A downhole heat exchange system and downhole heat exchange process

Abstract

The application provides a downhole heat exchange system and a downhole heat exchange process, and relates to the technical field of downhole heat exchange. The downhole heat exchange system comprises a heat exchange well, a casing pipe arranged in the heat exchange well, and a flow channel arranged on the wall of the heat exchange well. A flow disturbance system and a heat exchange system are arranged in the heat exchange well in sequence from bottom to top. The flow disturbance system comprises a suction pipe, a flow disturbance pump and a first fixing part. The lower end of the suction pipe is located in the range of the hot reservoir. The suction end of the flow disturbance pump is connected with the suction pipe. The flow disturbance pump is connected with the casing pipe through the first fixing part. The first fixing part is provided with a first flow hole. The output end of the flow disturbance pump is located above the first fixing part. The flow disturbance pump is used for sucking geothermal water. The lower end of the heat exchange system is soaked in the geothermal water. The downhole heat exchange technology in the prior art can be quickly recovered. The cooling speed is high during use. The heat compensation speed is slow. The downhole heat exchange technology can meet the requirement of large-area heating.

Description

Technical Field

[0001] This invention belongs to the field of downhole heat exchange technology, and more specifically, relates to 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 have been widely developed and utilized due to their cleanliness, environmental friendliness, safety, renewability, and wide distribution. Currently, the development and utilization of geothermal resources mainly employs a process of well injection and surface heat exchange. This involves simultaneously constructing extraction wells and reinjection wells in the target area. High-temperature formation water is extracted from the extraction well, its heat is extracted through a surface heat exchange device, and the cooled water is then transported to the reinjection well for injection into the formation. This process offers a large extraction range and high heat exchange efficiency per well, but it is only suitable for areas with abundant water resources and favorable 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 some 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 increasing awareness of the scientific and rational development of geothermal resources, various regions are gradually tightening regulations on new wells extracting geothermal water, 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 a single-well downhole heat exchange system, coaxial casing single-well closed heat extraction, and U-shaped wells.

[0003] Downhole heat exchange systems do not extract groundwater or geothermal fluids. The process is relatively simple, and it causes less pollution to the surface and underground, making it an environmentally friendly and sustainable heat extraction method. Downhole heat exchange systems (DHE) mainly come in two forms: U-tube downhole heat exchange systems and coaxial casing downhole heat exchange systems. Specifically, the heat extraction process involves suspending a U-tube or coaxial casing heat exchange system, sealed with an outer tube, inside the 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, completes its heat utilization at the surface, and is then recirculated back into the heat exchange system.

[0004] In formations without water, a coaxial casing downhole heat exchange system can be used, which utilizes the inner wall of the wellbore as a heat exchange interface to extract heat from the formation. After the geothermal well is completed, the wellbore is kept as a watertight closed system. A concentric tubing string is run into the geothermal well. During heat exchange, cool water is injected from the surface through the annulus, and after heat exchange in the thermal reservoir, it returns to the surface through the central tube, completing the heat extraction process.

[0005] U-shaped wells are also a hot topic in the research of "heat extraction without water extraction" technology. Cold water is injected from the wellhead of a horizontal well, and after heat exchange is completed in the horizontal section, it returns to the surface through another vertical well that is connected underground. This method requires drilling a horizontal well and a vertical well at the same time. In addition, underground connection technology is also the key to success, and the cost and technical requirements are relatively high.

[0006] The main problem with the above three heat extraction methods is that the geothermal water or well wall, which has cooled down after heat exchange, is reheated by heat conduction or natural micro-convection. Since the formation fluid is static, the micro-convection cannot quickly restore the temperature of the high-temperature section of the heat exchange. The cooling rate is fast, but the heat compensation rate is slow, resulting in low heat exchange efficiency, rapid power decay, and inability to meet the heating requirements of large areas. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a downhole heat exchange system and process, which solves the problems of existing downhole heat exchange technologies, such as difficulty in quickly restoring the high temperature of the heat exchange location, rapid cooling during use, slow thermal compensation, and difficulty in meeting the heating requirements of large areas.

[0008] To achieve the above objectives, the present invention provides a downhole heat exchange system, comprising:

[0009] A heat exchange well, which penetrates a non-thermal reservoir and a thermal reservoir sequentially from top to bottom, is equipped with a casing with a flow channel that communicates with the formation and includes a second permeable section located near the bottom of the well and a first permeable section located at intervals above the second permeable section.

