Liquid nitrogen foam generating device and method

Abstract

The invention provides a liquid nitrogen foam generating device and method, the device comprises a liquid nitrogen module, a foaming mixing module and a generator module, and the generator module comprises a liquid-liquid mixer and a high-pressure foam generator. The liquid nitrogen module, the foaming mixing module and the generator module are adopted, the liquid nitrogen module can conduct pressurization, heat exchange and flow monitoring on liquid nitrogen to obtain gaseous nitrogen, and the foaming mixing module can prepare a mixed solution of a foaming agent and a foam stabilizer according to a certain proportion; and finally, the generator module mixes gaseous nitrogen and the mixed solution according to a certain proportion to obtain foam fluid, the flow of each fluid can be monitored in real time and accurately adjusted in the operation process of each module, the prepared foam fluid is stable and uniform, and the sand carrying performance is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of low-pressure horizontal wellbore cleaning and sand flushing, and particularly relates to a liquid nitrogen foam generating device and a method thereof. Background Art

[0002] In view of the actual working conditions of oil and gas horizontal wells after multi-stage fracturing transformation and well shut-in, such as sand and scale coexisting with blowout and leakage, as well as serious leakage in old wells and inability to establish effective circulation, the conventional sand flushing and well washing process has low construction efficiency, poor sand carrying effect, high risk of drill sticking, etc. Based on the many advantages of nitrogen foam fluid such as fast foaming, long foam stabilization time, low density, low leakage, and good cuttings carrying effect, it can more effectively carry the sand produced by the formation to the ground and reduce the damage to the formation. The research has formed a continuous tubing nitrogen foam wellbore cleaning process technology.

[0003] One of the core devices of the continuous tubing nitrogen foam sand flushing process technology is the liquid nitrogen foam generating device. The existing devices on the market currently have a simple overall structure and cannot achieve real-time monitoring and precise adjustment of foam density. At the same time, the prepared foam fluid is not stable and uniform enough, and the sand carrying performance is greatly reduced. Summary of the invention

[0004] In order to solve at least one problem in the background technology, the present invention provides a liquid nitrogen foam generating device and a method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A liquid nitrogen foam generating device, comprising:

[0007] A liquid nitrogen module is used to pressurize liquid nitrogen and evaporate it to obtain gaseous nitrogen, which is then transported to the generator module;

[0008] A foaming and mixing module is used to mix a foaming agent and a foam stabilizer to obtain a foam liquid, and then pressurize the foam liquid and transport it to the generator module;

[0009] a generator module, including a liquid-liquid mixer and a high-pressure foam generator;

[0010] The liquid-liquid mixer is connected to the foaming mixing module and is used to pre-mix the foam liquid and the high-pressure water-based liquid, and then deliver them to the high-pressure foam generator;

[0011] The high-pressure foam generator is connected to the liquid-liquid mixer and the liquid nitrogen module respectively, and is used to react the pre-mixed foam liquid with the high-pressure water-based liquid and the gaseous nitrogen to form a foam fluid and discharge it.

[0012] Preferably, the liquid nitrogen module comprises a liquid nitrogen circuit, on which a liquid nitrogen inlet, a liquid nitrogen centrifugal pump, a liquid nitrogen plunger pump, a liquid nitrogen evaporator, a first flow meter, a first valve and a liquid nitrogen outlet are sequentially arranged, and the liquid nitrogen outlet is connected to the high-pressure foam generator;

[0013] The liquid nitrogen centrifugal pump is used to fill the liquid nitrogen plunger pump with liquid nitrogen;

[0014] The liquid nitrogen plunger pump is used to pressurize the liquid nitrogen;

[0015] The liquid nitrogen evaporator is used to evaporate liquid nitrogen to produce gaseous nitrogen;

[0016] The first flow meter is used to measure the flow rate of gaseous nitrogen passing through;

[0017] The first valve is used to control the opening of the liquid nitrogen circuit.

[0018] Preferably, the liquid nitrogen circuit is further connected to a liquid nitrogen branch, the inlet of the liquid nitrogen branch is located between the first flow meter and the first valve, and a second valve is installed at the outlet of the liquid nitrogen branch.

[0019] Preferably, the liquid nitrogen plunger pump is one of a triplex plunger pump and a quintuple plunger pump;

[0020] The liquid nitrogen evaporator is one of a water bath evaporator and a direct-fired evaporator.

