Existing salt cavern bottom transformation and solution diffusion method and salt cavern gas storage structure

Abstract

The invention relates to an existing salt cavern bottom transformation diffusion and dissolution method and a salt cavern gas storage structure. The method is suitable for the technical field of rock salt mining and salt cavity comprehensive utilization. The technical problem to be solved by the invention is to provide the existing salt cavern bottom transformation and diffusion method and the salt cavern gas storage structure. According to the technical scheme, the existing salt cavity bottom transformation and diffusion method comprises the following steps that S1, existing salt cavity data are collected, existing salt cavity screening work is carried out, and a salt cavity is selected; s2, newly drilling an inclined shaft near the selected salt cavern, wherein the end point of the inclined shaft is located at a designated position near the bottom of the selected salt cavern; s3, performing multi-step cavity construction at the appointed position by using an inclined shaft to form a new cavity; s4, communicating the new cavity with the bottom of the selected salt cavity to form a new salt cavern gas storage; s5, gas injection and brine discharge are conducted on the salt cavern gas storage firstly, and then corrosion is conducted on the bottom area of a cavity of the salt cavern gas storage; and S6, the step S5 is repeated until the brine in the salt cavern gas storage is completely discharged, and energy storage operation is carried out.

Description

Technical Field

[0001] The invention relates to the technical field of rock salt mining and comprehensive utilization of salt caverns, in particular to a method for transforming and dissolving an existing salt cavern bottom and a salt cavern gas storage structure. Background Art

[0002] Salt caverns are huge mine caves left behind after water-soluble mining. They are well sealed and are high-quality space resources for storing oil, natural gas, hydrogen, compressed air, etc.

[0003] There are currently two routes to the origin of salt cavities. One is to build a new dissolution cavity, that is, to use multi-layer casing to carry out positive and reverse circulation dissolution with the goal of high-quality salt cavities, and to use diesel, nitrogen, natural gas, etc. as dissolution inhibitors to control the upper dissolution. The cavity obtained under this approach has a regular shape, the roof is well protected, and it is safe and stable. However, it usually takes 3-4 years to build a cavity, and brine consumption can easily become a limiting factor. The other is an existing salt cavity, that is, a cavity that has been formed after salt companies have mined salt. Although the cavity shape is poor, it saves cavity building time and is more economical. Therefore, the compressed air energy storage projects currently being carried out basically use existing salt cavities.

[0004] Since there is no dissolution inhibitor in the salt mining process, especially in the early stage of mining, rapid water injection can easily lead to excessive dissolution. In addition, the salt layer of domestic salt mines is thin and there are many interlayers. Even if the injection and mining are controlled in time in the later stage, the soluble thickness of the top is very small. This leads to the following problems: the bottom of the salt cavity is not fully dissolved, and the sediment occupies the bottom of the salt cavity, resulting in very limited net space available in the salt cavity, while the top of the salt cavity is fully dissolved. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in view of the above-mentioned existing problems, a method for transforming and expanding the bottom of an existing salt cavity and a salt cavern gas storage structure are provided.

[0006] The technical solution adopted by the present invention is: a method for transforming and dissolving the bottom of an existing salt cavity, comprising the following steps:

[0007] S1. Collect existing salt cavity data, carry out existing salt cavity screening, and select salt cavities;

[0008] S2. Drill a new inclined well near the selected salt cavity, with the end point of the inclined well located at a designated position near the bottom of the selected salt cavity;

[0009] S3, using an inclined well to perform a multi-step cavity creation process at a designated location to form a new cavity;

[0010] S4, connecting the new cavity with the bottom of the selected salt cavity to form a new salt cavern gas storage;

[0011] S5. Firstly, inject gas into the salt cavern gas storage to remove brine, and then dissolve the bottom area of ​​the cavity;

[0012] S6. Repeat step S5 until the brine in the salt cavern gas storage is completely drained and energy storage operation is performed.

[0013] Through the above-mentioned technical means, directional drilling technology is used to drill an inclined well directly to the bottom of the salt cavity. Dissolution is first carried out at the bottom of the inclined well to form a cavity. The inclined well simultaneously becomes a brine discharge channel during the dissolution process, and the formed new cavity is connected with the existing salt cavity, so that the bottom sediment in the existing salt cavity falls into the dissolution space, thereby ensuring the thickness of the reserved salt layer on the top of the existing salt cavity, increasing the upper net space of the existing salt cavity, and realizing the reuse of the existing salt cavity.

