A method for enhanced oil recovery based on microbubble flooding

Abstract

The application discloses a kind of oil reservoir recovery enhancement methods based on microbubble oil displacement, applied to the water drive development process of low permeability reservoir;The method comprises the following steps: adding micron-sized bubbles in water injection flow, to obtain microbubble aqueous solution;The microbubble aqueous solution is injected into the oil reservoir through injection well;During the migration process of the microbubble aqueous solution into the oil reservoir, the micron-sized bubbles in the microbubble aqueous solution grow or shear to become smaller, to increase the flow resistance of the first type of permeation channel in the oil reservoir, while improving the displacement pressure of the water flow in the second type of permeation channel in the microbubble aqueous solution;The micron-sized bubbles of the application have good homogeneity and little damage to the formation;By using the micron-sized bubbles in the reservoir through the Jiamin effect, the effect of increasing viscosity and increasing pressure, the water drive swept volume of the oil reservoir is effectively expanded, the cost is low, and the recovery of the low permeability reservoir is improved, thereby achieving the purpose of increasing the crude oil production of the oilfield.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, and specifically relates to a method for improving reservoir recovery based on microbubble flooding. Background Technology

[0002] Low-permeability reservoirs are generally buried at greater depths, with air permeability ranging from 1 to 10 × 10⁻⁶. -3 μm 2 Low-permeability reservoirs exhibit strong heterogeneity, with pore throat radii ranging from 0.01 to 100 μm, and some reservoirs have well-developed microfractures. Currently, during water-drive development of low-permeability reservoirs, the crude oil displacement efficiency is less than 30%, and the final oil recovery rate is below 30%. For example, the average final oil recovery rate of water-drive development in a Triassic reservoir of a certain oilfield is only 19.9%. Therefore, for low-permeability reservoirs developed using water-drive, due to strong heterogeneity and the development of microfractures, more than 70% of the crude oil remains in the reservoir, resulting in reduced crude oil production and decreased economic benefits.

[0003] Currently, waterflooding remains one of the most effective and economical extraction methods for oilfield development. Foam has excellent plugging performance and selectivity for oil-water and heterogeneous bottom layers, making it one of the main means of stabilizing and increasing production in old oilfields. However, foam flooding has several drawbacks in its application, including poor foam stability, high injection pressure, defoaming upon contact with oil, short effective period, emulsification of produced fluid, severe adsorption of foaming agents, and high construction costs. These issues severely restrict the application and promotion of foam flooding technology.

[0004] In recent years, some scholars have also prepared microfoam systems by high-speed stirring and shearing. These systems have particle sizes between 10 and 100 μm, liquid film thicknesses between 4 and 10 μm, and foam release time and half-life greater than 24 hours, exhibiting good dynamic and coalescence stability. They have good applications in drilling, oil production, and waterflooding. However, microfoam systems generated by chemical foaming agents and stabilizers have problems such as poor foam homogeneity, significant formation damage, and high cost during use. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for improving reservoir recovery based on microbubble flooding, in order to solve the technical problems of poor foam homogeneity, significant formation damage, and high cost in existing microbubble flooding processes.

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

[0007] This invention provides a method for enhancing oil recovery based on microbubble flooding, applied to the waterflooding development process of low-permeability reservoirs; the method includes:

[0008] Micron-sized air bubbles are added to the water flow to obtain a microbubble aqueous solution;

[0009] The microbubble aqueous solution is injected into the oil reservoir through a water injection well;

[0010] During the migration process after the microbubble aqueous solution enters the reservoir, the micron-sized bubbles in the microbubble aqueous solution aggregate and grow or shear and shrink to increase the flow resistance of the first type of permeation channel in the reservoir, while increasing the displacement pressure of the water flow in the microbubble aqueous solution in the second type of permeation channel in the reservoir.

