Carbon dioxide response tackifying surfactant and application thereof in fracturing fluid

Abstract

The invention relates to a tackifying surfactant with carbon dioxide response and application of the tackifying surfactant in fracturing fluid, which comprises the following steps: 1, adding ethanol as a solvent, sequentially adding cyanuric chloride and long-chain fatty amine while stirring, controlling the reaction in an ice-water bath, and adjusting the pH value of the reaction system to 8-9 by using alkali in the reaction process until the reaction is ended to obtain an intermediate product (I); 2, hydroxyethyl piperazine is added into the intermediate product (I), stirring and mixing are conducted, the temperature is increased to 30-40 DEG C or below, after a heat preservation reaction is conducted for 1-2 h, the temperature continues to be increased while the ethyl alcohol is distilled off and recycled, when the temperature is increased to 80-95 DEG C, the heat preservation reaction is conducted for 5-6 h, the pH of a reaction system is adjusted to be 8-9 with alkali in the reaction process, and after the reaction is finished, the CO2 response tackifying surfactant is obtained. The protonation rate of tertiary amine groups is increased, more tertiary amine groups are contained in surfactant molecules to form multiple cations, then more stable wormlike micelles are formed through the surfactant molecules and small molecule salt, and the tackifying effect and the salt resistance are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of fracturing fluid thickeners, and in particular relates to a carbon dioxide responsive viscosity increasing surfactant and application thereof in fracturing fluids. Background Art

[0002] In the process of oilfield fracturing, fracturing fluid is used as a carrier to transmit pressure and transport proppant. The most widely used fracturing fluid is generally composed of water-soluble polymer as thickener (such as guar gum, acrylamide, polyvinyl alcohol, etc.) plus cross-linking agent (boron compound, zirconium compound, etc.). However, many years of field application and research have found that macromolecular adsorption blocks formation seepage channels, degelling fluid residue blocks proppant filling layer, and core filter cake damage.

[0003] In recent years, people have found that the clean fracturing fluid system with viscoelastic surfactant as thickener can successfully solve the defects of macromolecular adsorption blockage and alkaline fluid invasion damage. However, the existing conventional viscoelastic surfactant as a thickener in fracturing fluid cannot automatically break the gel during fracturing of natural gas, coalbed methane and other gas wells. Carbon dioxide responsive viscoelastic surfactants have emerged. For example, CN 114716392B introduces a piperazine CO2 / N2 responsive double-tail surfactant, which contains two tertiary amine groups in its molecular structure, CN 114773212B and CN 115029143B respectively introduce a CO2 responsive surfactant, which contains a tertiary amine group in its molecular structure; Zhang Chuan introduced the synthesis of a new triazine CO2 switch type surfactant (Chemical Engineer [J], 2023, 335 (8): 1-4). The above CO2 responsive viscosifying surfactants have shortcomings such as aqueous solution viscosifying effect, low viscosity of fracturing fluid formed with small molecule salts, weak sand carrying capacity, and salt resistance. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a carbon dioxide responsive viscosity-increasing surfactant and its application in fracturing fluid. The surfactant can increase the protonation rate of tertiary amine groups, and the surfactant molecules contain more tertiary amine groups to form multiple cations, thereby further improving the viscosity-increasing effect and salt resistance by forming more stable worm-like micelles with small molecule salts.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A carbon dioxide responsive viscosity increasing surfactant having the following general structural formula:

[0007]

[0008] Here, R is a long-chain hydrocarbon group having 16 or 18 carbon atoms.

[0009] The molecules of the carbon dioxide responsive viscosity-increasing surfactant contain four tertiary amine groups and two hydroxyl groups. The four tertiary amine groups have a super strong ability to bind protons, and combine with the protons generated by the carbon dioxide aqueous solution to form multiple strong cations. The two hydroxyl groups are used to improve the hydrophilicity of the surfactant, increase its solubility in water, and are conducive to the formation of mixed micelles to increase the viscosity of its aqueous solution.

[0010] A method for preparing a carbon dioxide responsive viscosity increasing surfactant comprises the following steps;

[0011] Step 1: In a reactor equipped with a reflux condensation recovery device, add ethanol of equal mass to cyanuric chloride as a solvent, add cyanuric chloride and a long-chain fatty amine in sequence while stirring, control the reaction in an ice-water bath, and adjust the pH of the reaction system to 8-9 with a base during the reaction until the reaction is terminated to obtain an intermediate product (I);

[0012] Step 2: Add hydroxyethylpiperazine to the intermediate product (I) obtained in step 1, stir and mix, heat to 30-40°C, keep warm for reaction for 1-2 hours, continue to heat while distilling out and recovering ethanol, until the temperature reaches 80-95°C, keep warm for reaction for 5-6 hours, adjust the pH of the reaction system to 8-9 with alkali during the reaction, and the reaction is completed to obtain a CO2 responsive viscosity-increasing surfactant.

[0013] In the step 1, the long-chain fatty amine is oleylamine or stearylamine, and the raw material feeding ratio in each step of the reaction is 1.0:1.05:2.05 according to the molar ratio of cyanuric chloride, long-chain fatty amine and hydroxyethylpiperazine.

