Double CO2 response type nanoparticle reinforced foam system as well as preparation method and application thereof

Abstract

The invention relates to a double CO2 response type nanoparticle reinforced foam system as well as a preparation method and application thereof. The foam system is composed of a CO2 response type surfactant, CO2 response type nanoparticles and water. According to the invention, a dual CO2 response mechanism of CO2 response type nanoparticles and a CO2 response type surfactant is utilized, and a dual CO2 response type nanoparticle reinforced foam system is creatively prepared. The system is sensitive to CO2 response, has the characteristics of stable and clean foam, reusability and the like, not only solves the technical defects of reservoir pollution and the like caused by poor foam stability, low cyclic utilization rate and difficulty in defoaming in oil and gas field exploitation work, but also is beneficial to efficient utilization and storage of CO2. The double CO2 response type nanoparticle reinforced foam system can be used in the fields of fracturing, chemical oil displacement and the like in the oil and gas field development engineering technology.

Description

Technical Field

[0001] This invention relates to a dual CO2-responsive nanoparticle-reinforced foam system, its preparation method, and its application, belonging to the field of oil and gas field development engineering technology. Background Technology

[0003] CO2-EOR (CO2-enhanced oil recovery) can effectively exploit unconventional oil and gas resources and is a crucial technology for CO2 capture, utilization, and storage (CCUS) in oil and gas field development. It not only utilizes CO2 to displace dissolved gases and increase the volume of crude oil, thereby reducing surface tension and improving fluidity to enhance oil and gas reservoir recovery, but also stores CO2 underground. However, current methods of using CO2 solely for fracturing or oil displacement are prone to gas channeling, and the low viscosity of the system often limits its application due to reservoir geological conditions. As a vital component of CO2-EOR, CO2 foam, with its unique property of liquid-encapsulated gas phase, low water consumption (typically less than 30%), and high viscosity, can effectively control gas channeling and reduce viscous fingering. This makes it suitable for many low-pressure, low-permeability, and water-sensitive reservoirs. Therefore, the research and application of CO2 foam systems are of great significance for the development of unconventional oil and gas resources and the application of CCUS in oil and gas field development.

[0004] CO2 foam systems generally consist of foaming agents and thickeners. Foaming agents are often single or compounded surfactants of different types, while thickeners are mostly polymers, such as guar gum and polyacrylamide. Although they can provide the system with high viscosity, resulting in stable foam, these thickeners can cause negative problems. First, insoluble residues generated by thickeners during oil displacement or fracturing can reduce utilization, contaminate formation water, and clog pores. Second, foam is sometimes difficult to eliminate during flowback, and the addition of defoamers can also contaminate the formation and increase costs. Finally, at certain temperatures (mostly 70°C), the stability of the foam decreases sharply during application, leading to reduced construction effectiveness. Therefore, a new type of CO2 foam system is urgently needed that can form stable foam while reducing damage to the formation and improving its own defoaming ability, thus solving the above difficulties.

[0005] Patent document CN114456792A (application number 202210086909.8) discloses a method for preparing a responsive particle-reinforced foam system for oil and gas development, and conducts some application evaluation tests. This method mainly involves compounding nanoparticles with a CO2-responsive surfactant, N-dodecyl-N,N-dimethyl tertiary amine, to form a CO2-responsive foam system. This system can form foam upon the introduction of CO2 and defoam upon the introduction of nitrogen or air, exhibiting a certain degree of CO2 responsiveness. This method can solve the problems of low utilization rate, formation contamination, and difficulty in defoaming associated with traditional CO2 foam systems. However, the foam formed by this system is difficult to adapt to fracturing reservoirs above 70°C, indicating poor foam stability and insufficient CO2 responsiveness, thus limiting its application conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a dual CO2-responsive nanoparticle-reinforced foam system, its preparation method, and its applications.

[0007] The enhanced foam system of this invention utilizes CO2-responsive surfactants and CO2-responsive nanoparticles. The CO2-responsive surfactants become cationic surfactants upon contact with CO2, further forming micelles. The CO2-responsive nanoparticles expand and aggregate upon contact with CO2 to generate foam and make it more stable, allowing it to penetrate into cracks or pores that traditional foams cannot reach. This enhances the fracturing, plugging, and oil displacement properties of the foam system, achieving dual CO2 response.

