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

Abstract

The invention provides nano rubber and carbon nanotube composite toughened oil well cement and a preparation method thereof. The nano rubber and carbon nanotube composite toughened oil well cement is prepared from the following raw materials in parts by weight: 90 to 120 parts of oil well cement, 40 to 60 parts of water, 2 to 10 parts of nano rubber, 0.02 to 0.1 part of carbon nanotube, 0.1 to 0.5 part of oil well cement dispersing agent and 0.2 to 1 part of defoaming agent. The invention also provides a preparation method of the cement. The set cement prepared from the nano rubber and carbon nanotube composite toughened oil well cement shows good mechanical and shrinkage properties at 30 DEG C, 60 DEG C and 90 DEG C, and has good construction performance, and the fluidity meets the well cementation construction requirements. The nano rubber and carbon nanotube composite toughened oil well cement can be used for design, research and development and application of a high-performance well cementation cement system, meets the long-acting sealing requirement of a cement sheath in a complex stress environment, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to a nano-rubber and carbon nanotube composite toughened oil well cement and a preparation method thereof, belonging to the technical field of oil and gas well cementing cement. Background Art

[0002] The long-term effective sealing of the cement sheath is an important guarantee for the safe production of oil and gas resources. In recent years, with the continuous deepening of exploration and development towards deep, low-permeability, unconventional and other resources, the proportion of complex oil and gas wells has increased year by year, and the service environment faced by the cement sheath of the well cementing is becoming increasingly harsh, putting forward higher requirements for the mechanical properties and volume stability of the oil well cement in the cementing project. As a brittle material, the cement stone has the characteristics of low tensile strength, poor impact resistance, weak deformation resistance, easy brittle cracking and easy shrinkage. Under the action of its own shrinkage stress, temperature and load in the well, the cement sheath is prone to micro-cracks and micro-annuli, forming a fluid channel for fluid flow, resulting in the failure of layer-by-layer sealing and affecting the long-term sealing of the wellbore. The oil and gas field is researching and developing toughened cement systems and micro-expansion cement systems to improve the sealing integrity of the cement sheath in complex environments. Generally, the elastic modulus is reduced and shrinkage is inhibited by separately adding elastic materials or expansion materials to the cement. However, while conventional elastic materials and expansion materials reduce the elastic modulus of the cement and improve shrinkage, they will have a greater adverse impact on the strength of the cement stone. How to reduce the elastic modulus of the cement stone and inhibit shrinkage without affecting the strength of the cement stone, so as to effectively improve the crack resistance, impact resistance and deformation resistance of the cement sheath, is the current technical difficulty and hot issue.

[0003] In the above research, rubber particles are a commonly used elastic material for cement stone. At present, the sizes of rubber particles incorporated into the oil well cement system are mainly above the micron level. Although it can achieve the effect of reducing the elastic modulus, due to the size effect of the rubber particles, the tensile performance of the cement stone is significantly reduced. On the other hand, due to the compatibility problem between materials, it is difficult to use elastic materials, expansion materials (such as magnesium oxide) and reinforcing materials (such as carbon nanotubes) simultaneously. At present, there is no oil well cement system with low elastic modulus, low shrinkage rate and high strength.

[0004] The prior art has disclosed various methods to solve the toughness problem of oil well cement. For example, CN201910340441.9 discloses a toughened oil well cement prepared 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 parameter of the toughness cement system of this technology still uses the traditional compressive strength instead of the tensile strength (the characteristic of the cement stone is low tensile strength), and there is no characterization description of the influence on the shrinkage performance. CN202210917661.5 discloses a physical method to modify the oil well cement slurry system toughened by natural rock asphalt. Compared with the cement stone without adding natural rock asphalt toughened by modification, the toughness of the cement stone formed after the hardening of the cement slurry body is increased by a large margin under the same curing temperature. However, this system lacks the comparison of the mechanical properties of the toughened cement at different temperatures, and the toughening effect at different temperatures needs to be clarified, and it also does not involve the description of the shrinkage performance of the cement stone.

[0005] The prior art represented by the above patents has certain effects in improving the elastic properties of the cement stone, etc., but in terms of comprehensive performance (elastic modulus, tensile strength, shrinkage rate and construction performance), it is still difficult to meet the long-term sealing requirements of the cement sheath under current and future harsh service conditions. Summary of the Invention

[0006] 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 its preparation method.

