CO2 responsive surfactant, preparation method thereof, fracturing fluid composition containing CO2 responsive surfactant and fracturing method

Abstract

The invention discloses a CO2 response type surfactant, a preparation method thereof, a fracturing fluid composition containing the CO2 response type surfactant and a fracturing method. The CO2 responsive surfactant has a structure of formula (I) wherein R is a C11-C23 hydrocarbyl group, and j is a positive integer, for example, 1, 2, 3 or 4. The preparation method of the CO2-responsive surfactant comprises the step of enabling R-COCl to react with aminoimidazole to obtain the CO2-responsive surfactant. The invention further provides a fracturing fluid composition which comprises the CO2 response type surface active agent. According to the CO2 response type surfactant, the applicable temperature of a fracturing fluid system can be remarkably increased to 90-120 DEG C from 80 DEG C or below, the CO2 response type surfactant can bear multiple CO2 / N2 cycles without performance attenuation, and the fracturing construction requirements of deep high-temperature reservoirs are met. (I).

Description

Technical Field

[0001] This disclosure relates to oilfield chemistry, and more specifically to CO2-responsive surfactants, their preparation methods, and their application in fracturing fluids. Background Technology

[0002] Driven by strategic goals, coalbed methane is an important alternative resource for achieving a clean and low-carbon transformation of the energy structure, and its efficient development has become one of the key paths for the transformation of my country's energy system. Fracturing fluid is a crucial working fluid for reservoir fracturing stimulation, and its performance directly determines the operational results. Traditional fracturing fluids suffer from problems such as high water consumption, incomplete gel breaking, high flowback fluid treatment costs, and environmental pollution. In recent years, intelligent fracturing fluids based on responsive surfactants have emerged. These fluids can trigger reversible changes in micelle structure through external stimuli (such as CO2 / N2), achieving a reversible cycle of solution "gel formation-gel breaking," providing a new approach for the reuse of fracturing fluids and cost reduction. Summary of the Invention

[0003] The inventors unexpectedly discovered that the CO2-responsive surfactant in this invention can significantly increase the applicable temperature of the fracturing fluid system from ≤80°C to 90-120°C, and can withstand multiple CO2 / N2 cycles without performance degradation, thus meeting the fracturing requirements of deep high-temperature reservoirs. This invention was obtained based on the above unexpected discovery.

[0004] In a first aspect of this disclosure, a CO2-responsive surfactant is provided having the structure of the following formula (I):

[0005] (I)

[0006] Where R is C 11 -C 23 The hydrocarbon group, and j can be a positive integer, such as 1, 2, 3 or 4.

[0007] In some embodiments, the hydrocarbon group may be saturated or unsaturated. For example, the hydrocarbon group may contain 1, 2, 3 or 4 unsaturated bonds, which may be, for example, C=C double bonds.

[0008] In some embodiments, R may be selected from undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl, tridecyl, 9-pentadecanyl, 11-heptadecyl, 9-nonadecanyl, 11-nonadecanyl, 9,12-heptadecadienyl, 6,9,12-heptadectrienyl, 9,12,15-heptadectrienyl, 5,8,11,14-nonadecantetraenyl, 9-heptadecyl and 13-teicosyl, preferably R may be selected from 9-heptadecyl, 13-teicosyl, pentadecyl, heptadecyl and dodecyl.

[0009] In some embodiments, the CO2-responsive surfactant may be selected from oleamide ethylimidazolium, erucamide ethylimidazolium, palmitamide ethylimidazolium, stearamide ethylimidazolium, behenamide ethylimidazolium, oleamide propylimidazolium, erucamide propylimidazolium, palmitamide propylimidazolium, stearamide propylimidazolium, behenamide propylimidazolium, oleamide butylimidazolium, erucamide butylimidazolium, palmitamide butylimidazolium, stearamide butylimidazolium, and behenamide butylimidazolium. Preferably, the CO2-responsive surfactant may be oleamide propylimidazolium or erucamide propylimidazolium.

[0010] In a second aspect of this disclosure, this disclosure provides a method for preparing a CO2-responsive surfactant according to the first aspect, which may include:

[0011] The CO2-responsive surfactant is obtained by reacting R-COCl with an aminoimidazolium of formula X.

[0012] (X)

[0013] R and j have the same limitations as in the first aspect.

