Salt-tolerant fracturing fluid thickening agent, preparation method and application thereof

Abstract

This invention relates to the field of oil displacement fracturing technology, specifically to a salt-resistant fracturing fluid thickener, its preparation method, and its application. This salt-resistant fracturing fluid thickener is polymerized from main-chain monomers, salt-resistant monomers, cationic monomers, crosslinking monomers, emulsifiers, oil solvents, initiators, and deionized water in a weight ratio of (25~35):(0.5~1.0):(23~37):(20~33):(0.08~1.2):(0.3~1.5):(1~8):(15~25). This salt-resistant fracturing fluid thickener, formed from main-chain monomers polyacrylamide, salt-resistant monomers, cationic monomers, crosslinking monomers acrylic acid, emulsifiers, and oil solvents, is a multifunctional emulsion-type fracturing fluid thickener with good stability, resistance to stratification, good water solubility, excellent proppant carrying capacity, good salt resistance, and simple on-site application.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology, specifically relating to a salt-resistant fracturing fluid thickener, its preparation method, and its application. Background Technology

[0002] With the continuous development of shale oil reservoirs, the water consumption for fracturing operations has been increasing year by year, leading to a severe shortage of on-site water resources. At the same time, the amount of produced water produced far exceeds the oilfield's reinjection capacity, and the remaining fluid after reinjection has no further use, resulting in a large accumulation of produced water. Therefore, how to achieve rapid and low-cost reuse of produced water has become an urgent problem to be solved.

[0003] Currently, the fracturing fluid system mainly used in shale oil is polymer-based fracturing fluid. Although synthetic polymer-based fracturing fluid thickeners leave no residue, their thickening ability in high-salinity water is limited, making it difficult to meet the requirements of oilfield produced water with high hardness and high salinity. Therefore, it is necessary to improve the salt resistance of polymer fracturing fluid systems so that they can be used for oilfield produced water preparation, expand the reuse pathways of oilfield produced water, and solve some of the oilfield produced water disposal problems.

[0004] In the prior art, patent application CN111732687A discloses a shear-resistant and salt-resistant fracturing fluid thickener. This thickener is prepared by polymerization of acrylamide and monomer A in deionized water, with the crosslinking agent N,N-methylenebisacrylamide and an initiator. Monomer A is one of acryloylglycine, acryloylglycine, or vinylguanidine. The initiator is ammonium persulfate or 2-hydroxy-2-methylpropanone. This thickener is a colloidal thickener prepared by polymerization of acrylamide and monomer A at a heating temperature of 40-50°C or under ultraviolet light irradiation. The thickener of this invention, by introducing a stable network structure formed by a reversible multiple hydrogen bond supramolecular structure, effectively resists the permanent damage to the system structure caused by high-speed shear, while improving the thickener's salt resistance.

[0005] Patent application CN114478909A discloses a fast-dissolving salt-resistant fracturing fluid thickener and its preparation method. It uses acrylamide and functional monomers as main raw materials, and is synthesized through reverse emulsion polymerization. The specific preparation method is as follows: First, a certain amount of white oil and oil-soluble and water-soluble emulsifiers are weighed and mixed in a reactor to form an oil phase. A certain amount of acrylamide, functional monomers, and pH adjuster are weighed and dissolved in deionized water to form an aqueous phase. Then, nitrogen gas is continuously introduced at 40–60°C, and the aqueous phase is transferred to the reactor and stirred and mixed with the oil phase for 20 minutes. An initiator is added, and after reacting for 3–5 hours, a terminator is added and stirred for 10 minutes. Finally, a reverse phase agent is added, and the mixture is stirred for 30 minutes to obtain the fast-dissolving salt-resistant fracturing fluid thickener. The fast-dissolving salt-resistant fracturing fluid thickener provided by this invention can dissolve in deionized water and standard brine within 1 minute and rapidly thickens. When the amount of thickener added is 1.5 to 2.0%, the viscosity of deionized water is ≥65 mPa·s, and the viscosity of standard brine is ≥45 mPa·s. Summary of the Invention

