Nitrogen injection foam well washing device and using method

Abstract

The invention relates to a nitrogen injection foam well washing device and a using method. During operation, a liquid nitrogen medium flows into a liquid nitrogen centrifugal pump through a liquid nitrogen low-pressure pipeline, and enters a liquid nitrogen plunger pump after being pressurized; the liquid nitrogen pressurized again flows into a water bath type evaporator to be heated and evaporated, and nitrogen is formed and enters a foam generator; high-temperature cooling water is pressurized and then enters a water bath type evaporator to heat liquid nitrogen; clear water flows into a low-pressure mixer through a clear water pipeline and is mixed with chemical additives pumped by a foaming agent pump and a foam stabilizer pump to form a low-pressure mixed solution; the low-pressure mixed liquid flows into a liquid phase inlet of the foam generator after being pressurized by the pumping pressure device, and is fully foamed with nitrogen at a gas phase inlet in a cavity of the foam generator to form foam fluid. The defects (such as the problems that on-site pipeline connection is complex, an efficient foam generating device is lacked, control dispersion is not beneficial to monitoring and foaming density is difficult to stabilize) of existing similar equipment are overcome, a new foam mixing well washing technology is adopted, the process is simplified, and the operation efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of low-pressure horizontal wellbore cleaning and sand flushing technology, specifically to a nitrogen injection foam well washing device and its usage method. Background Technology

[0002] As oilfield operations continue, there are a large number of shut-in wells and low-production wells. Most of these wells have experienced formation sand discharge and wellbore sand accumulation during long-term production, which blocks oil and gas channels, causing a decline in oil and gas well production and seriously affecting the implementation of potential tapping measures for old wells.

[0003] Nitrogen injection foam well washing equipment, as the core equipment of foam well washing process, produces low-density foam fluid through mechanical foaming. It has the advantages of strong sand carrying capacity, low density and high viscosity. When used as a sand flushing fluid and combined with a continuous sand flushing device, it can solve the problem of sand flushing in low-pressure lost circulation wells with simple procedures and low cost.

[0004] Existing foam flushing well washing equipment generally uses liquid storage tanks, nitrogen truck sets, foam generators, additive skids, cement pump trucks, and coiled tubing equipment. These equipment suffers from problems such as complex on-site pipeline connections, lack of efficient foam generation devices, dispersed control making monitoring difficult, difficulty in stabilizing foam density, and high rental costs for liquid nitrogen pump trucks. These issues severely restrict the development of foam fluid flushing technology.

[0005] Therefore, it is of great significance to develop miniaturized, automated, low-cost, and high-efficiency nitrogen foam well washing equipment. Summary of the Invention

[0006] This invention provides a miniaturized, automated, low-cost, and highly stable nitrogen foam well cleaning device and its usage method, which can effectively clean the wellbore of horizontal wells.

[0007] The technical solution adopted in this invention is: a nitrogen foam well washing device, characterized in that: it includes a liquid nitrogen centrifugal pump, a liquid nitrogen plunger pump, a water bath evaporator, a cooling water pump, a heat exchanger, a cooling water tank, a foam generator, a low-pressure mixer, a foaming agent pump, and a foam stabilizing agent pump. The liquid nitrogen medium flows into the liquid nitrogen centrifugal pump through a liquid nitrogen low-pressure pipeline. The outlet of the liquid nitrogen centrifugal pump is connected to the inlet of the liquid nitrogen plunger pump. The pressurized liquid nitrogen is injected into the liquid nitrogen plunger pump to maintain good suction conditions. The outlet of the liquid nitrogen plunger pump is connected to the inlet of the water bath evaporator. The repressurized liquid nitrogen flows into the water bath evaporator for heating and evaporation, forming nitrogen gas at 15~21℃, which is then output into the gas phase port of the foam generator. The heat required by the water bath evaporator mainly comes from the heat exchange system. The inlet of the water bath evaporator is connected to the outlet of the cooling water pump. The high-temperature cooling water from the cooling water tank is pressurized by the cooling water pump and enters the water bath evaporator to heat the liquid nitrogen. The outlet of the water bath evaporator is connected to the inlet of the heat exchanger. The cooled coolant enters the heat exchanger to recover heat from the hydraulic system, lubrication system and engine cylinder liner water, and finally flows into the cooling water tank to continue the circulation. The clean water line is connected to the low-pressure mixer. Clean water flows into the low-pressure mixer through the clean water line and mixes with the chemical additives pumped from the foaming agent pump and the foam stabilizer pump to form a low-pressure mixture. The outlet of the low-pressure mixer is connected to the inlet of the pump pressure device, and the outlet of the pump pressure device is connected to the liquid phase inlet of the foam generator. After being pressurized by the pump pressure device, the low-pressure mixture flows into the liquid phase inlet of the foam generator, where it fully foams with the nitrogen gas at the gas phase inlet in the foam generator cavity to form a stable, uniform, and dense foam fluid.