[0008] The foam system of this invention can be used as a working fluid for CO2 foam fracturing, CO2 foam flooding, and CO2 sealing. It not only solves the problems of traditional CO2 foam systems, such as the easy contamination of the formation by thickeners and the difficulty in eliminating foam during flowback, but is also suitable for reservoirs with a formation temperature of 90°C. Furthermore, this system allows for foam reuse by introducing CO2 gas / inert gas, exhibiting sensitive CO2 responsiveness.

[0009] This invention is achieved through the following technical solution:

[0010] A dual CO2-responsive nanoparticle-reinforced foam system is composed of the following raw materials by mass percentage:

[0011] 0.01-1.2% CO2-responsive surfactant, 1.0-1.2% CO2-responsive nanoparticles, balance water, calculated as 100%.

[0012] According to a preferred embodiment of the present invention, the CO2-responsive surfactant is a tertiary amine surfactant.

[0013] Tertiary amine surfactants are long-chain amphiphilic nonionic surfactants with a tertiary amine head group and an amide functional group. The presence of these two functional groups makes the surfactants highly responsive to CO2, resulting in good foaming and thickening properties.

[0014] According to a preferred embodiment of the present invention, the CO2-responsive surfactant is selected from any one or a mixture of two or more of palmitamide propyl dimethylamine, stearamide propyl dimethylamine, oleamide propyl dimethylamine, and erucamide propyl dimethylamine.

[0015] According to a preferred embodiment of the present invention, the inert gas used in the dual CO2-responsive nanoparticle-reinforced foam system is nitrogen or air.

[0016] This invention utilizes the unique properties of tertiary amine surfactants to generate and stabilize bubbles. Firstly, the surfactants themselves possess high surface activity; upon contact with CO2 in water, tertiary amine surfactants form cationic bicarbonate, and the hydrophobic and electrostatic interactions between the hydrocarbon chains contribute to their excellent foaming ability. Secondly, at specific concentrations, upon contact with CO2 in water, tertiary amine surfactants can form worm-like micelles that entangle, increasing the solution viscosity and improving foam stability. Upon introduction of an inert gas, the cationic bicarbonate surfactant transforms into a tertiary amine, decreasing surface activity and weakening the entanglement of the worm-like micelles, causing the foam to disappear and break. This achieves a reversible CO2-responsive process, improving the utilization rate of the dual CO2-responsive nanoparticle-reinforced foam system while mitigating contaminated formations and defoaming.

[0017] According to a preferred embodiment of the present invention, the CO2-responsive nanoparticles are prepared from the following raw materials in the indicated mass percentages:

[0018] 10-20% CO2-responsive component, 3-8% emulsifier, 1-5% stabilizer, 0.5-5% crosslinking agent, 3-10% initiator, balance water, calculated as 100%.

[0019] According to a preferred embodiment of the present invention, the CO2-responsive component is diethylaminoethyl methacrylate.

[0020] According to a preferred embodiment of the present invention, the emulsifier is polysorbate 80.

[0021] According to a preferred embodiment of the present invention, the stabilizer is polyethylene glycol monomethyl ether methacrylate.

[0022] According to a preferred embodiment of the present invention, the crosslinking agent is divinylbenzene.

[0023] According to a preferred embodiment of the present invention, the initiator is ammonium persulfate.

[0024] According to a preferred embodiment of the present invention, the CO2-responsive nanoparticles are prepared by the following method:

[0025] (1) According to the mass percentage of the raw materials, add the CO2 response component, emulsifier, crosslinking agent, stabilizer and water into a three-necked flask and stir evenly. After stirring, freeze the flask.

[0026] (2) Evacuate the inside of the three-necked flask and introduce N2 to expel the air, melt the raw materials, and repeat 1-5 times;

[0027] (3) Stir the liquid after melting and recycling in step (2), add an initiator, and obtain the product;

[0028] (4) Dialyze the product obtained in step (3) in deionized water, and dry it after dialysis to obtain CO2-responsive nanoparticles.

[0029] According to a preferred embodiment of the present invention, in step (1), the freezing is performed using liquid nitrogen.

[0030] According to a preferred embodiment of the present invention, in step (2), the vacuuming is performed using a vacuum pump, and the melting is performed in a constant temperature water bath at 65-75°C for 8-15 minutes.

[0031] According to a preferred embodiment of the present invention, in step (3), the stirring time is 8-15 hours and the stirring speed is 200-400 r / min.

[0032] According to a preferred embodiment of the present invention, in step (4), dialysis is performed using a dialysis bag, the water is deionized water, the water is changed every 6 hours, and the dialysis time is two days.

