Fracturing thickening agent, its preparation method and application

Abstract

The application belongs to the technical field of oil exploitation, and particularly relates to a thickening agent for fracturing and a preparation method and application thereof. The preparation method comprises the following steps: adding beta-cyclodextrin and DMF into a reactor, adding triethylamine, cooling, adding acryloyl chloride drop by drop, adding acetone, and performing suction filtration and drying to obtain a functional monomer; adding acrylamide, deionized water, the functional monomer, vinyl pyrrolidone, styrene sulfonic acid, 1-allyl-3-methyl imidazole bis(trifluoromethanesulfonyl) imidate salt and potassium dihydrogen phosphate into a reaction kettle in sequence and stirring uniformly; slowly adding an initiator into the reaction kettle, performing temperature increasing and heat preservation reaction, drying and granulating to obtain the thickening agent for fracturing. The thickening agent has the advantages of high apparent viscosity, good thermal stability and strong shear resistance.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a thickener for fracturing, its preparation method, and its application. Background Technology

[0002] Hydraulic fracturing, a core technology for enhancing oil and gas reservoir production, has been widely applied in global oil and gas field development. This technology involves injecting high-viscosity fracturing fluid containing proppant under high pressure to create a fracture network in underground rock formations, significantly improving oil and gas permeability. The performance of the fracturing fluid directly determines fracture propagation efficiency, proppant migration capacity, and formation damage. Thickeners, as the core component of fracturing fluids, primarily function to significantly increase the viscosity of the base fluid, suspending and transporting proppant, reducing pipeline friction, controlling filtration loss, and forming fractures. Technological breakthroughs in thickener technology have become a key factor restricting fracturing effectiveness.

[0003] Traditional water-based fracturing fluid thickeners are mainly composed of natural plant gums (such as guar gum and guar gum). The hydroxyl groups in their molecular chains are prone to degradation at high temperatures (>120℃), leading to a sharp drop in viscosity. Plant gum molecular chains are also susceptible to degradation, oxidation, or coiling, resulting in a drastic decrease in the viscosity of the fracturing fluid system and poor stability, making it difficult to meet the fracturing requirements of deep, high-temperature reservoirs. Although synthetic polymer thickeners (such as polyacrylamide) have improved temperature resistance, they are prone to shear degradation under high pressure, significantly weakening their proppant-carrying capacity.

[0004] CN1073194A discloses a method for preparing a fracturing fluid thickener suitable for fracturing operations in low-permeability oil and gas reservoirs. It is prepared by chemically modifying plant-based broad bean powder with ethanol, caustic soda, propylene oxide, and water. Its water-insoluble content is significantly lower than that of currently used plant-based broad bean gum thickeners in fracturing fluids, thus causing less formation damage and achieving increased production. However, compared to synthetic polymer thickeners, this fracturing fluid thickener has a higher residue content and poorer temperature resistance.

[0005] CN111019042A discloses a high-temperature resistant thickener for fracturing fluid, its preparation method, and its application. The thickener comprises acrylamide, a salt-resistant functional monomer, and a temperature-sensitive functional monomer free radical; the molar ratio of acrylamide, salt-resistant functional monomer, and temperature-sensitive functional monomer is 1:(0.01~0.08):(0.05~0.15). This invention introduces temperature-sensitive and salt-resistant units into the acrylamide molecular chain through solution copolymerization, endowing the copolymer with excellent high-temperature resistance and salt resistance, while also exhibiting good solubility, viscoelasticity, and proppant carrying capacity. However, because it does not actually solve the problem of crosslinking bond breakage in fracturing fluid thickeners at high temperatures, the stability of the fracturing fluid thickener is poor. Summary of the Invention

[0006] This invention addresses the shortcomings of the prior art by providing a fracturing thickener, its preparation method, and its application. The thickener of this invention has the advantages of high apparent viscosity, good thermal stability, and strong shear resistance.

[0007] The first objective of this invention is to disclose a method for preparing a thickener for fracturing, the specific steps of which are as follows:

[0008] (1) Preparation of functional monomers

[0009] β-cyclodextrin and DMF were added to the reactor and stirred to dissolve. Triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for at least 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0010] The structural formula of the functional unit is:

[0011]

[0012] Preferably, in this invention, the weight ratio of DMF, triethylamine, acryloyl chloride and β-cyclodextrin is 5-10:2-6:0.5-1.5:1.

