Device and method for negative pressure control and permeability monitoring of unconventional natural gas reservoir

Abstract

The invention discloses a negative pressure control and permeability monitoring device and method for an unconventional natural gas reservoir, and the device comprises a reservoir which is provided with a water injection well pipeline and a water pumping well pipeline, the water injection well pipeline is provided with a first water pressure gauge, and the water pumping well pipeline is provided with a second water pressure gauge; the air exhaust pipeline is provided with a barometer and is used for monitoring the pressure change in the air exhaust process; in the auxiliary pipeline, positive and negative electrode materials are arranged on the two sides in the length direction respectively, and external voltage is arranged at the top end; a porous material and a fixed end point are sequentially arranged in the auxiliary pipeline from top to bottom, the interior of the auxiliary pipeline is divided into an upper storage cavity, a middle storage cavity and a bottom storage cavity, pressure gauges are arranged in the upper storage cavity and the middle storage cavity respectively, the upper storage cavity is further provided with a flow meter, and a conductive sliding block is arranged in the bottom storage cavity and used for monitoring reservoir water level changes; a signal transceiver; and a central processor. The negative pressure can be accurately controlled, permeability monitoring lag is avoided, and the pressure and the permeability can be adjusted in real time in the reservoir exploitation process.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and in particular relates to a device and method for negative pressure control and permeability monitoring of unconventional natural gas reservoirs. Background Art

[0002] With the continuous growth of energy demand, the exploitation of traditional oil and gas resources is gradually facing exhaustion, but unconventional natural gas resources, including tight sandstone gas and shale gas, have become an important part of the global energy structure due to their abundant reserves and wide distribution. Unconventional natural gas has become an important alternative energy source. The exploitation technology of these resources is more challenging than that of traditional natural gas, especially in unconventional reservoirs such as shale gas and coalbed methane. Traditional development technology faces many challenges, such as low reservoir permeability and negative pressure generated during the exploitation process that affects the reservoir pressure.

[0003] In the process of unconventional natural gas extraction, negative pressure control and permeability monitoring are key technologies to improve recovery and ensure stable production of gas reservoirs. The generation of negative pressure may lead to instability of gas reservoirs and even cause environmental problems such as ground subsidence. Therefore, avoiding the generation of negative pressure is crucial to protecting gas reservoirs and environmental safety. In the prior art, common oil and gas development methods include water drive oil and gas, gas injection and other means, which can alleviate the negative pressure phenomenon to a certain extent and increase the production of oil and gas. However, the generation of negative pressure and changes in permeability are often difficult to monitor in real time, and the existing monitoring systems mostly rely on static monitoring methods and lack real-time and dynamic feedback control mechanisms. Therefore, when the negative pressure is too large or the permeability is too high, it often leads to reservoir instability or waste of resources, which in turn affects the extraction effect. How to efficiently control reservoir pressure and monitor permeability changes has become a key technology to improve the development efficiency of unconventional oil and gas reservoirs. Summary of the invention

[0004] Technical problems solved: In response to the above technical problems, the present invention provides a device and method for negative pressure control and permeability monitoring of unconventional natural gas reservoirs, which can accurately control the negative pressure, avoid permeability monitoring lag, and adjust the pressure and permeability in real time during reservoir exploitation.

[0005] Technical solution: A device for negative pressure control and permeability monitoring of an unconventional natural gas reservoir, wherein the reservoir is provided with a first aquifer and a second aquifer that are not connected;

[0006] The device comprises:

[0007] The water reservoir is connected to the first aquifer through an injection well pipeline and connected to the second aquifer through a pumping well pipeline; wherein a first water pressure gauge is provided on the injection well pipeline and a second water pressure gauge is provided on the pumping well pipeline;

[0008] The air extraction pipeline has an air inlet located in the reservoir and an air outlet connected to the atmosphere. A barometer is provided on the air extraction pipeline to monitor the pressure changes during the air extraction process.

