A wellbore structure and method for draining brine from a salt cavern.

Abstract

This invention relates to the field of brine drainage technology for salt caverns, and provides a wellbore structure for brine drainage from salt caverns, comprising at least: a gas injection well located above the salt cavern and extending from the surface into the salt cavern; a first row of brine wells located above the salt cavern and extending from the surface to the bottom of the salt cavern, with drill pipes installed in the first row of brine wells; and a second row of brine wells located outside the boundary of the salt cavern and extending from the surface beyond the bottom of the salt cavern, with the well body of the second row of brine wells extending towards the first row of brine wells so that the drill pipes at least partially extend into the second row of brine wells. In this wellbore structure for brine drainage from salt caverns, the first and second rows of brine wells are designed with vertical alignment, wherein the second row of brine wells is located at the edge of the salt cavern and extends towards the first row of brine wells via a double-angle drilling method, forming a connection with the first row of brine wells. This allows for the complete drainage of brine from the salt cavern, increasing the gas storage space.

Description

Technical Field

[0001] This invention relates to the field of brine drainage technology in salt caverns, specifically to a wellbore structure and method for brine drainage from salt caverns. Background Technology

[0002] Due to the extremely low permeability and good creep and damage recovery characteristics of salt rock, salt caverns are considered highly secure underground energy storage facilities and are referred to as strategically safe reserves. However, my country's salt deposits are mainly composed of terrestrial lacustrine layered salt layers, characterized by multiple interlayers and thick single interlayers. The resulting cavity formations are complex, making it difficult to completely drain the brine during the gas injection and brine drainage stages, which severely affects the storage volume of salt cavern gas storage facilities. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is that it is difficult to completely drain the brine during the gas injection and brine drainage stage, which seriously affects the storage volume of the salt cavern gas storage tank. Thus, a well structure and method for draining brine from a salt cavern is provided.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0005] A well structure for draining brine from a salt cavern includes at least: a gas injection well located above the salt cavern and extending from the surface into the salt cavern; a first row of brine wells located above the salt cavern and extending from the surface to the bottom of the salt cavern, wherein a drill pipe is installed in the first row of brine wells; and a second row of brine wells located outside the boundary of the salt cavern and extending from the surface beyond the bottom of the salt cavern, wherein the well body of the second row of brine wells located below the salt cavern extends toward the direction close to the first row of brine wells, such that the drill pipe at least partially extends into the second row of brine wells.

[0006] Furthermore, the second row of brine wells extends horizontally below the salt cavern cavity to below the first row of brine wells.

[0007] Furthermore, the well structure for the brine drainage of the salt cavern also includes a blowout preventer, which is installed at the wellhead of the first brine drainage well. The blowout preventer has a blocking state that restricts the discharge of brine and an open state that allows the brine to pass through.

[0008] Furthermore, the well structure for draining brine from the salt cavern also includes a casing installed inside the first brine draining well. The drill pipe is inserted inside the casing, and the casing is adapted to limit the pressure exerted by the rock mass inside the salt cavern on the drill pipe.

[0009] A method for draining brine from a salt cavern cavity includes the wellbore structure for draining brine from a salt cavern cavity as described in any of the above-mentioned methods, and the specific steps are as follows: First brine draining stage: sealing the second brine draining well, injecting high-pressure gas into the salt cavern cavity through the gas injection well, and draining brine through the first brine draining well; Second brine draining stage: sealing the first brine draining well and putting the drill pipe into a working state, injecting high-pressure gas into the salt cavern cavity through the gas injection well, and draining brine through the second brine draining well.

[0010] Furthermore, when sealing the second brine well during the first brine stage, the second brine well is sealed by filling it with clean water.

[0011] Furthermore, when the amount of brine discharged from the salt cavern reaches 30%-50% of the total volume of the cavern, the process switches from the first brine discharge stage to the second brine discharge stage.

[0012] Furthermore, the well body of the second row of brine wells located below the salt cavern cavity is formed by a double-inclined method, so that the well body structure extends from the bottom of the salt cavern cavity into the salt cavern cavity and connects with the first row of brine wells.

[0013] The technical solution of this invention has the following advantages:

[0014] The well structure for draining brine from a salt cavern provided by this invention features a vertical alignment design between the first and second rows of brine wells. The second row of brine wells is located at the edge of the salt cavern and extends toward the first row of brine wells via a double-inclined method, thus connecting with the first row of brine wells. This allows for the complete drainage of brine from the salt cavern, increasing the gas storage space. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the well structure for brine drainage in a salt cavern according to an embodiment of the present invention.

