CO2 reinforced micro-foam oil displacement system and preparation method, device and application thereof

Abstract

The invention belongs to the technical field of CO2 oil displacement, and particularly relates to a CO2 reinforced micro-foam oil displacement system and a preparation method, device and application thereof. The CO2 reinforced micro-foam oil displacement system is mainly generated by CO2 and reinforced foam base fluid in a micro-foam generator according to a certain proportion; wherein the reinforced foam base solution is composed of a temperature-resistant and salt-resistant surfactant, an inorganic cross-linking agent, an organic cross-linking agent and a polymer mother solution; wherein the polymer mother liquor is prepared by diluting polyacrylamide and simulated formation water into different concentrations. The average diameter of micro-foam in the CO2 reinforced micro-foam oil displacement system is 10-50 microns, the micro-foam is continuously generated and is good in uniformity, a foam liquid film is thick, a single bubble is spherical, the variation factor is 10%-30%, and a curve formed by connecting three surfaces does not exist.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 oil recovery, and in particular relates to a CO2 enhanced micro foam oil recovery system and a preparation method, a device and an application thereof. Background Art

[0002] Displacement technology is an important technology for improving oil recovery. By injecting displacing agents (such as water, gas or chemicals), the interaction force between oil and water or oil and gas phases is changed, and crude oil is moved to the inlet, thereby improving the recovery rate. Gas drive is a key technology for improving oil recovery. It uses air as an energy medium, is safe and convenient to use, and can achieve low-cost and high-efficiency production.

[0003] Displacement technologies can be roughly divided into the following two types: 1) The basic principle of water flooding technology is to preferentially penetrate and move crude oil in the reservoir through the relatively low viscosity and high flow rate of water, thereby promoting the crude oil to gather in the wellbore. The flow of injected water has a washing effect. As the crude oil is continuously produced, the pressure of the oil layer gradually decreases, forming a pressure difference. As the amount of injected water increases, the pressure in the oil layer can be increased to form a new pressure difference, pushing the crude oil to the production well. It is low-cost and pollution-free, but as the amount of injected water increases, the life of the oil well is shortened, which will cause certain damage to the formation. 2) Foam flooding uses foam as an oil displacement agent. It is a displacement method that uses various gases and foaming agents to form foam as a displacement medium. It can effectively increase the viscosity of the injected fluid, improve fluidity, and increase the sweep coefficient. It can also use the wetting, oil washing, emulsification, and liquid film replacement of surfactants to improve the oil displacement efficiency. Therefore, it is widely used in oil field exploitation and has great development prospects. Microfoam is to configure polymer and surfactant solution into a base liquid, introduce gas into the base liquid through stirring or airflow, and form a uniformly distributed micron-level foam. By utilizing the high viscosity of polymers and the gas resistance effect of microfoam, the gas mobility control ability is improved, thereby increasing the recovery rate. Microfoam flooding technology is an oil recovery method that uses microfoam as an oil displacement agent. Microfoam has the characteristics of high apparent viscosity, resistance factor increases with the increase of reservoir permeability, bursts when encountering oil, is stable when encountering water, and has the selective plugging ability for oil and water, so it can improve the recovery rate.

[0004] However, microfoam flooding still has the following problems: microfoam stability problem: if the microfoam stability is poor, it is difficult to form an effective oil recovery system; serious emulsification of produced fluid, environmental pollution problems of microfoam flooding, short validity period, poor compatibility with crude oil and other problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a CO2 enhanced micro-foam oil recovery system and a preparation method, device and application thereof.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a CO2 enhanced micro-foam flooding system, the CO2 enhanced micro-foam flooding system comprises CO2 and an enhanced foam base fluid, the enhanced foam base fluid is composed of a temperature-resistant and salt-resistant surfactant, an inorganic cross-linking agent, an organic cross-linking agent and a polymer mother liquid; wherein the polymer mother liquid is prepared by diluting polyacrylamide (HPAM) and simulated formation water to different concentrations. More specifically, the volume ratio of CO2 to the enhanced foam base fluid is less than 1:4.

