An adaptive self-cleaning micro-foam generator for low permeability reservoirs and injection method

Abstract

The application discloses a self-adaptive self-cleaning micro-foam generator for low-permeability reservoirs and an injection method, and belongs to the technical field of oil and gas field development. The micro-foam generator comprises, in sequence along the medium flow direction, a liquid inlet contraction assembly, a gas-liquid mixing bubble forming assembly, a dispersion shearing assembly, a contraction section assembly and a micro-foam diffusion and steady flow outlet assembly; the micro-foam generator can realize the introduction and mixing of the injected gas and the injected liquid in the gas-liquid mixing bubble forming assembly and the formation of micro-bubbles by using the continuous shearing and tearing function of the Venturi effect and the micropore structure of the circumferential uniform gas inlet module on the liquid; then, the micro-bubbles are continuously sheared and refined by the dispersion shearing assembly, and the micro-foam flow rate is improved by the second contraction assembly, so that stable micro-foam output with a narrow foam particle size distribution interval is obtained.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to an adaptive self-cleaning microfoam generator and injection method for low-permeability reservoirs. Background Technology

[0002] In the mid-to-late stages of oil and gas field development, especially for reservoirs with high water cut and severe heterogeneity, enhanced oil recovery (EOR) technologies using microfoam as a driving or conditioning medium are receiving increasing attention. Microfoam systems, due to their unique "Jamin effect," liquid film elasticity, and gas compressibility, can effectively regulate mobility ratios, block high-permeability channels, and expand swept volume, thereby improving crude oil recovery efficiency. The core of microfoam-driven technology lies in the efficient generation of micron-sized foam systems with suitable particle size, uniform distribution, and sufficient stability, either underground or on the surface. Among these, the pre-injection method on the surface is more promising due to its strong controllability of foam quality and flexible process; its effectiveness directly depends on the performance of the microfoam generator. However, existing microfoam generators still have the following problems: insufficient foam stability, and large foam particle size and wide particle size distribution, making it difficult to meet the requirements of low-permeability reservoirs. Low-permeability reservoirs have low porosity and poor permeability, requiring microfoam with smaller, more uniform particle size and higher stability. Summary of the Invention

[0003] To address the above problems, this invention provides an adaptive self-cleaning microfoam generator and injection method for low-permeability reservoirs.

[0004] The technical solution adopted in this invention is: A microfoam generator for low-permeability reservoirs includes a liquid inlet shrinkage assembly, a gas-liquid mixing and foaming assembly, a dispersion and shearing assembly, a shrinkage assembly, and a microfoam diffusion and flow stabilization outlet assembly that are detachably connected in sequence along the medium flow direction. The liquid inlet shrinkage assembly has a liquid inlet channel and a first liquid shrinkage channel; the gas-liquid mixing and foaming assembly has an air inlet and an air chamber connected to the air inlet; the air chamber has a circumferential uniform air inlet module, which includes a microporous ceramic filter layer and a microfoam generation channel located at the center of the microporous ceramic filter layer; the dispersion shearing assembly has a first liquid diffusion channel, and a spiral shearing assembly is installed at the rear section of the first liquid diffusion channel; the shrinkage assembly has a second liquid shrinkage channel and a Venturi tube section; the microfoam diffusion stable flow outlet assembly has a second liquid diffusion channel, and a combined microchannel and a microfoam outflow channel are sequentially connected at the rear section of the second liquid diffusion channel; the liquid inlet channel, the first liquid shrinkage channel, the microfoam generation channel, the first liquid diffusion channel, the second liquid shrinkage channel, the Venturi tube section, the second liquid diffusion channel, the combined microchannel, and the microfoam outflow channel are sequentially sealed and connected; The liquid inlet shrinkage assembly is used to connect upstream and downstream pipelines, increase the flow rate of the injected liquid, and create a pressure drop in the micro-foam generation channel; The gas-liquid mixing bubble-forming component uses the negative pressure generated by the liquid flow to introduce the gas phase, and then the gas phase is dispersed and refined by the microporous ceramic filter layer of the circumferential uniform air intake module before entering the micro foam generation channel, where it mixes with the injected liquid to form primary micro foam. The dispersion shearing component is used to further shear and refine microfoams, stabilize foam morphology, and reduce the foam particle size distribution range. The constriction section assembly is used to re-accelerate the fluid and enhance gas-liquid interface disturbances; The microbubble diffusion and flow stabilization outlet component is used to increase the flow rate of microbubbles and to perform final-stage refinement and homogenization of microbubbles, thereby stabilizing the output of microbubbles after final-stage shearing and refinement.

[0005] Furthermore, the circumferentially uniform air intake module is made of microporous ceramic material and is in the shape of a stepped cylinder with large ends and small middle. A through hole with a diameter equal to the small diameter end diameter of the first liquid contraction channel is opened in the center of the cylinder. The through hole is the micro foam generation channel. The circumferential sidewall of the small diameter section in the middle of the cylinder forms a ceramic microporous filter layer. The inner wall of the micro foam generation channel and the outer surface of the ceramic microporous filter layer are coated with a hydrophobic layer.

[0006] Furthermore, the equivalent diameter of the microfoam generation channel is 3~20mm, the porosity of the ceramic microporous filter layer is 30~60%, the pore size is 0.05~0.5mm, and the effective thickness of the ceramic microporous filter layer is 2~10mm.

[0007] Furthermore, the length of the first liquid contraction channel is 8~12mm, and the contraction angle is 10°~15°; the diffusion angle of the first liquid diffusion channel is 8°~12°, and the outlet length of the diffusion section is 4~6mm.