[0021] Preferably, the foaming and mixing module comprises a foaming circuit, a foam stabilizing circuit and a mixing circuit, and the bubble circuit and the foam stabilizing circuit are arranged in parallel and converge into the mixing circuit;

[0022] The foaming line is provided with a foaming agent inlet, a first upper liquid pump, a foaming box, a first booster pump and a fourth flow meter in sequence;

[0023] The foam stabilizing circuit is provided with a foam stabilizing agent inlet, a second upper liquid pump, a foam stabilizing tank, a second booster pump and a fifth flow meter in sequence;

[0024] The mixing circuit is provided with a foaming plunger pump, a third flow meter and a sixth valve in sequence, and the foaming plunger pump is connected to the outlets of the bubble circuit and the foam stabilizing circuit respectively.

[0025] Preferably, the generator module comprises a generator circuit;

[0026] The generator circuit is sequentially provided with a clean water inlet, a fourth valve, a second flow meter, a liquid-liquid mixer, a high-pressure foam generator, a third valve and a foaming fluid outlet.

[0027] Preferably, the generator module further comprises a generator branch, the inlet and outlet of the generator branch are both connected to the generator circuit;

[0028] The generator branch is provided with a fifth valve, and the inlet of the generator branch is located between the clean water inlet and the second flow meter, and the outlet is located between the third valve and the foaming fluid outlet.

[0029] A liquid nitrogen foam generating method comprises the following steps:

[0030] The liquid nitrogen is pressurized by a liquid nitrogen plunger pump in the liquid nitrogen module, and then evaporated by a liquid nitrogen evaporator in the liquid nitrogen module to obtain gaseous nitrogen, which is then transported to the generator module;

[0031] The foaming agent and the foam stabilizer are mixed through the foaming mixing module to obtain a foam liquid, which is then pressurized and transported to the generator module;

[0032] premixing the foam liquid and the high-pressure water-based liquid through a liquid-liquid mixer in the generator module and subsequently delivering them to the high-pressure foam generator;

[0033] The premixed foam liquid is reacted with the high-pressure water-based liquid and gaseous nitrogen through a high-pressure foam generator connected to the liquid-liquid mixer and the liquid nitrogen module to form a foam fluid and discharge it.

[0034] Preferably, after the foam fluid is discharged, the following steps are further included:

[0035] The density of the discharged foam fluid is tested. If the density of the foam fluid meets the target value, the foam fluid is discharged and used for well washing.

[0036] If the density of the foam fluid does not meet the target value, the foam fluid is discharged and the flow rate of the foam liquid and the flow rate of the liquid nitrogen are adjusted, and the density of the foam fluid is retested until the density of the foam fluid meets the target value.

[0037] Preferably, the temperature of the gaseous nitrogen in the liquid nitrogen evaporator is 15-21°C;

[0038] The maximum working pressure of the liquid nitrogen plunger pump is 103.5 MPa.

[0039] Beneficial effects of the present invention:

[0040] 1. The present invention adopts a liquid nitrogen module, a foaming and mixing module and a generator module, wherein the liquid nitrogen module can pressurize, heat exchange and flow rate monitor the liquid nitrogen to obtain gaseous nitrogen, the foaming and mixing module can configure a mixed solution of a foaming agent and a foam stabilizer in a certain proportion, and finally the generator module mixes the gaseous nitrogen and the mixed solution in a certain proportion to obtain a foam fluid. During the operation of each module, the flow rate of each fluid can be monitored in real time and accurately adjusted, the prepared foam fluid is stable and uniform, and the sand carrying performance is greatly improved;

[0041] 2. The present invention has various functions, including: (1) as a nitrogen foam device: it can be used for operations such as continuous pipe nitrogen foam sand washing and continuous pipe nitrogen foam drilling and grinding; (2) as a foam drainage device: it can be used for operations such as mixed water drainage and nitrogen foam drainage; (3) as a small liquid nitrogen pump device: it can be used for operations such as nitrogen gas lifting and pressure testing; (4) as a pipeline purge device, it can be used for operations such as nitrogen purge pipelines and continuous pipes;

[0042] 3. The present invention recycles the heat generated by the device through the heat exchange function of the liquid nitrogen evaporator to provide heat for liquid nitrogen gasification, with low energy consumption, energy saving and environmental protection, high energy utilization rate, reduced equipment investment, and low operating cost; in addition, the present invention adopts a liquid nitrogen plunger pump and a foaming plunger pump to pressurize the liquid nitrogen and the foam liquid, increase the mixing uniformity, and reduce the density of the foam fluid; finally, the present invention performs real-time detection of the density of the foam fluid, and adjusts the flow rate of the liquid nitrogen or the foam liquid according to the density, so that the density control is simple.

