Composite pipe for geothermal wellbore, wellbore structure and using method

Abstract

The invention relates to the technical field of energy, in particular to a composite pipe for a geothermal wellbore, a wellbore structure and a using method.The composite pipe comprises a pipe body, the pipe body comprises an upper heat insulation section and a lower heat insulation section, an annular cavity is formed in the lower heat insulation section in the axial direction, and the annular cavity is used for heat insulation; the upper heat insulation section comprises a heat-resistant plastic pipe layer, a heat insulation aerogel pipe layer and a rigid pipe layer which are sequentially and coaxially arranged from inside to outside. The pipe body is arranged to be of the structural design of the upper heat insulation section and the lower heat insulation section, compared with a traditional vacuum heat insulation pipe design, the upper heat insulation section adopts the low-cost composite pipe structural design, it is guaranteed that high-temperature fluid can be conveyed to the ground under small heat loss on the basis that the structural strength requirement is met, and the heat insulation effect is improved. The requirements for low heat loss and low cost input of the coaxial sleeve type heat exchange system are met, the energy-saving effect is improved, and key support is provided for efficient landing of the middle-deep layer geothermal heat'heat extraction without water 'technology.

Description

Technical Field

[0001] This invention relates to the field of energy technology, and in particular to a composite pipe for geothermal wells, well structure, and method of use. Background Technology

[0002] Medium-deep geothermal energy typically refers to geothermal resources buried at depths of 200 to 3000 meters. Its heat primarily originates from the decay of radioactive elements within the Earth, making it a highly promising clean and renewable energy source. Currently, it is being utilized on a large scale in various fields such as heating and power generation. Compared to shallow geothermal energy, it has larger reserves and a higher exploitable energy density per unit area; compared to deep geothermal energy above 3000 meters, its extraction is less difficult and less costly, making it more economical.

[0003] Existing medium-deep geothermal devices can be divided into two main technical routes based on the "heat extraction method": "heat extraction and water extraction" and "heat extraction without water extraction". The coaxial sleeve heat exchange system belongs to the "heat extraction without water extraction" technical route. Its core structure is to install coaxial double-layer pipes in the well to form an annulus and a central channel. Through the cooperation of the annulus and the central channel, the extraction of medium-deep geothermal energy can be achieved.

[0004] In the process of realizing this invention, the applicant discovered that for coaxial sleeve heat exchange systems, it is difficult to balance low heat loss and low cost due to the limitations of the pipe structure. Summary of the Invention

[0005] The purpose of this application is to provide a composite pipe, well structure, and usage method for geothermal wells, thereby solving the aforementioned technical problems existing in the prior art.

[0006] This application is implemented as follows: In a first aspect, this application provides a composite pipe for geothermal wells, comprising a pipe body, the pipe body comprising an upper insulation section and a lower insulation section, the lower insulation section having an annular chamber along the axial direction for heat insulation, and the upper insulation section comprising a heat-resistant plastic pipe layer, a heat-insulating aerogel pipe layer and a rigid pipe layer arranged coaxially from the inside to the outside.

[0007] Furthermore, the upper insulation section is used to correspond to the temperature range below 95°C in the wellbore.

[0008] Furthermore, the lower insulation section is designed to correspond to at least the temperature range of 95°C or above in the wellbore.

[0009] Furthermore, the lower insulation section includes a redundant area located near the upper insulation section, and the side of the redundant area away from the upper insulation section is used to correspond to the 95°C isotherm of the wellbore.

[0010] Furthermore, the annular chamber is a vacuum chamber; Alternatively, the annular cavity may be filled with heat-insulating material.

[0011] Furthermore, the heat-resistant plastic tube layer is at least one of polybutene, heat-resistant polyethylene type II, cross-linked polyethylene, polyvinylidene fluoride, polyether ether ketone, and glass fiber reinforced PP; And / or, the thermal insulation aerogel tube layer is at least one of nano-silica aerogel, carbon aerogel, alumina aerogel, and nanoporous thermal insulation board; And / or, the rigid tubular layer is made of stainless steel, nickel-based corrosion-resistant alloy, or titanium alloy.

[0012] Furthermore, the composite pipe also includes a transition section, and the upper insulation section is connected to the lower insulation section through the transition section.

[0013] Secondly, this application provides a wellbore structure, including a wellbore casing and the aforementioned composite pipe, wherein the composite pipe is coaxially disposed inside the wellbore casing, the inner channel of the composite pipe is configured as a hot fluid return channel, the gap between the composite pipe and the wellbore casing is configured as a cold fluid injection channel, and the bottom of the hot fluid return channel and the bottom of the cold fluid injection channel are connected.