[0008] Furthermore, the spiral shearing assembly includes a spiral guide block and a microporous sieve plate. The spiral guide block is used to apply swirling disturbance to the gas-liquid mixture, causing the fluid to form a velocity gradient and a secondary flow structure. The microporous sieve plate is disposed at the rear end of the spiral guide block and is used to shear and break up the gas-liquid mixture after swirling disturbance and refine microbubbles. The spiral shearing assembly is sequentially connected in series with the upstream first liquid diffusion channel and the downstream second liquid contraction channel. Through the combination of diffusion-shearing-contraction flow channels, the gas-liquid mixture is subjected to progressively enhanced treatment, thereby reducing the average particle size of microbubbles and improving the uniformity of foam particle size distribution.

[0009] Furthermore, the inlet section of the second liquid diffusion channel has a length of 8~12mm and a diffusion angle of 10°~15°.

[0010] Furthermore, the combined microchannel includes multiple constriction sections, throat sections, and expansion sections arranged in series along the medium flow direction. At least one throat section is provided with an adaptive variable throat unit. The adaptive elastic variable throat structure includes a limiting boss, a return gap, a fixed base, and an elastic adjustment plate. One end of the elastic adjustment plate is fixedly connected to the fixed base, and the other end extends obliquely into the throat region along the medium flow direction, forming a variable throat cross-section together with the opposite wall of the throat region. Under normal operating conditions, the elastic regulating plate is in its initial position, providing a smaller effective flow area in the throat region, thereby increasing local flow velocity and shear strength. When increased flow resistance occurs within the combined microchannel due to suspended particles, oil, organic deposits, or foam aggregation, the pressure difference across the throat region increases, increasing the force exerted by the fluid on the elastic regulating plate. The plate then elastically deflects towards its return gap, increasing the effective flow area in the throat region, thus reducing local flow resistance and alleviating clogging tendencies. When the flow resistance decreases or the pressure difference returns to normal, the elastic regulating plate resets under its own elastic restoring force, restoring the smaller effective flow area in the throat region and resuming its shearing and refining effect on the microfoam. During the deflection and reset of the elastic regulating plate, the local flow velocity distribution within the throat region changes, creating a turbulent scouring effect. This helps weaken the adhesion of deposits in the throat region and on the inner wall of the combined microchannel, thereby improving the adaptive anti-clogging and auxiliary self-cleaning capabilities of the microfoam diffusion and flow stabilization outlet component.

[0011] Furthermore, the low-permeability reservoir must simultaneously meet the following conditions: (1) Formation permeability ≤ 100 mD, porosity ≥ 0.10; (2) The formation pressure ranges from 5 MPa to 30 MPa, and the formation temperature is ≤120℃; (3) The salinity of the injected water is 1×10 4 mg / L ~ 2×10 5 mg / L, and the injected water contains suspended particles and inorganic scale-forming ions; (4) The oil layer is heterogeneous.

[0012] The microbubble generation method of any of the above-mentioned microbubble generators includes the following steps: S1: Connect the inlet of the microfoam generator to the air injection pump and the liquid injection pump respectively through pipelines, and connect the outlet to the low-permeability reservoir with a visualization observation window to establish a microfoam generation system; S2: Perform initial pre-saturation treatment on the microbubble generator to form a stable initial gas-liquid working condition in the system; S3: Maintain a constant gas injection rate while continuously injecting liquid to allow the gas-liquid system to enter a stable flow state within the microbubble generator; S4: The foaming state is monitored in real time through a visual observation window. When a continuous and stable micro-foam flow is observed to form in the channel, the foam morphology is confirmed by microscopic observation or image acquisition. S5: Adjust the liquid injection rate while keeping the gas injection rate constant, and synchronously control the gas injection flow rate according to the gas-liquid ratio (G / L) to achieve stable adjustment of the target gas-liquid ratio; S6: Adjust the gas flow rate while keeping the liquid injection rate constant, and regulate the micro-foam generation state by changing the gas-liquid ratio (G / L) to optimize the bubble size distribution and foam stability. S7: Real-time acquisition of the injected liquid flow rate Q l Gas flow rate Q of the injected gas g The pressure difference ΔP before and after the ceramic microporous hydrophobic nucleation module is used to adjust the gas-liquid ratio in real time based on the pressure difference ΔP. The gas-liquid ratio is denoted as G / L=Q. g / Q l The G / L value ranges from 0.1 to 1.0.

[0013] Furthermore, the microbubble generation method also includes step S8, that is, when the pressure difference ΔP continues to increase, the microbubble generator is cleaned online or offline. The cleaning steps include: pre-rinsing with clean water, circulating cleaning with a cleaning solution containing surfactant, and post-rinsing with clean water. The mass concentration of surfactant in the cleaning solution containing surfactant is less than 0.5 wt%.

[0014] Furthermore, the cleaning solution containing surfactant is one or more of anionic surfactants, nonionic surfactants, or amphoteric surfactants, wherein the mass concentration of the surfactant is less than 0.5 wt%; preferably 0.05 wt% to 0.45 wt%, more preferably 0.1 wt% to 0.3 wt%.

[0015] The beneficial effects of this invention are: By setting up a liquid inlet contraction component, a gas-liquid mixing and foaming component, a dispersion and shearing component, a contraction section component, and a microfoam diffusion and stable flow outlet component connected in sequence, the uniform introduction, dispersion and mixing of injected gas and liquid, and the formation of primary microfoams can be achieved by utilizing the synergistic effect of the Venturi effect, the circumferential uniform air inlet module, and the spiral shearing component. Then, the microfoam system is subjected to stepwise shearing, compression, expansion, and bubble diameter control through the spiral shearing component, Venturi tube section, and combined microchannels, which enhances the gas-liquid interface disturbance and foam redispersion process, resulting in a microfoam system with smaller average bubble diameter, more concentrated bubble diameter distribution, and better injection stability.