[0010] A turbulence system and a heat exchange system are sequentially arranged from bottom to top within the heat exchange well. The turbulence system includes an extraction pipe, a turbulence pump, a first fixing component, and a sealing component. The lower end of the extraction pipe is below the sealing component. One end of the turbulence pump is connected to the extraction pipe. The turbulence pump is connected to the casing through the first fixing component, and the first fixing component has a first flow passage hole. The first flow passage hole is located in the annulus formed by the extraction pipe and the casing. The other end of the turbulence pump is above the first fixing component. The sealing component is located between the first permeable section and the second permeable section, and the sealing component is connected to the extraction pipe and the casing.

[0011] The heat exchange system is immersed in geothermal water, which can circulate through the second permeable section, the extraction pipe, the turbulence pump, the first flow hole, the annulus formed between the extraction pipe and the sleeve, and the first permeable section. The heat exchange system can complete the heat exchange of the circulating heat exchange medium on the ground.

[0012] Optionally, the lower end of the casing in the thermal reservoir is the second permeable section, and the upper end of the casing in the thermal reservoir is the first permeable section. The first permeable section and the second permeable section are separated by the sealing member located between the extraction pipe and the casing.

[0013] Optionally, the heat exchange system is connected to the casing via a second fixing component, the turbulence pump is located below the heat exchange system, and the second fixing component is provided with an exhaust port to discharge the gas that escapes from the geothermal water during circulation, so that the geothermal water can fill the space from the turbulence pump to the wellhead.

[0014] Optionally, a connecting pipe is sleeved on the lower outer side of the heat exchange system, and a second flow hole is opened on the upper side wall of the connecting pipe. The output end of the turbulence pump is connected to the lower end of the connecting pipe.

[0015] Optionally, the heat exchange system is provided with a first cavity and a second cavity, and an injection pump is provided above the heat exchange system. The injection pump is connected to the first cavity and is used to inject the circulating heat exchange medium into the first cavity so that the circulating heat exchange medium can flow out to the ground through the second cavity.

[0016] Optionally, the heat exchange well is a vertical well, a horizontal well, a high-displacement well, or a branch well.

[0017] Optionally, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located in the horizontal section near the vertical section.

[0018] Optionally, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located in the vertical section near the horizontal section.

[0019] The present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0020] The heat exchange system is installed inside the heat exchange well, allowing it to be immersed in geothermal water.

[0021] A turbulence pump is used to extract geothermal water flowing from the second permeable section into the casing through an extraction pipe, and the geothermal water is then transported to the top of the first fixed component.

[0022] Geothermal water flows through the first flow hole into the annulus formed by the extraction pipe and the sleeve below the first fixed component;

[0023] Geothermal water enters the first permeable section through the annulus formed by the extraction pipe and the casing, and then enters the formation.

[0024] The circulating heat exchange medium is introduced into the heat exchange system, so that the circulating heat exchange medium can exchange heat in the heat exchange system, and the heat exchanged circulating heat exchange medium is transported to the ground for heat utilization.

[0025] Optionally, the extraction pipe extracts geothermal water that flows into the sleeve below the sealing component through the second permeable section, and the geothermal water flows through the first flow hole into the sleeve above the sealing component and out through the first permeable section.

[0026] This invention provides a downhole heat exchange system and process, the advantages of which are as follows: The downhole heat exchange system includes two parts: a surface circulating heat exchange medium and a geothermal water circulation system. The geothermal water circulation system uses a turbulence pump to extract geothermal water near the bottom of the heat exchange well through an extraction pipe, and then transports the geothermal water back to a location far from the bottom of the well. This method of driving the geothermal water circulation accelerates heat compensation within the geothermal reservoir, timely compensating for heat around the well wall, stabilizing the temperature field, and thus improving heat exchange efficiency and effect. The surface circulating heat exchange medium is installed inside the heat exchange well and immersed in geothermal water. The surface circulating heat exchange medium can be injected into the system, where it exchanges heat with the geothermal water. After the heat exchange medium's temperature rises, it flows back to the surface for heat utilization. The utilized circulating heat exchange medium is then injected back into the system for heat exchange and the next heat utilization cycle, thus achieving effective utilization of geothermal resources.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0028] 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.

[0029] Figure 1 A schematic diagram of a downhole heat exchange system according to Embodiment 1 of the present invention is shown.

[0030] Figure 2 A schematic diagram of a downhole heat exchange system according to Embodiment 2 of the present invention is shown.

