Salt cavern gas storage cavity creation method

Abstract

The application belongs to the technical field of natural gas storage, and discloses a salt cavern gas storage cavity forming method. The salt cavern gas storage cavity forming method comprises the following steps: S1, drilling a cavity forming well until a first salt layer below a thick interlayer is drilled to, installing a pipe string assembly in the cavity forming well, and extending the pipe string assembly into the first salt layer; S2, forming a first cavity in the first salt layer; S3, injecting gas into the first cavity, and making brine in the first cavity discharge through the pipe string assembly; S4, continuously injecting gas until the pressure in the first cavity reaches a preset pressure value P1; S5, discharging the gas in the first cavity until the pressure in the first cavity decreases to the atmospheric pressure; S6, extending the pipe string assembly into a second salt layer above the thick interlayer; and S7, forming a second cavity in the second salt layer until the thick interlayer collapses, and the second cavity is formed in the second salt layer and communicates with the first cavity. The salt cavern gas storage cavity forming method can promote the collapse of the interlayer and expand the effective gas storage space of the salt rock.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas storage, and particularly relates to a salt cavern gas storage cavity forming method. BACKGROUND

[0002] The salt cavern gas storage refers to a cavern cavity formed by using water-soluble salt mining in a salt layer or salt dome to store natural gas, which has the following three characteristics: 1. low proportion of cushion gas - the working gas accounts for about 65% of the total expansion proportion; 2. high flexibility - efficient and convenient switching between gas injection and extraction; 3. high safety - even if it encounters geological disasters or external attacks, it can still be safe and sound, which is an ideal natural gas storage method.

[0003] At present, the commonly used salt cavern gas storage is mostly constructed in the stratified salt rock of lacustrine sediment, which has the characteristics that the salt rock and the insoluble interlayer are alternately produced, the number of ore layers is large, and the thickness of single layer changes greatly; in the case that the thickness of the insoluble interlayer is small, the interlayer can collapse and fall during the water-soluble cavity forming process, thereby accumulating residual materials at the bottom of the salt cavity; the limit thickness of the traditional collapsible interlayer is about 10-20 meters, if there is an interlayer with a thickness greater than 20 meters (thick interlayer) in the stratum, the conventional cavity forming process needs to avoid the interlayer, and only a single cavity can be constructed above or below the thick interlayer, thereby causing problems such as low utilization rate of salt rock and small effective gas storage space of salt cavity. SUMMARY

[0004] The purpose of the present application is to provide a salt cavern gas storage cavity forming method, which can promote the collapse of the interlayer and expand the effective gas storage space of the salt rock.

[0005] To achieve this purpose, the present application adopts the following technical solutions:

[0006] The salt cavern gas storage cavity forming method comprises:

[0007] S1, drilling a cavity forming well downward from the ground until a first salt layer below the thick interlayer is drilled, installing a pipe column assembly in the cavity forming well, and extending the pipe column assembly into the first salt layer;

[0008] S2, using the pipe column assembly to form a first cavity in the first salt layer;

[0009] S3, injecting gas into the first cavity through the pipe column assembly, so that the brine produced by dissolving the first salt layer in the first cavity is discharged through the pipe column assembly;

[0010] S4, continue to inject the gas until the pressure in the first cavity reaches a preset pressure value P1;

[0011] S5. Use the tubing assembly to discharge the gas from the first cavity until the pressure in the first cavity drops to atmospheric pressure;

[0012] S6. Move the tubing assembly so that it extends into the second salt layer above the thick interlayer;

[0013] S7. Using the tubing assembly, create a cavity in the second salt layer until the thick interlayer collapses, forming a second cavity in the second salt layer, and the second cavity is connected to the first cavity.

[0014] Preferably, step S2, using the tubing assembly to create a cavity in the first salt layer, includes:

[0015] Fresh water is injected into the first salt layer through the tubing assembly;

[0016] The tubular assembly is used to drain the brine produced by the dissolution of the first salt layer, forming a first cavity in the first salt layer.

