Flexible geothermal heat removal pipe and geothermal heat removal construction method

Abstract

The invention discloses a flexible geothermal heat removal pipe and a geothermal heat removal construction method, the flexible geothermal heat removal pipe comprises a plurality of inner pipes arranged from front to back, and a hollow ball head is arranged between every two adjacent inner pipes; a ball socket is arranged in each ball seat structure, the multiple ball seat structures are arranged outside the multiple inner pipes in a sleeving mode and are in hinged fit with the ball heads of the multiple inner pipes through the ball sockets of the multiple ball seat structures, and in every two adjacent ball seat structures, the rear end of the front ball seat structure is movably connected with the front end of the rear ball seat structure in a sealed mode; the multiple inner pipes are communicated through the multiple ball seat structures to form a first channel, and the first channel can be communicated with a second channel to form a geothermal heating loop. When the flexible geothermal heat removal pipe is tripped into an operation well, the angle between the multiple inner pipes can be adaptively adjusted along with the angle of the operation well, a multi-branch structure is formed in a geothermal reservoir with the high geothermal temperature, the multiple flexible geothermal heat removal pipes are used for simultaneous heat removal, and the heat exchange area of the geothermal reservoir in the heat removal well is greatly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal utilization and multi-branch wells, and in particular to a flexible geothermal heat extraction pipe and a geothermal heat extraction construction method. Background Art

[0002] Geothermal energy is a clean and renewable energy source, so people are committed to developing and utilizing geothermal energy. In particular, the development of geothermal resources using ultra-short radius multi-branch wells has gradually become one of the key areas of focus for the development of new energy in countries around the world.

[0003] Currently, geothermal resource development and utilization encompasses not only direct uses such as heating and crop production but also geothermal cooling and medium- and high-temperature geothermal power generation. Geothermal energy occurs in various forms on Earth. Based on its storage form, geothermal resources can be categorized into five main types: steam, hot water, geopressured, hot dry rock, and lava.

[0004] Ultra-short radius horizontal wells play an important role in the transformation of old wells in oil and gas fields and geothermal extraction, but the commonly used geothermal heat pipe technology is difficult to adapt to the geothermal extraction of ultra-short radius multi-branch wells. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible geothermal heat extraction pipe and a geothermal heat extraction construction method to solve the technical problem that the current geothermal heat extraction pipe is difficult to adapt to geothermal extraction in ultra-short radius multi-branch wells.

[0006] The above-mentioned purpose of the present invention can be achieved by adopting the following technical solutions:

[0007] The present invention provides a flexible geothermal heat extraction pipe, comprising: a plurality of inner tubes arranged from front to back, with a hollow ball head provided between two adjacent inner tubes; a plurality of ball seat structures, each of which has a ball socket provided therein, the plurality of ball seat structures being sleeved outside the plurality of inner tubes and hingedly matched with the ball heads of the plurality of inner tubes through the ball sockets thereof, and in two adjacent ball seat structures, the rear end of the preceding ball seat structure is sealed and movably connected with the front end of the following ball seat structure; wherein the plurality of inner tubes are connected through the plurality of ball seat structures to form a first channel, and the first channel can be connected with a second channel to form a geothermal heat extraction circuit.

[0008] In an embodiment of the present invention, the flexible geothermal heat extraction pipe further comprises a guide shoe, which is sealingly and movably connected to the front end of the ball seat structure arranged at the front, and the inner tube arranged at the front extends into the guide shoe body.

[0009] In an embodiment of the present invention, there is a fitting gap between the rear end of the first ball seat structure and the front end of the second ball seat structure in the two adjacent ball seat structures, and between the front end of the ball seat structure arranged at the frontmost front and the guide shoe; the ball seat structure also includes a first sealing structure, which can seal the fitting gap and use its elastic deformation ability to provide movement space for the first ball seat structure and the guide shoe in the two adjacent ball seat structures.

[0010] In an embodiment of the present invention, the flexible geothermal heat extraction pipe further includes an outer pipe, which is sleeved on the plurality of ball seat structures, and the internal channel of the outer pipe constitutes the second channel.

[0011] In an embodiment of the present invention, the outer tube includes a plurality of spiral heat exchange tubes and a plurality of flexible connecting tubes. The plurality of spiral heat exchange tubes are arranged at intervals from front to back and are sleeved on the outside of the plurality of inner tubes. The plurality of spiral heat exchange tubes are connected through the plurality of flexible connecting tubes.

[0012] In an embodiment of the present invention, the flexible geothermal heat extraction pipe includes a closed guide shoe with a sealed inner cavity, and the outer pipe also includes a connecting outer pipe, which is passed through the closed guide shoe and is connected to the spiral heat exchange pipe arranged at the front through a flexible connecting pipe.

[0013] In an embodiment of the present invention, the second channel is the wellbore annulus between the flexible geothermal heat extraction pipe and the well wall of the operating well.

[0014] In an embodiment of the present invention, the flexible geothermal heat extraction pipe includes an open guide shoe, and the inner cavity of the open guide shoe is connected to the wellbore annulus.

[0015] In an embodiment of the present invention, the ball seat structure includes a front ball seat and a rear ball seat, the front end of the rear ball seat is fixedly connected to the rear end of the front ball seat and cooperates to form the ball socket, and in the two adjacent ball seat structures, the rear end of the rear ball seat of the previous ball seat structure is sealed and movably connected to the front end of the front ball seat of the latter ball seat structure.

[0016] In an embodiment of the present invention, the ball seat structure also includes a plurality of ball keys, which are arranged along the radial direction of the ball head, and the plurality of ball keys are arranged at intervals along the circumference of the ball head. The ball key has a hemispherical ball end, and the ball head is correspondingly provided with a plurality of hemispherical ball grooves. The ball ends of the plurality of ball keys pass through the front ball seat and cooperate with the plurality of ball grooves on the ball head.

