Fracturing viscosifier, method for preparing same, and fracturing fluid
By combining specific monomer ratios with nano-permeability enhancers, a temperature- and shear-resistant thickener for fracturing was prepared, which solved the problem of fracturing fluid damaging the reservoir, improved flowback rate and permeability, and achieved long-term stable production and high recovery rate of the gas field.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA NAT PETROLEUM CORP
- Filing Date
- 2024-12-23
- Publication Date
- 2026-06-23
AI Technical Summary
Existing fracturing fluids cause severe damage to the reservoir during high-volume, high-displacement operations, including fracturing fluid residue damage, fracturing fluid retention damage, water lock-in, and self-absorption damage. This leads to a decrease in reservoir gas phase permeability and affects the long-term stable production and recovery rate of the gas field.
A fracturing thickener with temperature, shear, and salt resistance was prepared by segmented initiation polymerization using a specific ratio of hydrophilic monomers, cationic monomers, anionic monomers, and composite supramolecular interaction monomers. This thickener was then used in conjunction with a nano-penetrating agent to form a fracturing fluid with low interfacial tension and low rupture fluid residue.
It significantly reduced the damage of fracturing fluid to the reservoir, increased the flowback rate and permeability, reduced the residue of fracturing fluid, improved the reservoir stimulation effect, and achieved long-term stable production and high recovery rate of the gas field.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to a thickener for fracturing, its preparation method, and fracturing fluid. Background Technology
[0002] Volumetric fracturing is a commonly used technique for unconventional reservoir stimulation. However, under the construction mode of large displacement and large fluid volume, the damage caused by fracturing fluid to the reservoir in three aspects cannot be ignored: damage from fracturing fluid residue, damage from fracturing fluid retention, and damage from water lock and self-priming.
[0003] Guar gum fracturing fluid remains widely used in volumetric fracturing operations due to its excellent uniform sand suspension properties, making it the most mainstream gel fracturing fluid. However, during the oxidative fracturing process of guar gum molecules, the dissociation rate of galactose in the side chains is much greater than that of mannose in the main chain, resulting in reduced solubility of guar gum molecules. This makes it difficult for fracturing agents to completely break down the guar gum molecules, and the residue after fracturing with guar gum fracturing fluid can reach 200-400 mg / L, which can cause significant damage to the reservoir.
[0004] During volumetric fracturing, the flowback rate of fracturing fluid is generally only 10-50% due to the propagation of complex fractures. Achieving rapid and effective flowback of fracturing fluid, as well as reducing soaking time and penetration depth, is key to fundamentally reducing fracturing fluid damage and improving reservoir recovery.
[0005] Volumetric fracturing creates a complex network of fractures with small capillary radii and large capillary forces. Under the influence of these capillary forces, large amounts of fluid are drawn into the deep formation, causing water-phase trapping damage.
[0006] The combined effects of the aforementioned reservoir damage significantly reduce reservoir gas permeability. Therefore, developing a new generation of multi-purpose fracturing fluids that can fully replace slickwater (with a drag reduction of up to 75%, salt resistance, and variable viscosity) and guar gum fracturing fluid (with high temperature resistance, shear resistance, and uniform proppant carrying capacity) in terms of performance, and comprehensively reduce the damage to the reservoir caused by fracturing fluids during volumetric fracturing in three aspects, in order to achieve long-term stable gas field production and improve recovery rate, is an urgent problem that needs to be solved in unconventional reservoir stimulation. Summary of the Invention
[0007] The purpose of this invention is to provide a technical solution that enables fracturing fluid to have low reservoir damage and excellent temperature resistance, shear resistance, salt resistance, and sand suspension performance.
[0008] To achieve the above objectives, the present invention provides the following technical solution.
[0009] In a first aspect, the present invention provides a method for preparing a thickener for fracturing, wherein the preparation method includes:
[0010] The monomer is reacted in an aqueous environment using an azo initiator and a redox initiator. The resulting product is then granulated, hydrolyzed, dried, and powdered to obtain the fracturing thickener.
[0011] The monomers, based on a total mass of 100%, comprise 65%-69% hydrophilic monomers, 3%-5% cationic monomers, 10%-15% a first anionic monomer, 3%-5% a second anionic monomer, and 10%-15% composite supramolecular interaction monomers. The hydrophilic monomer is selected from acrylamide; the cationic monomer is selected from at least one of dimethyl diallyl ammonium chloride; the first anionic monomer is selected from sodium acrylate; the second anionic monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid; and the composite supramolecular interaction monomer comprises a mixture of octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate in a mass ratio of 3.5-4:1.
[0012] The fracturing thickener preparation method provided by this invention utilizes a special hydrophilic monomer, cationic monomer, anionic monomer, and composite supramolecular interaction monomer (using a polymerizable surfactant) with specific monomer ratios, employing a segmented initiation process followed by hydrolysis to prepare the fracturing thickener. The fracturing thickener prepared by this method significantly enhances the surface activity and intermolecular supramolecular forces of the thickener, achieving a lower molecular weight while exhibiting excellent properties such as reducing interfacial tension, thickening, temperature and shear resistance, salt resistance, and sand carrying capacity. Simultaneously, it can significantly reduce the residue of the breaking fluid, minimizing residue damage to the reservoir and improving reservoir stimulation effectiveness.