[0008] Preferably, the liquid nitrogen plunger pump has a maximum liquid nitrogen discharge capacity of 61 L / min and a maximum working pressure of 70 MPa.

[0009] Preferably, the heat exchanger includes a hydraulic oil heat exchanger, a lubricating oil heat exchanger, and an engine cylinder liner water heat exchanger. The hydraulic oil heat exchanger and the lubricating oil heat exchanger are shell-and-tube heat exchangers, and the cylinder liner water heat exchanger is a plate heat exchanger.

[0010] Preferably, the foam generator includes a liquid phase inlet and a gas phase inlet, wherein the liquid containing the foaming agent and the foam stabilizer is foamed under pressurized nitrogen in the foam generator; the gas phase inlet is provided with a nozzle structure.

[0011] Preferably, the foam generator pipeline is provided with a spiral homogenization structure, which can shear and stir the pressurized foam fluid after mixing.

[0012] Preferably, the low-pressure mixer includes an additive inlet and a clean water inlet for low-pressure mixing of clean water with foaming agent and foam stabilizer; the low-pressure mixer is internally equipped with a turbine fan blade structure and a spiral homogenization structure, which can shear and stir the mixed liquid.

[0013] Preferably, the system also includes a power unit directly connected to the transfer case, which drives the hydraulic oil pump to rotate, and drives the motor to rotate through hydraulic internal energy, transferring mechanical energy to the liquid nitrogen centrifugal pump and the liquid nitrogen plunger pump. The total power of the power unit's engine is determined based on both the total power of the actuators and the liquid nitrogen vaporization displacement. The total power of the actuators is determined according to formula (1). Pump input shaft power P : (1) in: For pumping rated displacement; The rated pressure for pumping; The total efficiency of the pump includes mechanical efficiency and volumetric efficiency.

[0014] Preferably, the system also includes a control room and a control device. The control device is placed in the control room and monitors the operating status of each system of the equipment through temperature sensors, pressure sensors and speed sensors on the pipeline.

[0015] Preferably, a heater is also included, which can preheat the engine for operation in cold conditions, while the pipeline is insulated to meet the requirements of operation in environments as low as -30°C.

[0016] Preferably, the device is equipped with a foldable guardrail on the top to facilitate the installation of an additive storage tank on the top.

[0017] Preferably, the device is equipped with a fuel tank of >600L, which can meet the long-term continuous operation conditions of sand flushing and well washing operations.

[0018] Preferably, the device has a soundproof wall between the power unit and the control room, which can effectively absorb the noise generated by the engine and reduce the noise in the control room to below 85 dB, thus meeting the environmental protection requirements of the well site.

[0019] Preferably, the device is equipped with a gas storage cylinder of >140L, which provides a large gas output and facilitates the cleaning of pipelines and equipment after liquid addition operations.

