A nitrogen foam generator with variable foam diameter and foaming method and application

Abstract

The application discloses a nitrogen foam generating device with variable foam diameter and a foaming method and application, belongs to the technical field of oilfield development, and comprises a foam generating device, and the foam generating device is most commonly used in profile control, water plugging and oil displacement construction wells. The application is composed of a gas access end, a liquid access end, a foam generating mechanism and a control part of variable foam diameter, achieves the purpose of changing the foam diameter, and can improve foaming performance and foaming quality. Meanwhile, the utilization rate of the foam in water plugging, profile control, channeling sealing and other process measures in oilfields can be improved, the profile control, water plugging and channeling sealing needs of different types of oil reservoirs can be met, the foam system has good temperature resistance, and the needs of preventing gas channeling in steam huff and puff of heavy oil reservoirs and plugging large channels in steam drive of heavy oil reservoirs can be better met, support is provided for oilfield oil increase and production increase, and guarantee is provided for an energy security strategy.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, specifically a nitrogen foam generating device with variable foam diameter, a foaming method, and its application. Background Technology

[0002] During oilfield development, oil wells will eventually produce water, and the water content in the produced fluid gradually increases. Especially when the oilfield enters the water injection development stage, the water content of the oil well increases even faster, which will seriously affect the oil production of the oil well. Research has been carried out on oil well water plugging and water injection well profile adjustment technology to address water production in oil wells, and this technology has gradually become one of the important technological measures for stabilizing oilfield production.

[0003] Water injection well profile control involves selectively blocking high-permeability layers and large pores in water injection wells to adjust and improve the water absorption profile, allowing the injected water to advance more evenly, thereby increasing the swept volume of the injected water and improving water drive recovery. Water injection well profile control does not affect the normal production of oil wells. One water injection well profile control can benefit multiple oil wells. It is easy to implement and has a long effective period, making it one of the leading technologies for water control and oil stabilization during the high water-cut period of oilfield development.

[0004] For oil and water wells in oilfields, water shut-off, profile control, and channel sealing technologies are being developed, and these technologies are gradually becoming important measures for stabilizing oilfield production. Conventional oilfield water shut-off, profile control, and channel sealing operations mostly use liquid or liquid suspension as the constituent systems. Foam is also widely used in oilfields due to its good cost performance, temperature resistance, and elasticity. Due to the special properties of relatively homogeneous foam fluid, it is currently widely used in various aspects such as foam sand flushing, foam acid removal, foam mixing, foam acidizing, foam induced flow, foam bottom water suppression, foam profile control, foam oil displacement, foam underbalanced drilling, and foam fracturing, showing great application potential. The main device for foam generation is the foam generator.

[0005] Currently, the main problems with oilfield foam generator systems are as follows:

[0006] (1) The diameter of a single foam cannot be controlled, and the uniformity of the foam cluster cannot be controlled.

[0007] Currently used foam generators typically consist of a three-dimensional porous medium within a cavity. Liquid and gas mix inside, generating foam through this porous medium. The individual foam particles vary in diameter. Indoor studies show that the diameter difference between individual foam particles generated by conventional foam generators ranges from 5 to 20, meaning the ratio of large to small foam diameters is within this range. Due to this large diameter variation, foam stability deteriorates. Broken foam particles result in more liquid and less gas, reducing the effective foaming process.

[0008] (2) The plugging is not targeted at different types of reservoirs.

[0009] Currently, there are increasingly more methods to enhance oil recovery in different reservoirs. Foam water shut-off and foam flooding are becoming more and more adaptable to medium-high permeability reservoirs and medium-low permeability reservoirs. However, the permeability of medium-low permeability reservoirs varies significantly. Medium-low permeability reservoirs suitable for foam flooding are mostly concentrated in the range of 10mD-100mD, while medium-high permeability reservoirs are mostly concentrated in the range of 100mD-1000mD. Therefore, the size of the foam needs to be matched accordingly.

[0010] Indoor studies have shown that, based on experiments on the plugging rate of cores with different foam diameters, there is an optimal range for the selection of foam diameter for oil reservoirs with different permeability.

[0011] Table 1. Experimental results of foam diameter and core plugging rate at different permeabilities.