[0017] 1. Gas injection well; 2. First row of brine wells; 3. Second row of brine wells;

[0018] 4. Drill pipe; 5. Casing; 6. Salt cavern. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, 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 invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Figure 1 This is a schematic diagram of the wellbore structure for brine drainage in a salt cavern according to an embodiment of the present invention, as shown below. Figure 1 As shown, this embodiment provides a well structure for draining brine from a salt cavern, comprising at least: a gas injection well 1, located above a salt cavern 6 and extending from the surface into the salt cavern 6; a first row of brine wells 2, located above the salt cavern 6 and extending from the surface into the bottom of the salt cavern 6, with a drill pipe 4 installed in the first row of brine wells 2; and a second row of brine wells 3, located outside the boundary of the salt cavern 6 and extending from the surface beyond the bottom of the salt cavern 6, with the well body of the second row of brine wells 3 extending towards the first row of brine wells 2, so that the drill pipe 4 at least partially extends into the second row of brine wells 3.

[0024] Specifically, the injection well 1 only needs to reach the brine, while the first row of brine wells 2 can penetrate to the deepest part of the brine. A drilling rig is installed on the surface, and the drill rod 4 extends along the first row of brine wells 2 into the depth of the salt cavern 6. The second row of brine wells 3 extends downward from the edge of the salt cavern 6. The vertical shaft of the second row of brine wells 3 does not intersect with the salt cavern 6. When the vertical shaft of the second row of brine wells 3 reaches the lowest point of the salt cavern 6, the extension direction of the second row of brine wells 3 can be changed using directional drilling technology to form the horizontal shaft structure of the second row of brine wells 3. When the horizontal shaft of the second row of brine wells 3 extends directly below the first row of brine wells 2, directional drilling technology is used again to make the second row of brine wells 3 extend upward through the bottom of the salt cavern 6 and connect with the first row of brine wells 2. At this time, the drill rod 4 extends at least partially into the second row of brine wells 3. The specific brine discharge method will be described in detail in the following embodiment section.

[0025] The well structure for draining brine from the salt cavern provided in this embodiment features a vertical alignment design between the first row of brine wells 2 and the second row of brine wells 3. The second row of brine wells 3 is located at the edge of the salt cavern 6 and extends toward the first row of brine wells 2 via a double-inclined method, thus connecting with the first row of brine wells 2. This allows for the complete drainage of brine from the salt cavern 6, increasing the gas storage space.

[0026] Preferably, the well body of the second row of brine wells 3, located below the salt cavern 6, extends horizontally to below the first row of brine wells 2.

[0027] The well structure for draining brine from the salt cavern also includes a blowout preventer (BOP), located at the wellhead of the first brine well 2. The BOP has both a blocked state to restrict brine discharge and an open state to allow brine to pass through. When the first brine well 2 needs to drain brine, the BOP is in the open state; when the second brine well 3 needs to drain brine, the BOP is in the blocked state.

[0028] Preferably, the wellbore structure for draining brine from the salt cavern 6 also includes a casing 5, which is installed inside the first brine well 2. The drill pipe 4 is inserted inside the casing 5, and the casing 5 is adapted to limit the pressure exerted by the rock mass within the salt cavern 6 on the drill pipe 4. The presence of the casing 5 can block the rock mass surrounding the drill pipe 4, preventing damage to the drill pipe 4 due to rock mass compression.

[0029] Another embodiment provides a method for draining brine from a salt cavern cavity, including the well structure for draining brine from a salt cavern cavity as described above, with the following specific steps: First draining stage: The second brine well 3 is sealed, and high-pressure gas is injected into the salt cavern cavity 6 through the gas injection well 1. With the assistance of the high-pressure gas, the brine in the salt cavern cavity 6 can be drained through the first brine well 2; Second draining stage: The first brine well 2 is sealed by the blowout preventer and the drilling rig is started, so that the drill rod 4 is in a rotating working state to break up large insoluble particles at the inlet of the second brine well 3 to prevent blockage of the second brine well 3. High-pressure gas is injected into the salt cavern cavity 6 through the gas injection well 1. At this time, with the assistance of the high gas pressure, the brine in the salt cavern cavity 6 can be drained through the second brine well 3.

[0030] Preferably, when sealing the second brine well 3 during the first brine discharge stage, the sealing method is to fill the second brine well 3 with clean water.

[0031] Specifically, when the amount of brine discharged from the salt cavern cavity 6 reaches 30%-50% of the total volume of the cavity, the process switches from the first brine discharge stage to the second brine discharge stage. For example, the first brine discharge stage can be switched to the second brine discharge stage when the amount of brine discharged from the salt cavern cavity 6 reaches 40% of the total volume of the cavity.

