Salt cavern gas storage well structure and cavity forming method

Abstract

This invention discloses a brine discharge well structure for a salt cavern gas storage facility, comprising a wellbore extending from the ground to the salt cavern, a casing inside the wellbore, and a packer in the middle of the casing. The packer has a first state and a second state. In the first state, it divides the space inside the casing into an upper chamber and a lower chamber; in the second state, it connects the upper and lower chambers. A hanger is located at the top of the wellbore, and a drainage tubing string and a brine discharge pump are connected downwards to the hanger. The brine discharge pump is lowered by the hanger to above the packer, and the packer is in the second state when the brine discharge pump is performing brine discharge operations. This invention also discloses a cavity-making method for the salt cavern gas storage facility, in which the packer is in the first state, the brine discharge pump is lowered to a preset position in the middle of the casing; the packer is then in the second state, and brine is pumped out by the brine discharge pump until gas begins to rise, at which point the packer returns to the first state. This invention has high brine discharge efficiency and does not require pressurized injection-production conversion after brine discharge.

Description

Technical Field

[0001] This invention relates to the field of salt cavern well structure technology, and in particular to a brine discharge well structure and cavity creation method for a salt cavern gas storage facility. Background Technology

[0002] The gas storage device in the compressed air energy storage system utilizes underground salt caverns extracted from water. Due to the extremely low permeability and good creep and damage recovery characteristics of salt rock, salt caverns offer high safety as underground energy storage reservoirs. When using salt caverns as gas storage, all the brine within the cavity needs to be drained. Traditionally, brine drainage is achieved by injecting high-pressure air into the salt cavern using an air compressor or nitrogen compressor. Existing technology also employs a brine drainage pump directly through a drainage well extending into the bottom of the salt cavern. However, this method has the following drawbacks: First, the flow rate and head of the drainage pump are mutually restrictive; the higher the head, the lower the flow rate, and vice versa. A drainage pump extending into the bottom of the salt cavern has a high head but a low flow rate, making it difficult to improve drainage efficiency. Secondly, the process of creating a cavity and switching between injection and production after gas leakage occurs in the salt cavern is complex. Either the brine pump and part of the pipeline are left in the well, or if the brine pump is to be retrieved, pressurized operation is required, which is a high-risk and high-difficulty operation. Summary of the Invention

[0003] To address the shortcomings of the existing technology, this invention provides a brine discharge well structure for a salt cavern gas storage facility, solving the problems of low brine discharge efficiency and complex cavity construction and injection-production conversion. This invention also provides a cavity construction method for a salt cavern gas storage facility.

[0004] The technical solution of the present invention is as follows: A brine discharge well structure for a salt cavern gas storage facility includes a wellbore extending from the ground to the salt cavern. A casing is provided inside the wellbore, and a packer is provided in the middle of the casing. The packer has a first state and a second state. The first state is that the space inside the casing is divided into an upper chamber and a lower chamber. The second state is that the upper chamber and the lower chamber are connected. A hanger is provided at the top of the wellbore. A drainage pipe string and a brine discharge pump are connected downward to the hanger. The brine discharge pump is lowered by the hanger to the top of the packer. When the brine discharge pump is performing brine discharge operations, the packer is in the second state.

[0005] Furthermore, the packer is a spring packer, which maintains the first state in its natural state. The bottom of the discharge pump is provided with a top-opening short section. When the discharge pump is lowered into place, the top-opening short section opens the spring packer, causing the spring packer to maintain the second state.

[0006] Furthermore, the top of the hanger is connected to a four-way valve, and the interface of the four-way valve is connected to a brine discharge pipe and a clean water injection pipe.

[0007] Furthermore, a gate valve is provided between the hanger and the wellhead four-way valve.

[0008] Furthermore, the hanger is provided with a bottom four-way valve, through which the cable of the brine pump enters the wellbore.

[0009] Furthermore, the brine discharge pump is a multi-stage centrifugal deep well pump.