[0012]

[0013]

[0014] Experiments show that different foam diameters correspond to different permeability levels, resulting in a relatively ideal plugging rate. A good plugging rate of foam in the formation is a key indicator for successful foam water shut-off and foam oil displacement. Therefore, controlling the foam diameter becomes a crucial factor for the success of foam water shut-off and foam oil displacement.

[0015] (3) The foam generator produces poor foam quality and poor foaming stability.

[0016] Conventional foam generators produce foam with varying diameters. Indoor experiments show that foam clumps of different sizes also exhibit significant differences in stability.

[0017] Table 2 Half-life of foam clusters with different foam diameters

[0018]

[0019] Experiments show that when the foam size is nearly uniform, its half-life is the longest and the foam cluster is the most stable. Only a stable foam cluster can play a better role in sealing and displacing oil. Summary of the Invention

[0020] To overcome the above-mentioned defects, the present invention provides a nitrogen foam generating device with variable foam diameter, a foaming method and application, which solves the problems of uncontrollable individual foam diameter, uncontrollable foam cluster uniformity, weak targeting for sealing different types of oil reservoirs, poor foam quality of foam generator and poor foaming stability.

[0021] To achieve the above objectives, the present invention provides the following technical solution: a nitrogen foam generator with variable foam diameter, comprising a liquid inlet end and an air inlet end, one end of which is connected to the same atomizer. A baffle is provided in the middle of the atomizer, and the atomizer outputs a gas-liquid mixture. Three sets of fixed and rotatable impellers are provided on the gas-liquid mixture away from the atomizer. A first-stage variable-aperture impeller, a second-stage variable-aperture impeller, and a third-stage variable-aperture impeller are respectively provided between two opposite fixed and rotatable impellers. A variable-aperture adjustment knob is provided at the bottom of the three sets of fixed and rotatable impellers. The side of the third-stage variable-aperture impeller away from the atomizer is provided as a foam system, and a foam outlet end is provided on the foam system away from the third-stage variable-aperture impeller.

[0022] As a further embodiment of the present invention: the atomizer, baffle, fixed impeller, rotatable impeller, first-stage variable-aperture impeller, second-stage variable-aperture impeller, third-stage variable-aperture impeller, gas-liquid mixture and foam system are all integrated in a single housing, and the liquid inlet end and air inlet end are embedded in the housing, the variable-aperture adjustment knob is installed at the bottom of the housing, and the foam outlet end is embedded on the side of the housing away from the atomizer.

[0023] As a further aspect of the present invention: the fixed grinding wheel is provided with a plurality of grinding wheel holes one on the side away from the atomizer, and the rotatable grinding wheel is provided with a plurality of grinding wheel holes two on the side close to the atomizer.

[0024] As a further aspect of the present invention: both the liquid inlet end and the air inlet end are provided with one-way valves, which are used for the liquid and gas to flow towards the atomizer and to prevent the liquid and gas from flowing back.

[0025] A foaming method for a nitrogen foam generator with variable foam diameter, comprising the following foaming steps:

[0026] S1, Gas-liquid atomization

[0027] The foaming agent liquid and gas are introduced into the liquid inlet and gas inlet respectively, so that the foaming agent liquid and gas enter the atomizer through the one-way valve to form a fine and uniform gas-liquid mixture, with the gas being the continuous phase and the liquid being the dispersed phase.

[0028] S2, Foam generation

[0029] During the formation of a gas-liquid mixture, the micropores of the first-stage variable-pore wheel capture the droplets, which will generate a bubble-blowing effect. Some of the droplets that are not blown will continue to be captured by the second-stage and third-stage variable-pore wheels to complete the bubble-blowing effect, generating foam and eventually forming a foam system.

[0030] S3, Foam Diameter Control

[0031] After the gas-liquid mixture passes through the first-stage, second-stage, and third-stage variable-aperture grinding wheels, the droplets are captured by the micropores on these wheels. The overlapping holes of the fixed and rotatable grinding wheels change their diameters under the adjustment of the variable-aperture adjustment knob, and micropores of different diameters produce foams of different diameters.

[0032] As a further aspect of the present invention: in S1, the atomizer controls the size of the atomized droplets by controlling the pressure at its input end and the diameter of the nozzle.