[0017] Preferably, the tubular assembly includes an inner tube and an outer tube, the inner tube being inserted into the outer tube, and an annular section being formed between the inner tube and the outer tube. The inner tube is used to inject fresh water into the first salt layer, and the annular section is used to discharge the brine from the first salt layer.

[0018] Preferably, the process includes the following steps before step S6:

[0019] Monitor the integrity of the thick interlayer. If the thick interlayer does not show any deformation or damage, repeat steps S4 and S5 until the thick interlayer shows any deformation or damage.

[0020] Preferably, a monitoring well is drilled on one side of the cavity-forming well, and a microseismic monitoring instrument is installed in the monitoring well to monitor the integrity of the thick interlayer.

[0021] The beneficial effects of this invention are as follows:

[0022] The salt cavern gas storage cavity-building method provided by this invention first involves installing a tubing assembly in the drilled cavity-building well and extending the tubing assembly into a first salt layer to create a cavity, thereby enabling the storage of natural gas. Then, gas is injected into the first cavity through the tubing assembly until the pressure reaches a preset value. Subsequently, the gas in the first cavity is rapidly discharged until the pressure returns to normal atmospheric pressure. During this process, the upper thick interlayer is subjected to the intense pressure from gas injection and discharge, and undergoes deformation and damage under the pressure fluctuations, thus creating conditions for the later collapse of the thick interlayer. Afterwards, the tubing assembly... The material is moved to the second salt layer above the thick interlayer, and a cavity is created in the second salt layer to form a second cavity. Through this layered cavity-making method, a cavity is formed above the thick interlayer, causing the thick interlayer to lose its upper support layer, thus further disintegrating and eventually collapsing during the cavity-making process. Since a second cavity is formed above the thick interlayer, after the thick interlayer collapses, the first cavity and the second cavity connect and merge, expanding the effective gas storage space of the cavity. At the same time, the collapse of the thick interlayer greatly increases the cavity-making speed and reduces the cavity-making cost. This salt cavern gas storage cavity-making method can effectively utilize the bottom layer of salt rock containing thick interlayers to create cavities for gas storage, improving the space utilization rate of salt rock. Attached Figure Description

[0023] Figure 1 This is a flowchart of the salt cavern gas storage cavity creation method provided in a specific embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of step S3 provided in a specific embodiment of the present invention.

[0025] In the picture:

[0026] 100-thick interlayer;

[0027] 1-Cavity well;

[0028] 2-Tube assembly; 21-Outer tube; 22-Inner tube; 23-Annular section;

[0029] 3-Monitoring wells;

[0030] 4-Microseismic monitoring instrument. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0032] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0034] In the description of this embodiment, the terms "upper," "lower," "right," and "left," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0035] like Figure 1 and Figure 2 As shown, the present invention provides a method for creating a cavity in a salt cavern gas storage facility, the method comprising:

[0036] S1. Drill a cavity-making well 1 vertically downwards from the ground until reaching the first salt layer below the thick interlayer 100. Install a tubing assembly 2 in the cavity-making well 1 and extend the tubing assembly 2 into the first salt layer. In this embodiment, the construction personnel first drill a cavity-making well 1 vertically downwards from the ground until reaching the first salt layer below the thick interlayer 100. Then, they lower the tubing assembly 2 into the cavity-making well 1. One end of the tubing assembly 2 is located on the ground and connected to the ground water and gas injection equipment. The other end of the tubing assembly 2 extends into the first salt layer to prepare for cavity creation. Specifically, during the drilling of the cavity-making well 1, the construction personnel need to perform well logging and core sampling analysis on the drilled cavity-making well 1 to determine the location, composition, thickness, hardness, and other physical parameters of the thick interlayer 100, thereby obtaining the necessary information for subsequent cavity creation.

