CN113004472B

CN113004472B - Nano drag reducer, preparation method thereof and slickwater fracturing fluid

Info

Publication number: CN113004472B
Application number: CN202110199927.2A
Authority: CN
Inventors: 周福建; 李根生; 姚二冬; 李源; 周志澎; 王旻; 周翠红
Original assignee: Beijing Kemaishi Oil Field Chemical Agent Technology Co ltd; China University of Petroleum Beijing
Current assignee: Beijing Kemaishi Oil Field Chemical Agent Technology Co ltd; China University of Petroleum Beijing
Priority date: 2021-02-23
Filing date: 2021-02-23
Publication date: 2022-05-20
Anticipated expiration: 2041-02-23
Also published as: CN113004472A

Abstract

The invention discloses a nano drag reducer, a preparation method thereof and slickwater fracturing fluid. The preparation method comprises the following steps: performing surface modification on a molybdenum disulfide nanosheet by using acrylamide to obtain a molybdenum disulfide nanosheet with a surface modified functional group; and copolymerizing the comonomer with the molybdenum disulfide nanosheet with the surface modified functional group to obtain the polyacrylamide modified molybdenum disulfide nanosheet. According to the invention, after the surface of molybdenum disulfide is modified with functional groups, polyacrylamide is modified on the surface of the molybdenum disulfide in a copolymerization mode, and a polyacrylamide molecular chain is introduced into the surface of the molybdenum disulfide to form the nano drag reducer. The drag reducer prepared by the preparation method has the advantages of shear resistance, salt resistance and good sand suspension.

Description

Nano drag reducer, preparation method thereof and slickwater fracturing fluid

Technical Field

The invention relates to the field of oil and gas field working fluids, in particular to a nano drag reducer, a preparation method thereof and a slickwater fracturing fluid.

Background

Shale gas reservoirs generally have the characteristics of extremely low porosity, low permeability, small throat radius and extremely low natural productivity, and therefore, production increasing measures such as hydraulic fracturing and the like are often required to improve the yield of shale gas wells in the exploration and development process of shale gas reservoirs. When the shale reservoir is fractured, fracturing fluid is required to enter natural fractures of the stratum, more natural fractures are communicated through the self fluid loss action on the basis of forming a certain number of main fractures, so that a large number of highly communicated fracture networks are formed, and the effect of improving the seepage area of the reservoir is achieved. Therefore, the shale reservoir fracturing modification needs a volume fracturing modification mode with large liquid amount and large displacement, and a slickwater fracturing liquid system becomes the first choice.

98.0-99.5 percent of the components in the slickwater fracturing fluid are sand mixing water, and the additive generally accounts for 0.5-2.0 percent of the total volume of the slickwater and comprises a resistance reducing agent, a surfactant, a scale inhibitor, a clay stabilizer, a bactericide and the like. Drag reducers are the core additives for slickwater fracturing fluids.

The conventional slickwater fracturing fluid system has the advantages of low friction resistance, low viscosity, low damage and the like, and has been widely applied to various large oil fields at home and abroad in recent years. Along with the continuous development of shale gas resources, more requirements are provided for the performance of the slickwater fracturing fluid, although the conventional slickwater fracturing fluid system can meet the construction requirements of large discharge capacity and large liquid amount during the fracturing of shale reservoirs, the sand adding content during the construction is low due to the poor salt tolerance and the low sand carrying capacity, the use amount of the slickwater fracturing fluid needs to be increased in order to reach the sand amount required by the construction design, the fracturing construction cost is increased, the resource waste is caused, and the problems that a large amount of flowback fluid after the fracturing construction easily causes environmental pollution and the like are solved.

