A biomimetic capillary network-assisted CO2 expansion geothermal development system and method

Abstract

The present application belongs to the technical field of geothermal energy development and CO2 resource utilization, and provides a geothermal development system and method of bionic capillary network cooperating with CO2 expansion work, which realizes CO2 heating-expansion-fracturing synchronization through bionic capillary network structure, and strengthens the effect of reservoir reconstruction and heat energy extraction; through well pair type circulation structure, a stable interconnected artificial fracture network is formed between two horizontal wells, cross-well flow and continuous heat extraction of CO2 in the reservoir are realized; supercritical state CO2 with high temperature and high pressure and circulating water are simultaneously transported to the ground heat exchange and power generation device after being cooperatively heat-exchanged underground, and the geothermal energy and CO2 expansion energy are combined and converted, and the generated electric energy is preferentially used to drive the operation of the CO2 compression and circulating water system, and a closed cycle mode of heat energy cascade utilization and system energy self-sustaining is constructed. The process significantly reduces the dependence of the system on external energy.

Description

Technical Field

[0001] This invention belongs to the field of geothermal energy development and CO2 resource utilization technology, and particularly relates to a geothermal development system and method that uses a biomimetic capillary network to work in conjunction with CO2 expansion. It is especially suitable for the transformation and efficient heat extraction of dry hot rock reservoirs and enhanced geothermal systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Deep geothermal resources, such as hot dry rocks, are vast and represent a highly promising clean energy source. Enhanced Geothermal Systems (EGS) are technologies that extract heat energy by artificially modifying low-permeability geothermal reservoirs and establishing fluid circulation channels.

[0004] The mainstream approach to existing EGS development treats reservoir fracturing and water injection for heat extraction as two independent and sequential steps. While theoretically feasible, this approach faces a series of technical challenges in engineering practice, including low heat exchange efficiency and insufficient energy utilization. First, large-scale hydraulic fracturing is performed to create a fracture network, a process that consumes enormous energy. Subsequently, a cryogenic working fluid (usually water) is injected to extract heat within the fractures. This approach suffers from the following drawbacks: the artificial fracture network formed by fracturing often does not match the optimal heat exchange channels required for efficient and uniform heat extraction in terms of morphology, conductivity, and spatial distribution, leading to rapid decline in heat extraction efficiency and a tendency to form "thermal short circuits" during long-term operation. Furthermore, the system's operation is highly dependent on external power grid power to drive the high-pressure injection equipment, resulting in insufficient economic efficiency. Although some studies have attempted to use supercritical CO2 (injected state) as a heat extraction working fluid, the expansion energy rapidly generated during its heating and expansion process is usually not effectively guided and utilized for active and continuous reservoir modification. Summary of the Invention

[0005] To address at least one of the technical problems existing in the background art, the first aspect of the present invention provides a geothermal development system with biomimetic capillary network coordinating CO2 expansion to perform work. It achieves synchronization of CO2 heating-expansion-fracturing through a biomimetic capillary network structure, thereby enhancing reservoir stimulation and thermal energy extraction effects. Relying on a well-to-well circulation structure and a dual-medium heat exchange system, it achieves cascade recovery of thermal energy and system energy self-sufficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A biomimetic capillary network-assisted CO2 expansion geothermal development system includes: At least two horizontal wells form a well-to-well circulation network within the target geothermal layer, with the first horizontal well serving as an injection well and the second horizontal well serving as a production well. A biomimetic capillary network structure is installed and deployed in the horizontal well sections of the injection well and the production well, respectively, to construct a three-dimensional staged heat exchange network within the wellbore. A circulating water system, connected to the biomimetic capillary network structure, is used to inject circulating water into the biomimetic capillary network structure, so that the circulating water flows in the three-dimensional graded heat exchange network and exchanges heat with the geothermal layer. The CO2 injection and circulation system is connected to the wellbore of the injection well and the production well, and is used to inject and recover CO2 into the wellbore; The biomimetic capillary network structure is configured to work synergistically with CO2 injection after the circulating water system is running and a high-temperature environment is formed inside the wellbore: the injected supercritical CO2 is heated and expanded by the high-temperature environment and circulating water inside the wellbore, and the resulting volume expansion effect and pressure fluctuation directly act on the geothermal layer to form an artificial fracture network; the expanded supercritical CO2 enters the interconnected artificial fracture network to extract heat and is then produced from the production well, and together with the high-temperature circulating water produced from the biomimetic capillary network structure, it is transported to the surface for energy utilization.

[0007] As one implementation, the biomimetic capillary network structure includes: Multiple circumferential fluid distribution main pipes are arranged in sections at preset intervals along the axis of the well shaft and form a closed loop around the inner wall of the well shaft to distribute circulating water evenly in the circumference. Multiple sets of hollow heat exchange capillaries are distributed in parallel along the wellbore axis, connected between adjacent circumferential fluid distribution main pipes, and perpendicular to the circumferential fluid distribution main pipes, forming a three-dimensional graded heat exchange network that is staggered along the axial and circumferential directions within the wellbore.