[0020] Preferably, the water bath evaporator and the foam generator are connected by a high-pressure liquid nitrogen pipeline. The high-pressure liquid nitrogen pipeline is equipped with a nitrogen bypass port. When the main nitrogen outlet valve is closed and the nitrogen bypass valve is opened, the device can be used as a liquid nitrogen plunger pump injection device.

[0021] Preferably, the device includes not only a foaming agent pump and a foam stabilizer pump, but also generally has four liquid filling pump lines that can be used interchangeably. When the device switches the cooling of the hydraulic system from the heat exchanger to the water tank, the device can be used as an independent liquid filling skid.

[0022] Preferably, the device is equipped with two electric ball valve lines on the liquid additive pump discharge line. One line outputs to the low-pressure mixer, and the other line returns to the liquid additive pump inlet through the electric ball valve. Through software settings, it can achieve automated chemical additive output operation of 1~50L / min.

[0023] A method for preparing nitrogen foam fluid, using the aforementioned nitrogen injection foam well washing device, includes the following steps: S1. First, you need to prepare the corresponding water supply device (water tank or water tank), pump pressure device (1000 type pump truck or pump skid), and connect the corresponding pipelines according to the water supply device - foam well washing equipment - pump pressure device - foam well washing equipment; prepare 1 liquid nitrogen tank truck to supply liquid nitrogen at the specified pressure and flow rate to the foam well washing equipment, and connect the liquid nitrogen suction and discharge pipelines. S2. Liquid nitrogen flows from the tanker through a low-pressure liquid nitrogen pipeline into a centrifugal liquid nitrogen pump, where it is pressurized to a set pressure of 0.6~0.8MPa and continuously flows to a plunger pump to ensure sufficient suction. After being pressurized by the plunger pump, it is delivered to a water bath evaporator, where it continuously exchanges heat and heats up. Through a heat exchange system, heat from the equipment's power system, hydraulic system, and lubrication system is recovered, converting the liquid nitrogen into nitrogen gas. This gas is then delivered to a foam generator through a high-pressure liquid nitrogen pipeline. The operating pressure of the liquid nitrogen plunger pump is 0~70MPa, and the temperature of the converted nitrogen gas is 15~21℃. S3. The clean water in the water supply device is pumped to the clean water inlet of the foam well washing equipment by the booster pump. It flows through the low-pressure mixer, and the liquid addition pump and liquid addition pump are started to pump the foaming agent and foam stabilizer into the clean water pipeline according to the set discharge rate. In the low-pressure mixer, the clean water is fully mixed with the foaming agent and foam stabilizer. After flowing through the pump pressure device, it is pressurized and delivered to the foam generator. The pump pressure device is a well site configuration device, mainly used for pressurizing the mixed liquid. The foaming agent and foam stabilizer are stored in well site ton tanks. Considering the additive suction conditions during operation, the foam stabilizer ton tank can be placed on the skid top platform. S4. A liquid containing a foaming agent and a foam stabilizer is sprayed and mixed with high-pressure nitrogen in the cavity of a foam generator to form a uniform and dense foam fluid, which is then introduced into the well for flushing operations through a coiled tubing; the working pressure of the foam fluid is 0~70MPa and the density is 0.5~1.0g / cm3; S5. The density detection device is installed in the high-pressure discharge pipeline after the foam generator to detect the actual density of the foam fluid entering the well. Based on the density value, the nitrogen discharge rate and chemical additive discharge rate are adjusted in reverse to achieve density control. At the same time, the half-life of the return fluid and the density of the foam fluid are collected and calculated to evaluate the downhole foam washing status. S6. After construction is completed, close the nitrogen discharge valve, use compressed air to backflush the liquid filling pipeline, turn on the pump pressure device to operate at low displacement and low pressure, and clean the entire clean water pipeline.