[0011] The first type of infiltration channel includes infiltration pores with a water flow permeability of 3-125 mD, infiltration channels with a water flow permeability of 40-600 mD, and infiltration fractures with a water flow permeability of 300-1500 mD; the second type of infiltration channel includes infiltration pores with a water flow permeability of less than 3 mD, infiltration channels with a water flow permeability of less than 40 mD, and infiltration fractures with a water flow permeability of less than 300 mD.

[0012] Furthermore, the bubble diameter of the micron-sized bubbles matches the pore throat size of the reservoir.

[0013] Furthermore, the bubble diameter of the micron-sized bubbles is 1μm-100μm.

[0014] Furthermore, the process of adding micron-sized air bubbles into the injected water flow to obtain a microbubble aqueous solution is as follows:

[0015] A microbubble generator is installed on the high-pressure water injection pipeline of the water injection well. The microbubble generator includes a central exhaust pipe 1 and several micron-sized perforated plates 2. The central exhaust pipe 1 is concentrically arranged inside the outer cylinder 4 of the high-pressure water injection pipeline. One end of the central exhaust pipe 1 is connected to a gas source, and the other end is closed. Several exhaust ports are spaced apart on the central exhaust pipe 1, and the micron-sized perforated plates 2 are installed at the exhaust ports. Several micron-sized through holes are provided on the micron-sized perforated plates 2.

[0016] Water is introduced between the central exhaust pipe 1 and the outer cylinder 4, and high-pressure gas is introduced into the central exhaust pipe 1. When the high-pressure gas passes through the micron-sized perforated plate 2 at the exhaust port, it forms micron-sized bubbles and enters the water flow to mix and obtain a microbubble aqueous solution.

[0017] Furthermore, the high-pressure gas is one of air, N2, CO2, and natural gas.

[0018] Furthermore, the pressure value of the high-pressure gas is greater than the pressure value of the injected water flow.

[0019] Furthermore, the pressure difference between the high-pressure gas and the injection water flow is 0.3-0.5 MPa.

[0020] Furthermore, in the microbubble aqueous solution, the micron-sized bubbles are a uniformly dispersed phase, and the injected water flow is a continuous phase.

[0021] Furthermore, in the microbubble aqueous solution, the volume of the micron-sized bubbles accounts for 5%-30% of the volume of the injected water flow.

[0022] Furthermore, the apparent viscosity of the microbubble aqueous solution increases as the bubble diameter of the micron-sized bubbles decreases.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention provides a method for enhancing oil recovery based on microbubble flooding. By adding micron-sized bubbles to the injected water flow, the method leverages the characteristics of these bubbles—aggregation and growth or shear shrinkage during reservoir migration—to effectively increase the flow resistance in high-permeability channels within the reservoir, while simultaneously increasing the displacement pressure of the injected water flow in low-permeability channels. The micron-sized bubbles exhibit good homogeneity and cause minimal damage to the formation. Through the Jamin effect, viscosity enhancement, and pressurization, the water-driven sweep volume of the reservoir is effectively expanded, resulting in low cost and improved oil recovery in low-permeability reservoirs, ultimately achieving the goal of increasing crude oil production in the oilfield.

[0025] Furthermore, by matching the bubble diameter of the micron-sized bubbles with the pore throat scale of the reservoir, it is ensured that the micron-sized bubbles can be evenly distributed in the injection water flow, and the rising speed of the micron-sized bubbles is effectively reduced, thereby improving the stability of the micron-sized bubbles.

[0026] Furthermore, since the pore throat radius of low-permeability reservoirs is generally less than 100 μm, the bubble diameter of micron-sized bubbles is set to 1 μm-100 μm to ensure that the micron-sized bubbles can enter the reservoir depth with the injection water flow. The micron-sized bubbles exhibit characteristics such as shrinking under shear and increasing in size through aggregation during migration, ensuring their migration to the deep reservoir and plugging of large pore throats. Through continuous migration and plugging, the displacement of crude oil in low-permeability reservoirs is effectively improved, thereby expanding the water drive swept volume and increasing the crude oil recovery rate.

