A downhole heat exchanger, a downhole heat exchange system and a downhole heat exchange process

Abstract

This invention provides a downhole heat exchanger, a downhole heat exchange system, and a downhole heat exchange process, relating to the field of downhole heat exchange technology. The invention includes: a heat exchange tube, the lower end of which is closed; a baffle extending axially along the tube is disposed inside the tube, dividing it into a first chamber and a second chamber, with the lower ends of the first and second chambers connected; the upper ends of the first and second chambers are respectively used for injecting and discharging circulating heat exchange medium; the heat exchange tube includes a heat-extracting section and a non-heat-extracting section arranged sequentially from bottom to top, corresponding to the hot water section and non-hot water section of the heat exchange well, respectively; the hot water section is located below the static water level after well completion. The invention reduces the volume ratio of the internal material of the downhole heat exchanger, increases the flow area of ​​the circulating heat exchange medium, and releases more space for the circulating heat exchange medium. Simultaneously, due to the increased internal volume, the circulating fluid velocity increases under the same pump pressure conditions, resulting in an increase in total heat extraction.

Description

Technical Field

[0001] This invention belongs to the field of downhole heat exchange technology, and more specifically, relates to a downhole heat exchanger, a downhole heat exchange system, and a downhole heat exchange process. Background Technology

[0002] In recent years, with the increasing prominence of energy and environmental issues, geothermal resources, due to their cleanliness, environmental friendliness, safety, renewability, and wide distribution, have gradually been widely developed and utilized. Currently, the development and utilization of geothermal resources mainly adopts a process of well injection and surface heat exchange. This involves simultaneously constructing a water extraction well and a reinjection well in the target area. High-temperature formation water is extracted from the water extraction well, and after heat extraction through a surface heat exchange device, the cooled water is transported to the reinjection well for injection into the formation. This process offers a large resource extraction range and high heat exchange efficiency per well, but it is only suitable for areas with abundant water resources and superior physical properties in the target formation, and the construction cost of geothermal wells is high. Furthermore, because a large amount of formation water is extracted, cooled through surface heat exchange, and reinjected, it inevitably has a certain impact on the target formation and groundwater, and problems such as sand production and scaling occur during production, affecting the normal operation of the system. With the increasing awareness of the scientific and rational development of geothermal resources, various regions are gradually tightening the supervision of new wells for geothermal water extraction, making it increasingly difficult to obtain water extraction permits and mining permits. "Downhole heat exchange" technology, which does not extract geothermal fluids, has become one of the research hotspots. Currently, the main methods of "downhole heat exchange" include using U-shaped wells and using single-well downhole heat exchangers.

[0003] Using downhole heat exchangers (DHEs) eliminates the need to extract groundwater or geothermal fluids. The process is relatively simple and produces minimal pollution to both surface and underground environments, making it an environmentally friendly and sustainable heat extraction method. DHEs primarily come in two forms: U-tube downhole heat exchangers and coaxial sleeve downhole heat exchangers. The specific heat extraction process involves suspending a U-tube or coaxial sleeve heat exchanger (sealed with an outer tube) inside a wellbore at a high geothermal level. Cold water is injected at the surface and exchanges heat with the geothermal water through the U-tube or coaxial outer tube. The water then flows out through the other end of the U-tube or the central tube, completing its heat utilization at the surface before being recirculated back into the heat exchanger. The bottom of the geothermal well in this type of heat exchanger is either an open borehole or a perforated tube, allowing the water inside the well to undergo convective mass transfer with the geothermal reservoir.

[0004] In a U-shaped downhole heat exchanger, the circulating heat exchange medium is injected from one side and flows out from the other. The heat-extracting section of the heat exchanger is in contact with the geothermal water throughout, but its flow passage is small, resulting in high frictional resistance to the circulating heat exchange medium. In a coaxial casing downhole heat exchanger, the circulating heat exchange medium is injected from the annulus and flows out from the central tube. The central tube does not come into contact with the geothermal water, and its flow passage is small. In particular, the annulus injection of the circulating heat exchange medium results in a large contact area between the circulating heat exchange medium and the sidewall, leading to high frictional resistance to the circulating heat exchange medium.