[0014] Furthermore, a sealing head is detachably provided at the bottom of the lower insulation section.

[0015] Thirdly, this application provides a method of using the well casing structure as described above, including the following steps: introducing cold fluid into the bottom of the well casing through a cold fluid injection channel, and simultaneously introducing hot fluid from the bottom of the well casing into a heat exchanger through a hot fluid return channel.

[0016] The technical solution provided in this application can achieve the following beneficial effects: This application adopts a structural design with an upper insulation section and a lower insulation section for the pipe body. Compared with the traditional vacuum insulation pipe design, the upper insulation section adopts a low-cost composite pipe structure design. While meeting the structural strength requirements, it also ensures that the high-temperature fluid can be transported to the ground with minimal heat loss. This achieves both the low heat loss and low cost requirements of the coaxial sleeve heat exchange system, improves energy-saving performance, and provides key support for the efficient implementation of the "heat extraction without water extraction" technology for medium-deep geothermal energy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1This is a structural schematic diagram of the wellbore structure of this application; Figure 2 This is a cross-sectional schematic diagram of the geothermal wellbore of this application; Figure 3 This is a schematic diagram of the composite pipe structure of this application; Figure 4 This is a schematic diagram of the structure of the insulation section in this application; Figure 5 This is a schematic diagram of the working state of the geothermal wellbore in this application.

[0019] In the picture: 10. Pipe body; 20. Well casing; 30. Heat exchanger; 40. Cold fluid injection channel; 50. Hot fluid return channel; 100. Upper insulation section; 110. Heat-resistant plastic pipe layer; 120. Thermal insulation aerogel pipe layer; 130. Rigid pipe layer; 200. Lower insulation section; 201. Redundancy zone; 210. Annular chamber; 220. Upper outer pipe; 230. Lower outer pipe; 240. Upper inner pipe; 250. Lower inner pipe; 260. End cap; 300. Transition sub; 400. Protective pipe layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0022] In existing coaxial tube heat exchange systems, the core structure includes a double-layered coaxial pipe system installed inside the well, forming an annular channel and a central channel. During operation, a cryogenic fluid is injected through the annular channel. After heat exchange with the well wall, the cryogenic fluid heats up to become a high-temperature fluid. The high-temperature fluid returns to the surface heat exchanger through the central channel, where it releases heat and becomes cryogenic again, before being recirculated back into the annular channel. For the pipes installed inside the well, metal tubes or vacuum-insulated tubes are generally used due to mechanical strength requirements. However, single metal tubes have poor insulation and high heat loss. While vacuum-insulated tubes can effectively insulate and reduce heat loss, their manufacturing cost is high. This leads to a situation where existing coaxial tube heat exchange systems struggle to balance low heat loss with low-cost investment.

[0023] To address this, a composite pipe, well structure, and usage method for geothermal wells are provided. A double-layer metal pipe structure is used for insulation in the high-temperature section at the bottom of the well to prevent seal failure at high temperatures. A composite pipe consisting of steel, aerogel coating, and plastic material is used for insulation in the lower-temperature section at the top of the well. The steel provides mechanical strength and protection, the aerogel coating provides efficient insulation, and the high-temperature resistant plastic material ensures the stability of medium transport. This effectively overcomes traditional technical bottlenecks, significantly reduces well heat loss and cost, and improves energy efficiency. It provides crucial support for the efficient implementation of "heat extraction without water extraction" technology in medium-deep geothermal systems, as detailed in the following embodiments.

