1. The preparation method of the cement slurry toughening agent is characterized by comprising the following steps:

adding acid liquor into the carbon fiber with a clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber;

adding nanoparticles into a solvent, performing ultrasonic dispersion at 30 ℃ for 30min, adding aminopropyltriethoxysilane, stirring at 30-70 ℃ for 2-12 h, reacting the nanoparticles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing with absolute ethyl alcohol for multiple times, and performing vacuum drying at 70 ℃ for 24h to obtain surface-modified nanoparticles;

adding the surface-modified nano particles into methanol, performing ultrasonic dispersion for 30min, adding the surface-modified carbon fibers, stirring for 4-8 h at 60 ℃, reacting the surface-modified nano particles with the surface-modified carbon fibers in the stirring process, cooling to room temperature after reaction, washing for multiple times by water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

2. The preparation method of the cement slurry toughening agent according to claim 1, wherein the surface-modified nano particles are 0.1 to 0.5 part by weight, the methanol is 100 parts by weight, and the surface-modified carbon fibers are 1 to 5 parts by weight.

3. The preparation method of the cement slurry toughening agent according to claim 2, wherein the nano particles are 0.5 to 3 parts by weight, the solvent is 100 parts by weight, and the aminopropyltriethoxysilane is 0.3 to 3 parts by weight.

4. The method for preparing the cement slurry toughening agent according to claim 1, wherein the nano particles are nano alumina particles or nano silica particles.

5. The method for preparing the cement slurry toughening agent according to claim 1, wherein the solvent is a mixture of absolute ethyl alcohol and deionized water.

6. The preparation method of the cement slurry toughening agent according to claim 5, wherein the volume ratio of the absolute ethyl alcohol to the deionized water is 0:100, 50:50 or 70: 30.

7. The preparation method of the cement slurry toughening agent according to claim 1, wherein the acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid according to a volume ratio of 75: 25.

8. The preparation method of the cement slurry toughening agent according to claim 1, further comprising:

chopping carbon fibers, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours;

and after extraction is finished, washing the carbon fiber with water for multiple times, and drying the carbon fiber in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with clean surface.

9. The cement paste is characterized by comprising the following components in parts by weight:

100 parts of cement, 30-45 parts of a stabilizer, 0-70 parts of a density regulator, 35-65 parts of water, 0.5-2 parts of a dispersant, 0.5-5 parts of a fluid loss agent, 0.5-3 parts of a retarder, 0.1-1 part of a defoaming agent and 3-10 parts of a cement slurry toughening agent prepared by the preparation method of the cement slurry toughening agent according to any one of claims 1-8.

10. A method of preparing a cement slurry according to claim 9, characterized in that it comprises:

mixing cement, a cement slurry toughening agent, a stabilizing agent and a density regulator according to the weight parts of the components to obtain dry powder;

adding water into a mixing container, and adding a dispersing agent, a fluid loss agent, a retarder and a defoaming agent into the water to obtain an aqueous solution;

stirring the aqueous solution at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement paste.

Background

At present, shale gas which is an important component of national energy is mainly developed by means of staged volume fracturing. However, the pressure adopted by the sectional volume fracturing is high, the times are many, and frequent pressure changes can cause well-cemented cement stones to be easily damaged, so that the production life of the shale gas well is influenced. Because the set cement is formed after the cement paste is solidified, the toughness of the set cement can be improved by adding the cement paste toughening agent into the cement paste, so that the production life of the shale gas well is prolonged.

In the related art, the cement slurry toughening agent is mainly organic fiber, and the organic fiber can be polyvinyl alcohol fiber, cellulose fiber or polypropylene fiber and the like.

However, the organic fiber in the related art has poor temperature resistance, is unstable at high temperature, and has reduced mechanical properties, so that the toughness of the set cement cannot be effectively improved.

Disclosure of Invention

The embodiment of the application provides a preparation method of a cement slurry toughening agent, cement slurry and a preparation method thereof, which can effectively improve the toughness of set cement. The specific technical scheme is as follows:

in one aspect, an embodiment of the present application provides a preparation method of a cement slurry toughening agent, where the preparation method of the cement slurry toughening agent includes:

adding acid liquor into the carbon fiber with a clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber;

adding nanoparticles into a solvent, performing ultrasonic dispersion at 30 ℃ for 30min, adding aminopropyltriethoxysilane, stirring at 30-70 ℃ for 2-12 h, reacting the nanoparticles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing with absolute ethyl alcohol for multiple times, and performing vacuum drying at 70 ℃ for 24h to obtain surface-modified nanoparticles;

adding the surface-modified nano particles into methanol, performing ultrasonic dispersion for 30min, adding the surface-modified carbon fibers, stirring for 4-8 h at 60 ℃, reacting the surface-modified nano particles with the surface-modified carbon fibers in the stirring process, cooling to room temperature after reaction, washing for multiple times by water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

In one possible implementation manner, the surface-modified nanoparticles are 0.1 to 0.5 parts by weight, the methanol is 100 parts by weight, and the surface-modified carbon fibers are 1 to 5 parts by weight.