[0007] To achieve the above purpose, the present invention provides a nano-rubber and carbon nanotube composite toughened oil well cement, wherein, by weight, the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement includes:

[0008] 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 nanotube, 0.1 - 0.5 part of oil well cement dispersant, and 0.2 - 1 part of defoamer.

[0009] According to a specific embodiment of the present invention, preferably, by weight, the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement includes:

[0010] 100 parts of oil well cement, 44 parts of water, 4 parts of nano-rubber, 0.04 part of carbon nanotube, 0.2 part of oil well cement dispersant, and 0.5 part of defoamer.

[0011] According to a specific embodiment of the present invention, preferably, the oil well cement is G-class oil well cement.

[0012] According to a specific embodiment of the present invention, preferably, the nano-rubber is nitrile rubber. More preferably, the particle size of the nitrile rubber is 50-150 nm, and further preferably 50-100 nm.

[0013] According to a specific embodiment of the present invention, preferably, the carbon nanotubes are carboxylated multi-walled carbon nanotubes. More preferably, the length of the carbon nanotubes is 5-15 μm, the inner diameter is 3-5 nm, the outer diameter is 8-15 nm, and the specific surface area ≥ 250 m 2 / g.

[0014] 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.

[0015] According to a specific embodiment of the present invention, preferably, the oil well cement dispersant is a powdered sulfonated acetone formaldehyde condensate, in the form of a reddish-brown solid powder. The addition of the oil well cement dispersant can improve the rheology of the cement slurry.

[0016] According to a specific embodiment of the present invention, preferably, the carbon nanotube dispersant is TNWDIS with a long carbon chain structure as the main structure. One end of the carbon chain is an aromatic ring, and the other end is a hydrophilic group to form a non-ionic surfactant. 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 uniformly dispersed in water.

[0017] The core of the nano-rubber and carbon nanotube composite toughened oil well cement of the present invention is a nano-rubber material that can improve the elasticity and shrinkage characteristics of the cement stone, and a carbon nanotube that can enhance the strength of the cement stone: on the one hand, the incorporation of nano-rubber effectively reduces the free liquid of the oil well cement slurry, compensates for the autogenous shrinkage of the cement system, delays the setting time of the cement slurry, and reduces the elastic modulus of the cement stone. At the same time, based on the deficiency that the incorporation of a single nano-rubber leads to a reduction in compressive strength, carbon nanotubes are added to enhance the strength of the cement stone. Based on the ratio and preparation method of the present invention, the problem of compounding of nano-materials is solved, and the two materials can exert their respective properties, achieving that the cement stone has a low elastic modulus and a low shrinkage rate while having a high strength, meeting the long-term sealing requirements of the cement sheath under harsh mechanical environments.

[0018] The present invention also provides a preparation method of the above-mentioned nano-rubber and carbon nanotube composite toughened oil well cement, comprising the following steps:

[0019] Disperse the nano-rubber and carbon nanotubes respectively in an appropriate amount of water to prepare suspensions;

[0020] Mix the two suspensions, add well cement, well cement dispersant, and the remaining water, stir and mix, and add an antifoaming agent to obtain the nano-rubber and carbon nanotube composite toughened well cement.

[0021] According to a specific embodiment of the present invention, preferably, the preparation method includes the following specific steps:

[0022] (1) Prepare a nano-rubber suspension: Mix an appropriate amount of water with nano-rubber and stir, then perform ultrasonic dispersion to obtain a nano-rubber suspension;

[0023] (2) Prepare a carbon nanotube suspension: Mix an appropriate amount of water, carbon nanotubes, and a carbon nanotube dispersant and stir, then perform ultrasonic dispersion to obtain a carbon nanotube suspension;

[0024] (3) Prepare a nano-rubber / carbon nanotube toughened cement: Uniformly dry-mix well cement and a well cement dispersant to obtain a dry-mix, mix the nano-rubber suspension, carbon nanotube suspension, and the remaining water to obtain a mixed slurry, and under low-speed stirring, add the dry-mix to the mixed slurry, then stir at high speed and add an antifoaming agent to obtain the nano-rubber and carbon nanotube composite toughened well cement.

[0025] According to a specific embodiment of the present invention, preferably, the preparation method includes the following specific steps:

[0026] (1) Prepare a nano-rubber (NR) suspension (or solution): Take 150 g of mixing water in a beaker, place it on a magnetic stirrer, add the weighed NR, stir with a magnetic heating stirrer for 10 min, and after stirring, place it in an ultrasonic cleaner for ultrasonic dispersion for 20 min to obtain an NR suspension (or solution).

