Fracturing fluid thickener for hot rock hydraulic fracturing and preparation method thereof

Abstract

The present application belongs to the technical field of hot dry rock development, and particularly relates to a fracturing fluid thickening agent for hot dry rock hydraulic fracturing and a preparation method thereof. The fracturing fluid thickening agent for hot dry rock hydraulic fracturing comprises the following raw material components in parts by weight: acrylamide 14-18 parts, 2-acrylamide-2-methylpropanesulfonic acid 6-8 parts, methyl methacryloyloxymethyl trimethoxysilane 4-6 parts, sodium p-styrenesulfonate 3-5 parts, water 60 parts, emulsifier 4-6 parts, and white oil 25-45 parts. The fracturing fluid thickening agent for hot dry rock hydraulic fracturing provided by the present application can realize hydrophobic association thickening in water, has high drag reduction performance at low viscosity under high temperature, has good temperature resistance and shear resistance at high viscosity, has good stability, and can meet construction requirements.

Description

Technical Field

[0001] This invention belongs to the field of dry hot rock development technology, specifically relating to a thickener for hydraulic fracturing fluid in dry hot rock and its preparation method. Background Technology

[0002] Hot dry rock, as a renewable and clean energy source, possesses enormous resource reserves, zero pollution emissions, and high thermal utilization efficiency, exhibiting immense development potential. It holds significant strategic importance for optimizing the energy structure, alleviating my country's energy shortage pressure, and contributing to the achievement of the "dual-carbon" target. Future effective extraction of heat from hot dry rock typically involves using hydraulic fracturing technology in enhanced geothermal systems to permeate the reservoir. This process creates a complex network of hydraulic fracturing fractures with high heat exchange efficiency, increasing the heat exchange area and connecting injection and production wells. This provides a flow channel for the circulating medium, extracting the stored thermal energy from the hot dry rock and achieving efficient development of its thermal energy.

[0003] Due to the characteristics of hot dry rock, such as high temperature, high strength, high density, and high stress, traditional fracturing fluids have limited stability and drag-reducing properties at high temperatures during hydraulic fracturing operations. This leads to difficulties in fracture propagation, excessively high operating pressures, and situations where hydraulic fracturing fails to "inject" or "fracture," severely hindering the development of hot dry rock. Therefore, it is necessary to develop a fracturing fluid thickener for hot dry rock hydraulic fracturing to meet the requirements of hot dry rock fracturing operations and achieve efficient development of hot dry rock thermal energy.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a thickener for hydraulic fracturing fluid in hot dry rock and its preparation method; to solve the problems of high construction pressure and limited fracture extension caused by insufficient stability and drag reduction performance of fracturing fluid at high temperatures in current hot dry rock hydraulic fracturing operations.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A thickener for hydraulic fracturing fluid in hot dry rock comprises, by weight, the following raw material components: 14-18 parts acrylamide, 6-8 parts 2-acrylamide-2-methylpropanesulfonic acid, 4-6 parts methacryloyloxymethyltrimethoxysilane, 3-5 parts sodium p-styrenesulfonate, 60 parts water, 4-6 parts emulsifier, and 25-45 parts white oil.

[0008] Furthermore, the emulsifier is selected from Span-60 emulsifier or Tween-80 emulsifier, or a combination thereof.

[0009] Furthermore, the emulsifier is selected from a combination of Span-60 emulsifier and Tween-80 emulsifier.

[0010] Furthermore, the weight ratio of the span-60 emulsifier to the tween-80 emulsifier is (2.0 to 2.5):1.

[0011] In addition, the present invention also provides a method for preparing the fracturing fluid thickener for hot dry rock hydraulic fracturing as described above, comprising the following steps:

[0012] S1. Acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, methacryloyloxymethyltrimethoxysilane, sodium p-styrenesulfonate and water are mixed and stirred evenly. Then the pH value is adjusted to 7.5-9.0 with sodium hydroxide solution to obtain the aqueous phase.

[0013] S2. Mix the emulsifier and white oil, and stir until homogeneous to obtain the oil phase;

[0014] S3. After mixing the aqueous phase obtained in step S1 and the oil phase obtained in step S2, a mixture is obtained.