[0014] In some embodiments, in step S1, the geological resources, drilling data and salt mining data of the existing salt cavity are analyzed, and a selected salt cavity that meets the requirements is obtained through testing, and the basic morphological information and spatial location information of the selected salt cavity are obtained through surveying means.

[0015] In some embodiments, the selected salt cavity that meets the requirements is obtained through testing, the testing method is a water sealing test, and the surveying means includes sonar cavity surveying or three-dimensional seismic surveying means.

[0016] In some embodiments, in step 2, the inclined well includes a vertical section and a curved section, the bottom of the vertical section is connected to the curved section, the top end of the vertical section is not less than 150m away from the ground of the vertical well of the existing salt cavity, the minimum distance between the end point of the curved section and the cavity wall of the existing salt cavity is 5-10m, the distance between the end point of the curved section and the bottom plate of the salt layer is not less than 5m, the turning radius of the curved section is 2 / 3-4 / 5 of the ground distance from the top end of the vertical section to the vertical well of the existing salt cavity, and the turning angle of the curved section is 60°.

[0017] In some embodiments, in step 3, the inclined well adopts a two-layer tubing mode to create a cavity, a casing is provided on the inner wall of the inclined well, a center pipe is passed through the middle of the casing, and an annulus is provided between the casing and the center pipe.

[0018] In some embodiments, the multi-step cavity creation method comprises the following steps:

[0019] S31, inject clean water into the central tube, and use the annulus between the central tube and the casing to discharge the brine;

[0020] S32. During the dissolution process, gradually pull the central tube back and up to 10m from the tube mouth and keep it still;

[0021] S33. Inject clean water into the annulus between the central pipe and the casing, and use the central pipe to discharge the brine.

[0022] In some embodiments, in step S5, compressed air is injected into the vertical well of the existing salt cavity, and the brine in the net space of the existing salt cavity is discharged through the inclined well. After the brine is discharged, the injection of compressed air is stopped, the valve of the vertical well is closed, and clean water is injected into the central pipe inside the inclined well, and the brine is discharged through the annulus between the casing and the central pipe.

[0023] In some embodiments, in step S6, the gas injection, brine removal and bottom dissolution process in step S5 is repeated 3 to 5 times, and the last time high-pressure air is continuously injected into the vertical well in the existing salt cavity, and the valve of the annulus between the casing and the central pipe is closed so that only the central pipe can discharge brine. The central pipe is placed at the lowest point until the brine in the central pipe disappears, and the gas injection is stopped, the relevant valves are closed, and compressed air energy storage operation is performed.

[0024] In some embodiments, in step S4, the connection method is to use drilling tools or high-pressure water directional erosion of the cavity wall.

[0025] Another technical solution adopted by the present invention is: a salt cavern gas storage structure is prepared by adopting an existing salt cavern bottom transformation and dissolution method.

[0026] The beneficial effects of the present invention are:

[0027] 1. This application dissolves the salt layer near the bottom of the existing salt cavity by drilling a new inclined well to form a new salt cavity, and then connects the new salt cavity with the existing salt cavity, so that the bottom sediment falls into the dissolution space. On the one hand, the inclined well is used to re-dissolve the bottom of the existing salt cavity, and on the other hand, the inclined well can be used to discharge the brine at the bottom of the existing salt cavity, which not only increases the net space above the sediment, but also increases the pore space of the sediment. This method can fully utilize the existing salt cavity, protect the top of the salt cavity, expand the storage space of the salt cavity, and discharge the brine at the bottom. At the same time, compared with the construction period required for a new salt cavity, this method greatly shortens the construction period required, and can meet the requirements of the short-term construction period of some energy storage power stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flowchart of this application.

[0029] Figure 2 It is a schematic diagram of the transformation and dissolution expansion steps of this application.

[0030] Description of reference numerals:

[0031] 1. Salt layer; 2. Existing salt cavity; 3. Vertical well; 4. Inclined well; 5. New cavity; 21. Net space in the salt cavity; 22. Sediment; 41. Center pipe; 42. Casing.

