Fracturing fluid as well as preparation method and application thereof

Abstract

The invention provides fracturing fluid as well as a preparation method and application thereof. The fracturing fluid comprises a diversified ester-based solvent, nanoparticles and a water-soluble thickening agent, wherein the water-soluble thickening agent is polyacrylamide and a derivative thereof. According to the invention, the water-soluble thickening agent is used for replacing an oil-based thickening agent, a diversified ester-based solvent is introduced as a solvent, especially the water-soluble thickening agent is polyacrylamide and a derivative thereof, and the thickening agent can generate an effective suspension effect on water-soluble high-molecular polymer powder, so that the viscosity of a fracturing fluid system is further reduced; the stable low-viscosity fluid is obtained, so that the low-viscosity fluid has better diffusion and permeability, the resistance reduction performance is greatly improved, and the application prospect is wider.

Description

Technical Field

[0001] The present invention relates to the field of fracturing fluids for oil and gas field transformation, and in particular, to a fracturing fluid, a preparation method thereof, and an application thereof. Background Art

[0002] At present, for volume fracturing of low-permeability tight reservoirs, the fracturing fluid is required to have the characteristics of rapid swelling, excellent drag reduction, and controllable viscosity. Therefore, the reverse emulsion system and the oil-based suspension emulsion system with multiple effects in one agent have become the mainstream fracturing fluid systems for tight gas transformation. Among them, the molecular weight of the reverse emulsion system is less than 16 million, the drag reduction rate is good, and the salt tolerance performance is ≤40000 mg / L, but it is only applicable to the water quality environment with medium and low salinity. However, the oil-based suspension emulsion system has the characteristics of large polymer molecules, excellent drag reduction, adjustable salt tolerance, and wide suitability. However, these two types of fracturing fluid systems usually add a large amount of white oil and emulsifier during the synthesis or preparation process, which will cause the oil phase to emulsify with fluids such as reservoir condensate oil after entering the micro-pore throats of the low-permeability reservoir, thereby resulting in poor fluid flow ability and aggravating reservoir damage.

[0003] Based on this, scientific researchers have also studied strategies to solve the above problems. Among them, Ren Shan et al. prepared an aqueous drag reducer using polyols, alcohol ethers, polyhydric alcohols, ethanolamines, etc. as solvents in order to achieve the purpose of rapid dissolution of water-soluble polymers in water. However, due to the presence of a large number of hydroxyl groups, the viscosity of the prepared drag reducer itself is very high, and the viscosity of the drag reducer itself will further increase with the passage of time, which is not conducive to on-site suction and pumping, so its further popularization and use are limited.

[0004] In summary, the fracturing fluid systems in the prior art have problems such as large viscosity or poor drag reduction performance, which limits the further application of the fracturing fluid systems. Therefore, there is an urgent need to provide a fracturing fluid and a preparation method thereof to improve the above problems. Summary of the Invention

[0005] The main object of the present invention is to provide a fracturing fluid, a preparation method thereof, and an application thereof to solve the problems of large viscosity or poor drag reduction performance existing in the fracturing fluid systems in the prior art.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a fracturing fluid, which comprises a diversified ester-based solvent, nanoparticles, and a water-soluble thickening agent; wherein, the water-soluble thickening agent is polyacrylamide and its derivatives.

[0007] Further, by weight percentage, the components of the fracturing fluid include: 20-50% of a water-soluble thickening agent, 50-70% of a diversified ester-based solvent, and 0.5-5.0% of nanoparticles; preferably, the diversified ester-based solvent is selected from one or more of dimethyl succinate, dimethyl adipate, dimethyl phthalate, methyl lactate, or methyl oleate.

[0008] Further, the nanoparticles are selected from one or more of hydrophilic nano-silica, hydrophobically modified silica, or nano-cellulose; preferably, the particle size D50 of the nanoparticles is 50-150 nm.

[0009] Further, the components of the fracturing fluid include: 40-45% of a water-soluble thickening agent, 55-60% of a diversified ester-based solvent, and 0.3-2.5% of a nano-material; preferably, the polyacrylamide and its derivatives are selected from one or more of non-ionic polyacrylamide, poly(acrylamide-sodium acrylate), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt-long chain alkyl dimethyl allyl ammonium chloride), or poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt-fatty alcohol polyoxyethylene ether methacrylate); preferably, the weight-average molecular weight Mw of the water-soluble thickening agent is 4 million to 30 million; preferably, the water-soluble thickening agent is granular, and its average particle size is 120-180 μm.

