Directional repair string for salt cavern gas storage and directional repair method thereof

Abstract

The application discloses a directional repair string for a partial dissolution cavity of a salt cavern gas storage and a directional repair method thereof. The lower end of a production casing is located above the partial dissolution cavity of the salt cavern gas storage. The production casing is inserted with an intermediate pipe. The lower end of the intermediate pipe extends into the partial dissolution cavity of the salt cavern gas storage and the lower end port is located below the to-be-repaired undissolved stratum. The intermediate pipe is inserted with a center pipe. The lower end of the center pipe extends to the bottom of the partial dissolution cavity of the salt cavern gas storage. The lower part of the intermediate pipe is provided with a jet hole facing the to-be-repaired undissolved stratum on one side of the circumference. A packer is screwed in the center pipe. The rubber tube of the packer is set in the lower pipe port of the intermediate pipe and the jet hole. The packer is set first. Then, the anti-dissolution agent is injected into the annulus between the intermediate pipe and the center pipe to protect the upper salt layer. Then, fresh water or brine water is injected into the annulus between the intermediate pipe and the center pipe to quickly dissolve the to-be-repaired dissolved stratum, so that the deformed cavity is directionally repaired. The application can improve the repair efficiency of the partial dissolution cavity, ensure the stability of the cavity and the cavity forming rate.

Description

TECHNICAL FIELD

[0001] The present application relates to a directional repair pipe column, in particular to a directional repair pipe column for a salt cavern gas storage partial dissolution cavity, and relates to a directional repair method for a salt cavern gas storage partial dissolution cavity, and belongs to the technical field of repair of a salt cavern gas storage deformed cavity, and is suitable for repair and expansion of a cavity during a cavity forming period or a brine discharge period of a gas storage. BACKGROUND

[0002] A salt cavern gas storage is an underground gas storage facility that uses a man-made space formed by dissolution in underground salt rock to store natural gas or other gases, and can perform injection and production operations as needed, and has functions such as seasonal peak shaving, emergency supply, and strategic reserve.

[0003] During the cavity forming process of a salt cavern gas storage, due to the non-uniform distribution of insoluble substances in the underground salt layer in all directions on the plane and the uneven thickness in the vertical direction, the salt layer is not uniformly dissolved in all directions during the dissolution process. In the direction with high salt content and few insoluble substances, the dissolution rate is fast, and in the direction with relatively low salt content and many insoluble substances, the dissolution rate is slow, resulting in a "partial dissolution" phenomenon, which causes the cavity formed by dissolution to have a deformed cavity with one half having a large diameter and the other half having a small diameter. Such a shaped cavity has two problems: first, it has poor stability and may collapse during the later operation of the gas storage, and second, due to partial dissolution, the salt layer in the direction that has not been dissolved does not form an effective cavity, resulting in a small cavity volume and a low cavity formation rate, which wastes the underground salt layer gas storage space resources.

[0004] At present, in terms of repair of deformed cavities caused by partial dissolution, during the gas injection and brine discharge stage, natural gas injected as a dissolution inhibitor is used, and then reverse circulation is used to inject fresh water or brine into the cavity through the gas injection pipe column to repair the cavity. When the fresh water or brine injected in this way enters the cavity from the gas injection pipe, it is uniformly dissolved in all directions, which can repair the cavity to some extent, but it can easily cause excessive dissolution in the fully dissolved area, and cannot achieve the effect of strengthening dissolution in the undissolved direction, resulting in poor repair effect.

[0005] Chinese invention patent CN 108150220B discloses a salt cavern gas storage repair method, which requires a curved coiled tubing to be lowered into the cavity through a casing with a small diameter, which is difficult to achieve. On the other hand, the method proposes that the coiled tubing is extended radially along the cavity to face the undissolved formation to be repaired. In practice, it is basically impossible to stably face the repair point due to the swinging of the coiled tubing after injection of fresh water, so the repair effect is not achieved.