[0032] This specification includes references to "one embodiment" or "an embodiment." The appearance of the phrase "in one embodiment" or "in an embodiment" does not necessarily refer to the same embodiment. The particular features, structures or characteristics may be combined in any suitable manner consistent with the present disclosure.

[0033] The term "comprising" is open ended. As used in the appended claims, the term does not exclude additional structures or steps.

[0034] "First," "second," etc. As used herein, these terms act as labels for the nouns that precede them and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments.

[0036] Embodiment 1:

[0037] Combination Figure 1 to Figure 2 As shown, this embodiment is a method for transforming and expanding the bottom of an existing salt cavity, comprising the following steps:

[0038] S1. Collect the data of existing salt cavern 2, carry out the screening of existing salt cavern 2, and select the salt cavern;

[0039] S2, drilling a new inclined well 4 near the selected salt cavity, with the end point of the inclined well 4 being located at a designated position near the bottom of the selected salt cavity;

[0040] S3, using the inclined well 4 to perform a multi-step cavity creation process at a designated location to form a new cavity 5;

[0041] S4, connecting the new cavity 5 to the bottom of the selected salt cavity to form a new salt cavern gas storage;

[0042] S5. Firstly, inject gas into the salt cavern gas storage to remove brine, and then dissolve the bottom area of ​​the cavity;

[0043] S6. Repeat step S5 until the brine in the salt cavern gas storage is completely drained and energy storage operation is performed.

[0044] In some embodiments, in step S1, the geological resources, drilling data, and salt mining data of the existing salt cavity 2 are analyzed, and a selected salt cavity that meets the requirements is obtained through testing. The testing method in this embodiment is a water sealing test to determine whether the salt cavity is available. On the basis that the salt cavity is available, the basic morphological information and spatial position information of the selected salt cavity are obtained through surveying means. In this embodiment, the surveying means includes sonar cavity measurement or three-dimensional seismic surveying means.

[0045] In some embodiments, in step 2, the inclined well 4 includes a vertical section and a bending section, and the bottom of the vertical section is connected to the bending section. Specifically, in this embodiment, the top end of the vertical section is not less than 150m away from the ground of the vertical well 3 of the existing salt cavity 2, and the borehole continues to extend along the bending section. The minimum distance between the end point of the bending section and the cavity wall of the existing salt cavity 2 is 5 to 10m, and the distance between the end point of the bending section and the bottom plate of the salt layer 1 is not less than 5m. The turning radius of the bending section is the distance to the ground, and the turning angle of the bending section is 60°.

[0046] In some embodiments, in step 3, the inclined well 4 adopts a two-layer tubing mode to create a cavity, a casing 42 is provided on the inner wall of the inclined well 4, a central pipe 41 is passed through the middle of the casing 42, and an annulus is provided between the casing 42 and the central pipe 41, one is injected with clean water, and the other is discharged with brine, and the length is flexibly adjusted through the ground.

[0047] Furthermore, the multi-step cavity creation method includes the following steps:

[0048] S31, inject clean water into the central tube 41, and use the annulus between the central tube 41 and the casing 42 to discharge the brine;

[0049] S32, during the dissolution process, the central tube 41 is gradually withdrawn and lifted up to about 10m from the tube mouth, and kept motionless;

[0050] S33, injecting clean water into the annulus between the central pipe 41 and the casing 42, and using the central pipe 41 to discharge the brine.

[0051] In the early stage of cavity creation, the goal is to form a basic cavity structure as quickly as possible. The positive circulation cavity creation technology can directly dissolve the salt rock near the bottom of the inclined well 4, quickly establish the initial cavity, and effectively protect the top salt layer 1. As the cavity gradually expands, it is necessary to dissolve the surrounding salt rock more evenly to optimize the final shape of the cavity. At this time, switching to the reverse circulation cavity creation technology can allow clean water to contact a larger dissolution surface, ensuring that all parts of the cavity are fully dissolved to form a regular and stable structure.

[0052] In some embodiments, after forming the ideal new cavity 5 space, it is necessary to connect the new cavity 5 with the existing salt cavity 2. In step S4, the connection method is drilling with a drilling tool or directional erosion of the cavity wall with high-pressure water.

