Modified cellulose thickening agent for fracturing fluid, fracturing fluid and preparation method of modified cellulose thickening agent

Abstract

The invention provides a modified cellulose thickening agent for fracturing fluid, the fracturing fluid and a preparation method of the fracturing fluid, and relates to the technical field of oil and gas exploitation. Compared with hydroxy propyl cellulose and carboxymethyl cellulose, the cellulose derivative prepared by carrying out graft modification on carboxymethyl cellulose by utilizing amino-terminated polysiloxane is used as a thickening agent, and compared with the hydroxy propyl cellulose and the carboxymethyl cellulose, the cellulose derivative disclosed by the invention has higher temperature resistance and shear resistance, good swelling property, low residue content and good stability. And the damage to the stratum is reduced.

Description

Technical Field

[0001] This application relates to the technical field of oil and gas exploitation, and particularly relates to a modified cellulose thickener for fracturing fluid, a fracturing fluid and a preparation method thereof. Background Art

[0002] Fracturing technology, as an important production-increasing measure for oil and gas reservoirs, has been rapidly developed and widely applied. Fracturing fluid is an important part of fracturing technology. It is a heterogeneous and unstable chemical system formed by mixing various additives in a certain ratio. Its main function is to transfer the high pressure on the ground to the formation, and to transport proppants into the fractures and spread them in the fractures. In order to achieve effective transmission during transportation, fracturing fluid is required to have high suspension ability and high low-shear-rate viscosity. In recent years, thickeners are commonly used to achieve this effect. Currently, the commonly used thickeners in domestic water-based fracturing fluids include natural plant gums and their derivatives, cellulose derivatives, synthetic polymers, etc. Natural plant gums and their derivatives mainly include guar gum, hydroxypropyl guar gum, carboxymethyl guar gum, carboxymethyl hydroxypropyl guar gum, sesbania gum, modified coumarin gum, modified konjac gum, soapnut gum, and crucifer gum, etc.; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, etc.; synthetic polymers such as polyacrylamide, partially hydrolyzed polyacrylamide, methylene polyacrylamide, polyvinyl alcohol, and copolymers of acrylamide with hydrophobic monomers, 2-acrylamido-2-methylpropanesulfonic acid (sodium), vinyl pyrrolidone, polyvinyl alcohol, etc.

[0003] Cellulose is a natural resource widely existing in nature, with excellent thickening ability and compatibility. However, for ordinary cellulose derivatives such as carboxymethyl cellulose and hydroxypropyl cellulose, their heat resistance is poor. Carboxymethyl cellulose will accelerate degradation above 80°C and has poor salt resistance and shear resistance, while hydroxypropyl cellulose will rapidly degrade above 120°C and has poor shear resistance, both of which cannot meet the construction requirements of long fracturing sections. Therefore, in order to improve the applicability of cellulose in oil and gas reservoir development, people have started to modify it.

[0004] Patent CN117924718A discloses a modified sodium carboxymethyl cellulose and its preparation method. A hydrophobic quaternary ammonium salt is synthesized through epichlorohydrin and N,N-diethyl-N'-oleoyl ethylenediamine, and at the same time, free radical polymerization is carried out with acrylamide and 2-acrylamido-2-methylpropanesulfonic acid to obtain a polymer powder. Then the polymer powder is grafted onto sodium carboxymethyl cellulose through an etherification reaction to obtain the modified sodium carboxymethyl cellulose. However, the heat resistance of the modified sodium carboxymethyl cellulose prepared by this technology is only 120°C, and it cannot adapt to the development of oil and gas reservoirs at higher temperatures.

[0005] Patent CN110257041A discloses a guar gum-nanocellulose fiber crosslinking thickener for fracturing fluid. After crosslinking pyridine-type cationic nanocellulose fibers with guar gum, and then further moderately crosslinking with fatty alcohol polyoxyethylene ether and acrylic acid, and using nanoparticles in combination, it has excellent temperature and salt resistance, but does not solve the problems of high content of guar gum residues and easy secondary plugging after reservoir stimulation.