[0027] Furthermore, micron-sized bubbles with controllable concentration and diameter are injected into the injected water flow through a microbubble generator to form a microbubble aqueous solution. After the microbubble aqueous solution is injected into the formation, the water drive efficiency is increased by controlling the low-permeability reservoir to expand the water drive sweep volume, thereby improving crude oil production and ultimate recovery. The microbubble device uses a micron-sized perforated plate on the central tube. When gas passes through the micron-sized perforations at high speed, it is ejected to form micron-sized bubbles, which then enter the injected water flow to form a water-gas dispersion system of microbubble aqueous solution. The water-gas dispersion system of microbubble aqueous solution using the microbubble generator has bubble diameter and concentration that are related to the high-pressure gas flow velocity, perforated plate material, manufacturing method, water flow pressure and viscosity, etc. The gas-liquid ratio is adjustable and is not limited by temperature and pressure. The device has a simple structure and is easy to operate.

[0028] Furthermore, the high-pressure gas is one of air, N2, CO2, and natural gas to avoid damage to the formation caused by micron-sized bubbles. The performance of micron-sized bubbles is related to the nature and source of the gas source when different gas media are selected to make microbubbles. There are differences in the use of microbubbles when different gas media are selected. When using air, the corrosion of the tubing due to oxygen must be considered. When using N2, the cost of producing or purchasing and transporting N2 must be considered. When using CO2, the corrosion caused by producing CO2 and the consumption caused by the miscibility of CO2 with crude oil must be considered. When using natural gas, the cost of producing natural gas and the characteristics of high-pressure gas escape must be considered.

[0029] Furthermore, the pressure value of the high-pressure gas is set to be greater than the pressure value of the injected water flow. The high-pressure gas is squeezed into the injected water flow through the micron-sized perforated plate in the microbubble generator to produce an injected water flow containing micron-sized bubbles. The pressure value of the high-pressure gas needs to overcome the shear force of the special perforated plate and is related to the pressure of the injected water flow and the micron-sized perforated plate. It is determined by the pressure, bubble diameter, concentration, etc., of the microbubbles to be generated. Therefore, the pressure value of the high-pressure gas is set to be 0.3 to 0.5 MPa greater than the pressure of the high-pressure water flow.

[0030] Furthermore, the volume of the micron-sized bubbles accounts for 5%-30% of the volume of the injected water flow. The concentration of micron-sized bubbles in the injected water flow is determined according to the seepage conditions of the reservoir. Generally, when the injection pressure is relatively low, a higher concentration of micron-sized bubbles is used. Setting the volume fraction of micron-sized bubbles is necessary to ensure that the micron-sized bubbles can enter the deep reservoir and play a role in oil displacement, while also blocking high-permeability channels. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the micron-sized bubble generating device in this invention;

[0032] Figure 2This is a graph showing the effect of different gas-liquid ratios on the flow resistance and apparent viscosity of microbubble aqueous solutions in this invention.

[0033] Figure 3 This is a schematic diagram illustrating the effect of the pressure difference between air and water on the bubble diameter of micron-sized bubbles in this invention; wherein, Figure 3 a is a micron-sized bubble diagram with a gas-water pressure difference of 0.2 MPa. Figure 3 b is a micron-sized bubble diagram with a gas-water pressure difference of 0.5 MPa. Figure 3 c is a micron-sized bubble diagram with a gas-water pressure difference of 0.8 MPa;

[0034] Figure 4 This is a schematic diagram illustrating the effect of pressure on the bubble diameter of micron-sized bubbles in this invention.

[0035] The components include: 1. central exhaust pipe; 2. micron perforated plate; 3. gas connecting pipe; 4. outer cylinder; 5. internal connecting pipe; 6. internal filter; 7. internal one-way valve; and 8. pressure cap. Detailed Implementation

[0036] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0037] This invention provides a method for enhancing oil recovery based on microbubble flooding; the method is applied to the waterflooding development process of low-permeability reservoirs; the method specifically includes the following steps:

[0038] Step 1: Add micron-sized air bubbles to the water flow to obtain a microbubble aqueous solution.

