Low-damage fracturing fluid for coal rock gas well and preparation method of low-damage fracturing fluid

Abstract

The invention discloses a low-damage fracturing fluid for a coal rock gas well and a preparation method of the low-damage fracturing fluid, and relates to the technical field of petrochemical engineering. When the low-damage fracturing fluid for the coal rock gas well is prepared, firstly, allyl phosphorus dichloride and 4-(dimethylaminomethyl) phenol react to prepare a double-bond di-tert-amine intermediate; reacting the double-bond di-tert-amine intermediate with halogenated alkane to prepare a gemini quaternary ammonium hydrophobic monomer; the preparation method comprises the following steps: reacting N, N '-ethylenediamine disuccinic acid with allyl glycidyl ether to prepare a metal chelating monomer; acrylamide, acrylic acid, fumaric acid, a metal chelating monomer and a gemini quaternary ammonium hydrophobic monomer are copolymerized to prepare modified polyacrylamide; and mixing the modified polyacrylamide with water and an auxiliary agent to prepare the low-damage fracturing fluid for the coal rock gas well. The prepared low-damage fracturing fluid for the coal rock gas well has the advantages of being low in damage, capable of expanding pores and increasing permeability, anti-swelling, resistant to temperature and shear and resistant to salt.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum chemical industry, in particular to a low-damage fracturing fluid for coal rock gas well and a preparation method thereof. BACKGROUND

[0002] Coal rock gas, also known as coal mine gas, is a kind of clean combustible gas, more than 95% of which is methane. These gases are adsorbed on coal seams, mudstone and other substances. China is rich in coal resources, and the coal seam gas resources associated with the coal resources are also quite rich. Coal seam gas is a new type of energy due to its high methane content and large heat release after combustion. With the progress of exploration technology, more and more coal seam gas blocks are discovered, especially the deep coal seam gas below 2000m, which has huge reserves. For deep coal seam gas, the reservoir permeability is low, but the coal seam gas content is high, and through appropriate mining methods, considerable yield can be obtained, which can effectively improve the energy shortage and other problems.

[0003] However, due to the complex coal seam geological conditions in China, most coal reservoirs have low permeability and low pressure characteristics. The change of sedimentary environment and the complex geological structure lead to obvious heterogeneity and anisotropy of the coal seam itself. The coal seam is sensitive to external compounds, and the fracturing fluid after hydraulic fracturing causes serious damage to the coal reservoir. After the fracturing fluid is injected into the coal seam, water and additives are filtered into the coal reservoir, changing the physical and chemical properties of the coal seam, and having positive and negative effects on the permeability of the coal seam. The permeability characteristics of the coal seam are an important parameter to determine the efficiency of coal seam gas extraction. Therefore, the development of a low-damage fracturing fluid is of great significance to the efficient development of coal rock gas. SUMMARY

[0004] The purpose of the present application is to provide a low-damage fracturing fluid for coal rock gas well and a preparation method thereof to solve the problems in the prior art.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: A low-damage fracturing fluid for coal rock gas well, which is prepared by mixing modified polyacrylamide, water and additives. The modified polyacrylamide is prepared by copolymerization of acrylamide, acrylic acid, fumaric acid, metal chelating monomer and geminal quaternary ammonium hydrophobic monomer. The geminal quaternary ammonium hydrophobic monomer is prepared by reacting double bond di-tert-butyl amine intermediate with halogenated alkane. The double bond di-tert-butyl amine intermediate is prepared by reacting dichloroallyl phosphine with 4-(dimethylaminomethyl) phenol. The metal chelating monomer is prepared by reacting N,N'-ethylenediamine disuccinic acid with allyl glycidyl ether.

[0006] As an optimization, the additives include gel breaking additives, anti-swelling additives, water lock prevention additives and drag reduction agents.

[0007] As an optimization, the halogenated alkanes include chloroalkanes, bromoalkanes, iodoalkanes, and carbon chain lengths of 12-22.