[0005] The heat exchange principle of heat exchangers involves injecting cool surface water, exchanging heat with geothermal water in the wellbore, and then the hot water flows out. Therefore, the adequacy of the heat exchange between the surface water and the geothermal water is a key factor determining the heat extraction. Previous research indicates that the larger the contact area between the heat exchange interface and the geothermal water, and the faster the water flow velocity, the greater the heat extraction. Therefore, increasing the contact area between the heat exchange surface and the geothermal water, and increasing the flow velocity of the circulating surface water, are effective ways to improve heat extraction. Summary of the Invention

[0006] The purpose of this invention is to provide a downhole heat exchanger, a downhole heat exchange system, and a downhole heat exchange process, which reduces the volume ratio of the internal material of the downhole heat exchanger, increases the flow area of ​​the circulating heat exchange medium, and releases more space for the circulating heat exchange medium. At the same time, due to the increase in internal volume, the flow rate of the circulating fluid increases under the same pump pressure conditions, thereby increasing the total heat extraction.

[0007] To achieve the above objectives, the present invention provides a downhole heat exchanger, comprising:

[0008] The heat exchange tube is closed at its lower end. An axially extending baffle is provided inside the heat exchange tube, dividing it into a first chamber and a second chamber. The lower ends of the first and second chambers are connected. The upper ends of the first and second chambers are respectively used for injecting and discharging circulating heat exchange medium. The heat exchange tube includes a heat-extracting section and a non-heat-extracting section arranged sequentially from bottom to top. The heat-extracting section and the non-heat-extracting section correspond to the hot water section and the non-hot water section of the heat exchange well, respectively. The hot water section is located below the static water level after the heat exchange well is completed.

[0009] Optionally, the heat exchange tube in the heat extraction section is made of a thermally conductive material, while the heat exchange tube in the non-heat extraction section is made of a thermal insulation material.

[0010] Optionally, the partition is made of thermal insulation material.

[0011] Optionally, the heat exchange tube is a circular tube, and a sealing plate is provided at the lower end of the heat exchange tube. A gap is formed between the lower end of the partition plate and the sealing plate, and the lower ends of the first chamber and the second chamber are connected through the gap.

[0012] The present invention also provides a downhole heat exchange system, comprising:

[0013] A heat exchange well, which penetrates a non-thermal reservoir and a thermal reservoir sequentially from top to bottom, is equipped with a well casing. The thermal reservoir is connected to the well casing of the heat exchange well, and geothermal water enters the well casing through the connection point.

[0014] The aforementioned downhole heat exchanger is placed in the geothermal water of the heat exchange well. The heat extraction section of the heat exchange tube is located in the hot water section of the heat exchange well, and the non-heat extraction section of the heat exchange tube is located in the non-hot water section of the heat exchange well.

[0015] Optionally, at least a portion of the heat exchange tubes are immersed in geothermal water within the heat exchange well.

[0016] Optionally, the system also includes a pump, the output of which is connected to the upper end of the first chamber for injecting circulating heat exchange medium.

[0017] The present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0018] Inject circulating heat exchange medium into the first chamber;

[0019] The circulating heat exchange medium exchanges heat with the geothermal water through the heat exchange tubes, causing its temperature to rise.

[0020] The circulating heat exchange medium flows out through the second chamber to the ground for heat utilization.

[0021] Optionally, it also includes:

[0022] After heat utilization is completed, the circulating heat exchange medium is injected into the first chamber and circulated for heat exchange and utilization through the downhole heat exchanger.

[0023] Optionally, the circulating heat exchange medium may be water, a fluid with water as the continuous phase, or an organic liquid.

