Cavity building method for salt cavern gas storage

Abstract

The invention belongs to the technical field of natural gas storage, and discloses a salt cavern gas storage cavity building method. The salt cavern gas storage cavity building method comprises the steps that S1, a cavity building well is drilled till a first salt layer below a thick interlayer is drilled, a pipe column assembly is installed in the cavity building well, and the pipe column assembly extends into the first salt layer; s2, forming a cavity in the first salt layer to form a first cavity; s3, gas is injected into the first cavity, so that the brine in the first cavity is discharged through the tubular column assembly; s4, continuously injecting the 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 is reduced to atmospheric pressure; s6, enabling the tubular column assembly to extend into a second salt layer above the thick interlayer; and S7, a cavity is formed in the second salt layer until the thick interlayer collapses, and a second cavity is formed in the second salt layer and communicates with the first cavity. The cavity building method of the salt cavern gas storage can promote collapse of the interlayer and enlarge the effective gas storage space of the salt rock.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas storage, and in particular to a method for creating a cavity in a salt cavern gas storage. Background Art

[0002] Salt cavern gas storage refers to a cavern cavity formed by water-soluble salt in underground salt layers or salt domes to store natural gas. It has the following three characteristics: 1. Low proportion of bottom gas - the working gas volume accounts for about 65% of the total expansion capacity; 2. Strong flexibility - the switching of injection and production gas is efficient and convenient; 3. High safety - even in the event of geological disasters or external attacks, it can still be safe and sound, and is an ideal way to store natural gas.

[0003] Currently, most commonly used salt cavern gas storages are built in layered salt rocks deposited in lake phases. They are characterized by the alternating production of salt rocks and insoluble interlayers, with many layers and large variations in single-layer thickness. When the thickness of the insoluble interlayer is small, the interlayer may collapse and fall during the water-soluble cavity making process, thereby accumulating at the bottom of the salt cavity to form residue. The traditional maximum thickness of the interlayer that can collapse and fall is about 10-20 meters. If there is an interlayer with a thickness greater than 20 meters (thick interlayer) in the stratum, the current conventional cavity making process needs to avoid the interlayer, and only a single cavity can be built above or below the thick interlayer, resulting in low salt rock utilization and small effective gas storage space in the salt cavity. Summary of the invention

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

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for creating a cavern for a salt cavern gas storage comprises:

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

[0008] S2. Using the tubing assembly to create a cavity in the first salt layer to form a first cavity;

[0009] S3, injecting gas into the first cavity through the tubing assembly, so that the brine generated by the dissolution of the first salt layer in the first cavity is discharged through the tubing assembly;

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

[0011] S5, using the pipe column assembly to discharge the gas in the first cavity until the pressure in the first cavity drops to atmospheric pressure;

[0012] S6, moving the tubular column assembly so that the tubular column assembly extends into the second salt layer above the thick interlayer;

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

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

[0015] injecting fresh water into the first salt layer through the tubing assembly;

[0016] The pipe column assembly is used to discharge brine produced by dissolution of the first salt layer, thereby forming a first cavity in the first salt layer.

[0017] Preferably, the tubing assembly comprises an inner tube and an outer tube, the inner tube is inserted into the outer tube, an annulus section is formed between the inner tube and the outer tube, the inner tube is used to inject the fresh water into the first salt layer, and the annulus section is used to discharge the brine in the first salt layer.

[0018] Preferably, before step S6, the method further includes:

[0019] The integrity of the thick interlayer is monitored. If the thick interlayer is not deformed or damaged, steps S4 and S5 are repeated until the thick interlayer is deformed or damaged.

[0020] Preferably, a monitoring well is drilled on one side of the cavity making well, and a microseismic monitor is arranged in the monitoring well, and the microseismic monitor is used to monitor the integrity of the thick interlayer.