[0039] The preparation process of the microbubble aqueous solution is as follows:

[0040] A microbubble generator is installed on the high-pressure water injection pipeline of the water injection well; water is introduced between the central exhaust pipe 1 and the outer cylinder 4, and high-pressure gas is introduced into the central exhaust pipe 1; when the high-pressure gas passes through the micron-sized perforated plate 2 at the exhaust port, it forms micron-sized bubbles and enters the water injection flow to mix and obtain a microbubble aqueous solution.

[0041] As attached Figure 1As shown, the microbubble generator includes a central exhaust pipe 1, a microporous plate 2, a gas connecting pipe 3, an internal connecting pipe 5, an internal filter 6, an internal one-way valve 7, and a pressure cap 8. The central exhaust pipe 1 is concentrically arranged inside the outer cylinder 4 of the high-pressure water injection pipeline. One end of the central exhaust pipe 1 is connected to the gas source, and the other end is closed. The central exhaust pipe 1 is provided with a plurality of exhaust ports at intervals, and the microporous plate 2 is installed at the exhaust ports. The microporous plate 2 is provided with a plurality of micron-sized through holes.

[0042] The outer cylinder 4 has a mounting flange at its top, which includes an upper flange and a lower flange. The lower end of the lower flange is connected to the top end of the outer cylinder 4, and the upper end of the lower flange is fixedly connected to the upper flange. The upper flange and the lower flange each have a central through hole. The internal connecting pipe 5 is disposed in the central hole of the upper flange, and the upper end of the internal connecting pipe 5 is connected to the lower end of the gas connecting pipe 3. The upper end of the gas connecting pipe 3 is connected to a gas source. The internal filter 6 is disposed in the gas connecting pipe 3 for filtering high-pressure gas.

[0043] A pressure cap 8 is fitted on the outer side of the inner connecting pipe 5, and the pressure cap 8 is used to fix the inner connecting pipe 5 to the upper flange. An internal one-way valve 7 is provided at the upper end of the central through hole of the upper flange, and the internal one-way valve 7 is located between the upper flange and the pressure cap 8. A water inlet is provided on the upper side wall of the outer cylinder 4. The water inlet is connected to a water source through a pipeline. The water flow can enter the annular space between the outer cylinder 4 and the central exhaust pipe 1 through the water inlet, and mix with the micron-sized bubbles generated by the micron-sized perforated plate 2 to obtain a microbubble aqueous solution.

[0044] In this invention, micron-sized bubbles are formed by jetting through a micron-perforated plate. The radius of the bubbles matches the pore size of low-permeability rocks, the microbubble clusters are uniformly distributed, and the gas-liquid ratio is adjustable. The microbubble generating device meets the environmental conditions of 150℃ and 70MPa, and is suitable for high-temperature and high-pressure reservoir conditions.

[0045] Step 2: Inject the microbubble aqueous solution into the oil reservoir through a water injection well;

[0046] Step 3: During the migration process after the microbubble aqueous solution enters the reservoir, the micron-sized bubbles in the microbubble aqueous solution aggregate and grow or shear and shrink, thereby increasing the flow resistance of the first type of permeation channel in the reservoir and increasing the displacement pressure of the water flow in the microbubble aqueous solution in the second type of permeation channel in the reservoir.

[0047] The first type of infiltration channel includes infiltration pores with a water flow permeability of 3-125 mD, infiltration channels with a water flow permeability of 40-600 mD, and infiltration fractures with a water flow permeability of 300-1500 mD; the second type of infiltration channel includes infiltration pores with a water flow permeability of less than 3 mD, infiltration channels with a water flow permeability of less than 40 mD, and infiltration fractures with a water flow permeability of less than 300 mD.

