A CO2-responsive gemini imidazoline surfactant and its application in fracturing fluid

Abstract

The invention discloses a kind of CO2 responsive type gemini imidazoline surfactant and its application in fracturing fluid, tetraethylene pentamine and long-chain fatty acid are fed, using the dimethylbenzene of mass equal to long-chain fatty acid as water-carrying agent, being warming up to 125~140 DEG C and being refluxed, then continuing to be warming up to 190~220 DEG C and being reversed, being cooled to room temperature successively, obtain gemini imidazoline viscous liquid;Step 2:3 chloro-2 hydroxypropyltrimethylammonium chloride and the composition solution of acetone of equal mass are added dropwise to the gemini imidazoline of step one while stirring, then equimolar acid binding agent is added, reacted at room temperature, being warming up to 56~60 DEG C and distilling out acetone, CO2 responsive type gemini imidazoline surfactant can be obtained.The present invention can be used for the thickening agent of clean fracturing fluid, while improving the viscoelasticity of surfactant as thickening agent for preparing clean fracturing fluid, and the clean fracturing fluid formed is obviously stronger acidic, can dissolve the inorganic blockages such as carbonate rock in partial stratum.

Description

Technical Field

[0001] The present invention belongs to the technical field of fracturing fluid thickener preparation, and in particular relates to a CO2-responsive gemini imidazoline surfactant and its application in fracturing fluid. Background Art

[0002] Water-based clean fracturing fluids, also known as viscoelastic surfactant fracturing fluids, have been successfully applied to fracturing operations in oil wells and coal seams, achieving good economic benefits. However, existing clean fracturing fluids suffer from poor salt tolerance, complex preparation processes, and high costs. Applying CO2-responsive surfactants or polymers to clean fracturing fluid systems offers advantages such as simple control and ease of operation. Without the need for adding breakers, controllable breakage can be achieved simply by introducing an inert gas (such as N2, methane, or air), which can also be recycled. This approach conserves resources and reduces costs, effectively resolving the current pollution treatment issues associated with polymer fracturing flowback fluids, protecting the geological environment, and possessing significant practical significance for the economical and efficient development of unconventional oil and gas reservoirs and energy conservation and emission reduction. Consequently, CO2-responsive viscoelastic surfactants have emerged.

[0003] For example, CN 114716392B introduces a piperazine CO2 / N2-responsive double-tail surfactant, whose molecular structure contains two tertiary amine groups. CN 114773212B and CN 115029143B respectively introduce a CO2-responsive surfactant, each of which contains a tertiary amine group in its molecular structure. The CO2-sensitive viscosity-increasing surfactant molecules introduced in the above documents have few CO2-sensitive tertiary amine groups, weak response sensitivity to CO2, and the viscosity-increasing effect needs to be further improved. Summary of the Invention

[0004] In order to overcome the problems of the above prior art, the object of the present invention is to provide a CO2-responsive gemini imidazoline surfactant and its application in fracturing fluid. The surfactant molecule contains two imidazoline rings and a bridged tertiary amine group, a quaternary ammonium group and a hydroxyl group. The surfactant can be used as a thickener for clean fracturing fluid. While improving the viscoelasticity of the surfactant used as a thickener to prepare clean fracturing fluid, the resulting clean fracturing fluid is highly acidic and can dissolve inorganic blockages such as carbonate rocks in some strata. In addition, the responsive clean fracturing fluid can reduce viscosity by introducing air or nitrogen during fracturing, achieving gel breaking and smooth discharge.

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

[0006] A CO2-responsive gemini imidazoline surfactant having the following general structural formula:

[0007]

[0008] Here, R is a straight long-chain hydrocarbon group having 17 to 21 carbon atoms.

[0009] The structural characteristics of this CO2-responsive gemini imidazoline surfactant are that the molecule contains three tertiary amino groups, two imidazoline rings, a quaternary ammonium group and a hydroxyl group. The imidazoline ring and tertiary amino group can combine with the protons generated by the carbon dioxide aqueous solution to form multiple cations.

