Water-based fracturing fluid as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of oil exploitation, and particularly relates to a water-based fracturing fluid as well as a preparation method and application thereof. The preparation method comprises the following steps: adding 4-vinylaniline and a catalyst into a high-pressure reaction kettle, heating, introducing ethylene oxide, and carrying out heating and heat preservation reaction; cooling, adding sulfamic acid powder, heating, preserving heat, reacting, and cooling to obtain a first functional monomer; adding beta-cyclodextrin and DMF (Dimethyl Formamide) into a first reactor, stirring and dissolving, adding triethylamine, cooling, dropwise adding acryloyl chloride, and carrying out low-temperature reaction, suction filtration, washing and drying to obtain a second functional monomer; adding acrylamide, a first functional monomer, a second functional monomer, 3-[(3-acrylamidopropyl) dimethylammonium] propionate, distilled water and sodium dihydrogen phosphate into a second reactor, and uniformly stirring; and adding an initiator, carrying out heat preservation reaction, and cooling to obtain the water-based fracturing fluid. The water-based fracturing fluid disclosed by the invention has the advantages of high apparent viscosity, strong shear resistance and good salt resistance and hardness resistance.

Description

Technical Field

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

[0002] Hydraulic fracturing is a core technology for exploiting unconventional oil and gas resources (such as shale gas, tight oil, and coalbed methane) and for modifying low-permeability conventional reservoirs. Its principle is to inject fracturing fluid into the underground reservoir under high pressure, forming an artificial fracture network that provides efficient flow channels for oil and gas. The performance of the fracturing fluid directly determines the success or failure of the fracturing operation, the fracture conductivity, and the effectiveness of reservoir protection.

[0003] Currently, there are two main types of fracturing fluids: one is polymer-based water-based fracturing fluids using guar gum and its derivatives as thickeners. These have advantages such as low cost, high viscosity, and good sand-suspending performance. However, traditional guar gum fracturing fluids leave insoluble residues after breaking down, which can clog the proppant-filled layer and reservoir pores, severely reducing fracture conductivity and affecting production enhancement. The other type is water-based fracturing fluids using synthetic polymers as thickeners. These generally exhibit high shear stress (such as high-speed pumping or wellbore friction), where molecular chains are prone to mechanical breakage, leading to viscosity decay. In high-salinity formations, high-valence ions such as calcium and magnesium easily precipitate, causing the solution viscosity to decrease or even fail.

[0004] CN106336862B provides a clean fracturing fluid comprising the following components by weight: 2-4% thickener, 0-8% potassium chloride, 0-10% regulator, 2-5% temperature-resistant enhancer, and the balance being water for mixing. This fracturing fluid can be prepared using acidic or alkaline fresh water or high-salt acidizing fracturing flowback fluid. The high-salt flowback fluid can be used for fracturing in the next well after treatment to remove mechanical impurities, eliminating the need for pre-adjustment of the water quality and saving on chemical water treatment processes, thus greatly reducing operating costs. During on-site construction, the fracturing fluid is continuously mixed to achieve efficient proppant carrying, thereby achieving zero wastewater discharge during reservoir fracturing, acidizing, and oil and gas testing, realizing "zero pollution" at the downhole operation site and contributing to clean and efficient production. However, the apparent viscosity of this fracturing fluid at room temperature is only 30 mPa·s, and the viscosity will further decrease as the formation temperature rises, which will lead to poor fracturing effect. Summary of the Invention

[0005] This invention addresses the shortcomings of the prior art by providing a water-based fracturing fluid and its preparation method. The water-based fracturing fluid of this invention has advantages such as high apparent viscosity, strong shear resistance, and good salt and hardness resistance.

[0006] The first objective of this invention discloses a water-based fracturing fluid and its preparation method, the specific steps of which are as follows: (1) Add 4-ethyleneaniline and catalyst to a high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 88-92℃, repeat 2-3 times, slowly introduce ethylene oxide, heat and keep the reaction at the temperature; cool down to below 40℃, adjust the pH to 2-3 with sulfuric acid, add aminosulfonic acid powder, stir and heat, continue heating and keep the reaction at the temperature, cool down to below 40℃, and obtain the first functional monomer.

[0007] The molar ratio of ethylene oxide, aminosulfonic acid and 4-vinylaniline is 2-20:0.8-1.2:1.

[0008] (2) β-cyclodextrin and DMF were added to the first reactor and stirred to dissolve. Triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, acryloyl chloride was slowly added dropwise, the reaction was carried out at low temperature, acetone was added, crude functional monomer was precipitated, filtered, washed with acetone, and dried to obtain the second functional monomer.

