Cavity making system

Abstract

The invention discloses a cavity building system, and relates to the technical field of cavity building, the cavity building system comprises a vertical well and two horizontal wells, and the vertical well is arranged between the two horizontal wells; any horizontal well is provided with a vertical channel and at least two horizontal channels; all the horizontal channels are formed in the salt layer; all the horizontal channels are sequentially arranged from bottom to top, a through crack is formed between any two adjacent horizontal channels, one end of each horizontal channel is connected and communicated with the vertical channel, and the other end of each horizontal channel is connected and communicated with the vertical well; according to the invention, the cavity making efficiency is improved, the consumption of clear water is reduced, and the energy consumption of subsequent brine concentration treatment is reduced.

Description

Technical Field

[0001] This invention relates to the field of cavity creation technology, and in particular to a cavity creation system. Background Technology

[0002] Salt caverns, artificial caverns created in underground salt rock layers using water-soluble cavity-forming technology, have become key underground facilities for storing energy sources such as natural gas, oil, hydrogen, and compressed air due to their excellent sealing properties and enormous space. Salt cavern energy storage, as a large-scale, long-term energy storage technology, is increasingly demonstrating its importance.

[0003] The traditional water-soluble cavity-building technique for preparing salt caverns presents the following technical problems: 1. Low cavity formation efficiency and long cycle: Traditional cavity formation process has limited brine discharge flow rate and low contact area and efficiency between fluid and salt rock, resulting in slow cavity formation speed.

[0004] 2. Low resource utilization and substandard brine concentration: When using conventional vertical well injection for brine extraction, the fluid is prone to "short-circuiting," and the clean water is discharged before it can fully contact the salt rock. This results in low concentration and unsaturated brine, which wastes a lot of fresh water resources, reduces the efficiency of salt rock extraction, and increases the cost and energy consumption of subsequent brine concentration treatment. Summary of the Invention

[0005] The purpose of this invention is to provide a cavity-forming system to solve the problems existing in the prior art, improve the efficiency of cavity formation, reduce water consumption, and reduce energy consumption in subsequent brine concentration treatment.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a cavity-making system, comprising a vertical well and two horizontal wells, wherein the vertical well is positioned between the two horizontal wells; each of the horizontal wells has a vertical channel and at least two horizontal channels; all the horizontal channels are formed within a salt layer; all the horizontal channels are arranged sequentially from bottom to top, and any two adjacent horizontal channels are connected by a through fracture; one end of each horizontal channel is connected to and communicates with the vertical channel, and the other end of each horizontal channel is connected to and communicates with the vertical well.

[0007] Preferably, the system further includes a fracturing device. In any one of the horizontal wells, there are three horizontal channels, which are arranged from bottom to top as a lower channel, a middle channel, and an upper channel. The fracturing device is placed within the middle channel and is used to directionally fracture the salt rock and / or interlayers between the middle channel and the upper channel upwards to form a through fracture between the middle channel and the upper channel. The fracturing device is also used to directionally fracture the salt rock and / or interlayers between the middle channel and the lower channel downwards to form a through fracture between the middle channel and the lower channel.

[0008] Preferably, both the vertical well and the vertical channel are fixedly equipped with injection and discharge pipes and screen pipes. The screen pipe is placed below the injection and discharge pipe, and the top end of the screen pipe is fixedly connected to and communicates with the bottom end of the injection and discharge pipe. The bottom end of the screen pipe is open, and several screen slits are opened on the side wall of the screen pipe. The screen slits can block sediment, and the screen slits can allow brine to pass through.

[0009] Preferably, a production casing is fixedly installed in both the vertical well and the vertical channel. The production casing is fixedly sleeved outside the injection and discharge pipe and is positioned above the upper channel. An annular space is left between the production casing and the injection and discharge pipe. The annular space of the vertical well is used to fill the oil pad medium. The annular space of the vertical channel is used to discharge brine or to fill the oil pad medium.

[0010] Preferably, the sieve slots on the sieve tube are all located below the central channel.

[0011] Preferably, the vertical well and / or the vertical channel are used as injection-production wells after the cavity is created.

[0012] Preferably, the outer diameter of the injection / release pipe is equal to the outer diameter of the injection / production tubing string of the injection / production well.

[0013] Preferably, a packer is fixedly provided on the injection tube, the packer is placed inside the production sleeve, and the packer is positioned above the production sleeve shoe of the production sleeve. The packer is used to seal the inner side wall of the production sleeve after the cavity is formed.

