Method for rolling construction and putting into production of salt cavern gas storage

Abstract

The application provides a method for construction and production of a salt cavern gas storage, comprising the following steps: S1, constructing a single cavity dissolution well type and well pattern combined with a straight well and a directional well; wherein, a cavity construction and halogen discharge point is located at the bottom of the cavity; S2, dividing a cavity construction and operation stage into a slot construction period, a cavity construction period, a capacity expansion period and a gas storage period; S3, optimizing and combining the slot construction period, the cavity construction period, the capacity expansion period and the gas storage period with a static period, a gas injection period, a static period and a gas production period. By adjusting and deploying the cavity dissolution and gas storage linkage coupling of different construction stages in different injection and production cycle stages, the time for the cavity to play a gas storage capacity is advanced, the idle waste of effective gas storage space is avoided, the inefficient conditions such as re-injection or external discharge of low-concentration brine are avoided, the brine receiving capacity and production adjustment capacity of a salt enterprise are fully utilized, and the cavity formed is timely converted into effective gas storage space.

Description

Technical Field

[0001] This invention relates to the field of oil and gas storage technology, and in particular to a method for the rolling construction and commissioning of a salt cavern gas storage chamber and gas storage. Background Technology

[0002] Salt cavern gas storage facilities are large underground caverns constructed through water dissolution within sedimentary salt layers. Salt rock, due to its extremely high sealing properties and self-healing mechanical characteristics, is widely used for constructing natural gas, hydrogen, and compressed air storage. Currently, salt cavern gas storage cavities primarily utilize a vertical water circulation channel constructed using a single-well, center-pipe combination model. Once the cavity volume reaches the design target, dissolution is complete, and the natural gas injection / production tubing is set within the wellbore, transitioning the cavity into the injection / production operation phase. Current salt cavern gas storage construction, design, and operation methods have some significant drawbacks:

[0003] During the cavity-building phase in dissolution, the traditional single-well cavity-building tubing combination with intermediate pipe-intermediate pipe configuration increases circulating friction, raises cavity-building energy consumption, and increases the risk of tubing failure under water hammer damage. In deep salt rock and high-volume cavity-building processes, the energy loss and failure risk of traditional conventional-sized single-well cavity-building become even more apparent. Addressing current issues in large-diameter single-well drilling and cementing still presents challenges due to high investment and difficulty. Furthermore, the impact of salt rock creep under alternating stress and temperature on the integrity and sealing of the wellbore and cement sheath requires further investigation.

[0004] During the construction phase of salt cavern gas storage tanks, the limited internal space for circulation and mixing, coupled with the small contact surface between the salt rock and the storage tank walls, results in brine concentrations that are generally far below the required standards for receiving brine from salt chemical enterprises. This low-concentration brine must be reinjected into the cavern for salt dissolution. This process increases the energy consumption of cavern construction and significantly reduces the efficiency of salt dissolution and tank construction.

[0005] Traditional salt-based cavity construction typically uses diesel or nitrogen as an inhibitor to control the regular expansion of the cavity shape. However, both diesel and nitrogen inhibitors require temporary facilities for injection and storage, and the purchase or production system of the inhibitors is costly. When the cavity shape is complex and requires inhibitor protection for a large volume section at the top, neither diesel nor nitrogen can meet the required dosage for effective cavity protection and control.

[0006] In traditional cavity-building methods, the depth of the brine discharge string after cavity construction determines the effective drainage volume of the upper cavity and the resulting gas storage space. To avoid the risks of sludge inhalation and natural gas breakthrough into the brine discharge string, the brine discharge port is generally 3-5 meters below the sludge surface, and the final gas-water interface after discharge is approximately 3 meters above the discharge port. A significant amount of effective volume space below the gas-water interface and the gas storage space within the pores of the sludge accumulation area remain unutilized.

[0007] Traditional cavity construction methods can only be used to complete well completion operations and realize gas storage capacity after the cavity has been dissolved to the target shape and volume. Especially when the target volume of the cavity is large, the dissolution and construction time of a single cavity can be as long as 4 to 6 years. The cavity cannot fully realize its gas storage capacity after it has reached a certain volume, resulting in the waste and idleness of the cavity's effective space and prolonging the commissioning time of the salt cavern gas storage project.

[0008] Traditional wellbore construction processes connect the wellbore to the surface via a single wellbore channel. After gas injection and brine discharge, the natural gas injection and production tubing is sealed within the production casing inside the wellbore. If the tubing or sealing components inside the wellbore malfunction, it is impossible to effectively backfill the brine and release all the natural gas before commencing operations. This necessitates expensive and complex pressurized operations, and may even only allow for monitoring without effective intervention.

[0009] To maintain the stability of the cavity, a certain amount of natural gas must be left in the cavity to maintain the pressure inside the cavity under the traditional cavity injection and production operation mode. The natural gas at the bottom accounts for about 40% of the total storage capacity. In extreme emergency gas production situations, the space for releasing extreme gas production in the cavity is limited. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a method for the rolling construction and commissioning of salt cavern gas storage chambers and gas storage facilities, which addresses the shortcomings of the existing technology.

[0011] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for the rolling construction and commissioning of a salt cavern gas storage cavity and gas storage, comprising: S1, constructing a single-cavity dissolution well type and well network combining vertical wells and directional wells; wherein, the cavity creation and brine discharge point is located at the bottom of the cavity; S2, dividing the cavity construction and operation stages into a trenching period, a cavity building period, a capacity expansion period, and a gas storage period; S3, optimizing the combination of the trenching period, cavity building period, capacity expansion period, and gas storage period with the static period, gas injection period, static period, and gas production period.

[0012] The beneficial effects of adopting the technical solution of this invention are as follows: The cavity construction adopts a vertical dissolution single-cavity mode combining vertical and directional wells, and the cavity is divided into four stages according to the construction phase: trenching, cavity construction, expansion, and gas storage. The annual natural gas injection and production cycle is divided into four stages: spring stabilization, injection, autumn stabilization, and production. By coordinating the dissolution and gas storage linkage of the cavity at different construction stages in different injection and production cycle phases, the cavity's gas storage capacity is brought forward, avoiding the idle waste of effective gas storage space and the inefficiency of low-concentration brine reinjection or discharge. This fully utilizes the brine receiving capacity and production regulation capacity of the salt chemical enterprise, promptly converting the formed cavity into effective gas storage space. It increases the proportion of working gas within the cavity and solves the problem of low-concentration brine discharge during the trenching phase. Through a rolling construction and commissioning model, the limited brine digestion capacity of the salt chemical enterprise is fully utilized. Directional and vertical wells increase cavity construction discharge rate and single-cavity cavity construction speed without increasing well diameter or wellhead pump pressure. The brine discharge point is located at the lowest point of the cavity, which increases the brine concentration during the cavity-building stage and fully discharges the pore volume of sediment below the sediment surface, making full use of the potential gas storage space of the salt rock gas storage facility. In case of risks or malfunctions in the injection and production tubing, natural gas in the cavity can be discharged by reinjecting brine through directional wells, and routine repair work can be carried out on the injection and production tubing and equipment in the vertical well.