In another possible implementation manner, the nano particles are 0.5 to 3 parts by weight, the solvent is 100 parts by weight, and the aminopropyltriethoxysilane is 0.3 to 3 parts by weight.

In another possible implementation, the nanoparticles are nano alumina particles or nano silica particles.

In another possible implementation, the solvent is a mixture of absolute ethanol and deionized water.

In another possible implementation, the volume ratio of the absolute ethanol to the deionized water is 0:100, 50:50, or 70: 30.

In another possible implementation manner, the acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 75: 25.

In another possible implementation manner, the preparation method of the cement slurry toughening agent further includes:

chopping carbon fibers, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours;

and after extraction is finished, washing the carbon fiber with water for multiple times, and drying the carbon fiber in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with clean surface.

On the other hand, the embodiment of the application provides cement paste, which comprises the following components in parts by weight:

100 parts of cement, 30-45 parts of a stabilizer, 0-70 parts of a density regulator, 35-65 parts of water, 0.5-2 parts of a dispersant, 0.5-5 parts of a fluid loss agent, 0.5-3 parts of a retarder, 0.1-1 part of a defoaming agent and 3-10 parts of a cement slurry toughening agent prepared by the preparation method of the cement slurry toughening agent according to any one of claims 1-8.

On the other hand, the embodiment of the application also provides a preparation method of cement paste, and the preparation method of the cement paste comprises the following steps:

mixing cement, a cement slurry toughening agent, a stabilizing agent and a density regulator according to the weight parts of the components to obtain dry powder;

adding water into a mixing container, and adding a dispersing agent, a fluid loss agent, a retarder and a defoaming agent into the water to obtain an aqueous solution;

stirring the aqueous solution at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement paste.

The technical scheme provided by the embodiment of the application has the following beneficial effects:

the embodiment of the application provides a preparation method of a cement slurry toughening agent, the preparation method comprises the steps of modifying carbon fibers and nano particles respectively to obtain surface-modified carbon fibers and surface-modified nano particles, then controlling the temperature and time to enable the surface-modified nano particles to react with the surface-modified carbon fibers, and combining in a chemical bonding mode to obtain the cement slurry toughening agent.

Drawings

Fig. 1 is a flowchart of a preparation method of a cement slurry toughening agent provided in an embodiment of the present application.

Detailed Description

In order to make the technical solutions and advantages of the present application more clear, the following describes the embodiments of the present application in further detail.

The embodiment of the application provides a preparation method of a cement slurry toughening agent, and referring to fig. 1, the preparation method comprises the following steps:

step 101: and (2) chopping the carbon fibers, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours.

In this step, the carbon fiber can be chopped by a chopping machine, and the length of the chopped carbon fiber can be 1-3 mm.

In the embodiment of the application, the carbon fiber with the length can improve the dispersibility of the carbon fiber, so that the carbon fiber is uniformly dispersed in cement paste subsequently, the safety and performance of cement paste construction are not influenced, and the requirements of shale gas well cementing and cementing operation are met.

In the step, acetone is used as a solvent and added into the Soxhlet extractor, and the acetone is used for continuously extracting impurities on the surface of the carbon fiber, so that the cleaning effect is realized.

Step 102: and after extraction is finished, washing the carbon fiber with water for multiple times, and drying the carbon fiber in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with a clean surface.

In the step, the carbon fiber obtained in the step 101 can be washed by deionized water for multiple times, so that acetone can be prevented from remaining on the surface of the carbon fiber, and impurity ions can be prevented from being introduced.

Here, the number of washing may be set and changed as needed, for example, the number of washing may be 3 or 4.

In the embodiment of the application, the surface of the carbon fiber is cleaned before modification treatment is carried out on the carbon fiber, so that the modification effect can be improved.

Step 103: adding acid liquor into the carbon fiber with clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber.