[0014] Preferably, the distance between the middle channel and the upper channel is equal to the distance between the middle channel and the lower channel.

[0015] Preferably, the two horizontal wells are symmetrical about the vertical well.

[0016] The present invention achieves the following technical effects compared to the prior art: The cavity-building system provided by this invention, on the one hand, features horizontal wells with at least two horizontal channels, and each pair of adjacent horizontal channels has a through-crack, increasing the number of fluid seepage channels during the cavity-building process. This makes it easier for clear water or other injected fluids to flow and diffuse in the salt rock layer, promoting the dissolution of the salt rock. More fluid channels mean a more uniform and rapid dissolution effect, increasing the cavity-building speed. Simultaneously, the two horizontal wells increase the brine discharge flow rate, reduce the residence time of brine in the cavity, accelerate the cavity expansion process, and shorten the cavity-building time. Therefore, both fluid injection and discharge during the cavity-building process are optimized, significantly improving the overall efficiency of the cavity-building operation. This means that in the same time... The system allows for more cavity-making work to be completed within the space, reducing labor and equipment costs. Furthermore, the installation of two horizontal wells, each with at least two horizontal channels, connects one end of the horizontal channel to the vertical channel and the other end to the vertical well. This increases the contact area and time between the water and the salt rock, ensuring sufficient contact between the injected water and the salt rock. This allows for more uniform dissolution of the salt rock, resulting in the discharge of near-saturated high-concentration brine, reducing water consumption, increasing the recovery rate of salt rock mining, and achieving high resource utilization efficiency while minimizing waste. This not only improves cavity-making efficiency but also reduces energy consumption for subsequent brine concentration treatment, aligning with green mining principles. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the cavity creation system provided by the present invention; In the diagram: 1-Vertical well, 2-Horizontal well, 3-Surface casing, 4-Production casing, 5-Packer, 6-Salt layer, 7-Interlayer, 8-Build-up point, 9-Upper channel, 10-Middle channel, 11-Lower channel, 12-Through fracture, 13-Screen pipe, 14-Oil pad medium, 15-Injection and drainage pipe. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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] The purpose of this invention is to provide a cavity-forming system to solve the problems existing in the prior art, improve the efficiency of cavity formation, reduce water consumption, and reduce energy consumption in subsequent brine concentration treatment.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, the present invention provides a cavity-making system, including a vertical well 1 and two horizontal wells 2, with the vertical well 1 located between the two horizontal wells 2; each horizontal well 2 has a vertical channel and at least two horizontal channels; all horizontal channels are formed within a salt layer 6; all horizontal channels are arranged sequentially from bottom to top, and there is a through crack 12 between any two adjacent horizontal channels; one end of the horizontal channel is connected to and communicates with the vertical channel, and the other end of the horizontal channel is connected to and communicates with the vertical well 1.

[0023] The cavity-building system provided by this invention, on the one hand, features a horizontal well 2 with at least two horizontal channels, and each pair of adjacent horizontal channels is connected by a through fracture 12. This increases the number of fluid seepage channels during the cavity-building process, making it easier for clear water or other injected fluids to flow and diffuse in the salt rock layer, promoting the dissolution of the salt rock. More fluid channels mean a more uniform and rapid dissolution effect, increasing the cavity-building speed. Simultaneously, the two horizontal wells 2 increase the brine discharge flow rate, reduce the residence time of brine in the cavity, accelerate the cavity expansion process, and shorten the cavity-building time. Therefore, both fluid injection and discharge during the cavity-building process are optimized, significantly improving the overall efficiency of the cavity-building operation. This means that in the same... More cavity-making work can be completed within a short time, reducing labor and equipment costs. On the other hand, setting up two horizontal wells 2, each with at least two horizontal channels, with one end of the horizontal channel connected to and communicating with the vertical channel, and the other end of the horizontal channel connected to and communicating with the vertical well 1, increases the contact area and contact time between the clean water and the salt rock. This allows the clean water to fully contact the salt rock after injection, enabling the injected clean water to dissolve the salt rock more evenly. This allows for the discharge of near-saturated high-concentration brine, reducing clean water consumption, improving the recovery rate of salt rock mining, and achieving high resource utilization efficiency. It also reduces resource waste and not only improves the efficiency of cavity-making but also reduces the energy consumption of subsequent brine concentration treatment, which is in line with the concept of green mining.