[0013] Further, step S1 includes: S11, drilling a vertical well to the bottom depth of the cavity at the target cavity construction location and cementing the well; S12, drilling a directional well, connecting the bottom of the directional well with the vertical well, and reserving a 3-5m open hole section at the bottom of the directional well connecting the vertical well; S13, designing a well network layout pattern with three directional wells on one drilling platform.

[0014] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The design places three directional wells on one drilling platform, and the well layout pattern facilitates centralized scheduling of water circulation during cavity construction and operation. The brine discharge point is located at the lowest point of the cavity, resulting in extremely high brine concentration, fully utilizing the salt chemical enterprise's production capacity. In the event of risks or malfunctions in the injection and production tubing, natural gas within the cavity can be discharged through brine reinjection via the directional wells, allowing for routine repair work on the injection and production tubing and equipment in the vertical wells.

[0015] Further, step S2 includes: S21, during the trenching phase, a single-layer cavity-building string is installed in both the vertical and directional wells, and a vertical circulation mode of injecting fresh water into the directional well and extracting brine from the vertical well is used for trenching and cavity building; S22, during the cavity-building phase, a vertical reverse circulation mode of injecting fresh water into the vertical well and extracting brine from the directional well is used for trenching and cavity building, and the cavity shape development is controlled by adjusting the cavity-building string and the depth of the solvent inhibitor in the vertical well in stages until the top of the cavity is dissolved to the design depth; S23, during the expansion phase, the cavity-building string in the vertical well is replaced with a natural gas injection and production string, and the string is set to complete the well completion operation. The directional well serves as the injection and production channel for fresh water, fresh brine, and saturated brine until the cavity is expanded to the target shape and volume, and then all the brine in the cavity is discharged; S24, during the gas storage phase, the directional well is shut in, and the directional well serves as the channel for brine reinjection during vertical well workover and emergency gas production.

[0016] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: both directional wells and vertical wells require only one cavity-building string, which can increase the cavity-building discharge rate by more than 100% and the single-cavity cavity-building speed by more than 100% without increasing the well diameter and wellhead pump pressure. High-discharge trenching can fully open the sediment settling space, allowing the low-concentration brine generated to be injected into the cavity during the expansion period, avoiding the concentration limitations of brine export and fully utilizing the limited brine treatment capacity of the salt chemical enterprise. It also allows for balanced and stable utilization of the brine digestion and regulation capacity of the salt chemical enterprise, maximizing the gas storage capacity of the cavity during the expansion period, achieving 100% working gas without a bottom gas layer under optimal operating conditions. The gas storage capacity can be altered by adjusting the interface depth of the natural gas inhibitor. Conventional cavity-building strings are installed in directional wells for water injection and brine output throughout the cavity's entire life cycle, while gas-tight cavity-building strings are installed in vertical wells during the trenching and cavity-building periods for water injection and brine output.

[0017] Furthermore, before step S21, the following steps are included: comprehensively designing the cavity shape of the trenching and cavity building stages, and pre-setting the cavity shape generated by directional well injection of fresh brine or fresh water during the expansion stage.

[0018] The beneficial effects of adopting the above-mentioned further technical solutions are: designing the cavity shape during the trenching and cavity building stages, taking into account the development of cavity shape caused by directional well injection of brine or fresh water and dissolution during the expansion period, so as to meet the stability requirements of the cavity and cavity group.

[0019] Further, in step S21, the tail end of the cavity-making string of the directional well is connected to the head of the screen pipe, and the cavity-making string of the directional well is annularly connected to the production casing. The cavity-making string of the vertical well is a gas-tight string, and the cavity-making string of the vertical well is annularly connected to the production casing. Insoluble sediment is provided at the bottom of the vertical well. In step S23, the injection rate, concentration, and gas-water interface depth of fresh water or brine are designed using numerical simulation software.

[0020] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The directional well's cavity-making string is connected to a screen pipe head at the tail end to prevent insoluble substances from being drawn into the string during brine extraction. A liquid-phase inhibitory protective fluid needs to be injected into the annulus between the directional well's cavity-making string and the production casing. The vertical well's cavity-making string uses a gas-tight string, and natural gas is injected into its annulus with the production casing as an inhibitory solvent. Utilizing the pores of the cavity sediment increases the effective gas storage space, maximizing the gas storage capacity of the salt cavern cavity, lowering the threshold for salt rock grade requirements in salt cavern gas storage site selection, and improving the economic efficiency of salt cavern gas storage projects. For salt rock layers with high insoluble content, the volume of the sediment pores at the bottom of the cavity can be fully utilized, increasing the gas storage volume gain per unit thickness of salt layer.

[0021] Further, step S3 includes: S31, during the static period, the cavity is built and brine is extracted, and during emergency and phased gas injection, the cavity is actively and steadily adjusted to move the solvent interface downward during the cavity building period, and natural gas is stored in the cushion layer, or the cavity is injected during the expansion period to steadily replace the brine in the cavity.

[0022] S32. During the gas injection period, fully utilize the brine regulation capacity, use the expansion period cavity for stable gas injection and brine discharge, and use the storage period cavity to undertake the main and peak gas injection. S33. During the settling period, use the cavity construction period cavity for brine extraction. In case of emergency or phased gas extraction, choose to actively adjust the cavity construction period cavity to move the solvent interface upward for gas extraction, or start the large-volume trench construction of the trench construction period cavity and inject the unsaturated brine generated during trench construction into the expansion period cavity to replace the gas extraction. S34. During the gas extraction period, start the trench construction period cavity for trench construction, inject the stable unsaturated brine generated during trench construction into the expansion period cavity for gas extraction, and use the storage period cavity to undertake the main and peak gas extraction.

