Underground gas storage drainage system and drainage method thereof

Abstract

The invention discloses an underground gas storage drainage system and a drainage method thereof. The drainage system comprises a plurality of gas storage caverns arranged side by side, and a traffic tunnel is arranged between every two adjacent gas storage caverns; a first drainage pipe, a plurality of second drainage pipes and a plurality of third drainage pipes are arranged outside the gas storage cavern; the first drainage pipe is arranged at the bottom of the gas storage cavern; the second drainage pipes are arranged on the side wall of the gas storage cavern, and the multiple second drainage pipes are arranged at intervals in the length direction of the gas storage cavern; a plurality of third drainage pipes are arranged on each second drainage pipe at intervals in the length direction, and at least one water inlet hole is formed in the side wall of each third drainage pipe; one end of the third drainage pipe is communicated with the second drainage pipe, and the other end extends away from the gas storage cavern; one end of the first drainage pipe is communicated with the second drainage pipes, the other end of the first drainage pipe extends into the traffic hole, and a valve is arranged at the end, extending into the traffic hole, of the first drainage pipe. The drainage system solves the technical problem that in the prior art, the pressure of water outside a gas storage is large.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of compressed air energy storage, and particularly relates to a drainage system of an underground gas storage and a drainage method thereof. BACKGROUND

[0002] Compressed air energy storage refers to a method of storing air compressed by surplus power in a low valley of power grid in a high-pressure sealed facility, and releasing the air to drive an expander to drive a generator to generate power in a power peak. The compressed air energy storage system mainly comprises a compression system, an expansion and power generation system, a storage and heat exchange system, and a gas storage system, and the high-pressure gas discharged from the compression system is stored in the gas storage, and the maximum pressure of the gas can be higher than 10 MPa, which puts high requirements on the pressure bearing capacity and sealing property of the gas storage. At present, the underground artificial excavation gas storage gradually becomes one of the mainstream forms of the gas storage due to the advantages of flexible site selection, less restrictions, wide application area, large scale, and high gas storage pressure.

[0003] The underground artificial excavation gas storage is excavated in a rock mass at a certain depth by an artificial method to store gas in a cavern, and the rock mass cover weight and the ground stress are used to resist the gas pressure in the cavern to achieve the purpose of fully utilizing the surrounding rock to bear the internal high pressure. In order to maintain the air tightness of the cavern, a sealing layer is generally arranged in the gas storage cavern. Since the gas storage cavern is buried below 100 meters underground, the sealing layer of the gas storage cavern is subjected to the action of the underground water pressure. During the operation period, the maximum pressure in the gas storage can be higher than 10 MPa, and the external water pressure can be ignored. However, during the maintenance period, the external water pressure can cause the sealing layer to deform, buckle, or even be damaged, and therefore corresponding measures need to be taken to ensure the stability of the sealing layer against external pressure, which can cause the thickness of the sealing layer to be thickened, the cost of additional measures to be increased, and the investment to be high and the economy to be poor. In order to solve the above problems, relevant measures can be taken to reduce the underground water level outside the gas storage, so as to reduce the external water pressure of the sealing layer. Under the premise of ensuring the safety and stability of the gas storage and the air tightness, considering various influencing factors, how to design the drainage measures outside the gas storage to achieve the purpose of reducing the external water pressure of the gas storage is crucial to the structural stability of the gas storage cavern. SUMMARY

[0004] In view of the existing technical problems, the application aims to provide a drainage system of an underground gas storage and a drainage method thereof, which can solve the technical problem of high external water pressure of the gas storage in the prior art.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0006] The application discloses an underground gas storage drainage system, which comprises a plurality of gas storage caverns arranged side by side, and a traffic tunnel arranged between two adjacent gas storage caverns; the structural characteristics are that a first drainage pipe, a plurality of second drainage pipes and a plurality of third drainage pipes are arranged outside the gas storage cavern; the first drainage pipe is arranged on the bottom of the gas storage cavern along the length direction of the gas storage cavern; the second drainage pipe is arranged on the side wall of the gas storage cavern along the cross section direction of the gas storage cavern, and a plurality of second drainage pipes are arranged at intervals along the length direction of the gas storage cavern; a plurality of third drainage pipes are arranged at intervals along the length direction of each second drainage pipe, and at least one water inlet hole is arranged on the side wall of each third drainage pipe; one end of each third drainage pipe is connected with a second drainage pipe, and the other end of each third drainage pipe extends away from the gas storage cavern, and each third drainage pipe is arranged in an upward inclined manner; one end of the first drainage pipe is connected with a plurality of second drainage pipes, and the other end of the first drainage pipe extends into the traffic tunnel, and a valve is arranged on the end of the first drainage pipe extending into the traffic tunnel.