[0008] Furthermore, the average diameter of the microfoam in the CO2 enhanced microfoam flooding system is 10 μm to 50 μm, the single bubble is spherical, the variation factor is 10% to 30%, and there is no curve formed by three connected surfaces.

[0009] The second aspect of the present invention provides a preparation device for a CO2 enhanced microfoam oil recovery system, which comprises: a pipette, a magnetic stirrer, an intermediate container, a microfoam generator and a CO2 high-pressure gas cylinder; the pipette and the magnetic stirrer are used to coordinately configure a temperature-resistant and salt-resistant surfactant solution and a polymer mother solution; the intermediate container is used to store an enhanced foam base liquid, and the intermediate container is externally connected to an ISCO plunger pump; the microfoam generator comprises a high-temperature and high-pressure cavity, a multi-stage reactor, and a combined microchannel, and the high-temperature and high-pressure cavity is respectively provided with a liquid injection hole and a gas injection hole, the liquid injection hole is connected to the intermediate container, and the gas injection hole is connected to the CO2 high-pressure gas cylinder; the upper end of the high-temperature and high-pressure cavity is connected to an oscillation controller, a rotation controller, and a cavity controller, and the lower end is connected to a stirring motor; temperature sensors and pressure sensors are also provided on both sides of the high-temperature and high-pressure cavity, respectively; a high-speed camera and an ultra-depth-of-field microscope are also provided on the high-temperature and high-pressure cavity; and a gas flow meter is provided on the CO2 high-pressure gas cylinder.

[0010] Furthermore, the micro foam generator has a pressure range of 10MPa to 50MPa and a temperature range of 20°C to 200°C.

[0011] The third aspect of the present invention provides a method for preparing a CO2 enhanced microfoam oil recovery system, which is characterized in that a preparation device for the CO2 enhanced microfoam oil recovery system as described above is used; the preparation method comprises: pre-preparing a heat-resistant and salt-resistant surfactant solution and a polymer mother liquor with a concentration of 0.5%; adding the heat-resistant and salt-resistant surfactant solution to the polymer mother liquor under slow stirring, and then successively adding an inorganic cross-linking agent and an organic cross-linking agent to form an enhanced foam base liquid; mixing high-pressure CO2 and the enhanced foam base liquid to form CO2 microfoam, and then subjecting the CO2 microfoam to an aging reaction to obtain the CO2 enhanced microfoam oil recovery system.

[0012] Furthermore, the preparation method specifically comprises: (1) using anionic surfactant as the main body to generate a temperature-resistant and salt-resistant surfactant by fluorination; wherein the temperature-resistant and salt-resistant surfactant is an anionic fluorocarbon surfactant, specifically a fluorocarbon sulfonate type, and further preferably the temperature resistance condition can reach 150°C, and the salt resistance condition can reach 2×10 5 mg / L; (2) preparing surfactants of different concentrations by pipetting, setting the magnetic stirrer speed to 600RPM to mix them evenly, and screening out the optimal concentration of the heat-resistant and salt-resistant surfactant by the WaringBlender stirring evaluation method according to the comprehensive foam value associated with the product of the foaming volume and the precipitate half-life, thereby obtaining the surfactant system required for the reaction; (3) modifying the high molecular weight polymer polyacrylamide by using the heat-resistant and salt-resistant functional groups according to the structure-activity relationship, and preparing the polymer mother liquor by combining with simulated formation water; (4) adding the polymer to the polymer by pipetting The surfactant system is added to the mother liquor of the composition to form a foam base liquid, and an inorganic crosslinking agent and an organic crosslinking agent are added to obtain an enhanced foam base liquid; (5) the enhanced foam base liquid is placed in an intermediate container for standby use, connected to the liquid injection port of the microfoam generator, and a CO2 high-pressure gas cylinder is connected to the gas injection port of the microfoam generator. An ISCO plunger pump and a gas flow meter are used to set different injection gas-liquid ratios, and the gas-liquid two phases are passed through a combined microchannel that generates turbulent flow, laminar flow and counter-cavitation jets to continuously generate uniform, stable and efficient enhanced microfoam, and after high-temperature aging, the CO2 enhanced microfoam oil recovery system is obtained.

