CN114806535A - A modified nano-silica fluid and its preparation method and application, a slick water fracturing fluid and its application - Google Patents

Abstract

The invention provides a modified nano-silica fluid, a preparation method and application thereof, a slick water fracturing fluid and application thereof, belonging to the technical field of shale oil development. The modified nano-silica fluid of the present invention can enhance the interaction between the modified nano-silica and the slick water fracturing fluid through electrostatic action, etc., effectively reduce the oil-water interfacial tension, and change the wettability. The slick water fracturing fluid prepared by using the modified nano-silica fluid of the present invention can form a wedge-shaped structure in the oil-water-rock three-phase contact zone, and the generated structural separation pressure peels off the crude oil from the rock surface, thereby improving imbibition recovery rate. The results of the examples show that the maximum imbibition recovery rate of the modified nano-silica fluid reaches 12%, while the interfacial tension is reduced to 0.11mN/m, and the wetting transition reaches a maximum of 158°, and the oil droplets peel off in 8h. 151° was reached in the experiment.

Description

A modified nano-silica fluid and its preparation method and application, a slick water fracturing fluid and its application

technical field

The invention belongs to the technical field of shale oil development, and in particular relates to a modified nano-silica fluid, a preparation method and application thereof, a slick water fracturing fluid and its application.

Background technique

Shale oil has become a hot spot in the exploration and development of unconventional oil and gas resources in the world, affecting the strategic layout of energy in various countries. In the development process of shale oil, the imbibition replacement technology has become an important research direction to improve the single well production and prolong the production validity period. The driving of the well inlet fluid can spontaneously imbibe into the fine pores of the matrix rock, and through oil-water replacement, the crude oil is gradually collected into the large pores, thereby realizing the purpose of supplementing the formation energy and improving the final recovery rate.

Slippery hydraulic fracturing technology in dialysis replacement production technology has become one of the core technologies of shale oil production due to its low cost, little damage to the reservoir and high fracture conductivity of proppant. However, the existing slick water fracturing fluid is mainly composed of polymer drag reducing agent and a small amount of drainage aid and anti-swelling agent, and there is still the problem of low dialysis recovery.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a modified nano-silica fluid and its preparation method and application, a slick water fracturing fluid and its application, which can improve the recovery rate of shale oil reservoirs.

The invention provides a modified nano-silica fluid, comprising the following preparation raw materials:

The mass content of silica in the hydrophilic nano-silica sol is 20-40%;

The modifiers include alkyl glucoside, alkyl polyoxyethylene ether, sodium alkyl sulfate, sodium alkyl sulfonate, sodium α-alkenyl sulfonate, sodium alkyl alcohol phosphate, alkyl carboxybetaine and One or more of Alkyl Hydroxypropyl Sultaines.

Preferably, the average particle size of the hydrophilic nano-silica sol is 8-15 nm.

Preferably, the stabilizer includes a first low temperature stabilizer and a second low temperature stabilizer; the mass of the first low temperature stabilizer and the second low temperature stabilizer independently account for 5% of the modified nano-silica fluid. ~15%;

The first stabilizer includes one or more of sodium chloride, ammonium chloride and urea;

The second stabilizer includes one or more of isobutanol, propylene glycol, n-butanol, ethanol and methanol.

The present invention also provides a method for preparing the modified nano-silica fluid according to the above scheme, which includes the following steps: mixing and modifying the hydrophilic nano-silica sol, a modifier, a low-temperature stabilizer and water to obtain the modified nano-silica sol. Sexual nano silica fluid;

The temperature of the modification is 70-90°C.

The present invention also provides the application of the modified nano-silica fluid described in the above scheme or the modified nano-silica fluid prepared by the preparation method described in the above scheme in the development of shale oil.

The present invention also provides a slick water fracturing fluid, comprising the following components:

The modified nano-silica fluid is the modified nano-silica fluid described in the above scheme or the modified nano-silica fluid prepared by the preparation method described in the above scheme.