[0006] To address the problems of poor salt resistance and long viscous formation time in general polymer fracturing fluid systems, the present invention aims to provide a salt-resistant fracturing fluid thickener, its preparation method, and its application. By introducing salt-resistant groups such as sulfonic acid groups and hydrophilic groups such as cationic groups, the salt resistance of the polymer is increased, while exhibiting rapid dissolution characteristics. It can be used to prepare fracturing fluids with high salinity liquids such as produced water for reuse in fracturing operations. This can effectively alleviate the contradiction between the large amount of fracturing fluid used on site and the scarcity of water resources, partially solve the problem of mismatch between the water injection capacity of oil production plants and the amount of produced water in oil fields, save the amount of clean water used, and reduce the amount of sewage discharge and transportation for disposal.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a salt-resistant fracturing fluid thickener, which is polymerized from main-chain monomers, salt-resistant monomers, cationic monomers, crosslinking monomers, emulsifiers, oil solvents, initiators, and deionized water in a weight ratio of (25~35):(0.5~1.0):(23~37):(20~33):(0.08~1.2):(0.3~1.5):(1~8):(15~25).

[0008] Furthermore, the main chain monomer is polyacrylamide.

[0009] Furthermore, the salt-resistant monomer is one or more combinations of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone.

[0010] Furthermore, the cationic monomer is one or more combinations of acryloyloxyethyltrimethylammonium chloride, trimethylbenzylammonium chloride, and 2,3-epoxypropyltrimethylammonium chloride.

[0011] Furthermore, the crosslinking monomer is acrylic acid.

[0012] Furthermore, the emulsifier is one or more of Span80, Tween-80, and nonylphenol polyoxyethylene ether.

[0013] Furthermore, the oil solvent is one of white oil, liquid paraffin, cyclohexane, and kerosene.

[0014] Furthermore, the initiator is one of ammonium persulfate, potassium persulfate, and sodium bisulfite.

[0015] The second objective of this invention is to provide a method for preparing a salt-resistant fracturing fluid thickener, comprising the following steps: S1. Preparation of aqueous phase S101. Add the main chain monomer and crosslinking monomer to deionized water to obtain a mixed solution; the mass ratio of the main chain monomer, crosslinking monomer and deionized water is (25-35):(20~33):(15~25). S102. Slowly add the mixed solution to an aqueous sodium hydroxide solution to adjust the pH of the liquid to 6.5~7.5, then add the salt-tolerant monomer and the cationic monomer, and stir until homogeneous to obtain the aqueous phase; the mass ratio of the salt-tolerant monomer to the cationic monomer is (0.5~1.0):(23~37). S2. Preparation of the oil phase The emulsifier and oil solvent are mixed and stirred evenly to obtain the oil phase; the mass ratio of the emulsifier to the oil solvent is (0.08~1.2):(0.3~1.5). S3. Synthesis reaction The aqueous and oil phase solutions are mixed under stirring to obtain a uniform and stable water-in-oil emulsion. Nitrogen gas is introduced into the water-in-oil emulsion, and an initiator aqueous solution is added under the protection of inert nitrogen gas. At the same time, the temperature is raised to 40-55℃ and the reaction is maintained for 3-5 hours to obtain the target product, a salt-resistant fracturing fluid thickener.

[0016] Furthermore, in S3, the heating rate is 0.1℃ / 20~30s.

[0017] The third objective of this invention is to provide an application of a salt-resistant fracturing fluid thickener, wherein the application method is as follows: fracturing fluid is prepared using the aforementioned salt-resistant fracturing fluid thickener.

[0018] Further, the fracturing fluid comprises the following components by mass percentage: 0.5-1.2% salt-resistant fracturing fluid thickener, 0.03-0.05% breaker, and the balance being water.

[0019] Furthermore, the de-gelling agent is preferably ammonium persulfate capsules or ammonium persulfate.

[0020] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The thickener prepared by reverse emulsion polymerization in this invention is an emulsion thickener with good stability, is not easy to separate into layers, has good water solubility, and is easy to apply on site.

[0021] (2) This emulsion thickener can be prepared with high-mineralization water. Even when fracturing fluid is prepared with 100,000 mg / L water, it still has good temperature resistance and sand carrying performance.

[0022] The above description is merely an overview of the technical solution of the present invention. Other features and advantages of the present invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the present invention can be realized and obtained by means of the structures pointed out in the description, claims, and drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The rheological curve of the fracturing fluid prepared in Example 1 using 0.4% salt-resistant fracturing fluid thickener and water is shown.