[0033] As a further aspect of the present invention: in S2, the gas-liquid mixture forms foam by passing through a body with a certain pore size, and the resulting foam has a uniform size.

[0034] As a further aspect of the present invention: In S3, the foam size can be made homogeneous by using a first-stage variable-aperture wheel, a second-stage variable-aperture wheel, and a third-stage variable-aperture wheel. The foam diameter at different temperatures and pressures can be calculated using the gas state equation, which can match different types of reservoir water shut-off, profile control, and oil displacement.

[0035] An application of a nitrogen foam generator with variable foam diameter is disclosed. The foam generator is used for foam sand flushing, foam acid removal, foam mixing, foam acidizing, foam induction, foam bottom water suppression, foam profile control, foam oil displacement, foam underbalanced drilling, and foam fracturing. It is most commonly used in wells for profile control, water shut-off, and oil displacement.

[0036] The specific application of the foam generating device is achieved through the following construction process:

[0037] The foam base liquid is prepared in the mixing tank A, and gas is injected using the gas generator B. The base liquid and gas are mixed in the foam generator C to produce uniform foam of controllable size. The foam is then injected into the construction well E through the pump truck D to complete the on-site construction task.

[0038] The beneficial effects of this invention are as follows: Based on a gas inlet, a liquid inlet, a foam generating mechanism, and a control part with a variable foam diameter, this invention achieves the purpose of changing the foam diameter and can also improve foaming performance and foaming quality. At the same time, it can improve the utilization rate of foam in oilfield water shut-off, profile control, and channel sealing processes, meeting the needs of different types of reservoirs for profile control, water shut-off, and channel sealing. Because the foam system has good temperature resistance, it can also better meet the needs of heavy oil reservoirs for steam injection to prevent gas channeling and for steam drive to seal large channels in heavy oil reservoirs. Therefore, this application can provide technical support for increasing oil production in oilfields and provide technical guarantee for energy security strategy. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the foam generating device of the present invention;

[0040] Figure 2 This is a side view schematic diagram of the fixed and rotatable friction wheels of the present invention;

[0041] Figure 3 This is a flowchart illustrating the construction process of the present invention.

[0042] In the diagram: 1. Liquid inlet; 2. Air inlet; 3. One-way valve; 4. Atomizer; 5. Baffle; 6. Fixed grinding wheel; 7. Rotary grinding wheel; 8. First-stage variable-aperture grinding wheel; 9. Second-stage variable-aperture grinding wheel; 10. Third-stage variable-aperture grinding wheel; 11. Variable-aperture adjustment knob; 12. Foam outlet; 13. Gas-liquid mixture; 14. Foam system; 15. Grinding wheel hole one; 16. Grinding wheel hole two. Detailed Implementation

[0043] The technical solution of this patent will be further described in detail below with reference to specific embodiments.

[0044] like Figure 1-3 As shown, the present invention provides a technical solution: a nitrogen foam generator with variable foam diameter, including a liquid inlet end 1 and an air inlet end 2. One end of the liquid inlet end 1 and the air inlet end 2 are connected to the same atomizer 4. A baffle 5 is provided in the middle of the atomizer 4. The atomizer 4 outputs a gas-liquid mixture 13. Three sets of fixed grinding wheels 6 and rotatable grinding wheels 7 are provided in the gas-liquid mixture 13 away from the atomizer 4. A first-stage variable-aperture grinding wheel 8, a second-stage variable-aperture grinding wheel 9 and a third-stage variable-aperture grinding wheel 10 are respectively provided between two opposite fixed grinding wheels 6 and rotatable grinding wheels 7. A variable-aperture adjustment knob 11 is provided at the bottom of the three sets of fixed grinding wheels 6 and rotatable grinding wheels 7. A foam system 14 is provided on the side of the third-stage variable-aperture grinding wheel 10 away from the atomizer 4. A foam outlet end 12 is provided in the foam system 14 away from the third-stage variable-aperture grinding wheel 10.

[0045] The atomizer 4, baffle 5, fixed whirl wheel 6, rotatable whirl wheel 7, first-stage variable-aperture whirl wheel 8, second-stage variable-aperture whirl wheel 9, third-stage variable-aperture whirl wheel 10, gas-liquid mixture 13 and foam system 14 are all integrated in a single housing, with the liquid inlet 1 and air inlet 2 embedded in the housing, the variable-aperture adjustment knob 11 installed at the bottom of the housing, and the foam outlet 12 embedded on the side of the housing away from the atomizer 4.