Preferably, the drag reducing agent comprises one or more of polyacrylamide, partially hydrolyzed polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, guar gum, cationically modified guar gum and hydroxypropyl guar gum kind.

Preferably, the multifunctional additives include potassium chloride, copolymers of tetramethylpropylenediamine and dichloropropane, copolymers of tetramethylethylenediamine and dichloroethane, and polydiallyl dimethyl A mixture of one or more ammonium chlorides with glutaraldehyde and/or chlorophenoxide.

The present invention also provides the application of the slick water fracturing fluid described in the above solution in the development of shale oil.

Preferably, the application includes the following steps:

The slick water fracturing fluid is pumped into the formation, and after the fracture is formed, a mixture of slick water fracturing fluid and proppant is pumped into the formation to make the proppant support the fracture; The proppant is squeezed into the reservoir; no reverse drainage is performed, and the well is stuffed for 3 to 28 days.

The invention provides a modified nano-silica fluid, comprising the following preparation raw materials: hydrophilic nano-silica sol 30wt%; modifier 30wt%; low temperature stabilizer 20-30wt%; the balance is water; The mass content of silica in the hydrophilic nano-silica sol is 40%; the modifier includes alkyl glucoside, alkyl polyoxyethylene ether, sodium alkyl sulfate, sodium alkyl sulfonate, alpha - One or more of sodium alkenyl sulfonate, sodium alkyl alcohol phosphate, alkyl carboxybetaine and alkyl hydroxypropyl sulfobetaine. When the modified nano-silica fluid of the present invention is used in slick water fracturing fluid, the interaction between the modified nano-silica and slick water fracturing fluid can be enhanced by electrostatic action, van der Waals force, hydrogen bonding, etc. Reduce oil-water interfacial tension and change reservoir rock wettability. The slick water fracturing fluid prepared by using the modified nano-silica fluid of the present invention can be enriched in the oil-water-solid three-phase contact area, and form a wedge-shaped structure in the oil-water-rock three-phase contact area. Separation pressure strips crude oil from the rock surface, thereby enhancing imbibition recovery. The results of the examples show that the maximum imbibition recovery rate of the modified nano-silica fluid reaches 12%, while the interfacial tension is reduced to 0.11mN/m, and the wetting transition reaches a maximum of 158°, and the oil droplets peel off in 8h. 151° was reached in the experiment.

The present invention provides a slick water fracturing fluid. Through the synergistic effect between the modified nano-silica fluid, drag reducing agent and multifunctional additive, the slick water fracturing fluid of the present invention has excellent performance. Dispersion stability, drag reduction, sand carrying and seam-making ability. The results of the examples show that the maximum imbibition recovery rate of the slick water fracturing fluid provided by the present invention is 16.1%, and the maximum drag reduction rate is 83.5%.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative labor.

Fig. 1 is the SEM image of the hydrophilic nano-silica sol used in Comparative Examples 2-3 and Examples 1-8;

Fig. 2 is the SEM image of the modified nano-silica fluid prepared by comparative example 3;

3 is a DLS diagram of the hydrophilic nano-silica sol used in Comparative Examples 2-3 and Examples 1-8 and the modified nano-silica fluid prepared in Comparative Example 3. FIG.

Detailed ways

The invention provides a modified nano-silica fluid, comprising the following preparation raw materials:

The mass content of silica in the hydrophilic nano-silica sol is 20-40%;

The modifiers include alkyl glucoside, alkyl polyoxyethylene ether, sodium alkyl sulfate, sodium alkyl sulfonate, sodium α-alkenyl sulfonate, sodium alkyl alcohol phosphate, alkyl carboxybetaine and One or more of Alkyl Hydroxypropyl Sultaines.

The particle size of the modified nano-silica fluid in the present invention is preferably 1-100 nm, more preferably 5-20 nm.