[0024] The beneficial effects achieved by this invention are: 1. Overcome the shortcomings of existing similar equipment, such as: complex on-site pipeline connections, lack of efficient foam generation devices, decentralized control that is not conducive to monitoring, difficulty in stabilizing foam density, and high cost of liquid nitrogen pump truck rental, and provide a miniaturized, automated, low-cost, and highly stable foam well washing equipment; 2. The adoption of a new foam-mixed well washing process simplifies the procedure and improves operational efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the preparation principle of the nitrogen foam fluid of the present invention; Figure 2 This is a schematic diagram of the overall structure of the present invention; In the diagram: 1. Liquid nitrogen centrifugal pump; 2. Liquid nitrogen plunger pump; 3. Water bath evaporator; 4. Cooling water pump; 5. Heat exchanger; 6. Cooling water tank; 7. Foam generator; 8. Pump pressure device; 9. Low-pressure mixer; 10. Foaming agent pump; 11. Foam stabilizer pump; 12. Clean water pipeline; 13. Liquid nitrogen low-pressure pipeline; 14. Liquid nitrogen high-pressure pipeline; 15. Density detection device; 16. Control room; 17. Liquid nitrogen filling system; 18. Liquid nitrogen low-pressure assembly; 19. Hydraulic oil tank; 20. Liquid nitrogen high-pressure assembly; 21. Power assembly; 22. Heater; 23. Fuel tank; 24. Hydraulic oil pump assembly. Detailed Implementation

[0026] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1-2 As shown, a nitrogen foam well washing device of the present invention includes a liquid nitrogen centrifugal pump 1, a liquid nitrogen plunger pump 2, a water bath evaporator 3, a cooling water pump 4, a heat exchanger 5, a cooling water tank 6, a foam generator 7, a low-pressure mixer 9, a foaming agent pump 10, a foam stabilizer pump 11, a clean water pipeline 12, a liquid nitrogen low-pressure pipeline 13, a liquid nitrogen high-pressure pipeline 14, and a density detection device 15. The liquid nitrogen plunger pump 2 has a maximum liquid nitrogen discharge of 61 L / min and a maximum working pressure of 70 MPa.

[0028] The heat exchanger 5 includes a hydraulic oil heat exchanger, a lubricating oil heat exchanger, and an engine cylinder liner water heat exchanger. The hydraulic oil heat exchanger and the lubricating oil heat exchanger are preferably shell-and-tube heat exchangers, and the cylinder liner water heat exchanger is preferably a plate heat exchanger.

[0029] The foam generator 7 includes a liquid phase inlet and a gas phase inlet. The liquid containing the foaming agent and the foam stabilizer is foamed under pressurized nitrogen in the foam generator 7. In particular, the nitrogen inlet is equipped with a nozzle structure, which can make the liquid foam more uniform and dense. In particular, the foam generator 7 pipeline is equipped with a spiral homogenization structure, which can shear and stir the pressurized foam fluid after mixing.

[0030] The low-pressure mixer 9 includes an additive inlet and a clean water inlet for low-pressure mixing of clean water with foaming agents and foam stabilizers. In particular, the low-pressure mixer 9 is equipped with a turbine fan blade structure and a spiral homogenizing structure, which can shear and stir the mixed liquid.

[0031] The liquid nitrogen low-pressure pipeline 13 includes an inlet pipeline and a return pipeline, which can be used for low-pressure circulation testing and liquid nitrogen tank return during operation, greatly saving the amount of liquid nitrogen used.

[0032] During normal operation, liquid nitrogen medium flows into liquid nitrogen centrifugal pump 1 through the inlet of liquid nitrogen low-pressure pipeline 13. The outlet of liquid nitrogen centrifugal pump 1 is connected to the suction port of liquid nitrogen plunger pump 2. The pressurized liquid nitrogen is injected into liquid nitrogen plunger pump 2 to maintain good suction conditions.

[0033] The outlet of the liquid nitrogen plunger pump 2 is connected to the inlet of the water bath evaporator 3. The repressurized liquid nitrogen flows into the water bath evaporator 3 for heating and evaporation, forming nitrogen gas at 15~21℃, which is then output into the gas phase port of the foam generator 7.

