A single-well circulating hydrothermal underground heat extraction system and method

Abstract

The present invention belongs to the field of geothermal resource development technology, and specifically discloses a single-well circulation hydrothermal underground heat extraction system and method, the heat extraction system includes a vertical well, an outer ring pipe, a first transverse pipe, an inner pipe, a second transverse pipe and a heat pump system, the lower end of the outer ring pipe is provided with at least one first transverse pipe, one end of the first transverse pipe is connected with the lower end of the outer ring pipe, and the other end penetrates the side wall of the vertical well and is arranged in the lateral soil layer of the vertical well; the lower end of the inner pipe penetrates the lower end of the outer ring pipe and extends to the bottom of the vertical well, the lower end of the inner pipe is provided with at least one second transverse pipe, one end of the second transverse pipe is connected with the inner pipe, and the other end penetrates the side wall of the vertical well and is arranged in the lateral soil layer of the vertical well. The present invention avoids the well body safety problem that may be caused by the flow scouring along the well wall caused by direct water injection. And it effectively expands the amount and area of ​​water involved in the circulation, and solves the thermal short circuit problem caused by the return of cold water in the vicinity.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal resource development, and in particular relates to a single-well circulating hydrothermal underground heat extraction system and method. Background Art

[0002] As global energy demand grows, clean energy is gradually gaining more and more attention. Geothermal energy, as a renewable, clean and stable energy resource, is gaining more and more attention and application around the world.

[0003] As a clean and renewable way of utilizing energy, underground heat exchange has received extensive attention in recent years. Compared with the traditional air source heat pump system, the underground heat exchange system has the advantages of more stable heat source temperature, higher thermal efficiency, and less energy consumption. In the underground heat exchange system, hot water circulates through the U-shaped pipe buried underground to transfer heat, exchange heat with the surrounding soil underground, and then transfers it back to the ground for heating or cooling.

[0004] In underground heat exchange systems, the single-well circulation mode is a commonly used system form. Injection of water from different layers in the same well is mostly done directly by drilling holes in the well body. Although the pressure is increased by a ground pressure pump, it is still difficult to obtain a high pressure after thousands of meters. In addition, the material and pressure limitations of the well body and pipe wall make the water flow farther laterally. The existing vertical pipes in different layers in the prior art are close to the heat collector, which can easily cause the seepage water to flow along the well wall, resulting in safety problems of the well, and also cause thermal short circuit problems. Summary of the invention

[0005] In view of the above-mentioned problems, the purpose of the present invention is to provide a single-well circulating hydrothermal underground heat extraction system and method to prevent seepage water from flowing along the well wall, thereby improving the safety of the well and effectively avoiding the problem of thermal short circuit.

[0006] The technical solution of the present invention is: a single-well circulating hydrothermal underground heat extraction system, comprising:

[0007] vertical well;

[0008] The outer ring pipe is arranged in the vertical well along the well depth direction of the vertical well and is arranged coaxially with the vertical well; at least one first transverse pipe is arranged at the lower end of the outer ring pipe, one end of the first transverse pipe is connected to the lower end of the outer ring pipe, and the other end penetrates the side wall of the vertical well and is arranged in the lateral soil layer of the vertical well, and the other end of the first transverse pipe is used to be placed in the first aquifer of the heat storage;

[0009] The inner pipe is arranged along the length direction of the outer ring pipe and is coaxially arranged with the outer ring pipe; the lower end of the inner pipe penetrates the lower end of the outer ring pipe and extends to the bottom of the vertical well, and at least one second transverse pipe is arranged at the lower end of the inner pipe, one end of the second transverse pipe is connected to the inner pipe, and the other end penetrates the side wall of the vertical well and is arranged in the lateral soil layer of the vertical well, and the other end of the second transverse pipe is used to be placed in the second aquifer containing heat storage water; the first aquifer is located above the second aquifer, and there is a weak permeable layer between the first aquifer and the second aquifer;

[0010] The heat pump system has a hot water inlet and a cold water outlet. The hot water inlet is connected to the upper end of the inner tube, and the cold water outlet is connected to the upper end of the outer ring tube. The heat pump system is used for heat exchange with hot water storage.