[0013] Furthermore, the preparation method also includes: (6) observing the morphology and microscopic state of the CO2 enhanced microfoam flooding system by a high-speed camera and an ultra-depth microscope, which is used as data for exploring the Oswald ripening mechanism of enhanced microfoam in a reservoir-like environment.

[0014] Furthermore, the step (4) specifically includes: firstly adding an inorganic crosslinking agent to the formed foam base liquid to form preliminary crosslinking, and then adding an organic crosslinking agent to form a three-dimensional network structure to obtain a reinforced foam base liquid; the step (5) specifically includes: introducing the reinforced foam base liquid and a certain amount of CO2 into a micro-foam generator under a pressure of 50 MPa, setting the temperature to 150°C for aging, and finally forming a CO2-enhanced micro-foam oil recovery system.

[0015] The fourth aspect of the present invention provides the use of the CO2 enhanced microfoam oil recovery system as described above in the field of oil recovery.

[0016] Furthermore, the target reservoir for the application is a deep fracture-cave carbonate reservoir with a burial depth of ≥3000m, an oil layer thickness of ≥20m, a net-to-total thickness ratio of >0.5, and an oil-bearing area of ​​>0.15km 2 .

[0017] Furthermore, the target reservoir temperature is 100°C and the pressure is 50MPa.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] Micro foam has high stability and unique structure. The gas volume fraction of ordinary foam is generally greater than 90%, while that of micro foam is usually 40% to 70%. Micro foam has a larger specific surface area and a much lower gas volume fraction than ordinary foam. Micro foam has higher stability than ordinary foam. The pressure that micro foam can withstand is about 10 times the pressure range that ordinary foam can withstand.

[0020] The plugging effect of microfoam is stronger than that of ordinary foam. The plugging effect of microfoam in reservoir pore displacement is mainly manifested in three aspects: 1. When the diameter of microfoam is smaller than the diameter of pore, microfoam temporarily plugs in a disordered manner in the form of cluster accumulation; 2. When the diameter of microfoam is equivalent to the pore, the additional pressure caused by the Jamin reaction when entering the pore causes the foam to deform, thereby increasing the resistance of the fluid; 3. When the diameter of microfoam is larger than the pore diameter, the adsorption of polymer forms a high-viscosity liquid film on the pore surface, causing the pore diameter to become smaller, further increasing the resistance.

[0021] Micro foam has better injectability than ordinary foam. Micro foam is a dispersed system with high stability formed by high-speed stirring of the prepared base liquid and gas. It has a large viscosity, and the gravity effect in the wellbore is much greater than the buoyancy effect, thereby reducing the wellbore friction. The ordinary foam injection method is generally gas-liquid co-injection and gas-liquid alternating injection, but both methods will increase the wellbore friction, making the generated foam uneven and the injectability poor.

[0022] Micro foam has a wider sweep volume. In the process of ordinary foam moving in the reservoir, it moves forward by generating, bursting, and regenerating. The Jamin reaction of the foam increases the seepage resistance, expands the sweep area of ​​the fluid, and inhibits gas channeling to a certain extent. When the diameter of the generated foam is larger than the pore diameter, it is not easy to enter the area with a smaller diameter for plugging. For micro foam, the micro foam with a larger diameter will preferentially enter and block the high permeability channel, and the micro foam with a smaller diameter can enter the low permeability channel that the large bubbles cannot enter, forcing the gas to move deeper inside, thereby improving the sweep efficiency.

[0023] The temperature-resistant and salt-resistant surfactant system constructed by the present invention can be applied to high temperature (temperature higher than 150°C) and high salt (mineralization degree greater than 2×10 5 mg L -1) under specific conditions, it maintains strong stability. The foam base liquid configured by the present invention adopts an optimal composite cross-linking system method, uses an inorganic cross-linking agent to quickly cross-link through the carboxyl group of HPAM to improve the strength of the liquid film in the initial stage of foaming, and uses an organic cross-linking agent to form a covalent bond with the amide group of HPAM to finally form a three-dimensional network structure, which further enhances the stability of the formed micro-foam.