[0024] This invention provides a downhole heat exchanger, a downhole heat exchange system, and a downhole heat exchange process. Its advantages lie in the following: the lower end of the heat exchange tube in the downhole heat exchanger is sealed. A partition is installed inside the heat exchange tube to divide its internal space into a first chamber and a second chamber. A gap is left between the lower end of the partition and the sealed position, allowing the lower ends of the first and second chambers to communicate. The circulating heat exchange medium can be injected into the first chamber and flow out of the second chamber. The heat-extracting section and the non-heat-extracting section of the heat exchange tube correspond to the hot water section and the non-hot water section of the heat exchange well, respectively. The circulating heat exchange medium can be injected into the first chamber and flow out of the second chamber. In the hot section, heat exchange occurs between the heat exchanger and geothermal water through heat exchange tubes, raising the temperature and enabling the utilization of geothermal resources at the surface. This downhole heat exchanger reduces the volume ratio of internal materials, increases the flow area of ​​the circulating heat exchange medium, and frees up more space for the circulating heat exchange medium. At the same time, due to the increased internal volume, the flow velocity of the circulating fluid increases under the same pump pressure, resulting in an increase in total heat extraction. Compared with existing U-shaped and coaxial heat exchangers, the increased flow area leads to more thorough heat exchange, higher flow velocity under the same pump pressure, and greater heat extraction.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0026] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0027] Figure 1 A schematic diagram of a downhole heat exchanger according to Embodiment 1 of the present invention is shown.

[0028] Figure 2 A top view of the heat exchange tubes of a downhole heat exchanger according to Embodiment 1 of the present invention is shown.

[0029] Figure 3 A schematic diagram of a downhole heat exchange system according to Embodiment 2 of the present invention is shown.

[0030] Figure 4 A flowchart of a downhole heat exchange process according to Embodiment 3 of the present invention is shown.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1. Heat exchange tube; 2. Baffle; 3. First chamber; 4. Second chamber; 5. Thermal reservoir; 6. Non-thermal reservoir; 7. Gap; 8. Well casing; 9. Geothermal water. Detailed Implementation

[0033] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0034] This invention provides a downhole heat exchanger, comprising:

[0035] The heat exchange tube is closed at its lower end. Inside the heat exchange tube, there is a baffle extending axially along the heat exchange tube. The baffle divides the heat exchange tube into a first chamber and a second chamber, and the lower ends of the first chamber and the second chamber are connected. The upper ends of the first chamber and the second chamber are used for injecting circulating heat exchange medium and for flowing out circulating heat exchange medium, respectively. The heat exchange tube includes a heat extraction section and a non-heat extraction section arranged sequentially from bottom to top. The heat extraction section and the non-heat extraction section correspond to the hot water section and the non-hot water section of the heat exchange well, respectively. The hot water section is below the static water level after the heat exchange well is completed.

[0036] Specifically, the lower end of the heat exchange tube in this downhole heat exchanger is sealed. The interior of the heat exchange tube is equipped with a partition that divides its internal space into a first chamber and a second chamber. A gap is left between the lower end of the partition and the sealed position, allowing the lower ends of the first and second chambers to connect. The circulating heat exchange medium can be injected into the first chamber and flow out of the second chamber. The heat-extracting and non-heat-extracting sections of the heat exchange tube correspond to the heat-extracting and non-heat-extracting sections of the heat exchange well, respectively. The circulating heat exchange medium can exchange heat with geothermal water through the heat exchange tube in the heat-extracting section, increasing its temperature and enabling the utilization of geothermal resources at the surface. This downhole heat exchanger reduces the volume ratio of internal materials, increases the flow area of ​​the circulating heat exchange medium, and frees up more space for the circulating heat exchange medium. Simultaneously, due to the increased internal volume, the flow velocity of the circulating fluid increases under the same pump pressure conditions, resulting in an increase in total heat output. Compared to existing U-shaped and coaxial heat exchangers, this technology increases the flow area, resulting in more thorough heat exchange, higher flow velocity under the same pump pressure conditions, and greater heat output.