[0013] The fracturing thickener preparation method provided by this invention uses a specific ratio of polymerizable surfactants octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate as composite supramolecular interaction monomers, combined with a specific ratio of hydrophilic monomers, cationic monomers, and anionic monomers. A segmented initiation polymerization followed by hydrolysis process is employed to prepare the fracturing thickener. Compared to thickeners prepared using conventional supramolecular interaction monomers, the fracturing thickener prepared by this invention significantly enhances the supramolecular interaction forces between molecules, achieving good thickening, temperature and shear resistance, salt resistance, and sand carrying capacity at a lower molecular weight. Simultaneously, it significantly enhances the surface activity of the thickener, resulting in a substantial decrease in the interfacial tension of the fracturing fluid prepared using this thickener. This is beneficial for flowback and improved permeability of the fracturing fluid, significantly reducing the residue of the breaking fluid, minimizing residue damage to the reservoir, and improving reservoir stimulation effectiveness. Furthermore, the long hydrophobic segments of the fracturing thickener prepared by the method of the present invention can penetrate into the nano-permeability enhancer structure in the fracturing fluid provided by the present invention, and have a synergistic effect with the nano-permeability enhancer to promote the formation and stability of the nanostructure.
[0014] According to a preferred embodiment of the first aspect, preferably, the azo initiator is azobisisobutyramidine hydrochloride.
[0015] According to a preferred embodiment of the first aspect, preferably, the amount of azo initiator is 0.015%-0.025% based on the total mass of the monomers as 100%.
[0016] According to a preferred embodiment of the first aspect, preferably, the redox reaction initiator includes sodium bisulfite and sodium persulfate;
[0017] More preferably, based on the total mass of the monomers, the amount of sodium bisulfite is 0.01%-0.02% and the amount of sodium persulfate is 0.02%-0.04%.
[0018] The preferred embodiment of the above-mentioned method for preparing fracturing thickener, by selecting the type of initiator and appropriately increasing the amount of redox reaction initiator, accelerates the polymerization reaction rate. While ensuring that the thickener still has good thickening, temperature and shear resistance, salt resistance, and sand carrying properties, it further reduces the molecular weight of the polymer and further reduces the liquid residue after delamination.
[0019] According to a preferred embodiment of the first aspect, preferably, the mass content of the monomer is 28%-30% based on the total mass of water and monomer in the aquatic environment being 100%.
[0020] According to the preferred embodiment of the first aspect, preferably, the aquatic environment also contains urea; the amount of urea used is 4%-8% based on the total mass of the monomers as 100%;
[0021] The addition of urea can improve the solubility of the thickener and accelerate the dissolution rate.
[0022] According to the preferred embodiment of the first aspect, preferably, the aquatic environment also contains potassium chloride; the amount of potassium chloride used is 3%-6% based on the total mass of the monomers as 100%;
[0023] The addition of potassium chloride can adjust the length of the hydrophobic monomer microblocks in the thickener, thereby regulating the hydrophobic properties of the thickener.
[0024] According to a preferred embodiment of the first aspect, preferably, the aquatic environment also contains sodium formate; the amount of sodium formate is 0.02%-0.06% based on the total mass of the monomers as 100%;
[0025] The addition of sodium formate can inhibit water-insoluble substances during the polymerization process.
[0026] According to the preferred embodiment of the first aspect, preferably, the aquatic environment also contains EDTA-2Na; the amount of EDTA-2Na is 0.1%-0.2% based on the total mass of the monomers as 100%;
[0027] The addition of EDTA-2Na can control the rate of polymerization and improve the stability of the prepared product by chelating metal ions.
[0028] According to a preferred embodiment of the first aspect, hydrolysis is preferably carried out by adding an aqueous sodium hydroxide solution and op-10;
[0029] More preferably, the mass concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 30%-40%;
[0030] More preferably, the amount of sodium hydroxide aqueous solution used is 2%-5% based on the mass of the granulated particles (100%).
[0031] More preferably, the amount of op-10 used is 0.3%-0.6% based on the mass of the granulated particles obtained by granulation, which is 100%.
[0032] More preferably, hydrolysis is carried out at 80-90°C;
[0033] More preferably, the hydrolysis time is 1.5-3 hours.
[0034] According to a preferred embodiment of the first aspect, preferably, the method for preparing the thickener for fracturing includes:
[0035] 1) Prepare a first solution; wherein the first solution contains various components, monomers, and azo initiators in an aqueous environment;
[0036] 2) Heat the first solution to the target temperature; under heat preservation conditions, deoxygenate the first solution and mix it with the redox reaction initiator, and then carry out the reaction in an oxygen-free atmosphere;
[0037] 3) The product obtained from the reaction in step 2) is granulated, hydrolyzed, dried and powdered in sequence to obtain the thickener for fracturing.
[0038] According to a preferred embodiment of the first aspect, preferably, the pH value of the first solution is 6.90-7.30.
[0039] According to a preferred embodiment of the first aspect, preferably, the target temperature is 18-22°C.
[0040] According to the preferred embodiment of the first aspect, preferably, the deoxygenation process is carried out by introducing nitrogen gas; more preferably, the nitrogen gas is introduced for 30-45 minutes.
[0041] According to the preferred embodiment of the first aspect, preferably, the oxygen-free atmosphere is a nitrogen atmosphere;
[0042] In one specific embodiment, the nitrogen atmosphere is provided by purging nitrogen into a sealed reaction vessel until no more nitrogen can be introduced.