[0007] When the underground gas storage is in normal operation, the valve on the first drainage pipe is closed, and the underground water outside the gas storage can provide support for the internal pressure of the gas storage cavern; when the underground gas storage needs to be overhauled, the gas storage cavern needs to be emptied, and in order to ensure the structural stability of the gas storage cavern, the underground water outside the gas storage needs to be drained; at this time, the valve on the first drainage pipe is opened, the underground water of the gas storage is collected through the third drainage pipe, is collected into the first drainage pipe on the bottom of the gas storage through the second drainage pipe, and is drained into the traffic tunnel through the first drainage pipe; when the water pressure outside the gas storage cavern is reduced to below a safety value, the gas storage cavern is emptied for overhaul. The underground gas storage drainage system of the application drains the underground seepage water around the gas storage cavern into the connecting tunnel through the first drainage pipe, the second drainage pipe and the third drainage pipe, thereby solving the technical problem of high water pressure outside the gas storage.

[0008] Specifically, the gas storage cavern has a rectangular structure, and round corners are arranged at four corners of the gas storage cavern, and the cross section shape of the gas storage cavern is circular; the second drainage pipe is arranged along the circumferential direction of the gas storage cavern, and the third drainage pipe is arranged along the circumferential diameter direction of the gas storage cavern.

[0009] Preferably, a water collecting pit is arranged in the traffic tunnel, the end of the first drainage pipe extending towards the traffic tunnel is connected with the water collecting pit, and the first drainage pipe is inclined towards the water collecting pit; the underground water outside the gas storage cavern is collected into the water collecting pit through the first drainage pipe, the second drainage pipe and the third drainage pipe; when the tunnel opening of the traffic tunnel is lower than the water collecting pit, the water is drained out of the tunnel through the traffic tunnel by gravity; when the tunnel opening of the traffic tunnel is higher than the water collecting pit, the water can be pumped out of the tunnel.

[0010] Specifically, the gas storage chamber comprises a first long-side chamber and a second long-side chamber arranged in parallel, the first long-side chamber and the second long-side chamber are connected by end chambers between both end portions, and the second long-side chamber is located on the side close to the traffic tunnel; the bottom wall of the first long-side chamber is provided with slopes towards both end portions from the middle portion, and both end portions are sloped towards the middle portion of the second long-side chamber through the end chambers, and the first drainage pipe is laid along the bottom wall of the gas storage chamber. The water in the first drainage pipe flows from the middle portion of the first long-side chamber to both end portions along the slopes, and flows to the middle portion of the second long-side chamber through the end chambers, and then flows into the traffic tunnel.

[0011] Preferably, the first drainage pipe and the second drainage pipe are both made of steel drainage pipes, the diameter of the first drainage pipe is 0.07m-0.15m; the diameter of the second drainage pipe is 0.05m-0.08m, and the spacing between two adjacent second drainage pipes is 2.0m-5.0m; the third drainage pipe is made of hot-rolled seamless steel pipes, the diameter of the third drainage pipe is 0.05m-0.07m, the length of the third drainage pipe is 2.5m-4.5m, and the spacing between two adjacent third drainage pipes on the same second drainage pipe is 2.0m-5.0m. The service life of the compressed air energy storage underground gas storage is more than 30 years, in order to ensure the effectiveness of the drainage system, the drainage pipe is made of hot-rolled seamless steel pipes.

[0012] Preferably, the spacing between the lowest third drainage pipe on the second drainage pipe and the bottom of the gas storage chamber is not less than 1 / 2 of the diameter of the gas storage chamber, and the included angle between the axial center line of the third drainage pipe and the horizontal plane is 15°-90°. The third drainage pipe is arranged on the upper half of the second drainage pipe.