[0016] The detachable connection structure allows for easy replacement and cleaning of the circumferential uniform air intake module when it becomes clogged. The circumferential uniform air intake module, located in the gas-liquid mixing and foaming assembly, effectively prevents brittle fracture under pressure, thus ensuring stable micro-foam output.

[0017] 3. By incorporating an adaptive variable throat structure in the throat section of the combined microchannel, the device possesses the adaptive capability to passively adjust to changes in pressure differential. Specifically, when the flow resistance increases due to suspended particles, oil, organic deposits, or foam aggregation in the combined microchannel, microporous ceramic filter layer, or inner wall of the flow channel, the pressure differential across the throat section rises. Under the action of fluid pressure and scouring force, the elastic regulating plate elastically deflects towards the return gap, increasing the effective flow area of ​​the throat, thereby reducing local pressure drop, alleviating the tendency to blockage, and maintaining continuous output of microfoam. When the pressure differential decreases or the flow resistance returns to normal, the elastic regulating plate resets under its own elastic restoring force, reducing the effective flow area of ​​the throat, thereby restoring local flow velocity and shear strength, achieving continuous refinement and stable control of microfoam particle size.

[0018] 4. By combining an adaptive variable throat structure with online or offline cleaning processes, the device acquires auxiliary self-cleaning capabilities. When deposits adhere to the combined microchannels, microporous ceramic filter layers, or the inner walls of the flow channels due to suspended particles, oil, organic sediments, or foam aggregation, the elastic regulating plate deflects and resets under pressure differential changes. This alters the effective flow area and local velocity distribution in the throat region, creating disturbances and pressure fluctuations near the throat, thereby weakening the adhesion of deposits to the throat region, combined microchannels, microporous ceramic filter layers, and the inner walls of the flow channels. Furthermore, combined with pre-rinsing with clean water, circulating cleaning with surfactant-containing cleaning solution, and post-rinsing with clean water, oil, organic sediments, and suspended particles adhering to the inner walls of the flow channels, microporous ceramic filter layers, combined microchannels, and the surface of the microporous sieve plate can be peeled off and discharged, restoring flow channel patency and stable microfoam output capability. This improves the continuous operation stability, anti-clogging ability, and maintenance convenience of the microfoam generator under complex injection water conditions in low-permeability reservoirs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the microbubble generator of the present invention.

[0020] Figure 2 This is a flowchart of the cleaning process for the microbubble generator of the present invention.

[0021] Figure 3 This is a partial cross-sectional view of the adaptive variable throat unit in the combined microchannel of the present invention.

[0022] Figure 4 This is a microbubble state diagram observed in the visualization observation section of Embodiment 2 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and preferred embodiments. Example 1

[0024] See Figure 1 This embodiment provides a microfoam generator, including a liquid inlet and contraction assembly 1, a gas-liquid mixing and foaming assembly 2, a dispersion and shearing assembly 3, a contraction section assembly 4, and a microfoam diffusion and flow stabilization outlet assembly 5, which are detachably connected in sequence along the medium flow direction. The liquid inlet and contraction assembly 1 is provided with a liquid inlet channel 11 and a first liquid contraction channel 12. The gas-liquid mixing and foaming assembly 2 is provided with an air inlet 13 and an air chamber 15 communicating with the air inlet. The air chamber 15 is provided with a circumferentially uniform air inlet module 14, which is provided with a microporous ceramic filter layer communicating with the air chamber 15. The microporous ceramic filter layer is provided with a microfoam generation channel, and uniform ceramic micropores are distributed in the microporous ceramic filter layer, with a diameter of approximately 0.5 mm. mm; the dispersion shearing assembly 3 is provided with a first liquid diffusion channel 33, and the rear section of the first liquid diffusion channel 33 is equipped with a spiral shearing assembly 34; the contraction section assembly 4 is provided with a second liquid contraction channel 41 and a venturi tube section 42; the micro foam diffusion steady flow outlet assembly 5 is provided with a second liquid diffusion channel 51, and the rear section of the second liquid diffusion channel 51 is sequentially connected to a combined microchannel 55 and a micro foam outflow channel 54; the liquid inlet channel 11, the first liquid contraction channel 12, the micro foam generation channel, the first liquid diffusion channel 33, the second liquid contraction channel 41, the venturi tube section 42, the second liquid diffusion channel 51, the combined microchannel 55 and the micro foam outflow channel 54 are sequentially sealed and connected.

[0025] The inlet channel 11, the first liquid contraction channel 12, the microfoam generation channel, the first liquid diffusion channel 33, the second liquid contraction channel 41, the second liquid diffusion channel 51, and the microfoam outlet channel 54 are sequentially connected to form a connected channel with a Venturi effect. The first liquid diffusion channel 41 and the second liquid contraction channel 51 are connected to form a Venturi diffusion section, the inlet channel 11 and the first liquid contraction channel 21 are connected to form a Venturi contraction section, and the microfoam generation channel forms a Venturi throat. The injected liquid enters through the inlet channel 11, and its flow rate increases under the contraction effect of the first liquid contraction channel 12, forming a localized bubble within the gas-liquid mixing and foaming assembly 2. Pressure drop; Under negative pressure suction, the injected gas is drawn into the gas chamber 15 through the air inlet 13, and dispersed and refined by the microporous ceramic filter layer of the circumferential uniform air intake module 14 before entering the main liquid channel, where it mixes with the injected liquid to form primary microfoam; the gas-liquid mixture carrying the primary microfoam enters the first liquid diffusion channel 33, where it is decelerated and pressurized. The primary microfoam is further broken and refined by the spiral shear component 34. Subsequently, the gas-liquid mixture passes through the spiral shear component 34, where it generates swirling disturbance, velocity gradient, and shearing and breaking action under the spiral guidance and microporous sieving action, further refining the primary microfoam. The microfoam after spiral shearing enters the contraction section component 4, where it is accelerated and the gas-liquid interface disturbance is enhanced again under the action of the second liquid contraction channel 41 and the Venturi tube section 42, causing larger bubbles to continue to be broken and refined. Subsequently, the microfoam enters the microfoam diffusion and stabilization outlet component 5, undergoes final refinement and homogenization treatment through the second liquid diffusion channel 51 and the combined microchannel 55, and is finally stably output through the microfoam outflow channel 54.

