A drag reducer for shale oil fracturing and preparation method thereof

Abstract

The invention belongs to the technical field of petroleum extraction, and specifically relates to a drag reducer for shale oil fracturing and a preparation method thereof. The drag reducer raw materials include 5-15 parts of halloysite nanotubes, 0.01-0.5 parts of an intercalating agent, 35-45 parts of acrylamide, 10-30 parts of a functional monomer, 0.2-0.5 parts of an initiator, 1-3 parts of a cross-linking agent, 1-3 parts of a surfactant, and 50-70 parts of deionized water. The specific preparation method comprises the following steps: firstly mixing the halloysite nanotubes, the intercalating agent, and deionized water, heating the mixture, allowing the mixture to stand, lowering the temperature, and adding acrylamide and a surfactant; then adding the functional monomer and mixing the mixture uniformly, then adding the initiator and the surfactant, mixing the mixture uniformly, adjusting the pH, heating the mixture with stirring, then adding the cross-linking agent, and continuing to heat the mixture with stirring to obtain the drag reducer; and the drag reducer effectively improves the stability of the drag reducer, has excellent high temperature resistance and shear resistance, effectively ensures a high drag reduction effect, and has an antibacterial effect, thereby helping to reduce environmental pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and particularly relates to a drag reducer for shale oil fracturing and a preparation method thereof. Background Art

[0002] Fracturing technology is a crucial process in oil and gas field development, and fracturing fluid plays a crucial role in the fracturing operation. With the advancement of fracturing technology and the development of fracturing fluids, slickwater fracturing fluid has gained widespread application due to its low viscosity and low friction. Slickwater fracturing is the primary means for achieving efficient development of shale reservoirs. Fracturing fluid, the lifeblood of fracturing, determines the success or failure of fracturing operations. Drag reducers are key components of slickwater fracturing fluid and largely determine its performance. The operational characteristics of slickwater fracturing fluid result in significant frictional drag within the wellbore. To overcome this high frictional drag and effectively reduce pumping costs, drag reducers with high drag reduction efficiency are typically used. These drag reducers significantly improve the fluidity of the fracturing fluid, reduce frictional resistance, and thus enhance shale oil and gas recovery.

[0003] At present, polyacrylamide drag reducers have become the most common drag reducers used on site due to their excellent drag reduction performance and low cost. In addition, the prior art has provided a variety of acrylamide polymers, such as cationic, anionic and zwitterionic, or drag reducers generated by copolymerization of one or more different monomers.

[0004] Currently used polyacrylamide copolymers, such as patent application number CN202310867907.7, disclose a drag reducer for fracturing and its preparation method, which have the characteristics of good drag reduction effect, small dosage, strong adaptability, and environmental protection, and have achieved good indoor evaluation and field application results; however, under high temperature and shear conditions, the polymer is still destroyed, resulting in a decrease in drag reduction; currently, nanomaterials with small size and high specific surface area are added to the drag reducer matrix to increase temperature resistance and shear resistance, such as the production method of salt-resistant drag reducer for oil well fracturing disclosed in application number CN202411256887.0. Although the salt resistance is improved, there are still problems with poor temperature resistance and poor shear resistance. Summary of the Invention

[0005] In response to the current technical problems, the present invention provides a drag reducer for shale oil fracturing and a preparation method thereof. The prepared drag reducer effectively improves the stability of the drag reducer, has excellent high temperature resistance and shear resistance, effectively ensures the drag reduction effect, and has antibacterial effects, which helps to reduce environmental pollution.

[0006] The technical solutions of the present invention are as follows:

[0007] A drag reducer for shale oil fracturing, comprising, by weight, 5-15 parts of halloysite nanotubes, 0.01-0.5 parts of an intercalating agent, 35-45 parts of acrylamide, 10-30 parts of a functional monomer, 0.2-0.5 parts of an initiator, 1-3 parts of a cross-linking agent, 1-3 parts of a surfactant, and 50-70 parts of deionized water;

[0008] The intercalating agent is one or any combination of dimethyl sulfoxide, potassium acetate and methylamide; and the functional monomer is a sulfonic acid monomer and 2,4-hexadienoic acid.