[0013] Preferably, the third drainage pipes on two adjacent second drainage pipes are arranged alternately, and the third drainage pipes are wrapped with geotextiles. In order to prevent silt from entering the third drainage pipe and blocking the pipe, the third drainage pipes are wrapped with geotextiles.

[0014] Preferably, the side wall of the gas storage chamber is sequentially provided with a sealing layer, a concrete layer and a water-resisting layer from inside to outside, the thickness of the sealing layer is 0.01m-0.03m, and the thickness of the concrete layer is 0.5m-1.0m; the water-resisting layer is arranged close to the surrounding rock, the first drainage pipe and the second drainage pipe are arranged between the water-resisting layer and the surrounding rock, and the third drainage pipe extends into the surrounding rock. The sealing layer can be made of steel plates, the surface of the steel plate is subjected to corrosion prevention treatment, and the sealing layer can also be replaced by organic materials such as glass steel, polyurea and rubber. The concrete layer can transmit the high pressure inside the sealing layer to the surrounding rock, so as to achieve the purpose of bearing the surrounding rock. The water-resisting layer can be made of waterproof paint and waterproof coiled material, so as to further isolate water outside the gas storage chamber. The underground gas storage drainage system of the application fully utilizes the surrounding rock to share the internal high pressure, reduces the amount of sealing material and the cost by using the flat adit chamber gas storage with the internal concrete and sealing layer.

[0015] Preferably, the traffic hole is provided with an osmometer, and the osmometer and the valve are electrically connected with the control system. The osmometer can be buried in the surrounding rock of the traffic hole, and the control system can be arranged in the ground workshop. The control system can monitor the groundwater pressure of the surrounding rock of the gas storage in real time, and open or close the valve on the first drainage pipe according to the need.

[0016] Based on the same inventive concept, the application also provides a gas storage drainage method. The underground gas storage drainage system is used. During normal operation of the gas storage chamber, the valve is closed. When the gas storage chamber needs to be overhauled, the valve is opened, the underground seepage water outside the gas storage chamber is discharged outward through the third drainage pipe, the second drainage pipe and the first drainage pipe, and the gas storage chamber is overhauled after the water pressure outside the gas storage chamber is reduced to below the safety value.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] 1. The underground gas storage drainage system of the application sets up a rock wall drainage system outside the gas storage chamber concrete, collects the underground water outside the gas storage chamber into the first drainage pipe through the third drainage pipe, and discharges it to the outside of the hole, thereby effectively reducing the underground water level.

[0019] 2. The underground gas storage drainage method of the application effectively avoids the anti-external pressure instability phenomenon of the sealing layer during the internal overhaul and emptying of the gas storage chamber, reduces the additional measures for the sealing layer to resist external pressure, thins the thickness of the sealing layer increased for resisting external pressure, and is expected to reduce the thickness of the sealing layer of the gas storage chamber by 1 / 10-1 / 5, thereby effectively reducing the sealing cost. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the underground gas storage drainage system of the application;

[0021] Figure 2 is Figure 1 a schematic diagram of the arrangement structure of the first drainage pipe, the second drainage pipe and the third drainage pipe in the gas storage chamber;

[0022] Figure 3 is Figure 2 a schematic diagram of the cross-sectional structure;

[0023] Figure 4 is Figure 1 a schematic diagram of the overhead structure of two adjacent gas storage chambers (the arrow direction is a schematic diagram of the water flow direction in the first drainage pipe);

[0024] Figure 5 is Figure 1 a schematic diagram of the first drainage pipe connection structure at the bottom of the gas storage chamber.

[0025] In the drawings

[0026] 1 - sump, 2 - surrounding rock, 3 - gas storage cavern, 301 - first long side cavern, 302 - second long side cavern, 303 - end cavern, 4 - connecting roadway, 5 - traffic tunnel, 6 - first drainage pipe, 7 - sealing layer, 8 - concrete layer, 9 - second drainage pipe, 10 - third drainage pipe, 11 - water-resisting layer, 12 - valve, 13 - osmometer, 14 - control system. DETAILED DESCRIPTION

[0027] The application will be described in detail below with reference to the drawings and in conjunction with the embodiments. It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. For the convenience of description, if the terms “upper”, “lower”, “left”, “right” appear in the following, they only mean consistent with the upper, lower, left and right directions of the drawings themselves, and do not limit the structure.