[0009] The auxiliary pipeline has a filter screen at its bottom end, which is located at the bottom of the reservoir, and the top end is connected to the air inlet of the exhaust pipeline; the interior of the auxiliary pipeline: positive electrode materials and negative electrode materials are respectively provided on both sides along the length direction, and the top ends of the positive electrode materials and the negative electrode materials are provided with external voltages; porous materials and fixed end points are provided in sequence from top to bottom, and the interior of the auxiliary pipeline is divided into an upper storage chamber, a middle storage chamber and a bottom storage chamber, and pressure gauges are respectively provided in the upper storage chamber and the middle storage chamber, and a flow meter is also provided in the upper storage chamber, and a conductive slider is provided in the bottom storage chamber, and the conductive slider, the positive electrode material, the negative electrode material, and the external voltage form a water level gauge for monitoring changes in the reservoir water level;

[0010] a signal transceiver, which is in telecommunication connection with the first water pressure gauge, the second water pressure gauge, the air pressure gauge, the pressure gauge, the flow meter and the water level gauge, and is used to transmit real-time data of the first water pressure gauge, the second water pressure gauge, the air pressure gauge, the pressure gauge, the flow meter and the water level gauge to the central processor, and transmit operation instructions of the central processor to the water injection well pipeline and the water pumping well pipeline;

[0011] The central processing unit is connected to the signal transceiver by telecommunication, and is used for receiving and processing the above real-time data and issuing operation instructions.

[0012] Preferably, a two-way valve is provided on the water injection well pipeline.

[0013] Preferably, a one-way valve is provided on the pumping well pipeline to control the flow of water from the second aquifer to the water reservoir.

[0014] Preferably, the water reservoir is also provided with a water storage pipeline, and the water storage pipeline is provided with a two-way valve.

[0015] Preferably, the fixed end point is an insulator.

[0016] Preferably, the air inlet of the air extraction pipe is a porous structure.

[0017] A method for negative pressure control and permeability monitoring of unconventional natural gas reservoirs comprises the following steps:

[0018] S1. Obtain the air pressure in the reservoir from the air pressure indication, calculate the permeability from the pressure gauge and flow meter indications, and obtain the reservoir water level from the water level gauge;

[0019] S2. Determine the operation of the reservoir according to the gas pressure, permeability and water level in the reservoir: inject water, pump water or maintain the original state, and adjust the water flow rate in combination with the first water pressure gauge or the second water pressure gauge;

[0020] S3. Repeat steps S1 and S2 to maintain the stability of the reservoir.

[0021] Preferably, the calculation formula of the permeability in step S1 is:

[0022]

[0023] Wherein, K is the permeability; Q is the flow rate, which is determined by the flowmeter; S is the area through which the fluid passes through the porous material; P0 is the atmospheric pressure; P1 and P2 are the pressure indications of the upper storage chamber and the middle storage chamber, respectively; L is the path length of the fluid through the porous material; μ is the fluid dynamic viscosity; for this test environment, the cross-sectional area S, length L, fluid dynamic viscosity μ and atmospheric pressure P0 are all known constants.

[0024] Preferably, the readings of the first water pressure gauge and the second water pressure gauge are both positively correlated with the water flow velocity.

[0025] Preferably, in step S2, the judgment process is as follows:

[0026] Standard 1: When the gas pressure in the reservoir (1) is less than that in the aquifer (3), it is negative pressure, water injection is performed; when the gas pressure in the reservoir (1) is greater than that in the aquifer (3), it is positive pressure, and when the positive pressure is greater than a certain critical value, water pumping is performed;

[0027] Standard 2: When the permeability is less than the permeability of water flowing through the porous material (15), water is pumped out; when the permeability is greater than the permeability of natural gas flowing through the porous material (15), water is injected; when the permeability is between the permeability of water flowing through the porous material (15) and the permeability of natural gas flowing through the porous material (15), the state is maintained;

[0028] Standard three: the highest water level is when the conductive slider (22) reaches the fixed end point (16), and the lowest water level is when the conductive slider (22) is located at the bottom of the positive electrode material (13) and the negative electrode material (14). When the water level is at the highest value, water is pumped out; when the water level is at the lowest value, water is injected; when the water level is between the lowest value and the highest value, the water level is maintained as it is.

[0029] When standards 1, 2 and 3 conflict, standard 1 takes precedence, standard 2 comes second, and standard 3 comes last.