[0025] Figure 2 The rheological curve of the fracturing fluid prepared in Example 2 using 0.8% salt-resistant fracturing fluid thickener and produced water is shown.

[0026] Figure 3 The rheological curve of the fracturing fluid prepared in Example 4 using 1.2% multifunctional cleaning fracturing fluid thickener + 100,000 mg / L NaCl brine is shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In a typical embodiment of this application, a salt-resistant fracturing fluid thickener is proposed, which is polymerized from main chain monomer, salt-resistant monomer, cationic monomer, crosslinking monomer, emulsifier, oil solvent, initiator, and deionized water in a weight ratio of (25~35):(0.5~1.0):(23~37):(20~33):(0.08~1.2):(0.3~1.5):(1~8):(15~25).

[0029] In some preferred embodiments, the main chain monomer is further defined as polyacrylamide. The salt-resistant monomer is one or more combinations of sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and N-vinylpyrrolidone. The cationic monomer is one or more combinations of acryloyloxyethyltrimethylammonium chloride, trimethylbenzylammonium chloride, and 2,3-epoxypropyltrimethylammonium chloride. The crosslinking monomer is acrylic acid.

[0030] The emulsifier is preferably one or more of Span 80, Tween-80, and nonylphenol polyoxyethylene ether. The oil solvent is preferably one of white oil, liquid paraffin, cyclohexane, and kerosene. The initiator is one of ammonium persulfate, potassium persulfate, and sodium bisulfite.

[0031] In another typical embodiment of this application, a method for preparing a salt-resistant fracturing fluid thickener is proposed, the method comprising the following steps: S1. Preparation of aqueous phase S101. Add the main chain monomer and crosslinking monomer to deionized water to obtain a mixed solution; the mass ratio of the main chain monomer, crosslinking monomer and deionized water is (25-35):(20~33):(15~25). S102. Add the mixed solution to an aqueous sodium hydroxide solution to adjust the pH of the liquid to 6.5~7.5, then add the salt-tolerant monomer and the cationic monomer, and stir until homogeneous to obtain the aqueous phase; the mass ratio of the salt-tolerant monomer to the cationic monomer is (0.5~1.0):(23~37). S2. Preparation of the oil phase The emulsifier and oil solvent are mixed and stirred evenly to obtain the oil phase; the mass ratio of the emulsifier to the oil solvent is (0.08~1.2):(0.3~1.5). S3. Synthesis reaction The aqueous and oil phase solutions are mixed under stirring to obtain a uniform and stable water-in-oil emulsion. Nitrogen gas is introduced into the water-in-oil emulsion, and an initiator aqueous solution is added under the protection of inert nitrogen gas. At the same time, the temperature is raised to 40-55℃ and the reaction is maintained for 3-5 hours to obtain the target product, a salt-resistant fracturing fluid thickener.

[0032] Furthermore, in S3, the heating rate is 0.1℃ / 20~30s.

[0033] The third objective of this invention is to propose an application of a salt-resistant fracturing fluid thickener, specifically, the application method being: using the aforementioned salt-resistant fracturing fluid thickener to prepare fracturing fluid.

[0034] In some preferred embodiments, the fracturing fluid comprises the following components by mass percentage: 0.5-1.2% salt-resistant fracturing fluid thickener, 0.03-0.05% breaker, and the balance being water.

[0035] As a further improvement to the present invention, the de-gelling agent is ammonium persulfate capsules or ammonium persulfate.

[0036] The following specific embodiments illustrate the composition, preparation process, and effects of the fracturing fluid system.

[0037] Example 1 This embodiment prepares a salt-resistant fracturing fluid thickener, and the specific preparation method is as follows: S1. Preparation of aqueous phase: S101. Add 23 parts of polyacrylamide and 24 parts of acrylic acid to 20 parts of deionized water; S102. Slowly add sodium hydroxide aqueous solution to adjust the pH of the liquid to 6.5, then add 0.5 parts of salt-tolerant monomer sodium p-styrene sulfonate and 25 parts of cationic monomer acryloyloxyethyltrimethylammonium chloride, and stir until homogeneous to obtain the aqueous phase.

[0038] S2. Oil phase preparation: Eight parts of emulsifier and 35 parts of oil solvent were mixed and stirred evenly to obtain the oil phase; wherein the emulsifier was a mixture of Span80 and nonylphenol polyoxyethylene ether in a mass ratio of 4:1; and the oil solvent was white oil.