[0006] Therefore, although certain progress has been made in the research of thickeners, the current thickeners still need to be improved. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the present application provides a modified cellulose thickener for fracturing fluid, a fracturing fluid and its preparation method, which have good temperature resistance, low residue content after gel breaking, and little damage to the formation.

[0008] To achieve the above object, the technical solutions adopted in the present application are as follows: According to one aspect of the present application, there is provided a modified cellulose thickener for fracturing fluid, including a carboxymethyl cellulose derivative prepared by grafting and modifying carboxymethyl cellulose with bis-terminal amino polysiloxane.

[0009] Further, the mass ratio of the carboxymethyl cellulose to the bis-terminal amino polysiloxane is 1:(1 - 1.8).

[0010] Preferably, the mass ratio of the carboxymethyl cellulose to the bis-terminal amino polysiloxane is 1:1.3.

[0011] Further, the molecular weight of the carboxymethyl cellulose is 20,000 - 100,000, and the carboxymethyl substitution degree is 0.54 - 0.68, preferably the carboxymethyl substitution degree is 0.61.

[0012] Further, the molecular weight of the bis-terminal amino polysiloxane is 2000 - 8000.

[0013] Preferably, the molecular weight of the bis-terminal amino polysiloxane is 5000.

[0014] The amount of monohydroxy-terminated polysiloxane should not be too much, which will lead to a decrease in swelling property. Control the introduction amount and carboxymethyl degree to make it maintain excellent swelling degree and have excellent temperature resistance, etc.

[0015] Further, the preparation method of the above-mentioned cellulose derivative includes the following steps: Dissolve carboxymethyl cellulose in the solvent dimethyl sulfoxide, add bis-terminal amino polysiloxane, add the catalyst p-toluenesulfonic acid, react at 50 - 60 °C for 12 - 24 h, cool after the reaction is completed, filter by suction, and dry to obtain the cellulose derivative.

[0016] Optionally, the mass ratio of the carboxymethyl cellulose to the solvent dimethyl sulfoxide is 1:(5 - 10).

[0017] Optionally, the dosage of the catalyst is 0.1 - 1% of the weight of the carboxymethyl cellulose.

[0018] In this application, the carboxymethyl cellulose is graft - modified with bis - terminal amino polysiloxane. The amino group in the bis - terminal amino polysiloxane undergoes an amidation reaction with the carboxyl group in the carboxymethyl cellulose to form a cellulose derivative with polysiloxane branches. Compared with carboxymethyl cellulose, the polysiloxane chain segment is introduced into the cellulose derivative, making it have higher temperature and shear resistance.

[0019] Some of the amino groups in the bis - terminal amino polysiloxane do not react. When preparing the fracturing fluid, they will cross - link with the cross - linker and other components to a certain extent. Therefore, it is necessary to control the dosage and molecular weight of the bis - terminal amino polysiloxane to avoid excessive proportion or large molecular weight of the bis - terminal amino polysiloxane, which may lead to excessive cross - linking of the fracturing fluid, making it difficult to break gel completely during gel breaking, resulting in more cross - linked structures remaining after gel breaking and increasing the residue content. Excessive dosage or large molecular weight of the bis - terminal amino polysiloxane will also affect the uniformity of the formed solution, the temperature and shear resistance, and the salt tolerance. In addition, it will also affect the gel - breaking performance of the fracturing fluid. Therefore, this application preferably uses bis - terminal amino polysiloxane with a molecular weight of 2000 - 8000, controls the carboxymethyl substitution degree of the carboxymethyl cellulose in the range of 0.54 - 0.68, the mass ratio of the bis - terminal amino polysiloxane in the range of 1:(1 - 1.8), and the carboxymethyl degree of the carboxymethyl cellulose, so as to control the branch length, carboxyl content, etc., making it have both high temperature and shear resistance and excellent swelling and gel - breaking properties.