[0009] The weight ratio of DMF, triethylamine, acryloyl chloride and β-cyclodextrin is 5-10:4-6:0.4-0.8:1.

[0010] (3) Add acrylamide, first functional monomer, second functional monomer, 3-[(3-acrylamidopropyl)dimethylammonium]propionate, distilled water, and sodium dihydrogen phosphate to the second reactor. Adjust the pH to 7-8 with sodium hydroxide solution and stir evenly. Purge the reactor with nitrogen, add initiator, keep the reaction at a constant temperature, cool down to below 40°C, and adjust the pH to 7-8 to obtain water-based fracturing fluid.

[0011] The weight ratio of the first functional monomer, the second functional monomer, 3-[(3-acrylamidopropyl)dimethylammonium]propionate to acrylamide is 0.1-0.2:0.2-0.5:0.1-0.2:1.

[0012] Preferably, in step (1), the catalyst is sodium hydroxide or potassium hydroxide, and the weight ratio of the catalyst to 4-ethyleneaniline is 0.1-0.2:1.

[0013] Preferably, in step (1), the heating and heat preservation reaction temperature is 90-120℃ and the time is 1-4h.

[0014] Preferably, in step (1), the continued heating and heat preservation reaction temperature is 80-110℃, and the time is 2-6h.

[0015] Preferably, in step (2), the low-temperature reaction temperature is 5-20℃ and the time is 1-4h.

[0016] Preferably, in step (3), the weight ratio of distilled water, sodium dihydrogen phosphate and acrylamide is 12-15:0.1-0.2:1.

[0017] Preferably, in step (3), the initiator is one of potassium persulfate, sodium persulfate, or ammonium persulfate, and the weight ratio of the initiator to acrylamide is 0.05-0.2:1.

[0018] Preferably, in step (3), the heat preservation reaction temperature is 60-80℃ and the time is 1-4h.

[0019] The synthesis reaction equation for the water-based fracturing fluid of this invention is as follows:

[0020]

[0021]

[0022]

[0023] Another objective of this invention discloses a water-based fracturing fluid, the molecular structure of which is as follows:

[0024] in: a = 30000 - 300000; b = 1000 - 50000; c = 600 - 15000; d = 1000 - 20000; n = 2 - 20.

[0025] Preferably, the viscosity-average molecular weight of the fracturing fluid is 15,000,000-25,000,000.

[0026] The third objective of this invention is to disclose the application of the above-mentioned water-based fracturing fluid in oil and gas reservoir fracturing.

[0027] The water-based fracturing fluid of this invention is a quaternary polymer obtained by modifying the molecular structure of polyacrylamide, and has a high apparent viscosity. The long chain on the side of the first functional monomer allows the thickener to penetrate the aqueous phase better, strengthens the interaction with the aqueous phase, and also has the property of reducing filtration loss; the second functional monomer is a rigid monomer, which can significantly improve the shear resistance of this invention; 3-[(3-acrylamidopropyl)dimethylammonium]propionate is an amphoteric surfactant, which can improve the salt and hardness resistance of the fracturing fluid.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The water-based fracturing fluid of the present invention has a high apparent viscosity, and the viscosity can reach 80 mPa•s after being diluted with 50 times the weight of distilled water. (2) The water-based fracturing fluid of the present invention has good shear resistance at 170S. -1 Under these conditions, after continuous shearing for 120 minutes, the viscosity retention rate can reach 97%. (3) The water-based fracturing fluid of the present invention has good salt and hardness resistance. When diluted 50 times with simulated formation water containing 40,000 mg / L sodium chloride and 10,000 mg / L calcium chloride, the viscosity can reach 73 mPa•s. Detailed Implementation

[0029] 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.

[0030] Example 1 1. Preparation of the first functional monomer (1) Add 0.1 mol of 4-ethylene aniline and 1.19 g of sodium hydroxide to a high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 90°C, repeat twice, slowly introduce 0.2 mol of ethylene oxide, heat to 90°C, and keep the reaction at this temperature for 1 h. (2) Cool down to below 40°C, adjust pH to 2-3 with sulfuric acid, add 0.08 mol aminosulfonic acid powder, heat while stirring, heat to 80°C, keep the reaction at this temperature for 6 hours, cool down to below 40°C, and obtain the first functional monomer.

[0031] 2. Preparation of the second functional monomer 20g of β-cyclodextrin and 100g of DMF were added to the first reactor and stirred to dissolve. 80g of triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and 8g of acryloyl chloride was slowly added dropwise. The reaction was carried out at 5°C for 2 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the second functional monomer.