[0024] Example 1 This embodiment provides a composite pipe for geothermal well casings, such as... Figures 1-4 As shown, the device includes a tube body 10, which includes an upper insulation section 100 and a lower insulation section 200. The lower insulation section 200 has an annular chamber 210 arranged along the axial direction. The annular chamber 210 is used for heat insulation. The upper insulation section 100 includes a heat-resistant plastic tube layer 110, a heat-insulating aerogel tube layer 120, and a rigid tube layer 130 arranged coaxially from the inside to the outside. Based on the above structural design, the lower part of the geothermal well is located in a high-temperature section with high pressure. A lower insulation section 200, employing a double-layer metal tubing structure, provides strength support, allowing the low-temperature fluid passing through the annular channel to exchange heat with the well wall and rise to become a high-temperature fluid. This fluid then enters the composite pipe from the bottom of the geothermal well. At this point, the annular chamber 210 in the lower insulation section 200 insulates the rising high-temperature fluid within the pipe. The upper part of the geothermal well is located in a low-temperature section. The corresponding upper insulation section 100 uses a composite pipe composed of steel, aerogel coating, and plastic material for insulation. The heat-resistant plastic pipe layer 110 directly contacts the hot fluid, utilizing its high-temperature resistance to ensure the stability of the medium transport and prevent damage to the pipeline from high temperatures. Insulation gas... The gel tube layer 120 achieves high-efficiency thermal insulation with its nanoscale porous structure, significantly reducing heat conduction efficiency and minimizing heat loss to the external environment. The rigid tube layer 130 uses high-strength metal materials to provide the necessary mechanical support and resistance to external pressure for the entire composite tube, ensuring structural stability under complex well conditions. Compared to traditional vacuum insulation tube designs, the upper insulation section 100 adopts a low-cost composite tube structure design, which, while meeting structural strength requirements, ensures that high-temperature fluids can be transported to the surface with minimal heat loss. This achieves a balance between low heat loss and low-cost investment requirements for coaxial sleeve heat exchange systems, improving energy efficiency and providing key support for the efficient implementation of "heat extraction without water extraction" technology in medium-deep geothermal energy.

[0025] In some embodiments, to ensure the stability and safety of the device operating within a geothermal well, the upper insulation section 100 can be configured to correspond to the temperature range below 95°C of the well. Due to the material of the upper insulation section 100, and to prevent damage to its structure from high temperatures in the formation, a corresponding temperature line is defined for its installation. The upper insulation section 100 is used in lower temperature regions for adaptation. Through the synergistic effect of the heat-resistant plastic pipe layer 110, the heat-insulating aerogel pipe layer 120, and the rigid pipe layer 130, excellent thermal insulation performance and mechanical strength are maintained at the design temperature, effectively preventing heat loss and pipe deformation, and ensuring the temperature stability of the hot fluid and the structural integrity of the pipeline during transportation. Correspondingly, in this embodiment, the heat-resistant plastic pipe layer 110 preferably uses heat-resistant polyethylene type II (PE-RT II, ​​a material copolymerized from high-density polyethylene and hexene or butene, with a continuous operating temperature up to 95°C and a short-term temperature resistance of 110°C to 120°C, possessing good chemical corrosion resistance and anti-aging properties, and adaptable to the environmental requirements of the wellhead to 95°C temperature range). The heat-insulating aerogel pipe layer 120 uses nano-silica aerogel, and the rigid pipe layer uses 316L stainless steel. With the aerogel coating as the core insulation layer, taking advantage of its ultra-low thermal conductivity (≤0.018W / (m·K)), combined with the protection of the inner heat-resistant plastic pipe layer 110 and the structural support of the outer stainless steel rigid pipe layer 130, the upper insulation section 100 is adapted to the temperature range below 95°C of the wellbore.

[0026] In some embodiments, the thickness of the thermal insulation aerogel tube layer 120 can be set to 3-5 mm to avoid increasing costs due to excessive thickness of the thermal insulation tube layer 120, and to prevent the thermal insulation effect from falling short of expectations when the thermal insulation tube layer 120 is too thin. The thickness of the heat-resistant plastic tube layer 110 can be 5-8 mm, and the thickness of the rigid tube layer 130 can be 5-8 mm to ensure structural strength while controlling costs and avoiding excessive increase in the outer diameter of the tube.

[0027] Specifically, the lower insulation section 200 can be set to correspond to at least the temperature range of 95°C or above in the wellbore. Specifically, the lower insulation section 200 can be made of 316L stainless steel and is installed at the bottom of the geothermal wellbore with stable mechanical support and thermal insulation performance, so that the lower insulation section 200 can work stably in high temperature and high pressure environment.

[0028] In some embodiments, to enhance the thermal insulation performance of the annular chamber 210 on the lower insulation section 200, the annular chamber 210 can be set to a vacuum state, or thermal insulation material can be filled in the annular chamber 210. This effectively insulates and preserves the high-temperature fluid rising from the bottom within the lower insulation section 200, reducing heat loss during the ascent and improving energy efficiency. In this embodiment, it is preferable to set the annular chamber 210 to a vacuum state. Specifically, the annular chamber 210 can be connected to a vacuum pump via a pipe, and the vacuum pump can then evacuate the annular chamber 210.

[0029] In some embodiments, to avoid insulation failure at temperature boundaries, the lower insulation section 200 may include a redundant region 201 located near the upper insulation section 100. The side of the redundant region 201 furthest from the upper insulation section 100 corresponds to the 95°C isotherm of the wellbore. This design ensures the composite pipe maintains a safe distance from the 95°C isotherm, allowing it to effectively cope with temperature changes in the geothermal wellbore. This ensures the lower insulation section 200 covers the entire high-temperature reservoir region above 95°C, preventing structural failure of the composite pipe due to high temperatures and guaranteeing the stability of the insulation effect at temperature boundaries. Preferably, the axial length of the redundant region 201 is 50m.

