NANO rubber and carbon nanotube composite toughened oil well cement and preparation method therefor

Abstract

The present invention provides nano rubber and carbon nanotube composite toughened oil well cement and a preparation method therefor. In parts by weight, the raw material composition comprises: 90-120 parts of oil well cement, 40-60 parts of water, 2-10 parts of nano rubber, 0.02-0.1 part of carbon nanotubes, 0.1-0.5 part of an oil well cement dispersant, and 0.2-1 part of a defoaming agent. The present invention also provides a preparation method for the cement. Cement stone prepared by the present invention shows desirable mechanical and shrinkage performance, satisfies well cementation construction requirements in fluidity, can be used for high-performance well cementation cement system design, research, development and application, and satisfies long-acting sealing requirements of a cement ring in a complex stress environment.

Description

Nano-rubber and carbon nanotube composite toughened oil well cement and preparation method thereof

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on November 28, 2023, with application number 202311605302.7 and invention name “A nano-rubber and carbon nanotube composite toughened oil well cement and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The invention relates to a nano-rubber and carbon nano-tube composite toughened oil well cement and a preparation method thereof, belonging to the technical field of oil and gas well cementing cement. Background Art

[0004] The long-term and effective sealing of the cement sheath is an important guarantee for the safe production of oil and gas resources. In recent years, as exploration and development continue to deepen towards deep, low-permeability, and unconventional resources, the proportion of complex oil and gas wells has increased year by year. The service environment faced by cement sheaths has become increasingly harsh, and higher requirements have been placed on the mechanical properties and volume stability of oil well cement in cementing projects. As a brittle material, cement stone has the characteristics of low tensile strength, poor impact resistance, weak deformation resistance, and susceptibility to brittle cracking and shrinkage. Under the action of its own shrinkage stress, temperature, and load in the wellbore, the cement sheath is prone to microcracks and microannuli, forming fluid crossflow channels, causing interlayer isolation to fail and affecting the long-term sealing of the wellbore. The oil and gas field is developing toughened cement systems and micro-expansive cement systems to improve the sealing integrity of cement sheaths in complex environments. Generally, elastic materials or expansive materials are added separately to the cement to reduce the elastic modulus and inhibit shrinkage, respectively. However, while conventional elastic materials and expansive materials reduce the elastic modulus of cement and improve shrinkage, they also have a significant adverse effect on the strength of cement paste. How to reduce the elastic modulus of cement paste and inhibit shrinkage without affecting the strength of cement paste, thereby effectively improving the crack resistance, impact resistance and deformation resistance of the cement sheath, is a technical difficulty and hot issue in current research.

[0005] In the aforementioned research, rubber particles are a commonly used elastic material in cement paste. Currently, the rubber particles incorporated into oil-well cement systems are primarily micron-sized and larger. While this can reduce the elastic modulus, the size effect of the rubber particles significantly reduces the tensile properties of the cement paste. Furthermore, due to compatibility issues, the simultaneous use of elastic materials, expansive materials (such as magnesium oxide), and reinforcing materials (such as carbon nanotubes) is difficult. Currently, no oil-well cement system has achieved both low elastic modulus, low shrinkage, and high strength.

[0006] The prior art has disclosed a variety of methods to solve the toughness problem of oil well cement. For example, CN201910340441.9 discloses a toughened oil well cement made from a composite material of nano-carbon black and carbon nanotubes. The toughened oil well cement stone has the characteristics of low elastic modulus and high ultimate compressive strength. However, the characterization parameters of the toughness cement system of this technology still use traditional compressive strength rather than tensile strength (the characteristic of cement stone is low tensile strength). At the same time, there is no characterization description of the impact on shrinkage performance. CN202210917661.5 discloses an oil well cement slurry system toughened by natural rock asphalt modified by physical methods. The cement stone formed after the cement slurry hardens is compared with the cement stone toughened by unmodified natural rock asphalt. At the same curing temperature, the toughness of the cement stone is greatly improved. However, the toughened cement of this system lacks a comparison of the mechanical properties of the toughened cement at different temperatures. The toughening effect at different temperatures needs to be clarified, and there is also no description of the shrinkage performance of the cement stone.