In terms of mass percentage, the preparation raw materials of the modified nano-silica fluid provided by the present invention include 20-40 wt% of hydrophilic nano-silica sol, more preferably 25-35 wt%; the hydrophilic nano-silica The mass content of silica in the sol is 20-40 wt %, more preferably 25-35 wt %. In the present invention, the average particle size of the hydrophilic nano-silica sol is preferably 8-15 nm, more preferably 10-12 nm; the density is preferably 1.28-1.30 g/mL, more preferably 1.29 g/mL; The pH value is preferably 7 to 11, and more preferably 7.5 to 9.5.

The preparation raw material of the modified nano-silica fluid provided by the present invention includes 20-40 wt% of the modifier, more preferably 25-35 wt%. In the present invention, the modifier includes alkyl glucoside, alkyl polyoxyethylene ether, sodium alkyl sulfate, sodium alkyl sulfonate, sodium α-alkenyl sulfonate, sodium alkyl alcohol phosphate, alkyl alcohol One or more of carboxybetaine and alkylhydroxypropyl sulfobetaine, preferably two or more modifiers, more preferably three modifiers. In the present invention, the number of C atoms in the modifier is preferably 12-16, more preferably 13-15. In the embodiment of the present invention, the number of specific C atoms selected is 12 (such as sodium dodecyl sulfonate, dodecyl hydroxypropyl sulfobetaine) and/or 14 (such as tetradecyl carboxy betaine) Alkali, sodium tetradecyl sulfate, tetradecyl polyoxyethylene ether) modifier. The function of the modifier in the present invention is to modify the hydrophilic nano-silica sol to make it active.

The preparation raw materials of the modified nano-silica fluid provided by the present invention include 10-30 wt% of a low-temperature stabilizer. In the present invention, the stabilizer preferably includes a first low temperature stabilizer and a second low temperature stabilizer; the quality of the first low temperature stabilizer and the second low temperature stabilizer preferably respectively independently account for the modified nano-dioxide 5 to 15% of the silicon fluid, more preferably 8 to 12 wt%. In the present invention, the first stabilizer preferably includes one or more of sodium chloride, ammonium chloride and urea; the second stabilizer preferably includes isobutanol, propylene glycol, n-butanol, ethanol and methanol one or more of. In the present invention, the function of the first stabilizer is to reduce the freezing point of the modified nano-silica fluid and prevent the hydrophilic nano-silica sol and the modifier from precipitation at low temperature; the function of the second stabilizer is to reduce the The freezing point of the modified nano-silica fluid is reduced, the viscosity of the modified nano-silica fluid is reduced, and the injectability is enhanced. The low-temperature stabilizer enables the modified nano-silica fluid to maintain a uniform system without freezing when the storage temperature is -5 °C and above.

The present invention also provides a method for preparing the modified nano-silica fluid according to the above scheme, which includes the following steps: mixing and modifying the hydrophilic nano-silica sol, a modifier, a low-temperature stabilizer and water to obtain the modified nano-silica sol. Sexual nano silica fluid;

The temperature of the modification is 70-90°C.

In the present invention, the mixing of the hydrophilic nano-silica sol, the modifier, the low-temperature stabilizer and the water preferably includes: heating the water to a modified temperature, adding the low-temperature stabilizer to the water during the heating, and then adding the low-temperature stabilizer to the water. The hydrophilic nano-silica sol is added to the obtained first mixed solution, and then a modifier is added to the obtained second mixed solution.

In the present invention, the mixing is preferably carried out under stirring conditions. The present invention preferably stirs for 1h after adding the hydrophilic nano-silica sol.

In the present invention, the modification temperature is 70-90°C, preferably 75-85°C; the modification time is preferably 2-5h, more preferably 3-4h. In the present invention, the modification is preferably carried out under stirring conditions. After modification, the activity of the nanofluid increases, and the temperature and salt resistance performance is enhanced. When the temperature of modification is controlled within the above range, the effect of modification is the best and the system after modification is stable. If the temperature is too high or too low, the product properties are unstable and the reaction efficiency is poor.