[0028] As shown in Figure 1 , the underground gas storage drainage system of the embodiment comprises two gas storage caverns 3 arranged side by side, and the two gas storage caverns 3 are connected through the connecting roadway 4. A traffic tunnel 5 is arranged between the two adjacent gas storage caverns 3, and the osmometer 13 is arranged in the traffic tunnel 5. Figure 1 、 Figure 2 and Figure 5 , the first drainage pipe 6, the second drainage pipes 9 and the third drainage pipes 10 are arranged outside the gas storage cavern 3. The first drainage pipe 6 is arranged at the bottom of the gas storage cavern 3 along the length direction of the gas storage cavern 3. The second drainage pipes 9 are arranged on the side wall of the gas storage cavern 3 along the cross-sectional direction of the gas storage cavern 3, and the second drainage pipes 9 are arranged at intervals along the length direction of the gas storage cavern 3. The third drainage pipes 10 are arranged at intervals along the length direction of each second drainage pipe 9, the third drainage pipes 10 on the adjacent two second drainage pipes 9 are arranged staggered, and the side wall of the third drainage pipe 10 is provided with a plurality of water inlet holes. One end of the third drainage pipe 10 is connected with the second drainage pipe 9, the other end of the third drainage pipe 10 extends away from the gas storage cavern 3, and the third drainage pipe 10 is arranged inclined upward. As shown in Figure 1 and Figure 5 , one end of the first drainage pipe 6 is connected with the second drainage pipes 9, the other end of the first drainage pipe 6 extends into the traffic tunnel 5, and the valve 12 is arranged on the end of the first drainage pipe 6 extending into the traffic tunnel 5. The osmometer 13 and the valve 12 are electrically connected with the control system 14. As shown in Figure 4 , the gas storage cavern 3 has a rectangular structure, and the four corners are provided with rounded corners. As shown in Figure 2 and Figure 3As shown, the cross-sectional shape of the gas storage chamber 3 is circular, and the second drain pipe 9 is arranged along the circumferential direction of the gas storage chamber 3. The gas storage chamber 3 comprises a first long-side chamber 301 and a second long-side chamber 302 arranged in parallel, and the two ends of the first long-side chamber 301 and the second long-side chamber 302 are connected by an end chamber 303. The second long-side chamber 302 is located on the side close to the traffic tunnel 5. The bottom wall of the first long-side chamber 301 is provided with slopes towards the two ends from the middle part, and the slopes of the two ends are directed towards the middle part of the second long-side chamber 302 through the end chamber 303. The first drain pipe 6 is laid along the bottom wall of the gas storage chamber 3. Figure 3 As shown, the side wall of the gas storage chamber 3 is sequentially provided with a sealing layer 7, a concrete layer 8 and a water-blocking layer 11 from inside to outside, and the water-blocking layer 11 is arranged immediately adjacent to the surrounding rock 2. The first drain pipe 6 and the second drain pipe 9 are arranged between the water-blocking layer 11 and the surrounding rock 2, and the third drain pipe 10 extends into the surrounding rock 2. The thickness of the sealing layer 7 is 0.01m-0.03m, and the thickness of the concrete layer 8 is 0.5m-1.0m. The water-blocking layer 11 is formed by spraying waterproof material, and the thickness is 5mm. Systematic drainage holes are drilled in the surrounding rock 2 on the upper half of the gas storage chamber 3, the angle between the drainage holes and the horizontal direction is not equal to 15°-90°, the hole depth is 3m, the hole diameter is 56mm, and the circumferential spacing of the drainage holes is 3m. Along the axial direction of the gas storage chamber 3, the spacing of the drainage holes is also 3m. The third drain pipe 10 is inserted into the drainage hole, the third drain pipe 10 is made of hot-rolled seamless steel pipe with an outer diameter of 50mm and a wall thickness of 3.5mm, the length is 2.5m, the water inlet hole with a diameter of 8mm is drilled around the wall of the third drain pipe 10, and the third drain pipe 10 is wrapped with geotextile to prevent the pipeline from being blocked by silt. The diameter of the second drain pipe 9 is 60mm, and the spacing between the adjacent two second drain pipes 9 along the length direction of the gas storage chamber 3 is 3m. A first drain pipe 6 is buried at the bottom of the chamber along the whole length of the chamber, and the diameter of the first drain pipe 6 is 90mm. The first drain pipe 6 and the second drain pipe 9 are both made of hot-rolled seamless steel pipe. Figure 4 and Figure 5 As shown, after the first drain pipe 6 is arranged along the whole length of the chamber, the first drain pipes 6 at the bottoms of the adjacent two gas storage chambers 3 are connected and then extended to the sump 1 in the traffic tunnel 5.