[0032] 3. Preparation of water-based fracturing fluid (1) Add 10g acrylamide, 2g first functional monomer, 2g second functional monomer, 2g 3-[(3-acrylamidopropyl)dimethylammonium]propionate, 120g distilled water, and 1g sodium dihydrogen phosphate to the second reactor, adjust the pH to 7-8 with sodium hydroxide solution, and stir evenly; (2) Purge the reactor with nitrogen, add 0.5g sodium persulfate, heat to 60℃, keep the reaction at this temperature for 4h, cool down to below 40℃, adjust the pH to 7-8, and obtain water-based fracturing fluid.

[0033] Example 2 1. Preparation of the first functional monomer (1) Add 0.1 mol of 4-ethylene aniline and 1.25 g of sodium hydroxide to a high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 88°C, repeat twice, slowly introduce 0.6 mol of ethylene oxide, heat to 100°C, and keep the reaction at this temperature for 1 h. (2) Cool down to below 40°C, adjust pH to 2-3 with sulfuric acid, add 0.12 mol aminosulfonic acid powder, heat while stirring, heat to 90°C, keep the reaction at this temperature for 4 hours, cool down to below 40°C, and obtain the first functional monomer.

[0034] 2. Preparation of the second functional monomer 20g of β-cyclodextrin and 120g of DMF were added to the first reactor and stirred to dissolve. 120g of triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and 16g of acryloyl chloride was slowly added dropwise. The reaction was carried out at 20°C for 1 hour. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the second functional monomer.

[0035] 3. Preparation of water-based fracturing fluid (1) Add 10g acrylamide, 1.8g first functional monomer, 3g second functional monomer, 1.7g 3-[(3-acrylamidopropyl)dimethylammonium]propionate, 125g distilled water, and 1.2g sodium dihydrogen phosphate to the second reactor, adjust the pH to 7-8 with sodium hydroxide solution, and stir evenly; (2) Purge the reactor with nitrogen, add 1g of sodium persulfate, heat to 65°C, keep the reaction at this temperature for 3 hours, cool down to below 40°C, adjust the pH to 7-8, and obtain water-based fracturing fluid.

[0036] Example 3 1. Preparation of the first functional monomer (1) Add 0.1 mol 4-ethylene aniline and 1.55 g sodium hydroxide to the high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 92°C, repeat 3 times, slowly introduce 1 mol ethylene oxide, heat to 110°C, and keep the reaction at this temperature for 2 h. (2) Cool down to below 40°C, adjust pH to 2-3 with sulfuric acid, add 0.09 mol aminosulfonic acid powder, heat while stirring, heat to 110°C, keep the reaction at this temperature for 2 hours, cool down to below 40°C, and obtain the first functional monomer.

[0037] 2. Preparation of the second functional monomer 20g of β-cyclodextrin and 150g of DMF were added to the first reactor and stirred to dissolve. 100g of triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and 10g of acryloyl chloride was slowly added dropwise. The reaction was carried out at 15°C for 2 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the second functional monomer.

[0038] 3. Preparation of water-based fracturing fluid (1) Add 10g acrylamide, 1.6g first functional monomer, 4g second functional monomer, 1.5g 3-[(3-acrylamidopropyl)dimethylammonium]propionate, 130g distilled water, and 1.4g sodium dihydrogen phosphate to the second reactor, adjust the pH to 7-8 with sodium hydroxide solution, and stir evenly; (2) Purge the reactor with nitrogen, add 1.5g of potassium persulfate, heat to 70°C, keep the reaction at this temperature for 2 hours, cool down to below 40°C, adjust the pH to 7-8, and obtain water-based fracturing fluid.

[0039] Example 4 1. Preparation of the first functional monomer (1) Add 0.1 mol of 4-ethylene aniline and 2.14 g of potassium hydroxide to a high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 89°C, repeat 3 times, slowly introduce 1.5 mol of ethylene oxide, heat to 110°C, and keep the reaction at this temperature for 4 h. (2) Cool down to below 40°C, adjust pH to 2-3 with sulfuric acid, add 0.11 mol aminosulfonic acid powder, heat while stirring, heat to 100°C, keep the reaction at this temperature for 4 hours, cool down to below 40°C, and obtain the first functional monomer.

[0040] 2. Preparation of the second functional monomer 20g of β-cyclodextrin and 200g of DMF were added to the first reactor and stirred to dissolve. 90g of triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and 12g of acryloyl chloride was slowly added dropwise. The reaction was carried out at 10°C for 4 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the second functional monomer.