[0043] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 A schematic diagram of the system layout of a liquid nitrogen foam generating device of the present invention is shown;

[0046] Figure 2 A schematic structural diagram of a liquid nitrogen foam generating device of the present invention is shown;

[0047] Figure 3 A flow chart of liquid nitrogen foam generation according to the present invention is shown.

[0048] In the figure: 1. liquid nitrogen inlet; 2. liquid nitrogen centrifugal pump; 3. liquid nitrogen plunger pump; 4. liquid nitrogen evaporator; 5. first flow meter; 6. first valve; 7. second valve; 8. high-pressure foam generator; 9. third valve; 10. foaming fluid outlet; 11. liquid-liquid mixer; 12. second flow meter; 13. fourth valve; 14. clean water inlet; 15. fifth valve; 16. sixth valve; 17. third flow meter; 18. foaming plunger pump; 19. fourth flow meter; 20. first booster pump; 21. foaming tank; 22. first upper liquid pump; 23. foaming agent inlet; 24. fifth flow meter; 25. second booster pump; 26. foam stabilizing tank; 27. second upper liquid pump; 28. foam stabilizing agent inlet; 29. ​​carrying device. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] A liquid nitrogen foam generating device, such as Figure 1 The example shown includes a liquid nitrogen module, a foaming and mixing module, and a generator module. The liquid nitrogen module is used to pressurize liquid nitrogen and evaporate it to obtain gaseous nitrogen, which is then transported to the generator module; the foaming and mixing module is used to mix a foaming agent and a foam stabilizer to obtain a foam liquid, which is then pressurized and transported to the generator module; the generator module includes a liquid-liquid mixer 11 and a high-pressure foam generator 8, wherein the liquid-liquid mixer 11 is connected to the foaming and mixing module to pre-mix the foam liquid and the high-pressure water-based liquid, which is then transported to the high-pressure foam generator 8; the high-pressure foam generator 8 is respectively connected to the liquid-liquid mixer 11 and the liquid nitrogen module to react the pre-mixed foam liquid with the high-pressure water-based liquid and the gaseous nitrogen to form a foam fluid and discharge it.

[0051] like Figure 2 As shown, the liquid nitrogen module, the foaming module and the generator module are all integrated in the carrying device 29. Specifically, the carrying device 29 can be one of a chassis vehicle, a trailer chassis, and a skid frame.

[0052] Furthermore, combined with Figure 1It can be seen that the liquid nitrogen module includes a liquid nitrogen circuit, on which a liquid nitrogen inlet 1, a liquid nitrogen centrifugal pump 2, a liquid nitrogen plunger pump 3, a liquid nitrogen evaporator 4, a first flowmeter 5, a first valve 6 and a liquid nitrogen outlet are sequentially arranged, and the liquid nitrogen outlet is connected to a high-pressure foam generator 8; wherein the liquid nitrogen centrifugal pump 2 is used to fill the liquid nitrogen plunger pump 3 with liquid nitrogen to ensure that the liquid nitrogen plunger pump 3 is fully inhaled. The liquid nitrogen plunger pump 3 is used to pressurize the liquid nitrogen; the liquid nitrogen evaporator 4 is used to evaporate the liquid nitrogen to produce gaseous nitrogen; the first flowmeter 5 is used to measure the flow of gaseous nitrogen passing through; and the first valve 6 is used to control the opening of the liquid nitrogen circuit. At the same time, the liquid nitrogen circuit is also connected to a liquid nitrogen branch, the inlet of the liquid nitrogen branch is located between the first flowmeter 5 and the first valve 6, and a second valve 7 is installed at the outlet of the liquid nitrogen branch.

[0053] It should be noted that the liquid nitrogen plunger pump 3 is one of a three-cylinder liquid nitrogen pump and a five-cylinder plunger pump, adopts a reinforced heavy-duty structure, and its maximum pressure is about 15,000 psi. The liquid nitrogen evaporator 4 is one of a water bath evaporator and a direct-fired evaporator. The water bath evaporator evaporates liquid nitrogen by exchanging heat with a high-temperature heat source through a shell and tube heat exchanger. The heat exchanger includes a water brake, a hydraulic oil heat exchanger, an engine cooling heat exchanger, and a lubricating oil heat exchanger. The direct-fired liquid nitrogen evaporator heats the liquid nitrogen to evaporate by the heat of direct oil combustion, and includes a combustion chamber assembly, a heat exchanger, a control system, and a fuel system.

