Multi-branch middle-deep geothermal well efficient heat exchange system

Abstract

The invention discloses a multi-branch middle-deep geothermal well efficient heat exchange system which comprises a main well, a plurality of branch wells and heat exchange pipes extending downwards in the main well in the vertical direction. The main well comprises a first well opening section and a second well opening section, the first well opening section extends downwards from the ground in the vertical direction to be communicated with an upper port of the second well opening section, a lower port of the second well opening section extends downwards in the vertical direction to a geothermal water layer, and an upper port of each branch well is communicated with the second well opening section. The lower port of each branch well obliquely and downwards extends to the geothermal water layer in the direction gradually away from the second opening well section; the vertical distances between the upper ports of the multiple branch wells and the ground are different, and a heat conduction metal stranded wire is arranged in each branch well in the extension direction of the branch well. The medium-deep geothermal well is designed to be of a multi-branch directional well structure, the heat conduction metal stranded wires are arranged in the branch wells in the extension directions of the branch wells, and therefore the geothermal energy taking capacity and the heat transfer efficiency of the stratum far away from the medium-deep geothermal well are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal energy development and application, and particularly relates to a high-efficiency heat exchange system for multi-branch medium-deep geothermal wells. Background Art

[0002] In the medium-deep heat exchange type of geothermal energy development, "only heat is taken and no water is taken", which has almost no impact on underground water resources and the geological environment. Its basic principle is to bury a buried pipe heat exchanger composed of a heat-insulating inner pipe and a heat-conducting outer pipe in the formation to extract the heat of the underground rock and soil mass and transport it to the surface. At present, with the progress of technology and the further improvement of the heat extraction capacity requirements, the well depth of medium-deep heat exchange type geothermal wells is getting deeper and deeper, exceeding 3000m and even approaching 4000m, and the formation temperature is also getting higher and higher. A high-vacuum metal heat-insulating inner pipe with a thermal conductivity less than 0.02W / m·K, a compressive strength greater than 40MPa, and that can be used in medium-deep geothermal wells with a temperature greater than 150°C for a long time is being widely promoted, and the heat extraction capacity of medium-deep geothermal wells has been greatly improved.

[0003] However, the improvements in the prior art only start from the heat-insulating performance of the heat-insulating inner pipe, trying to minimize the heat loss of the geothermal energy that has been extracted by the heat transfer medium during the transportation to the surface, without considering how to introduce the geothermal energy of the rock and soil mass within a certain distance around the medium-deep geothermal well into the geothermal well. Most of the existing medium-deep heat exchange type geothermal wells are straight wells, directional wells or horizontal docking wells with relatively high costs. Due to the generally low thermal conductivity of the formation rock and soil mass, the medium-deep heat exchange type geothermal well can only extract the geothermal energy of the rock and soil mass within a limited range around the wellbore in a short time and efficiently, and the geothermal energy farther away from the geothermal well cannot be efficiently transmitted to the geothermal well. With the continuous long-term heat extraction activities, the heat extraction capacity of the medium-deep heat exchange type geothermal well will quickly decline and remain at a low level. Summary of the Invention

[0004] In view of the defects and deficiencies in the prior art, the present invention provides a high-efficiency heat exchange system for multi-branch medium-deep geothermal wells, which uses a single-well heat exchange method to extract medium-deep geothermal energy, so as to solve the technical problem of low heat extraction efficiency of the heat exchange system of medium-deep geothermal wells for the geothermal energy of the rock and soil mass within a certain range around the geothermal well in the prior art.

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

[0006] A high-efficiency heat exchange system for multi-branch medium-deep geothermal wells, comprising a main well, a plurality of branch wells, and a heat exchange pipe extending vertically downward in the main well;

[0007] The main well includes an initial drilling section and a secondary drilling section. The initial drilling section extends vertically downward from the ground to communicate with the upper port of the secondary drilling section. The lower port of the secondary drilling section extends vertically downward to the geothermal water layer. The upper port of each branch well communicates with the secondary drilling section, and the lower port of each branch well extends obliquely downward in a direction gradually away from the secondary drilling section to the geothermal water layer;

[0008] The vertical distances from the upper ports of the multiple branch wells to the ground are different, and a heat-conducting metal stranded wire is arranged in each branch well along the extension direction of the branch well.

