CO2 responsive gemini imidazoline surfactant and application thereof in fracturing fluid

Abstract

The invention discloses a CO2 response type gemini imidazoline surfactant and application thereof in fracturing fluid, tetraethylenepentamine and long-chain fatty acid are fed, dimethylbenzene with the mass equal to that of the long-chain fatty acid is used as a water carrying agent, the temperature is raised to 125-140 DEG C for reflux, then the temperature is continuously raised to 190-220 DEG C for reflux, the temperature is sequentially reduced to room temperature, and the CO2 response type gemini imidazoline surfactant is obtained. A gemini imidazoline viscous liquid is obtained; and step 2, dropwise adding a composition solution of 3-chloro-2-hydroxypropyl trimethyl ammonium chloride and acetone with the same mass into the gemini imidazoline in the step 1 while stirring, then adding an acid-binding agent with the same mole, reacting at room temperature, heating to 56-60 DEG C, distilling out acetone, and thus obtaining the CO2 response type gemini imidazoline surfactant. The surfactant can be used as a thickening agent of the clean fracturing fluid, the viscoelasticity of the clean fracturing fluid prepared by using the surfactant as the thickening agent is improved, and the formed clean fracturing fluid shows relatively strong acidity and can corrode inorganic blockages such as carbonic rock in part of a stratum.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of fracturing fluid thickeners, and specifically relates to a CO2 responsive gemini imidazoline surfactant and application thereof in fracturing fluids. Background Art

[0002] Water-based clean fracturing fluid, also known as viscoelastic surfactant fracturing fluid, has been successfully applied to fracturing construction of oil wells and coal seams, and has achieved good economic benefits. However, existing clean fracturing fluids have problems such as poor salt resistance, complex preparation process, and high cost. Applying CO2-responsive surfactants or polymers to clean fracturing fluid systems has the advantages of simple control and easy operation. It does not require the addition of debonding agents to the system. Only inert gas (such as N2, methane, air, etc.) is required to achieve controllable debonding, and it can be recycled. It saves resources and reduces costs, effectively solves the current pollution treatment problem of polymer fracturing flowback fluids, protects the geological environment, and has important practical significance for the economical and efficient development of unconventional oil and gas reservoirs and energy conservation and emission reduction. Therefore, carbon dioxide-responsive viscoelastic surfactants came into being.

[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 fewer 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 existing in the above prior art, the purpose 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 formed clean fracturing fluid is relatively acidic and can dissolve inorganic blockages such as carbonate rocks in some formations. In addition, the responsive clean fracturing fluid can reduce viscosity by introducing air or nitrogen during fracturing, achieve gel breaking, and discharge smoothly.

[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 the CO2-responsive gemini imidazoline surfactant are that the molecule contains three tertiary amine groups, two imidazoline rings, a quaternary ammonium group and a hydroxyl group. The imidazoline ring and tertiary amine 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, and 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, making the viscosity of the surfactant solution decrease. This process can be repeated.

[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 the same mass as the long-chain fatty acid is used as a water-carrying agent, and the temperature is raised to 125-140° C. for reflux 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 then the refluxed xylene solvent is collected through the switch at the bottom of the water separator, and the temperature is successively lowered to room temperature to obtain a viscous liquid of gemini imidazoline;

[0013] Step 2: Add a solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and acetone of equal mass to the gemini imidazoline 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 to distill out the acetone, and the CO2-responsive gemini imidazoline surfactant can be obtained.

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

[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, and 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 for 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 carbon dioxide response and thickening provided by the present invention can significantly increase the viscosity of the system after carbon dioxide is introduced into the system, and has super sand carrying capacity.

[0021] (2) The carbon dioxide viscosity-enhancing fracturing fluid provided by the present invention can be debonded by displacement of an 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 part of the formation, thereby increasing the permeability of the reservoir rock.

[0023] (4) The carbon dioxide viscosity-enhanced 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 H NMR 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 further described in detail below in conjunction with the accompanying drawings.

[0029] The following is a description of the principles and features of the present invention, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional 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.

[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. for reflux 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 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 the temperature is successively lowered 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 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, react at room temperature for 3 to 4 hours, heat to 56 to 60°C to distill off acetone, and a CO2-responsive gemini imidazoline surfactant can be obtained.

[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, and then the refluxed xylene solvent is collected through the bottom switch of the water separator, and the temperature is successively lowered to room temperature 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, and the reaction is carried out at room temperature for 4h. The temperature is raised to 56-60°C to distill out the acetone, and the CO2-responsive gemini imidazoline surfactant can be obtained, and its nuclear magnetic resonance spectrum is shown in Figure 1 shown.