[0031] Figure 3A schematic diagram of a downhole heat exchange system according to Embodiment 3 of the present invention is shown.

[0032] Figure 4 A schematic diagram of a downhole heat exchange system according to Embodiment 4 of the present invention is shown.

[0033] Figure 5 A flowchart of a downhole heat exchange process according to Embodiment 5 of the present invention is shown.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Thermal reservoir; 2. Heat exchange system; 3. Extraction pipe; 4. Turbulence pump; 5. First fixed component; 6. First flow passage; 7. First open sleeve; 8. Second open sleeve; 11. Sealing component; 12. Water stopper; 13. Second fixed component; 14. Connecting pipe; 15. Second flow passage; 16. Heat exchange pipe; 17. Central insulation pipe; 18. First permeable section; 19. Second permeable section. Detailed Implementation

[0036] 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.

[0037] To address the problems of existing downhole heat exchange technologies, such as difficulty in quickly restoring high temperatures at the heat exchange location, rapid cooling during use, slow thermal compensation, and inability to meet large-area heating requirements, this invention provides a downhole heat exchange system, comprising:

[0038] 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 casing with a flow channel that communicates with the formation. It includes a second permeable section located near the bottom of the well and a first permeable section located at intervals above the second permeable section.

[0039] The turbulence system and heat exchange system are arranged sequentially from bottom to top in the heat exchange well. The turbulence system includes an extraction pipe, a turbulence pump, a first fixed component, and a sealing component. The lower end of the extraction pipe is below the sealing component. One end of the turbulence pump is connected to the extraction pipe. The turbulence pump is connected to the casing through the first fixed component, and the first fixed component has a first flow hole. The first flow hole is located in the annulus formed by the extraction pipe and the casing. The other end of the turbulence pump is above the first fixed component. The sealing component is located between the first permeable section and the second permeable section. The sealing component is connected to the extraction pipe and the casing.

[0040] The heat exchange system is immersed in geothermal water, which can circulate through the second permeable section, extraction pipe, turbulence pump, first flow hole, annulus formed between extraction pipe and casing, and the first permeable section. The heat exchange system can complete the heat exchange of the circulating heat exchange medium on the ground.

[0041] Specifically, the downhole heat exchange system comprises two parts: surface circulating heat exchange medium circulation and geothermal water circulation. The geothermal water circulation part utilizes a turbulence pump to extract geothermal water near the bottom of the heat exchange well through an extraction pipe, and then returns the geothermal water to a location further away from the bottom. This method of driving the geothermal water circulation accelerates heat compensation within the geothermal reservoir, promptly compensating for heat around the well wall, stabilizing the temperature field, and thus improving heat exchange efficiency and effect. The surface circulating heat exchange medium circulation part utilizes a heat exchange system installed inside the heat exchange well, immersed in geothermal water. Surface circulating heat exchange medium can be injected into the system, where it exchanges heat with the geothermal water. After the heated medium flows back to the surface for heat utilization, it is injected back into the system for further heat exchange and utilization, thus achieving effective utilization of geothermal resources.

[0042] Furthermore, this downhole heat exchange system requires only one geothermal well to achieve closed-loop heat extraction, eliminating the need for drilling and reinjection wells. The system exchanges heat through the outer wall of its heat exchange tubes, allowing for the development and utilization of geothermal resources without extracting groundwater or damaging the formation. The outer wall of the heat exchange tubes is immersed in geothermal water, resulting in a large contact area and high heat exchange efficiency. Circulating the geothermal water using a turbulence pump promptly compensates for heat loss around the well wall, stabilizing the temperature field and improving heat exchange efficiency. The turbulence pump does not need to be placed at the bottom of the well, simplifying the drilling and completion process, and making it easy to remove for maintenance. This downhole heat exchange system is easily converted from a conventional hydrothermal geothermal well, and can also be easily modified into a hydrothermal geothermal well or a reinjection well.

[0043] In this embodiment, the inlet of the turbulence pump is below the packer, and the outlet is above the packer. However, in other embodiments, the inlet and outlet of the turbulence pump can be reversed, as long as the geothermal water circulation can be formed. That is, the turbulence pump draws geothermal water from the first permeable section and discharges geothermal water from the second permeable section.

[0044] Optionally, the circulating heat exchange medium is water, a fluid with water as the continuous phase, or an organic liquid.

[0045] Specifically, water and fluids with water as the continuous phase are preferred.