[0037] S2. A cavity is created in the first salt layer using the tubing assembly 2, forming a first cavity. In this embodiment, the construction personnel use the leaching method to create the cavity, that is, fresh water is injected into the first salt layer through the tubing assembly 2. The fresh water will dissolve the salt rock in the first salt layer to generate brine. As more fresh water is injected into the first salt layer, the first salt layer will gradually dissolve from bottom to top to form the first cavity. As more fresh water is injected, some of the brine will also be discharged through the tubing assembly 2 until the brine fills the first cavity, and the bottom of the thick interlayer 100 is immersed in the brine in the first cavity.

[0038] S3. Gas is injected into the first cavity through the tubing assembly 2, causing the brine produced by the dissolution of the first salt layer in the first cavity to be discharged through the tubing assembly 2. In this embodiment, after the cavity is created, the construction personnel inject nitrogen into the brine-filled first cavity through the tubing assembly 2. The brine in the first cavity will be discharged through the tubing assembly 2 under the pressure of the injected nitrogen. Specifically, the tubing assembly 2 includes an outer tube 21 and an inner tube 22 sleeved together. The inner tube 22 is placed inside the outer tube 21, and an annular section 23 is formed between the inner tube 22 and the outer tube 21. Before injecting nitrogen into the first cavity, the construction personnel first lift the outer tube 21 upwards so that the bottom end of the outer tube 21 is located in the cavity-creating well 1, and the top end of the outer tube 21 is connected to the gas injection equipment on the ground, so that nitrogen is injected into the cavity-creating well 1 from the annular section 23 between the outer tube 21 and the inner tube 22, thereby pressing the brine in the first cavity upwards into the inner tube 22 and discharging it. In another embodiment, air can also be injected into the first cavity.

[0039] S4. Continue injecting gas until the pressure in the first chamber reaches the preset pressure value P1. In this embodiment, nitrogen is continued to be injected into the first chamber through the annular section 23 until all the brine in the first chamber is discharged. The nitrogen pressure in the first chamber at this time is set as the preset pressure value P1. Specifically, a pressure detection device is installed on the top of the outer pipe 21 at the ground, which can detect the pressure value in the first chamber.

[0040] For example, in a project where the bottom depth of the thick interlayer 3 is 1420 meters, the pressure required to completely drain the brine is P1 = ρgh = 1.2 × 9.8 × 1420 ≈ 17 MPa, where ρ is the density of the brine, taken as 1.2 kg / m³. 3 Based on the actual engineering conditions, the first cavity is determined to be approximately a cylindrical space with a diameter of 50 meters, and the height for injecting nitrogen is set at 2 meters. Therefore, based on the above results, the required volume V2 of nitrogen to be injected is calculated as follows:

[0041] According to the gas law: pV = nRT

[0042] We know that: V2=(P1V1·R2T2) / R1T1·P2

[0043] In the formula,

[0044] P1—Nitrogen pressure at a depth of 1420m, MPa;

[0045] The volume of nitrogen injected at a depth of V1—1420m, in m 3 ;

[0046] R2—Nitrogen gas constant under standard temperature and pressure conditions, J / K·mol;

[0047] T2—Standard temperature, 273K;

[0048] The nitrogen gas constant under pressure and temperature conditions at a depth of 1420m, J / K·mol;

[0049] T1—Temperature at a depth of 1420m, in K;

[0050] P2 — Atmospheric pressure, MPa.

[0051] Therefore, the required nitrogen volume V2 to be injected from the ground under standard pressure and temperature conditions can be calculated to be approximately 600,000 m³. 3 .

[0052] S5. Use the tubing assembly 2 to purge the gas from the first cavity until the pressure in the first cavity drops to atmospheric pressure. In this embodiment, when the nitrogen pressure in the first cavity reaches the preset pressure value P1, the construction personnel stop injecting nitrogen and close the valve on the tubing assembly 2, allowing the first cavity to remain pressurized for a period of time. Then, the construction personnel open the valve on the tubing assembly 2 and quickly purge the nitrogen from the first cavity through the annular section 23. During this process, the thick interlayer 100 above the first cavity is subjected to the excitation pressure brought by the injection and venting of gas, and undergoes deformation damage under the pressure fluctuation of nitrogen, thus creating conditions for the collapse of the thick interlayer 100 later. Specifically, the tubing assembly 2 is equipped with a pressure detection device at the top of the ground, which can detect the pressure value in the first cavity. When the pressure detection device detects that the pressure in the first cavity has returned to the normal atmospheric pressure value, it means that the venting process is over.

