Multifunctional emulsion type clean fracturing fluid thickening agent, preparation method thereof and fracturing fluid

Abstract

The invention provides a multifunctional emulsion type clean fracturing fluid thickening agent, a preparation method thereof and a fracturing fluid. The thickening agent is prepared by polymerizing the following components in parts by weight: 40-55 parts of beta-cyclodextrin, 15-20 parts of acrylamide, 10-15 parts of a polymer skeleton, 3-8 parts of maleic anhydride, 1-3 parts of a functional monomer, 5-10 parts of an emulsifier, 75-85 parts of an oil solvent, 2-4 parts of an initiator and 90-110 parts of water. The sand-carrying agent is prepared from beta-cyclodextrin, acrylamide, a polymer skeleton, maleic anhydride and a functional monomer through inverse emulsion polymerization, is high in viscosity at high temperature, excellent in sand-carrying performance and good in salt resistance, and can be prepared from multiple types of flow-back fluids. The thickening agent is good in stability, not prone to layering, good in water solubility and easy and convenient to construct on site. The fracturing fluid prepared from the thickening agent is good in temperature resistance, the viscosity is kept at 150 mPas or above after the fracturing fluid is sheared at 180 DEG C for 2 h, and the fracturing fluid has good temperature resistance. The emulsion thickening agent can be prepared by using high-salinity water, and fracturing fluid prepared by using 100000mg / L water still has good temperature resistance and sand carrying performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas development, and particularly relates to a multifunctional emulsion-type clean fracturing fluid thickening agent, a preparation method thereof, and a fracturing fluid. Background Art

[0002] The main functions of fracturing fluid are to conduct ground pressure to form fractures in the formation; carry proppants and make the proppants spread in the fractures; and reduce the filtration loss of external liquids in the formation. It is required that the fracturing fluid has high viscosity at high temperature, high shear resistance, good sand-carrying capacity, little damage to the formation, and good gel-breaking properties. At present, the water-based fracturing fluids used in China mainly rely on guar gum and its derivatives. This type of thickening agent system has good thickening effect, but the plant gum system has a limit temperature resistance of 177 °C. Once exceeded, it will degrade rapidly, and contains a large amount of water-insoluble plant fibers. A large amount of residue will block the fracture pores after gel-breaking, causing damage and affecting the fracturing effect.

[0003] During the fracturing transformation of existing oil and gas reservoirs, volume fracturing has the characteristic of large liquid consumption, and correspondingly, a large amount of flowback fluid will be generated. Only in Changqing Oilfield, more than 2 million cubic meters of flowback fluid are generated in one year. The components of various types of flowback fluids are complex, with high salinity, high suspended solids and bacteria content, and are difficult to treat and recycle. The use of flowback fluid for guar gum system is greatly affected by bacteria, salinity and boron ions, and is prone to spoilage or poor performance after crosslinking.

[0004] The existing clean fracturing fluid system is mainly a viscoelastic surfactant system, which has the characteristics of no residue and no damage to the formation after gel-breaking, but its use cost is high.

[0005] CN202210554376.1 discloses a clean fracturing fluid composition, a clean fracturing fluid and its application. The clean fracturing fluid composition includes a deep eutectic solvent, and the preparation method of the deep eutectic solvent includes: reacting a hydrogen bond acceptor and a hydrogen bond donor; and based on the total weight of the clean fracturing fluid composition, the dosage of the deep eutectic solvent is 0.5-5% by weight. The present invention adopts a deep eutectic solvent, which greatly improves the imbibition efficiency of the clean fracturing fluid, but has poor high-temperature resistance, and the micelles cannot expand in a high-salt environment, which is restricted in the use of flowback fluid. Summary of the Invention

[0006] The purpose of the present invention is to provide a multifunctional emulsion-type clean fracturing fluid thickening agent, which has high viscosity at high temperature, excellent sand-carrying performance, good salt resistance, and can be prepared with various types of flowback fluids.