[0023] The beneficial effects of adopting the above-mentioned further technical solutions are: multi-stage cavity construction planning and multi-level injection-production allocation maximize the exploitation of external support conditions and inherent gas storage potential. By optimizing the combination of the trenching period, cavity construction period, expansion period, and gas storage period within the spring stabilization period, injection period, autumn stabilization period, and gas production period within one year, the highest concentration of brine for external transmission and discharge is achieved, maximizing the available gas storage capacity. Except for the unsaturated brine generated during the first cavity trenching period, which needs to be exported or recirculated into the cavity, the low-concentration brine generated during subsequent trenching periods is injected into the cavity during the expansion period to increase the proportion of working gas in the cavity. For salt rock strata with high insoluble content, the pore volume of sediment at the bottom of the cavity can be fully utilized, greatly improving the gas storage volume gain rate per unit thickness of salt layer. During the expansion period, the cavity is reinjected with unsaturated brine to ensure that all natural gas in the favorable gas storage space is working gas, without any bottom gas. The construction of the cavity is divided into different stages. By combining different gas injection and extraction stages with the cavity dissolution and gas storage requirements of different stages, the cavity can have gas storage capacity at an earlier stage, avoiding inefficient situations such as reinjection or discharge of low-concentration brine. This fully utilizes the brine receiving capacity and production regulation capacity of the salt chemical enterprise, and promptly transforms the formed cavity into an effective gas storage space.

[0024] Furthermore, in step S34, during the gas production period, unsaturated brine generated in the cavity during the trenching period is injected into the cavity during the expansion period through a directional well to replace the natural gas in the cavity; in step S32, during the gas injection period, natural gas is injected through a vertical well, and most of the brine in the effective cavity and sediment pores is discharged through the directional well, completing one expansion cycle until the entire cavity reaches the target shape and volume, and the cavity is converted to the gas storage period.

[0025] The beneficial effects of adopting the above-mentioned further technical solution are as follows: by optimizing the construction and commissioning of cavity-making wells in batches and stages, the cavity can have preliminary gas storage capacity during the cavity construction period and gas storage capacity without a bottom gas during the expansion period, thus advancing the entire cavity gas storage stage. This avoids the disadvantages of the traditional cavity-making mode, which has a long cavity construction time and the cavity being idle before well completion and unable to exert its gas storage capacity. At the same time, this invention fully utilizes the limited brine receiving and regulation capabilities of salt chemical enterprises.

[0026] Furthermore, the distance between the wellhead of a directional well and the wellhead of a vertical well is calculated using the following formula:

[0027] L = (P + D) / 2, where L is the distance between the wellhead of the directional well and the wellhead of the vertical well, P is the safety pillar spacing designed between two adjacent cavities, and D is the maximum designed diameter of a single cavity.

[0028] The beneficial effect of adopting the above-mentioned further technical solution is that it facilitates the directional well shot trajectory to maintain a corresponding safe distance from the designed cavity wall.

[0029] The advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] Figure 1 This is a schematic flowchart illustrating the method for the rolling construction and commissioning of salt cavern gas storage chambers and gas storage facilities provided in an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the salt cavern gas storage tank and the water-soluble construction of the gas storage tank during rolling construction and commissioning, provided in an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the salt cavern gas storage cavity and the gas storage rolling construction, commissioning, injection, and production well completion provided in an embodiment of the present invention.

[0033] Figure 4 A schematic diagram of the salt cavern gas storage cavity and the rolling construction well network for gas storage provided in an embodiment of the present invention.

[0034] Explanation of reference numerals: 1. Vertical well; 2. Directional well; 3. Natural gas pipeline; 4. Cavity-making natural gas inhibitor; 5. Cavity-making string for directional well; 6. Cavity-making string for vertical well; 7. Insoluble sediment; 8. Screen pipe inlet for directional well; 9. Protective fluid for directional well; 10. First injection / production string; 11. Packer; 12. Second injection / production string; 13. Natural gas. Detailed Implementation

[0035] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] like Figure 1 As shown, this embodiment of the invention provides a method for the rolling construction and commissioning of a salt cavern gas storage cavity and gas storage, including: S1, constructing a single-cavity dissolution well type and well network combining vertical wells and directional wells; wherein, the cavity creation and brine discharge point is located at the bottom of the cavity; S2, dividing the cavity construction and operation stages into a trenching period, a cavity construction period, a capacity expansion period, and a gas storage period; S3, optimizing the combination of the trenching period, cavity construction period, capacity expansion period, and gas storage period with the static period, gas injection period, static period, and gas production period.

[0037] The beneficial effects of adopting the technical solution of this invention are as follows: The cavity construction adopts a vertical dissolution single-cavity mode combining vertical and directional wells, and the cavity is divided into four stages according to the construction phase: trenching, cavity construction, expansion, and gas storage. The annual natural gas injection and production cycle is divided into four stages: spring stabilization, injection, autumn stabilization, and production. By coordinating the dissolution and gas storage linkage of the cavity at different construction stages in different injection and production cycle phases, the cavity's gas storage capacity is brought forward, avoiding the idle waste of effective gas storage space and the inefficiency of low-concentration brine reinjection or discharge. This fully utilizes the brine receiving capacity and production regulation capacity of the salt chemical enterprise, promptly converting the formed cavity into effective gas storage space. It increases the proportion of working gas within the cavity and solves the problem of low-concentration brine discharge during the trenching phase. Through a rolling construction and commissioning model, the limited brine digestion capacity of the salt chemical enterprise is fully utilized. Directional and vertical wells increase cavity construction discharge rate and single-cavity cavity construction speed without increasing well diameter or wellhead pump pressure. The brine discharge point is located at the lowest point of the cavity, which increases the brine concentration during the cavity-building stage and fully discharges the pore volume of sediment below the sediment surface, making full use of the potential gas storage space of the salt rock gas storage facility. In case of risks or malfunctions in the injection and production tubing, natural gas in the cavity can be discharged by reinjecting brine through directional wells, and routine repair work can be carried out on the injection and production tubing and equipment in the vertical well.

[0038] Further, step S1 includes: S11, drilling a vertical well to the bottom depth of the cavity at the target cavity construction location and cementing the well; S12, drilling a directional well, connecting the bottom of the directional well with the vertical well, and reserving a 3-5m open hole section at the bottom of the directional well connecting the vertical well; S13, designing a well network layout pattern with three directional wells on one drilling platform.