[0006] The Chinese invention patent with the publication number CN 218598242U discloses a cavity repair simulation device for salt cavern gas storage. Salt bricks are used to simulate underground salt layers, and an outer pipe and an inner pipe are lowered into the salt brick cavity. Fresh water enters the cavity through the annulus to dissolve the target layer below the gas-liquid interface layer by layer, thereby achieving cavity repair simulation. This method lacks targeting and cannot achieve directional repair of the layer to be repaired. The repair distance is short, the effect is poor, and the fully dissolved area is also over-dissolved, causing the cavity to be more irregular and less stable.

[0007] The Chinese invention patent with the publication number CN 219084341U discloses an experimental device for simulating repair of a deformed salt cavity. A container is used to simulate the underground cavity, and a gas pipe column and a water pipe column are installed in the container. A shooting device is installed on the external guide rail of the container. This device is mainly used for observing the brine flow field changes in the container and studying the development and change law of the brine flow field in the deformed salt cavity during the repair process. The repair method is omnidirectional dissolution, and directional repair is not achieved.

[0008] In summary, there is an urgent need for a partial dissolution cavity directional repair technology that can forcibly dissolve the undissolved direction and minimize dissolution in the fully dissolved area, thereby effectively repairing the partial dissolution deformed cavity. SUMMARY

[0009] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions cannot be used to limit the scope of the present application.

[0010] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0011] The primary purpose of the present application is to overcome the low repair efficiency and poor effect of the deformed cavity of the salt cavern gas storage in the prior art, and to provide a directional repair pipe column for the deformed cavity of the salt cavern gas storage. The directional repair pipe column can forcibly dissolve the salt layer in the undissolved direction, improve the repair efficiency of the deformed cavity, improve the repair effect, and ensure the stability of the cavity and the cavity formation rate.

[0012] To solve the above technical problems, the directional repair string of the partial dissolution cavity of the salt cavern gas storage of the application comprises a production casing, the lower end of the production casing is located above the partial dissolution cavity of the salt cavern gas storage, the production casing is inserted with an intermediate pipe, the lower end of the intermediate pipe extends into the partial dissolution cavity of the salt cavern gas storage and the lower end port is located below the to-be-repaired unsolved stratum, the intermediate pipe is inserted with a central pipe, the lower end of the central pipe extends to the bottom of the partial dissolution cavity of the salt cavern gas storage; the lower part of the circumference of the intermediate pipe is provided with a nozzle facing the to-be-repaired unsolved stratum, the central pipe is screwed with a packer, and the rubber sleeve of the packer is set between the lower pipe port and the nozzle of the intermediate pipe.

[0013] Further, the intermediate pipe is screwed with a centralizer, and the slip of the centralizer is supported on the inner wall of the lower part of the production casing.

[0014] Further, the upper part of the partial dissolution cavity of the salt cavern gas storage is injected with a dissolution inhibitor, and the interface between the dissolution inhibitor and the brine is located above the to-be-repaired unsolved stratum.

[0015] Further, the dissolution inhibitor is nitrogen during the cavity forming process.

[0016] Further, the dissolution inhibitor is natural gas during the gas injection and brine discharge process.

[0017] Further, the intermediate pipe is a brine discharge pipe, and the central pipe is a gas injection pipe during the gas injection and brine discharge process; the distance between the lower edge of the nozzle of the intermediate pipe and the lower pipe port of the intermediate pipe is 3 meters, the distance between the centralizer and the shoe of the production casing is 3-5 meters, and the setting position of the packer is 1-2 meters away from the lower pipe port of the intermediate pipe.

[0018] Another object of the application is to overcome the low repair efficiency and poor effect of the partial dissolution cavity of the salt cavern gas storage in the prior art, and to provide a directional repair method for the partial dissolution cavity of the salt cavern gas storage, which can forcibly dissolve the salt layer in the unsolved direction, improve the repair efficiency of the partial dissolution cavity, improve the repair effect, and ensure the stability of the cavity and the cavity forming rate.