[0037] Furthermore, this downhole heat exchanger requires only one well to achieve closed-loop heat extraction, eliminating the need for reinjection wells. Heat exchange occurs through the walls of the heat exchange tubes, allowing for the development and utilization of geothermal resources without extracting groundwater or damaging the formation. The heat exchange tubes are immersed in geothermal water, resulting in a large contact area and high heat exchange efficiency. After heat exchange, the geothermal water compensates for the heat around the well wall through temperature transfer, stabilizing the temperature field. The structural design of the heat exchange tubes increases the fluid flow area and reduces fluid resistance during heat exchange, further improving heat exchange efficiency. Compared to coaxial tube heat exchangers, taking a 2000m heat exchanger as an example, under the same conditions, the internal volume of the outer tube is reduced by 30%-50%, the contact area between the inner tube and the circulating heat exchange medium is reduced by 15%-25%, and the heat extraction is increased by more than 30%.

[0038] The heat exchange tubes can be segmented, and the length requirements of the heat exchange tubes can be met by connecting the segments. The closed position near the bottom of the heat exchange tube has no baffles or the baffles have gaps, so that a gap is formed between the heat exchange tube and the closed position at the bottom. This gap is used to connect the first chamber and the second chamber. The heat exchange tubes are circular tubes or corrugated tubes. Different sections of the heat exchange tubes can be connected by a locking device. The locking device can include a threaded connection structure or a butt locking structure. Taking the threaded connection structure as an example, two heat exchange tubes can be connected by threads. When tightened, the baffles inside the two heat exchange tubes are aligned. A sealing structure, such as a sealing strip, can be set at the end of the baffle to achieve a sealed connection between the baffles of the two heat exchange tubes.

[0039] Optionally, the heat exchange tubes in the heat extraction section are made of thermally conductive material, while the heat exchange tubes in the non-heat extraction section are made of thermal insulation material.

[0040] Optionally, the thermal conductivity of the heat extraction section is not lower than that of the non-heat extraction section.

[0041] Specifically, in the downhole heat exchanger, the heat exchange circulating medium exchanges heat with the geothermal water through the outer wall of the heat exchange tube in the heat extraction section. The outer wall of the heat exchange tube in the heat extraction section is made of a high thermal conductivity material, such as stainless steel, copper, or cast iron, to ensure the heat exchange effect.

[0042] Optionally, the partition is made of thermal insulation material.

[0043] Specifically, the partition uses insulation materials with low thermal conductivity, such as plexiglass, plastic, resin, and sandwich structures filled with insulation materials, to prevent the injected and outflowing heat exchange circulating water from exchanging heat.

[0044] Furthermore, the heat exchange tubes in the heat extraction section are made of high thermal conductivity materials, such as stainless steel, copper, and cast iron, while the heat exchange tubes in the non-heat extraction section are made of insulation materials; the partition materials are insulation materials, such as plexiglass, plastic, resin, and plywood filled with insulation materials.

[0045] Optionally, the heat exchange tube is a circular tube, and a sealing plate is provided at the lower end of the heat exchange tube. A gap is formed between the lower end of the baffle and the sealing plate, and the lower ends of the first chamber and the second chamber are connected through the gap.

[0046] Specifically, the sealing plate is connected to the lower end of the heat exchange tube to seal the lower end of the heat exchange tube, so that the circulating hot water in the heat exchange tube does not come into contact with the geothermal water, and heat exchange only occurs through the tube wall. The gap between the lower end of the partition plate and the sealing plate allows the lower ends of the first chamber and the second chamber to be connected, so that the circulating heat exchange medium can enter the second chamber from the first chamber.

[0047] Furthermore, this downhole heat exchanger can be used for heat extraction from water-bearing formations.

[0048] The present invention also provides a downhole heat exchange system, comprising:

[0049] The heat exchange well penetrates the non-thermal reservoir and the thermal reservoir sequentially from top to bottom. The heat exchange well is equipped with a well casing. The thermal reservoir is connected to the well casing of the heat exchange well, and geothermal water enters the well casing through the connection point.

[0050] The aforementioned downhole heat exchanger is placed in the geothermal water of the heat exchange well. The heat extraction section of the heat exchange tube is located in the hot water section of the heat exchange well, and the non-heat extraction section of the heat exchange tube is located in the non-hot water section of the heat exchange well.