[0039] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The design places three directional wells on one drilling platform, and the well layout pattern facilitates centralized scheduling of water circulation during cavity construction and operation. The brine discharge point is located at the lowest point of the cavity, resulting in extremely high brine concentration, fully utilizing the salt chemical enterprise's production capacity. In the event of risks or malfunctions in the injection and production tubing, natural gas within the cavity can be discharged through brine reinjection via the directional wells, allowing for routine repair work on the injection and production tubing and equipment in the vertical wells.

[0040] It should be noted that the number of directional wells in this embodiment of the invention may be, but is not limited to, three. Users can choose the number of directional wells according to their time needs.

[0041] S101: Each cavity construction unit includes a vertical well 1 and a directional well 2, with the directional well 2 drilled to the bottom of the vertical well 1 for connection;

[0042] S102: Lay the natural gas pipeline 3 from the injection and production station to the vertical well site for the injection and recovery of the natural gas inhibitor 4 for cavity creation and natural gas injection and production during the storage period;

[0043] S103: A conventional directional well cavity-making string 5 is run into directional well 2 for water injection and brine production throughout the cavity's life cycle. During the trenching and cavity-making periods, a vertical well cavity-making string 6 (which can be a gas-tight cavity-making string for vertical wells) is run into the vertical well for water injection and brine production. During the expansion period, the vertical well cavity-making string 6 is replaced with the first gas injection and production string 12 (which can be a gas-tight injection and production string) and set.

[0044] Further, step S2 includes: S21, during the trenching phase, a single-layer cavity-building string is installed in both the vertical and directional wells, and a vertical circulation mode of injecting fresh water into the directional well and extracting brine from the vertical well is used for trenching and cavity building; S22, during the cavity-building phase, a vertical reverse circulation mode of injecting fresh water into the vertical well and extracting brine from the directional well is used for trenching and cavity building, and the cavity shape development is controlled by adjusting the cavity-building string and the depth of the solvent inhibitor in the vertical well in stages until the top of the cavity is dissolved to the design depth; S23, during the expansion phase, the cavity-building string in the vertical well is replaced with a natural gas injection and production string, and the string is set to complete the well completion operation. The directional well serves as the injection and production channel for fresh water, fresh brine, and saturated brine until the cavity is expanded to the target shape and volume, and then all the brine in the cavity is discharged; S24, during the gas storage phase, the directional well is shut in, and the directional well serves as the channel for brine reinjection during vertical well workover and emergency gas production.

[0045] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: both directional wells and vertical wells require only one cavity-building string, which can increase the cavity-building discharge rate by more than 100% and the single-cavity cavity-building speed by more than 100% without increasing the well diameter and wellhead pump pressure. High-discharge trenching can fully open the sediment settling space, allowing the low-concentration brine generated to be injected into the cavity during the expansion period, avoiding the concentration limitations of brine export and fully utilizing the limited brine treatment capacity of the salt chemical enterprise. It also allows for balanced and stable utilization of the brine digestion and regulation capacity of the salt chemical enterprise, maximizing the gas storage capacity of the cavity during the expansion period, achieving 100% working gas without a bottom gas layer under optimal operating conditions. The gas storage capacity can be altered by adjusting the interface depth of the natural gas inhibitor. Conventional cavity-building strings are installed in directional wells for water injection and brine output throughout the cavity's entire life cycle, while gas-tight cavity-building strings are installed in vertical wells during the trenching and cavity-building periods for water injection and brine output.

[0046] The construction and operation phases of the gas cavity are divided into the trench construction phase, the cavity construction phase, the capacity expansion phase, and the gas storage phase, including the following:

[0047] S201: Unsaturated brine generated during the construction phase is injected into the expansion phase cavity to replace the natural gas inside the cavity;

[0048] S202: During the initial construction phase, the cavity has preliminary gas storage capacity. The gas storage capacity can be changed by adjusting the interface depth of the natural gas inhibitor.

[0049] S203: The expansion chamber has fully utilized its gas storage capacity. The expansion chamber only accepts the reinjection of unsaturated brine or fresh water generated by the tank construction chamber for expansion.

[0050] S204: During the gas storage period, the cavity is completely converted into an injection-production well, and depressurization operation is adopted. Only during critical emergency periods or well workover periods, brine is reinjected through directional wells to replace part or all of the natural gas.

[0051] Furthermore, before step S21, the following steps are included: comprehensively designing the cavity shape of the trenching and cavity building stages, and pre-setting the cavity shape generated by directional well injection of fresh brine or fresh water during the expansion stage.

[0052] The beneficial effects of adopting the above-mentioned further technical solutions are: designing the cavity shape during the trenching and cavity building stages, taking into account the development of cavity shape caused by directional well injection of brine or fresh water and dissolution during the expansion period, so as to meet the stability requirements of the cavity and cavity group.

[0053] Further, in step S21, the tail end of the cavity-making string of the directional well is connected to the head of the screen pipe, and the cavity-making string of the directional well is annularly connected to the production casing. The cavity-making string of the vertical well is a gas-tight string, and the cavity-making string of the vertical well is annularly connected to the production casing. Insoluble sediment is provided at the bottom of the vertical well. In step S23, the injection rate, concentration, and gas-water interface depth of fresh water or brine are designed using numerical simulation software.

[0054] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The directional well's cavity-making string is connected to a screen pipe head at the tail end to prevent insoluble substances from being drawn into the string during brine extraction. A liquid-phase inhibitory protective fluid needs to be injected into the annulus between the directional well's cavity-making string and the production casing. The vertical well's cavity-making string uses a gas-tight string, and natural gas is injected into its annulus with the production casing as an inhibitory solvent. Utilizing the pores of the cavity sediment increases the effective gas storage space, maximizing the gas storage capacity of the salt cavern cavity, lowering the threshold for salt rock grade requirements in salt cavern gas storage site selection, and improving the economic efficiency of salt cavern gas storage projects. For salt rock layers with high insoluble content, the volume of the sediment pores at the bottom of the cavity can be fully utilized, increasing the gas storage volume gain per unit thickness of salt layer.