[0009] The surfactant is an anionic surfactant.

[0010] The initiators are persulfate and sodium bisulfite;

[0011] The crosslinking agents are trimethylolpropane triglycidyl ether and triethylenediamine.

[0012] Preferably, the intercalant is any two or three of dimethyl sulfoxide, potassium acetate, and methylamide.

[0013] Preferably, the intercalating agent is dimethyl sulfoxide, potassium acetate, and methylamide. More preferably, the mass ratio of dimethyl sulfoxide, potassium acetate, and methylamide is (1-2):1:(1-3).

[0014] Preferably, the sulfonic acid monomer is one or both of sodium styrene sulfonate and 2-acrylamido-2-methylpropanesulfonic acid.

[0015] More preferably, the mass ratio of the sulfonic acid monomer to 2,4-hexadienoic acid is (1-5):(5-20).

[0016] Preferably, the anionic surfactant is one or more of sodium lignin sulfonate, sodium dodecylbenzene sulfonate, and sodium dialkyl sulfosuccinate. The surfactant is beneficial for dispersing and stabilizing the reaction system.

[0017] Preferably, the mass ratio of persulfate to sodium bisulfite is (1-2):(1-2).

[0018] Preferably, the mass ratio of trimethylolpropane triglycidyl ether to triethylenediamine is 1:(1-2).

[0019] A method for preparing a drag reducer for shale oil fracturing, the specific preparation steps are as follows:

[0020] (1) First, halloysite nanotubes, intercalation agent and deionized water were mixed, heated to 65-80 °C, ultrasonically vibrated for 30-60 min, and allowed to stand for 50-120 min;

[0021] (2) Then, lower the temperature, add acrylamide and surfactant, and ultrasonicate for 15-30 minutes;

[0022] (3) Add functional monomers, mix well, then add initiator and surfactant, mix well, add pH regulator to adjust pH, heat and stir for 10-30 minutes, then add cross-linking agent, continue to heat and stir for 5-15 minutes to obtain drag reducer for shale oil fracturing.

[0023] Preferably, the temperature is lowered to 20-30°C in step (2).

[0024] Preferably, in step (3), the temperature is raised to 40-70°C and the pH is adjusted to 5-8.

[0025] Preferably, the pH regulator is acetate. For example, the acetate can be one or both of sodium acetate and potassium acetate.

[0026] The halloysite nanotubes (HNTs) used in this invention are a natural clay mineral that is well-crystallized, inexpensive, and environmentally friendly due to their unique intratube space. HNTs have a long, straight tubular structure. Their large aspect ratio gives them fibrous properties, which can improve the mechanical properties, temperature resistance, and shear resistance of the drag reducer. The outer surface of HNTs is primarily composed of siloxane, which has low chemical activity. In contrast, the inner surface of HNTs is composed of aluminol, which is highly chemically active and can form stable chemical bonds with many organic compounds. Due to the small interlayer spacing of HNTs, the Al—OH groups on the interlayer surface are blocked by strong hydrogen bonds with adjacent layers. Intercalating agents can embed organic or inorganic substances into the interlayer structure without disrupting the HNT interlayer structure, thereby expanding the interlayer spacing of the HNTs and facilitating the entry of macromolecules.

[0027] In the present invention, acrylamide (AM) is used as a main chain monomer, which can easily form a high molecular weight polymer through free radical polymerization, providing an excellent drag reduction effect; 2,4-hexadienoic acid is used to introduce carboxyl groups into acrylamide, which helps to improve the dispersion of the polymer in water, makes it easier to form a stable solution, and facilitates on-site preparation and transportation. In addition, 2,4-hexadienoic acid has antibacterial and antioxidant effects, is environmentally friendly and degradable, and reduces pollution to the environment. The conjugated double bond structure of 2,4-hexadienoic acid can enhance the flexibility of the molecular chain, and in combination with the sulfonic acid monomer, helps to achieve a dynamic balance of "high viscosity-low friction" under the shear thinning effect; the sulfonic acid monomer and the introduction of sulfonic acid groups into acrylamide help to improve temperature resistance and shear resistance; and through the cross-linking agent, a more highly ordered three-dimensional network structure is formed, which is conducive to improving sand carrying capacity, salt resistance, shear resistance, and temperature resistance.

