Preparation method of resistance reducing agent for slickwater fracturing

Abstract

The invention relates to a preparation method of a resistance reducing agent for slickwater fracturing, and belongs to the technical field of chemical agents for oil and gas fields. The method comprises the following steps: providing a mixed solution composed of acrylamide, acrylic acid, sodium p-styrenesulfonate, allyl polyoxyethylene ether, a molecular weight regulator, a metal ion inhibitor and water, adjusting the pH value of the mixed solution to 6-8, adding an initiator under an anaerobic condition, carrying out a reaction at 40-60 DEG C for 6-10 h, and carrying out granulation after the reaction is finished; the mass ratio of the acrylamide to the acrylic acid to the styrene sulfonate to the allyl polyoxyethylene ether is (65-75): (10-15): (5-10): (10-15), the allyl polyoxyethylene ether is CH2 = CHCH2O (CH2CH2O) mH, and m is 6-10. According to the method, different functional monomers are introduced for polymerization, so that the prepared resistance reducing agent for slickwater fracturing has multiple functions, and has the functions of reducing resistance, preventing swelling, assisting discharge, reducing viscosity of thickened oil and displacing oil at the same time.

Description

Technical Field

[0001] The present invention relates to a preparation method of a drag reducer for slickwater fracturing, belonging to the technical field of chemical agents for oil and gas fields. Background Technique

[0002] In recent years, with the large-scale development of unconventional oil and gas, reservoir stimulation technologies represented by volume fracturing have developed rapidly and been widely applied. Slickwater is a new type of fracturing fluid system studied and applied for unconventional tight oil and gas volume fracturing. This system mainly consists of a drag reducer, an anti-swelling agent, a flowback aid, and water. Compared with conventional gel fracturing fluids, it has many advantages: ① Greatly reduce the friction during fracturing construction; ② Easily generate complex fractures; ③ Increase the reservoir stimulation volume; ④ Low cost and easy flowback; ⑤ Less damage to the reservoir. However, with the continuous increase in usage, some problems of slickwater have gradually emerged, such as a large variety of additives, single functions, cumbersome preparation procedures, and long preparation time, etc.

[0003] As the core component of slickwater, the drag reducer is gradually developing towards the direction of low cost and multi-function. Some multi-functional drag reducer products have achieved functions such as drag reduction, anti-swelling, flowback assistance, or drag reduction, flowback assistance, and oil displacement in one. For example, the Chinese invention patent application with the publication number CN107964399A discloses a multi-functional nanoemulsion drag reducer for shale gas fracturing, which is prepared by inverse emulsion polymerization of an aqueous phase solvent and an oil phase solvent. This drag reducer integrates functions of drag reduction, sterilization, anti-swelling, and flowback assistance. Another example is the Chinese invention patent application with the publication number CN106832111A, which discloses a preparation method of a multi-functional drag reducer, solving the problem of slow dispersion and dissolution of the drag reducer. This method is made by applying the principle of inverse emulsion polymerization reaction to develop a drag reducer with functions of drag reduction and flowback assistance. Still another example is the Chinese invention patent application with the publication number CN106543354A, which discloses a polymer drag reducer, which is a polymer prepared from monomers such as acrylamide, acryloyloxyethyl trimethyl ammonium chloride, and 2-acrylamido-2-methylpropanesulfonic acid, having functions of drag reduction and anti-swelling. Although the drag reducers disclosed in these prior arts are no longer limited to single functions, they still have problems such as fewer functions, limited applicable range of oil and gas reservoirs, and cannot meet the on-site requirements of integrated viscosity reduction during fracturing of medium-low permeability heavy oil reservoirs and integrated oil displacement during fracturing of condensate oil and gas reservoirs. Summary of the Invention