[0055] Further, step S3 includes: S31. During the static period, when the cavity is built up and brine is extracted, and during emergency and phased gas injection, the cavity is actively and steadily adjusted to lower the barrier solvent interface to store natural gas using the cushion layer, or the cavity is injected during the expansion period to smoothly replace the brine in the cavity; S32. During the gas injection period, the brine's regulating capacity is fully utilized, and the cavity is used for stable gas injection and brine discharge during the expansion period, while the cavity is used for main and peak gas injection; S33. During the static period, when the cavity is built up and brine is extracted, and during emergency and phased gas extraction, the cavity is actively adjusted to raise the barrier solvent interface to extract gas, or the cavity is started to build a large-volume trench during the trench construction period, and the unsaturated brine generated during trench construction is injected into the cavity during the expansion period to replace the gas extracted; S34. During the gas extraction period, the cavity is started to build a trench during the trench construction period, and the stable unsaturated brine generated during the trench construction period is injected into the cavity during the expansion period to extract gas, while the cavity is used for main and peak gas extraction.

[0056] The beneficial effects of adopting the above-mentioned further technical solutions are: multi-stage cavity construction planning and multi-level injection-production allocation maximize the exploitation of external support conditions and inherent gas storage potential. By optimizing the combination of the trenching period, cavity construction period, expansion period, and gas storage period within the spring stabilization period, injection period, autumn stabilization period, and gas production period within one year, the highest concentration of brine for external transmission and discharge is achieved, maximizing the available gas storage capacity. Except for the unsaturated brine generated during the first cavity trenching period, which needs to be exported or recirculated into the cavity, the low-concentration brine generated during subsequent trenching periods is injected into the cavity during the expansion period to increase the proportion of working gas in the cavity. For salt rock strata with high insoluble content, the pore volume of sediment at the bottom of the cavity can be fully utilized, greatly improving the gas storage volume gain rate per unit thickness of salt layer. During the expansion period, the cavity is reinjected with unsaturated brine to ensure that all natural gas in the favorable gas storage space is working gas, without any bottom gas. The construction of the cavity is divided into different stages. By combining different gas injection and extraction stages with the cavity dissolution and gas storage requirements of different stages, the cavity can have gas storage capacity at an earlier stage, avoiding inefficient situations such as reinjection or discharge of low-concentration brine. This fully utilizes the brine receiving capacity and production regulation capacity of the salt chemical enterprise, and promptly transforms the formed cavity into an effective gas storage space.

[0057] The annual natural gas injection and production cycle is divided into four phases: the spring settling period, the injection period, the autumn settling period, and the production period, including the following:

[0058] S301: During the spring settling period, the cavity is built and brine is extracted. During this period, emergency and phased gas injection is carried out. First, the cavity is actively and steadily adjusted to move the solvent interface downward during the cavity building period, and natural gas is stored in the cushion layer. Second, the cavity is injected during the expansion period to steadily replace the brine in the cavity.

[0059] S302: During the gas injection period, the brine regulation capacity of the salt chemical enterprise is fully utilized to smoothly inject gas and discharge the brine in the cavity during the expansion period. During the gas storage period, the cavity undertakes the main and peak gas injection.

[0060] S303: During the autumn settling period, the cavity is built during the cavity construction period for brine extraction. During emergency and phased gas extraction during this period: First, the cavity during the cavity construction period is selected to actively adjust the interface of the inhibitory solvent to move upward and extract the stored natural gas without affecting the cavity construction control; Second, the cavity during the trench construction period is started with a large-volume trench construction, and the unsaturated brine generated during the trench construction is injected into the cavity during the expansion period to replace the gas extraction.

[0061] S304: During the gas extraction period, control the start-up of the trenching chamber, inject the stable unsaturated brine generated by the trenching chamber into the expansion chamber for gas extraction, and utilize the gas storage chamber to undertake the main and peak gas extraction.

[0062] Furthermore, in step S34, during the gas production period, unsaturated brine generated in the cavity during the trenching period is injected into the cavity during the expansion period through a directional well to replace the natural gas in the cavity; in step S32, during the gas injection period, natural gas is injected through a vertical well, and most of the brine in the effective cavity and sediment pores is discharged through the directional well, completing one expansion cycle until the entire cavity reaches the target shape and volume, and the cavity is converted to the gas storage period.

[0063] The beneficial effects of adopting the above-mentioned further technical solution are as follows: by optimizing the construction and commissioning of cavity-making wells in batches and stages, the cavity can have preliminary gas storage capacity during the cavity construction period and gas storage capacity without a bottom gas during the expansion period, thus advancing the entire cavity gas storage stage. This avoids the disadvantages of the traditional cavity-making mode, which has a long cavity construction time and the cavity being idle before well completion and unable to exert its gas storage capacity. At the same time, this invention fully utilizes the limited brine receiving and regulation capabilities of salt chemical enterprises.

[0064] Furthermore, the distance between the wellhead of a directional well and the wellhead of a vertical well is calculated using the following formula:

[0065] L = (P + D) / 2, where L is the distance between the wellhead of the directional well and the wellhead of the vertical well, P is the safety pillar spacing designed between two adjacent cavities, and D is the maximum designed diameter of a single cavity.

[0066] The beneficial effect of adopting the above-mentioned further technical solution is that it facilitates the directional well shot trajectory to maintain a corresponding safe distance from the designed cavity wall.

[0067] A method for the rolling construction and commissioning of a salt cavern gas storage facility's cavitation chamber and gas storage, the specific technical solution of which is as follows:

[0068] Step 1: Well Type and Well Pattern: Constructing a single-cavity, high-efficiency dissolution well type and well pattern combining vertical and directional wells.

[0069] S110: Each cavity is constructed and injected using a combination of one vertical well 1 and one directional well 2.

[0070] As a preferred option, a vertical well is drilled to the bottom depth of the cavity at the target cavity construction location and cemented. The depth of the production casing entering the salt layer and the depth of the casing shoe to the top neck of the cavity both meet the cavity design and operation requirements.

[0071] As a preferred option, the wellhead of directional well 2 is (P+D) / 2 away from the wellhead of vertical well 1. The bottom of vertical well 1 is the target point of the directional well. The well trajectory of directional well 2 should maintain a corresponding safe distance from the designed cavity wall. It is designed to connect with the bottom of vertical well 1 only at the target point depth. A 3-5m open hole section is reserved at the bottom of vertical well 1 where directional well 2 connects to the directional well 1. The entire section of directional well 2 is cemented.

[0072] Where: P is the safety pillar spacing designed between two adjacent chambers; D is the maximum diameter designed for a single chamber.

[0073] S120: Vertical well 1 serves as a water injection channel during the trenching and cavity construction phases, and as a natural gas injection and production channel during the expansion phase and thereafter; directional well 2 serves as a freshwater and brine injection and production channel throughout the entire construction and operation cycle.

