Method and device for nitrogen blocking solution in salt cavern gas storage

Abstract

The application provides a salt cavern gas storage nitrogen solution blocking cavity forming method and device, the method comprises the following steps: according to the well depth and the stratum parameter, the top depth of the target cavity and the depth of the initial time cavity string are determined; the first cavity forming process is cyclically executed to form the cavity in the slotting stage; the first cavity forming process comprises the following steps: the position of the cavity string is adjusted; nitrogen is injected until the gas-water interface reaches the depth of the current cavity outer pipe; the cavity is expanded until the first expansion time is passed; nitrogen is injected again until the gas-water interface reaches the depth of the cavity outer pipe; the cavity is expanded until the second expansion time is passed; the second cavity forming process is cyclically executed to form the cavity in the cavity forming stage; the third cavity forming process is cyclically executed to form the target cavity in the sealing top stage. By expanding the cavity gas volume through short time expansion of the open hole section first, and then injecting a large amount of nitrogen for expansion again, the cavity forming process is simplified, and the cavity forming cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of natural gas storage, and in particular to a method and device for forming a nitrogen blocking cavity of a salt cavern gas storage. BACKGROUND

[0002] The salt cavern gas storage is mainly built by a water blocking method. A blocking agent needs to be injected to control the shape of the cavity during the cavity forming process. Nitrogen has gradually replaced diesel as the main blocking agent due to its lower cost and environmental friendliness. During the nitrogen blocking cavity forming process of the salt cavern gas storage, nitrogen injection equipment needs to be set up on site to supplement the nitrogen underground to stabilize the position and change rate of the gas-water interface.

[0003] The cavity forming process needs to go through multiple stages. When the designed interface of a certain cavity forming stage is located in the open hole section, the nitrogen storage space in the well section is small, and the nitrogen is highly compressible, which leads to low monitoring accuracy of the gas-water interface during the cavity forming. Under the designed gas cushion thickness, a small amount of nitrogen needs to be injected multiple times by the ground nitrogen injection pry to accurately control the position of the gas-water interface, and the cavity forming process is relatively complicated.

[0004] Therefore, there is a need for a method for forming a nitrogen blocking cavity of a salt cavern gas storage to simplify the cavity forming process and reduce the cavity forming cost. SUMMARY

[0005] The present application provides a method and device for forming a nitrogen blocking cavity of a salt cavern gas storage to simplify the cavity forming process and reduce the cavity forming cost.

[0006] In a first aspect, the present application provides a method for forming a nitrogen blocking cavity of a salt cavern gas storage, comprising:

[0007] determining the top depth of the target cavity and the depth of the cavity forming string at the initial time according to the well depth and the formation parameters; wherein the cavity forming string comprises a cavity forming inner pipe and a cavity forming outer pipe;

[0008] cyclically executing a first cavity forming process to form the cavity of the slot building stage; wherein the first cavity forming process comprises: adjusting the position of the cavity forming string; injecting nitrogen until the gas-water interface reaches the depth of the current cavity forming outer pipe; expanding the cavity until a first expansion time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity forming outer pipe; expanding the cavity until a second expansion time elapses; wherein the first expansion time is less than the second expansion time;

[0009] cyclically executing a second cavity forming process to form the cavity of the cavity building stage; and cyclically executing a third cavity forming process to form the target cavity of the top sealing stage.

[0010] Optionally, the second cavity forming process comprises:

[0011] If the current gas-water interface is located below the open hole, adjust the position of the cavity-creating string;

[0012] inject nitrogen gas until the gas-water interface reaches a first design position, which is located below the top depth of the cavity currently formed, and perform cavity dissolution until a third dissolution time elapses.

[0013] Optionally, the second cavity-creating process comprises:

[0014] If the current gas-water interface is located within the open hole, adjust the current gas-water interface to reach a current second design position, which is located within the open hole, and perform cavity dissolution until a fourth dissolution time elapses.

[0015] release all the nitrogen gas downhole and adjust the position of the cavity-creating string, inject nitrogen gas until the gas-water interface reaches a current third design position, which is located between the second design position and the top depth of the cavity currently formed, and perform cavity dissolution until a fifth dissolution time elapses.

[0016] Optionally, the third cavity-creating process is repeatedly performed to form the target cavity in the ceiling-sealing stage, comprising:

[0017] determine a fourth design position, which is located below the top depth of the target cavity;

[0018] according to the fourth design position, repeatedly perform the third cavity-creating process until the target cavity in the ceiling-sealing stage is formed; wherein the third cavity-creating process comprises: injecting nitrogen gas until the gas-water interface reaches the fourth design position, performing cavity dissolution until the gas-water interface moves up to the top depth of the target cavity, injecting nitrogen gas again until the gas-water interface reaches the fourth design position, and performing cavity dissolution until a sixth dissolution time elapses.

[0019] Optionally, the cavity dissolution until the sixth dissolution time elapses comprises:

[0020] performing cavity dissolution until the sixth dissolution time elapses, and during the sixth dissolution time, monitoring and controlling the gas-water interface in real time to be no higher than the top depth of the target cavity.

[0021] In a second aspect, the present application provides a nitrogen-dissolution cavity-creating device for a salt cavern gas storage, comprising:

[0022] an initialization module configured to determine the top depth of the target cavity and the depth of the cavity-creating string at the initial time according to the well depth and the formation parameters; wherein the cavity-creating string comprises a cavity-creating inner tube and a cavity-creating outer tube.

[0023] The circulation cavity-forming module is configured to cyclically execute a first cavity-forming process to form a cavity in a slotting stage, wherein the first cavity-forming process comprises: adjusting a position of a cavity-forming string; injecting nitrogen until a gas-water interface reaches a depth of a current cavity-forming outer pipe; performing a first dissolution of the cavity until a first dissolution time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity-forming outer pipe; performing a second dissolution of the cavity until a second dissolution time elapses; and wherein the first dissolution time is less than the second dissolution time.

[0024] The circulation cavity-forming module is further configured to cyclically execute a second cavity-forming process to form a cavity in a cavity-forming stage, and cyclically execute a third cavity-forming process to form the target cavity in a capping stage.

[0025] Optionally, the circulation cavity-forming module is specifically configured to:

[0026] If the current gas-water interface is below the open hole, the position of the cavity-forming string is adjusted.

[0027] Nitrogen is injected until the gas-water interface reaches a first design position, the first design position is below a top depth of the cavity currently formed, and a third dissolution of the cavity is performed until a third dissolution time elapses.

[0028] Optionally, the circulation cavity-forming module is specifically configured to:

[0029] If the current gas-water interface is in the open hole, the current gas-water interface is adjusted to reach a current second design position, the second design position is in the open hole, and a fourth dissolution of the cavity is performed until a fourth dissolution time elapses.