[0004] The object of the present invention is also to provide a preparation method of a drag reducer for slickwater fracturing to solve the problem of fewer functions of existing drag reducers.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method of a drag reducer for slick water fracturing, comprising the following steps: providing a mixed solution composed of acrylamide, acrylic acid, styrene sulfonate, allyl polyoxyethylene ether, molecular weight regulator, metal ion inhibitor and water, adjusting the pH of the mixed solution to 6-8, adding an initiator under anaerobic conditions and reacting at 40-60 °C for 6-10 h, and granulating after the reaction; the mass ratio of acrylamide, acrylic acid, styrene sulfonate, and allyl polyoxyethylene ether is 65-75:10-15:5-10:10-15, and the allyl polyoxyethylene ether is CH2=CHCH2O(CH2CH2O) m H, where m is 6-10.

[0007] In the preparation method of the drag reducer for slick water fracturing of the present invention, different functional monomers are introduced for polymerization. Among them, acrylamide can improve the drag reduction and thickening and viscosity increasing functions, acrylic acid can improve the instant solubility function, styrene sulfonate can improve the anti-swelling and oil displacement functions, and allyl polyoxyethylene ether can improve the drainage assistance and heavy oil viscosity reduction functions. Thus, the prepared drag reducer for slick water fracturing has multiple functions, and simultaneously has functions of drag reduction, anti-swelling, drainage assistance, heavy oil viscosity reduction, and oil displacement.

[0008] The preparation method of the drag reducer for slick water fracturing of the present invention has a simple process and can meet the on-site requirements of slick water fracturing in tight / shale oil and gas reservoirs, integrated fracturing and viscosity reduction in medium and low-permeability heavy oil reservoirs, and integrated fracturing and oil displacement in condensate oil and gas reservoirs.

[0009] Further, the temperature of the reaction is 40-50 °C and the time is 6-8 h. Controlling the temperature and time of the reaction within the above ranges can effectively control the polymerization reaction rate, promote the polymerization of various monomers, and reduce the by-products generated by the reaction.

[0010] Too high or too low pH value of the reaction system will affect the progress of the polymerization reaction. To further promote the progress of the polymerization reaction, the pH of the mixed solution is adjusted to 7-7.5. The anaerobic environment is formed by introducing nitrogen into the system to replace the atmosphere.

[0011] Further, the mass ratio of acrylamide and water in the mixed solution is 65-75:230-330. Controlling the mass ratio of acrylamide and water in the mixed solution within the above ranges is beneficial to the introduction of other functional monomers and makes the comprehensive performance of the generated polymer better. The styrene sulfonate is preferably sodium styrene sulfonate.

[0012] Further, when adjusting the pH, a sodium hydroxide solution with a mass fraction of 20-40% is used. Using this concentration of sodium hydroxide solution to adjust the pH is fast and simple, and a smaller amount can be used to reach the required pH value.

[0013] The molecular weight regulator can promote the dissolution and mixing of monomers and control the molecular weight of the polymer. Further, the molecular weight regulator is isobutanol and / or n-butanol; the mass ratio of the molecular weight regulator to acrylamide is 5-10:65-75. Using isobutanol and / or n-butanol in the above dosage as the molecular weight regulator can achieve a narrow molecular weight distribution of the polymer.

[0014] The metal ion inhibitor can chelate and passivate metal ions in the reaction system, reducing the interference of metal ions on the polymerization reaction. Further, the metal ion inhibitor is disodium ethylenediaminetetraacetate and / or tetrasodium ethylenediaminetetraacetate, and the mass ratio of the metal ion inhibitor to acrylamide is 0.03-0.05:65-75. Using disodium ethylenediaminetetraacetate and / or tetrasodium ethylenediaminetetraacetate in the above dosage as the metal ion inhibitor can better reduce the interference of metal ions in the system on the reaction.

[0015] Further, the initiator is sulfite and persulfate, and the mass ratio of sulfite to persulfate is 0.3-0.6:1, for example, 0.33-0.54:1.