[0010] According to another aspect of the present invention, there is also provided a preparation method of the above fracturing fluid, which includes: Step S1: Dispersing the nanoparticles in the diversified ester-based solvent and performing a primary shearing treatment to obtain a pseudo-fluid; Step S2, adding the water-soluble thickening agent to the pseudo-fluid and performing a secondary shearing treatment to obtain the fracturing fluid.

[0011] Further, both the primary shearing treatment and the secondary shearing treatment are performed in a high-speed shearing machine; preferably, the shearing power of the primary shearing treatment is 25-50 kW, the shearing speed is 9000-10000 rpm, and the shearing time is 1-1.5 h; preferably, the shearing power of the secondary shearing treatment is 25-50 kW, the shearing speed is 9000-10000 rpm, and the shearing time is 2-3 h.

[0012] Further, the preparation process is carried out in a reaction kettle. Preferably, the temperature inside the reaction kettle is controlled at 10-40 °C by cooling water in the jacket of the reaction kettle; preferably, the temperature of the cooling water is -10 to -20 °C.

[0013] Further, by weight percentage, the addition amount of the nanoparticles accounts for 2-2.5 wt% of the weight of the diversified ester-based solvent.

[0014] Further, by weight percentage, the weight ratio of the water-soluble thickening agent to the nanoparticles is (0.06 - 0.08):1.

[0015] According to another aspect of the present invention, there is also provided an application of the above fracturing fluid in the field of reservoir reconstruction in oil and gas fields; preferably, the fracturing fluid is used to prepare an oil and gas field fracturing working fluid. When the addition amount is 0.05 - 0.2% wt, a slickwater fracturing fluid is prepared, and its drag reduction rate ≥ 70%; when the addition amount is 0.5 - 1.5% wt, a high-viscosity sand-carrying fracturing fluid is prepared, and its apparent viscosity at 90°C and 170 s -1 Shearing for 2 h is ≥ 50 mPa·s.

[0016] In the fracturing fluid system in the prior art, the commonly used thickening agent is an oil-based thickening agent, which makes the viscosity of the fracturing fluid relatively large during the application process and the viscosity is uncontrollable, resulting in huge challenges in pumping the fracturing fluid on site, thus limiting its further application. Moreover, in the existing oil-based suspension emulsion system containing an oil-based thickening agent, the oil phase therein is extremely likely to enter the tiny pore throats of low-permeability reservoirs and emulsify with fluids such as reservoir condensate oil, resulting in poor fluid flow ability and poor drag reduction performance, and further aggravating reservoir damage. However, the present invention creatively replaces the oil-based thickening agent with a water-soluble thickening agent and introduces a diversified ester-based solvent as the solvent. In particular, the water-soluble thickening agent is polyacrylamide and its derivatives. This thickening agent can effectively suspend the water-soluble polymer powder, thereby further reducing the viscosity of the fracturing fluid system, obtaining a stable low-viscosity fluid, making it have good diffusion and penetration performance, greatly improving the drag reduction performance, and having a broader application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 Shows the rheological curve of an aqueous solution with a concentration of 0.5% prepared with clear water of the fracturing fluid in Example 5 at 90°C;

[0020] Figure 2 Shows the rheological curve graph of an aqueous solution with a concentration of 1.0% prepared with clear water of the fracturing fluid in Example 5 at 90°C; and

[0021] Figure 3Shows the rheological curve of an aqueous solution with a concentration of 1.5% prepared with 20% standard salinity brine for the fracturing fluid in Example 5 at 90°C. Detailed implementation manners

[0022] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] Combined with the technical status of the fracturing fluid in Changqing Oilfield, it is necessary to break through the technical defects and development bottlenecks of the existing fracturing fluid system. Aiming at the reservoir conditions, with the main purpose of reducing the potential damage of the thickening agent, avoiding the use of oil-based thickening agents, creatively introducing diversified ester groups as the continuous phase and modified nanomaterials as the thixotropic agent, and adopting a high-speed shear dispersion process to obtain a low-viscosity fluid with low stability, which can effectively suspend the water-soluble polymer powder, and prepare an oil-free functional fracturing fluid.

