Underground circulating heat removal system and method

Abstract

The invention provides an underground circulating heat removal system and method, and belongs to the crossing field of geothermal development and petroleum engineering. The system comprises a sleeve, a formation water underground circulation assembly and an underground heat exchange device, wherein the formation water underground circulation assembly and the underground heat exchange device are arranged in the sleeve; the underground heat exchange device is connected with the formation water underground circulation assembly; and formation water in the geothermal water reservoir enters the underground heat exchange device along the formation water underground circulating assembly, and the formation water subjected to heat exchange is recharged into the geothermal water reservoir along the formation water underground circulating assembly to form circulating heat removal. By means of the underground formation water circulation assembly, formation water completely circulates underground and does not make contact with the outside, pollution to the formation water in the conveying process is reduced to a certain degree, and blockage of geothermal well rock stratum gaps is avoided as much as possible; according to the method, the same-layer reinjection of the formation water of the single well is realized through sidetrack drilling of the branch well sections, drilling of multiple wells is avoided, and the well drilling cost is saved.

Description

Technical Field

[0001] The present invention belongs to the intersection of geothermal development and petroleum engineering, and specifically relates to a downhole circulating heat extraction system and method, which is used for downhole circulating heat extraction of geothermal wells, and is a technology for transitioning from a "water extraction and reinjection" geothermal extraction mode to a "heat extraction without water extraction" geothermal extraction mode. Background Art

[0002] Geothermal energy is a green, low-carbon, recyclable renewable energy with the characteristics of large reserves, wide distribution, clean and environmentally friendly, stable and reliable. It is one of the main directions of energy development at this stage and in the future, and has huge social and economic benefits and important strategic significance.

[0003] Traditional geothermal resource exploitation mainly relies on the "water extraction and re-injection" method. This geothermal exploitation model requires the formation water to be drawn out of the ground during the heat extraction process, and the tail water is then injected back into the formation after absorbing heat energy through the ground heat exchanger. In the long-distance transportation process of "underground-ground-underground", there may be a risk of formation water contamination; and during re-injection, due to the tiny impurities carried during the long-distance transportation, it is likely to cause the blockage of the pores in the geothermal well rock formation, especially in some heat storage blocks with strong heterogeneity or poor porosity and permeability; insufficient re-injection will cause a series of problems such as groundwater level drop, surface subsidence, and soil salinization; in addition, according to the requirements of geothermal water re-injection in the same layer, this exploitation method means that at least two wells must be drilled in the same heat reservoir system to achieve water extraction and re-injection respectively, which will undoubtedly greatly increase the initial investment and operation and maintenance costs. In addition, various local policies and regulations have also imposed varying degrees of restrictions on the traditional geothermal exploitation method of "water extraction and re-injection".

[0004] In the face of the limitations of traditional "water extraction and re-injection", a feasible breakthrough direction is to develop a geothermal resource development and utilization model based on "extracting heat without taking water", which generally uses a coaxial downhole heat exchanger to extract geothermal energy. Its essence is that the heat exchange medium circulates in the downhole heat exchanger while indirectly contacting the heat storage for heat exchange. However, the current research on this heat extraction mode is still in the experimental exploration stage, and there are still technical bottlenecks such as small heat exchange capacity and an order of magnitude difference in power compared with the traditional extraction and injection mode. Therefore, the direction of indirect extraction of geothermal energy by coaxial downhole heat exchangers is still in the stage of development and improvement, and cannot perfectly replace "water extraction and re-injection".

[0005] In view of this, another feasible direction is to improve the traditional "water extraction and re-injection" mining model so that the improved model can avoid the negative effects brought about by the traditional "water extraction and re-injection" model to a certain extent, and at the same time comply with the requirements of relevant local policies and regulations on "extracting heat but not water". Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, to provide a downhole circulating heat extraction system and method, and to provide a feasible technology for the transition from "water extraction and reinjection" to "heat extraction without water extraction".

[0007] The present invention is achieved through the following technical solutions:

[0008] A first aspect of the present invention provides a downhole circulation heat extraction system, the system comprising a casing, and a formation water downhole circulation assembly and a downhole heat exchange device arranged in the casing;

[0009] The downhole heat exchange device is connected to the formation water downhole circulation component;

[0010] The formation water in the geothermal water reservoir enters the downhole heat exchange device along the formation water downhole circulation component, and the formation water after heat exchange is re-injected into the geothermal water reservoir along the formation water downhole circulation component to form a circulation heat extraction.