[0008] A preparation method of a low-damage fracturing fluid for coal rock gas wells, comprising the following preparation steps: (1) Under a nitrogen atmosphere, 2-3 parts of 4-(dimethylaminomethyl) phenol and 15-30 parts of diethylene glycol monomethyl ether are mixed uniformly, 1.3-1.96 parts of triethylamine is added dropwise at a rate of 4-10 ml / min at room temperature and 200-300 r / min, 0.04-0.08 parts of hydroquinone is then added and mixed uniformly, the mixture is cooled to 0-2°C in an ice water bath, and 3.34-5 parts of a 30wt% allyl phosphorus dichloride diethylene glycol monomethyl ether solution is added dropwise at a rate of 1-1.8 ml / min, after the dropwise addition is completed, the mixture is reacted at room temperature and 300-400 r / min for 10-14 h, and then heated to 55-65°C for continued reaction for 4-6 h, the filtrate is obtained by filtration, the solvent is removed by rotary evaporation, and the product is extracted with dichloromethane and saturated sodium chloride aqueous solution, washed, concentrated and purified to obtain a double bond di-tert-butylamine intermediate; (2) 3-4 parts of the double bond di-tert-butylamine intermediate, 0.008-0.012 parts of hydroquinone, 0.2-0.3 parts of potassium iodide and 20-30 parts of acetonitrile are mixed uniformly, a halogenated alkane is added in a molar ratio of 1:(2-2.2) of the double bond di-tert-butylamine intermediate to the halogenated alkane, the mixture is stirred at reflux at 80-85°C and 300-500 r / min for 12-16 h, the solvent is removed by rotary evaporation, and the product is purified by recrystallization and then vacuum dried at 50-60°C for 8-10 h to obtain a Gemini quaternary ammonium hydrophobic monomer; (3) 3-4 parts of N,N'-ethylenediamine disuccinic acid is dissolved in 40-50 parts of pure water, and the pH is adjusted to 10-11 with a 1 mol / L sodium hydroxide solution, 4.3-5.73 parts of a 30wt% allyl glycidyl ether ethanol solution is added under a nitrogen atmosphere, the mixture is stirred at reflux at 65-70°C and 300-400 r / min for 10-12 h, the mixture is cooled to 0-4°C in an ice water bath, the pH is adjusted to 6.5-7 with a 1 mol / L hydrochloric acid solution, the mixture is dialyzed using a dialysis membrane with a molecular weight cut-off of 300 Da at 0-4°C, the pure water is replaced every 3-4 h, the dialysis is performed until the conductivity is less than 5 μs / cm, the mixture is concentrated by rotary evaporation to 10%-20% of the original volume, and the mixture is freeze-dried for 24-30 h to obtain a metal chelating monomer; (4) 13-17 parts by mass of acrylamide, 6-8 parts of acrylic acid, 0.13-0.15 parts of fumaric acid, 2.5-2.8 parts of emulsifier, 40-50 parts of pure water are mixed uniformly, the pH is adjusted to 7-8, 2.1-2.3 parts of metal chelating monomer, 1.4-1.8 parts of Gemini quaternary ammonium hydrophobic monomer, 0.09-0.12 parts of initiator are added under the atmosphere of nitrogen, and the reaction is carried out at 75-80 DEG C and 300-400 r / min for 10-12 h, and then the mixture is naturally cooled to room temperature, cut, washed with anhydrous ethanol for 3-4 times, vacuum dried at 50-60 DEG C for 10-12 h, and then ground and sieved through a 120 mesh screen to obtain modified polyacrylamide; (5) 0.1-1 parts of modified polyacrylamide and 100-110 parts of pure water are mixed uniformly, stirred at 300-400 r / min for 30-40 min at room temperature, and then the pH is adjusted to 6-6.5 to obtain a low-damage fracturing fluid for coal rock gas wells.

[0009] As an optimization, the reaction process of the double bond di-tert-butylamine intermediate in step (1) is as follows: .

[0010] As an optimization, the reaction process of the Gemini quaternary ammonium hydrophobic monomer in step (2) is as follows: .

[0011] As an optimization, the reaction process of the metal chelating monomer in step (3) is as follows: .

[0012] As an optimization, the emulsifier in step (4) is OP-10, and the initiator is azobisisobutyronitrile or azobisisopropylimidazoline hydrochloride.

[0013] Compared with the prior art, the present application has the following beneficial effects: In the preparation of the low-damage fracturing fluid for coal rock gas wells, the allyl phosphine dichloride is first reacted with 4-(dimethylaminomethyl) phenol to obtain a double bond di-tert-butylamine intermediate, the double bond di-tert-butylamine intermediate is then reacted with a halogenated alkane to obtain a Gemini quaternary ammonium hydrophobic monomer, N,N'-ethylenediamine disuccinic acid is reacted with allyl glycidyl ether to obtain a metal chelating monomer, acrylamide, acrylic acid, fumaric acid, the metal chelating monomer and the Gemini quaternary ammonium hydrophobic monomer are copolymerized to obtain modified polyacrylamide, and the modified polyacrylamide is mixed with water and an additive to obtain the low-damage fracturing fluid for coal rock gas wells.

[0014] Firstly, the double bond secondary amine intermediate is prepared by reacting allyl dichloride phosphorus with 4-(dimethylaminomethyl) phenol, the two phosphoryl chloride groups on the allyl dichloride phosphorus are substituted with the phenol group on the 4-(dimethylaminomethyl) phenol, thereby obtaining a double-substituted product, and obtaining a double bond secondary amine intermediate containing two tertiary amine groups and a double bond, the double bond allows it to participate in subsequent copolymerization, the two tertiary amines can form a gemini quaternary ammonium salt with a halogenated hydrocarbon, and the two rigid benzene rings are also provided, thereby improving the thermal stability; the gemini quaternary ammonium hydrophobic monomer is prepared by reacting the double bond secondary amine intermediate with a halogenated alkane, the halogen atom on the halogenated alkane is quaternized with the tertiary amine group on the double bond secondary amine intermediate, thereby forming a gemini quaternary ammonium hydrophobic monomer with two hydrophobic carbon chains, two quaternary ammonium groups, two benzene rings and a double bond, one monomer simultaneously has two quaternary ammonium groups and two hydrophobic carbon chains, which greatly improves the local hydrophobicity, the concentrated quaternary ammonium cation can be adsorbed on the negatively charged coal and clay surface, neutralizing the ionic charge thereon, while the hydrophobic carbon chain extends outward, causing the chemical bond of the oxygen-containing functional group on the coal matrix surface to break, and the mineral composition to fall off, so that it is in a hydrophobic state, avoiding the swelling caused by water intrusion, inhibiting the permeability damage caused by the water-sensitive swelling of clay, and the long hydrophobic carbon chain can also reduce the surface tension, reduce the permeability damage caused by microfracture water lock, and increase the desorption and diffusion channels of coalbed methane.