[0015] S4. The mixture obtained in step S3 is deoxygenated by passing nitrogen gas through it under stirring conditions and heated to a certain temperature. Then, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise and a polymerization reaction is carried out under constant temperature conditions. After the reaction is completed, the thickener for hydraulic fracturing fluid for hot dry rock is obtained.

[0016] Further, in step S1, the concentration of the sodium hydroxide solution is 15%.

[0017] Further, in step S4, after heating to 50-70°C, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise.

[0018] Further, in step S4, the amount of 2,2'-azobisisobutylamidine dihydrochloride added is 0.02 to 0.04 wt.% of the weight of the mixture.

[0019] Furthermore, in step S4, the polymerization reaction time is 3 to 5 hours.

[0020] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0021] The thickener for hydraulic fracturing fluid in hot dry rock provided by this invention can achieve hydrophobic association and thickening in water. Moreover, it has high drag reduction performance at low viscosity and good temperature and shear resistance at high viscosity, as well as good stability, which can meet the construction requirements. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0023] Figure 1 This is a temperature and shear rheological diagram of Example 2. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0025] The endpoints and any values ​​of the ranges disclosed in this invention 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 in this invention.

[0026] According to a first aspect of the present invention, a thickener for hydraulic fracturing of hot dry rock is provided, comprising, by weight, the following raw material components: 14-18 parts of acrylamide (e.g., 14, 15, 16, 17, or 18 parts), 6-8 parts of 2-acrylamido-2-methylpropanesulfonic acid (e.g., 6, 7, or 8 parts), 4-6 parts of methacryloyloxymethyltrimethoxysilane (e.g., 4, 5, or 6 parts), 3-5 parts of sodium p-styrenesulfonate (e.g., 3, 4, or 5 parts), 60 parts of water, 4-6 parts of emulsifier (e.g., 4, 5, or 6 parts), and 25-45 parts of white oil (e.g., 25, 30, 35, 40, or 45 parts).

[0027] The weight portions described in this invention mainly include the disclosed numerical range, any value (including integers and decimals) within the disclosed range, or an interval between any two values, or multiple discontinuous intervals. It also includes values ​​or numerical ranges whose effects are expected to be similar to the endpoints of the numerical range, such as 5-10 parts. This does not only include 5, 6, 7, 8, 9, 10 parts, or any interval between any two parts. Other numerical ranges, not listed individually, are all included in this invention. Therefore, this invention also includes sub-ranges of any directly disclosed numerical range or any specific value within that range.

[0028] In the aforementioned thickener for hydraulic fracturing of hot dry rock, as a preferred embodiment, the emulsifier is selected from Span-60 emulsifier or Tween-80 emulsifier, or a combination thereof. Preferably, the emulsifier is selected from a mixture of Span-60 emulsifier and Tween-80 emulsifier; more preferably, the weight ratio of Span-60 emulsifier to Tween-80 emulsifier is (2.0 to 2.5):1 (e.g., 2:1, 2.2:1, 2.5:1, 2.4:1).

[0029] According to a second aspect of the present invention, a method for preparing a fracturing fluid thickener for hot dry rock hydraulic fracturing as described above is provided, comprising the following steps:

[0030] S1. Acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, methacryloyloxymethyltrimethoxysilane, sodium p-styrenesulfonate and water are mixed and stirred evenly. Then the pH value is adjusted to 7.5-9.0 with sodium hydroxide solution to obtain the aqueous phase.

[0031] S2. Mix the emulsifier and white oil, and stir until homogeneous to obtain the oil phase;

[0032] S3. After mixing the aqueous phase obtained in step S1 and the oil phase obtained in step S2, a mixture is obtained.

[0033] S4. The mixture obtained in step S3 is deoxygenated by passing nitrogen gas through it under stirring conditions and heated to a certain temperature. Then, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise and a polymerization reaction is carried out under constant temperature conditions. After the reaction is completed, the thickener for hydraulic fracturing fluid for hot dry rock is obtained.