[0024] The average diameter of the microfoam produced by the present invention is 10 to 50 μm, which is continuously generated with good uniformity, has a thick protective film, and the bubbles are spherical. The variation factor is 10% to 30%, and there is no curve formed by three surfaces connected (called plateau boundary). The produced microfoam can withstand a pressure of 50 MPa and has high stability. It can achieve the blocking of pores with smaller diameters, improve the blocking effect of microfoam, enter lower permeation channels for blocking, force gas to move to deeper layers, inhibit the occurrence of gas channeling to a certain extent, greatly increase the affected area and improve the efficiency of the affected area. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the technical description of the present invention.

[0026] Figure 1 It is a schematic diagram of the composite cross-linking process of an inorganic cross-linking agent and an organic cross-linking agent;

[0027] Figure 2 It is a schematic diagram of the three-dimensional network structure after composite cross-linking;

[0028] Figure 3 This is a flow chart of the production of CO2 enhanced micro foam of the present invention;

[0029] Figure 4 It is a micro-foam generator that strengthens the micro-foam micro-generation process; wherein a is continuous foam generation, b is a combined microchannel, c is a reactor, reactor 1 can screen foam with a diameter of less than 200 μm, reactor 2 can screen foam with a diameter of less than 80 μm, and reactor 3 can screen foam with a diameter of less than 50 μm;

[0030] Figure 5 is a photograph of the CO2-enhanced microfoam after generation of the present invention;

[0031] Figure 6 is a microscopic photograph of the CO2 enhanced microfoam of the present invention;

[0032] Figure 7 It is the frequency distribution histogram of the micro-bubble radius size analyzed under the micro-bubble statistical calculation program;

[0033] Figure 8The recovery factors are compared under three different displacement modes: water flooding, foam flooding, and CO2 enhanced micro-foam flooding of the present invention. DETAILED DESCRIPTION

[0034] In the 1970s, foreign scholars such as SEBBA pioneered the introduction of a unique micron-scale foam system, which is widely referred to as colloidal gas foam or microfoam by the academic community due to its colloidal properties and fine structure. Microfoam is composed of tightly packed spherical bubbles with a diameter of 10 to 100 μm. It has a unique three-layer structure - gas core, thickening water layer and peripheral liquid phase, and each layer is densely covered with surfactant molecules. Research experimental data show that the pressure that microfoam can withstand is much higher than the pressure bearing capacity of ordinary foam, about 10 times the pressure, with a longer liquid discharge time and half-life, high liquid film strength, high stability and no Plateau boundary. It is precisely because of the existence of the thickening water layer that the protective film of microfoam is thicker, bubbles are less likely to gather together, and the stability is higher. Its structure and properties are significantly different from those of ordinary foam. The gas in ordinary foam is surrounded by a single layer of surfactant, rather than three layers of surfactant, and lacks the wrapping of the thickening water layer, so ordinary foam is more likely to coalesce than microfoam. Ordinary foam is a continuous phase with a polyhedral structure, while microfoam is a dispersed phase, independently suspended in the liquid phase. Its gas volume fraction is generally 40% to 70%, while the gas volume fraction of ordinary foam is generally greater than 90%, and the gas volume fraction of microfoam is much lower than that of ordinary foam.

[0035] The inventors have found that although the application of microfoam in biomedicine, water purification, soil restoration and oil exploration has shown remarkable results, and has initially revealed its potential in improving oil recovery, the microscopic oil-displacing agent in unconventional oil reservoirs is still unclear. It is urgent to explore in depth and optimize the preparation method of microfoam suitable for improving oil recovery in unconventional oil reservoirs. The existing preparation methods include high-speed stirring method, microfluidic control method and special filter sieve plates, etc., and the existing preparation methods all have certain limitations.

[0036] At present, there are many studies on the properties and applications of air microfoam, but there are few studies on microfoam of other gas media. CO2 can not only be mixed with crude oil and drive oil, but also is one of the effective ways to achieve carbon emission reduction through geological storage. The size of the microfoam bubbles is controllable, which can enter smaller pores and increase the swept volume; it has a reinforced liquid film, strong stability, and effectively blocks the water flow channel.