[0014] In the step 1, the temperature is controlled at 0-5° C. in an ice-water bath to carry out the reaction for 0.5-1.0 h.

[0015] The alkali solution added in each step of the reaction to adjust the pH value of the system is an aqueous solution of sodium hydroxide or sodium carbonate, and the mass concentration of the solution is 5% to 10%.

[0016] The CO2 responsive viscosity increasing surfactant can be used as a thickener for preparing fracturing fluid. The viscosity of the fracturing fluid can be increased by introducing CO2, and the viscosity of the fracturing fluid can be greatly reduced by introducing inert gas N2, thereby achieving recycling.

[0017] When inert gas N2 is passed through the surfactant solution, as the carbon dioxide concentration in the solution decreases, the proton concentration in the surfactant aqueous solution gradually decreases, and these cationic tertiary amine groups bound to protons lose the bound protons and become neutral tertiary amine groups, making the viscosity of the surfactant solution decrease. This process can be circulated by alternating the introduction of CO2 / N2 and can be reused. The protonation of the four tertiary amines and the two hydroxyl groups synergistically improve the ability to resist divalent salt ions.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The surfactant provided by the present invention has four tertiary amine CO2 responsive groups, forming a super strong carbon dioxide responsive viscosity increasing effect, forming a recyclable acidic fracturing fluid with good sand carrying capacity, and the acidic fracturing fluid is beneficial to dissolving some inorganic blockages such as carbonate rocks.

[0020] (2) The carbon dioxide responsive viscosifying surfactant fracturing fluid provided by the present invention can achieve gel breaking through the displacement effect of inert gas (nitrogen, air or methane), thereby overcoming the problem that traditional clean fracturing fluid cannot automatically break gel.

[0021] (3) The CO2-responsive viscosity-increasing surfactant provided by the present invention forms multiple super-strong cations after the introduction of CO2, and has a significant ability to resist minerals in groundwater, thereby reducing the impact of underground minerals on the viscosity of the fracturing fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the CO2 responsive viscosity-increasing surfactant of Example 1.

[0023] Figure 2 The viscosity change of CO2-responsive viscosifying surfactant fracturing fluid after alternate introduction of CO2 / N2.

[0024] Figure 3 Schematic diagram of the change in viscosity of CO2-responsive thickening surfactant with concentration. DETAILED DESCRIPTION

[0025] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0026] Example 1

[0027] In 60 mL of ethanol solvent, 46 g of cyanuric chloride and 70 g of oleylamine were mixed, and the reaction was carried out at a temperature of 0-5 ° C in an ice-water mixed bath. During the reaction, the pH value of the reaction system was adjusted to 8-9 with a 5% sodium hydroxide solution. After the reaction was kept warm for 0.5 h, 65 g of hydroxyethylpiperazine was added, and the mixture was stirred and heated to 38-40 ° C. After the reaction was kept warm for 1 h, the ethanol was distilled out and recovered while the temperature was increased. When the temperature reached 85-87 ° C, the reaction was kept warm for 6 h. During the whole reaction process, the pH value of the reaction system was continuously adjusted with a 5% sodium hydroxide solution so that the pH value of the reaction system was always maintained between 8 and 9. At the end of the reaction, a viscous CO2-responsive viscosity-increasing surfactant was obtained.

[0028] The structure of CO2-responsive viscosity-increasing surfactant is:

[0029]

[0030] Where: R is C 18 H 35

[0031] A surfactant with carbon dioxide responsive viscosity-increasing properties was used as a fracturing fluid thickener. When preparing clean fracturing fluid, it was dissolved in water to prepare a solution with a mass fraction of 2.5% and a viscosity test was performed. The measured viscosity was 25 mPa·s. After carbon dioxide was introduced into the prepared fracturing fluid for 15 minutes, the solution viscosity was measured to be 105 mPa·s.

[0032] Example 2

[0033] When the carbon dioxide-responsive viscosity-increasing surfactant is used as a thickener to prepare clean fracturing fluid, it is dissolved in water to prepare a solution with a mass fraction of 5.0% and a viscosity test is performed, and the viscosity is measured to be 35 mPa·s. After carbon dioxide is introduced into the prepared solution for 15 minutes, the solution viscosity is measured to be 315 mPa·s.

[0034] Example 3

[0035] When the carbon dioxide-responsive viscosity-increasing surfactant is used as a thickener to prepare clean fracturing fluid, it is dissolved in water to prepare a solution with a mass fraction of 4% and a viscosity test is performed, and the viscosity is measured to be 27mPa·s. After carbon dioxide is introduced into the prepared solution for 20 minutes, the solution viscosity is measured to be 185mPa·s.