[0021] The beneficial effects of the present invention are:

[0022] The method for making a cavity in a salt cavern gas storage provided by the present invention comprises the following steps: firstly, a pipe column assembly is installed in a well drilled for making a cavity, and the pipe column assembly is extended into a first salt layer, and a cavity is made in the first salt layer to form a first cavity, so that natural gas can be stored; then, gas is injected into the first cavity through the pipe column assembly until the pressure in the first cavity reaches a preset pressure value, and then the gas in the first cavity is quickly discharged until the pressure in the first cavity is restored to a normal atmospheric pressure level. In this process, the thick interlayer above is subjected to the excited pressure brought by the gas injection and exhaust, and is deformed and damaged under the pressure fluctuation of the gas, thereby creating collapse conditions for the thick interlayer in the later stage; then, the pipe column assembly is installed in the wellbore for making a cavity, and the gas is injected into ... The device is moved to the second salt layer above the thick interlayer, and the second salt layer is cavitated to form a second cavity. Through the layered cavitation method, a cavity is formed above the thick interlayer, so that the thick interlayer loses the upper supporting layer, thereby further disintegrating and breaking during the cavitation process and finally collapsing. Since the second cavity is formed by cavitation above the thick interlayer, after the thick interlayer collapses, the first cavity is connected and merged with the second cavity, thereby expanding the effective gas storage space of the cavity. At the same time, the collapse of the thick interlayer greatly increases the speed of cavitation and reduces the cost of cavitation. The cavitation method for salt cavern gas storage can effectively utilize the salt rock bottom layer containing thick interlayers to cavity and store gas, thereby improving the space utilization rate of salt rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of a method for creating a cavity in a salt cavern gas storage provided by a specific embodiment of the present invention;

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

[0025] In the figure:

[0026] 100-thick sandwich;

[0027] 1-Cavity well;

[0028] 2- pipe string assembly; 21- outer pipe; 22- inner pipe; 23- annulus section;

[0029] 3- Monitoring wells;

[0030] 4-Microseismic monitor. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0032] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] In the description of this embodiment, the terms "upper", "lower", "right", "left" and other directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the 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 reservoir, and the method for creating a cavity in a salt cavern gas storage reservoir comprises:

[0036] S1. Drill a cavity well 1 downward from the ground until the first salt layer below the thick interlayer 100 is drilled, install a pipe string assembly 2 in the cavity well 1, and extend the pipe string assembly 2 into the first salt layer. In this embodiment, the construction personnel first vertically drill a cavity well 1 downward on the ground until the first salt layer below the thick interlayer 100 is drilled, and then the pipe string assembly 2 is lowered into the cavity well 1. One end of the pipe string assembly 2 is located on the ground and connected to the water injection and gas injection equipment on the ground. The other end of the pipe string assembly 2 extends into the first salt layer to prepare for cavity making; specifically, in the process of drilling the cavity well 1, the construction personnel need to perform well logging and coring analysis on the drilled cavity well 1 to determine the location, composition, thickness, hardness and other physical parameters of the thick interlayer 100, so as to obtain necessary information for subsequent cavity making.

[0037] S2. Use the pipe string assembly 2 to create a cavity in the first salt layer to form a first cavity. In this embodiment, the construction personnel use the solution mining method to create the cavity, that is, inject fresh water into the first salt layer through the pipe string 2 assembly, and the fresh water will dissolve the salt rock in the first salt layer to generate brine. Continue to inject fresh water into the first salt layer, and the first salt layer will gradually dissolve from bottom to top to form a first cavity. As more fresh water is injected, a portion of the brine will also be discharged through the pipe string 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, injecting gas into the first cavity through the pipe string assembly 2, so that the brine produced by the dissolution of the first salt layer in the first cavity is discharged through the pipe string assembly 2. In this embodiment, after the cavity is completed, the construction personnel inject nitrogen into the first cavity filled with brine through the pipe string assembly 2, and the brine in the first cavity will be discharged through the pipe string assembly 2 under the pressure of the injected nitrogen; specifically, the pipe string assembly 2 includes an outer tube 21 and an inner tube 22 which are sleeved together, and the inner tube 22 is arranged in the outer tube 21, and an annulus 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 upward, so that the bottom end of the outer tube 21 is located in the cavity well 1, and the top end of the outer tube 21 is connected to the gas injection equipment on the ground, so that the nitrogen is injected into the cavity well 1 from the annulus section 23 between the outer tube 21 and the inner tube 22, and then the brine in the first cavity is pressed upward into the inner tube 22 and discharged; in another embodiment, air can also be injected into the first cavity.

