of high-performance toughening agent, 48 parts by weight of nano oxide, 13 parts by weight of expansion agent, 3 parts by weight of chemical activator, 1-2 parts by weight of high-temperature water loss reducing agent, 1-2 parts by weight of high-temperature retarder, 0.25-0.8 parts by weight of dispersant, and 0.4-0.8 parts by weight of defoamer.

[0010] The above-mentioned active material is volcanic ash that has been hydrophobically modified by aminosilane coupling agent and vinylsilane coupling agent; the mass ratio of aminosilane coupling agent, volcanic ash and vinylsilane coupling agent is (2-3):10:1.

[0011] Furthermore, the aforementioned volcanic ash is finely ground volcanic rock waste, with an aluminate content of 20-40% and a density of 2.6-3.0 g / cm³. 3 The average particle size is 5-10 μm; the 3-day activity index of the above active materials is 150-200%.

[0012] Preferably, the mass ratio of aminosilane coupling agent, volcanic ash, and vinylsilane coupling agent is 2:10:1.

[0013] The preparation process of the above-mentioned active material is as follows: Anhydrous ethanol and deionized water are mixed as solvents to prepare solutions of aminosilane coupling agent and vinylsilane coupling agent, each with a content of 0.5 wt%; Volcanic ash is first added to the above-mentioned solution of aminosilane coupling agent, and the pH is adjusted with glacial acetic acid to carry out the first grafting reaction; then it is added to the above-mentioned solution of vinylsilane coupling agent to carry out the second grafting reaction, and then washed and dried to obtain the final product.

[0014] The mass ratio of anhydrous ethanol to deionized water is 1:9; the grafting reaction is carried out by ultrasonic dispersion during the preparation of the active material; glacial acetic acid is used to adjust the pH to 4-5; the first grafting reaction is carried out at 58-60℃ for 2.5-3 hours, and the second grafting reaction is carried out at 28-30℃ for 1-1.5 hours.

[0015] Preferably, the preparation process of the active material is as follows: Volcanic ash is first added to the above solution of aminosilane coupling agent, the pH of the solution is adjusted to 4-5 with glacial acetic acid, and the reaction is carried out at 60°C for 3 hours. Then, it is grafted into the above solution of vinylsilane coupling agent, which has been reacted at 30°C for 1 hour. Ultrasonic dispersion is used to ensure uniform dispersion of the volcanic ash and sufficient contact with the silane. The grafted volcanic ash needs to be centrifuged and washed three times with anhydrous ethanol to remove unreacted silane, and then vacuum dried at 60°C for 12 hours to avoid desorption of the coupling agent due to high-temperature drying.

[0016] The aforementioned volcanic ash is made from finely ground volcanic rock waste. Its active components can undergo a secondary hydration reaction with Ca(OH)2 in water, generating more hydrated calcium silicate (CSH) gel and hydrated calcium aluminate, among other hydration products. These hydration products have high heat resistance, which can improve the high-temperature resistance of cement stone.

[0017] The aforementioned high-performance toughening agent is a composite of fiber and emulsion polymer. The fiber is a mixture of graphene oxide-modified carbon fiber, modified basalt fiber, and coconut fiber; the mass ratio of graphene oxide-modified carbon fiber, modified basalt fiber, and coconut fiber is (1-1.5):1:0.5. Preferential mixing of the fiber and emulsion polymer ensures uniform dispersion of the fiber and polymer in the cement matrix, avoiding performance degradation due to localized aggregation.

[0018] The emulsion polymer in the high-performance toughening agent is dispersed in the cement paste. As the cement hydrates, the polymer particles gradually form a film, creating an organic-inorganic interpenetrating three-dimensional network structure with the cement hydration products. Simultaneously, the fibers form a high-strength interface with the cement, further enhancing the overall strength and toughness of the cement.

[0019] The preparation process of high-performance toughening agents is as follows:

[0020] a) Weigh the fiber and emulsion polymer according to the above proportions;

[0021] b) Place the weighed raw materials into the mixer and mix for 10-15 minutes to ensure that the components are mixed evenly;

[0022] c) Add the well-mixed mixture to an appropriate amount of deionized water to form a suspension. Use a high-shear mixer to stir the suspension for 30 minutes at a speed of 2000 rpm to ensure that the fiber and emulsion polymer are evenly dispersed in the water.

[0023] d) Heat the suspension to 60°C and maintain the temperature while stirring for 30 minutes to further improve the dispersibility and stability of each component;

[0024] e) Add 0.1-0.3% of the total suspension volume of polycarboxylic acid dispersant to the cooled suspension, stir evenly, and enhance the stability and dispersibility of the toughening agent;

[0025] f) Spray dry the stabilized suspension and let it stand.

[0026] The above dispersant is a long-side-chain polyether modified polycarboxylic acid shrinkage reducing agent with a solid content of 30%.