[0037] The present invention is described in detail below in conjunction with specific implementation modes.

[0038] Example 1

[0039] A preparation method of a CO2 enhanced micro-foam flooding system: pre-mix a heat-resistant and salt-resistant surfactant solution and a polymer mother liquor with a concentration of 0.5% by a pipette gun and a magnetic stirrer, add the heat-resistant and salt-resistant surfactant solution to the polymer mother liquor under slow stirring, and then add an inorganic cross-linking agent and an organic cross-linking agent in sequence to form an enhanced foam base liquid, and inject high-pressure CO2 and the enhanced foam base liquid into a micro-foam generator in a certain proportion by a gas flow meter and an ISCO plunger pump to form CO2 micro-foam, and then perform an aging reaction under the conditions of a temperature of 150°C and a pressure of 50MPa to obtain the CO2 enhanced micro-foam flooding system. The specific preparation method of CO2 enhanced micro-foam is as follows:

[0040] (1) Anionic surfactants are used as the main body, and anionic fluorocarbon surfactants are generated by fluorination, specifically fluorocarbon sulfonate type, which have good temperature and salt resistance. The further preferred temperature resistance can reach 150°C, and the salt resistance can reach 2×10 5 mg / L;

[0041] (2) Prepare surfactants of different concentrations by pipetting, set the magnetic stirrer speed to 600RPM to mix them evenly, and screen out the optimal concentration of the heat-resistant and salt-resistant surfactant in (1) by the Waring Blender stirring evaluation method according to the foam comprehensive value associated with the product of the foaming volume and the half-life of the liquid separation, and obtain the desired surfactant system. It should be noted that the optimal concentration of the heat-resistant and salt-resistant surfactant is based on the comprehensive value, which is calculated by the bubble volume × half-life. As the concentration of the surfactant solution continues to increase, the comprehensive value also continues to increase, but the growth trend is large at the beginning, and as the concentration continues to increase, the growth trend gradually slows down and gradually approaches 0. Therefore, the optimal concentration is selected when the growth slope approaches 0.25, which is the optimal concentration.

[0042] (3) Based on the structure-activity relationship, the high molecular weight polymer HPAM was modified using functional groups with heat and salt resistance characteristics, and the polymer mother solution was prepared by combining it with simulated formation water;

[0043] (4) Adding the surfactant system to the polymer mother solution through a pipette gun to form a foam base solution, first adding an inorganic crosslinking agent to form a preliminary crosslinking, and then adding an organic crosslinking agent. The schematic diagram of the composite crosslinking process of the inorganic crosslinking agent and the organic crosslinking agent is shown in FIG. Figure 1 As shown, a three-dimensional network structure is formed to obtain a reinforced foam base liquid, and a schematic diagram of the three-dimensional network structure after composite cross-linking is shown in Figure 2 As shown;

[0044] (5) The enhanced foam base liquid is placed in an intermediate container for standby use, which is connected to the liquid injection port of the microfoam generator, and the CO2 high-pressure gas cylinder is connected to the gas injection port of the microfoam generator. Different injection gas-liquid ratios are set by an ISCO plunger pump and a gas flow meter, and the gas-liquid two-phase is passed through a combined microchannel that generates turbulent flow, laminar flow and counter-cavitation jets to continuously generate uniform, stable and efficient enhanced microfoam, and after high-temperature aging, the CO2 enhanced microfoam oil recovery system is obtained.

[0045] (6) The morphology and microscopic state of the CO2-enhanced microfoam flooding system were observed by high-speed camera and ultra-depth microscope, which was used as data to explore the Oswald ripening mechanism of enhanced microfoam in a reservoir-like environment.