[0030] All nitrogen in the downhole is released, the position of the cavity-forming string is adjusted, nitrogen is injected until the gas-water interface reaches a current third design position, the third design position is between the second design position and a top depth of the cavity currently formed, and a fifth dissolution of the cavity is performed until a fifth dissolution time elapses.

[0031] Optionally, the circulation cavity-forming module is specifically configured to:

[0032] A fourth design position is determined, the fourth design position is below a top depth of the target cavity.

[0033] According to the fourth design position, the third cavity-forming process is cyclically executed until the target cavity in the capping stage is formed, wherein the third cavity-forming process comprises: injecting nitrogen until the gas-water interface reaches the fourth design position; performing a sixth dissolution of the cavity until the gas-water interface moves to the top depth of the target cavity; injecting nitrogen again until the gas-water interface reaches the fourth design position; and performing a seventh dissolution of the cavity until a sixth dissolution time elapses.

[0034] Optionally, the circulating cavity-forming module is further configured to:

[0035] The cavity is dilated until a sixth dilution time is reached, and during the sixth dilution time, the gas-water interface is monitored and controlled in real time to be no higher than the target cavity top depth.

[0036] In a third aspect, the present application provides an electronic device, comprising:

[0037] at least one processor; and

[0038] a memory in communication with the at least one processor; wherein

[0039] The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the salt cavern gas storage nitrogen blocking dissolution cavity forming method as described in the first aspect.

[0040] In a fourth aspect, the present application provides a computer-readable storage medium, the computer-readable storage medium stores computer execution instructions, and the computer execution instructions are executed by a processor to implement the salt cavern gas storage nitrogen blocking dissolution cavity forming method as described in the first aspect.

[0041] The present application provides a salt cavern gas storage nitrogen blocking dissolution cavity forming method, device, electronic device and storage medium, the method comprising: determining the target cavity top depth and the initial time cavity string depth according to the well depth and the formation parameters; cyclically executing a first cavity forming process to form a cavity in the trench building stage; wherein the first cavity forming process comprises: adjusting the position of the cavity string; injecting nitrogen until the gas-water interface reaches the depth of the current cavity outer pipe; dilating the cavity until a first dilution time is reached; injecting nitrogen again until the gas-water interface reaches the depth of the cavity outer pipe; dilating the cavity until a second dilution time is reached; wherein the first dilution time is less than the second dilution time; cyclically executing a second cavity forming process to form a cavity in the cavity building stage; and cyclically executing a third cavity forming process to form the target cavity in the top sealing stage. By dilating the open hole section for a short time first to expand the cavity gas volume, and then injecting a large amount of nitrogen for dilution, the number of nitrogen injection times in the cavity forming process is reduced, the problems of nitrogen loss and inaccurate detection are avoided, the cavity forming process is simplified, and the cavity forming cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0043] Figure 1 The application scenario schematic diagram provided for the examples of the present application;

[0044] Figure 2 A salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the first embodiment of the application;

[0045] Figure 3 Another salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the first embodiment of the application;

[0046] Figure 4 A salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the second embodiment of the application;

[0047] Figure 5 A salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the third embodiment of the application;

[0048] Figure 6 A salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the fourth embodiment of the application;

[0049] Figure 7 A salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the fifth embodiment of the application;

[0050] Figure 8 Another salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the fifth embodiment of the application;

[0051] Figure 9 Another salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the fifth embodiment of the application;

[0052] Figure 10 Another salt cave gas storage nitrogen blocking solution cavity forming method flow chart provided for the fifth embodiment of the application;

[0053] Figure 11 A salt cave gas storage nitrogen blocking solution cavity forming device structure diagram provided for the sixth embodiment of the application;

[0054] Figure 12 A structure diagram of an electronic device provided for the seventh embodiment of the application.

[0055] Through the above-mentioned drawings, the specific embodiments of the application have been shown, and will be described in more detail hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the application by any means, but to illustrate the concept of the application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0056] The exemplary embodiments will be described in detail herein with reference to the accompanying drawings. In the following description, like reference numerals refer to like elements throughout the description. The following exemplary embodiments described herein represent illustrations only. That is, those of ordinary skill in the art will recognize that the applications described herein with respect to the exemplary embodiments in no way represents all the variations applicable to the applications. Instead, they represent typical variations understood to be within the scope of the applications as set forth in the appended claims.

[0057] Figure 1 The application scenarios of the examples of the present application are schematically shown in FIGS. 1-3. Figure 1 As shown in FIG. 1, the nitrogen blocking solution forming cavity of the salt cavern gas storage is aimed to form a target cavity shown in FIG. 2, which is a pear-shaped gas storage cavity expanded in the underground rock layer to store natural gas. Figure 1 As shown in FIG. 1, the nitrogen blocking solution forming cavity of the salt cavern gas storage is aimed to form a target cavity shown in FIG. 2, which is a pear-shaped gas storage cavity expanded in the underground rock layer to store natural gas.

[0058] The salt cavern gas storage is mainly constructed by the water solution forming cavity method, and a blocking solution needs to be injected during the cavity forming process to control the shape of the cavity. Nitrogen has gradually replaced diesel as the main blocking solution due to its lower cost and environmental friendliness. During the nitrogen blocking solution forming cavity process of the salt cavern gas storage, nitrogen injection equipment needs to be set up on site to supplement the nitrogen underground to stabilize the position and change rate of the gas-water interface.

[0059] Figure 1 In FIG. 4, 1 is the annulus volume V1 between the production casing and the cavity forming outer pipe, 2 is the annulus volume V2 between the open hole and the cavity forming outer pipe, 3 is the volume V3 of the nitrogen storage space at the top of the cavity, 4 represents the cavity forming outer pipe, 5 represents the cavity forming inner pipe, 6 represents the production casing, 7 represents the slightly expanded open hole section, and 8 represents the top of the cavity. The open hole section generally refers to the part above the top of the cavity formed in the current cavity forming stage. The cavity forming process needs to go through multiple stages. When the design interface of a certain cavity forming stage is located in the open hole section, due to the small nitrogen storage space in the section and the strong compressibility of nitrogen, the gas-water interface fluctuates greatly in this case, resulting in low monitoring accuracy of the gas-water interface during cavity forming. Under the designed gas cushion thickness, a small amount of nitrogen needs to be injected multiple times through the ground nitrogen injection pry to accurately control the position of the gas-water interface, which involves more interface detection and nitrogen injection processes, resulting in a relatively complicated cavity forming process.