[0043] According to the preferred embodiment of the first aspect, preferably, the reaction time is 3-5 hours during the reaction process carried out in an oxygen-free atmosphere.
[0044] In a second aspect, the present invention provides a thickener for fracturing, wherein the thickener for fracturing can be prepared by the preparation method of the thickener for fracturing provided in the first aspect of the invention.
[0045] The thickener for fracturing provided by this invention is a pentagonal copolymer produced by a segmented initiation process using a special ratio of hydrophilic monomers, cationic monomers, a first anionic monomer, a second anionic monomer, a composite supramolecular monomer, and a special monomer.
[0046] Thirdly, the present invention provides the application of the fracturing thickener provided in the second aspect of the present invention as a thickener in slickwater fracturing fluid and / or gel fracturing fluid.
[0047] According to a preferred embodiment of the third aspect, preferably, the amount of the thickener for fracturing provided in the second aspect of the present invention is 0.02%-0.1% based on the total mass of the slickwater fracturing fluid as 100%.
[0048] According to the preferred embodiment of the third aspect, preferably, the amount of the thickener for fracturing provided in the second aspect of the present invention is greater than 0.1% and not more than 0.6% based on the total mass of the fracturing fluid as 100%.
[0049] Fourthly, the present invention provides a fracturing fluid comprising a thickener and a nano-penetrating agent provided in the second aspect of the present invention; based on the total mass of the fracturing fluid as 100%, the mass content of the thickener is 0.02%-0.6%, and the mass content of the nano-penetrating agent is 0.1%-0.5%.
[0050] The raw material components of the nano-penetrating agent include limonene, water, modified flake molybdenum disulfide nanofluid solution, dodecanol, Tween-80, and Span-80 in a mass ratio of 2.5-3.5:2:4.5-5.5:0.8-1.2:0.4-0.6:0.4-0.6.
[0051] Among them, the modified sheet-like molybdenum disulfide nanofluid solution is a dihexyldimethylammonium chloride modified sheet-like molybdenum disulfide nanofluid solution.
[0052] The fracturing fluid provided by this invention uses a specific thickener combined with a nano-penetrating agent. The nano-penetrating agent is a surfactant with a particle size of nanometers. Utilizing the adsorption effect of the modified lamellar molybdenum disulfide material in the nano-penetrating agent, the fracturing fluid forms an oriented adsorption film on the rock, transforming the original high-energy surface of the rock into a low-energy surface. This results in a self-repellent phenomenon where the low-energy liquid cannot wet the solid rock surface, reducing fracturing fluid retention, mitigating water lock and self-absorption damage. At the same time, the nano-penetrating agent can positively synergize with the thickener molecules from a molecular structure perspective, improving the fracturing fluid's drag reduction, sand suspension, and surface tension reduction properties, while reducing the amount of thickener required.
[0053] In the fracturing fluid provided by this invention, the long hydrophobic segments of the thickener can penetrate deep into the nano-permeability enhancer structure and have a synergistic effect with the nano-permeability enhancer, promoting the formation and stability of the nanostructure.
[0054] The fracturing fluid provided by this invention uses nano-sheet molybdenum disulfide. Compared with spherical silica, the concentration of sheet molybdenum disulfide is lower, its interfacial free energy is smaller, and it is easier to adsorb onto the rock surface, thus improving the modification efficiency of the rock surface. Furthermore, the sheet molybdenum disulfide has a better synergistic effect with the octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate monomers in the thickener, further reducing the surface and interfacial tension of the fracturing fluid.
[0055] According to a preferred embodiment of the fourth aspect, preferably, the modified sheet-like molybdenum disulfide nanofluid solution can be prepared by the following method:
[0056] Water, nanosheet molybdenum disulfide, and dihexadecyl dimethyl ammonium chloride are mixed to obtain a first mixture; wherein, based on the total mass of water as 100%, the amount of nanosheet molybdenum disulfide is 0.4%-0.6%, and the amount of dihexadecyl dimethyl ammonium chloride (i.e., dimethyl dihexadecyl ammonium chloride) is 1.5%-2.5%.
[0057] After adjusting the pH of the first mixture to 9.8-10.2, it was subjected to ultrasonic dispersion to obtain a modified flake-like molybdenum disulfide nanofluid solution.
[0058] More preferably, during the process of adjusting the pH value of the first mixture to 9.8-10.2, a sodium hydroxide solution is used for pH adjustment; even more preferably, the concentration of sodium hydroxide in the sodium hydroxide solution is 1.8-2.2 mol / L, based on the volume of the sodium hydroxide solution.
[0059] More preferably, during the process of adjusting the pH value of the first mixture to 9.8-10.2, the first mixture is stirred at a stirring speed of 800-1200 r / min;
[0060] More preferably, the ultrasonic dispersion frequency is 35-45kHz, and the ultrasonic dispersion treatment time is 1-1.5h.
[0061] According to a preferred embodiment of the fourth aspect, preferably, the nano-permeability enhancer can be prepared by the following method:
[0062] A nano-penetrating agent was obtained by mixing limonene, water, modified flake molybdenum disulfide nanofluid solution, dodecanol, Tween-80, and Span-80.
[0063] More preferably, the mixing is achieved by stirring at 4500-5500 r / min for 2-5 min.
[0064] The median particle size of the nano-permeability enhancer prepared by the above preferred embodiment is ≤30nm.