[0010] When CO2 is introduced into the solution, the surfactant molecules are fully stretched and hydrophilic, forming mixed worm-like micelles with bicarbonate ions and interweaving with each other, which increases the viscosity of the aqueous solution and significantly reduces the surface tension, showing the characteristics of multiple cationic surfactants. When N2 is introduced into the surfactant solution again, as the carbon dioxide concentration in the solution decreases, the proton concentration in the surfactant aqueous solution gradually decreases. These cationic groups bound to protons will lose the bound protons and become neutral groups. The water solubility of the surfactant molecules becomes worse, the molecular chains become curled, and the micelles dissociate, which makes the viscosity of the surfactant solution decrease. This process can be cyclic.

[0011] A method for preparing a CO2-responsive gemini imidazoline surfactant comprises the following steps:

[0012] Step 1: In a reactor equipped with a stirrer and a water separator, tetraethylenepentamine and a long-chain fatty acid are added, and xylene of equal mass to the long-chain fatty acid is used as a water-carrying agent. The temperature is raised to 125-140° C. and refluxed for 1-2 hours. The temperature is then further raised to 190-220° C. and reacted for 5-6 hours. During the reaction, water generated by the reaction is continuously released from the switch at the bottom of the water separator, and the refluxed xylene solvent is then collected through the switch at the bottom of the water separator. The mixture is cooled to room temperature to obtain a viscous gemini imidazoline liquid.

[0013] Step 2: Add a solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and acetone of equal mass to the gemini imidazoline prepared in step 1 while stirring, then add an equimolar amount of an acid-binding agent, react at room temperature for 3 to 4 hours, raise the temperature to 56 to 60°C, distill off the acetone, and obtain a CO2-responsive gemini imidazoline surfactant.

[0014] In the step 1, the molar ratio of tetraethylenepentamine to long-chain fatty acid is 1.05:2.0. When the water generated by the reaction is close to 4 times the molar number of the tetraethylenepentamine fed, the reaction is terminated.

[0015] In the step 2, the molar ratio of gemini imidazoline, 3-chloro-2-hydroxypropyltrimethylammonium chloride and the acid binding agent is 1:1:1.

[0016] The acid binding agent is one or a mixture of sodium carbonate, potassium carbonate, magnesium hydroxide and triethylamine.

[0017] The CO2-responsive gemini imidazoline surfactant is used as a fracturing fluid thickener. The specific application process is: dissolving the CO2-responsive gemini imidazoline surfactant in water at a mass ratio of 2.0-5.0%, and then adding a small molecule salt and stirring and dissolving to obtain a CO2-sensitive clean fracturing fluid.

[0018] The small molecule salt is one of sodium chloride, potassium chloride, sodium salicylate, and sodium p-toluenesulfonate.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The surfactant with super strong carbon dioxide response and thickening provided by the present invention can significantly increase the viscosity after carbon dioxide is introduced into the system, and has super strong sand carrying capacity.

[0021] (2) The carbon dioxide viscosity-enhancing fracturing fluid provided by the present invention can achieve gel breaking through the displacement effect of inert gas (nitrogen, air, methane).

[0022] (3) The clean fracturing fluid formed by the present invention has strong acidity and can dissolve inorganic blockages in some formations, thereby increasing the permeability of reservoir rocks.

[0023] (4) The carbon dioxide viscosity-enhancing fracturing fluid formed by the present invention has a more significant salt resistance and can reduce the influence of underground minerals on the viscosity of the fracturing fluid.

[0024] (5) The CO2 viscosity-increasing surfactant has the advantages of easy-to-obtain raw materials, stable reaction process, no need for purification and separation, and low preparation cost, and is suitable for large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is a schematic diagram of the nuclear magnetic resonance hydrogen spectrum of the CO2-responsive gemini imidazoline surfactant.

[0026] Figure 2 Shown is the viscosity cycle diagram of CO2-responsive gemini imidazoline surfactant solution.

[0027] Figure 3 Shown is the viscosity cycle diagram of CO2-responsive gemini imidazoline surfactant fracturing fluid. DETAILED DESCRIPTION

[0028] The present invention will be described in further detail below with reference to the accompanying drawings.

[0029] The following is a description of the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0030] A method for preparing a CO2-responsive gemini imidazoline surfactant comprises the following steps:

[0031] Step 1: In a reactor equipped with a stirrer and a water separator, tetraethylene pentamine and long-chain fatty acids are added in a molar ratio of 1.05:2.0, and xylene of the same mass as the long-chain fatty acids is used as a water-carrying agent. The temperature is raised to 125-140° C. and refluxed for 1-2 hours, and then the temperature is further raised to 190-220° C. and reacted for 5-6 hours. During the reaction, water generated by the reaction is continuously released from the bottom switch of the water separator. When the water generated by the reaction is close to 4 times the molar number of the tetraethylene pentamine added, the reaction is basically completed, and then the refluxed xylene solvent is collected through the bottom switch of the water separator and cooled to room temperature to obtain a viscous gemini imidazoline liquid.