[0027] The emulsion polymer is mainly composed of ethylene-vinyl acetate copolymer, with an average particle size of 50-100 nm, preferably 60-80 nm. The ratio of total fiber content to emulsion polymer content is (3-8):(1-5).

[0028] The above-mentioned graphene oxide modified carbon fiber is obtained through the following steps: Weigh artificial graphite and NaNO3 in a mass ratio of (1.5-2):1, add concentrated H2SO4, and mix thoroughly under ice bath conditions; add KMnO4 in three portions; after ice bath for 30-35 minutes, raise the temperature to 35-40℃ and maintain the temperature for 24-26 hours; pour the mixture into deionized water, add 30% H2O2 dropwise until the solution turns golden yellow; finally, separate by ultrasonication, wash with deionized water to obtain an aqueous solution of graphene oxide; pretreat the carbon fiber under concentrated nitric acid (69.7%), immerse the pretreated carbon fiber in the aqueous solution of graphene oxide, adjust the pH of the solution to 2-3 with hydrochloric acid, react at 78-80℃ for 2-2.5 hours, and then heat-treat at 180-185℃ for 48-50 hours to obtain the modified carbon fiber; the amount of potassium permanganate used is 3 times the mass of artificial graphite.

[0029] The specific preparation process of the above-mentioned graphene oxide modified carbon fiber is as follows: Weigh 5g of artificial graphite and 2.5g of NaNO3, add them to a three-necked flask, and then add 180ml of concentrated H2SO4. Continuously stir mechanically under ice bath conditions to ensure complete mixing, maintaining the temperature below 4℃. Add 15g of KMnO4 in three portions to prevent vigorous reaction. After ice bath for 30 minutes, raise the temperature to 35℃ and maintain this temperature for 24 hours. Pour the mixture into deionized water and add 30% H2O2 dropwise until no bubbles are generated and the solution turns golden yellow. Finally, sonicate for 15 minutes, wash with deionized water, and dialyze to neutral to obtain an aqueous solution of graphene oxide. Wash the carbon fiber with acetone under reflux for 48 hours to remove the surface adhesive layer, and then dry at 100℃. Next, immerse the carbon fiber sample in 150ml of concentrated nitric acid (69.7%), reflux for 2 hours, wash with deionized water until neutral, and then vacuum dry the sample. Pretreated carbon fibers were immersed in an aqueous solution of graphene oxide, and the pH of the solution was adjusted to 3 with hydrochloric acid. The reaction was carried out at 78°C for 2 hours, followed by heat treatment at 180°C for 48 hours to obtain modified carbon fibers. The graphene on the carbon fibers can be chemically linked with the amino groups on the volcanic ash to form a network structure.

[0030] The modified basalt fiber is obtained through the following steps: the basalt fiber is ultrasonically soaked in a 1:1 mixture of ethanol and acetone for 1 hour, rinsed with deionized water, and then dried in an oven at 55-60℃ for 7-8 hours; the pretreated basalt fiber is mixed with an amination reagent or a vinyl esterification reagent, ultrasonically dispersed and heated, and after the reaction is completed, it is washed and dried to obtain the modified basalt fiber.

[0031] The preparation process of the modified basalt fiber is as follows: Basalt fiber is ultrasonically soaked in a 1:1 ethanol-acetone mixed solution for 1 hour to remove impurities from the fiber surface. It is then rinsed with deionized water and dried in a 60℃ oven for 8 hours. The pretreated basalt fiber is mixed with an amination reagent (such as APTES) or a vinyl esterifying reagent, ultrasonically dispersed, and heated to allow the reagent to be uniformly adsorbed onto the fiber surface and react chemically with the active groups on the fiber surface to form chemical bonds. After the reaction is complete, the fiber is washed with deionized water to remove unreacted reagents and dried to obtain the modified basalt fiber. The modified basalt fiber is mixed with volcanic ash and a composite material is prepared through an appropriate process (such as manual lay-up or resin transfer molding). During the composite process, the amino or vinyl groups on the fiber surface chemically bond with the amino or vinyl groups on the volcanic ash, forming a large network structure that enhances the overall performance of the composite material.

[0032] The above-mentioned coconut fiber is obtained through the following steps: after the coconut shell is crushed, it is treated with 10% m / v sodium hydroxide, then bleached with sodium chlorite and acetic acid, and dried at 70-72℃ for 110-120 min.

[0033] The aforementioned nano-oxides are a mixture of SiO2 and Al2O3, wherein the particle size of both SiO2 and Al2O3 ranges from 10-15 nm, and the weight ratio of SiO2 to Al2O3 is 1:(0.3-0.5). The nano-silica in this application exhibits high activity, capable of chemically reacting with other components in cement to form stable hydration products, thereby improving the high-temperature resistance of the cement. Furthermore, the nano-alumina has a small particle size and a large specific surface area, enabling it to better bond with the cement matrix, forming a dense structure, reducing porosity and defects within the cement at high temperatures, thus improving the high-temperature resistance of the cement.