[0030] Beneficial effects: The negative pressure control and permeability monitoring device for unconventional natural gas reservoirs of the present invention can realize real-time negative pressure monitoring and permeability testing, ensuring that during the reservoir exploitation process, the reservoir pressure and permeability are always maintained at the best state, avoiding exploitation problems caused by excessive negative pressure or excessive permeability changes. Through the pressure gauge and flow meter on the auxiliary pipeline, real-time monitoring of permeability is achieved, providing data support for optimizing exploitation. The setting of the conductive slider and the fixed end point realizes the monitoring of the groundwater level while protecting the porous material from damage. The use of the filter screen improves the durability and reliability of the system. The present invention can effectively improve the development efficiency of unconventional oil and gas reservoirs, reduce resource waste, and avoid irreversible damage to the reservoir due to pressure imbalance by automatically adjusting the negative pressure control and permeability management. In addition, the integrated and intelligent design of the present invention enables it to efficiently and accurately adjust the exploitation parameters of the reservoir in practical applications, thereby improving the safety and economy of the oil and gas exploitation process.

[0031] The present invention provides a comprehensive and intelligent reservoir exploitation control solution, which improves the utilization efficiency of oil and gas resources while ensuring the long-term stability and safety of the reservoir development process. The present invention can achieve efficient negative pressure control and permeability monitoring in unconventional natural gas reservoirs, improve the extraction efficiency of natural gas, and reduce the impact on the environment, which helps to improve the efficient utilization and sustainable development of energy and promote the widespread application of unconventional natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the device structure of the present invention;

[0033] Figure 2 It is a schematic diagram of the structure of the auxiliary pipeline;

[0034] The numbers in the figure represent the following: 1. reservoir; 2. first aquifer; 3. second aquifer; 4. water storage reservoir; 5. injection well pipeline; 6. pumping well pipeline; 7. first water pressure gauge; 8. second water pressure gauge; 9. suction pipeline; 10. air pressure gauge; 11. auxiliary pipeline; 12. filter; 13. positive electrode material; 14. negative electrode material; 15. porous material; 16. fixed end point; 17. upper storage chamber; 18. middle storage chamber; 19. bottom storage chamber; 20. pressure gauge; 21. flow meter; 22. conductive slider; 23. water storage pipeline; 24. cap layer; 25. shale; 26. bedrock; 27. fault. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] like Figure 1 and Figure 2 As shown, a device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs, wherein the geological environment of the unconventional natural gas reservoir 1 is: from top to bottom, it includes a cap rock 24, an impermeable layer 25, a reservoir 1 and a bedrock 26. Affected by a fault 27, a first aquifer 2 and a second aquifer 3 that are not connected are formed in the reservoir 1; the first aquifer 2 and the second aquifer 3 are both bottom water layers of the oil and gas reservoir 1, and the exploitation process may cause bottom water to flow into the oil and gas reservoir 1. It is necessary to use the following device to test whether the exploitation will cause bottom water intrusion, how much the flow rate is, and whether the well can be flooded.

[0038] The device comprises:

[0039] The water reservoir 4 is connected to the first aquifer 2 through the water injection well pipeline 5 and is connected to the second aquifer 3 through the water pumping well pipeline 6; wherein the water injection well pipeline 5 is provided with a first water pressure gauge 7, and the water pumping well pipeline 6 is provided with a second water pressure gauge 8;

[0040] The air extraction pipeline 9 has an air inlet disposed in the reservoir 1 and an air outlet connected to the atmosphere. A barometer 10 is provided on the air extraction pipeline 9 to monitor the pressure change during the air extraction process to ensure that the air extraction process does not cause excessive negative pressure to the reservoir 1;

[0041] The auxiliary pipe 11 has a filter screen 12 at its bottom, which is located at the bottom of the reservoir 1 and can effectively intercept suspended matter and particles in the water, filter impurities in the pipe, and protect internal components; its top is connected to the air inlet of the exhaust pipe 9; the inside of the auxiliary pipe 11: positive electrode materials 13 and negative electrode materials 14 are respectively provided on both sides along the length direction, and the tops of the positive electrode materials 13 and the negative electrode materials 14 are provided with external voltages; porous materials 15 and fixed end points 16 are provided in sequence from top to bottom, dividing the inside of the auxiliary pipe 11 into an upper storage chamber 17, a middle storage chamber 1 8 and a bottom storage chamber 19, a pressure gauge 20 is respectively arranged in the upper storage chamber 17 and the middle storage chamber 18, a flow meter 21 is also arranged in the upper storage chamber, a conductive slider 22 is arranged in the bottom storage chamber 19, the conductive slider 22, the positive electrode material 13, the negative electrode material 14, and the external voltage form a water level gauge for monitoring the water level change of the reservoir 1, when the conductive slider 22 floating on the horizontal plane moves in the bottom storage chamber 19 with the water level change, the circuit resistance of the water level gauge changes, thereby causing the current to change, so that the water level change in the reservoir 1 can be reflected in real time;