After completing the modification, the present invention preferably stirs the obtained modified product until its temperature drops to room temperature to obtain a modified nano-silica fluid.

The present invention also provides the application of the modified nano-silica fluid described in the above scheme or the modified nano-silica fluid prepared by the preparation method described in the above scheme in the development of shale oil.

In the present invention, the application preferably includes the following steps: pumping the active nanofluid into the formation for 3-28 days and then opening the well for production.

In the present invention, the suitable shale oil reservoir conditions for the modified nano-silica fluid are preferably a salinity between 0 and 80000 mg/L, and a temperature between room temperature and 120°C.

The present invention also provides a slick water fracturing fluid, comprising the following components:

The modified nano-silica fluid is the modified nano-silica fluid described in the above scheme or the modified nano-silica fluid prepared by the preparation method described in the above scheme.

In terms of mass percentage, the slick water fracturing fluid provided by the present invention comprises 0.05-0.5wt% of modified nano-silica fluid, preferably 0.1-0.4wt%, more preferably 0.2-0.3wt%.

The slick water fracturing fluid provided by the present invention includes 0.05-0.5wt% of drag reducing agent, preferably 0.1-0.4wt%, more preferably 0.2-0.3wt%. The drag reducing agent of the present invention preferably comprises one or more of polyacrylamide, partially hydrolyzed polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, guar gum, cationically modified guar gum and hydroxypropyl guar gum species, more preferably amphoteric polyacrylamide. In the present invention, the molecular weight of the polyacrylamide is preferably 1 to 9 million, the molecular weight of the cationic polyacrylamide is preferably 1 to 6 million, and the molecular weight of the amphoteric polyacrylamide is preferably 1 to 5 million. The degree of hydrolysis of the partially hydrolyzed polyacrylamide is preferably 1-10%, and the molecular weight is preferably 1-7 million.

When the drag reducing agent preferably includes polyacrylamide with a molecular weight of 1 to 9 million, a degree of hydrolysis of 1 to 10%, a partially hydrolyzed polyacrylamide with a molecular weight of 1 to 7 million, and an amphoteric polyacrylamide with a molecular weight of 1 to 5 million , the sum of the mass of the above three drag reducing agents shall not be less than 80% of the total mass of the drag reducing agents.

When the drag reducing agent preferably includes cationic polyacrylamide, guar gum, cationic modified guar gum and hydroxypropyl guar gum with a molecular weight of 1 million to 6 million, the sum of the masses of the above four drag reducing agents shall not be greater than 20% of the total mass of the resist.

In the present invention, the cationic polyacrylamide and the cationic modified guar gum with a molecular weight of 1 to 6 million in the drag reducing agent must not be polymerized with a partially hydrolyzed polymer with a degree of hydrolysis of 1 to 10% and a molecular weight of 1 to 7 million. Acrylamide is used simultaneously. If used at the same time, it will fail to converge.

The slick water fracturing fluid provided by the present invention comprises 0.1-0.5wt% of multifunctional additives, preferably 0.2-0.4%. In the present invention, the multifunctional additive preferably includes potassium chloride, a copolymer of tetramethylpropylenediamine and dichloropropane, a copolymer of tetramethylethylenediamine and dichloroethane, and polydiallyl A mixture of one or more of dimethylammonium chloride with glutaraldehyde and/or chlorophenoxide.

In the present invention, the copolymerization ratio of the tetramethylpropylenediamine and dichloropropane copolymer is preferably 1:0.9-0.95, more preferably 1:0.92-0.94; the tetramethylethylenediamine and dichloropropane copolymer The copolymerization ratio of the ethylene chloride copolymer is preferably 1:0.9 to 0.95, and more preferably 1:0.92 to 0.94.