[0007] Although the existing technology represented by the above-mentioned patent has certain effects in improving the elastic properties of cement stone, it is still difficult to meet the long-term sealing requirements of cement rings under current and future harsh service conditions in terms of comprehensive performance (elastic modulus, tensile strength, shrinkage rate and construction performance).

[0008] Summary of the Invention

[0009] In order to solve the above technical problems, the purpose of the present invention is to provide a nano-rubber and carbon nanotube composite toughened oil well cement and a preparation method thereof.

[0010] To achieve the above-mentioned object, the present invention provides a nano-rubber and carbon nanotube composite toughened oil well cement, wherein the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement comprises, in parts by weight:

[0011] 90-120 parts of oil well cement, 40-60 parts of water, 2-10 parts of nano rubber, 0.02-0.1 parts of carbon nanotubes, 0.1-0.5 parts of oil well cement dispersant, and 0.2-1 parts of defoaming agent.

[0012] According to a specific embodiment of the present invention, preferably, the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement comprises, in parts by weight:

[0013] 100 parts of oil well cement, 44 parts of water, 4 parts of nano rubber, 0.04 parts of carbon nanotubes, 0.2 parts of oil well cement dispersant, and 0.5 parts of defoaming agent.

[0014] According to a specific embodiment of the present invention, preferably, the oil well cement is Grade G oil well cement.

[0015] According to a specific embodiment of the present invention, preferably, the nano rubber is a nitrile rubber. More preferably, the particle size of the nitrile rubber is 50-150 nm, and further preferably 50-100 nm.

[0016] According to a specific embodiment of the present invention, preferably, the carbon nanotubes are carboxylated multi-walled carbon nanotubes. More preferably, the carbon nanotubes have a length of 5-15 μm, an inner diameter of 3-5 nm, an outer diameter of 8-15 nm, and a specific surface area of ​​≥250 m 2 / g.

[0017] According to a specific embodiment of the present invention, preferably, the nano-rubber and carbon nanotube composite toughened oil well cement further comprises 0.04 parts of a carbon nanotube dispersant.

[0018] According to a specific embodiment of the present invention, preferably, the oil well cement dispersant is a powdery sulfonated acetone formaldehyde condensation product in the form of reddish-brown solid powder. The addition of the oil well cement dispersant can improve the rheological properties of the cement slurry.

[0019] According to a specific embodiment of the present invention, preferably, the carbon nanotube dispersant is TNWDIS, the main structure of which is a long carbon chain structure, one end of the carbon chain is an aromatic ring, and the other end is a non-ionic surfactant composed of a hydrophilic group. In the carbon nanotube suspension, the aromatic ring at one end is connected to the surface of the carbon nanotube, and the hydrophilic group at the other end can be effectively and evenly dispersed in water.

[0020] The core of the nano-rubber and carbon nanotube composite toughened oil well cement of the present invention is a nano-rubber material that improves the elasticity and shrinkage properties of the cement paste, and carbon nanotubes that enhance the strength of the cement paste. On the one hand, the incorporation of the nano-rubber effectively reduces the free liquid in the oil well cement slurry, while compensating for the self-shrinkage of the cement system, delaying the setting time of the cement slurry, and reducing the elastic modulus of the cement paste. Furthermore, the addition of carbon nanotubes enhances the strength of the cement paste, as the incorporation of nano-rubber alone reduces compressive strength. The present invention's proportioning and configuration method solves the problem of compounding nanomaterials, allowing the two materials to fully utilize their respective properties, achieving a cement paste with a low elastic modulus and low shrinkage rate while also possessing high strength, meeting the long-term sealing requirements of cement sheaths in harsh mechanical environments.

[0021] The present invention also provides a method for preparing the nano-rubber and carbon nanotube composite toughened oil well cement, comprising the following steps:

[0022] Dispersing nano rubber and carbon nanotubes in appropriate amount of water to prepare suspension;

[0023] The two suspensions are mixed, and oil well cement, oil well cement dispersant and the remaining water are added, stirred and mixed, and a defoamer is added to obtain the nano-rubber and carbon nanotube composite toughened oil well cement.