[0065] According to a preferred embodiment of the fourth aspect, preferably, when the fracturing fluid is a slickwater fracturing fluid, the mass content of the thickener is 0.02%-0.1% and the mass content of the nano-penetrating agent is 0.1%-0.3%, based on the total mass of the fracturing fluid as 100%.
[0066] According to the preferred embodiment of the fourth aspect, preferably, when the fracturing fluid is a gel-water fracturing fluid, the mass content of the thickener is greater than 0.1% and not more than 0.6% based on the total mass of the fracturing fluid as 100%, and the mass content of the nano-penetrating agent is 0.2%-0.5%.
[0067] The fracturing fluid provided by this invention possesses excellent temperature resistance, shear resistance, salt resistance, and proppant-carrying properties, while also exhibiting low damage from broken gel residue, low damage from fracturing fluid retention, and low damage from water lock and self-priming. Compared with existing technologies, the technical solution provided by this invention has the following beneficial effects:
[0068] 1. The thickener for fracturing provided by this invention can be used to formulate slickwater fracturing fluid and gel fracturing fluid by changing its concentration. The slickwater fracturing fluid prepared by this invention has a drag reduction of over 70%, a salt tolerance of over 60,000 ppm, and a linearly adjustable viscosity of 2-30 mPa·s. The gel fracturing fluid prepared by this invention can uniformly carry sand like gum, has a temperature resistance of over 180℃, and has a residue of ≤30 ppm after breaking the gel, which is more than 85% lower than that of gum. The thickener for fracturing provided by this invention has an ultra-low critical association concentration, which is <500 mg / L.
[0069] 2. The fracturing fluid provided by this invention incorporates a nano-permeability enhancer. After treatment with the fracturing fluid containing the nano-permeability enhancer, the water phase contact angle of the core sample is ≥90°, and the rock surface changes from hydrophilic to hydrophobic, significantly reducing the damage to the reservoir caused by fracturing fluid intrusion, improving the flowback rate, and reducing water lock and self-absorption damage. The relative permeability of the gas phase after treatment with the fracturing fluid provided by this invention increases by ≥10% compared to treatment with conventional fracturing fluids (e.g., polyacrylamide fracturing fluids, guar gum fracturing fluids). The surface tension of the broken fracturing fluid obtained after breaking the gel provided by this invention is ≤24 mN / m, and the interfacial tension is ≤1 mN / m. Attached Figure Description
[0070] Figure 1 The graph shows the drag reduction rate of the slickwater fracturing fluid A provided in Example 1 over time.
[0071] Figure 2 The graph shows the drag reduction rate of the slickwater fracturing fluid B provided in Example 1 over time.
[0072] Figure 3 This is a comparison chart of the thickening properties of the fracturing thickener provided in Example 1 and a conventional fracturing thickener.
[0073] Figure 4 Comparison of suspended sand morphology between gel fracturing fluid A and gel fracturing fluid B provided in Example 2.
[0074] Figure 5 The temperature and shear resistance diagram is for the gel hydraulic fracturing fluid A provided in Example 2.
[0075] Figure 6 This is a comparison diagram of the morphology of the gel breaking liquid in Example 2.
[0076] Figure 7 The image shows the water phase contact angle test results of the glass plate and rock plate after treatment with slickwater fracturing fluid A in Example 1.
[0077] Figure 8 This is a comparison chart of the relative gas phase permeability of the support crack after treatment with adhesive fracturing fluid A and after treatment with adhesive fracturing fluid B in Example 2. Detailed Implementation
[0078] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.
[0079] Example 1
[0080] This embodiment provides a thickener, a nano-penetrating agent, and a fracturing fluid for fracturing.
[0081] The thickener for fracturing is prepared by the following method:
[0082] Add 500 kg of water to the reactor, along with 134 kg of acrylamide, 8 kg of dimethyl diallyl ammonium chloride, 30 kg of sodium acrylate, 8 kg of 2-acrylamido-2-methylpropanesulfonic acid, and 20 kg of a mixture obtained by mixing octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate in a mass ratio of 3.5:1. Add 8 kg of urea, 8 kg of potassium chloride, 0.3 kg of EDTA-2Na, 0.08 kg of sodium formate, and 0.04 kg of azobisisobutyramidine hydrochloride. Dissolve all components thoroughly and adjust the pH to 7.05 to obtain the first solution. Heat the reactor containing the first solution to... At 20℃, under heat preservation conditions, nitrogen gas was introduced for 40 minutes to remove oxygen. Then, redox reaction initiators were added: 0.02 kg of sodium bisulfite and 0.04 kg of ammonium persulfate. The nitrogen gas was increased and nitrogen was continued until no more could be introduced. The reaction was continued for 4 hours to complete the reaction. The obtained product was granulated, and 4% sodium hydroxide aqueous solution (sodium hydroxide concentration in the sodium hydroxide aqueous solution was 40%) and 0.4% OP-10 were added to the granulated particles. After mixing evenly, the mixture was hydrolyzed in an oven at 80℃ for 2 hours, and then dried. The dried product was then pulverized through a 100-mesh sieve to obtain the fracturing thickener.