[0017] In an embodiment of the present invention, a heat insulating layer is provided between the ball seat structure and the inner tube; the heat insulating layer is an air layer or a heat insulating material layer filled with heat insulating material.

[0018] In an embodiment of the present invention, the flexible geothermal heat extraction pipe also includes a three-way hollow casing and a bender. The bender is used to be installed in the main well of the working well and is located below the wellhead of the branch well of the working well. The front end of the three-way hollow casing is connected to the rear end of the bender. The three-way hollow casing is provided with a side hole corresponding to the wellhead of the branch well. The bender is provided with a guide slope for guiding the flexible geothermal heat extraction pipe from the side hole into the branch well.

[0019] The present invention also provides a geothermal heat extraction construction method for using the flexible geothermal heat extraction pipe described above for geothermal heat extraction, the construction method comprising the following steps: side-drilling multiple branch wells in the main well of the working well to penetrate into the geothermal reservoir; lowering multiple flexible geothermal heat extraction pipes into the multiple branch wells and establishing a geothermal heat extraction circuit; wherein, multiple inner tubes of the flexible geothermal heat extraction pipes are connected to form a first channel, and a second channel is formed by utilizing the wellbore annulus between the flexible geothermal heat extraction pipe and the well wall of the working well, or by arranging multiple spiral heat exchange pipes outside the multiple inner tubes to connect and form the second channel, and the first channel and the second channel are connected to form the geothermal heat extraction circuit; injecting a cold heat exchange medium into the first channel, the cold heat exchange medium well exchanges heat with the formation to form a hot heat exchange medium, and the hot heat exchange medium flows back to the second channel; or injecting a cold heat exchange medium into the second channel, the cold heat exchange medium well exchanges heat with the formation to form a hot heat exchange medium, and the hot heat exchange medium flows back to the first channel.

[0020] In an embodiment of the present invention, lowering the plurality of flexible geothermal heat pipes into the plurality of branch wells comprises the following steps: S1, placing a whipstock below the wellhead of the branch well in the main well; S2, lowering a three-way hollow casing into the main well and connecting it to the whipstock; S3, lowering the flexible geothermal heat pipe into the three-way hollow casing, and then entering the branch well from the side hole of the three-way hollow casing along the guide slope of the whipstock until the rear end of the flexible geothermal heat pipe is stuck in the side hole; S4, repeating the above steps S1 to S3, and lowering the plurality of flexible geothermal heat pipes into the plurality of branch wells in sequence from bottom to top.

[0021] The characteristics and advantages of the present invention are:

[0022] The flexible geothermal heat extraction pipe of the present invention is configured such that a hollow ball head is arranged between a plurality of inner tubes, and the ball sockets of a plurality of ball seat structures are hingedly matched with the ball heads of the plurality of inner tubes, and the rear end of a preceding ball seat structure is sealed and movably connected with the front end of a following ball seat structure, thereby connecting the plurality of inner tubes to form a first channel, and ensuring that the fluid in the first channel will not be affected by the outside. At the same time, the flexible geothermal heat extraction pipe has a certain flexibility, so that when the flexible geothermal heat extraction pipe is lowered into an operating well, the angles between the plurality of inner tubes can be adaptively adjusted according to the angle of the operating well, and the first channel can be connected with a second channel to form a geothermal heat extraction loop, and then the heat exchange medium is injected from the wellhead through the geothermal heat extraction loop and returns to the wellhead after absorbing geothermal heat underground, thereby realizing the exploitation of geothermal heat underground in the operating well.

[0023] The geothermal heat extraction construction method of the present invention uses a common main well to form a multi-branch structure in the geothermal reservoir with a high geothermal temperature and utilizes multiple flexible geothermal heat extraction pipes to extract heat simultaneously, thereby greatly increasing the heat exchange area of ​​the geothermal reservoir in the heat extraction well and significantly improving the heat extraction capacity of a single heat extraction well. Under the premise of increasing the project cost by 0.5 times to 1 times, the heat extraction capacity is increased by 3 times to 5 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A three-dimensional schematic diagram of a flexible geothermal heat pipe according to an embodiment of the present invention;

[0026] Figure 2 A longitudinal cross-sectional view of a flexible geothermal heat pipe according to an embodiment of the present invention;

[0027] Figure 3 This is a three-dimensional schematic diagram of an inner tube in one embodiment of the present invention;

[0028] Figure 4 A longitudinal sectional view of an inner tube in one embodiment of the present invention;

[0029] Figure 5 A perspective schematic diagram of a front ball seat in one embodiment of the present invention;

[0030] Figure 6 A longitudinal sectional view of a front ball seat according to an embodiment of the present invention;

[0031] Figure 7 is a cross-sectional view of a front ball seat in one embodiment of the present invention;

[0032] Figure 8 A three-dimensional schematic diagram of a ball key in one embodiment of the present invention;

[0033] Figure 9 A perspective schematic diagram of a rear ball seat in one embodiment of the present invention;

[0034] Figure 10 A longitudinal sectional view of a rear ball seat according to an embodiment of the present invention;

[0035] Figure 11 Schematic diagram of the three-way hollow sleeve in the present invention;

[0036] Figure 12 is a three-dimensional schematic diagram of the whipstock in the present invention;

[0037] Figure 13 This is a schematic diagram of the engineering process of lowering the flexible geothermal heat extraction pipe into the first branch well in the present invention;

[0038] Figure 14 This is a schematic diagram of the process of placing the flexible geothermal heat pipe into the second branch well in the present invention;

[0039] Figure 15 is a three-dimensional schematic diagram of a spiral heat exchange tube in one embodiment of the present invention;

[0040] Figure 16 A state diagram of heat extraction by a flexible geothermal heat pipe according to an embodiment of the present invention;

[0041] Figure 17 A schematic perspective view of a flexible geothermal heat pipe according to another embodiment of the present invention;

[0042] Figure 18 A longitudinal cross-sectional view of a flexible geothermal heat pipe according to another embodiment of the present invention;

[0043] Figure 19 A perspective schematic diagram of an open guide shoe in another embodiment of the present invention;

[0044] Figure 20 A longitudinal sectional view of an open guide shoe in another embodiment of the present invention;

[0045] Figure 21 This is a state diagram of heat extraction by a flexible geothermal heat pipe in another embodiment of the present invention.