[0011] A further improvement of the present invention is:

[0012] The formation water downhole circulation assembly comprises: a circulation power device, an oil pipe and an insulated oil pipe;

[0013] The oil pipe is coaxially arranged with the heat-insulating sleeve, and the inner diameter of the oil pipe is larger than the inner diameter of the heat-insulating oil pipe.

[0014] A further improvement of the present invention is:

[0015] The downhole heat exchange device and the circulating power device are arranged above the oil pipe and the heat-insulated oil pipe;

[0016] The upper end of the heat-insulating oil pipe is connected to the inlet of the circulating power device, the outlet of the circulating power device is connected to the inlet of the downhole heat exchange device, and the upper end of the annulus between the heat-insulating oil pipe and the oil pipe is connected to the outlet of the downhole heat exchange device.

[0017] Preferably, a filtering device is provided at the bottom of the heat-insulated oil pipe.

[0018] A further improvement of the present invention is:

[0019] The casing comprises two sections, namely a first casing and a second casing;

[0020] The inner diameter of the first sleeve is greater than the inner diameter of the second sleeve, and the lower end of the first sleeve is connected to the upper end of the second sleeve.

[0021] Preferably, the first sleeve and the second sleeve are coaxially arranged.

[0022] A further improvement of the present invention is:

[0023] A first packer is arranged in the annulus between the oil pipe and the second casing;

[0024] A second packer is arranged in the annulus between the heat-insulated oil pipe and the second casing;

[0025] The first packer is located above the lower end surface of the oil pipe, and the second packer is located below the lower end surface of the oil pipe.

[0026] The second aspect of the present invention provides a method for underground circulating heat extraction, which includes: drilling a vertical well section extending from the ground to a geothermal water reservoir, and a side-drilled branch well section extending obliquely downward, wherein the end of each side-drilled branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir; lowering the above-mentioned underground circulating heat extraction system; and reinjecting formation water in the geothermal water reservoir into the geothermal water reservoir after heat exchange through the underground circulating heat extraction system to achieve circulating heat extraction.

[0027] A further improvement of the present invention is:

[0028] The method comprises:

[0029] (1) drilling out the first completion section and running the first casing;

[0030] (2) drilling a second completion section and running a second casing;

[0031] (3) drilling a sidetrack branch well section;

[0032] (4) Open up the geothermal water reservoir, install the formation water downhole circulation assembly and downhole heat exchange device, and then circulate and extract heat.

[0033] A further improvement of the present invention is:

[0034] The operation of step (3) includes:

[0035] A side drilling window drilling operation is performed at the lower part of the second casing. After the window drilling is completed, directional side drilling of the branch section is performed to obtain multiple side drilling branch well sections. The end of the side drilling branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir.

[0036] A further improvement of the present invention is:

[0037] The operation of step (4) includes:

[0038] Perforating the bottom of the second casing to penetrate the geothermal water reservoir, and placing a filter device in the perforation;

[0039] The heat-insulating oil pipe and the second packer are sequentially lowered and hung and fixed, and the lower end of the heat-insulating oil pipe is extended to the lower end of the second casing and is located below the connection between the side-drilling branch well section and the second casing;

[0040] Connect the upper end of the heat-insulated oil pipe to the inlet of the circulating power unit;

[0041] The oil pipe and the first packer are lowered and hung and fixed, the lower end of the oil pipe is located above the connection between the side drilling branch well section and the second casing, and the first packer is located above the lower end surface of the oil pipe;

[0042] Connect the outlet of the circulating power device to the inlet of the downhole heat exchange device;

[0043] Connect the annulus of the oil pipe and the insulated oil pipe to the outlet of the downhole heat exchange device;

[0044] Start the underground heat exchange device and circulating power device to circulate heat.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] A first aspect of the present invention provides a downhole circulation heat extraction system, the system comprising a casing, and a formation water downhole circulation assembly and a downhole heat exchange device arranged in the casing;

[0047] The downhole heat exchange device is connected to the formation water downhole circulation component;

[0048] The formation water in the geothermal water reservoir enters the downhole heat exchange device along the formation water downhole circulation component, and the formation water after heat exchange is re-injected into the geothermal water reservoir along the formation water downhole circulation component to form a circulation heat extraction.