[0083] The nano-penetrating agent was prepared by the following method:
[0084] At room temperature, 0.42 kg of nanosheet molybdenum disulfide washed with anhydrous ethanol and 1.67 kg of dihexadecyldimethylammonium chloride were added to 81.24 kg of deionized water to obtain a first mixture. The electric stirrer was set to a speed of 1000 r / min, and a 2 mol / L sodium hydroxide solution was added to the first mixture in portions to adjust the pH to 10.0, with stirring continued for 1 h. The mixture was then ultrasonically dispersed at a frequency of 40 kHz for 1 h to obtain a homogeneous modified nanofluid solution of molybdenum disulfide nanosheets. According to the mass ratio of limonene:water:modified flake molybdenum disulfide nanofluid solution:dodecyl alcohol:Tween-80:Span-80 of 3:2:5:1:0.5:0.5, limonene, water, modified flake molybdenum disulfide nanofluid solution, dodecyl alcohol, Tween-80, and Span-80 were placed in a mixer and mixed. The mixture was stirred at 5000 r / min for 2 min to obtain 200 kg of transparent, stable, and homogeneous nano-penetrating agent.
[0085] Fracturing fluid is prepared by the following method:
[0086] The fracturing thickener and nano-penetrating agent provided in this embodiment were dissolved in water to prepare slickwater fracturing fluid A with a fracturing thickener concentration of 0.02% (based on 100% of the total mass of the slickwater fracturing fluid) and a nano-penetrating agent concentration of 0.3% (based on 100% of the total mass of the slickwater fracturing fluid). The drag reduction rate reached 74.72%, and the dissolution time was 28 seconds (e.g., Figure 1 (As shown). After treatment with slickwater fracturing fluid A, the water phase contact angle of the glass plate was 101°; after treatment with slickwater fracturing fluid A, the water phase contact angle of the rock plate was 96°, and the surface changed from hydrophilic to hydrophobic (as shown). Figure 7 (As shown).
[0087] The fracturing thickener and nano-penetrating agent provided in this embodiment were dissolved in 60,000 ppm sodium chloride brine to prepare slickwater fracturing fluid B with a fracturing thickener concentration of 0.03% (based on 100% of the total mass of the slickwater fracturing fluid) and a nano-penetrating agent concentration of 0.3% (based on 100% of the total mass of the slickwater fracturing fluid). The drag reduction rate reached 75.2%, and the dissolution time was 19 seconds (e.g., ...). Figure 2 (As shown).
[0088] Fracturing fluids with different mass concentrations of fracturing thickener (0.01%, 0.02%, 0.03%, 0.05%, 0.1%, 0.15%, 0.2%, 0.3%) and nano-penetrating agent (0.3% mass of fracturing fluid, based on 100% of the total mass of the fracturing fluid) were prepared by dissolving the conventional fracturing thickener (a polyacrylamide-based fracturing thickener purchased from Sichuan Chuanqing Well Technology Co., Ltd.) in water. Fracturing fluids with different mass concentrations of fracturing thickener (0.01%, 0.02%, 0.03%, 0.05%, 0.1%, 0.15%, 0.2%, 0.3%) were then prepared. The concentrations of each prepared fracturing fluid were tested, and the results are as follows: Figure 3 As shown.
[0089] The fracturing thickener and nano-penetrating agent provided in this embodiment were dissolved in water to prepare fracturing fluids with different mass concentrations of thickener and a mass concentration of 0.3% of nano-penetrating agent (based on the total mass of fracturing fluid being 100%). The surface tension of each fracturing fluid was tested, and the critical association concentration of the thickener was determined to be 482 mg / L by the surface tension method.
[0090] Example 2
[0091] This embodiment provides a thickener, a nano-penetrating agent, and a fracturing fluid for fracturing.
[0092] The thickener for fracturing is prepared by the following method:
[0093] Add 470 kg of water to the reactor, along with 135 kg of acrylamide, 8 kg of dimethyl diallyl ammonium chloride, 24 kg of sodium acrylate, 8 kg of 2-acrylamido-2-methylpropanesulfonic acid, and 25 kg of a mixture obtained by mixing octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate in a mass ratio of 3.5:1. Add 12 kg of urea, 10 kg of potassium chloride, 0.4 kg of EDTA-2Na, 0.1 kg of sodium formate, and 0.03 kg of azobisisobutyramidine hydrochloride. Dissolve thoroughly and adjust the pH to 7.12 to obtain the first solution. Heat the reactor containing the first solution to 20 °C. ℃; Under heat preservation conditions, nitrogen gas is introduced for 40 minutes to remove oxygen, and then redox reaction initiators: sodium bisulfite 0.025 kg and ammonium persulfate 0.045 kg are added. The nitrogen gas is increased and nitrogen is continued to be introduced until no more can be introduced. The reaction is continued to be kept at the temperature for 4 hours to complete the reaction. The obtained product is granulated, and 3.5% sodium hydroxide aqueous solution (sodium hydroxide concentration in sodium hydroxide aqueous solution is 38%) and 0.35% OP-10 are added to the granulated granules. After mixing evenly, the mixture is hydrolyzed in an oven at 80℃ for 2 hours, and then dried. The dried product is then crushed and passed through a 100-mesh sieve to obtain the fracturing thickener.