In the step, the acid solution is a mixture of concentrated nitric acid and concentrated sulfuric acid, wherein the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 75: 25. The concentrated nitric acid and the concentrated sulfuric acid have strong oxidation effect, and the carbon fiber can be oxidized by the concentrated nitric acid and the concentrated sulfuric acid to be modified, so that the surface modified carbon fiber is obtained. Moreover, the carbon fibers and the acid liquor can be fully mixed through ultrasonic dispersion, and the oxidation of the acid liquor is promoted. In addition, standing for 3h can make the acid solution fully oxidize the carbon fiber.

In this step, the carbon fiber after the treatment may be washed by deionized water, and the number of washing times may be set and changed as needed, which is not specifically limited in this embodiment of the application.

Step 104: adding nanoparticles into a solvent, performing ultrasonic dispersion at 30 ℃ for 30min, adding aminopropyltriethoxysilane, stirring at 30-70 ℃ for 2-12 h, reacting the nanoparticles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing with absolute ethanol for multiple times, and performing vacuum drying at 70 ℃ for 24h to obtain the surface-modified nanoparticles.

In the step, the nanoparticles are added into the solvent to be dissolved in the solvent, the nanoparticles and aminopropyltriethoxysilane are subjected to chemical reaction in the stirring process, the siloxy groups in the aminopropyltriethoxysilane have reaction activity on inorganic matters, the nanoparticles can be grafted onto the aminopropyltriethoxysilane by controlling the temperature and time, and the aminopropyltriethoxysilane are combined in a chemical bonding mode to form stable covalent bonds, so that the surface-modified nanoparticles are obtained. Because the nanoparticles and the aminopropyltriethoxysilane are combined through covalent bonds and are relatively stable, the stability of the obtained surface-modified nanoparticles under a high-temperature condition can be ensured.

In the present embodiment, the nanoparticles may be nano alumina (Al)₂O₃) Granular or nanosilica (SiO)₂) And (3) granules. The nano-particles are inorganic nano-particles, and the nano-particles obtained by modifying the inorganic nano-particles can effectively improve the cohesiveness and toughness of the cement matrix on the basis of ensuring the original performance of the carbon fibers.

In one possible implementation, the amount of the nanoparticles is 0.5 to 3 parts by weight, the amount of the solvent is 100 parts by weight, and the amount of aminopropyltriethoxysilane is 0.3 to 3 parts by weight.

In one possible implementation, the solvent may be a mixture of absolute ethanol and deionized water. The ratio of absolute ethanol to deionized water can be 0:100, 50:50, or 70:30 by volume.

Step 105: adding the surface-modified nano particles into methanol, dispersing for 30min after overtime, adding the surface-modified carbon fibers, stirring for 4-8 h at 60 ℃, reacting the surface-modified nano particles with the surface-modified carbon fibers in the stirring process, cooling to room temperature after reaction, washing for multiple times by water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

In the step, the surface modified nano particles are added into methanol to be dissolved in the methanol, amino in aminopropyltriethoxysilane has reaction activity on organic matters, the surface modified carbon fibers are oxidized into carboxyl by acid liquor after being treated by the acid liquor, and the carboxyl and the amino are subjected to chemical reaction, so that the surface modified nano particles and the surface modified carbon fibers are combined together.

Wherein the surface-modified nanoparticles are 0.1 to 0.5 part by weight, the methanol is 100 parts by weight, and the surface-modified carbon fibers are 1 to 5 parts by weight.

In the embodiment of the application, one side of aminopropyltriethoxysilane is connected with nanoparticles in a chemical bonding mode, the other side of aminopropyltriethoxysilane is also connected with carbon fibers in a chemical bonding mode, and a firm and stable grafting layer is formed on the surface of the carbon fibers, so that the stability of the cement slurry toughening agent under a high-temperature condition can be ensured. In addition, the nanoparticles on the surface of the surface-modified carbon fiber can induce and generate a large amount of hydration products with uniform size on the surface of the carbon fiber under the action of the nano crystal nucleus sites, so that the adhesion of a cement matrix on the surface of the carbon fiber is effectively improved. In addition, the nano particles belong to cement mineral components, can participate in cement hydration reaction by self to promote the development of early strength of cement, and ensure the development of compressive strength while improving the toughness of the set cement.

The embodiment of the application provides a preparation method of a cement slurry toughening agent, the preparation method comprises the steps of modifying carbon fibers and nano particles respectively to obtain surface-modified carbon fibers and surface-modified nano particles, then controlling the temperature and time to enable the surface-modified nano particles to react with the surface-modified carbon fibers, and combining in a chemical bonding mode to obtain the cement slurry toughening agent.