[0028] The halloysite nanotubes introduced in the present invention have a unique internal space and can regulate the reaction with the polymer. Monomers such as acrylamide are embedded into the internal space of the halloysite nanotubes through the halloysite nanotubes, forming a stable network structure inside and outside the halloysite nanotubes, which is beneficial to improving the temperature resistance and shear resistance of the drag reducer. The polymer has strong adsorption groups such as amide, carboxyl, and sulfonic acid. These adsorption groups are not easily decomposed at high temperatures and can still be adsorbed on the surface of the halloysite nanotubes at high temperatures, thereby forming a network structure that makes the product have good high temperature resistance and shear resistance. At the same time, the drag reducer also has antibacterial and antioxidant effects. The halloysite nanotubes and 2,4-hexadienoic acid used are environmentally friendly, reducing pollution to the environment and reducing damage to the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1 An exemplary embodiment of the infrared spectrum of the drag reducer for shale oil fracturing according to Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0032] The experimental methods described in the examples are conventional methods unless otherwise specified, and the reagents and materials used are commercially available unless otherwise specified.

[0033] The halloysite nanotubes described below generally have a tube length of 0.2 to 1.5 μm, an inner diameter of 10 to 50 nm, and an outer diameter of 30 to 150 nm.

[0034] Example 1

[0035] In an exemplary embodiment of the present invention, a drag reducer for shale oil fracturing comprises:

[0036] The raw materials are 5 parts by mass of halloysite nanotubes, 0.03 parts of intercalating agent (dimethyl sulfoxide, potassium acetate and methylamide in a mass ratio of 1:1:1), 35 parts of acrylamide, 10 parts of functional monomer (2-acrylamido-2-methylpropanesulfonic acid and 2,4-hexadienoic acid in a mass ratio of 3:7), 0.2 parts of initiator (sodium persulfate and sodium bisulfite in a mass ratio of 2:1), 1 part of cross-linking agent (trimethylolpropane triglycidyl ether and triethylenediamine in a mass ratio of 1:1), 1 part of surfactant (sodium lignin sulfonate), and 50 parts of deionized water;

[0037] The specific preparation steps are as follows:

[0038] (1) First, halloysite nanotubes, intercalation agent and deionized water were mixed, heated to 65 °C, ultrasonically vibrated (1000W) for 30 min, and allowed to stand for 120 min;

[0039] (2) Then, the temperature was lowered by 20°C, acrylamide and surfactant were added, and ultrasonic vibration (800w) was applied for 15 minutes;

[0040] (3) Add functional monomers and mix well, then add initiator and surfactant, mix well, adjust pH to 6.5 with potassium acetate, heat to 40°C, stir for 30 minutes, then add cross-linker, continue to heat to 50°C and stir for 15 minutes to obtain drag reducer.

[0041] Example 2

[0042] In an exemplary embodiment of the present invention, a drag reducer for shale oil fracturing comprises:

[0043] The raw materials are 10 parts by mass of halloysite nanotubes, 0.1 parts of intercalating agent (dimethyl sulfoxide, potassium acetate and methylamide in a mass ratio of 1:1:1), 38 parts of acrylamide, 20 parts of functional monomer (sodium styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid and 2,4-hexadienoic acid in a mass ratio of 1.5:1.5:7), 0.3 parts of initiator (sodium persulfate and sodium bisulfite in a mass ratio of 1:1), 2 parts of crosslinking agent (trimethylolpropane triglycidyl ether and triethylenediamine in a mass ratio of 1:1), 2 parts of surfactant (sodium dodecylbenzenesulfonate and sodium dialkylsulfosuccinate in a mass ratio of 1:1), and 65 parts of deionized water;

[0044] The specific preparation steps are as follows:

[0045] (1) First, halloysite nanotubes, intercalation agent and deionized water were mixed, heated to 75 °C, ultrasonically vibrated (1000W) for 60 min, and allowed to stand for 60 min;

[0046] (2) Then, the temperature was lowered to 30°C, acrylamide and surfactant were added, and ultrasonic vibration (800w) was applied for 30 min;

[0047] (3) Add functional monomers and mix well, then add initiator and surfactant, mix well, adjust pH to 7.5 with potassium acetate, heat to 50°C, stir for 25 minutes, then add cross-linker, continue to heat to 60°C and stir for 10 minutes to obtain drag reducer.

[0048] Example 3

[0049] In an exemplary embodiment of the present invention, a drag reducer for shale oil fracturing comprises:

[0050] The raw materials are 15 parts by mass of halloysite nanotubes, 0.5 parts of intercalating agent (dimethyl sulfoxide, potassium acetate and methylamide in a mass ratio of 1:1:1), 45 parts of acrylamide, 30 parts of functional monomer (sodium styrene sulfonate and 2,4-hexadienoic acid in a mass ratio of 3:7), 0.5 parts of initiator (potassium persulfate and sodium bisulfite in a mass ratio of 1:2), 3 parts of cross-linking agent (trimethylolpropane triglycidyl ether and triethylenediamine in a mass ratio of 1:1), 3 parts of surfactant (sodium dodecylbenzene sulfonate), and 70 parts of deionized water;

[0051] The specific preparation steps are as follows:

[0052] (1) Halloysite nanotubes, intercalation agent and deionized water were mixed, heated to 80 °C, ultrasonically vibrated (1000 W) for 50 min, and allowed to stand for 80 min;

[0053] (2) Then, the temperature was lowered to 25°C, acrylamide and surfactant were added, and ultrasonic vibration (800w) was applied for 30 min;

[0054] (3) Add functional monomers and mix well, then add initiator and surfactant, mix well, adjust pH to 7 with potassium acetate, heat to 65℃, stir for 20min, then add cross-linker, continue to heat to 70℃ and stir for 10min to obtain drag reducer.

[0055] Example 4

[0056] The difference from Example 1 is that potassium acetate is used as the intercalant, and the other steps are the same as those in Example 1.

[0057] Example 5

[0058] The difference from Example 1 is that the intercalating agents used are dimethyl sulfoxide and potassium acetate, and the mass ratio of dimethyl sulfoxide to potassium acetate is 1:1. The other conditions are the same as those of Example 1.

[0059] Example 6

[0060] The difference from Example 1 is that the intercalating agents used are dimethyl sulfoxide, potassium acetate and methylamide, and the mass ratio of dimethyl sulfoxide, potassium acetate and methylamide is 2:1:3. Others are the same as Example 1.

[0061] Example 7

[0062] The difference from Example 1 is that the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to 2,4-hexadienoic acid in the functional monomers used is 1:10, and the other aspects are the same as Example 1.

[0063] Comparative Example 1

[0064] The difference from Example 1 is that the amount of intercalant used is 0, and the rest is the same as Example 1.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that the usage amount of the functional monomer is 0, and the rest is the same as Example 1.

[0067] Comparative Example 3

[0068] The difference from Example 1 is that the functional monomer is 2-acrylamido-2-methylpropanesulfonic acid, and the other steps are the same as those in Example 1.

[0069] Comparative Example 4

[0070] The difference from Example 1 is that the functional monomer is 2,4-hexadienoic acid, and the rest is the same as Example 1.

[0071] Comparative Example 5

[0072] The difference from Example 1 is that the surfactant used is Span, and the rest is the same as Example 1.

[0073] Comparative Example 6

[0074] Common commercially available polyacrylamide drag reducer.

[0075] Performance Testing

[0076] High temperature resistance and shear resistance test

[0077] The specific method is as follows: According to the petroleum and natural gas industry standard "SY / T 6376-2008 General Technical Conditions for Fracturing Fluids" and the petroleum and natural gas industry standard "SY / T 5107-2005 Performance Evaluation Method for Water-Based Fracturing Fluids", the viscosity (mPa˙s) of the products of Examples 1-7 and Comparative Examples 1-6 after shearing for 2 hours at 90°C, 120°C, and 150°C was measured respectively. The results are shown in Table 1.