[0019] To solve the above technical problems, the directional repair method for the partial dissolution cavity of the salt cavern gas storage of the application comprises the following steps in sequence:

[0020] Step 1, determining the to-be-repaired area of the partial dissolution cavity of the salt cavern gas storage, determining the orientation and depth of the to-be-repaired unsolved stratum through the cavity measurement result of the cavity measurement instrument;

[0021] Step 2, directionally punching a nozzle within a certain angle range on the pipe wall near the pipe port of the intermediate pipe;

[0022] Step 3, the intermediate pipe with a centralizer is lowered into the directional hole, and the centralizer is lowered to a depth of 3-5 meters from the shoe of the production casing; the depth of the directional hole is equivalent to the depth of the undissolved formation to be repaired;

[0023] Step 4, after the gyroscope is lowered into the intermediate pipe to measure the direction, the pipe string is rotated to ensure that the directional hole on the intermediate pipe is directed to the undissolved formation to be repaired;

[0024] Step 5, the central pipe is lowered into the intermediate pipe, and the central pipe is rotatably connected with the packer; the pipe string is lowered to a predetermined depth, and the packer is positioned at a distance of 1-2 meters from the pipe mouth of the intermediate pipe; the wellhead is pressed to seat the packer, and the passage downward from the pipe mouth of the intermediate pipe is blocked;

[0025] Step 6, during the cavity forming process, the blocking agent is injected into the annulus between the intermediate pipe and the central pipe to ensure that the interface between the blocking agent and the brine is located at the designed depth to protect the upper salt layer;

[0026] Step 7, fresh water or brine is injected into the annulus between the intermediate pipe and the central pipe, and the fresh water or brine is sprayed from the spray hole to quickly dissolve the dissolved formation to be repaired, reduce the dissolution of the fully dissolved area, and thus realize the directional repair of the abnormal cavity.

[0027] Further, in step 2, the size and number of the spray holes are determined by the injection displacement, the injection pressure and the distance of the undissolved formation to be repaired from the wellbore.

[0028] Further, in step 2, the central angle between the spray hole and the center of the intermediate pipe is 15°-30°.

[0029] Further, in step 7, the effective repair distance of the water flow sprayed from the directional hole is optimized and determined by the injection displacement, the injection pressure of the fresh water or brine, and the flow area of the directional hole, to ensure that the dissolved formation to be repaired can be quickly and efficiently dissolved.

[0030] Further, in the blocking cavity forming stage, the blocking agent is nitrogen.

[0031] Further, in the gas injection and brine discharge process, the intermediate pipe is a brine discharge pipe, the central pipe is a gas injection pipe, and the blocking agent is natural gas.

[0032] Compared with the prior art, the present application has the following beneficial effects: 1, the present application performs directional drilling on the wall of the intermediate pipe (or the gas injection pipe), and the injected water flow is sprayed through the directional hole on the wall, and the directional hole is directed to the undissolved formation to be repaired, so as to achieve the target of targeted repair.

[0033] 2. The injected water flow direction is definite, the flow rate is controllable, the repair speed is fast, the efficiency is high, and the effect is good. It also greatly reduces the impact on the fully dissolved area and reduces over-dissolution in the fully dissolved area. It enables the rapid dissolution of the formation in the undissolved area. The repair direction is controllable, the repair distance is adjustable, and it can achieve the goal of expanding the radius of the irregular side. At the same time, based on directional repair, factors such as the stability of the tubing string are considered, which has strong field operability.

[0034] 3. This invention can quickly and effectively repair misaligned cavities in salt cavern gas storage facilities. For cavities with uneven dissolution caused by formation heterogeneity, it minimizes dissolution in already sufficiently dissolved areas and forces dissolution in undissolved areas, thus making the cavity more regular and effectively repairing the misaligned cavities. This results in better stability and higher salt layer utilization. Compared to currently used repair methods, this invention offers a relatively shorter repair time and higher efficiency, ensuring the gas storage facility can be put into operation as soon as possible.

