Gradient sealing connection structure and method for sectional type middle-deep layer geothermal heat exchanger
By employing a segmented design and a gradient sealing connection structure, the problems of high heat loss and insufficient sealing reliability of coaxial heat exchangers in downhole environments have been solved, enabling efficient and reliable development of medium-deep geothermal energy.
Patent Information
- Application Number
- CN202511374899.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-25
- Publication Date
- 2025-11-07
AI Technical Summary
Existing coaxial heat exchangers fail to effectively adapt to changes in the thermal conductivity of underground rock formations and geostress gradients, resulting in large heat losses, low efficiency, and insufficient sealing reliability. Traditional connection methods cannot guarantee absolute sealing for long periods in complex underground environments.
The segmented design utilizes heat exchange tube sections of different materials and wall thicknesses, combined with gradient sealing connection components and multiple dynamic sealing mechanisms, to ensure that the connection can maintain sealing strength and adapt to tube expansion and contraction when downhole temperature and pressure change. The inner tube filling material and the outer tube work together to optimize heat exchange efficiency.
It improves the heat exchange efficiency and sealing reliability of the heat exchanger, reduces material and operating costs, and ensures long-term trouble-free operation, making it suitable for large-scale promotion and application.
Smart Images
Figure CN120907251A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of geothermal energy development, and particularly relates to a segmented middle-deep geothermal heat exchanger gradient sealing connection structure and method. BACKGROUND
[0002] Geothermal energy is a kind of renewable clean energy with abundant reserves and stable reliability. The coaxial casing heat exchanger (also known as "casing underground heat exchanger") is the core equipment for middle-deep geothermal development (2000-3000 meters or less), which exchanges heat with the rock formation through the circulating working medium closed in the wellbore, realizes the non-interference development of "taking heat without taking water", and has the advantages of environmental protection, wide applicability, etc. However, the existing coaxial heat exchanger technology has obvious defects, which restricts its heat exchange efficiency, long-term reliability and economy; the existing heat exchanger usually adopts a single material and a uniform wall thickness casing from the wellhead to the bottom of the well; but in fact, the thermal conductivity of the underground rock formation is not uniform and constant, and the ground stress increases approximately linearly with the increase of depth; the heat exchanger with a single structure cannot adapt to this gradient change, resulting in excessive heat loss in the shallow section due to the excessively high thermal conductivity of the pipe wall, and the deformation risk in the deep section due to the insufficient strength or thickness of the pipe wall, or the high material cost due to the overly conservative design; the circulating working medium obtains heat in the deep part and flows through the shallow low-temperature area during the process of returning to the ground; if the heat exchanger has good heat conduction performance in the shallow section, a large amount of heat will be lost to the surrounding low-temperature rock formation, resulting in a decrease in effective output heat and a decrease in system efficiency; and if a segmented design is adopted, the key problem is the connection between the segments; the downhole environment is harsh, with high temperature, high pressure, corrosive fluid in the formation and thermal expansion and contraction effect; the traditional welding or threaded connection method cannot guarantee absolute sealing under such complex dynamic load for a long time; once leakage occurs, the entire system will fail, and the maintenance cost is extremely high; at present, there is a lack of an effective connection scheme that can simultaneously meet the requirements of high strength, high sealing, fatigue resistance and adaptation to the axial expansion of the pipe body.
[0003] Therefore, in view of the above problems, a segmented middle-deep geothermal heat exchanger gradient sealing connection structure and method is proposed, which combines segmented adaptation to geological gradient, multiple dynamic sealing and rigid structure connection to solve the problems of low efficiency, poor reliability and high cost in the field of middle-deep geothermal heat exchanger for a long time, and provides reliable technical equipment support for efficient and large-scale development of geothermal energy. SUMMARY
[0004] In order to overcome the problems of large heat loss in the shallow layer, low efficiency and insufficient sealing reliability of the coaxial heat exchanger in the prior art without considering the gradient difference of the geological conditions in the application.