[0034] The heat required by the water bath evaporator 3 mainly comes from the heat exchange system. Its inlet is connected to the outlet of the cooling water pump 4. The high-temperature cooling water from the cooling water tank 6 is pressurized by the cooling water pump 4 and enters the water bath evaporator 3 to heat the liquid nitrogen. The outlet of the water bath evaporator 3 is connected to the inlet of the heat exchanger 5. The cooled coolant enters the heat exchanger to recover heat from the hydraulic system, lubrication system and engine cylinder liner water respectively, and finally flows into the cooling water tank 6 to continue the circulation.

[0035] The clean water line 2 is connected to the low-pressure mixer 9. Clean water flows into the low-pressure mixer through the clean water line 2 and mixes with the chemical additives pumped from the foaming agent pump 10 and the foam stabilizer pump 11 to form a low-pressure mixture.

[0036] The outlet of the low-pressure mixer 9 is connected to the inlet of the pumping device 8, and the outlet of the pumping device 9 is connected to the liquid phase inlet of the foam generator 7. After being pressurized by the pumping device 8, the low-pressure mixture flows into the liquid phase inlet of the foam generator 7 and fully foams with the nitrogen gas at the gas phase inlet in the cavity of the foam generator 7 to form a stable, uniform, and dense foam fluid.

[0037] The nitrogen foam well washing device of the present invention also includes a power unit. The power unit is directly connected to the transfer case to drive the hydraulic oil pump to rotate. The hydraulic internal energy drives the motor to rotate, and mechanical energy is transmitted to the liquid nitrogen centrifugal pump 1 and liquid nitrogen plunger pump 2 and other actuators. The total power of the engine is determined based on the total power of the actuators and the liquid nitrogen vaporization displacement. The total power of the actuators is determined according to formula (1). The maximum liquid nitrogen displacement of the device is 61L / min. The total heat required to convert it into nitrogen gas at 15-21℃ can be determined. Therefore, a CAT C13 engine is preferred.

[0038] Pump input shaft power PUnit (kW): (1) in: Rated pump displacement, in L / min; The rated pumping pressure is expressed in MPa. The total efficiency of the pump includes mechanical efficiency and volumetric efficiency.

[0039] The nitrogen injection foam well washing device of the present invention also includes a control room 16 and a control device. The control device is placed in the control room 16. The control device can accurately monitor the operating status of each system of the equipment through sensors such as temperature, pressure and speed on the pipeline. An automatic control system for foam fluid has been developed, which can realize automatic stable operation of nitrogen, automatic stable operation of additives, automatic clean water ratio operation of additives, and automatic stable operation of foam fluid density.

[0040] The nitrogen foam well washing device of the present invention is also equipped with a heater 22, which can preheat the engine in cold conditions. At the same time, the pipeline is insulated to meet the requirements of operation in an environment of -30℃.

[0041] The nitrogen foam well washing device of the present invention is equipped with a foldable guardrail on the top to facilitate the operation of installing an additive storage tank on the top.

[0042] The nitrogen foam well washing device of the present invention is equipped with a fuel tank of >600L, which can meet the long-term continuous operation conditions of sand flushing well washing operation.

[0043] The nitrogen foam well washing device of the present invention has a soundproof wall between the power unit and the control room, which can effectively absorb the noise generated by the engine and reduce the noise of the control room to below 85 dB, thus meeting the environmental protection requirements of the well site.

[0044] The nitrogen foam well washing device of the present invention is equipped with a gas storage cylinder of >140L, which has a large gas output and facilitates the cleaning of pipelines and equipment after liquid addition operations.

[0045] The water bath evaporator 3 and the foam generator 7 are connected by a liquid nitrogen high-pressure pipeline 14. The liquid nitrogen high-pressure pipeline 14 is equipped with a nitrogen bypass port. When the main nitrogen outlet valve is closed and the nitrogen bypass valve is opened, the device can be used as a liquid nitrogen plunger pump injection device.

