Modified nano SiO2 multi-component salt-tolerant copolymer suitable for deep coal rock gas fracturing, preparation method and fracturing fluid

Abstract

The invention discloses a modified nano SiO2 multi-element salt-tolerant copolymer suitable for deep coal rock gas fracturing, a preparation method and fracturing fluid, and relates to the technical field of preparation of thickening agents. The preparation method of the salt-tolerant copolymer comprises the following steps: taking 2-acrylamido-2-methylpropanesulfonic acid, a hydrophobic monomer containing a quaternary ammonium group and modified nano SiO2 as raw materials, and obtaining a polymer as a salt-tolerant monomer through an aqueous solution polymerization method; then acrylamide and the prepared salt-tolerant monomer are used as raw materials, and a salt-tolerant copolymer is prepared through an inverse emulsion polymerization method and can be used as a fracturing fluid thickening agent. The whole preparation process is simple, the prepared salt-tolerant copolymer is good in salt tolerance, and the requirement for yield increase and transformation of high-salt and high-salinity compact deep coal bed gas is met.

Description

Technical Field

[0001] The present invention relates to the technical field of thickener preparation, and in particular to a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep-seated coal-rock gas fracturing, a preparation method and a fracturing fluid. Background Art

[0002] Hydraulic fracturing, a widely used reservoir stimulation technique, primarily creates highly conductive fractures around the wellbore, shifting radial flow near the wellbore to a near-linear flow. This not only reduces fluid resistance near the wellbore but also increases the drainage area of the well, thereby increasing production. In recent years, with the increasing proportion of low-permeability, ultra-low-permeability, tight oil and gas reservoirs, and unconventional oil and gas resources, hydraulic fracturing has become an essential production-enhancing measure for oil and gas exploration. Approximately 70% of oil wells and 90% of gas wells require hydraulic fracturing before they can be put into production. During the fracturing process, the fracturing fluid acts as a carrier for transmitting pressure and transporting proppant, and its performance impacts the overall effectiveness of the fracturing operation. As oil and gas development progresses toward deeper reservoirs, the sensitivity of conventional fracturing fluids to water quality, particularly in high-salinity and high-mineralization reservoirs, has led to increasing technical challenges. As the core medium for reservoir transformation, the salt resistance of fracturing fluid has become a key factor restricting the efficiency of deep oil and gas development.

[0003] Extensive research has been conducted on fracturing operations in highly salinized formations. However, both natural and synthetic polymer thickeners exhibit suboptimal thickening performance under high salinity conditions. This engineering challenge has led to the development of a variety of salt-tolerant thickening polymers. In recent years, polyacrylamide (PAA), due to its unique physical and chemical properties derived from its hydrolyzable amide groups, has been widely used in fracturing. Research has enhanced its salt tolerance by introducing specific salt-tolerant monomers into the PAA molecular chain and increasing its molecular weight. However, the technical challenge remains that its salt tolerance is insufficient. This suggests that further improvement is needed in existing technologies. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, wherein the copolymer prepared by the method has good salt resistance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps in sequence:

[0007] a. Preparing a salt-tolerant monomer: dissolving 2-acrylamido-2-methylpropanesulfonic acid, a hydrophobic monomer containing a quaternary ammonium group, and modified nano-SiO2 in deionized water in a mass ratio of 3.5-4:3.5-4:2-3, adjusting the pH of the resulting solution to 6-8, and introducing nitrogen for 20-40 minutes; sequentially adding an electrolyte dispersant, an ionic chain transfer agent, and a thermal decomposition free radical initiator to the resulting solution, reacting at a temperature of 40-70° C. for 6-8 hours to obtain a gel copolymer, and treating the gel copolymer to obtain a salt-tolerant monomer;

[0008] b. Prepare a salt-tolerant copolymer by dissolving acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 6-8:2-4 as the aqueous phase; dissolving an emulsifier in white oil as the oil phase; slowly adding the aqueous phase to the oil phase, adding a thermal decomposition free radical initiator, and reacting at 30-60° C. for 4-6 hours to obtain the copolymer.