[0046] Example 2

[0047] A preparation device for a CO2 enhanced microfoam oil recovery system, the preparation device comprising: a CO2 high-pressure gas cylinder, a pipette, a magnetic stirrer, an ISCO plunger pump, an intermediate container, a microfoam generator, a high-speed camera, and an ultra-depth-of-field microscope; wherein the microfoam generator comprises a high-temperature and high-pressure cavity, a multi-stage reactor, and a combined microchannel, wherein the high-temperature and high-pressure cavity is provided with a gas injection hole and a liquid injection hole, respectively, wherein the gas injection hole is provided with a gas injection valve, and the liquid injection hole is provided with a liquid injection valve; the upper end of the high-temperature and high-pressure cavity is connected to an oscillation controller, a rotation controller, and a cavity controller, and the lower end is connected to a stirring motor; temperature sensors and pressure sensors are respectively provided on both sides of the high-temperature and high-pressure cavity; wherein the intermediate container is externally connected to an ISCO plunger pump, and the CO2 high-pressure gas cylinder is provided with a gas flowmeter. The specific preparation device process is as follows: Figure 3 As shown. In the micro-foam generator, CO2 and enhanced foam base liquid generate a large amount of foam in a certain proportion in the combined microchannel through high-frequency shear, collision and cavitation. The micro-foam reactor in the combined microchannel screens out micro-foam with a diameter less than 50μm layer by layer. The reactor in the combined microchannel can screen foam with a diameter of less than 200μm, less than 80μm, and less than 50μm, respectively. The specific micro-foam generator enhances the microscopic generation process of micro-foam as shown in the figure. Figure 4 shown.

[0048] Example 3

[0049] 100 mL of the heat-resistant and salt-resistant amphoteric surfactant solution and sodium dodecyl sulfate solution prepared by the present invention with the same concentration of 0.5% were selected by pipetting and placed in a standard environment (temperature of 25°C, mineralization of 100 mg / L) and a high-temperature and high-salt environment (temperature of 150°C, mineralization of 2×10 5mg / L), and then added the same concentration of polymer mother solution to form a foam base liquid, which were placed in a stirring cup respectively, and the stirrer was started, the speed was set to 8000r / min, the stirring time was 3min, the change of foam volume was recorded regularly, and the foaming volume after the stirring was completed was recorded. The statistical time when the foam precipitated to 50mL was the precipitate half-life. The data were plotted into a graph. The results are shown in Table 1.

[0050] Table 1 Comparison of foaming volume and liquid separation half-life under different conditions and foams

[0051]

[0052] It can be seen from Table 1 that the performance of ordinary surfactants (sodium dodecyl sulfate) is poor under high temperature and high salt conditions; whether in a standard environment or a high temperature and high salt environment, the temperature-resistant and salt-resistant amphoteric surfactant system produced by the present invention has good foaming performance and a long liquid separation half-life, that is, strong stability.

[0053] Example 4

[0054] The foam images are analyzed by software, stable bubbles are selected, and the average diameter of the micro-foam and the variation factor (which describes the uniformity of the bubbles, the lower the variation factor, the more uniform the foam formed) are calculated. The average diameter calculation formula is:

[0055]

[0056] Where: d av ——average diameter of microfoam (m);

[0057] d i ——The diameter of the ith bubble (m);

[0058] n i ——The i-th bubble.

[0059] The formula for calculating the variation factor is:

[0060]

[0061] Where: CV——variation factor of microfoam;

[0062] δ——Standard deviation of microfoam.

[0063] The CO2 enhanced microfoam of the present invention is photographed, such as Figure 5 The micro foam produced by the present invention is photographed under an electron microscope, as shown in FIG. Figure 6As shown in the figure, after software analysis, the proportion of foam diameters in the range of 10 to 50 μm is about 86%, and the foam diameters are all below 50 μm. The diameters of micro foams are mainly concentrated in the range of 10 to 30 μm. Figure 7 shown.

[0064] Embodiment 5:

[0065] CO2 enhanced microfoam displacement experiment: (i) Build a one-dimensional sand-filled tube experimental device, select quartz sand with a mesh size of 100, fill the sand-filled tube model and compact it, with a target permeability of 500mD, use a vacuum pump to evacuate the inside of the sand-filled tube model and saturate it with simulated formation water, inject 500mL of crude oil with a viscosity of 37mPa·s, and slowly saturate the oil at an injection rate of 0.2mL / min; (ii) Inject 0.3PV of CO2 enhanced microfoam produced by the process of Example 1 into the sand-filled tube, and the injection rate is 1mL / min; (iii) Observe and record the oil production at the outlet end. After data sorting, the oil production is 296mL. Analysis shows that the CO2 enhanced microfoam recovery is 58.6%.