[0049] (1) The design of the double casing with different apertures of the present invention provides a favorable location for the layout of the downhole heat exchange system and the formation water circulation system;

[0050] (2) The application of the underground heat exchange device of the present invention effectively reduces the heat exchange pipeline and improves the thermal insulation effect to a certain extent;

[0051] (3) The present invention uses a downhole formation water circulation component to allow the formation water to circulate completely downhole without contacting the outside world, thereby reducing the pollution of the formation water during the transportation process to a certain extent and avoiding the blockage of the pores in the geothermal well rock formation as much as possible;

[0052] (4) The present invention realizes the same-layer reinjection of formation water in a single well by side-drilling branch well sections, avoiding the need to drill multiple wells and saving drilling costs;

[0053] (5) The downhole heat exchange device and circulating power device of the present invention are arranged in the first casing close to the ground and with a larger wellbore diameter, which is convenient for maintenance and overhaul.

[0054] (6) The various components of the present invention cooperate with each other to complete heat extraction and energy exchange, providing a new idea for the efficient development and utilization of geothermal energy in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A schematic structural diagram of the underground circulating heat extraction system of the present invention.

[0056] In the figure: 1 is a downhole heat exchange device; 2 is a circulating power device; 3 is an oil pipe; 4 is an insulated oil pipe; 5 is a first packer; 6 is a second packer; 7 is a side drilling branch well section; 8 is a first casing; 9 is a second casing. DETAILED DESCRIPTION

[0057] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0058] like Figure 1 As shown, the present invention provides a downhole circulating heat extraction system, which includes a casing, and a formation water downhole circulation component and a downhole heat exchange device arranged in the casing; the downhole heat exchange device is connected to the formation water downhole circulation component; the formation water in the geothermal water reservoir enters the downhole heat exchange device along the formation water downhole circulation component, and the formation water after heat exchange is recharged into the geothermal water reservoir along the formation water downhole circulation component to form circulating heat extraction.

[0059] When using the system of the present invention, it is necessary to drill a vertical well section and a side-drilled branch well section extending from the ground to the geothermal water reservoir. The vertical well section is a carrier for production operation, and the side-drilled branch well section and the vertical well section can serve as carriers for formation water to flow into and out of the circulation channel, and part of them can serve as the circulation channel itself. The side-drilled branch well section can generally include two side-drilled channels, which are symmetrically excavated on both sides of the vertical well section and connected to the vertical well section. The lower end of the vertical well section is located in the geothermal water reservoir, each side-drilled branch well section extends obliquely downward, and the end of each side-drilled branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir.

[0060] The embodiments of the underground circulating heat extraction system of the present invention are as follows:

[0061] Embodiment 1:

[0062] The formation water downhole circulation assembly includes: a circulation power device 2, an oil pipe 3 and an insulated oil pipe 4. The oil pipe 3 is coaxially arranged with the insulated casing 4, and the inner diameter of the oil pipe 3 is larger than the inner diameter of the insulated oil pipe 4. The circulation power device 2 can provide power for the circulation of formation water downhole, and can adopt any existing power structure, such as a screw pump, a submersible electric pump, and other power devices that match production. The oil pipe 3 and the insulated oil pipe 4 can be any combination of pipe strings suitable for fluid circulation.

[0063] The inner cavity of the heat-insulated oil pipe 4 is used as an upper water channel, and the annulus between the outer wall of the heat-insulated oil pipe 4 and the inner wall of the oil pipe 3 is used as a lower water channel, and the upper water channel and the lower water channel constitute a water circulation channel. The downhole heat exchange device 1 and the circulation power device 2 are arranged above the oil pipe 3 and the heat-insulated oil pipe 4, and the upper end of the heat-insulated oil pipe 4 is connected to the inlet of the circulation power device 2, the outlet of the circulation power device 2 is connected to the inlet of the downhole heat exchange device 1, and the upper end of the annulus between the heat-insulated oil pipe 4 and the oil pipe 3 is connected to the outlet of the downhole heat exchange device 1.