[0046] The fixed grinding wheel 6 has several grinding wheel holes 15 on the side away from the atomizer 4, and the rotatable grinding wheel 7 has several grinding wheel holes 16 on the side close to the atomizer 4.

[0047] Both the liquid inlet 1 and the air inlet 2 are equipped with one-way valves 3. The one-way valves 3 are used for the flow of liquid and gas towards the atomizer 4 and to prevent the backflow of liquid and gas.

[0048] A foaming method for a nitrogen foam generator with variable foam diameter, comprising the following foaming steps:

[0049] S1, Gas-liquid atomization

[0050] The foaming agent liquid and gas are introduced into the liquid inlet 1 and the gas inlet 2 respectively, so that the foaming agent liquid and gas enter the atomizer 4 through the one-way valve 3 to form a fine and uniform gas-liquid mixture 13, with the gas being the continuous phase and the liquid being the dispersed phase.

[0051] S2, Foam generation

[0052] During the formation of the gas-liquid mixture 13, the micropores of the first-stage variable-pore wheel 8 will capture the bubble-blowing effect. Some of the unbubbled droplets will be captured by the second-stage variable-pore wheel 9 and the third-stage variable-pore wheel 10 to complete the bubble-blowing effect, generate foam, and finally form a foam system 14.

[0053] S3, Foam Diameter Control

[0054] After the gas-liquid mixture 13 passes through the first-stage variable-aperture wheel 8, the second-stage variable-aperture wheel 9, and the third-stage variable-aperture wheel 10, the droplets are captured by the micropores on the first-stage variable-aperture wheel 8, the second-stage variable-aperture wheel 9, and the third-stage variable-aperture wheel 10. The overlapping holes of the fixed wheel 6 and the rotatable wheel 7 change their aperture under the adjustment of the variable-aperture adjustment knob 11. Micropores of different diameters produce foams of different diameters.

[0055] In S1, the atomizer 4 controls the size of the atomized droplets by controlling the pressure at its input end and the diameter of the nozzle.

[0056] In S2, the gas-liquid mixture 13 forms foam by passing through a body with a certain pore size, and the resulting foam has a uniform size.

[0057] In S3, the first-stage variable porosity grinding wheel 8, the second-stage variable porosity grinding wheel 9, and the third-stage variable porosity grinding wheel 10 can make the foam size homogeneous. The foam diameter under different temperatures and pressures can be calculated by the gas state equation, which can match different types of reservoir water shut-off, profile control, and oil displacement.

[0058] An application of a nitrogen foam generator with variable foam diameter. The foam generator is used for foam sand flushing, foam acid removal, foam mixing, foam acidizing, foam induction, foam bottom water suppression, foam profile control, foam oil displacement, foam underbalanced drilling, and foam fracturing. It is most commonly used in wells for profile control, water shut-off, and oil displacement.

[0059] The specific application of foam generators is achieved through the following construction process:

[0060] The foam base liquid is prepared in the mixing tank A, and gas is injected using the gas generator B. The base liquid and gas are mixed in the foam generator C to produce uniform foam of controllable size. The foam is then injected into the construction well E through the pump truck D to complete the on-site construction task.

[0061] Example 1:

[0062] Using this application, a statistical analysis of foam diameter range was conducted indoors. The experiment showed that the median foam size generated by the foam generator was relatively concentrated, with the median particle size being close to the grinding wheel aperture. Large-diameter and small-diameter foams accounted for a small proportion, and the median foam diameter was greater than 80%. The experimental data on the proportion of foam cluster diameter are shown in Table 3.

[0063] Table 3. Experimental results on the proportion of foam cluster diameter.

[0064]

[0065]

[0066] Note: The experimental conditions were indoor atmospheric pressure. The foam under high pressure needed to be converted using the "ideal gas law". The foam size was measured by observing the diameter of a sample of the foam mass under a microscope.

