A micro-crosslinked polymer drag reducer for fracturing fluid and preparation method thereof

Abstract

The present invention provides a micro-crosslinked polymer drag reducer for fracturing fluid and a preparation method thereof. The raw materials include a water-soluble monomer, a pH regulator, a functional monomer, an initiator, a crosslinking agent and water. The water-soluble monomer has a sulfonic acid group and an unsaturated double bond; the functional monomer has an amide group and an unsaturated double bond; and the crosslinking agent has two unsaturated double bonds. The drag reducer of the present invention has high drag reduction efficiency, low cost, environmental friendliness, and a simple synthesis process, and has high practical application value.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum fracturing fluids, and in particular relates to a micro-crosslinked polymer drag reducer for fracturing fluids and a preparation method thereof. Background Art

[0002] Unconventional oil and gas resources play a crucial role in current oil and gas exploration and development. Given the low porosity and permeability of unconventional oil and gas reservoirs, which present significant challenges in extraction, reservoir fracturing is a key measure to achieve industrial production capacity. By injecting fracturing fluid into the formation, complex fractures are created under pressure, and proppants are used to prevent the fractures from closing. This promotes efficient flow of oil and gas from the low-porosity, low-permeability reservoir into the wellbore, thereby increasing oil and gas production. Therefore, significantly reducing the friction of the working fluid in the fracturing pipeline during fracturing operations is crucial for safe and efficient transportation, energy conservation and emission reduction, and improved fracturing efficiency. The drag reducer used in fracturing fluid formulation is a key factor in determining the performance of the fracturing process. Current fracturing fluid drag reducers can be categorized into emulsion-based and solid particle-based types, each with its own advantages. At higher concentrations, solid particle-based drag reducers can be used as thickeners for fracturing fluids.

[0003] CN 112778460 B discloses an acrylamide-α-olefin copolymer, a drag reducer, and a preparation method thereof. The acrylamide-α-olefin copolymer features a high degree of polymerization and a large molecular weight. Long alkyl succinimide and hydroxyalkyl side chains are introduced to diversify the side chain structure, which not only reduces the stereoregularity and crystallinity of the drag reducer molecules but also enhances product stability and solubility in hydrocarbon media such as crude oil, facilitating rapid dispersion and effectiveness during use. Furthermore, the diversified side chain structure acts as a buffer, enhancing the flexibility and shear resistance of the drag reducer molecules. This results in excellent drag reduction, making it particularly suitable for heavy oil pipeline transportation. However, the synthesis process is relatively complex, and during use, the drag reducer suspension must be mixed with a nano-drainage aid and a dispersant, increasing application costs. CN103013488 A discloses a drag reducer for slickwater fracturing fluid and its preparation method. The selected monomers are acrylamide and functional monomers, the mass ratio of surfactant to base oil is (2-3):10, and the selected base oil is one or more of white oil, kerosene, cyclohexane, and isoparaffin. The drag reduction effect can reach 30-65%. CN 112126422A also discloses a highly stable drag reducer and its preparation method and application. The synthetic raw materials of the drag reducer include acrylamide monomer, a crosslinking agent, a dispersant, an oil solvent, a surfactant, an initiator, and water. Because the synthesis method uses reverse polymerization and emulsification of the water phase and the oil phase, and the oil phase accounts for 40%, the production cost is relatively high, and there are environmental pollution problems during actual application.

[0004] In summary, regarding drag reducers, the existing technology has technical deficiencies such as complex synthesis process, high requirements for process equipment, high cost of use, and easy environmental pollution during application. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a micro-crosslinked polymer drag reducer for fracturing fluid and a preparation method thereof, which has high drag reduction efficiency, low cost, environmental friendliness and simple synthesis process, and has high practical application value.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a slightly cross-linked polymer drag reducer for fracturing fluid, the raw materials of which include water-soluble monomers, pH regulators, functional monomers, initiators, cross-linking agents and water.

