Enhanced geothermal system U-shaped well heat exchange method based on multistage fracturing permeation enhancement

Abstract

The invention relates to an enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing permeation enhancement, and relates to the technical field of geothermal development. Optimizing a heat exchange medium; and heat exchange control. An oil and gas reservoir fracturing technology is innovatively transplanted to the field of geothermal development, and the core lies in that multi-stage directional hydraulic fracturing is carried out on a horizontal heat exchange section of a U-shaped well, a high-density branch fracture network is constructed, and a capillary type heat exchange structure is formed. Compared with a traditional geothermal development technology, the heat exchange area is increased in an exponential level mode, and the effective heat exchange area is increased to be more than 10 times that of a traditional smooth well wall through a crack network; the heat extraction efficiency is improved by 40-70%, and the temperature of tail water is increased by 15-25 DEG C; the fracture network delays the thermal breakthrough phenomenon, and the economic exploitation period is prolonged; the cost advantage is that the mature fracturing process is utilized, and the cost is reduced by more than 30% compared with drilling of an ultra-long horizontal well.

Description

Technical Field

[0001] The present invention relates to the field of geothermal development technology, and more specifically, to a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing and permeability enhancement. Background Art

[0002] With the growing global demand for clean energy, geothermal energy, as a stable, clean, and renewable energy source, is attracting increasing attention for its development and utilization. However, traditional geothermal development technologies have limitations in terms of heat exchange efficiency and cost control, which restricts the large-scale and efficient development of geothermal energy.

[0003] Traditional U-shaped butt-jointed wells rely on the limited contact area between the vertical and horizontal well sections for water-rock heat transfer. This results in limited heat transfer area, low heat extraction efficiency, and rapid tailwater temperature decay. While existing technologies have attempted to increase the length of the horizontal section or injection flow rates, significant improvements are difficult due to geological constraints and energy efficiency.

[0004] In summary, there is an urgent need for an enhanced geothermal system U-well heat exchange method based on multi-stage fracturing and permeability enhancement to solve the above problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an enhanced geothermal system U-well heat exchange method based on multi-stage fracturing and permeability enhancement, which solves the problems of small heat exchange area, low heat extraction efficiency, and rapid tail water temperature decay in existing heat exchange methods.

[0006] To achieve the above objectives, the present invention provides a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing and permeability enhancement, comprising the following steps: S1. Fracture network construction: Form multiple tree-like fracture clusters in the horizontal well section; including segmented perforation technology and temporary plugging and diversion technology; S101, staged perforation technology: setting perforation points at different locations in the horizontal well to provide initial fracture cluster opening locations for hydraulic fracturing; specifically, the following steps are included: S1011. Review existing technical information Specifically, before officially carrying out segmented perforating operations, professional and technical personnel need to conduct in-depth research on the geological data of the target area; by analyzing core samples, they can obtain the rock's compressive strength, elastic modulus, porosity and other mechanical and physical properties, and determine key parameters such as perforating depth, aperture and density.

[0007] S1012, Geophysical Exploration With the help of geological radar, seismic exploration and other technical means, we can accurately grasp the stratum structure and ground stress distribution, identify the weak layers and stress concentration areas of underground rocks, and provide a basis for the selection of perforation locations.

[0008] S1013, On-site inspection Conduct a comprehensive inspection of the horizontal heat exchange section of the U-shaped well. Use downhole television, calipers, and other testing tools to check for wellbore collapse, shrinkage, scaling, and other issues. If any irregularities are found, workover operations are necessary. Use an underreamer to expand the shrinkage area and remove scale and debris from the wellbore to ensure the perforating tool can be lowered smoothly to the intended location.

[0009] S1014, comprehensive division of sub-segments The horizontal heat exchange section of a U-shaped well is divided into multiple subsections based on geological conditions and design requirements. Specialized perforating tools are then used to perform perforation operations at specific locations in each subsection.

[0010] Specifically, perforation parameters such as depth, diameter, and density require precise calculation and design to ensure the formation of appropriate initial fractures in the rock while avoiding excessive damage to the wellbore wall. The perforation depth must be sufficient to penetrate the compacted zone near the wellbore wall, while the diameter and density must be optimized based on the rock hardness and the injectivity of the fracturing fluid to create optimal conditions for subsequent hydraulic fracturing.

