High-toughness micro-expansive cement paste suitable for high-temperature well cementation as well as preparation method and application of high-toughness micro-expansive cement paste

Abstract

The invention provides high-toughness micro-expansive cement paste suitable for high-temperature well cementation. The cement paste comprises the following raw materials in parts by weight: 60-90 parts of G-grade oil well cement, 20-40 parts of an active material, 3-12 parts of a high-performance toughening agent, 3-10 parts of nano oxide, 0.5-5 parts of an expanding agent, 3-5 parts of a chemical exciting agent, 1-3 parts of a high-temperature fluid loss agent, 0.5-3 parts of a high-temperature retarder and 0.1-1 part of a dispersing agent, and 0.2-1 part by weight of a defoaming agent. By adding the active material, the high-performance toughening agent, the nano oxide and the expanding agent, the high-temperature resistance and toughness of the cement paste, the cementation quality of a cement sheath and the like are improved; through the combined action of the four components, the high-temperature resistance, toughness and surrounding rock interface cementation performance of the cement are comprehensively improved; and the cement paste is matched with other components for use, so that the cement paste has the advantages of good stability, low water loss, good rheological property and the like, is suitable for underground gas storage well cementation, can improve the well cementation quality of a stratum sealing section, and ensures the sealing integrity of a cement sheath under frequent injection and production.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well cementing, and particularly relates to a high-toughness micro-expansive cement slurry suitable for high-temperature cementing, a preparation method thereof, and an application thereof. Background Art

[0002] The cement used for cementing belongs to portland cement, which has the disadvantages of low tensile strength, poor impact strength, and easy brittle cracking. When the assembly is subjected to external forces, the cement sheath is very likely to crack, damage, and fail first. 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-expansive cement slurry system.

[0003] CN117228979A discloses a high-temperature-resistant low-density cement slurry system. By using additives such as cement for cementing, high-temperature retarder, high-temperature fluid loss reducer, hollow microspheres, reinforcing materials, laterite nickel slag, and high-temperature-resistant elastic materials, a low-density cement slurry is prepared according to the GB / T19139 standard, and the sealing section of the formation with a low pressure coefficient is balanced.

[0004] CN110937857A discloses a high-temperature-resistant anti-channeling emulsion elastic and tough cement slurry and a preparation method thereof. The high-temperature-resistant anti-channeling emulsion elastic and tough cement slurry comprises the following components in parts 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 expansion agent, 1-12 parts of high-temperature-resistant fluid loss reducer, 0.1-10 parts of high-temperature retarder, 0.5-3 parts of defoaming agent, 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 used in cementing, a cement slurry, and a preparation method thereof. The high-temperature strength stabilizer is composed of 73% - 75% of a reinforcing agent, 22% - 24% of a crystal phase stabilizing component, and 2% - 4% of a pH regulator by mass percentage. The reinforcing agent includes crystalline silicon dioxide and can undergo a hydration reaction with portland cement at a temperature above 200°C to generate acicular tobermorite and fibrous xonotlite crystals; the crystal 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 a temperature above 200°C to generate fibrous aluminum-substituted xonotlite crystals; the pH regulator is solid sodium silicate with a modulus of 1 - 2. The present invention can effectively prevent the late strength decline of the cement sheath, improve the compactness of the cement stone, and meet the cementing requirements of ultra-deep and ultra-high-temperature wells.

[0006] Although the toughness and high-temperature strength degradation of cement stone have been improved by adding certain tough and high-temperature resistant materials to the cement slurry, the interface bonding performance between the cement sheath and the rock formation is poor when meeting the high-temperature resistance and toughness requirements. This makes it difficult to ensure 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] In order to solve the technical problems existing in the prior art such as poor interface bonding performance between cement sheath and surrounding rock, poor impact strength of consolidated cement, and brittle cracking, the present application provides a high-toughness micro-expansive cement slurry suitable for high-temperature cementing, and its preparation method and application. The cement slurry has the characteristics of high temperature resistance, high toughness, strong bonding, etc., which can meet the cementing quality requirements of gas storage and the sealing integrity of cement sheath under injection and production throughout the life cycle, thereby ensuring the safe and efficient operation of the gas storage.

[0008] A high-toughness, slightly expansive cement slurry suitable for high-temperature well cementing, the cement slurry 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 additive, 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 defoaming agent;

[0009] Preferably, the cement slurry comprises the following raw materials in parts by weight: 6580 parts by weight of G-grade 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 stimulant, 1-2 parts by weight of high-temperature fluid loss additive, 1-2 parts by weight of high-temperature retarder, 0.250.8 parts by weight of dispersant, and 0.40.8 parts by weight of defoaming agent.