[0014] In some embodiments, the method may further include reacting R-COOH with an acyl chloride reagent to obtain R-COCl. Specifically, the acyl chloride reagent is selected from oxalyl chloride, thionyl chloride, phosphorus trichloride, phosphorus pentachloride, and phosgene.

[0015] In a third aspect of this disclosure, this disclosure provides fracturing fluid compositions that may contain the CO2-responsive surfactants described in the first aspect.

[0016] In some embodiments, the fracturing fluid composition may further comprise anionic aromatic surfactants. Specifically, the anionic aromatic surfactants are selected from salicylic acid and its salts, benzoic acid and its salts, benzenesulfonic acid and its salts, p-toluenesulfonic acid and its salts, p-styrenesulfonic acid and its salts, and p-hydroxybenzenesulfonic acid and its salts.

[0017] In some embodiments, the fracturing fluid composition may also contain a stabilizer. Specifically, the stabilizer is selected from potassium salts, sodium salts, and ammonium salts.

[0018] In some embodiments, the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 1:1 to 4:1.

[0019] In some embodiments, the fracturing fluid composition may further contain CO2, specifically, 1) by introducing CO2 gas into a fracturing fluid composition without added CO2 at ambient pressure to form a gel, or 2) by mixing supercritical CO2 with a fracturing fluid composition without added CO2 under pressurized conditions to form a foam, wherein the fracturing fluid composition obtained in embodiment 2) has a liquid volume ratio of 20 to 40% and a gas volume ratio of 60 to 80%.

[0020] In a fourth aspect of this disclosure, a fracturing method is provided, which may include: providing the fracturing fluid composition according to the third aspect to the location to be fracturing.

[0021] In some embodiments, the fracturing method may further include, after providing the fracturing fluid composition, introducing CO2 gas into the location to be fracturing to gel, wherein the fracturing fluid composition is the fracturing fluid composition according to the first aspect.

[0022] In some embodiments, the fracturing method may further include introducing an inert gas into the location to be fracturing to break up the gel.

[0023] The CO2-responsive surfactant of this invention exhibits better thermal stability, outstanding temperature resistance, and recyclability. Therefore, fracturing fluid compositions containing this surfactant possess at least one of the following advantages: meeting the fracturing requirements of high-temperature reservoirs at 90-120°C; maintaining good temperature resistance even after multiple CO2-responsive thickening and N2 gel breaking processes; and excellent temperature resistance and recyclability, making the fracturing fluid compositions of this invention promising for deep coalbed methane fracturing. Furthermore, the method of this invention has the advantages of low raw material costs and easy synthesis. Attached Figure Description

[0024] The accompanying drawings illustrate exemplary embodiments of this disclosure and, together with the foregoing description, are intended to provide a better understanding of the technical aspects of this disclosure; therefore, this disclosure is not to be construed as limited to the drawings.

[0025] Figure 1 The 1H NMR spectrum of oleamide propyl imidazole in Example 1;

[0026] Figure 2 The temperature resistance and shear viscosity test curve of the VES clean fracturing fluid in Example 3 after CO2 response;

[0027] Figure 3 The image shows the VES-CO2 foam fracturing fluid of Example 4 after foaming, as observed through a viewing window.

[0028] Figure 4 The graph shows the cyclic performance test curve of the VES clean fracturing fluid in Example 3; and

[0029] Figure 5 The graph shows the cyclic performance test curve of the VES-CO2 foam fracturing fluid in Example 4. Detailed Implementation

[0030] This disclosure will be described in more detail below to aid in understanding it.

[0031] It should be understood that the terms or words used in this specification and the appended claims should not be construed as limited to their general or dictionary meanings, but rather interpreted based on their meanings and concepts corresponding to the technical aspects of this disclosure, on the basis of the principle that the inventors are allowed to define terms appropriately for the purpose of best illustration.

[0032] It should be further understood that, unless otherwise expressly stated, when used in the specification, "comprising" or "including" indicates the presence of the said element and does not exclude the presence or addition of one or more other elements.

[0033] As used herein, a range is used as a shorthand to describe the individual values ​​within the range and each value. Any value within the range can be chosen as an endpoint of the range. Thus, the ranges 1 to 5 specifically include 1, 2, 3, 4, and 5, as well as subranges such as 2 to 5, 3 to 5, 2 to 3, 2 to 4, 1 to 4, etc.

[0034] As used in this article, "selected from" means selecting one, two or more candidates.

[0035] As used herein, the term "acyl chloride reagent" refers to a reagent capable of converting carboxylic acids into acyl chlorides, which may be selected from one or more of oxalyl chloride, thionyl chloride, phosphorus trichloride, phosphorus pentachloride, and phosgene.