[0067] Example 2:

[0068] Using this application, an indoor foam half-life experiment was conducted. The experiment showed that the foam generated by the foam generating device had a half-life that was more than three times that of foam generated by conventional foaming. The comparison data of foam half-life are shown in Table 4.

[0069] Table 4 Comparison of foam half-life

[0070]

[0071] Note: The experimental conditions are indoor atmospheric pressure conditions. The foam needs to be converted using the "ideal gas law" under high pressure.

[0072] Based on Examples 1 and 2, it can be concluded that the diameter of individual foams and the uniformity of foam clusters are effectively controlled. Indoor experiments show that the diameter difference of individual foams generated by this foam generating device is 1-5, and the ratio of large foam diameter to small foam diameter is in the range of 1-5.

[0073] Example 3:

[0074] The specific application of foam generating devices includes the following construction steps:

[0075] Applications in wells for profile control, water shut-off, and oil displacement

[0076] Well selection principles for profile control wells:

[0077] ① For reservoir types, choose medium-low permeability reservoirs. Foam profile control is not suitable for reservoirs with interconnected fractures.

[0078] ② Well groups with relatively clear correspondence between oil and water wells, either one-to-one or one-to-many, with wells having clear correspondence detected by tracers being the preferred selection.

[0079] ③ Oil reservoirs with mineralization ≤10mg / l, underground crude oil viscosity ≤100mpa.s, and formation temperature ≤150℃.

[0080] Well selection principles for water plugging:

[0081] ① For reservoirs with medium to low permeability, foam water shut-off is not suitable.

[0082] ② Oil wells with water content ≤95% exhibit obvious bottom water ridges and edge water surges.

[0083] ③ Oil reservoirs with mineralization ≤10mg / l, underground crude oil viscosity ≤100mpa.s, and formation temperature ≤150℃.

[0084] Before construction, the liquid inlet and air inlet are connected to the foam generator, the foam outlet is connected to the wellhead, and the construction pipeline is connected to debug the process flow to meet the construction requirements of no puncture and no leakage.

[0085] Based on the designed gas and liquid ratio, the underground volume ratio of gas and liquid is calculated using the "ideal gas law".

[0086] For example, profile adjustment work is being carried out on a certain well:

[0087] Reservoir temperature: 100℃, reservoir pressure: 10MPa, permeability: 2mD, porosity: 30%, reservoir thickness: 20 meters, design subsurface treatment radius: 15 meters. The calculations using the formula are as follows:

[0088] The total amount of plug used in the formation working section is calculated according to the formula:

[0089]

[0090] In the formula:

[0091] R—the radius (m) reached by the plugging agent in a high-permeability layer;

[0092] h——oil layer penetration thickness (m);

[0093] —Porosity of the oil layer (%);

[0094] α — Longitudinal coefficient (%);

[0095] β — Direction coefficient (%)

[0096] The well is known If h = 10m, R = 15m, α = 60%, and β = 50%, then the amount of plugging agent required can be calculated as follows:

[0097] V=3.14*15*15*20*0.30*0.6*0.5=1271.7m 3

[0098] The design value is a total foam volume of 1300 m³. 3 If the underground gas-liquid ratio is 1:1, then the following can be calculated using the gas law:

[0099] Foam base liquid 650m 3 Gas 48584.2 Nm 3 The ratio of underground gas to surface gas compression is 75:1.

[0100] Adjust the orifice diameters of the first-stage variable-aperture grinding wheel 8, the second-stage variable-aperture grinding wheel 9, and the third-stage variable-aperture grinding wheel 10 to obtain the desired diameter;

[0101] ① The ratio of the diameter of a single foam to its volume expansion is 1:2. The volume ratio is calculated based on the formation pore throat radius and subsurface state equation in the reservoir description, and then the pore diameters of the first-stage variable pore wheel 8, the second-stage variable pore wheel 9, and the third-stage variable pore wheel 10 are determined.

[0102] ② The orifice diameters of the first-stage variable-aperture wheel 8, the second-stage variable-aperture wheel 9, and the third-stage variable-aperture wheel 10 are adjusted by the construction pressure. During the profile control and water plugging construction, due to the limitations of the formation fracturing pressure and the main line pressure, there is an upper limit to the construction pressure. On-site, the orifice diameters of the first-stage variable-aperture wheel 8, the second-stage variable-aperture wheel 9, and the third-stage variable-aperture wheel 10 can be adjusted according to the construction pressure to meet the needs of the construction pressure.