[0042] A signal transceiver is connected to the first water pressure gauge 7, the second water pressure gauge 8, the barometer 10, the pressure gauge 20, the flow meter 21 and the water level gauge by telecommunication, and is used to transmit the real-time data of the first water pressure gauge 7, the second water pressure gauge 8, the barometer 10, the pressure gauge 20, the flow meter 21 and the water level gauge to the central processor, and transmit the operation instructions of the central processor to the injection well pipeline 5 and the pumping well pipeline 6;

[0043] The central processing unit is connected to the signal transceiver by telecommunication, and is used for receiving and processing the above real-time data and issuing operation instructions.

[0044] Among them, a two-way valve is provided on the injection well pipeline 5. The two-way valve has an automatic adjustment function, which can flexibly switch the injection and pumping processes, and automatically adjust the injection and pumping volumes according to the changes in the pressure and permeability of the reservoir 1 during the injection and pumping processes to prevent excessive negative pressure or inappropriate permeability, ensure a reasonable balance of water in the reservoir 1, and optimize the water drive oil and gas process.

[0045] The pumping well pipeline 6 is provided with a one-way valve for controlling the water flow to flow from the second aquifer 3 to the water reservoir 4 in one direction.

[0046] The water reservoir 4 is also provided with a water storage pipeline 23, and a two-way valve is provided on the water storage pipeline 23.

[0047] The fixed end point 16 is an insulator with sufficient strength, which can limit the movement of the conductive slider 22 and prevent the porous material 15 from being damaged.

[0048] The air inlet of the air extraction pipeline 9 is a porous structure, which can quickly extract unconventional natural gas.

[0049] The pressure gauge 20 has high-precision measurement capability to ensure the accuracy of permeability monitoring. The conductive slider 22 is made of corrosion-resistant material to adapt to the chemical environment of the aquifer. The positive electrode material 13 and the negative electrode material 14 have a conductive function, but do not short-circuit in a water vapor environment.

[0050] The above device forms an intelligent control system through the feedback data of the first water pressure gauge 7, the second water pressure gauge 8, the barometer 10, the pressure gauge 20, the flow meter 21 and the water level gauge, in conjunction with the automatic adjustment function of the two-way valve. This intelligent control system can not only improve the mining efficiency, but also greatly reduce the impact on the environment, so it has the following advantages: the system can monitor the pressure, water level changes and permeability data of the reservoir 1 in real time, automatically adjust the injection and pumping volume, and ensure that the negative pressure and permeability of the reservoir 1 are always maintained in the best state. The use of the barometer 10 can automatically trigger the water injection program when the negative pressure of the reservoir 1 is too large, balance the pressure of the reservoir 1, and prevent the instability of the reservoir 1. Through the accurate data of the pressure gauge 20 and the flow meter 21, the system can calculate the permeability of the reservoir 1 in real time, optimize the mining process, and avoid the situation where the permeability is too high or too low. The design of multiple sensors and high-efficiency filter 12 ensures the stability and reliability of the system during long-term operation, while reducing system failures caused by impurities and damage. Through intelligent negative pressure control and permeability regulation, this system can improve the efficiency of natural gas extraction, reduce resource waste, and avoid the environmental impact caused by excessive pumping or injection, and has good sustainability.