[0039] S3. Synthesis reaction: Adjust the stirrer speed to mix the aqueous and oil phase solutions to obtain a uniform and stable water-in-oil emulsion. In the water-in-oil emulsion, nitrogen gas is introduced for 30 minutes, and 1 part of the initiator ammonium persulfate aqueous solution is slowly added while the temperature is raised (it is worth mentioning that the rate of addition of the initiator ammonium persulfate is controlled by temperature changes, and the heating rate is maintained at 0.15℃ / 20-30s). After the temperature is raised to 45℃, the reaction is maintained for about 4 hours to obtain salt-resistant fracturing fluid thickener A.

[0040] Salt-resistant fracturing fluid thickener A was prepared with water to form a fracturing fluid with a mass concentration of 0.4%.

[0041] In the 170s -1 The viscosity of the fracturing fluid system as a function of temperature and time was tested at 70℃, as shown in the figure. Figure 1As shown, the initial viscosity of the system was 72.2 mPa∙s, and the viscosity after shearing for 110 min was 51.3 mPa∙s.

[0042] Example 2 This embodiment prepares a salt-resistant fracturing fluid, and the specific preparation method is as follows: Aqueous phase preparation: S101. Add 27 parts of polyacrylamide and 28 parts of acrylic acid to 20 parts of deionized water; S102. Slowly add sodium hydroxide aqueous solution to adjust the pH of the liquid to 7, then add 0.8 parts of salt-tolerant monomer sodium p-styrene sulfonate and 28 parts of cationic monomer trimethylbenzylammonium chloride, and stir until homogeneous to obtain the aqueous phase.

[0043] Oil phase preparation: Mix 5 parts of emulsifier and 30 parts of oil solvent evenly to obtain the oil phase; wherein the emulsifier is a mixture of Span80 and nonylphenol polyoxyethylene ether in a mass ratio of 4:1, and the oil solvent is white oil.

[0044] Synthesis reaction: Adjust the stirrer speed to mix the aqueous and oil phase solutions to obtain a uniform and stable water-in-oil emulsion. In the water-in-oil emulsion, purge nitrogen gas for 40 minutes, then slowly add 1.5 parts of potassium persulfate aqueous solution as initiator while simultaneously raising the temperature. Control the rate of potassium persulfate addition by changing the temperature, maintaining a heating rate of 0.1℃ / 20-30s. Raise the temperature to 50℃ and maintain the reaction for about 4 hours to obtain salt-resistant fracturing fluid thickener B.

[0045] Salt-resistant fracturing fluid thickener B was prepared into a fracturing fluid with a mass concentration of 0.8% using produced water (mineralization 41370 mg / L).

[0046] In the 170s -1 The viscosity of the fracturing fluid system as a function of temperature and time was tested at 70℃, as shown in the figure. Figure 2 As shown, the initial viscosity of the system was 56.3 mPa∙s, and the viscosity after shearing for 110 min was 54.4 mPa∙s.

[0047] Example 3 Aqueous phase preparation: S101. Add 30 parts of polyacrylamide and 30 parts of acrylic acid to 25 parts of deionized water; S102. Slowly add sodium hydroxide aqueous solution to adjust the pH of the liquid to 7, then add 1.0 part of salt-tolerant monomer N-vinylpyrrolidone and 28 parts of cationic monomer 2,3-epoxypropyltrimethylammonium chloride, and stir until homogeneous to obtain the aqueous phase; Oil phase preparation: Six parts of emulsifier Span80 and 28 parts of oil solvent white oil were mixed and stirred evenly to obtain the oil phase; wherein the emulsifier was a mixture of Span80 and nonylphenol polyoxyethylene ether in a mass ratio of 4:1, and the oil solvent was white oil.

[0048] Synthesis reaction: Adjust the stirrer speed to mix the aqueous and oil phase solutions under stirring conditions to obtain a uniform and stable water-in-oil emulsion. In the water-in-oil emulsion, nitrogen gas is introduced for 45 minutes. Under the protection of inert nitrogen gas, 2 parts of sodium bisulfite aqueous solution as initiator are slowly added while the temperature is raised. The rate of addition of sodium bisulfite is controlled by temperature changes, and the heating rate is maintained at 0.1℃ / 20-30s. After the temperature is raised to 48℃, the reaction is maintained for about 4 hours to obtain salt-resistant fracturing fluid thickener C.