[0053] S6. Move the tubing assembly 2 so that it extends into the second salt layer above the thick interlayer 100. In this embodiment, the construction personnel lift the tubing assembly 2 upwards so that the bottom end of the tubing assembly 2 extends into the second salt layer above the thick interlayer 100, in preparation for the next step of cavity creation.

[0054] S7. Using the tubing assembly 2, a cavity is created in the second salt layer until the thick interlayer 100 collapses, forming a second cavity in the second salt layer, which is connected to the first cavity. In this embodiment, the same method as creating a cavity in the first salt layer is used to create a cavity in the second salt layer. During the cavity creation process in the second salt layer, the second salt layer gradually dissolves, the thick interlayer 100 is suspended and loses its upper support layer. As the space of the second cavity expands and the salt layer gradually dissolves, the thick interlayer 100 gradually crumbles and eventually collapses. Since a second cavity is formed above the thick interlayer 100, after the thick interlayer 100 collapses, the first cavity and the second cavity are connected and merged, expanding the effective gas storage space of the cavity. This method of creating a cavity in a salt cavern gas storage tank can effectively utilize the bottom layer of salt rock containing the thick interlayer 100 to create a cavity for gas storage, improving the space utilization rate of the salt rock.

[0055] Further, step S2, using the tubing assembly 2 to create a cavity in the first salt layer, includes: injecting fresh water into the first salt layer through the tubing assembly 2; and using the tubing assembly 2 to discharge the brine generated by the dissolution of the first salt layer, thus forming a first cavity in the first salt layer. In this embodiment, the cavity creation in both the first and second salt layers is carried out using the dissolution mining method. That is, fresh water is injected into the first salt layer through the tubing assembly 2, and the fresh water will dissolve the salt rock in the first salt layer to generate brine. As more fresh water is injected into the first salt layer, the first salt layer will gradually dissolve from bottom to top to form the first cavity. As more fresh water is injected, a portion of the brine will also be discharged through the tubing assembly 2 until the brine fills the first cavity, and the bottom of the thick interlayer 100 is immersed in the brine in the first cavity.

[0056] Specifically, such as Figure 2 As shown, the tubular assembly 2 includes an inner tube 22 and an outer tube 21. The inner tube 22 is inserted into the outer tube 21, and an annular section 23 is formed between the inner tube 22 and the outer tube 21. The inner tube 22 is used to inject fresh water into the first salt layer, and the annular section 23 is used to discharge brine from the first salt layer. In this embodiment, the tubular assembly 2 includes an outer tube 21 and an inner tube 22 nested together. The inner tube 22 is disposed inside the outer tube 21, and an annular section 23 is formed between the inner tube 22 and the outer tube 21. The top end of the inner tube 22 is connected to a water injection device on the ground. The water injection device is used to inject fresh water into the first salt layer through the inner tube 22. Valves are provided at the top ends of both the inner tube 22 and the outer tube 21 on the ground. When using the leaching method to create a cavity, the construction personnel open the valves of the inner tube 22 and the outer tube 21 to inject fresh water into the inner tube 22. The fresh water is injected into the first salt layer through the inner tube 22, and the brine generated by the dissolution of the salt layer is discharged to the ground through the annular section 23, thereby forming a cavity-creating process of "injecting and extracting simultaneously". The water injection and drainage do not interfere with each other, which speeds up the cavity-creating process.

[0057] Furthermore, before step S6, the process includes: monitoring the integrity of the thick interlayer 100. If the thick interlayer 100 does not show any deformation or damage, steps S4 and S5 are repeated until the thick interlayer 100 shows deformation or damage. In this embodiment, before creating a cavity in the second salt layer, the damage condition of the thick interlayer 100 needs to be detected. If the thick interlayer 100 does not show any deformation or damage, steps S4 and S5 need to be repeated to perform multiple gas injection and degassing processes on the first cavity, so that the thick interlayer 100 shows deformation or damage, creating favorable conditions for the subsequent collapse of the thick interlayer 100.