[0008] In one implementation, the biomimetic capillary network structure has a contracted state and an expanded state: before being lowered into the wellbore, the circumferential fluid distribution main pipe and the hollow heat exchange capillary are in an axial and radial contracted state; after reaching the preset well section, circulating water is injected into the pipe to make the internal pressure higher than the wellbore annular pressure, and under the action of the internal and external pressure difference, radial elastic expansion and axial reset are achieved to adhere to the well wall.

[0009] In one embodiment, the circulating water system includes a water conveying motor, an inlet pipe, an outlet pipe, and a spiral return water collection pipe; the water conveying motor is connected to one end of the inlet pipe, the other end of the inlet pipe is connected to one end of the circumferential fluid distribution main pipe, the other end of the circumferential fluid distribution main pipe is connected to one end of the spiral return water collection pipe, and the other end of the spiral return water collection pipe transmits high-temperature circulating water to the ground through the outlet pipe.

[0010] In one embodiment, the spiral return water collection pipe is arranged in a spiral shape along the axis of the wellbore.

[0011] In one embodiment, the system further includes a power transmission line and a heat exchanger. The CO2 injection and circulation system includes an electrically driven compressor, and the heat exchanger is electrically connected to the electrically driven compressor and the water supply motor via the power transmission line.

[0012] As one implementation, one end of the biomimetic capillary network structure is provided with a closed end positioning constraint cap for downhole axial positioning.

[0013] To address the aforementioned issues, a second aspect of this invention provides a geothermal development method that utilizes a biomimetic capillary network to facilitate CO2 expansion and work. This method achieves synchronized CO2 heating, expansion, and fracturing through a biomimetic capillary network structure, thereby enhancing reservoir stimulation and thermal energy extraction. Furthermore, it leverages a well-to-well circulation structure and a dual-medium heat exchange system to achieve cascaded thermal energy recovery and system energy self-sufficiency.

[0014] To achieve the above objectives, the present invention adopts the following technical solution: A geothermal development method using biomimetic capillary networks in conjunction with CO2 expansion for work includes the following steps: Step 1: Drill at least two horizontal wells within the target geothermal layer as injection and production wells, and install a biomimetic capillary network structure within the horizontal well sections; Step 2: Inject circulating water into the biomimetic capillary network structure. The circulating water exchanges heat with the geothermal layer through the capillary wall, creating a stable high-temperature heat exchange field inside the wellbore. Step 3: Inject supercritical CO2 into the wellbore. When the supercritical CO2 flows through the biomimetic capillary network structure, it undergoes heat exchange with the high-temperature environment and circulating water, causing it to expand. The resulting volume expansion effect and pressure wave action act on the geothermal layer, forming the initial artificial fracture network. Step 4: Enhance fracturing by simultaneously or alternately performing CO2 expansion work in the injection well and production well, thereby expanding and connecting the artificial fracture network around the two wells to form a connected artificial fracture network system. Step 5: Continuously inject supercritical CO2 into the injection well. After the CO2 expands in the wellbore, it flows into the artificial fracture network to extract heat and is produced from the production well. At the same time, the circulating water collected by the biomimetic capillary network structure in the two wells is transported to the surface. The high-temperature and high-pressure supercritical CO2 and circulating water are recycled back into the biomimetic capillary network structure and wellbore of the injection well after the energy is utilized on the surface, forming a closed loop.

[0015] In one implementation, in step 2, the deployment of the biomimetic capillary network structure is achieved by injecting circulating water into the circumferential fluid distribution main pipe, making the pressure inside the pipe higher than the annular pressure in the wellbore, thereby driving the circumferential fluid distribution main pipe and the hollow heat exchange capillary tube, which are in a contracted state, to undergo radial elastic deployment and axial repositioning, and attach to the well wall.

[0016] In one implementation, step 3 involves heat exchange heating of supercritical CO2, including indirect heat exchange through the wall of a hollow heat exchange capillary tube and direct contact heat exchange between CO2 and high-temperature circulating water in a spiral return water collection pipe.

[0017] The beneficial effects of this invention are: 1. This invention constructs an integrated CO2 geothermal development system that combines active expansion-induced fracturing, synergistic heat extraction, and energy self-sufficiency. It elevates the role of CO2 in geothermal systems from a traditional passive heat extraction medium to an active synergistic working medium that integrates expansion-induced fracturing, enhanced heat exchange, and energy recovery. Supercritical CO2 is rapidly heated and expands in a high specific surface area heat exchange environment constructed by a biomimetic capillary network. During this process, a volume expansion effect and pressure fluctuation are rapidly generated. Its expansion energy can directly act on the geothermal reservoir rock mass, realizing expansion-induced enhanced fracturing without additional hydraulic fracturing. It forms and expands an artificial fracture network around and between wells, thereby simultaneously completing reservoir stimulation and heat exchange channel construction.