[0034] The reaction equation is as follows:

[0035] (Molecular weight is 6-7 million).

[0036] In the above preparation method, as a preferred embodiment, in step S1, the concentration of the sodium hydroxide solution is 15%.

[0037] In the above preparation method, as a preferred embodiment, in step S4, after heating to 50-70°C, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise.

[0038] In the above preparation method, as a preferred embodiment, in step S4, the amount of 2,2'-azobisisobutylamidine dihydrochloride added is 0.02 to 0.04 wt.% (e.g., 0.02 wt.%, 0.025 wt.%, 0.03 wt.%, 0.035 wt.%, 0.04 wt.%) of the weight of the mixture.

[0039] In the above preparation method, as a preferred embodiment, in step S4, the polymerization reaction time is 3 to 5 hours (e.g., 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours).

[0040] The present invention will now be described in detail with reference to embodiments thereof. These examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0041] In the embodiments of the present invention, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0042] Example 1

[0043] A thickener for hydraulic fracturing of hot dry rock is prepared by the following method:

[0044] S1. Mix 14 parts by weight of acrylamide, 6 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 4 parts by weight of methacryloyloxymethyltrimethoxysilane, 3 parts by weight of N,N-dimethyl-4-vinylbenzamide and 60 parts by weight of water until homogeneous, and adjust the pH to 8.0 with 15% sodium hydroxide solution to obtain an aqueous phase mixture.

[0045] S2. Mix 4 parts by weight of emulsifier and 25 parts by weight of white oil evenly to obtain an oil phase mixture; wherein the emulsifier is a mixture of span-60 and tween-80, with a weight ratio of 2:1.

[0046] S3. Mix the oil phase mixture and the water phase mixture evenly, remove oxygen by purging with nitrogen under stirring, and heat to 50°C. Add 0.02 wt.% of 2,2'-azobisisobutylamidine dihydrochloride and continue the reaction at this temperature for 3 hours to obtain the fracturing fluid thickener for hot dry rock hydraulic fracturing in this embodiment.

[0047] Example 2

[0048] A thickener for hydraulic fracturing of hot dry rock is prepared by the following method:

[0049] S1. Mix 15 parts by weight of acrylamide, 8 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 5 parts by weight of methacryloyloxymethyltrimethoxysilane, 4 parts by weight of N,N-dimethyl-4-vinylbenzamide and 60 parts by weight of water until homogeneous, and adjust the pH to 7.5 with 15% sodium hydroxide solution to obtain an aqueous phase mixture.

[0050] S2. Mix 5 parts by weight of emulsifier and 35 parts by weight of white oil evenly to obtain an oil phase mixture; wherein the emulsifier is a mixture of span-60 and tween-80, with a weight ratio of 2.2:1.

[0051] S3. Mix the oil phase mixture and the water phase mixture evenly, remove oxygen by purging with nitrogen under stirring, and heat to 55°C. Add 0.03 wt.% of 2,2'-azobisisobutylamidine dihydrochloride and continue the reaction at this temperature for 4 hours to obtain the fracturing fluid thickener for hot dry rock hydraulic fracturing in this embodiment.

[0052] Example 3

[0053] A thickener for hydraulic fracturing of hot dry rock is prepared by the following method:

[0054] S1. Mix 16 parts by weight of acrylamide, 7 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 4 parts by weight of methacryloyloxymethyltrimethoxysilane, 5 parts by weight of N,N-dimethyl-4-vinylbenzamide and 60 parts by weight of water until homogeneous, and adjust the pH to 8.5 with 15% sodium hydroxide solution to obtain an aqueous phase mixture.

[0055] S2. Mix 6 parts by weight of emulsifier and 30 parts by weight of white oil evenly to obtain an oil phase mixture; wherein the emulsifier is a mixture of span-60 and tween-80, with a weight ratio of 2.5:1.

[0056] S3. Mix the oil phase mixture and the water phase mixture evenly, remove oxygen by purging with nitrogen under stirring, and heat to 60°C. Add 0.04 wt.% of 2,2'-azobisisobutylamidine dihydrochloride and continue the reaction at this temperature for 5 hours to obtain the fracturing fluid thickener for hot dry rock hydraulic fracturing in this embodiment.