[0026] The liquid inlet shrinkage assembly 1 and the microfoam diffusion and flow stabilization outlet assembly 5 are used to connect to external pipelines during the installation and use of the microfoam generator. In this embodiment, the liquid inlet shrinkage assembly 1 is a stepped cylinder with an axial through hole in its center, which serves as a liquid inlet channel 11. A liquid inlet is provided at the entrance of the liquid inlet channel 11, and a first liquid shrinkage channel 21 is provided in its center. The first liquid shrinkage channel 21 includes an inlet section of equal diameter and a shrinkage section with a reduced diameter. In this embodiment, the length of the inlet section is 10 mm, the shrinkage angle of the shrinkage section is 12°, and the minimum diameter of the shrinkage section is equal to the diameter of the microfoam generation channel, which has a diameter of 3 mm. In other embodiments, the length of the inlet section of the first liquid shrinkage channel 21 can be selected from 8 to 12 mm (excluding 10 mm), the shrinkage angle can be selected from 10 to 15° (excluding 12°), and the diameter of the microfoam generation channel can be selected from 3 to 20 mm (excluding 3 mm). For easy connection, the small-diameter end of the first contraction component 2 is provided with an external thread. The liquid inlet contraction component 1 and the gas-liquid mixing foaming component 2 are detachably connected by the thread. To prevent leakage, a sealing gasket can be installed on the connection surface. The structural design principle of the microfoam diffusion and flow stabilizing outlet component 5 is the same as that of the liquid inlet contraction component 1. In this embodiment, the microfoam diffusion and flow stabilizing outlet component 5 is a cylindrical shape with a constant diameter. A microfoam outflow channel 54 is opened in the center of the microfoam outflow channel 54, and a liquid outlet is provided at the outlet end of the microfoam outflow channel 54.

[0027] In this embodiment, the gas-liquid mixing bubble-forming assembly 2 mainly consists of a cylindrical shell with an outer diameter equal to the diameter of the large end of the first liquid contraction channel 21 and a circumferentially uniform air intake module 14. The circumferentially uniform air intake module 14 is disposed in the gas chamber 15 and is made of microporous ceramic material. Its surface is provided with uniformly arranged ceramic micropores with a diameter of 0.5 mm. After the gas enters the gas chamber 15 through the air inlet 13, it enters the main liquid channel uniformly through the microporous ceramic filter layer of the circumferentially uniform air intake module 33, thereby improving the uniformity of gas phase dispersion and reducing the formation of large bubbles and foam aggregation.

[0028] The circumferential uniform air intake module 14 is cylindrical with larger ends and a smaller middle section. The diameter of the larger ends is equal to the inner diameter of the circular through hole in the center of the cylindrical shell, and the diameter of the middle section is much smaller than that of the two ends. The circumferential uniform air intake module 14 is inserted into the circular through hole of the cylindrical shell through its larger ends. The annular cavity formed between the smaller diameter section in the middle section and the cylindrical shell is the air chamber 15. The two end faces of the circumferential uniform air intake module 14 are flush with the two end faces of the circular through hole of the cylindrical shell, so that the circumferential uniform air intake module 14 can be press-fitted and fixed in the cylindrical shell by the liquid inlet shrinkage component 1 and the dispersion shearing component 3.

[0029] The cylindrical center of the circumferential uniform air intake module 14 has a through hole with a diameter equal to that of the small-diameter end of the first liquid contraction channel. This through hole serves as a microfoam generation channel, and the circumferential sidewall of the small-diameter section in the middle forms a ceramic microporous filter layer. In one embodiment of the present invention, the porosity of the ceramic microporous filter layer is selected to be 30%~60%, and the effective thickness is 2mm~10mm. Under these conditions, the foam generation capacity and anti-clogging performance of the circumferential uniform air intake module 14 can be effectively balanced, which can generate fine bubbles while avoiding micropore clogging caused by high-mineralized water or particulate impurities.

[0030] In one embodiment of the present invention, the inner wall of the microfoam generation channel and the outer surface of the ceramic microporous filter layer are coated with a hydrophobic layer, such as a fluoropolymer coating, a silanized coating, or an inorganic-organic composite hydrophobic coating. The function of the hydrophobic layer is to reduce the tendency of liquid to wet the micropores, thereby making it easier for gas to nucleate and form uniform primary microfoams; and the hydrophobic coating can also effectively prevent water accumulation in the micropores, ensuring stable foam generation and adapting to low-permeability reservoirs with high mineralization and high hardness water.

[0031] In this embodiment, the dispersing shearing assembly 3 includes a shearing shell and a spiral shearing assembly 34. A first liquid diffusion channel 33 is provided at the center of the shearing shell. The first liquid diffusion channel 33 includes a diffusion section communicating with the gas-liquid mixing and foaming assembly 2 and an outlet section of equal diameter. The spiral shearing assembly 34 is located at the rear section of the first liquid diffusion channel 33 and is used to shear, break down, and refine the gas-liquid mixture carrying primary microfoam. The first liquid diffusion channel 33 is provided at the center of the diffusion shell. The first liquid diffusion channel 33 includes a diffusion section communicating with the microfoam generation channel and an outlet section of equal diameter. In this embodiment, the diffusion angle of the diffusion section is 10°, and the length of the outlet section is 6 mm. In other embodiments, the diffusion angle of the diffusion section can be selected within the range of 8~12° (excluding 10°), and the length of the outlet section can be selected within the range of 4~6 mm (excluding 6 mm). The diffusion shell is threadedly connected to the shell of the gas-liquid mixing and foaming assembly 2 through its small-diameter end. To prevent leakage, a sealing gasket can be installed on the connecting surface.