[0024] According to a specific embodiment of the present invention, preferably, the preparation method comprises the following specific steps:

[0025] (1) preparing a nano rubber suspension: mixing an appropriate amount of water with the nano rubber, stirring, and then performing ultrasonic dispersion to obtain a nano rubber suspension;

[0026] (2) preparing a carbon nanotube suspension: mixing an appropriate amount of water, carbon nanotubes, and a carbon nanotube dispersant, and then performing ultrasonic dispersion to obtain a carbon nanotube suspension;

[0027] (3) preparing nano-rubber / carbon nanotube toughened cement: uniformly dry-mixing oil well cement and oil well cement dispersant to obtain a dry mixture, mixing the nano-rubber suspension, carbon nanotube suspension and remaining water to obtain a mixed slurry, adding the dry mixture to the mixed slurry under low-speed stirring, and then stirring at high speed and adding a defoaming agent to obtain the nano-rubber and carbon nanotube composite toughened oil well cement.

[0028] According to a specific embodiment of the present invention, preferably, the preparation method comprises the following specific steps:

[0029] (1) Prepare nano rubber (NR) suspension (or solution): Take 150 g of mixing water in a beaker, place it on a magnetic stirrer, add weighed NR, stir with a magnetic heating stirrer for 10 minutes, and after stirring, place it in an ultrasonic cleaner for ultrasonic dispersion for 20 minutes to obtain a NR suspension (or solution).

[0030] (2) Prepare carbon nanotube (CNT) suspension (or solution): Take 100 g of the mixed water and place it in a beaker. Weigh CNT and its dispersant TNWDIS in a mass ratio of 1:1. First, add the dispersant TNWDIS to the beaker and place it on a magnetic heating stirrer and stir until dissolved. Then add CNT and stir for 20 minutes. Finally, place it in an ultrasonic cleaner and ultrasonically disperse it for 40 minutes to obtain a CNT suspension (or solution).

[0031] (3) Preparation of nano-rubber / carbon nanotube toughened cement slurry: Weigh the oil well cement and cement dispersant and mix them evenly. Pour the prepared suspension (or solution) and the remaining mixing water into the slurry cup. Place the slurry cup on the base of the corrugated mixer. Turn on the low speed gear of the mixer (4000 r / min) and stir for 15 seconds. During this period, slowly pour the dry-mixed oil well cement and cement dispersant into the slurry cup (water-cement ratio of about 0.44). Then switch the mixer gear to high speed gear (12000 r / min) and continue stirring for 35 seconds. During this period, add an appropriate amount of defoaming agent to defoam the cement slurry. At this point, the cement slurry preparation is complete.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) Taking the ratio of tensile strength to elastic modulus as the toughening index, compared with the 3-day-old cement paste without the addition of nanomaterials, the toughening index of the cement paste made of the nano-rubber and carbon nanotube composite toughened oil well cement of the present invention, which was cured at 30°C, 60°C, and 90°C for 3 days, was increased by 28.0%, 34.4%, and 41.3%, respectively.

[0034] (2) Compared with cement paste without adding nanomaterials, the autogenous shrinkage value of the cement paste made of the nano-rubber and carbon nanotube composite toughened oil well cement of the present invention after 72 hours is significantly reduced under different temperature curing, that is, the nano-rubber / carbon nanotube composite nanomaterial has the effect of compensating for cement shrinkage.

[0035] (3) The nano-rubber and carbon nanotube composite toughened oil well cement of the present invention fully utilizes the effect of nano-rubber in reducing the elastic modulus and the effect of carbon nanotubes in increasing the strength. The addition of the composite nanomaterial can effectively reduce the free liquid in the cement slurry and has little effect on the rheological properties. It has good working performance and meets the needs of on-site cementing construction.

[0036] (4) The toughening material of the present invention uses nanomaterials, which are nano-sized and have a larger specific surface area. They can play a filling role in the cement matrix, improve the pore structure, and reduce the porosity; at the same time, they provide nucleation sites for cement hydration and accelerate cement hydration; in addition, the nanomaterials can also reduce the size of calcium hydroxide crystals generated by hydration and optimize the microstructure of the gel composite material.

[0037] In summary, the cement paste made from the nano-rubber and carbon nanotube composite toughened oil-well cement of the present invention exhibits excellent mechanical and shrinkage properties at 30°C, 60°C, and 90°C, along with good workability and fluidity that meets cementing requirements. This nano-rubber and carbon nanotube composite toughened oil-well cement can be used in the design, development, and application of high-performance cement systems for high-temperature, high-pressure gas wells, unconventional oil and gas wells, and gas storage wells. It meets the requirements for long-term cement sheath sealing in complex stress environments and has promising application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 shows the autogenous shrinkage curve of cement paste under different temperature curing.