[0048] In this invention, the bubble diameter of the micron-sized bubbles matches the pore throat size of the reservoir; preferably, the bubble diameter of the micron-sized bubbles is 1μm-100μm; the high-pressure gas is one of air, N2, CO2 and natural gas; the pressure value of the high-pressure gas is greater than the pressure value of the injected water flow; wherein, the difference between the pressure value of the high-pressure gas and the pressure value of the injected water flow is 0.3-0.5 MPa.

[0049] In this invention, the microbubble aqueous solution is injected into the oil reservoir through a water injection well; wherein, in the microbubble aqueous solution, micron-sized bubbles are a uniformly dispersed phase, and the injected water flow is a continuous phase; in the microbubble aqueous solution, the volume of the micron-sized bubbles accounts for 5%-30% of the volume of the injected water flow; the apparent viscosity of the microbubble aqueous solution is more than twice the apparent viscosity of water; the apparent viscosity of the microbubble aqueous solution increases as the bubble diameter of the micron-sized bubbles decreases.

[0050] The oil recovery enhancement method based on microbubble flooding described in this invention involves the microbubble aqueous solution undergoing aggregation and growth or shear reduction during its migration into the reservoir, thereby increasing the flow resistance of high-permeability channels within the reservoir and simultaneously increasing the displacement pressure of the injected water flow in low-permeability channels within the reservoir.

[0051] The present invention provides a method for enhancing oil recovery based on microbubble flooding. In the process of waterflooding development of low-permeability reservoirs, as the water-bearing channel forms, the oilfield gradually enters the medium-to-high water-cut stage. The remaining oil is mainly located in the area not fully reached by waterflooding, and the oilfield's crude oil production gradually decreases, with the final recovery rate less than 30%. By using the microbubble flooding method, micron-sized bubbles are added during the waterflooding development process. After entering the reservoir with high-pressure water injection, the bubbles increase the water flow resistance in the waterflooding channel, thereby increasing the driving pressure of the unwaterflooded reservoir, expanding the waterflooding volume, improving waterflooding efficiency, increasing crude oil production, and ultimately improving the oilfield's final recovery rate.

[0052] Working principle:

[0053] The oil recovery enhancement method based on microbubble flooding described in this invention involves adding micron-sized bubbles to the injected water flow to obtain a microbubble aqueous solution. During the migration of the microbubble aqueous solution into the reservoir, the micron-sized bubbles aggregate and grow or shrink due to shearing. The micron-sized bubbles increase the flow resistance of high-permeability channels in the reservoir through the Jamin effect, viscosity enhancement, and pressure enhancement. At the same time, they increase the displacement pressure of the injected water flow in low-permeability channels within the reservoir, expand the water-driven swept volume of the reservoir, and increase crude oil production to improve the recovery rate.

[0054] The oil recovery enhancement method based on microbubble flooding described in this invention effectively increases the seepage resistance factor and expands the water drive sweep area during the oil displacement process using microbubble aqueous solution, thereby improving the recovery rate. As shown in Table 1 below, Table 1 presents the test results of the resistance factor and recovery rate of porous cores improved by microbubble aqueous solution.

[0055] As can be seen from Table 1, the microbubble aqueous solution can effectively control the core flow rate ratio in low-permeability reservoirs, expand the sweep area, and thus improve the oil recovery rate.

[0056] Table 1. Test results of microbubble aqueous solution improving the resistance factor and recovery rate of porous cores.

[0057] Penetration rate, mD seepage resistance factor Increase the recovery rate by % 0.57 4.89 8.42 5.3 3.74 10 40.5 1.92 16.83

[0058] In this invention, two low-permeability outcrops with a permeability difference of 10 times are bonded and compacted to establish a longitudinally connected two-layer low-permeability heterogeneous long core model. The core is first water-driven, with a water recovery rate as low as 35.5%. Then, an ultra-low IFT surfactant system is used for displacement, increasing the EOR by 1.5%. Finally, a microbubble aqueous solution is used for displacement, resulting in a cumulative increase in EOR of 17%, as shown in Table 2 below.