[0024] As described in the background art section of the present invention, the fracturing fluid system in the prior art has problems such as relatively high viscosity or poor drag reduction performance, which limits the further application of the fracturing fluid system. In view of the above problems, the present invention provides a fracturing fluid, which includes a diversified ester-based solvent, nanoparticles, and a water-soluble thickening agent; wherein, the water-soluble thickening agent is polyacrylamide and its derivatives.

[0025] In the existing fracturing fluid system, the commonly used thickening agent is an oil-based thickening agent, which makes the viscosity relatively high and uncontrollable during the application of the fracturing fluid, resulting in huge challenges in the on-site suction and pumping of the fracturing fluid, thus limiting its further application. Moreover, in the existing oil-based suspension emulsion system containing an oil-based thickening agent, the oil phase is very likely to enter the tiny pore throats of the low-permeability reservoir and emulsify with fluids such as reservoir condensate oil, resulting in poor fluid flow ability and poor drag reduction performance, and further aggravating reservoir damage. However, the present invention creatively replaces the oil-based thickening agent with a water-soluble thickening agent and introduces a diversified ester-based solvent as the solvent. In particular, the water-soluble thickening agent is polyacrylamide and its derivatives. This thickening agent can effectively suspend the water-soluble polymer powder, thereby further reducing the viscosity of the fracturing fluid system, obtaining a stable low-viscosity fluid, making it have good diffusion and penetration performance, and greatly improving the drag reduction performance, with a broader application prospect.

[0026] In a preferred embodiment, by weight percentage, the components of the fracturing fluid include: 20-50% of a water-soluble thickening agent, 50-70% of a diversified ester-based solvent, and 0.5-5.0% of a nanomaterial; to further improve the comprehensive performance of the fracturing fluid, preferably the diversified ester-based solvent is selected from one or more of dimethyl succinate, dimethyl adipate, dimethyl phthalate, methyl lactate, or methyl oleate. Using this diversified ester-based solvent as the continuous phase can further improve the viscosity controllability of the fracturing fluid system, endowing it with good diffusion and penetration properties and significantly improving its drag reduction performance.

[0027] To further improve the viscosity controllability of the fracturing fluid system and endow it with good diffusion and penetration properties, preferably the nanoparticles are selected from one or more of hydrophilic nano-silica, hydrophobically modified silica, or nano-cellulose; more preferably, the particle size D50 of the nanoparticles is 50-150 nm. The above-mentioned nanoparticles can be, for example, hydrophilic nano-silica of model HDK-N20 produced by Wacker Chemie AG in Germany, hydrophobically modified silica of model HDK-H20, or nano-cellulose CNF produced by Nippon Paper Industries Co., Ltd. in Japan.

[0028] In a preferred embodiment, the components of the fracturing fluid include: 40-45% of a water-soluble thickening agent, 55-60% of a diversified ester-based solvent, and 0.3-2.5% of a nanomaterial; to further obtain a stable low-viscosity fluid with good diffusion and penetration properties, preferably the polyacrylamide and its derivatives are selected from one or more of non-ionic polyacrylamide, poly(acrylamide-sodium acrylate), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid-long-chain alkyl dimethyl allyl ammonium chloride), or poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid-fatty alcohol polyoxyethylene ether methacrylate); preferably, the weight-average molecular weight Mw of the water-soluble thickening agent is 4 million to 30 million; and the water-soluble thickening agent is in granular form with an average particle size of 120-180 μm.

[0029] For example, the model 6919G produced by Shandong Nuoer Biotechnology Co., Ltd. is non-ionic polyacrylamide with a molecular weight of 10 million - 12 million; NR-GS708 is post-hydrolyzed polyacrylamide with a molecular weight of 28 million; the model NR556 is a copolymer of acrylamide and sodium acrylate with a molecular weight of 20 million; the model NR566 is a terpolymer of acrylamide, sodium acrylate, and 2-acrylamide-2-methylpropanesulfonic acid with a molecular weight of 20 million.