[0064] Through the circulation power device 2, formation water can be pumped from the bottom of the well into the insulated oil pipe 4, and then go up along the insulated oil pipe 4 to enter the downhole heat exchange device 1, where it exchanges heat with the heat exchange medium on the user side. After the heat exchange is completed, the formation water goes down along the annulus between the insulated oil pipe 4 and the oil pipe 3. In actual use, the lower end of the insulated oil pipe 4 is directly extended into the thermal reservoir where the bottom of the well is located. At the same time, a filtering device can be set at the bottom of the insulated oil pipe 4 (the existing filtering device can be used, which will not be repeated here). The lower end of the oil pipe 3 is set above the opening of the side-drilling branch well section. In this way, the formation water after the heat exchange can be guided back to the side-drilling branch well section through the annulus between the insulated oil pipe 4 and the oil pipe 3, and re-injected into the original hot stratum, thereby realizing the reinjection of formation water.

[0065] Embodiment 2:

[0066] The downhole heat exchange device 1 can adopt a heat exchanger of any geometric shape and size that is beneficial to the working medium to complete heat exchange efficiently, and the heat exchange working medium used in the heat exchanger can be any fluid medium suitable for circulating heat exchange.

[0067] Embodiment three:

[0068] The sleeve includes two sleeves, namely a first sleeve 8 and a second sleeve 9. The inner diameter of the first sleeve 8 is larger than the inner diameter of the second sleeve 9, and the lower end of the first sleeve 8 is connected to the upper end of the second sleeve 9.

[0069] Preferably, the first casing 8 and the second casing 9 are coaxially arranged. Accordingly, the vertical well section in the formation includes two connected completion sections, namely the first completion section and the second completion section, and the inner diameter of the first completion section is larger than the inner diameter of the second completion section. Under the premise of ensuring the stability of the formation well wall and the smooth circulation of the fluid, the completion method of these two sections can adopt any completion method suitable for the thermal reservoir. The lower end of the second casing 9 is blocked by cementing cement, and a hole is opened on the lower wall of the second casing 9, and a filtering device is installed in the hole.

[0070] The first casing 8 has a large inner diameter and is used to place the downhole heat exchange device 1 and the circulation power device 2. The second casing 9 has a small inner diameter and is used to arrange the formation water downhole circulation component.

[0071] Embodiment 4:

[0072] Furthermore, a first packer 5 is provided in the annulus between the oil pipe 3 and the second casing 9, and a second packer 6 is provided in the annulus between the heat-insulated oil pipe 4 and the second casing 9. The first packer 5 is located above the lower end surface of the oil pipe 3, and the second packer 6 is located below the lower end surface of the oil pipe 3. When in use, after drilling a hole in the lower part of the second casing 9, the side-drilled branch section 7 is drilled out, the first packer 5 is located above the connection between the side-drilled branch section 7 and the second casing 9, and the second packer 6 is located below the connection between the side-drilled branch section 7 and the second casing 9. In this way, the two packers ensure that the formation water after the heat exchange is re-injected from the side-drilled branch section 7 into the geothermal reservoir.

[0073] During the production process, driven by the circulating power device 2, a low-pressure area is formed inside the insulating casing 4, and the formation water in the geothermal water reservoir is sucked in and goes up along the insulating oil pipe 4 to the downhole heat exchange device 1, where it indirectly contacts and exchanges heat with the user-side heat exchange medium, and then is discharged into the annulus between the insulating oil pipe 4 and the casing 3, and is injected back into the original geothermal water reservoir through the side-drilled branch section 7 under the action of gravity.

[0074] The present invention also provides a method for underground circulating heat extraction, which comprises: drilling a vertical well section extending from the ground to a geothermal water reservoir, and a side-drilled branch well section extending obliquely downward, wherein the end of each side-drilled branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir; lowering the above-mentioned underground circulating heat extraction system, and reinjecting formation water in the geothermal water reservoir into the geothermal water reservoir after heat exchange through the underground circulating heat extraction system, thereby realizing circulating heat extraction.