[0032] In this embodiment, the spiral shearing assembly 34 is a single-stage spiral shearing structure, including a spiral guide block and a microporous sieve plate. The spiral guide block is used to apply a spiral guiding effect to the gas-liquid mixture, causing the fluid to form swirling disturbances, velocity gradients, and secondary flow structures. The microporous sieve plate is disposed at the rear end of the spiral guide block and is used to further shear and break up the gas-liquid mixture after swirling disturbance and refine microbubbles. The spiral shearing assembly 34 is arranged in series with the upstream first liquid diffusion channel 33 and the downstream second liquid contraction channel 41. Through the combination of diffusion-shearing-contraction flow channels, the gas-liquid mixture is subjected to progressively enhanced treatment, thereby reducing the average particle size of microbubbles and improving the uniformity of bubble size distribution.

[0033] In this embodiment, the contraction section assembly 4 is located downstream of the dispersing shear assembly 3. The contraction section assembly 4 includes a second liquid contraction channel 41 and a Venturi tube section 42. The second liquid contraction channel 41 is used to further accelerate the microfoam processed by the spiral shear assembly 34, while the Venturi tube section 42 creates localized compression, acceleration, and shearing effects to further enhance gas-liquid interface disturbance, causing larger foams to continue to break down and refine. In this embodiment, the inlet length of the second liquid contraction channel 41 is 8–12 mm, and the contraction angle is 10°–15°.

[0034] In this embodiment, the microfoam diffusion and flow stabilization outlet component 5 is located downstream of the contraction section component 4. The microfoam diffusion and flow stabilization outlet component 5 includes a second liquid diffusion channel 51, and a combined microchannel 55 is installed at the rear end of the second liquid diffusion channel 51. The second liquid diffusion channel 51 is used to diffuse and restore the pressure of the microfoam processed by the contraction section component 4, while the combined microchannel 55 is used for final-stage refinement, homogenization, and stable output processing of the microfoam.

[0035] In this embodiment, the combined microchannel 55 includes multiple constriction sections 56, throat sections 52, and expansion sections 53 arranged in series along the medium flow direction. Microfoams are accelerated and locally compressed when flowing through the constriction sections, subjected to high shear when flowing through the throat sections, and undergo deceleration expansion and interfacial stretching when flowing through the expansion sections. This results in larger foam particles being continuously stretched, compressed, and broken up, further reducing foam particle size, stabilizing foam morphology, and improving the uniformity of foam particle size distribution.

[0036] See Figure 3 In this embodiment, at least one throat segment of the combined microchannel 55 is provided with an adaptive variable throat structure.

[0037] The adaptive elastic variable throat structure includes a limiting boss 551, a return gap 552, a fixed base 553, and an elastic adjusting plate 554. The fixed base 553 is disposed on one side wall of the throat region. One end of the elastic adjusting plate 554 is fixedly connected to the fixed base 553, and the other end extends obliquely into the throat region along the medium flow direction, forming a variable flow cross-section together with the opposite wall of the throat region. The return gap 552 is disposed on the side of the elastic adjusting plate 554 facing away from the flow channel, providing space for the elastic deflection and reset of the elastic adjusting plate 554. The limiting boss 551 is disposed on the deformation path of the elastic adjusting plate 554, limiting the maximum deflection stroke of the elastic adjusting plate 554 and preventing excessive deformation of the elastic adjusting plate 554 due to excessive pressure difference.

[0038] Under normal operating conditions, the elastic regulating plate 554 is in its initial position, providing a smaller effective flow area in the throat region, thereby increasing local flow velocity and shear strength. When the combined microchannel 55 or the inner wall of the flow channel experiences increased flow resistance due to suspended particles, oil, organic deposits, or foam aggregation, the pressure difference across the throat region increases. This increases the force exerted by the fluid on the elastic regulating plate 554, causing it to elastically deflect towards the return gap 552, increasing the effective flow area in the throat region and thus reducing local flow resistance and alleviating the tendency to clog. When the clog tendency weakens or the pressure difference returns to normal, the elastic regulating plate 554 resets under its own elastic restoring force, reducing the effective flow area in the throat region to restore local flow velocity and shear refinement.

[0039] During the deflection and reset of the elastic regulating plate 554, the local flow velocity distribution in the throat area changes and generates a disturbance scouring effect, which helps to weaken the adhesion of oil, organic deposits, suspended particles and foam aggregates to the throat area and the inner wall of the combined microchannel 55, thereby improving the adaptive anti-clogging and auxiliary self-cleaning ability of the microfoam diffusion and flow stabilization outlet component 5.

[0040] The elastic adjustment sheet 554 can be made of 316L stainless steel, Hastelloy, PEEK, PTFE-coated metal sheet or other corrosion-resistant elastic materials. Its surface can be coated with fluoropolymer, wear-resistant ceramic or oleophobic and hydrophobic coating to reduce the probability of oil, organic deposits and suspended particles adhering to the throat area. Example 2

[0041] Method and performance evaluation of generating microbubbles using the microbubble generator described in Example 1: Selecting suitable reservoirs: The following low-permeability reservoirs were selected as experimental subjects: formation permeability < 100 mD, reservoir porosity > 0.10, formation pressure 30 MPa, formation temperature < 120℃, and injected water salinity 8.2 × 10⁻⁶. 4 mg / L, suspended particulate matter content 65 mg / L, injection temperature 45℃, injection volume 2.0 mg / L. 3 The injection pressure is 17 MPa, the injected gas is nitrogen, and the gas flow rate is 0.15~0.50 m³ / h. The oil content of this low-permeability reservoir is 150 m³.