[0039] Figure 2 is the cumulative pore size distribution curve of cement stone.

[0040] FIG3 is a scanning electron microscope microstructure of cement stone prepared in the embodiment. DETAILED DESCRIPTION

[0041] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0042] The raw materials of embodiment and comparative example are as follows:

[0043] Nano rubber is nitrile rubber with a particle size of 50-150nm;

[0044] The carbon nanotubes are carboxylated multi-walled carbon nanotubes, produced by Shenzhen Suiheng Technology Co., Ltd., CAS: 308068-56-6; the length is 5-15 μm, the inner diameter is 3-5 nm, the outer diameter is 8-15 nm, and the specific surface area is 250 m 2 / g-270m 2 / g;

[0045] Oil well cement dispersants are powdered sulfonated acetone formaldehyde condensation products;

[0046] The carbon nanotube dispersant is TNWDIS, which has a long carbon chain structure as its main body. One end of the carbon chain is an aromatic ring, and the other end is a non-ionic surfactant composed of a hydrophilic group.

[0047] The defoaming agent is an organophosphate defoaming agent.

[0048] Example

[0049] This embodiment provides a nano-rubber and carbon nanotube composite toughened oil well cement. The raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement includes: 600g G-grade oil well cement + 264g water + 24g nano-rubber + 0.24g carbon nanotubes + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0050] The nano rubber and carbon nanotube composite toughened oil well cement is prepared by the following steps:

[0051] The nano rubber and carbon nanotubes were dispersed in water to obtain their respective dispersion solutions. The carbon nanotubes were dispersed with the aid of a carbon nanotube dispersant. The mixture was magnetically stirred for 10 minutes and then ultrasonicated for 45 minutes.

[0052] The two solutions are mixed, and G-grade oil well cement and oil well cement dispersant are added, and stirred at high speed to obtain a uniformly mixed cement slurry. A defoaming agent is added during the high-speed stirring.

[0053] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the requirements of GB 10238-2015.

[0054] Comparative Example 1

[0055] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement+264g water+1.2g oil well cement dispersant+3g defoaming agent.

[0056] The oil well cement slurry is prepared by the following steps: uniformly dry-mixing G-grade oil well cement and cement dispersant, weighing mixing water according to a water-cement ratio of 0.44 and pouring it into a slurry cup, and placing the slurry cup on the base of a corrugated mixer; turning on the low speed gear (4000r / min) of the mixer and stirring for 15 seconds, during which time the dry-mixed oil well cement and cement dispersant are slowly poured into the slurry cup, and then switching the mixer gear to high speed gear (12000r / min), and continuing stirring for 35 seconds, during which time an appropriate amount of defoaming agent is added to defoam the cement slurry, and the cement slurry preparation is completed.

[0057] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0058] Comparative Example 2

[0059] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement+264g water+12g nano rubber+1.2g oil well cement dispersant+3g defoaming agent.

[0060] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the nano rubber in water, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0061] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a 60°C water bath for 3 days, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0062] Comparative Example 3

[0063] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement+264g water+24g nano rubber+1.2g oil well cement dispersant+3g defoaming agent.

[0064] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the nano rubber in water, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0065] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a 60°C water bath for 3 days, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0066] Comparative Example 4

[0067] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement+264g water+36g nano rubber+1.2g oil well cement dispersant+3g defoaming agent.

[0068] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the nano rubber in water, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0069] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a 60°C water bath for 3 days, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0070] Comparative Example 5

[0071] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement + 264g water + 0.12g carbon nanotubes + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0072] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing carbon nanotubes in water, using a carbon nanotube dispersant for the dispersion of the carbon nanotubes, magnetic stirring for 10 minutes and then ultrasonication for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0073] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0074] Comparative Example 6

[0075] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement + 264g water + 0.24g carbon nanotubes + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0076] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing carbon nanotubes in water, using a carbon nanotube dispersant for the dispersion of the carbon nanotubes, magnetic stirring for 10 minutes and then ultrasonication for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0077] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0078] Comparative Example 7