[0018] 2. This invention constructs a three-dimensional heat exchange system using a biomimetic capillary network and a dual-medium synergy. Within this capillary network, circulating water and CO2 can be simultaneously injected into the wellbore, forming a truly dual-medium synergistic heat exchange system. On one hand, the circulating water flows along the capillary wall, continuously exchanging heat indirectly with the surrounding rock mass, providing a stable heat source for the expansion and work done by CO2 downhole. On the other hand, during the expansion and work done by the injected CO2, it directly contacts the high-temperature circulating water surrounding the capillary bundle and the return water in the spiral return pipe, exchanging energy and enhancing heating. Through the synchronous flow and mutual heat exchange of water and CO2, the downhole heat exchange process becomes more uniform, continuous, and controllable, maximizing the extraction of reservoir heat and fully utilizing the CO2 expansion energy, while ensuring the cascade recovery of heat energy and the synergistic conversion of downhole energy.

[0019] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is the overall layout of the well-to-well geothermal well network system provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the unfolded state of the biomimetic capillary network structure provided in this embodiment of the invention in a dual-well configuration; Figure 3 This is a schematic diagram of the biomimetic capillary network structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram showing a partial detail of the biomimetic capillary network structure provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the dual-medium synergistic heat exchange and CO2 expansion work enhancement fracturing process provided in the embodiments of the present invention; Figure 6 This is a schematic diagram of the simultaneous dual-well fracturing heat extraction and CO2-water closed-loop operation provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the geothermal development method using a biomimetic capillary network in conjunction with CO2 expansion to perform work, provided in an embodiment of the present invention. In the diagram, 1. Geothermal layer; 2. Mudstone strata; 3. Electrically driven compressor; 4. Power transmission line; 5. Heat exchanger; 6. Water conveying motor; 7. Outlet pipe; 8. Inlet pipe; 9. Artificial fracture network; 10. Bionic capillary network structure; 11. Supercritical CO2; 12. Fracture channel; 13. High-temperature and high-pressure supercritical CO2; 14. Hollow heat exchange capillary; 15. Circumferential fluid distribution trunk pipe; 16. Spiral return water collection pipe; 17. Closed end positioning and constraint end cap; 18. Injection well; 19. Production well. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] In this invention, terms such as "upper," "lower," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, nor should they be construed as limiting this invention.

[0026] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0027] The technical problem this invention aims to solve is to overcome the systemic deficiencies in existing technologies for geothermal development, CO2 utilization, and energy conversion in hot dry rock formations. It provides a synergistic solution integrating reservoir fracturing, enhanced heat exchange, energy recovery, and carbon sequestration, specifically addressing the following key technical pain points: 1) The problem of disconnect between reservoir fracturing and thermal energy extraction: Existing enhanced geothermal systems mostly adopt a serial mode of hydraulic fracturing first and then water injection for heat extraction. Fracturing consumes a lot of energy and is disconnected from the subsequent heat extraction process, resulting in low energy utilization efficiency. At the same time, the fracture network formed by traditional fracturing has poor matching degree with the ideal heat exchange channel, resulting in rapid decline in long-term heat extraction efficiency.

[0028] 2) Problems of low downhole heat exchange efficiency and uneven heat recovery: Existing technologies mainly rely on the flow of injected working fluid in natural or artificial fractures for heat exchange. The effective heat exchange area is limited, which easily leads to "thermal short circuits", resulting in slow and uneven heat extraction rate from the reservoir and low overall heat recovery rate.

[0029] 3) The problem of ineffective utilization of CO2 expansion work and high system energy consumption: Existing CO2 working geothermal systems mostly regard it as a simple heat extraction fluid, failing to actively control and fully utilize the huge expansion energy generated during its expansion work to continuously transform the reservoir; at the same time, the system operation relies on external electric power to drive equipment such as injection pumps, lacking an effective internal energy recovery and self-sufficiency mechanism, thus limiting its economic efficiency.

[0030] The core of this invention is to construct an integrated system that combines "biomimetic capillary network structure for synchronous heat exchange and fracturing + dual-medium synergistic heat exchange enhancement + well-to-well energy self-circulation" to simultaneously solve technical problems in existing technologies such as hydraulic fracturing-heat extraction separation, low heat exchange efficiency, and insufficient energy utilization. Ultimately, this invention aims to achieve multiple objectives, including efficient geothermal reservoir transformation, maximum thermal energy extraction, and low-carbon self-sustaining operation of the system.

[0031] Example 1 This embodiment provides a geothermal development system that utilizes a biomimetic capillary network in conjunction with CO2 expansion to perform work, including: At least two horizontal wells form a well-to-well circulation network within the target geothermal layer 1, wherein the first horizontal well serves as an injection well 18 and the second horizontal well serves as a production well 19. The biomimetic capillary network structure 10 is inserted and deployed in the horizontal well sections of the injection well 18 and the production well 19 respectively, and is used to construct a three-dimensional graded heat exchange network in the wellbore. The circulating water system is connected to the biomimetic capillary network structure 10 and is used to inject circulating water into the biomimetic capillary network structure 10, so that the circulating water flows in the three-dimensional graded heat exchange network and exchanges heat with the geothermal layer 1. The CO2 injection and circulation system is connected to the wellbore of injection well 18 and production well 19 and is used to inject and recover CO2 into the wellbore. The biomimetic capillary network structure 10 is configured to work synergistically with CO2 injection after the circulating water system is running and a high-temperature environment is formed inside the wellbore: the injected supercritical CO2 11 is heated and expanded by the high-temperature environment and circulating water inside the wellbore, and the volume expansion effect and pressure fluctuation generated by its expansion directly act on the geothermal layer 1 to form an artificial fracture network 9; after the supercritical CO2 enters the artificial fracture network and flows to extract heat, it is produced from the production well 19 and transported to the surface for energy utilization together with the high-temperature circulating water produced from the biomimetic capillary network structure 10.