[0054] Furthermore, combined with Figure 1 It can be seen that the foaming mixing module includes a foaming circuit, a foam stabilizing circuit and a mixing circuit, and the bubble circuit and the foam stabilizing circuit are arranged in parallel and converge into the mixing circuit; wherein, the bubble circuit is sequentially provided with a foaming agent inlet 23, a first upper liquid pump 22, a foaming tank 21, a first boosting pump 20 and a fourth flow meter 19; meanwhile, the foam stabilizing circuit is sequentially provided with a foam stabilizing agent inlet 28, a second upper liquid pump 27, a foam stabilizing tank 26, a second boosting pump 25 and a fifth flow meter 24; the mixing circuit is sequentially provided with a foaming plunger pump 18, a third flow meter 17 and a sixth valve 16, and the foaming plunger pump 18 is respectively connected to the outlets of the bubble circuit and the foam stabilizing circuit.

[0055] It should be noted that, in the foaming line, the foaming agent enters from the foaming agent inlet 23, is transported to the foaming tank 21 through the first upper liquid pump 22, and then enters the mixing line through the first booster pump 20. At the same time, the flow of the foaming agent is measured by the fourth flowmeter 19, so as to accurately measure the displacement data and maintain the optimal suction pressure of the foaming plunger pump 18. Similarly, in the foam stabilizing line, the foam stabilizing agent enters from the foam stabilizing agent inlet 28, and then enters the foam stabilizing tank 26 through the second upper liquid pump 27. Then, the second booster pump 25 pressurizes the foam stabilizing agent and enters the mixing line. At the same time, the fifth flowmeter 24 measures the flow of the foam stabilizing agent.

[0056] In addition, in the foaming and mixing module, the entire pipeline, valves and other liquid circulation pipelines are all made of stainless steel, and the foaming plunger pump 18 generally adopts a foaming liquid pump driven by a motor or a multi-cylinder plunger pump driven by a motor.

[0057] Furthermore, combined with Figure 1 It can be seen that the generator module includes a generator circuit and a generator branch, and the inlet and outlet of the generator branch are connected to the generator circuit. The generator circuit is sequentially provided with a clean water inlet 14, a fourth valve 13, a second flow meter 12, a liquid-liquid mixer 11, a high-pressure foam generator 8, a third valve 9 and a foaming fluid outlet 10. A fifth valve 15 is provided on the generator branch, and the inlet of the generator branch is located between the clean water inlet 14 and the fourth valve 13, and the outlet is located between the third valve 9 and the foaming fluid outlet 10.

[0058] It should be noted that the high-pressure foam generator 8 is used to mix nitrogen, foam liquid, and clean water (high-pressure water-based liquid) to form a foam fluid; the high-pressure foam generator 8 can continuously and stably produce high-quality foam with fine and dense particles; the liquid-liquid mixer 11 and the mixing line are connected by a "T"-shaped pipe, and the foam fluid is generated by the injection and suction of the air flow and the mixing of clean water mixed with a foaming agent.

[0059] It should be further explained that in Figure 1 In the liquid nitrogen line, the left side of the liquid nitrogen plunger pump 3 is a low-pressure pipeline, and the right side is a high-pressure pipeline; Figure 1 In the foaming line, foam stabilizing line and mixing line, the left side of the foaming plunger pump 18 is a low-pressure pipeline, and the right side is a high-pressure pipeline. The fluid is mostly high-pressure fluid, and its maximum working pressure can reach 103.5MPa.

[0060] Furthermore, the liquid nitrogen foam generating device is also equipped with a power system, which is generally one of an engine and a motor, wherein the engine is one of an electric start and a gas start. The power system is connected to a power distribution system, and the power distribution system can drive the hydraulic system to make the booster pump, liquid nitrogen pump and upper liquid pump in the hydraulic system work. The power distribution system is one of a one-input three-outlet type and a one-input four-outlet type.