[0024] As a preferred embodiment of the present invention, the cavity-making system provided by the present invention further includes a fracturing device. On any horizontal well 2, there are three horizontal channels, and the three horizontal channels are arranged from bottom to top as a lower channel 11, a middle channel 10, and an upper channel 9. The fracturing device is used to be placed in the middle channel 10. The fracturing device is used to perform upward directional fracturing of the salt rock and / or interlayer 7 between the middle channel 10 and the upper channel 9 to form a through fracture 12 between the middle channel 10 and the upper channel 9. The fracturing device is also used to perform downward directional fracturing of the salt rock and / or interlayer 7 between the middle channel 10 and the lower channel 11 to form a through fracture 12 between the middle channel 10 and the lower channel 11. The structure is relatively simple, easy to manufacture, and improves the efficiency of construction operations.

[0025] In this embodiment, during specific construction, vertical well 1 is drilled to the target layer. During the drilling of vertical well 1, well logging is used to determine the formation distribution, particularly the distribution of salt layer 6. Both horizontal wells 2 employ a three-section wellbore structure. After drilling horizontal well 2 to the second casing shoe, based on the well logging data from vertical well 1, a thicker section of salt layer 6 is selected. Three build-up points 8 are sequentially arranged from bottom to top, and horizontal drilling is performed using a side-drilling method until the target point of vertical well 1 is reached, forming a lower channel 11, a middle channel 10, and an upper channel 9. Adjacent horizontal sections ( The spacing of the horizontal channels is such that the designed salt cavern height is divided into three equal parts (for example, if the salt cavern height is about 90m, then the spacing between adjacent drilling horizontal sections (horizontal channels) is about 30m). After the horizontal well 2 is drilled, the fracturing device is sent to the middle channel 10. The fracturing device fractures the salt rock and / or interlayer 7 between the middle channel 10 and the upper channel 9 upwards to form a through fracture 12 between the middle channel 10 and the upper channel 9. The fracturing device also fractures the salt rock and / or interlayer 7 between the middle channel 10 and the lower channel 11 downwards to form a through fracture 12 between the middle channel 10 and the lower channel 11.

[0026] In a preferred embodiment of the present invention, injection and discharge pipes 15 and screen pipes 13 are fixedly installed in both the vertical well 1 and the vertical channel. The screen pipe 13 is placed below the injection and discharge pipe 15, and its top end is fixedly connected to and communicates with the bottom end of the injection and discharge pipe 15. The bottom end of the screen pipe 13 is open, and several screen slots are opened on the side wall of the screen pipe 13. The screen slots can block sediment and allow brine to pass through. After fracturing is completed, the fracturing device is removed, and the injection and discharge pipe 15 and screen pipe 13 are lowered into the vertical channel of the horizontal well 2. The bottom end of the screen pipe 13 reaches the directional point 8 of the lower channel 11. The screen slots on the side wall of the screen pipe 13 enable the brine to pass through during the cavity-making process. Even if sludge blockage occurs after dissolution, normal brine discharge can still be maintained through the screen gaps, ensuring high reliability of brine discharge (strong anti-clogging ability). This effectively avoids operation interruptions caused by blockage, improves the stability and reliability of the system, extends the service life of the equipment, and reduces maintenance costs. At the same time, the screen tube 13 is equivalent to adding a filter device. When rock salt dissolves, the sludge (such as insoluble impurities) produced will be blocked by the screen tube 13, preventing the sludge from entering the injection and discharge pipe 15 and causing blockage inside the injection and discharge pipe 15. Meanwhile, the screen tube 13 allows brine to pass smoothly, ensuring the continuity of brine discharge. It is especially suitable for long-term operation and ensures the smooth progress of the cavity-making process.