[0009] The above-mentioned method for preparing a modified nano-SiO2 multi-salt-resistant copolymer suitable for deep coal gas fracturing, in step a, the preparation method of modified nano-SiO2 is: dissolving nano-SiO2 in anhydrous ethanol, adding a hydrolyzed silane coupling agent thereto, stirring and reacting at a temperature of 40-60°C for 4-6 hours, and centrifuging, washing, and drying the obtained product in sequence.

[0010] The above-mentioned method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, in step a, the hydrophobic monomer containing a quaternary ammonium group is an allyl-type quaternary ammonium salt monomer, a styrene-type quaternary ammonium salt monomer or a siloxane-type quaternary ammonium salt monomer.

[0011] In the above-mentioned method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing, in step a, the electrolyte dispersant is sodium chloride, magnesium chloride or sodium sulfate.

[0012] In the above-mentioned method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, in step a, the ionic chain transfer agent is a carboxylate chain transfer agent.

[0013] In the above-mentioned method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing, in step a, the thermal decomposition type free radical initiator is a persulfate initiator.

[0014] In the above-mentioned method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing, in step b, the emulsifier is Span-60 or Tween-80.

[0015] Another object of the present invention is to provide a modified nano-SiO2 multi-salt-resistant copolymer suitable for deep coal-rock gas fracturing, which is prepared by the above-mentioned preparation method. The salt-resistant copolymer is configured as a solution with a mass ratio of 1%. The viscosity of the solution at room temperature is measured to be 35.0 mPa·s~45.0 mPa·s, and its viscosity gradually increases with the increase of salt content. When the salt content is greater than 100,000 mg / L, or the total mineralization is greater than 150,000 mg / L, the solution viscosity at room temperature is greater than 80.0 mPa·s, and the viscosity at 80°C is greater than 15.0 mPa·s.

[0016] Another object of the present invention is to provide a salt-resistant fracturing fluid, which comprises the above-mentioned modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, a drainage aid and a stabilizer.

[0017] In the above-mentioned salt-resistant fracturing fluid, the drainage aid is a betaine drainage aid, and the stabilizer is clay.

[0018] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0019] (1) The present invention provides a method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep-seated coal-rock gas fracturing. First, 2-acrylamido-2-methylpropanesulfonic acid, a hydrophobic monomer containing a quaternary ammonium group, and modified nano-SiO2 are used as raw materials to obtain a salt-tolerant monomer by aqueous solution polymerization. Then, acrylamide and the obtained salt-tolerant monomer are used as raw materials to obtain a modified nano-SiO2 multi-component copolymer suitable for deep-seated coal-rock gas fracturing by inverse emulsion polymerization, which is used as a fracturing fluid thickener. The amine groups in the thickener molecules are cross-linked through an amidation reaction, thereby enhancing the viscosity of the system. Therefore, the method has the advantage of avoiding the use of a cross-linking agent and reducing production costs.

[0020] (2) The salt-tolerant polymer used as a thickener for deep coal-rock gas fracturing fluid is prepared into a solution at a mass ratio of 1%. The viscosity of the solution at room temperature is measured to be 35.0 mPa·s to 45.0 mPa·s. The viscosity gradually increases with the increase of salt content. When the salt content is greater than 100,000 mg / L and the salinity is greater than 150,000 mg / L, the viscosity of the solution at room temperature is greater than 80.0 mPa·s. The method of the present invention has a simple preparation process, good salt tolerance, and an economical and reasonable price, and can meet the needs of production increase and transformation of high-salinity and dense deep coal-bed methane reservoirs.

[0021] (3) The present invention also discloses the use of the modified nano-SiO2 multi-polymer suitable for deep coal-bed gas fracturing as a thickener for fracturing fluid in the deep coal-bed gas fracturing process. Since it contains sulfonic acid groups, which are strong polar groups, it can effectively inhibit the hydrolysis of amide groups in acrylamide, thereby enhancing the salt resistance of the product. The salt-resistant polymer used as a thickener for deep coal-bed gas fracturing fluid can have a reservoir salt content of up to 100,000 mg / L and a mineralization of up to 150,000 mg / L. It also contains quaternary ammonium groups, which can balance the charge with the sulfonic acid groups, reduce the charge shielding effect of salt ions, and utilize the "anti-polyelectrolyte effect" to improve salt resistance and effectively enhance the viscosity of the system. The modified nano-SiO2 is linked to the polymer through covalent bonds, which can limit the excessive curling of the polymer chain and maintain the integrity of the three-dimensional network structure. At the same time, it can resist the compression of salt ions through the steric effect, slow down the collapse of the molecular chain, and effectively improve the salt resistance of the polymer. Since no cross-linking agent is used, damage to the formation is reduced, and production costs are reduced. The salt-resistant thickener has high salt content resistance and good shear resistance, and can realize the effective application of salt-resistant fracturing fluid in high-salt deep coalbed methane reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the accompanying drawings:

[0023] Figure 1 This is a test chart of the salt resistance of the copolymers prepared in Example 6, Comparative Example 1, and Comparative Example 2;

[0024] Figure 2 This is a test diagram of the shear resistance performance of the copolymers prepared in Example 6, Comparative Example 1, and Comparative Example 2;

[0025] Figure 3 The salt-tolerant thickener prepared in Example 6 is formulated into a 1% by mass solution, and the schematic diagram of the change in solution viscosity with salt content;

[0026] Figure 4 The salt-tolerant thickener prepared in Example 6 is formulated into a 1% by mass solution, and the schematic diagram of the change in solution viscosity with salinity content;

[0027] Figure 5 Schematic diagram of the viscosity change of the salt-tolerant thickener prepared in Example 6 at different shear rates, prepared as a 1% solution at a salinity of 35,000 mg / L;

[0028] Figure 6 The salt-tolerant thickener prepared in Example 6 was prepared into a 1% solution at a salinity of 35000 mg / L. The solution was stirred at a shear rate of 170 s -1 Schematic diagram of viscosity change at different temperatures. DETAILED DESCRIPTION

[0029] The present invention proposes a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, a preparation method and a fracturing fluid. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below with reference to specific embodiments.

[0030] The hydrophobic monomer containing a quaternary ammonium group described in the present invention is an allyl-type quaternary ammonium salt monomer, a styrene-type quaternary ammonium salt monomer, or a siloxane-type quaternary ammonium salt monomer. The electrolyte dispersant is sodium chloride, magnesium chloride, or sodium sulfate. The ionic chain transfer agent is a carboxylate chain transfer agent, such as sodium formate. The thermal decomposition free radical initiator is a persulfate initiator, such as potassium persulfate or ammonium persulfate. The emulsifier is Span-60 or Tween-80.

[0031] The preparation method of the modified nano-SiO2 described in the present invention is: dissolving nano-SiO2 in anhydrous ethanol, adding the hydrolyzed silane coupling agent thereto, stirring and reacting at a temperature of 40-60°C for 4-6 hours, and centrifuging, washing and drying the obtained product in sequence.

[0032] The present invention is described in detail below with reference to specific embodiments.

[0033] Example 1:

[0034] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0035] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 50°C with stirring for 4 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, an allyl quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 6 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 20 minutes. Then, add sodium chloride as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and potassium persulfate as a thermal decomposition free radical initiator. React at 40°C for 6 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(allyl quaternary ammonium salt monomer):w(modified nano-SiO2) is 3.5:3.5:3, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0036] Step 2: Prepare a salt-tolerant copolymer: Dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 6:4 as the aqueous phase, and adjust the pH of the aqueous phase to 7. Slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 40 minutes, add potassium persulfate, a thermal decomposition free radical initiator, and react at 30°C for 4 hours to obtain the salt-tolerant copolymer. The structural formula of the salt-tolerant copolymer prepared in this example is shown in Formula (1).

[0037]

[0038] Example 2:

[0039] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0040] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 50°C with stirring for 5 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, a styrene-type quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 6 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 30 minutes. Then, add magnesium chloride (electrolyte dispersant), sodium formate (ionic chain transfer agent), and ammonium persulfate (thermal decomposition free radical initiator). The reaction is continued at 50°C for 7 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(styrene-type quaternary ammonium salt monomer):w(modified nano-SiO2) is 4:3.5:2.5, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0041] Step 2: Prepare a salt-tolerant copolymer: dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 7:3 as the aqueous phase, and adjust the pH of the aqueous phase to 7; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 40 minutes, add a thermal decomposition free radical initiator, ammonium persulfate, and react at 40°C for 4 hours to obtain the copolymer.