[0027] (2) Prepare a carbon nanotube (CNT) suspension (or solution): Take 100 g of mixing water in a beaker, weigh CNT and its dispersant TNWDIS according to a mass ratio of 1:1. First, add the dispersant TNWDIS to the beaker and stir on a magnetic heating stirrer until dissolved, then add CNT and stir for 20 min. Finally, place it in an ultrasonic cleaner and perform ultrasonic dispersion for 40 min to obtain a CNT suspension (or solution).

[0028] (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 (4000 r / min) of the mixer 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 is 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.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) Taking the ratio of tensile strength to elastic modulus as the toughening index, compared with the 3-day-old cement paste without adding 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 cured at 30°C, 60°C, and 90°C for 3 days was increased by 28.0%, 34.4%, and 41.3%, respectively.

[0031] (2) Compared with cement paste without adding nanomaterials, the self-shrinkage value of cement paste made of nano-rubber and carbon nanotube composite toughened oil well cement after 72 hours under different temperature curing is significantly reduced, that is, the nano-rubber / carbon nanotube composite nanomaterial has the effect of compensating for cement shrinkage.

[0032] (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 improving the strength. The addition of composite nanomaterials can effectively reduce the free liquid in cement slurry and has little effect on the rheology. It has good working performance and meets the needs of on-site cementing construction.

[0033] (4) The toughening material of the present invention uses nanomaterials, which are nanoscale in size 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.

[0034] In summary, the cement stone made of the nano-rubber and carbon nanotube composite toughened oil well cement of the present invention exhibits good mechanical and shrinkage properties at 30°C, 60°C and 90°C, has good construction performance, and the fluidity meets the requirements of cementing construction. The nano-rubber and carbon nanotube composite toughened oil well cement can be used for the design, development and application of high-performance cementing systems such as high-temperature and high-pressure gas wells, unconventional oil and gas wells, and gas storage wells, meeting the long-term sealing requirements of cement rings under complex stress environments, and has good application prospects. Brief Description of the Drawings

[0035] Figure 1 It is the autogenous shrinkage curve of hardened cement paste cured at different temperatures.

[0036] Figure 2 It is the cumulative curve of pore size distribution of hardened cement paste.

[0037] Figure 3 It is the SEM microstructure of the hardened cement paste prepared in the example. Detailed Description of the Invention

[0038] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0039] The raw materials of the examples and comparative examples are as follows:

[0040] The nano-rubber is nitrile rubber with a particle size of 50 - 150 nm;

[0041] The carbon nanotubes are carboxylated multi-walled carbon nanotubes produced by Shenzhen Suiheng Technology Co., Ltd., CAS: 308068 - 56 - 6; with 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 - 270 m 2 / g;

[0042] The oil well cement dispersant is a powdered sulfonated acetone formaldehyde condensate;

[0043] The carbon nanotube dispersant is TNWDIS with a main structure of a long carbon chain structure, a non-ionic surfactant with an aromatic ring at one end of the carbon chain and a hydrophilic group at the other end;

[0044] The defoaming agent is an organophosphate defoaming agent.

[0045] Example

[0046] This example provides a nano-rubber and carbon nanotube composite toughened oil well cement, and the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement includes: 600 g of G-class oil well cement + 264 g of water + 24 g of nano-rubber + 0.24 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoaming agent.

[0047] The nano-rubber and carbon nanotube composite toughened oil well cement is prepared by the following steps:

[0048] Dispersing the nano rubber and carbon nanotubes in water to obtain their respective dispersion solutions, wherein the carbon nanotubes need to be dispersed with the aid of a carbon nanotube dispersant, and then subjected to magnetic stirring for 10 minutes and ultrasonication for 45 minutes;

[0049] 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, and a defoaming agent is added during the high-speed stirring.

[0050] 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 paste was removed from the mold and the compressive strength, tensile strength and elastic modulus of the cement paste were tested according to the requirements of GB 10238-2015.

[0051] Comparative Example 1

[0052] This comparative example provides an oil well cement slurry, and 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.

[0053] 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 agitator and stirring for 15s, during which time the dry-mixed oil well cement and cement dispersant are slowly poured into the slurry cup, and then the agitator gear is switched to the high speed gear (12000r / min), and stirring is continued for 35s, during which time an appropriate amount of defoaming agent is added to defoam the cement slurry, and the cement slurry configuration is now complete.