[0094] The nano-penetrating agent was prepared by the following method:
[0095] At room temperature, 0.5 kg of nanosheet molybdenum disulfide washed with anhydrous ethanol and 2 kg of dihexadecanyldimethylammonium chloride were added to 80.83 kg of deionized water to obtain a first mixture. The electric stirrer was set to 1000 r / min, and a 2 mol / L sodium hydroxide solution was added to the first mixture in portions to adjust the pH to 10.0, with stirring continued for 1.5 h. The mixture was then ultrasonically dispersed at a frequency of 40 kHz for 1.5 h to obtain a homogeneous modified nanofluid solution of molybdenum disulfide nanosheets. According to the mass ratio of limonene:water:modified flake molybdenum disulfide nanofluid solution:dodecyl alcohol:Tween-80:Span-80 of 3:2:5:1:0.5:0.5, limonene, water, modified flake molybdenum disulfide nanofluid solution, dodecyl alcohol, Tween-80, and Span-80 were placed in a mixer and mixed for 5 minutes at 5000 rpm to obtain 200 kg of transparent, stable, and homogeneous nano-penetrating agent.
[0096] Fracturing fluid is prepared by the following method:
[0097] The fracturing thickener and nano-penetrating agent provided in this embodiment were dissolved in water to prepare a gel-type fracturing fluid A with a fracturing thickener concentration of 0.03% (based on 100% of the total mass of the slickwater fracturing fluid) and a nano-penetrating agent concentration of 0.3% (based on 100% of the total mass of the slickwater fracturing fluid). A conventional fracturing thickener (purchased from Sichuan Chuanqing Well Technology Co., Ltd., a polyacrylamide-based fracturing thickener) was dissolved in water to prepare a gel-type fracturing fluid B with a fracturing thickener concentration of 0.03% (based on 100% of the total mass of the slickwater fracturing fluid). The dynamic proppant-carrying capacity of both was tested. The proppant suspension in gel-type fracturing fluid B was piled up and strip-shaped, while the proppant suspension in gel-type fracturing fluid A was more uniformly distributed, resembling gel-like proppant suspension. Figure 4 As shown. The residue obtained after fracturing with gel-fracturing fluid A was only 5 ppm; compared with the residue of 231 ppm obtained after fracturing with guar gum, this represents a reduction of 97.8%; compared with the residue of 133 ppm obtained after fracturing with gel-fracturing fluid B, this represents a reduction of 96.2%. The morphology of the residue obtained after fracturing with each gel-fracturing fluid is as follows. Figure 6 As shown. The relative permeability of the gas phase in the supported fracture increased by 21.58% after treatment with fracturing fluid A compared to treatment with fracturing fluid B (e.g., Figure 8 (As shown).
[0098] The gel hydraulic fracturing fluid A provided in this embodiment was tested using a Hacker rheometer, with the temperature increased to 180°C at a rate of 3°C / min, and the temperature was measured within 100 seconds. -1 The shear test of the prepared gel hydraulic fracturing fluid for 2 hours yielded the following results: Figure 5 As shown, the prepared gel fracturing fluid A has a temperature resistance of up to 180℃.
[0099] Comparative Example 1
[0100] This comparative example provides a thickener for fracturing.
[0101] The preparation method of the fracturing thickener provided in this comparative example differs from the preparation method of the fracturing thickener provided in Example 1 only in that: instead of adding octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate, 20 kg of hexadecyl dimethyl allyl ammonium chloride is added.
[0102] Comparative Example 2
[0103] This comparative example provides a thickener for fracturing.
[0104] The preparation method of the fracturing thickener provided in this comparative example differs from the preparation method of the fracturing thickener provided in Example 1 only in that: instead of adding octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate, 20 kg of a mixture of octadecyl dimethyl allyl ammonium chloride and hexadecyl dimethyl allyl ammonium chloride in a mass ratio of 1:1 is added.
[0105] Comparative Example 3
[0106] This comparative example provides a thickener for fracturing.
[0107] The preparation method of the fracturing thickener provided in this comparative example differs from the preparation method of the fracturing thickener provided in Example 1 only in that: instead of adding octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate, 20 kg of a mixture of hexadecyl dimethyl allyl ammonium chloride and octadecyl dimethyl allyl ammonium chloride in a mass ratio of 3.5:1 is added.
[0108] Comparative Example 4
[0109] This comparative example provides a thickener for fracturing.
[0110] The preparation method of the fracturing thickener provided in this comparative example differs from the preparation method of the fracturing thickener provided in Example 1 only in that: nonylphenol polyoxyethylene ether acrylate is not added, but only 20 kg of octylphenol polyoxyethylene ether acrylate is added.
[0111] Comparative Example 5
[0112] This comparative example provides a thickener for fracturing.
[0113] The preparation method of the fracturing thickener provided in this comparative example differs from the preparation method of the fracturing thickener provided in Example 1 only in that: the mass ratio of octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate is 1:1, and the total mass of octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate is 20 kg.
[0114] Experimental Example 1
[0115] Fracturing fluids with a thickening agent concentration of 0.1% (based on 100% of the total mass of the fracturing fluid) and a nano-penetrating agent concentration of 0.3% (based on 100% of the total mass of the fracturing fluid) were prepared by dissolving the thickening agents provided in Examples 1, 1, 2, 3, 4, and 5, and the nano-penetrating agent concentration in Example 1, respectively, in water. The surface tension and interfacial tension of each fracturing fluid were tested, and the results are shown in Table 1.
[0116] Table 1
[0117] Sources of thickeners for fracturing Surface tension / mN / m Interfacial tension / mN / m Comparative Example 1 39 15 Comparative Example 2 35 13 Comparative Example 3 31 10 Comparative Example 4 29 9 Comparative Example 5 27 9 Example 1 23 5
[0118] Example 3
[0119] This embodiment provides a thickener for fracturing.