[0053] In some embodiments, in step S5, after the new cavity 5 is connected with the existing cavity, compressed air is injected into the vertical well 3 of the existing salt cavity 2, and the brine in the net space 21 in the existing salt cavity is discharged by the inclined well 4. This process can also push the sediment 22 into the space of the new cavity 5 under the action of water flow and gravity. After the brine is discharged, the injection of compressed air is stopped, the valve of the vertical well 3 is closed, and then clean water is injected into the central pipe 41 inside the inclined well 4, and the brine is discharged by the annulus between the casing 42 and the central pipe 41, so as to further dissolve the bottom of the existing salt cavity 2.

[0054] In some embodiments, in step S6, the gas injection, brine removal and bottom dissolution process in step S5 are repeated 3 to 5 times, and the last time, high-pressure air is continuously injected into the vertical well 3 of the existing salt cavity 2, and the valve of the annulus between the casing 42 and the central pipe 41 is closed, so that only the central pipe 41 can discharge brine. The central pipe 41 is placed at the lowest point to ensure that as much brine as possible is discharged until the brine in the central pipe 41 disappears, and the gas injection is stopped, and the relevant valves are closed to perform compressed air energy storage operation.

[0055] Furthermore, if you want to dissolve the bottom, you can inject clean water from one end of the inclined well 4 during the energy release stage, and use the vertical well 3 of the existing salt cavity 2 to release gas. When storing energy, compressed air is injected from one end of the vertical well 3, and brine is discharged from one end of the inclined well 4.

[0056] The implementation principle of a method for reforming and dissolving the bottom of an existing salt cavern according to an embodiment of the present invention is as follows:

[0057] Near the existing salt cavity 2, a directional drilling technology is used to drill an exploration well directly to the bottom of the existing salt cavity 2. The inclined well 4 can provide a channel for subsequent bottom dissolution, and also serve as a channel for brine removal and monitoring. Clean water or other appropriate solvents are injected through the inclined well 4 to dissolve the undissolved area at the bottom of the salt cavity again. During the bottom dissolution process, the original sediment 22 will gradually sink into the newly formed dissolution space, freeing up more effective storage space. After the bottom re-dissolution, not only the space capacity of the bottom is increased, but also the top salt layer 1 is better protected, indirectly increasing the net space on the top. For old cavities that were originally in poor shape, the maximum utilization of resources can be achieved.

[0058] Through the inclined shaft 4 and multi-step cavity making technology, precise dissolution of the bottom area is achieved, solving the problem of insufficient bottom dissolution that is difficult to handle with traditional methods. The cavity structure is optimized and the effective storage space is increased, especially for old cavities whose efficiency is affected by the accumulation of sediment 22. This method is highly flexible and can flexibly adjust the dissolution strategy according to actual needs to ensure that the final cavity meets the design requirements. The dissolution rate and range are strictly controlled throughout the process to protect the roof and other key parts and improve the safety of the overall structure. Compared with the construction of a new dissolution cavity, this method has lower costs and shorter time, and can adapt to market demand more quickly.

[0059] If the inclined well 4 is first connected to the existing salt cavity 2 and then a new cavity is created at the connection point, the brine in the main cavity will inevitably be diluted when fresh water is injected into the inclined well, which will cause synchronous dissolution. Therefore, the present application adopts the method of first creating a new cavity and then connecting the new cavity with the existing salt cavity 2. This method can be independent when the new cavity dissolves, the water consumption can be controlled, and it is easier to directionally dissolve the new cavity.

[0060] Embodiment 2:

[0061] This embodiment is a salt cavern gas storage structure, which is manufactured by the existing salt cavern bottom transformation and dissolution expansion method described in the first embodiment.

[0062] Embodiment three:

[0063] This embodiment is an example of applying the method for transformation and dissolution expansion of the bottom of an existing salt cavern in Embodiment 1 to an existing salt cavern expansion and transformation project.