[0074] S130: The design involves three directional wells on one drilling platform, and a well network layout pattern is designed to facilitate centralized scheduling of water circulation during cavity construction and operation.

[0075] Step 2: Cavity shape design: The cavity construction phase is divided into the trenching phase, cavity construction phase, expansion phase and gas storage phase, which requires an overall design of the shape development of the entire cavity in multiple stages.

[0076] As a preferred option, during the expansion period, the cavity has been dissolved to the target final cavity top depth. During the gas production period each year, all natural gas is extracted by injecting unsaturated brine or fresh water generated by the trench well through directional well 2. During the gas injection period, natural gas is injected through vertical well 1 and most of the brine in the effective cavity and sediment pores is discharged through directional well 2 to complete an expansion cycle until the entire cavity reaches the target shape and volume, and the cavity is converted to the gas storage period.

[0077] As a preferred option, the cavity shape is designed during the trenching and cavity construction stages, taking into account the cavity shape development caused by the injection of fresh brine or fresh water and dissolution during the expansion period of the directional well, so as to meet the stability requirements of the cavity and cavity group.

[0078] Step 3: Trenching period: Single-layer cavity-building tubing is installed in both wells with single cavities, and a vertical circulation mode of injecting fresh water in directional well 2 and extracting brine in vertical well 1 is adopted for trenching and cavity building.

[0079] As a preferred option, the tail end of the cavity-making string 5 of the directional well is connected to the screen pipe head (directional well screen pipe inlet 8) to prevent insoluble substances from being sucked into the string during brine extraction. The annulus between the cavity-making string 5 of the directional well and the production casing needs to be injected with a liquid phase solvent inhibitor.

[0080] As a preferred option, the cavity-making string 6 of the vertical well adopts a gas-tight string, which is injected with natural gas as an inhibitor into the annulus of the production casing.

[0081] Step 4: Cavity building period: Vertical reverse circulation cavity building (groove construction) is adopted by injecting fresh water into vertical wells and extracting brine from directional wells. The cavity shape development is controlled by adjusting the cavity building tubing 6 and the cavity building natural gas inhibitor 4 in stages.

[0082] Step 5: Expansion Period: After the cavity construction period, the cavity top has been dissolved to the design depth. The cavity construction string 6 of the vertical well is replaced with a natural gas injection / production string, and well completion operations such as string setting and sealing are carried out. During this stage, only directional well 2 is used as the injection / production channel for fresh water, fresh brine, and saturated brine.

[0083] Preferably, the injection rate and concentration requirements of fresh water or brine, as well as the design for controlling the gas-water interface depth, should be carried out under the guidance of numerical simulation software.

[0084] Step 6: Gas storage period: After the cavity is expanded to the target shape and volume, all brine in the cavity is discharged, and the cavity is put into the gas storage period. The directional well 2 is safely shut in. After that, the directional well 2 is only used as a channel for brine reinjection during vertical well workover or extreme emergency gas production.

[0085] Step 7: Rolling Construction and Commissioning Design of the Concentration Chamber and Gas Storage: By optimizing the combination of the tank construction period, cavity construction period, expansion period, and gas storage period within one year, including the spring settling period, gas injection period, autumn settling period, and gas extraction period, the goal is to achieve the highest concentration of brine for external transmission and discharge, and the maximum usable gas storage capacity. Specific details are as follows:

[0086] S610: During the spring quiescent period, the cavity is built and brine is extracted. During emergency and phased gas injection during this period, the cavity is first selected to actively and steadily adjust the downward movement of the anti-solvent interface for gas storage during the cavity building period; the cavity is then selected to inject gas and discharge brine for gas storage during the expansion period.

[0087] S620: During the gas injection period, it makes full use of the brine regulation capacity, uses the expansion period cavity to smoothly inject gas and discharge brine, and uses the gas storage period cavity to undertake the main and peak gas injection.

[0088] S630: During the autumn settling period, the cavity is built up during the cavity construction period for brine extraction. During emergency and phased gas extraction during this period, without affecting the cavity construction control, the cavity is first selected to actively adjust the anti-solvent interface upwards for gas extraction; then, the cavity is started with a large-volume sinking during the sinking period, and the unsaturated brine generated during the sinking period is injected into the cavity during the expansion period for gas extraction.

[0089] S640: During the gas extraction period, the trenching of the cavity is initiated during the trenching period. The stable unsaturated brine generated during the trenching period is injected into the expansion cavity for gas extraction. The cavity during the gas storage period is used to undertake the main and peak gas extraction.

[0090] Compared with the prior art, the present invention has the following advantages and effects:

[0091] Both directional and vertical wells have only one cavity-making string. Without increasing the well diameter and wellhead pump pressure, the cavity-making discharge rate can be increased by more than 100%, and the single-cavity cavity-making speed can be increased by more than 100%.

[0092] Except for the unsaturated brine produced during the initial construction period of the cavity, which needs to be transported out or recirculated into the cavity, the low-concentration brine produced during the subsequent construction period is injected into the cavity during the expansion period to increase the proportion of working gas in the cavity; the cavity brine discharge point is located at the lowest point of the cavity, with extremely high brine concentration, making full use of the salt chemical enterprise's production capacity.

[0093] For salt rock layers with high insoluble content, the volume of sediment pores at the bottom of the cavity can be fully utilized, greatly improving the gas storage volume gain per unit thickness of salt layer. During the expansion period, the cavity can achieve favorable gas storage space by reinjecting unsaturated brine. All natural gas in the gas storage space is working gas, with no bottom gas.

[0094] When there are risks or malfunctions in the gas injection and production tubing, natural gas in the cavity can be discharged by reinjecting brine through the directional well, and routine repair work can be carried out on the gas injection and production tubing and equipment in the vertical well.

[0095] By optimizing the construction and commissioning of cavity-making wells in batches and stages, the cavity can have preliminary gas storage capacity during the cavity construction period and gas storage capacity without a base gas during the expansion period. This advances the entire cavity gas storage stage and avoids the drawbacks of the traditional cavity-making mode, such as long cavity construction time and the cavity being idle before well completion and unable to exert its gas storage capacity. At the same time, it makes full use of the limited brine receiving and regulation capacity of salt chemical enterprises.