[0033] The CO2-responsive nanoparticles prepared by this invention are responsive to CO2. After contact with CO2 gas, the particle size of the CO2-responsive nanoparticles increases, resulting in a swelling effect. This enables expansion and flow regulation in matrix pores that traditional foam cannot penetrate, allowing them to accumulate in the fracture matrix and achieve a CO2 sealing and channeling effect. The increased surface energy also enables the CO2-responsive nanoparticles to synergistically stabilize the foam while replacing the thickener of traditional CO2 foam fracturing fluid, thus reducing formation pollution and damage.

[0034] The present invention also provides a method for preparing the above-mentioned dual CO2 responsive nanoparticle reinforced foam system.

[0035] The preparation method of the above-mentioned dual CO2-responsive nanoparticle-reinforced foam system includes the following steps:

[0036] 1) Take CO2-responsive nanoparticles and water according to the mass percentage of the raw materials, add the CO2-responsive nanoparticles to the water and stir evenly to obtain a CO2-responsive nanoparticle solution, and disperse the solution evenly.

[0037] 2) Add the CO2-responsive surfactant to the CO2-responsive nanoparticle solution prepared in step 1) by mass percentage;

[0038] 3) Introduce CO2 gas into the solution from step 2) and stir the solution to obtain nanoparticle-enhanced CO2-responsive foam fracturing fluid.

[0039] According to a preferred embodiment of the present invention, in step 1), the dispersion is performed by ultrasonic treatment at an ultrasonic frequency of 10-30 kHz for 8-15 minutes.

[0040] According to a preferred embodiment of the present invention, in step 3), the flow rate of CO2 gas introduced is 10-30 mL / min, and the introduction time is 1-8 min.

[0041] According to a preferred embodiment of the present invention, in step 3), the stirring process uses a warping blender, the stirring speed is 3000-5000 r / min, and the stirring time is 1-6 min.

[0042] Introducing an inert gas into a dual CO2-responsive nanoparticle-reinforced foam system that has already been infused with CO2 gas can eliminate foam and reduce viscosity. Introducing CO2 gas into the dual CO2-responsive nanoparticle-reinforced foam system that has already been infused with inert gas can enable reuse and increase viscosity.

[0043] Tertiary amine surfactants react with CO2 in water to form bicarbonates, i.e., cationic surfactants. A concentration of 0.01-1.2% of cationic surfactants not only induces foaming but also generates worm-like micelles to stabilize the foam. The introduction of CO2-responsive nanoparticles further enhances foam stability by increasing lamellar viscosity. Furthermore, the nanoparticles adsorb at the water-air interface of the foam, enhancing the elastic modulus of the foam film. The dual CO2-responsive mechanism of tertiary amine surfactants and CO2-responsive nanoparticles makes the fracturing fluid system more sensitive to CO2. Simultaneously, the co-adsorption of tertiary amine surfactants and CO2-responsive nanoparticles on the liquid film surface synergistically stabilizes the foam.

[0044] Technical features and beneficial effects of the present invention:

[0045] 1. This invention creatively prepares a dual CO2-responsive nanoparticle-reinforced foam system by utilizing the dual CO2-responsive mechanism of CO2-responsive nanoparticles and CO2-responsive surfactants. This foam system is highly responsive to CO2 and features stable, clean, and reusable foam. When using the dual CO2-responsive nanoparticle-reinforced foam system of this invention, a large amount of foam can be obtained simply by introducing CO2 gas and stirring, and the viscosity of the fracturing fluid is greatly increased; while defoaming and viscosity reduction can be achieved by introducing an inert gas, a simple and thorough method that allows the dual CO2-responsive nanoparticle-reinforced foam to eliminate foam during the flowback process.

[0046] 2. Tertiary amine surfactants and CO2-responsive nanoparticles can synergistically stabilize foam. Tertiary amine surfactants react with CO2 in water to form cationic surfactants, greatly increasing the surface activity of the solution and generating foam. A 1.2% concentration of surfactant can further stabilize the foam by forming worm-like micelles. Nanoparticles can adsorb at the water-air interface of the foam, enhancing the elastic modulus of the foam liquid film. The co-adsorption of tertiary amine surfactants and CO2-responsive nanoparticles on the liquid film surface further stabilizes the foam.

[0047] 3. The dual CO2-responsive nanoparticle-reinforced foam system of the present invention has good reproducible CO2 response. 2 / The solution exhibits inert gas responsiveness; its viscosity increases after 3 minutes of CO2 gas introduction into a solution composed of tertiary amine surfactants and CO2-responsive nanoparticles. Even after four introductions of either CO2 or inert gas, the nanoparticle-reinforced CO2-responsive foam fracturing fluid maintains a stable foaming volume and foam half-life.