[0042] Example 3:

[0043] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0044] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 50°C with stirring for 6 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, a siloxane-type quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 7 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 40 minutes. Add potassium sulfate as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and ammonium persulfate as a thermal decomposition free radical initiator. React at 50°C for 7 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(siloxane-type quaternary ammonium salt monomer):w(modified nano-SiO2) is 3.5:4:2.5, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0045] Step 2: Prepare a salt-tolerant copolymer: dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 6:4 as the aqueous phase, and adjust the pH of the aqueous phase to 9; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 60 minutes, add a thermal decomposition free radical initiator, ammonium persulfate, and react at 60°C for 6 hours to obtain the copolymer.

[0046] Example 4:

[0047] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0048] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 50°C with stirring for 5 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, an allyl quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 8 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 20 minutes. Add potassium sulfate as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and ammonium persulfate as a thermal decomposition free radical initiator. React at 70°C for 8 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(allyl quaternary ammonium salt monomer):w(modified nano-SiO2) is 3.5:3.5:3, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0049] Step 2: Prepare a salt-tolerant copolymer: dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 7:3 as the aqueous phase, and adjust the pH of the aqueous phase to 7; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 50 minutes, add a thermal decomposition free radical initiator, and react at 40°C for 5 hours to obtain the copolymer.

[0050] Example 5:

[0051] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0052] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 50°C with stirring for 5 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, an allyl quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 8 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 40 minutes. Then, add sodium sulfate as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and potassium persulfate as a thermal decomposition free radical initiator. The mixture is reacted at 50°C for 5 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(allyl quaternary ammonium salt monomer):w(modified nano-SiO2) is 4:3.5:2.5, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0053] Step 2: Prepare a salt-tolerant copolymer: dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 8:2 as the aqueous phase, and adjust the pH of the aqueous phase to 8; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 40 minutes, add a thermal decomposition free radical initiator potassium persulfate, and react at 50°C for 6 hours to obtain the copolymer.

[0054] Example 6:

[0055] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0056] Step 1: Prepare a salt-tolerant monomer: Dissolve nano-SiO2 in anhydrous ethanol, disperse using an ultrasonicator, then add the hydrolyzed silane coupling agent and react at 60°C with stirring for 6 hours. The product is centrifuged, washed, and dried to obtain modified nano-SiO2. Add 2-acrylamido-2-methylpropanesulfonic acid, a styrene-type quaternary ammonium salt monomer, and modified nano-SiO2 to a beaker. Adjust the solution to pH 8 with deionized water. Transfer the solution to a round-bottom flask and deoxygenate with nitrogen for 30 minutes. Then, add sodium chloride as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and potassium persulfate as a thermal decomposition free radical initiator. The mixture is reacted at 60°C for 6 hours. The ratio of w(2-acrylamido-2-methylpropanesulfonic acid):w(styrene-type quaternary ammonium salt monomer):w(modified nano-SiO2) is 4:4:2, resulting in a white gel-like copolymer. The gel-like copolymer is chopped, granulated, washed, and dried to obtain a salt-tolerant monomer.

[0057] Step 2: Prepare a salt-tolerant copolymer: dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 8:2 as the aqueous phase, and adjust the pH of the aqueous phase to 9; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 50 minutes, add a thermal decomposition free radical initiator, and react at 50°C for 6 hours to obtain the copolymer.

[0058] In order to characterize the performance of the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing, the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing synthesized in Example 6 was prepared into a 1% solution by mass with water of different salt contents, and the viscosity was tested. The results are shown in the figure. Figure 3 、 Figure 4 It can be seen that the solution viscosity of the synthesized modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal gas fracturing prepared at a mass ratio of 1% gradually increases with the increase of salt content. When the salt content is greater than 100,000 mg / L, or the total mineralization is greater than 150,000 mg / L, the solution viscosity is greater than 80.0 mPa·s. This is because it contains sulfonic acid groups, which are strong polar groups and can effectively inhibit the hydrolysis of amide groups in acrylamide, thereby enhancing the salt resistance of the product. At the same time, it contains quaternary ammonium groups, which can balance the charge with the sulfonic acid groups, reduce the charge shielding effect of salt ions, and utilize the "anti-polyelectrolyte effect" to improve salt resistance and effectively enhance the viscosity of the system; the modified nano-SiO2 is linked to the polymer through covalent bonds, which can limit the excessive curling of the polymer chain and maintain the integrity of the three-dimensional network structure. At the same time, it can resist the compression of salt ions through the steric effect, slow down the collapse of the molecular chain, and effectively improve the salt resistance of the polymer.