[0046] The nitrogen foam well washing device of the present invention includes not only a foaming agent pump 10 and a foam stabilizing agent pump 11, but also generally has 4 liquid injection pump pipelines that can be mutually redundant; when the device switches the heat dissipation of the hydraulic system from the heat exchanger 5 to the cooling water tank 6, the device can be used as an independent liquid injection skid device.

[0047] The nitrogen foam well washing device of the present invention has two electric ball valve lines installed on the discharge pipeline of the liquid additive pump. One line outputs to the low-pressure mixer 9 for operation, and the other line returns to the suction port of the liquid additive pump through the electric ball valve. Through software settings, it can realize the automated chemical additive output operation of 1~50L / min.

[0048] A method for preparing nitrogen foam fluid according to the present invention, using the above-mentioned nitrogen injection foam well washing device, includes the following steps: S1. First, you need to prepare the corresponding water supply device (water tank or water tank), pump pressure device (1000 type pump truck or pump skid), and connect the corresponding pipelines according to the water supply device - foam well washing equipment - pump pressure device - foam well washing equipment; prepare 1 liquid nitrogen tank truck to supply liquid nitrogen at the specified pressure and flow rate to the foam well washing equipment, and connect the liquid nitrogen suction and discharge pipelines. S2. Liquid nitrogen flows from the tanker truck through the low-pressure liquid nitrogen pipeline 13 into the liquid nitrogen centrifugal pump 1, where it is pressurized to a set pressure of 0.6~0.8MPa and continuously flows to the liquid nitrogen plunger pump 2, ensuring sufficient suction. After being pressurized by the liquid nitrogen plunger pump 2, it is delivered to the water bath evaporator 3, where it continuously exchanges heat and heats up. Through the heat exchange system, heat from the equipment's power system, hydraulic system, and lubrication system is recovered, converting the liquid nitrogen into nitrogen gas. This nitrogen gas is then delivered to the foam generator 7 through the high-pressure liquid nitrogen pipeline 14. The operating pressure of the liquid nitrogen plunger pump 2 is 0~70MPa, and the temperature of the converted nitrogen gas is 15~21℃. S3. The clean water in the water supply device is pumped to the clean water inlet of the foam well washing equipment by the booster pump. It flows through the low-pressure mixer 9, and the liquid addition pumps 10 and 11 are started to pump the foaming agent and foam stabilizer into the clean water pipeline 12 according to the set discharge rate. In the low-pressure mixer 9, the clean water is fully mixed with the foaming agent and foam stabilizer. It flows through the pump pressure device 8 and is pressurized before being delivered to the foam generator 7. The pump pressure device 8 is a well site configuration device, mainly used for pressurizing the mixed liquid. The foaming agent and foam stabilizer are stored in well site ton containers. Considering the additive suction conditions during operation, the foam stabilizer ton container can be placed on the skid top platform. S4. A liquid containing a foaming agent and a foam stabilizer is sprayed and mixed with high-pressure nitrogen in the cavity of the foam generator 7 to form a uniform and dense foam fluid, which is then introduced into the downhole flushing operation through the coiled tubing; the working pressure of the foam fluid is 0~70MPa and the density is 0.5~1.0g / cm3; S5, the density detection device 15 is installed in the high-pressure discharge pipeline after the foam generator 7. It is used to detect the actual density of the foam fluid entering the well. Based on the density value, the nitrogen discharge rate and the chemical additive discharge rate are adjusted in reverse to achieve density control. At the same time, the half-life of the return fluid and the density of the foam fluid are collected and calculated to evaluate the downhole foam washing status. S6. After construction is completed, close the nitrogen discharge valve, use compressed air to backflush the liquid filling pipeline, turn on the pump pressure device 8 for low-discharge and low-pressure operation, and clean the entire clean water pipeline 12.