[0061] The liquid nitrogen booster pump is a centrifugal pump or a screw pump, driven by a hydraulic motor or an electric motor, and is used to fill the liquid nitrogen plunger pump 3 with liquid nitrogen to ensure that the liquid nitrogen plunger pump 3 is fully inhaled and realize stable high-pressure operation of the liquid nitrogen plunger pump 3.

[0062] Furthermore, the liquid nitrogen foam generating device is also equipped with a hydraulic system, which is generally one or both of an open system and a closed system. Specifically, it includes a hydraulic oil tank, a filter, a thermostat, a hydraulic oil heat exchanger, a flow control valve, etc. The hydraulic system mainly drives the hydraulic pump to drive the motor and other actuators through the transfer case, and finally drives the liquid nitrogen plunger pump 3, the liquid nitrogen centrifugal pump 2, the foaming agent pump, the foam stabilizer pump, the foaming plunger pump 18, the valves (the first valve 6 to the sixth valve 16), etc. to operate.

[0063] Furthermore, the liquid nitrogen foam generating device is also equipped with a gas circuit system and a control system, wherein the gas circuit system corresponds to an air compressor, a gas storage tank, a one-way valve, a pipeline and a valve, etc., for opening the pneumatic valve. The control system includes an electrical control system, a liquid nitrogen evaporation control system, and a foam fluid mixing control system. The electrical control system includes an electrical control cabinet, a control module, a sensor, an instrument, etc., and the electrical control cabinet is made of stainless steel. The liquid nitrogen evaporation control system and the foam fluid mixing control system are installed in the control cabinet for monitoring data, automatic control, and adjusting parameters.

[0064] A liquid nitrogen foam generation method, such as Figure 3 As shown, the following steps are included:

[0065] S1: The liquid nitrogen is pressurized by the liquid nitrogen plunger pump 3 in the liquid nitrogen module, and then evaporated by the liquid nitrogen evaporator 4 in the liquid nitrogen module to obtain gaseous nitrogen, which is then transported to the generator module; specifically, the liquid nitrogen enters the liquid nitrogen circuit through the liquid nitrogen inlet 1, and then enters the liquid nitrogen plunger pump 3 through the liquid nitrogen centrifugal pump 2 for pressurization, and after pressurization, enters the liquid nitrogen evaporator 4 for heat exchange, and then enters the high-pressure foam generator 8.

[0066] S2: The foaming agent and the foam stabilizer are mixed through the foaming mixing module to obtain a foam liquid, which is then pressurized and transported to the generator module; specifically, the foaming agent and the foam stabilizer are mixed and pressurized in a certain proportion in the foaming plunger pump 18, and then enter the liquid-liquid mixer 11, while the third flowmeter 17 measures its flow rate and controls its opening through the sixth valve 16.

[0067] S3: pre-mix the foam liquid and the high-pressure water-based liquid through the liquid-liquid mixer 11 in the generator module, and then transport them to the high-pressure foam generator 8; react the pre-mixed foam liquid with the high-pressure water-based liquid and gaseous nitrogen through the high-pressure foam generator 8 connected to the liquid-liquid mixer 11 and the liquid nitrogen module to form a foam fluid and discharge it. Specifically, the high-pressure water-based liquid (clean water) enters the generator line through the clean water inlet 14, then enters the liquid-liquid mixer 11 through the fourth valve 13 and the second flowmeter 12 in sequence, and finally enters the high-pressure foam generator 8 to form a foam fluid, and the foam fluid can pass through the third valve 9 and the foaming fluid outlet 10 in sequence, and finally be discharged.

[0068] S4: Density testing is performed on the discharged foam fluid. If the density of the foam fluid meets the target value, the foam fluid is discharged and used for well washing. If the density of the foam fluid does not meet the target value, the foam fluid is discharged and the flow rate of the foam liquid and the flow rate of the liquid nitrogen are adjusted, and the density of the foam fluid is retested until the density of the foam fluid meets the target value.

[0069] S5: Clean the liquid nitrogen foam generating device.

[0070] Further, the temperature of gaseous nitrogen in the liquid nitrogen evaporator 4 is 15-21°C;

[0071] The maximum working pressure of the liquid nitrogen plunger pump 3 and the foaming plunger pump 18 is 103.5 MPa.

[0072] It should be noted that the liquid nitrogen line is also connected to a liquid nitrogen branch, which is used for nitrogen operations. When the first valve 6 is closed and the second valve 7 is opened, the liquid nitrogen branch can be used alone as a liquid nitrogen pumping device to provide liquid nitrogen for subsequent pipelines (not shown in the figure).