[0030] The type I polyacrylamide for oil displacement produced by Shandong Baomo Biochemical Co., Ltd. is a copolymer of acrylamide and sodium acrylate, with a molecular weight of 20 million; the type II polyacrylamide for oil displacement is a terpolymer of acrylamide and sodium acrylate, with a molecular weight of 22 million; the temperature and salt tolerance polymer is a terpolymer of acrylamide, sodium acrylate and 2-acrylamido-2-methylpropanesulfonic acid sodium salt, with a molecular weight of 25 million;

[0031] The 3402 type polyacrylamide for fracturing produced by SNF (China) Flocculants Co., Ltd. is a copolymer of acrylamide and sodium acrylate, with a molecular weight of 25 million; the CK3200X type salt-tolerant polyacrylamide for fracturing is a terpolymer of sodium acrylate and 2-acrylamido-2-methylpropanesulfonic acid sodium salt, with a molecular weight of 20 million; the hydrophobic associating polyacrylamide fracturing thickener, model AM / AA / AMPS / D18, is a quaternary copolymer of acrylamide, sodium acrylate, 2-acrylamido-2-methylpropanesulfonic acid sodium salt and long-chain alkyl dimethyl allyl ammonium chloride, with a molecular weight of 6 million; the model AM / AA / AMPS / OM is a copolymer of acrylamide, sodium acrylate, 2-acrylamido-2-methylpropanesulfonic acid sodium salt and fatty alcohol polyoxyethylene ether methacrylate, with a molecular weight of 8 million.

[0032] Another aspect of the present invention provides a preparation method of a fracturing fluid, which includes: Step S1: Dispersing nanoparticles in a polybasic ester-based solvent, and performing a primary shearing treatment to obtain a pseudoplastic fluid; Step S2, adding a water-soluble thickening agent to the pseudoplastic fluid, and performing a secondary shearing treatment to obtain a fracturing fluid.

[0033] Those skilled in the art can first disperse nanoparticles in a polybasic ester-based solvent and perform a primary shearing treatment to obtain a pseudoplastic fluid, and then add a water-soluble thickening agent to the pseudoplastic fluid and perform a secondary shearing treatment to obtain a fracturing fluid. This fracturing fluid has a low viscosity, excellent permeability and dispersibility, and relatively good drag reduction performance. This preparation method is simple, easy to operate, has mild preparation conditions, is suitable for large-scale production, and has broad application prospects.

[0034] In a preferred embodiment, both the primary shearing treatment and the secondary shearing treatment are carried out in a high-speed shearing machine; further preferably, the shearing power of the primary shearing treatment is 25-50 kw, the shearing speed is 9000-10000 rpm, and the shearing time is 1-1.5 h; so as to further obtain a pseudoplastic fluid and prepare for the preparation of a fracturing fluid with controllable viscosity and excellent drag reduction performance; preferably, the shearing power of the secondary shearing treatment is 25-50 kw, the shearing speed is 9000-10000 rpm, and the shearing time is 1-1.5 h, so as to obtain a fracturing fluid system with excellent comprehensive performance.

[0035] To further avoid the influence of heat on the system performance during the preparation of the fracturing fluid, the preparation process is carried out in a reaction kettle. Preferably, the temperature in the reaction kettle is controlled at 10-40°C by cooling water in the jacket of the reaction kettle; more preferably, the temperature of the cooling water is -10 to -20°C. To further improve the preparation efficiency of the fracturing fluid, save resources and production costs, by weight percentage, preferably the nanoparticles account for 2-2.5 wt% of the weight of the diversified ester-based solvent; more preferably, the weight ratio of the water-soluble thickening agent to the nanoparticles is (0.06-0.08):1.

[0036] Specifically, the following preparation method can be adopted: Add the metered diversified ester solvent into a 5-ton reaction kettle. A high-speed shearer is connected to the bottom of the reaction kettle. After sealing, start the stirring of the reaction kettle and the high-speed shearer. Connect a self-suction pipe at the inlet of the high-speed shearer, insert the self-suction pipe into the nano material package for feeding, and perform high-speed shearing for a period of time after the feeding is completed. Then continue to add the metered polyacrylamide and its derivative solid powder, and continue to perform high-speed shearing for a period of time after adding.

[0037] Another aspect of the present invention also provides an application of a fracturing fluid, or a fracturing fluid obtained by the above-mentioned preparation method of the fracturing fluid, in the field of oil and gas field reservoir reconstruction. As described above, this fracturing fluid has excellent drag reduction performance and low viscosity, so it has broad application prospects.