[0046] In the picture:

[0047] 100. Flexible geothermal heat pipe;

[0048] 1. Inner tube; 11. Ball head;

[0049] 2. Ball seat structure; 21. Front ball seat; 211. Ball groove; 22. Rear ball seat; 23. Ball socket; 24. Ball key; 25. First sealing structure; 26. Second sealing structure;

[0050] 3. Outer tube; 31. Spiral heat exchange tube; 32. Flexible connecting tube; 33. Connecting outer tube;

[0051] 41. Closed guide shoe; 42. Open guide shoe; 421. Sieve hole;

[0052] 5. Thermal insulation layer;

[0053] 6. Three-way hollow sleeve; 61. Side hole; 62. Limiting protrusion;

[0054] 7. Whipstock; 71. Guide slope; 72. Limiting groove; 73. Buffer groove;

[0055] 200, operating well; 201, main well; 202, lower branch well; 203, upper branch well;

[0056] 301, geothermal heat extraction main pipe; 302, injection main pipe; 303, lowering pipe string;

[0057] 400. Ground heat exchange circuit; 401. Heat exchange device; 402. Pumping device; 403. Three-way valve. DETAILED DESCRIPTION

[0058] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0059] Implementation Method 1

[0060] like Figures 1 to 7 As shown, the present invention provides a flexible geothermal heat extraction pipe 100, comprising: a plurality of inner tubes 1, arranged from front to back, with a hollow ball head 11 provided between two adjacent inner tubes 1; a plurality of ball seat structures 2, each of which has a ball socket 23 provided therein, the plurality of ball seat structures 2 being sleeved outside the plurality of inner tubes 1 and hingedly engaged with the ball heads 11 of the plurality of inner tubes 1 through their ball sockets 23, and the rear end of the preceding ball seat structure 2 being sealed and movably connected to the front end of the following ball seat structure 2 between two adjacent ball seat structures 2; wherein the plurality of inner tubes 1 are connected through the plurality of ball seat structures 2 to form a first channel, and the first channel can be connected to a second channel to form a geothermal heat extraction circuit. For ease of description, the present invention defines the forward and backward directions of the flexible geothermal heat extraction pipe 100 when lowered into the operating well 200 as the forward and backward directions.

[0061] The flexible geothermal heat extraction pipe 100 of the present invention is configured with a hollow ball head 11 between multiple inner tubes 1, and the ball sockets 23 of multiple ball seat structures 2 are hingedly matched with the ball heads 11 of multiple inner tubes 1, and the rear end of the previous ball seat structure 2 is sealed and movably connected with the front end of the next ball seat structure 2, so that the multiple inner tubes 1 can be connected to form a first channel, and it can be ensured that the fluid in the first channel will not be affected by the outside. At the same time, it also has a certain flexibility, so that when the flexible geothermal heat extraction pipe 100 is lowered into the working well 200, the angles between the multiple inner tubes 1 can be adaptively adjusted according to the angle of the working well 200, and the first channel can be connected with a second channel to form a geothermal heat extraction loop, and then the heat exchange medium is injected from the wellhead through the geothermal heat extraction loop and returns to the wellhead after absorbing geothermal heat underground, thereby realizing the exploitation of geothermal heat in the working well 200.

[0062] Specifically, such as Figure 3 and Figure 4 As shown, the ball head 11 is generally a spherical hollow shell structure and can be installed at the rear end of the front inner tube 1. Of course, the ball head 11 can also be formed by a ball joint of two hemispherical hollow shells, with the outer diameter of one hemispherical hollow shell matching the inner diameter of the other hemispherical hollow shell, the hemispherical hollow shell being installed at the rear end of the front inner tube 1, and the other hemispherical hollow shell being installed at the front end of the rear inner tube 1. The sealed movable connection between the rear end of the front ball seat structure 2 and the front end of the rear ball seat structure 2 specifically means that the front ball seat structure 2 can rotate in any direction by a preset angle relative to the rear ball seat structure 2, and the seal between adjacent ball seat structures 2 can be maintained. Therefore, when the ball head 11 of the front inner tube 1 rotates within the ball socket of the rear ball seat structure 2 to adapt to the angle of the working well 200, the front ball seat structure 2 disposed outside the front inner tube 1 can also adaptively rotate relative to the rear ball seat structure without interfering with the rotation of the front inner tube 1.

[0063] like Figure 1 and Figure 2 As shown, in the embodiment of the present invention, there is a matching gap between the rear end of the first ball seat structure 2 and the front end of the second ball seat structure 2 in the two adjacent ball seat structures 2; Figure 5 As shown, the ball seat structure 2 also includes a first sealing structure 25. The first sealing structure 25 can seal the mating gap and use its elastic deformation ability to provide movement space for the preceding ball seat structure 2 of the two adjacent ball seat structures 2. Due to the elastic deformation ability of the first sealing structure 25, the preceding ball seat structure 2 can squeeze the first sealing structure 25 and rotate in any direction relative to the following ball seat structure 2.

[0064] Specific, combined Figure 5 、 Figure 6 as well as Figure 9 and Figure 10As shown, the fitting clearance may not be specifically limited and may be set according to a preset angle. The fitting clearance includes a circumferential fitting clearance and / or an axial fitting clearance, and the first sealing structure 25 includes a sealing ring installed in the circumferential fitting clearance or a sealing ring installed in the axial fitting clearance. An annular boss protrudes from the end face of the front end of the ball seat structure 2, and the rear end of the previous ball seat structure 2 can be sleeved on the annular boss of the next ball seat structure 2. The gap between the inner wall surface of the rear end of the previous ball seat structure 2 and the outer wall surface of the annular boss of the next ball seat structure 2 is the circumferential fitting clearance, and the gap between the end face of the rear end of the previous ball seat structure 2 and the end face of the front end of the next ball seat structure 2 is the axial fitting clearance.