In the present invention, among the multifunctional additives, potassium chloride, tetramethylpropylenediamine and dichloropropane copolymer, tetramethylethylenediamine and dichloroethane copolymer, polydiallyl dimethyl The weight sum of one or more ammonium chlorides is preferably 40% to 60% of the total amount of the multifunctional additive, and the balance is preferably glutaraldehyde and/or chlorophenoxide. The chlorophenoxide is preferably chlorobenzene oxide or chlorophenidol. The functions of the multifunctional additive in the present invention are anti-swelling and sterilization.

The present invention has no special requirements on the preparation method of the slick water fracturing fluid, and the components can be directly mixed uniformly. In the embodiment of the present invention, it is specifically as follows: adding the modified nano-silica fluid and multifunctional additives into water and stirring for 5-10 minutes, and then adding a drag reducing agent and stirring for 10-35 minutes to obtain a slick water fracturing fluid.

Through the synergistic effect among the drag reducing agent, the modified nano-silica fluid and the multifunctional additive, the present invention not only has the excellent drag reducing property, sand carrying property and creating property better than the conventional slick water fracturing fluid At the same time, it has unique interfacial activity, which can effectively reduce interfacial tension, change wettability and oil droplet peeling, so that it has excellent oil absorption and drainage ability.

The present invention also provides the application of the slick water fracturing fluid described in the above solution in the development of shale oil. The method of said application preferably comprises the following steps:

The slick water fracturing fluid is pumped into the formation, and after the fracture is formed, a mixture of slick water fracturing fluid and proppant is pumped into the formation to make the proppant support the fracture; The proppant is squeezed into the reservoir; no reverse drainage is performed, and the well is stuffed for 3 to 28 days.

The present invention has no special requirements on the implementation conditions of each step in the application process, and the implementation conditions well known to those skilled in the art can be used.

On the premise that the slick water fracturing fluid system of the present invention meets the requirements of shale oil reservoir fracturing construction, it does not need backflow after fracturing construction, and can fully utilize fracturing energy and fracturing fluid, and then directly fill up wells for 3-28 Tianhou opened a well for production, which is green and environmentally friendly, reducing costs and increasing efficiency.

In order to further illustrate the present invention, a modified nano-silica fluid and its preparation method and application, a slick water fracturing fluid and its application provided by the present invention are described in detail below with reference to the accompanying drawings and examples, but not They are to be understood as limiting the scope of protection of the present invention.

Modified Nano Silica Fluid

The preparation methods of the modified nano-silica fluids of Comparative Examples 1-3 and Examples 1-8, the steps are as follows:

Heat the water to 80°C, add the first low-temperature stabilizer and the first low-temperature stabilizer to the water and stir evenly, slowly add the hydrophilic nano-silica sol to the reaction vessel and continue stirring for 1 h, and slowly add the modifier to the reaction After the container was stirred for 3 hours, the heating was stopped, and the residual heat was used to continue stirring until it was cooled to room temperature to obtain the modified nano-silica fluid.

In Comparative Examples 1-3 and Examples 1-8, the total mass of the modified nano-silica fluid is 100 g, and the amount of water used is 100 g of the total mass of the modified nano-silica fluid - the amount of other components.

The preparation methods of Comparative Examples 1 to 3 are the same as those of Examples 1 to 8, and the content of silica in the used nano-silica silica sol hydrophilic nano-silica sol is 40%. The average particle size of the silica sol is 10 nm; the density is 1.109 g/mL, and the pH is 9. The differences are shown in Table 1.

Table 1 Preparation raw materials, dosage and modification temperature of Comparative Examples 1-3 and Examples 1-8

Add 0.1 g of the modified nano-silica fluids of Comparative Examples 1 to 3 and Examples 1 to 8 into 99.9 g of water, respectively. After stirring evenly, the particle size distribution was evaluated by DLS instrument, and the oil-water interfacial tension was tested by rotating drop method. , the contact angle evaluation device was used to evaluate its wetting transition ability and oil droplet peeling ability, and the imbibition bottle was used to evaluate its imbibition recovery rate. The evaluation results are shown in Table 2.