[0060] When a large amount of nitrogen is injected, the phenomenon of gas-water interface fluctuation will be significantly reduced, and the upward movement speed of the gas-water interface is very slow within the cavity forming period of about three months in each stage. If a sufficient gas cushion thickness is designed, nitrogen can be avoided to be supplemented in a single cavity forming stage, and strict monitoring of the gas-water interface is not necessary, which will simplify the cavity forming process to reduce the cavity forming cost.

[0061] The position of the gas-water interface during the cavity forming process can be detected by using a fiber interface instrument or a numerical simulation calculation method, and the volume of nitrogen can be calculated by using a theoretical calculation method. The volume of the nitrogen storage space underground is calculated as follows:

[0062]

[0063] Among them, V n The volume of the downhole nitrogen storage space, in meters (m). 3 V1 represents the annulus volume between the downhole production casing and the cavity-forming outer casing, in meters. 3 V2 represents the spatial volume of the open hole and the annulus outside the cavity, in meters. 3 V3 is the volume of the space at the top of the cavity where nitrogen is stored, in meters. 3 D1 is the inner diameter of the production casing, in meters; D2 is the outer diameter of the cavity outer casing, in meters; D3 is the outer diameter of the cavity inner casing, in meters; k is the wellbore enlargement ratio; D4 is the drill bit diameter, in meters; D5 is the cavity top diameter, in meters; H1 is the production casing depth, in meters; H2 is the length of the downhole open hole section, equal to the cavity top depth minus the production casing depth, in meters; H3 is the cavity top gas cushion thickness, in meters.

[0064] The nitrogen injection volume under standard conditions is as follows:

[0065]

[0066] Among them, Q n T0 represents the nitrogen injection volume, in Nm3 (standard cubic meters); T0 is the absolute temperature of the gas at the wellhead, taken as 293 K. This represents the average pressure of the gas inside the wellbore, expressed in MPa, and can be calculated based on the wellhead pressure. P0 is the average compressibility factor of the gas inside the wellbore; P0 is the standard atmospheric pressure, with a value of 0.101 MPa. In this application, all calculations involving nitrogen volume are expressed in standard cubic units.

[0067] Furthermore, when the gas-water interface is located in the naked eye, V n =V1+V2, when the gas-water interface is located inside the cavity top, V n =V1+V2+V3.

[0068] The technical solutions of this application will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. In the description of this application, unless otherwise expressly specified and limited, the terms should be broadly understood within the art. The embodiments of this application will now be described with reference to the accompanying drawings.

[0069] Example 1

[0070] Figure 2 This is a schematic flowchart of the nitrogen-dissolution-resistant cavity creation method for salt cavern gas storage provided in Embodiment 1 of this application, as shown below. Figure 2 As shown, the method includes:

[0071] S101: determining the top depth of the target cavity and the depth of the initial cavity-forming string according to the well depth and the stratum parameters;

[0072] S102: cyclically performing a first cavity-forming process to form the cavity in the trench-building stage;

[0073] S103: cyclically performing a second cavity-forming process to form the cavity in the cavity-building stage;

[0074] S104: cyclically performing a third cavity-forming process to form the target cavity in the top-sealing stage.

[0075] The embodiment is exemplarily described in combination with a specific application scenario. The nitrogen dissolution cavity forming for a salt cavern gas storage usually adopts a cavity-forming string composed of an inner cavity-forming pipe and an outer cavity-forming pipe, and a production casing installed on the ground and penetrating into the top of the underground salt layer. The production casing is used to excavate the open hole section, the cavity-forming string is lowered into the production casing, and the cavity is formed by opening the well and injecting water.

[0076] The nitrogen used is usually of a purity of 99.99%, the production casing is lowered into the open hole section and has a size of d1, the outer cavity-forming pipe is lowered into the production casing and has a size of d2, and the inner cavity-forming pipe is lowered into the outer cavity-forming pipe and has a size of d3. The specific sizes are selected according to the actual geological conditions and the target cavity, and d3 < d2 < d1, which can be used to calculate the nitrogen injection amount in the well.

[0077] Generally, a common size combination is: d3 = 7", and another feasible size combination is: d2 = 7",

[0078] The cavity forming needs to go through multiple cavity-forming stages, and the cavity is formed from bottom to top. According to the position of the cavity to be formed in the cavity-forming stage, the cavity-forming stage can be divided into a trench-building stage, a cavity-building stage and a top-sealing stage. Generally, the trench-building refers to building a pit for loading the upper insoluble substances in the initial stage of cavity forming, generally adopting 3-4 cavity-forming processes; the cavity-building refers to building the main part of the salt cavern gas storage, generally adopting a positive circulation or a reverse circulation, a total of 4-6 cavity-forming processes; and the top-sealing refers to building an arch-shaped cavity top with higher stability, generally adopting 2-3 positive circulation or reverse circulation cavity-forming processes. In each cavity-forming process, the target gas-water interface position and the target cavity shape are obtained by numerical simulation through a computer according to the actual demand and the local geological conditions. The positive circulation or the reverse circulation generally refers to the water flow direction of the inner and outer cavity-forming pipes. Specifically, after the cavity is dissolved by water injection, brine is generated in the cavity, and the brine needs to be continuously discharged and fresh water needs to be injected. When the inner pipe is used to inject fresh water and the outer pipe is used to discharge brine, the process is called positive circulation, and vice versa, which needs to be selected according to the preset shape of the cavity.

[0079] Before the cavity forming starts, the top depth of the target cavity and the depth of the initial cavity forming string need to be determined according to the well depth and the formation parameters; wherein, the cavity forming string includes a cavity forming inner tube and a cavity forming outer tube. The production casing bottom position is located at or below the top of the salt layer. The cavity forming inner tube and the cavity forming outer tube are used for the cavity forming in the positive circulation or the reverse circulation, the cavity forming inner tube is higher than the well bottom position, the cavity forming outer tube is higher than the cavity forming inner tube, and the cavity forming inner tube is inside the cavity forming outer tube. Generally, the cavity forming outer tube is about 30m above the well bottom, and the cavity forming inner tube is 1-2m above the well bottom. Then the cavity forming starts, and the first cavity forming process is executed in circulation to form the cavity in the slotting stage.

[0080] Figure 3 A flowchart of another nitrogen blocking dissolution cavity forming method for the salt cavern gas storage provided in Embodiment One of the present application is provided to illustrate the first cavity forming process. As shown in FIG. 2, the first cavity forming process in S102 specifically includes: Figure 3

[0081] S105: adjusting the position of the cavity forming string;

[0082] S106: injecting nitrogen until the gas-water interface reaches the depth of the current cavity forming outer tube;

[0083] S107: expanding the cavity until the first expansion time is reached;

[0084] S108: injecting nitrogen again until the gas-water interface reaches the depth of the cavity forming outer tube;

[0085] S109: expanding the cavity until the second expansion time is reached.