[0007] Furthermore, the water-soluble monomer has a sulfonic acid group and an unsaturated double bond; the functional monomer has an amide group and an unsaturated double bond; the initiator is a redox initiator; and the cross-linking agent has two unsaturated double bonds.

[0008] Furthermore, in terms of mass percentage, the raw materials include 10% to 20% water-soluble monomers, 1% to 8% pH regulators, 4% to 12% functional monomers, 0.02% to 0.15% initiators, 0.05% to 0.15% cross-linking agents, and the remainder is water. The sum of the mass percentages of the above components is 100%.

[0009] Furthermore, the water-soluble monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid.

[0010] Furthermore, the pH regulator is a NaOH solution with a mass concentration of 20%.

[0011] Furthermore, the functional monomer is N,N'-diethyl-2-acrylamide.

[0012] Furthermore, the initiator is ammonium persulfate or potassium persulfate.

[0013] Furthermore, the cross-linking agent is selected from N,N'-methylenebisacrylamide.

[0014] The present invention provides a method for preparing a micro-crosslinked polymer drag reducer for fracturing fluid, which comprises the following steps:

[0015] S1 adjusts the pH value of the water-soluble monomer solution to neutral using a pH adjuster to obtain a mixed solution 1;

[0016] S2: adding functional monomers to the mixed solution 1, heating to 50°C to 65°C under a protective atmosphere, and reacting to obtain a mixed solution 2;

[0017] S3: adding the initiator solution dropwise into the mixed solution 2 and stirring to obtain the mixed solution 3;

[0018] S4: dripping the cross-linking agent solution into the mixed solution 3, stirring, reacting for 4 to 6 hours under sealed and protective atmosphere conditions, precipitating, and drying to obtain a micro-cross-linked polymer drag reducer sample for fracturing fluid.

[0019] Furthermore, in terms of mass percentage, the amount of water-soluble monomer is 10% to 20%, the amount of pH regulator is 1% to 8%, the amount of functional monomer is 4 to 12%, the amount of initiator is 0.02% to 0.15%, the amount of cross-linking agent is 0.05% to 0.15%, and the balance is water. The sum of the mass percentage contents of the above components is 100%.

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

[0021] The present invention provides a micro-cross-linked polymer drag reducer for fracturing fluid. The synthetic raw materials are few in variety and only include water-soluble monomers, pH regulators, functional monomers, initiators, and cross-linking agents. The water-soluble monomers are used, which is environmentally friendly. Following the principle of free radical polymerization, the water-soluble monomers and functional monomers undergo polymerization reaction under the action of a large number of free radicals generated by the initiator to produce a large number of long molecular chains, wherein the side chain group -CONHC(CH3)2CH2SO3Na of the water-soluble monomer can significantly enhance the steric hindrance between polymer groups, thereby improving the rigidity of the molecular chain, which helps to enhance the stability of the molecular chain after polymerization and is not easily broken by external forces. Moreover, the unsaturated double bonds of the water-soluble monomers and the functional monomers can make the polymerization reaction easy to occur and the degree of polymerization is high. Furthermore, the two unsaturated double bonds in the cross-linking agent can effectively connect the partially polymerized long molecular chains to form a micro-cross-linked structure, which can improve its shear resistance, thereby achieving the goals of high drag reduction and low loss, reducing construction time, saving costs and increasing efficiency, and having good industrial application value.

[0022] The drag reducer of the present invention is prepared by a homogeneous solution polymerization method, has a simple synthesis process, and has the advantages of easy control and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a picture of an indoor sample of the polymer drag reducer prepared by the present invention.

[0024] Figure 2 This is a microstructure diagram of the polymer drag reducer prepared in the present invention under a cryo-scanning electron microscope. DETAILED DESCRIPTION

[0025] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the invention is further described below in conjunction with embodiments and drawings, but it should not be understood as limiting the scope of implementation of the present invention.