[0042] (2) Constructing a microfoam generation system: See Figure 2The air injection pump 15, gas valve 17, gas intermediate container 16, one-way valve 18, and pipeline filter with a filtration accuracy of 50μm are connected sequentially to the air injection port of the microfoam generator 23 through the first pipeline. The liquid injection pump 19, liquid valve 21, and liquid intermediate container 20 are connected sequentially to one inlet of the six-way valve 22 through the second pipeline. The cleaning fluid storage tank 27, heater 26, cleaning fluid circulation pump 25, and filter 24 are connected sequentially to the other inlet of the six-way valve 22 through the third pipeline. The outlet of the six-way valve 22 is connected to the liquid inlet shrinkage component 1 of the microfoam generator through a pipeline. After connecting the microfoam diffusion and stabilizing outlet component 5 of the microfoam generator, it is connected to the inlet of the second six-way valve 28 through the outlet end component 7. One outlet of the second six-way valve 28 is connected to the sewage tank 29 through the fourth pipeline. The other outlet of the second six-way valve 28 is connected sequentially to the low-permeability reservoir 30 with a viewing window, back pressure valve 31, and measuring cylinder 32 through the fifth pipeline. Pressure gauges or differential pressure sensors are installed at the front and rear ends of the circumferential uniform air intake module 33 of the microbubble generator to monitor the differential pressure changes of the circumferential uniform air intake module 14 and its microporous ceramic filter layer. The ceramic microporous filter layer of the microfoam generator 23 has a porosity of 45%, an effective thickness of 5 mm, a ceramic micropore diameter of 0.5 mm, and is coated with a hydrophobic layer containing fluoropolymer. The inlet section of the first liquid contraction channel 21 has a length of 10 mm and a contraction angle of 12°; the diameter of the microfoam generation channel is 3 mm and the length is 25 mm; the diffusion angle of the first liquid diffusion channel 41 is 10° and the outlet length of the diffusion section is 5 mm; the spiral shear assembly 34 is a single-stage spiral shear structure, including a spiral guide block and a microporous sieve plate. The pitch of the spiral guide block is 10 mm, the hydraulic diameter of the spiral channel is 4 mm, the radius of curvature is 20 mm, the pore density of the microporous sieve plate is 120 pores / mm², and the pore diameter is 0.5 mm; the contraction angle of the second liquid contraction channel 51 is 12°, and the throat diameter of the Venturi tube section 42 is 1 mm; the rear section of the second liquid diffusion channel 51 is provided with a combined microchannel 55. The combined microchannel 55 includes a three-stage series-connected contraction section, throat section, and expansion section, used for final-stage refinement and homogenization of the dispersed and sheared microfoam; the first throat section is provided with an adaptive variable throat structure, used to adjust the effective flow area of ​​the throat according to the pressure difference.

[0043] (3) Generate microfoam and inject it into the reservoir: disconnect the third and fourth pipelines to connect the microfoam generator 23 with the first, second and fifth pipelines; start the injection pump 19 to inject the pretreated liquid into the microfoam generator through the liquid inlet shrinkage assembly 1, and control the liquid flow rate Q. l 2.0m 3 / h; Simultaneously start the gas injection pump 15 to introduce nitrogen gas through the injection port and control the gas flow rate Q. g 0.5m 3 / h, corresponding to a gas-liquid ratio G / L of 0.25. The injected gas and injected liquid form microbubbles in the microbubble generator 23, and after stable output, they are injected into the low-permeability reservoir 30. The displaced oil flows into the measuring cylinder 32 through the back pressure valve 31.

[0044] During operation, when the inlet pressure P is monitored in Increase or increase liquid flow rate Q l When the flow rate decreases, it is determined that there is a tendency for blockage in the microporous ceramic filter layer, the combined microchannel 55, or the inner wall of the flow channel. By adjusting the gas injection flow rate, liquid injection flow rate, or gas-liquid ratio, the local flow resistance is reduced and the stable output of microbubbles is maintained.

[0045] (4) Cleaning, maintenance, and adaptive parameter adjustment: See Figure 2After the device operated continuously for a period of time, the pressure difference ΔP across the circumferential uniform air intake module increased from the initial 0.18 MPa to 0.31 MPa, the system liquid flow rate decreased by approximately 12%, and the uniformity of the outlet foam decreased, indicating a tendency for deposition and blockage in the nucleation zone. At this point, the first, second, and fifth pipelines were disconnected, connecting the microfoam generator 23 to the third and fourth pipelines. First, clean water was introduced for pre-rinsing for 15 minutes, while simultaneously opening the drain valve to discharge loose particles and silt. Then, a chemical cleaning solution was switched to circulating cleaning. This chemical cleaning solution was a mixture of a surfactant-containing cleaning solution or a weakly acidic cleaning solution with a chelating agent, circulated at 40°C for 30 minutes. After cleaning, the cleaning solution was discharged, and the device was rinsed with clean water for 20 minutes until the drain was clean. Finally, the valve assembly was restored to normal operating conditions, and the equipment was restarted. After cleaning, the pressure difference across the circumferential uniform air intake module recovered to 0.20 MPa, and the liquid flow rate recovered to over 95% of the original design value, indicating that the cleaning and maintenance were effective. Optionally, when oil, organic deposits, or suspended particulate matter are present on the surface of the ceramic microporous filter layer, microfoam generating channel, or microporous sieve plate, a surfactant may be added to the chemical cleaning solution to form a surfactant-containing compound cleaning solution. The surfactant is one or more of anionic, nonionic, or amphoteric surfactants, and its mass concentration is less than 0.5 wt%, preferably 0.05 wt% to 0.45 wt%, more preferably 0.1 wt% to 0.3 wt%. The surfactant is used to reduce the interfacial adhesion between oil, organic deposits, and suspended particulate matter and the surface of the ceramic microporous filter layer, microfoam generating channel, and microporous sieve plate, thereby improving the cleaning effect. Meanwhile, due to the pressure difference change, when the flow resistance inside the combined microchannel 55 increases, the elastic adjustment plate 554 is elastically deflected towards the return gap 552 under the action of fluid pressure and scouring force, which increases the opening of the variable throat, thereby reducing the local flow resistance of the final microchannel and generating a disturbance and scouring effect on the deposits near the throat. When the pressure difference returns to the normal range after cleaning, the elastic adjustment plate 554 resets under its own elastic restoring force, which reduces the opening of the variable throat and restores the shearing and refining effect on the microfoam.