[0038] The water-soluble fracturing fluid of the present invention can be used to prepare the fracturing working fluid for oil and gas fields. The addition amount of 0.05-0.2% wt can prepare the slickwater fracturing fluid with a drag reduction rate ≥ 70%. The addition amount of 0.5-1.5% wt can prepare the high-viscosity sand-carrying fracturing fluid. The addition amount of 1.0% wt has an apparent viscosity ≥ 50 mPa·s at 90°C and 170 s- 1 Shearing for 2 h.

[0039] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0040] Example 1

[0041] Add 3250 kg of dimethyl succinate to a 5-ton reactor. A high-speed shearer is connected to the bottom of the reactor. Open the cooling water in the jacket to control the temperature in the reactor at 20°C, and the temperature of the cooling water is -10°C. After sealing, start the stirring of the reactor and the high-speed shearer. Connect a self-suction pipe at the inlet of the high-speed shearer, insert the self-suction pipe into the hydrophilic nanomaterial package for feeding. After adding 75 kg of hydrophilic nano-silica, carry out high-speed shearing for 1 h, with a power of 25 kW and a rotation speed of 9500 rpm. The particle size D50 of the nanoparticles is 75 nm. Then continue to add 1675 kg of polyacrylamide NR-GS708, with a weight-average molecular weight Mw of 1675 kDa, a residue on a 80-mesh sieve of 0.5%, a residue on a 100-mesh sieve of 2%, and an average particle size of 135 μm. After adding, continue high-speed shearing for 2 h, with a power of 25 kW and a rotation speed of 9000 rpm to obtain a fracturing fluid. The composition of this fracturing fluid includes: 33.5% water-soluble thickening agent, 65% diversified ester-based solvent, and 1.5% nanoparticles. Among them, the nanoparticles are hydrophilic nano-silica of model HDK-N20 produced by Wacker Chemie AG of Germany, and the water-soluble thickening agent is NR-GS708, which is post-hydrolyzed polyacrylamide with a molecular weight of 28 million.

[0042] Example 2

[0043] The difference from Example 1 is: add 3500 kg of methyl oleate, 100 kg of hydrophilic nano-silica, and 1400 kg of polyacrylamide type II for enhanced oil recovery. The composition of this fracturing fluid includes: 28% water-soluble thickening agent, 70% diversified ester-based solvent, and 2% nanoparticles.

[0044] Example 3

[0045] The difference from Example 1 is: add 3000 kg of dimethyl adipate, 75 kg of hydrophobic nano-silica, and 1925 kg of NR556. The composition of this fracturing fluid includes: 38.5% water-soluble thickening agent, 60% diversified ester-based solvent, and 1.5% nanoparticles. NR556 is a copolymer of acrylamide and sodium acrylate with a molecular weight of 20 million.

[0046] Example 4

[0047] The differences from Example 1 are as follows: 2750 kg of methyl lactate, 62.5 kg of hydrophobic nano-silica, and 2225 kg of 6919G are added. The components of this fracturing fluid include: 44.5% of water-soluble thickening agent, 55% of diversified ester-based solvent, and 0.5% of nano-particles. The water-soluble thickening agent is non-ionic polyacrylamide with the model number 6919G produced by Shandong Nuoer Biotechnology Co., Ltd., with a molecular weight of 10 million - 12 million. The nano-particles are hydrophobic nano-silica with the model number HDK-H20 produced by Wacker Chemie AG of Germany.

[0048] Example 5

[0049] The differences from Example 1 are as follows: 2950 kg of dimethyl phthalate, 50 kg of nano-cellulose CNF, and 2000 kg of polyacrylamide for fracturing with the model number 3402 are added. The components of this fracturing fluid include: 40% of water-soluble thickening agent, 59% of diversified ester-based solvent, and 1% of nano-particles. The nano-particles are nano-cellulose CNF produced by Nippon Paper Industries Co., Ltd. of Japan. The water-soluble thickening agent is polyacrylamide for fracturing with the model number 3402 produced by SNF (China) Flocculants Co., Ltd., which is a copolymer of acrylamide and sodium acrylate, with a molecular weight of 25 million.