[0032] This invention constructs an integrated system that combines "biomimetic capillary network structure for synchronous heat exchange and fracturing, dual-medium synergistic heat exchange enhancement, and well-to-well energy self-circulation," simultaneously addressing technical issues in existing technologies such as hydraulic fracturing-heat extraction separation, low heat exchange efficiency, and insufficient energy utilization. Ultimately, it achieves multiple objectives, including efficient geothermal layer transformation, maximized thermal energy extraction, and low-carbon self-sustaining operation of the system.

[0033] The following is combined Figures 1-5 Detailed explanation of the implementation process of this invention: Please refer to Figure 1 Select the target dry hot rock geothermal layer, and drill at least two horizontal wells in the geothermal layer 1. The first horizontal well is used as an injection well 18, and the second horizontal well is used as a production well 19. The two horizontal wells form a well-to-well circulation network in space.

[0034] It should be noted that, in other embodiments, those skilled in the art can set the number of horizontal wells according to the specific working conditions.

[0035] like Figure 2 and Figure 3 As shown, the biomimetic capillary network structure 10 includes multiple circumferential fluid distribution trunk pipes 15 and multiple sets of hollow heat exchange capillaries 14. Multiple circumferential fluid distribution main pipes 15 serve as the skeleton structure of the biomimetic capillary network structure 10. They are arranged in segments along the well shaft axis at preset intervals. Each circumferential fluid distribution main pipe 15 is arranged in a closed loop around the inner wall of the well shaft to uniformly distribute circulating water in the circumference. Before being lowered into the wellbore, the circumferential fluid distribution main pipe 15 is in a state of bidirectional contraction in both the axial and radial directions to reduce the overall outer diameter and adapt to the wellbore lowering conditions. Adjacent circumferential fluid distribution main pipes 15 are interconnected by multiple sets of hollow heat exchange capillaries 14. The multiple sets of hollow heat exchange capillaries 14 are distributed in parallel along the well shaft axis and perpendicular to the corresponding circumferential fluid distribution main pipes 15, thereby forming a three-dimensional graded heat exchange network that is staggered along the axial and circumferential directions in the well shaft. This structure simulates the hierarchical mass and heat transfer mechanism of "artery-capillary-vein" in a living organism, enabling circulating water to be evenly distributed to each level of capillary bundle through the main pipe and fully exchange heat with the high-temperature rock mass along the well shaft axis, thus forming a continuous and efficient heat transfer path. This overcomes the problems of limited heat exchange area and easy "thermal short circuit" in traditional single pipes or fractures.

[0036] Furthermore, the circumferential fluid distribution main pipe 15 and the hollow heat exchange capillary tube 14 are made of elastic material and can expand from a radially contracted state under the action of internal fluid pressure to adhere to the well wall.

[0037] Furthermore, a closed-end positioning and constraint end cap 17 is provided near the tail of the well in the biomimetic capillary network structure 10 to achieve downhole positioning and axial stability constraint, preventing the circumferential fluid distribution trunk 15 from directly hitting the tail of the well during the unfolding process of the capillary network structure.

[0038] Before being lowered into the wellbore, the hollow heat exchange capillary tube 14 is also in a state of axial and radial contraction, and it works in conjunction with the circumferential fluid distribution main tube 15 to form a compact, lowerable structure.

[0039] When the biomimetic capillary network structure 10 reaches the preset well section, circulating water is injected into the circumferential fluid distribution main pipe 15, so that the internal pressure of the main pipe and the hollow heat exchange capillary 14 connected thereto is higher than the annular pressure of the wellbore. Under the action of the internal and external pressure difference, the circumferential fluid distribution main pipe 15 and the hollow heat exchange capillary 14 undergo radial elastic expansion and return to the preset spacing state in the axial direction, thereby forming a stable three-dimensional biomimetic capillary network structure attached to the well wall in the wellbore.

[0040] Please refer to Figure 3 and Figure 4The circulating water system includes a water conveying motor 6, an inlet pipe 8, an outlet pipe 7, and a spiral return water collection pipe 16. The water conveying motor 6 is connected to one end of the inlet pipe 8, and the other end of the inlet pipe 8 is connected to one end of the circumferential fluid distribution main pipe 15. The other end of the circumferential fluid distribution main pipe 15 is connected to one end of the spiral return water collection pipe 16, and the other end of the spiral return water collection pipe 16 is connected to one end of the outlet pipe 7. The other end of the outlet pipe 7 is connected to the ground heat exchanger 5 for energy conversion. The generated electrical energy is preferentially used to drive the electric compressor 3 and the water conveying motor 6 via the transmission line 4, so as to realize the self-sustaining operation of the system.