[0054] 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 specification requirements.

[0055] Comparative Example 2

[0056] This comparative example provides an oil well cement slurry, and 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.

[0057] The oil well cement slurry is prepared through the following steps: weighing the above materials, dispersing the nano-rubber into water, magnetically stirring for 10 min and then ultrasonically treating for 45 min, adding Class G oil well cement and an oil well cement dispersant, and obtaining a uniformly mixed cement slurry by high-speed stirring, and adding an antifoaming agent during the high-speed stirring.

[0058] Test the conventional properties of the cement slurry, and pour the slurry into corresponding mechanical test molds, where the size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The size of the elastic modulus mold is Cure for 3 d in a water bath at 60 °C, remove the mold to take out the hardened cement, and test the compressive strength, tensile strength and elastic modulus of the hardened cement according to the specification requirements.

[0059] Comparative Example 3

[0060] This comparative example provides an oil well cement slurry, and the raw material composition of the oil well cement slurry includes: 600 g of Class G oil well cement + 264 g of water + 24 g of nano-rubber + 1.2 g of an oil well cement dispersant + 3 g of an antifoaming agent.

[0061] The oil well cement slurry is prepared through the following steps: weighing the above materials, dispersing the nano-rubber into water, magnetically stirring for 10 min and then ultrasonically treating for 45 min, adding Class G oil well cement and an oil well cement dispersant, and obtaining a uniformly mixed cement slurry by high-speed stirring, and adding an antifoaming agent during the high-speed stirring.

[0062] Test the conventional properties of the cement slurry, and pour the slurry into corresponding mechanical test molds, where the size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The size of the elastic modulus mold is Cure for 3 d in a water bath at 60 °C, remove the mold to take out the hardened cement, and test the compressive strength, tensile strength and elastic modulus of the hardened cement according to the specification requirements.

[0063] Comparative Example 4

[0064] This comparative example provides an oil well cement slurry, and the raw material composition of the oil well cement slurry includes: 600 g of Class G oil well cement + 264 g of water + 36 g of nano-rubber + 1.2 g of an oil well cement dispersant + 3 g of an antifoaming agent.

[0065] The oil well cement slurry is prepared through the following steps: weighing the above materials, dispersing the nano-rubber into water, magnetically stirring for 10 min and then ultrasonically treating for 45 min, adding Class G oil well cement and an oil well cement dispersant, and obtaining a uniformly mixed cement slurry by high-speed stirring, and adding an antifoaming agent during the high-speed stirring.

[0066] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. The size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The size of the elastic modulus mold is Cure for 3 days in a water bath at 60 °C, remove the mold and take out the hardened cement. Test the compressive strength, tensile strength and elastic modulus of the hardened cement according to the specification requirements.

[0067] Comparative Example 5

[0068] This comparative example provides an oil well cement slurry. The raw material composition of the oil well cement slurry includes: 600 g of G-class oil well cement + 264 g of water + 0.12 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoamer.

[0069] The oil well cement slurry is prepared by the following steps: Weigh the above materials, disperse the carbon nanotubes in water. The dispersion of carbon nanotubes requires the aid of a carbon nanotube dispersant. After magnetic stirring for 10 min, ultrasonic for 45 min, add G-class oil well cement and oil well cement dispersant, and obtain a uniformly mixed cement slurry by high-speed stirring. Add the defoamer during high-speed stirring.

[0070] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. The size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The size of the elastic modulus mold is Cure for 3 days in water baths at 30 °C, 60 °C and 90 °C respectively. Remove the mold and take out the hardened cement. Test the compressive strength, tensile strength and elastic modulus of the hardened cement according to the specification requirements.

[0071] Comparative Example 6

[0072] This comparative example provides an oil well cement slurry. The raw material composition of the oil well cement slurry includes: 600 g of G-class oil well cement + 264 g of water + 0.24 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoamer.

[0073] The oil well cement slurry is prepared by the following steps: Weigh the above materials, disperse the carbon nanotubes in water. The dispersion of carbon nanotubes requires the aid of a carbon nanotube dispersant. After magnetic stirring for 10 min, ultrasonic for 45 min, add G-class oil well cement and oil well cement dispersant, and obtain a uniformly mixed cement slurry by high-speed stirring. Add the defoamer during high-speed stirring.

[0074] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. The size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The mold size of the elastic modulus is Cure for 3 days in a water bath at 30 °C, 60 °C, and 90 °C respectively. Demold and take out the hardened cement paste, and test the compressive strength, tensile strength, and elastic modulus of the hardened cement paste according to the specification requirements.