[0048] 4. The dual-CO2 responsive nanoparticle-reinforced foam system for fracturing of this invention possesses certain application capabilities under medium- and high-temperature conditions. The experimental test results of the foaming performance, static proppant carrying capacity, and temperature and shear resistance of the dual-CO2 responsive nanoparticle-reinforced foam system for fracturing at 90℃ still meet the construction standards. At 90℃, the foaming volume of 100mL of the dual-CO2 responsive nanoparticle-reinforced foam system is 290mL, and the foam half-life is 78min; when the proppant is 20-40 mesh ceramsite and the sand ratio is 10%, the settling time of the proppant in the dual-CO2 responsive nanoparticle-reinforced foam fracturing fluid is 50min. At a shear rate of 100s... -1 Under these conditions, after a shear test lasting 5400 s, the viscosity of the dual CO2-responsive nanoparticle-reinforced foam system remained above 28 mPa·s. The dual CO2-responsive nanoparticle-reinforced foam system of this invention, applicable to oil displacement, showed an increased final recovery rate of 54% after core displacement experiments. Attached Figure Description

[0049] Figure 1 A roadmap for the preparation of CO2-responsive nanoparticles for a dual CO2-responsive nanoparticle-reinforced foam system;

[0050] Figure 2 The infrared spectrum of the CO2-responsive nanoparticles prepared in Example 1 is shown below.

[0051] Figure 3 The graph shows the particle size change of the CO2-responsive nanoparticles prepared in Example 1 after alternating introduction of CO2 gas and inert gas.

[0052] Figure 4 The changes in foam volume and foam half-life of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 at different temperatures;

[0053] Figure 5 The changes in foam volume and foam half-life of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 after alternating introduction of CO2 gas and inert gas;

[0054] Figure 6 The changes in the state of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 before and after alternating introduction of CO2 gas and inert gas;

[0055] Figure 7 The viscosity change of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 after alternating introduction of CO2 gas and inert gas;

[0056] Figure 8 The image shows the change of foam suspension over time in the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 at 90°C. The proppant is 20-40 mesh ceramsite, and the sand ratio is 10%. Figure 8 (a)(b)(c)(d)(e) are records of changes after every ten minutes;

[0057] Figure 9 The viscosity of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 2 under shear conditions at 90°C changes over time.

[0058] Figure 10 The data curves are from the core flooding experiment of the dual CO2-responsive nanoparticle-reinforced foam system used in Example 3. Detailed Implementation

[0059] The present invention will now be described in detail and completely with reference to the embodiments. However, these embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0060] Unless otherwise stated, all percentages in the following examples are mass percentages based on the total weight of the nanoparticle-reinforced CO2-responsive foam fracturing fluid.

[0061] Unless otherwise stated, the raw materials for preparing the tertiary amine surfactant and CO2-responsive nanoparticles in the embodiments of this application were all purchased commercially.

[0062] Example 1

[0063] The preparation method of CO2-responsive nanoparticles includes the following steps:

[0064] Step (1): Add 14g of CO2 response component diethylaminoethyl methacrylate, 4g of emulsifier polysorbate 80, 2g of stabilizer polyethylene glycol monomethyl ether methacrylate and 1g of crosslinking agent divinylbenzene to a three-necked flask containing 75g of deionized water. Place the three-necked flask in a constant temperature water bath and stir the mixture evenly.

[0065] Step (2): Freeze the three-necked flask after stirring with liquid nitrogen; after a period of time, use a vacuum pump to evacuate the inside of the three-necked flask and introduce N2 gas to expel the air.

[0066] Step (3): Place the three-necked flask in a constant temperature water bath for 10 minutes at a temperature of 70°C, and repeat the melting process twice.

[0067] Step (4): Stir the liquid in the three-necked flask and add ammonium persulfate as an initiator to obtain the product. Place the product in a dialysis bag and dialyze it in deionized water, changing the water every 6 hours for two days. After dialysis, dry the product to obtain CO2-responsive nanoparticle powder.

[0068] The CO2-responsive nanoparticles were analyzed using infrared spectroscopy, such as... Figure 2 As shown, Figure 2 The infrared spectrum of CO2-responsive nanoparticles is shown at 1100 cm⁻¹. -1 The stretching vibration of COC at this point indicates the retention of the feed chain, while at 1250-1150cm... -1 The asymmetric stretching vibration peak at COC at 1720 cm⁻¹ indicates the formation of the ester group, while the peak at 1720 cm⁻¹... -1 The stretching vibrations of the carbon-oxygen double bond at the point also indicate the success of the esterification reaction, and the presence of these stretching vibration peaks proves the successful synthesis of CO2-responsive nanoparticles.