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

[0011] Furthermore, the volcanic ash is ground volcanic rock waste, and its aluminate content is 20-40%; its density is 2.6-3.0g / cm 3 , with an average particle size of 5-10 μm; and a 3-day activity index of the above active material 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 active material is as follows: Mix absolute ethanol and deionized water as solvents to prepare solutions with a content of 0.5 wt% of both amino-silane coupling agent and vinyl-silane coupling agent respectively; First add the volcanic ash into the above solution of the amino-silane coupling agent, adjust the pH with glacial acetic acid and then carry out the first grafting reaction; Then add it into the above solution of the vinyl-silane coupling agent to carry out the second grafting reaction, and then wash and dry to obtain it.

[0014] The mass ratio of the above absolute ethanol to deionized water is 1:9; Ultrasonic dispersion is used for the grafting reaction during the preparation process of the active material; Glacial acetic acid is used to adjust the pH to 4 - 5; The conditions for the first grafting reaction are to react at 58 - 60 °C for 2.5 - 3 hours, and the conditions for the second grafting reaction are to react at 28 - 30 °C for 1 - 1.5 hours.

[0015] Preferably, the preparation process of the active material is specifically as follows: First add the volcanic ash into the above solution of the amino-silane coupling agent, adjust the pH of the solution to 4 - 5 with glacial acetic acid, react at 60 °C for 3 hours, and then add it into the above solution of the vinyl-silane coupling agent that reacts at 30 °C for 1 hour for grafting. Use ultrasonic dispersion to ensure that the volcanic ash is evenly dispersed and in full contact with the silane to obtain. The grafted volcanic ash needs to be centrifugally washed 3 times with absolute ethanol to remove the unreacted silane, and vacuum dried at 60 °C for 12 hours to avoid the desorption of the coupling agent caused by high-temperature drying.

[0016] The above volcanic ash uses the ground volcanic rock waste residue, and its active components can undergo a secondary hydration reaction with Ca(OH)₂ in water to generate more hydrated calcium silicate (C-S-H) gel and hydrated calcium aluminate and other hydration products. These hydration products have high heat resistance and can improve the high-temperature resistance of the cement stone.

[0017] The above high-performance toughening agent is a composite of fibers and emulsion polymers. The above fibers are a mixture of graphene oxide-modified carbon fibers, modified basalt fibers, and coconut fibers; The mass dosage ratio of graphene oxide-modified carbon fibers, modified basalt fibers, and coconut fibers is (1 - 1.5):1:0.5. Mixing the fibers and emulsion polymers first can ensure the uniform dispersion of the fibers and polymers in the cement matrix and avoid the performance decline caused by local aggregation.

[0018] The emulsion polymer in the high-performance toughening agent is dispersed in the cement paste. With the hydration reaction of the cement, the polymer particles gradually form a film and form an organic-inorganic interpenetrating three-dimensional network structure with the cement hydration products. At the same time, the fibers form an interface with high bonding strength with the cement, further improving the overall strength and toughness of the cement.

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

[0020] a) Weigh the fibers and emulsion polymer respectively according to the above ratios.

[0021] b) Put the weighed raw materials into a mixer and mix and stir for 10 - 15 minutes to ensure that each component is evenly mixed.

[0022] c) Add the evenly mixed mixture to an appropriate amount of deionized water to form a suspension, and use a high - shear mixer to stir the suspension for 30 minutes at a rotation speed of 2000 revolutions per minute to ensure that the fibers and emulsion polymer are evenly dispersed in water.

[0023] d) Heat the suspension to 60 °C and keep stirring at a constant temperature for 30 minutes to further improve the dispersibility and stability of each component.

[0024] e) Add a polycarboxylic acid - type dispersant accounting for 0.1 - 0.3% of the total amount of the suspension to the cooled suspension and stir evenly to enhance the stability and dispersibility of the toughening agent.

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

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

[0027] Among them, the main component of the emulsion polymer is ethylene - vinyl acetate copolymer, with an average particle size of 50 - 100 nm, preferably 60 - 80 nm. The ratio of the total amount of fibers used to the amount of emulsion polymer used 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 with a mass ratio of (1.5 - 2):1, then add concentrated H2SO4 and mix evenly under ice - bath conditions; add KMnO4 in three portions; after ice - bath for 30 - 35 minutes, raise the temperature to 35 - 40 °C and keep warm for 24 - 26 hours; pour the mixture into deionized water, and dropwise add 30% H2O2 until the solution turns golden yellow; finally, perform ultrasonic separation, wash with deionized water to obtain an aqueous solution of graphene oxide; pretreat the carbon fiber under the condition of concentrated nitric acid (69.7%), immerse the pretreated carbon fiber into the aqueous solution of graphene oxide, adjust the pH of the solution to 2 - 3 with hydrochloric acid, react at 78 - 80 °C for 2 - 2.5 hours, and then perform heat treatment at 180 - 185 °C for 48 - 50 hours to obtain the modified carbon fiber; the dosage of potassium permanganate is 3 times the mass of artificial graphite.