[0036] As used in this article, the inert gas is selected from nitrogen, argon, and helium, etc.

[0037] As used in this article, the term "anionic aromatic surfactant" refers to a class of surfactants whose molecular structure contains both an aromatic ring and a negatively charged hydrophilic group (anionic) that can ionize in aqueous solution.

[0038] As used in this article, the term "viscoelastic surfactant (VES)" is a special surfactant that can form worm-like micelles. It has properties such as high viscoelasticity, self-breaking gel upon contact with oil and water, and resistance to high temperature and high salt. It is mainly used in fracturing fluids and drilling fluids in oil extraction, which can effectively improve oil and gas recovery. It is also used in cosmetics, fluid drag reduction and other fields.

[0039] As used herein, the term "CO2-responsive surfactant" refers to a surfactant whose molecular structure contains a functional group capable of undergoing a reversible acid-base reaction with CO2. Upon introduction of CO2, this functional group protonates, causing a change in molecular morphology or aggregation state; upon removal of CO2 (e.g., introduction of N2), the functional group deprotonates, restoring its original state. This CO2-responsive surfactant can form stable worm-like micelles under CO2 stimulation, exhibiting excellent viscoelasticity, and is therefore a responsive viscoelastic surfactant.

[0040] As used in this article, the term "stabilizer" refers to a stabilizer that not only inhibits clay swelling, but also whose ions ionized in water can compress the electric double layer formed by micelles, which is beneficial for micelles to entangle and thicken in solution and increase adsorption density at the gas-liquid interface.

[0041] In a first aspect of this disclosure, a CO2-responsive surfactant is provided having the structure of the following formula (I):

[0042] (I)

[0043] Where R is C 11 -C 23 The hydrocarbon group, and j can be a positive integer, such as 1, 2, 3 or 4.

[0044] In some embodiments, the hydrocarbon group may be saturated or unsaturated. For example, the hydrocarbon group may contain 1, 2, 3 or 4 unsaturated bonds, which may be, for example, C=C double bonds.

[0045] In some embodiments, R may be selected from undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl, tridecyl, 9-pentadecanyl, 11-heptadecyl, 9-nonadecanyl, 11-nonadecanyl, 9,12-heptadecadienyl, 6,9,12-heptadectrienyl, 9,12,15-heptadectrienyl, 5,8,11,14-nonadecantetraenyl, 9-heptadecyl and 13-teicosyl, preferably R may be selected from 9-heptadecyl, 13-teicosyl, pentadecyl, heptadecyl and dodecyl.

[0046] In some embodiments, the CO2-responsive surfactant may be selected from oleamide ethylimidazolium, erucamide ethylimidazolium, palmitamide ethylimidazolium, stearamide ethylimidazolium, behenamide ethylimidazolium, oleamide propylimidazolium, erucamide propylimidazolium, palmitamide propylimidazolium, stearamide propylimidazolium, behenamide propylimidazolium, oleamide butylimidazolium, erucamide butylimidazolium, palmitamide butylimidazolium, stearamide butylimidazolium, and behenamide butylimidazolium. Preferably, the CO2-responsive surfactant may be oleamide propylimidazolium or erucamide propylimidazolium.

[0047] The CO2-responsive surfactant disclosed in this paper undergoes protonation under the action of CO2, thereby forming a cationic surfactant and micelles. After the CO2 is removed by an inert gas such as N2, the protonated imidazole undergoes deprotonation and de-micelle formation, restoring the original state. Furthermore, the gelation-de-micelle process can be repeated multiple times, exhibiting the characteristic of multiple recycling. The response mechanism is as follows:

[0048] .

[0049] In a second aspect of this disclosure, this disclosure provides a method for preparing a CO2-responsive surfactant according to the first aspect, which may include:

[0050] The CO2-responsive surfactant is obtained by reacting R-COCl with an aminoimidazolium of formula X.

[0051] (X)

[0052] R and j have the same limitations as in the first aspect.

[0053] In some embodiments, the method may further include reacting R-COOH with an acyl chloride reagent to obtain R-COCl. Specifically, the acyl chloride reagent is selected from oxalyl chloride, thionyl chloride, phosphorus trichloride, phosphorus pentachloride, and phosgene.