[0020] According to another aspect of the present application, a fracturing fluid is provided. The fracturing fluid contains the modified cellulose thickener for fracturing fluid and a cross - linker described above; wherein, The dosage of the modified cellulose thickener for fracturing fluid accounts for 0.30 - 45% of the total weight of the fracturing fluid; The dosage of the cross - linker accounts for 0.1 - 0.3% of the total weight of the fracturing fluid.

[0021] Furthermore, the cross - linker is selected from at least one of organic boron cross - linkers, borates, and organic boron zirconium cross - linkers. For example, it can be triethanolamine borate, ethylene glycol borate, zirconium hydroxide, tetrabutyl zirconate, etc.

[0022] Furthermore, the fracturing fluid also contains a guar gum derivative. The dosage of the guar gum derivative accounts for 0.05 - 0.1% of the total weight of the fracturing fluid. The guar gum derivative is selected from any one of hydroxypropyl guar gum, carboxymethyl guar gum, and carboxymethyl hydroxypropyl guar gum, and the molecular weight of the guar gum derivative is 200,000 - 500,000.

[0023] Furthermore, the fracturing fluid further contains a bactericide, and the dosage of the bactericide accounts for 0-0.1% of the total weight of the fracturing fluid, preferably 0.05-0.1%; the bactericide is selected from at least one of formaldehyde or isothiazolinone bactericides.

[0024] Furthermore, the fracturing fluid further contains a clay stabilizer, and the dosage of the clay stabilizer accounts for 0-1% of the total weight of the fracturing fluid, preferably 0.5-1%; the clay stabilizer is selected from at least one of potassium chloride, ammonium chloride, and sodium chloride.

[0025] Furthermore, the fracturing fluid further contains a flowback aid, and the dosage of the flowback aid accounts for 0-1% of the total weight of the fracturing fluid, preferably 0.5-1%; the flowback aid is selected from at least one of fluorocarbon surfactants and alkylphenol polyoxyethylene ethers.

[0026] Furthermore, the fracturing fluid further contains a pH regulator, and the pH regulator is added to adjust the pH of the fracturing fluid to 10-11; the pH regulator is selected from sodium hydroxide or sodium carbonate.

[0027] Furthermore, the fracturing fluid further contains a breaker, and the dosage of the breaker accounts for 0-0.05% of the total weight of the fracturing fluid, preferably 0.005-0.05%; the breaker is selected from potassium persulfate or sodium persulfate.

[0028] In a further preferred embodiment, sulfonated nano-montmorillonite is further added to the fracturing fluid, and the addition amount of the sulfonated nano-montmorillonite in the fracturing fluid is 0-0.5%, preferably 0.2-0.5% by weight.

[0029] The lamellar structure of nano-montmorillonite can remain relatively stable at high temperatures. Adding it to the fracturing fluid can improve the temperature and shear resistance. However, the dispersibility of nano-montmorillonite is poor and it is prone to agglomeration in the fracturing fluid, so it cannot achieve a good strengthening effect. In this application, sulfonated nano-montmorillonite modified with vinyl silane coupling agent and polymerizable monomers containing sulfonic acid groups has improved dispersibility, so that it can exert the effect of nano-montmorillonite in enhancing temperature and shear resistance. There can also be stable chemical bonding and other interactions between sulfonated nano-montmorillonite and cellulose molecules, thereby further improving the temperature and shear resistance of the thickener, making it have a high viscosity retention rate at high temperatures and high shear rates. However, nano-montmorillonite will increase the crosslinked network structure of the fracturing fluid, increase the crosslinking density, and reduce the breaking performance. In this application, introducing a polymer formed by vinyl silane coupling agent and polymerizable monomers containing sulfonic acid groups on the surface of nano-montmorillonite can also adjust the interfacial properties of the fracturing fluid to a certain extent, reduce the surface tension, make the breaker easier to penetrate, and thus improve the breaking performance.