[0075] The embodiments of the method of the present invention are as follows:

[0076] Embodiment five:

[0077] The method comprises:

[0078] (1) Drill out the first completion section and run the first casing:

[0079] Drilling construction of the first completion section (i.e., the first opening) is generally carried out using a Φ444.5 mm drill bit (the drill bit size can be adjusted according to actual needs), drilling to a well depth of not less than 300 m, and lowering a Φ339.7 mm first casing 8 (the casing size can be adjusted according to actual needs) into the first completion section, and sealing the annulus between the casing and the formation with cement;

[0080] (2) Drill out the second completion section and run the second casing:

[0081] The drilling construction of the second completion section (i.e., the second opening) is carried out. The second opening can use a Φ311.2mm drill bit (the drill bit size can be adjusted according to actual needs) to drill to the target reservoir (i.e., the geothermal water reservoir), and then the second casing 9 is lowered into the second completion section, and the annulus between the casing and the formation is sealed with cement, thus completing the completion operation of the vertical well section. Note that at this time, the wellbore and the target reservoir are sealed with cement and are not yet connected.

[0082] (3) Drilling the sidetrack branch section:

[0083] Side drilling window drilling operations are performed at a suitable position at the bottom of the second casing 9. After the window drilling is completed, directional side drilling of the branch section is performed. The side drilling target can be formulated according to actual conditions to obtain multiple side drilling branch well sections. The end of the side drilling branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir.

[0084] (4) Open up the geothermal water reservoir, install the formation water downhole circulation assembly and downhole heat exchange device, and then circulate and extract heat:

[0085] Perforation is performed at the bottom of the second casing 9 to open up the geothermal water reservoir, and a filter device is lowered into the perforation. Water is tested at the wellhead. If the water test meets the design requirements, the insulating oil pipe 4 and the second packer 6 are sequentially lowered and hung and fixed. The lower end of the insulating oil pipe 4 extends all the way to the lower end of the second casing 9. The second packer 6 is located in the annulus between the insulating oil pipe 4 and the second casing 9, and is located below the connection between the side drilling branch well section and the second casing. Connect the upper end of the insulated oil pipe 4 to the inlet of the circulation power device 2, then lower the oil pipe 3 and the first packer 5 and hang and fix them. The lower end of the oil pipe 3 is located above the connection between the side drilling branch section and the second casing. The first packer 5 is located in the annulus between the oil pipe 3 and the second casing 9, and is located above the lower end surface of the oil pipe 3. Finally, connect the outlet of the circulation power device 2 to the inlet of the downhole heat exchange device 1, and connect the annulus between the oil pipe 3 and the insulated oil pipe 4 to the outlet of the downhole heat exchange device 1. In this way, a closed circulation loop of formation water is established. Start the downhole heat exchange device 1 and the circulation power device 2 to realize the downhole heat exchange and downhole circulation of heat without water. During the production process, the hot reservoir water does not leave the wellhead, first goes up along the insulated casing 4, goes down along the annulus after heat exchange in the downhole heat exchange device 1, and finally is injected back into the same geothermal water reservoir.

[0086] The present invention has the following characteristics: the thermal reservoir water does not leave the ground and the transportation distance is short, and heat exchange and energy extraction can be achieved with only a single well. After using the side-drilled branch well section, the same-layer recharge can be achieved with a single well, and the two side-drilled branch sections can improve the recharge efficiency to a certain extent. Two sections of casing with different diameters are used, and the circulating power device and the downhole heat exchange device are arranged in the first casing with a larger diameter, which is closer to the ground and is convenient for later maintenance and repair. The second casing is not affected during maintenance and repair, which reduces the maintenance and repair costs. In addition, after using the present invention, most of the formation water circulates in the insulated oil pipe and the oil pipe, which can avoid impurities from mixing into the formation water to the greatest extent.

[0087] In summary, the present invention proposes a system for underground circulation of formation water and underground heat exchange, which can alleviate or overcome the problem of tail water reinjection caused by the existing "water extraction and reinjection" technology, and promote the transformation to the geothermal extraction mode of "extracting heat without extracting water"; the present invention has the characteristics of single-well operation and underground heat exchange, and has the characteristics of relatively small footprint, relatively high space utilization, and relatively low drilling cost.