[0011] Furthermore, there are a plurality of the first transverse tubes, and the plurality of first transverse tubes are distributed along the circumference of the outer annular tube and are all connected to the outer annular tube;

[0012] The end of each of the first transverse tubes away from the outer ring tube is closed, a first opening is formed on the side wall of the first transverse tube close to the end, and a first filter is arranged on the first opening.

[0013] Furthermore, there are multiple second transverse tubes, which are distributed along the circumference of the inner tube and are all connected to the outer annular tube;

[0014] The end of each of the second transverse tubes away from the inner tube is closed, a second opening is formed on the side wall of the second transverse tube close to the end, and a second filter is arranged on the second opening.

[0015] Furthermore, the length of the first transverse tube is L1, the length of the second transverse tube is L2, and L2<L1.

[0016] Furthermore, it also includes a telescopic device, the first transverse tube is a telescopic structure, the telescopic device has a telescopic end, the telescopic end is connected to the end of the first transverse tube away from the outer ring tube, and the telescopic device is used to drive the first transverse tube to telescope to adjust the length of the first transverse tube.

[0017] Furthermore, the first transverse tube comprises:

[0018] A base pipe, one end of which is connected to the lower end of the outer ring pipe;

[0019] The telescopic pipe is slidably sleeved on the end of the base pipe away from the outer ring pipe;

[0020] The telescopic end of the telescopic device is connected to the telescopic tube and is used to drive the telescopic tube to move along the tube length direction of the base tube.

[0021] Further, the angle between the first transverse tube and the horizontal direction is α, then 0°≤α≤5°;

[0022] The angle between the second transverse tube and the horizontal direction is β, then 0°≤β≤5°.

[0023] Furthermore, it also includes a circulation pump group, which is respectively connected to the outer ring pipe and the inner pipe, and is used to provide power to the outer ring pipe to discharge the hot storage water after heat exchange from the first transverse pipe to the first aquifer through the outer ring pipe. The circulation pump group is also used to provide power to the inner pipe to lift the hot storage water in the second aquifer from the second transverse pipe through the inner pipe to the heat pump system.

[0024] Furthermore, the circulating pump group comprises:

[0025] Submersible pumps, the number of which corresponds to the number of the second transverse pipes, and are arranged one by one in one in the second transverse pipe near the inner pipe, and the submersible pumps are used to pump the hot water stored in the second aquifer into the second transverse pipe;

[0026] A lifting pump, whose water inlet is connected to the inner pipe and whose water outlet is connected to the heat pump system, is used to lift the hot stored water to the ground;

[0027] A circulation pump, whose water inlet is connected to the heat pump system and whose water outlet is connected to the outer ring pipe, is used to discharge the hot stored water after heat exchange into the outer ring pipe.

[0028] A single-well circulating hydrothermal underground heat extraction method, utilizing the underground heat extraction system to extract heat, comprises the following steps:

[0029] Determine the drilling position of the geothermal well, drill the well, lower the vertical casing and fix it; use the downhole diverter to perform side drilling and window opening in the formation at the first horizontal pipe depth position, complete the second opening drilling operation, and lower the horizontal casing; use the downhole diverter to perform side drilling and window opening in the formation at the second horizontal pipe depth position, complete the second opening drilling operation, and lower the horizontal casing;

[0030] The second transverse pipe, the first transverse pipe, the inner pipe, and the outer ring pipe are sequentially lowered, and the thermal insulation material is laid; the space between the second transverse pipe and the inner pipe, and between the first transverse pipe and the outer ring pipe are sequentially sealed;

[0031] Connect the heat pump system to the outer ring pipe and inner pipe to complete the connection and fixation of the ground system:

[0032] Operation: hot water enters the heat pump system from the second aquifer through the second horizontal pipe and the inner pipe. The heat pump system is used to exchange heat with the hot storage water with a higher temperature and then supply it to the demand side. The hot storage water with a lower temperature after heat exchange is injected into the first aquifer through the outer ring pipe and the first horizontal pipe, and then penetrates into the second aquifer through the weak permeable layer. During this period, it completes sufficient heat exchange with the formation to increase its own temperature, replenishes the water pumped away from the second aquifer, and maintains its temperature field and pressure field.