[0009] The present invention also has the following technical features:

[0010] Specifically, a spearhead assembly is further connected to the front end of the heat-conducting metal stranded wire, and the spearhead assembly is used to fix the heat-conducting metal stranded wire in the branch well.

[0011] Furthermore, the spearhead assembly includes a spearhead body. A heat-conducting metal stranded wire fixing mechanism is arranged at the rear end of the spearhead body, and at least one elastic card positioning mechanism is further arranged at the front end of the spearhead body;

[0012] The elastic card positioning mechanism includes a pin shaft and a limiting block arranged on the upper surface of the spearhead body. A spring is sleeved on the pin shaft, and two ends of the spring are respectively connected with elastic cards capable of rotating around the pin shaft. The limiting block can abut against the side wall of the elastic card.

[0013] Furthermore, a serrated structure is further arranged on the side of the elastic card away from the pin shaft.

[0014] Furthermore, the heat-conducting metal stranded wire fixing mechanism includes a pressing plate and a fastening bolt. The fastening bolt passes through an installation hole opened on the pressing plate and is connected to the spearhead body.

[0015] Furthermore, the heat exchange tube includes an outer tube and a heat-insulating inner tube sleeved coaxially. A hanger is arranged at the top end of the outer tube. After the heat-insulating inner tube passes through the hanger, it is communicated with a water supply pipe through a water supply adapter pipe; a water return port is opened on the side wall of the outer tube, and the water return port is communicated with a water return pipe through a water return adapter pipe.

[0016] Furthermore, a water supply valve is arranged on the water supply pipe, and a water return valve is arranged on the water return pipe;

[0017] Furthermore, the heat-conducting metal stranded wire includes a copper stranded wire, an aluminum stranded wire and an alloy stranded wire.

[0018] Further, a primary cementing casing is arranged in the first open hole section, and a primary cementing thermal insulation layer is arranged between the primary cementing casing and the inner wall of the first open hole section; a secondary cementing casing is arranged in the second open hole section, and a secondary cementing thermal insulation layer is arranged between the secondary cementing casing and the inner wall of the second open hole section;

[0019] Further, a through hole is formed in the middle of the hanger, a master bushing is coaxially sleeved in the through hole, and the heat preservation inner pipe passes through the master bushing.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] (1) The multi-branch medium-deep geothermal well high-efficiency heat exchange system provided by the present invention is designed as a multi-branch directional well structure, and heat-conducting metal strands are arranged along the extending direction of each branch well, thereby greatly improving the heat extraction capacity and heat transfer efficiency of geothermal energy from strata far away from the medium-deep geothermal well.

[0022] (2) By designing a spearhead assembly at the front end of the heat-conducting metal strand, the present invention can reliably anchor the heat-conducting metal strand at the bottom of the branch well, with a simple structure and convenient operation.

[0023] (3) In the present invention, a heat preservation inner pipe with a thermal conductivity less than 0.02 W / m·K is adopted, whereby it can be ensured that during the process of the heat transfer medium transporting geothermal energy, the heat loss is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 is a schematic diagram of the structure of the bullet clamping positioning mechanism in the open state;

[0026] Figure 3 is a schematic diagram of the structure of the bullet clamping positioning mechanism in the retracted state.