[0086] Specifically, the position of the cavity forming string is adjusted, and the cavity forming string is adjusted to the corresponding position of the target cavity shape in this stage according to the actual situation; then a small amount of nitrogen is injected until the gas-water interface reaches the depth of the current cavity forming outer tube; the cavity is expanded until the first expansion time is reached, which is generally 1-2 weeks, and the wellbore diameter is expanded to 2-5m according to the demand. At this time, the lowermost open hole section has sufficient gas storage space. Nitrogen is injected again until the gas-water interface reaches the depth of the cavity forming outer tube, and the cavity is expanded until the second expansion time is reached, which is usually about 2 months. At this time, the cavity will reach the design volume in this stage; wherein, the first expansion time is less than the second expansion time.

[0087] After the circulation cavity forming in the slotting stage is completed, the cavity forming stage in the cavity building stage needs to be performed according to the position of the gas-water interface, and the cavity forming stage also needs to be performed in circulation to form the preset cavity body. When the partial expansion of the body is completed, the circulation cavity forming work of the cavity top needs to be performed below the reserved salt layer top plate. ​

[0088] The embodiment provides a salt cavern gas storage nitrogen blocking dissolution cavity forming method, which comprises the following steps: determining the top depth of a target cavity and the depth of an initial cavity forming string according to well depth and stratum parameters; cyclically performing a first cavity forming process to form a cavity in a slotting stage; wherein the first cavity forming process comprises the following steps: adjusting the position of the cavity forming string; injecting nitrogen until the gas-water interface reaches the depth of a current cavity forming outer pipe; expanding the cavity until a first expansion time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity forming outer pipe; expanding the cavity until a second expansion time elapses; cyclically performing a second cavity forming process to form a cavity in a cavity forming stage; and cyclically performing a third cavity forming process to form the target cavity in a sealing stage. By expanding the cavity for a short time to expand the gas storage volume of the cavity in the open hole section, and then injecting a large amount of nitrogen to expand the cavity, the number of nitrogen injection times in the cavity forming process is reduced, the problems of nitrogen loss and inaccurate detection are avoided, the cavity forming process is simplified, and thus the cavity forming cost is reduced.

[0089] Embodiment two

[0090] Figure 4 A flowchart of the salt cavern gas storage nitrogen blocking dissolution cavity forming method provided by the embodiment two is shown in FIG. 2, which is based on any one of the other embodiments and comprises the following steps: Figure 4 The second cavity forming process in S103 can specifically comprise the following steps:

[0091] S201: If the current gas-water interface is located below the open hole, the position of the cavity forming string is adjusted.

[0092] S202: Nitrogen is injected until the gas-water interface reaches a first design position, and the first design position is located below the top depth of the cavity formed at present.

[0093] S203: The cavity is expanded until a third expansion time elapses.

[0094] The embodiment is exemplarily described in combination with a specific application scenario: the embodiment provides a cavity forming method when the gas-water interface is located at the top of the cavity. After the slotting stage is completed, if it is the first cavity forming stage, the cavity formed at present is the cavity formed at the end of the slotting stage, and if it is not the first cavity forming stage, the cavity formed at present refers to the cavity formed at the end of the previous cavity forming process.

[0095] If the current gas-water interface is located below the open hole, i.e., near the top of the cavity, the position of the cavity-forming string is adjusted to the target position to prepare for cavity formation; then a large amount of nitrogen is injected at one time, and the amount of nitrogen needs to be calculated according to the preset gas cushion thickness, so that the gas-water interface reaches the first design position below the top depth of the current cavity, and the cavity is expanded for a long time at this position until the third expansion time of about three months. Cycle until the final target cavity of the cavity formation stage meets the results of data simulation.

[0096] The salt cavern gas storage nitrogen dissolution-resistant cavity forming method provided by the embodiment adjusts the position of the cavity-forming string if the current gas-water interface is located below the open hole; nitrogen is injected until the gas-water interface reaches the first design position below the top depth of the current cavity; and the cavity is expanded until the third expansion time. By injecting a large amount of nitrogen to expand the cavity opened at the top for a long time, the frequent control of the gas-water interface by multiple cycles of nitrogen injection is avoided, the cavity forming process is simplified, and the cavity forming cost is reduced.

[0097] Embodiment three

[0098] Figure 5 The flowchart of the salt cavern gas storage nitrogen dissolution-resistant cavity forming method provided by the third embodiment of the present application is shown in FIG. 3, which is based on any other embodiment and can specifically include the second cavity forming process in S103. Figure 5

[0099] S301: If the current gas-water interface is located in the open hole, adjust the current gas-water interface to reach the current second design position;

[0100] S302: Expand the cavity until the fourth expansion time;

[0101] S303: Release all the nitrogen downhole and adjust the position of the cavity-forming string;

[0102] S304: Inject nitrogen until the gas-water interface reaches the current third design position;

[0103] S305: Expand the cavity until the fifth expansion time.

[0104] It should be noted that according to the different gas-water interfaces during the cavity formation period, the actual situation can be used to adopt the implementation mode described in the embodiment or the implementation mode described in the previous embodiment, and the different cavity forming processes can also be arbitrarily selected for separate implementation or combined implementation, but the gas-water interface needs to be adjusted to the required position by pre-charging and discharging.

[0105] ​As an example, after the slotting stage, the cavity building process based on the present embodiment can be directly performed, i.e. in each cycle of performing the second cavity building process, the situation that the gas-water interface is located in the open hole is considered. As another example, after the slotting stage, the cavity building process based on the aforementioned embodiment two can be performed first. For example, assuming that at the end of the slotting stage, the gas-water interface is located below the open hole, the second cavity building process based on embodiment two can be performed, and during the cavity building stage, if it is found that the current gas-water interface moves into the open hole, the second cavity building process based on embodiment three can be performed. Similarly, during the cavity building stage based on the present embodiment, if the current gas-water interface is located below the open hole, the cavity building can also be performed in combination with the second cavity building process based on embodiment two.

[0106] The present embodiment is exemplarily described in combination with a specific application scenario: when the current gas-water interface is located in the open hole above the current cavity roof, the current gas-water interface needs to be adjusted to the second design position in the open hole by adjusting the nitrogen. Generally, the second design position can be located at 15-20 m above the current cavity roof. At this position, the cavity is preliminarily expanded for about two weeks, so that the diameter of the open hole section at this position and below is expanded, and the gas storage capacity is significantly increased. At this time, after the preliminary expansion is completed, the well needs to be shut down to release all the nitrogen, and the cavity building string depth is adjusted to perform the cavity building process. After the adjustment, a third design position is set, which is located between the second design position and the top depth of the cavity formed currently, and generally, it is about 5 m below the second design position. A large amount of nitrogen is injected to move the gas-water interface to this position or slightly above this position, and long-term expansion is performed for about three months to form the cavity of the cavity building process until the cavity shape meets the requirements of the numerical simulation.