[0035] 4. This invention is applicable to the repair of deformed cavities in salt cavern gas storage facilities during the cavity construction process (or gas injection and brine discharge process). After application, it can effectively repair deformed cavities caused by factors such as partial dissolution, thereby improving cavity stability and salt layer utilization, expanding cavity storage capacity, and greatly increasing the subsequent gas injection and production volume and the service life of the cavity. The adoption of this invention in the repair of deformed cavities in various salt cavern gas storage facilities in China has generated very significant economic and social benefits. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit the present invention. Wherein:

[0037] Figure 1 This is a plan view of the deformed cavity caused by partial dissolution;

[0038] Figure 2 This is a structural diagram of the directional repair tubing for the partial dissolution cavity of the salt cavern gas storage tank of the present invention;

[0039] Figure 3 Cross-sectional view of directional repair of the partial cavity;

[0040] In the diagram: 1. Production casing; 2. Centralizer; 3. Solvent barrier; 4. Solvent barrier and brine interface; 5. Intermediate pipe; 6. Packer; 7. Central pipe; A. Undissolved formation to be repaired. Detailed Implementation

[0041] In the following description of the present application, the terms "upper", "lower", "front", "back", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, only for the purpose of facilitating the description of the present application and simplifying the description, and do not mean that the device must have a particular orientation.

[0042] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0044] As Figure 2 shown, the directional repair string of the present application is used for nitrogen blocking and dissolving cavity stage or gas injection and halogen discharge stage of salt cavern gas storage partial dissolution cavity, the packer 6 is screwed on the specified depth of the center pipe 7 or halogen discharge pipe, used for sealing the annulus between the center pipe 7 and the intermediate pipe 5, the hole is punched on the side of the intermediate pipe 5 or gas injection pipe, used for the discharge of clean water or brine water when the cavity is directionally repaired, the centralizer 2 is installed at the specified depth of the intermediate pipe 5 or gas injection pipe, used for ensuring the stability of the string during the repair process. Clean water or brine water is injected from the annulus between the center pipe 7 (or halogen discharge pipe) and the intermediate pipe 5 (or gas injection pipe), the jet hole direction is towards the unsolved salt layer, and directional dissolution repair is carried out in this direction.

[0045] In the blocking and dissolving cavity stage, the directional repair method of the salt cavern gas storage partial dissolution cavity of the present application comprises the following steps in sequence:

[0046] Step 1, as Figure 1 shown, the to-be-repaired area of the salt cavern gas storage partial dissolution cavity is determined, and the orientation and depth of the to-be-repaired unsolved formation A are determined by the cavity measurement result of the cavity measurement instrument;

[0047] Step 2, directional punching is carried out within a certain angle range on the pipe wall of the intermediate pipe 5 about 3 meters away from the pipe mouth 3, and the size and number of the punched jet hole are determined by the injection displacement, injection pressure and distance of the to-be-repaired unsolved formation A from the wellbore;

[0048] Step 3, in the nitrogen blocking and dissolving cavity stage, the intermediate pipe 5 with the centralizer 2 and the directional hole is lowered, and the depth of the centralizer 2 is 5 meters away from the shoe 3 of the production casing 1 after being lowered, and the centralizer 2 functions to reduce the influence of the backflow force generated by the water flow on the stability of the string when clean water or brine water is injected for cavity repair in the later stage; the depth of the directional hole is equivalent to the depth of the to-be-repaired unsolved formation A.

[0049] Step 4, after measuring the direction with the gyroscope lowered from the middle pipe 5, rotate the pipe column to ensure that the directional hole on the middle pipe 5 is directed towards the un-dissolved formation A to be repaired;

[0050] Step 5, lower the center pipe 7 with the packer 6 screwed thereon from the middle pipe 5. Lower the pipe column to the designed depth (generally inserted into the cavity bottom), and ensure that the packer 6 is located at a distance of 1-2 meters from the pipe mouth of the middle pipe 5, and press and set the packer 6 at the well mouth to block the passage downwards at the pipe mouth of the middle pipe 5;

[0051] Step 6, during the cavity forming process, inject the blocking solvent 3 such as nitrogen from the annulus between the middle pipe 5 and the center pipe 7 to ensure that the blocking solvent and the brine interface 4 are located at the designed depth to protect the upper salt layer;

[0052] Step 7, as shown in Figure 2 , Figure 3 , inject fresh water or fresh brine from the annulus between the middle pipe 5 and the center pipe 7, and determine the effective repair distance after the water flow is ejected from the directional hole according to the injection discharge, injection pressure, and flow area of the directional hole, to ensure that the dissolved formation to be repaired can be dissolved quickly and efficiently, and the dissolution of the fully dissolved area is reduced, so as to achieve the goal of directional repair of the deformed cavity.