[0051] The method for negative pressure control and permeability monitoring of unconventional natural gas reservoirs using the above device comprises the following steps:

[0052] S1. The air pressure in the reservoir 1 is obtained from the reading of the barometer 10, the permeability is calculated from the readings of the pressure gauge 20 and the flow meter 21, and the water level of the reservoir 1 is obtained from the water level gauge; wherein the calculation formula of the permeability is:

[0053]

[0054] In the formula, K is the permeability; Q is the flow rate, which is determined by the flow meter 21; S is the area of ​​the fluid passing through the porous material 15; P0 is the atmospheric pressure; P1 and P2 are the readings of the pressure gauge 20 of the upper storage chamber 17 and the middle storage chamber 18 respectively; L is the path length of the fluid through the porous material 15; μ is the fluid dynamic viscosity; for this test environment, the cross-sectional area S, the length L, the fluid dynamic viscosity μ and the atmospheric pressure P0 are all known constants.

[0055] S2. According to the gas pressure, permeability and water level of reservoir 1, the operation of reservoir 1 is determined: water injection, water extraction or maintaining the original state. The determination process is as follows:

[0056] Standard 1: When the gas pressure in the reservoir (1) is less than that in the aquifer (3), it is negative pressure, water injection is performed; when the gas pressure in the reservoir (1) is greater than that in the aquifer (3), it is positive pressure, and when the positive pressure is greater than a certain critical value, water pumping is performed;

[0057] Standard 2: When the permeability is less than the permeability of water flowing through the porous material (15), water is pumped out; when the permeability is greater than the permeability of natural gas flowing through the porous material (15), water is injected; when the permeability is between the permeability of water flowing through the porous material (15) and the permeability of natural gas flowing through the porous material (15), the state is maintained;

[0058] Standard three: the highest water level is when the conductive slider (22) reaches the fixed end point (16), and the lowest water level is when the conductive slider (22) is located at the bottom of the positive electrode material (13) and the negative electrode material (14). When the water level is at the highest value, water is pumped out; when the water level is at the lowest value, water is injected; when the water level is between the lowest value and the highest value, the water level is maintained as it is.

[0059] When standards 1, 2 and 3 conflict, standard 1 takes precedence, standard 2 comes second, and standard 3 comes last.

[0060] The water flow rate is then adjusted in combination with the indication of the first water pressure gauge 7 or the second water pressure gauge 8. The indications of the first water pressure gauge 7 and the second water pressure gauge 8 are both positively correlated with the water flow rate.

[0061] S3. Repeat steps S1 and S2 to maintain the stability of reservoir 1.

[0062] The present invention provides a comprehensive and intelligent reservoir 1 exploitation control solution, which improves the utilization efficiency of oil and gas resources while ensuring the long-term stability and safety of the reservoir 1 development process. The present invention can achieve efficient negative pressure control and permeability monitoring in the unconventional natural gas reservoir 1, improve the efficiency of natural gas exploitation, and reduce the impact on the environment, which is helpful to improve the efficient utilization and sustainable development of energy and promote the widespread application of unconventional natural gas.

Claims

1. A device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs, characterized in that: The reservoir (1) is provided with a first aquifer (2) and a second aquifer (3) which are not connected; The device comprises: A water reservoir (4) is connected to a first aquifer (2) via an injection well pipeline (5) and is connected to a second aquifer (3) via a pumping well pipeline (6); wherein a first water pressure gauge (7) is provided on the injection well pipeline (5) and a second water pressure gauge (8) is provided on the pumping well pipeline (6); An air extraction pipeline (9), the air inlet of which is arranged in the reservoir (1), the air outlet of which is connected to the atmosphere, and a barometer (10) is arranged on the air extraction pipeline (9) for monitoring the pressure change during the air extraction process; An auxiliary pipeline (11) is provided with a filter screen (12) at its bottom end, and is located at the bottom of the reservoir (1), and its top end is connected to the air inlet of the air extraction pipeline (9); inside the auxiliary pipeline (11): positive electrode materials (13) and negative electrode materials (14) are respectively provided on both sides along the length direction, and the top ends of the positive electrode materials (13) and the negative electrode materials (14) are provided with external voltages; porous materials (15) and fixed end points (16) are provided in sequence from top to bottom, and the inside of the auxiliary pipeline (11) is divided into an upper storage chamber (17), a middle storage chamber (18) and a bottom storage chamber (19); pressure gauges (20) are respectively provided in the upper storage chamber (17) and the middle storage chamber (18); a flow meter (21) is also provided in the upper storage chamber (17); and a conductive slider (22) is provided in the bottom storage chamber (19); the conductive slider (22) forms a water level gauge with the positive electrode materials (13), the negative electrode materials (14) and the external voltage, and is used to monitor the water level change of the reservoir (1); a signal transceiver, which is connected to the first water pressure gauge (7), the second water pressure gauge (8), the air pressure gauge (10), the pressure gauge (20), the flow meter (21) and the water level gauge by telecommunication, and is used to transmit real-time data of the first water pressure gauge (7), the second water pressure gauge (8), the air pressure gauge (10), the pressure gauge (20), the flow meter (21) and the water level gauge to the central processor, and transmits operation instructions of the central processor to the water injection well pipeline (5) and the water pumping well pipeline (6); The central processing unit is connected to the signal transceiver by telecommunication, and is used for receiving and processing the above real-time data and issuing operation instructions.