Research shows that the molybdenum disulfide is added into the slickwater, so that the salt resistance and temperature resistance of a slickwater system can be improved, and the sand carrying performance of the slickwater fracturing fluid is improved. Firstly, the synthesis methods of molybdenum disulfide nanosheets are numerous, but the method for obtaining 1T-type molybdenum disulfide nanosheets by a hydrothermal synthesis method is few. Secondly, Chinese patent application CN109554169A mentions that molybdenum disulfide is taken as an additive, and a drag reducer for coiled tubing is prepared by compounding different substances. Chinese patent application CN110551493A discloses a method for preparing slickwater from molybdenum disulfide dispersion. The introduction of the molybdenum disulfide is to form a crossed network structure in a polymer matrix, and the thermodynamic performance of the material is effectively improved. However, molybdenum disulfide as an inorganic material is not easy to be uniformly dispersed in a polymer, so that organic matters, particularly polymer modified molybdenum disulfide, are paid particular attention and attention, and have become the focus and hot spot of research and development of novel slickwater fracturing fluids.

Disclosure of Invention

Based on the above background art, a first object of the present invention is to provide a method for preparing a nano drag reducer, in which a functional group is modified on a surface of molybdenum disulfide, polyacrylamide is modified on the surface of the molybdenum disulfide in a copolymerization manner, and a polyacrylamide molecular chain is introduced on the surface of the molybdenum disulfide to form the nano drag reducer.

The second purpose of the invention is to provide a nanometer drag reducer obtained by the preparation method.

The third purpose of the invention is to provide a slickwater fracturing fluid containing the nano drag reduction.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for preparing a nano drag reducer, comprising the steps of:

performing surface modification on a molybdenum disulfide nanosheet by using acrylamide to obtain a molybdenum disulfide nanosheet with a surface modified functional group;

and copolymerizing the comonomer with the molybdenum disulfide nanosheet with the surface modified functional group to obtain the polyacrylamide modified molybdenum disulfide nanosheet.

According to the preparation method of the present invention, preferably, the specific process of the copolymerization comprises:

adding a comonomer and a molybdenum disulfide nanosheet with a surface modified functional group into water, then adding a catalyst, and carrying out polymerization reaction under a vacuum condition; and after the reaction is finished, washing with acetone and ethanol in sequence to remove unreacted monomers, and drying to obtain the polyacrylamide modified molybdenum disulfide nanosheet.

According to the preparation method provided by the invention, preferably, the mass ratio of the comonomer to the molybdenum disulfide nanosheet with the surface modification functional group is 1: 1-1000: 1; preferably 1:1 to 100:1, and more preferably 8:1 to 40: 1.

According to the preparation method provided by the invention, preferably, the polyacrylamide modified molybdenum disulfide nanosheet is further crushed and sieved to enable the particle size to be 100-140 meshes.

According to the preparation method of the present invention, preferably, the comonomer includes one or a combination of two or more of Acrylic Acid (AA), Acrylamide (AM) and 2-acrylamido-2-methylpropanesulfonic Acid (AMPS).

According to the preparation method of the present invention, preferably, the catalyst in the polymerization reaction is ammonium persulfate-sodium bisulfite, potassium persulfate, sodium formaldehyde sulfoxylate or azobisisobutyramidine hydrochloride.

According to the preparation method of the invention, preferably, the addition amount of the catalyst is 0.1-0.5% of the total mass of the comonomer and the molybdenum disulfide nanosheet with the surface modification functional group.

According to the preparation method of the invention, preferably, the temperature of the polymerization reaction is 50-90 ℃ and the time is 3-8 h;

according to the preparation method provided by the invention, preferably, the drying temperature of the polyacrylamide modified molybdenum disulfide nanosheet is 40-60 ℃.

According to the preparation method of the invention, preferably, the process of surface modification of molybdenum disulfide nanosheets with acrylamide comprises:

adding molybdenum disulfide nanosheets and acrylamide into deionized water, stirring and reacting for 12-24 h, preferably 24h, then washing the product with the deionized water to remove unreacted acrylamide, and drying to obtain the molybdenum disulfide nanosheets with the surface modified functional group.

According to the preparation method provided by the invention, preferably, the mass ratio of the molybdenum disulfide nanosheet to the acrylamide is 1: 1-1: 10; preferably 1: 1.

According to the preparation method provided by the invention, preferably, after the molybdenum disulfide nanosheet and acrylamide are added into deionized water, ultrasonic treatment is carried out at room temperature for 15min to 60min, preferably 30min, and then stirring reaction is carried out at room temperature.