[0057] Example 4

[0058] A thickener for hydraulic fracturing of hot dry rock is prepared by the following method:

[0059] S1. Mix 17 parts by weight of acrylamide, 6 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 5 parts by weight of methacryloyloxymethyltrimethoxysilane, 4 parts by weight of N,N-dimethyl-4-vinylbenzamide and 60 parts by weight of water until homogeneous, and adjust the pH to 9.0 with 15% sodium hydroxide solution to obtain an aqueous phase mixture.

[0060] S2. Mix 5 parts by weight of emulsifier and 40 parts by weight of white oil evenly to obtain an oil phase mixture; wherein the emulsifier is a mixture of span-60 and tween-80, with a weight ratio of 2.4:1.

[0061] S3. Mix the oil phase mixture and the water phase mixture evenly, remove oxygen by purging with nitrogen under stirring, and heat to 65°C. Add 0.025 wt.% of 2,2'-azobisisobutylamidine dihydrochloride and continue the reaction at this temperature for 3 hours to obtain the fracturing fluid thickener for hot dry rock hydraulic fracturing in this embodiment.

[0062] Example 5

[0063] A thickener for hydraulic fracturing of hot dry rock is prepared by the following method:

[0064] S1. Mix 18 parts by weight of acrylamide, 8 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 6 parts by weight of methacryloyloxymethyltrimethoxysilane, 3 parts by weight of N,N-dimethyl-4-vinylbenzamide and 60 parts by weight of water until homogeneous, and adjust the pH to 8.0 with 15% sodium hydroxide solution to obtain an aqueous phase mixture.

[0065] S2. Mix 4 parts by weight of emulsifier and 45 parts by weight of white oil evenly to obtain an oil phase mixture; wherein the emulsifier is a mixture of span-60 and tween-80, with a weight ratio of 2.3:1.

[0066] S3. Mix the oil phase mixture and the water phase mixture evenly, remove oxygen by purging with nitrogen under stirring, and heat to 70°C. Add 0.035 wt.% of 2,2'-azobisisobutylamidine dihydrochloride and continue the reaction at this temperature for 4 hours to obtain the fracturing fluid thickener for hot dry rock hydraulic fracturing in this embodiment.

[0067] Effect test

[0068] 1. Drag-reducing properties of low-viscosity fracturing fluid

[0069] The target materials obtained in Examples 1-5 were first aged in a roller furnace at 240°C for 6 hours, and then prepared into a 0.1% aqueous solution. The drag reduction performance was evaluated according to the standard "NB / T 14003.1-2015 Shale Gas Fracturing Fluid Part 1: Slickwater Performance Indicators and Evaluation Methods". The test results are shown in Table 1.

[0070] Table 1

[0071] Example 1 Example 2 Example 3 Example 4 Example 5 Drag reduction rate, % 73.4 75.1 74.3 72.6 73.7 Viscosity, mPa·s 3.1 3.4 3.5 3.8 3.6

[0072] As shown in Table 1, the drag reduction rate of the fracturing fluid thickeners for hot dry rock hydraulic fracturing prepared in Examples 1-5 is greater than 70%, indicating that the fracturing fluid thickeners for hot dry rock hydraulic fracturing of the present invention have good drag reduction performance and can effectively reduce the on-site construction pressure of hot dry rock hydraulic fracturing.

[0073] 2. Temperature and shear resistance of high-viscosity fracturing fluid

[0074] The target compounds prepared in Examples 1-5 were prepared into an aqueous solution at a ratio of 0.8 wt.% (target compound content), and then subjected to standard treatment at 240°C for 100 seconds. -1 Under the specified conditions, it was sheared for 120 minutes, and then its viscosity after shearing was tested. The temperature and shear rheological diagrams are shown below. Figure 1 As shown, the test results are shown in Table 2:

[0075] Table 2

[0076]

[0077] As shown in Table 2, the shear viscosity of the fracturing fluid thickeners for hot dry rock hydraulic fracturing prepared in Examples 1-5 is all above 50 mPa·s, which meets the standard requirements. This indicates that the fracturing fluid thickener for hot dry rock hydraulic fracturing of the present invention has good temperature and shear resistance at high temperatures.