[0069] The prepared CO2-responsive nanoparticles were configured into a 0.1% (w / w) CO2-responsive nanoparticle dispersion. After passing CO2 or an inert gas through the dispersion, the particle size was measured, and the results are as follows: Figure 3 As shown. Figure 3 The results show that under alkaline conditions in an inert gas environment, the particle dispersion is stable and conducive to injection. However, under acidic conditions, i.e., after the introduction of CO2, the particle size expands from about 42 nm to about 236 nm. This helps stabilize the foam and facilitates the foam to enter micropores or cracks, thereby enhancing the system's fracturing, plugging, and oil displacement capabilities.

[0070] Example 2

[0071] The preparation method of the dual CO2-responsive nanoparticle-reinforced foam system includes the following specific steps:

[0072] (1) Weigh 0.5g of CO2-responsive nanoparticle powder prepared in Example 1, add it to a beaker containing 98.3g of water while stirring, stir at room temperature for 10 minutes, and after stirring, put the CO2-responsive nanoparticle solution into an ultrasonic processor, set it to 20kHz and ultrasonically disperse the solution for 10 minutes.

[0073] (2) Weigh 1.2g of erucamide propyl dimethylamine and add it to the ultrasonically prepared CO2-responsive nanoparticle solution and stir to obtain a compound solution. After the compound solution is stirred evenly, let it stand in an oven at the required measurement temperature for 60 minutes.

[0074] (3) Pour the compound solution from step (2) into the waring blender, introduce CO2 gas into the compound solution at a flow rate of 20 mL / min to make it in a CO2 environment, seal and start the waring blender, adjust the speed to 4000 r / min, and stir for 3 min.

[0075] (4) Pour the mixture in the warning blender into a container such as a measuring cylinder to obtain a dual CO2-responsive nanoparticle reinforced foam system suitable for fracturing.

[0076] Experimental Example 1:

[0077] To better illustrate the application effect of the dual CO2-responsive nanoparticle-reinforced foam system of the present invention as a fracturing fluid, the following research was conducted:

[0078] 1. Foaming performance experiment at different temperatures

[0079] The dual-CO2 responsive nanoparticle-reinforced foam system prepared in Example 2 was quickly poured into a 500mL graduated cylinder. The height of the graduated cylinder mark at this point was recorded as the foam volume of the dual-CO2 responsive nanoparticle-reinforced foam system, i.e., the foaming volume. After recording, the dual-CO2 responsive nanoparticle-reinforced foam system in the graduated cylinder was quickly poured into a pressure-resistant bottle and sealed. The pressure-resistant bottle was placed in an oven at the required measurement temperature, and a stopwatch was started. The timing was stopped when the foaming volume of the dual-CO2 responsive nanoparticle-reinforced foam system reached the 50mL volume mark of the pressure-resistant bottle, which was measured and marked beforehand. This time was the time required for 100mL of the dual-CO2 responsive nanoparticle-reinforced foam system to precipitate 50mL of foam, which is the foam half-life of the dual-CO2 responsive nanoparticle-reinforced foam system. The experimental results of the foaming performance of the dual-CO2 responsive nanoparticle-reinforced foam system at different temperatures are as follows. Figure 4 As shown. From Figure 4 It can be seen that the foaming performance of the dual CO2-responsive nanoparticle-reinforced foam system is good from 30℃ to 90℃. At 90℃, its foaming performance is 290mL, and the foam half-life is 78min, indicating that the foam quality of the dual CO2-responsive nanoparticle-reinforced foam system is good.

[0080] 2. Foaming / defoaming experiment with alternating introduction of CO2 gas and inert gas.

[0081] The procedure is as follows: Pour the dual CO2-responsive nanoparticle-reinforced foam system prepared in Example 2 into a waring blender. Inert gas is introduced into the system at a flow rate of 30 mL / min to immerse it in an inert gas environment. Seal and start the waring blender, adjusting the speed to 4000 rpm. After stirring for 3 minutes, pour the mixture from the blender into a graduated cylinder and observe and record the foam volume. After recording, pour the mixture back into the blender and introduce CO2 gas at a flow rate of 20 mL / min to immerse it in a CO2 environment. Finally, seal and start the waring blender, adjusting the speed to 4000 rpm. After stirring for 3 minutes, pour the dual CO2-responsive nanoparticle-reinforced foam system from the blender into a graduated cylinder. While observing the foam volume, start a stopwatch. Stop the stopwatch when 50 mL of the dual CO2-responsive nanoparticle-reinforced foam system has precipitated; this time is the foam half-life. Repeat the entire experimental process four times in alternating cycles at an experimental temperature of 30°C. Experimental results are as follows Figure 5 As shown, after introducing inert gas, the foam volume of the dual CO2-responsive nanoparticle-reinforced foam system decreased from the original 395 mL to about 145 mL.