[0041] As a further implementation, the spiral return water collection pipe 16 is arranged spirally along the axis of the wellbore, causing the circulating water to rise along the spiral path during the return flow, thereby extending the return path and improving the heat exchange and energy exchange efficiency during the return flow. At the same time, the circulating water reheats the CO2 in the middle of the wellbore during the return flow through the spiral return water collection pipe to accelerate expansion.

[0042] Through the above technical solution, the circulating water after heat exchange in each hollow heat exchange capillary tube 14 is collected step by step in the well barrel and enters the spiral return water collection pipe 16. The spiral return water collection pipe 16 is used to stably transport the high-temperature circulating water collected in the biomimetic capillary network structure 10 to the ground heat exchange and energy utilization system.

[0043] like Figure 2 As shown, the CO2 injection and circulation system includes an electrically driven compressor 3. The system also includes a power transmission line 4 and a heat exchanger 5. The heat exchanger 5 is electrically connected to the electrically driven compressor 3 and the water conveying motor 6 via the power transmission line 4. One end of the heat exchanger 5 is connected to the outlet pipe 7, and the other end is connected to the power transmission line 4 to drive the electrically driven compressor 3 and the water conveying motor 6 with the electrical energy generated by the high-temperature CO213 and circulating water through the outlet pipe 7.

[0044] By coordinating the heat exchange pathways of geothermal rock mass-circulating water and circulating water-CO2, a dual-path synergistic heat exchange mode is constructed, enabling the circulating water to heat CO2 while completing geothermal heat extraction, thus promoting the temperature rise, heat exchange, and expansion of CO2 to perform work.

[0045] The working principle of this invention is as follows: Select a target geothermal area and drill at least two horizontal wells within that area. The first horizontal well will serve as an injection well (18), and the second horizontal well will serve as a production well (19). Both horizontal wells will penetrate the overlying mudstone strata (2) and extend into the target geothermal layer (1), and will be arranged in a well-to-well configuration to form a subsequently interconnected fluid circulation channel within the geothermal layer (1). The injection well (18) and the production well (19) together constitute a well-to-well circulation network, providing the basic wellbore conditions for the cross-well flow of CO2 and circulating water and for continuous heat extraction.

[0046] After selecting the target dry hot rock geothermal layer and drilling to form injection well 18 and production well 19, biomimetic capillary network structure 10 is simultaneously installed in the preset horizontal well sections of the two horizontal wells.

[0047] Before being lowered into the wellbore, the biomimetic capillary network structure 10 in both injection well 18 and production well 19 is in a bidirectional contraction state, both axially and radially. Hollow heat exchange capillaries 14 at each stage are arranged close to their corresponding fluid distribution main pipes 15 to reduce the overall outer diameter and meet the wellbore lowering requirements. By connecting the fluid distribution main pipes 15 in each well to their corresponding inlet pipes 8, and using the main pipes as a load-bearing and guiding structure, the biomimetic capillary network structure 10 is advanced to the target well sections of the two horizontal wells.

[0048] Once the biomimetic capillary network structure 10 reaches the preset position, the water delivery motors 6 corresponding to the two wells are started respectively, injecting circulating water into the fluid distribution main pipes 15 in their respective wellbores through the water inlet pipes 8. As the internal pressure of the main pipe 15 and its connected hollow heat exchange capillary 14 gradually increases, making its internal pressure higher than the wellbore annular pressure, under the action of the internal and external pressure difference, the circumferential fluid distribution main pipe 15 and the hollow heat exchange capillary 14 simultaneously undergo radial elastic expansion and return to the preset spacing state in the axial direction, thereby forming a stable three-dimensional biomimetic capillary network structure attached to the well wall in the injection well 18 and the production well 19 respectively.

[0049] After deployment, the circulating water that has completed heat exchange in the hollow heat exchange capillary tubes 14 at each stage is collected in the wellbore and enters the spiral return water collection pipe 16 set in the middle of the corresponding wellbore, providing a stable downhole structure and heat exchange basis for subsequent dual-well synchronous heat exchange and CO2 expansion to enhance fracturing.

[0050] like Figure 5 In the horizontal well sections of injection well 18 and production well 19, biomimetic capillary network structures 10 are installed and deployed to stably attach to the corresponding well walls. Then, the water conveying motors 6 of the two wells are started to transport circulating water through their respective inlet pipes 8 to the fluid distribution main pipes 15 in the corresponding wells.

[0051] After being distributed in stages by the fluid distribution main pipe 15 in each well, the circulating water enters the multi-stage hollow heat exchange capillary tubes 14 and flows along the capillary network. It continuously exchanges heat indirectly with the surrounding high-temperature geothermal layer 1 through the capillary wall, so that a stable high-temperature heat exchange environment is formed in both wells.

[0052] Based on the synchronous and stable operation of the above-mentioned circulating water heat exchange process, the electric-driven compressors 3 corresponding to the two wells are started respectively to synchronously inject supercritical CO211 into the wellbore of injection well 18 and production well 19. When the supercritical CO211 flows through the biomimetic capillary network structure 10 in their respective wellbore, it undergoes enhanced heat exchange with the hollow heat exchange capillary tubes 14 that have been heated by the formation and the high-temperature circulating water around them. The temperature and pressure gradually increase, and rapid volume expansion occurs.