[0039] S4, continue to inject gas until the pressure in the first cavity reaches the preset pressure value P1. In this embodiment, nitrogen is continuously injected into the first cavity through the annular section 23 until all the brine in the first cavity is discharged, and the nitrogen pressure in the first cavity at this time is set to the preset pressure value P1; specifically, a pressure detection device is provided at the top of the outer tube 21 located on the ground, which can detect the pressure value in the first cavity.

[0040] For example, in a project where the bottom depth of the thick interlayer 3 is 1420 meters, the pressure value required to discharge all the brine is P1=ρgh=1.2×9.8×1420≈17MPa, where ρ is the density of the brine, which is 1.2kg / m 3 According to the actual engineering situation, the first cavity is determined to be approximately a cylindrical space with a diameter of 50 meters, and the height of the nitrogen injection is set at 2 meters; based on the above results, the volume V2 of nitrogen to be injected is calculated as follows:

[0041] According to the gas state equation: pV = nRT

[0042] It can be seen that: V2 = (P1V1·R2T2) / R1T1·P2

[0043] In the formula,

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

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

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

[0047] T2—standard temperature, 273K;

[0048] R1—Nitrogen gas constant under pressure and temperature conditions at a depth of 1420 m, J / K·mol;

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

[0050] P2—atmospheric pressure, MPa.

[0051] Therefore, it can be calculated that the volume of nitrogen V2 that needs to be injected from the ground under standard pressure and temperature conditions is about 600,000 m 3 .

[0052] S5. Use the pipe string assembly 2 to discharge the gas in 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 pipe string assembly 2, so that the first cavity is pressurized and left to stand for a period of time; then the construction personnel open the valve of the pipe string assembly 2 and quickly discharge the nitrogen in the first cavity from the annular section 23. During this process, the thick interlayer 100 above the first cavity is subjected to the exciting pressure caused by gas injection and exhaust, and deforms and is damaged under the pressure fluctuation of nitrogen, thereby creating collapse conditions for the thick interlayer 100 in the later stage; specifically, the pipe string assembly 2 is located at the top of the ground and is provided with a pressure detection device, 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 exhaust process is over.

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

[0054] S7. Use the pipe column assembly 2 to create a cavity in the second salt layer until the thick interlayer 100 collapses, and a second cavity is formed in the second salt layer, and the second cavity is connected to the first cavity. In this embodiment, the same method as the cavity creation in the first salt layer is used to create a cavity in the second salt layer; during the cavity creation in the second salt layer, the second salt layer will gradually dissolve, the thick interlayer 100 will be suspended and lose the upper support layer, and as the second cavity space expands and the salt layer gradually dissolves, the thick interlayer 100 will gradually break and eventually collapse; since the second cavity is formed by cavity creation above the thick interlayer 100, after the thick interlayer 100 collapses, the first cavity is connected and merged with the second cavity, expanding the effective gas storage space of the cavity; the salt cavern gas storage cavity creation method can effectively utilize the salt rock bottom layer containing the thick interlayer 100 to create a cavity and store gas, thereby improving the space utilization rate of the salt rock.

[0055] Furthermore, in 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; using the tubing assembly 2 to discharge the brine generated by the dissolution of the first salt layer, and forming a first cavity in the first salt layer. In this embodiment, the cavity creation in the first salt layer and the second salt layer is carried out by the solution 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, and the fresh water will continue to be injected into the first salt layer. The first salt layer will gradually dissolve from bottom to top to form a first cavity, and 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, 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. An annulus 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 annulus section 23 is used to discharge brine in the first salt layer. In this embodiment, the pipe column assembly 2 includes an outer pipe 21 and an inner pipe 22 which are sleeved together. The inner pipe 22 is arranged in the outer pipe 21. An annulus section 23 is formed between the inner pipe 22 and the outer pipe 21. The top of the inner pipe 22 is connected to the water injection equipment on the ground. The water injection equipment is used to inject fresh water into the first salt layer through the inner pipe 22. The tops of the inner pipe 22 and the outer pipe 21 located on the ground are both provided with valves. When the solution mining method is used for cavity making, the construction personnel open the valves of the inner pipe 22 and the outer pipe 21, and inject fresh water into the inner pipe 22. The fresh water is injected into the first salt layer through the inner pipe 22, and the brine generated by the dissolution of the salt layer is discharged from the ground through the annulus section 23, thereby forming a "simultaneous injection and mining" cavity making process. The water injection and drainage do not interfere with each other, which speeds up the cavity making speed.