[0016] In order to effectively initiate the polymerization reaction of various functional monomers, further, the sulfite is sodium sulfite or sodium bisulfite, and the persulfate is ammonium persulfate or potassium persulfate. The mass ratio of the initiator to acrylamide is 0.2-0.4:65-75.

[0017] Further, the preparation method of the drag reducer for slickwater fracturing of the present invention further includes the following step: drying the granulated particles and then pulverizing them. Detailed Embodiments

[0018] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0019] Examples 1-9

[0020] The preparation methods of the drag reducers for slickwater fracturing in Examples 1-9 include the following steps:

[0021] Add deionized water by mass parts in a reactor equipped with a stirrer and a thermometer, then start stirring and add acrylamide, acrylic acid, sodium styrenesulfonate, allyl polyoxyethylene ether (specifically CH2=CHCH2O(CH2CH2O) m H, where m is 6-10), the molecular weight regulator, and the metal ion inhibitor, and stir until completely dissolved; adjust the pH value of the reaction solution with an aqueous sodium hydroxide solution, raise the temperature to the reaction temperature, pass nitrogen until the oxygen is removed completely, quickly and uniformly add the initiator to the reaction system, stop stirring after stirring evenly, keep the temperature for the reaction, and after the reaction is completed, obtain the drag reducer for slickwater fracturing through shear granulation, drying, and pulverization.

[0022] Among them, the allyl polyoxyethylene ether used in Examples 1 to 2 is specifically CH2=CHCH2O(CH2CH2O)6H, the allyl polyoxyethylene ether used in Examples 3 to 4 is specifically CH2=CHCH2O(CH2CH2O)7H, the allyl polyoxyethylene ether used in Examples 5 to 6 is specifically CH2=CHCH2O(CH2CH2O)8H, the allyl polyoxyethylene ether used in Examples 7 to 8 is specifically CH2=CHCH2O(CH2CH2O)9H, and the allyl polyoxyethylene ether used in Example 9 is specifically CH2=CHCH2O(CH2CH2O) 10 H.

[0023] The mass fractions of acrylamide, acrylic acid, sodium styrene sulfonate, allyl polyoxyethylene ether, molecular weight regulator, metal ion inhibitor, water and initiator used in Examples 1 to 9, the mass fraction of the sodium hydroxide solution used, the pH end point value of the adjusted reaction solution, the nitrogen purging time, the reaction temperature and time are shown in Table 1.

[0024] Table 1 Raw materials and process conditions of Examples 1 to 9

[0025]

[0026]

[0027] In Table 1: "-" indicates not used.

[0028] Comparative Example 1

[0029] The drag reducer of this comparative example is a drag reducer prepared by using the preparation method of the multifunctional clean drag reducer for shale gas fracturing in Example 1 of the Chinese invention patent application with the application publication number of CN108192587A.

[0030] Comparative Example 2

[0031] The drag reducer of this comparative example is a drag reducer prepared by using the preparation method of the multifunctional slickwater fracturing fluid drag reducer in Example 1 of the Chinese invention patent application with the application publication number of CN106832111A.

[0032] Comparative Example 3

[0033] The difference between the preparation method of the drag reducer of this comparative example and that of the drag reducer in Example 1 is only that: the mass fraction of the acrylamide monomer used in this comparative example is 80 parts, and the mass fraction of the acrylic acid monomer is 5 parts.

[0034] Comparative Example 4

[0035] The difference between the preparation method of the drag reducer in this comparative example and the drag reducer in Example 4 lies only in that: in this comparative example, the mass fraction of sodium styrene sulfonate monomer is 15 parts, and the mass fraction of allyl polyoxyethylene ether monomer is 5 parts.

[0036] Comparative Example 5

[0037] The difference between the preparation method of the drag reducer in this comparative example and the drag reducer in Example 9 lies only in that: in this comparative example, m in the allyl polyoxyethylene ether used is 20.