[0030] In some embodiments, the heat-resistant plastic tube layer 110 may be made of at least one of polybutene, heat-resistant polyethylene type II, cross-linked polyethylene, polyvinylidene fluoride, polyether ether ketone, and glass fiber reinforced PP. These materials have excellent high-temperature resistance and chemical stability, enabling them to operate stably for a long time in high-temperature environments and ensuring the safe transport of hot fluids. The heat-insulating aerogel tube layer 120 may be made of at least one of nano-silica aerogel, carbon aerogel, alumina aerogel, and nanoporous heat insulation board. These aerogel materials have extremely low thermal conductivity, effectively preventing heat transfer and improving heat insulation efficiency. The rigid tube layer 130 may be made of stainless steel, nickel-based corrosion-resistant alloy, or titanium alloy. These metal materials have high strength and corrosion resistance, providing reliable mechanical support and protection for the composite tube and ensuring that the composite tube is not damaged in complex wellbore environments. Different materials can be selected for the heat-resistant plastic tube layer 110, the heat-insulating aerogel tube layer 120, and the rigid tube layer 130. The 95℃ isotherm can also be adjusted accordingly to ensure that the upper insulation section 100 can balance structural safety and thermal insulation. Furthermore, the isotherm corresponding to the upper insulation section 100 can be selected and adjusted as needed, taking into account the corrosion resistance of the material.

[0031] In some embodiments, the lower insulation section 200 may be configured to include an upper inner tube 240, a lower inner tube 250, an upper outer tube 220, and a lower outer tube 230. The lower inner tube 250 is disposed inside the lower outer tube 230. The bottom outer peripheral wall of the lower inner tube 250 is expanded to the inner peripheral wall of the lower outer tube 230. The top of the lower inner tube 250 is provided with a first groove. The bottom of the upper inner tube 240 is provided with a first protrusion that matches the first groove. The upper inner tube 240 is disposed inside the upper outer tube 220. The top of the upper outer tube 220 is sealed to the outer peripheral wall of the upper inner tube 240. The bottom of the upper outer tube 220 is provided with a second protrusion. The top of the lower outer tube 230 is provided with a second groove that matches the second protrusion. A portion of the outer peripheral wall of the upper inner tube 240, a portion of the inner peripheral wall of the upper outer tube 220, and a portion of the inner peripheral wall of the lower outer tube 230 cooperate to form an annular chamber 210. Preferably, the first groove is an annular groove located on the inner wall of the lower inner tube 250 port, and the second groove is an annular groove located on the inner wall of the lower outer tube 230 port. A sealing head 260 is provided at the bottom opening of the lower outer tube 230. Preferably, the sealing head 260 and the bottom opening of the lower outer tube 230 are expanded together. The sealing head 260 abuts against the lower inner tube 250. By adjusting the axial position of the upper inner tube 240 downwards, axial pressure is applied to the lower inner tube 250, changing the degree of expansion between the lower inner tube 250 and the lower outer tube 230. When the lower inner tube 250 and the lower outer tube 230 are fully expanded, the lower inner tube 250 pushes the sealing head 260 out of the lower outer tube 230, thus connecting the bottom of the hot fluid return channel 50 and the bottom of the cold fluid injection channel 40.

[0032] In some embodiments, to achieve a stable connection between the upper insulation section 100 and the lower insulation section 200, the composite pipe may further include a transition section 300, through which the upper insulation section 100 and the lower insulation section 200 are connected. Specifically, the top of the upper inner tube 240 protrudes from the upper outer tube 220, and the internal thread at the bottom of the transition section 300 engages with the external thread at the top of the upper inner tube 240 to achieve a threaded connection. The rigid tube layer 130 at the bottom of the upper insulation section 100 protrudes from the heat-resistant plastic tube layer 110 and the heat-insulating aerogel tube layer 120, and the internal thread at the bottom of the protruding rigid tube layer 130 engages with the external thread at the top of the transition section 300 to achieve a threaded connection, thus achieving a stable and safe connection between the upper insulation section 100 and the lower insulation section 200. Preferably, the transition section 300 is covered with a protective tube layer 400, which covers the connection area between the upper insulation section 100 and the transition section 300, as well as the connection area between the lower insulation section 200 and the transition section 300. The protective tube layer 400 forms an external mechanical constraint at the connection between the upper insulation section 100 and the lower insulation section 200, isolating the formation medium from corrosion and compensating for the stiffness of the connection.