Table 2 Experimental results of Comparative Examples 1-3 and Examples 1-8

It can be seen from Table 2 that the interfacial tension, wetting transition, oil droplet exfoliation and imbibition recovery of the modified nanofluid are significantly higher than those of the conventional surfactant solution and the unmodified nanofluid.

It can be seen from Table 2 that when the type and amount of modifier and low-temperature stabilizer are the same, the higher the modification temperature, the higher the interfacial tension, wetting transition, oil droplet exfoliation and imbibition recovery of the modified nanofluid. it is good.

It can be seen from Table 2 that the type and amount of stabilizer at low temperature are the same, and the amount of modifier is the same. The effect of composite modification is better than that of binary composite modification than that of single modifier.

It can be seen from Table 2 that when the type and amount of low-temperature stabilizer are the same, the total amount and type of modifier are the same, and when the amount of different modifiers is the same, the interfacial tension, wettability, and oil droplet of the modified nanofluid will be reduced. Strippability and imbibition recovery are better.

The hydrophilic nano-silica sols (SiO ₂ before modification) used in Comparative Examples 2-3 and Examples 1-8 were analyzed by SEM and DLS, and the results are shown in Figures 1 and 3;

The modified nano-silica fluid (modified SiO ₂ ) prepared in Comparative Example 3 was analyzed by SEM and DLS, and the results are shown in FIG. 2 and FIG. 3 . It can be seen from the comprehensive analysis of Figures 1-3 that the particle size of the modified nanofluid is about 10 nm.

Slippery water fracturing fluid

Preparation methods of the slick water fracturing fluids of Comparative Examples 4 to 15 and Examples 9 to 14:

A certain amount of the modified nano-silica fluid prepared in the example was added to water and stirred, multi-functional additives were added to stir, and a certain amount of drag reducing agent was added to stir, and a total amount of 100 g of active nano-fluid was used to strengthen the slick water fracturing fluid system.

The preparation methods of the slick water fracturing fluids of Comparative Examples 4 to 15 and Examples 9 to 14 are different, and the differences are shown in Table 3.

Table 3 Raw materials and dosages of slick water fracturing fluids of Comparative Examples 4 to 15 and Examples 9 to 14

The drag reduction rates of the slick water fracturing fluids of Comparative Examples 4 to 15 and Examples 9 to 14 were evaluated under a pipe inner diameter of 10 cm and a displacement of 35 L/min. The experimental results are shown in Table 4.

The slick water fracturing fluids of Comparative Examples 4 to 15 and Examples 9 to 14 were sheared at 1000 s ⁻¹ for 30 min to obtain gel breaking fluid. The imbibition recovery rate of broken gel was evaluated by imbibition bottle. The experimental results are shown in Table 4.

Table 4 compares the experimental results of the slick water fracturing fluids of 1-12 and Examples 1-6

It can be seen from Table 4 that, compared with the conventional slick water only adding drag reducing agent, the drag reduction rate and imbibition recovery rate of the activated nanofluid enhanced slick water fracturing fluid system are better. rate and imbibition recovery.

It can be seen from Table 4 that under the same amount of modified nanofluid, an excessive amount of drag reducer is not conducive to its drag reduction and imbibition.

It can be seen from Table 4 that under the same amount of nanofluid and drag reducing agent, the drag reduction rate and recovery rate of amphoteric polyacrylamide as drag reducing agent are better than that of polyacrylamide, partially hydrolyzed polyacrylamide, cationic polyacrylamide, guanidine gum, cationically modified guar gum and hydroxypropyl modified guar gum.

Drainage performance of stuffy wells in different systems

The shale oil dynamic displacement evaluation device was used to evaluate the dynamic displacement of the modified nanofluid, the ordinary slick water gel breaker in Comparative Example 17 and the slick water fracturing fluid gel breakers in Examples 15 to 18 under different well boring times. The preparation method of the glue breaking fluid is as follows: stirring ordinary slick water or slick water fracturing fluid at a speed of 3000 rpm for 5 minutes to obtain ordinary slick water glue breaking fluid or slick water fracturing fluid glue breaking fluid. The results are shown in Table 5.