[0011] The inspected and qualified perforating guns and perforating charges are assembled according to design specifications to form a perforating string. The string is then slowly lowered into the well through the wellhead assembly. When the string reaches the first predetermined perforation location, an electrical signal is transmitted from the surface control system to the cable within the string, detonating the perforating charge. The resulting shaped jet instantly penetrates the wellbore wall and surrounding rock, forming the perforation hole.

[0012] S1015, perforation section movement and repeated operation After completing a perforating section, lift or lower the perforating string to the next predetermined perforating position and repeat the above ignition and perforating steps. When moving the perforating string, pay attention to controlling the speed and distance to ensure that the perforating position is accurate.

[0013] S1016, perforation effect inspection After the perforation operation is completed, downhole imaging, acoustic logging and other technical means are used to detect parameters such as the shape, depth, aperture and density of the perforation holes to evaluate whether the perforation effect meets the design requirements.

[0014] S102, temporary blocking and steering technology Temporary plugging and diversion technology involves starting hydraulic fracturing operations after completing staged perforation. During the fracturing process, a temporary plugging agent is injected into the well to temporarily plug existing fractures, forcing the subsequently injected high-pressure fluid to seek new weak points, thereby forming new fractures. Ultimately, multiple groups of tree-like fracture clusters are formed in the horizontal well section. The specific steps include: S1021, injection of fracturing fluid Specifically, high-pressure fracturing fluid is injected into the well. Under the action of pressure, the fracturing fluid enters the rock from the perforation position and gradually forms initial cracks.

[0015] S1022, inject temporary plugging agent Specifically, when a group of cracks expands to a certain extent, a temporary plugging agent is injected into the well; the temporary plugging agent can enter the formed cracks, block the crack channels, and increase the flow resistance within the cracks.

[0016] S1023, repeated injection Specifically, through repeated injection of temporary plugging agents and fracturing fluids, multiple groups of tree-branching fracture clusters are gradually formed in the horizontal well section, constructing a complex fracture network.

[0017] As a preferred embodiment of the present invention, the temporary blocking agent is a degradable granular material or a gel material.

[0018] As a preferred embodiment of the present invention, the expansion and morphology of the fractures must be precisely controlled throughout the fracture network construction process. By monitoring parameters such as pressure and flow during the fracturing process, and combining geological models with numerical simulation techniques, parameters such as the fracturing fluid injection rate, pressure, and the amount of temporary plugging agent injected can be adjusted in real time. Based on the mechanical properties of the rock and the distribution of in-situ stresses, the perforation orientation and fracturing sequence are optimized to ensure that the resulting fracture network meets the requirements of geothermal development.

[0019] S2. Optimization of heat exchange medium: Water is injected into the production well as the main medium, forming turbulent flow through the fracture network to achieve full surface contact heat exchange with the rock mass; S3. Heat exchange control: Regulate flow resistance through crack opening and inclination design to extend the retention time of the medium in the high-temperature rock formation.

[0020] As a preferred embodiment of the present invention, the crack opening is controlled to be 0.5-5 mm.

[0021] As a preferred embodiment of the present invention, the inclination angle is controlled to be 15°-45° with respect to the vertical direction.

[0022] As a preferred embodiment of the present invention, the expansion radius of a single fracture cluster is 30-100 meters.

[0023] As a preferred embodiment of the present invention, the fracture clusters evenly cover the horizontal well section and present a tree-like branching structure.