[0082] Figure 6 The image shows a before-and-after comparison of the appearance of the dual-CO2 responsive nanoparticle reinforced foam fracturing fluid after CO2 is introduced and stirred, and the dual-CO2 responsive nanoparticle reinforced foam system after inert gas is introduced and stirred. As can be seen from the image, after inert gas is introduced, the foam in the dual-CO2 responsive nanoparticle reinforced foam system is basically eliminated, and the foam is difficult to observe with the naked eye.

[0083] 3. Viscosity test experiment with alternating introduction of CO2 gas / inert gas

[0084] The operating method is as follows: The dual CO2-responsive nanoparticle-reinforced foam system prepared in Example 2 is poured into the graduated cylinder of the Hakke Mars 60 high-temperature and high-pressure rheometer. A CC41 Ti rotor is selected to connect to the rheometer system. A pre-set program is used to perform a constant shear test on the dual CO2-responsive nanoparticle-reinforced foam system. The test time is 600 s, with data collected every 10 s, and the shear rate is 100 s². -1 The test temperature was 30℃. After the test, the average of 60 data points was taken and recorded, which is the apparent viscosity of the dual CO2-responsive nanoparticle-reinforced foam system at 30℃. Subsequently, the defoaming experiment in Example 3 was performed on the dual CO2-responsive nanoparticle-reinforced foam system after the test. After introducing inert gas and stirring, the mixture was poured into the graduated cylinder of the Hakke Mars 60 high-temperature and high-pressure rheometer. A CC41 Ti rotor was used to connect to the rheometer system, and viscosity was tested under the same conditions as the dual CO2-responsive nanoparticle-reinforced foam system. The entire experimental process was repeated four times. The results are as follows: Figure 7 As shown, after the introduction of inert gas, the viscosity of the dual CO2-responsive nanoparticle-reinforced foam system decreased from 196 mPa·s to about 17 mPa·s. After the introduction of CO2 gas and stirring, the viscosity returned to 196 mPa·s, indicating that the dual CO2-responsive nanoparticle-reinforced foam system has good repeatable CO2 / inert gas responsiveness.

[0085] 4. Static sand-carrying performance test experiment

[0086] The operating method is as follows: The dual CO2-responsive nanoparticle-reinforced foam system prepared in Example 2 and the proppant are poured into a warping blender. The blender is sealed and started. The speed is adjusted to 4000 r / min, and after stirring for 3 minutes, the mixture is poured into a 500 mL graduated cylinder. The cylinder is placed in a 90℃ oven and a timer is started. The cylinder's changes are recorded by taking a picture every 10 minutes. The proppant is 20-40 mesh ceramsite, and the sand ratio is 10%. The results are as follows: Figure 8As shown in the figure. It took 50 minutes for the proppant in the dual-CO₂-responsive nanoparticle enhanced foam system to completely sink to the bottom of the graduated cylinder, indicating that the dual-CO₂-responsive nanoparticle enhanced foam system has good sand-carrying capacity at 90°C.

[0087] 5. Temperature and shear resistance performance test experiment

[0088] The operation method is as follows: Pour the dual-CO₂-responsive nanoparticle enhanced foam system prepared in Example 2 into a high-temperature and high-pressure reaction kettle equipped with a Hakke Mars 60 high-temperature and high-pressure rheometer. Select the PZ 38HA rotor to connect to the rheometer system, and select the pre-set program to conduct the temperature and shear resistance test on the dual-CO₂-responsive nanoparticle enhanced foam system. The test time is 5400 s, and the shear rate is 170 s -1 , and the final test temperature is 90°C. The test results are as Figure 9 shown. As the temperature increases and shear progresses, the viscosity of the dual-CO₂-responsive nanoparticle enhanced foam system finally stabilizes above 28 mPa·s, which can meet some reservoirs for medium-high temperature fracturing construction.