[0034] The above-mentioned expanding agent is a magnesium oxide and calcium oxide composite expanding agent, with a weight ratio of MgO to CaO of 1:(1-2);

[0035] The MgO used is a multi-stage active MgO mixture. Different active MgOs have different hydration rates, forming a staged and continuous expansion effect, which can provide continuous expansion compensation at different stages of concrete hydration. The mass ratio of high-activity MgO, medium-activity MgO and low-activity MgO is (3-4):(3-4):(2-3).

[0036] High-activity MgO is obtained by calcining magnesite at 800-900℃ for 0.5-1h followed by rapid cooling and crushing; medium-activity MgO is obtained by calcining magnesite at 900–1100℃ for 0.5-1h followed by medium-speed cooling and crushing; low-activity MgO is obtained by calcining magnesite at 1100–1300℃ for 0.5-1h followed by natural cooling in air and crushing. The rapid cooling method is air quenching with an air flow rate of 20-40m / s; the medium-speed cooling method is air quenching with an air flow rate of 10-15m / s.

[0037] High-activity MgO can limit the volume shrinkage of cement slurry during the solidification period; calcium oxide plays a role in the early stage of cement slurry hardening, reducing the micro-gap between the cement sheath and the casing and formation, thereby improving the cement sheath bonding quality; magnesium oxide and calcium oxide work together to effectively compensate for the volume shrinkage of cement slurry throughout the cementing process, improving cementing quality and further enhancing interfacial bonding; medium-activity MgO has a slower hydration rate and continues to exert an expansion effect in the middle stage of hydration; low-activity MgO has a slow hydration rate and releases an expansion effect for a long time in the later stage of hydration. Using a multi-stage active MgO mixture can provide targeted expansion compensation at different hydration stages of cementing, optimizing its fracture resistance, improving cementing quality, and enhancing service stability.

[0038] The particle size of the aforementioned G-grade oil well cement is 3-80 μm, preferably 575 μm, and more preferably 870 μm. Under these preferred values, the cement hydration rate is moderate, and the thickening time and rheological properties are easily adjustable. The aforementioned chemical activator is selected from any one of lithium sulfate, lithium carbonate, sodium sulfate, sodium hydroxide, calcium hydroxide, calcium sulfate, triethanolamine, calcium formate, sodium acetate, sodium gluconate, and potassium sodium tartrate. The high-temperature water loss reducing agent is selected from 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), and propylene. The cement slurry contains any one of the following: acetic acid (AA) and N-vinylpyrrolidone (NVP); a high-temperature retarder is selected from any one of lignin sulfonate, AMPS, and double-layer hydrotalcite to reduce the hydration rate of cement at high temperatures and prevent premature setting of the cement ring; a polycarboxylic acid dispersant is selected to deagglomerate and disperse cement particles in the cement slurry, release free water, improve the fluidity of the cement slurry, and prevent thixotropy that could affect cementing operations; and a defoamer is selected from any one of polyether defoamers, polysiloxanes, and polyether-modified silicone oils.

[0039] A method for preparing a high-toughness micro-expansion cement slurry suitable for high-temperature cementing includes the following steps: (1) uniformly mixing G-grade oil well cement, active materials, nano-silica, dispersant, and expansion agent to obtain a dry material; (2) uniformly mixing a chemical activator, high-performance toughening agent, high-temperature fluid loss reducing agent, high-temperature retarder, and defoamer with water to obtain a liquid material; (3) uniformly mixing the dry material and liquid material according to GB / T19139 standard to obtain a cement slurry system. The water-cement ratio of the high-toughness micro-expansion cement slurry suitable for high-temperature cementing in this application is 0.4.

[0040] High-toughness micro-expansion cement slurry suitable for high-temperature cementing can be applied to cementing in high-temperature gas storage facilities. Compared with conventional cementing slurries, it features high temperature resistance, high toughness, and strong bonding, which can improve the cementing quality of the formation sealing section and ensure the integrity of the cement sheath seal under frequent injection and production. This cement slurry solves the problems of poor cementing quality and annular pressure after several injection and production cycles in existing technologies for this type of well application.

[0041] This application has the following advantages over the prior art:

[0042] (1) The cement slurry of this application not only possesses characteristics such as high temperature resistance, high toughness, and strong bonding, but also exhibits good high-temperature slurry stability and low filtration loss. This invention improves the high-temperature resistance, toughness, and bonding quality of the cement sheath by adding active materials, high-performance toughening agents, nano-oxides, and expanding agents; these four components work together to comprehensively improve the high-temperature resistance, toughness, and bonding performance of the cement at the surrounding rock interface. Furthermore, by using it in combination with other components, the cement slurry possesses advantages such as good stability, low water loss, and good rheological properties, making it suitable for cementing underground gas storage facilities. It can improve the cementing quality of the formation sealing section and ensure the sealing integrity of the cement sheath under frequent injection and production.