[0059] Table 2. Test Results of Microbubble Drive Improving Recovery Rate of Fractured Cores

[0060]

[0061] This invention studies the microbubble generation principle through experiments. When gas passes through the micropores on the microporous plate at high speed, turbulent flow occurs in the local areas above and below the micropores. The pressure difference, the gas-water interfacial tension at the micropore edge, and the shearing effect at the edge cause the gas passing through the micropores to form discrete micron-sized bubbles. During high-pressure water injection, the high-speed gas jet from the micropores of the microporous plate forms a high-pressure microbubble system with a bubble diameter of 1μm-100μm, which enters the reservoir. By adjusting the displacement pressure, the resistance of the water drive dominant channel is increased, the water drive pressure of the low-permeability channel is increased, and the water drive sweep efficiency is expanded.

[0062] (1) Evaluation of Enhanced Oil Recovery in Heterogeneous Reservoirs

[0063] Two low-permeability outcrops with a permeability difference of 10 times (1.9 mD and 22 mD respectively) were bonded and compacted to establish a longitudinally connected two-layer low-permeability heterogeneous long core model. Using a water / N2 microbubble system, the water-drive recovery rate was increased from 36.50% to 50.62%; using a water / CO2 microbubble system, the water-drive recovery rate was increased from 35.40% to 53.56%. Through displacement of the low-permeability heterogeneous long cores, it was verified that the microbubble system can effectively increase the recovery rate after water-drive by more than 10% and expand the swept volume by more than 20%. The performance of the water / CO2 microbubble system is superior to that of the water / N2 microbubble system.

[0064] (2) Evaluation of Enhanced Oil Recovery in Porous Reservoirs

[0065] Using core samples with a permeability of 21.4 mD, a water / microbubble displacement evaluation test was conducted. Injected water could increase the reservoir recovery rate to 53.2%, while microbubble displacement could increase the recovery rate to 65.3%. This shows that microbubble displacement has a significant effect on improving the recovery rate in low-permeability environments. The test results indicate that microbubble displacement improves the recovery rate gradually, has a long duration of action, and has a significant effect.

[0066] Example

[0067] Taking the application of microbubble aqueous solution in a long layer of an oilfield as an example.

[0068] The oil reservoir in a certain oilfield is a long-form lithological reservoir. The main rock and mineral composition is grayish-green silty to fine-grained lithic feldspathic sandstone, with chlorite and ferrocalcite as the main interstitial materials. The average porosity is 12.69%, and the permeability is 1.81 mD, which is a low-porosity and ultra-low-permeability reservoir. The original formation pressure of the oil layer is 12.2 MPa, the temperature is 54.73℃, the crude oil viscosity is 1.95 mPa·s, the asphaltene content is 2.96%, the formation water salinity is 82 g / L, the chloride ion content is 50481 mg / L, the pH value is 5.9-6, and it belongs to the CaCl2 water type.

[0069] In November 2020, microbubble aqueous solutions were injected into four test wells to conduct enhanced oil recovery applications; as of October 2021, 145.4 × 10⁻⁶ gas had been injected. 4 Nm 3The completion rate was 11.7%, and the overall operation was stable. In the four microbubble aqueous solution test well groups, the daily oil production increased from the original 23.0t to 26.6t, and the water cut decreased from the original 64.8% to 60.1%. Among them, the daily oil production of the central well increased from the original 0.3t to 1.45t, and the water cut decreased from the original 95.3% to 76.8%, with a cumulative increase of 2445t of oil and an input-output ratio of 1:1.13, achieving good initial results. The stage decline decreased from the original 6.57% to 21.06%, and the water cut increase rate decreased from the original 20.93% to -14.33%, with a significant effect of water reduction and oil increase.