[0030] Further, the sulfonated nano-montmorillonite is prepared by sequentially modifying nano-montmorillonite with a vinyl silane coupling agent and a polymerizable monomer containing a sulfonic acid group. Its preparation method includes the following steps: (1) Disperse the nano-montmorillonite powder in Solvent I, add a vinyl silane coupling agent and react. After the reaction, filter and dry to obtain an intermediate product; (2) Disperse the intermediate product in Solvent II, add a polymerizable monomer containing a sulfonic acid group, add an initiator and react. After the reaction, filter and dry to obtain the sulfonated nano-montmorillonite.

[0031] Optionally, the weight ratio of the nano-montmorillonite, the vinyl silane coupling agent, and the polymerizable monomer containing a sulfonic acid group is 1:(1 - 2):(0.5 - 0.7).

[0032] Optionally, in step (1), the particle size of the nano-montmorillonite is 200 - 600 nm.

[0033] Optionally, in step (1), the vinyl silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltripropoxysilane, and vinyltris(β - methoxyethoxy)silane.

[0034] Optionally, in step (1), Solvent I is selected from any one of n - hexane, n - heptane, dichloromethane, and toluene, and the mass ratio of the nano-montmorillonite powder to Solvent I is 1:10 - 15.

[0035] Optionally, in step (1), the temperature of the reaction is 80 - 100 °C and the time is 3 - 10 h.

[0036] Optionally, in step (2), Solvent II is selected from any one of N,N - dimethylformamide, dimethyl sulfoxide, N - methylpyrrolidone, and N,N - dimethylacetamide.

[0037] Optionally, in step (2), the polymerizable monomer containing a sulfonic acid group is selected from at least one of 2 - methylacrylamide - 2 - methylpropanesulfonic acid, 2 - acrylamidoethanesulfonic acid, 2 - acryloyloxyethanesulfonic acid, 2 - methacryloyloxyethanesulfonic acid, 3 - acryloyloxypropanesulfonic acid, and 2 - methacryloyloxypropanesulfonic acid.

[0038] Optionally, in step (2), the initiator is selected from azo initiators and peroxide initiators, and exemplary ones include but are not limited to azobisisobutyronitrile, 2,2'-azobis-(2 - methylbutyronitrile), azobis(2,4 - dimethylvaleronitrile), azobisisoheptonitrile, dilauroyl peroxide, or tert - butyl peroxyneodecanoate, benzoyl peroxide, diisopropylbenzene peroxide, etc.

[0039] Optionally, in step (2), the reaction temperature is 70-90 °C and the time is 2-6 h.

[0040] According to another aspect of the present application, there is provided a method for preparing a fracturing fluid, comprising the following steps: S1. Add water to the guanidine gum derivative and stir to swell for 5-10 min, then add a bactericide, a clay stabilizer, and a flowback aid and mix evenly. Use a pH regulator to adjust the pH to 10-11, and add a crosslinking agent to obtain a base fluid; S2. Add a modified cellulose thickener for fracturing fluid to the base fluid, add a breaker, and stir to form a network gel, thus obtaining the fracturing fluid.

[0041] Furthermore, the above operations are all carried out at room temperature.

[0042] Compared with the prior art, the present application has the following beneficial effects: 1. The present application provides a modified cellulose thickener for fracturing fluid. This thickener is a cellulose derivative prepared by modifying carboxymethyl cellulose with a double-ended amino polysiloxane. Compared with conventional cellulose derivative thickeners such as carboxymethyl cellulose, the cellulose derivative of the present application has higher temperature and shear resistance. The fracturing fluid prepared with the guanidine gum derivative has a temperature resistance of over 160 °C, and the residue content is low, reducing the damage to the formation.

[0043] 2. The present application also provides a fracturing fluid containing the above thickener, which has complete gel breaking and low residue, and meets the construction requirements of reservoirs with a temperature of ≥160 °C.

[0044] 3. Sulfonated nano-montmorillonite is also added to the fracturing fluid of the present application. After sulfonation, the dispersibility of nano-montmorillonite in the fracturing fluid is improved, which can improve the temperature and shear resistance of the fracturing fluid and also help to improve the gel breaking performance. Specific Embodiments

[0045] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present application, but do not limit the present application in any way. The following content is only an exemplary description of the scope claimed in the present application. Those skilled in the art can make various changes and modifications to the invention of the present application based on the disclosed content, and they should also fall within the scope claimed in the present application.