[0054] In some embodiments, R-COOH represents long-chain saturated fatty acids and monounsaturated fatty acids with a carbon chain length of 12 to 24. In some embodiments, preferably, R-COOH may have a structure of formula (M) or formula (N):

[0055] (M) or (N), where m is an integer from 5 to 9, n is an integer from 2 to 5, and k is an integer from 7 to 20. Preferably, n is 5, m is 5-9, and k is 12-18. More preferably, n is 5, m is 5 or 9, and k is 12, 14, or 18. In some embodiments, R-COOH is selected from oleic acid, erucic acid, palmitic acid, stearic acid, and behenic acid. The method disclosed herein is simple to synthesize, and the reaction raw materials are readily available and economical.

[0056] In a third aspect of this disclosure, this disclosure provides fracturing fluid compositions that may contain the CO2-responsive surfactants described in the first aspect.

[0057] In some embodiments, the fracturing fluid composition may further comprise anionic aromatic surfactants. Specifically, the anionic aromatic surfactants are selected from salicylic acid and its salts, benzoic acid and its salts, benzenesulfonic acid and its salts, p-toluenesulfonic acid and its salts, p-styrenesulfonic acid and its salts, and p-hydroxybenzenesulfonic acid and its salts. Anionic aromatic surfactants and CO2-responsive surfactants can interact through electrostatic attraction and hydrogen bonding, thereby increasing the temperature resistance and stability of the worm-like micelles.

[0058] In some embodiments, the fracturing fluid composition may further comprise a stabilizer. Specifically, the stabilizer is selected from potassium salts, sodium salts, and ammonium salts. In some embodiments, the stabilizer may be selected from KCl, NH4Cl, NaCl, etc.

[0059] In some embodiments, the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 1:1 to 4:1. In some embodiments, the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 1:1 to 3:1. In some embodiments, the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 1:1 to 2:1. In some embodiments, the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 2:1.

[0060] In some embodiments, the fracturing fluid composition may comprise a CO2-responsive surfactant, an anionic aromatic surfactant, a stabilizer, and water. In some embodiments, the fracturing fluid composition may comprise 1 to 3 wt% of a CO2-responsive surfactant, 0.5 to 1.5 wt% of anionic aromatic surfactant, 0.5 to 1 wt% of stabilizer, and water.

[0061] In some embodiments, the fracturing fluid composition may further contain CO2, specifically, 1) by introducing CO2 gas into a fracturing fluid composition without added CO2 at ambient pressure to form a gel, or 2) by mixing supercritical CO2 with a fracturing fluid composition without added CO2 under pressurized conditions to form a foam, wherein the fracturing fluid composition obtained in embodiment 2) has a liquid phase volume ratio of 20% to 40% and a gas volume ratio of 60% to 80%. The liquid phase volume and gas volume are determined based on the initial space distribution within the reactor before mixing, wherein the liquid phase volume is the volume of the added fracturing fluid composition, and the gas volume is the gas phase space volume within the reactor not occupied by the fracturing fluid composition and used for introducing supercritical CO2. In some embodiments, the fracturing fluid composition obtained in embodiment 2) has a liquid phase volume ratio of 20% to 40% and a gas volume ratio of 60% to 80%. In some embodiments, the fracturing fluid composition obtained in embodiment 2) has a liquid phase volume ratio of 25% to 40% and a gas volume ratio of 60% to 75%. In some embodiments, the fracturing fluid composition obtained in embodiment 2) has a liquid phase volume ratio of 30% to 40% and a gas volume ratio of 60% to 70%. In some embodiments, the fracturing fluid composition may include VES clean fracturing fluid and VES-CO2 foam fracturing fluid. The VES clean fracturing fluid can be obtained by gelling a fracturing fluid composition without added CO2 by introducing CO2 gas. The VES-CO2 foam fracturing fluid is obtained by mixing supercritical CO2 with a fracturing fluid composition without added CO2 under pressurized conditions to form a foam.

[0062] In a fourth aspect of this disclosure, a fracturing method is provided, which may include: providing the fracturing fluid composition according to the third aspect to the location to be fracturing.

[0063] In some embodiments, the fracturing method may further include, after providing the fracturing fluid composition, introducing CO2 gas into the location to be fracturing to gel, wherein the fracturing fluid composition is the fracturing fluid composition according to the first aspect.

[0064] In some embodiments, the fracturing method may further include introducing an inert gas into the location to be fracturing to break up the gel.