[0033] Repeat the operation steps to achieve continuous heat extraction.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention is based on the first horizontal pipe and the second horizontal pipe, which avoids the wellbore safety problem caused by the flow scouring along the well wall caused by the long-term direct water injection of the vertical pipe in the traditional technology. It also effectively expands the amount and area of ​​water involved in the circulation, and solves the thermal short circuit problem caused by the cold water reflux near the vertical pipe caused by the long-term direct water injection in the traditional technology.

[0036] Moreover, although the present application adds transverse pipe branches of the first transverse pipe and the second transverse pipe, it is still based on a single well structure, that is, it still has the advantages of small single well investment and short construction period. In addition, the actual number and layout of the first transverse pipe and the second transverse pipe can be arranged in different ways according to geological conditions, which has the advantage of a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0038] Figure 2 is a schematic structural diagram of Embodiment 2 of the present invention;

[0039] Figure 3 It is a schematic diagram of the partial structure of the first transverse tube of Example 2 of the present invention;

[0040] Figure 4 It is a structural schematic diagram of other layouts of the first transverse tube and the second transverse tube of the present invention;

[0041] Figure 5 It is a structural schematic diagram of other layouts of the first transverse tube and the second transverse tube of the present invention.

[0042] Among them, 1-vertical well, 2-outer ring pipe, 3-first horizontal pipe, 30-first filter, 31-base pipe, 32-telescopic pipe, 4-inner pipe, 5-second horizontal pipe, 50-second filter, 6-heat pump system, 7-telescopic device, 71-motor, 72-screw, 73-nut, 8-circulating pump group, 81-submersible pump, 82-lifting pump, 83-circulating pump, DETAILED DESCRIPTION

[0043] The following is combined with Figure 1 -Attached Figure 5, the specific embodiments of the present invention are described in detail. In the description of the present invention, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0044] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0045] It should be noted that the circuit connections involved in the present invention all adopt conventional circuit connection methods and do not involve any innovation.

[0046] Example 1

[0047] like Figure 1 A single-well circulating hydrothermal underground heat extraction system is shown, comprising a vertical well 1, an outer ring pipe 2, a first horizontal pipe 3, an inner pipe 4, a second horizontal pipe 5 and a heat pump system 6.

[0048] The outer ring pipe 2 is arranged in the vertical well 1 along the depth direction of the vertical well 1 and is coaxially arranged with the vertical well 1; at least one first transverse pipe 3 is arranged at the lower end of the outer ring pipe 2, one end of the first transverse pipe 3 is connected to the lower end of the outer ring pipe 2, and the other end passes through the side wall of the vertical well 1 and is arranged in the lateral soil layer of the vertical well 1, and the other end of the first transverse pipe 3 is used to be placed in the first aquifer of the heat storage.

[0049] The inner pipe 4 is arranged along the length direction of the outer ring pipe 2 and is coaxially arranged with the outer ring pipe 2; the lower end of the inner pipe 4 passes through the lower end of the outer ring pipe 2 and extends to the bottom of the vertical well 1, and at least one second transverse pipe 5 is arranged at the lower end of the inner pipe 4, one end of the second transverse pipe 5 is connected to the inner pipe 4, and the other end passes through the side wall of the vertical well 1 and is arranged in the lateral soil layer of the vertical well 1, and the other end of the second transverse pipe 5 is used to be placed in the second aquifer containing heat storage water; the first aquifer is located above the second aquifer, and there is a weakly permeable layer between the first aquifer and the second aquifer.

[0050] The heat pump system 6 has a hot water inlet and a cold water outlet. The hot water inlet is connected to the upper end of the inner tube 4, and the cold water outlet is connected to the upper end of the outer ring tube 2. The heat pump system 6 is used for heat exchange with the hot water storage.