[0070] In this embodiment, the relationship curve between the water cut increase rate and the geological reserve recovery rate of the test well group shows that the water cut increase was controlled after the microbubble aqueous solution test. In particular, the water cut decrease was significant after the injection of microbubble aqueous solution. From November 2020 to the present, the geological reserve recovery rate of the four microbubble aqueous solution test well groups has increased by 0.23% compared with water drive, and it is expected to increase by 5.75% in 25 years.

[0071] In this embodiment, a microbubble flooding test was conducted in one block of the aforementioned oilfield, involving four water injection wells and 19 corresponding evaluation wells. The test was carried out on-site for 18 months. The crude oil production rate decreased from 6.57% to 21.06%, resulting in an increase of 3776.8 tons of oil. The production of the four core wells in the microbubble flooding test increased from 0.3 tons / day to 1.45 tons / day, and the water cut decreased from 95.3% to 76.8%, achieving good initial results.

[0072] As attached Figure 2 As shown, attached Figure 2 The effects of different gas-liquid ratios on the flow resistance and apparent viscosity of microbubble aqueous solutions are presented in the attached graphs. Figure 2 As can be seen from the data, for homogeneous cores, microbubble aqueous solutions can effectively regulate the mobility ratio of ultra-low permeability and low permeability cores, expand the swept volume, and improve the oil recovery rate, but the effect on medium and high permeability cores is not obvious.

[0073] As attached Figure 3 As shown, attached Figure 3 The diagram illustrates the effect of the pressure difference between air and water on the bubble diameter of micron-sized bubbles; among which, Figure 3 a is a micron-sized bubble diagram with a gas-water pressure difference of 0.2 MPa. Figure 3 b is a micron-sized bubble diagram with a gas-water pressure difference of 0.5 MPa. Figure 3 c represents a micron-sized bubble diagram with a gas-water pressure difference of 0.8 MPa; from the attached diagram... Figure 3 As can be seen, the greater the pressure difference between air and water, the larger the bubble diameter. Reasonable control of the pressure difference is the key to bubble diameter control. Under the same conditions, a pressure difference of 0.2 MPa produces a bubble diameter of 300 μm; 0.5 MPa produces a bubble diameter of 500 μm; and 0.8 MPa produces a bubble diameter of 1500 μm.

[0074] As attached Figure 4 As shown, attached Figure 4 The diagram shows the effect of pressure on the bubble diameter of micron-sized bubbles; from the appendix... Figure 4 As can be seen, the bubble diameter decreases significantly after pressurization; in the N2 microbubble flooding system: 300μm bubbles are generated at 12MPa on the ground, and after migrating to the formation location, the bubble diameter becomes 10μm when the pressure is increased by 15MPa.

[0075] The oil recovery enhancement method based on microbubble flooding described in this invention applies micron-sized bubbles during water injection development in low-permeability reservoirs. These micron-sized bubbles are injected into the reservoir with high-pressure water flow. During migration within the reservoir, they aggregate and grow or shrink due to shearing, increasing the flow resistance in high-permeability channels, raising the displacement pressure in low-permeability channels, expanding the water-drive sweep volume, improving water-drive efficiency, increasing well production, and enhancing oilfield recovery. During high-pressure water injection, an orifice plate method is used, where high-speed gas injection through the orifice plate micropores forms high-pressure microbubbles with a diameter of 1μm-100μm, and the gas-liquid ratio is adjustable. The microbubbles are uniformly distributed in the high-pressure water injection at a concentration of 5%-30%, with water as the continuous phase and microbubbles as the dispersed phase. The microbubbles effectively expand the sweep efficiency in low-permeability, high-residual-oil-saturated areas. The adjustable bubble diameter (1μm-100μm) in the high-pressure microbubble aqueous solution matches the pore throat of low-permeability reservoirs. The microbubble clusters are uniformly distributed, with reduced microbubble rising speed and increased stability. Viscosity increases as bubble diameter decreases, and the gas can be one of air, N2, CO2, or natural gas. Among them, the apparent viscosity of CO2 microbubble aqueous solution can be more than 2 times higher than that of water and more than 50 times higher than that of CO2. A microbubble generator is installed on the high-pressure injection pipeline of the injection well. High-pressure gas passes through the microbubble generator to generate microbubbles, which are uniformly distributed in the high-pressure water. The microbubble generator consists of inner and outer structures. High-pressure gas in the central tube is squeezed out through the core tube orifice plate and enters the high-pressure water between the inner and outer tubes. It enters the injection well with the high-pressure water flow and controls the water drive mobility ratio during the migration process into the reservoir, thereby expanding the water drive swept volume. The gas type is matched with the reservoir and needs to be pressurized by a gas booster pump. The pressure is usually 0.3 to 0.5 MPa higher than the injection pressure and is related to the reservoir injection pressure.