[0065] Example

[0066] The effects and functions of this disclosure will be described in more detail below through specific embodiments thereof. However, these embodiments are for illustrative purposes only, and the scope of the claims of this disclosure is not determined thereto.

[0067] Example 1: Preparation of oleic acid amyl propyl imidazole

[0068] 7.06 g of oleic acid (25 mmol) was added to a round-bottom flask containing 25 mL of dichloromethane to obtain a mixed solution. Then, 15.9 g of oxaloyl chloride (125 mmol) was added dropwise to the mixed solution. After the addition of oxaloyl chloride, the reaction mixture was stirred at room temperature for 12 hours. After the reaction was complete, the solvent was removed by vacuum distillation to obtain a pale yellow liquid crude product, oleic acid acyl chloride. This crude product did not require further separation and was used directly in the next step.

[0069] Next, 3.76 g of 1-(3-aminopropyl)imidazole (30 mmol) and 10.1 g of triethylamine (100 mmol) were added to a round-bottom flask containing 50 mL of dichloromethane and cooled to 0°C to obtain a mixed solution. Then, 7.52 g of oleic acid chloride (25 mmol) was dissolved in 25 mL of dichloromethane and added dropwise to the mixed solution. After the dropwise addition, the reaction mixture was stirred at room temperature for 12 hours. After the reaction was completed, the organic phase was washed with water, the organic solvent was removed under reduced pressure, and the mixture was separated by column chromatography (dichloromethane / methanol = 20:1) to give a viscous, pale yellow liquid (yield: 87%). Figure 1 The image shows the 1H NMR spectrum of oleamide propyl imidazole from Example 1.

[0070] Example 2 Preparation of erucic acid amyl propyl imidazole

[0071] 8.46 g of erucic acid (25 mmol) was added to a round-bottom flask containing 25 mL of dichloromethane to obtain a mixed solution. Then, 15.9 g of oxaloyl chloride (125 mmol) was added dropwise to the mixed solution. After the addition of oxaloyl chloride, the reaction mixture was stirred at room temperature for 12 hours. After the reaction was complete, the solvent was removed by vacuum distillation to obtain a pale yellow liquid crude product, erucic acid chloride, which could be used directly in the next step without further separation.

[0072] Next, 3.76 g of 1-(3-aminopropyl)imidazole (30 mmol) and 10.1 g of triethylamine (100 mmol) were added to a round-bottom flask containing 50 mL of dichloromethane and cooled to 0°C to obtain a mixed solution. Then, 8.92 g of erucic acid chloride (25 mmol) was dissolved in 25 mL of dichloromethane and added dropwise to the mixed solution. After the dropwise addition, the reaction mixture was stirred at room temperature for 12 hours. After the reaction was complete, the organic phase was washed with water, the organic solvent was removed under reduced pressure, and the product was separated by column chromatography (dichloromethane / methanol = 20:1) to give a pale yellow solid product (yield: 85%).

[0073] Example 3: Preparation of VES Clean Fracturing Fluid

[0074] 96.5 g of deionized water was placed in a 200 mL beaker, stirred with a rotor, and heated to 45°C. Then, 2 g of erucamide propylimidazole, 1 g of sodium p-toluenesulfonate, and 0.5 g of potassium chloride were added to the beaker and dissolved. Stirring was continued for 10 minutes to ensure complete dissolution, yielding a fracturing fluid composition containing 2 wt% erucamide propylimidazole (the initial system was a white emulsion). CO2 was then introduced into this fracturing fluid composition at a flow rate of 0.5 L / min while stirring. After 2 minutes, the solution gradually became clear and viscous; after 8-10 minutes, the solution completely transformed into a clear, transparent, high-viscosity fluid, yielding VES clean fracturing fluid.

[0075] Example 4: Preparation of VES-CO2 foam fracturing fluid

[0076] 96.5 g of deionized water was placed in a 200 mL beaker, stirred with a rotor, and heated to 45°C. Then, 2 g of oleamidopropyl imidazole, 1 g of sodium p-hydroxybenzenesulfonate, and 0.5 g of potassium chloride were added to the beaker and dissolved. Stirring continued for 10 minutes to ensure complete dissolution, yielding a fracturing fluid composition containing 2 wt% oleamidopropyl imidazole (the initial system was a pale yellow emulsion). 100 mL of this fracturing fluid composition was transferred to a high-temperature, high-pressure, visual reactor (total reactor volume 400 mL). The vent valve was opened, and CO2 was introduced to purge air from the reactor. The vent valve was then closed, and CO2 was continued to be introduced using a gas booster pump until the pressure inside the reactor reached 15 MPa. Simultaneously, the reactor was heated to 100°C using a constant-temperature oil bath. At this point, the CO2 inside the reactor was in a supercritical state. The stirrer was turned on and stirred at 3000 to 5000 r / min for 2-5 minutes to induce foaming, thus obtaining VES-CO2 foam fracturing fluid. In Example 4, the liquid phase accounted for 25% of the volume and the gas phase accounted for 75% of the volume.