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

[0036]

[0037] Where R = C 17 H 33 .

[0038] When preparing clean fracturing fluid, the CO2-responsive gemini imidazoline surfactant was used as a thickener and mixed with water in a certain proportion and dissolved to prepare a 3.0% solution and perform a viscosity test, which measured a viscosity of 25 mPa·s. After carbon dioxide was introduced into the prepared solution for 15 minutes, the solution viscosity was measured to be 106 mPa·s.

[0039] Example 2

[0040] When preparing clean fracturing fluid, the CO2-responsive gemini imidazoline surfactant was used as a thickener and mixed with water in a certain proportion and dissolved to prepare a 2.5% solution and perform a viscosity test, which measured a viscosity of 20 mPa·s. After carbon dioxide was introduced into the prepared solution for 15 minutes, the solution viscosity was measured to be 110 mPa·s.

[0041] Example 3

[0042] When preparing clean fracturing fluid, the CO2-responsive gemini imidazoline surfactant was used as a thickener and mixed with water in a certain proportion and dissolved to prepare a 3.5% solution and perform a viscosity test, which measured a viscosity of 15 mPa·s. After carbon dioxide was introduced into the prepared 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. When preparing clean fracturing fluid, it was mixed and dissolved with water in a certain proportion to prepare a 3.5% solution and tested for viscosity. The viscosity was 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 to measure the viscosity values ​​in turn. The above cycle was repeated 5 times. The solution viscosity change results were 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 (sodium salicylate is used 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 measured viscosity is 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 measured viscosity change of the fracturing fluid is as follows: Figure 3 As shown. Figure 2 It can be seen that the carbon dioxide responsive viscosity-increasing gemini imidazoline surfactant and the small molecule salt compound show a good viscosity-increasing effect, and the viscosity of the fracturing fluid aqueous solution after nitrogen is introduced into the gel breaking is small, which can meet the requirements of on-site construction of fracturing fluid.

[0047] The present invention aims at the defects of unsatisfactory viscosity enhancement effect and poor salt resistance that are common in CO2 responsive surfactants used as fracturing fluid thickeners. According to the measurement, when the CO2 aqueous solution is saturated, only 50% of the tertiary amine groups are protonated to become cations. Therefore, more tertiary amine groups are contained in the surfactant molecule to produce strong multiple cations, and then by forming better worm-like micelles with small molecule salts (organic and inorganic acid radical ions), the viscosity enhancement effect and the ability to resist salt substances are further improved. The present invention provides a bisimidazoline quaternary ammonium salt surfactant thickener, which contains a bisimidazoline ring and a bridged tertiary amine in the molecule to coordinate 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 to the preparation of clean fracturing fluid. In addition, the responsive clean fracturing fluid can break the gel by introducing air or nitrogen during fracturing, without adding a gel breaker, reducing damage to the formation, saving the amount of chemical agents, etc.

Claims

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

2. A CO2-responsive gemini imidazoline surfactant according to claim 1, characterized in that: The CO2-responsive gemini imidazoline surfactant contains three tertiary amine groups, two imidazoline rings, a quaternary ammonium group and a hydroxyl group in its molecule. The imidazoline ring and the tertiary amine group can combine with the protons generated by the carbon dioxide aqueous solution to form multiple cations.

3. A method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 1 or 2, 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 the same mass as the long-chain fatty acid is used as a water-carrying agent, and the temperature is raised to 125-140° C. for reflux 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 then the refluxed xylene solvent is collected through the switch at the bottom of the water separator, and the temperature is successively lowered to room temperature to obtain a viscous liquid of gemini imidazoline; Step 2: Add a solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and acetone of equal mass to the gemini imidazoline 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 to distill out the acetone, and the CO2-responsive gemini imidazoline surfactant can be obtained.

4. The method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 3, characterized in that: In the step 1, the molar ratio of tetraethylenepentamine to long-chain fatty acid is 1.05:2.0, and the reaction is terminated when the water generated by the reaction is close to 4 times the molar number of the tetraethylenepentamine fed.

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

1.

6. The method for preparing a CO2-responsive gemini imidazoline surfactant according to claim 3, characterized in that: The acid binding agent is one or a mixture of sodium carbonate, potassium carbonate, magnesium hydroxide and triethylamine.

7. The use of the CO2-responsive gemini imidazoline surfactant according to any one of claims 1 to 6, characterized in that: 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.

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

Images