[0046] Optionally, the first fixing component is a perforated annular septum or a perforated packer.

[0047] Optionally, the lower end of the casing in the thermal reservoir is the second permeable section, and the upper end of the casing in the thermal reservoir is the first permeable section. The first permeable section and the second permeable section are separated by a sealing component located between the extraction pipe and the casing.

[0048] Optionally, the heat exchange system is connected to the casing via a second fixed component, and the turbulence pump is located below the heat exchange system. The second fixed component is provided with an exhaust port to discharge the gas that escapes during the circulation of the geothermal water and to allow the geothermal water to fill the space from the turbulence pump to the wellhead.

[0049] Optionally, a connecting pipe is sleeved on the lower outer side of the heat exchange system, and a second flow hole is opened on the upper side wall of the connecting pipe. The output end of the turbulence pump is connected to the lower end of the connecting pipe.

[0050] Optionally, the heat exchange well is a two-section geothermal well structure, and the casing includes a first-section casing and a second-section casing. The lower part of the second-section casing is located in the thermal reservoir. A connecting pipe is sleeved on the lower outer side of the heat exchange system. A second flow hole is opened on the upper side wall of the connecting pipe. The output end of the turbulence pump is connected to the lower end of the connecting pipe.

[0051] A second permeable section is set near the bottom of the thermal reservoir, and a first permeable section is set at the location of the thermal reservoir further away from the bottom of the well. A sealing component is set between the first and second permeable sections, and the sealing component is connected to the inner wall of the extraction pipe and the second casing.

[0052] Specifically, in the two-stage geothermal well structure, the upper part of the thermal reservoir is a non-thermal reservoir. Foamed cement is used for cementing within the non-thermal reservoir area, while foamed cement or ordinary cement is used for cementing within the thermal reservoir area. The first permeable section can be perforated, and the bottom of the thermal reservoir is the second permeable section, which can be completed using open hole, perforation, or screen pipe. The second and first permeable sections are separated by a packer, allowing geothermal water from the second permeable section to enter the wellbore and be extracted through the extraction pipe. The first permeable section is used for geothermal water reinjection. In this way, the geothermal water after heat exchange is reinjected back into the formation from the first permeable section, and the geothermal water used for heat exchange is continuously extracted from the second permeable layer, ensuring that the temperature of the geothermal water used for heat exchange remains high, maintaining a good heat exchange effect and efficiency.

[0053] Optionally, a water stop, a straightener, or a packer is also provided inside the double-sleeve between the first and second permeable sections to ensure that the extraction pipe is centered.

[0054] Furthermore, the heat exchange system can adopt a U-tube heat exchange system or a coaxial sleeve heat exchange system, etc.

[0055] Optionally, the upper part of the heat exchange system is set inside a first open sleeve, the heat exchange system is connected to the first open sleeve through a second fixed component, and the turbulence pump is set inside a second open sleeve.

[0056] Specifically, the height of the heat exchange system is 200-700m. The second fixed component at the upper end of the heat exchange system is a wellhead device, which fixes and seals the wellhead. The wellhead device is equipped with an exhaust port. The bottom of the heat exchange system is 10-50m away from the output end of the turbulence pump.

[0057] Optionally, the heat exchange system is provided with a first chamber and a second chamber, and a pump is provided above the heat exchange system. The injection pump is connected to the first chamber and is used to inject the circulating heat exchange medium into the first chamber so that the circulating heat exchange medium can flow out to the ground through the second chamber.

[0058] Specifically, the injection pump can be installed on the ground. The injection pump pressurizes the circulating heat exchange medium and injects it into the first cavity. Taking the coaxial tube heat exchange system as an example, the first cavity is the annular part, and the second cavity is the central tube. After the circulating heat exchange medium completes heat exchange in the heat exchange system, it flows upward through the second cavity to the ground for heat utilization.

[0059] Optionally, the heat exchange well can be a vertical well, a horizontal well, a high-displacement well, or a branch well.

[0060] Specifically, this downhole heat exchange system is suitable for vertical wells, horizontal wells, extended reach wells, and branch wells, and has a wide range of applications.

[0061] In one example, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located at the position of the horizontal section near the vertical section.

[0062] When the heat exchange well is a horizontal well, the second permeable section is set near the bottom of the horizontal section, and the first permeable section is set in the horizontal section closer to the vertical section.

[0063] In another example, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located in the vertical section near the horizontal section.