[0053] During the gas injection and brine discharge process, the directional repair method of the partial dissolution cavity of the salt cavern gas storage according to the present application comprises the following steps in sequence:

[0054] Step 1, as shown in Figure 1 , determine the repair area of the partial dissolution cavity of the salt cavern gas storage, and determine the direction and depth of the un-dissolved formation A to be repaired according to the cavity measurement result of the cavity measurement instrument;

[0055] Step 2, perform directional drilling within a certain angle range on the pipe wall of the gas injection pipe at a distance of about 3 meters from the pipe mouth, and the size and number of the drilled injection holes are determined according to the injection discharge, injection pressure, and distance of the un-dissolved formation A to be repaired from the wellbore;

[0056] Step 3, during the gas injection and brine discharge stage, lower the gas injection pipe with the directional hole drilled thereinto and the centralizer 2, and the depth of the centralizer 2 is 3-5 meters from the shoe 3 of the production casing 1 after being lowered; the depth of the directional hole is equivalent to the depth of the un-dissolved formation A to be repaired;

[0057] Step 4, after measuring the direction with the gyroscope lowered from the gas injection pipe, rotate the pipe column to ensure that the directional hole on the gas injection pipe is directed towards the un-dissolved formation A to be repaired;

[0058] Step 5, the halogen discharge pipe is lowered into the gas injection pipe, and the packer 6 is screwed on the halogen discharge pipe. The pipe string is lowered to the designed depth (generally inserted into the cavity bottom), and the packer 6 is positioned at a distance of 1-2 meters from the pipe mouth of the gas injection pipe. The well mouth is pressed to seat the packer 6, and the passage downward from the pipe mouth of the gas injection pipe is blocked;

[0059] Step 6, during the cavity forming process, natural gas is injected as the blocking solvent 3 from the annulus between the gas injection pipe and the halogen discharge pipe, and the interface 4 between the blocking solvent and the brine is located at the designed depth to protect the upper salt layer;

[0060] Step 7, as shown in Figure 2 、 Figure 3 , fresh water or fresh brine is injected from the annulus between the gas injection pipe and the halogen discharge pipe, and the effective repair distance after the water flow is ejected from the directional hole is determined by the injection discharge, injection pressure, flow area of the directional hole and other parameters, so that the to-be-repaired dissolved formation can be quickly and efficiently dissolved, and the dissolution of the fully dissolved area is reduced, thereby achieving the goal of directional repair of the abnormal cavity.

[0061] The above only describes the preferred embodiments of the present application, shows and describes the basic principles, main features and advantages of the present application, and does not limit the patent protection scope of the present application. It should be understood by those skilled in the art that the present application is not limited by the above embodiments. In addition to the above embodiments, the present application can have other implementation manners without departing from the spirit and scope of the present application. The present application can also have various changes and improvements, and any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope of the present application. The protection scope of the present application is defined by the appended claims and their equivalents. The technical features not described in the present application can be realized by or using the prior art, which will not be described here.

Claims

1. A directional repair string for a partially dissolved cavern of a salt cavern gas storage, comprising a production casing, the lower end of the production casing being located above the partially dissolved cavern of the salt cavern gas storage, characterized in that, The production casing is inserted with an intermediate pipe, the lower end of the intermediate pipe extends into the partial solution cavity of the salt cavern gas storage and the lower port is below the unsolved formation to be repaired, a central pipe is inserted in the intermediate pipe, the lower end of the central pipe extends to the bottom of the partial solution cavity of the salt cavern gas storage; the lower part of the circumference of the intermediate pipe is provided with a nozzle facing the unsolved formation to be repaired, a packer is screwed on the central pipe, the rubber sleeve of the packer is set in the lower port of the intermediate pipe and the nozzle.

2. The directional remedial string for a salt cavern gas storage facility partial dissolution cavity of claim 1, wherein: A centralizer is screwed in the intermediate pipe, the slips of the centralizer are supported on the inner wall of the lower part of the production casing.