[0075] Comparative Example 7

[0076] This comparative example provides an oil well cement slurry. The raw material composition of the oil well cement slurry includes: 600 g of G-class oil well cement + 264 g of water + 0.48 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoamer.

[0077] The oil well cement slurry is prepared by the following steps: Weigh the above materials, disperse the carbon nanotube material in water. The dispersion of carbon nanotubes requires the aid of a carbon nanotube dispersant. After magnetic stirring for 10 min, ultrasonicate for 45 min. Add G-class oil well cement and oil well cement dispersant, and obtain a uniformly mixed cement slurry by high-speed stirring. Add the defoamer during high-speed stirring.

[0078] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. Among them, the compressive mold size is 50.8 mm × 50.8 mm × 50.8 mm, and the tensile mold size is The mold size of the elastic modulus is Cure for 3 days in a water bath at 30 °C, 60 °C, and 90 °C respectively. Demold and take out the hardened cement paste, and test the compressive strength, tensile strength, and elastic modulus of the hardened cement paste according to the specification requirements.

[0079] Comparative Example 8

[0080] This comparative example provides an oil well cement slurry. The raw material composition of the oil well cement slurry includes: 600 g of G-class oil well cement + 264 g of water + 0.60 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoamer.

[0081] The oil well cement slurry is prepared by the following steps: Weigh the above materials, disperse the carbon nanotube material in the aqueous solution. The dispersion of carbon nanotubes requires the aid of a carbon nanotube dispersant. After magnetic stirring for 10 min, ultrasonicate for 45 min. Add G-class oil well cement and oil well cement dispersant, and obtain a uniformly mixed cement slurry by high-speed stirring. Add the defoamer during high-speed stirring.

[0082] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. Among them, the compressive mold size is 50.8 mm × 50.8 mm × 50.8 mm, and the tensile mold size is The mold size of the elastic modulus is Cure for 3 days in a water bath at 30°C, 60°C, and 90°C respectively. Demold and take out the hardened cement paste, and test the compressive strength, tensile strength, and elastic modulus of the hardened cement paste according to the specification requirements.

[0083] Comparative Example 9

[0084] This comparative example provides an oil well cement slurry. The raw material composition of the oil well cement slurry includes: 600 g of G-class oil well cement + 264 g of water + 24 g of nano-rubber + 0.24 g of carbon nanotubes + 1.2 g of oil well cement dispersant + 0.24 g of carbon nanotube dispersant + 3 g of defoamer.

[0085] The oil well cement slurry is prepared by the following steps: Weigh the above materials, disperse the nano-rubber and carbon nanotubes together in water. The dispersion of carbon nanotubes requires the aid of a carbon nanotube dispersant. After magnetic stirring for 10 min, ultrasonic for 45 min, add G-class oil well cement and oil well cement dispersant, and obtain a uniformly mixed cement paste by high-speed stirring. Add the defoamer during high-speed stirring.

[0086] Test the conventional properties of the cement slurry, and pour the slurry into the corresponding mechanical test molds. The size of the compressive mold is 50.8 mm × 50.8 mm × 50.8 mm, and the size of the tensile mold is The size of the elastic modulus mold is Cure for 3 days in a water bath at 30°C, 60°C, and 90°C respectively. Demold and take out the hardened cement paste, and test the compressive strength, tensile strength, and elastic modulus of the hardened cement paste according to the specification requirements.

[0087] (1) Evaluation of the engineering properties of the cement slurry

[0088] Table 1 Construction performance of the cement slurry in the examples

[0089] Name Free liquid content / % Fluidity / cm pH value Example 3.05 25.6 10.0 Comparative Example 1 3.97 27.3 10.0

[0090] 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 the conventional cement system, and at the same time has good fluidity, meeting the pumping requirements of on-site construction.

[0091] (2) Evaluation of the mechanical properties of the hardened cement paste

[0092] Table 2 Comparison of the mechanical properties of the hardened cement paste made from the examples and the comparative examples

[0093]

[0094]

[0095] The data in Table 2 show that 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 anti-deformation ability (tensile strength / elastic modulus) is increased by 34.3%. Compared with the single nano-rubber system (Comparative Examples 2-4), both the compressive and tensile strengths are greatly improved, and the anti-deformation ability is increased 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 increase in the anti-deformation ability of 9.1%-24.6%. Compared with the direct mixing system of two nano-materials with the same ratio (Comparative Example 9), both the compressive and tensile strengths are improved, and the anti-deformation ability is increased by 11.0%.