[0065] Optionally, two adjacent ball seat structures 2 can be fitted with a ball joint or a universal joint, so that the front inner tube 1 and the front ball seat structure 2 can be rotated in any direction relative to the rear ball seat structure 2 and the rear inner tube 1 to adjust the angle between the two adjacent inner tubes 1 to adapt to the angle of the working well 200.

[0066] like Figure 1 、 Figure 2 as well as Figure 7 As shown, in an embodiment of the present invention, the ball seat structure 2 includes a front ball seat 21 and a rear ball seat 22. The front end of the rear ball seat 22 is fixedly connected to the rear end of the front ball seat 21 and cooperates to form a ball socket 23. Moreover, in two adjacent ball seat structures 2, the rear end of the rear ball seat 22 of the front ball seat structure 2 is sealed and movable with the front end of the front ball seat 21 of the rear ball seat structure 2. The front ball seat 21 and the rear ball seat 22 are assembled into the ball seat structure 2 and cooperate to form the ball socket 23, which is easy to process and disassemble.

[0067] Specific, combined Figure 5 、 Figure 6 as well as Figure 9 and Figure 10 As shown, for ease of assembly and disassembly, the front end of the rear ball seat 22 is detachably fixedly connected to the rear end of the front ball seat 21. The ball head 11 is provided at the rear end of the inner tube 1. The rear end of the front ball seat 21 defines a front spherical groove, and the front end of the rear ball seat 22 defines a rear spherical groove. During assembly, the front end of the front inner tube 1 is passed through the rear end of the front ball seat 21 and then extended. The front end of the rear ball seat 22 is then plugged and fixed to the rear end of the front ball seat 21, so that the front spherical groove of the front ball seat 21 and the rear spherical groove of the rear ball seat 22 cooperate to form a ball socket 23, and the ball head of the front inner tube 1 fits into the ball socket 23. The next ball seat structure 2 and the rear inner tube 1 are then assembled in the same manner. The front end of the rear inner tube 1 is then inserted into the rear ball seat 22 of the front ball seat structure 2, and the rear end of the rear ball seat 22 of the front ball seat structure 2 is sealed and movably connected to the front end of the front ball seat 21 of the rear ball seat structure 2.

[0068] like Figures 5 to 8As shown, to ensure stable rotation of the ball head 11 of the inner tube 1 within the ball socket 23, in an embodiment of the present invention, the front ball seat 21 is connected to the ball head 11 via multiple ball keys 24. The ball keys 24 are arranged radially along the ball head 11 and are spaced apart circumferentially. The ball keys 24 have hemispherical ends, correspondingly provided with multiple hemispherical ball grooves 211 on the ball head 11. The ball ends of the multiple ball keys 24 pass through the front ball seat 21 and engage with the ball head 11. The multiple ball keys 24 are preferably evenly spaced. The provision of multiple ball keys 24 ensures that when the ball head 11 of the inner tube 1 rotates within the ball socket 23, the ball head 11 remains stably connected to the front ball seat 21 via the ball keys 24. Furthermore, a second sealing structure 26 is provided between the ball head 11 and the ball socket 23 to maintain a seal between the ball head 11 and the ball socket 23 when the ball head 11 rotates within the ball socket 23.

[0069] like Figure 2 As shown in FIG. 1 , in the embodiment of the present invention, a heat insulating layer 5 is provided between the ball seat structure 2 and the inner tube 1. Specifically, as Figure 5 、 Figure 6 as well as Figure 9 and Figure 10 As shown, both the front ball seat 21 and the rear ball seat 22 are generally hollow tubular structures, and the inner diameter of the tubular structure is larger than the outer diameter of the inner tube 1, so that a gap is provided between the rear ball seat 22 and the inner tube 1. This gap allows for the provision of a heat insulation layer 5 between the rear ball seat 22 and the inner tube 1, thereby preventing the injected cold heat exchange medium from absorbing the heat of the returning hot heat exchange medium, thereby improving heat exchange efficiency. The heat insulation layer 5 is a layer of air or a heat insulation material filled with heat insulation material.

[0070] like Figure 1 and Figure 2 As shown, in an embodiment of the present invention, the flexible geothermal heat pipe 100 further includes a guide shoe, which is sealably and movably connected to the front end of the ball seat structure 2 arranged at the front end (i.e., the ball seat structure 2 arranged at the head end). The inner tube 1 arranged at the front end (i.e., the inner tube 1 arranged at the head end) extends into the guide shoe. Under the guidance of the guide shoe, the inner tube 1 arranged at the front end advances synchronously with the guide shoe in the operating well 200, thereby driving the inner tubes 1 behind it to advance in sequence, thereby facilitating smoother lowering of multiple inner tubes 1 into the operating well 200.

[0071] Specifically, there is a fitting gap between the front end of the ball seat structure 2 arranged at the front and the guide shoe. The fitting gap can be sealed by the first sealing structure 25 and its elastic deformation ability is used to provide a movable space for the guide shoe. That is, the connection method between the front end of the ball seat structure 2 arranged at the front and the guide shoe is the same as the connection method between the two adjacent ball seat structures 2, which will not be repeated here. The material of the guide shoe is preferably carbon steel and / or other high-temperature alloys, and of course it can also be other materials with high hardness and good strength. The guide shoe is generally a cylindrical structure with a conical front end. The outer diameter of the guide shoe is large, so that the guide shoe constitutes the part with the largest outer diameter of the flexible geothermal heat extraction pipe 100, thereby removing obstacles on the well wall in the front during the process of guiding the flexible geothermal heat extraction pipe 100 to be lowered, reducing the resistance encountered by the flexible geothermal heat extraction pipe 100 to be lowered. In addition, in order to better replace the guide shoe, the guide shoe is detachably connected to the front end of the front ball seat 21 of the ball seat structure 2 arranged at the front.