[0027] The reference numerals in the drawings represent:

[0028] 1 - main well, 2 - branch well, 3 - heat exchange pipe, 4 - heat-conducting metal strand, 5 - spearhead assembly, 6 - delivery pipe, 7 - hanger, 8 - water supply adapter, 9 - water supply pipe, 10 - return water adapter, 11 - return water pipe, 12 - water supply valve, 13 - return water valve, 14 - primary cementing casing; 15 - primary cementing thermal insulation layer, 16 - secondary cementing thermal insulation layer, 17 - master bushing;

[0029] 31 - outer pipe, 32 - heat preservation inner pipe;

[0030] 51 - spearhead body, 52 - heat-conducting metal strand fixing mechanism, 53 - bullet clamping positioning mechanism;

[0031] 101 - Open hole section 1, 102 - Open hole section 2;

[0032] 521 - Pressure plate, 522 - Fastening bolt;

[0033] 531 - Pin shaft, 532 - Limit block, 533 - Spring clip;

[0034] 5331 - Serrated structure. Detailed implementation manners

[0035] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0036] When the present invention describes directions, it should be understood that the directions are described with reference to Figure 1 the directions shown. The orientation or positional relationship indicated by terms such as "upper", "lower", "front", "rear", "left", "right", etc. is 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 should not be construed as a limitation to the present invention.

[0037] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0038] Unless otherwise specified, all components in the present invention are commercially available.

[0039] Embodiment

[0040] Following the above technical solution, as Figure 1 shown, this embodiment provides a high-efficiency heat exchange system for multi-branch medium-deep geothermal wells, including a main well 1, a plurality of branch wells 2, and a heat exchange pipe 3 extending vertically downward in the main well 1. The heat exchange pipe can be a coaxial casing. The main well 1 is a vertical well, and the main well 1 includes an open hole section 101 and an open hole section 102. The open hole section 101 extends vertically downward from the ground to communicate with the upper port of the open hole section 12. The lower port of the open hole section 102 extends vertically downward to the geothermal water layer. An open hole cementing casing 14 is arranged in the open hole section 101, and an open hole cementing insulation layer 15 is arranged between the open hole cementing casing 14 and the inner wall of the open hole section 101. A second open hole cementing casing 16 is arranged in the open hole section 102, and a second open hole cementing insulation layer 17 is arranged between the second open hole cementing casing 16 and the inner wall of the open hole section 102.

[0041] The number of branch wells can be selected according to actual needs. In this embodiment, 4 branch wells are adopted. The upper ports of each branch well 2 are all connected to the second-opening well section 102, and the lower ports of each branch well 2 extend obliquely downward in a direction gradually away from the second-opening well section 102 to the geothermal water layer.

[0042] The vertical distances from the upper ports of the multiple branch wells 2 to the ground are different from each other. The distance between the upper ports of adjacent branch wells is greater than 50 meters. That is, the multiple branch wells 2 are located at different well depths and different orientations, and a heat-conducting metal stranded wire 4 is arranged in each branch well 2 along the extending direction of the branch well 2. The heat-conducting metal stranded wire 4 is composed of a stranded wire bundle wound by copper wire, aluminum wire or alloy wire, and has both high heat conductivity and flexibility, and is conveyed through the central through hole of a delivery pipe 6 made of an oil pipe or a drill pipe.

[0043] As a preferred solution of this embodiment, one end of the heat-conducting metal stranded wire 4 far from the upper port of the branch well 2 is also connected with a spearhead assembly 5. The spearhead assembly 5 is used to fix the heat-conducting metal stranded wire 4 in the branch well 2, and the rear end of the heat-conducting metal stranded wire 4 is connected to the pipe wall of the second-opening cementing casing 16.

[0044] As a preferred solution of this embodiment, the spearhead assembly 5 includes a spearhead body 51. A heat-conducting metal stranded wire fixing mechanism 52 is arranged at the rear end of the spearhead body 51. The heat-conducting metal stranded wire fixing mechanism 52 is mainly used to fix the heat-conducting metal stranded wire 4. At least one spring clip positioning mechanism 53 is also arranged at the front end of the spearhead body 51;

[0045] The spring clip positioning mechanism 53 includes a pin shaft 531 and a limit block 532 arranged on the upper surface of the spearhead body 51. A spring is sleeved on the pin shaft 531. The two ends of the spring are respectively connected with spring clips 533 capable of rotating around the pin shaft 531. The limit block 532 can abut against the side wall of the spring clip 533. After the spearhead body 51 is pushed out of the delivery pipe, the spring clips 533 open under the action of the spring and penetrate into the well wall for fixation. The limit block 532 can prevent the spring clips 533 from reversing and flipping, and further ensure the reliable anchoring of the spearhead body.