[0015] Secondly, the metal chelating monomer is prepared by reacting N,N'-ethylenediamine disuccinic acid with allyl glycidyl ether, the epoxy group on the allyl glycidyl ether reacts with the secondary amine group on the N,N'-ethylenediamine disuccinic acid, thereby obtaining a metal chelating monomer with a metal chelating group and a polymerizable double bond, N,N'-ethylenediamine disuccinic acid has strong metal chelating ability, which can capture metal ions in coal and clay during fracturing operation, and assist the gemini quaternary ammonium hydrophobic monomer in fragmenting the coal matrix and clay minerals, thereby expanding the pore size and the number of pores, achieving the effect of pore expansion and permeability improvement, and improving the efficiency of methane desorption.

[0016] Finally, acrylamide, acrylic acid, fumaric acid, metal chelating monomer, Gemini quaternary ammonium hydrophobic monomer are copolymerized to prepare modified polyacrylamide. Acrylamide and acrylic acid are used as the backbone of the modified polyacrylamide, the average bond energy is high, the main chain property is stable, the tackifying and drag reducing performance is strong, the Gemini quaternary ammonium hydrophobic monomer and the metal chelating monomer are used as the main functional side groups on the chain segment, the Gemini quaternary ammonium hydrophobic monomer contains two long carbon chains, two quaternary ammonium cations and two benzene ring rigid groups, which can greatly improve the temperature resistance and shear resistance, the cationic groups can improve the salt resistance of the polymer molecules, the hydrophobic long carbon chain can increase the space network structure of the fracturing fluid through hydrophobic association, thereby improving the viscosity and enhancing the sand carrying performance, and after the polymer is broken, part of the chain segment contains both hydrophobic and hydrophilic groups, which improves the surface activity of the fracturing fluid, effectively reduces the surface tension of the broken gel, is beneficial to the flowback of the broken gel, and the quaternary ammonium salt small molecules formed after the gel is broken can also adhere to the surface of clay minerals to inhibit the hydration and migration of the clay minerals and reduce the permeability reduction caused by the pore throat blockage; the addition of the fumaric acid monomer can play a certain isolation role on the main chain, so that the hydrophobic side groups are randomly distributed in a comb type; the addition of the metal chelating monomer introduces a strong chelating group, which has very strong metal chelating ability, and the anion carries a negative charge, which combines with the quaternary ammonium cation with a positive charge to form an amphoteric structure, has obvious "counterion effect", and effectively improves the salt resistance. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] The following all examples and comparative examples use the following raw materials: Halogenated alkane: 1-bromohexadecane; Emulsifier: OP-10; Initiator: azobis isopropyl imidazole hydrochloride.

[0019] Example 1: A preparation method of a low-damage fracturing fluid for coal rock gas wells, the preparation method of the low-damage fracturing fluid for coal rock gas wells comprises the following preparation steps: (1) Under nitrogen atmosphere, 2 parts of 4-(dimethylaminomethyl) phenol and 15 parts of diethylene glycol monomethyl ether were mixed uniformly, 1.3 parts of triethylamine was added dropwise at 4 ml / min and 200 r / min at room temperature, and then 0.04 parts of hydroquinone was added and mixed uniformly, and the mixture was cooled to 0 DEG C in an ice water bath, and 3.34 parts of 30 wt% allyl phosphine dichloride solution in diethylene glycol monomethyl ether was added dropwise at 1 ml / min, and after the dropwise addition was completed, the mixture was reacted at 300 r / min for 14 h at room temperature and then heated to 55 DEG C and reacted for another 6 h, and then the mixture was filtered, and the filtrate was rotary evaporated to remove the solvent, and then the mixture was extracted with dichloromethane and saturated sodium chloride aqueous solution, washed, concentrated and purified to obtain a double bond di-t-amine intermediate; (2) Under nitrogen atmosphere, 3 parts of the double bond di-t-amine intermediate, 0.008 parts of hydroquinone, 0.2 parts of potassium iodide and 20 parts of acetonitrile were mixed uniformly, and a halogenated alkane was added in a molar ratio of 1:2 of the double bond di-t-amine intermediate to the halogenated alkane, and then the mixture was stirred at 300 r / min at 80 DEG C for 16 h, and then the solvent was removed by rotary evaporation, and the mixture was recrystallized and purified, and then the mixture was vacuum dried at 50 DEG C for 10 h to obtain a geminal quaternary ammonium hydrophobic monomer; (3) Under nitrogen atmosphere, 3 parts of N,N'-ethylenediamine disuccinic acid was dissolved in 40 parts of pure water, and the pH was adjusted to 10 with 1 mol / L sodium hydroxide solution, and then 4.3 parts of 30 wt% allyl glycidyl ether in ethanol was added, and the mixture was stirred at 300 r / min at 65 DEG C for 12 h, and then the mixture was cooled to 0 DEG C in an ice water bath, and the pH was adjusted to 6.5 with 1 mol / L hydrochloric acid solution, and then the mixture was dialyzed with a dialysis membrane with a molecular weight cut-off of 300 Da at 0 DEG C, and the pure water was changed every 3 h, and the dialysis was continued until the conductivity was less than 5 μs / cm, and then the mixture was concentrated by rotary evaporation to 10% of the original volume, and then the mixture was freeze-dried for 24 h to obtain a metal chelating monomer; (4) 13 parts of acrylamide, 6 parts of acrylic acid, 0.13 parts of fumaric acid, 2.5 parts of an emulsifier and 40 parts of pure water were mixed uniformly, and the pH was adjusted to 7, and then 2.1 parts of the metal chelating monomer, 1.4 parts of the geminal quaternary ammonium hydrophobic monomer and 0.09 parts of an initiator were added under nitrogen atmosphere, and then the mixture was reacted at 300 r / min at 75 DEG C for 12 h, and then the mixture was naturally cooled to room temperature, and then the mixture was cut, washed with anhydrous ethanol for 3 times, and then the mixture was vacuum dried at 50 DEG C for 12 h, and then the mixture was ground into powder, and then the mixture was sieved through a 120 mesh sieve to obtain modified polyacrylamide; (5) 0.5 parts of the modified polyacrylamide and 100 parts of pure water were mixed uniformly, and then the mixture was stirred at 300 r / min at room temperature for 40 min, and then the pH was adjusted to 6 to obtain a low-damage fracturing fluid for coal and rock gas wells.