[0079] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement + 264g water + 0.48g carbon nanotubes + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0080] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the carbon nanotube material into water, using a carbon nanotube dispersant to disperse the carbon nanotubes, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0081] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0082] Comparative Example 8

[0083] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement + 264g water + 0.60g carbon nanotubes + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0084] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the carbon nanotubes into an aqueous solution, using a carbon nanotube dispersant to disperse the carbon nanotubes, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0085] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0086] Comparative Example 9

[0087] This comparative example provides an oil well cement slurry, the raw material composition of the oil well cement slurry includes: 600g G-grade oil well cement + 264g water + 24g nano rubber + 0.24g carbon nanotube + 1.2g oil well cement dispersant + 0.24g carbon nanotube dispersant + 3g defoaming agent.

[0088] The oil well cement slurry is prepared by the following steps: weighing the above materials, dispersing the nano rubber and carbon nanotubes in water, using a carbon nanotube dispersant to disperse the carbon nanotubes, magnetically stirring for 10 minutes and then ultrasonicating for 45 minutes, adding G-grade oil well cement and oil well cement dispersant, stirring at high speed to obtain a uniformly mixed cement slurry, and adding a defoaming agent during the high-speed stirring.

[0089] Test the conventional properties of cement slurry and pour the slurry into the corresponding mechanical test molds, where the compression mold size is 50.8mm×50.8mm×50.8mm and the tensile mold size is Elastic modulus mold size is After curing in a water bath at 30°C, 60°C and 90°C for 3 days respectively, the cement stone was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement stone were tested according to the specifications.

[0090] (1) Cement slurry engineering performance evaluation

[0091] Table 1 Construction performance of cement slurry in Examples and Comparative Examples

[0092] The data in Table 1 show that the free liquid ratio of the composite toughened oil well cement of the present invention is lower than that of conventional cement systems, and at the same time, it has good flow properties and meets the pumping requirements of on-site construction.

[0093] (2) Evaluation of mechanical properties of cement paste

[0094] Table 2 Comparison of mechanical properties of cement stone made in Example and cement stone made in Comparative Example

[0095] The data in Table 2 show that at 60°C, the elastic modulus of the cement stone made from the composite toughened oil well cement of the present invention is lower than that of the conventional cement system (Comparative Example 1), the tensile strength is higher than that of the conventional system, and the deformation resistance (tensile strength / elastic modulus) is improved by 34.3%. Compared with the single nano rubber system (Comparative Examples 2-4), the compressive and tensile strengths are greatly improved, and the deformation resistance is improved by 10.6%-20.0%. Compared with the single carbon nanotube system (Comparative Examples 5-8), although the compressive and tensile strengths are reduced, the elastic modulus decreases even more, resulting in an improvement of 9.1%-24.6% in deformation resistance. Compared with the system with the same ratio but two nano materials directly mixed (Comparative Example 9), the compressive and tensile strengths are improved, and the deformation resistance is improved by 11.0%.

[0096] (3) Shrinkage performance evaluation

[0097] FIG1 is the autogenous shrinkage curve of cement paste under different temperature curing, B, N4 and N4C4 correspond to comparative example 1, comparative example 3 and embodiment, respectively.

[0098] Figure 1 shows that at 30°C, 60°C, and 90°C, the shrinkage of the cement stone made from the composite toughened oil well cement slurry system of the present invention is significantly smaller than that of the conventional cement system (Comparative Example 1), and is generally equivalent to that of the system with only nano-rubber added (Comparative Example 3), indicating that the nano-rubber can exert its expansion performance according to the configuration method and ratio provided by the present invention.

[0099] (4) Temperature adaptability evaluation

[0100] Table 3 Mechanical properties of cement stones prepared in Examples and Comparative Examples under different temperature conditions

[0101] The data in Table 3 show that at 30°C, 60°C, and 90°C, the cement stone made from the composite toughened oil well cement slurry system of the present invention has good deformation resistance. Compared with the conventional system (Comparative Example 1), the deformation resistance is improved by 28.0%, 34.4%, and 41.3%, respectively, and the system has good temperature adaptability.

[0102] (5) Microstructure evaluation

[0103] FIG2 is a cumulative curve of pore size distribution of cement stone, where B, N4 and N4C4 correspond to comparative example 1, comparative example 3 and embodiment, respectively.