[0057] Furthermore, before step S6, it also includes: monitoring the integrity of the thick interlayer 100, and if the thick interlayer 100 is not deformed or damaged, repeating steps S4 and S5 until the thick interlayer 100 is deformed or damaged. In this embodiment, before the second salt layer is cavitated, it is necessary to detect the damage of the thick interlayer 100, and if the thick interlayer 100 is not deformed or damaged, it is necessary to repeat steps S4 and S5, and perform multiple gas injection and exhaust processes on the first cavity to cause deformation and damage to the thick interlayer 100, thereby creating favorable conditions for the subsequent collapse of the thick interlayer 100.

[0058] Specifically, Figure 2 As shown, a monitoring well 3 is drilled on one side of the cavity well 1, and a microseismic monitor 4 is arranged in the monitoring well 3. The microseismic monitor 4 is used to monitor the integrity of the thick interlayer 100. In this embodiment, the microseismic monitor 4 is a commonly used detection instrument in the field, which is mainly used to monitor the activity and fracture of the underground rock mass. Its main working principle is to determine the location and scale of the rock mass vibration by receiving the vibration wave of the underground rock mass. A monitoring well 3 is drilled on one side of the cavity well 1. The microseismic monitor 4 is placed in the monitoring well 3 and connected to the computer on the ground. The microseismic monitor 4 can accurately monitor the deformation and damage of the thick interlayer 100. When the construction personnel detect the deformation and damage of the thick interlayer 100 through the microseismic monitor 4 and the damage amount reaches the predetermined value, the gas injection and exhaust of the first cavity are stopped, and the second salt layer above the thick interlayer 100 is prepared for cavity construction; if the microseismic monitor 4 detects that the deformation and damage amount of the thick interlayer 100 does not reach the predetermined value, the gas injection and exhaust 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 embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for creating a cavern for a salt cavern gas storage, characterized in that: include: S1, drilling a cavity-making well (1) downward from the ground until reaching a first salt layer below a thick interlayer (100), installing a pipe column assembly (2) in the cavity-making well (1), and extending the pipe column assembly (2) into the first salt layer; S2, using the tubular column assembly (2) to create a cavity in the first salt layer to form a first cavity; S3, injecting gas into the first cavity through the tubing assembly (2), so that brine generated by dissolution of the first salt layer in the first cavity is discharged through the tubing assembly (2); S4, continue to inject the gas until the pressure in the first cavity reaches a preset pressure value P1; S5, using the pipe column assembly (2) to discharge the gas in the first cavity until the pressure in the first cavity drops to atmospheric pressure; S6, moving the tubular column assembly (2) so that the tubular column assembly (2) extends into the second salt layer above the thick interlayer (100); S7. Use the tubular column assembly (2) to create a cavity in the second salt layer until the thick interlayer (100) collapses, and a second cavity is formed in the second salt layer, and the second cavity is connected to the first cavity.

2. The method for creating a salt cavern gas storage chamber according to claim 1, characterized in that: In step S2, using the tubular column assembly (2) to create a cavity in the first salt layer comprises: injecting fresh water into the first salt layer through the tubing assembly (2); The pipe column assembly (2) is used to discharge brine produced by dissolution of the first salt layer, thereby forming a first cavity in the first salt layer.

3. The method for creating a cavern for a salt cavern gas storage according to claim 2, characterized in that: The tubular column assembly (2) comprises an inner tube (22) and an outer tube (21); the inner tube (22) is inserted into the outer tube (21); an annulus 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 annulus section (23) is used to discharge the brine in the first salt layer.

4. The method for creating a cavern for a salt cavern gas storage according to claim 1, characterized in that: Before step S6, the method further includes: The integrity of the thick interlayer (100) is monitored; if the thick interlayer (100) is not deformed or damaged, steps S4 and S5 are repeated until the thick interlayer (100) is deformed or damaged.

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

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