[0026] The present invention provides a slightly cross-linked polymer drag reducer for fracturing fluid. The synthetic raw material components and their mass percentages are: 10-20% of water-soluble monomer, 1-8% of pH regulator, 4-12% of functional monomer, 0.02-0.15% of initiator, 0.05-0.15% of cross-linking agent, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0027] In the above-mentioned slightly cross-linked polymer drag reducer for fracturing fluid, the water-soluble monomer is selected from 2-acrylamido-2-methyl-1-propanesulfonic acid having a sulfonic acid group and an unsaturated double bond.

[0028] In the above-mentioned slightly cross-linked polymer drag reducer for fracturing fluid, the pH regulator is a NaOH solution with a mass concentration of 20%.

[0029] In the above-mentioned micro-cross-linked polymer drag reducer for fracturing fluid, the functional monomer is selected from N,N'-diethyl-2-acrylamide having an amide group and an unsaturated double bond. The amide group has excellent hydrolysis stability and thermal stability, which is conducive to strengthening the rigidity of the molecular chain produced by polymerization and is not easily affected by external forces and broken. Moreover, after the polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid and N,N'-diethyl-2-acrylamide, the molecular chain is not easily affected by ions in salt water, causing the molecular chain to curl up, thereby also reflecting a certain salt resistance.

[0030] In the above-mentioned slightly cross-linked polymer drag reducer for fracturing fluid, the initiator is selected to be a redox initiator with low cost and easy initiation, specifically one of ammonium persulfate and potassium persulfate.

[0031] In the above-mentioned micro-crosslinked polymer drag reducer for fracturing fluid, the crosslinking agent is selected as N,N'-methylenebisacrylamide having two unsaturated double bonds, thereby achieving the purpose of connecting long molecular chains to form a micro-crosslinked structure.

[0032] like Figure 1 As shown, in the above-mentioned slightly cross-linked polymer drag reducer for fracturing fluid, the product form is white granular powder, which has the advantages of convenient transportation and easy storage.

[0033] The present invention provides a method for preparing a micro-crosslinked polymer drag reducer for fracturing fluid, which adopts a homogeneous solution polymerization method and follows the principle of free radical polymerization, and has the advantages of easy control and low cost, comprising the following steps:

[0034] S1: Weigh a certain amount of water-soluble monomer and an appropriate amount of deionized water, mix them thoroughly, and then dropwise add a pH adjuster to adjust the pH value of the solution to neutral to obtain a mixed solution 1;

[0035] S2 then adds an appropriate amount of functional monomer to the mixed solution 1, stirs it thoroughly to dissolve it, and then pours it into a three-necked flask and slowly stirs it to dissolve it evenly, while passing N2 to deoxygenate for 30 minutes, and then raises the reaction temperature to 50°C to 65°C. At this time, the C=C bonds in the molecular structures of the water-soluble monomer and the functional monomer are opened at the reaction temperature, thereby obtaining mixed solution 2;

[0036] S3 dissolves a certain amount of initiator in a certain amount of deionized water, and then drips it into the mixed solution 2 at a uniform speed. The initiator generates a large number of free radicals in the aqueous solution, and the polymerization reaction begins. It is stirred with a stirrer at a speed of 200-300 r·min -1 , react for 1 hour, at which point the mixed system polymerizes to produce a large number of long molecular chains, obtaining mixed solution 3;

[0037] S4: A certain amount of cross-linking agent is dissolved in a certain amount of deionized water, and then dripped into the mixed solution 3 at a uniform speed, and continued to stir. The C=C bond in the cross-linking agent is opened, and the long molecular chains that have been partially polymerized are connected to form a cross-linked structure. The mixed solution 3 is placed in a sealed condition and reacted for another 4h~6h under N2 protection. The product is taken out, precipitated with ethanol, and vacuum dried at 40℃ to obtain a micro-cross-linked polymer drag reducer sample for fracturing fluid. The microstructure is as follows Figure 2 shown.