[0049] It should be noted that the above description of the technical solutions is exemplary, and this specification may be embodied in different forms and should not be construed as limiting it to the technical solutions set forth herein. Rather, providing these descriptions will ensure that the disclosure of this invention is thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Furthermore, the technical solutions of this invention are defined only by the scope of the claims.

[0050] Finally, it should be noted that the above embodiments are merely representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention should be considered within the protection scope of the present invention.

Claims

1. A nitrogen foam well washing device, characterized in that: The system includes a liquid nitrogen centrifugal pump (1), a liquid nitrogen plunger pump (2), a water bath evaporator (3), a cooling water pump (4), a heat exchanger (5), a cooling water tank (6), a foam generator (7), a low-pressure mixer (9), a foaming agent pump (10), and a foam stabilizer pump (11). Liquid nitrogen medium flows into the liquid nitrogen centrifugal pump (1) through the liquid nitrogen low-pressure pipeline (13). The outlet of the liquid nitrogen centrifugal pump (1) is connected to the inlet of the liquid nitrogen plunger pump (2). The pressurized liquid nitrogen is injected into the liquid nitrogen plunger pump (2). The outlet of the liquid nitrogen plunger pump (2) is connected to the inlet of the water bath evaporator (3). The repressurized liquid nitrogen flows into the water bath evaporator (3) for heating and evaporation, forming nitrogen gas, which is then output into the gas phase port of the foam generator (7). The inlet of the water bath evaporator (3) is connected to the outlet of the cooling water pump (4). The high-temperature cooling water from the cooling water tank (6) is pressurized by the cooling water pump (4) and enters the water bath evaporator (3) to heat the liquid nitrogen. The outlet of the water bath evaporator (3) is connected to the inlet of the heat exchanger (5). The cooled liquid enters the heat exchanger (5) and flows into the cooling water tank (6) to continue circulating. The clean water line (12) is connected to the low-pressure mixer (9). Clean water flows into the low-pressure mixer (9) through the clean water line (12) and mixes with the chemical additives pumped from the foaming agent pump (10) and the foam stabilizer pump (11) to form a low-pressure mixture. The outlet of the low-pressure mixer (9) is connected to the inlet of the pump pressure device (8), and the outlet of the pump pressure device (8) is connected to the liquid phase inlet of the foam generator (7). After being pressurized by the pump pressure device (8), the low-pressure mixture flows into the liquid phase inlet of the foam generator (7) and fully foams with the nitrogen gas at the gas phase inlet in the cavity of the foam generator (7) to form a foam fluid.

2. The nitrogen foam well washing device according to claim 1, characterized in that: The liquid nitrogen plunger pump (2) has a maximum liquid nitrogen discharge capacity of 61 L / min and a maximum working pressure of 70 MPa.

3. The nitrogen foam well washing device according to claim 1, characterized in that: The heat exchanger (5) includes a hydraulic oil heat exchanger, a lubricating oil heat exchanger and an engine cylinder liner water heat exchanger. The hydraulic oil heat exchanger and the lubricating oil heat exchanger are shell-and-tube heat exchangers, and the cylinder liner water heat exchanger is a plate heat exchanger.

4. The nitrogen foam well washing device according to claim 1, characterized in that: The foam generator (7) has a spiral homogenizing structure in its pipeline, which can shear and stir the pressurized foam fluid after mixing; the low-pressure mixer (9) includes an additive inlet and a clean water inlet, which is used for low-pressure mixing of clean water with foaming agent and foam stabilizer; the low-pressure mixer (9) has a turbine fan blade structure and a spiral homogenizing structure inside, which can shear and stir the mixed liquid.

5. The nitrogen foam well washing device according to claim 1, characterized in that: It also includes a power unit, which is directly connected to the transfer case to drive the hydraulic oil pump to rotate. The hydraulic internal energy drives the motor to rotate, and mechanical energy is transferred to the liquid nitrogen centrifugal pump (1) and the liquid nitrogen plunger pump (2). The total power of the engine of the power unit is determined based on the total power of the actuators and the liquid nitrogen vaporization displacement. The total power of the actuators is determined according to formula (1). Pump input shaft power P : （1） in: For pumping rated displacement; The pump's rated pressure; The total efficiency of the pump includes mechanical efficiency and volumetric efficiency.