[0046] In the present application, the "double-terminal amino polysiloxane refers to a polysiloxane having two primary amino groups at the end group, and the two primary amino groups are respectively located at two different end groups of the polysiloxane". The double-terminal amino polysiloxane of the present application can achieve the effect of the present application as long as the two ends are capped with primary amino groups and the molecular weight is in the range of 2000-8000, and there is no other limitation. The double-terminal amino polysiloxane can be a commercially available double-terminal amino polydimethylsiloxane or a homemade product. The preparation method is as follows: 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and octamethylcyclotetrasiloxane are used as raw materials, and the double-terminal amino polysiloxane is reacted under the action of a catalyst tetramethylammonium hydroxide pentahydrate to obtain the double-terminal amino polysiloxane. The raw material ratio and dosage are adjusted according to the required molecular weight.

[0047] In the following specific embodiments, methylisothiazolinone (CAS: 2682-20-4) is selected as the bactericide, potassium chloride is selected as the clay stabilizer, octylphenol polyoxyethylene ether (CAS: 9036-19-5) is selected as the drainage agent, 20% by mass sodium hydroxide solution is selected as the pH adjuster, potassium persulfate is selected as the degumming agent, and triethanolamine borate is selected as the cross-linking agent. The selection of the above materials does not constitute a limitation on the present application. It can be understood that the effect of the present application can also be achieved by replacing other materials.

[0048] The present application is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present application are obtained through conventional commercial channels.

[0049] Example 1 A modified cellulose thickener for fracturing fluid is prepared by the following method: Dissolve carboxymethyl cellulose in 5 times the weight of dimethyl sulfoxide, add diamino polysiloxane in a mass ratio of 1:1, add terephthalic acid at a rate of 0.1% by weight of carboxymethyl cellulose, react at 50°C for 12 hours, cool after the reaction is complete, filter, and dry to obtain the product, which is recorded as thickener 1#.

[0050] In this embodiment, the molecular weight of carboxymethyl cellulose is 20,000, and the degree of carboxylmethyl is 0.54; the molecular weight of double-terminated amino polysiloxane is 2,000.

[0051] Example 2 A modified cellulose thickener for fracturing fluid is prepared by the following method: Dissolve carboxymethyl cellulose in 10 times the weight of dimethyl sulfoxide, add diamino polysiloxane in a mass ratio of carboxymethyl cellulose to diamino polysiloxane of 1:1.3, react at 60°C for 18 hours, cool after the reaction, filter and dry to obtain the thickener 2#.

[0052] In this embodiment, the molecular weight of carboxymethyl cellulose is 80,000 and the degree of carboxymethyl substitution is 0.61; the molecular weight of the double-terminal amino polysiloxane is 5,000.

[0053] Example 3 A modified cellulose thickener for fracturing fluid is prepared by the following method: Dissolve carboxymethyl cellulose in 10 times by weight of dimethyl sulfoxide, add double-terminal amino polysiloxane according to the mass ratio of carboxymethyl cellulose to double-terminal amino polysiloxane of 1:1.8, react at 60 °C for 24 hours, cool after the reaction is completed, filter by suction, and dry to obtain, denoted as thickener 3#.

[0054] In this embodiment, the molecular weight of carboxymethyl cellulose is 100,000 and the degree of carboxymethyl substitution is 0.68; the molecular weight of the double-terminal amino polysiloxane is 8,000.

[0055] Example 4 The difference from Example 2 is that the degree of carboxymethyl substitution of carboxymethyl cellulose is 0.51, and the rest is the same as in Example 2. The obtained product is denoted as thickener 4#.

[0056] Example 5 The difference from Example 2 is that the degree of carboxymethyl substitution of carboxymethyl cellulose is 0.76, and the rest is the same as in Example 2. The obtained product is denoted as thickener 5#.