[0073] The generator line is also connected to a generator branch. When the fourth valve 13 is closed and the fifth valve 15 is opened, clean water can flow directly out of the foaming fluid outlet 10 through the generator branch. The foaming fluid outlet 10 will be connected to other equipment. After the clean water enters these equipment, the subsequent equipment can be cleaned and circulated to prevent the equipment from being blocked.

[0074] It should be noted that in steps S1 to S5, the operation process can switch between manual and automatic modes. The foam fluid mixing control system can collect the flow and pressure of clean water, the temperature, pressure, and flow of nitrogen, and the pressure and flow of foam fluid. In addition, the entire operation process can be controlled by the control cabinet, and the nitrogen displacement and foaming liquid displacement can be automatically adjusted according to the foam fluid displacement and density setting value to achieve the gas-liquid ratio set for the operation, realize the continuous adjustment of the foam fluid density, and meet the set requirements of the well washing operation.

[0075] In addition, manual operation control includes engine start, throttle lifting, flameout, emergency stop, overpressure reset, displacement clearing and manual operation corresponding to the above automatic operation, etc. Equipment control logic: According to the principle of mechanical foaming process, low-temperature liquid nitrogen is pressurized and vaporized into high-pressure, room-temperature nitrogen, and foamed with foaming agent (foaming agent + foam stabilizer) and clean water in the high-pressure foam generator 8. At the same time, according to the real-time measured clean water displacement and density value, the foam monitoring system controls the nitrogen and foaming agent displacement to automatically control the online density of the foam fluid.

[0076] The device of the present invention also includes the following adjustment steps during operation:

[0077] The foaming liquid speed is set, and the speed of the foaming plunger pump 18 is adjusted according to this value.

[0078] Set the N2 displacement and adjust the speed of the liquid nitrogen plunger pump 3 according to this value.

[0079] When the heat of the liquid nitrogen evaporator 4 is insufficient to heat the liquid nitrogen, the nitrogen discharge temperature is set, and the temperature is adjusted by adjusting the opening degree of the water brake according to the set temperature.

[0080] The normal working range of the discharge pressure of the liquid nitrogen centrifugal pump 2 is set, and according to this range, the speed of the liquid nitrogen centrifugal pump is adjusted to ensure that the discharge pressure is within the set range.

[0081] In addition, in step S2, the liquid level of the foaming agent / foam stabilizer tank is set, and the speed of the foaming agent / foam stabilizer upper liquid pump is adjusted according to the set value to maintain the foaming agent / foam stabilizer tank liquid level at the set value. At the same time, the foaming agent / foam stabilizer flow rate is set, and the speed of the foaming agent / foam stabilizer booster pump is adjusted according to the set value to maintain the foaming agent / foam stabilizer tank flow rate at the set value.

[0082] Furthermore, in S1, a normal working range of the discharge pressure of the liquid nitrogen centrifugal pump 2 is set, and according to this range, the speed of the liquid nitrogen booster pump is adjusted to ensure that the discharge pressure of the liquid nitrogen booster pump is within the set range.

[0083] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid nitrogen foam generating device, characterized in that: include: A liquid nitrogen module is used to pressurize liquid nitrogen and evaporate it to obtain gaseous nitrogen, which is then transported to the generator module; A foaming and mixing module is used to mix a foaming agent and a foam stabilizer to obtain a foam liquid, and then pressurize the foam liquid and transport it to the generator module; A generator module, comprising a liquid-liquid mixer (11) and a high-pressure foam generator (8); The liquid-liquid mixer (11) is connected to the foaming mixing module and is used to pre-mix the foam liquid and the high-pressure water-based liquid, and then transport them to the high-pressure foam generator (8); The high-pressure foam generator (8) is connected to the liquid-liquid mixer (11) and the liquid nitrogen module respectively, and is used to react the pre-mixed foam liquid with the high-pressure water-based liquid and the gaseous nitrogen to form a foam fluid and discharge it.