[0013] (2) Preparation of thickener

[0014] ① Add acrylamide, deionized water, functional monomer, vinylpyrrolidone, styrene sulfonic acid, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipeline with nitrogen gas to replace the air in the reaction vessel.

[0015] ② Slowly add the initiator dropwise to the reactor. After the addition is complete, raise the temperature to 60-70℃ and keep the temperature for 1-2 hours to obtain a viscous liquid.

[0016] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0017] In this invention, preferably, the mass ratio of the functional monomer, vinylpyrrolidone, styrene sulfonic acid, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to acrylamide is 0.2-0.4:0.2-0.4:0.1-0.2:0.05-0.1:1.

[0018] Preferably, the weight ratio of deionized water, potassium dihydrogen phosphate, and acrylamide in step ① is 12-15:0.2-0.4:1.

[0019] In this invention, preferably, the initiator in step ② is a mixed solution of persulfate and sodium bisulfite, wherein the concentration of persulfate is 6-10 wt% and the concentration of sodium bisulfite is 3-5 wt%.

[0020] Preferably, the weight ratio of the initiator to acrylamide is 0.3-0.6:1.

[0021] More preferably, the persulfate is one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0022] The synthesis reaction equation for the fracturing thickener of the present invention is as follows:

[0023]

[0024] Another objective of this invention is to disclose a thickener prepared by the above-described method, wherein the molecular structural formula of the thickener is as follows:

[0025]

[0026] in,

[0027] a = 20000 - 200000;

[0028] b = 150 - 3000;

[0029] c = 2500 - 50000;

[0030] d = 1000 - 200000;

[0031] e = 200 - 4000.

[0032] Preferably, the viscosity-average molecular weight of the thickener is 10,000,000-20,000,000.

[0033] The third objective of this invention is to disclose the application of the above-mentioned thickener in hydraulic fracturing of oil and gas reservoirs.

[0034] The fracturing thickener of this invention is obtained by modifying the molecular structure of the conventional thickener polyacrylamide. The main monomer polymerized is acrylamide, and the monomers involved in the modification include functional monomers, vinylpyrrolidone, styrene sulfonic acid, and 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. Among them, the functional monomer has a β-cyclodextrin structure, and its molecule has multiple hydroxyl groups, which can react with multiple hydrophobic groups simultaneously, or link different polymer chains together through its own cross-linking effect, thus significantly increasing the viscosity of the thickener. Vinylpyrrolidone is a typical rigid monomer, which can increase the shear resistance of the thickener. Styrene sulfonic acid can reduce the interfacial tension and frictional resistance, and the presence of a benzene ring in the molecule can increase the shear resistance. 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can improve the temperature resistance of the thickener, significantly reduce frictional resistance, and improve the tolerance to different pH values.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) The thickener of the present invention has a high apparent viscosity, with a viscosity of 3000 mg / L reaching 105 mPa·s or more;

[0037] (2) The thickener of the present invention has good shear resistance, 170s -1 After shearing at a rate of 120 min, the viscosity retention rate reached over 98%. Detailed Implementation

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] Example 1

[0040] (1) Preparation of functional monomers

[0041] 20g of β-cyclodextrin and 100g of DMF were added to the reactor and stirred to dissolve. 40g of triethylamine was added, the temperature was lowered to 3°C, nitrogen gas was introduced, and 10g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0042] (2) Preparation of thickener

[0043] ① Add 10g acrylamide, 120g deionized water, 2g functional monomer, 2g vinylpyrrolidone, 1g styrene sulfonic acid, 0.5g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 2g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0044] ② Slowly add 3g of initiator to the reaction vessel. The initiator contains 10wt% sodium persulfate and 5wt% sodium bisulfite. After the addition is complete, raise the temperature to 60℃ and keep the reaction at this temperature for 2 hours to obtain a viscous liquid.