[0089] Example 3

[0090] The preparation method of the dual-CO₂-responsive nanoparticle enhanced foam system is as follows:

[0091] (1). Weigh 0.5 grams of CO₂-responsive nanoparticle powder, add it to a beaker containing 99.1 grams of water under stirring, stir at room temperature for 10 minutes. After stirring, put the CO₂-responsive nanoparticle solution into an ultrasonic processor, adjust it to 20 kHz, and ultrasonically disperse the solution for 10 minutes;

[0092] (2). Weigh 0.6 grams of palmitamidopropyl dimethylamine, add it to the ultrasonically treated CO₂-responsive nanoparticle solution and stir to obtain a compound solution. After the compound solution is stirred evenly, let it stand in an oven at the required measurement temperature for 60 minutes;

[0093] (3). Pour the compound solution into a waring blender, and introduce CO₂ gas into the compound solution at a flow rate of 20 mL / min to make it in a CO₂ environment. Finally, seal and start the waring blender, adjust the rotation speed to 4000 r / min, and stir for 2 min;

[0094] (4). Pour the mixture in the waring blender into a graduated cylinder and other containers to prepare a dual-CO₂-responsive nanoparticle enhanced foam system suitable for oil displacement.

[0095] Experimental Example 2:

[0096] To better illustrate the application effect of the dual CO2-responsive nanoparticle-reinforced foam system of the present invention as an oil displacement fluid, the following research was conducted:

[0097] Oil displacement performance test experiment

[0098] The operating procedure is as follows: The main experimental setup consists of an ISCO pump and a core holder. The crude oil used in the experiment had a viscosity of 1.38 mPa·s and a density of 0.841 g / cm³ under surface conditions. 3 The porosity and permeability of the experimental core were measured using a porosimeter with nitrogen gas. The core permeability was 2.28 mD, and the porosity was 13.26%. The dry weight of the dried core was weighed, and after vacuum saturation with simulated water, the wet weight was measured and the pore volume (PV) was calculated. The core was saturated with crude oil at 90℃ until bound water saturation was reached, and the pore volume was calculated. First, the outlet backpressure valve pressure of the ISCO pump was set, and CO2 was injected at a certain flow rate until no oil was produced in the core. Then, the dual CO2-responsive nanoparticle-reinforced foam system prepared in Example 3 was injected into the core at a certain flow rate until no oil was produced. Finally, formation water was injected, and other conditions remained unchanged throughout the experiment. After the experiments with both oil displacement methods, the oil production, water production, and pressure were recorded, and the recovery rate was calculated. The results are as follows: Figure 10 As shown, the subsequent recovery rate of the dual-CO2 responsive nanoparticle-enhanced foam flooding reached 54%, indicating that the foam system has moderate viscosity, effectively blocking the flow channels mainly composed of micro-fractures, and can guide subsequent fluids to enter the low-permeability portion of the core, significantly improving the oil recovery rate. This demonstrates that the dual-CO2 responsive nanoparticle-enhanced foam system possesses certain oil displacement and plugging capabilities in low-permeability oil and gas reservoirs.

[0099] Comparative Example 1

[0100] The preparation method of the dual CO2-responsive nanoparticle-reinforced foam system is as follows:

[0101] (1) Weigh 1g of CO2-responsive nanoparticle powder and add it to a beaker containing 97.8g of water while stirring. Stir at room temperature for 10 minutes. After stirring, put the CO2-responsive nanoparticle solution prepared in Example 1 into an ultrasonic processor and set it to 20kHz to ultrasonically disperse the solution for 10 minutes.

[0102] (2) Pour the solution into the waring blender, introduce CO2 gas into the solution at a flow rate of 20 mL / min to make it in a CO2 environment, seal and start the waring blender, adjust the speed to 4000 r / min, and stir for 3 min;

[0103] (3) Pour the mixture in the warning blender into a container such as a measuring cylinder to obtain a dual CO2-responsive nanoparticle reinforced foam system suitable for fracturing.

[0104] This comparative example did not include a CO2-responsive surfactant, and the nanoparticle solution alone was difficult to foam.

[0105] Comparative Example 2

[0106] The preparation method of the dual CO2-responsive nanoparticle-reinforced foam system is as follows:

[0107] Weigh 1.2 g of erucamide propyl dimethylamine and add it to 98.8 g of deionized water. Pass CO2 gas through the mixture at a flow rate of 20 mL / min, seal the container, and start the warning blender. Adjust the speed to 4000 r / min and stir for 3 min. Transfer the mixture to a measuring cylinder or other container to obtain a CO2-responsive foam system suitable for fracturing.