[0043] (2) This application uses volcanic rock slag as raw material, which greatly reduces the environmental pressure caused by solid waste. The material is green and environmentally friendly, and has low cost. The addition of volcanic ash particles can fill the tiny pores in cement stone, improve its pore structure, reduce porosity, and reduce the effects of heat conduction and thermal expansion at high temperatures, thereby improving the high-temperature resistance of cement stone. Some mineral components in volcanic ash have high thermal stability and are not easily decomposed or undergo phase transformation at high temperatures. They can exist stably in cement stone, thereby improving the overall thermal stability of cement stone.

[0044] (3) Using aminosilane alone may lead to an imbalance of surface charge in volcanic ash particles, causing agglomeration; using vinylsilane alone may result in uneven dispersion due to excessive hydrophobicity. This application uses aminosilane (hydrophilic) and vinylsilane (hydrophobic) to synergistically adjust the surface polarity of volcanic ash, improve the uniformity of particle dispersion in cement paste, and maximize the active filling effect of volcanic ash. The two coupling agents work together to construct a "rigid-flexible" interface structure: aminosilane enhances bonding strength, and vinylsilane improves deformation capacity, thereby transferring stress more efficiently;

[0045] (4) Carbon fiber provides high strength and high modulus support, basalt fiber enhances interfacial bonding and stress dispersion, while coconut fiber further improves toughness through flexibility and energy absorption. Composite fibers further optimize the microstructure and improve the overall performance of the material by filling pores and microcracks;

[0046] (5) The cement slurry provided in this application can meet the cementing requirements of gas storage wells. Compared with conventional cementing slurry, it has the characteristics of high temperature resistance, high toughness, micro-expansion, and strong bonding, which can improve the cementing quality of the formation sealing section and ensure the integrity of the cement sheath seal under frequent injection and production. This system is suitable for use in gas storage well cementing. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0048] Unless otherwise specified, the following examples and comparative examples were conducted under standard conditions. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0049] The graphene oxide-modified carbon fibers in the following examples and comparative examples were obtained through the following steps: 5g of artificial graphite and 2.5g of NaNO3 were weighed and added to a three-necked flask, followed by 180ml of concentrated H2SO4. The mixture was continuously mechanically stirred under ice bath conditions to ensure complete mixing, with the temperature maintained below 4°C. 15g of KMnO4 was added in three portions to prevent vigorous reaction. After 30 minutes in an ice bath, the temperature was raised to 35°C and maintained for 24 hours. The mixture was poured into deionized water, and 30% H2O2 was added dropwise until no bubbles were generated and the solution turned golden yellow. Finally, the mixture was ultrasonically separated for 15 minutes, washed with deionized water, and dialyzed to neutral to obtain an aqueous solution of graphene oxide. The carbon fibers were refluxed with acetone for 48 hours to remove the surface adhesive layer, and then dried at 100°C. The carbon fiber sample was then immersed in 150ml of concentrated nitric acid (69.7%), refluxed for 2 hours, washed with deionized water until neutral, and then vacuum dried. The pretreated carbon fibers were immersed in an aqueous solution of graphene oxide, the pH of the solution was adjusted to 3 with hydrochloric acid, the reaction was carried out at 78°C for 2 hours, and then heat-treated at 180°C for 48 hours to obtain the modified carbon fibers.

[0050] The modified basalt fibers in the various embodiments and comparative examples were obtained through the following steps: Basalt fibers were ultrasonically soaked in a 1:1 mixture of ethanol and acetone for 1 hour to remove impurities from the fiber surface, rinsed with deionized water, and then dried in an oven at 60°C for 8 hours. The pretreated basalt fibers were mixed with an amination reagent (such as APTES) or a vinyl esterifying reagent, ultrasonically dispersed, and heated to allow the reagent to be uniformly adsorbed onto the fiber surface and chemically react with the active groups on the fiber surface to form chemical bonds. After the reaction was complete, the fibers were washed with deionized water to remove unreacted reagents, and then dried to obtain the modified basalt fibers. The modified basalt fibers were mixed with volcanic ash, and a composite material was prepared through an appropriate process (such as manual lay-up or resin transfer molding). During the composite process, the amino or vinyl groups on the fiber surface formed chemical bonds with the amino or vinyl groups on the volcanic ash, forming a large network structure and enhancing the overall performance of the composite material.

[0051] The preparation process of the high-performance toughening agent in each embodiment and comparative example is as follows:

[0052] a) Weigh the fiber and emulsion polymer according to the above proportions;

[0053] b) Place the weighed raw materials into the mixer and mix for 10-15 minutes to ensure that the components are mixed evenly;

[0054] c) Add the well-mixed mixture to an appropriate amount of deionized water to form a suspension. Use a high-shear mixer to stir the suspension for 30 minutes at a speed of 2000 rpm to ensure that the fiber and emulsion polymer are evenly dispersed in the water.