[0046] As a preferred solution of this embodiment, a serrated structure 5331 is also arranged on the side of the spring clip 533 far from the pin shaft 531.

[0047] As a preferred solution of this embodiment, the heat-conducting metal stranded wire fixing mechanism 52 includes a pressing plate 521 and a fastening bolt 522. The fastening bolt 522 passes through the installation hole opened on the pressing plate 521 and is connected with the spearhead body 51.

[0048] As a preferred solution of this embodiment, the heat exchange tube 3 includes an outer tube 31 and a heat-insulating inner tube 32 coaxially sleeved. A hanger 7 is arranged at the top of the outer tube 31. After the heat-insulating inner tube 32 passes through the hanger 7, it is communicated with the water supply pipe 9 through a water supply adapter 8; a water return port is formed on the side wall of the outer tube 31, and the water return port is communicated with the water return pipe 11 through a water return adapter 10.

[0049] As a preferred solution of this embodiment, a water supply valve 12 is arranged on the water supply pipe 9, and a water return valve 13 is arranged on the water return pipe 11;

[0050] As a preferred solution of this embodiment, the heat-conducting metal stranded wire 4 includes a copper stranded wire, an aluminum stranded wire and an alloy stranded wire.

[0051] As a preferred solution of this embodiment, a cementing casing 14 is arranged in the first open hole section 101, and a first open hole cementing heat-insulating layer 15 is arranged between the cementing casing 14 and the inner wall of the first open hole section 101. A second open hole cementing casing is arranged in the second open hole section 102, and a second open hole cementing heat-insulating layer 16 is arranged between the second open hole cementing casing and the inner wall of the second open hole section 102;

[0052] In this embodiment, both the first open hole cementing heat-insulating layer 15 and the second open hole cementing heat-insulating layer 16 are heat-conducting cement layers, which can enhance the heat transfer capacity from the formation to the fluid medium in the well.

[0053] As a preferred solution of this embodiment, a through hole is formed in the middle of the hanger 7, and a bushing 17 is coaxially sleeved in the through hole, and the heat-insulating inner tube 32 passes through the bushing 17. The through hole provides a lowering channel for the heat-insulating inner tube string 32. The coupling of the heat-insulating inner tube 32 is seated on the bushing 17. The bushing 17 adopts an inverted frustum structure, which mainly functions to support the inner heat-insulating tube 32, seal the annulus and fix the inner heat-insulating tube 32.

[0054] When the present invention is in use, the drilling construction of the first open hole section 101 and the second open hole section 102 is completed by using a conventional drilling process. After the cementing of the second open hole section 102 is completed, the drilling operations of each branch well 2 are carried out in sequence. According to the pre-designed branch well drilling process, the lowering length of the heat-conducting metal stranded wire 4 in each branch well is determined. The central through hole of the delivery pipe 6 composed of tubing or drill pipe is used as the lowering and installation channel for the heat-conducting metal stranded wire 4. High-pressure mud or water is pumped by a mud pump to push the heat-conducting metal stranded wire 4 to the bottom of the branch well. After the heat-conducting metal stranded wire 4 is sent to the set position, the spring clips of the spear assembly 5 are spread out, and the serrated structure pierces into the wellbore formation of the branch well 2 to anchor the heat-conducting metal stranded wire 4 in the branch well 2. Finally, high heat-conducting cementing cement is poured to cement the branch well to increase the heat transfer capacity from the rock mass to the heat-conducting metal stranded wire in the branch well.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention; for those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-efficiency heat exchange system for multi-branch medium-deep geothermal wells, comprising a main well (1), a plurality of branch wells (2), and a heat exchange pipe (3) extending vertically downward in the main well (1). Characterized in that, The main well (1) includes an open-hole section (101) and a second open-hole section (102). The open-hole section (101) extends vertically downward from the ground to communicate with the upper port of the second open-hole section (102). The lower port of the second open-hole section (102) extends vertically downward to the geothermal water layer. The upper port of each branch well (2) is communicated with the second open-hole section (102), and the lower port of each branch well (2) extends obliquely downward in a direction gradually away from the second open-hole section (102) to the geothermal water layer; The vertical distances from the upper ports of the plurality of branch wells (2) to the ground are different, and a heat-conducting metal stranded wire (4) is arranged in each branch well (2) along the extending direction of the branch well (2).