[0064] According to the geological resources, drilling data and salt mining data of the salt cavern, the salt layer 1 where the salt cavern is located is 200m thick and buried at a depth of -650m to -850m. The grade of salt layer 1 is 70-82%, and there are insoluble interlayers ranging from 3m to 10m in the middle, with a total thickness of 60m. There are fewer interlayers in the lower and upper sections of the salt layer 1, and the thickness of the salt rock is relatively large. When the salt company mined salt in the early stage, due to the problem of controlling the amount of water injected and mined, the upper dissolution was faster and soon reached the middle section. After the discovery, the amount and time of water injected and mined were adjusted, and the upper dissolution of salt layer 1 was reasonable and the dissolution was relatively sufficient.

[0065] A water sealing test was carried out on the salt chamber, which showed that the sealing performance was good and it was feasible to store compressed air.

[0066] The sonar survey of the salt cavern showed that the top of the existing salt cavern 2 is at -623m, the sediment 22 interface is at about -700m, and the net space of the cavern is about 121,000 cubic meters. In order to better match the ground installed capacity, the existing salt cavern 2 needs to be expanded and renovated. Since the reserved salt layer 1 above is relatively thin and the surroundings are fully dissolved, this method is suitable for renovation and expansion.

[0067] Before the transformation, the bottom position and range of the existing salt cavity 2 were known based on the previous data and three-dimensional seismic data. The bottom of the existing salt cavity 2 is at -845m, and the bottom dissolution radius is about 6m. Based on this, the inclined well 4 is drilled at an interval of about 4 times the maximum dissolution radius of the vertical well 3 (about 180m here). The inclination is started when drilling to -750m, with a turning radius of 60°, and the end of the inclination is the position of the outer casing 42. Continue drilling to a position 10m away from the bottom of the existing salt cavity 2, stop drilling, and complete cementing. Lower the central pipe 41 in the casing 42 of the inclined well 4 so that the central pipe 41 is located at the front side of the borehole.

[0068] The inclined well 4 is used to create a cavity, clean water is injected into the central pipe 41, and brine is discharged from the annulus of the casing 42. The central pipe 41 is lifted every two months, and the lifting is about 10 to 20 meters. After lifting 3 to 5 times, the central pipe 41 is retreated to about 10 meters from the pipe mouth and remains motionless. At this time, clean water is injected into the annulus of the casing 42, and brine is discharged from the central pipe 41. This cavity dissolution process lasts for about 9 to 12 months.

[0069] During the dissolution process of the new cavity 5, the side close to the existing salt cavity 2 will also be dissolved, but the reserved distance is not enough to dissolve through. Therefore, the new cavity 5 and the existing cavity are connected by drilling tools or directional high-pressure water.

[0070] After the two chambers are connected, compressed air is injected into the vertical well 3 of the existing salt chamber 2, and part of the brine is discharged through the inclined well 4. After the brine in the net space is discharged, the vertical well 3 is closed. The position of the central pipe 41 is moved forward to the end of the existing salt chamber 2, and clean water is injected into the central pipe 41 of the inclined well 4, and the brine is discharged from the annulus of the casing 42, so that the bottom area of ​​the cavity is dissolved. The position of the central pipe 41 can be appropriately adjusted during the dissolution process to more accurately determine the bottom position of the dissolution.

[0071] At regular intervals, the steps of gas injection, brine removal and bottom dissolution are repeated 3-5 times until the last gas injection, when no brine can be discharged from the central pipe 41 of the inclined well 4, the valve of the inclined well 4 is closed and compressed air energy storage operation is performed.

[0072] If you want to dissolve the bottom again, you can inject clean water from the end of the inclined well 4 during the energy release stage, and release gas from the vertical well 3. When storing energy, compressed air is injected from the end of the vertical well 3, and brine is discharged from the end of the inclined well 4.

[0073] When the cavity volume reaches the storage requirement, only brine needs to be injected into the inclined well 4 when releasing energy, and the gas is released from the vertical well 3. When storing energy, compressed air is injected from the end of the vertical well 3, and brine is discharged from the end of the inclined well 4.

[0074] The above-mentioned operation mode is isobaric operation. During operation, the inclined well 4 can be closed on a daily basis, and only the vertical well 3 can be used for gas injection and production to implement variable pressure operation.