2. The device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs according to claim 1, characterized in that: A two-way valve is provided on the water injection well pipeline (5).

3. The device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs according to claim 1, characterized in that: The pumping well pipeline (6) is provided with a one-way valve for controlling the flow of water from the second aquifer (3) to the water storage reservoir (4).

4. The device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs according to claim 1, characterized in that: The water storage reservoir (4) is also provided with a water storage pipeline (23), and a two-way valve is provided on the water storage pipeline (23).

5. The device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs according to claim 1, characterized in that: The fixed end point (16) is an insulator.

6. The device for negative pressure control and permeability monitoring of unconventional natural gas reservoirs according to claim 1, characterized in that: The air inlet of the air extraction pipeline (9) is a porous structure.

7. A method for negative pressure control and permeability monitoring of unconventional natural gas reservoirs using the device according to any one of claims 1 to 6, characterized in that: The steps include: S1. The air pressure in the reservoir (1) is obtained by the barometer (10), the permeability is calculated by the pressure gauge (20) and the flow meter (21), and the water level of the reservoir (1) is obtained by the water level meter; S2. Determine the operation of the reservoir (1) according to the gas pressure, permeability and water level of the reservoir (1): water injection, pumping or maintaining the original state, and adjust the water flow rate in combination with the first water pressure gauge (7) or the second water pressure gauge (8); S3. Repeat steps S1 and S2 to maintain the stability of the reservoir (1).

8. The method according to claim 7, characterized in that The calculation formula of the permeability in step S1 is: In the formula, K is the permeability; Q is the flow rate, which is determined by the flow meter (21); S is the area of ​​the fluid passing through the porous material (15); P0 is the atmospheric pressure; P1 and P2 are the readings of the pressure gauge (20) of the upper storage chamber (17) and the middle storage chamber (18), respectively; L is the path length of the fluid passing through the porous material (15); μ is the fluid dynamic viscosity; under the present test environment, the cross-sectional area S, the length L, the fluid dynamic viscosity μ and the atmospheric pressure P0 are all known constants.

9. The method according to claim 7, characterized in that: The readings of the first water pressure gauge (7) and the second water pressure gauge (8) are both positively correlated with the water flow velocity.

10. The method according to claim 7, characterized in that In step S2, the judgment process is as follows: Standard 1: When the gas pressure in the reservoir (1) is less than that in the aquifer (3), it is negative pressure, water injection is performed; when the gas pressure in the reservoir (1) is greater than that in the aquifer (3), it is positive pressure, and when the positive pressure is greater than a certain critical value, water pumping is performed; Standard 2: When the permeability is less than the permeability of water flowing through the porous material (15), water is pumped out; when the permeability is greater than the permeability of natural gas flowing through the porous material (15), water is injected; when the permeability is between the permeability of water flowing through the porous material (15) and the permeability of natural gas flowing through the porous material (15), the state is maintained; Standard three: the highest water level is when the conductive slider (22) reaches the fixed end point (16), and the lowest water level is when the conductive slider (22) is located at the bottom of the positive electrode material (13) and the negative electrode material (14). When the water level is at the highest value, water is pumped out; when the water level is at the lowest value, water is injected; when the water level is between the lowest value and the highest value, the water level is maintained as it is. When standards 1, 2 and 3 conflict, standard 1 takes precedence, standard 2 comes second, and standard 3 comes last.

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