[0051] Specifically, the heat exchanger tubes in the heat-extracting section are inserted into the geothermal water in the heat exchange well, while the non-heat-extracting section is inserted into the non-hot water section of the heat exchange well. The heat-extracting section heats the geothermal water in the heat exchange well. After heat exchange with the circulating heat exchange medium, the cooled geothermal water exchanges heat with the well casing and the thermal reservoir to replenish the heat exchanged in the well and maintain the stability of the output. The geothermal water layer outside the well wall of the heat exchange well is a porous medium region, and heat exchange occurs simultaneously through natural convection and conduction.

[0052] Optionally, at least part of the heat exchange tubes are immersed in geothermal water within the heat exchange well.

[0053] Specifically, the geothermal water comes from the thermal reservoir corresponding to the heat exchange well. The heat extraction section of the heat exchange pipe is completely immersed in the geothermal water, exchanging heat with the geothermal water with a large contact area to ensure the heat exchange effect.

[0054] Optionally, it also includes a pump, the output of which is connected to the upper end of the first chamber for injecting circulating heat exchange medium.

[0055] Specifically, the pump can be installed on the ground. The pump pressurizes the circulating heat exchange medium, injects the circulating heat exchange medium into the first chamber, and allows the circulating heat exchange medium to flow out from the second chamber to the ground, thus achieving circulation.

[0056] The present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0057] Inject circulating heat exchange medium into the first chamber;

[0058] The circulating heat exchange medium exchanges heat with the geothermal water through the heat exchange tubes, causing its temperature to rise.

[0059] The circulating heat exchange medium flows out through the second chamber to the ground for heat utilization.

[0060] Specifically, the first chamber of the heat exchanger is connected to a pump on the ground, through which cool ground water, i.e., the circulating heat exchange medium, is injected into the first chamber. In the heat extraction section, the cool water exchanges heat with the geothermal water through the heat exchange tubes of the heat exchanger, and its temperature rises. When the circulating heat exchange medium reaches the bottom of the heat exchanger, it flows back up into the second chamber through the gap between the baffle and the sealing plate, flows upward, and continues to exchange heat in the heat extraction section. Finally, it flows out from the top of the second chamber to the ground for heat utilization, thus realizing the utilization of geothermal resources.

[0061] Optionally, it also includes:

[0062] After heat utilization is completed, the circulating heat exchange medium is injected into the first chamber and circulated for heat exchange and utilization through the downhole heat exchanger.

[0063] Specifically, after the heat utilization is completed, the circulating heat exchange medium is pumped back into the first chamber from the ground, and then flows out to the ground through the second chamber for heat utilization. This cycle repeats continuously, enabling the downhole heat exchange system to continuously extract heat and utilize geothermal resources.

[0064] Optionally, the circulating heat exchange medium may be water, a fluid with water as the continuous phase, or an organic liquid.

[0065] Specifically, the preferred circulating heat exchange medium is water or a fluid with water as the continuous phase.

[0066] Example 1

[0067] like Figure 1 and Figure 2 As shown, the present invention provides a downhole heat exchanger, comprising:

[0068] The heat exchange tube 1 is closed at its lower end. Inside the heat exchange tube 1, there is a baffle 2 extending axially along the heat exchange tube 1. The baffle 2 divides the heat exchange tube 1 into a first chamber 3 and a second chamber 4. The lower ends of the first chamber 3 and the second chamber 4 are connected. The upper ends of the first chamber 3 and the second chamber 4 are used for injecting circulating heat exchange medium and for flowing out circulating heat exchange medium, respectively. The heat exchange tube 1 includes a heat extraction section and a non-heat extraction section arranged sequentially from bottom to top. The heat extraction section and the non-heat extraction section correspond to the hot water section and the non-hot water section of the heat exchange well, respectively. The hot water section is below the static water level after the heat exchange well is completed.