[0029] The construction method of the underground gas storage drainage system of the embodiment has the following steps:

[0030] Step S1, after the gas storage excavation support, first use hand drill or drill rig drill drainage hole, then insert the third drainage pipe 10 in the drainage hole; after the third drainage pipe 10 construction, immediately install the second drainage pipe 9, the second drainage pipe 9 is connected by tee by multiple curved prefabricated seamless steel pipes, install the second drainage pipe 9 on the side wall of the chamber and fix, the end of the third drainage pipe 10 in the drainage hole is connected with the second drainage pipe 9 through tee; while the second drainage pipe 9 is constructed, the first drainage pipe 6 is buried on the ground at the bottom of the chamber, and the valve 12 is installed, the first drainage pipe 6 is connected with each second drainage pipe 9 through tee; the outer end of the first drainage pipe 6 extends to the sump 1 through the tee interface;

[0031] Step S2, after the drainage pipe system construction is completed, the surface is sprayed with waterproof material; then if the sealing layer 7 is made of steel, after the sealing layer 7 construction, the concrete layer 8 is poured and the concrete pouring is ensured to be dense; if the sealing layer 7 is made of flexible material, the concrete is poured first, and then the sealing layer 7 is constructed on the inner side of the concrete layer 8.

[0032] The embodiment also provides a kind of underground gas storage drainage method, using the underground gas storage drainage system as described above, during normal operation of gas storage chamber 3, internal gas pressure of gas storage chamber 3 is much higher than external water pressure, without external underground water, by control system 14 closes the valve 12 on the first drainage pipe 6;When gas storage chamber 3 needs to be overhauled empty, by control system 14 opens the valve 12 on the first drainage pipe 6, underground seepage water outside gas storage chamber 3 is discharged outward through third drainage pipe 10, second drainage pipe 9 and first drainage pipe 6.Simultaneously, using the osmometer 13 buried in the surrounding rock of traffic tunnel 5, underground water pressure of gas storage can be monitored, open valve 12 in advance before overhaul emptying, when detecting that water pressure outside gas storage chamber 3 reduces to below safety value, empty gas storage chamber 3 for overhaul.

[0033] The underground gas storage drainage system of the embodiment collects underground water above the gas storage through the third drainage pipe 10, collects to the first drainage pipe 6 at the bottom of the gas storage through the second drainage pipe 9, and discharges to the traffic tunnel 5 through the first drainage pipe 6, so as to ensure the structural stability of the gas storage chamber during overhaul, and solve the technical problem of large water pressure outside the gas storage.

[0034] The content illustrated in the above embodiment should be understood as that the embodiment is only used to more clearly illustrate the application, and is not used to limit the scope of the application, and after reading the application, the modification of various equivalent forms of the embodiment by the person skilled in the art falls within the scope defined by the appended claims of the application.

Claims

1. A drainage system for underground gas storage, comprising a plurality of gas storage caverns (3) arranged side by side, a traffic tunnel (5) being arranged between two adjacent gas storage caverns (3); characterized in that: The gas storage chamber (3) is provided with a first drain pipe (6), multiple second drain pipes (9) and multiple third drain pipes (10) outside. The first drain pipe (6) is arranged at the bottom of the gas storage chamber (3) along the length direction of the gas storage chamber (3); the second drain pipes (9) are arranged on the side wall of the gas storage chamber (3) along the cross-sectional direction of the gas storage chamber (3), and the multiple second drain pipes (9) are arranged at intervals along the length direction of the gas storage chamber (3). Each of the second drain pipes (9) is provided with multiple third drain pipes (10) at intervals along its length, and each third drain pipe (10) has at least one water inlet hole on its side wall. One end of the third drain pipe (10) is connected to the second drain pipe (9), and the other end of the third drain pipe (10) extends away from the gas storage chamber (3). The third drain pipe (10) is set at an upward inclination. One end of the first drain pipe (6) is connected to multiple second drain pipes (9), and the other end of the first drain pipe (6) extends into the traffic tunnel (5). A valve (12) is provided on the end of the first drain pipe (6) that extends into the traffic tunnel (5).