[0033] Example 2 This embodiment provides a wellbore structure, including a wellbore casing 20 and a composite pipe as described in the above embodiment. The composite pipe is coaxially disposed inside the wellbore casing 20. The inner channel of the composite pipe is configured as a hot fluid return channel 50, and the gap between the composite pipe and the wellbore casing 20 is configured as a cold fluid injection channel 40. The bottom of the hot fluid return channel 50 and the bottom of the cold fluid injection channel 40 are connected. This structural design allows the cold fluid and hot fluid to form an effective circulation within the wellbore. Cold fluid is introduced into the bottom of the wellbore casing 20 through the cold fluid injection channel 40. After exchanging heat with the well wall, the cold fluid heats up to form a high-temperature fluid. The high-temperature fluid returns to the surface through the hot fluid return channel 50 and flows to the heat exchanger 30, realizing the extraction and utilization of heat.

[0034] In some embodiments, when the composite pipe is installed into the geothermal well, in order to prevent downhole liquid in the geothermal well from entering the composite pipe, a plug head 260 can be detachably installed at the bottom of the lower insulation section 200. When the composite pipe is installed in place, the plug head 260 can be removed to allow the bottom of the hot fluid return channel 50 and the cold fluid injection channel 40 to be connected, and the geothermal mining operation can be started.

[0035] Example 3 This embodiment provides a method for using the wellbore structure as described in the above embodiments, such as... Figure 1 and Figure 5 As shown, the procedure includes the following steps: cold fluid is introduced into the bottom of the well casing 20 through the cold fluid injection channel 40, and at the same time, hot fluid at the bottom of the well casing 20 is introduced into the heat exchanger 30 through the hot fluid return channel 50.

[0036] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0037] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite pipe for geothermal well casings, characterized in that, The device includes a tube body, which includes an upper insulation section and a lower insulation section. The lower insulation section has an annular chamber along the axial direction for heat insulation. The upper insulation section includes a heat-resistant plastic tube layer, a heat-insulating aerogel tube layer, and a rigid tube layer arranged coaxially from the inside to the outside.

2. A composite pipe for geothermal wells according to claim 1, characterized in that, The upper insulation section is used to correspond to the temperature range below 95°C in the wellbore.

3. A composite pipe for geothermal wells according to claim 1, characterized in that, The lower insulation section is designed to correspond to at least the temperature range of 95°C or above in the wellbore.

4. A composite pipe for geothermal wells according to claim 3, characterized in that, The lower insulation section includes a redundant area located near the upper insulation section, and the side of the redundant area away from the upper insulation section is used to correspond to the 95°C isotherm of the wellbore.

5. A composite pipe for geothermal wells according to any one of claims 1 to 4, characterized in that, The annular chamber is a vacuum chamber; Alternatively, the annular cavity may be filled with heat-insulating material.

6. A composite pipe for geothermal wells according to any one of claims 1 to 4, characterized in that, The heat-resistant plastic tube layer is at least one of polybutene, heat-resistant polyethylene type II, cross-linked polyethylene, polyvinylidene fluoride, polyether ether ketone, and glass fiber reinforced PP; And / or, the thermal insulation aerogel tube layer is at least one of nano-silica aerogel, carbon aerogel, alumina aerogel, and nanoporous thermal insulation board; And / or, the rigid tubular layer is made of stainless steel, nickel-based corrosion-resistant alloy, or titanium alloy.

7. A composite pipe for geothermal wells according to any one of claims 1 to 4, characterized in that, The composite pipe also includes a transition section, and the upper insulation section is connected to the lower insulation section through the transition section.

8. A well shaft structure, characterized in that, The invention includes a well casing and a composite pipe as described in any one of claims 1 to 7, wherein the composite pipe is coaxially disposed inside the well casing, the inner channel of the composite pipe is configured as a hot fluid return channel, the gap between the composite pipe and the well casing is configured as a cold fluid injection channel, and the bottom of the hot fluid return channel and the bottom of the cold fluid injection channel are connected.

9. A well shaft structure according to claim 8, characterized in that, The bottom of the lower insulation section is detachably equipped with a sealing head.

10. A method of using the wellbore structure as described in claim 8 or 9, characterized in that, The process includes the following steps: introducing cold fluid into the bottom of the well casing through the cold fluid injection channel, and simultaneously introducing hot fluid from the bottom of the well casing into the heat exchanger through the hot fluid return channel.

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