[0077] Comparative Example 1

[0078] The VES cleaning fracturing fluid of Comparative Example 1 was prepared in the same manner as in Example 3, except that erucamide propyl dimethylamine was used instead of erucamide propyl imidazole in Example 3.

[0079] Comparative Example 2

[0080] The VES-CO2 foam fracturing fluid of Comparative Example 2 was prepared in the same manner as in Example 4, except that oleamidopropyl dimethylamine was used instead of oleamidopropyl imidazole in Example 4.

[0081] Experimental Example

[0082] Experimental Example 1: Temperature and Shear Resistance Test of VES Clean Fracturing Fluid in Example 3

[0083] The VES clean fracturing fluid from Example 3 was poured into a sealed container equipped with a HAAKE MARS 60 rheometer. High-temperature shear viscosity and high-temperature viscoelasticity tests were performed using a PZDG38 dual-slit rotor. The high-temperature shear viscosity test conditions were as follows: the system temperature was raised from room temperature (25°C) to a high temperature of 110°C over 2500 seconds, followed by a shear viscosity test at 110°C for 5000 seconds. The shear rate during the entire process was 170 seconds per second. -1 High-temperature viscoelasticity testing includes stress scanning and frequency scanning, with oscillation frequency scanning performed at a stress of 0.5 Pa (scanning range 0.01-10 Hz).

[0084] Test results show that the viscosity of the VES clean fracturing fluid at 110°C is 54.7 mPa·s, which meets the construction requirements (>25 mPa·s). Stress scanning results show that the linear viscoelastic range of the VES clean fracturing fluid after CO2 response is 0.01-4 Pa; frequency scanning results show that the storage modulus G' of the VES clean fracturing fluid after CO2 response is always greater than the loss modulus G'' in the range of 0.01-10 Hz, indicating that a three-dimensional network structure is formed inside the fracturing fluid, and it still has good viscoelasticity at high temperatures, ensuring its proppant carrying capacity at high temperatures.

[0085] Figure 2 The temperature resistance and shear viscosity test curve of the VES clean fracturing fluid of Example 3 after CO2 response.

[0086] Comparative Experiment Example 1: Temperature and Shear Resistance Test of VES Clean Fracturing Fluid in Comparative Example 1

[0087] Temperature shear resistance tests were conducted under the same conditions as in Experimental Example 1, except that the high-temperature shear viscosity test conditions involved raising the system temperature from room temperature (25°C) to a high temperature (90°C). The test results showed that the viscosity of the VES clean fracturing fluid in Comparative Example 1 was only 9.42 mPa·s at 90°C, indicating that the fracturing fluid had broken down at this temperature. Upon returning to room temperature, its viscosity was only 12.9 mPa·s, rendering it unusable. Therefore, the high temperature damaged the micelle network structure, causing it to lose its recyclability. The temperature shear resistance test results are shown in Table 1 below.

[0088] Table 1

[0089]

[0090] Experimental Example 2: High-Temperature Stability Test of VES-CO2 Foam Fracturing Fluid in Example 4

[0091] VES-CO2 foam fracturing fluid was prepared as described in Example 4. The stirrer was turned off, and the foam separation half-life was recorded through the viewing window.

[0092] Test results show that the foam exudate half-life is 246 minutes, indicating that the foam stability meets the requirements of high-temperature reservoir fracturing operations.

[0093] Figure 3 The image shows the condition of the VES-CO2 foam fracturing fluid in Example 4 after foaming, as observed through a viewing window.