[0007] Another object of the present invention is to provide a preparation method of a multifunctional emulsion-type clean fracturing fluid thickening agent. Using β-cyclodextrin as the main body, and taking advantage of the unique cavity structure of its macrocyclic compound with hydrophilic exterior and hydrophobic interior to recognize and include specific groups, a new inclusion system is formed through host-guest inclusion interaction.

[0008] Another object of the present invention is to provide a multifunctional clean fracturing fluid to overcome the above technical problems existing in the prior art.

[0009] For this reason, the technical solution provided by the present invention is as follows: A multifunctional emulsion-type clean fracturing fluid thickening agent is polymerized from the following components in parts by weight: 40-55 parts of β-cyclodextrin, 15-20 parts of acrylamide, 10-15 parts of polymer skeleton, 3-8 parts of maleic anhydride, 1-3 parts of functional monomer, 5-10 parts of emulsifier, 75-85 parts of oil solvent, 2-4 parts of initiator, and 90-110 parts of water. The polymer skeleton is chitosan, cellulose or starch.

[0010] The functional monomer is dimethyldiallylammonium chloride, trimethylbenzylammonium chloride or 4-chloro-2-methylphenol.

[0011] The emulsifier is one or more of Span80, T-80, OP-10, nonylphenol polyoxyethylene ether.

[0012] The oil solvent is white oil, liquid paraffin, cyclohexane or kerosene.

[0013] The initiator is ammonium persulfate, potassium persulfate or azobisisobutyramidine hydrochloride.

[0014] A preparation method of a multifunctional emulsion-type clean fracturing fluid thickening agent includes the following steps: Step 1) Add the formulated amounts of β-cyclodextrin, acrylamide, polymer skeleton, maleic anhydride, and functional monomer to the formulated amount of water, and stir and mix evenly to obtain an aqueous solution; Step 2) Stir the formulated amounts of emulsifier and oil solvent until evenly mixed to obtain an oil phase solution; Step 3) Stir and mix the aqueous solution and the oil phase solution to obtain a uniform and stable water-in-oil emulsion; Step 4) Introduce nitrogen into the water-in-oil emulsion for 30-45 minutes, stir at high speed, slowly drop the initiator into the emulsion for initiation, and carry out a polymerization reaction at 40-60 °C for 4-8 hours to obtain the product.

[0015] A multifunctional clean fracturing fluid is composed of the following substances in mass percentages: 0.8-1.5% of thickening agent, 0.2-0.4% of temperature resistance enhancer, 0.04-0.05% of breaker, and the balance is water.

[0016] The temperature-resistant enhancer is a complex of zirconium salt and polyol surfactant, and the mass ratio of the two is 4:3.

[0017] The zirconium salt is zirconium tetrachloride or a complex of zirconium tetrachloride and borax, and the polyol is ethylene glycol, glycerol, ethanolamine or diethanolamine.

[0018] The beneficial effects of the present invention are as follows: The multifunctional emulsion-type clean fracturing fluid thickener provided by the present invention is polymerized from β-cyclodextrin, acrylamide, polymer skeleton, maleic anhydride and functional monomers. It has high viscosity at high temperature, excellent sand-carrying performance, good salt resistance, and can be prepared with multiple types of flowback fluids.

[0019] This thickener is prepared by inverse emulsion polymerization, with good stability, not easy to delaminate, good water solubility, and simple on-site construction. The fracturing fluid prepared with this thickener has good temperature resistance. After shearing at 180°C for 2 hours, the viscosity remains above 150 mPa∙s, showing good temperature resistance. This emulsion thickener can be prepared with high salinity water, and the fracturing fluid prepared with 100000 mg / L water still has good temperature resistance and sand-carrying performance.