[0088] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0089] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0090] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A downhole circulating heat extraction system, characterized in that: The system includes a casing, and a formation water downhole circulation component and a downhole heat exchange device arranged in the casing; The downhole heat exchange device is connected to the formation water downhole circulation component; The formation water in the geothermal water reservoir enters the downhole heat exchange device along the formation water downhole circulation component, and the formation water after heat exchange is re-injected into the geothermal water reservoir along the formation water downhole circulation component to form a circulation heat extraction.

2. The underground circulating heat extraction system according to claim 1 is characterized in that: The formation water downhole circulation assembly comprises: a circulation power device, an oil pipe and an insulated oil pipe; The oil pipe is coaxially arranged with the heat-insulating sleeve, and the inner diameter of the oil pipe is larger than the inner diameter of the heat-insulating oil pipe.

3. The underground circulating heat extraction system according to claim 2 is characterized in that: The downhole heat exchange device and the circulating power device are arranged above the oil pipe and the heat-insulated oil pipe; The upper end of the heat-insulating oil pipe is connected to the inlet of the circulating power device, the outlet of the circulating power device is connected to the inlet of the downhole heat exchange device, and the upper end of the annulus between the heat-insulating oil pipe and the oil pipe is connected to the outlet of the downhole heat exchange device.

4. The underground circulating heat extraction system according to claim 2 is characterized in that: A filtering device is arranged at the bottom of the heat-insulated oil pipe.

5. The underground circulating heat extraction system according to claim 1 is characterized in that: The casing comprises two sections, namely a first casing and a second casing; The inner diameter of the first sleeve is greater than the inner diameter of the second sleeve, and the lower end of the first sleeve is connected to the upper end of the second sleeve.

6. The underground circulating heat extraction system according to claim 5 is characterized in that: The first sleeve and the second sleeve are coaxially arranged.

7. The underground circulating heat extraction system according to claim 5, characterized in that: A first packer is arranged in the annulus between the oil pipe and the second casing; A second packer is arranged in the annulus between the heat-insulated oil pipe and the second casing; The first packer is located above the lower end surface of the oil pipe, and the second packer is located below the lower end surface of the oil pipe.

8. A downhole circulating heat extraction method, characterized in that: The method comprises: drilling a vertical well section extending from the ground into a geothermal water reservoir, and a side-drilled branch well section extending obliquely downward, wherein the end of each side-drilled branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir; inserting a downhole circulating heat extraction system as described in any one of claims 1 to 7; and reinjecting formation water in the geothermal water reservoir into the geothermal water reservoir after heat exchange through the downhole circulating heat extraction system, thereby realizing circulating heat extraction.

9. The underground circulating heat extraction method according to claim 8, characterized in that: The method comprises: (1) drilling out the first completion section and running the first casing; (2) drilling a second completion section and running a second casing; (3) drilling a sidetrack branch well section; (4) Open up the geothermal water reservoir, install the formation water downhole circulation assembly and downhole heat exchange device, and then circulate and extract heat.

10. The underground circulating heat extraction method according to claim 9, characterized in that: The operation of step (3) includes: A side drilling window drilling operation is performed at the lower part of the second casing. After the window drilling is completed, directional side drilling of the branch section is performed to obtain multiple side drilling branch well sections. The end of the side drilling branch well section and the lower end of the vertical well section are located in the same geothermal water reservoir.

11. The underground circulating heat extraction method according to claim 9, characterized in that: The operation of step (4) includes: Perforating the bottom of the second casing to penetrate the geothermal water reservoir, and placing a filter device in the perforation; The heat-insulating oil pipe and the second packer are sequentially lowered and hung and fixed, and the lower end of the heat-insulating oil pipe is extended to the lower end of the second casing and is located below the connection between the side-drilling branch well section and the second casing; Connect the upper end of the heat-insulated oil pipe to the inlet of the circulating power unit; The oil pipe and the first packer are lowered and hung and fixed, the lower end of the oil pipe is located above the connection between the side drilling branch well section and the second casing, and the first packer is located above the lower end surface of the oil pipe; Connect the outlet of the circulating power device to the inlet of the downhole heat exchange device; Connect the annulus of the oil pipe and the insulated oil pipe to the outlet of the downhole heat exchange device; Start the underground heat exchange device and circulating power device to circulate heat.

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