[0059] In order to characterize the shear resistance of the solution of the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing synthesized at a mass ratio of 1% under the condition of a salinity of 35000 mg / L, the viscosity of the solution prepared by the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing synthesized in Example 6 was tested at different shear rates at room temperature. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that as the shear rate increases, the viscosity value continues to decrease. When the shear rate reaches 450s -1 After that, the viscosity value tends to be flat. When the shear rate is further increased, the viscosity value is still 28.0mPa·s, which shows that the synthesized modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal gas fracturing has good shear resistance under the condition of salinity of 35000mg / L.

[0060] In order to characterize the temperature resistance of the solution of the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing synthesized at a mass ratio of 1% under the condition of a salinity of 35000 mg / L, the solution prepared by the modified nano-SiO2 multi-polymer salt-resistant thickener for deep coal-rock gas fracturing synthesized in Example 6 was subjected to a shear rate of 170s -1 The viscosity test was carried out at different temperatures. The results are as follows Figure 6 As shown. Figure 6 As can be seen, the solution viscosity decreases with increasing temperature, reaching a viscosity greater than 15.0 mPa·s at 80°C. This demonstrates that the modified nano-SiO2 multi-polymer salt-tolerant thickener for deep coalbed methane fracturing has good temperature resistance at a salinity of 35,000 mg / L and can be used in deep coalbed methane wells at 80°C.

[0061] Example 7:

[0062] A salt-tolerant fracturing fluid comprises the salt-tolerant copolymer prepared in Example 6, a betaine drainage aid, and clay stabilizer.

[0063] Comparative Example 1:

[0064] A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0065] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, styrene-type quaternary ammonium salt monomer and modified nano-SiO2 are used as raw materials, dissolved in deionized water, the pH of the solution is adjusted, gas is passed through to deoxygenate, an electrolyte dispersant, an ionic chain transfer agent, and a thermal decomposition free radical initiator are added, and the mixture is reacted under heating conditions to obtain a gel copolymer, which is then shredded, granulated, washed, and dried.

[0066] Comparative Example 2:

[0067] A method for preparing a multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing comprises the following steps:

[0068] Step 1: 2-acrylamido-2-methylpropanesulfonic acid and styrene-type quaternary ammonium salt monomer are added to a beaker, deionized water is used as the solvent, and the solution pH is adjusted to 8. The above solution is transferred to a round-bottom flask, and nitrogen is passed through to deoxygenate for 30 minutes. Then, sodium chloride as an electrolyte dispersant, sodium formate as an ionic chain transfer agent, and potassium persulfate as a thermal decomposition type free radical initiator are added. The reaction is carried out at 60°C for 6 hours, wherein the ratio of w (2-acrylamido-2-methylpropanesulfonic acid) to w (styrene-type quaternary ammonium salt monomer) is 4:4 to obtain a white gel copolymer. The gel copolymer is chopped, granulated, washed, and dried to obtain a monomer.

[0069] Step 2: Dissolve Span-80 and Tween-80 in white oil at a ratio of 1:1 as the oil phase; dissolve acrylamide and monomer in deionized water at a mass ratio of 8:2 as the aqueous phase, and adjust the pH of the aqueous phase to 9; slowly add the aqueous phase to the oil phase under high-speed stirring, deoxygenate with nitrogen for 50 minutes, add a thermal decomposition free radical initiator, and react at 50°C for 6 hours to obtain the product.

[0070] The salt resistance of the copolymers prepared in Comparative Example 1 and Comparative Example 2 was tested using the same test method as in Example 6. The test results are shown in FIG. Figure 1 .