[0020] The present invention uses β-cyclodextrin as the main body, and utilizes the unique cavity structure of its macrocyclic compound with hydrophilic exterior and hydrophobic interior to recognize and include specific groups, and forms a new inclusion system through host-guest inclusion interaction. At room temperature, the strong hydrogen bond interaction within the polymer material molecule attracts the structural units, and the molecule is in a weakly stretched state, and the fracturing fluid system has low viscosity. As the temperature rises, the single supramolecular hydrogen bond interaction weakens, the structural units quickly stretch, and at the same time, non-covalent interactions occur between supramolecules, and the system quickly increases in viscosity, realizing the technical goal of high-viscosity sand-carrying in the reservoir. Description of the Drawings

[0021] Figure 1 It is the temperature resistance and shear resistance curve of the fracturing fluid prepared with the thickener in Example 2; Figure 2 It is the temperature resistance and shear resistance curve of the fracturing fluid prepared with the thickener in Example 3; Figure 3 It is the temperature resistance and shear resistance curve of the fracturing fluid prepared with the thickener in Example 4; Figure 4 It is the temperature resistance and shear resistance curve of the fracturing fluid prepared with the thickener + 100000 mg / L NaCl brine in Example 5. Detailed Embodiments

[0022] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0023] Exemplary embodiments of the present invention are now introduced. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art.

[0024] Unless otherwise specified, the terms used herein (including scientific and technical terms) have the ordinary meaning understood by those skilled in the art. Additionally, it can be understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant fields, and should not be understood in an idealized or overly formal sense.

[0025] Example 1 The present invention provides a multifunctional emulsion-type clean fracturing fluid thickener, which is polymerized from the following components in parts by weight: 40 - 55 parts of β-cyclodextrin, 15 - 20 parts of acrylamide, 10 - 15 parts of a polymer skeleton, 3 - 8 parts of maleic anhydride, 1 - 3 parts of a functional monomer, 5 - 10 parts of an emulsifier, 75 - 85 parts of an oil solvent, 2 - 4 parts of an initiator, and 90 - 110 parts of water. The polymer skeleton is chitosan, cellulose, or starch.

[0026] The functional monomer is dimethyldiallylammonium chloride, trimethylbenzylammonium chloride, or 4-chloro-2-methylphenol.

[0027] The emulsifier is one or more of Span80, T-80, OP-10, and nonylphenol polyoxyethylene ether.

[0028] The oil solvent is white oil, liquid paraffin, cyclohexane, or kerosene.

[0029] The initiator is ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride.

[0030] A multifunctional clean fracturing fluid is composed of the following substances in mass percentages: 0.8 - 1.5% of a thickener, 0.2 - 0.4% of a temperature-resistant enhancer, 0.04 - 0.05% of a breaker, and the balance is water.

[0031] The temperature-resistant enhancer is a complex of a zirconium salt and a polyol surfactant, and the mass ratio of the two is 4:3.

[0032] The zirconium salt is zirconium tetrachloride or a complex of zirconium tetrachloride and borax, and the polyol is ethylene glycol, glycerol, ethanolamine, or diethanolamine.

[0033] The multifunctional emulsion-type clean fracturing fluid thickener provided by the present invention is prepared by inverse emulsion polymerization using β-cyclodextrin, acrylamide, a polymer skeleton, maleic anhydride, and a functional monomer. It has high viscosity at high temperature, excellent sand carrying performance, and good salt resistance, and can be prepared using multiple types of flowback fluids.