[0010] Another technical solution of the present invention is as follows: a cavity-making method for a salt cavern gas storage tank, based on the aforementioned brine discharge well structure of the salt cavern gas storage tank, comprising: placing the packer in a first state, lowering the brine discharge pump to a preset position in the middle of the casing; placing the packer in a second state, and pumping brine by the brine discharge pump until the gas begins to rise, and then returning the packer to the first state.

[0011] Another technical solution of the present invention is as follows: a cavity-making method for a salt cavern gas storage tank, based on the aforementioned brine discharge well structure of the salt cavern gas storage tank, comprising: placing the packer in a first state, lowering the brine discharge pump to a preset position in the middle of the casing, opening the packer with a top-opening short section to keep the packer in the second state, pumping brine with the brine discharge pump until the gas begins to rise, raising the brine discharge pump to disengage the top-opening short section from the packer and return the packer to the first state.

[0012] Furthermore, when the brine pump is pumping out brine, gas is injected through the gas injection well connected to the top of the salt cavern to return the packer to its first state. Then, the injection and production pipe is lowered into the brine pump until it passes through the packer at the bottom.

[0013] Compared with the prior art, the advantages of the technical solution provided by the present invention are as follows: By installing a brine discharge pump and packer in the middle of the casing, the pump head is reduced, the brine discharge flow rate is increased, efficiency is improved, the gas injection and brine discharge cycle is shortened, and the construction cost of the gas storage facility is reduced. In the preferred embodiment, a top-opening short section on the brine discharge pump allows the packer's state to automatically switch according to the pump's height, making operation more convenient.

[0014] Meanwhile, a brine pump is installed above the packer. After the brine is drained, the brine pump and the corresponding drain tubing can be lifted without pressurized operation due to the separation of the packer, and then replaced with injection tubing. The conversion between cavity creation and injection is simple. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the initial state structure of the brine discharge well of the salt cavern gas storage facility as an example.

[0016] Figure 2 This is a schematic diagram of the brine discharge state structure of the brine discharge well structure of the salt cavern gas storage facility as an example.

[0017] Figure 3 This is a schematic diagram of the brine discharge well structure of the salt cavern gas storage facility, illustrating the brine discharge process and the replacement injection-production process after the brine discharge is completed. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. After reading this description, any modifications of this description in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0019] Please combine Figures 1 to 3 As shown, the brine discharge well structure of the salt cavern gas storage facility involved in this embodiment includes a wellbore formed by drilling that extends from the ground to the salt cavern 12. The wellbore is equipped with a casing 1, which constitutes the basic channel for the creation of the salt cavern 12 cavity and subsequent gas storage operation.

[0020] A hanger 2 is installed at the top of the wellbore at the wellhead position. It is used to support and suspend the brine pump 3 and related tubing, and to ensure that the downhole equipment is stably positioned at the target location.

[0021] In a preferred embodiment, the brine discharge pump 3 is a multi-stage centrifugal deep well pump, which consists of multiple pump stages connected in series. Each stage comprises an impeller and a guide vane (stator). The pump body, impeller, and guide vane, which are in direct contact with the brine, are preferably made of duplex stainless steel. The brine discharge pump 3 operates using a variable frequency speed control method, and a slow-closing check sieve structure is installed at the pump outlet. The brine discharge pump 3 is located at the bottom of the discharge tubing string 4 and is arranged via a hanger 2. The brine discharge pump 3 is not located at the bottom of the well, but is suspended in the middle section of the casing 1, i.e., at the middle depth of the wellbore. Brine is discharged at this position to reduce the brine discharge head, increase the brine discharge flow rate, and meet the requirements for rapid cavity creation.

[0022] To ensure the brine discharge of the brine pump 3 at its intermediate position and to effectively seal the salt cavern 12 after discharge, a packer 5 is installed in the middle section of the casing, located below the brine pump 3. The packer 5 is controlled and has two states: a first state and a second state.