[0064] The second permeable section is located near the bottom of the well in the horizontal section, while the first permeable section is located in the horizontal section closer to the vertical section.

[0065] Specifically, when the heat exchange well is a horizontal well, the first permeable section can be located in the vertical section or the horizontal section.

[0066] The present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0067] The heat exchange system is installed inside the heat exchange well, allowing it to be immersed in geothermal water.

[0068] A turbulence pump is used to extract geothermal water flowing from the second permeable section into the casing through an extraction pipe, and the geothermal water is then transported to the top of the first fixed component.

[0069] Geothermal water flows through the first flow hole into the annulus formed by the extraction pipe and the sleeve below the first fixed component;

[0070] Geothermal water enters the first permeable section through the annulus formed by the extraction pipe and the casing, and then enters the formation.

[0071] The circulating heat exchange medium is introduced into the heat exchange system, so that the circulating heat exchange medium can exchange heat in the heat exchange system, and the heat exchanged circulating heat exchange medium is transported to the ground for heat utilization.

[0072] Specifically, the heat exchange system can be fixed at the wellhead of the heat exchange well via a wellhead device, allowing the system to be immersed in geothermal water. Activating the turbulence pump allows geothermal water near the bottom of the heat exchange well to be drawn through the extraction pipe and transported above the first fixed component. This geothermal water then exchanges heat with the circulating heat exchange medium within the system, raising its temperature for heat utilization. The geothermal water flows downwards through the first flow hole, circulating under the action of the turbulence pump, thereby improving heat exchange efficiency and effect. Simultaneously, the circulated heat exchange water flows upwards within the heat exchange system to the surface for heat utilization.

[0073] Optionally, the extraction pipe extracts geothermal water that flows into the sleeve below the sealing component through the second permeable section, and the geothermal water flows through the first overflow hole into the sleeve above the sealing component and out through the first permeable section.

[0074] Optionally, when the heat exchange well is a two-section geothermal well structure, the casing includes a first-section casing and a second-section casing. The lower part of the second-section casing is located in the geothermal reservoir. A second permeable section is set in the wellbore near the bottom of the well. A first permeable section is set in the geothermal reservoir section at a position far from the wellbore. A sealing component is set between the first and second permeable sections. The sealing component is connected to the inner wall of the extraction pipe and the second-section casing. The extraction pipe extracts the geothermal water that flows into the wellbore through the second permeable section. The geothermal water flows through the first flow hole to the annulus between the extraction pipe and the casing, and then flows into the formation through the first permeable section.

[0075] Specifically, the heat exchange well can adopt a two-section geothermal well structure. A second permeable section is set in the wellbore near the bottom of the well, and a first permeable section is set in the geothermal reservoir section at a position far from the bottom of the well. A sealing component is set between the first and second permeable sections. The sealing component is connected to the inner wall of the extraction pipe and the two-section casing. The second permeable section is used for the extraction of geothermal water, and the first permeable section is used for the reinjection of geothermal water. Through the extraction and reinjection of geothermal water, the temperature of the geothermal water used for heat exchange is kept at a high level, maintaining a good heat exchange effect and heat exchange efficiency.

[0076] Example 1

[0077] like Figure 1 As shown, the present invention provides a downhole heat exchange system, comprising:

[0078] The heat exchange well penetrates the non-thermal reservoir and the thermal reservoir 1 from top to bottom. The heat exchange well is equipped with a casing with a flow channel that is connected to the formation. The casing includes a second permeable section 19 located near the bottom of the well and a first permeable section 18 located above the second permeable section 19 at intervals.

[0079] The turbulence system and heat exchange system 2 are arranged sequentially from bottom to top in the heat exchange well. The turbulence system includes an extraction pipe 3, a turbulence pump 4, a first fixing component 5, and a sealing component 11. The lower end of the extraction pipe 3 is below the sealing component 11. One end of the turbulence pump 4 is connected to the extraction pipe 3. The turbulence pump 4 is connected to the casing through the first fixing component 5. The first fixing component 5 has a first flow hole 6, which is located in the annulus formed by the extraction pipe 3 and the casing. The other end of the turbulence pump 4 is above the first fixing component 5. The sealing component 11 is located between the first permeable section 18 and the second permeable section 19. The sealing component 11 is connected to the extraction pipe 3 and the casing.

[0080] The heat exchange system 2 is immersed in geothermal water, which can circulate through the second permeable section 19, the extraction pipe 3, the turbulence pump 4, the first flow hole 6, the annulus formed between the extraction pipe 3 and the sleeve, and the first permeable section 18. The heat exchange system 2 can complete the heat exchange of the circulating heat exchange medium on the ground.