[0094] High-Temperature Rheological Properties Test of VES-CO2 Foam Fracturing Fluid in Example 3 and Example 4

[0095] VES-CO2 foam fracturing fluid was prepared according to Example 4. The agitator was turned on and stirred at 3000 to 5000 r / min for 10 minutes. Then the reactor was inverted, and stirring continued for another 10 minutes. Simultaneously, the sealed container equipped with a HAAKE MARS 60 rheometer was preheated to 100°C. The pipeline connecting the reactor and the rheometer's sealed container was opened, and the connecting valve was opened to inject the VES-CO2 foam fracturing fluid into the rheometer. The pressure in the rheometer's sealed container was adjusted to 15 MPa using the reactor's hand-cranked valve, and then the connecting valve was closed. Then, a double-slit rotor PZDG38 was used at a shear rate of 170 seconds... -1 A high-temperature shear viscosity test was conducted for 7200 seconds. The test results show that the fracturing fluid can maintain a viscosity of 30.68 mPa·s at 100°C, which meets the construction requirements.

[0096] Comparative Experiment Example 2: High-Temperature Stability Test of VES-CO2 Foam Fracturing Fluid in Comparative Example 2

[0097] The high-temperature stability of the VES-CO2 foam fracturing fluid in Comparative Example 2 was tested under the same conditions as in Experimental Example 2. The results showed that the foam separation half-life of the VES-CO2 foam fracturing fluid in Comparative Example 2 decreased to 52 minutes at 15 MPa and 100°C, which could no longer meet the construction requirements.

[0098] High-Temperature Rheological Properties Test of VES-CO2 Foam Fracturing Fluid in Comparative Experiment Example 3 and Comparative Experiment Example 2

[0099] High-temperature rheological tests were conducted on the VES-CO2 foam fracturing fluid of Comparative Example 2 under the same conditions as in Experimental Example 3. The test results showed that the viscosity of the VES-CO2 foam fracturing fluid of Comparative Example 2 was only 3.4 mPa·s at 15 MPa and 100°C, thus losing its recyclability. The test results are shown in Table 2 below.

[0100] Table 2

[0101]

[0102] Experimental Example 4: Recyclability Test of VES Clean Fracturing Fluid in Example 3

[0103] Pour the VES-cleaned fracturing fluid from Example 3 into a 200 mL beaker. At room temperature (25°C), add a rotor stirrer and alternately introduce CO2 and N2 at a rate of 0.5 L / min. Then, use a rheometer to measure the flux at 170 seconds... -1 The shear rate was measured to study the viscosity of VES clean fracturing fluid after each cycle, following CO2-induced viscosity increase and N2-induced viscosity breakdown, in order to investigate its recycling performance.

[0104] The results show that the viscosity of the VES-cleaned fracturing fluid in Example 3 after four cycles of gel breaking, following a CO2 response, remained at 193.9 mPa·s, comparable to the initial system viscosity, indicating excellent recyclability. Furthermore, the VES-cleaned fracturing fluid after four cycles underwent another temperature and shear resistance test. The results showed that the viscosity at 110°C remained at 51.58 mPa·s, demonstrating good high-temperature stability and further proving its excellent recyclability.

[0105] Figure 4 The graph shows the cyclic performance test curve of the VES cleaning fracturing fluid in Example 3.

[0106] Experimental Example 5: Recycling Test of VES-CO2 Foam Fracturing Fluid in Example 4

[0107] The VES-CO2 foam fracturing fluid composition from Example 4 was poured into a 200 mL beaker, and a rotor was added for stirring at room temperature (25°C). CO2 and N2 were alternately introduced into the mixture at a rate of 0.5 L / min. A rheometer was then used to measure the reaction temperature over 170 seconds.-1 The viscosity of the foam fracturing fluid after CO2-responsive thickening and N2-induced gel breaking was measured by shear rate to study its recycling performance.

[0108] The results showed that after four cycles of gel breaking, the viscosity of the VES-CO2 foam fracturing fluid after CO2 response remained at 107.1 mPa·s, with no significant difference from the initial viscosity, indicating excellent recyclability. Furthermore, the VES-CO2 foam fracturing fluid, after multiple cycles, was reinjected into a high-temperature, high-pressure, visual reactor and foamed at 100°C and 15 MPa. The half-life of the foam was recorded and compared with the initial half-life. It was found that after four cycles, the half-life of the VES-CO2 foam fracturing fluid remained at 233 minutes, maintaining good high-temperature stability, further demonstrating its excellent recyclability.

[0109] Figure 5 The graph shows the cyclic performance test curve of the VES-CO2 foam fracturing fluid in Example 4.

[0110] Therefore, compared with existing CO2-responsive surfactants, this disclosure significantly increases the applicable temperature range of fracturing fluid systems from ≤80°C to 90-120°C, and it can withstand multiple CO2 / N2 cycles without performance degradation, meeting the fracturing requirements of deep, high-temperature reservoirs. Furthermore, the CO2-responsive surfactant disclosed herein has the advantages of low raw material costs and simple synthesis steps.