[0038] Experimental Example 1

[0039] 1) Respectively prepare aqueous solutions with a mass fraction of 0.1 wt% of the drag reducers of Examples 1 to 9 and Comparative Examples 1 to 5, and evaluate the drag reduction rate, surface and interfacial tension, and CST ratio (anti-swelling function); respectively prepare aqueous solutions with a mass fraction of 0.3 wt% of the drag reducers of Examples 1 to 9 and Comparative Examples 1 to 5, and evaluate the oil displacement efficiency and heavy oil viscosity reduction rate.

[0040] 2) Respectively prepare slickwater (0.3 wt% drag reducer + 0.3 wt% drainage aid + 0.3 wt% anti-swelling agent) with the drag reducers prepared in Example 1 and Comparative Examples 1 to 2, and evaluate the oil displacement efficiency and heavy oil viscosity reduction rate; and respectively prepare slickwater (0.1 wt% drag reducer + 0.3 wt% drainage aid + 0.3 wt% anti-swelling agent) with the drag reducers prepared in Example 1 and Comparative Examples 1 to 2 to evaluate the drag reduction rate, surface and interfacial tension, and CST ratio (anti-swelling function); the drainage aid used for preparing the slickwater is a commercially available non-ionic surfactant product, and the anti-swelling agent is a commercially available quaternary ammonium salt compound product.

[0041] Among them, the drag reduction rate is measured by an acid-resistant fracturing fluid drag reduction instrument; the surface and interfacial tension are measured by a K100 surface and interfacial tension instrument; the anti-swelling function is determined according to the capillary absorption time. The reference standards for these three indicators are "Shale Gas Fracturing Fluid - Part 1: Performance Indicators and Evaluation Methods of Slickwater" (NB / T 14003.1 - 2015).

[0042] The viscosity reduction rate was measured using a DV-Ⅲ viscometer produced by Brookfield Company. The reference standard was Q / SHCG 65-2013 "Technical Requirements for Viscosity Reducing Agents for Heavy Oil". For the evaluation, heavy oil with a viscosity of 2835 mPa·s at 50°C was selected, and the viscosity reduction rate of the heavy oil with a 0.3 wt% concentration drag reducing agent solution was tested. The formula for calculating the viscosity reduction rate was Δη(%) = ((η0 - η) / η0) × 100%, where η0 (mPa·s) and η (mPa·s) refer to the viscosity of the heavy oil before and after the reaction, respectively; the oil displacement efficiency was characterized by the increased oil recovery value compared with water flooding with a 0.3 wt% concentration drag reducing agent solution. The test method was to first measure the air permeability and porosity of the sand-packed tube, then saturate it with crude oil, record the volume as V0, conduct water flooding, collect the produced liquid with a 10 mL graduated cylinder until the water cut of the produced liquid reached 98%, record the volume of the produced oil V1, and calculate the water flooding oil displacement efficiency E1 = (V1 / V0) × 100%. After the water flooding was completed, a designed volume of the drag reducing agent solution was injected at a flow rate of 0.5 mL / min until the water cut of the produced liquid reached 98%, collect the produced liquid with a 10 mL graduated cylinder, and record the volume of the produced oil V2. Finally, the oil displacement efficiency E = ((V1 + V2) / V0) × 100%. Calculate the increased oil recovery of the drag reducing agent solution E2 = E - E1. The evaluation results are shown in Table 2.

[0043] Table 2 Comparison of Evaluation Results of Drag Reducing Agents Prepared in Examples with Other Drag Reducing Agents and Blended Slickwater

[0044]

[0045]

[0046] It can be easily seen from Table 2 that the drag reducing agent prepared by the present invention is more excellent in all aspects compared with the drag reducing agents prepared in Comparative Examples 1-5. When the drag reducing agent prepared by the present invention is compounded with commercially available wellbore cleanup agents and swelling inhibitors to form a slickwater solution, the performance is improved to a certain extent, and it is overall better than the slickwater prepared in Comparative Examples 1 and 2, especially having greater advantages in terms of oil displacement effect and heavy oil viscosity reduction effect.