[0081] In this embodiment, the first fixing component 5 is a perforated annular partition.

[0082] In this embodiment, the heat exchange system 2 is a coaxial tube heat exchanger.

[0083] In this embodiment, the outer diameter of the extraction pipe 3 is smaller than the inner diameter of the casing. The bottom end of the extraction pipe 3 is 20-50m away from the bottom of the heat exchange well, or the bottom end of the extraction pipe 3 reaches the bottom of the well. A water inlet hole is opened in the pipe wall within a range of 20-100m from the lower end of the extraction pipe 3. The top end of the extraction pipe 3 is 500-800m away from the ground.

[0084] In this embodiment, the heat exchange well is a two-section geothermal well structure. The casing includes a first-section casing 7 and a second-section casing 8. The lower part of the second-section casing 8 is located in the thermal reservoir 1, and the upper part of the second-section casing 8 is located in the non-thermal reservoir. The second permeable section 19 is 50m above the bottom of the well. The second permeable section 1600m is located between 1500m and 1580m. The sealing component 11 is connected to the inner wall of the extraction pipe 3 and the second-section casing 8.

[0085] In this embodiment, a water stopper 12 may also be provided inside the double-opening sleeve 8 located between the first permeable section 18 and the second permeable section 19.

[0086] In this embodiment, the sealing component 11 is a packer.

[0087] In this embodiment, the upper part of the heat exchange system 2 is disposed inside the first open sleeve 7, and the heat exchange system 2 is connected to the first open sleeve 7 through the second fixing component 13. The turbulence pump 4 is disposed inside the second open sleeve 8.

[0088] In this embodiment, the height of the heat exchange system 2 is 200-700m. The second fixing component 13 at the upper end of the heat exchange system 2 is a wellhead device. The wellhead is fixed and sealed by the wellhead device. The wellhead device has an exhaust hole. The heat exchange system 2 is 10-50m away from the output end of the turbulence pump 4.

[0089] In this embodiment, the heat exchange system 2 is provided with a first cavity and a second cavity. A pump is provided above the heat exchange system 2. The injection pump is connected to the first cavity and is used to inject the circulating heat exchange medium into the first cavity so that the circulating heat exchange medium can flow out to the ground through the second cavity.

[0090] Figure 1 The middle arrow indicates the flow direction of the circulating heat exchange medium.

[0091] In this embodiment, the heat exchange well is a vertical well.

[0092] In summary, when the downhole heat exchange system in this embodiment is applied in a vertical well, the wellbore has a two-section structure. The bottom of the well employs open-hole completion, perforated completion, or perforated screen pipe. The two-section casing 8 at the top of the thermal reservoir 1 is perforated, and a packer is installed below the perforated section. An extraction pipe 3 is lowered to a depth of 300-800m from the surface, with its bottom 20-50m from the bottom of the well, or the extraction pipe 3 reaches the bottom of the well, with a water inlet 20-100m below it. The extraction pipe 3 passes through the perforated section and packer in the upper part of the thermal reservoir 1. The top of the extraction pipe 3 is connected to... A turbulence pump 4 is connected to a second casing 8. There is an annular baffle with a first flow passage 6 between the turbulence pump 4 and the second casing 8, through which fluid can pass. The lower extraction end of the turbulence pump 4 is located in the extraction pipe 3, and the output end is located in the second casing 8. Above the turbulence pump 4 in the wellbore is a coaxial casing heat exchange system 2, which includes a heat exchange tube 16 and a central insulation tube 17. The coaxial casing heat exchange system 2 is 200-700m deep, and its upper end is fixed by a wellhead device. The heat exchange tube 16 is made of a material with good thermal conductivity and is suspended in the geothermal water in the heat exchange well. The central insulation tube 17 is made of a low thermal conductivity insulation material.

[0093] Example 2

[0094] like Figure 2 As shown, the difference between this embodiment and Embodiment 1 is that:

[0095] In this embodiment, a connecting pipe 14 is sleeved on the lower outer side of the heat exchange system 2, and a second flow hole 15 is opened on the upper side wall of the connecting pipe 14. The output end of the turbulence pump 4 is connected to the lower end of the connecting pipe 14.