[0029] The preparation process of the above-mentioned graphene oxide modified carbon fiber is as follows: Weigh 5 g of artificial graphite and 2.5 g of NaNO3, add them into a three-necked flask, and then add 180 ml of concentrated H2SO4. Continuously stir mechanically under ice bath conditions to completely mix the mixture, and keep the temperature below 4 °C. Add 15 g of KMnO4 in three portions to prevent violent reactions. After ice bath for 30 minutes, raise the temperature to 35 °C and keep it warm for 24 hours. Pour the mixture into deionized water, and dropwise add 30% H2O2 until no bubbles are generated and the solution turns golden yellow. Finally, perform ultrasonic separation for 15 minutes, wash with deionized water, and dialyze until neutral to obtain an aqueous solution of graphene oxide. The carbon fiber is refluxed and washed with acetone for 48 hours to remove the surface glue layer, and then dried at 100 °C. Then immerse the carbon fiber sample into 150 ml of concentrated nitric acid (69.7%), perform condensation reflux for 2 hours, wash with deionized water until neutral, and then vacuum dry the sample. Immerse the pretreated carbon fiber into the aqueous solution of graphene oxide, adjust the pH of the solution to 3 with hydrochloric acid, react at 78 °C for 2 hours, and then perform heat treatment at 180 °C for 48 hours to obtain the modified carbon fiber. The graphene on the carbon fiber can be chemically connected to the amino groups on the volcanic ash to form a network structure.

[0030] The above-mentioned modified basalt fiber is obtained through the following steps: Ultrasonically soak the basalt fiber in a mixed solution of ethanol-acetone at a ratio of 1:1 for 1 h, then rinse with deionized water, and then dry in an oven at 55-60 °C for 7-8 h; Mix the pretreated basalt fiber with an amination reagent or a vinylation reagent, ultrasonically disperse and heat it. After the reaction is completed, wash and dry to obtain the modified basalt fiber.

[0031] The preparation process of the above-mentioned modified basalt fiber is as follows: Ultrasonically soak the basalt fiber in a mixed solution of ethanol-acetone at a ratio of 1:1 for 1 h to remove impurities on the fiber surface, rinse with deionized water, and then dry in an oven at 60 °C for 8 h. Mix the pretreated basalt fiber with an amination reagent (such as APTES) or a vinylation reagent, ultrasonically disperse and heat it to make the reagent evenly adsorb on the fiber surface and chemically react with the active groups on the fiber surface to form chemical bonds. After the reaction is completed, wash with deionized water to remove the unreacted reagent, and dry to obtain the modified basalt fiber. Mix the modified basalt fiber with volcanic ash and prepare a composite material through an appropriate process (such as manual layup 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 to form a large network structure, enhancing the overall performance of the composite material.

[0032] The above-mentioned coconut fiber is obtained through the following steps: After crushing the coconut shell, treat it with 10% m / v sodium hydroxide, then bleach it with sodium chlorite and acetic acid, and dry at 70-72 °C for 110-120 min.

[0033] The above-mentioned nano-oxides are a mixture of SiO2 and Al2O3. Among them, the particle size ranges of both SiO2 and Al2O3 are 10 - 15 nm, and the weight ratio of SiO2 to Al2O3 is 1:(0.3 - 0.5). The nano-silicon oxide in the nano-oxides of this application has high activity and can chemically react with other components in the cement to form stable hydration products, thereby improving the high-temperature resistance of the cement. Moreover, the nano-aluminum oxide has a small particle size and a large specific surface area, which can better combine with the cement matrix to form a dense structure, reduce the pores and defects inside the cement at high temperatures, and thus improve the high-temperature resistance of the cement.

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

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

[0036] High-active MgO is obtained by calcining magnesite at 800 - 900 °C for 0.5 - 1 h and then rapidly cooling and crushing; medium-active MgO is obtained by calcining magnesite at 900–1100 °C for 0.5 - 1 h and then moderately cooling and crushing; low-active MgO is obtained by calcining magnesite at 1100–1300 °C for 0.5 - 1 h and then naturally cooling in the air and crushing; the above rapid cooling method is: air quenching, and the air flow rate is 20 - 40 m / s; the above medium-speed cooling method is: air quenching, and the air flow rate is 10 - 15 m / s.

[0037] High-active MgO can limit the volume shrinkage of the cement paste during the waiting for solidification period; calcium oxide plays a role in the initial stage of the hardening of the cement paste, reducing the micro-gap between the cement sheath and the casing and the formation, thereby improving the cementing quality of the cement sheath; magnesium oxide and calcium oxide cooperate with each other to effectively compensate for the volume shrinkage of the cement paste during the whole process of well cementing, improve the well cementing quality, and further improve the interface cementing; the hydration rate of medium-active MgO is relatively slow, and it continues to play an expansion role in the middle stage of hydration; the hydration rate of low-active MgO is slow, and it 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 well cementing cement, optimize its crack resistance performance, improve the well cementing quality, and enhance the service stability.