[0045] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0046] Example 2

[0047] (1) Preparation of functional monomers

[0048] 20g of β-cyclodextrin and 200g of DMF were added to the reactor and stirred to dissolve. 120g of triethylamine was added, the temperature was lowered to 3°C, nitrogen gas was introduced, and 30g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0049] (2) Preparation of thickener

[0050] ① Add 10g acrylamide, 150g deionized water, 2g functional monomer, 2.5g vinylpyrrolidone, 1.5g styrene sulfonic acid, 0.6g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 4g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0051] ② Slowly add 6g of initiator to the reaction vessel. The initiator contains 6wt% sodium persulfate and 3wt% sodium bisulfite. After the addition is complete, raise the temperature to 70℃ and keep the reaction at this temperature for 1 hour to obtain a viscous liquid.

[0052] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0053] Example 3

[0054] (1) Preparation of functional monomers

[0055] 20g of β-cyclodextrin and 120g of DMF were added to the reactor and stirred to dissolve. 60g of triethylamine was added, the temperature was lowered to 3°C, nitrogen gas was introduced, and 15g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0056] (2) Preparation of thickener

[0057] ① Add 10g acrylamide, 130g deionized water, 4g functional monomer, 2g vinylpyrrolidone, 2g styrene sulfonic acid, 1g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 3g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0058] ② Slowly add 4g of initiator to the reaction vessel. The initiator contains 8wt% potassium persulfate and 4wt% sodium bisulfite. After the addition is complete, raise the temperature to 65℃ and keep the reaction at this temperature for 2 hours to obtain a viscous liquid.

[0059] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0060] Example 4

[0061] (1) Preparation of functional monomers

[0062] 20g of β-cyclodextrin and 140g of DMF were added to the reactor and stirred to dissolve. 80g of triethylamine was added, the temperature was lowered to 2℃, nitrogen gas was introduced, and 20g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0063] (2) Preparation of thickener

[0064] ① Add 10g acrylamide, 140g deionized water, 3.5g functional monomer, 3g vinylpyrrolidone, 1g styrene sulfonic acid, 0.7g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 3.5g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0065] ② Slowly add 4g of initiator to the reaction vessel. The initiator contains 8wt% potassium persulfate and 3wt% sodium bisulfite. After the addition is complete, raise the temperature to 60℃ and keep the reaction at this temperature for 2 hours to obtain a viscous liquid.

[0066] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0067] Example 5

[0068] (1) Preparation of functional monomers

[0069] 20g of β-cyclodextrin and 180g of DMF were added to the reactor and stirred to dissolve. 100g of triethylamine was added, the temperature was lowered to 3°C, nitrogen gas was introduced, and 25g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 2 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0070] (2) Preparation of thickener

[0071] ① Add 10g acrylamide, 150g deionized water, 3g functional monomer, 4g vinylpyrrolidone, 2g styrene sulfonic acid, 0.8g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 3g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0072] ② Slowly add 5g of initiator to the reaction vessel. The initiator contains 9wt% ammonium persulfate and 4wt% sodium bisulfite. After the addition is complete, raise the temperature to 70℃ and keep the reaction at this temperature for 1 hour to obtain a viscous liquid.

[0073] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0074] Example 6

[0075] (1) Preparation of functional monomers

[0076] 20g of β-cyclodextrin and 160g of DMF were added to the reactor and stirred to dissolve. 80g of triethylamine was added, the temperature was lowered to 2℃, nitrogen gas was introduced, and 20g of acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for 2 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer.

[0077] (2) Preparation of thickener

[0078] ① Add 10g acrylamide, 150g deionized water, 3g functional monomer, 3g vinylpyrrolidone, 1.5g styrene sulfonic acid, 0.8g 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and 3g potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipelines with nitrogen to replace the air in the reaction vessel;

[0079] ② Slowly add 5g of initiator to the reaction vessel. The initiator contains 7wt% ammonium persulfate and 3wt% sodium bisulfite. After the addition is complete, raise the temperature to 70℃ and keep the reaction at this temperature for 1.2h to obtain a viscous liquid.

[0080] ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing.

[0081] Example 7: Apparent viscosity test

[0082] The thickener for fracturing according to the present invention (Examples 1-6) was prepared into a solution with a concentration of 3000 mg / L using deionized water, and then subjected to fracturing at 60°C for 170 seconds. -1 Under the given conditions, the apparent viscosity μ0 was tested using the DV-III Brinell viscosity tester.