[0047] Experimental Example 2

[0048] The powdery acrylamide (monomer A) used in Example 1 was respectively prepared into an aqueous solution with a concentration of 0.3 wt% (denoted as solution A); the liquid acrylic acid (monomer B) was prepared into an aqueous solution with a concentration of 0.3 wt% (denoted as solution B); the liquid sodium styrene sulfonate (monomer C) was prepared into an aqueous solution with a concentration of 0.3 wt% (denoted as solution C); the liquid allyl polyoxyethylene ether (monomer D) was prepared into an aqueous solution with a concentration of 0.3 wt% (denoted as solution D); monomers A, B, C, and D were compounded in a mass ratio of 7:1:1:1 to prepare an aqueous solution with a concentration of 0.3 wt% (denoted as solution E), and then the drag reduction rate, drainage aid performance, viscosity reduction rate, anti-swelling function, and oil displacement effect of each aqueous solution were respectively tested according to the test method in the experimental example. The results are shown in Table 3.

[0049] Table 3 Performance test results of each solution

[0050]

[0051]

[0052] It is not difficult to see from Table 2 and Table 3 that the drag reducer prepared by the present invention has more excellent performance than the single agent or the compound system of each single agent.

[0053] Through two groups of comparisons, the drag reducer prepared by the present invention has good drag reduction performance, lower use concentration, lower surface and interfacial tension, better anti-swelling function, and at the same time has the functions of viscosity reduction and improvement of oil displacement efficiency, and its comprehensive performance is more excellent.

Claims

1. A preparation method of a drag reducer for slippery water fracturing, characterized in that: It includes the following steps: A mixed solution composed of acrylamide, acrylic acid, styrene sulfonate, allyl polyoxyethylene ether, molecular weight regulator, metal ion inhibitor and water is provided. The pH of the mixed solution is adjusted to 6-8, and an initiator is added under anaerobic conditions and reacted at 40-60 °C for 6-10 h. After the reaction is completed, granulation is carried out; the mass ratio of acrylamide, acrylic acid, styrene sulfonate, and allyl polyoxyethylene ether is 65-75:10-15:5-10:10-15, and the allyl polyoxyethylene ether is CH2=CHCH2O(CH2CH2O) m H, where m is 6-10.

2. The preparation method of the drag reducer for slippery water fracturing according to claim 1, characterized in that: The temperature of the reaction is 40 - 50 °C and the time is 6 - 8 h.

3. The preparation method of the drag reducer for slippery water fracturing according to claim 1, characterized in that: The mass ratio of acrylamide to water in the mixed solution is 65 - 75:230 - 330.

4. The preparation method of the drag reducer for slippery water fracturing according to claim 1 or 2 or 3, characterized in that: When adjusting the pH, a sodium hydroxide solution with a mass fraction of 20 - 40% is used.

5. The preparation method of the drag reducer for slippery water fracturing according to claim 1 or 2 or 3, characterized in that: The molecular weight regulator is isobutanol and / or n-butanol; the mass ratio of the molecular weight regulator to acrylamide is 5 - 10:65 - 75.

6. The preparation method of the drag reducer for slippery water fracturing according to claim 1, characterized in that: The metal ion inhibitor is disodium ethylenediaminetetraacetate and / or tetrasodium ethylenediaminetetraacetate, and the mass ratio of the metal ion inhibitor to acrylamide is 0.03 - 0.05:65 - 75.

7. The preparation method of the drag reducer for slippery water fracturing according to claim 1 or 2 or 3, characterized in that: The initiator is sulfite and persulfate, and the mass ratio of sulfite to persulfate is 0.3 - 0.6:

1.

8. The preparation method of the drag reducer for slippery water fracturing according to claim 7, wherein: The sulfite is sodium sulfite or sodium bisulfite, and the persulfate is ammonium persulfate or potassium persulfate.

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