[0069] In this embodiment, the partition 2 is arranged along the diameter of the heat exchange tube 1, so that the first cavity and the second cavity are symmetrical structures, dividing the internal space of the heat exchange tube 1 equally.

[0070] In this embodiment, the heat exchange tube in the heat extraction section is made of a thermally conductive material, while the heat exchange tube in the non-heat extraction section is made of a thermal insulation material.

[0071] In this embodiment, the thermal conductivity of the heat extraction section is not lower than that of the non-heat extraction section.

[0072] In this embodiment, the partition is made of thermal insulation material.

[0073] In this embodiment, the partition 2 must be made of a thermal insulation material with low thermal conductivity to prevent the injected and outflowing circulating heat exchange medium from exchanging heat and affecting the heat extraction effect; the heat exchange tube 1 in the heat extraction section is made of a thermally conductive material with high thermal conductivity, which is beneficial to the heat exchange between the circulating heat exchange medium and the geothermal water 9; the heat exchange tube 1 in the non-heat extraction section is made of a thermal insulation material to prevent the hot water after heat exchange from exchanging heat with the surrounding environment and cooling down.

[0074] In this embodiment, the heat exchange tube 1 is a circular tube, and a sealing plate is provided at the lower end of the heat exchange tube 1. A gap 7 is formed between the lower end of the partition plate 2 and the sealing plate. The lower ends of the first chamber 3 and the second chamber 4 are connected through the gap 7.

[0075] In this embodiment, the distance between the partition 2 and the sealing plate is 20-50 meters.

[0076] Example 2

[0077] like Figure 3 As shown, the present invention also provides a downhole heat exchange system, comprising:

[0078] The heat exchange well penetrates the non-thermal reservoir 6 and the thermal reservoir 5 from top to bottom. The heat exchange well is equipped with a well casing 8. The thermal reservoir and the well casing of the heat exchange well are connected, and the geothermal water enters the well casing through the connection point.

[0079] The aforementioned downhole heat exchanger is placed in the geothermal water of the heat exchange well. The heat extraction section of the heat exchange tube is located in the hot water section of the heat exchange well, and the non-heat extraction section of the heat exchange tube is located in the non-hot water section of the heat exchange well.

[0080] like Figure 3 As shown, the arrows indicate the flow direction of the circulating heat exchange medium.

[0081] In this embodiment, at least a portion of the heat exchange tube 1 is immersed in the geothermal water 9 within the heat exchange well.

[0082] In this embodiment, a pump is also included, the output end of which is connected to the upper end of the first chamber 3 for injecting circulating heat exchange medium.

[0083] Example 3

[0084] like Figure 4 As shown, the present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0085] Inject circulating heat exchange medium into the first chamber 3;

[0086] The circulating heat exchange medium exchanges heat with the geothermal water 9 through heat exchange tube 1, and its temperature rises.

[0087] The circulating heat exchange medium flows out through the second chamber 4 to the ground for heat utilization.

[0088] In this embodiment, it also includes:

[0089] After the heat utilization is completed, the circulating heat exchange medium is injected into the first chamber 3, and the heat exchange and utilization are carried out in a circulating manner through the downhole heat exchanger.

[0090] In this embodiment, the circulating heat exchange medium is water, a fluid with water as the continuous phase, or an organic liquid.

[0091] Taking a simulated implementation as an example: the heat exchange well is equipped with a 193.7mm well casing 8, the wall thickness of the well casing 8 is 10mm, the wellbore length of the heat exchange well is 2100m, the geothermal water 9 is 500m below the ground surface, and the water temperature is 65℃; the injected circulating heat exchange medium is water, the water temperature is 15℃, and the circulation flow rate is 50m³ / h. 3 / h; Calculations were performed using the aforementioned downhole heat exchange system and the coaxial casing downhole heat exchange system with a coaxial heat exchanger. The heat exchanger tube 1 of the heat exchanger was selected as 152mm in diameter, 10mm in thickness, and 2000m in length. The partition plate 2 was 10mm thick. The central tube of the coaxial heat exchanger was selected as the optimized tube diameter of 102mm and the thickness of 10mm.