3. The directional remedial string for a salt cavern gas storage facility partial dissolution cavity of claim 1, wherein: The upper part of the partial solution cavity of the salt cavern gas storage is injected with a solution inhibitor, the interface of the solution inhibitor and the brine is above the unsolved formation to be repaired.

4. The directional remedial string for a salt cavern gas storage gasholder of claim 3, wherein: The solution inhibitor is nitrogen during the cavity forming process.

5. The directional remedial string for a salt cavern gas storage gasholder of claim 3, wherein: The solution inhibitor is natural gas during the gas injection and brine displacement process.

6. The directional remedial string for a salt cavern gas storage facility partial dissolution cavity of claim 2, wherein: During the gas injection and brine displacement process, the intermediate pipe is a brine displacement pipe, the central pipe is a gas injection pipe; the distance between the lower edge of the nozzle of the intermediate pipe and the lower port of the intermediate pipe is 3 meters, the distance between the centralizer and the shoe of the production casing is 3-5 meters, and the setting position of the packer is 1-2 meters away from the lower port of the intermediate pipe.

7. A method for directional repair of a solution cavity of a salt cavern gas storage, characterized in that, The steps are as follows: Step 1, determine the repair area of the partial solution cavity of the salt cavern gas storage, determine the position and depth of the unsolved formation to be repaired through the cavity measurement results of the cavity measurement instrument; Step 2, directionally drill nozzles within a certain angle range on the pipe wall of the intermediate pipe near the port; Step 3, lower the intermediate pipe with the centralizer into the drilled directional hole, the depth of the centralizer after being lowered is 3-5 meters away from the shoe of the production casing, and the depth of the directional hole is equivalent to the depth of the unsolved formation to be repaired; Step 4, after the direction is measured by the gyroscope lowered by the cable from the intermediate pipe, rotate and adjust the pipe column to ensure that the directional hole on the intermediate pipe is directed towards the unsolved formation to be repaired; Step 5, lower the central pipe from the intermediate pipe, the central pipe is screwed with a packer; lower the pipe column to the specified depth and ensure that the position of the packer is 1-2 meters away from the port of the intermediate pipe, press and set the packer at the wellhead to block the downward passage at the port of the intermediate pipe; Step 6, during the cavity forming process, inject the solution inhibitor into the annulus between the intermediate pipe and the central pipe to ensure that the interface of the solution inhibitor and the brine is at the designed depth to protect the upper salt layer; Step 7, inject fresh water or fresh brine into the annulus between the intermediate pipe and the central pipe, the fresh water or fresh brine is sprayed from the nozzle to quickly dissolve the dissolved formation to be repaired, reduce the dissolution of the fully dissolved area, and thus realize the directional repair of the abnormal cavity.

8. The method of targeted repair of a salt cavern gas storage facility partial dissolution cavity according to claim 7, wherein: In step 2, the size and number of the drilled nozzles are determined by the injection displacement, injection pressure and distance of the unsolved formation to be repaired from the wellbore.

9. The method of claim 7, wherein: In step 2, the central angle between the nozzle and the pipe core of the intermediate pipe is 15°-30°.

10. The method of claim 7, wherein: In step 7, the effective repair distance of the water flow sprayed from the directional hole is optimized and determined by the injection displacement, injection pressure and flow area of the directional hole of the fresh water or fresh brine, to ensure that the dissolved formation to be repaired can be quickly and efficiently dissolved.

11. The method of targeted repair of a salt cavern gas storage facility partial dissolution cavity of claim 7, wherein: During the solution inhibition cavity forming stage, the solution inhibitor is nitrogen.

12. The method of targeted repair of a salt cavern gas storage facility offset cavity according to claim 7, wherein: During the gas injection and brine displacement process, the intermediate pipe is a brine displacement pipe, the central pipe is a gas injection pipe, and the solution inhibitor is natural gas.

13. The method of targeted repair of a salt cavern gas storage facility offset cavity according to claim 7, wherein: The horizontal area covered by the orifice is determined by the horizontal projected area of the undissolved formation, and the vertical area covered by the orifice is determined by the thickness of the undissolved formation. The horizontal area covered by the orifice is determined by the horizontal projected area of the undissolved formation, and the vertical area covered by the orifice is determined by the thickness of the undissolved formation.

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