[0051] It should be noted that the arrangement of the first transverse pipe 3 and the second transverse pipe 5 avoids the wellbore safety problem that may be caused by the flow scouring along the well wall caused by the long-term direct water injection of the vertical pipe in the traditional technology. It also effectively expands the amount and area of ​​water involved in the circulation, and solves the thermal short circuit problem caused by the cold water reflux in the vicinity caused by the long-term direct water injection of the vertical pipe in the traditional technology.

[0052] Preferably, there are multiple first transverse tubes 3, which are distributed along the circumference of the outer ring tube 2 and are all connected to the outer ring tube 2; the end of each first transverse tube 3 away from the outer ring tube 2 is closed, and a first opening is provided on the side wall of the first transverse tube 3 close to the end, and a first filter 30 is provided on the first opening. In this embodiment, there are two first transverse tubes 3, and the two first transverse tubes 3 are arranged on both sides of the outer ring tube 2 in a straight line structure.

[0053] Preferably, there are multiple second transverse tubes 5, which are distributed along the circumference of the inner tube 4 and are all connected to the outer ring tube 2; the end of each second transverse tube 5 away from the inner tube 4 is closed, and a second opening is provided on the side wall of the second transverse tube 5 close to the end, and a second filter 50 is provided on the second opening. In this embodiment, there are two second transverse tubes 5, which are arranged on both sides of the inner tube 4 in a straight line structure. And the outer ring tube 2, the first transverse tube 3, the inner tube 4, and the second transverse tube 5 form a V-shaped structure as a whole.

[0054] It should be noted that: Figure 4 As shown, when the number of the first transverse pipe 3 and the second transverse pipe 5 is one each, they are preferably arranged in a staggered manner, that is, the first transverse pipe 3 and the second transverse pipe 5 are respectively located on opposite sides of the vertical shaft 1. Figure 5 As shown, when the number of the first transverse pipe 3 and the second transverse pipe 5 is two, they can also be arranged in a staggered and mutually perpendicular manner, which can further expand the circulating water activity area. In actual implementation, it is necessary to make a field selection based on different geological conditions, construction technology and permeability, taking into account factors such as construction difficulty, system reliability, and injection and drainage pressure. In addition, the number of the first transverse pipe 3 and the second transverse pipe 5 can also be an integer greater than 2, but it is not recommended to exceed 5.

[0055] The first filter element 30 and the second filter element 50 are both commercially available filter elements.

[0056] Preferably, the length of the first transverse tube 3 is L1, the length of the second transverse tube 5 is L2, and L2 < L1. It should be noted that the length of the first transverse tube 3 is L1, and the length of the second transverse tube 5 is L2, which are both related to the heat removal Q, heat removal influence radius R, and penetration time T of the heat removal system.

[0057] Among them, L1 = k1·QR / T, that is, it is positively correlated with Q and R, and negatively correlated with the penetration time T, wherein the k1 value is a constant value, and the value of k1 is related to the geological conditions. According to the actual engineering projects and the simulation results of the numerical model, the head radius during the long-term operation temperature field influence period is 20-30m, therefore, the length of L1 is generally not less than 15m, and the value of L1 in this embodiment is 20m.

[0058] Among them, L2 = k2·QR / T, that is, it is positively correlated with Q and R, and negatively correlated with the penetration time T, wherein the k2 value is a constant value, and the value of k2 is related to the geological conditions. In this embodiment, the value of L2 is 15m.

[0059] Preferably, it also includes a circulation pump group 8, which is respectively connected to the outer ring pipe 2 and the inner pipe 4, and is used to provide power to the outer ring pipe 2 to discharge the hot storage water after heat exchange from the first transverse pipe 3 to the first aquifer through the outer ring pipe 2. The circulation pump group 8 is also used to provide power to the inner pipe 4 to lift the hot storage water in the second aquifer from the second transverse pipe 5 through the inner pipe 4 to the heat pump system 6.