[0034] Example 2 Based on Example 1, this example provides a multifunctional emulsion-type clean fracturing fluid thickener, which is polymerized by the following components in parts by weight: 55 parts of β-cyclodextrin, 15 parts of acrylamide, 10 parts of polymer skeleton, 3 parts of maleic anhydride, 1 part of functional monomer, 5 parts of emulsifier, 85 parts of oil solvent, 2 parts of initiator, and 90 parts of water. The preparation method of the thickener comprises the following steps: Step 1) adding a formulated amount of β-cyclodextrin, acrylamide, polymer skeleton, maleic anhydride, and functional monomer to a formulated amount of water, stirring and mixing to obtain an aqueous phase solution; Step 2) Stirring the formulated emulsifier and oil solvent until they are evenly mixed to obtain an oil phase solution; Step 3) stirring the aqueous phase solution and the oil phase solution to obtain a uniform and stable water-in-oil emulsion; Step 4) nitrogen was introduced into the water-in-oil emulsion for 30 minutes, and the initiator was slowly dripped into the emulsion at a formulated amount for initiation. The polymerization reaction was carried out at 40° C. for 6 hours to obtain an emulsion thickener A.

[0035] Clean fracturing fluid preparation: The thickener A was prepared into a 1.3% solution, 0.2% of the temperature resistance enhancer was added, and the solution was stirred thoroughly to obtain a clean fracturing fluid.

[0036] In this embodiment, the polymer skeleton is chitosan, the functional monomer is dimethyl diallyl ammonium chloride; the emulsifier is a mixture of Span80 and nonylphenol polyoxyethylene ether, with a mass ratio of 1:0.5; the oil solvent is white oil, and the initiator is potassium persulfate.

[0037] The heat resistance enhancer is a compound of zirconium tetrachloride and polyols in a mass ratio of 4:3, wherein the polyol is a compound of ethylene glycol and propylene glycol in a mass ratio of 1:1.

[0038] Example 3 Based on Example 1, this example provides a multifunctional emulsion-type clean fracturing fluid thickener, which is polymerized by the following components in parts by weight: 40 parts of β-cyclodextrin, 20 parts of acrylamide, 13 parts of a polymer skeleton, 8 parts of maleic anhydride, 3 parts of a functional monomer, 10 parts of an emulsifier, 80 parts of an oil solvent, 2 parts of an initiator, and 110 parts of water. The preparation process is the same as that in Example 2. The difference lies in that: in step 4), nitrogen is introduced into the water-in-oil emulsion for 45 min, and high-speed stirring is carried out. The formulated amount of initiator is slowly dropped into the emulsion for initiation, and the polymerization reaction is carried out at 60 °C for 8 h to obtain the emulsion thickener B.

[0039] Preparation of clean fracturing fluid: The thickener B is formulated into a 1.0% solution, and 0.4% temperature-resistant enhancer is added. After sufficient stirring, the clean fracturing fluid is obtained.

[0040] In this example, the polymer backbone is cellulose, the functional monomer is 4-chloro-2-methylphenol; the emulsifier is a mixture of Span80 and OP-10 with a mass ratio of 1:1; the oil solvent is a mixture of white oil and kerosene with a mass ratio of 1:0.1, and the initiator is potassium persulfate.

[0041] The temperature-resistant enhancer is a compound of zirconium salt and polyol with a mass ratio of 4:3. Among them, the zirconium salt is compounded according to the mass ratio of zirconium tetrachloride to borax of 5:1, and the polyol is compounded according to the mass ratio of glycerol, ethanolamine, and ethylene glycol of 2:1:1.

[0042] Example 4 On the basis of Example 1, this example provides a multifunctional emulsion-type clean fracturing fluid thickener, which is polymerized from the following components in parts by weight: 55 parts of β-cyclodextrin, 18 parts of acrylamide, 15 parts of polymer backbone, 5 parts of maleic anhydride, 1 part of functional monomer, 5 parts of emulsifier, 85 parts of oil solvent, 4 parts of initiator, and 95 parts of water. The preparation process is the same as that in Example 2. The difference lies in that: in step 4), nitrogen is introduced into the water-in-oil emulsion for 40 min, and high-speed stirring is carried out. The formulated amount of initiator is slowly dropped into the emulsion for initiation, and the polymerization reaction is carried out at 52 °C for 6 h to obtain the emulsion thickener C.