[0053] Meanwhile, in the two wells, the high-temperature circulating water after heat exchange in the hollow heat exchange capillary tubes 14 is collected into the corresponding spiral return water collection pipes 16. During the spiral ascent, it directly contacts and exchanges heat with CO2 in the well, further promoting the heating and expansion process of CO2, and enhancing its volume expansion effect and pressure fluctuation intensity.

[0054] The volume expansion effect and pressure fluctuations generated by the simultaneous expansion of CO2 in the two wells act on the geothermal layer 1 around the corresponding wells, causing the surrounding rock mass to fracture and simultaneously forming and expanding artificial fracture networks 9 around injection well 18 and production well 19.

[0055] like Figure 6 The circulating water system and CO2 injection system of the two wells are started, and the circulating water heat exchange and CO2 expansion work are carried out simultaneously to enhance the fracturing operation. Supercritical CO211 is heated by indirect heat exchange in the capillary network 10 and direct contact heat exchange in the spiral return water collection pipe 16, and expands into high-temperature and high-pressure supercritical CO213, which produces a volume expansion effect and pressure fluctuation, which acts on the geothermal layer 1, causing the fracture channel 12 to continue to expand and form a stable artificial fracture network 9 around the two wells.

[0056] High-temperature, high-pressure supercritical CO213 and high-temperature circulating water flow in a dual-medium flow within the fracture network 9 and the wellbore, further absorbing heat from the geothermal layer 1. The high-temperature, high-pressure supercritical CO213 and circulating water are transported to the surface heat exchanger 5 via the outlet pipe 7 for energy conversion. The generated electrical energy is preferentially used via the transmission line 4 to drive the electric compressor 3 and the water-carrying motor 6, achieving self-sustaining operation of the system. After energy utilization, the high-temperature, high-pressure supercritical CO213 is cooled and pressure-regulated before being reinjected into the injection well 18, achieving closed-loop CO2 recycling and partial geological sequestration. Simultaneously, the recycled water, after energy utilization, flows back to the wellbore via the inlet pipe 8 to continue participating in the downhole heat exchange cycle.

[0057] Through the above operations, injection well 18 and production well 19 remain synchronized throughout the fracturing and heat extraction process, enabling the downhole CO2 and circulating water to form a continuous and stable dual-medium flow field, thus achieving a highly integrated geothermal development model that combines reservoir stimulation, enhanced heat exchange, energy recovery, and CO2 resource sequestration.

[0058] Example 2 like Figure 7 As shown, this embodiment provides a geothermal development method using a biomimetic capillary network in conjunction with CO2 expansion to perform work, including the following steps: Step 1: Target reservoir selection and biomimetic capillary network structure deployment: Drill at least two horizontal wells as injection wells 18 and production wells 19 in the target geothermal layer 1, and deploy a biomimetic capillary network structure 10 in its horizontal well section; As a further implementation, in step 1, the biomimetic capillary network structure 10 uses the circumferential fluid distribution main pipes 15 arranged in segments along the well shaft axis as the skeleton structure. Each circumferential fluid distribution main pipe 15 is arranged sequentially along the well shaft axis at a preset interval. Each circumferential fluid distribution main pipe 15 is arranged in a closed loop around the inner wall of the well shaft to uniformly distribute the circulating water in the circumference.

[0059] Before being lowered into the wellbore, the circumferential fluid distribution main pipe 15 is in a bidirectional contraction state, both axially and radially, to reduce its overall outer diameter and adapt to the wellbore lowering conditions. Adjacent circumferential fluid distribution main pipes 15 are interconnected by multiple sets of hollow heat exchange capillaries 14. These hollow heat exchange capillaries are arranged along the wellbore axis and perpendicular to the corresponding circumferential fluid distribution main pipe 15, thereby forming a biomimetic capillary network structure that is staggered along the axial and circumferential directions within the wellbore.

[0060] The hollow heat exchange capillary tube 14 is also in an axial and radial contraction state before being lowered into the wellbore, and it works in conjunction with the circumferential fluid distribution main pipe 15 to form a compact, lowerable structure.

[0061] When the biomimetic capillary network structure 10 reaches the preset well section, circulating water is injected into the circumferential fluid distribution main pipe 15, so that the internal pressure of the main pipe and the hollow heat exchange capillary 14 connected thereto is higher than the annular pressure of the wellbore. Under the action of the internal and external pressure difference, the circumferential fluid distribution main pipe 15 and the hollow heat exchange capillary 14 undergo radial elastic expansion and return to the preset spacing state in the axial direction, thereby forming a stable three-dimensional biomimetic capillary network structure attached to the well wall in the wellbore.

[0062] After heat exchange, the circulating water in each hollow heat exchange capillary tube 14 is collected step by step in the wellbore and enters the spiral return water collection pipe 16 located in the middle of the wellbore. The spiral return water collection pipe 16 is arranged along the axis of the wellbore and is used to stably transport the high-temperature circulating water collected in the biomimetic capillary network structure 10 to the ground heat exchange and energy utilization system.