[0049] Salt-resistant fracturing fluid thickener C was prepared into a fracturing fluid with a mass concentration of 1.2% using 100,000 mg / L standard saline solution.

[0050] In the 170s -1 The viscosity of the fracturing fluid system as a function of temperature and time was tested at 70℃, as shown in the figure. Figure 3 As shown, the initial viscosity of the system was 53 mPa∙s, and the viscosity after shearing for 110 min was 41.4 mPa∙s.

[0051] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A salt-resistant fracturing fluid thickener, characterized in that, This salt-resistant fracturing fluid thickener is polymerized from main chain monomers, salt-resistant monomers, cationic monomers, crosslinking monomers, emulsifiers, oil solvents, initiators, and deionized water in a weight ratio of (25~35):(0.5~1.0):(23~37):(20~33):(0.08~1.2):(0.3~1.5):(1~8):(15~25).

2. The salt-resistant fracturing fluid thickener as described in claim 1, characterized in that: The main chain monomer is polyacrylamide; the crosslinking monomer is acrylic acid.

3. The salt-resistant fracturing fluid thickener as described in claim 1, characterized in that: The salt-resistant monomer is one or more combinations of sodium p-styrenesulfonate, 2-acrylamide-2-methylpropanesulfonic acid, and N-vinylpyrrolidone.

4. The salt-resistant fracturing fluid thickener as described in claim 1, characterized in that: The cationic monomer is one or more combinations of acryloyloxyethyltrimethylammonium chloride, trimethylbenzylammonium chloride, and 2,3-epoxypropyltrimethylammonium chloride.

5. The salt-resistant fracturing fluid thickener as described in claim 1, characterized in that: The emulsifier is one or more of Span80, Tween-80, and nonylphenol polyoxyethylene ether; The oil solvent is one of white oil, liquid paraffin, cyclohexane, and kerosene; The initiator is one of ammonium persulfate, potassium persulfate, and sodium bisulfite.

6. A method for preparing the salt-resistant fracturing fluid thickener according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Preparation of aqueous phase S101. Add the main chain monomer and crosslinking monomer to deionized water to obtain a mixed solution; the mass ratio of the main chain monomer, crosslinking monomer and deionized water is (25-35):(20~33):(18~30). S102. Add the mixed solution to an aqueous sodium hydroxide solution to adjust the pH of the liquid to 6.5~7.5, then add the salt-tolerant monomer and the cationic monomer, and stir until homogeneous to obtain the aqueous phase; the mass ratio of the salt-tolerant monomer to the cationic monomer is (0.5~1.0):(23~37). S2. Preparation of the oil phase The emulsifier and oil solvent are mixed and stirred evenly to obtain the oil phase; the mass ratio of the emulsifier to the oil solvent is (0.08~1.2):(0.3~1.5). S3. Synthesis reaction The aqueous and oil phase solutions are mixed under stirring to obtain a uniform and stable water-in-oil emulsion. Nitrogen gas is introduced into the water-in-oil emulsion, and an initiator aqueous solution is added under the protection of inert nitrogen gas. At the same time, the temperature is raised to 40-55℃ and the reaction is maintained for 3-5 hours to obtain the target product, a salt-resistant fracturing fluid thickener.

7. The method for preparing the salt-resistant fracturing fluid thickener as described in claim 6, characterized in that: In S3, the heating rate is 0.1℃ / 20-30s.

8. The application of a salt-resistant fracturing fluid thickener, characterized in that, The application method is as follows: fracturing fluid is prepared using the salt-resistant fracturing fluid thickener described in any one of claims 1-5, or the salt-resistant fracturing fluid thickener prepared by the preparation method described in any one of claims 6-7.

9. The application of the salt-resistant fracturing fluid thickener as described in claim 8, characterized in that: The fracturing fluid comprises the following components by mass percentage: 0.5-1.2% salt-resistant fracturing fluid thickener, 0.03-0.05% breaker, and the balance being water.

10. The application of the salt-resistant fracturing fluid thickener as described in claim 9, characterized in that: The de-icing agent is ammonium persulfate capsules or ammonium persulfate.

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