[0038] Example 1:

[0039] The synthetic raw material components and mass percentages of the polymer drag reducer of this embodiment are: 10.8 g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 4.6 g of pH adjuster (20% mass concentration NaOH solution), 9.2 g of functional monomer N,N'-diethyl-2-acrylamide, 0.10 g of initiator ammonium persulfate, 0.08 g of cross-linking agent N,N'-methylenebisacrylamide, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0040] The preparation process is as follows:

[0041] A certain amount of 2-acrylamido-2-methyl-1-propanesulfonic acid and an appropriate amount of deionized water were weighed and thoroughly mixed, and then a 20% mass concentration NaOH solution was added dropwise to adjust the pH value to neutral; then an appropriate amount of N,N'-diethyl-2-acrylamide was added and thoroughly stirred to dissolve it, and then poured into a three-necked flask and slowly stirred to dissolve it evenly, while nitrogen was passed through for deoxygenation for 30 minutes; then the reaction temperature was raised to 60°C, and the initiator ammonium persulfate was dissolved in a certain amount of deionized water and then uniformly added dropwise to the three-necked flask. The reaction began and was stirred with a stirrer at a speed of 200-300 r·min. -1 After 1 hour of reaction, the crosslinker, N,N'-methylenebisacrylamide, was dissolved in a certain amount of deionized water and then added dropwise to the three-necked flask at a uniform rate. Stirring was continued, and the flask was sealed. The reaction continued under nitrogen for another 5 hours. Finally, the product was removed, precipitated with ethanol, and dried under vacuum at 40°C to obtain a polymer drag reducer sample.

[0042] Example 2: This example only describes the differences from Example 1, and the similarities are not repeated here.

[0043] The synthetic raw material components and mass percentages of the polymer drag reducer of this embodiment are: 14.2 g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 6.4 g of pH adjuster (20% mass concentration NaOH solution), 5.8 g of functional monomer N,N'-diethyl-2-acrylamide, 0.10 g of initiator potassium persulfate, 0.08 g of cross-linking agent N,N'-methylenebisacrylamide, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0044] Example 3:

[0045] This embodiment only describes the differences from Example 1, and the similarities are not repeated here.

[0046] The synthetic raw material components and mass percentages of the polymer drag reducer of this embodiment are: 14.2 g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 6.4 g of pH adjuster (20% mass concentration NaOH solution), 5.8 g of functional monomer N,N'-diethyl-2-acrylamide, 0.05 g of initiator ammonium persulfate, 0.123 g of cross-linking agent N,N'-methylenebisacrylamide, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0047] Example 4:

[0048] This embodiment only describes the differences from Example 1, and the similarities are not repeated here.

[0049] The synthetic raw material components and mass percentages of the polymer drag reducer of this embodiment are: 20g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 8g of pH adjuster (20% mass concentration NaOH solution), 4g of functional monomer N,N'-diethyl-2-acrylamide, 0.02g of initiator ammonium persulfate, 0.05g of cross-linking agent N,N'-methylenebisacrylamide, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0050] Example 5:

[0051] This embodiment only describes the differences from Example 1, and the similarities are not repeated here.

[0052] The synthetic raw material components and mass percentages of the polymer drag reducer of this embodiment are: 10g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 1g of pH adjuster (20% mass concentration NaOH solution), 12g of functional monomer N,N'-diethyl-2-acrylamide, 0.15g of initiator ammonium persulfate, 0.15g of cross-linking agent N,N'-methylenebisacrylamide, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0053] Comparative Example:

[0054] This comparative example only describes the differences from Example 3, and the similarities are not repeated here.

[0055] The synthetic raw material components and mass percentages of the polymer drag reducer of this comparative example are: 14.2 g of water-soluble monomer 2-acrylamido-2-methyl-1-propanesulfonic acid, 6.4 g of pH regulator (20% mass concentration of NaOH solution), 5.8 g of functional monomer N,N'-diethyl-2-acrylamide, 0.05 g of initiator ammonium persulfate, no crosslinking agent N,N'-methylenebisacrylamide is added, and the balance is water. The sum of the mass percentages of the above components is 100%.