[0027] In a preferred embodiment of the present invention, a production casing 4 is fixedly installed in both the vertical well 1 and the vertical channel. The production casing 4 is fixedly sleeved outside the injection / discharge pipe 15 and positioned above the upper channel 9. An annular space is left between the production casing 4 and the injection / discharge pipe 15. The annular space of the vertical well 1 is used to fill the oil pad medium 14 (a water-insoluble fluid, such as diesel oil). The annular space of the vertical channel is used for draining brine or for filling the oil pad medium 14. In the early stage of cavity creation, the annular space of the vertical channel is used for draining brine, increasing the brine discharge flow rate. In the middle stage of cavity creation, the annular space of the vertical channel is used for filling the oil pad medium. The medium 14 is mixed with the oil pad medium 14 filling the annular space of the vertical well 1 to form a double oil pad. The oil pad floats above the brine, forming a barrier, precisely controlling the fluid interface, controlling the dissolution direction, limiting the dissolution range, ensuring the controllability of the cavity shape, preventing upward dissolution of the salt rock, and thus effectively preventing upward dissolution of the cavity. The cavity control precision is high, protecting the salt cavern roof from erosion, protecting the integrity of the salt cavern roof, providing good sealing and uniformity for later use of the salt cavern (such as compressed air energy storage), improving the safety and availability of the cavity, reducing the need for repair or reinforcement, and improving the reliability of long-term operation.

[0028] In a preferred embodiment of the present invention, the sieve slots on the sieve tube 13 are all located below the middle channel 10, so that the clean water injected into the vertical well 1 in the early stage moves horizontally from bottom to top along the lower channel 11, the middle channel 10 and the upper channel 9, preventing the clean water from entering the upper channel 9 in advance and causing dissolution; during the cavity making process, the brine cannot directly enter the injection and discharge pipe 15 from the upper channel 9, and all brine or fresh water can only enter and exit through the sieve slots below the injection and discharge pipe 15 and the bottom opening of the sieve tube 13.

[0029] In a preferred embodiment of the present invention, the vertical well 1 and / or the vertical channel are used as injection-production wells after the cavity is built. Both the vertical well 1 and the horizontal well 2 are also equipped with surface casing 3. The well structure, well quality, and various parameters of the tubing of the vertical channel of the vertical well 1 and the horizontal well 2 are designed and constructed in accordance with the requirements of injection-production wells (e.g., considering well structure, material pressure resistance, corrosion resistance, and sealing requirements) during the cavity building stage. This avoids additional drilling or large-scale modification work. After the cavity is built, it can be directly used for injection-production wells (such as compressed air energy storage injection-production wells), realizing the multi-functional reuse of wells, reducing engineering duplication and coordination time, reducing the risk of failure due to well incompatibility, shortening the construction period of the power plant gas storage system, and reducing the overall project cost.

[0030] In a preferred embodiment of the present invention, the outer diameter of the injection-exit pipe 15 is equal to the outer diameter of the injection-production string of the injection-production well, which facilitates the subsequent use of the injection-exit pipe 15 as the injection-production string. At the same time, the use of a large-size injection-exit pipe 15 reduces flow resistance, increases brine discharge flow rate, and greatly shortens the cavity creation time. It works in synergy with the through fracture 12 to avoid brine discharge delay caused by flow restriction or obstructed passage. In this embodiment, the outer diameter of the injection-exit pipe 15 is 339.7 mm.

[0031] In a preferred embodiment of the present invention, a packer 5 is fixedly provided on the injection / extraction pipe 15. The packer 5 is placed inside the production casing 4 and is positioned above the production casing shoe of the production casing 4. The packer 5 is used to set on the inner wall of the production casing 4 after the cavity is created. After the cavity is created, the portion below the packer 5 on the injection / extraction pipe 15 is cut by cutting the pipe, and then the packer 5 is set. The injection / extraction pipe 15 is used as an injection / production string.

[0032] In a preferred embodiment of the present invention, the distance between the middle channel 10 and the upper channel 9 is equal to the distance between the middle channel 10 and the lower channel 11, which facilitates construction and improves cavity creation efficiency.

[0033] As a preferred embodiment of the present invention, the two horizontal wells 2 are symmetrical about the vertical well 1, which facilitates construction and improves cavity-making efficiency.