[0050] Example 6

[0051] The differences from Example 1 are as follows: 2925 kg of dimethyl succinate, 75 kg of hydrophilic nano-silica, and 2000 kg of salt-tolerant polyacrylamide for fracturing with the model number CK3200X are added. The components of this fracturing fluid include: 40% of water-soluble thickening agent, 58.5% of diversified ester-based solvent, and 1.5% of nano-particles. The water-soluble thickening agent is salt-tolerant polyacrylamide for fracturing with the model number CK3200X, which is a terpolymer of sodium acrylate and 2-acrylamido-2-methylpropanesulfonic acid sodium, with a molecular weight of 20 million.

[0052] Example 7

[0053] The differences from Example 1 are as follows: 2875 kg of dimethyl adipate, 50 kg of hydrophobic nano-silica, and 2000 kg of AM / AA / AMPS / D18 are added. The components of this fracturing fluid include: 40% of water-soluble thickening agent, 57.5% of diversified ester-based solvent, and 2.5% of nano-particles. The water-soluble thickening agent is a hydrophobic associating polyacrylamide fracturing thickening agent with the model number AM / AA / AMPS / D18, which is a quaternary copolymer of acrylamide, sodium acrylate, 2-acrylamido-2-methylpropanesulfonic acid sodium, and long-chain alkyl dimethyl allyl ammonium chloride, with a molecular weight of 6 million.

[0054] Example 8

[0055] The differences from Example 1 are as follows: 2875 kg of dimethyl succinate, 125 kg of hydrophilic nano-silica, and 2000 kg of AM / AA / AMPS / OM are added. The components of this fracturing fluid include: 40% water-soluble thickening agent, 57.5% diversified ester-based solvent, and 2.5% nano-particles. The water-soluble thickening agent is a copolymer of acrylamide, sodium acrylate, 2-acrylamido-2-methylpropanesulfonic acid sodium salt, and fatty alcohol polyoxyethylene ether methacrylate with the model AM / AA / AMPS / OM and a molecular weight of 8 million.

[0056] Performance Test

[0057] Take the fracturing fluids of the examples and comparative examples, prepare a solution with a concentration of 0.1% with clear water, measure its viscosity with a capillary viscometer and its drag reduction rate with a drag reduction rate measuring instrument; prepare aqueous solutions with concentrations of 0.5% and 1.0% with clear water, and measure the viscosity after 5 minutes of dissolution with a six-speed viscometer, and the test temperature is 25°C; prepare aqueous solutions with concentrations of 0.5% and 1.0% with clear water, and prepare a 1.5% solution with 20% standard salinity brine, and then test its temperature and shear resistance at 90°C; prepare solutions with concentrations of 0.5 and 1.0% with standard mineralized water (85000 mg / L), and measure the viscosity after 5 minutes of dissolution with a six-speed viscometer.

[0058] Specifically:

[0059] (1) Take the oil-free fracturing thickening agents prepared in Examples 1 to 8, prepare an aqueous solution with a concentration of 0.1% with clear water, measure its viscosity with a capillary viscometer and its drag reduction rate with a drag reduction rate measuring instrument, and the test conditions are: 25°C. The results are shown in the following table:

[0060]

[0061] (2) Take the oil-free fracturing thickening agents prepared in Examples 1 to 8, prepare aqueous solutions with concentrations of 0.5% and 1.0% with clear water, and measure the viscosity after 5 minutes of dissolution with a six-speed viscometer. The results are shown in the following table:

[0062]

[0063] (3) Take the oil-free fracturing thickening agents prepared in Examples 5 to 8, prepare an aqueous solution with a concentration of 1.0% with standard mineralized water (85000 mg / L), and measure the viscosity after 5 minutes of dissolution with a six-speed viscometer. The results are shown in the following table:

[0064]

[0065] Experimental Example 4

[0066] The fracturing fluid prepared in Example 5 was respectively formulated into aqueous solutions with 0.5% and 1.0% of fresh water, and an aqueous solution with 1.5% was formulated with standard mineralized water, and then its temperature and shear resistance performance at 90 °C was tested. Among them, Figure 1 shows the rheological curve of the aqueous solution with a concentration of 0.5% prepared with fresh water at 90 °C; Figure 2 shows the rheological curve graph of the aqueous solution with a concentration of 1.0% prepared with fresh water at 90 °C; Figure 3 shows the rheological curve graph of the aqueous solution with a concentration of 1.5% prepared with 20% standard salinity brine at 90 °C. According to the rheological curve, it can be clearly seen that the fracturing fluid of the present invention has good temperature and shear resistance performance after application.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fracturing fluid, characterized in that, the fracturing fluid comprises a diversified ester-based solvent, nanoparticles and a water-soluble thickening agent; wherein, the water-soluble thickening agent is polyacrylamide and its derivatives.