According to the preparation method of the invention, the power of the ultrasound is preferably 10 Hz-25 Hz, preferably 19.2 Hz; the rotation speed of the stirring is 500rpm to 1500rpm, preferably 1000 rpm.

According to the preparation method of the invention, the drying temperature is preferably 50-90 ℃, preferably 50 ℃.

According to the preparation method of the present invention, preferably, the size of the molybdenum disulfide nanosheet is 20nm × 30nm to 30nm × 50 nm.

According to the preparation method of the present invention, preferably, the molybdenum disulfide nanosheets are prepared by a hydrothermal synthesis method, including the steps of:

s101, adding a molybdenum source, a sulfur source and a reducing agent into water for mixing;

s102, carrying out hydrothermal reaction on the mixed solution of S101 at 160-240 ℃ for 6-12 h; more preferably, the temperature of the hydrothermal reaction is 180 ℃ and the time is 8 h;

and S103, washing a product after the hydrothermal reaction is finished with deionized water to obtain the molybdenum disulfide nanosheet.

The molybdenum disulfide has three crystal forms, namely 1T, 2H and 3R. 2H type in nature; because the surface of the 1T-type molybdenum disulfide nanosheet has defects, namely active sites, the modification can be carried out to obtain the composite material. Currently, molybdenum disulfide in 1T form obtained in a laboratory is usually subjected to lithium intercalation and ultrasonic treatment, and the molybdenum disulfide nanosheet in 1T form can be obtained through hydrothermal synthesis. According to the invention, the molybdenum disulfide nanosheet in the 1T shape is obtained by controlling the temperature, the molybdenum-sulfur ratio and the reducing agent.

Currently, different preparation methods are greatly different with respect to the size of the molybdenum disulfide nanosheet. The CVD method can prepare molybdenum disulfide nanosheets of any size, but are basically 2H type. Ultrasonic stripping method, which is 2H type if directly stripped; if the lithium intercalation method is adopted, 1T-type nanosheets can be obtained, but the size of the nanosheets is more than 80 nm. The size of the hydrothermal synthesis method is more than 60nm as reported in the literature. Therefore, no nanosheet below 50nm has been reported at present. It is well known that control of the size of nanomaterials is a very difficult problem. Therefore, the invention provides a method for the first time, which can realize the minimum size of about 20nm multiplied by 30nm by adopting a hydrothermal synthesis method.

The conventional drag reducer is a high polymer with a carbon chain structure, and when the drag reducer is subjected to shearing or high temperature, chain links are easily broken, so that the original functions are lost. Macroscopically, it appears as a decrease in the drag reduction ratio. When a divalent ion or a hypersalinity solution is encountered, the polymer molecular chain is limited in stretching and thus curls, or even precipitates from the solution. In order to increase the salt and temperature resistance of the drag reducer, increasing the rigidity of the molecules, such as increasing the temperature resistant functional group (sulfonic acid group), increasing the molecular weight, and the like, is often used. The invention adopts a nano composite structure to improve the temperature resistance and salt tolerance of molecules.

According to the preparation method of the present invention, preferably, the molybdenum source includes one or a combination of two or more of molybdenum trioxide, ammonium molybdate and sodium molybdate; more preferably, the molybdenum source is molybdenum trioxide.

According to the production method of the present invention, preferably, the sulfur source includes one or a combination of two or more of thiourea, sodium sulfide, and thiocarbamide.

According to the preparation method of the invention, preferably, the reducing agent in the preparation process of the molybdenum disulfide nanosheet comprises one or a combination of two or more of citric acid, hydrazine hydrate, urea, sodium sulfite and glucose.

According to the preparation method of the invention, preferably, the molar ratio of the molybdenum source to the sulfur source is 1: 2-1: 30, the reducing agent is 0.5-3 times of the total mass of the molybdenum source and the sulfur source.