[0066] Comparative Example 1:

[0067] Water flooding experiment: (i) Maintain the same step 1 process as in Example 5; (ii) Perform water flooding injection into the sand filling pipe at an injection rate of 1 mL / min and an injection volume of 0.3 PV; (iii) Observe and record the oil production at the outlet. After data collation, the oil production was 199 mL. Analysis showed that the water flooding recovery was 39.8%.

[0068] Comparative Example 2:

[0069] Ordinary foam displacement experiment: (i) Keep the same step 1 process as in Example 5; (ii) Inject ordinary foam (made of sodium dodecyl sulfate solution and CO2) into the sand filling pipe at an injection rate of 1 mL / min and an injection volume of 0.3 PV; (iii) Observe and record the oil production at the outlet. After data collation, the oil production is 257.5 mL. Analysis shows that the foam flooding recovery is 51.5%.

[0070] The recovery rate data of CO2 enhanced micro foam flooding in Example 5, water flooding in Comparative Example 1, and ordinary foam flooding in Comparative Example 2 under the same conditions are as follows: Figure 8 The recovery rate of different displacement methods is shown in the figure. The water drive recovery rate is 39.8%, the foam drive recovery rate is 51.5%, and the CO2 enhanced micro foam recovery rate is 58.6%. It can be seen from the figure that CO2 enhanced micro foam has the best oil recovery efficiency and the highest recovery rate. Foam drive has a significant effect on improving oil recovery compared to water drive, and CO2 enhanced micro foam has a better effect on improving oil recovery compared to foam drive.

[0071] Those skilled in the art can understand that the above-mentioned embodiments are specific examples for implementing the present application, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the present application. Any person skilled in the art can make their own changes and modifications without departing from the spirit and scope of the present application, so the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A CO2 enhanced microfoam flooding system, characterized in that: The CO2 enhanced micro-foam flooding system comprises CO2 and an enhanced foam base fluid, wherein the enhanced foam base fluid is composed of a temperature-resistant and salt-resistant surfactant, an inorganic cross-linking agent, an organic cross-linking agent and a polymer mother liquid; The polymer mother solution is prepared by diluting polyacrylamide and simulated formation water into different concentrations.

2. The CO2 enhanced microfoam flooding system according to claim 1, characterized in that: The average diameter of the microfoam in the CO2 enhanced microfoam flooding system is 10 μm to 50 μm, a single bubble is spherical, the variation factor is 10% to 30%, and there is no curve formed by three connected surfaces.

3. A preparation device for a CO2 enhanced microfoam flooding system, characterized in that: The preparation device comprises: a pipette gun, a magnetic stirrer, an intermediate container, a micro-foam generator and a CO2 high-pressure gas cylinder; The pipette gun and the magnetic stirrer are used to coordinately prepare the temperature-resistant and salt-resistant surfactant solution and the polymer mother solution; The intermediate container is used to store the enhanced foam base liquid, and the intermediate container is externally connected to an ISCO plunger pump; The micro-foam generator comprises a high-temperature and high-pressure cavity, a multi-stage reactor, and a combined microchannel. The high-temperature and high-pressure cavity is provided with a liquid injection hole and a gas injection hole, respectively. The liquid injection hole is connected to the intermediate container, and the gas injection hole is connected to the CO2 high-pressure gas cylinder; the upper end of the high-temperature and high-pressure cavity is connected to an oscillation controller, a rotation controller, and a cavity controller, and the lower end is connected to a stirring motor; temperature sensors and pressure sensors are also provided on both sides of the high-temperature and high-pressure cavity; a high-speed camera and an ultra-depth-of-field microscope are also provided on the high-temperature and high-pressure cavity; The CO2 high-pressure gas cylinder is provided with a gas flow meter.