[0103] Start the liquid pump and gas pump in pump truck D to complete the foaming process.

[0104] The foam base liquid is prepared in the mixing tank A, and gas is injected using the gas generator B. The base liquid and gas are mixed in the foam generator C to produce uniform foam of controllable size. The foam is then injected into the construction well E through the pump truck D to complete the on-site construction task.

[0105] Example 4:

[0106] Analysis of the profile control effect using a nitrogen foam generator with variable foam diameter:

[0107] (1) Nitrogen foam profile control during steam injection in a well:

[0108] During the steam injection process for this well, nitrogen foam was injected to regulate the steam injection and control the bottom water coning at the well's edge. A total of over 50,000 cubic meters of nitrogen and 3 tons of high-temperature foaming agent were injected. After the well started production, the overall water cut decreased by 15% compared to the previous injection cycle. To date, the oil production has increased by more than 1,000 tons compared to the same period of the previous cycle, and the well is still in a stable oil production period, achieving good economic benefits.

[0109] (2) Nitrogen foam profile control during steam injection in a well:

[0110] The well has an oil layer thickness of 9.1m. During the first cycle, the steam injection dryness was 64%, temperature 335℃, pressure 15.4MPa, and injection rate 2677t. Sand control was achieved using a combination of coated sand and wire mesh. Initial production was 67.7t of fluid, 14.5t of oil, 77.7% water cut, and a dynamic fluid level of 121.8m. Peak production was 51.3t of fluid, 17.5t of oil, 65.1% water cut, and a dynamic fluid level of 136.5m. Production lasted 87 days, producing a total of 1303t of oil and 3882t of water, with a water recovery rate of 1.45%. During the second cycle, the steam injection dryness was 63%, temperature 344℃, pressure 15.5MPa, and injection rate 2836t. The initial production of the product was 77.6t of liquid, 9.0t of oil, 88.4% water content, and a dynamic liquid level of 65.1m. The peak production was also 77.6t of liquid, 9.0t of oil, 88.4% water content, and a dynamic liquid level of 65.1m. Currently, the liquid volume is 76.5t, the oil volume is 2.6t, the water content is 96.6%, and the dynamic liquid level is 266.7m. The product has been in production for 258 days. 130,000 standard cubic meters of nitrogen, 2,700 tons of steam, and 10 tons of foaming agent have been injected. The nitrogen injection pressure has been maintained at 14-15 MPa. After profile control, the liquid volume is 74.2t, the oil volume is 6.1t, the water content is 91.8%, and the cumulative increase in oil volume is 1,637.7t.

[0111] Indoor and field experiments show that the uniform foam system generated by using a "nitrogen foam generator with variable foam diameter" can achieve better construction results, providing a new technological approach for water shut-off, profile control, and enhanced oil recovery measures.

[0112] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0113] The preferred embodiments of this patent have been described in detail above. However, this patent is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this patent.

Claims

1. A nitrogen foam generator with variable foam diameter, comprising a liquid inlet (1) and a gas inlet (2), characterized in that: One end of the liquid inlet (1) and the air inlet (2) are connected to the same atomizer (4). The middle part of the atomizer (4) is provided with a baffle (5). The atomizer (4) outputs a gas-liquid mixture (13). The gas-liquid mixture (13) is provided with three sets of fixed grinding wheels (6) and rotatable grinding wheels (7) at a position away from the atomizer (4). Between the two opposite fixed grinding wheels (6) and rotatable grinding wheels (7), there are respectively a first-stage variable-aperture grinding wheel (8), a second-stage variable-aperture grinding wheel (9) and a third-stage variable-aperture grinding wheel (10). The bottom of the three sets of fixed grinding wheels (6) and rotatable grinding wheels (7) is provided with a variable-aperture adjustment knob (11). The side of the third-stage variable-aperture grinding wheel (10) away from the atomizer (4) is provided with a foam system (14). The foam system (14) is provided with a foam outlet end (12) at a position away from the third-stage variable-aperture grinding wheel (10).