[0020] Example 2 A preparation method of a low-damage fracturing fluid for coal and rock gas wells, the preparation method of the low-damage fracturing fluid for coal and rock gas wells comprises the following preparation steps: (1) Under nitrogen atmosphere, 2.5 parts of 4-(dimethylaminomethyl) phenol and 22 parts of diethylene glycol monomethyl ether were mixed uniformly, 1.63 parts of triethylamine was added dropwise at 7 ml / min and 250 r / min at room temperature, and then 0.06 parts of hydroquinone was added and mixed uniformly, and the mixture was cooled to 1℃ in an ice water bath, and 4.17 parts of 30 wt% allyl phosphine dichloride solution in diethylene glycol monomethyl ether was added dropwise at 1.4 ml / min, and after the dropwise addition was completed, the mixture was reacted at 350 r / min for 12 h at room temperature and then heated to 60℃ and reacted for another 5 h, and then the mixture was filtered, and the filtrate was rotary evaporated to remove the solvent, and then extracted with dichloromethane and saturated sodium chloride aqueous solution, washed, concentrated and purified to obtain a double bond di-t-butylamine intermediate; (2) Under nitrogen atmosphere, 3.5 parts of the double bond di-t-butylamine intermediate, 0.01 parts of hydroquinone, 0.25 parts of potassium iodide and 25 parts of acetonitrile were mixed uniformly, and a halogenated alkane was added according to a molar ratio of the double bond di-t-butylamine intermediate to the halogenated alkane of 1:2.1, and then the mixture was stirred at 80℃ and 400 r / min for 14 h, and then the solvent was removed by rotary evaporation, and the mixture was recrystallized and purified, and then vacuum dried at 55℃ for 9 h to obtain a Gemini quaternary ammonium hydrophobic monomer; (3) Under nitrogen atmosphere, 3.5 parts of N,N'-ethylenediamine disuccinic acid was dissolved in 45 parts of pure water, and the pH was adjusted to 10.5 with 1 mol / L sodium hydroxide solution, and then 5.01 parts of 30 wt% allyl glycidyl ether in ethanol was added, and the mixture was stirred at 65℃ and 350 r / min for 11 h, and then the mixture was cooled to 2℃ in an ice water bath, and the pH was adjusted to 6.5 with 1 mol / L hydrochloric acid solution, and then the mixture was dialyzed with a dialysis membrane with a molecular weight cut-off of 300 Da at 2℃, and the pure water was changed every 3.5 h, and the dialysis was continued until the conductivity was less than 5 μs / cm, and then the mixture was concentrated by rotary evaporation to 15% of the original volume, and then the mixture was freeze-dried for 27 h to obtain a metal chelating monomer; (4) Under nitrogen atmosphere, 15 parts of acrylamide, 7 parts of acrylic acid, 0.14 parts of fumaric acid, 2.6 parts of an emulsifier and 45 parts of pure water were mixed uniformly, and the pH was adjusted to 7.5, and then 2.2 parts of the metal chelating monomer, 1.6 parts of the Gemini quaternary ammonium hydrophobic monomer and 0.105 parts of an initiator were added, and the mixture was reacted at 80℃ and 350 r / min for 11 h, and then the mixture was naturally cooled to room temperature, and then the mixture was cut and washed with anhydrous ethanol for 3 times, and then the mixture was vacuum dried at 55℃ for 11 h, and then the mixture was ground and sieved through a 120 mesh sieve to obtain a modified polyacrylamide; (5) Under nitrogen atmosphere, 0.6 parts of the modified polyacrylamide and 105 parts of pure water were mixed uniformly, and then the mixture was stirred at 350 r / min for 35 min at room temperature, and then the pH was adjusted to 6 to obtain a low-damage fracturing fluid for coal rock gas wells.