[0024] Compared with the existing technology, the technical solution of this application has the following beneficial effects: This invention demonstrates a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing to increase permeability. This innovative approach applies oil and gas reservoir fracturing technology to geothermal development. Its core principle is to implement multi-stage directional hydraulic fracturing in the horizontal heat exchange section of the U-shaped well, creating a high-density branching fracture network and forming a "capillary" heat exchange structure. Compared with traditional geothermal development technologies, this method exponentially increases the heat exchange area: the fracture network increases the effective heat exchange area to more than 10 times that of a traditional smooth wellbore. It also offers a breakthrough in heat extraction efficiency: the heat extraction rate per well increases by 40%-70%, and the tailwater temperature rises by 15-25°C. System life is extended: the fracture network delays thermal breakthrough, extending the economic recovery cycle. Furthermore, the cost advantage is achieved by utilizing mature fracturing technology, reducing costs by over 30% compared to drilling ultra-long horizontal wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing and permeability enhancement in one embodiment of the present application; Figure 2 This is a schematic diagram of a process for constructing a fracture network in a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing and permeability enhancement in one embodiment of the present application; Figure 3 This is a flow chart of the segmented perforation technology in the U-shaped well heat exchange method of the enhanced geothermal system based on multi-stage fracturing and permeability enhancement in one embodiment of the present application; Figure 4 This is a flow chart of the temporary plugging and diverting technology in the U-shaped well heat exchange method of the enhanced geothermal system based on multi-stage fracturing and permeability enhancement in one embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0027] Example 1

[0028] The present invention provides a U-shaped well heat exchange method for an enhanced geothermal system based on multi-stage fracturing and permeability enhancement, such as Figure 1 As shown, the following steps are included: S1. Fracture network construction: multiple groups of tree-like fracture clusters are formed in the horizontal well section; Figure 2 As shown, the specific steps include: S101. Staged perforation technology: Staged perforation provides the initial crack opening position for hydraulic fracturing.

[0029] As a preferred embodiment of the present invention, the segmented perforation is to set perforation points at different positions of the horizontal well to provide initial crack opening positions for hydraulic fracturing; Figure 3 As shown, the specific steps include: S1011. Review existing technical information Before officially commencing staged perforation operations, professional technicians must thoroughly study the geological data of the target area. By analyzing core samples, they can determine the rock's mechanical and physical properties, such as compressive strength, elastic modulus, and porosity, and determine key parameters such as perforation depth, hole diameter, and hole density.

[0030] S1012, Geophysical Exploration With the help of geological radar, seismic exploration and other technical means, we can accurately grasp the stratum structure and ground stress distribution, identify the weak layers and stress concentration areas of underground rocks, and provide a basis for the selection of perforation locations.

[0031] S1013, On-site inspection Conduct a comprehensive inspection of the horizontal heat exchange section of the U-shaped well. Use downhole television, calipers, and other testing tools to check for wellbore collapse, shrinkage, scaling, and other issues. If any irregularities are found, workover operations are necessary. Use an underreamer to expand the shrinkage area and remove scale and debris from the wellbore to ensure the perforating tool can be lowered smoothly to the intended location.

[0032] S1014, comprehensive division of sub-segments The horizontal heat exchange section of a U-shaped well is divided into multiple subsections based on geological conditions and design requirements. Specialized perforating tools are then used to perforate specific locations within each subsection. Parameters such as perforation depth, hole diameter, and hole density require precise calculation and design to ensure appropriate initial fractures in the rock while avoiding excessive damage to the wellbore wall. The perforation depth must be sufficient to penetrate the compacted zone near the wellbore wall, while the hole diameter and hole density are optimized based on the rock hardness and the injectivity of the fracturing fluid to create optimal conditions for subsequent hydraulic fracturing.

[0033] The inspected and qualified perforating guns and perforating charges are assembled according to the design specifications to form the perforating string. The perforating string is then slowly lowered into the well through the wellhead assembly. During lowering, parameters such as cable tension, string lowering speed, and depth are closely monitored to prevent string obstruction and drill sticking. When the perforating string reaches the first predetermined perforation location, an electrical signal is transmitted through the ground control system to the cable within the string, detonating the perforating charge. The resulting shaped jet instantly penetrates the wellbore wall and surrounding rock, forming the perforation hole.

[0034] S1015, perforation section movement and repeated operation After completing a perforating section, the perforating string is raised or lowered to the next predetermined perforating location and the above ignition and perforating steps are repeated. When moving the perforating string, pay attention to controlling the speed and distance to ensure the perforation location is accurate.