[0063] Step 2: System initialization and establishment of stable heat exchange cycle: Inject circulating water into the biomimetic capillary network structure 10. The circulating water exchanges heat with the geothermal layer 1 through the capillary wall, and a stable high-temperature heat exchange field is built in the well. As a further implementation, in step 2, after the biomimetic capillary network structure 10 has been deployed and stably attached to the wall, the surface circulating water system is activated to continuously inject circulating water into the capillary network in the two horizontal wells. The circulating water is evenly distributed to the hollow heat exchange capillaries 14 at each level through the fluid distribution main pipe 15 and flows along the capillary network. The circulating water continuously exchanges heat with the surrounding high-temperature geothermal rock mass through the walls of the hollow heat exchange capillaries 14, keeping the entire capillary network cage at a high temperature, thereby constructing a stable and continuous downhole heat exchange field within the wellbore, providing heat source conditions for the subsequent CO2 expansion and work process.

[0064] Step 3: CO2 injection and expansion work to enhance fracturing: Supercritical CO211 is injected into the wellbore. When the supercritical CO2 flows through the biomimetic capillary network structure 10, it exchanges heat with the high temperature environment and circulating water, is rapidly heated and expands. The resulting volume expansion effect and pressure wave act on the geothermal layer 1 to form the initial artificial fracture network 9. As a further implementation, in step 3, after the circulating water heat exchange process has stabilized, supercritical CO211 is continuously injected into the wellbore of both wells. When the supercritical CO211 flows through the well section equipped with the biomimetic capillary network structure 10, it undergoes sufficient heat exchange with the walls of the hollow heat exchange capillaries 14, which have already been heated by the formation. The temperature and pressure gradually increase, and volume expansion occurs. As the CO2 continues to be heated, it undergoes significant volume expansion, generating a strong volume expansion effect and pressure fluctuations. This pressure effect is effectively transmitted to the geothermal layer through the wellbore, causing the reservoir rock to fracture and forming an initial artificial fracture network around the two horizontal wells. Simultaneously, the spiral return water collection pipe 16 installed inside the wellbore collects the high-temperature circulating water flowing out of the capillary network, allowing it to directly contact and exchange heat with the CO2 inside the wellbore during its spiral ascent, further improving the heating efficiency and expansion work of the CO2.

[0065] Step 4: Fracture network expansion and inter-well connection: By simultaneously or alternately performing CO2 expansion work in injection well 18 and production well 19 to enhance fracturing, the artificial fracture network 9 around the two wells is expanded and connected to form a connected artificial fracture network system. Step 5: Dual-well coupled heat extraction and closed-loop energy circulation: Supercritical CO211 is continuously injected into injection well 18. After expanding in the wellbore, CO2 flows into the artificial fracture network 9 to extract heat and is produced from production well 19. At the same time, circulating water collected in the biomimetic capillary network structure 10 in the two wells is transported to the surface. The high-temperature and high-pressure supercritical CO213 produced (i.e., the state after the reservoir absorbs heat) and circulating water are re-injected into the biomimetic capillary network structure 10 and wellbore of injection well 18 after surface energy utilization, forming a closed loop.

[0066] As a further implementation method, in step 5, after the artificial fracture network formed by the two horizontal wells is stably connected, the system enters the dual-well collaborative heat extraction operation stage. Supercritical CO211 is continuously injected into the injection well. Under the indirect heat exchange effect of the biomimetic capillary network and the direct contact heat exchange effect of the spiral return water pipeline, the supercritical CO211 fully expands and performs work, then enters the connected artificial fracture network, flows in the fractures and absorbs heat from the geothermal layer, ultimately being produced from production well 19. Simultaneously, the circulating water collected by the spiral return water pipelines in the two horizontal wells is transported to the surface, heated by the heat extraction device, and then reinjected into the capillary network, forming a stable circulating water heat exchange loop. The high-temperature, high-pressure supercritical CO2 produced from the production well is transported to the surface power generation device for energy conversion. The generated electricity is preferentially used to drive the CO2 compression equipment, circulating water pump, and control system, achieving system energy self-sufficiency. After energy utilization, the CO2 is cooled and pressure regulated before being reinjected into the injection well, achieving closed-loop CO2 recycling.