[0021] Example 3: The application discloses a preparation method of a low-damage fracturing fluid for coal rock gas wells. (1) 3 parts of 4-(dimethylaminomethyl) phenol and 30 parts of diethylene glycol monomethyl ether are uniformly mixed under a nitrogen atmosphere, 1.96 parts of triethylamine is added dropwise at a rate of 10 ml / min at 300 r / min at room temperature, 0.08 parts of hydroquinone is added and uniformly mixed, the mixture is cooled to 2 DEG C in an ice water bath, 5 parts of 30wt% allyl phosphine dichloride diethylene glycol monomethyl ether solution is added dropwise at a rate of 1.8 ml / min, after the dropwise addition is completed, the mixture is reacted at 400 r / min at room temperature for 10 h, and then heated to 65 DEG C and continuously reacted for 4 h, the mixture is filtered, the filtrate is subjected to rotary evaporation to remove the solvent, and the mixture is extracted with dichloromethane and saturated sodium chloride aqueous solution, washed, concentrated and purified to obtain a double bond di-tert-butyl amine intermediate; (2) 4 parts of the double bond di-tert-butyl amine intermediate, 0.012 parts of hydroquinone, 0.3 parts of potassium iodide and 30 parts of acetonitrile are uniformly mixed, a halogenated alkane is added according to a molar ratio of the double bond di-tert-butyl amine intermediate to the halogenated alkane of 1:2.2, the mixture is stirred at 85 DEG C at 500 r / min under reflux for 12 h, the solvent is removed through rotary evaporation, and the mixture is recrystallized and purified and then vacuum dried at 60 DEG C for 8 h to obtain a geminal quaternary ammonium hydrophobic monomer; (3) 4 parts of N,N'-ethylenediamine disuccinic acid is dissolved in 50 parts of pure water, a 1 mol / L sodium hydroxide solution is used to adjust the pH to 11, 5.73 parts of 30wt% allyl glycidyl ether ethanol solution is added under a nitrogen atmosphere, the mixture is stirred at 400 r / min at 70 DEG C under reflux for 10 h, the mixture is cooled to 4 DEG C in an ice water bath, a 1 mol / L hydrochloric acid solution is used to adjust the pH to 7, the mixture is subjected to dialysis by using a dialysis membrane with a molecular weight cut-off of 300 Da at 4 DEG C, the pure water is replaced every 4 h, the dialysis is performed until the conductivity is less than 5 μs / cm, the mixture is concentrated to 20% of the original volume through rotary evaporation, and then freeze-dried for 30 h to obtain a metal chelating monomer; (4) 17 parts of acrylamide, 8 parts of acrylic acid, 0.15 parts of fumaric acid, 2.8 parts of an emulsifier and 50 parts of pure water are uniformly mixed, the pH is adjusted to 8, 2.3 parts of the metal chelating monomer, 1.8 parts of the geminal quaternary ammonium hydrophobic monomer and 0.12 parts of an initiator are added under a nitrogen atmosphere, the mixture is reacted at 80 DEG C at 400 r / min for 10 h, the mixture is naturally cooled to room temperature, cut into pieces, washed with anhydrous ethanol for 4 times, vacuum dried at 60 DEG C for 10 h, ground into powder, and then sieved through a 120-mesh sieve to obtain modified polyacrylamide; (5) 0.7 parts of the modified polyacrylamide and 110 parts of pure water are uniformly mixed, the mixture is stirred at 400 r / min at room temperature for 30 min, and the pH is adjusted to 6.5 to obtain the low-damage fracturing fluid for coal rock gas wells.

[0022] Comparative Example 1 The preparation method of the low-damage fracturing fluid for coal rock gas wells of Comparative Example 1 is different from that of Example 2 in that step (2) is modified, and step (2) is modified as follows: 3.5 parts of double bond di-tert-butyl amine intermediate, 0.01 parts of hydroquinone, 0.25 parts of potassium iodide, and 25 parts of acetonitrile are uniformly mixed, 1-bromopropane is added in a molar ratio of double bond di-tert-butyl amine intermediate to 1-bromopropane of 1:2.1, reflux stirring is carried out at 80°C and 400 r / min for 14h, the solvent is removed by rotary evaporation, and the double-headed quaternary ammonium hydrophobic monomer is prepared after recrystallization and purification and vacuum drying at 55°C for 9h. The rest of the steps are the same as in Example 2.