In a preferred embodiment of the present invention, a method for preparing a nano drag reducer comprises the steps of:

s100, preparing a molybdenum disulfide nanosheet by a hydrothermal synthesis method, wherein the molybdenum disulfide nanosheet specifically comprises S101-S103;

s101, adding a molybdenum source, a sulfur source and a reducing agent into water, and stirring for 30 min;

s102, pouring the mixed solution of the S101 into a hydrothermal reaction kettle, and carrying out hydrothermal reaction for 6-12 h at 160-240 ℃;

s103, washing a product after the hydrothermal reaction is finished with deionized water to obtain molybdenum disulfide nanosheets;

s200, adding the synthesized molybdenum disulfide nanosheet and acrylamide into deionized water, and carrying out ultrasonic treatment for 30min at room temperature under 19.2 Hz; then stirring for 24 hours at the room temperature of 1000rpm, and modifying the surface functional group of the molybdenum disulfide nanosheet; then washing with deionized water to remove unreacted acrylamide, and drying to obtain a molybdenum disulfide nanosheet with a surface modified functional group;

s300, mixing a comonomer and the molybdenum disulfide nanosheet with the surface modified functional group in a mass ratio of 1: 1-1000: 1, adding the mixture into a Schlenk bottle, taking deionized water as a reaction solvent, then adding a catalyst, vacuumizing, and sealing a tube to perform polymerization reaction; and after the reaction is finished, repeatedly washing by using a large amount of acetone and ethanol to remove unreacted monomers, drying, further crushing and screening to obtain the polyacrylamide modified molybdenum disulfide nanosheet with the particle size of 100-140 meshes.

In a second aspect, the present invention provides a nano drag reducer obtained by the above preparation method. The drag reducer prepared by the preparation method has the advantages of shear resistance, salt resistance and good sand suspension.

When the nanometer drag reducer is dissolved in water, the nanometer sheets are used as crosslinking points to better wind and connect molecular chains together, so that the viscoelasticity of the solution is increased, and the sand suspending capacity of the solution is increased.

In a third aspect, the present invention provides a slickwater fracturing fluid comprising the above nano drag reducer.

Compared with the prior art, the invention has the beneficial effects that:

1) the invention obtains the small-size molybdenum disulfide nanosheet through a hydrothermal synthesis method.

2) The preparation method of the invention can effectively solve the defects of insufficient salt resistance and temperature resistance and poor sand suspension performance of the existing drag reducer. The polymer is copolymerized and grafted on the nano-sheets, so that the rigidity and the strength of the polymer can be increased, and the salt and temperature resistance can be improved. The polymer is spontaneously coiled in an aqueous solution, and when the nanosheet is added for modification, physical cross-linking points are increased, so that the viscosity of the solution is improved, and the sand suspension property is increased.

3) By modifying the surface of the molybdenum disulfide with functional groups, the dispersion condition of the molybdenum disulfide in the polymer can be improved, and the stability of the nanosheet material can be increased.

4) The nano drag reducer has small dosage, and the slickwater fracturing fluid with good performance can be obtained when the dosage of the drag reducer is 0.05-0.4% according to different construction conditions.

Drawings

Figure 1 is XPS experimental data for 1T-type molybdenum disulfide nanosheets prepared in example 1.

Fig. 2 is raman spectral data of 1T-type molybdenum disulfide nanosheets prepared in example 1.

Fig. 3 is an SEM image of molybdenum disulfide nanoplates prepared in example 1.

Fig. 4 is a schematic structural diagram of a molybdenum disulfide nanosheet with a surface modification functional group in example 1 of the present invention.

FIG. 5 is a graph of experimental data showing drag reduction rate with flow rate for a 20w mineralization of 0.1% drag reducing agent in example 4 and comparative example 4, respectively.

Fig. 6 is the nano drag reducer rheology as tested in example 5.

Detailed Description

In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.

All numerical designations herein (e.g., temperature, time, concentration, and weight, etc., including ranges for each) may generally be approximated as varied (+) or (-) in increments of 0.1 or 1.0, as appropriate. All numerical designations should be understood to be preceded by the term "about".