[0072] like Figures 11 to 14 As shown, in an embodiment of the present invention, the flexible geothermal heat extraction pipe 100 further includes a three-way hollow casing 6 and a whipstock 7. The whipstock 7 is used to be installed in the main well 201 of the working well 200 and is located below the wellhead of the branch well of the working well 200. The front end of the three-way hollow casing 6 is connected to the rear end of the whipstock 7. The three-way hollow casing 6 is provided with a side hole 61 corresponding to the wellhead of the branch well. The whipstock 7 is provided with a guide slope 71 for guiding the flexible geothermal heat extraction pipe 100 from the side hole 61 into the branch well. By providing the three-way hollow casing 6 and the whipstock 7, the wellhead position of the branch well is determined, thereby ensuring smooth lowering of the flexible geothermal heat extraction pipe 100.

[0073] Specifically, after the flexible geothermal heat extraction pipe 100 is lowered into the branch well, the rear end of the flexible geothermal heat extraction pipe 100 can be stuck in the side hole 61. The rear end of the whipstock 7 is provided with a limiting boss, which is provided with a guiding bevel 71. The front end of the three-way hollow sleeve 6 is sleeved on the limiting boss, and the front end of the three-way hollow sleeve 6 is provided with a limiting protrusion 62. The outer side surface of the rear end of the whipstock 7 is provided with a limiting groove 72 that cooperates with the limiting protrusion 62. In addition, a buffer groove 73 is also provided on the guiding bevel 71. When the flexible geothermal heat extraction pipe 100 is lowered into the three-way hollow sleeve 6, the side of the guide shoe contacts the guiding bevel 71, and the tip of the guide shoe extends into the buffer groove 73, thereby reducing the impact force on the tip of the guide shoe during lowering and preventing damage to the tip of the guide shoe. Then, under the guidance of the guiding bevel 71, the guide shoe is lowered into the branch well through the side hole 61 of the three-way hollow sleeve 6.

[0074] like Figure 1 and Figure 2As shown, in some embodiments of the present invention, the flexible geothermal heat extraction pipe 100 further includes an outer tube 3, which is sleeved onto the multiple ball seat structures 2. The internal channel of the outer tube 3 constitutes a second channel. Since the first channel is located inside the flexible geothermal heat extraction pipe 100 and the second channel is located outside the flexible geothermal heat extraction pipe 100, the fluid in the second channel can better exchange heat with the formation. Therefore, the second channel is preferably used as an injection channel for injecting cold heat exchange medium from the wellhead to exchange heat with the formation, while the first channel is used as a return channel for returning the hot heat exchange medium generated by absorbing geothermal heat to the wellhead. Of course, in other embodiments of the present invention, the second channel can also be used as a return channel, while the first channel can be used as an injection channel.

[0075] Specific, combined Figure 1 、 Figure 2 as well as Figure 15 As shown, the outer tube 3 includes a plurality of spiral heat exchange tubes 31 and a plurality of flexible connecting tubes 32. The plurality of spiral heat exchange tubes 31 are arranged in an intermittent manner from front to back and are sheathed outside the plurality of inner tubes 1. The plurality of spiral heat exchange tubes 31 are connected to each other through the plurality of flexible connecting tubes 32 to form a second channel. The spiral heat exchange tubes 31 are a tube structure made of a rigid material, which gives the flexible geothermal heat extraction pipe 100 better structural strength. The flexible connecting tubes 32 are a hose, and the material of the flexible connecting tubes 32 includes but is not limited to rubber, plastic or other polymer materials. The plurality of flexible connecting tubes 32 are arranged in a one-to-one correspondence with the front ball seats 21 of the plurality of ball seat structures 2, that is, the plurality of flexible connecting tubes 32 are mainly sheathed outside the plurality of front ball seats 21, while the plurality of spiral heat exchange tubes 31 are arranged in a one-to-one correspondence with the rear ball seats 22 of the plurality of ball seat structures 2, that is, the plurality of spiral heat exchange tubes 31 are mainly sheathed outside the plurality of rear ball seats 22. The helix angle of the spiral heat exchange tube 31 is 8° to 25°, and the pitch of the spiral heat exchange tube 31 is 2 to 5 times the outer diameter of the tube.

[0076] Combine Figure 16As shown, the flexible geothermal heat extraction pipe 100 is first lowered into the branch well by lowering the pipe string 303. The rear end of the inner pipe 1 of the flexible geothermal heat extraction pipe 100, which is arranged at the rear, is then connected to the geothermal heat extraction main pipe 301, and the rear end of the outer pipe 3 of the flexible geothermal heat extraction pipe 100 is connected to the injection main pipe 302. Alternatively, the flexible geothermal heat extraction pipe 100 is first connected to the geothermal heat extraction main pipe 301 and the injection main pipe 302, and then the geothermal heat extraction main pipe 301 and the injection main pipe 302 are lowered into the branch well by lowering the geothermal heat extraction main pipe 301 and the injection main pipe 302 into the main well 201. In addition, the geothermal heat extraction main pipe 301 and the injection main pipe 302 are connected to the ground heat exchange circuit 400, thereby connecting the geothermal heat extraction circuit and the ground heat exchange circuit 400 to form a heat exchange medium circulation pipeline. The ground heat exchange circuit 400 is provided with a pumping device 402 and a ground heat exchange device 401, wherein the pumping device 402 is used to provide conveying power to the heat exchange medium circulation pipeline. The hot heat exchange medium after absorbing geothermal heat flows back to the ground heat exchange device 401 to form a cold heat exchange medium after heat exchange, and then can flow into the injection pipeline to exchange heat with the formation.