[0038] The particle size of the above-mentioned G-class oil well cement is 3 - 80 μm, preferably 5 - 75 μm, and more preferably 8 - 70 μm. At this preferred value, the cement hydration rate is moderate, and the thickening time and rheology are easy to adjust; the above-mentioned 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 fluid loss reducer is selected from any one of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), acrylic acid (AA), and N-vinylpyrrolidone (NVP); the high-temperature retarder is selected from any one of lignosulfonates, AMPS-based, and double-electron layer hydrotalcite-based to reduce the hydration rate of the cement at high temperatures and avoid premature final setting of the cement sheath; the dispersant is a polycarboxylate dispersant, which can depolymerize and disperse the agglomerated cement particles in the cement slurry, release free water, improve the fluidity of the cement slurry, and avoid thixotropy, which affects the cementing construction; the defoamer is selected from any one of polyether defoamers, polysiloxanes, and polyether-modified silicone oils.

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

[0040] The high-toughness and slightly expandable cement slurry suitable for high-temperature cementing can be applied to high-temperature gas storage well cementing. Compared with conventional cement slurries for cementing, it has characteristics such as high temperature resistance, high toughness, and strong cementation, 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 annulus pressure after several injection and production cycles in the application of existing technologies in such wells.

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

[0042] (1) The cement slurry of this application not only has characteristics such as high temperature resistance, high toughness, and strong cementation, but also has good high-temperature slurry stability and fluid loss. In this invention, by adding active materials, high-performance toughening agents, nano-oxides, and expansion agents, the high-temperature resistance ability, toughness, and cementation quality of the cement sheath of the cement slurry are improved; the four act together to comprehensively improve the high-temperature resistance ability, toughness, and cementation performance at the interface with the surrounding rock of the cement. And by cooperating with other components, the cement slurry has advantages such as good stability, low water loss, and good rheology, is suitable for cementing of underground gas storage wells, can improve the cementing quality of the formation sealing section, and ensure the integrity of the cement sheath seal under frequent injection and production.

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

[0044] (3) Using amino silane alone may cause charge imbalance on the surface of volcanic ash particles, leading to agglomeration; using only vinyl silane may cause uneven dispersion due to excessive hydrophobicity. This application uses amino silane (hydrophilic) and vinyl silane (hydrophobic) to synergistically adjust the surface polarity of volcanic ash, improve the dispersion uniformity of particles in the cement paste, and maximize the active filling effect of volcanic ash. The combined action of the two coupling agents can construct an interface structure of "rigidity and flexibility": amino silane enhances the bonding strength, and vinyl silane improves the deformation ability, so as to transfer stress more efficiently;

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

[0046] (5) The cement paste provided by this application can meet the requirements of gas storage well cementing construction. Compared with conventional cementing cement paste, it has characteristics such as 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 gas storage well cementing. Detailed Embodiment

[0047] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0048] For those not specifying specific conditions in the following examples and comparative examples, they are carried out according to conventional conditions. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase channels.

[0049] In the following examples and comparative examples, the graphene oxide modified carbon fiber is obtained through the following steps: Weigh 5 g of artificial graphite and 2.5 g of NaNO3, add them to a three-necked flask, and then add 180 ml of concentrated H2SO4. Continuously mechanically stir under ice bath conditions to completely mix the mixture, and keep the temperature below 4 °C. Add 15 g of KMnO4 in three portions to prevent violent reactions. After 30 minutes of ice bath, raise the temperature to 35 °C and keep it warm for 24 hours. Pour the mixture into deionized water, and dropwise add 30% H2O2 until no bubbles are generated and the solution turns golden yellow. Finally, perform ultrasonic separation for 15 minutes, wash with deionized water, and dialyze until neutral to obtain an aqueous solution of graphene oxide. The carbon fiber is refluxed and washed with acetone for 48 hours to remove the surface glue layer, and then dried at 100 °C. Then immerse the carbon fiber sample in 150 ml of concentrated nitric acid (69.7%), carry out reflux condensation for 2 hours, wash with deionized water until neutral, and then vacuum dry the sample. Immerse the pretreated carbon fiber in the aqueous solution of graphene oxide, adjust the pH of the solution to 3 with hydrochloric acid, react at 78 °C for 2 hours, and then perform heat treatment at 180 °C for 48 hours to obtain the modified carbon fiber.

[0050] In each of the examples and comparative examples, the modified basalt fiber is obtained through the following steps: Ultrasonically soak the basalt fiber in a mixed solution of ethanol-acetone at a ratio of 1:1 for 1 h to remove impurities on the fiber surface, rinse with deionized water, and then dry in an oven at 60 °C for 8 h. Mix the pretreated basalt fiber with an amination reagent (such as APTES) or a vinylation reagent, ultrasonically disperse and heat it to make the reagent uniformly adsorb on the fiber surface and chemically react with the active groups on the fiber surface to form chemical bonds. After the reaction is completed, wash with deionized water to remove the unreacted reagent, and obtain the modified basalt fiber after drying. Mix the modified basalt fiber with volcanic ash and prepare a composite material through an appropriate process (such as manual lay-up or resin transfer molding). During the composite process, the amino or vinyl group on the fiber surface chemically bonds with the amino or vinyl group on the volcanic ash to form a large network structure, enhancing the overall performance of the composite material.