Example 1

This example produces a nano drag reducer comprising the steps of:

1) adding 1g of molybdenum trioxide powder, 5g of thiocarbamide and 8g of citric acid into 100mL of deionized water, and stirring for 30 min; then the mixed solution is poured into a hydrothermal reaction kettle and reacted for 12 hours at 180 ℃. And then, washing with deionized water to obtain the molybdenum disulfide nanosheet. Figure 1 is XPS experimental data of molybdenum disulfide nanoplates, with the average binding energy of molybdenum disulfide type 1T being 227,231ev and the average binding energy of molybdenum disulfide type 2H being 229ev, 232 ev; FIG. 2 is Raman spectrum data of molybdenum disulfide nanosheets, wherein the Raman spectrum is 146cm^-1The characteristic peak of (A) shows that the molybdenum disulfide is 1T type molybdenum disulfide. FIG. 3 is an SEM image of molybdenum disulfide nanosheets, with dimensions ranging from 23.4nm to 41.1 nm.

2) Adding the synthesized molybdenum disulfide nanosheet and acrylamide into deionized water according to the mass ratio of 1:1, and performing ultrasonic treatment for 30min at room temperature; then, the mixture was stirred at 1000rpm at room temperature for 24 hours. And then washing with deionized water to remove unreacted acrylamide, and drying at 50 ℃ to obtain the molybdenum disulfide nanosheet with the surface modified functional group. Fig. 4 is a structural schematic diagram of a molybdenum disulfide nanosheet with a surface modified functional group.

3) Adding 1g of molybdenum disulfide nanosheet with surface modified functional groups and 10g of acrylamide into a Schlenk bottle, taking deionized water as a reaction solvent, then adding 0.02g of catalyst (ammonium persulfate-sodium bisulfite), vacuumizing and sealing a tube to perform polymerization reaction; after the reaction is finished, a large amount of ethanol is used for washing to remove unreacted monomers, and polyacrylamide modified molybdenum disulfide nanosheets with the particle size of 100-140 meshes are obtained after drying at 50 ℃, further crushing and screening.

Example 2

This example produces a nano drag reducer comprising the steps of:

1) adding 0.1g of molybdenum trioxide powder, 1g of sodium sulfide and 0.6g of hydrazine hydrate into 50mL of deionized water, and stirring for 30 min; then the mixed solution was poured into a hydrothermal reaction kettle and reacted at 220 ℃ for 6 hours. And then, washing with deionized water to obtain the molybdenum disulfide nanosheet.

2) Adding the synthesized molybdenum disulfide nanosheet and acrylamide into deionized water according to the mass ratio of 1:1, and performing ultrasonic treatment for 30min at room temperature; then, the mixture was stirred at 1000rpm at room temperature for 24 hours. And then washing with deionized water to remove unreacted acrylamide, and drying at 50 ℃ to obtain the molybdenum disulfide nanosheet with the surface modified functional group.

3) Adding 0.1g of molybdenum disulfide nanosheet with surface modified functional groups and 4g of acrylamide into a Schlenk bottle, taking deionized water as a reaction solvent, then adding 0.01g of catalyst (ammonium persulfate-sodium bisulfite), vacuumizing and sealing a tube to perform polymerization reaction; after the reaction is finished, a large amount of ethanol is used for washing to remove unreacted monomers, and polyacrylamide modified molybdenum disulfide nanosheets with the particle size of 100-140 meshes are obtained after drying at 50 ℃, further crushing and screening.

Example 3

This example produces a nano drag reducer comprising the steps of:

1) adding 1g of molybdenum trioxide powder, 8g of thiourea, 3g of sodium sulfide and 10g of urea into 100mL of deionized water, and stirring for 30 min; then the mixed solution is poured into a hydrothermal reaction kettle and reacted for 10 hours at 200 ℃. And then, washing with deionized water to obtain the molybdenum disulfide nanosheet.

3) Adding 1g of molybdenum disulfide nanosheet with a surface modified functional group, 4g of acrylamide and 4g of acrylic acid into a Schlenk bottle, taking deionized water as a reaction solvent, then adding 0.04g of catalyst (ammonium persulfate-sodium bisulfite), vacuumizing and sealing a tube to perform polymerization reaction; after the reaction is finished, a large amount of ethanol is used for washing to remove unreacted monomers, and polyacrylamide modified molybdenum disulfide nanosheets with the particle size of 100-140 meshes are obtained after drying at 50 ℃, further crushing and screening.