[0077] When there are multiple branch wells, the geothermal heat extraction main pipe 301 is lowered into the main well 201 and connected to the inner pipe 1 of multiple flexible geothermal heat extraction pipes 100, and multiple injection main pipes 302 are lowered into the main well 201 and connected to the outer pipe 3 of multiple flexible geothermal heat extraction pipes 100. Then, the multiple flexible geothermal heat extraction pipes 100 are lowered into multiple branch wells from bottom to top, and then the multiple output pipes of the ground heat exchange loop 400 are connected to the multiple injection main pipes 302. The multiple input pipes of the ground heat exchange loop 400 can be connected to the geothermal heat extraction main pipe 301 through a multi-way structure. The multi-way structure can be a joint structure or a valve structure with one input end and multiple output ends. For example, when there are two branch wells, the two input pipes of the ground heat exchange loop 400 are connected to the geothermal heat extraction main pipe 301 through a three-way joint or a three-way valve 403.

[0078] In addition, if Figure 1 and Figure 2 As shown, to prevent the heat exchange medium from contacting the wellbore wall and thus ensure the stability of the wellbore wall, the guide shoe is a closed guide shoe 41 with a sealed inner cavity. The outer tube 3 also includes a connecting outer tube 33, which is installed on the closed guide shoe 41 and connected to the spiral heat exchange tube 31 arranged at the front through a flexible connecting tube 32. The front end of the connecting outer tube 33 can be directly connected to the front end of the inner tube 1 arranged at the front, or it can be connected to the inner tube 1 arranged at the front through the sealed inner cavity of the closed guide shoe 41. The outer diameter of the closed guide shoe 41 is slightly larger than the spiral outer diameter of the spiral heat exchange tube 31.

[0079] like Figure 17 、 Figure 18 as well as Figure 21As shown, in other embodiments of the present invention, the second channel is the wellbore annulus between the flexible geothermal heat extraction pipe 100 and the wellbore wall of the operating well 200. Because the first channel is located within the flexible geothermal heat extraction pipe 100, the fluid in the second channel can directly contact the wellbore wall, thereby better enabling heat exchange with the formation. Therefore, the second channel is preferably used as an injection channel for injecting cold heat exchange medium from the wellhead for heat exchange with the formation, while the first channel is used as a return channel for returning the hot heat exchange medium generated by absorbing geothermal heat to the wellhead. Of course, in other embodiments of the present invention, the second channel can also be used as a return channel, while the first channel can be used as an injection channel.

[0080] Specifically, such as Figure 19 and Figure 20 As shown, the second channel can be directly connected to the first channel, or, as in this embodiment, the second channel and the first channel can be connected via a guide shoe. The guide shoe is an open guide shoe 42, the inner cavity of which is connected to the wellbore annulus. The open guide shoe 42 can be connected to the wellbore annulus by providing multiple sieve holes 421. The sieve holes 421 can also intercept large impurities, preventing large impurities from flowing into the open guide shoe 42 along with the heat exchange medium after absorbing geothermal heat through the multiple sieve holes 421 and then entering the inner tube 1, causing blockage of the inner tube 1. The outer diameter of the open guide shoe 42 is slightly larger than the outer diameter of the ball seat structure 2.

[0081] Combine Figure 21 As shown, the flexible geothermal heat extraction pipe 100 is first lowered into the branch well by lowering the pipe string 303, and then the rear end of the inner pipe 1 of the flexible geothermal heat extraction pipe 100 arranged at the rear is connected to the geothermal heat extraction main pipe 301; or the flexible geothermal heat extraction pipe 100 is first connected to the geothermal heat extraction main pipe 301, and then the geothermal heat extraction main pipe 301 is lowered into the main well 201 to lower the flexible geothermal heat extraction pipe 100 into the branch well. In addition, the input pipeline of the ground heat exchange loop 400 is connected to the output end of the geothermal heat extraction main pipe 301, and the output pipeline of the ground heat exchange loop 400 is connected to the wellhead of the main well 201, thereby connecting the geothermal heat extraction loop and the ground heat exchange loop 400 to form a heat exchange medium circulation pipeline. The specific structure of the ground heat exchange loop 400 is the same as that of the above embodiment and will not be repeated here.

[0082] Implementation Method 2

[0083] like Figure 13 、 Figure 14 、 Figure 16 as well as Figure 21 As shown, the present invention also provides a geothermal heat extraction construction method for geothermal heat extraction using a flexible geothermal heat extraction pipe 100. The specific structure, working principle and beneficial effects of the flexible geothermal heat extraction pipe 100 in this embodiment are the same as those of the flexible geothermal heat extraction pipe 100 in embodiment 1, and will not be repeated here.

[0084] The construction method includes the following steps: drilling multiple branch wells in the main well 201 of the working well 200 to penetrate into the geothermal reservoir; lowering multiple flexible geothermal heat extraction pipes 100 into the multiple branch wells and establishing a geothermal heat extraction circuit; wherein, multiple inner tubes 1 of the flexible geothermal heat extraction pipes 100 are connected to form a first channel, and a second channel is formed by utilizing the wellbore annulus between the flexible geothermal heat extraction pipes 100 and the well wall of the working well 200 or by arranging multiple spiral heat exchange pipes 31 on the outer surface of the multiple inner tubes 1 to connect and form a second channel, and the first channel and the second channel are connected to form a geothermal heat extraction circuit; injecting a cold heat exchange medium into the first channel, the cold heat exchange medium well exchanges heat with the formation to form a hot heat exchange medium, and the hot heat exchange medium flows back to the second channel; or injecting a cold heat exchange medium into the second channel, the cold heat exchange medium well exchanges heat with the formation to form a hot heat exchange medium, and the hot heat exchange medium flows back to the first channel.