[0043] Preparation of clean fracturing fluid: The thickener C is formulated into a 1.3% solution, and 0.3% temperature-resistant enhancer is added. After sufficient stirring, the clean fracturing fluid is obtained.

[0044] In this example, the polymer backbone is cellulose, the functional monomer is dimethyldiallylammonium chloride; the emulsifier is a mixture of T-80 and nonylphenol polyoxyethylene ether with a mass ratio of 1:1.5; the oil solvent is a mixture of white oil and cyclohexane with a mass ratio of 1:0.05, and the initiator is a mixture of potassium persulfate and azodiisobutyramidine hydrochloride with a mass ratio of 1:0.1.

[0045] The heat resistance enhancer is a compound of zirconium salt and polyol in a mass ratio of 4:3, wherein the zirconium salt is compounded according to a mass ratio of zirconium tetrachloride to borax of 4:1, and the polyol is compounded according to a mass ratio of ethylene glycol to diethanolamine of 1:1.

[0046] Example 5 On the basis of Example 1, this example provides a multifunctional emulsion-type clean fracturing fluid thickener, which is polymerized by the following components in parts by weight: 50 parts of β-cyclodextrin, 15 parts of acrylamide, 12 parts of polymer skeleton, 6 parts of maleic anhydride, 1 part of functional monomer, 8 parts of emulsifier, 85 parts of oil solvent, 2 parts of initiator, and 100 parts of water. The preparation process is the same as that of Example 2. An emulsion thickener D is obtained.

[0047] Clean fracturing fluid preparation: The thickener D was prepared into a 1.5% solution, 0.4% of the temperature resistance enhancer was added, and the solution was stirred thoroughly to obtain a clean fracturing fluid.

[0048] In this embodiment, the polymer skeleton is starch, the functional monomer is trimethylbenzyl ammonium chloride; the emulsifier is a mixture of OP-10 and nonylphenol polyoxyethylene ether, the mass ratio is 1:1; the oil solvent is white oil, and the initiator is a mixture of potassium persulfate and azobisisobutylamidine hydrochloride, the mass ratio is 1:0.3. The heat resistance enhancer is a compound of zirconium tetrachloride and polyols, the mass ratio is 4:3, wherein the polyols are a compound of ethylene glycol and glycerol, the mass ratio is 1:1.

[0049] The heat resistance enhancer is a compound of zirconium salt and polyol in a mass ratio of 4:3, wherein the zirconium salt is compounded according to a mass ratio of zirconium tetrachloride to borax of 4:1, and the polyol is compounded according to a mass ratio of ethylene glycol, propylene glycol and diethanolamine of 2:1:1.

[0050] Performance Testing: 1. Heat and shear resistance After filling the viscometer sample cup with fracturing fluid, heat the sample. Control the heating rate to 3℃ / min, start the test from 30℃, and rotate the rotor at a shear rate of 170s-1. When the temperature reaches 180℃, keep the shear rate and temperature unchanged until 120min. See the temperature and shear resistance curves. Figures 1 - 4 ,in, Figure 4 This is the temperature and shear resistance curve of the fracturing fluid prepared with thickener + 100000 mg / L NaCl brine in Example 5. The results are shown in Table 1.

[0051] Table 1 Viscosity after shearing for 120 min at 180°C

[0052] 2. Gel breaking performance test In the fracturing fluids prepared in Example 2, 0.02%-0.08% ammonium persulfate solution was added respectively, and they were placed in a 95°C water bath to test the viscosity of the gel-breaking fluid. The results are shown in Table 2.

[0053] Table 2 Viscosity of the gel-breaking fluid

[0054] In the fracturing fluids prepared in Examples 3, 4, and 5, 0.04% and 0.05% ammonium persulfate solutions were added respectively, and they were placed in a 95°C water bath. After 2 h, the viscosity of the gel-breaking fluid was tested. The results are shown in Table 3. Table 3 Viscosity of the gel-breaking fluid Dosage of breaker Example 3 Example 4 Example 5 0.04% ammonium persulfate 3.58 2.47 4.63 0.05% ammonium persulfate 2.12 2.25 3.69 The results show that when the dosage of ammonium persulfate is 0.04%, complete gel breaking can occur at 95°C in 2 h.