[0041] 3. Preparation of water-based fracturing fluid (1) Add 10g acrylamide, 1.3g first functional monomer, 4.5g second functional monomer, 1.2g 3-[(3-acrylamidopropyl)dimethylammonium]propionate, 140g distilled water, and 1.8g sodium dihydrogen phosphate to the second reactor, adjust the pH to 7-8 with sodium hydroxide solution, and stir evenly; (2) Purge the reactor with nitrogen, add 2g of potassium persulfate, heat to 80℃, keep the reaction at this temperature for 1h, cool down to below 40℃, adjust the pH to 7-8, and obtain water-based fracturing fluid.

[0042] Example 5 1. Preparation of the first functional monomer (1) Add 0.1 mol 4-ethylene aniline and 2.38 g potassium hydroxide to the high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 91°C, repeat 3 times, slowly introduce 2 mol ethylene oxide, heat to 120°C, and keep the reaction at this temperature for 3 h. (2) Cool down to below 40°C, adjust pH to 2-3 with sulfuric acid, add 0.1 mol aminosulfonic acid powder, heat while stirring, heat to 110°C, keep the reaction at this temperature for 5 hours, cool down to below 40°C, and obtain the first functional monomer.

[0043] 2. Preparation of the second functional monomer 20g of β-cyclodextrin and 200g of DMF were added to the first reactor and stirred to dissolve. 100g of triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, and 14g of acryloyl chloride was slowly added dropwise. The reaction was carried out at 10°C for 4 hours. Acetone was added to precipitate the crude functional monomer. The product was filtered, washed with acetone, and dried to obtain the second functional monomer.

[0044] 3. Preparation of water-based fracturing fluid (1) Add 10g acrylamide, 1g first functional monomer, 5g second functional monomer, 1g 3-[(3-acrylamidopropyl)dimethylammonium]propionate, 150g distilled water, and 2g sodium dihydrogen phosphate to the second reactor, adjust the pH to 7-8 with sodium hydroxide solution, and stir evenly. (2) Purge the reactor with nitrogen, add 1.5g of ammonium persulfate, heat to 70°C, keep the reaction at this temperature for 2 hours, cool down to below 40°C, adjust the pH to 7-8, and obtain water-based fracturing fluid.

[0045] Example 6: Apparent viscosity test The water-based fracturing fluid of the present invention (Examples 1-5) was diluted with 50 times its weight of distilled water to prepare the test solution. The apparent viscosity μ0 was tested at 60°C according to SY / T 6376-2008 "General Technical Conditions for Fracturing Fluids". The test results are shown in Table 1. A comparative experiment was conducted using PAM (concentration 1500 mg / L) from Shengli Petrochemical Co., Ltd.

[0046] As shown in Table 1, the apparent viscosity of the water-based fracturing fluid of the present invention (Examples 1-5) reached 70 mPa•s or higher after dilution with 50 times its weight of distilled water, with the highest reaching 80 mPa•s; while the apparent viscosity of PAM (concentration of 1500 mg / L) from Shengli Petrochemical Co., Ltd., a comparative example, was 42 mPa•s, which is significantly lower than that of the present invention. Therefore, the water-based fracturing fluid of the present invention has a higher apparent viscosity.

[0047] Example 7 Shear resistance test The solution from Example 6 was subjected to 60°C for 170 seconds. -1 Under these conditions, the apparent viscosity μ1 was tested after continuous shearing for 2 hours.

[0048] Shear resistance is denoted as η. η = μ1 / μ0 × 100% The test results are shown in Table 1. A comparative experiment was conducted using PAM from Shengli Petrochemical Co., Ltd.

[0049] As can be seen from Table 1, the water-based fracturing fluid of the present invention (Examples 1-5) has a 170S... -1 Under the specified conditions, after continuous shearing for 120 minutes, the shear resistance of the fluid reached 91% or higher, with a maximum of 97%. In contrast, the shear resistance of PAM from Shengli Petrochemical Co., Ltd., a comparative example, was 64%, significantly lower than that of the present invention. Therefore, the water-based fracturing fluid of the present invention exhibits superior shear resistance.

[0050] Example 8 Salt and Hardness Resistance Test The testing method is the same as in Example 6, except that the distilled water is replaced with simulated formation water.

[0051] Add 40g of sodium chloride and 10g of calcium chloride to a beaker, dissolve them, and make up to 1000ml to obtain simulated formation water containing 40000mg / L of sodium chloride and 10000mg / L of calcium chloride.