[0032] Step 2: Add a solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and acetone of equal mass to the gemini imidazoline prepared in step 1 while stirring, and then add an equimolar amount of an acid-binding agent. The molar ratio of the gemini imidazoline, 3-chloro-2-hydroxypropyltrimethylammonium chloride and the acid-binding agent obtained in step 1 is 1:1:1. The mixture is reacted at room temperature for 3 to 4 hours, and the temperature is raised to 56 to 60°C to distill off the acetone to obtain a CO2-responsive gemini imidazoline surfactant.

[0033] Example 1

[0034] In a reactor equipped with a stirrer and a water separator, 49.5g of tetraethylenepentamine, 141g of oleic acid, and 141g of xylene are used as water-carrying agents, heated to 137-140°C for reflux reaction for 1h, and then continued to heat to 190-192°C for reaction for 6h. During the reaction, the water generated by the reaction is continuously released from the bottom switch of the water separator. When the water generated by the reaction is close to 18g, the reaction is basically completed. Then, the refluxed xylene solvent is collected through the bottom switch of the water separator and cooled to room temperature in turn to obtain a viscous liquid of gemini imidazoline. While continuing to stir, a solution formed by 47g of 3-chloro-2-hydroxypropyltrimethylammonium chloride and 47g of acetone is added dropwise to the reactor, and then 15g of sodium carbonate, the total mass of the reaction materials, is added. The reaction is carried out at room temperature for 4h, and the temperature is raised to 56-60°C to distill out the acetone to obtain a CO2-responsive gemini imidazoline surfactant. Its nuclear magnetic resonance spectrum is shown in FIG. Figure 1 shown.

[0035] The structure of CO2-responsive gemini imidazoline surfactant is

[0036]

[0037] Where R = C 17 H 33 .

[0038] A CO2-responsive gemini imidazoline surfactant was used as a thickener in the preparation of clean fracturing fluid. It was mixed and dissolved in water at a specific ratio to create a 3.0% solution. The viscosity was tested, revealing a viscosity of 25 mPa·s. After carbon dioxide was introduced into the solution for 15 minutes, the resulting solution viscosity was measured to be 106 mPa·s.

[0039] Example 2

[0040] A CO2-responsive gemini imidazoline surfactant was used as a thickener in the preparation of clean fracturing fluid. It was mixed and dissolved in water to create a 2.5% solution. The viscosity was tested, revealing a viscosity of 20 mPa·s. After bubbling carbon dioxide into the solution for 15 minutes, the solution viscosity was measured to be 110 mPa·s.

[0041] Example 3

[0042] A CO2-responsive gemini imidazoline surfactant was used as a thickener in the preparation of clean fracturing fluid. It was mixed and dissolved in water to create a 3.5% solution. The viscosity was tested, revealing a viscosity of 15 mPa·s. After bubbling carbon dioxide into the solution for 20 minutes, the solution viscosity was measured to be 128 mPa·s.

[0043] Example 4

[0044] The CO2-responsive gemini imidazoline surfactant was used as a thickener to prepare a clean fracturing fluid. It was mixed and dissolved with water in a certain proportion to prepare a 3.5% solution and subjected to a viscosity test. The viscosity was measured to be 15 mPa·s. The solution viscosity was measured after carbon dioxide was introduced for 15 minutes, and then the viscosity was measured after nitrogen was introduced for 15 minutes. CO2 and N2 were introduced alternately for 15 minutes each and the viscosity values ​​were measured in turn. The above cycle was repeated 5 times. The measured solution viscosity change results are shown as follows: Figure 1 As shown. Figure 1 It can be seen that the viscosity of the carbon dioxide-responsive thickening surfactant aqueous solution has good repeatability and the viscosity hardly decays during repeated use.