The cement slurry toughening agent prepared by the preparation method can keep better stability under the high-temperature condition, so the cement slurry toughening agent is suitable for cement slurry used for deep shale gas-solid wells. In addition, the preparation method has the advantages of simple process, convenient operation and good product consistency.

The embodiment of the application provides cement paste which comprises the following components in parts by weight:

100 parts of cement, 30-45 parts of a stabilizer, 0-70 parts of a density regulator, 35-65 parts of water, 0.5-2 parts of a dispersing agent, 0.5-5 parts of a fluid loss agent, 0.5-3 parts of a retarder, 0.1-1 part of a defoaming agent and 3-10 parts of a cement slurry toughening agent prepared by the preparation method of the cement slurry toughening agent.

In one possible implementation, the cement may be a high sulfate-resistant class G oil well cement.

In one possible implementation, the stabilizer is a high temperature stabilizer including at least one of silicon powder and microsilica. In this implementation, the weight fraction of the stabilizer can be set and changed as desired, for example, the weight fraction of the stabilizer can be 30, 32, 35, 38, 40, 42, or 45.

In one possible implementation, the density regulator can be iron ore powder or barite. In this implementation, the weight fraction of the density modifier may be set and changed as desired, for example, the weight fraction of the density modifier may be 0, 10, 20, 30, 40, 50, 60, or 70.

In one possible implementation, the dispersant includes at least one of a formaldehyde acetone condensate and sodium polystyrene sulfonate. In this implementation, the weight fraction of the dispersant can be set and changed as desired, for example, the weight fraction of the dispersant can be 0.5, 0.8, 1, 1.5, 1.8, or 2.

In one possible implementation, the fluid loss additive includes at least one of carboxymethyl cellulose and hydroxyethyl cellulose. In this implementation, the weight parts of the fluid loss agent may be set and changed as needed, for example, the weight parts of the fluid loss agent may be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5.

In one possible implementation, the retarder includes at least one of sodium lignosulfonate, sodium gluconate, and citric acid. In this implementation, the weight parts of the retarder can be set and changed as desired, for example, the weight parts of the retarder can be 0.5, 0.8, 1, 1.5, 1.8, 2, 2.5, or 3.

In one possible implementation, the defoamer can be a polyvinyl ether. In this implementation, the weight fraction of the anti-foaming agent can be set and changed as desired, for example, the weight fraction of the anti-foaming agent can be 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 0.9, or 1.

In one possible implementation, the weight parts of the cement slurry toughening agent may be set and changed as needed, for example, the weight parts of the cement slurry toughening agent may be 3, 4, 5, 6, 7, 8, 9, or 10.

The embodiment of the application provides cement slurry, a cement slurry toughening agent is added into the cement slurry, the toughness of set cement can be improved by adding the cement slurry toughening agent, and the cement slurry toughening agent is compounded with other components in a synergistic manner, so that the compressive strength of the set cement can be improved, the fracturing operation requirement is ensured, the cement slurry toughening agent can be uniformly dispersed in water, the construction safety and performance of the cement slurry are not influenced, and the cementing operation requirement of shale gas well cementing can be met.

The embodiment of the application also provides a preparation method of the cement paste, which comprises the following steps:

step 201: according to the weight parts of the components, the cement paste toughening agent, the stabilizing agent and the density regulator are mixed to obtain dry powder.

Step 202: adding water into the mixing container, and adding a dispersing agent, a fluid loss agent, a retarder and a defoaming agent into the water to obtain an aqueous solution.

Step 203: stirring the aqueous solution at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement slurry.

In this step, the aqueous solution and the mixture of the aqueous solution and the dry powder may be stirred by a stirrer.

The preparation method of the cement paste has simple process and convenient operation,

the technical solution of the present application will be described in detail by specific embodiments below.

In the following examples, those whose operations are not subject to the conditions indicated, are carried out according to the conventional conditions or conditions recommended by the manufacturer. The raw materials are conventional products which can be obtained commercially by manufacturers and specifications.

Example 1

Preparation of cement slurry toughening agent

Step 1: and (3) chopping the carbon fibers to 1-3 mm, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours. And after extraction is finished, washing the carbon fiber with deionized water for 3 times, and drying in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with a clean surface.

Step 2: adding acid liquor into the carbon fiber with clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber with deionized water to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber.

Wherein the acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid according to the volume ratio of 75: 25.