[0120] The difference between the preparation method of the fracturing thickener provided in this embodiment and the preparation method of the fracturing thickener provided in Example 1 is only that: the amount of sodium bisulfite added is 0.06% of the total mass of the monomers and the amount of ammonium persulfate added is 0.012% of the total mass of the monomers.
[0121] Example 4
[0122] This embodiment provides a thickener for fracturing.
[0123] The difference between the preparation method of the fracturing thickener provided in this embodiment and the preparation method of the fracturing thickener provided in Example 1 is only that: the amount of sodium bisulfite added is 0.008% of the total mass of the monomers and the amount of ammonium persulfate added is 0.015% of the total mass of the monomers.
[0124] Example 5
[0125] This embodiment provides a thickener for fracturing.
[0126] The difference between the preparation method of the fracturing thickener provided in this embodiment and the preparation method of the fracturing thickener provided in Example 1 is only that: the amount of azobisisobutyramidine hydrochloride added is 0.03% of the total mass of monomers, the amount of sodium bisulfite added is 0.006% of the total mass of monomers, and the amount of ammonium persulfate added is 0.012% of the total mass of monomers.
[0127] Example 6
[0128] This embodiment provides a thickener for fracturing.
[0129] The difference between the preparation method of the fracturing thickener provided in this embodiment and the preparation method of the fracturing thickener provided in Example 1 is only that: the amount of sodium bisulfite added is 0.008% of the total mass of the monomers and the amount of ammonium persulfate added is 0.015% of the total mass of the monomers.
[0130] Example 7
[0131] This embodiment provides a thickener for fracturing.
[0132] The only difference between the preparation method of the fracturing thickener provided in this embodiment and the preparation method of the fracturing thickener provided in Example 1 is that the amount of azobisisobutyramidine hydrochloride added is 0.03% of the total mass of the monomers.
[0133] Experiment Example 2
[0134] The fracturing thickeners provided in Examples 1, 3, 4, 5, 6, and 7, along with the nano-penetrating agent provided in Example 1, were dissolved in water to prepare fracturing fluids with a thickener concentration of 0.5% (based on 100% of the total mass of the fracturing fluid) and a nano-penetrating agent concentration of 0.3% (based on 100% of the total mass of the fracturing fluid). The residue content of the broken fracturing fluid after breaking the gel of each prepared fracturing fluid was tested, and the results are shown in Table 2.
[0135] Table 2
[0136]
[0137]
[0138] Comparative Example 6
[0139] This comparative example provides a nano-permeability enhancer.
[0140] The preparation method of the nano-penetrating agent provided in this comparative example differs from the preparation method of the nano-penetrating agent provided in Example 1 only in that: instead of using nano-sheet molybdenum disulfide, nano-silica is used.
[0141] Experimental Example 3
[0142] The nano-penetrating agent provided in Example 1 and Comparative Example 1, and the fracturing thickener provided in Example 1 were dissolved in water to prepare fracturing thickener with a mass concentration of 0.3% (based on the total mass of the fracturing fluid of 000%) and nano-penetrating agent with a mass concentration of 0.3% (based on the total mass of the fracturing fluid of 100%). The surface tension and interfacial tension of the fracturing fluid obtained after breaking the gel were then tested, and the results are shown in Table 3.
[0143] At the same concentration, nano-penetration enhancers prepared using nano-laminated molybdenum disulfide have lower interfacial free energy compared to those prepared using traditional nano-silica, making them easier to adsorb onto rock surfaces and improving surface modification efficiency. Furthermore, the synergistic effect of the lamellar molybdenum disulfide with the octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate monomers in the thickener is better, further reducing the surface and interfacial tension of the broken fluid obtained after fracturing fluid breakdown.
[0144] Table 3
[0145] Sources of thickeners for fracturing Surface tension of the gel breaking liquid / mN / m Interfacial tension of the gel breaking liquid / mN / m Comparative Example 6 22.50 1.44 Example 1 21.70 0.07
[0146] The embodiments described above are for the purpose of better explaining the present invention. For those skilled in the art, it is not difficult to make various modifications to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and variations made to the present invention by those skilled in the art based on the principles and spirit of the present invention should be within the scope of protection of the present invention.
Claims
1. A method for preparing a thickener for fracturing, wherein, The preparation method includes: The monomer is reacted in an aqueous environment using an azo initiator and a redox initiator. The resulting product is then granulated, hydrolyzed, dried, and powdered to obtain the fracturing thickener. The monomers, based on a total mass of 100%, comprise 65%-69% hydrophilic monomers, 3%-5% cationic monomers, 10%-15% a first anionic monomer, 3%-5% a second anionic monomer, and 10%-15% composite supramolecular interaction monomers. The hydrophilic monomer is selected from acrylamide; the cationic monomer is selected from at least one of dimethyl diallyl ammonium chloride; the first anionic monomer is selected from sodium acrylate; the second anionic monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid; and the composite supramolecular interaction monomer comprises a mixture of octylphenol polyoxyethylene ether acrylate and nonylphenol polyoxyethylene ether acrylate in a mass ratio of 3.5-4:
1.