[0023] Comparative Example 2: The preparation method of the low-damage fracturing fluid for coal rock gas wells of Comparative Example 2 is different from that of Example 2 in that steps (1) and (2) are not performed, and step (4) is modified as follows: 15 parts of acrylamide, 7 parts of acrylic acid, 0.14 parts of fumaric acid, 2.6 parts of emulsifier, and 45 parts of pure water are uniformly mixed, the pH is adjusted to 7.5, 2.2 parts of metal chelating monomer and 0.105 parts of initiator are added under a nitrogen atmosphere, reaction is carried out at 80°C and 350 r / min for 11h, natural cooling is carried out to room temperature, cutting is performed, washing is performed with anhydrous ethanol for 3 times, vacuum drying is performed at 55°C for 11h, grinding is performed, and the modified polyacrylamide is prepared by sieving through a 120 mesh sieve. The rest of the steps are the same as in Example 2.

[0024] Comparative Example 3: The preparation method of the low-damage fracturing fluid for coal rock gas wells of Comparative Example 3 is different from that of Example 2 in that step (3) is not performed, and step (4) is modified as follows: 15 parts of acrylamide, 7 parts of acrylic acid, 0.14 parts of fumaric acid, 2.6 parts of emulsifier, and 45 parts of pure water are uniformly mixed, the pH is adjusted to 7.5, 1.6 parts of double-headed quaternary ammonium hydrophobic monomer and 0.105 parts of initiator are added under a nitrogen atmosphere, reaction is carried out at 80°C and 350 r / min for 11h, natural cooling is carried out to room temperature, cutting is performed, washing is performed with anhydrous ethanol for 3 times, vacuum drying is performed at 55°C for 11h, grinding is performed, and the modified polyacrylamide is prepared by sieving through a 120 mesh sieve. The rest of the steps are the same as in Example 2.

[0025] Comparative Example 4: The preparation method of the low-damage fracturing fluid for coal and rock gas well of Comparative Example 4 is different from that of Example 2 in that step (4) is modified as follows: 15 parts of acrylamide, 7 parts of acrylic acid, 2.6 parts of emulsifier, and 45 parts of pure water are uniformly mixed, the pH is adjusted to 7.5, 2.2 parts of metal chelating monomer, 1.6 parts of gemini quaternary ammonium hydrophobic monomer, and 0.105 parts of initiator are added under a nitrogen atmosphere, and the mixture is reacted at 80°C and 350 r / min for 11 h, and then naturally cooled to room temperature. The mixture is cut, washed with anhydrous ethanol for 3 times, and vacuum dried at 55°C for 11 h. The modified polyacrylamide is obtained by grinding and sieving through a 120-mesh sieve. The remaining steps are the same as those of Example 2.

[0026] Test Example 1 Salt-tolerant, temperature-tolerant and shear-tolerant performance test: The apparent viscosity, temperature-tolerant viscosity retention rate, and salt-tolerant viscosity retention rate of the prepared low-damage fracturing fluid for coal and rock gas well are tested to evaluate the temperature-tolerant performance and salt-tolerant performance. The specific test method is as follows: Apparent viscosity: 500 ml of the prepared low-damage fracturing fluid for coal and rock gas well is taken in a beaker, and the apparent viscosity of the low-damage fracturing fluid for coal and rock gas well at room temperature and a shear rate of 170 s -1 is measured by a ZNND six-speed rotary viscometer. Each group of samples is tested in parallel for 5 times, and the average value is recorded; Temperature-tolerant and shear-tolerant performance: The prepared low-damage fracturing fluid for coal and rock gas well is heated at 90°C for 2 h, and the viscosity of the low-damage fracturing fluid for coal and rock gas well at a shear rate of 170 s -1 is measured by a ZNND six-speed rotary viscometer, and the viscosity retention rate is calculated as the temperature-tolerant viscosity retention rate. Each group is tested in parallel for 5 times, and the average value is recorded; Salt-tolerant performance: Inorganic salt is mixed in a ratio of 5.5% sodium chloride + 2.0% potassium chloride + 0.45% magnesium chloride + 0.55% calcium chloride to prepare standard salt water with a salinity of 85000 mg / L. The pure water in step (5) is replaced with the standard salt water to prepare a sample. The viscosity of the sample at room temperature and a shear rate of 170 s -1 is measured by a ZNND six-speed rotary viscometer as the salt-tolerant viscosity. Each group is tested in parallel for 5 times, and the average value is recorded.

[0027] The results are shown in Table 1.

[0028] Table 1 ; From the experimental data of Examples 1-3 and Comparative Examples 1-4 in Table 1, it can be found that the low-damage fracturing fluid for coal and rock gas well prepared by the present application has good temperature-tolerant, shear-tolerant, and salt-tolerant performance.

[0029] By comparing the data in the table, the apparent viscosity data of examples 1-3 shows that as the amount of modified polyacrylamide increases, the viscosity also increases, which has the characteristic of viscosity change, and the construction site can flexibly match according to the demand. At the same time, due to the presence of quaternary ammonium cations and carboxyl anions provided by metal chelating monomers in the modified polyacrylamide segment, the zwitterionic structure has the "antipolyelectrolyte effect", and the viscosity does not decrease but increases in high salinity brine, which has good salt tolerance.

[0030] By comparing the data in the table, the data of comparative example 1 shows that the longer hydrophobic carbon chain has hydrophobic association effect, which can effectively improve the apparent viscosity and temperature resistance of the fracturing fluid.