2. The nitrogen foam generator with variable foam diameter as described in claim 1, characterized in that: The atomizer (4), baffle (5), fixed grinding wheel (6), rotatable grinding wheel (7), first-stage variable-aperture grinding wheel (8), second-stage variable-aperture grinding wheel (9), third-stage variable-aperture grinding wheel (10), gas-liquid mixture (13) and foam system (14) are all integrated in a single housing, and the liquid inlet (1) and air inlet (2) are embedded in the housing. The variable-aperture adjustment knob (11) is installed at the bottom of the housing, and the foam outlet (12) is embedded on the side of the housing away from the atomizer (4).

3. The nitrogen foam generator with variable foam diameter as described in claim 1, characterized in that: The fixed grinding wheel (6) has several grinding wheel holes (15) on the side away from the atomizer (4), and the rotatable grinding wheel (7) has several grinding wheel holes (16) on the side close to the atomizer (4).

4. The nitrogen foam generator with variable foam diameter as described in claim 1, characterized in that: Both the liquid inlet (1) and the air inlet (2) are provided with one-way valves (3). The one-way valves (3) are used to allow liquid and gas to flow towards the atomizer (4) and to prevent liquid and gas from flowing back.

5. A foaming method for a nitrogen foam generator with variable foam diameter, characterized in that, The nitrogen foam generator with variable foam diameter as described in any one of claims 1-4, wherein the foaming step is as follows: S1, Gas-liquid atomization The foaming agent liquid and gas are introduced into the liquid inlet (1) and the gas inlet (2) respectively, so that the foaming agent liquid and gas enter the atomizer (4) through the one-way valve (3) to form a fine and uniform gas-liquid mixture (13), with the gas being the continuous phase and the liquid being the dispersed phase. S2, Foam generation During the formation of the gas-liquid mixture (13), the micropores of the first-stage variable-pore wheel (8) will capture the bubble-blowing effect. Some of the unblown droplets will continue to be captured by the second-stage variable-pore wheel (9) and the third-stage variable-pore wheel (10) to complete the bubble-blowing effect, generate foam, and finally form a foam system (14). S3, Foam Diameter Control After the gas-liquid mixture (13) passes through the first-stage variable-aperture wheel (8), the second-stage variable-aperture wheel (9), and the third-stage variable-aperture wheel (10), the droplets are captured by the micropores on the first-stage variable-aperture wheel (8), the second-stage variable-aperture wheel (9), and the third-stage variable-aperture wheel (10). The overlapping holes of the fixed wheel (6) and the rotatable wheel (7) change their aperture under the adjustment of the variable-aperture adjustment knob (11). Micropores of different diameters produce foams of different diameters.

6. The foaming method of a nitrogen foam generator with variable foam diameter as described in claim 5, characterized in that: In S1, the atomizer (4) controls the size of the atomized droplets by controlling the pressure at its input end and the diameter of the nozzle.

7. The foaming method of a nitrogen foam generator with variable foam diameter as described in claim 5, characterized in that: In S2, the gas-liquid mixture (13) forms foam by passing through a body with a certain pore size, and the resulting foam has a uniform size.

8. The foaming method of a nitrogen foam generator with variable foam diameter as described in claim 5, characterized in that: In S3, the first-stage variable porosity grinding wheel (8), the second-stage variable porosity grinding wheel (9) and the third-stage variable porosity grinding wheel (10) can make the foam size homogeneous. The foam diameter at different temperatures and pressures can be calculated by the gas state equation, which can match different types of reservoir water shut-off profile control and oil displacement.

9. An application of a nitrogen foam generator with variable foam diameter, characterized in that, The nitrogen foam generating device with variable foam diameter according to any one of claims 1-4 is applied to foam sand flushing, foam acid removal, foam mixing, foam acidizing, foam induction, foam bottom water suppression, foam profile control, foam oil displacement, foam underbalanced drilling, and foam fracturing.

10. The application of the nitrogen foam generator with variable foam diameter as described in claim 9, characterized in that, The specific application of the foam generating device is achieved through the following construction process: The foam base liquid is prepared in the mixing tank A, and gas is injected using the gas generator B. The base liquid and gas are mixed in the foam generator C to produce uniform foam of controllable size. The foam is then injected into the construction well E through the pump truck D to complete the on-site construction task.

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