[0058] Specifically, such as Figure 2 As shown, a monitoring well 3 is drilled on one side of the cavity-making well 1, and a microseismic monitoring instrument 4 is installed in the monitoring well 3. The microseismic monitoring instrument 4 is used to monitor the integrity of the thick interlayer 100. In this embodiment, the microseismic monitoring instrument 4 is a commonly used detection instrument in the field, mainly used to monitor the activity and fracturing of underground rock masses. Its main working principle is to determine the location and scale of rock mass vibration by receiving vibration waves from underground rock masses. The monitoring well 3 is drilled on one side of the cavity-making well 1, and the microseismic monitoring instrument 4 is placed in the monitoring well 3 and connected to a computer on the ground. The microseismic monitoring instrument 4 can accurately monitor the deformation and damage of the thick interlayer 100. When the construction personnel detect deformation and damage in the thick interlayer 100 through the microseismic monitoring instrument 4 and the damage reaches a predetermined value, the gas injection and venting of the first cavity is stopped, and preparation is made to create a cavity in the second salt layer above the thick interlayer 100. If the microseismic monitoring instrument 4 detects that the deformation and damage of the thick interlayer 100 has not reached the predetermined value, the gas injection and venting of the first cavity are repeated.

[0059] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for creating a cavity in a salt cavern gas storage tank, characterized in that, include: S1. Drill a cavity-making well (1) from the ground down until you reach the first salt layer below the thick interlayer (100). Install a tubing assembly (2) in the cavity-making well (1) and extend the tubing assembly (2) into the first salt layer. S2. Using the tubing assembly (2), a cavity is created in the first salt layer to form a first cavity; S3. Gas is injected into the first cavity through the tubing assembly (2) so that the brine produced by the dissolution of the first salt layer in the first cavity is discharged through the tubing assembly (2); S4. Continue injecting the gas until the pressure in the first cavity reaches the preset pressure value P1, and then let the first cavity stand under pressure for a period of time. S5. Use the tubing assembly (2) to quickly discharge the gas in the first cavity until the pressure in the first cavity drops to atmospheric pressure; Step S6 is preceded by: Monitor the integrity of the thick interlayer (100). If the thick interlayer (100) does not show any deformation or damage, repeat steps S4 and S5 until the thick interlayer (100) shows any deformation or damage. S6. Move the tubing assembly (2) so that the tubing assembly (2) extends into the second salt layer above the thick interlayer (100); S7. Using the tubing assembly (2), a cavity is created in the second salt layer until the thick interlayer (100) collapses, forming a second cavity in the second salt layer, and the second cavity is connected to the first cavity.

2. The method for creating a cavity in a salt cavern gas storage tank according to claim 1, characterized in that, Step S2, using the tubing assembly (2) to create a cavity in the first salt layer, includes: Fresh water is injected into the first salt layer through the tubing assembly (2); The tubular assembly (2) is used to drain the brine produced by the dissolution of the first salt layer, forming a first cavity in the first salt layer.

3. The method for creating a cavity in a salt cavern gas storage tank according to claim 2, characterized in that, The tubular assembly (2) includes an inner tube (22) and an outer tube (21). The inner tube (22) is inserted into the outer tube (21), and an annular section (23) is formed between the inner tube (22) and the outer tube (21). The inner tube (22) is used to inject the fresh water into the first salt layer, and the annular section (23) is used to discharge the brine in the first salt layer.

4. The method for creating a cavity in a salt cavern gas storage tank according to claim 1, characterized in that, A monitoring well (3) is drilled on one side of the cavity well (1), and a microseismic monitoring instrument (4) is installed in the monitoring well (3). The microseismic monitoring instrument (4) is used to monitor the integrity of the thick interlayer (100).

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