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

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

[0053] b) Put the weighed raw materials into a mixer, mix and stir for 10 - 15 minutes to ensure that each component is evenly mixed;

[0054] c) Add the evenly mixed mixture to an appropriate amount of deionized water to form a suspension, and use a high-shear mixer to stir the suspension for 30 minutes at a rotation speed of 2000 revolutions per minute to ensure that the fiber and the emulsion polymer are evenly dispersed in water;

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

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

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

[0058] The dispersant is a long-side-chain polyether modified polycarboxylic acid shrinkage reducing agent (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 the total amount of fibers used to the amount of emulsion polymer used is 2:1.

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

[0060] The preparation process of the active material in each example and comparative example is as follows: First, mix anhydrous ethanol and deionized water (mass ratio 1:9) as a solvent, and prepare solutions with both an amino-silane coupling agent and a vinyl-silane coupling agent at a content of 0.5 wt%; first add the volcanic ash to the above solution of the amino-silane coupling agent, adjust the pH of the solution to 4 with glacial acetic acid, react at 60 °C for 3 hours, and then add it to the above solution of the vinyl-silane coupling agent that has reacted at 30 °C for 1 hour for grafting. Use ultrasonic dispersion to ensure that the volcanic ash is evenly dispersed and in full contact with the silane. The grafted volcanic ash needs to be centrifugally washed 3 times with anhydrous ethanol to remove the unreacted silane, and vacuum dried at 60 °C for 12 hours to avoid the desorption of the coupling agent caused by high-temperature drying.

[0061] The mass ratio of the amino-silane coupling agent, volcanic ash, and vinyl-silane coupling is 2:10:1.

[0062] In Examples 1-7, the particle size ranges of both SiO2 and Al2O3 are 10 nm.

[0063] In each example and comparative example, highly active MgO is obtained by calcining magnesite at 800 °C for 1 h and then rapidly cooling and crushing; medium-active MgO is obtained by calcining magnesite at 1000 °C for 1 h and then medium-speed cooling and crushing; low-active MgO is obtained by calcining magnesite at 1300 °C for 1 h and then naturally cooling in air and crushing; the rapid cooling method is: air quenching with an air flow rate of 30 m / s; the medium-speed cooling method is: air quenching with an air flow rate of 15 m / s.

[0064] In each of the examples and comparative examples, the chemical activator is sodium acetate, the high-temperature fluid loss reducer is acrylamide, the defoamer is a polyether defoamer (Jiangsu Tengda Auxiliary 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] Mix 70 parts by weight of G-class oil well cement, 30 parts by weight of active material, 3 parts by weight of chemical activator, 6 parts by weight of a new toughening agent, and 2 parts by weight of an expansive agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 3:4:2) evenly to obtain a mixture; mix 6 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 3 parts by weight of high-temperature fluid loss reducer, 0.25 parts by weight of dispersant, 0.25 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a cement slurry system J1 with a density of 1.91 g / cm 3 ³.

[0067] Example 2

[0068] Mix 75 parts by weight of G-class oil well cement, 25 parts by weight of active material, 4 parts by weight of chemical activator, 9 parts by weight of a new toughening agent, and 1.5 parts by weight of an expansive agent (the weight ratio of MgO to CaO is 1:1, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 3:4:3) evenly to obtain a mixture; mix 9 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 1 part by weight of high-temperature fluid loss reducer, 0.4 parts by weight of dispersant, 0.2 parts by weight of defoamer, 1 part by weight of high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a cement slurry system J2 with a density of 1.91 g / cm 3 ³.

[0069] Example 3

[0070] Mix 65 parts by weight of G-class oil well cement, 35 parts by weight of active material, 5 parts by weight of chemical activator, 11 parts by weight of a new toughening agent, and 1 part by weight of an expansion agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 3:3:2) evenly to obtain a mixture; mix 5 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 1 part by weight of a high-temperature fluid loss reducer, 0.3 part by weight of a dispersant, 0.4 part by weight of an antifoaming agent, 1 part by weight of a high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a well cement slurry system J3 with a density of 1.91 g / cm 3 3.

[0071] Example 4

[0072] Mix 80 parts by weight of G-class oil well cement, 35 parts by weight of active material, 3 parts by weight of chemical activator, 8 parts by weight of a new toughening agent, and 3 parts by weight of an expansion agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 3:3:3) evenly to obtain a mixture; mix 8 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 2 parts by weight of a high-temperature fluid loss reducer, 0.5 part by weight of a dispersant, 0.6 part by weight of an antifoaming agent, 2 parts by weight of a high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a well cement slurry system J4 with a density of 1.91 g / cm 3 4.