[0092] Conclusion: A coaxial heat exchanger with an outer tube volume of 27.36 m³ was successfully used. 3 The central tube occupies a volume of 5.77m³. 3 It accounts for 21%, and the contact area between the inlet and outlet circulating heat exchange medium and the pipe wall is 1984.48 m². 3 The heat exchange tube 1 of the aforementioned downhole heat exchanger has a volume of 27.36 m³. 3 The volume occupied by partition 2 is 2.64m³. 3 It accounts for 9.65%, which is 14.6% larger than the circulating heat exchange medium volume in a coaxial heat exchanger, and the contact area between the inlet and outlet circulating heat exchange medium and the tube wall is 1356.96 m². 2 It reduces the number of heat exchangers by 31.6% compared to coaxial heat exchangers.

[0093] The aforementioned downhole heat exchanger has a calculated temperature rise of 20.5℃ and a heat output of 1197kW. Under the same pump pressure conditions, the temperature rise of the coaxial sleeve heat exchanger is 14.8℃ and the heat output is 864kW. The heat output of the aforementioned downhole heat exchanger is increased by 39%.

[0094] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A downhole heat exchanger, characterized in that, include: The heat exchange tube is closed at its lower end. An axially extending baffle is provided inside the heat exchange tube, dividing it into a first chamber and a second chamber. The lower ends of the first and second chambers are connected. The upper ends of the first and second chambers are respectively used for injecting and discharging circulating heat exchange medium. The heat exchange tube includes a heat-extracting section and a non-heat-extracting section arranged sequentially from bottom to top. The heat-extracting section and the non-heat-extracting section correspond to the hot water section and the non-hot water section of the heat exchange well, respectively. The hot water section is located below the static water level after the heat exchange well is completed.

2. The downhole heat exchanger of claim 1, wherein, The heat exchange tubes in the heat extraction section are made of thermally conductive material, while the heat exchange tubes in the non-heat extraction section are made of thermal insulation material.

3. The downhole heat exchanger of claim 1, wherein, The partition is made of thermal insulation material.

4. The downhole heat exchanger according to claim 1, characterized in that, The heat exchange tube is a circular tube, and a sealing plate is provided at the lower end of the heat exchange tube. A gap is formed between the lower end of the partition plate and the sealing plate, and the lower ends of the first chamber and the second chamber are connected through the gap.

5. A downhole heat exchange system, characterized in that, include: A heat exchange well, which penetrates a non-thermal reservoir and a thermal reservoir sequentially from top to bottom, is equipped with a well casing. The thermal reservoir is connected to the well casing of the heat exchange well, and geothermal water enters the well casing through the connection point. According to any one of claims 1-4, the downhole heat exchanger is placed in the geothermal water of the heat exchange well, the heat extraction section of the heat exchange tube is located in the hot water section of the heat exchange well, and the non-heat extraction section of the heat exchange tube is located in the non-hot water section of the heat exchange well.

6. The downhole heat exchange system according to claim 5, characterized in that, At least a portion of the heat exchange tubes are immersed in geothermal water within the heat exchange well.

7. The downhole heat exchange system according to claim 5, characterized in that, It also includes a pump, the output end of which is connected to the upper end of the first chamber for injecting circulating heat exchange medium.

8. A downhole heat exchange process, utilizing the downhole heat exchange system according to any one of claims 5-7, characterized in that, include: Inject circulating heat exchange medium into the first chamber; The circulating heat exchange medium exchanges heat with the geothermal water through the heat exchange tubes, causing its temperature to rise. The circulating heat exchange medium flows out through the second chamber to the ground for heat utilization.

9. The downhole heat exchange process according to claim 8, characterized in that, Also includes: After heat utilization is completed, the circulating heat exchange medium is injected into the first chamber and circulated for heat exchange and utilization through the downhole heat exchanger.

10. The downhole heat exchange process according to claim 8, characterized in that, The circulating heat exchange medium is water, a fluid with water as the continuous phase, or an organic liquid.

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