Example 4

In this example, the drag reducer prepared in example 2 is tested for drag reduction performance, and the test includes the following steps:

1) preparing 2% KCl aqueous solution;

2) slowly adding the nanometer resistance reducing agent into a KCl aqueous solution at room temperature and 1500rad/min to prepare a 0.1 percent resistance reducing agent solution;

3) and (3) carrying out a drag reduction rate test on the straight pipe drag reduction rate test device. The results are shown in table 1 below and in fig. 5 for the nanodiamond drag reducer.

TABLE 1

Flow velocity m/s	1.38	2.76	4.14	5.53	6.91	8.29	9.67	11.05	12.43
										The resistance reduction rate%	52.6	67.1	69.3	73.9	78.0	78.5	80.1	79.1	79.5

As can be seen from FIG. 5, the nano drag reducer has good drag reduction performance, the highest drag reduction rate reaches 80%, and the nano drag reducer is superior to the conventional drag reducer in the market and meets the requirements of site construction.

Comparative example 4

The comparative example tests the resistance reducing agent of the resistance reducing agent PJ-1 prepared by compounding molybdenum disulfide nanosheets and polyacrylamide for resistance reducing performance, and the method comprises the following steps:

1) preparing 2% KCl aqueous solution;

2) slowly adding PJ-1 into a KCl aqueous solution at room temperature and 1500rad/min to prepare a 0.1% resistance reducing agent solution;

3) and (4) carrying out a drag reduction rate test on the straight pipe drag reduction rate test device. The results are shown in Table 2 below and in the PJ-1 curve in FIG. 5.

TABLE 2

Flow velocity m/s	1.38	2.76	4.14	5.53	6.91	8.29	9.67	11.05	12.43
										The resistance reduction rate%	21.1	52.6	55.0	69.9	72.3	72.2	74.6	72.6	71.8

As can be seen from FIG. 5, the drag reduction rate of PJ-1 is lower than that of the nano drag reducer, and the highest drag reduction rate of PJ-1 is 74.6% and lower than 80% of that of the nano drag reducer.

Example 5

This example performed a nano drag reducer rheological property test on the drag reducer prepared in example 2.

Preparing a fracturing fluid according to a formula, fully fracturing in a viscometer sample cup, and heating a sample. Controlling the temperature rise speed to be 3 ℃/min +/-0.2 ℃/min, starting the test from 30 ℃, and simultaneously enabling the rotor to have a shear rate of 170s^-1Rotating, and continuously shearing for 60min after the temperature reaches the temperature (130 ℃) required to be tested. And determining the temperature resistance and the shearing resistance of the fracturing fluid by using the relation among time, temperature and apparent viscosity corresponding to the value of the whole process. The results of the experiment are shown in FIG. 6.

And (3) analyzing an experimental result:

the drag reducer prepared in example 2 was formulated into a slickwater fracturing fluid at 0.4% according to the method of example 4. After the temperature rise is completed, 170s^-1The viscosity in the initial stage in the shearing process is high and reaches more than 200 mPas, the viscosity is reduced rapidly along with the shearing time, and the viscosity in the later stage is stabilized at 70 mPas.

The viscosity of the conventionally used slippery aqueous solution is about 5 mPas, so that the viscous sand suspending effect is not good. The slickwater fracturing fluid can reach 70 mPas. Effectively suspending sand with viscosity. The static sand suspension experiment can reach 40 minutes, which is far beyond the sand suspension time of conventional slickwater.

It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.