[0078] 3. Performance after debonding

[0079] Referring to the standard "SY / T 7627-2021 Technical Requirements for Water-Based Fracturing Fluids", 0.8 wt.% (target substance content) fracturing fluid prepared from the target substances obtained in Examples 1-5 was mixed with 0.015% ammonium persulfate capsule breaker, and a rupture test was conducted by heating at 240℃ for 120 min. The viscosity of the ruptured fluid, residue, and core damage rate were tested. Specific test results are shown in Table 3 below.

[0080] Table 3

[0081] Test Project Example 1 Example 2 Example 3 Example 4 Example 5 Viscosity after gel breaking, mPa·s 3.7 3.2 3.4 3.5 3.3 Residue content, mg / L 9.0 8.3 9.6 9.2 8.9 Core damage rate, % 9.3 8.9 9.8 9.5 9.1

[0082] As shown in Table 3, the fracturing fluid prepared from the target materials obtained in Examples 1-5 has a viscosity of 3.2-3.7 mPa·s after gel breaking, a core damage rate of less than 10%, and a residue content of less than 10.0 mg / L, and does not cause secondary damage to the artificial thermal reservoir constructed by hydraulic fracturing.

[0083] The foregoing has described and evaluated some embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, still fall within the protection scope of the present invention.

Claims

1. A thickener for hydraulic fracturing fluid in hot dry rock, characterized in that, By weight, it includes the following raw material components: 14-18 parts acrylamide, 6-8 parts 2-acrylamide-2-methylpropanesulfonic acid, 4-6 parts methacryloyloxymethyltrimethoxysilane, 3-5 parts sodium p-styrenesulfonate, 60 parts water, 4-6 parts emulsifier, and 25-45 parts white oil.

2. The thickener for hydraulic fracturing fluid in hot dry rock according to claim 1, characterized in that, The emulsifier is selected from Span-60 emulsifier or Tween-80 emulsifier, or a combination thereof.

3. The thickener for hydraulic fracturing fluid in hot dry rock according to claim 2, characterized in that, The emulsifier is selected from a combination of Span-60 emulsifier and Tween-80 emulsifier.

4. The thickener for hydraulic fracturing fluid in hot dry rock according to claim 3, characterized in that, The weight ratio of the span-60 emulsifier to the tween-80 emulsifier is (2.0 to 2.5):

1.

5. A method for preparing a thickening agent for hydraulic fracturing of hot dry rock as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, methacryloyloxymethyltrimethoxysilane, sodium p-styrenesulfonate and water are mixed and stirred evenly. Then the pH value is adjusted to 7.5-9.0 with sodium hydroxide solution to obtain the aqueous phase. S2. Mix the emulsifier and white oil, and stir until homogeneous to obtain the oil phase; S3. After mixing the aqueous phase obtained in step S1 and the oil phase obtained in step S2, a mixture is obtained. S4. The mixture obtained in step S3 is deoxygenated by passing nitrogen gas through it under stirring conditions and heated to a certain temperature. Then, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise and a polymerization reaction is carried out under constant temperature conditions. After the reaction is completed, the thickener for hydraulic fracturing fluid for hot dry rock is obtained.

6. The preparation method according to claim 5, characterized in that, In step S1, the concentration of the sodium hydroxide solution is 15%.

7. The preparation method according to claim 5, characterized in that, In step S4, after heating to 50-70°C, 2,2'-azobisisobutylamidine dihydrochloride is added dropwise.

8. The preparation method according to claim 5, characterized in that, In step S4, the amount of 2,2'-azobisisobutylamidine dihydrochloride added is 0.02 to 0.04 wt.% of the weight of the mixture.

9. The preparation method according to claim 5, characterized in that, In step S4, the polymerization reaction time is 3 to 5 hours.

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