[0057] Example 6 The difference from Example 2 is that the mass ratio of carboxymethyl cellulose to double-terminal amino polysiloxane is 1:0.8, and the rest is the same as in Example 2. The obtained product is denoted as thickener 6#.

[0058] Example 7 The difference from Example 2 is that the mass ratio of carboxymethyl cellulose to double-terminal amino polysiloxane is 1:0.2, and the rest is the same as in Example 2. The obtained product is denoted as thickener 7#.

[0059] Example 8 The difference from Example 2 is that the molecular weight of the double-terminal amino polysiloxane is 1,000, and the rest is the same as in Example 2. The obtained product is denoted as thickener 8#.

[0060] Example 9 The difference from Example 2 is that the molecular weight of the double-terminal amino polysiloxane is 10,000, and the rest is the same as in Example 2. The obtained product is denoted as thickener 9#.

[0061] Example 10 A preparation method of a fracturing fluid includes the following steps: S1. Add water to the guar gum derivative and stir to swell for 5 min. Add a bactericide, a clay stabilizer, and a flowback aid, mix well, adjust the pH to 10 using a pH regulator, and add a crosslinking agent and mix evenly to obtain the base fluid; S2. Add a thickening agent and a gel breaker to the base fluid, stir to form a gel, and that's it; Each component in the fracturing fluid is calculated by weight percentage and includes: carboxymethyl guar gum 0.05 - 0.1%, thickening agent 0.30 - 0.45%, crosslinking agent 0.1 - 0.3%, bactericide 0.05 - 0.1%, clay stabilizer 0.5 - 1%.

[0062] The following fracturing fluids are prepared according to the above method: Fracturing fluid 1# Carboxymethyl guar gum (molecular weight 200,000) 0.1%, thickening agent 1# 0.30%, crosslinking agent 0.1%, bactericide 0.05%, clay stabilizer 0.5%.

[0063] Fracturing fluid 2# Carboxymethyl hydroxypropyl guar gum (molecular weight 200,000) 0.05%, thickening agent 2# 0.45%, crosslinking agent 0.3%, bactericide 0.1%, clay stabilizer 01%.

[0064] Fracturing fluid 3# Carboxymethyl hydroxypropyl guar gum (molecular weight 200,000) 0.05%, thickening agent 3# 0.45%, crosslinking agent 0.3%, bactericide 0.1%, clay stabilizer 01%.

[0065] Fracturing fluid 4# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 4# prepared in the above Example 4.

[0066] Fracturing fluid 5# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 5# prepared in the above Example 5.

[0067] Fracturing fluid 6# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 6# prepared in the above Example 6.

[0068] Fracturing fluid 7# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 7# prepared in the above Example 7.

[0069] Fracturing fluid 8# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 8# prepared in the above Example 8.

[0070] Fracturing fluid 9# The difference from fracturing fluid 2# is that the thickening agent is the thickening agent 9# prepared in Example 9 above.

[0071] Fracturing fluid 10# The difference from fracturing fluid 2# is that it further contains 0.2% sulfonated nano-montmorillonite, and the sulfonated nano-montmorillonite is prepared by the following method: (1) Disperse nano-montmorillonite powder with a particle size of 600 nm in 10 times the weight of toluene, add vinyltriethoxysilane for reaction, and after the reaction, filter and dry to obtain an intermediate product (i.e., silane coupling agent-modified nano-montmorillonite); (2) Disperse the intermediate product in 20 intermediate N,N-dimethylformamide, add 2-methylacrylamide-2-methylpropanesulfonic acid, add an initiator for reaction, and after the reaction, filter and dry to obtain sulfonated nano-montmorillonite; the weight ratio of nano-montmorillonite powder, vinyltriethoxysilane, and 2-methylacrylamide-2-methylpropanesulfonic acid is 1:1:0.5.