[0034] The specific cavity creation process of the cavity creation system provided by this invention is as follows: In the early stage of cavity construction, oil pad medium 14 is filled into the annular space of vertical well 1 to form an oil pad layer to prevent dissolution after water injection. In the early stage, the bottom of the oil pad layer of vertical well 1 is located 5m to 10m above the upper channel 9. Oil pad medium 14 is not injected into horizontal well 2 for the time being. In the early stage, brine is discharged simultaneously in the annular space of the injection and discharge pipe 15 of horizontal well 2 and the vertical channel. In the early stage, it is required that the water injected from the injection and discharge pipe 15 of vertical well 1 can enter the vertical channel through the lower channel 11, the middle channel 10 and the upper channel 9 for stable brine discharge. In the middle stage, once oil pad medium 14 is found in the annular space of the vertical channel of horizontal well 2, water injection is stopped and oil pad medium 14 is injected into the annular space of the vertical channel of horizontal well 2 under pressure. 4. To form a complete oil cushion layer on the upper part of the upper channel 9, completely preventing the salt cavity from dissolving upwards; at the same time, due to the creep of the salt rock, the through fracture 12 may be at risk of closure. In the mid-term stage, a reverse well method is adopted, injecting a large amount of clean water from the two horizontal wells 2, closing the vertical well 1, increasing the pressure in the salt cavity, expanding the through fracture 12, and making the lower channel 11, middle channel 10 and upper channel 9 completely connected vertically. Then, the vertical well 1 is opened to drain the brine, and the cycle is repeated multiple times. In the later stage, in order to extract saturated brine and ensure that the salt rock particles in the salt cavity are fully dissolved and improve the cavity-making efficiency, water is mainly injected from one horizontal well 2 and brine is drained from the other horizontal well 2 and the vertical well 1, or water is injected from the vertical well 1 and brine is drained from the two horizontal wells 2.

[0035] During the cavity-making process, the following requirements apply: Since crystallization is prone to occur during the brine discharge process, if the brine discharge rate is found to be continuously decreasing, backwashing is required by switching wells; Overpressure injection and production are not allowed during the water injection and brine discharge process to prevent the packer 5 from being prematurely set.

[0036] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A cavity-building system, characterized in that: It includes one vertical well and two horizontal wells, with the vertical well positioned between the two horizontal wells; Each of the horizontal wells has a vertical passage and at least two horizontal passages; All of the aforementioned horizontal channels are formed within the salt layer; All the horizontal channels are arranged sequentially from bottom to top, and there is a through crack between any two adjacent horizontal channels. One end of the horizontal channel is connected to and communicates with the vertical channel, and the other end of the horizontal channel is connected to and communicates with the vertical well.

2. The cavity-creating system according to claim 1, characterized in that: It also includes a fracturing device. In any one of the horizontal wells, there are three horizontal channels, which are arranged from bottom to top as a lower channel, a middle channel, and an upper channel. The fracturing device is placed in the middle channel and is used to directionally fracture the salt rock and / or interlayers between the middle channel and the upper channel upward to form a through fracture between the middle channel and the upper channel. The fracturing device is also used to directionally fracture the salt rock and / or interlayers between the middle channel and the lower channel downward to form a through fracture between the middle channel and the lower channel.

3. The cavity-creating system according to claim 2, characterized in that: Both the vertical well and the vertical channel are fixedly equipped with injection and discharge pipes and screen pipes. The screen pipe is placed below the injection and discharge pipe. The top end of the screen pipe is fixedly connected to and communicates with the bottom end of the injection and discharge pipe. The bottom end of the screen pipe is open. Several screen slits are opened on the side wall of the screen pipe. The screen slits can block sediment and allow brine to pass through.

4. The cavity-creating system according to claim 3, characterized in that: Both the vertical well and the vertical channel are equipped with a production casing, which is fixedly sleeved outside the injection and discharge pipe. The production casing is positioned above the upper channel, and an annular space is left between the production casing and the injection and discharge pipe. The annular space of the vertical well is used to fill the oil pad medium. The annular space of the vertical channel is used to discharge brine or to fill the oil pad medium.

5. The cavity-building system according to claim 3, characterized in that: The sieve slots on the sieve tube are all located below the central channel.

6. The cavity-building system according to claim 4, characterized in that: The vertical well and / or the vertical channel are used as injection-production wells after the cavity is created.

7. The cavity-building system according to claim 6, characterized in that: The outer diameter of the injection and drainage pipe is equal to the outer diameter of the injection and production tubing string of the injection and production well.

8. The cavity-building system according to claim 6, characterized in that: A packer is fixedly installed on the injection tube. The packer is placed inside the production sleeve and above the production sleeve shoe of the production sleeve. The packer is used to seal the inner wall of the production sleeve after the cavity is created.

9. The cavity-creating system according to claim 2, characterized in that: The distance between the middle channel and the upper channel is equal to the distance between the middle channel and the lower channel.

10. The cavity-creating system according to claim 2, characterized in that: The two horizontal wells are symmetrical about the vertical well.

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