[0096] This invention proposes a single-cavity well design for creating a vertical cavity using a combination of vertical and directional wells. By using the lowest point at the bottom of the cavity as the cavity creation and brine discharge point, the brine concentration during the cavity creation stage is maximized. At the same time, the volume of sediment pores below the sediment surface of the cavity can be fully discharged, making full use of the potential gas storage space of the salt rock gas storage facility. This design is highly effective in addressing the shortcomings of common salt rock storage facilities, such as multiple interlayers and low overall NaCl content.

[0097] The construction of the cavity is divided into different stages. By combining different gas injection and extraction stages with the cavity dissolution and gas storage requirements of different stages, the cavity can have gas storage capacity at an earlier stage, avoiding inefficient situations such as reinjection or discharge of low-concentration brine. This fully utilizes the brine receiving capacity and production regulation capacity of the salt chemical enterprise, and promptly transforms the formed cavity into an effective gas storage space.

[0098] An embodiment of the present invention provides a method for the rolling construction and commissioning of a salt cavern gas storage cavity and gas storage, which can be a method for constructing a gas storage cavity through convection between two wells in layered salt rock, comprising the following steps:

[0099] Example 1: Taking a salt mine in a certain area as an example, the effectiveness of this technical method is further illustrated, and the implementation of the present invention is described as follows:

[0100] S100: A salt mine is located in a basin. Salt layers 12-37 in this basin are currently the optimal reservoir construction section, with an average total thickness of 201.4m at the sedimentary center, a salt layer thickness of 99.8m, and an interlayer thickness of 101.6m. Salt layers 1-11 serve as the reservoir's roof, with a total thickness of 82.5m. The overall NaCl content of salt layers 12-37 in the reservoir construction section is 50.3%, the cavity top depth is 935m, and the designed cavity height is 150m. The final cavity shape design is as follows... Figures 2 to 4 The cavity volume estimate is shown in Table 1.

[0101] Table 1. Shapes of a single cavity in a salt mine in a certain area

[0102]

[0103] S200: Drill a vertical well to a depth of 1085m, run production casing to 905m and cement it. The directional wellhead is 120m from the vertical wellhead. Drill the directional well to the bottom of the vertical well, leaving a 3m open hole section. Run production casing and cement the remaining sections. The production casing size for both the vertical and directional wells is 9-5 / 8". The cavity-building string for both the vertical and directional wells is 7" tubing. Connect the natural gas injection / production pipeline to the vertical wellhead. Inject natural gas as a solvent inhibitor into the annulus of the cavity-building string and production casing in the vertical well. The section before the cavity-building string in the directional well is a screen pipe string, which is in the open hole section below the casing shoe depth. Inject diesel fuel as a solvent inhibitor into the annulus of the cavity-building string and production casing in the directional well.

[0104] S300: During the trenching phase, fresh water is injected through directional wells and brine is discharged through vertical wells; during the cavity construction phase, the cavity shape is constructed by adjusting the water injection depth of the cavity-making tubing and the depth of the natural gas inhibitor interface in stages; during the expansion phase, the cavity-making tubing in the vertical well is replaced with an injection-production tubing and set, and the corresponding safety control downhole tool combination is installed.

[0105] S400: For this region, the volume of the dissolution space during the three stages of trenching, cavity building, and expansion is limited to 1×10⁻⁶. 4 m 3 28×104 m 3 Fresh water is reinjected during the expansion period of the cavity, or unsaturated brine produced in the cavity during the construction period (assuming an average concentration of 180 g / L).

[0106] Table 2. Cavity volume expansion under different reinjection modes

[0107]

[0108] S500: During the expansion period, to ensure that the natural gas-brine interface is not too low, causing natural gas to break through and spray out from the directional wellhead, the minimum interface depth between natural gas and brine is set at 1065m, with a 20-30m brine height reserved to ensure gas injection safety. It is assumed that the reserved space at the bottom accounts for 20% of the total sediment space. Table 2 shows the number of cycles required for the cavity shape and volume to develop to the required volume during the gas storage period under different reinjection expansion modes. At the same time, the initial volume of the cavity during the expansion period can be adjusted according to the overall gas storage construction needs and brine regulation capacity.

[0109] S600: The freshwater replenishment for the cavity-making process in this region can be sourced from a certain location. The brine receiving capacity of the salt chemical enterprise is approximately 1000 cubic meters per hour. During the construction phase, the discharge rate of each cavity is 200 cubic meters per hour. Approximately 85% of the brine volume returned to the salt production line is freshwater from the salt chemical plant. The maximum freshwater return from the salt production line is set to meet the utilization standards for external transmission and discharge, up to 30%. In other words, the ratio of freshwater return to brine from the salt chemical enterprise can be adjusted and fluctuated within the range of 58% to 85% in the cavity-making system.

[0110] Based on the geological conditions of the region, this receiving capacity can create a dissolution space volume of 2.29 million cubic meters, of which 460,000 cubic meters is above the sediment surface and 660,000 cubic meters is in the sediment pores. The operating pressure range for this deep salt cavity gas storage period is 7-17 MPa, generating approximately 100 million cubic meters of working gas annually.

[0111] like Figure 2 As shown, a water-soluble cavity-building system for a salt cavern gas storage facility, used to realize the above-mentioned method for rolling construction and commissioning of the salt cavern gas storage facility's cavity and gas storage, is disclosed. The water-soluble cavity-building system includes: a vertical well 1, a directional well 2, a natural gas pipeline 3, a cavity-building natural gas inhibitor 4, a cavity-building tubing string 5 for the directional well, a cavity-building tubing string 6 for the vertical well, insoluble sediment 7, a directional well screen pipe opening 8, and a directional well protective fluid 9. The vertical well 1 is vertically arranged, and the bottom of the directional well 2 is connected to the bottom of the vertical well 1. The natural gas pipeline 3 and the cavity-building tubing string 6 of the vertical well are both arranged in the vertical well 1. The cavity-building natural gas inhibitor 4 is located outside the cavity-building tubing string 6 of the vertical well. The insoluble sediment 7 and the directional well screen pipe opening 8 are both located at the bottom of the vertical well 1. The cavity-building tubing string 5 of the directional well is located in the directional well 2, and the directional well protective fluid 9 is located outside the cavity-building tubing string 5 of the directional well.