[0035] S1016, perforation effect inspection After the perforation operation is complete, downhole imaging and sonic logging are used to examine parameters such as perforation shape, depth, diameter, and density to assess whether the perforation results meet design requirements. Downhole imaging allows for intuitive visualization of the distribution and morphological characteristics of the perforations on the wellbore, while sonic logging can detect damage to the rock surrounding the perforations and changes in permeability.

[0036] S102, temporary blocking and steering technology Temporary plugging and diversion technology involves injecting temporary plugging agents into the well during the fracturing process to temporarily plug the existing cracks, forcing the subsequently injected high-pressure fluid to find new weak points, thereby forming new cracks, and ultimately forming multiple groups of tree-like branching crack clusters in the horizontal well section.

[0037] like Figure 4 As shown, the specific steps include: S1021, injection of fracturing fluid Specifically, high-pressure fracturing fluid is injected into the well. Under the action of pressure, the fracturing fluid enters the rock from the perforation position and gradually forms initial cracks.

[0038] S1022, inject temporary plugging agent Specifically, when a group of cracks expands to a certain extent, a temporary plugging agent is injected into the well; the temporary plugging agent can enter the formed cracks, block the crack channels, and increase the flow resistance within the cracks.

[0039] S1023, repeated injection Specifically, through repeated injection of temporary plugging agents and fracturing fluids, multiple groups of tree-branching fracture clusters are gradually formed in the horizontal well section, constructing a complex fracture network.

[0040] Temporary plugging agents, typically biodegradable granules or gels, can penetrate existing fractures, blocking their passageways and increasing flow resistance. This forces subsequent injections of high-pressure fracturing fluid to seek out new weak spots, leading to the formation of new fractures elsewhere. Repeated injections of temporary plugging agents and fracturing fluid gradually form multiple tree-like fracture clusters within the horizontal well section, creating a complex fracture network.

[0041] It is particularly important to note that during the entire process of constructing the fracture network, the expansion and morphology of the fractures need to be precisely controlled. By monitoring parameters such as pressure and flow during the fracturing process, combined with geological models and numerical simulation technology, parameters such as the injection rate of the fracturing fluid, pressure, and injection volume of the temporary plugging agent can be adjusted in real time. For example, when it is found that the fractures in a certain direction are expanding too quickly, the injection volume of the temporary plugging agent in the fractures in that direction can be increased to guide the fracturing fluid to expand in other directions; when a more complex fracture morphology needs to be formed, the injection rate of the fracturing fluid can be appropriately reduced to allow the fractures more time to extend in different directions. In addition, according to the mechanical properties of the rock and the distribution of ground stress, the perforation orientation and fracturing sequence are optimized to ensure that the final fracture network can meet the needs of geothermal development.

[0042] The fracture propagation radius of a single cluster is an important parameter for measuring the scale of a fracture network. In this application, the fracture propagation radius of a single cluster is 30-100 meters. Determining this parameter requires comprehensive consideration of multiple factors, including the mechanical properties of the rock (such as compressive strength and elastic modulus), the magnitude and direction of in-situ stress, the properties of the fracturing fluid (such as viscosity and flow rate), and the duration of the fracturing operation. Generally speaking, the weaker the rock, the lower the in-situ stress, and the better the fracturing fluid performance, the larger the fracture propagation radius. In actual engineering, field tests and numerical simulations are needed to study and optimize the fracture propagation radius under different conditions to ensure that fractures can expand within a reasonable range and form a fracture network of sufficient size, while also avoiding resource waste and construction risks caused by excessive fracture propagation.

[0043] Secondly, fracture density refers to the number of fractures per unit length of a well section. This application increases fracture density by 3-5 times. A higher fracture density can significantly increase the contact area between the rock and the heat exchange medium, improving heat exchange efficiency. Fracture density is controlled primarily by adjusting the spacing between segmented perforations and the number of temporary plugging and diversions. The smaller the segmented perforation spacing, the more initial fractures are formed within the same well section, which is conducive to increasing fracture density. The greater the number of temporary plugging and diversions, the more branch fractures can be formed, further increasing fracture density.