[0032] Among them, the well body of the second row of brine wells 3 located below the salt cavern cavity 6 adopts a double-inclined method to form a well body structure, so that the well body structure extends from the bottom of the salt cavern cavity 6 into the salt cavern cavity 6 and connects with the first row of brine wells 2.

[0033] The well drilling and brine removal process is as follows:

[0034] Vertical well construction:

[0035] The vertical well setup mainly consists of a first row of brine wells 2 and a second row of brine wells 3. The first row of brine wells 2 is constructed above the overall salt cavern 6, with the casing inside being lowered into the salt cavern 6. The second row of brine wells 3 is constructed at the edge of the cavern, drilling to an undeveloped salt layer. Through directional drilling technology, two consecutive sections are created to connect with the first row of brine wells 2.

[0036] Vertical well brine discharge working principle:

[0037] First, at the construction location of the first row of brine wells 2, a drilling rig and blowout preventer are installed, and drill rod 4 is lowered into the second row of brine wells 3.

[0038] Secondly, at the beginning of the gas injection and brine discharge process, clean water is injected into the second brine well 3, and the amount of clean water injected is consistent with the internal volume of the production casing in the second brine well 3.

[0039] Then, high-pressure air is injected into the injection well 1, the outlet of the second row of brine wells 3 is closed, and the brine outlet of the first row of brine wells 2 is opened. Brine is discharged using the first row of brine wells 2. When the amount of brine discharged from the salt cavern 6 reaches 40% of the total volume of the salt cavern 6, the brine outlet of the first row of brine wells 2 is closed. For example, a blowout preventer can also be installed at the outlet of the second row of brine wells 3.

[0040] Subsequently, the brine outlet of the second row of brine wells 3 was opened, the blowout preventer was activated, the drilling rig was started, and the gas injection well 1 continued to work. The brine was discharged from the second row of brine wells 3. The normal operation of the drilling rig ensured that large particles of insoluble matter could not clog the wellhead of the second row of brine wells 3.

[0041] Finally, all the brine in the cavity was drained, the drill rod 4 of the drilling rig was removed from the first brine well 2, and the brine injection and drainage project of the salt cavern gas storage was completed. All wellheads can be used as gas storage and gas transmission channels for the gas storage facility.

[0042] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A wellbore structure for draining brine from a salt cavern, characterized in that, At least including: The gas injection well is located above the salt cavern and extends from the surface into the salt cavern. The first row of brine wells is located above the salt cavern and extends from the surface to the bottom of the salt cavern. Drill rods are installed in the first row of brine wells. The second row of brine wells is located outside the boundary of the salt cavern cavity and extends from the surface to a position beyond the bottom of the salt cavern cavity. The well body of the second row of brine wells extends towards the direction close to the first row of brine wells. The second row of brine wells extends horizontally below the salt cavern cavity to below the first row of brine wells. The second row of brine wells passes upward through the bottom of the salt cavern cavity and connects with the first row of brine wells, so that the drill pipe extends at least partially into the second row of brine wells.

2. The well structure for brine drainage in a salt cavern according to claim 1, characterized in that, It also includes a blowout preventer, which is installed at the wellhead of the first brine well. The blowout preventer has a blocking state that restricts the discharge of brine and an open state that allows the brine to pass through.

3. The well structure for brine drainage in a salt cavern according to claim 1, characterized in that, It also includes a casing installed in the first brine well, with the drill pipe inserted inside the casing. The casing is adapted to limit the pressure exerted on the drill pipe by the rock mass within the salt cavern cavity.

4. A method for draining brine from a salt cavern, characterized in that, The wellbore structure including the brine drainage system of any one of claims 1-3 comprises the following specific steps: First stage of brine removal: The second brine well is sealed, high-pressure gas is injected into the salt cavern cavity through the gas injection well, and brine is removed through the first brine well; The second stage of brine removal involves sealing the first brine well and putting the drill pipe into operation. High-pressure gas is injected into the salt cavern cavity through the gas injection well, and brine is removed through the second brine well.

5. The method for draining brine from a salt cavern according to claim 4, characterized in that, When sealing the second brine well during the first brine stage, the second brine well is sealed by filling it with clean water.

6. The method for draining brine from a salt cavern according to claim 4, characterized in that, When the amount of brine discharged from the salt cavern reaches 30%-50% of the total volume of the cavern, the process switches from the first brine discharge stage to the second brine discharge stage.

7. The method for draining brine from salt caverns according to claim 4, characterized in that, The second row of brine wells, located below the salt cavern cavity, employs a double-inclined construction method to form the well body structure, allowing the well body structure to extend from the bottom of the salt cavern cavity into the cavity and connect with the first row of brine wells.

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