[0096] (3) Shrinkage performance evaluation

[0097] Figure 1 is the autogenous shrinkage curve of the cement stone cured at different temperatures. B, N4, and N4C4 correspond to Comparative Example 1, Comparative Example 3, and the Example respectively.

[0098] Figure 1 shows that under the conditions of 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 single nano-rubber system (Comparative Example 3), indicating that according to the configuration method and ratio provided by the present invention, the nano-rubber can exert its swelling performance.

[0099] (4) Temperature adaptability evaluation

[0100] Table 3 Mechanical properties of the cement stone made from the Example and Comparative Examples under different temperature conditions

[0101]

[0102]

[0103] The data in Table 3 show that under the conditions of 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 anti-deformation ability. Compared with the conventional system (Comparative Example 1), the anti-deformation ability is increased by 28.0%, 34.4%, and 41.3% respectively, and the system has good temperature adaptability.

[0104] (5) Microstructure evaluation

[0105] Figure 2 is the cumulative pore size distribution curve of the cement stone. B, N4, and N4C4 correspond to Comparative Example 1, Comparative Example 3, and the Example respectively.

[0106] Figure 2It 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 system 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 system density is less affected by the compounding.

[0107] Figure 3 It is the SEM microstructure of the cement stone made from the example. Figure 3 It shows that the nano-materials of the composite toughened oil well cement slurry system of the present invention provide nucleation sites for cement hydration, and at the same time can also reduce the crystal size of calcium hydroxide generated by hydration and optimize the microstructure of the gel composite material.

[0108] In summary, the results of the present invention can effectively reduce the free liquid of the cement slurry while maintaining the rheological properties of the cement slurry, effectively reduce the elastic modulus of the cement stone, inhibit shrinkage, and at the same time improve the tensile strength of the cement stone, so as to achieve the toughening and anti-shrinkage effects of the cement stone. The results of the present invention have good application prospects in cementing operations of special wells such as high-temperature and high-pressure gas wells, unconventional oil and gas wells, gas storage wells, deep and ultra-deep wells, etc. The content of the present invention is not limited to the above embodiments, and those skilled in the art in the same field can easily propose other embodiments within the technical guiding ideology of the present invention, but such embodiments are all included within the scope of the present invention.

Claims

1. A nano-rubber and carbon nanotube composite toughened oil well cement, wherein, Based on parts by weight, the raw material composition of the nano-rubber and carbon nanotube composite toughened oil well cement includes: 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 nanotube, 0.1 - 0.5 part of oil well cement dispersant, and 0.2 - 1 part of defoamer.

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

3. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein, The oil well cement is G-grade 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 - 150 nm.

6. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 1 or 2, wherein, The carbon nanotube is a carboxylated multi-walled carbon nanotube.

7. The nano-rubber and carbon nanotube composite toughened oil well cement according to claim 6, wherein, The length of the carbon nanotubes 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.

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

9. The preparation method of the nano-rubber and carbon nanotube composite toughened oil well cement according to any one of claims 1 - 8, comprising the following steps: Disperse the nano-rubber and carbon nanotube separately in an appropriate amount of water to prepare suspensions; Mix the two suspensions, add the oil well cement, oil well cement dispersant, and the remaining water, stir and mix, and add the defoamer to obtain the nano-rubber and carbon nanotube composite toughened oil well cement.

10. The preparation method according to claim 9, wherein, The preparation method includes the following specific steps: (1) Prepare the nano-rubber suspension: Mix and stir an appropriate amount of water and nano-rubber, and then perform ultrasonic dispersion to obtain the nano-rubber suspension; (2) Prepare the carbon nanotube suspension: Mix and stir an appropriate amount of water, carbon nanotube, and carbon nanotube dispersant, and then perform ultrasonic dispersion to obtain the carbon nanotube suspension; (3) Prepare the nano-rubber / carbon nanotube toughened cement: Uniformly dry-mix the oil well cement and oil well cement dispersant to obtain a dry-mix, mix the nano-rubber suspension, carbon nanotube suspension, and the remaining water to obtain a mixed slurry, and under low-speed stirring, add the dry-mix to the mixed slurry, then stir at high speed and add the defoamer to obtain the nano-rubber and carbon nanotube composite toughened oil well cement.

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