[0044] Finally, the distribution and morphology of fracture clusters have a significant impact on the overall performance of geothermal wells. Ideally, fracture clusters should evenly cover horizontal well sections, avoiding localized overcrowding or sparse fractures. Fracture clusters should exhibit a tree-like branching structure to maximize the surface area and connectivity of the fractures. During the design process, parameters such as the starting position, branching angle, and extension direction of the fracture clusters need to be determined based on geological conditions and geothermal extraction requirements. In areas with high rock permeability, the number of fracture clusters can be appropriately reduced, while the size of individual fracture clusters can be increased. In areas with low rock permeability, the number of fracture clusters should be increased to improve heat exchange efficiency.

[0045] By implementing this technology at multiple geothermal well sites, a complex fracture network was successfully constructed. Microseismic monitoring, downhole imaging, and other techniques were used to monitor and evaluate the morphology and distribution of the fracture network in real time. The results showed that the resulting fracture network was consistent with design expectations, with both the single-cluster fracture extension radius and fracture density meeting design targets.

[0046] In terms of heat exchange effectiveness, a comparison of geothermal well operating data before and after implementation revealed that the construction of the fracture network increased the effective heat exchange area to over 10 times that of a traditional smooth wellbore, boosted the heat extraction rate per well by 40%-70%, and increased tailwater temperature by 15-25°C, significantly improving geothermal extraction efficiency. Furthermore, the fracture network delays thermal breakthrough, significantly extending the economic recovery cycle of geothermal wells, validating the effectiveness and practicality of this fracture network construction technology in geothermal development.

[0047] With this technology, the radius of a single fracture cluster can reach 30-100 meters, increasing fracture density by 3-5 times compared to traditional methods. This high-density fracture network significantly increases the contact area between the rock and the heat transfer medium, laying a solid foundation for efficient heat transfer.

[0048] S2. Optimization of heat exchange medium: Water is injected into the production well as the main medium, forming turbulent flow through the fracture network to achieve full surface contact heat exchange with the rock mass; This application uses water as the primary heat exchange medium injected into the production well. Water has advantages such as good thermal conductivity, wide availability, and low cost, making it an ideal heat exchange medium in geothermal development.

[0049] The heat exchange principle employed is that the injected water flows through the fracture network created by hydraulic fracturing. Due to the complex structure of the fracture network, the water forms a turbulent flow. This turbulent flow allows the water to achieve full surface contact with the rock mass for heat exchange, significantly improving heat exchange efficiency compared to laminar flow, allowing the water to more fully absorb heat from the rock mass.

[0050] S3. Heat exchange control: Regulate flow resistance by designing the fracture opening and inclination, thereby extending the retention time of the medium in the high-temperature rock formation; By precisely designing the fracture aperture to between 0.5 and 5 mm and the inclination angle to between 15 and 45 degrees from the vertical, effective control of flow resistance is achieved. A smaller fracture aperture increases resistance to fluid flow, while a properly designed inclination angle can guide the fluid's flow path within the rock formation.

[0051] This design can extend the retention time of the medium in the high-temperature rock formation by 50%-200% compared to conventional wells. This longer retention time means the heat exchange medium has more time to exchange heat with the rock mass, thereby improving heat extraction efficiency.

[0052] This application was implemented in a granite thermal reservoir: a U-shaped well pair was drilled to a depth of 800 meters, and six fracture stages were performed in the 600-meter horizontal section, creating a network structure with a total fracture area exceeding 20,000 square meters. The measured heat exchange power reached 8MW, a 3.2-fold increase compared to an unfractured well of the same specification.

[0053] Reservoir fracturing technology has matured in the field of oil and gas extraction. It uses hydraulic fracturing to create a fracture network, enhancing the permeability of oil and gas. This application innovatively applies this technology to geothermal development. Based on similar principles of fluid flow and rock mechanics, multi-stage directional hydraulic fracturing is implemented in the horizontal heat exchange section of a U-shaped well to construct a high-density branching fracture network, forming a "capillary" heat exchange structure, thereby enhancing the heat exchange efficiency between the geothermal resource and the heat exchange medium.