And step 3: adding 1 part by weight of nano alumina particles into 100 parts of solvent, performing ultrasonic dispersion at 30 ℃ for 30min, then adding 2 parts by weight of aminopropyltriethoxysilane, stirring for 6h at 50 ℃ by using a magnetic stirrer, reacting the nano particles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing for 3 times by using absolute ethyl alcohol, and performing vacuum drying at 70 ℃ for 24h to obtain the surface-modified nano particles.

Wherein the solvent is obtained by mixing absolute ethyl alcohol and deionized water according to the volume ratio of 70: 30.

And 4, step 4: adding 0.5 part by weight of surface-modified nano particles into 100 parts by weight of methanol, performing ultrasonic dispersion for 30min, adding 1 part by weight of surface-modified carbon fibers, performing magnetic stirring for 4h at 60 ℃, cooling to room temperature, washing for 3 times with deionized water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

Secondly, preparation of cement paste

Step 1: 100 parts by weight of cement, 0-10 parts by weight of cement slurry toughening agent, 30 parts by weight of silicon powder and 40 parts by weight of iron ore powder are mixed to obtain dry powder.

Wherein the cement slurry toughening agent is 0, 3, 5 and 7 in parts by weight respectively.

Step 2: 40 parts by weight of water was added to the mixing vessel, and 1.5 parts by weight of a formaldehyde acetone condensate, 4 parts by weight of hydroxyethyl cellulose, 3 parts by weight of sodium gluconate, and 0.2 part by weight of polyvinyl ether were added to the water to obtain an aqueous solution.

And step 3: stirring the aqueous solution by a stirrer at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement paste.

Example 2

Preparation of cement slurry toughening agent

Step 1: and (3) chopping the carbon fibers to 1-3 mm, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours. And after extraction is finished, washing the carbon fiber with deionized water for 3 times, and drying in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with a clean surface.

Step 2: adding acid liquor into the carbon fiber with clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber with deionized water to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber.

Wherein the acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid according to the volume ratio of 75: 25.

And step 3: adding 1.5 parts by weight of nano silicon dioxide particles into 100 parts of deionized water, performing ultrasonic dispersion at 30 ℃ for 30min, then adding 3 parts by weight of aminopropyltriethoxysilane, stirring for 4h at 30 ℃ by using a magnetic stirrer, reacting the nano particles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing for 3 times by using absolute ethyl alcohol, and performing vacuum drying at 70 ℃ for 24h to obtain the surface-modified nano particles.

And 4, step 4: adding 0.3 part by weight of surface-modified nano particles into 100 parts by weight of methanol, performing ultrasonic dispersion for 30min, adding 3 parts by weight of surface-modified carbon fibers, performing magnetic stirring for 6h at 60 ℃, cooling to room temperature, washing for 3 times with deionized water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

Secondly, preparation of cement paste

Step 1: mixing 100 parts by weight of cement, 0-10 parts by weight of cement paste toughening agent, 35 parts by weight of silicon powder and 5 parts by weight of micro silicon powder to obtain dry powder.

Wherein the cement slurry toughening agent is 0, 3, 5 and 7 in parts by weight respectively.

Step 2: adding 45 parts by weight of water into a mixing container, and adding 2 parts by weight of sodium styrene sulfonate, 3.5 parts by weight of carboxymethyl cellulose, 3 parts by weight of sodium gluconate and 0.2 part by weight of polyvinyl ether into the water to obtain an aqueous solution.

And step 3: stirring the aqueous solution by a stirrer at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement paste.

Example 3

Preparation of cement slurry toughening agent

Step 1: and (3) chopping the carbon fibers to 1-3 mm, putting the chopped carbon fibers into a Soxhlet extractor, adding acetone, and extracting for 48 hours. And after extraction is finished, washing the carbon fiber with deionized water for 3 times, and drying in vacuum at 70 ℃ for 24 hours to obtain the carbon fiber with a clean surface.

Step 2: adding acid liquor into the carbon fiber with clean surface, performing ultrasonic dispersion for 30min at 65 ℃, standing for 3h, washing the treated carbon fiber with deionized water to be neutral, and performing vacuum drying for 24h at 70 ℃ to obtain the surface-modified carbon fiber.

Wherein the acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid according to the volume ratio of 75: 25.