[0107] The salt cavern gas storage nitrogen blocking dissolution cavity building method provided by the present embodiment adjusts the current gas-water interface to the current second design position if the current gas-water interface is located in the open hole; expands the cavity until the fourth expansion time elapses; releases all the nitrogen downhole and adjusts the position of the cavity building string; injects nitrogen until the gas-water interface reaches the current third design position; and expands the cavity until the fifth expansion time elapses. For the case that the design interface is located in the open hole, the open hole is first expanded to have enough space to accommodate nitrogen downhole, then the well is shut down to release the gas, and a large amount of nitrogen is injected at one time after adjusting the position of the cavity building string to perform long-term expansion, thereby avoiding the problems of gas-water interface fluctuation due to small gas storage capacity of the open hole section and the need for multiple injections of small amounts of nitrogen for gas-water interface adjustment, simplifying the cavity building process and reducing the cavity building cost.

[0108] Embodiment four

[0109] Figure 6 The flowchart of the salt cavern gas storage nitrogen blocking dissolution cavity building method provided by the present embodiment is shown in Figure 6As shown, S104 specifically comprises, on the basis of any other embodiment:

[0110] S401: determining a fourth design position, which is below the top depth of the target cavity;

[0111] S402: according to the fourth design position, cyclically performing a third cavity-forming process until the target cavity in the capping stage is formed.

[0112] The fourth design position is below the final target cavity obtained by software simulation, and generally needs to leave a space of at least 5 m to ensure that the gas-water interface in the capping stage is strictly controlled below the top depth of the target cavity, and a sufficient salt layer thickness is left.

[0113] The third cavity-forming process comprises: injecting nitrogen until the gas-water interface reaches the fourth design position; performing preliminary dissolution on the cavity at this position, so that the gas-water interface naturally moves upward until the gas-water interface moves to the top depth of the target cavity or a warning depth below the top depth; then injecting nitrogen again until the gas-water interface reaches the fourth design position; and performing dissolution on the cavity until a sixth dissolution time of about 3 months is reached. During the sixth dissolution time, the gas-water interface is monitored and controlled in real time to be not higher than the top depth of the target cavity. Generally, during the dissolution process, the upward movement of the gas-water interface is generally not higher than the position of the top depth of the target cavity, but needs to be monitored by a fiber interface instrument or the like to strictly ensure that the gas-water interface position does not exceed the limit and the salt roof above the top depth of the target cavity is not corroded.

[0114] The nitrogen dissolution-blocking cavity-forming method for a salt cavern gas storage provided by the embodiment determines a fourth design position, which is below the top depth of the target cavity; according to the fourth design position, a third cavity-forming process is cyclically performed until the target cavity in the capping stage is formed; wherein the third cavity-forming process comprises: injecting nitrogen until the gas-water interface reaches the fourth design position; performing dissolution on the cavity until the gas-water interface moves to the top depth of the target cavity; injecting nitrogen again until the gas-water interface reaches the fourth design position; and performing dissolution on the cavity until a sixth dissolution time is reached. Through the dissolution of the top part in the capping stage, there is sufficient gas storage space below the open hole, a large amount of nitrogen is injected at one time in the capping stage, the gas-water interface is slowly moved upward through natural dissolution, the engineering quantity of multiple nitrogen injection precise control is avoided, the cavity-forming process is simplified, and the cavity-forming cost is reduced.

[0115] Embodiment five

[0116] The embodiment five of the present application combines the foregoing various embodiments to specifically illustrate the application and operation of the method.

[0117] Figure 7 A salt cavern gas storage nitrogen blocking solution cavity method provided for the fifth embodiment of the present application, to illustrate the specific application of the method in the slot building stage. As shown in Figure 7 , the figure: 1 is the initial nitrogen gas cushion, 2 is the cavity forming outer tube, 3 is the design gas-water interface, 4 is the cavity forming inner tube, 5 is the new well bore, 6 is the well bottom position, 7 is the cavity forming inner tube bottom position, 8 is the gas-water interface depth after moving up, 9 is the first time to expand the solution cavity boundary, 10 is the second injection of a large amount of nitrogen gas cushion, 11 is the nitrogen gas cushion after a period of expansion, 12 is the final gas-water interface, 13 is the final cavity boundary. It should be noted that the case shown in the figure is only an example of a certain slot building process, and the 12 and 13 may result in different results in different slot building processes.

[0118] A certain gas storage, numerical simulation shows that the depth of the new well bottom 6 needs to be built is 1250m, the inner diameter of the production casing D1 = 0.22052m, the depth is 1000m, the new well bore 5 diameter is equal to D4*k = 0.311*1.1 = 0.3421m, the cavity forming inner tube 4 outer diameter D3 = 41 / 2" = 0.1143m, the cavity forming inner tube bottom 7 depth is 1248m, the cavity forming outer tube 2 outer diameter D2 = 7" = 0.1778m, the depth is 1230m, the gas-water interface 3 depth is equal to the cavity forming outer tube 2 depth 1230m, as shown in Figure 7 a, the first nitrogen injection amount is calculated as follows:

[0119] The annular volume V1 between the downhole production casing and the cavity forming outer tube:

[0120]

[0121] The annular volume V2 between the downhole open hole and the cavity forming outer tube:

[0122]

[0123] The downhole nitrogen storage space volume Vn is calculated as follows:

[0124] V n = V1+V2 = 13.36+15.43 = 28.97 (5)

[0125] The amount of nitrogen injected at standard conditions is as follows:

[0126]

[0127] Wherein, Simplify the wellhead pressure; T0 = 293K; P0 = 0.101MPa.

[0128] The first nitrogen injection volume at standard conditions is 4014 Nm3.

[0129] After 1 week of open hole circulation, the gas-water interface 8 was detected to move up to 1226.5 m by the fiber interface instrument, and the first expanded cavity 9 had a top diameter of 2.5 m, as shown in Fig. 2a. Figure 7 b. If the wellhead gas pressure is 14 MPa, and the gas-water interface is pressed down to the original design position 1230 m by injecting nitrogen again, as shown in Fig. 2b. Figure 7 c. Then the nitrogen gas cushion thickness is 3.5 m, and the nitrogen gas amount is calculated as follows:

[0130] The nitrogen gas space volume V3 stored at the top of the cavity after moving up is:

[0131]

[0132] The amount of nitrogen gas 10 needed to be injected again is:

[0133]

[0134] That is, 2395 cubic meters of nitrogen gas need to be injected again to press the gas-water interface to the original design position 1230 m.