[0108] Experimental Example 3

[0109] The foaming performance of Comparative Example 2 was tested at different temperatures and compared with the dual CO2-responsive nanoparticle-reinforced foam system in Example 1. The experimental results are shown in Table 1 below:

[0110] Table 1

[0111]

[0112] As can be seen from Table 1, in Comparative Example 2 without the addition of CO2-responsive nanoparticles, the foam volume of the CO2-responsive foam system at different temperatures is slightly larger than that of the double CO2-responsive nanoparticle-reinforced foam system. However, its foam half-life is greatly reduced, even by as much as five times at 90℃, indicating that the CO2-responsive nanoparticles have excellent foam stabilization performance.

[0113] Therefore, CO2-responsive nanoparticles and CO2-responsive surfactants are key to obtaining stable foam volume and foam half-life, and neither can be omitted.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual CO2-responsive nanoparticle-reinforced foam system, composed of the following raw materials by mass percentage: 0.01-1.2% CO2-responsive surfactant, 1.0-1.2% CO2-responsive nanoparticles, balance water, calculated as 100%.

2. The dual CO2-responsive nanoparticle-reinforced foam system according to claim 1, characterized in that, The CO2-responsive surfactant is a tertiary amine surfactant, and the CO2-responsive surfactant is selected from any one or a mixture of two or more of palmitamide propyl dimethylamine, stearamide propyl dimethylamine, oleamide propyl dimethylamine, and erucamide propyl dimethylamine.

3. The dual CO2-responsive nanoparticle-reinforced foam system according to claim 1, characterized in that, The inert gas used in the dual CO2-responsive nanoparticle-reinforced foam system is nitrogen or air.

4. The dual CO2-responsive nanoparticle-reinforced foam system according to claim 1, characterized in that, The CO2-responsive nanoparticles are prepared from the following raw materials in the indicated mass percentages: 10-20% CO2-responsive component, 3-8% emulsifier, 1-5% stabilizer, 0.5-5% crosslinking agent, 3-10% initiator, balance water, calculated as 100%; The CO2-responsive component is diethylaminoethyl methacrylate, the emulsifier is polysorbate 80, the stabilizer is polyethylene glycol monomethyl ether methacrylate, the crosslinking agent is divinylbenzene, and the initiator is ammonium persulfate.

5. The dual CO2-responsive nanoparticle-reinforced foam system according to claim 1, characterized in that, The CO2-responsive nanoparticles were prepared by the following method: (1) According to the mass percentage of the raw materials, add the CO2 response component, emulsifier, crosslinking agent, stabilizer and water into a three-necked flask and stir evenly. After stirring, freeze the flask. (2) Evacuate the inside of the three-necked flask and introduce N2 to expel the air, melt the raw materials, and repeat 1-5 times; (3) Stir the liquid after melting and recycling in step (2), add an initiator, and obtain the product; (4) Dialyze the product obtained in step (3) in deionized water, and dry it after dialysis to obtain CO2-responsive nanoparticles.

6. The dual CO2-responsive nanoparticle-reinforced foam system according to claim 5, characterized in that, In step (1), the freezing is performed using liquid nitrogen. In step (2), the vacuuming is performed using a vacuum pump. The melting is performed in a constant temperature water bath at 65-75℃ for 8-15 minutes. In step (3), the stirring time is 8-15 hours and the stirring speed is 200-400 r / min. In step (4), the dialysis is performed using a dialysis bag and deionized water. The water is changed every 6 hours and the dialysis time is two days.

7. The preparation method of the dual CO2-responsive nanoparticle-reinforced foam system according to claim 1, comprising the following steps: 1) Take CO2-responsive nanoparticles and water according to the mass percentage of the raw materials, add the CO2-responsive nanoparticles to the water and stir evenly to obtain a CO2-responsive nanoparticle solution, and disperse the solution evenly. 2) Add the CO2-responsive surfactant to the CO2-responsive nanoparticle solution prepared in step 1) by mass percentage; 3) Introduce CO2 gas into the solution from step 2) and stir the solution to obtain nanoparticle-enhanced CO2-responsive foam fracturing fluid.

8. The preparation method according to claim 7, characterized in that, In step 1), the dispersion is achieved by ultrasonic treatment at an ultrasonic frequency of 10-30 kHz for 8-15 minutes.

9. The preparation method according to claim 7, characterized in that, In step 3), the flow rate of CO2 gas is 10-30 mL / min, and the introduction time is 1-8 min.

10. The preparation method according to claim 7, characterized in that, In step 3), the stirring process uses a warping blender with a stirring speed of 3000-5000 r / min and a stirring time of 1-6 min.

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