2. The high-efficiency heat exchange system for multi-branch medium-deep geothermal wells according to claim 1, Characterized in that, An open-hole cementing casing (14) is arranged in the open-hole section (101), and an open-hole cementing insulation layer (15) is arranged between the open-hole cementing casing (14) and the inner wall of the open-hole section (101). A second open-hole cementing casing is arranged in the second open-hole section (102), and a second open-hole cementing insulation layer (16) is arranged between the second open-hole cementing casing and the inner wall of the second open-hole section (102).

3. The high-efficiency heat exchange system for multi-branch medium-deep geothermal wells according to claim 2, Characterized in that, The front end of the heat-conducting metal stranded wire (4) is further connected with a spearhead assembly (5). The spearhead assembly (5) is used to fix the heat-conducting metal stranded wire (4) in the branch well (2), and the rear end of the heat-conducting metal stranded wire (4) is connected to the pipe wall of the second open-hole cementing casing (16).

4. The high-efficiency heat exchange system for multi-branch medium-deep geothermal wells according to claim 3, Characterized in that, The spearhead assembly (5) includes a spearhead body (51). A heat-conducting metal stranded wire fixing mechanism (52) is arranged at the rear end of the spearhead body (51), and at least one elastic card positioning mechanism (53) is further arranged at the front end of the spearhead body (51); The elastic card positioning mechanism (53) includes a pin shaft (531) and a limit block (532) arranged on the upper surface of the spearhead body (51). A spring is sleeved on the pin shaft (531), and the two ends of the spring are respectively connected with an elastic card (533) capable of rotating around the pin shaft (531). The limit block (532) can be in contact with the side wall of the elastic card (533).

5. The high-efficiency heat exchange system for multi-branch medium-deep geothermal wells according to claim 4, Characterized in that, A serrated structure (5331) is further arranged on the side of the elastic card (533) away from the pin shaft (531).

6. The high-efficiency heat exchange system for multi-branch medium-deep geothermal wells according to claim 4, Characterized in that, The heat-conducting metal strand fixing mechanism (52) comprises a pressing plate (521) and a fastening bolt (522), wherein the fastening bolt (522) passes through a mounting hole provided on the pressing plate (521) and is connected to the spearhead body (51).

7. The multi-branch medium-deep geothermal well high-efficiency heat exchange system according to claim 1, It is characterized in that The heat exchange tube (3) comprises an outer tube (31) and an insulating inner tube (32) which are coaxially sleeved. A hanger (7) is provided at the top end of the outer tube (31). After passing through the hanger (7), the insulating inner tube (32) is connected to a water supply pipe (9) via a water supply transfer pipe (8). A water return port is provided on the side wall of the outer tube (31). The water return port is connected to a water return pipe (11) via a water return transfer pipe (10).

8. The multi-branch medium-deep geothermal well high-efficiency heat exchange system according to claim 7, It is characterized in that The water supply pipe (9) is provided with a water supply valve (12), and the water return pipe (11) is provided with a water return valve (13).

9. The multi-branch medium-deep geothermal well high-efficiency heat exchange system according to claim 1, It is characterized in that The heat-conducting metal stranded wire (4) comprises copper stranded wire, aluminum stranded wire and alloy stranded wire.

10. The multi-branch medium-deep geothermal well high-efficiency heat exchange system according to claim 7, It is characterized in that A through hole is provided in the middle of the hanger (7), a bushing (17) is coaxially sleeved in the through hole, and the insulation inner tube (32) is passed through the bushing (17).

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