2. A liquid nitrogen foam generating device according to claim 1, characterized in that: The liquid nitrogen module comprises a liquid nitrogen circuit, on which a liquid nitrogen inlet (1), a liquid nitrogen centrifugal pump (2), a liquid nitrogen plunger pump (3), a liquid nitrogen evaporator (4), a first flow meter (5), a first valve (6) and a liquid nitrogen outlet are sequentially arranged, and the liquid nitrogen outlet is connected to a high-pressure foam generator (8); The liquid nitrogen centrifugal pump (2) is used to fill the liquid nitrogen plunger pump (3) with liquid nitrogen; The liquid nitrogen plunger pump (3) is used to pressurize the liquid nitrogen; The liquid nitrogen evaporator (4) is used to evaporate liquid nitrogen to produce gaseous nitrogen; The first flow meter (5) is used to measure the flow rate of gaseous nitrogen passing through; The first valve (6) is used to control the opening degree of the liquid nitrogen circuit.

3. A liquid nitrogen foam generating device according to claim 2, characterized in that: The liquid nitrogen circuit is also connected to a liquid nitrogen branch, the inlet of the liquid nitrogen branch is located between the first flow meter (5) and the first valve (6), and a second valve (7) is installed at the outlet of the liquid nitrogen branch.

4. A liquid nitrogen foam generating device according to claim 3, characterized in that: The liquid nitrogen plunger pump (3) is one of a triplex plunger pump and a quintuple plunger pump; The liquid nitrogen evaporator (4) is one of a water bath evaporator and a direct-fired evaporator.

5. A liquid nitrogen foam generating device according to claim 1, characterized in that: The foaming and mixing module comprises a foaming circuit, a foam stabilizing circuit and a mixing circuit, wherein the foaming circuit and the foam stabilizing circuit are arranged in parallel and converge into the mixing circuit; The foaming line is provided with a foaming agent inlet (23), a first liquid pump (22), a foaming tank (21), a first boosting pump (20) and a fourth flow meter (19) in sequence; The foam stabilizing circuit is provided with a foam stabilizing agent inlet (28), a second upper liquid pump (27), a foam stabilizing tank (26), a second boosting pump (25) and a fifth flow meter (24) in sequence; The mixing circuit is provided with a foaming plunger pump (18), a third flow meter (17) and a sixth valve (16) in sequence, and the foaming plunger pump (18) is connected to the outlets of the bubble circuit and the bubble stabilizing circuit respectively.

6. A liquid nitrogen foam generating device according to any one of claims 1 to 4, characterized in that: The generator module includes a generator circuit; The generator circuit is provided with a clean water inlet (14), a fourth valve (13), a second flow meter (12), a liquid-liquid mixer (11), a high-pressure foam generator (8), a third valve (9) and a foaming fluid outlet (10) in sequence.

7. A liquid nitrogen foam generating device according to claim 6, characterized in that: The generator module also includes a generator branch, the inlet and outlet of the generator branch are both connected to the generator circuit; A fifth valve (15) is provided on the generator branch, and the inlet of the generator branch is located between the clean water inlet (14) and the second flow meter (12), and the outlet is located between the third valve (9) and the foaming fluid outlet (10).

8. A method for generating liquid nitrogen foam, characterized in that: The following steps are involved: The liquid nitrogen is pressurized by a liquid nitrogen plunger pump (3) in the liquid nitrogen module, and then evaporated by a liquid nitrogen evaporator (4) in the liquid nitrogen module to obtain gaseous nitrogen, which is then transported to the generator module; The foaming agent and the foam stabilizer are mixed through the foaming mixing module to obtain a foam liquid, which is then pressurized and transported to the generator module; Premixing the foam liquid and the high-pressure water-based liquid through a liquid-liquid mixer (11) in the generator module and then delivering them to the high-pressure foam generator (8); The premixed foam liquid, high-pressure water-based liquid and gaseous nitrogen are reacted by a high-pressure foam generator (8) connected to a liquid-liquid mixer (11) and a liquid nitrogen module to form a foam fluid and discharge it.

9. A liquid nitrogen foam generating method according to claim 8, characterized in that: After the foam fluid is discharged, the following steps are also included: The density of the discharged foam fluid is tested. If the density of the foam fluid meets the target value, the foam fluid is discharged and used for well washing. If the density of the foam fluid does not meet the target value, the foam fluid is discharged and the flow rate of the foam liquid and the flow rate of the liquid nitrogen are adjusted, and the density of the foam fluid is retested until the density of the foam fluid meets the target value.

10. A liquid nitrogen foam generating method according to claim 8, characterized in that: The temperature of the gaseous nitrogen in the liquid nitrogen evaporator (4) is 15-21°C; The maximum working pressure of the liquid nitrogen plunger pump (3) is 103.5 MPa.

Images