[0036] Example 4

[0037] When the carbon dioxide-responsive viscosity-increasing surfactant is used as a thickener to prepare clean fracturing fluid, it is dissolved in water to prepare a solution with a mass fraction of 3.5% and a viscosity test is performed. The viscosity is measured to be 25 mPa·s. Then, carbon dioxide and nitrogen are alternately introduced for 15 minutes each, and the viscosity of the solution is measured respectively. The cycle is repeated 5 times, and the measured solution viscosity change results are as follows: Figure 1 As shown in the table, it can be seen that the viscosity of the carbon dioxide responsive thickening surfactant aqueous solution has good repeatability.

[0038] The viscosity of the CO2-responsive viscosity-increasing surfactant aqueous solution in the above example varies with concentration. Figure 2 As shown in the figure, it can be seen that the viscosity increases rapidly with the increase of surfactant concentration, which greatly improves its sand carrying performance and mineral resistance.

[0039] From the attached Figure 3 It can be seen that the viscosity increases rapidly with the increase of surfactant concentration.

[0040] The present invention aims at the two shortcomings of the current CO2 responsive surfactants with tertiary amine groups, namely, unsatisfactory viscosity enhancement and poor salt resistance. According to the measurement that the pH of a CO2 saturated aqueous solution is about 5.6, at this time, only about 50% of the surfactants containing only a single tertiary amine type are protonated, so as to increase the protonation rate of the tertiary amine group and contain more tertiary amine groups in the surfactant molecules to produce strong multiple cations, and then further improve the viscosity enhancement effect and the ability to resist salt substances by forming worm-like micelles with stronger cohesion with small molecule salts. The present invention provides a super CO2 sensitive viscosity enhancing surfactant in which a triazine structure surfactant molecule contains a triazine ring, four tertiary amines of pipercyclazine, two hydroxyl groups and a secondary amine group, and is used for the preparation of clean fracturing fluid.

Claims

1. A carbon dioxide responsive viscosity increasing surfactant, characterized in that: Has the following structural formula Here, R is a long-chain hydrocarbon group having 16 or 18 carbon atoms.

2. A carbon dioxide responsive viscosity increasing surfactant according to claim 1, characterized in that: The molecules of the carbon dioxide responsive viscosity-increasing surfactant contain four tertiary amine groups and two hydroxyl groups. The four tertiary amine groups have a super strong ability to bind protons, and combine with the protons generated by the carbon dioxide aqueous solution to form multiple strong cations. The two hydroxyl groups are used to improve the hydrophilicity of the surfactant and increase its solubility in water.

3. The method for preparing a carbon dioxide responsive viscosity increasing surfactant according to claim 1 or 2, characterized in that: The steps include: Step 1: In a reactor equipped with a reflux condensation recovery device, add ethanol of equal mass to cyanuric chloride as a solvent, add cyanuric chloride and a long-chain fatty amine in sequence while stirring, control the reaction in an ice-water bath, and adjust the pH of the reaction system to 8-9 with a base during the reaction until the reaction is terminated to obtain an intermediate product (I); Step 2: Add hydroxyethylpiperazine to the intermediate product (I) obtained in step 1, stir and mix, heat to 30-40°C, keep warm for reaction for 1-2 hours, continue to heat while distilling out and recovering ethanol, until the temperature reaches 80-95°C, keep warm for reaction for 5-6 hours, adjust the pH of the reaction system to 8-9 with alkali during the reaction, and the reaction is completed to obtain a CO2 responsive viscosity-increasing surfactant.

4. The method for preparing a carbon dioxide responsive viscosity increasing surfactant according to claim 3, characterized in that: In the step 1, the long-chain fatty amine is oleylamine or stearylamine, and the raw material feeding ratio in each step of the reaction is 1.0:1.05:2.05 according to the molar ratio of cyanuric chloride, long-chain fatty amine and hydroxyethylpiperazine.

5. The method for preparing a carbon dioxide responsive viscosity increasing surfactant according to claim 3, characterized in that: In the step 1, the temperature is controlled at 0-5° C. in an ice-water bath to carry out the reaction for 0.5-1.0 h.

6. The method for preparing a carbon dioxide responsive viscosity increasing surfactant according to claim 3, characterized in that: The alkali solution added in each step of the reaction to adjust the pH value of the system is an aqueous solution of sodium hydroxide or sodium carbonate, and the mass concentration of the solution is 5% to 10%.

7. The use of a CO2 responsive viscosity increasing surfactant according to any one of claims 1 to 6, characterized in that: The CO2 responsive viscosity increasing surfactant can be used as a thickener for preparing fracturing fluid. The viscosity of the fracturing fluid can be increased by introducing CO2, and the viscosity of the fracturing fluid can be greatly reduced by introducing inert gas N2, thereby achieving recycling.

8. The use of the CO2 responsive viscosity increasing surfactant according to claim 7, characterized in that: When inert gas N2 is passed through the surfactant solution, as the carbon dioxide concentration in the solution decreases, the proton concentration in the surfactant aqueous solution gradually decreases, and the cationic tertiary amine groups bound to the protons lose the bound protons and become neutral tertiary amine groups, making the viscosity of the surfactant solution decrease. This process is cyclically realized by alternating the introduction of CO2 / N2 and can be reused. The protonation of the four tertiary amines and the two hydroxyl groups synergistically improve the ability to resist divalent salt ions.

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