[0055] d) Heat the suspension to 60°C and maintain the temperature while stirring for 30 minutes to further improve the dispersibility and stability of each component;

[0056] e) Add 0.2% of the total amount of polycarboxylic acid dispersant to the cooled suspension, stir evenly, and enhance the stability and dispersibility of the toughening agent;

[0057] f) Spray dry the stabilized suspension and let it stand.

[0058] The dispersant is a long-side-chain polyether-modified polycarboxylate shrinkage reducer (Wuhan Huaxuan High-Tech Co., Ltd.), with a solid content of 30%. The average particle size of the emulsion polymer is 80 nm. The ratio of total fiber content to emulsion polymer content is 2:1.

[0059] In Examples 1-3, the mass ratio of graphene oxide-modified carbon fiber, modified basalt fiber, and coconut fiber was 1:1:0.5; in Examples 4-7, the mass ratio of graphene oxide-modified carbon fiber, modified basalt fiber, and coconut fiber was 1.5:1:0.5.

[0060] The preparation process of the active materials in each embodiment and comparative example is as follows: First, anhydrous ethanol and deionized water (1:9 mass ratio) were mixed as solvents to prepare solutions of 0.5 wt% each of aminosilane coupling agent and vinylsilane coupling agent. Volcanic ash was first added to the above solution of aminosilane coupling agent, and the pH of the solution was adjusted to 4 with glacial acetic acid. The reaction was carried out at 60°C for 3 hours. Then, the volcanic ash was added to the above solution of vinylsilane coupling agent, which had been reacted at 30°C for 1 hour, for grafting. Ultrasonic dispersion was used to ensure that the volcanic ash was uniformly dispersed and fully contacted with the silane. The grafted volcanic ash was washed three times by centrifugation with anhydrous ethanol to remove unreacted silane, and then vacuum dried at 60°C for 12 hours to avoid desorption of the coupling agent due to high-temperature drying.

[0061] The mass ratio of aminosilane coupling agent, volcanic ash, and vinylsilane coupling agent is 2:10:1.

[0062] In Examples 1-7, the particle size range of SiO2 and Al2O3 is 10 nm.

[0063] In all embodiments and comparative examples, high-activity MgO was obtained by calcining magnesite at 800℃ for 1 hour followed by rapid cooling and crushing; medium-activity MgO was obtained by calcining magnesite at 1000℃ for 1 hour followed by medium-speed cooling and crushing; and low-activity MgO was obtained by calcining magnesite at 1300℃ for 1 hour followed by natural cooling in air and crushing. The rapid cooling method was air quenching with an air flow rate of 30 m / s; and the medium-speed cooling method was air quenching with an air flow rate of 15 m / s.

[0064] In all examples and comparative examples, the chemical activator is sodium acetate, the high-temperature water loss reducing agent is acrylamide, the defoamer is a polyether defoamer (Jiangsu Tengda Additives Co., Ltd.), the high-temperature retarder is sodium lignosulfonate, and the dispersant is a polycarboxylic acid dispersant (Wuhan Huaxuan High-Tech Co., Ltd.).

[0065] Example 1

[0066] 70 parts by weight of Grade G oil well cement, 30 parts by weight of active material, 3 parts by weight of chemical activator, 6 parts by weight of novel toughening agent, and 2 parts by weight of expansion agent (MgO and CaO in a weight ratio of 1:2, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 3:4:2) were mixed evenly to obtain a mixture. 6 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 3 parts by weight of high-temperature water loss reducing agent, 0.25 parts by weight of dispersant, 0.25 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 The cementing slurry system J1.

[0067] Example 2

[0068] 75 parts by weight of Grade G oil well cement, 25 parts by weight of active material, 4 parts by weight of chemical activator, 9 parts by weight of new toughening agent, and 1.5 parts by weight of expanding agent (MgO and CaO in a weight ratio of 1:1, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 3:4:3) were mixed evenly to obtain a mixture. 9 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 1 part by weight of high-temperature water loss reducing agent, 0.4 parts by weight of dispersant, 0.2 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J2 is a cementing slurry system for well cementing.

[0069] Example 3

[0070] 65 parts by weight of Grade G oil well cement, 35 parts by weight of active material, 5 parts by weight of chemical activator, 11 parts by weight of new toughening agent, and 1 part by weight of expansion agent (MgO and CaO in a weight ratio of 1:2, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 3:3:2) were mixed evenly to obtain a mixture. 5 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 1 part by weight of high-temperature water loss reducing agent, 0.3 parts by weight of dispersant, 0.4 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J3 is a cementing slurry system for well cementing.

[0071] Example 4

[0072] 80 parts by weight of Grade G oil well cement, 35 parts by weight of active material, 3 parts by weight of chemical activator, 8 parts by weight of new toughening agent, and 3 parts by weight of expansion agent (MgO and CaO in a weight ratio of 1:2, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 3:3:3) were mixed evenly to obtain a mixture. 8 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 2 parts by weight of high-temperature water loss reducing agent, 0.5 parts by weight of dispersant, 0.6 parts by weight of defoamer, 2 parts by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J4 is a cementing slurry system for well cementing.