[0135] The wellhead gas pressure is calculated at 14 MPa for each cavity forming stage described below.

[0136] After 2 months of cavity forming, no nitrogen gas needs to be supplemented, the cavity reaches the designed volume, the cavity is expanded again, the gas-water interface moves up slightly to a depth of 12, 1228 m, which is 2 m away from the original design position, which meets the cavity gas-water interface position control, and the cavity volume and shape have little effect. The final cavity shape is shown in Fig. 2d. Figure 7 d.

[0137] Figure 8 Another nitrogen dissolution cavity forming method for a salt cavern gas storage provided in Embodiment Five is shown in the schematic diagram, which is used to illustrate the specific application of the method when the gas-water interface is located at the top of the cavity during the trench building stage. As shown in Fig. 3, in the figure: 1 is the cavity top depth and the designed gas-water interface depth, 2 is the initial gas-water interface, 3 is the initial cavity boundary, 4 is the designed gas-water interface depth, and 5 is the final cavity boundary. Figure 8 For the initial boundary 3 of the cavity during the cavity building period, the value of the cavity top depth 1 is 1100 m, and the designed gas-water interface depth at this time is equal to the cavity depth 1. The cavity top diameter is 10 m, and the calculation method is similar to that during the trench building period. The annular space volume V1 between the production casing and the cavity forming outer pipe is 13.36 m3, the annular space volume V2 between the open hole and the cavity forming outer pipe is 6.71 m3, the cavity top gas cushion design thickness is 1 m, and the cavity top nitrogen gas storage space is 78.54 m.

[0138]

[0139] ​The nitrogen storage space volume Vn in the well can be V1+V2+V3=13.36+6.71+78.54=98.61 m3, and the first injection amount of nitrogen is calculated to be 13746 standard cubic meters, as shown in Figure 8 a.

[0140] Subsequently, the well is opened for reverse circulation for 3 months, and no nitrogen is supplemented during the process. The new gas-water interface 4 does not move upward, and the cavity is greatly expanded. The new cavity is as shown in Figure 8 b. The thickness of the nitrogen gas cushion at the top of the cavity is reduced, and there is still a sufficient thickness of the gas cushion at the top of the cavity. The top diameter is expanded to 30 m.

[0141] Figure 9 Another method for forming a cavity by nitrogen blocking dissolution of a salt cavern gas storage provided in Embodiment Five is schematically shown in FIG. 5, which is used to illustrate the specific application of the method when the gas-water interface is located in the open hole during the trench building stage. As shown in FIG. 5, in the figure: 1 is the initial gas-water interface depth; 2 is the designed gas-water interface depth; 3 is the gas-water interface depth after nitrogen injection; 4 is the initial cavity boundary; and 5 is the final cavity boundary. Figure 9

[0142] The initial cavity boundary 4 is as shown in Figure 9 a. The initial gas-water interface 1 is at a depth of 1100 m, and the designed gas-water interface 2 is located in the open hole above the top of the cavity formed in the previous cavity forming stage, at a depth of 1080 m. A small amount of nitrogen needs to be released during the current cavity forming process, and the gas-water interface is detected by using the optical fiber interface instrument. The gas-water interface is adjusted to the designed position 2 at a depth of 1080 m, and the cavity forming is continued for two weeks. The diameter of the open hole between the cavity top 1 and the designed gas-water interface 2 is expanded to 5 m, as shown in Figure 9 b. The well is shut down, and all the nitrogen in the well is released. The depth of the cavity forming string is adjusted.

[0143] The adjusted cavity forming string is as shown in Figure 9 c. At this time, the open hole in the well has been expanded, and a large amount of nitrogen is injected for the first time, so that the gas-water interface depth is 1085 m. The required amount of nitrogen is calculated as follows: the annular space volume V1 between the production casing and the cavity forming outer pipe is 13.36 m3, the annular space volume V2 between the open hole and the cavity forming outer pipe is 5.37 m3, the designed thickness of the cavity top gas cushion is 5 m, and the cavity top storage space V3 is 98.17 m3.

[0144] At this time, the nitrogen storage space volume Vn in the well can be V1+V2+V3=13.36+5.37+98.17=116.91 m3, and the first injection amount of nitrogen is calculated to be 16297 standard cubic meters. After the nitrogen is injected, the cavity forming is continued for 3 months, and no nitrogen needs to be supplemented. The gas-water interface only moves a small amount during the process, but it is still below the designed gas-water interface 2. The final cavity boundary 5 is as shown in Figure 9 d.

[0145] Figure 10 ​Another method for forming a nitrogen blocking cavity of a salt cavern gas storage provided in the fifth embodiment of the present application is shown in the schematic diagram, which is used to illustrate the capping stage, and the specific application of the method. As shown in Figure 10 , in the figure: 1 is the initial gas-water interface depth; 2 is the designed gas-water interface depth; 3 is the gas-water interface depth after nitrogen injection; 4 is the initial cavity boundary; 5 is the final cavity boundary;

[0146] The gas-water interface during the capping stage is usually in the open hole well, and the initial cavity boundary 4 is as shown in Figure 10 a, the depth of the designed gas-water interface 2 is 1015 m, which is 15 m away from the bottom end depth of the production casing, and at least 15 m thick salt layer is left as the salt roof. The first injection of nitrogen controls the gas-water interface 5 m below the designed depth, i.e. the position of the gas-water interface 1 is 1020 m. The method for calculating the first nitrogen injection amount is as follows: the annular space volume V1 between the production casing and the cavity forming outer pipe is 13.36 m3, the annular space volume V2 between the open hole and the cavity forming outer pipe is 1.34 m3, Vn = V1 + V2 = 13.36 + 1.34 = 14.7 m3, and 2050 standard cubic meters of nitrogen needs to be injected. After a period of cavity forming, generally 2 weeks, the optical fiber interface instrument is used to detect the position of the gas-water interface, and when it moves up to the designed depth 2, 1015 m, the cavity roof diameter is expanded to 5 m, as shown in Figure 10 b. If the gas-water interface is pressed back to 1020 m, the amount of nitrogen that needs to be supplemented is calculated as follows: the nitrogen storage space V3 in the cavity roof is 98.17 m3, and the amount of nitrogen that needs to be supplemented is calculated as 13685 standard cubic meters, as shown in Figure 10 c. After that, no nitrogen is supplemented, and the cavity is formed for about 3 months, during which the optical fiber interface instrument needs to be used to monitor the depth of the gas-water interface, and the gas-water interface is always ensured to be below the designed value, and the final cavity boundary 5 is as shown in Figure 10 d.