[0096] Specifically, the connection pipe 14 enables the output end of the turbulence pump 4 to connect with the lower part of the heat exchange system 2. The turbulence pump 4 extracts geothermal water near the bottom of the well and delivers it into the connection pipe 14. The connection pipe 14 is sleeved on the lower outer side of the heat exchange system 2. The geothermal water in the connection pipe 14 soaks the heat exchange system 2 and exchanges heat with the circulating heat exchange medium in the heat exchange system 2. The geothermal water in the connection pipe 14 can flow out through the second flow hole 15 opened on the upper side wall of the connection pipe 14, and then flow downward. After passing through the first flow hole 6, it can be reinjected.

[0097] Example 3

[0098] like Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that:

[0099] In this embodiment, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section. The extraction pipe 3 includes a vertical part and a horizontal part arranged sequentially from top to bottom. The two-section casing 8 includes a vertical casing and a horizontal casing. The second permeable section 19 is located at the bottom of the horizontal section, and the first permeable section 18 is located at a distance from the bottom of the horizontal section.

[0100] Specifically, in this embodiment, the first permeable section 18 and the second permeable section 19 are both in the horizontal section of the horizontal well.

[0101] In this embodiment, the packer 11 is disposed between the first permeable section 18 and the second permeable section 19.

[0102] Example 4

[0103] like Figure 4 As shown, the difference between this embodiment and Embodiment 3 is that:

[0104] In this embodiment, when the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section. The extraction pipe 3 includes a vertical part and a horizontal part arranged sequentially from top to bottom. The two-stage casing 8 includes a vertical casing and a horizontal casing. The second permeable section 19 is located at the bottom of the horizontal section, and the first permeable section 18 is located at the vertical section of the thermal reservoir.

[0105] Specifically, in this embodiment, the first permeable section 9 is in the horizontal section of the horizontal well, and the second permeable section 10 is in the vertical section of the horizontal well.

[0106] Example 5

[0107] like Figure 5 As shown, the present invention also provides a downhole heat exchange process, utilizing the above-mentioned downhole heat exchange system, comprising:

[0108] Heat exchange system 2 is installed inside the heat exchange well so that the lower end of heat exchange system 2 can be immersed in geothermal water;

[0109] The turbulence pump 4 is used to extract the geothermal water flowing from the second permeable section 19 into the casing through the extraction pipe 3, and the geothermal water is transported to the top of the first fixed component 5;

[0110] Geothermal water flows through the first flow hole 6 into the annulus formed by the extraction pipe 3 and the sleeve below the first fixed component 5;

[0111] The circulating heat exchange medium is introduced into the heat exchange system 2, so that the circulating heat exchange medium can exchange heat in the heat exchange system 2, and the heat exchanged circulating heat exchange medium is transported to the ground for heat utilization.

[0112] In this embodiment, when the heat exchange well is a two-section geothermal well structure, the casing includes a first-section casing 7 and a second-section casing 8. The lower part of the second-section casing 8 is located in the thermal reservoir 1, and the upper part of the second-section casing 8 is located in the non-thermal reservoir. The second permeable section 19 is located at the bottom of the horizontal section of the well, and the first permeable section 18 is located at the vertical section of the thermal reservoir. A sealing component 11 is provided between the second permeable section 19 and the first permeable section 18. When the sealing component 11 is connected to the inner wall of the extraction pipe 3 and the second-section casing 8, the extraction pipe 3 extracts the geothermal water flowing into the second-section casing 8 below the sealing component 11 through the second permeable section 19. The geothermal water flows through the first flow hole 6 to the second-section casing 8 above the sealing component 11 and flows out through the first permeable section 10.

[0113] Taking one implementation as an example: a conventional hydrothermal geothermal well with a borehole depth of 2000m and a geothermal reservoir depth of 500m is converted into the downhole heat exchange system described above; perforation is performed at a depth of 1500m, with a perforation section length of 80m; extraction pipe 3 is run in, with its upper end 500m from the wellhead, and it extends directly to the bottom of the well, with perforations at the bottom. The length of the perforated section is 200m. The extraction pipe 3 is aligned using a centralizer, and a packer is installed at 1600m to seal the extraction pipe 3 from the casing. A pump chamber section is set up at 500m, with the inlet of the turbulence pump 4 inside the extraction pipe 3 and the outlet inside the casing. The cable of the turbulence pump 4 is connected to the wellhead. A heat exchange system 2 with a depth of 350m is lowered into the well. The top of the heat exchange system 2 is connected to the surface wellhead device, fixed, and sealed. The heat exchange system 2 is connected to the injection pump on the surface, and the circulating heat exchange medium on the surface is circulated through the heat exchange system 2, which also exchanges heat with the geothermal water. The turbulence pump 4 is started, and the geothermal water circulates under the pressure of the turbulence pump 4, replenishing heat from the formation, maintaining a stable temperature inside the wellbore, and ensuring heat exchange efficiency and effect.