[0072] Fracturing fluid 11# The difference from fracturing fluid 2# is that it further contains 0.5% sulfonated nano-montmorillonite, and the sulfonated nano-montmorillonite is prepared by the following method: (1) Disperse nano-montmorillonite powder with a particle size of 200 nm in 20 times the weight of toluene, add 3-acryloxypropylsulfonic acid for reaction, and after the reaction, filter and dry to obtain an intermediate product (i.e., silane coupling agent-modified nano-montmorillonite); (2) Disperse the intermediate product in 20 intermediate N,N-dimethylformamide, add 2-methylacrylamide-2-methylpropanesulfonic acid, add an initiator for reaction, and after the reaction, filter and dry to obtain sulfonated nano-montmorillonite; the weight ratio of nano-montmorillonite powder, vinyltriethoxysilane, and 2-methylacrylamide-2-methylpropanesulfonic acid is 1:2:0.7.

[0073] Fracturing fluid 12# The difference from fracturing fluid 10# is that in the preparation process of sulfonated nano-montmorillonite, the weight ratio of nano-montmorillonite powder, vinyltriethoxysilane, and 2-methylacrylamide-2-methylpropanesulfonic acid is 1:3:1.

[0074] Fracturing fluid 13# The difference from fracturing fluid 10# is that 2-methylacrylamide-2-methylpropanesulfonic acid in the preparation process of sulfonated nano-montmorillonite is replaced with an equal amount of acrylic acid.

[0075] Fracturing fluid 14# The difference from fracturing fluid 10# is that sulfonated nano-montmorillonite is replaced with the silane coupling agent-modified nano-montmorillonite prepared in step (1).

[0076] Comparative Example 1 The difference from fracturing fluid 2# is that the thickener is replaced with an equal amount of hydroxypropyl cellulose to obtain fracturing fluid 15#.

[0077] Comparative Example 2 The difference from fracturing fluid 2# is that the thickener is replaced with an equal amount of carboxymethyl cellulose to obtain fracturing fluid 16#.

[0078] Test Example 1 The temperature resistance, salt resistance and shear resistance of the above thickeners 1~9# were tested and compared with carboxymethyl cellulose; the specific method is as follows: (1) At room temperature, thickeners 1 to 9 and carboxymethyl cellulose were added to water to prepare a solution with a mass fraction of 0.5%. After swelling stabilized, the viscosity A at room temperature was tested (shear speed was 170 s -1 ); Then the viscosity B and C after shearing for 180 minutes at 120℃ were tested respectively, and the viscosity retention rate was calculated to evaluate its heat resistance and anti-shear performance; (2) Thickeners 1 to 9 and carboxymethyl cellulose were added to 20,000 ppm NaCl solution to prepare a solution with a mass fraction of 0.5%. After swelling stabilized, the viscosity D was measured at room temperature (shear speed was 170 s -1 ), the viscosity retention rate was calculated according to the formula D / A to evaluate its salt resistance.

[0079] The measured results are shown in Table 1 below.

[0080] Table 1

[0081] As shown in the table, compared with carboxymethyl cellulose, the cellulose derivative provided in the present application has excellent temperature resistance, shear resistance, and salt resistance, which makes up for the defects of existing cellulose derivative thickeners.

[0082] Test Example 2 According to SYT5107-2016 "Water-based Fracturing Fluid Performance Evaluation Method", the viscosity of the above fracturing fluids 1 to 16# after shearing at 120℃ and 160℃ for 180 minutes was tested, and the viscosity retention rate and the residue content after complete gel breaking were calculated. The results are shown in Table 2 below.

[0083] Table 2

[0084] As shown in the table, compared with the use of hydroxyethyl cellulose and carboxymethyl hydroxyethyl cellulose (fracturing fluids 15# and 16#), fracturing fluids 1-3# use cellulose derivatives as thickeners, and have higher temperature and shear resistance. They can still maintain a relatively high viscosity under long-term shearing at 120°C and 160°C, and can withstand a high temperature of 160°C. Compared with fracturing fluids 1-3#, fracturing fluids 10 and 11# have a higher viscosity retention rate under long-term shearing at 120°C and 160°C, and their temperature and shear resistance are further improved.

[0085] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. Obviously, those who are familiar with the technology in this field can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, this application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of this application according to the disclosure of this application should be within the protection scope of this application.