4. The preparation device of the CO2 enhanced microfoam flooding system according to claim 3, characterized in that: The micro foam generator has a pressure range of 10MPa to 50MPa and a temperature range of 20°C to 200°C.

5. A method for preparing a CO2 enhanced microfoam flooding system, characterized in that: A preparation device for a CO2 enhanced micro-foam oil recovery system as described in claim 3 or 4 is used; the preparation method comprises: pre-preparing a heat-resistant and salt-resistant surfactant solution and a polymer mother liquor with a concentration of 0.5%; adding the heat-resistant and salt-resistant surfactant solution to the polymer mother liquor under slow stirring, and then sequentially adding an inorganic cross-linking agent and an organic cross-linking agent to form an enhanced foam base liquid; mixing high-pressure CO2 and the enhanced foam base liquid to form CO2 micro-foam, and then subjecting the CO2 micro-foam to an aging reaction to obtain the CO2 enhanced micro-foam oil recovery system.

6. The method for preparing CO2-enhanced microfoam according to claim 5, characterized in that: The preparation method specifically comprises: (1) Anionic surfactants are used as the main components to generate heat-resistant and salt-resistant surfactants through fluorination; wherein the heat-resistant and salt-resistant surfactant is an anionic fluorocarbon surfactant, specifically a fluorocarbon sulfonate type, and the further preferred heat-resistant condition can reach 150°C, and the salt-resistant condition can reach 2×10 5 mg / L; (2) preparing surfactants of different concentrations by a pipette, setting the magnetic stirrer speed to 600 RPM to mix them evenly, and screening out the optimal concentration of the temperature-resistant and salt-resistant surfactant according to the comprehensive foam value associated with the product of the foaming volume and the liquid separation half-life by the Waring Blender stirring evaluation method, thereby obtaining the surfactant system required for the reaction; (3) Based on the structure-activity relationship, high molecular weight polymer polyacrylamide was modified by using functional groups with heat and salt resistance characteristics, and the polymer mother solution was prepared by combining with simulated formation water; (4) adding the surfactant system to the polymer mother solution by a pipette gun to form a foam base solution, and adding an inorganic crosslinking agent and an organic crosslinking agent to obtain a reinforced foam base solution; (5) The enhanced foam base liquid is placed in an intermediate container for standby use, which is connected to the liquid injection port of the microfoam generator, and the CO2 high-pressure gas cylinder is connected to the gas injection port of the microfoam generator. Different injection gas-liquid ratios are set by an ISCO plunger pump and a gas flow meter, and the gas-liquid two-phase is passed through a combined microchannel that generates turbulent flow, laminar flow and counter-cavitation jets to continuously generate uniform, stable and efficient enhanced microfoam, and after high-temperature aging, the CO2 enhanced microfoam oil recovery system is obtained.

7. The method for preparing CO2 enhanced microfoam according to claim 6, characterized in that: The preparation method also includes: (6) The morphology and microscopic state of the CO2-enhanced microfoam flooding system were observed by high-speed camera and ultra-depth microscope, which was used as data to explore the Oswald ripening mechanism of enhanced microfoam in a reservoir-like environment.

8. The method for preparing CO2 enhanced microfoam according to claim 6, characterized in that: The step (4) specifically comprises: firstly adding an inorganic crosslinking agent to the foam base liquid to form a preliminary crosslink, and then adding an organic crosslinking agent to form a three-dimensional network structure to obtain a reinforced foam base liquid; The step (5) specifically includes: introducing the enhanced foam base liquid and a certain amount of CO2 into a micro-foam generator under a pressure of 50 MPa, setting the temperature to 150°C for aging, and finally forming a CO2 enhanced micro-foam flooding system.

9. Application of the CO2 enhanced microfoam oil recovery system as claimed in claim 1 or 2 in the field of oil recovery.

10. The use according to claim 9, characterized in that: The target reservoirs for the application are deep fracture-cavity carbonate reservoirs with a burial depth of ≥3000m, an oil layer thickness of ≥20m, a net-to-total thickness ratio of >0.5, and an oil-bearing area of ​​>0.15km 2 .

Images