[0147] The embodiment provides a nitrogen blocking cavity forming method for a salt cavern gas storage, which comprises the following steps: determining the top depth of a target cavity and the depth of a cavity forming pipe string at an initial time according to well depth and stratum parameters; cyclically executing a first cavity forming process to form a cavity at a trench building stage; wherein the first cavity forming process comprises the following steps: adjusting the position of the cavity forming pipe string; injecting nitrogen until the gas-water interface reaches the depth of a current cavity forming outer pipe; expanding the cavity until a first expansion time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity forming outer pipe; expanding the cavity until a second expansion time elapses; cyclically executing a second cavity forming process to form a cavity at a cavity building stage; and cyclically executing a third cavity forming process to form the target cavity at a capping stage. By expanding the cavity gas storage volume through short-time expansion of the open hole well section first, and then injecting a large amount of nitrogen for expansion, the number of nitrogen injection in the cavity forming process is reduced, the problems of nitrogen loss and inaccurate detection are avoided, the cavity forming process is simplified, and thus the cavity forming cost is reduced.

[0148] Embodiment six

[0149] The embodiment six of the present application also provides a nitrogen blocking dissolution cavity forming device for salt cavern gas storage to realize the foregoing method. Figure 11 A structural schematic diagram of the nitrogen blocking dissolution cavity forming device for salt cavern gas storage provided by the embodiment six of the present application is shown in Figure 11 The device comprises:

[0150] The initialization module 61 is configured to determine the top depth of the target cavity and the depth of the initial cavity forming pipe string according to the well depth and the formation parameters; wherein the cavity forming pipe string comprises a cavity forming inner pipe and a cavity forming outer pipe.

[0151] The cycle cavity forming module 62 is configured to cyclically execute a first cavity forming process to form the cavity in the trench building stage; wherein the first cavity forming process comprises: adjusting the position of the cavity forming pipe string; injecting nitrogen until the gas-water interface reaches the depth of the current cavity forming outer pipe; expanding the cavity until a first expansion time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity forming outer pipe; expanding the cavity until a second expansion time elapses; wherein the first expansion time is less than the second expansion time.

[0152] The cycle cavity forming module 62 is further configured to cyclically execute a second cavity forming process to form the cavity in the cavity building stage, and cyclically execute a third cavity forming process to form the target cavity in the top sealing stage.

[0153] In one example, the cycle cavity forming module 62 is specifically configured to:

[0154] If the current gas-water interface is below the open hole, adjust the position of the cavity forming pipe string;

[0155] Inject nitrogen until the gas-water interface reaches a first design position, the first design position being below the top depth of the cavity currently formed; expand the cavity until a third expansion time elapses.

[0156] By injecting a large amount of nitrogen to expand the cavity opened at the top for a long time, the frequent control of the gas-water interface by multiple cycles of nitrogen injection is avoided, the cavity forming process is simplified, and the cavity forming cost is reduced.

[0157] In one example, the cycle cavity forming module 62 is specifically configured to:

[0158] If the current gas-water interface is in the open hole, adjust the current gas-water interface to reach a current second design position, the second design position being in the open hole; expand the cavity until a fourth expansion time elapses.

[0159] Releasing all nitrogen gas downhole, and adjusting the position of the cavity-creating string; injecting nitrogen gas until the gas-water interface reaches the current third design position, which is between the second design position and the top depth of the currently formed cavity; and performing cavity expansion until the fifth expansion time elapses.

[0160] For the case where the design interface is located in the open hole, the open hole is first expanded to provide sufficient space for nitrogen gas downhole, and then the well is shut in to release the gas, a large amount of nitrogen gas is injected in one go after adjusting the position of the cavity-creating string, and long-time expansion is performed to avoid the problem of gas-water interface fluctuation due to insufficient gas storage in the open hole section, the need for multiple injections of small amounts of nitrogen gas for gas-water interface adjustment, and the simplification of the cavity-creating process to reduce the cost of cavity creation.

[0161] In one example, the cyclic cavity-creating module 62 is specifically used for:

[0162] determining a fourth design position below the top depth of the target cavity;

[0163] According to the fourth design position, the third cavity-creating process is cyclically performed until the target cavity in the sealing stage is formed; wherein the third cavity-creating process includes: injecting nitrogen gas until the gas-water interface reaches the fourth design position; expanding the cavity until the gas-water interface moves up to the top depth of the target cavity; injecting nitrogen gas again until the gas-water interface reaches the fourth design position; and expanding the cavity until the sixth expansion time elapses.

[0164] By expanding the top of the sealing stage, sufficient gas storage space is provided downhole, a large amount of nitrogen gas is injected in one go during the sealing stage, and the gas-water interface slowly moves up through natural expansion, avoiding the engineering quantity of multiple nitrogen injection precise control, simplifying the cavity-creating process and reducing the cost of cavity creation.

[0165] In one example, the cyclic cavity-creating module 62 is further used for:

[0166] expanding the cavity until the sixth expansion time elapses, and monitoring and controlling the gas-water interface in real time during the sixth expansion time to ensure that the gas-water interface is not higher than the top depth of the target cavity.

[0167] The monitoring and control of the gas-water interface can strictly ensure that the gas-water interface position does not exceed the limit, and protect the salt roof above the top depth of the target cavity from being corroded.

[0168] The embodiment provides a nitrogen blocking dissolution cavity device for a salt cavern gas storage, comprising: an initialization module configured to determine the top depth of a target cavity and the depth of an initial cavity-forming pipe string according to well depth and stratum parameters; wherein the cavity-forming pipe string comprises a cavity-forming inner pipe and a cavity-forming outer pipe; a circulating cavity-forming module configured to cyclically execute a first cavity-forming process to form a cavity in a slotting stage; wherein the first cavity-forming process comprises: adjusting the position of the cavity-forming pipe string; injecting nitrogen until the gas-water interface reaches the depth of the current cavity-forming outer pipe; expanding the cavity until a first expansion time elapses; injecting nitrogen again until the gas-water interface reaches the depth of the cavity-forming outer pipe; expanding the cavity until a second expansion time elapses; wherein the first expansion time is less than the second expansion time; the circulating cavity-forming module is further configured to cyclically execute a second cavity-forming process to form a cavity in a cavity-forming stage; and cyclically execute a third cavity-forming process to form the target cavity in a top-sealing stage. By expanding the cavity gas storage volume by expanding the cavity for a short time first, and then injecting a large amount of nitrogen for expansion, the number of nitrogen injection times in the cavity-forming process is reduced, the problems of nitrogen loss and inaccurate detection are avoided, the cavity-forming process is simplified, and thus the cavity-forming cost is reduced.