Table 5 Test results of dynamic displacement of modified nanofluids, ordinary slick water and slick water fracturing fluids

It can be seen from Table 5 that the oil recovery rate of slick water fracturing fluid with active nanofluids is significantly higher than that of modified nanofluids and slick water gel breaking fluid; and the oil recovery rate increases with the longer the well boring time.

Although the above embodiment has made a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can also be obtained according to the present embodiment without creativity. It belongs to the protection scope of the present invention.

Claims (10)

1. The modified nano-silica fluid is characterized by comprising the following preparation raw materials:

20-40 wt% of hydrophilic nano silica sol;

20-40 wt% of a modifier;

10-30 wt% of a low-temperature stabilizer;

the balance of water;

the mass content of silicon dioxide in the hydrophilic nano silicon dioxide sol is 20-40%;

the modifier comprises one or more of alkyl glucoside, alkyl polyoxyethylene ether, alkyl sodium sulfate, alkyl sodium sulfonate, alpha-alkenyl sodium sulfonate, alkyl alcohol phosphate sodium, alkyl carboxyl betaine and alkyl hydroxypropyl sulfobetaine.

2. The modified nanosilica fluid of claim 1, wherein the hydrophilic nanosilica sol has an average particle size of from 8 to 15 nm.

3. The modified nanosilica fluid of claim 1, wherein the stabilizer comprises a first low temperature stabilizer and a second low temperature stabilizer; the mass of the first low-temperature stabilizer and the mass of the second low-temperature stabilizer respectively and independently account for 5-15% of the modified nano silicon dioxide fluid;

the first stabilizer comprises one or more of sodium chloride, ammonium chloride and urea;

the second stabilizer comprises one or more of isobutanol, propylene glycol, n-butanol, ethanol, and methanol.

4. A method for preparing the modified nanosilica fluid of any of claims 1 to 3, comprising the steps of: mixing hydrophilic nano-silica sol, a modifier, a low-temperature stabilizer and water for modification to obtain modified nano-silica fluid;

the modification temperature is 70-90 ℃.

5. Use of the modified nanosilica fluid according to any of claims 1 to 3 or the modified nanosilica fluid obtained by the method of claim 4 in shale oil development.

6. The slickwater fracturing fluid is characterized by comprising the following components:

0.05-0.5 wt% of modified nano silicon dioxide fluid;

0.05 to 0.5 wt% of a drag reducer;

0.1-0.5 wt% of multifunctional additive;

the balance of water;

the modified nano-silica fluid is the modified nano-silica fluid described in any one of claims 1 to 3 or the modified nano-silica fluid prepared by the preparation method described in claim 4.

7. The slickwater fracturing fluid of claim 6, wherein the drag reducer comprises one or more of polyacrylamide, partially hydrolyzed polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, guar gum, cationic modified guar gum, and hydroxypropyl guar gum.

8. The slickwater fracturing fluid of claim 6 wherein the multifunctional additive comprises a mixture of one or more of potassium chloride, a copolymer of tetramethylpropylenediamine and dichloropropane, a copolymer of tetramethylethylenediamine and dichloroethane, and polydiallyldimethylammonium chloride with glutaraldehyde and/or chlorobenzene oxide.

9. Use of the slickwater fracturing fluid of any one of claims 5 to 8 in shale oil development.

10. The application according to claim 9, characterized in that it comprises the following steps:

pumping slickwater fracturing fluid into a stratum to form a crack, and pumping a mixture of slickwater fracturing fluid and a propping agent into the stratum to enable the propping agent to prop the crack; then continuously pumping slickwater fracturing fluid, and extruding the proppant in the shaft into the reservoir stratum; and (4) carrying out reverse drainage, and closing the well for 3-28 days.

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