[0073] Example 5

[0074] 85 parts by weight of Grade G oil well cement, 25 parts by weight of active material, 4 parts by weight of chemical activator, 4 parts by weight of novel toughening agent, and 3 parts by weight of expansion agent (MgO and CaO in a weight ratio of 1:2, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 3:4:2) were mixed evenly to obtain a mixture. 4 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 2 parts by weight of high-temperature water loss reducing agent, 0.8 parts by weight of dispersant, 0.8 parts by weight of defoamer, 2 parts by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J5 cement slurry system for well cementing.

[0075] Example 6

[0076] 90 parts by weight of Grade G oil well cement, 40 parts by weight of active material, 5 parts by weight of chemical activator, 12 parts by weight of novel toughening agent, and 5 parts by weight of expansion agent (MgO and CaO weight ratio of 1:2, high-activity MgO, medium-activity MgO, and low-activity MgO mass ratio of 4:4:2) were mixed evenly to obtain a mixture. 10 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3, weight ratio of 1:0.4), 3 parts by weight of high-temperature water loss reducing agent, 1 part by weight of dispersant, 1 part by weight of defoamer, 3 parts by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J6 is a cementing slurry system for well cementing.

[0077] Example 7

[0078] 60 parts by weight of Grade G oil well cement, 20 parts by weight of active material, 3 parts by weight of chemical activator, 3 parts by weight of novel toughening agent, and 0.5 parts by weight of expanding agent (MgO and CaO in a weight ratio of 1:2, with high-activity MgO, medium-activity MgO, and low-activity MgO in a mass ratio of 4:3:3) were mixed evenly to obtain a mixture. 3 parts by weight of nano-oxide (a mixture of SiO2 and Al2O3 in a weight ratio of 1:0.4), 1 part by weight of high-temperature water loss reducing agent, 0.1 part by weight of dispersant, 0.2 parts by weight of defoamer, 0.5 parts by weight of high-efficiency retarder, and water were mixed to obtain slurry water. The slurry water and the above mixture were then stirred together in a high-speed mixer at a speed of 4000 rpm to obtain a density of 1.91 g / cm³. 3 J7 is a cementing slurry system for well cementing.

[0079] Comparative Example 1

[0080] Mixing 80 parts by weight of Grade G oil well cement, 3 parts by weight of high-temperature fluid loss reducing agent, 0.25 parts by weight of high-efficiency polycarboxylate dispersant, 0.25 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water, a solution with a density of 1.91 g / cm³ was obtained. 3 J10 cement slurry system for cementing wells.

[0081] Comparative Example 2

[0082] The difference compared to Example 1 is that Comparative Example 2 added unmodified volcanic ash, resulting in a density of 1.91 g / cm³. 3 The cementing slurry system J 11.

[0083] Comparative Example 3

[0084] The difference compared to Example 1 is that Comparative Example 3 added volcanic ash modified with an aminosilane coupling agent, resulting in a density of 1.92 g / cm³. 3The cementing slurry system J 12.

[0085] Comparative Example 4

[0086] Compared to Example 1, the difference lies in the mass ratio of aminosilane coupling agent, volcanic ash, and vinylsilane coupling agent in the active material of Comparative Example 4: 1:5:2. This resulted in a density of 1.92 g / cm³. 3 The cementing slurry system J 13.

[0087] Comparative Example 5

[0088] The difference compared to Example 1 is that Comparative Example 5 only uses graphene oxide modified carbon fiber.

[0089] Comparative Example 6

[0090] The difference from Example 1 is that the mass ratio of graphene oxide modified carbon fiber, modified basalt fiber, and coconut fiber in Comparative Example 6 is (1-1.5):1:1.

[0091] Comparative Example 7

[0092] The difference compared to Example 1 is that the mass ratio of graphene oxide modified carbon fiber, modified basalt fiber, and coconut fiber in Comparative Example 7 is (1-1.5):1.5:0.5.

[0093] Comparative Example 8

[0094] Compared with Example 1, the difference is that the high-performance toughening agent in Comparative Example 8 is only fiber, which is a mixture of graphene oxide modified carbon fiber, modified basalt fiber and coconut fiber with a mass ratio of 1:1:0.5. The amount of fiber is the same as in Example 1.

[0095] Comparative Example 9

[0096] The difference compared to Example 1 is that the particle size range of the 9 nm oxide in the comparative example is 10-15 nm.

[0097] Comparative Example 10

[0098] Compared with Example 1, the difference is that the MgO in the expanding agent in Comparative Example 10 was obtained by calcining at 1000°C for 0.5-1h, followed by rapid cooling in air quenching and crushing.

[0099] Comparative Example 11

[0100] Compared with Example 1, the difference is that the MgO in the expanding agent in Comparative Example 11 was obtained by calcining at 700°C for 0.5-1h and then naturally cooling and crushing.

[0101] Comparative Example 12

[0102] The difference compared to Example 1 is that the MgO in the expanding agent in Comparative Example 12 is only highly active magnesium oxide.