[0054] Hydraulic fracturing uses high-pressure fluids to create cracks in underground rock, enhancing the flow of oil and gas. In geothermal development, high-pressure fluids (primarily water-based fracturing fluids) are similarly used to create cracks in the rock within the horizontal heat exchange section of a U-shaped well. However, unlike fracturing for oil and gas reservoirs, geothermal development focuses on creating a high-density, multi-branched fracture network to enhance heat exchange. Therefore, specialized techniques such as staged perforation and temporary plugging and diversion are required to achieve this goal.

[0055] Thereby achieving the following technical effects: 1. Exponential growth in heat exchange area By constructing a high-density fracture network, the effective heat exchange area is increased to more than 10 times that of a traditional smooth wellbore. This significantly increased heat exchange area provides more channels and contact interfaces for the transfer of heat energy, fundamentally improving the heat exchange capacity of geothermal development and creating favorable conditions for subsequent efficient heat extraction.

[0056] 2. Breakthrough in heat extraction efficiency Improved heat extraction rate: The heat extraction rate per well has increased by 40%-70%. This significant improvement allows geothermal wells to capture more heat in the same amount of time, increasing the efficiency of geothermal energy production and enhancing the economic benefits of geothermal development projects.

[0057] Tailwater temperature increase: Tailwater temperature increases by 15-25°C. Higher tailwater temperature indicates that the heat transfer medium has absorbed more heat from the rock mass, providing a higher-quality heat source for subsequent thermal energy utilization, which helps improve the energy utilization rate of the entire geothermal system.

[0058] 3. Extended system life The presence of a fracture network delays thermal breakthrough, a phenomenon in which the heat exchange medium prematurely removes heat from the rock formation as geothermal extraction progresses, resulting in insufficient heat for subsequent extraction. This technology, through rational fracture design, allows for more uniform and sustained heat extraction, thereby extending the economic life of geothermal wells and reducing the long-term costs of geothermal development projects.

[0059] 4. Cost advantage Because this technology leverages proven fracturing techniques used in oil and gas reservoir development, it eliminates the need for redeveloping complex extraction technologies, reducing R&D costs. Furthermore, compared to drilling ultra-long horizontal wells to increase heat exchange area, this technology can reduce costs by over 30%. This cost reduction makes geothermal development projects more economically viable and will help promote the large-scale development and application of geothermal energy.

[0060] Through integrated geological and engineering design, this solution transforms the secondary pore network formed by fracturing into an efficient heat exchange interface, solving the core bottleneck problem of "extracting heat without extracting water" in geothermal development and providing a revolutionary technical path for the economic development of medium and low-temperature geothermal resources.

[0061] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. An enhanced geothermal system U-well heat exchange method based on multi-stage fracturing and permeability enhancement is characterized by: The following steps are involved: S1. Fracture network construction: multiple groups of tree-like fracture clusters are formed in the horizontal well section; S2. Optimization of heat exchange medium: Water is injected into the production well as the main medium, forming turbulent flow through the fracture network to achieve full surface contact heat exchange with the rock mass; S3. Heat exchange control: Regulate flow resistance through crack opening and inclination design to extend the retention time of the medium in the high-temperature rock formation.

2. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 1 is characterized by: The step S1 includes a segmented perforation technique and a temporary plugging and diversion technique.

3. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 2 is characterized by: The segmented perforation technology specifically includes the following steps: S1011. Review existing technical information; S1012, geophysical exploration; S1013, on-site inspection; S1014, comprehensive division of sub-segments; S1015, perforation section movement and repetitive operation; S1016. Check the perforation effect.

4. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 3 is characterized by: The temporary blocking and steering technology specifically includes the following steps: S1021, injecting fracturing fluid; S1022, injecting temporary plugging agent; S1023. Repeat the injection multiple times.

5. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 1 is characterized in that: The crack opening is controlled at 0.5-5 mm.

6. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 1 is characterized by: The inclination angle is controlled to be 15°-45° with respect to the vertical direction.

7. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 1 is characterized by: The expansion radius of a single fracture cluster is 30-100 meters.

8. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 1 is characterized by: The fracture clusters evenly cover the horizontal well section and present a tree-like branching structure.

9. The enhanced geothermal system U-shaped well heat exchange method based on multi-stage fracturing and permeability enhancement according to claim 4, characterized in that: The temporary blocking agent is a degradable granular material or a gel material.

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