[0031] By comparing the data in the table, the data of comparative example 2 shows that the double-headed quaternary ammonium hydrophobic monomer contains a rigid benzene ring, which can effectively improve the temperature resistance, and when the quaternary ammonium cation is lost, the "antipolyelectrolyte effect" no longer exists, and the salt tolerance decreases.

[0032] By comparing the data in the table, the data of comparative example 3 shows that the metal chelating monomer provides a large number of anions combined with quaternary ammonium cations to provide "antipolyelectrolyte effect". When not added, the number of anions decreases, the "antipolyelectrolyte effect" decreases, and the salt resistance of the metal chelating monomer itself is lost.

[0033] Test example 2: Coal core permeability damage rate and anti-swelling performance test: The prepared coal rock gas well low damage fracturing fluid is tested for matrix permeability damage rate and anti-swelling rate to evaluate its damage to coal core permeability and anti-swelling performance. The specific test method is as follows: Matrix permeability damage rate test: The prepared coal rock gas well low damage fracturing fluid is tested for matrix permeability damage rate according to the coal core matrix permeability damage test procedure in standard NB / T 10034-2016. The filtrate collection method of the prepared coal rock gas well low damage fracturing fluid is carried out according to the plant glue fracturing fluid filtrate collection method in the standard. The gel breaker is ammonium persulfate. The permeability damage rate η is calculated and recorded according to the formula in the standard. d Each group is tested in parallel for 5 times, and the average value is recorded.

[0034] Anti-swelling rate test: The prepared coal rock gas well low damage fracturing fluid is tested for anti-swelling rate according to the anti-swelling rate test method in standard SY / T 5971-2016. The centrifugal method is used, and the anti-swelling rate is calculated and recorded according to the formula in the standard. Each group is tested in parallel for 5 times, and the average value is recorded.

[0035] The sodium-based bentonite used for anti-swelling rate test is purchased from Shaanxi Shangnan County Dongzheng Chemical Co., Ltd. and meets the requirements in the standard.

[0036] The results are shown in Table 2.

[0037] Table 2 ; From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-4 in Table 2, it can be found that the coal rock gas well low-damage fracturing fluid prepared by the present application has low damage, hole expansion and permeation, and good anti-swelling performance.

[0038] Through the comparison of the data in the table, the permeability damage rate of Examples 1-3 is negative, which indicates that after the treatment of the coal rock gas well low-damage fracturing fluid, the permeability of the coal rock matrix does not decrease but increases, which indicates that the coal rock gas well low-damage fracturing fluid has the performance of hole expansion and permeation.

[0039] Through the comparison of the data in the table, the data of Comparative Example 1 indicates that the long carbon chain of the Gemini quaternary ammonium hydrophobic monomer has the ability to reduce the surface tension and provide hydrophobic effect, which can effectively reduce the water lock damage and the permeability decrease caused by adsorption, and the provision of hydrophobic performance can effectively improve the anti-swelling performance.

[0040] Through the comparison of the data in the table, the data of Comparative Example 2 indicates that the addition of the Gemini quaternary ammonium hydrophobic monomer and the metal chelating monomer synergistically improves the hole expansion and permeation, reduces the damage to the permeability of the coal rock matrix, and effectively inhibits the water-sensitive swelling of bentonite.

[0041] Through the comparison of the data in the table, the data of Comparative Example 3 indicates that the strong metal chelating ability of the metal chelating monomer can capture the metal cations in the coal rock matrix and clay minerals, and at the same time, the hydrophobicity provided by the Gemini quaternary ammonium hydrophobic monomer can effectively reduce the damage to the permeability of the coal rock matrix and effectively inhibit the water-sensitive swelling of bentonite.

[0042] Through the comparison of the data in the table, the data of Comparative Example 4 indicates that the addition of fumaric acid promotes the random distribution of the hydrophobic side groups into a comb type, reduces the damage to the permeability of the coal rock matrix, and improves the anti-swelling performance.

[0043] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A low-damage fracturing fluid for coal rock gas wells, characterized in that, The coal rock gas well low-damage fracturing fluid is prepared by mixing modified polyacrylamide, water and additives; The modified polyacrylamide is prepared by copolymerization of acrylamide, acrylic acid, fumaric acid, metal chelating monomer and gemini quaternary ammonium hydrophobic monomer; The gemini quaternary ammonium hydrophobic monomer is prepared by reaction of double bond di-tert-amine intermediate and halogenated alkane; The double bond di-tert-amine intermediate is prepared by reaction of allyl phosphine dichloride and 4-(dimethylaminomethyl)phenol; The metal chelating monomer is prepared by reaction of N,N'-ethylenediamine disuccinic acid and allyl glycidyl ether.

2. The low-damage fracturing fluid for coal rock gas wells according to claim 1, characterized in that, The additives include gel breaking additives, anti-swelling additives, water lock prevention additives and drag reduction agents.

3. The low-damage fracturing fluid for coal rock gas well according to claim 1, characterized in that, The halogenated alkane includes chloroalkane, bromoalkane and iodoalkane, and the carbon chain length is 12-22.