2. The preparation method according to claim 1, wherein, The azo initiator selected is azobisisobutyramidine hydrochloride; the amount of azo initiator is 0.02%-0.035% based on the total mass of the monomers (100%). The redox initiators include sodium bisulfite and sodium persulfate; based on the total mass of the monomers (100%), the amount of sodium bisulfite is 0.01%-0.02%, and the amount of sodium persulfate is 0.02%-0.04%.
3. The preparation method according to claim 1, wherein, Based on the total mass of water and monomers in the aquatic environment being 100%, the mass content of monomers is 28%-30%.
4. The preparation method according to claim 1, wherein, The aquatic environment also contains at least one of the following: urea, potassium chloride, sodium formate, and EDTA-2Na. Based on the total mass of monomers as 100%, the amount of urea used is 4%-8%; Based on the total mass of monomers as 100%, the amount of potassium chloride used is 3%-6%; Based on the total mass of monomers as 100%, the amount of sodium formate used is 0.02%-0.06%; Based on the total mass of monomers as 100%, the amount of EDTA-2Na used is 0.1%-0.2%.
5. The preparation method according to claim 1, wherein, Hydrolysis was carried out by adding sodium hydroxide aqueous solution and OP-10. The mass concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 30%-40%; Based on the mass of the granulated particles obtained by granulation as 100%, the amount of sodium hydroxide aqueous solution used is 2%-5%; Based on the mass of the granulated granules as 100%, the amount of op-10 used is 0.3%-0.6%; Preferably, hydrolysis is carried out at 80-90°C; Preferably, the hydrolysis time is 1.5-3 hours.
6. The preparation method according to any one of claims 1-5, wherein, Methods for preparing thickeners for fracturing include: 1) Prepare a first solution; wherein the first solution contains various components, monomers, and azo initiators in an aqueous environment; 2) Heat the first solution to the target temperature; under heat preservation conditions, deoxygenate the first solution and mix it with the redox reaction initiator, and then carry out the reaction in an oxygen-free atmosphere; 3) The product obtained from the reaction is granulated, hydrolyzed, dried and powdered in sequence to obtain the thickener for fracturing.
7. The preparation method according to claim 6, wherein, The pH of the first solution is 6.85-7.25; and / or The target temperature is 18-22℃; and / or During the reaction process under an oxygen-free atmosphere, the reaction time is 3-5 hours.
8. The preparation method according to claim 6, wherein, During the deoxygenation process, nitrogen gas is introduced to remove oxygen; preferably, the nitrogen gas introduction time is 30-45 minutes; and / or Nitrogen atmosphere is used for oxygen-free atmosphere.
9. A thickener for fracturing, wherein, The thickener for fracturing can be prepared by the method for preparing the thickener for fracturing according to any one of claims 1-8.
10. An application of the fracturing thickener of claim 9, wherein the application is the use of the fracturing thickener of claim 9 as a thickener in slickwater fracturing fluid and / or gel fracturing fluid.
11. The application according to claim 10, wherein, Based on the total mass of the slickwater fracturing fluid being 100%, the amount of the thickener used for fracturing is 0.02%-0.1%. Based on the total mass of the fracturing fluid as 100%, the amount of the thickener used for fracturing is greater than 0.1% and not more than 0.6%.
12. A fracturing fluid comprising the thickener for fracturing as described in claim 9 and a nano-penetrating agent; wherein, based on the total mass of the fracturing fluid as 100%, the mass content of the thickener is 0.02%-0.6%, and the mass content of the nano-penetrating agent is 0.1%-0.5%; in, The raw material components of the nano-penetrating agent include limonene, water, modified flake molybdenum disulfide nanofluid solution, dodecanol, Tween-80, and Span-80 in a mass ratio of 2.5-3.5:2:4.5-5.5:0.8-1.2:0.4-0.6:0.4-0.
6. Among them, the modified sheet-like molybdenum disulfide nanofluid solution is a dihexyldimethylammonium chloride modified sheet-like molybdenum disulfide nanofluid solution.
13. The fracturing fluid according to claim 12, wherein, Modified sheet-like molybdenum disulfide nanofluid solutions can be prepared by the following method: Water, nanosheet molybdenum disulfide, and dihexadecyl dimethyl ammonium chloride are mixed to obtain a first mixture; wherein, based on the total mass of water as 100%, the amount of nanosheet molybdenum disulfide is 0.4%-0.6%, and the amount of dihexadecyl dimethyl ammonium chloride is 1.5%-2.5%. After adjusting the pH of the first mixture to 9.8-10.2, it was subjected to ultrasonic dispersion to obtain a modified flake-like molybdenum disulfide nanofluid solution. Preferably, during the process of adjusting the pH value of the first mixture to 9.8-10.2, a sodium hydroxide solution is used for pH adjustment; more preferably, the concentration of sodium hydroxide in the sodium hydroxide solution is 1.8-2.2 mol / L, based on the volume of the sodium hydroxide solution.
14. The fracturing fluid according to claim 12, wherein, When the fracturing fluid is slickwater fracturing fluid, the thickener content is 0.02%-0.1% by mass and the nano-penetrating agent content is 0.1%-0.3% based on the total mass of the fracturing fluid (100%).
15. The fracturing fluid according to claim 12, wherein, When the fracturing fluid is a gel-water fracturing fluid, the thickener content is greater than 0.1% and not more than 0.6% by mass, and the nano-penetrating agent content is 0.2%-0.5%, based on the total mass of the fracturing fluid as 100%.