[0112] like Figure 3 As shown, a system for the rolling construction and commissioning of a salt cavern gas storage cavity and gas storage after injection and production completion is used to realize the above-mentioned method for the rolling construction and commissioning of the salt cavern gas storage cavity and gas storage. The system after injection and production completion includes: a vertical well 1, a directional well 2, a first injection and production gas string 10, a packer 11, a second injection and production gas string 12, and natural gas 13. The first injection and production gas string 10 is located at the top of the vertical well 1, the second injection and production gas string 12 is located at the bottom of the vertical well 1, the packer 11 is located between the first injection and production gas string 10 and the second injection and production gas string 12, the natural gas 13 is stored in the second injection and production gas string 12, and the bottom of the directional well 2 is connected to the bottom of the vertical well 1.

[0113] In this invention, multiple directional wells 2 are arranged adjacent to each other, and multiple vertical wells 1 are located in the radial direction around the directional wells 2. Each vertical well 1 is connected to one of the directional wells 2 in a one-to-one correspondence, forming a triangular well network. It should be noted that this invention is merely an example of a triangular well network; those skilled in the art can design well networks of different shapes according to actual needs.

[0114] like Figure 4 As shown, Figure 4 The diagram illustrates the well network layout, where the outer ring wells are all vertical wells (1). To demonstrate the triangular well network relationship, an exemplary design of 18 wells is provided. The inner ring wells, located in the center, are directional wells (2) that connect to each vertical well (1). Because directional wells (2) are managed intensively, only 3 directional wells are needed per well site. The dashed arrows in the diagram represent the flow trajectory and direction of natural gas.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for the rolling construction and commissioning of a salt cavern gas storage tank's cavitation chamber and gas storage, characterized in that, include: S1. Construct a single-cavity dissolution well type and well pattern combining vertical and directional wells; wherein, the cavity creation and brine discharge point is located at the bottom of the cavity; S2. The construction and operation phases of the cavity are divided into the trench construction period, the cavity construction period, the expansion period, and the gas storage period. S3. Optimize the combination of trenching period, cavity construction period, capacity expansion period and gas storage period with static period, gas injection period, static period and gas extraction period. Step S2 includes: S21. During the trenching phase, a single-layer cavity-building string is installed in both vertical and directional wells. A vertical circulation mode is adopted for trenching and cavity building, with fresh water injection in directional wells and brine extraction in vertical wells. S22. During the cavity construction period, a vertical reverse circulation mode of injecting fresh water into vertical wells and extracting brine from directional wells is adopted to construct the cavity. The cavity shape development is controlled by adjusting the cavity construction tubing and solvent depth in the vertical wells in stages until the cavity top is dissolved to the design depth. S23. During the expansion period, the cavity-making string of the vertical well is replaced with a natural gas injection and production string, and the string is set to complete the well completion operation. The directional well serves as the injection and production channel for fresh water, fresh brine and saturated brine until the cavity is expanded to the target shape and volume, and then all the brine in the cavity is discharged. S24. During the gas storage period, the directional well is shut in, serving as a channel for brine reinjection during vertical well workover and emergency gas production. Step S3 includes: S31. During the quiescent period, brine is extracted from the cavity during the cavity building period, and during emergencies and phased gas injection, the cavity during the cavity building period is actively and steadily adjusted to move the solvent interface downward and use the cushion layer to store natural gas, or the cavity during the expansion period is injected to steadily replace the brine in the cavity. S32. During the gas injection period, make full use of the brine's regulating capacity, use the expansion period cavity to smoothly inject gas and discharge brine, and use the gas storage period cavity to undertake the main and peak gas injection. S33. During the settling period, the cavity is built during the cavity construction period for brine extraction. In case of emergency or phased gas extraction, the cavity is actively adjusted during the cavity construction period to move the interface of the inhibitory solvent upward for gas extraction. Alternatively, the cavity is started during the tank construction period with a large discharge capacity to build the tank, and the unsaturated brine generated during the tank construction period is injected into the cavity during the expansion period to replace the gas extraction. S34. During the gas extraction period, start the trenching of the trenching chamber, inject the stable unsaturated brine generated during the trenching period into the expansion chamber for gas extraction, and utilize the gas storage chamber to undertake the main and peak gas extraction.

2. The method for the rolling construction and commissioning of a salt cavern gas storage chamber and gas storage as described in claim 1, characterized in that, Step S1 includes: S11. Drill a vertical well to the bottom depth of the cavity at the target cavity construction location and cement the well. S12. Drill a directional well, connect the bottom of the directional well to the bottom of the vertical well, and reserve a 3-5m open hole section at the bottom of the position where the directional well connects to the vertical well; S13. Three directional wells are placed on one drilling platform, and a well layout pattern for building a reservoir network is designed.

3. The method for the rolling construction and commissioning of a salt cavern gas storage tank and its gas storage chamber according to claim 1, characterized in that, Before step S21, the following steps are included: comprehensively designing the cavity shape of the trenching and cavity building stages, and pre-setting the cavity shape generated by directional injection of fresh brine or fresh water during the expansion stage.

4. The method for the rolling construction and commissioning of a salt cavern gas storage tank and its gas storage chamber according to claim 1, characterized in that, In step S21, the tail end of the cavity-making string of the directional well is connected to the head of the screen pipe, and the cavity-making string of the directional well is set up in annulus with the production casing. The cavity-making string of the vertical well adopts a gas-tight string, and the cavity-making string of the vertical well is set up in annulus with the production casing. Insoluble sediment is provided at the bottom of the vertical well. In step S23, the injection rate, concentration and gas-water interface depth of fresh water or brine are designed using numerical simulation software.

5. The method for the rolling construction and commissioning of a salt cavern gas storage tank and its gas storage chamber according to claim 1, characterized in that, In step S34, during the gas production period, unsaturated brine generated in the trenching cavity during the trenching period is injected into the expansion cavity through a directional well to replace the natural gas in the cavity. In step S32, natural gas is injected through a vertical well during the gas injection period, and most of the brine in the effective cavity and sediment pores is discharged through a directional well, completing one expansion cycle until the entire cavity reaches the target shape and volume, and the cavity is converted to the gas storage period.

6. The method for the rolling construction and commissioning of a salt cavern gas storage tank and its gas storage chamber according to claim 1, characterized in that, The distance between the wellhead of a directional well and the wellhead of a vertical well is calculated using the following formula: L=(P+D) / 2, where L is the distance between the wellhead of the directional well and the wellhead of the vertical well, P is the safety pillar spacing designed between two adjacent cavities, and D is the maximum designed diameter of a single cavity.

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