[0114] 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 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 casing with a flow channel that communicates with the formation and includes a second permeable section located near the bottom of the well and a first permeable section located at intervals above the second permeable section. A turbulence system and a heat exchange system are sequentially arranged from bottom to top within the heat exchange well. The turbulence system includes an extraction pipe, a turbulence pump, a first fixing component, and a sealing component. The lower end of the extraction pipe is below the sealing component. One end of the turbulence pump is connected to the extraction pipe. The turbulence pump is connected to the casing through the first fixing component, and the first fixing component has a first flow passage hole. The first flow passage hole is located in the annulus formed by the extraction pipe and the casing. The other end of the turbulence pump is above the first fixing component. The sealing component is located between the first permeable section and the second permeable section, and the sealing component is connected to the extraction pipe and the casing. The heat exchange system is immersed in geothermal water, which can circulate through the second permeable section, the extraction pipe, the turbulence pump, the first flow hole, the annulus formed between the extraction pipe and the sleeve, and the first permeable section. The heat exchange system can complete the heat exchange of the circulating heat exchange medium on the ground.

2. The downhole heat exchange system according to claim 1, characterized in that, The lower end of the casing located in the thermal reservoir is the second permeable section, and the upper end of the casing located in the thermal reservoir is the first permeable section. The first permeable section and the second permeable section are separated by the sealing component located between the extraction pipe and the casing.

3. The downhole heat exchange system according to claim 2, characterized in that, The heat exchange system is connected to the casing through a second fixing component. The turbulence pump is located below the heat exchange system. The second fixing component is provided with an exhaust port to discharge the gas that escapes from the geothermal water during circulation and to allow the geothermal water to fill the space from the turbulence pump to the wellhead.

4. The downhole heat exchange system according to claim 1, characterized in that, A connecting pipe is sleeved on the lower outer side of the heat exchange system, and a second flow hole is opened on the upper side wall of the connecting pipe. The output end of the turbulence pump is connected to the lower end of the connecting pipe.

5. The downhole heat exchange system according to claim 1, characterized in that, The heat exchange system is provided with a first cavity and a second cavity. An injection pump is provided above the heat exchange system. The injection pump is connected to the first cavity and is used to inject the circulating heat exchange medium into the first cavity so that the circulating heat exchange medium can flow out to the ground through the second cavity.

6. The downhole heat exchange system according to claim 2, characterized in that, The heat exchange well can be a vertical well, a horizontal well, a high-displacement well, or a branch well.

7. The downhole heat exchange system according to claim 6, characterized in that, When the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located in the horizontal section near the vertical section.

8. The downhole heat exchange system according to claim 6, characterized in that, When the heat exchange well is a horizontal well, the heat exchange well includes a vertical section and a horizontal section, the extraction pipe includes a vertical part and a horizontal part arranged sequentially from top to bottom, the casing includes a vertical casing and a horizontal casing, the second permeable section is located at the bottom of the horizontal section, and the first permeable section is located in the vertical section near the horizontal section.

9. A downhole heat exchange process, utilizing the downhole heat exchange system according to any one of claims 1-8, characterized in that, include: The heat exchange system is installed inside the heat exchange well, allowing it to be immersed in geothermal water. A turbulence pump is used to extract geothermal water flowing from the second permeable section into the casing through an extraction pipe, and the geothermal water is then transported to the top of the first fixed component. Geothermal water flows through the first flow hole into the annulus formed by the extraction pipe and the sleeve below the first fixed component; Geothermal water enters the first permeable section through the annulus formed by the extraction pipe and the casing, and then enters the formation. The circulating heat exchange medium is introduced into the heat exchange system, so that the circulating heat exchange medium can exchange heat in the heat exchange system, and the heat exchanged circulating heat exchange medium is transported to the ground for heat utilization.

10. The downhole heat exchange process according to claim 9, characterized in that, The extraction pipe draws geothermal water that flows into the sleeve below the sealing component through the second permeable section. The geothermal water flows through the first overflow hole into the sleeve above the sealing component and then out through the first permeable section.

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