Claims

1. A method for preparing a nano drag reducer, the method comprising the steps of:

performing surface modification on the 1T-type molybdenum disulfide nanosheet by using acrylamide to obtain a molybdenum disulfide nanosheet with a surface modified functional group;

copolymerizing a comonomer with a molybdenum disulfide nanosheet with a surface modified functional group to obtain a polyacrylamide modified molybdenum disulfide nanosheet, namely a nano drag reducer;

the comonomer is acrylamide or a combination of acrylamide and acrylic acid;

the 1T-type molybdenum disulfide nanosheet is prepared through a hydrothermal synthesis method, and comprises the following steps:

the molybdenum source is one or the combination of more than two of molybdenum trioxide, ammonium molybdate and sodium molybdate; the sulfur source is one or the combination of more than two of thiourea, sodium sulfide and thiocarbamide; the reducing agent is one or the combination of more than two of citric acid, hydrazine hydrate, urea, sodium sulfite and glucose; the molar ratio of the molybdenum source to the sulfur source is 1: 2-1: 30, and the reducing agent is 0.5-3 times of the total mass of the molybdenum source and the sulfur source;

s102, carrying out hydrothermal reaction on the mixed solution of S101 at 160-240 ℃ for 6-12 h;

s103, washing a product after the hydrothermal reaction is finished with deionized water to obtain a 1T-type molybdenum disulfide nanosheet;

the process for performing surface modification on the 1T-type molybdenum disulfide nanosheet by using acrylamide comprises the following steps:

adding the 1T-type molybdenum disulfide nanosheet and acrylamide into deionized water, stirring and reacting for 12-24 h, then washing the product with the deionized water to remove unreacted acrylamide, and drying to obtain a molybdenum disulfide nanosheet with a surface modified functional group;

the specific process of the copolymerization comprises the following steps:

adding a comonomer and a molybdenum disulfide nanosheet with a surface modified functional group into water, then adding a catalyst, and carrying out polymerization reaction under a vacuum condition; and after the reaction is finished, washing to remove unreacted monomers, and drying to obtain the polyacrylamide modified molybdenum disulfide nanosheet.

2. The preparation method according to claim 1, wherein the mass ratio of the comonomer to the molybdenum disulfide nanosheet with the surface modification functional group is 1: 1-1000: 1.

3. The preparation method according to claim 1, wherein the polyacrylamide modified molybdenum disulfide nanosheets are further pulverized and sieved to have a particle size of 100-140 mesh.

4. The method of claim 1, wherein the catalyst is ammonium persulfate-sodium bisulfite, potassium persulfate, or azobisisobutyramidine hydrochloride.

5. The preparation method according to claim 1, wherein the addition amount of the catalyst is 0.1-0.5% of the total mass of the comonomer and the molybdenum disulfide nanosheet with the surface modification functional group.

6. The process according to claim 1, wherein the polymerization is carried out at a temperature of 50 ℃ to 90 ℃ for a time of 3 to 8 hours.

7. The production method according to claim 1, wherein the temperature of drying during the copolymerization is 40 ℃ to 60 ℃.

8. The preparation method according to claim 1, wherein in the process of surface modification of the 1T-type molybdenum disulfide nanosheets with acrylamide, the mass ratio of the 1T-type molybdenum disulfide nanosheets to the acrylamide is 1: 1-1: 10.

9. The preparation method of claim 1, wherein 1T-type molybdenum disulfide nanosheets and acrylamide are added to deionized water, and then subjected to ultrasonic treatment at room temperature for 15-60 min, and then stirred at room temperature for reaction.

10. The method according to claim 9, wherein the power of the ultrasound is 10Hz to 25 Hz; the rotating speed of the stirring is 500-1500 rpm.

11. The preparation method according to claim 1, wherein the drying temperature is 50-90 ℃ during the surface modification of the 1T-type molybdenum disulfide nanosheets with acrylamide.

12. The preparation method according to claim 1, wherein the size of the 1T-type molybdenum disulfide nanosheet is 20nm x 30nm to 30nm x 50 nm.

13. The preparation method according to claim 1, wherein the temperature of the hydrothermal reaction is 180 ℃ and the time is 8 h.

14. The method of claim 1, wherein the molybdenum source is molybdenum trioxide.

15. A nanodiamond drag reducer obtained by the method of any one of claims 1-14.

16. A slickwater fracturing fluid comprising the nano drag reducer of claim 15.