[0073] Example 5

[0074] Mix 85 parts by weight of G-class oil well cement, 25 parts by weight of active material, 4 parts by weight of chemical activator, 4 parts by weight of a new toughening agent, and 3 parts by weight of an expansion agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 3:4:2) evenly to obtain a mixture; mix 4 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 2 parts by weight of a high-temperature fluid loss reducer, 0.8 part by weight of a dispersant, 0.8 part by weight of an antifoaming agent, 2 parts by weight of a high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a well cement slurry system J5 with a density of 1.91 g / cm 3 6.

[0075] Example 6

[0076] Mix 90 parts by weight of G-class oil well cement, 40 parts by weight of active material, 5 parts by weight of chemical activator, 12 parts by weight of a new toughening agent, and 5 parts by weight of an expansive agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 4:4:2) evenly to obtain a mixture; mix 10 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 3 parts by weight of high-temperature fluid loss reducer, 1 part by weight of dispersant, 1 part by weight of defoamer, 3 parts by weight of high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a cement slurry system J6 with a density of 1.91 g / cm 3 of the well cementing slurry system J6.

[0077] Example 7

[0078] Mix 60 parts by weight of G-class oil well cement, 20 parts by weight of active material, 3 parts by weight of chemical activator, 3 parts by weight of a new toughening agent, and 0.5 part by weight of an expansive agent (the weight ratio of MgO to CaO is 1:2, and the mass ratio of high-activity MgO, medium-activity MgO, and low-activity MgO is 4:3:3) evenly to obtain a mixture; mix 3 parts by weight of nano-oxides (a mixture of SiO2 and Al2O3 with a weight ratio of 1:0.4), 1 part by weight of high-temperature fluid loss reducer, 0.1 part by weight of dispersant, 0.2 part by weight of defoamer, 0.5 part by weight of high-efficiency retarder, and water to obtain slurry-making water; then mix the slurry-making water with the above mixture on a high-speed mixer at a speed of 4000 revolutions per minute to obtain a cement slurry system J7 with a density of 1.91 g / cm 3 of the well cementing slurry system J7.

[0079] Comparative Example 1

[0080] Mix 80 parts by weight of G-class oil well cement, 3 parts by weight of high-temperature fluid loss reducer, 0.25 part by weight of high-efficiency polycarboxylate dispersant, 0.25 part by weight of defoamer, 1 part by weight of high-efficiency retarder, and water to obtain a cement slurry system J10 with a density of 1.91 g / cm 3 of the well cementing slurry system J10.

[0081] Comparative Example 2

[0082] Compared with Example 1, the difference is that in Comparative Example 2, unmodified volcanic ash is added to obtain a cement slurry system J11 with a density of 1.91 g / cm 3 of the well cementing slurry system J11.

[0083] Comparative Example 3

[0084] Compared with Example 1, the difference is that in Comparative Example 3, volcanic ash modified with an amino-silane coupling agent is added to obtain a cement slurry system J11 with a density of 1.92 g / cm 3The well cement slurry system J 12.

[0085] Comparative Example 4

[0086] Compared with Example 1, the difference is that in Comparative Example 4, the mass ratio of the amino silane coupling agent, pozzolan, and vinyl silane coupling agent in the active material is 1:5:2. The obtained well cement slurry system J 13 has a density of 1.92 g / cm 3

[0087] Comparative Example 5

[0088] Compared with Example 1, the difference is that in Comparative Example 5, only graphene oxide modified carbon fiber is used.

[0089] Comparative Example 6

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

[0091] Comparative Example 7

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

[0093] Comparative Example 8

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

[0095] Comparative Example 9

[0096] Compared with Example 1, the difference is that in Comparative Example 9, the particle size range of the nano-oxide is 10 - 15 nm.

[0097] Comparative Example 10

[0098] Compared with Example 1, the difference is that in Comparative Example 10, the MgO in the expansive agent is obtained by calcining at 1000 °C for 0.5 - 1 h and then rapidly cooled by air quenching and crushed.

[0099] Comparative Example 11

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

[0101] Comparative Example 12

[0102] Compared with Example 1, the difference lies in that: in Comparative Example 12, the MgO in the expansive agent is only highly reactive magnesium oxide.

[0103] The upper and lower density differences of the cement slurry systems obtained in the above examples and comparative examples are all 0.

[0104] The cement slurry systems Jn and the combined body of surrounding rock cement stone obtained in the above examples and comparative examples were cured for 24 h, 72 h and 7 days in an environment of 90 °C to obtain the corresponding cement stones Sn.