[0078] Table 1 is the test data of the products of Examples 1-7 and Comparative Examples 1-6

[0079]

[0080] It can be clearly seen from the above data that the heat resistance and shear resistance of Examples 1-7 are significantly higher than those of Comparative Example 6, and the heat resistance and shear resistance of the drag reducer prepared by the present invention are significantly better than those of the commercially available polyacrylamide drag reducer; Example 4 selects a single intercalant relative to Example 1 and Example 6, and Example 5 selects two intercalants relative to Example 1. It can be clearly seen from the data comparison that the heat resistance and shear resistance of Examples 4 and 5 are worse than those of Examples 1 and 6. This is because the intercalation effect of a single or two intercalants is significantly worse than that of three intercalants, which in turn affects the heat resistance and shear resistance of the final synthesized drag reducer; Comparative Examples 3 and 4 adjust the amount of sulfonic acid monomer and 2,4-hexadienoic acid in the functional performance monomer relative to Example 1. The effect of using only sulfonic acid monomer or 2,4-hexadienoic acid is significantly worse than that of using both. In the product of Example 1 using a sulfonic acid monomer and 2,4-hexadienoic acid, the introduction of sulfonic acid groups is beneficial to improving the heat resistance and shear resistance. The lubricating film formed by the 2,4-hexadienoic acid molecules in the fluid has higher mechanical strength and thermal stability, and its drag reduction effect can still maintain a good effect under high temperature, high mineralization and high shear conditions. The conjugated double bond structure of 2,4-hexadienoic acid can enhance the flexibility of the molecular chain. Under the joint action of the sulfonic acid monomer and 2,4-hexadienoic acid, it helps to achieve a dynamic balance of "high viscosity-low friction" under the shear thinning effect, which helps to improve the temperature resistance and shear resistance of the drag reducer; Comparative Example 5 replaces the surfactant relative to Example 1, and its heat resistance and shear resistance decrease compared with Example 1 because the surfactant is conducive to dispersing and stabilizing the reaction system, which helps to form the network structure of the drag reducer and improve its stability.

[0081] refer to Figure 1 As shown, Figure 1 The infrared spectrum of the drag reducer for shale oil fracturing in Example 1 of the present application is shown, with a brief description, 3510 cm -1 NH and OH stretching characteristic absorption peak, 1680 cm -1 It is the amide I band, C=O stretching characteristic absorption peak, 1570 cm -1 The amide II band, NH bending characteristic absorption peak, 1735 cm -1 is the characteristic absorption peak of carboxylic acid C=O stretching, 1100 cm -1 is the characteristic absorption peak of sulfonic acid group, 1150 cm -1 It is the characteristic absorption peak of Si-O-Si halloysite.

[0082] Antibacterial rate test

[0083] Referring to the Chinese Petroleum and Natural Gas Industry Standard SY / T0532-1993 "Oilfield Injection Water Bacteria Analysis Method - Extinction Dilution Method", the antibacterial rates of the drag reducers of Examples 1-3 were measured. The results are shown in Table 2 below:

[0084] Table 2 Determination of the antibacterial rate of the drag reducer of Examples 1-3

[0085]

[0086] The drag reducer prepared by the present invention has a very excellent antibacterial effect due to the addition of 2,4-hexadienoic acid. Without adding an additional bactericidal agent, the antibacterial rate is above 94%. The drag reducer prepared by the present invention has a very excellent antibacterial effect.

[0087] Since the synthetic raw materials of the drag reducer of the present invention are environmentally friendly substances such as halloysite nanotubes and 2,4-hexadienoic acid, damage to the core is reduced and pollution to the environment is reduced.