[0060] Preferably, the circulation pump group includes a submersible pump 81, a lifting pump 82 and a circulation pump 83. The number of the submersible pumps 81 corresponds to the number of the second transverse pipes 5, and they are arranged one by one in the second transverse pipe 5 on one side close to the inner pipe 4. The submersible pump 81 is used to pump the hot water storage in the second aquifer into the second transverse pipe 5; the water inlet of the lifting pump 82 is connected to the inner pipe 4, and the water outlet is connected to the heat pump system 6, and is used to lift the hot water storage to the ground; the water inlet of the circulation pump 83 is connected to the heat pump system 6, and the water outlet is connected to the outer ring pipe 2, and is used to discharge the hot water storage after heat exchange into the outer ring pipe 2.

[0061] The inner tube 4 and the second transverse tube 5 constitute a water intake pipeline, and the water intake pipeline cooperates with the submersible pump 81 and the lifting pump 82 to lift the hot water storage in the second aquifer to the heat pump system 6. The heat pump system 6 is used to exchange heat with the hot water storage. The outer ring tube 2 and the first transverse tube 3 constitute a water injection pipeline. The water injection pipeline cooperates with the circulating pump 83 to discharge the hot water storage after heat exchange in the heat pump system 6 into the first aquifer.

[0062] A single-well circulating hydrothermal underground heat extraction method, utilizing an underground heat extraction system to extract heat, comprises the following steps:

[0063] Step 1: Determine the geothermal well drilling location based on geological data, including horizontal positioning and depth positioning.

[0064] Step 2: Drill the vertical shaft, lower the vertical casing and secure it.

[0065] Step 3: Use a downhole diverter to perform side drilling and window opening in the stratum at the first horizontal pipe depth position, complete the secondary drilling operation, and lower the horizontal casing; Use a downhole diverter to perform side drilling and window opening in the stratum at the second horizontal pipe depth position, complete the secondary drilling operation, and lower the horizontal casing.

[0066] The second transverse pipe 5, the first transverse pipe 3, the inner pipe 4 and the outer ring pipe 2 are sequentially lowered, and the thermal insulation material is laid.

[0067] Step 4: Seal the space between the second transverse pipe 5 and the inner pipe 4 and between the first transverse pipe 3 and the outer ring pipe 2 in sequence; and lower the submersible pump 81 and its control line into the water intake section.

[0068] The heat pump system 6 is connected to the outer ring pipe 2 and the inner pipe 4, and the lifting pump 82 and the circulation pump 83 are connected to complete the connection and fixation of the ground system.

[0069] Step 5: The system is running, the lifting pump 82 and the submersible pump 81 are turned on, and the hot water enters the heat pump system 6 from the second aquifer through the second transverse pipe 5 and the inner pipe 4. The heat pump system 6 is used to supply the demand side after heat exchange with the hot storage water with a higher temperature; after a period of time, the circulation pump 83 is turned on, and the hot storage water with a lower temperature after heat exchange is injected into the first aquifer through the outer ring pipe 2 and the first transverse pipe 3, and then penetrates into the second aquifer through the weak permeable layer. During this period, sufficient heat exchange is completed with the formation to increase its own temperature, replenish the water volume pumped out of the second aquifer, and maintain its temperature field and pressure field.

[0070] Repeat the operation steps to achieve continuous heat extraction.

[0071] Example 2

[0072] The difference from Example 1 is that: preferably, Figure 2 As shown, it also includes a telescopic device 7. The first transverse tube 3 is a telescopic structure. The telescopic device 7 has a telescopic end, which is connected to the end of the first transverse tube 3 away from the outer ring tube 2. The telescopic device 7 is used to drive the first transverse tube 3 to telescope to adjust the length of the first transverse tube 3.

[0073] Preferably, Figure 3 As shown, the first transverse pipe 3 includes a base pipe 31 and a telescopic pipe 32. One end of the base pipe 31 is connected to the lower end of the outer ring pipe 2; the telescopic pipe 32 is slidably sleeved on the end of the base pipe 31 away from the outer ring pipe 2.

[0074] The telescopic end of the telescopic device 7 is connected to the telescopic tube 32, and is used to drive the telescopic tube 32 to move along the tube length direction of the base tube 31. The telescopic device 7 includes a motor 71, a lead screw 72 and a nut 73. The motor 71 is fixedly arranged on the base tube 31, the lead screw 72 is connected to the output end of the motor 71 through a coupling, and the nut 73 is threadedly connected to the lead screw 72. The nut 73 is fixedly arranged on the telescopic tube 32.