[0105] According to GB_T 19139-2012 Test Methods for Oil Well Cement, the density, fluidity, bleeding water amount and upper and lower density difference of the cement slurry systems and the properties of the cement stones obtained in each example and comparative example were tested. The density, fluidity, bleeding water amount and upper and lower density difference of the obtained well cementing slurry system were all measured under the conditions of 25 °C and normal pressure. The test results are shown in Table 1 below:

[0106] Table 1

[0107]

[0108]

[0109] It can be seen from the results in Table 1 that the compressive strength, bonding strength, linear expansion rate and 7-day elastic modulus of the cement stones obtained in Examples 1-7 have better effects compared with other comparative examples.

[0110] Compared with the conventional cement stone of Comparative Example 1, the elasticity and toughness of the cement stones obtained in Examples 1-7 increased significantly, the bonding strength with the surrounding rock interface increased greatly, the compressive strength increased at high temperature, and the expansion rate was large;

[0111] In Comparative Example 2, unmodified active materials were added, and the obtained cement stone had low strength and low bonding strength; in Comparative Example 3, pozzolan modified with an amino silane coupling agent was added, and the obtained cement stone had high strength and high bonding strength; but compared with Example 1, the performance was still slightly inferior;

[0112] In Comparative Example 4, an excessive amount of vinyl silane coupling agent was added, which excessively restricted the hydration process, hindered its chemical bonding with the hydration products (such as Ca(OH)2, C-S-H gel) in the cement slurry, reduced the interface bonding strength, resulting in a decrease in mechanical properties, and the compressive strength of the obtained cement stone and the interface bonding strength with the surrounding rock both decreased;

[0113] Comparative Example 5 added carbon fibers modified only with graphene oxide, without the combined action of coconut fibers and modified basalt fibers, resulting in a low strength of the cement stone and a low bonding strength; Comparative Example 6 added an excessive amount of coconut fibers, and the strength of the resulting cement stone decreased compared to Example 1; Comparative Example 7 added an excessive amount of basalt fibers, and the strength of the resulting cement stone decreased compared to Example 1, while the elastic modulus increased; in Comparative Example 8, the toughening agent was only fibers, and due to the lack of emulsion polymers, the fiber dispersibility decreased and the performance decreased due to local aggregation; the combination of the modified carbon fibers, modified basalt fibers and coconut fibers provided in the present application can well improve the overall performance of the cement stone;

[0114] Comparative Example 9 added nano-oxides with too large particle sizes, and the strength and elastic modulus of the resulting cement stone decreased compared to Example 1;

[0115] Comparative Example 10 added MgO calcined at too high a temperature, and the expansion rate decreased due to partial inactivation; Comparative Example 11 added MgO cooled naturally, and the MgO grains had sufficient time to grow, forming large-sized crystals, resulting in a decrease in specific surface area and a reduction in active sites, leading to a decrease in the expansion rate; in Comparative Example 12, the MgO in the expansive agent was only highly active magnesium oxide, and it could not continuously and effectively compensate for the late shrinkage of the cement, resulting in a decrease in the expansion rate.

[0116] In summary, by using the active materials, toughening materials and expansive agents in combination with other components, the cement slurry of the present invention can endow the cement slurry with advantages such as high temperature resistance, high toughness, micro-expansion, strong bonding, good rheology, etc., is suitable for cementing in underground gas storage caverns, can improve the cementing quality of the formation section, and ensure the sealing integrity of the cement sheath under frequent injection and production.

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

Claims

1. A high-toughness and slightly expansive cement slurry applicable to high-temperature well cementing, characterized in that, The cement slurry comprises the following raw materials in parts by weight: 60-90 parts by weight of G-class 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 expansive agent, 3-5 parts by weight of chemical activator, 1-3 parts by weight of high-temperature fluid loss reducer, 0.5-3 parts by weight of high-temperature retarder, 0.1-1 part by weight of dispersant, and 0.2-1 part by weight of defoamer; The active material is volcanic ash hydrophobically modified by a combination of amino-silane coupling agent and vinyl-silane coupling agent; the mass ratio of amino-silane coupling agent, volcanic ash, and vinyl-silane 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.

2. The highly ductile slightly expanding cement slurry applicable to high-temperature well cementing according to claim 1, wherein The preparation process of the active material is as follows: Mix anhydrous ethanol and deionized water as the solvent, and prepare solutions with a content of 0.5 wt% of both amino-silane coupling agent and vinyl-silane coupling agent respectively; first add the volcanic ash to the above solution of amino-silane coupling agent, adjust the pH with glacial acetic acid and then carry out the first grafting reaction; then add it to the above solution of vinyl-silane coupling agent for the second grafting reaction, and then wash and dry to obtain.

3. The highly ductile slightly expandable cement slurry applicable to high-temperature well cementing according to claim 2, wherein: The mass ratio of anhydrous ethanol to deionized water is 1:9; ultrasonic dispersion is used for the grafting reaction during the preparation process of the active material; glacial acetic acid adjusts the pH to 4-5; the conditions for the first grafting reaction are reaction at 58-60 °C for 2.5-3 hours, and the conditions for the second grafting reaction are reaction at 28-30 °C for 1-1.5 hours.