[0111] Although several embodiments of this disclosure have been described and illustrated herein, those skilled in the art will readily contemplate a variety of other ways and / or structures for performing the functions described herein and / or obtaining the results described herein and / or one or more advantages, and each such variation and / or modification is considered to be within the scope of this disclosure.

Claims

1. A CO2-responsive surfactant having the structure of the following formula (I): （I） Where R is C 11 -C 23 The hydrocarbon group, and j is a positive integer, such as 1, 2, 3 or 4.

2. The CO2-responsive surfactant according to claim 1, wherein the hydrocarbon group is saturated or unsaturated, for example, the hydrocarbon group contains 1, 2, 3 or 4 unsaturated bonds, the unsaturated bonds being, for example, C=C double bonds.

3. The CO2-responsive surfactant according to claim 1 or 2, wherein R is selected from undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl, tridecyl, 9-pentadecanyl, 11-heptadecyl, 9-nonadecanyl, 11-nonadecanyl, 9,12-heptadecadienyl, 6,9,12-heptadectrienyl, 9,12,15-heptadectrienyl, 5,8,11,14-nonadecantetraenyl, 9-heptadecyl and 13-teicosyl, preferably R is selected from 9-heptadecyl, 13-teicosyl, pentadecyl, heptadecyl and dodecyl.

4. The CO2-responsive surfactant according to any one of claims 1 to 3, wherein the CO2-responsive surfactant is selected from oleamide ethylimidazol, erucamide ethylimidazol, palmitamide ethylimidazol, stearamide ethylimidazol, behenamide ethylimidazol, oleamide propylimidazol, erucamide propylimidazol, palmitamide propylimidazol, stearamide propylimidazol, behenamide propylimidazol, oleamide butylimidazol, erucamide butylimidazol, palmitamide butylimidazol, stearamide butylimidazol, and behenamide butylimidazol, preferably, the CO2-responsive surfactant is oleamide propylimidazol or erucamide propylimidazol.

5. A method for preparing a CO2-responsive surfactant according to any one of claims 1 to 4, comprising: The CO2-responsive surfactant is obtained by reacting R-COCl with an aminoimidazolium of formula X. （X） Where R and j are the same as those defined in claims 1 to 4.

6. The method of claim 5, further comprising: R-COOH is reacted with an acyl chloride reagent to obtain R-COCl, specifically the acyl chloride reagent selected from oxalyl chloride, thionyl chloride, phosphorus trichloride, phosphorus pentachloride and phosgene.

7. A fracturing fluid composition comprising: The CO2-responsive surfactant according to any one of claims 1 to 4.

8. The fracturing fluid composition according to claim 7, further comprising anionic aromatic surfactants, specifically selected from salicylic acid and its salts, benzoic acid and its salts, benzenesulfonic acid and its salts, p-toluenesulfonic acid and its salts, p-styrenesulfonic acid and its salts, and p-hydroxybenzenesulfonic acid and its salts.

9. The fracturing fluid composition according to claim 7 or 8, further comprising a stabilizer, specifically selected from potassium salts, sodium salts, and ammonium salts.

10. The fracturing fluid composition according to claim 8 or 9, wherein the weight ratio of the CO2-responsive surfactant to the anionic aromatic surfactant is 1:1 to 4:

1.

11. The fracturing fluid composition according to any one of claims 7 to 10, further comprising CO2, Specifically, 1) CO2 gas is introduced into the fracturing fluid composition without CO2 under ambient pressure to form a gel, or 2) CO2 in a supercritical state is mixed with the fracturing fluid composition without CO2 under pressurized conditions to form a foam, wherein the fracturing fluid composition obtained in scheme 2) has a liquid volume ratio of 20 to 40% and a gas volume ratio of 60 to 80%.

12. A fracturing method, comprising: Provide the fracturing fluid composition according to any one of claims 7 to 11 to the location to be fracturing.

13. The fracturing method according to claim 12, further comprising: After the fracturing fluid composition is provided, CO2 gas is introduced into the location to be fracturing to gel, wherein the fracturing fluid composition is the fracturing fluid composition according to any one of claims 7 to 10.

14. The fracturing method according to claim 12 or 13, further comprising: Inert gas is introduced into the location to be fracturing to break up the gel.

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