[0104] Figure 2 shows that compared with the conventional cement system (Comparative Example 1), the cement stone made from the composite toughened oil well cement slurry system of the present invention has a lower porosity and better density, which is close to that of the single nano-rubber system (Comparative Example 3), indicating that according to the configuration method and ratio provided by the present invention, the density of the system is less affected by the compounding.

[0105] Figure 3 shows the electron microscope scanning microstructure of the cement paste prepared in the embodiment. Figure 3 shows that the nanomaterials in the composite toughened oil well cement slurry system of the present invention provide nucleation sites for cement hydration, while also reducing the size of calcium hydroxide crystals generated by hydration, thereby optimizing the microstructure of the gel composite material.

[0106] In summary, the present invention can effectively reduce the free liquid in cement slurry while maintaining the rheological properties of the cement slurry, effectively reduce the elastic modulus of the cement paste, inhibit shrinkage, and simultaneously increase the tensile strength of the cement paste, thereby achieving the toughening and shrinkage resistance of the cement paste. The present invention has good application prospects in cementing operations in special wells such as high-temperature and high-pressure gas wells, unconventional oil and gas wells, gas storage wells, deep wells, and ultra-deep wells. The content of the present invention is not limited to the above-mentioned embodiments. Engineers and technicians in the same field can easily propose other embodiments within the technical guidance of the present invention, but such embodiments are all included in the scope of the present invention.

Claims

1. A nano rubber and carbon nanotube composite toughened oil well cement, wherein: The raw material composition of the nano rubber and carbon nano tube composite toughened oil well cement includes, by weight: 90-120 parts of oil well cement, 40-60 parts of water, 2-10 parts of nano rubber, 0.02-0.1 parts of carbon nanotubes, 0.1-0.5 parts of oil well cement dispersant, and 0.2-1 parts of defoaming agent.

2. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1, wherein: The raw material composition of the nano rubber and carbon nano tube composite toughened oil well cement includes, by weight: 100 parts of oil well cement, 44 parts of water, 4 parts of nano rubber, 0.04 parts of carbon nanotubes, 0.2 parts of oil well cement dispersant, and 0.5 parts of defoaming agent.

3. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein: The oil well cement is Grade G oil well cement.

4. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein: The nano rubber is nitrile rubber.

5. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 4, wherein: The particle size of the nitrile rubber is 50-150nm.

6. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein: The carbon nanotubes are multi-walled carbon nanotubes that have been carboxylated.

7. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 6, wherein: The carbon nanotube has a length of 5-15 μm, an inner diameter of 3-5 nm, an outer diameter of 8-15 nm, and a specific surface area of ​​≥250 m 2 / g.

8. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein: The nano-rubber and carbon nano-tube composite toughened oil well cement also includes 0.04 parts of carbon nano-tube dispersant.

9. The method for preparing the nano-rubber and carbon nanotube composite toughened oil well cement according to any one of claims 1 to 8, comprising the following steps: Dispersing nano rubber and carbon nanotubes in appropriate amount of water to prepare suspension; The two suspensions are mixed, and oil well cement, oil well cement dispersant and the remaining water are added, stirred and mixed, and a defoamer is added to obtain the nano rubber and carbon nano tube composite toughened oil well cement.

10. The preparation method according to claim 9, wherein: The preparation method comprises the following specific steps: (1) preparing a nano rubber suspension: mixing an appropriate amount of water and the nano rubber, stirring, and then performing ultrasonic dispersion to obtain a nano rubber suspension; (2) Prepare carbon nanotube suspension: Mix appropriate amount of water, carbon nanotubes and carbon nanotube dispersant and stir. Then, ultrasonic dispersion is performed to obtain a carbon nanotube suspension; (3) preparing nano-rubber / carbon nanotube toughened cement: uniformly dry-mixing oil well cement and oil well cement dispersant to obtain a dry-mixed material, mixing the nano-rubber suspension, carbon nanotube suspension and remaining water to obtain a mixed slurry, adding the dry-mixed material to the mixed slurry under low-speed stirring, and then stirring at high speed and adding a defoaming agent to obtain the nano-rubber and carbon nanotube composite toughened oil well cement.

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