[0085] In an embodiment of the present invention, multiple flexible geothermal heat pipes 100 are lowered into multiple branch wells, including the following steps: S1, placing a whipstock 7 below the wellhead of the branch well in the main well 201; S2, lowering a three-way hollow casing 6 into the main well 201 and connecting it to the whipstock 7; S3, lowering the flexible geothermal heat pipe 100 into the three-way hollow casing 6, and then entering the branch well from the side hole 61 of the three-way hollow casing 6 along the guide inclined surface 71 of the whipstock 7 until the rear end of the flexible geothermal heat pipe 100 is stuck in the side hole 61; S4, repeating the above steps S1 to S3, and lowering the multiple flexible geothermal heat pipes 100 into the multiple branch wells in sequence from bottom to top.

[0086] The following is a detailed description of the geothermal heat extraction construction method of the present invention using a specific embodiment, which specifically includes the following steps:

[0087] Step 1: Determine the ground construction location of the main well 201 of the geothermal well (i.e., the operating well 200), the number of branch wells, and the depth of the main well 201 and each branch well based on the location of the geothermal reservoir;

[0088] Step 2: Drilling is performed at the ground construction location of the main well 201, and cementing is performed using at least one fixed casing according to the geological conditions; for example, one fixed casing is used for cementing in this embodiment;

[0089] Step 3: Drilling the upper branch well 203 and the lower branch well 202 in the open hole portion of the main well 201 and on the upper side of the fixed casing;

[0090] Step 4: After the upper branch well 203 and the lower branch well 202 are drilled in an open-hole manner, the whipstock 7 is retained below the lower branch well 202, and a three-way hollow casing 6 is lowered into the main well 201 to cooperate with the whipstock 7, so that the side hole 61 of the three-way hollow casing 6 faces the wellhead of the lower branch well 202. A flexible heat exchange and heat extraction pipe is then lowered into the lower branch well 202 until the rear end of the flexible heat exchange and heat extraction pipe is stuck in the side hole 61 of the three-way hollow casing 6 to prevent it from falling off;

[0091] Step 4: Place another whipstock 7 below the upper branch well 203, and lower another three-way hollow casing 6 to cooperate with the whipstock 7, so that the side hole 61 of the three-way hollow casing 6 faces the wellhead of the lower branch well 202. Then, lower another flexible heat exchange and heat extraction pipe into the upper branch well 203, and the rear end of the flexible heat exchange and heat extraction pipe is locked in the side hole 61 of the three-way hollow casing 6;

[0092] Step 6: After the main well 201 is flushed, the geothermal heat extraction main pipe 301 is lowered into the main well 201 and connected to the inner pipe 1 of the two flexible heat exchange pipes, and the input ends of the two ground heat exchange loops 400 are connected to the geothermal heat extraction main pipe 301; then, two injection main pipes 302 are lowered to connect to the outer pipes 3 of the two flexible heat exchange pipes, and the two injection pipes are connected to the output ends of the two ground heat exchange loops 400; or the output ends of the two ground heat exchange loops 400 are connected to the wellbore annulus between the geothermal heat extraction main pipe 301 and the working well.

[0093] Step 7: The cold heat exchange medium output by the two ground heat exchange loops 400 flows into the second channels in the two branch wells to absorb geothermal heat to form hot heat exchange medium, which then flows back to the first channels of the two flexible heat exchange pipes, and finally flows back to the ground heat exchange loop 400 through the geothermal heat extraction main pipe 301.

[0094] The flexible geothermal heat extraction pipe 100 and geothermal heat extraction construction method provided by the present invention have the following beneficial effects:

[0095] First, the present invention connects multiple inner tubes 1 through multiple ball seat structures 2, so that the flexible geothermal heat pipe 100 is highly flexible and can adapt to the well trajectory of ultra-short radius multi-branch wells to the greatest extent, ensuring the extraction and utilization of geothermal energy.

[0096] Second, the present invention can be disassembled and assembled into two types of flexible geothermal heat pipes 100; when the outer tube 3 is not assembled and the flexible geothermal heat pipe 100 adopts the open guide shoe 42, the heat exchange medium can be in direct contact with the well wall, which is beneficial to improving the heat exchange efficiency; when the outer tube 3 is assembled and the flexible geothermal heat pipe 100 adopts the closed guide shoe 41, the heat exchange medium can be prevented from directly contacting the well wall, which is beneficial to ensuring the stability of the well wall.

[0097] Third, the flexible geothermal heat pipe 100 of the present invention is highly maneuverable and does not require special processing and operation. All operations can be completed by normal drilling workers.

[0098] Fourth, the present invention can successfully achieve heat extraction from multi-branch wells by drilling multiple branch wells in the geothermal reservoir in steps and coordinating the operation mode of step-by-step lowering of the three-way hollow casing 6 and the bevel device 7 to determine the position of the multi-branch wellbore, thereby ensuring the accurate placement of the flexible geothermal heat extraction pipe 100 and achieving heat extraction from the multi-branch wells.

[0099] Fifth, the present invention uses a shared main well 201 to extract heat from geothermal reservoirs with high geothermal temperatures using a multi-branch structure, thereby greatly increasing the heat exchange area of ​​the geothermal reservoir in the heat extraction well and significantly improving the heat extraction of a single heat extraction well. Under the premise of increasing the project cost by 0.5 to 1 times, the heat extraction is increased by 3 to 5 times.

[0100] The above descriptions are only several embodiments of the present invention. Those skilled in the art may make various changes or modifications to the embodiments of the present invention based on the contents disclosed in the application documents without departing from the spirit and scope of the present invention.

Claims

1. A flexible geothermal heat pipe, characterized in that: include: A plurality of inner tubes are arranged from front to back, and a hollow ball head is provided between two adjacent inner tubes; A plurality of ball seat structures, each of which has a ball socket provided therein, wherein the plurality of ball seat structures are sleeved outside the plurality of inner tubes and are hingedly engaged with the ball heads of the plurality of inner tubes through the ball sockets thereof, and wherein the rear end of the preceding ball seat structure is sealed and movably connected to the front end of the succeeding ball seat structure between two adjacent ball seat structures; Wherein, a plurality of the inner tubes are connected through a plurality of the ball seat structures to form a first channel, and the first channel can be connected with a second channel to form a geothermal heat extraction circuit.