[0055] III. Evaluation of core damage performance: The core damage performance was evaluated using the determination procedure for core matrix permeability damage in SY / T5107-2016, and the test results are shown in Table 4. The fracturing fluids prepared in Examples 2-5 were used.

[0056] Table 4 Core damage rate

[0057] From the experimental results, it can be seen that the core damage rates are 9.58%, 9.83%, 9.65%, and 9.68%, and the gel-breaking fluid has little damage to the core permeability.

[0058] IV. Drag reduction rate test Aqueous solutions of thickeners A, B, C, and D with a mass concentration of 0.1% were prepared, and the drag reduction rate was measured using the indoor drag reduction rate determination method for fracturing fluids in SY / T5107-2016. The results are shown in Table 5.

[0059] Table 5 Drag reduction rate

[0060] From the experimental results, it can be seen that the maximum drag reduction rate of this system can reach more than 70%, and it has good drag reduction performance.

[0061] The above examples are only illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A multifunctional emulsion-type clean fracturing fluid thickening agent, characterized in that: The invention is polymerized by the following components in parts by weight: 40-55 parts of beta-cyclodextrin, 15-20 parts of acrylamide, 10-15 parts of polymer skeleton, 3-8 parts of maleic anhydride, 1-3 parts of functional monomer, 5-10 parts of emulsifier, 75-85 parts of oil solvent, 2-4 parts of initiator and 90-110 parts of water.

2. The multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, characterized in that: The polymer skeleton is chitosan, cellulose or starch.

3. The multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, wherein: The functional monomer is dimethyldiallylammonium chloride, trimethylbenzylammonium chloride or 4-chloro-2-methylphenol.

4. The multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, characterized in that: The emulsifier is one or more of Span80, T-80, OP-10 and nonylphenol polyoxyethylene ether.

5. A multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, characterized in that: The oil solvent is white oil, liquid paraffin, cyclohexane or kerosene.

6. The multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, characterized in that: The initiator is ammonium persulfate, potassium persulfate or azobisisobutyramidine hydrochloride.

7. The preparation method of a multifunctional emulsion-type clean fracturing fluid thickening agent according to claim 1, characterized in that: The following steps are involved: Step 1) adding a formulated amount of β-cyclodextrin, acrylamide, polymer skeleton, maleic anhydride, and functional monomer to a formulated amount of water, stirring and mixing to obtain an aqueous phase solution; Step 2) Stirring the formulated emulsifier and oil solvent until they are evenly mixed to obtain an oil phase solution; Step 3) stirring the aqueous phase solution and the oil phase solution to obtain a uniform and stable water-in-oil emulsion; Step 4) Into the water-in-oil emulsion, nitrogen is introduced for 30-45 minutes, and the mixture is stirred at high speed. An initiator is slowly dripped into the emulsion for initiation. The polymerization reaction is carried out at 40-60° C. for 4-8 hours. The product is obtained.

8. A multifunctional clean fracturing fluid, characterized in that: The invention is composed of the following substances in percentage by mass: 0.8-1.5% of the thickener according to any one of claims 1 to 6, 0.2-0.4% of a heat resistance enhancer, 0.04-0.05% of a debonder, and the balance being water.

9. A multifunctional clean fracturing fluid according to claim 8, characterized in that: The temperature resistance enhancer is a composite of zirconium salt and polyol surfactant, and the mass ratio of the two is 4:

3.

10. A multifunctional clean fracturing fluid according to claim 9, characterized in that: The zirconium salt is zirconium tetrachloride or a compound of zirconium tetrachloride and borax, and the polyol is ethylene glycol, glycerol, ethanolamine or diethanolamine.

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