A carbon dioxide-responsive viscosity-increasing surfactant and its application in fracturing fluid

Abstract

A surfactant with carbon dioxide-responsive viscosity-increasing properties and its application in fracturing fluids comprises the following steps: step 1: adding ethanol as a solvent, sequentially adding cyanuric chloride and a long-chain fatty amine while stirring, controlling the reaction in an ice-water bath, adjusting the pH of the reaction system to 8-9 with a base during the reaction, and terminating the reaction to obtain an intermediate product (I); step 2: adding hydroxyethylpiperazine to the intermediate product (I), stirring and mixing, heating the mixture to 30-40°C, and maintaining the temperature for 1-2 hours. Ethanol is then distilled off and recovered while heating the mixture until the temperature reaches 80-95°C, and the temperature is maintained for 5-6 hours. During the reaction, the pH of the reaction system is adjusted to 8-9 with a base, and the reaction is terminated to obtain a surfactant with carbon dioxide-responsive viscosity-increasing properties. The present invention improves the protonation rate of tertiary amine groups, so that the surfactant molecules contain more tertiary amine groups to form multiple cations, which further improve the viscosity-increasing effect and salt resistance by forming more stable worm-like micelles with small molecule salts.

Description

Technical Field

[0001] The invention belongs to the technical field of fracturing fluid thickener preparation, and particularly relates to a carbon dioxide-responsive viscosity-increasing surfactant and its application in fracturing fluid. Background Art

[0002] During oilfield fracturing, fracturing fluid acts as a carrier for transmitting pressure and transporting proppant. Currently, the most widely used fracturing fluids typically use water-soluble polymers as thickeners (such as guar gum, acrylamide, and polyvinyl alcohol) combined with crosslinkers (boron compounds, zirconium compounds, etc.). However, years of field application and research have revealed shortcomings such as macromolecular adsorption that blocks formation seepage channels, residual breaker fluid that clogs the proppant packing layer, and damage to core filter cakes.

[0003] In recent years, people have found that clean fracturing fluid systems with viscoelastic surfactants as thickeners can successfully solve the problems of macromolecular adsorption blockage and alkaline fluid intrusion damage. However, the existing conventional viscoelastic surfactants as thickeners in fracturing fluids cannot automatically break the gel when fracturing 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 one tertiary amine group in its molecular structure. Zhang Chuan introduced the synthesis of a new triazine CO2 switchable 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 viscosifying surfactant and its application in fracturing fluid. The active agent 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 viscosifying 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 thickening surfactant contain four tertiary amino groups and two hydroxyl groups. The four tertiary amino groups have a super strong proton-binding ability 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 condenser recovery device, add ethanol as a solvent in an amount equal to that of cyanuric chloride, 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 and react for 1-2 hours, continue to heat while distilling out and recovering ethanol, until the temperature reaches 80-95°C, keep warm and react 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 of the ice-water bath is controlled at 0-5° C. and the reaction is carried out 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 introduction of CO2 increases the viscosity of the fracturing fluid, while the introduction of inert gas N2 significantly reduces the viscosity of the fracturing fluid, 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 smaller. 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 for 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), overcoming the problem that traditional clean fracturing fluid cannot automatically break gel.

[0021] (3) The CO2-responsive viscosifying 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, which can reduce 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 injection 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. The examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In the examples, where specific conditions are not specified, conventional conditions or manufacturer-recommended conditions were used. Reagents or instruments used where the manufacturer is not specified are 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 to 5 ° C in an ice-water mixed bath. During the reaction, 5% sodium hydroxide solution was used to adjust the pH of the reaction system to between 8 and 9. 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 to 40 ° C. After the reaction was kept warm for 1 h, ethanol was distilled out and recovered while the temperature was increased. When the temperature reached 85 to 87 ° C, the reaction was kept warm for 6 h. During the entire reaction process, 5% sodium hydroxide solution was continuously used to adjust the pH of the reaction system so that the pH 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 viscosifying 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 2.5% solution by mass and subjected to a viscosity test. 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 a CO2-responsive viscosifying surfactant was used as a thickener in the preparation of a clean fracturing fluid, it was dissolved in water to prepare a 5.0% solution. The viscosity of the solution was measured to be 35 mPa·s. After CO2 was introduced into the solution for 15 minutes, the viscosity was measured to be 315 mPa·s.

[0034] Example 3

[0035] When a CO2-responsive viscosifying surfactant was used as a thickener in the preparation of a clean fracturing fluid, it was dissolved in water to create a 4% solution. The viscosity of the solution was measured at 27 mPa·s. After bubbling CO2 through the solution for 20 minutes, the solution viscosity was measured at 185 mPa·s.

[0036] Example 4

[0037] When a carbon dioxide-responsive viscosifying surfactant is used as a thickener to prepare a clean fracturing fluid, it is dissolved in water to prepare a 3.5% solution and subjected to a viscosity test. 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 immediately after each cycle. The results of the measured solution viscosity change 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 thickening surfactant aqueous solution in the above embodiment 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 addresses the two shortcomings of current CO2-responsive surfactants with tertiary amine groups, namely, unsatisfactory viscosity enhancement and poor salt resistance. According to the measurement of the pH of a CO2-saturated aqueous solution at about 5.6, only about 50% of the surfactants containing only a single tertiary amine are protonated. In order to increase the protonation rate of the tertiary amine group, more tertiary amine groups must be contained in the surfactant molecule to produce strong multiple cations, which in turn form worm-like micelles with stronger cohesion with small molecule salts, thereby further improving the viscosity enhancement effect and salt resistance. The present invention provides an s-triazine structure surfactant molecule that contains a s-triazine ring, four tertiary amines of pipecyclizine, two hydroxyl groups and one 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. The method for preparing the carbon dioxide responsive viscosity-increasing surfactant according to claim 1, wherein: The following steps are included: Step 1: In a reactor equipped with a reflux condenser recovery device, add ethanol as a solvent in an amount equal to that of cyanuric chloride, and sequentially add cyanuric chloride and a long-chain fatty amine while stirring. The reaction is controlled in an ice-water bath. During the reaction, the pH of the reaction system is adjusted to 8-9 with a base 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 and react for 1-2 hours, continue to heat while distilling out and recovering ethanol, until the temperature reaches 80-95°C, keep warm and react 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.

3. The method for preparing the carbon dioxide responsive viscosity-increasing surfactant according to claim 2, wherein: In the step 1, the long-chain fatty amine is oleylamine or stearylamine, and the raw material feed 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.

4. The method for preparing the carbon dioxide responsive viscosity-increasing surfactant according to claim 2, wherein: In the step 1, the temperature of the ice-water bath is controlled between 0 and 5° C. and the reaction is carried out for 0.5 to 1.0 h.

5. The method for preparing the carbon dioxide responsive viscosity-increasing surfactant according to claim 2, wherein: 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%.

6. The use of the CO2 responsive viscosity increasing surfactant according to claim 1, characterized in that: The CO2-responsive viscosity-increasing surfactant can be used as a thickener for preparing fracturing fluid. The introduction of CO2 increases the viscosity of the fracturing fluid, while the introduction of inert gas N2 significantly reduces the viscosity of the fracturing fluid, thereby achieving recycling.

7. The use of the CO2 responsive viscosity increasing surfactant according to claim 6, 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, which reduces the viscosity of the surfactant solution. This process is 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.

Images