[0023] In the first state, the packer 5 completely separates the upper and lower sides, thus dividing the space inside the sleeve 1 into an upper chamber and a lower chamber, with the brine pump 3 located in the upper chamber. In the second state, the packer 5 allows the upper and lower chambers to be connected.

[0024] To facilitate automatic control of the packer 5 and link the operation of the brine pump 3 with the state of the packer 5, in a preferred embodiment, the packer 5 is selected as a spring packer with a self-closing sealing plate 5a that can be opened downwards. After the packer 5 is set in a predetermined position, in its natural state, the self-closing sealing plate 5a closes the channel of the packer 5 by elastic action, forming the first state. At the same time, in conjunction with the spring packer, a top-opening short section 3a is provided at the bottom of the brine pump 3. When the brine pump 3 is lowered to the working position, the top-opening short section 3a on the brine pump 3 cooperates with the spring packer to open the self-closing sealing plate 5a, opening the brine flow channel between the upper and lower chambers. When the downhole liquid level drops to near the suction port of the brine discharge pump 3 and the gas begins to rise, the brine discharge pump 3 is lifted to disengage the top-opening short section from the spring packer. The self-closing sealing plate 5a of the spring packer automatically closes the flow channel under the elastic recovery action, thereby cutting off the gas upward path and realizing automatic termination of brine discharge or pump stop protection.

[0025] The brine discharge well structure of the salt cavern gas storage facility also includes a wellhead device and control system. The wellhead device includes a gate valve 6, a bottom four-way valve, a wellhead four-way valve 7, a clean water injection pipe 8, a brine discharge pipe 9, and a cable passage sealing assembly. The bottom four-way valve is located at the hanger 2, and the cable passage sealing assembly is located at the side port of the bottom four-way valve, allowing the power cable 10 to pass through and enter the casing 1 while ensuring pressure sealing at the wellhead. The top of the hanger 2 is connected to the wellhead four-way valve 7 via the gate valve 6. The side port of the wellhead four-way valve 7 is connected to the brine discharge pipe 9 to discharge brine to the surface, and the top port of the wellhead four-way valve 7 is connected to the clean water injection pipe 8 to inject clean water into the well.

[0026] The control system mainly includes an electrical control cabinet, a frequency converter control unit, a flow monitoring unit, a pressure monitoring unit, and a liquid level / operating condition identification unit. It is mainly used to adjust the amount of clean water injected, the speed of the deep well pump, and the flow rate of the brine discharge, as well as to control the pump to stop or further alarm based on the operating condition of the brine discharge pump.

[0027] The method for creating a cavity using the brine discharge well structure of the salt cavern gas storage facility of the present invention is as follows: A gas injection well 11 and a brine discharge well are formed by drilling in the salt cavern, wherein the gas injection well 11 extends from the surface to the top of the salt cavern 12; Install a hanger 2 at the wellhead of the brine discharge well, and send the brine discharge pump 3, brine discharge tubing 4 and power cable 10 into the well to the target depth; Install wellhead equipment, including gate valve 6 and wellhead four-way valve 7; The power cable 10 of the brine pump 3 passes through the bottom four-way side opening of the hanger 2 and is sealed. The side interface of the wellhead four-way 7 is connected to the brine discharge pipe 9, and the top interface is connected to the clean water injection pipe 8; Open the packer 5 to put it in the second state. As a preferred embodiment, select a spring packer and a matching brine pump 3 with a top opening short section 3a. When the brine pump 3 is sent to the target height, the packer 5 is already in the second state. Start the brine pump 3 and inject gas through the gas injection well 11 to continuously lift the generated brine from the well to the ground and discharge it through the brine discharge pipe 9. The flow rate at the wellhead determines whether the brine pump 3 discharges only brine or a mixture of brine and gas. Since the brine well extends to the bottom of the salt cavern 12 during construction, the emergence of gas indicates that there is little brine remaining in the cavity, at which point the brine discharge process can be considered complete. By sealing the packer 5 to its first state, the brine pump 3 and the brine discharge tubing 4 can be extracted. In a preferred embodiment, a spring packer and a matching brine pump 3 with a top-opening short section 3a are selected. After the brine discharge process is completed, the brine pump 3 and the brine discharge tubing 4 can be directly extracted, with the top-opening short section 3a of the brine pump 3 disengaging from the packer 5, placing the packer 5 in its first state. Then, the injection / production pipe 13 is lowered and connected to the packer 5. The packer 5 is opened to carry out gas storage and release work. When a spring packer is used, the injection / production pipe 13 pushes open the self-closing sealing plate 5a of the spring packer 5 to carry out gas storage and release work.