[0071] like Figure 1 As shown, the viscosity of the polymers synthesized by the three methods in clear water is greater than 10.0 mPa·s, and Example 6 has the highest viscosity and the best effect; with the increase of salt content, the viscosity of Comparative Example 1 and Comparative Example 2 does not change significantly, while the viscosity of Example 6 shows an increasing trend. When the salt content is 100,000 mg / L, the solution viscosity is greater than 80.0 mPa·s at room temperature.

[0072] The shear resistance of the copolymers prepared in Comparative Examples 1 and 2 was tested using the same test method as in Example 6. The test results are shown in FIG. Figure 2 .

[0073] like Figure 2 As shown in the figure, under the condition of mineralization of 35000 mg / L, the viscosity of the polymers synthesized by the three methods has been decreasing with the increase of shear rate. -1 The viscosity value tends to level off after that. By comparison, it is found that Example 6 has the highest viscosity and the best effect. Therefore, the polymer prepared by the present invention has the best salt resistance.

[0074] Parts not described in the present invention can be implemented by referring to the existing technology.

[0075] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for preparing a modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, characterized in that: The following steps are included in sequence: a. Preparing a salt-tolerant monomer: dissolving 2-acrylamido-2-methylpropanesulfonic acid, a hydrophobic monomer containing a quaternary ammonium group, and modified nano-SiO2 in deionized water in a mass ratio of 3.5-4:3.5-4:2-3, adjusting the pH of the resulting solution to 6-8, and introducing nitrogen for 20-40 minutes; sequentially adding an electrolyte dispersant, an ionic chain transfer agent, and a thermal decomposition free radical initiator to the resulting solution, reacting at a temperature of 40-70° C. for 6-8 hours to obtain a gel copolymer, and treating the gel copolymer to obtain a salt-tolerant monomer; b. Prepare a salt-tolerant copolymer by dissolving acrylamide and a salt-tolerant monomer in deionized water at a mass ratio of 6-8:2-4 as the aqueous phase; The emulsifier is dissolved in white oil as the oil phase; the water phase is slowly added to the oil phase, and a thermal decomposition type free radical initiator is added, and the reaction is carried out at 30-60° C. for 4-6 hours to obtain the product.

2. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step a, the preparation method of modified nano-SiO2 is: dissolving nano-SiO2 in anhydrous ethanol, adding the hydrolyzed silane coupling agent thereto, stirring and reacting at a temperature of 40-60°C for 4-6 hours, and centrifuging, washing, and drying the obtained product in sequence.

3. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step a, the hydrophobic monomer containing a quaternary ammonium group is an allyl-type quaternary ammonium salt monomer, a styrene-type quaternary ammonium salt monomer or a siloxane-type quaternary ammonium salt monomer.

4. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step a, the electrolyte dispersant is sodium chloride, magnesium chloride or sodium sulfate.

5. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step a, the ionic chain transfer agent is a carboxylate chain transfer agent.

6. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step a, the thermal decomposition type free radical initiator is a persulfate initiator.

7. The method for preparing a modified nano-SiO2 multi-component salt-tolerant copolymer suitable for deep coal-rock gas fracturing according to claim 1, characterized in that: In step b, the emulsifier is Span-60 or Tween-80.

8. A modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing, characterized in that: The salt-resistant copolymer is prepared by the preparation method described in any one of claims 1 to 7. The salt-resistant copolymer is configured as a solution with a mass ratio of 1%. The viscosity of the solution at room temperature is measured to be 35.0 mPa·s to 45.0 mPa·s, and the viscosity gradually increases with the increase of salt content. When the salt content is greater than 100,000 mg / L or the total mineralization is greater than 150,000 mg / L, the solution viscosity is greater than 80.0 mPa·s at room temperature, and the viscosity is greater than 15.0 mPa·s at 80°C.

9. A salt-resistant fracturing fluid, characterized in that: It comprises the modified nano-SiO2 multi-component salt-resistant copolymer suitable for deep coal-rock gas fracturing as described in claim 8, a drainage aid and a stabilizer.

10. The salt-resistant fracturing fluid according to claim 9, characterized in that: The drainage aid is a betaine drainage aid, and the stabilizer is clay.

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