[0052] The test results are shown in Table 1. A comparative experiment was conducted using PAM from Shengli Petrochemical Co., Ltd.

[0053] Table 1. Test results of apparent viscosity, shear resistance, salt resistance, and hardness resistance. <![CDATA[μ0,mPa•s]]> η, % <![CDATA[μ2,mPa•s]]> Example 1 70 91 68 Example 2 72 93 68 Example 3 75 93 70 Example 4 80 96 73 Example 5 78 97 71 Comparative Example 42 64 26 As shown in Table 1, the water-based fracturing fluid of this invention (Examples 1-5), when diluted 50 times with simulated formation water containing 40,000 mg / L sodium chloride and 10,000 mg / L calcium chloride, all achieved a viscosity of 68 mPa•s or higher, with the highest reaching 73 mPa•s. In contrast, the viscosity of PAM from Shengli Petrochemical Co., Ltd., the comparative example, was 26 mPa•s, significantly lower than that of this invention. Therefore, the water-based fracturing fluid of this invention exhibits good salt and hardness resistance.

[0054] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0056] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A water-based fracturing fluid and its preparation method, characterized in that, The specific steps of the preparation method are as follows: (1) Add 4-ethyleneaniline and catalyst to a high-pressure reactor, purge the reactor with nitrogen, evacuate, heat to 88-92℃, repeat 2-3 times, slowly introduce ethylene oxide, heat and keep the reaction at the temperature; cool down to below 40℃, adjust the pH to 2-3 with sulfuric acid, add aminosulfonic acid powder, stir and heat, continue heating and keep the reaction at the temperature, cool down to below 40℃, and obtain the first functional monomer; The molar ratio of ethylene oxide, aminosulfonic acid, and 4-vinylaniline is 2-20:0.8-1.2:1; (2) β-cyclodextrin and DMF were added to the first reactor and stirred to dissolve. Triethylamine was added, the temperature was lowered to below 5°C, nitrogen gas was introduced, acryloyl chloride was slowly added dropwise, the reaction was carried out at low temperature, acetone was added, crude functional monomer was precipitated, filtered, washed with acetone, and dried to obtain the second functional monomer. The weight ratio of DMF, triethylamine, acryloyl chloride, and β-cyclodextrin is 5-10:4-6:0.4-0.8:

1. (3) Add acrylamide, first functional monomer, second functional monomer, 3-[(3-acrylamidopropyl)dimethylammonium]propionate, distilled water, and sodium dihydrogen phosphate to the second reactor. Adjust the pH to 7-8 with sodium hydroxide solution and stir evenly. Purge the reactor with nitrogen, add initiator, keep the reaction at a constant temperature, cool down to below 40°C, and adjust the pH to 7-8 to obtain water-based fracturing fluid. The weight ratio of the first functional monomer, the second functional monomer, 3-[(3-acrylamidopropyl)dimethylammonium]propionate to acrylamide is 0.1-0.2:0.2-0.5:0.1-0.2:

1.

2. The preparation method according to claim 1, characterized in that, In step (1), the catalyst is sodium hydroxide or potassium hydroxide, and the weight ratio of sodium hydroxide to 4-ethyleneaniline is 0.1-0.2:

1.

3. The preparation method according to claim 1, characterized in that, In step (1), the heating and heat preservation reaction temperature is 90-120℃ and the time is 1-4h; the continued heating and heat preservation reaction temperature is 80-110℃ and the time is 2-6h.

4. The preparation method according to claim 1, characterized in that, In step (2), the low-temperature reaction temperature is 5-20℃ and the time is 1-4h.

5. The preparation method according to claim 1, characterized in that, In step (3), the weight ratio of distilled water, sodium dihydrogen phosphate, and acrylamide is 12-15: 0.1-0.2：1。 6. The preparation method according to claim 1, characterized in that, In step (3), the initiator is one of potassium persulfate, sodium persulfate, or ammonium persulfate, and the weight ratio of the initiator to acrylamide is 0.05-0.2:

1.

7. The preparation method according to claim 1, characterized in that, In step (3), the heat preservation reaction temperature is 60-80℃ and the time is 1-4h.

8. The water-based fracturing fluid prepared by the preparation method according to any one of claims 1-7.

9. The water-based fracturing fluid according to claim 8, characterized in that, The molecular structure of the fracturing fluid is as follows: ， in: a=30000-300000； b=1000-50000； c=600-15000； d=1000-20000； n=2-20； The viscosity-average molecular weight of the fracturing fluid is 15,000,000-25,000,000.

10. The application of the water-based fracturing fluid according to claim 8 in oil and gas reservoir fracturing.

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