6. The nitrogen foam well washing device according to claim 5, characterized in that: It also includes a control room (16) and a control device, with the control device placed in the control room (16); the control device monitors the operating status of each system through sensors arranged on the pipeline; a soundproof wall is provided between the control room (16) and the power unit (21).

7. The nitrogen foam well washing device according to claim 1, characterized in that: The water bath evaporator (3) and the foam generator (7) are connected by a liquid nitrogen high-pressure pipeline (14). The liquid nitrogen high-pressure pipeline (14) is equipped with a nitrogen bypass port. When the main nitrogen outlet valve is closed and the nitrogen bypass valve is opened, the device can be used as a liquid nitrogen plunger pump injection device.

8. A method of using a nitrogen injection foam well washing device, employing the nitrogen injection foam well washing device as described in any one of claims 1 to 7, comprising the following steps: S1. Prepare the corresponding water supply device and pump pressure device, and connect the corresponding pipelines according to the water supply device-foam well washing device-pump pressure device-foam well washing device; prepare liquid nitrogen tanker trucks for supplying liquid nitrogen to the foam well washing device, and connect the liquid nitrogen suction pipeline and discharge pipeline. S2. Liquid nitrogen flows from the liquid nitrogen tanker through the liquid nitrogen low-pressure pipeline (13) into the liquid nitrogen centrifugal pump (1) for pressurization, and continues to flow to the liquid nitrogen plunger pump (2) to ensure sufficient suction of the liquid nitrogen plunger pump (2); and after being pressurized by the liquid nitrogen plunger pump (2), it is transported to the water bath evaporator (3), where it continuously exchanges heat and heats up. Through the heat exchange system, the liquid nitrogen is converted into nitrogen gas, which is then transported to the foam generator (7) through the liquid nitrogen high-pressure pipeline (14). S3. The clean water in the water supply device is pumped to the clean water inlet of the foam well washing device by the booster pump. It flows through the low-pressure mixer (9), and the liquid addition pump (10) and liquid addition pump (11) are started to pump the foaming agent and foam stabilizer into the clean water pipeline (12) according to the set displacement. The clean water is fully mixed with the foaming agent and foam stabilizer in the low-pressure mixer (9). After being pressurized by the pump pressure device (8), it is delivered to the foam generator (7). S4. Liquid containing foaming agent and foam stabilizer is sprayed and mixed with high-pressure nitrogen in the cavity of foam generator (7) to form foam fluid, which enters the well flushing operation through the coiled tubing; S5. The density detection device (15) is installed in the high-pressure discharge pipeline after the foam generator (7) to detect the actual density of the foam fluid entering the well. Based on the density value, the nitrogen discharge rate and chemical additive discharge rate are adjusted in reverse to achieve density control. At the same time, the half-life of the return fluid and the density of the foam fluid are collected and calculated to evaluate the downhole foam washing status. S6. After the construction is completed, close the nitrogen discharge valve, use compressed air to backflush the liquid filling pipeline, turn on the pump pressure device (8) to operate at low discharge and low pressure, and clean the entire clean water pipeline (12).

9. The method of using the nitrogen injection foam well washing device according to claim 8, characterized in that: In step S2, liquid nitrogen flows from the liquid nitrogen tanker through the liquid nitrogen low-pressure pipeline (13) into the liquid nitrogen centrifugal pump (1) and is pressurized to a set pressure of 0.6~0.8MPa; the working pressure of the liquid nitrogen plunger pump (2) is 0~70MPa, and the temperature of the converted nitrogen is 15~21℃.

10. The method of using the nitrogen injection foam well washing device according to claim 8, characterized in that: In step S4, the working pressure of the foam fluid is 0~70MPa and the density is 0.5~1.0g / cm3.

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