[0083] The acid fracturing fluid from Henan Daochun New Material Technology Co., Ltd. was used as a comparative sample, and the test results are shown in Table 1.

[0084] As can be seen from Table 1, the fracturing thickener of the present invention (Examples 1-6) has a high apparent viscosity at 60°C and 170 seconds. -1 Under the specified conditions, the viscosity reached over 105 mPa·s when the concentration was 3000 mg / L, with a maximum of 140 mPa·s; while the apparent viscosity of the comparative example was 60 mPa·s, which was significantly lower than that of the present invention.

[0085] Example 8 Shear resistance test

[0086] The solution from Example 7 was subjected to 60°C for 170 seconds. -1 Under these conditions, the apparent viscosity μ1 was tested after continuous shearing for 120 min.

[0087] Shear resistance is denoted as η.

[0088] η = μ1 / μ0 × 100%

[0089] The acid fracturing fluid from Henan Daochun New Material Technology Co., Ltd. was used as a comparative sample, and the test results are shown in Table 1.

[0090] Table 1. Results of Apparent Viscosity and Shear Resistance Tests

[0091] Example 1 106 98.4 Example 2 114 98.5 Example 3 120 99 Example 4 125 98.8 Example 5 140 99.2 Example 6 138 99 Comparative Example 60 92

[0092] As can be seen from Table 1, the thickener for fracturing of the present invention (Examples 1-6) has good shear resistance at 60℃ and 170 seconds. -1 Under the specified conditions, after shearing for 120 minutes, the viscosity retention rate reached over 98%, with a maximum of 99.2%; while the viscosity retention rate of the comparative example was 92%, which is significantly lower than that of this invention.

[0093] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a viscosifier for fracturing, characterized in that, The specific steps of the preparation method are as follows: (1) Preparation of functional monomers; β-cyclodextrin and DMF were added to the reactor and stirred to dissolve. Triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and acryloyl chloride was slowly added dropwise. After the addition was completed, stirring was continued for at least 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the functional monomer. The weight ratio of DMF, triethylamine, acryloyl chloride, and β-cyclodextrin is 5-10:2-6:0.5-1.5:1; (2) Preparation of thickener; ① Add acrylamide, deionized water, functional monomer, vinylpyrrolidone, styrene sulfonic acid, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and potassium dihydrogen phosphate to the reaction vessel in sequence, stir well, adjust the pH to 7-8 with sodium hydroxide solution, and purge the reaction vessel and pipeline with nitrogen gas to replace the air in the reaction vessel. ② Slowly add the initiator dropwise to the reactor. After the addition is complete, raise the temperature to 60-70℃ and keep the temperature for 1-2 hours to obtain a viscous liquid. ③ The above viscous liquid is dried and granulated to obtain a thickener for fracturing; The mass ratio of the functional monomer, vinylpyrrolidone, styrene sulfonic acid, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to acrylamide is 0.2-0.4:0.2-0.4:0.1-0.2:0.05-0.1:

1.

2. The method of claim 1, wherein, The weight ratio of deionized water, potassium dihydrogen phosphate, and acrylamide mentioned in step ① is 12-15: 0.2-0.4：1。 3. The preparation method according to claim 1, characterized in that, The initiator mentioned in step ② is a mixed solution of persulfate and sodium bisulfite, wherein the concentration of persulfate is 6-10 wt% and the concentration of sodium bisulfite is 3-5 wt%.

4. The method of claim 1 or 3, wherein the compound is prepared by the method of claim 2. The weight ratio of the initiator to acrylamide is 0.3-0.6:

1.

5. The preparation method according to claim 3, characterized in that, The persulfate is one of potassium persulfate, ammonium persulfate, or sodium persulfate.

6. The preparation method according to claim 1, characterized in that, The structural formula of the functional unit is:

7. The thickener prepared by the preparation method according to any one of claims 1-6.

8. The thickener according to claim 7, characterized in that, The molecular structure of the thickener is as follows: in, a＝20000-200000； b＝150-3000； c＝2500-50000； d＝1000-200000； e＝200-4000。 9. The thickener according to claim 8, characterized in that, The viscosity-average molecular weight of the thickener is 10,000,000-20,000,000.

10. The application of the thickener according to any one of claims 7-9 in hydraulic fracturing of oil and gas reservoirs.

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