[0103] The density difference between the upper and lower parts of the cement slurry system obtained in the above embodiments and comparative examples is 0.

[0104] The cement slurry system Jn and the surrounding rock cement stone assembly obtained from the above embodiments and comparative examples were cured at 90℃ for 24h, 72h and 7 days to obtain the corresponding cement stone Sn.

[0105] According to GB / T 19139-2012 Oil Well Cement Test Method, the cement slurry systems and cement stone properties obtained in each example and comparative example were tested. The density, fluidity, water separation, and density difference of the obtained cement slurry systems were all measured under normal pressure and at 25℃. The test results are shown in Table 1 below:

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from the results in Table 1, the cement stone obtained in Examples 1-7 has better compressive strength, bonding strength, linear expansion rate and 7-day elastic modulus compared with other comparative examples.

[0110] Compared with the conventional cement stone of Comparative Example 1, the cement stone obtained in Examples 1-7 showed a significant increase in elasticity and toughness, a substantial increase in bonding strength with the surrounding rock interface, increased compressive strength at high temperatures, and a larger expansion rate.

[0111] Comparative Example 2, with the addition of unmodified active materials, resulted in cement stone with low strength and low bonding strength; Comparative Example 3, with the addition of volcanic ash modified by aminosilane coupling agent, resulted in cement stone with high strength and high bonding strength; however, compared with Example 1, the performance was still slightly inferior.

[0112] In Comparative Example 4, the addition of excessive vinyl silane coupling agent excessively restricted the hydration process, hindered its chemical bonding with hydration products (such as Ca(OH)2 and CSH gel) in cement paste, reduced the interfacial bonding strength, and resulted in a decrease in mechanical properties. The compressive strength of the cement stone and the interfacial bonding strength of the surrounding rock both decreased.

[0113] Comparative Example 5, which only uses graphene oxide-modified carbon fiber without the synergistic effect of coconut fiber and modified basalt fiber, resulted in cement stone with low strength and low bonding strength. Comparative Example 6, which added excessive coconut fiber, resulted in cement stone with lower strength compared to Example 1. Comparative Example 7, which added excessive basalt fiber, resulted in cement stone with lower strength compared to Example 1, but higher elastic modulus. Comparative Example 8, which used only fiber as a toughening agent, lacked emulsion polymer, leading to reduced fiber dispersion and performance degradation due to localized aggregation. The combination of modified carbon fiber, modified basalt fiber, and coconut fiber provided in this application can effectively improve the overall performance of cement stone.

[0114] In Comparative Example 9, the addition of nano-oxides with excessively large particle sizes resulted in a decrease in the strength and elastic modulus of the cement stone compared to Example 1.

[0115] Comparative Example 10 added MgO calcined at excessively high temperatures, which resulted in a decrease in expansion rate due to partial deactivation; Comparative Example 11 added MgO that had cooled naturally, which allowed the MgO grains sufficient time to grow and form large-sized crystals, resulting in a decrease in specific surface area and a reduction in active sites, leading to a decrease in expansion rate; Comparative Example 12 added MgO in the expansion agent, which was only highly active magnesium oxide, which could not continuously and effectively compensate for the shrinkage of cement in the later stages, resulting in a decrease in expansion rate.

[0116] In summary, the cement slurry of the present invention, by combining active materials, toughening materials, and expanding agents with other components, can give the cement slurry advantages such as high temperature resistance, high toughness, micro-expansion, strong bonding, and good rheological properties. It is suitable for cementing underground gas storage facilities, can improve the cementing quality of the formation section, and ensure the integrity of the cement sheath seal under frequent injection and production.

[0117] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-toughness micro-expansion cement slurry suitable for high-temperature cementing, characterized in that, The cement slurry comprises the following raw materials in parts by weight: 60-90 parts of G-grade oil well cement, 20-40 parts of active material, 3-12 parts of high-performance toughening agent, 3-10 parts of nano-oxide, 0.5-5 parts of expansion agent, 3-5 parts of chemical activator, 1-3 parts of high-temperature water loss reducing agent, 0.5-3 parts of high-temperature retarder, 0.1-1 parts of dispersant, and 0.2-1 parts of defoamer; The active material is volcanic ash that has been hydrophobically modified by aminosilane coupling agent and vinylsilane coupling agent; the mass ratio of aminosilane coupling agent, volcanic ash and vinylsilane coupling agent is (2-3):10:1; The high-performance toughening agent is a composite of fiber and emulsion polymer, and the fiber is a mixture of graphene oxide modified carbon fiber, modified basalt fiber and coconut fiber; the mass ratio of graphene oxide modified carbon fiber, modified basalt fiber and coconut fiber is (1-1.5):1:0.