[0169] Embodiment seven

[0170] Figure 12 A structural schematic diagram of an electronic device provided in the embodiment seven of the present application is shown in the figure, Figure 12 The electronic device comprises:

[0171] The processor 291, the electronic device further comprises a memory 292; can further comprise a communication interface 293 and a bus 294. Among them, the processor 291, the memory 292, the communication interface 293, can complete the communication between each other through the bus 294. The communication interface 293 can be used for information transmission. The processor 291 can call the logic instruction in the memory 294 to execute the method of the above-mentioned embodiment.

[0172] In addition, the logic instruction in the memory 292 described above can be realized in the form of a software function unit and sold or used as an independent product, which can be stored in a computer readable storage medium.

[0173] The memory 292 as a kind of computer readable storage medium, can be used to store software program, computer executable program, such as the program instruction / module corresponding to the method in the embodiment of the present application. The processor 291 runs the software program, instruction and module stored in the memory 292, thereby executing function application and data processing, that is, realizing the method in the above-mentioned method embodiment.

[0174] The memory 292 can include a program storage area and a data storage area, where the program storage area can store an operating system, application programs required by at least one function; the data storage area can store data created according to the use of the terminal device, etc. In addition, the memory 292 can include a high-speed random access memory, and can also include a nonvolatile memory.

[0175] The embodiments of the present application further provide a computer readable storage medium, wherein computer execution instructions are stored in the computer readable storage medium, and the computer execution instructions are used for implementing the method in any of the embodiments when executed by a processor.

[0176] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0177] It should be understood that the application is not limited to the precise construction that has been described above and shown in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is limited only by the claims that follow.

Claims

1. A method for creating a nitrogen-resistant cavity in a salt cavern gas storage tank, characterized in that, include: Based on the well depth and formation parameters, determine the top depth of the target cavity and the initial depth of the cavity-building string; wherein, the cavity-building string includes an inner cavity-building tube and an outer cavity-building tube; The first cavity-building process is executed cyclically to form the cavity in the tank-building stage; wherein the first cavity-building process includes: adjusting the position of the cavity-building tubing; injecting nitrogen gas until the gas-water interface reaches the depth of the current cavity-building outer tube; expanding the cavity until a first expansion time has elapsed to increase the gas storage volume of the cavity; injecting nitrogen gas again until the gas-water interface reaches the depth of the cavity-building outer tube; expanding the cavity until a second expansion time has elapsed; wherein the first expansion time is less than the second expansion time; The second cavity-building process is executed cyclically to form the cavity in the cavity-building stage; and the third cavity-building process is executed cyclically to form the target cavity in the capping stage; The second cavity creation procedure includes: If the current gas-water interface is below the naked eye, adjust the position of the cavity-forming column; Nitrogen gas is injected until the gas-water interface reaches the first designed position, which is located below the top depth of the currently formed cavity; the cavity is diffused until the third diffusion time has elapsed. If the current air-water interface is within the naked eye, adjust the current air-water interface to the current second design position, which is within the naked eye; then perform diffusion dissolution on the cavity until the fourth diffusion dissolution time has elapsed; Release all downhole nitrogen and adjust the position of the cavity-forming string; inject nitrogen until the gas-water interface reaches the current third design position, which is located between the second design position and the top depth of the currently formed cavity; expand the cavity until the fifth expansion time has elapsed.

2. The method according to claim 1, characterized in that, The cyclic execution of the third cavity-building process to form the target cavity in the capping stage includes: Determine a fourth design location, which is located below the top depth of the target cavity; According to the fourth design position, the third cavity-building process is executed cyclically until the target cavity in the capping stage is formed; wherein, the third cavity-building process includes: injecting nitrogen until the gas-water interface reaches the fourth design position; expanding the cavity until the gas-water interface moves up to the top depth of the target cavity; injecting nitrogen again until the gas-water interface reaches the fourth design position; expanding the cavity until the sixth expansion time has elapsed.

3. The method according to claim 2, characterized in that, The process of diluting the cavity until the sixth diluting time has elapsed includes: The cavity is expanded and dissolved until the sixth expansion and dissolution time has elapsed, and during the sixth expansion and dissolution time, the gas-water interface is monitored and controlled in real time to ensure that it does not exceed the top depth of the target cavity.

4. A nitrogen-blocking cavity-forming device for a salt cavern gas storage tank, characterized in that, include: An initialization module is used to determine the top depth of the target cavity and the initial depth of the cavity-building string based on the well depth and formation parameters; wherein, the cavity-building string includes an inner cavity tube and an outer cavity tube; A circulating cavity-building module is used to repeatedly execute the first cavity-building process to form a cavity in the tank-building stage. The first cavity-building process includes: adjusting the position of the cavity-building tubing; injecting nitrogen until the gas-water interface reaches the depth of the current cavity-building outer tube; expanding the cavity until a first expansion time has elapsed to increase the cavity's gas storage volume; injecting nitrogen again until the gas-water interface reaches the depth of the cavity-building outer tube; and expanding the cavity until a second expansion time has elapsed. The first expansion time is shorter than the second expansion time. The cyclic cavity-building module is also used to cyclically execute the second cavity-building process to form the cavity in the cavity-building stage; and to cyclically execute the third cavity-building process to form the target cavity in the capping stage; The cyclic cavity creation module is specifically used for: If the current gas-water interface is below the naked eye, adjust the position of the cavity-forming column; Nitrogen gas is injected until the gas-water interface reaches the first designed position, which is located below the top depth of the currently formed cavity; the cavity is diffused until the third diffusion time has elapsed. If the current air-water interface is within the naked eye, adjust the current air-water interface to the current second design position, which is within the naked eye; then perform diffusion dissolution on the cavity until the fourth diffusion dissolution time has elapsed; Release all downhole nitrogen and adjust the position of the cavity-forming string; inject nitrogen until the gas-water interface reaches the current third design position, which is located between the second design position and the top depth of the currently formed cavity; expand the cavity until the fifth expansion time has elapsed.

5. The apparatus according to claim 4, characterized in that, The cyclic cavity creation module is specifically used for: Determine a fourth design location, which is located below the top depth of the target cavity; According to the fourth design position, the third cavity-building process is executed cyclically until the target cavity in the capping stage is formed; wherein, the third cavity-building process includes: injecting nitrogen until the gas-water interface reaches the fourth design position; expanding the cavity until the gas-water interface moves up to the top depth of the target cavity; injecting nitrogen again until the gas-water interface reaches the fourth design position; expanding the cavity until the sixth expansion time has elapsed.

6. The apparatus according to claim 5, characterized in that, The circulating cavity module is also used for: The cavity is expanded and dissolved until the sixth expansion and dissolution time has elapsed, and during the sixth expansion and dissolution time, the gas-water interface is monitored and controlled in real time to ensure that it does not exceed the top depth of the target cavity.

7. An electronic device, comprising: At least one processor; as well as A memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method as described in any one of claims 1-3.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the method as described in any one of claims 1-3.

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