[0088] The halloysite nanotubes introduced in the present invention have a unique internal space and can regulate the reaction with the polymer. Monomers such as acrylamide are embedded into the internal space of the halloysite nanotubes through the halloysite nanotubes, forming a stable network structure inside and outside the halloysite nanotubes, which is beneficial to improving the temperature resistance and shear resistance of the drag reducer. The polymer has strong adsorption groups such as amide, carboxyl, and sulfonic acid. These adsorption groups are not easy to decompose at high temperatures and can still be adsorbed on the surface of the halloysite nanotubes at high temperatures, thereby forming a network structure that makes the product have good high temperature resistance and shear resistance. At the same time, the drag reducer also has the effects of adsorption cleaning, antibacterial and antioxidant. The halloysite nanotubes and 2,4-hexadienoic acid used are environmentally friendly, reducing environmental pollution and reducing damage to the formation.

[0089] In this specification, references to the same or similar parts between the various embodiments can be made to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0090] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A drag reducer for shale oil fracturing, characterized in that: The raw materials include, by weight, 5-15 parts of halloysite nanotubes, 0.01-0.5 parts of intercalating agent, 35-45 parts of acrylamide, 10-30 parts of functional monomer, 0.2-0.5 parts of initiator, 1-3 parts of cross-linking agent, 1-3 parts of surfactant, and 50-70 parts of deionized water; The intercalant is one or any combination of dimethyl sulfoxide, potassium acetate, and methylamide; The functional monomers are sulfonic acid monomers and 2,4-hexadienoic acid; The surfactant is an anionic surfactant; The initiators are persulfate and sodium bisulfite; The crosslinking agents are trimethylolpropane triglycidyl ether and triethylenediamine.

2. A drag reducer for shale oil fracturing according to claim 1, characterized in that: The intercalating agent is any two or three of dimethyl sulfoxide, potassium acetate and methylamide.

3. The drag reducer for shale oil fracturing according to claim 2, characterized in that: The intercalating agent is dimethyl sulfoxide, potassium acetate and methylamide; wherein the mass ratio of dimethyl sulfoxide, potassium acetate and methylamide is (1-2):1:(1-3).

4. The drag reducer for shale oil fracturing according to claim 1, characterized in that: The sulfonic acid monomer is one or both of sodium styrene sulfonate and 2-acrylamido-2-methylpropane sulfonic acid.

5. A drag reducer for shale oil fracturing according to claim 1 or 4, characterized in that: The mass ratio of the sulfonic acid monomer to 2,4-hexadienoic acid is (1-5): (5-20).

6. The drag reducer for shale oil fracturing according to claim 1, characterized in that: The anionic surfactant is one or more of sodium lignin sulfonate, sodium dodecylbenzene sulfonate, and sodium dialkyl sulfosuccinate; and / or the mass ratio of persulfate to sodium bisulfite is (1-2):(1-2); And / or the mass ratio of trimethylolpropane triglycidyl ether and triethylenediamine is 1:(1-2).

7. The method for preparing a drag reducer for shale oil fracturing according to any one of claims 1 to 6, characterized in that: The specific preparation steps are as follows: (1) First, halloysite nanotubes, intercalation agent and deionized water were mixed, heated to 65-80 °C, ultrasonically vibrated for 30-60 min, and allowed to stand for 50-120 min; (2) Then, lower the temperature, add acrylamide and surfactant, and ultrasonicate for 15-30 minutes; (3) Add functional monomers, mix well, then add initiator and surfactant, mix well, add pH regulator to adjust pH, heat and stir for 10-30 minutes, then add cross-linking agent, continue to heat and stir for 5-15 minutes to obtain drag reducer for shale oil fracturing.

8. The method for preparing a drag reducer for shale oil fracturing according to claim 7, characterized in that: In step (2), the temperature is lowered to 20-30°C.

9. The method for preparing a drag reducer for shale oil fracturing according to claim 7, characterized in that: In step (3), the temperature is raised to 40-70°C and the pH is adjusted to 5-8.

10. The method for preparing a drag reducer for shale oil fracturing according to claim 7, characterized in that: The pH regulator is acetate, and the acetate is one or both of sodium acetate and potassium acetate.

Images