5. The expanding agent is a magnesium oxide and calcium oxide composite expanding agent, with a MgO to CaO weight ratio of 1:(1-2); the MgO is a multi-stage active MgO mixture, wherein the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is (3-4):(3-4):(2-3); the high-activity MgO is obtained by calcining magnesite at 800-900℃ for 0.5-1h followed by rapid cooling and crushing; the medium-activity MgO is obtained by calcining magnesite at 900–1100℃ for 0.5-1h followed by medium-speed cooling and crushing; the low-activity MgO is obtained by calcining magnesite at 1100–1300℃ for 0.5-1h followed by natural cooling in air and crushing. The preparation process of the active material is as follows: Anhydrous ethanol and deionized water are mixed as solvents to prepare solutions of aminosilane coupling agent and vinylsilane coupling agent, each with a content of 0.5 wt%; volcanic ash is first added to the above solution of aminosilane coupling agent, and the pH is adjusted with glacial acetic acid to carry out the first grafting reaction; then it is added to the above solution of vinylsilane coupling agent to carry out the second grafting reaction, and then washed and dried to obtain the final product; The graphene oxide-modified carbon fiber is obtained through the following steps: Weigh artificial graphite and NaNO3 in a mass ratio of (1.5-2):1, add concentrated H2SO4, and mix thoroughly under ice bath conditions; add KMnO4 in three portions; after ice bath for 30-35 minutes, raise the temperature to 35-40℃ and maintain the temperature for 24-26 hours; pour the mixture into deionized water, add 30% H2O2 dropwise until the solution turns golden yellow; finally, separate by ultrasonication, wash with deionized water to obtain an aqueous solution of graphene oxide; pretreat the carbon fiber under concentrated nitric acid conditions, immerse the pretreated carbon fiber in the aqueous solution of graphene oxide, adjust the pH of the solution to 2-3 with hydrochloric acid, react at 78-80℃ for 2-2.5 hours, and then heat-treat at 180-185℃ for 48-50 hours to obtain the modified carbon fiber; the amount of potassium permanganate used is 3 times the mass of the artificial graphite. The modified basalt fiber is obtained through the following steps: basalt fiber is ultrasonically soaked in a 1:1 ethanol-acetone mixed solution for 1 hour, rinsed with deionized water, and then dried in an oven at 55-60℃ for 7-8 hours; the pretreated basalt fiber is mixed with an amination reagent or a vinyl esterification reagent, ultrasonically dispersed and heated, and after the reaction is completed, washed and dried to obtain the modified basalt fiber. The coconut fiber is obtained through the following steps: after the coconut shell is crushed, it is treated with 10% m / v sodium hydroxide, then bleached with sodium chlorite and acetic acid, and dried at 70-72℃ for 110-120 min. The nano-oxide is a mixture of SiO2 and Al2O3, wherein the weight ratio of SiO2 to Al2O3 is 1:(0.3-0.5).

2. The high-toughness micro-expansion cement slurry suitable for high-temperature cementing according to claim 1, characterized in that: The mass ratio of anhydrous ethanol to deionized water is 1:9; the grafting reaction is carried out by ultrasonic dispersion during the preparation of the active material; glacial acetic acid is used to adjust the pH to 4-5; the first grafting reaction is carried out at 58-60℃ for 2.5-3 hours, and the second grafting reaction is carried out at 28-30℃ for 1-1.5 hours.

3. The high-toughness micro-expansion cement slurry suitable for high-temperature cementing according to claim 1, characterized in that: The chemical activator is selected from any one of lithium sulfate, lithium carbonate, sodium sulfate, sodium hydroxide, calcium hydroxide, calcium sulfate, triethanolamine, calcium formate, sodium acetate, sodium gluconate, and potassium sodium tartrate; the high-temperature water loss reducing agent is selected from any one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), acrylic acid (AA), and N-vinylpyrrolidone (NVP); the high-temperature retarder is selected from any one of lignin sulfonates, AMPS, and double-electron-layer hydrotalcite; the dispersant is a polycarboxylic acid dispersant; and the defoamer is selected from any one of polyether defoamers, polysiloxanes, and polyether-modified silicone oils.

4. A method for preparing a high-toughness micro-expansion cement slurry suitable for high-temperature cementing as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix G-grade oil well cement, active materials, nano-oxides, dispersants and expansion agents evenly to obtain dry material; (2) Mix chemical activator, high-performance toughening agent, high-temperature water loss reducer, high-temperature retarder and defoamer with water evenly to obtain liquid material; (3) After the dry material is evenly mixed, slowly add the liquid material; after the liquid material is completely added, continue stirring for 1-2 minutes to ensure that the cement is completely uniform and obtain cement slurry system.

5. The application of a high-toughness micro-expansion cement slurry suitable for high-temperature cementing in high-temperature gas storage well cementing, characterized in that: The high-toughness micro-expansion cement slurry suitable for high-temperature cementing is the high-toughness micro-expansion cement slurry suitable for high-temperature cementing as described in any one of claims 1-3 or the high-toughness micro-expansion cement slurry suitable for high-temperature cementing obtained by the preparation method described in claim 4.

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