2. The flexible geothermal heat pipe according to claim 1, characterized in that: The flexible geothermal heat extraction pipe further comprises a guide shoe, which is sealingly and movably connected to the front end of the ball seat structure arranged at the front, and the inner tube arranged at the front extends into the guide shoe body.

3. The flexible geothermal heat pipe according to claim 2, characterized in that: There is a fitting gap between the rear end of the first ball seat structure and the front end of the second ball seat structure in two adjacent ball seat structures, and between the front end of the ball seat structure arranged at the front and the guide shoe; The ball seat structure further includes a first sealing structure, which can seal the fitting gap and utilize its elastic deformation ability to provide movement space for the first ball seat structure and the guide shoe of the two adjacent ball seat structures.

4. The flexible geothermal heat pipe according to claim 1 or 2, characterized in that: The flexible geothermal heat extraction pipe further includes an outer pipe, which is sleeved on the plurality of ball seat structures, and the inner channel of the outer pipe constitutes the second channel.

5. The flexible geothermal heat pipe according to claim 4, characterized in that: The outer tube includes a plurality of spiral heat exchange tubes and a plurality of flexible connecting tubes. The plurality of spiral heat exchange tubes are arranged at intervals from front to back and are sleeved outside the plurality of inner tubes. The plurality of spiral heat exchange tubes are connected through the plurality of flexible connecting tubes.

6. The flexible geothermal heat pipe according to claim 5, characterized in that: The flexible geothermal heat extraction pipe includes a closed guide shoe with a sealed inner cavity, and the outer pipe also includes a connecting outer pipe. The connecting outer pipe is passed through the closed guide shoe and is connected to the spiral heat exchange pipe arranged at the front through a flexible connecting pipe.

7. The flexible geothermal heat pipe according to claim 1 or 2, characterized in that: The second channel is the wellbore annulus between the flexible geothermal heat extraction pipe and the well wall of the operating well.

8. The flexible geothermal heat pipe according to claim 7, characterized in that: The flexible geothermal heat extraction pipe includes an open guide shoe, and the inner cavity of the open guide shoe is connected to the wellbore annulus.

9. The flexible geothermal heat pipe according to claim 1, characterized in that: The ball seat structure includes a front ball seat and a rear ball seat, the front end of the rear ball seat is fixedly connected to the rear end of the front ball seat and cooperates to form the ball socket, and in the two adjacent ball seat structures, the rear end of the rear ball seat of the previous ball seat structure is sealed and movably connected to the front end of the front ball seat of the latter ball seat structure.

10. The flexible geothermal heat pipe according to claim 9, characterized in that: The ball seat structure also includes multiple ball keys, which are arranged along the radial direction of the ball head. The multiple ball keys are arranged at intervals along the circumference of the ball head. The ball key has a hemispherical ball end, and the ball head is correspondingly provided with multiple hemispherical ball grooves. The ball ends of the multiple ball keys pass through the front ball seat and cooperate with the multiple ball grooves on the ball head.

11. The flexible geothermal heat pipe according to claim 1, characterized in that: A heat insulation layer is provided between the ball seat structure and the inner tube; the heat insulation layer is an air layer or a heat insulation material layer filled with heat insulation material.

12. The flexible geothermal heat pipe according to claim 1, characterized in that: The flexible geothermal heat extraction pipe also includes a three-way hollow casing and a bender. The bender is used to be installed in the main well of the working well and is located below the wellhead of the branch well of the working well. The front end of the three-way hollow casing is connected to the rear end of the bender. The three-way hollow casing is provided with a side hole corresponding to the wellhead of the branch well. The bender is provided with a guide slope for guiding the flexible geothermal heat extraction pipe from the side hole into the branch well.

13. A geothermal heat extraction construction method, characterized in that: For geothermal heat extraction using the flexible geothermal heat extraction pipe according to any one of claims 1 to 12, the construction method comprises the following steps: Drill multiple branch wells from the main well of the operating well to penetrate into the geothermal reservoir; Lowering a plurality of the flexible geothermal heat extraction pipes into a plurality of the branch wells to establish a geothermal heat extraction loop; wherein, a plurality of inner tubes of the flexible geothermal heat extraction pipes are connected to form a first channel, a second channel is formed by utilizing the wellbore annulus between the flexible geothermal heat extraction pipes and the well wall of the operating well, or a plurality of spiral heat exchange pipes are disposed outside the plurality of the inner tubes to form the second channel, and the first channel and the second channel are connected to form the geothermal heat extraction loop; Injecting cold heat exchange medium into the first channel, the cold heat exchange medium well exchanges heat with the formation to form hot heat exchange medium, and the hot heat exchange medium flows back to the second channel; or A cold heat exchange medium is injected into the second channel, the cold heat exchange medium well exchanges heat with the formation to form a hot heat exchange medium, and the hot heat exchange medium flows back to the first channel.

14. The geothermal heat extraction construction method according to claim 13, characterized in that: The step of lowering the plurality of flexible geothermal heat pipes into the plurality of branch wells comprises the following steps: S1. placing a whipstock below the wellhead of the branch well in the main well; S2, running a three-way hollow casing into the main well and connecting it to the whipstock; S3, lowering the flexible geothermal heat extraction pipe into the three-way hollow casing, and then entering the branch well from the side hole of the three-way hollow casing along the guide slope of the whipstock, until the rear end of the flexible geothermal heat extraction pipe is stuck in the side hole; S4. Repeat the above steps S1 to S3 to sequentially lower the multiple flexible geothermal heat extraction pipes into the multiple branch wells from bottom to top.

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