[0056] The drag reduction performance and shear resistance of the embodiment and the comparative example were tested respectively, and the results are shown in Table 1. The drag reduction effect was tested according to the SY / T 6578-2003 standard, and the drag reduction rate was calculated using the formula DR = (ΔP0-ΔP r ) / △P0×100%, where △P0 is the friction pressure drop at both ends of the pipeline when no drag reducer is added, Pa; △P rThe frictional pressure drop across the pipeline at the same flow rate (velocity) after adding the drag reducer, in Pa. The drag reduction system used in this invention has a circulation pipe diameter of 10 mm and an experimental flow rate of 5 m / s. The drag reducer dosage is 100 ppm. Shear resistance is assessed by comparing the drag reduction rate after the liquid circulates through the pipeline for a certain period of time to the initial drag reduction rate. A larger ratio indicates better shear resistance.

[0057] Table 1 Performance test results of examples and comparative examples

[0058]

[0059]

[0060] As can be seen from Table 1, compared to Example 1, the polymer drag reducer of Example 2, which increases the specific gravity of the water-soluble monomer, has better drag reduction performance. Compared to Example 2, the polymer drag reducer synthesized in Example 3, which reduces the initiator content and increases the crosslinker content, has significantly improved shear resistance. In addition, the slight decrease in initiator content makes the polymerization process more gentle and the polymer molecular weight longer, thereby improving the drag reduction rate to a certain extent. In the comparative example, no crosslinker was added, and the resulting polymer drag reducer was weaker in drag reduction and shear resistance than the polymer drag reducer in Example 3. In summary, the micro-crosslinked structure of the polymer drag reducer helps improve the overall performance of the drag reducer molecule, especially the shear resistance is significantly improved, and the drag reduction performance is also improved to a certain extent.

Claims

1. A micro-crosslinked polymer drag reducer for fracturing fluid, characterized in that: The raw materials include a water-soluble monomer, a pH regulator, a functional monomer, an initiator, a cross-linking agent and water, wherein the water-soluble monomer has a sulfonic acid group and an unsaturated double bond; the functional monomer has an amide group and an unsaturated double bond; and the cross-linking agent has two unsaturated double bonds. Calculated by mass percentage, the raw materials include 10% to 20% of a water-soluble monomer, 1% to 8% of a pH adjuster, 4% to 12% of a functional monomer, 0.02% to 0.15% of an initiator, 0.05% to 0.15% of a cross-linking agent, and the balance is water. The sum of the mass percentages of the above components is 100%. The water-soluble monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid; the pH value of the water-soluble monomer solution is adjusted to neutral using a pH adjuster; The functional monomer is N,N'-diethyl-2-acrylamide.

2. The micro-crosslinked polymer drag reducer for fracturing fluid according to claim 1, characterized in that: The pH regulator is a NaOH solution with a mass concentration of 20%.

3. The micro-crosslinked polymer drag reducer for fracturing fluid according to claim 1, characterized in that: The initiator is a redox initiator.

4. The micro-crosslinked polymer drag reducer for fracturing fluid according to claim 1, characterized in that: The initiator is ammonium persulfate or potassium persulfate.

5. The micro-crosslinked polymer drag reducer for fracturing fluid according to claim 1, characterized in that: The cross-linking agent is N,N'-methylenebisacrylamide.

6. The method for preparing a slightly cross-linked polymer drag reducer for fracturing fluid according to claim 1, characterized in that: S1 adjusts the pH value of the water-soluble monomer solution to neutral using a pH adjuster to obtain a mixed solution 1; S2 adds functional monomer to mixed solution 1, raises the temperature to 50°C~65°C under protective atmosphere, and reacts to obtain mixed solution 2; S3: adding the initiator solution dropwise into the mixed solution 2 and stirring to obtain the mixed solution 3; S4: dripping the crosslinking agent solution into the mixed solution 3, stirring, reacting for 4 to 6 hours under sealed and protective atmosphere conditions, precipitating, and drying to obtain a micro-crosslinked polymer drag reducer sample for fracturing fluid.

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