4. The highly ductile and slightly expandable cement slurry applicable to high-temperature well cementing according to claim 1, characterized in that, 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, then add concentrated H2SO4, and mix evenly under ice bath conditions; add KMnO4 in three portions; after ice bath for 30-35 minutes, raise the temperature to 35-40 °C and keep warm for 24-26 hours; pour the mixture into deionized water, dropwise add 30% H2O2 until the solution turns golden yellow; finally, perform ultrasonic separation, wash with deionized water to obtain an aqueous solution of graphene oxide; pretreat the carbon fiber under the condition of 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 °C for 2-2.5 hours, and then heat-treat at 180-185 °C for 48-50 hours to obtain the modified carbon fiber; the dosage of potassium permanganate is 3 times the mass of artificial graphite.

5. The highly ductile slightly expandable cement slurry applicable to high-temperature well cementing according to claim 1, characterized in that The modified basalt fiber is obtained through the following steps: Ultrasonically soak the basalt fiber in a mixed solution of ethanol-acetone at a ratio of 1:1 for 1 h, then rinse with deionized water, and then dry in an oven at 55-60 °C for 7-8 h; mix the pretreated basalt fiber with an amino-functionalizing reagent or a vinyl-functionalizing reagent, ultrasonically disperse and heat, and after the reaction is completed, wash and dry to obtain the modified basalt fiber.

6. The highly ductile slightly expanding cement slurry applicable to high-temperature well cementing according to claim 1, characterized in that, The coconut fiber is obtained through the following steps: after the coconut shell is shredded, it is treated with 10% m / v sodium hydroxide, then bleached with sodium chlorite and acetic acid, and dried at 70 - 72 °C for 110 - 120 min.

7. The highly ductile slightly expandable cement slurry applicable to high-temperature well cementing according to claim 1, characterized in that: The nano-oxide is a mixture of SiO2 and Al2O3. Among them, the particle size ranges of both SiO2 and Al2O3 are 10 - 15 nm, and the weight ratio of SiO2 to Al2O3 is 1:(0.3 - 0.5).

8. The highly ductile and slightly expandable cement slurry applicable to high-temperature cementing according to claim 1, characterized in that: The expansive agent is a magnesium oxide-calcium oxide composite expansive agent, and the weight ratio of MgO to CaO is 1:(1 - 2); the MgO adopts a multi-stage active MgO mixture, in which the mass ratio of high-active MgO, medium-active MgO, and low-active MgO is (3 - 4):(3 - 4):(2 - 3); the high-active MgO is obtained by calcining magnesite at 800 - 900 °C for 0.5 - 1 h and then rapidly cooling, cooling, and crushing; the medium-active MgO is obtained by calcining magnesite at 900 - 1100 °C for 0.5 - 1 h and then moderately cooling and crushing; the low-active MgO is obtained by calcining magnesite at 1100 - 1300 °C for 0.5 - 1 h and then naturally cooling in the air and crushing; the rapid cooling method is: air quenching, and the air flow rate is 20 - 40 m / s; the medium cooling method is: air quenching, and the air flow rate is 10 - 15 m / s.

9. The highly ductile slightly expandable cement slurry applicable to high-temperature well 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 fluid loss reducer is selected from any one of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), acrylic acid (AA), and N-vinylpyrrolidone (NVP); the high-temperature retarder is selected from any one of lignosulfonates, AMPS types, and double-layer hydrotalcite types; the dispersant is a polycarboxylate dispersant; the defoamer is selected from any one of polyether defoamers, polysiloxanes, and polyether-modified silicone oils.

10. A method for preparing a highly ductile and slightly expansive cement slurry applicable to high-temperature well cementing, as described in any one of claims 1-9, characterized in that, It includes the following steps: (1) uniformly mix G-class oil well cement, active materials, nano-silica, dispersant, and expansive agent to obtain dry materials; (2) uniformly mix the chemical activator, high-performance toughening agent, high-temperature fluid loss reducer, high-temperature retarder, and defoamer with water to obtain liquid materials; (3) after the dry materials are uniformly mixed, start to slowly add the liquid materials. After the liquid materials are completely added, continue to stir for 1 - 2 minutes to ensure that the cement is completely uniform, and a cement slurry system is obtained.

11. Application of a high-toughness and slightly expanding cement slurry suitable for high-temperature well cementing in well cementing of high-temperature gas storage reservoirs, characterized in that: The high-toughness slightly expansive cement slurry applicable to high-temperature well cementing is the high-toughness slightly expansive cement slurry applicable to high-temperature well cementing described in any one of claims 1 - 9 or the high-toughness slightly expansive cement slurry applicable to high-temperature well cementing obtained by the preparation method described in claim 10.

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