2. The fracturing fluid according to claim 1, characterized in that, by weight percentage, the components of the fracturing fluid include: 20-50% of the water-soluble thickening agent, 50-70% of the diversified ester-based solvent and 0.5-5.0% of the nanoparticles; Preferably, the diversified ester-based solvent is selected from one or more of dimethyl succinate, dimethyl adipate, dimethyl phthalate, methyl lactate or methyl oleate.

3. The fracturing fluid according to claim 1 or 2, characterized in that, the nanoparticles are selected from one or more of hydrophilic nano-silica, hydrophobically modified silica or nano-cellulose; Preferably, the particle size D50 of the nanoparticles is 50-150 nm.

4. The fracturing fluid according to any one of claims 1 to 3, characterized in that, the components of the fracturing fluid include: 40-45% of the water-soluble thickening agent, 55-60% of the diversified ester-based solvent and 0.3-2.5% of the nano-material; Preferably, the polyacrylamide and its derivatives are selected from one or more of non-ionic polyacrylamide, poly(acrylamide-sodium acrylate), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt), poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt-long chain alkyl dimethyl allyl ammonium chloride) or poly(acrylamide-sodium acrylate-2-acrylamide-2-methylpropanesulfonic acid sodium salt-fatty alcohol polyoxyethylene ether methyl acrylate); Preferably, the weight average molecular weight Mw of the water-soluble thickening agent is 4 million to 30 million; Preferably, the water-soluble thickening agent is granular, and its average particle size is 120-180 μm.

5. A preparation method of the fracturing fluid according to any one of claims 1 to 4, characterized in that, the preparation method includes: Step S1: Dispersing the nanoparticles in the diversified ester-based solvent, and performing a first shearing treatment to obtain a pseudoplastic fluid; Step S2: Adding the water-soluble thickening agent to the pseudoplastic fluid, and performing a second shearing treatment to obtain the fracturing fluid.

6. The preparation method of the fracturing fluid according to claim 5, characterized in that, both the first shearing treatment and the second shearing treatment are performed in a high-speed shearing machine; Preferably, the shearing power of the first shearing treatment is 25-50 kW, the shearing speed is 9000-10000 rpm, and the shearing time is 1-1.5 h; Preferably, the shearing power of the second shearing treatment is 25-50 kW, the shearing speed is 9000-10000 rpm, and the shearing time is 2-3 h.

7. The preparation method of the fracturing fluid according to claim 5 or 6, characterized in that, the preparation process is carried out in a reaction kettle. Preferably, the jacket of the reaction kettle needs to be cooled with water to control the temperature in the reaction kettle at 10-40 °C; Preferably, the temperature of the cooling water is -10 to -20 °C.

8. The method for preparing a fracturing fluid according to any one of claims 5 to 7, characterized in that by weight percentage, the addition amount of the nanoparticles accounts for 2 to 2.5 wt% of the weight of the diversified ester-based solvent.

9. The method for preparing a fracturing fluid according to any one of claims 5 to 8, characterized in that by weight percentage, the weight ratio of the water-soluble thickening agent to the nanoparticles is (0.06 to 0.08):

1.

10. Use of a fracturing fluid according to any one of claims 1 to 4, or a fracturing fluid obtained by the preparation method of a fracturing fluid according to any one of claims 5 to 9, in the field of reservoir reconstruction in oil and gas fields; preferably, the fracturing fluid is used to prepare a fracturing working fluid for oil and gas fields. When the addition amount is 0.05 to 0.2% wt, a slickwater fracturing fluid is prepared, and its drag reduction rate ≥ 70%; when the addition amount is 0.5 to 1.5% wt, a high-viscosity sand-carrying fracturing fluid is prepared, and its apparent viscosity at 90 °C and 170 s -1 shearing for 2 h is ≥ 50 mPa·s.

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