Claims

1. A modified cellulose thickener for fracturing fluid, characterized in that, It includes a carboxymethyl cellulose derivative prepared by modifying carboxymethyl cellulose with diaminopolysiloxane; the mass ratio of the carboxymethyl cellulose to the diaminopolysiloxane is 1:(1 - 1.8).

2. The modified cellulose thickener for fracturing fluid according to claim 1, wherein The molecular weight of the carboxymethyl cellulose is 20,000 - 100,000, and the carboxymethyl substitution degree DS is 0.54 - 0.

68.

3. The modified cellulose thickener for fracturing fluid according to claim 1, wherein The molecular weight of the diaminopolysiloxane is 2,000 - 8,000.

4. The modified cellulose thickener for fracturing fluid according to any one of claims 1-3, characterized in that, The preparation method of the carboxymethyl cellulose derivative includes the following steps: Add carboxymethyl cellulose into a solvent, add diaminopolysiloxane, add a catalyst, react at 60 - 80 °C for 12 - 24 h, cool after the reaction is completed, filter by suction, and dry to obtain.

5. A fracturing fluid, characterized in that, The fracturing fluid contains the modified cellulose thickener for fracturing fluid according to any one of claims 1 - 4, and a crosslinking agent; wherein, The dosage of the modified cellulose thickener for fracturing fluid accounts for 0.30 - 0.45% of the total weight of the fracturing fluid; The dosage of the crosslinking agent accounts for 0.1 - 0.3% of the total weight of the fracturing fluid.

6. The fracturing fluid according to claim 5, wherein The fracturing fluid also contains a guar gum derivative, and the dosage of the guar gum derivative accounts for 0.05 - 0.1% of the total weight of the fracturing fluid.

7. The fracturing fluid according to claim 6, wherein The fracturing fluid also contains the following components: A bactericide, and the dosage of the bactericide accounts for 0 - 0.1% of the total weight of the fracturing fluid; and / or A clay stabilizer, and the dosage of the clay stabilizer accounts for 0 - 1% of the total weight of the fracturing fluid; and / or A flowback aid, and the dosage of the flowback aid accounts for 0 - 1% of the total weight of the fracturing fluid; and / or A pH regulator, and the pH regulator is added to adjust the pH of the fracturing fluid to 10 - 11; and / or A breaker, and the dosage of the breaker accounts for 0 - 0.05% of the total weight of the fracturing fluid.

8. The fracturing fluid according to claim 7, wherein Sulfonated nano - montmorillonite is also added to the fracturing fluid, and the addition amount of the sulfonated nano - montmorillonite in the fracturing fluid is 0 - 0.5%; The sulfonated nano - montmorillonite is prepared by successively modifying nano - montmorillonite with a vinyl silane coupling agent and a polymerizable monomer containing a sulfonic acid group; The weight ratio of the nano - montmorillonite, the vinyl silane coupling agent, and the polymerizable monomer containing a sulfonic acid group is 1:(1 - 2):(0.5 - 0.7).

9. The fracturing fluid according to claim 8, wherein, The polymerizable monomer containing a sulfonic acid group is selected from at least one of 2 - methacrylamide - 2 - methylpropanesulfonic acid, 2 - acrylamidoethanesulfonic acid, 2 - acryloyloxyethanesulfonic acid, 2 - methacryloyloxyethanesulfonic acid, 3 - acryloyloxypropanesulfonic acid, and 2 - methacryloyloxypropanesulfonic acid.

10. The preparation method of the fracturing fluid according to any one of claims 6-9, characterized in that, It includes the following steps: S1. Stir and swell the guar gum derivative in water for 5 - 10 min, then add the bactericide, the clay stabilizer, and the flowback aid and mix evenly, use the pH regulator to adjust the pH to 10 - 11, and add the crosslinking agent to obtain a base fluid; S2. Add the modified cellulose thickener for fracturing fluid to the base fluid, add the breaker, and stir to form a network - like gel, thus obtaining.

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