[0067] Through the above operations, injection well 18 and production well 19 remain synchronized throughout the fracturing and heat extraction process, enabling downhole CO2 and circulating water to form a continuous and stable dual-medium flow field, thus achieving a highly integrated geothermal development model that combines reservoir stimulation, enhanced heat exchange, and energy recovery.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A geothermal development system using a biomimetic capillary network in conjunction with CO2 expansion for work generation, characterized in that: include: At least two horizontal wells form a well-to-well circulation network within the target geothermal layer (1), wherein the first horizontal well is used as an injection well (18) and the second horizontal well is used as a production well (19). A biomimetic capillary network structure (10) is installed and deployed in the horizontal well sections of the injection well (18) and the production well (19) respectively, for constructing a three-dimensional graded heat exchange network in the wellbore; The circulating water system is connected to the biomimetic capillary network structure (10) and is used to inject circulating water into the biomimetic capillary network structure (10) so that the circulating water flows in the three-dimensional graded heat exchange network and exchanges heat with the geothermal layer (1). The CO2 injection and circulation system is connected to the wellbore of the injection well (18) and the production well (19) and is used to inject and recover CO2 into the wellbore; The biomimetic capillary network structure (10) is configured to work synergistically with CO2 injection after the circulating water system is running and a high-temperature environment is formed in the wellbore: the injected supercritical CO2 (11) is heated and expanded by the high-temperature environment and circulating water in the wellbore, and the resulting volume expansion effect and pressure fluctuation directly act on the geothermal layer (1) to form an artificial fracture network (9); the expanded supercritical CO2 (11) enters the connected artificial fracture network (9) to flow and extract heat, and is produced from the production well (19), and is transported to the ground for energy utilization together with the high-temperature circulating water produced from the biomimetic capillary network structure (10); The biomimetic capillary network structure (10) includes: Multiple circumferential fluid distribution main pipes (15) are arranged in sections at preset intervals along the axis of the well shaft and form a closed ring around the inner wall of the well shaft for uniform circumferential distribution of circulating water. Multiple sets of hollow heat exchange capillaries (14) are distributed in parallel along the well shaft axis, connected between adjacent circumferential fluid distribution main pipes (15), and perpendicular to the circumferential fluid distribution main pipes (15), forming a three-dimensional graded heat exchange network that is staggered along the axial and circumferential directions in the well shaft. The biomimetic capillary network structure (10) has a contracted state and an expanded state: before being lowered into the wellbore, the circumferential fluid distribution main pipe (15) and the hollow heat exchange capillary (14) are in an axial and radial contracted state; after reaching the preset well section, the internal pressure is made higher than the wellbore annular pressure by injecting circulating water into the pipe, and under the action of the internal and external pressure difference, radial elastic expansion and axial reset are achieved so as to adhere to the well wall; The circulating water system includes a water conveying motor (6), an inlet pipe (8), an outlet pipe (7), and a spiral return water collection pipe (16). The water conveying motor (6) is connected to one end of the inlet pipe (8), and the other end of the inlet pipe (8) is connected to one end of the circumferential fluid distribution main pipe (15). The other end of the circumferential fluid distribution main pipe (15) is connected to one end of the spiral return water collection pipe (16). The other end of the spiral return water collection pipe (16) transmits high-temperature circulating water to the ground through the outlet pipe (7).

2. The geothermal development system with biomimetic capillary network synergistic CO2 expansion for work as described in claim 1, characterized in that, The spiral return water collection pipe (16) is arranged in a spiral shape along the axis of the well.

3. The geothermal development system with biomimetic capillary network and CO2 expansion for work as described in claim 1, characterized in that, The system also includes a power transmission line (4) and a heat exchanger (5). The CO2 injection and circulation system includes an electrically driven compressor (3). The heat exchanger (5) is electrically connected to the electrically driven compressor (3) and the water supply motor (6) via the power transmission line (4).

4. The geothermal development system with biomimetic capillary network and CO2 expansion for work as described in claim 1, characterized in that, One end of the biomimetic capillary network structure (10) is provided with a closed end positioning constraint cap (17) for downhole axial positioning.

5. A geothermal development method based on a biomimetic capillary network synergistically utilizing CO2 expansion for work, as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Drill at least two horizontal wells in the target geothermal layer (1) as injection wells (18) and production wells (19), and install a biomimetic capillary network structure (10) in its horizontal well section. Step 2: Inject circulating water into the biomimetic capillary network structure (10). The circulating water exchanges heat with the geothermal layer (1) through the capillary wall, and a stable high-temperature heat exchange field is built in the well. Step 3: Inject supercritical CO2 into the wellbore (11). When the supercritical CO2 flows through the biomimetic capillary network structure (10), it undergoes heat exchange with the high-temperature environment and circulating water, resulting in expansion. The volume expansion effect and pressure wave generated act on the geothermal layer (1) to form an initial artificial fracture network (9). Step 4: By simultaneously or alternately performing CO2 expansion work in the injection well (18) and production well (19) to enhance fracturing, the artificial fracture network (9) around the two wells is expanded and connected to form a connected artificial fracture network system. Step 5: Continuously inject supercritical CO2 (11) into the injection well (18). After the CO2 expands and does work in the wellbore, it enters the artificial fracture network (9) to flow and take heat, and is produced from the production well (19). At the same time, the circulating water collected by the biomimetic capillary network structure (10) in the two wells is transported to the surface. The high temperature and high pressure supercritical CO2 (13) produced and the circulating water are re-injected into the biomimetic capillary network structure (10) and wellbore of the injection well (18) after the surface energy is utilized, forming a closed loop. In step 2, the biomimetic capillary network structure (10) is deployed by injecting circulating water into the circumferential fluid distribution main pipe (15) to make the pressure inside the pipe higher than the wellbore annular pressure, thereby driving the circumferential fluid distribution main pipe (15) and the hollow heat exchange capillary (14) in a contracted state to undergo radial elastic deployment and axial repositioning, and attach to the well wall.

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