[0075] It should be noted that: in this embodiment, the base pipe 31 is 20m, the telescopic pipe 32 is 10m, and the overlap section between the base pipe 31 and the telescopic pipe 32 is 5m, that is, the effective length of the first transverse pipe 3 is 25-30m, and the actual length of the first transverse pipe 3 is actually determined according to the ground temperature attenuation. The telescopic device 7 is connected to the ground power supply and the controller, and according to the temperature of the taken out hot water, in addition to adjusting the injection flow rate, the controller can be used to adjust the length of the telescopic pipe 32 through the telescopic device 7, so as to expand or reduce the heat exchange path and area of ​​the injected water, which plays a role in regulating the heat exchange time and ensuring the water intake temperature.

[0076] Example 3

[0077] The difference from Example 1 is that: preferably, the angle between the first transverse pipe 3 and the horizontal direction is α, then 0°≤α≤5°; the angle between the second transverse pipe 5 and the horizontal direction is β, then 0°≤β≤5°. In actual construction, it is necessary to adapt to different geological conditions, construction processes and permeability, and comprehensively consider factors such as construction difficulty, system reliability, and injection and drainage pressure. In actual construction, both the first transverse pipe 3 and the second transverse pipe 5 can be arranged at a small angle.

[0078] The specific models of the above electronic components are not specially specified, and ordinary commercial products can be selected as long as they can meet the use requirements of the present invention.

[0079] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A single-well circulating hydrothermal underground heat extraction system, characterized in that: include: Vertical shaft (1); The outer ring pipe (2) is arranged in the vertical well (1) along the well depth direction of the vertical well (1) and is arranged coaxially with the vertical well (1); at least one first transverse pipe (3) is arranged at the lower end of the outer ring pipe (2); one end of the first transverse pipe (3) is connected to the lower end of the outer ring pipe (2), and the other end penetrates the side wall of the vertical well (1) and is arranged in the lateral soil layer of the vertical well (1); the other end of the first transverse pipe (3) is used to be placed in the first aquifer of the heat storage; The inner tube (4) is arranged along the length direction of the outer ring tube (2) and is coaxially arranged with the outer ring tube (2); the lower end of the inner tube (4) penetrates the lower end of the outer ring tube (2) and extends to the bottom of the vertical well (1); at least one second transverse tube (5) is arranged at the lower end of the inner tube (4); one end of the second transverse tube (5) is connected to the inner tube (4), and the other end penetrates the side wall of the vertical well (1) and is arranged in the lateral soil layer of the vertical well (1); the other end of the second transverse tube (5) is used to be placed in the second aquifer containing heat storage water; the first aquifer is located above the second aquifer, and there is a weak permeable layer between the first aquifer and the second aquifer; The heat pump system (6) has a hot water inlet and a cold water outlet, wherein the hot water inlet is connected to the upper end of the inner tube (4), and the cold water outlet is connected to the upper end of the outer ring tube (2), and the heat pump system (6) is used to perform heat exchange with the hot water storage; There are a plurality of the first transverse tubes (3), and the plurality of first transverse tubes (3) are distributed along the circumference of the outer annular tube (2) and are all connected to the outer annular tube (2); The end of each of the first transverse tubes (3) away from the outer ring tube (2) is closed, a first opening is provided on the side wall of the first transverse tube (3) close to the end, and a first filter element (30) is provided on the first opening; There are a plurality of the second transverse tubes (5), the plurality of second transverse tubes (5) are distributed along the circumference of the inner tube (4) and are all connected to the outer annular tube (2); The end of each second transverse tube (5) away from the inner tube (4) is closed, and a second opening is provided on the side wall of the second transverse tube (5) close to the end, and a second filter element (50) is provided on the second opening.

2. A single-well circulating hydrothermal underground heat extraction system as claimed in claim 1, characterized in that: The length of the first transverse tube (3) is L1, the length of the second transverse tube (5) is L2, and L2 is less than L1.