[0075] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reforming and dissolving the bottom of an existing salt cavern, characterized in that: The steps include: S1. Collect data on existing salt cavities (2), conduct screening of existing salt cavities (2), and select salt cavities; S2, drilling a new inclined well (4) near the selected salt cavity, wherein the end point of the inclined well (4) is located at a designated position near the bottom of the selected salt cavity; S3, using the inclined well (4) to perform a multi-step cavity creation process at a designated location to form a new cavity (5); S4, connecting the new cavity (5) to the bottom of the selected salt cavity to form a new salt cavern gas storage; S5. Firstly, inject gas into the salt cavern gas storage to remove brine, and then dissolve the bottom area of ​​the cavity; S6. Repeat step S5 until the brine in the salt cavern gas storage is completely drained and energy storage operation is performed.

2. The method for transforming and dissolving an existing salt cave bottom according to claim 1, characterized in that: In step S1, the geological resources, drilling data and salt mining data of the existing salt cavity (2) are analyzed, and a selected salt cavity that meets the requirements is obtained through testing, and basic morphological information and spatial position information of the selected salt cavity are obtained through surveying means.

3. The method for transforming and dissolving an existing salt cave bottom according to claim 2, characterized in that: The selected salt cavity that meets the requirements is obtained through testing, the testing method is a water sealing test, and the surveying means includes sonar cavity surveying or three-dimensional seismic surveying means.

4. The method for transforming and dissolving an existing salt cave bottom according to claim 1, characterized in that: In step 2, the inclined well (4) comprises a vertical section and a curved section, the bottom of the vertical section is connected to the curved section, the top end of the vertical section is at least 150 m away from the ground of the vertical well (3) of the existing salt cavity (2), the minimum distance between the end point of the curved section and the cavity wall of the existing salt cavity (2) is 5 to 10 m, the distance between the end point of the curved section and the bottom plate of the salt layer (1) is not less than 5 m, the turning radius of the curved section is 2 / 3 to 4 / 5 of the ground distance from the top end of the vertical section to the vertical well (3) of the existing salt cavity (2), and the turning angle of the curved section is 60°.

5. The method for transforming and expanding the bottom of an existing salt cavern according to claim 1, characterized in that: In step 3, the inclined well (4) is cavity-made by adopting a two-layer pipe string mode, a casing (42) is provided on the inner wall of the inclined well (4), a central pipe (41) is passed through the middle of the casing (42), and an annulus is provided between the casing (42) and the central pipe (41).

6. The method for transforming and dissolving the bottom of an existing salt cavern according to claim 5, characterized in that: The multi-step cavity creation method comprises the following steps: S31, injecting clean water into the central tube (41), and using the annulus between the central tube (41) and the casing (42) to discharge the brine; S32, during the dissolution process, gradually pull the central tube (41) back and up, pull it back to 10m from the tube mouth, and keep it still; S33, injecting clean water into the annulus between the central pipe (41) and the casing (42), and using the central pipe (41) to discharge the brine.

7. The method for transforming and dissolving an existing salt cave bottom according to claim 5, characterized in that: In the step S5, compressed air is injected into the vertical well (3) of the existing salt cavity (2), and the brine in the net space of the existing salt cavity (2) is discharged by using the inclined well (4). After the brine is discharged, the injection of compressed air is stopped, the valve of the vertical well (3) is closed, and clean water is injected into the central pipe (41) inside the inclined well (4), and the brine is discharged by using the annulus between the casing (42) and the central pipe (41).

8. The method for transforming and dissolving an existing salt cave bottom according to claim 5, characterized in that: In step S6, the gas injection, brine removal and bottom dissolution process in step S5 is repeated 3 to 5 times, and high-pressure air is continuously injected into the vertical well (3) of the existing salt cavity (2) for the last time, and the valve of the annulus between the casing (42) and the central pipe (41) is closed so that only the central pipe (41) can discharge brine. The central pipe (41) is placed at the lowest point until the brine in the central pipe (41) disappears, and the gas injection is stopped, and the relevant valves are closed to perform compressed air energy storage operation.

9. The method for transforming and dissolving an existing salt cave bottom according to claim 1, characterized in that: In step S4, the connection method is to use drilling tools or high-pressure water directional erosion of the cavity wall.

10. A salt cavern gas storage structure, characterized in that: The salt cavity (2) is prepared by the bottom transformation and dissolution expansion method of an existing salt cavity (2) as described in any one of claims 1 to 9.

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