[0076] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for enhancing oil recovery based on microbubble flooding, characterized in that, A method applied to the waterflooding development of low-permeability reservoirs; the method includes: Micron-sized air bubbles are added to the water flow to obtain a microbubble aqueous solution; The microbubble aqueous solution is injected into the oil reservoir through a water injection well; During the migration process after the microbubble aqueous solution enters the reservoir, the micron-sized bubbles in the microbubble aqueous solution aggregate and grow or shear and shrink to increase the flow resistance of the first type of permeation channel in the reservoir, while increasing the displacement pressure of the water flow in the microbubble aqueous solution in the second type of permeation channel in the reservoir. The first type of infiltration channels includes infiltration pores with a water flow permeability of 3-125 mD, infiltration channels with a water flow permeability of 40-600 mD, and infiltration fractures with a water flow permeability of 300-1500 mD; the second type of infiltration channels includes infiltration pores with a water flow permeability of less than 3 mD, infiltration channels with a water flow permeability of less than 40 mD, and infiltration fractures with a water flow permeability of less than 300 mD. The diameter of the micron-sized bubbles is matched to the pore throat size of the reservoir; The diameter of the micron-sized bubbles is 1μm-100μm; The process of adding micron-sized air bubbles into the injected water flow to obtain a microbubble aqueous solution is as follows: A microbubble generator is installed on the high-pressure water injection pipeline of the water injection well. The microbubble generator includes a central exhaust pipe (1) and several micro-perforated plates (2). The central exhaust pipe (1) is concentrically arranged inside the outer cylinder (4) of the high-pressure water injection pipeline. One end of the central exhaust pipe (1) is connected to the gas source, and the other end is closed. Several exhaust ports are provided at intervals on the central exhaust pipe (1), and the micro-perforated plates (2) are installed at the exhaust ports. Several micro-perforated holes are provided on the micro-perforated plates (2). Water is introduced between the central exhaust pipe (1) and the outer cylinder (4), and high-pressure gas is introduced into the central exhaust pipe (1). When the high-pressure gas passes through the micron-sized perforated plate (2) at the exhaust port, it forms micron-sized bubbles and enters the water flow to mix and obtain a microbubble aqueous solution. The pressure difference between the high-pressure gas and the injection water flow is 0.3-0.5 MPa.

2. The method for enhancing oil recovery based on microbubble flooding according to claim 1, characterized in that, The high-pressure gas is one of air, N2, CO2, and natural gas.

3. The method for enhancing oil recovery based on microbubble flooding according to claim 1, characterized in that, The pressure value of the high-pressure gas is greater than the pressure value of the injected water flow.

4. The method for enhancing oil recovery based on microbubble flooding according to claim 1, characterized in that, In the microbubble aqueous solution, the micron-sized bubbles are a uniformly dispersed phase, and the injected water flow is a continuous phase.

5. The method for enhancing oil recovery based on microbubble flooding according to claim 1, characterized in that, In the microbubble aqueous solution, the volume of the micron-sized bubbles accounts for 5%-30% of the volume of the injected water flow.

6. The method for enhancing oil recovery based on microbubble flooding according to claim 1, characterized in that, The apparent viscosity of the microbubble aqueous solution increases as the diameter of the micron-sized bubbles decreases.

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