4. The method for preparing the low-damage fracturing fluid for coal rock gas well according to claim 1, characterized in that, The preparation steps include: (1) under nitrogen atmosphere, 4-(dimethylaminomethyl)phenol and diethylene glycol monomethyl ether are uniformly mixed, triethylamine is added dropwise under stirring at room temperature, hydroquinone is added and uniformly mixed, the temperature is lowered, allyl phosphine dichloride solution is added dropwise, after the dropwise addition is completed, the reaction is carried out under stirring at room temperature, heating is continued, filtration is carried out, the filtrate is purified, and the double bond di-tert-amine intermediate is prepared; (2) the double bond di-tert-amine intermediate, hydroquinone, potassium iodide and acetonitrile are uniformly mixed, halogenated alkane is added, reflux stirring reaction is carried out, drying is carried out after purification, and the gemini quaternary ammonium hydrophobic monomer is prepared; (3) N,N'-ethylenediamine disuccinic acid is dissolved in pure water, the pH is adjusted, under nitrogen atmosphere, allyl glycidyl ether solution is added, reflux stirring reaction is carried out, the temperature is lowered, the pH is adjusted, drying is carried out after separation and purification, and the metal chelating monomer is prepared; (4) acrylamide, acrylic acid, fumaric acid, emulsifier and pure water are uniformly mixed, the pH is adjusted, under nitrogen atmosphere, the metal chelating monomer, gemini quaternary ammonium hydrophobic monomer and initiator are added, stirring reaction is carried out, the temperature is lowered, shearing is carried out, washing is carried out, drying is carried out, grinding is carried out, and the modified polyacrylamide is prepared; (5) the modified polyacrylamide and pure water are uniformly mixed, stirring is carried out at room temperature, the pH is adjusted, and the coal rock gas well low-damage fracturing fluid is prepared.

5. The method according to claim 4, characterized in that, In step (1), under nitrogen atmosphere, 2-3 parts of 4-(dimethylaminomethyl)phenol and 15-30 parts of diethylene glycol monomethyl ether are uniformly mixed, 1.3-1.96 parts of triethylamine is added dropwise at 4-10 ml / min under stirring at room temperature, 0.04-0.08 parts of hydroquinone is added and uniformly mixed, the temperature is lowered to 0-2℃ in an ice water bath, 3.34-5 parts of 30wt% allyl phosphine dichloride solution in diethylene glycol monomethyl ether is added dropwise at 1-1.8 ml / min, after the dropwise addition is completed, stirring reaction is carried out at room temperature for 10-14 h, heating is continued to 55-65℃, and reaction is continued for 4-6 h, filtration is carried out, the solvent is removed from the filtrate by rotary evaporation, and extraction, washing, concentration and purification are carried out.

6. The method according to claim 4, characterized in that, The Gemini quaternary ammonium hydrophobic monomer in step (2) is prepared by mixing 3-4 parts of double bond di-tert-butyl amine intermediate, 0.008-0.012 parts of hydroquinone, 0.2-0.3 parts of potassium iodide and 20-30 parts of acetonitrile, adding halogenated alkane in a molar ratio of double bond di-tert-butyl amine intermediate to halogenated alkane of 1:(2-2.2), stirring at 80-85°C under reflux for 12-16 hours, removing the solvent by rotary evaporation, purifying by recrystallization, and vacuum drying at 50-60°C for 8-10 hours.

7. The method according to claim 4, characterized in that, The metal chelating monomer in step (3) is prepared by dissolving 3-4 parts of N,N'-ethylenediamine disuccinic acid in 40-50 parts of pure water, adjusting the pH to 10-11, adding 4.3-5.73 parts of 30wt% allyl glycidyl ether ethanol solution under nitrogen atmosphere, stirring at 65-70°C under reflux for 10-12 hours, cooling to 0-4°C in an ice water bath, adjusting the pH to 6.5-7 with hydrochloric acid solution, separating and purifying, and freeze-drying for 24-30 hours.

8. The method according to claim 4, characterized in that, The modified polyacrylamide in step (4) is prepared by mixing 13-17 parts of acrylamide, 6-8 parts of acrylic acid, 0.13-0.15 parts of fumaric acid, 2.5-2.8 parts of emulsifier, 40-50 parts of pure water, adjusting the pH to 7-8, adding 2.1-2.3 parts of metal chelating monomer, 1.4-1.8 parts of Gemini quaternary ammonium hydrophobic monomer, and 0.09-0.12 parts of initiator under nitrogen atmosphere, stirring at 75-80°C for 10-12 hours, naturally cooling to room temperature, cutting, washing, drying, grinding, passing through a 120-mesh sieve, and obtaining.

9. The method according to claim 4, characterized in that, The emulsifier in step (4) is OP-10, and the initiator is azobisdimethyl isobutyronitrile or azobisdimethyl isopropyl imidazoline hydrochloride.

10. The method according to claim 4, characterized in that, The coal rock gas well low-damage fracturing fluid in step (5) is prepared by mixing 0.1-1 parts of modified polyacrylamide and 100-110 parts of pure water, stirring at room temperature for 30-40 minutes, and adjusting the pH to 6-6.5.