2. The underground gas storage reservoir drainage system of claim 1, wherein: The gas storage chamber (3) is a rectangular structure with rounded corners at the four corners, and the cross-sectional shape of the gas storage chamber (3) is circular; the second drain pipe (9) is arranged along the circumference of the gas storage chamber (3), and the third drain pipe (10) is arranged along the circumference diameter of the gas storage chamber (3).

3. The underground gas storage drainage system according to claim 2, characterized in that: The traffic tunnel (5) is equipped with a water collection pit (1). The first drainage pipe (6) extends into the traffic tunnel (5) and is connected to the water collection pit (1). The first drainage pipe (6) slopes towards the water collection pit (1).

4. The underground gas storage drainage system according to claim 2, characterized in that: The gas storage chamber (3) includes a first long side chamber (301) and a second long side chamber (302) arranged in parallel. The two ends of the first long side chamber (301) and the second long side chamber (302) are connected by an end chamber (303). The second long side chamber (302) is located on the side closer to the traffic tunnel (5). The bottom wall of the first long side chamber (301) is sloped from the middle to both ends, and both slope towards the middle of the second long side chamber (302) through the end chamber (303). The first drainage pipe (6) is laid along the bottom wall of the gas storage chamber (3).

5. The drainage system for an underground gas storage facility according to any one of claims 1 to 4, characterized in that: The first drain pipe (6) and the second drain pipe (9) are both made of steel drain pipes. The diameter of the first drain pipe (6) is 0.07m to 0.15m. The diameter of the second drain pipe (9) is 0.05m to 0.08m. The distance between two adjacent second drain pipes (9) is 2.0m to 5.0m. The third drain pipe (10) is made of hot-rolled seamless steel pipe. The diameter of the third drain pipe (10) is 0.05m to 0.07m. The length of the third drain pipe (10) is 2.5m to 4.5m. The distance between two adjacent third drain pipes (10) on the same second drain pipe (9) is 2.0m to 5.0m.

6. The drainage system for an underground gas storage facility according to any one of claims 1 to 4, characterized in that: The distance between the third drain pipe (10), located at the lowest point on the second drain pipe (9), and the bottom of the gas storage chamber (3) is not less than 1 / 2 of the diameter of the gas storage chamber (3), and the angle between the axial center line of the third drain pipe (10) and the horizontal plane is 15° to 90°.

7. The drainage system for an underground gas storage facility according to any one of claims 1 to 4, characterized in that: The third drainage pipes (10) on the two adjacent second drainage pipes (9) are staggered, and the third drainage pipes (10) are wrapped with geotextile.

8. The underground gas storage drainage system according to any one of claims 1 to 4, characterized in that: The sidewall of the gas storage cavern (3) is provided with a sealing layer (7), a concrete layer (8) and a water-proof layer (11) from the inside to the outside. The thickness of the sealing layer (7) is 0.01m to 0.03m, and the thickness of the concrete layer (8) is 0.5m to 1.0m. The water-proof layer (11) is set adjacent to the surrounding rock (2). The first drainage pipe (6) and the second drainage pipe (9) are both set between the water-proof layer (11) and the surrounding rock (2). The third drainage pipe (10) extends into the surrounding rock (2).

9. The underground gas storage drainage system according to any one of claims 1 to 4, characterized in that: The traffic tunnel (5) is equipped with a piezometer (13), and the piezometer (13) and the valve (12) are electrically connected to the control system (14).

10. A drainage method for an underground gas storage facility, characterized in that: Using the underground gas storage drainage system according to any one of claims 1 to 9, during normal operation of the gas storage cavern (3), the valve (12) is closed; when the gas storage cavern (3) needs to be repaired, the valve (12) is opened, and the underground seepage water outside the gas storage cavern (3) is discharged to the outside through the third drainage pipe (10), the second drainage pipe (9) and the first drainage pipe (6). After the water pressure outside the gas storage cavern (3) drops below the safe value, the gas storage cavern (3) is emptied for repair.

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