[0046] Comparative Example 1 Comparative Example 1 was set up to evaluate the microfoam and ordinary foam: The difference between Comparative Example 1 and Example 1 is that the circumferential uniform air intake module 14 is replaced with the same ordinary material as the housing of the gas-liquid mixing bubble-forming component, and the air intake 13 is directly connected to the Venturi throat.

[0047] Under the condition that the composition of the liquid system, the type of gas, the gas-liquid ratio and the total amount injected are basically the same, the comparative example is run using the same method as in Example 1.

[0048] See Figure 4 As can be seen from the view window, the microbubbles generated in this embodiment are smaller in size, have a more concentrated bubble diameter distribution, and have a more uniform and dense appearance, resulting in a more stable output process; while the bubbles in Comparative Example 1 are larger in size, have a wider bubble diameter distribution, and are more prone to large bubbles, aggregation, and fluctuations.

[0049] Depend on Figure 4 It can be seen that the microbubbles flow continuously within the observation section, with the foam phase distributed along the channel axis. No obvious large bubble aggregation, gas short circuit, or intermittent flow interruption was observed. This result indicates that the circumferential uniform air intake module (33) can uniformly introduce the gas phase into the main liquid channel through the microporous ceramic filter layer. The spiral shear component (42), the Venturi tube section (52), and the combined microchannel (55) can continuously shear, disturb, and refine the gas-liquid mixture, thereby forming a continuous and stable microbubble flow.

[0050] After running for a period of time, the oil recovery rate in the measuring cylinder was collected. The experimental results showed that the final recovery rate of ordinary foam flooding was 66.5%, while the final recovery rate of the micro foam flooding of this invention was 79.8%. Compared with the comparative ratio, the present invention improved by 13.3 percentage points, an increase of 20.0%.

[0051] (5) Evaluation of Field Application Effect: In another application method of this embodiment, the microfoam generator described in Example 1 was applied to a field test of microfoam flooding in a low-permeability reservoir. This reservoir is in the high water-cut development stage, with strong reservoir heterogeneity and relatively dispersed remaining oil distribution, and the sweep volume of conventional water flooding is limited. The field test of microfoam flooding was conducted using an injection-production well group, which included 16 injection wells and 68 production wells, covering an annual oil production of approximately 2.3 × 10⁻⁶. 4 The on-site injection pressure was 17 MPa to 20 MPa, and the injected gas was nitrogen. The gas displacement, converted to ground metering conditions, was 0.15 m³. 3 / h~0.50 m 3 / h.

[0052] Field statistics show that, under the aforementioned low-permeability reservoir conditions, the use of the microfoam generator and injection method described in this invention increased the dynamic recovery rate of the test well group by approximately 2.4 percentage points, achieving a production-to-input ratio of 1.54. This result indicates that this invention can adapt to high-pressure, low-flow-rate gas injection conditions of 17 MPa–20 MPa, achieving stable gas-liquid mixing, micropore nucleation, and multi-stage dispersion and refinement. This is beneficial for improving the stability of microfoam flooding injection, expanding the swept volume, and enhancing the utilization of remaining oil in low-permeability reservoirs.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also within the protection scope of the present invention.

Claims

1. A microfoam generator for low-permeability reservoirs, characterized in that, It includes a liquid inlet shrinkage assembly (1), a gas-liquid mixing and foaming assembly (2), a dispersion and shearing assembly (3), a shrinkage section assembly (4), and a micro-foam diffusion and steady flow outlet assembly (5), which are detachably connected in sequence along the medium flow direction. The liquid inlet shrinkage assembly (1) is provided with a liquid inlet channel (11) and a first liquid shrinkage channel (12). The gas-liquid mixing foaming assembly (2) is provided with an air inlet (13) and an air chamber (15) connected to the air inlet. The air chamber (15) is provided with a circumferential uniform air inlet module (14). The circumferential uniform air inlet module (14) includes a microporous ceramic filter layer and a microfoam generation channel located in the center of the microporous ceramic filter layer. The dispersion shearing assembly (3) is provided with a first liquid diffusion channel (33). The rear section of the first liquid diffusion channel is equipped with a spiral shearing assembly (34). The shrinkage section assembly (4) is provided with a first liquid diffusion channel (33). The microfoam diffusion and steady flow outlet assembly (5) is provided with a second liquid diffusion channel (51) and a venturi tube section (42). The rear section of the second diffusion channel is connected to a combined microchannel (55) and a microfoam outlet channel (54). The inlet channel (11), the first liquid contraction channel (12), the microfoam generation channel, the first liquid diffusion channel (33), the second liquid contraction channel (41), the venturi tube section (42), the second liquid diffusion channel (51), the combined microchannel (55), and the microfoam outlet channel (54) are sequentially sealed and connected. The liquid inlet shrinkage assembly (1) is used to connect the upstream and downstream pipelines, increase the flow rate of the injected liquid, and form a pressure drop in the micro-foam generation channel; The gas-liquid mixing bubble-forming component (2) introduces the gas phase using the negative pressure generated by the liquid flow, and the gas phase is dispersed and refined by the microporous ceramic filter layer of the circumferential uniform air intake module (14) before entering the micro foam generation channel, where it mixes with the injected liquid to form primary micro foam. The dispersion shearing component (3) is used to further shear and refine the microfoam, stabilize the foam morphology, and reduce the foam particle size distribution range; The contraction section assembly (4) is used to further accelerate the fluid and enhance the gas-liquid interface disturbance; The microfoam diffusion and flow stabilization outlet component (5) is used to increase the flow rate of microfoam and to perform final-stage refinement and homogenization of microfoam, so as to stably output the microfoam after final-stage shearing and refinement.

2. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The circumferential uniform air intake module (14) is made of microporous ceramic material and is a stepped cylinder with large ends and small middle. A through hole with the same diameter as the small diameter end of the first liquid contraction channel (12) is opened in the center of the cylinder. The through hole is the micro foam generation channel. The circumferential sidewall of the small diameter section in the middle of the cylinder forms a ceramic microporous filter layer. The inner wall of the micro foam generation channel and the outer surface of the ceramic microporous filter layer are coated with a hydrophobic layer.

3. A microfoam generator for low-permeability reservoirs according to claim 2, characterized in that, The equivalent diameter of the microfoam generation channel is 3~20mm, the porosity of the ceramic microporous filter layer is 30~60%, the pore size is 0.05~0.5mm, and the effective thickness of the ceramic microporous filter layer is 2~10mm.

4. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The inlet section of the first liquid contraction channel (12) has a length of 8~12mm and a contraction angle of 10°~15°; the diffusion angle of the first liquid diffusion channel (33) has a length of 8°~12° and a diffusion section outlet length of 4~6mm.

5. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The spiral shearing assembly (34) includes a spiral guide block and a microporous sieve plate. The spiral guide block is used to apply swirling disturbance to the gas-liquid mixture, so that the fluid forms a velocity gradient and a secondary flow structure. The microporous sieve plate is set at the rear end of the spiral guide block and is used to shear and break up the gas-liquid mixture after swirling disturbance and refine the microbubbles.

6. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The inlet section of the second liquid diffusion channel (51) has a length of 8~12mm and a diffusion angle of 10°~15°.

7. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The combined microchannel (55) includes multiple constriction sections, throat sections, and expansion sections arranged in series along the medium flow direction, at least one throat section having an adaptive variable throat structure; the adaptive elastic variable throat structure includes a limiting boss (551), a return gap (552), a fixed base (553), and an elastic adjustment plate (554); one end of the elastic adjustment plate (554) is fixedly connected to the fixed base (553), and the other end extends obliquely into the throat region along the medium flow direction, and together with the opposite wall of the throat region, defines a variable flow cross section; the return gap (552) The limiting boss (551) is located on the side of the elastic adjustment plate (554) facing away from the flow channel, and is used to provide deformation space for the elastic deflection and reset of the elastic adjustment plate (554); the limiting boss (551) is located on the deformation path of the elastic adjustment plate (554), and is used to limit the maximum deflection stroke of the elastic adjustment plate (554); when the pressure difference between the front and rear of the throat region increases or the fluid scouring force increases, the elastic adjustment plate (554) is elastically deflected towards the return gap (552) under the action of fluid pressure, so as to increase the effective flow area of ​​the throat region, thereby reducing local flow resistance and alleviating the blockage tendency; When the pressure difference across the throat region decreases or the fluid scouring force decreases, the elastic adjustment plate (554) resets under its own elastic restoring force, thereby reducing the effective flow area of ​​the throat region to restore local flow velocity and shear strength.

8. A microfoam generator for low-permeability reservoirs according to claim 1, characterized in that, The low-permeability reservoir must simultaneously meet the following conditions: (1) Formation permeability ≤ 100 mD, porosity ≥ 0.10; (2) The formation pressure ranges from 5 MPa to 30 MPa, and the formation temperature is ≤120℃; (3) The salinity of the injected water is 1×10 4 mg / L ~ 2×10 5 mg / L, and the injected water contains suspended particles and inorganic scale-forming ions; (4) The oil layer is heterogeneous.

9. A method for generating microbubbles using the microbubble generator according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Connect the inlet end of the micro foam generator to the air injection pump and the liquid injection pump respectively through pipelines, and connect the outlet end to the low-permeability reservoir with a visualization observation window (30) to establish a micro foam generation system; S2: Perform initial pre-saturation treatment on the microbubble generator to form a stable initial gas-liquid working condition in the system; S3: Maintain a constant gas injection rate while continuously injecting liquid to allow the gas-liquid system to enter a stable flow state within the microbubble generator; S4: The foaming state is monitored in real time through the visualization observation window (30). When a continuous and stable micro foam flow is observed to form in the channel, the foam morphology is confirmed by microscopic observation or image acquisition. S5: Adjust the injection speed and simultaneously adjust the gas injection flow rate according to the target gas-liquid ratio G / L to achieve stable control of the target gas-liquid ratio; S6: Adjust the gas flow rate while keeping the liquid injection rate constant, and regulate the micro-foam generation state by changing the gas-liquid ratio G / L to optimize the bubble size distribution and foam stability. S7: Real-time acquisition of the injected liquid flow rate Q l Gas flow rate Q of the injected gas g And the pressure difference ΔP before and after the circumferential uniform air intake module (14); the gas-liquid ratio is adjusted in real time according to the pressure difference ΔP, and the gas-liquid ratio is denoted as G / L=Q. g / Q l .

10. The microbubble generation method according to claim 9, characterized in that, It also includes step S8, which is to perform online or offline cleaning of the microbubble generator when the pressure difference ΔP continues to increase; the cleaning steps include: pre-rinsing with clean water, circulating cleaning with a cleaning solution containing surfactant, and post-rinsing with clean water.

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