3. A single-well circulating hydrothermal underground heat extraction system as claimed in claim 1, characterized in that: It also includes a telescopic device (7), wherein the first transverse tube (3) is a telescopic structure, and the telescopic device (7) has a telescopic end, wherein the telescopic end is connected to an end of the first transverse tube (3) away from the outer ring tube (2), and the telescopic device (7) is used to drive the first transverse tube (3) to telescope so as to adjust the length of the first transverse tube (3).

4. A single-well circulating hydrothermal underground heat extraction system as claimed in claim 3, characterized in that: The first transverse tube (3) comprises: A base pipe (31), one end of which is connected to the lower end of the outer ring pipe (2); A telescopic tube (32) is slidably sleeved on an end of the base tube (31) away from the outer ring tube (2); The telescopic end of the telescopic device (7) is connected to the telescopic tube (32) and is used to drive the telescopic tube (32) to move along the tube length direction of the base tube (31).

5. The single-well circulating hydrothermal underground heat extraction system according to claim 1, characterized in that: The angle between the first transverse tube (3) and the horizontal direction is α, then 0°≤α≤5°; The included angle between the second transverse tube (5) and the horizontal direction is β, and then 0°≤β≤5°.

6. The single-well circulating hydrothermal underground heat extraction system according to claim 1, characterized in that: The invention also comprises a circulation pump group (8) which is respectively connected to the outer ring pipe (2) and the inner pipe (4) and is used for providing power to the outer ring pipe (2) so as to discharge the hot water after heat exchange from the first transverse pipe (3) to the first aquifer through the outer ring pipe (2). The circulation pump group (8) is also used for providing power to the inner pipe (4) so ​​as to lift the hot water in the second aquifer from the second transverse pipe (5) through the inner pipe (4) to the heat pump system (6).

7. A single-well circulating hydrothermal underground heat extraction system as claimed in claim 6, characterized in that: The circulating pump group comprises: Submersible pumps (81), the number of which corresponds to the number of the second transverse pipes (5), and are arranged one-to-one in a side of the second transverse pipe (5) close to the inner pipe (4), and the submersible pumps (81) are used to pump the hot water stored in the second aquifer into the second transverse pipe (5); A lifting pump (82), the water inlet of which is connected to the inner pipe (4) and the water outlet of which is connected to the heat pump system (6), is used to lift the hot stored water to the ground; A circulation pump (83) has a water inlet connected to the heat pump system (6) and a water outlet connected to the outer ring pipe (2), and is used to discharge the hot stored water after heat exchange into the outer ring pipe (2).

8. A single-well circulating hydrothermal underground heat extraction method, characterized in that: Using the underground heat extraction system described in any one of claims 1 to 7 to extract heat comprises the following steps: Determine the drilling position of the geothermal well, drill the well, lower the vertical casing and fix it; use the downhole diverter to perform side drilling and window opening in the formation at the first horizontal pipe depth position, complete the second opening drilling operation, and lower the horizontal casing; use the downhole diverter to perform side drilling and window opening in the formation at the second horizontal pipe depth position, complete the second opening drilling operation, and lower the horizontal casing; The second transverse pipe (5), the first transverse pipe (3), the inner pipe (4), and the outer annular pipe (2) are sequentially lowered, and the thermal insulation material is laid; the space between the second transverse pipe (5) and the inner pipe (4), and the space between the first transverse pipe (3) and the outer annular pipe (2) are sequentially sealed; Connect the heat pump system (6) with the outer ring pipe (2) and the inner pipe (4) to complete the connection and fixation of the ground system: Operation: hot water enters the heat pump system (6) from the second aquifer through the second transverse pipe (5) and the inner pipe (4). The heat pump system (6) is used to exchange heat with the hot storage water with a higher temperature and then supply it to the demand side. The hot storage water with a lower temperature after the heat exchange is injected into the first aquifer through the outer ring pipe (2) and the first transverse pipe (3), and then penetrates into the second aquifer through the weakly permeable layer. During this period, sufficient heat exchange is completed with the formation to increase its own temperature, replenish the amount of water pumped out of the second aquifer, and maintain its temperature field and pressure field. Repeat the operation steps to achieve continuous heat extraction.

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