[0045] Example 5

[0046] The CO2-responsive gemini imidazoline surfactant is used as a thickening agent. When preparing clean fracturing fluid, it is mixed and dissolved with water and small molecule salt in a certain proportion. The proportion of water, surfactant, and small molecule salt (taking sodium salicylate as an example) is used to make a solution, wherein the carbon dioxide-responsive thickening surfactant is 3.5% and sodium salicylate is 5.0%. The viscosity of the prepared fracturing solution is tested, and the viscosity is measured to be less than 33mPa·s. The viscosity of the prepared fracturing fluid is tested, specifically, the viscosity is measured after passing CO2 for 20 minutes, and then the viscosity is measured after passing N2 for 20 minutes. This test is repeated 5 times, and the viscosity of the fracturing fluid is measured as follows: Figure 3 As shown. Figure 2 It can be seen that the carbon dioxide-responsive thickening gemini imidazoline surfactant and small molecule salt compound shows a good thickening effect, and the viscosity of the fracturing fluid aqueous solution after nitrogen is introduced into the gel is low, which can meet the on-site construction requirements of the fracturing fluid.

[0047] The present invention addresses the common defects of CO2-responsive surfactants used as fracturing fluid thickeners, such as unsatisfactory viscosity-increasing effects and poor salt resistance. According to measurements, only 50% of the tertiary amine groups are protonated to become cations when the CO2 aqueous solution is saturated. Therefore, more tertiary amine groups must be contained in the surfactant molecule to produce strong multiple cations, which in turn form better worm-like micelles with small molecule salts (organic and inorganic acid radical ions), thereby further improving the viscosity-increasing effect and salt resistance. The present invention provides a bisimidazoline quaternary ammonium salt surfactant thickener, the molecule of which contains a bisimidazoline ring and a bridged tertiary amine to cooperate with triple cations, thereby increasing the CO2 response ability. A quaternary ammonium group and a hydroxyl group in the molecule can improve the water solubility of the imidazoline surfactant, which is beneficial for the preparation of clean fracturing fluid. In addition, the responsive clean fracturing fluid can achieve gel breaking by introducing air or nitrogen during fracturing, without the need to add a gel breaker, reducing damage to the formation, and saving the amount of chemical agents.

Claims

1. A CO2-responsive gemini imidazoline surfactant, characterized in that: It has the following general structural formula: Wherein, R is a straight long-chain hydrocarbon group having 17 to 21 carbon atoms.

2. A method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 1, characterized in that: The following steps are involved: Step 1: In a reactor equipped with a stirrer and a water separator, tetraethylenepentamine and a long-chain fatty acid are added, and xylene of equal mass to the long-chain fatty acid is used as a water-carrying agent. The temperature is raised to 125-140°C and refluxed for 1-2 hours, and then the temperature is further raised to 190-220°C for reaction for 5-6 hours. During the reaction, the water generated by the reaction is continuously released from the switch at the bottom of the water separator, and the refluxed xylene solvent is then collected through the switch at the bottom of the water separator. The mixture is cooled to room temperature to obtain a viscous gemini imidazoline liquid. Step 2: Add a solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and acetone of equal mass to the gemini imidazoline prepared in step 1 while stirring, then add an equimolar amount of an acid-binding agent, react at room temperature for 3-4 hours, raise the temperature to 56-60°C to distill off the acetone, and a CO2-responsive gemini imidazoline surfactant can be obtained.

3. A method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 2, characterized in that: In the step 1, the molar ratio of tetraethylene pentamine to long-chain fatty acid is 1.05:2.

0. When the water generated by the reaction is close to 4 times the molar number of the tetraethylene pentamine fed, the reaction is terminated.

4. A method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 2, characterized in that: In the step 2, the molar ratio of gemini imidazoline, 3-chloro-2-hydroxypropyltrimethylammonium chloride and acid binding agent is 1:1:

1.

5. A method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 2, characterized in that: The acid binding agent is one or a mixture of sodium carbonate, potassium carbonate, magnesium hydroxide and triethylamine.

6. The use of the CO2-responsive gemini imidazoline surfactant according to claim 1, wherein The CO2-responsive gemini imidazoline surfactant is used as a fracturing fluid thickener. The CO2-responsive gemini imidazoline surfactant is dissolved in water at a mass ratio of 2.0-5.0%, and then a small molecule salt is added and stirred to dissolve to obtain a CO2-sensitive clean fracturing fluid.

7. The use of the CO2-responsive gemini imidazoline surfactant according to claim 6, wherein The small molecule salt is one of sodium chloride, potassium chloride, sodium salicylate, and sodium p-toluenesulfonate.

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