And step 3: adding 3 parts by weight of nano silicon dioxide particles into 100 parts of solvent, performing ultrasonic dispersion at 30 ℃ for 30min, then adding 3 parts by weight of aminopropyltriethoxysilane, stirring for 10h at 70 ℃ by using a magnetic stirrer, reacting the nano particles with the aminopropyltriethoxysilane during stirring, cooling to room temperature after reaction, performing centrifugal precipitation, filtering, washing for 3 times by using absolute ethyl alcohol, and performing vacuum drying at 70 ℃ for 24h to obtain the surface-modified nano particles.

Wherein the solvent is obtained by mixing absolute ethyl alcohol and deionized water according to the volume ratio of 50: 50.

And 4, step 4: adding 0.4 part by weight of surface-modified nano particles into 100 parts by weight of methanol, performing ultrasonic dispersion for 30min, adding 2 parts by weight of surface-modified carbon fibers, performing magnetic stirring for 4h at 60 ℃, cooling to room temperature, washing for 3 times with deionized water, performing suction filtration, and performing vacuum drying for 24h at 70 ℃ to obtain the cement slurry toughening agent.

Secondly, preparation of cement paste

Step 1: mixing 100 parts by weight of cement, 0-10 parts by weight of cement slurry toughening agent, 35 parts by weight of silicon powder, 5 parts by weight of micro silicon powder and 20 parts by weight of iron ore powder to obtain dry powder.

Wherein the cement slurry toughening agent is 0, 3, 5 and 7 in parts by weight respectively.

Step 2: adding 45 parts by weight of water into a mixing container, and adding 2 parts by weight of sodium styrene sulfonate, 3 parts by weight of carboxymethyl cellulose, 3 parts by weight of sodium lignin sulfonate and 0.1 part by weight of polyvinyl ether into the water to obtain an aqueous solution.

And step 3: stirring the aqueous solution by a stirrer at 3800-4200 rpm, adding the dry powder within 15s, and continuously stirring for 35s at 11500-12500 rpm to obtain cement paste.

Application examples

In the application embodiment, the cement slurries prepared in the embodiments 1 to 3 are respectively tested. Wherein, the engineering performance and the compression strength of the cement paste are mainly tested according to the GB/T19139 standard, and the tensile strength and the Young modulus of the cement paste are tested according to the NB/T14004.2 standard. The conditions for testing the thickening time of the cement paste prepared in example 1 were: 130 ℃ multiplied by 90MPa (temperature rise time is 70min), and the cement curing conditions are as follows: 130 ℃ X21 MPa X7 d, the thickening time test conditions for the cement slurries prepared in example 2 are: the temperature is 120 ℃ and 70MPa (the temperature rise time is 60min), and the cement curing conditions are as follows: 120 ℃ X21 MPa X7 d, the thickening time test conditions for the cement slurries prepared in example 3 were: 135 ℃ and 90MPa (the temperature rise time is 70min), and the cement curing conditions are as follows: 135 ℃ X21 MPa X7 d.

Tables 1 to 3 show experimental data obtained by testing the slurries prepared in examples 1 to 3, respectively.

Table 1 experimental data obtained by testing the cement slurries prepared in example 1

Table 2 experimental data obtained by testing the cement slurries prepared in example 2

Table 3 experimental data obtained by testing the cement slurries prepared in example 3

The tensile strength tests in tables 1 to 3 employ the brazilian split test method.

As can be seen from the experimental data in table 1: when the cement paste toughening agent is not added, the compressive strength of the set cement is 24.02MPa, and after the cement paste toughening agent is added, the compressive strength of the set cement is improved to different degrees. In addition, when the cement paste toughening agent is not added, the tensile strength of the set cement is 2.15MPa, and after the cement paste toughening agent is added, the tensile strength of the set cement is 2.95MPa, 3.88MPa and 4.21MPa respectively, so that the following conditions can be seen: the tensile strength of the set cement is obviously improved. In addition, the Young's modulus of the set cement was 7525MPa when no cement slurry toughening agent was added, and the Young's modulus of the set cement was 6685MPa, 5759MPa and 5348MPa respectively after the cement slurry toughening agent was added, from which it can be seen that: the Young's modulus of the set cement is obviously reduced. The smaller the Young's modulus is, the better the elastic deformation capability of the set cement is, and the better the resilience under high pressure is.

The above conclusion can be obtained from the experimental data in tables 2 and 3, and therefore, the cement slurry toughening agent provided by the embodiment of the application has good stability at high temperature, and can obviously improve the compressive strength and tensile strength of cement stones for well cementation and reduce the young modulus of the cement stones when added into cement slurry.

The above description is only for facilitating the understanding of the technical solutions of the present application by those skilled in the art, and is not intended to limit the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.