Claims

1. A brine discharge well structure for a salt cavern gas storage facility, comprising a wellbore extending from the ground to the salt cavern, wherein a casing is provided inside the wellbore, characterized in that, A packer is provided in the middle of the casing. The packer has a first state and a second state. The first state is to divide the space inside the casing into an upper chamber and a lower chamber. The second state is to connect the upper chamber and the lower chamber. A hanger is provided at the top of the wellbore. The hanger is connected downward to a drain tubing string and a brine pump. The brine pump is lowered by the hanger to the top of the packer. When the brine pump is performing brine drainage operation, the packer is in the second state.

2. The brine discharge well structure of the salt cavern gas storage facility according to claim 1, characterized in that, The packer is a spring packer. The spring packer maintains the first state in its natural state. The bottom of the discharge pump is provided with a top-opening short section. When the discharge pump is lowered into place, the top-opening short section opens the spring packer, so that the spring packer maintains the second state.

3. The brine discharge well structure of the salt cavern gas storage facility according to claim 1, characterized in that, The top of the hanger is connected to a four-way valve, and the interface of the four-way valve is connected to a brine discharge pipe and a clean water injection pipe.

4. The brine discharge well structure of the salt cavern gas storage facility according to claim 3, characterized in that, A gate valve is provided between the hanger and the wellhead four-way valve.

5. The brine discharge well structure of the salt cavern gas storage facility according to claim 1, characterized in that, The hanger is equipped with a bottom four-way valve, and the cable of the brine pump enters the wellbore through the side opening of the bottom four-way valve.

6. The brine discharge well structure of the salt cavern gas storage facility according to claim 1, characterized in that, The brine discharge pump is a multi-stage centrifugal deep well pump.

7. A method for creating a cavity in a salt cavern gas storage tank, characterized in that, Based on the brine discharge well structure of the salt cavern gas storage facility according to any one of claims 1 to 6, the method includes: placing the packer in a first state and lowering the brine discharge pump to a preset position in the middle of the casing; placing the packer in a second state and pumping brine by the brine discharge pump until the gas begins to rise, then returning the packer to the first state.

8. The cavity-building method for a salt cavern gas storage tank according to claim 7, characterized in that, When the brine pump is pumping out brine, gas is injected through the gas injection well connected to the top of the salt cavern to return the packer to its first state. Then, the injection and production pipe is lowered into the brine pump until it passes through the packer at the bottom.

9. A method for creating a cavity in a salt cavern gas storage tank, characterized in that, Based on the brine discharge well structure of the salt cavern gas storage facility as described in claim 2, the method includes: placing the packer in a first state, lowering the brine discharge pump to a preset position in the middle of the casing, opening the packer with a jacking section to keep the packer in the second state, pumping brine with the brine discharge pump until the gas begins to rise, raising the brine discharge pump to disengage the jacking section from the packer and return the packer to the first state.

10. The cavity-building method for a salt cavern gas storage tank according to claim 9, characterized in that, When the brine pump is pumping out brine, gas is injected through the gas injection well connected to the top of the salt cavern to return the packer to its first state. Then, the injection and production pipe is lowered into the brine pump until it passes through the packer at the bottom.

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