[0005] The technical scheme of the present application is: a sectional middle-deep geothermal heat exchanger gradient sealing connection structure, comprising: At least two sections of heat exchange pipe sections made of different materials and / or having different wall thicknesses are arranged in sequence along the depth direction of the geothermal well, the material selection and structural parameters of the heat exchange pipe sections are adaptively designed based on the thermal conductivity of the rock stratum and the ground stress gradient in the depth interval where the heat exchange pipe sections are located; the heat exchange pipe section comprises an inner pipe and an outer sleeve pipe arranged coaxially; the outer diameter of the inner pipe is slightly smaller than the inner diameter of the outer sleeve pipe, and the outer wall of the inner pipe is in close contact with the inner wall of the outer sleeve pipe; A gradient sealing connection assembly is used to connect two adjacent heat exchange pipe sections to form a complete wellbore, the gradient sealing connection assembly comprises a sealing sleeve coaxially sleeved outside the butt joint ends of the two heat exchange pipe sections, and a plurality of dynamic sealing mechanisms arranged between the sealing sleeve and the heat exchange pipe sections; The plurality of dynamic sealing mechanisms are configured to maintain the static sealing strength and dynamic sealing followability at the connection when the heat exchange pipe sections expand and contract axially due to changes in downhole temperature and pressure; An inner pipe filling material is filled in the inner pipe of the heat exchange pipe section, and the thermal conductivity of the inner pipe filling material is configured to cooperate with the material of the outer sleeve pipe of the corresponding depth section.
[0006] Preferably, in the present application, at least two sections of heat exchange pipe sections made of different materials and / or having different wall thicknesses are arranged in sequence along the depth direction of the geothermal well, the material selection and structural parameters of the heat exchange pipe sections are adaptively designed based on the detailed geological survey data of the thermal conductivity of the rock stratum and the ground stress gradient in the depth interval where the heat exchange pipe sections are located, thereby optimizing the cost and performance under the premise of safety; the gradient sealing connection assembly is used to connect two adjacent heat exchange pipe sections to form a complete and continuous pressure boundary; the assembly is a sealing sleeve coaxially sleeved outside the butt joint ends of the two heat exchange pipe sections; a plurality of dynamic sealing mechanisms are arranged in the annular space between the sealing sleeve and the heat exchange pipe sections; the mechanisms are specially configured to not only provide static sealing strength in the initial state, but also maintain effective contact of the sealing surface when the heat exchange pipe sections expand and contract axially due to changes in downhole temperature and pressure, i.e. have dynamic sealing followability, which is the key to ensuring long-term sealing; an inner pipe filling material is filled in the inner pipe of the heat exchange pipe section; the thermal conductivity of the inner pipe filling material is selected to have a synergistic effect with the material of the outer sleeve pipe of the corresponding depth section, high-thermal-conductivity filling materials are used in deep sections to strengthen heat exchange, and low-thermal-conductivity filling materials are used in shallow sections to assist in heat preservation, thereby optimizing the heat exchange efficiency in the entire well depth range and reducing invalid heat loss.
[0007] As a preferred, the at least two sections of heat exchange pipe sections comprise a shallow section, a middle-deep section and a deep section; The outer sleeve pipe of the shallow section (0-500m) adopts low thermal conductivity alloy steel, and the wall thickness is determined based on the shallow geological pressure and corrosion prevention requirements; the core function is to keep warm and reduce the heat loss of the uplink working medium; The outer sleeve pipe of the middle-deep section (500-1500m) adopts alloy steel with medium thermal conductivity and high strength, and the wall thickness is strengthened based on the gradient geostress in this depth interval; optimized by finite element analysis to ensure that it can withstand huge external pressure without unnecessary cost and weight increase due to overdesign; The outer sleeve pipe of the deep section (1500-2000m and below) adopts special alloy steel with high thermal conductivity, ultra-high strength and high corrosion resistance, and the wall thickness is determined based on the maximum geostress and high temperature creep performance; the inner and outer walls can be coated with high-performance corrosion-resistant coating, and the annular space between the inner and outer pipes can be filled with high-thermal-conductivity medium for efficient and safe absorption of geothermal energy in extreme environments.
[0008] As a preferred, the gradient sealing connection assembly is specifically arranged between the shallow section and the middle-deep section, and between the middle-deep section and the deep section; The thermal expansion coefficient of the sealing sleeve is between the thermal expansion coefficients of the materials of the two heat exchange pipe sections connected at its two ends, for forming a thermal stress transition zone; When the temperature changes, the shear stress generated at the connection of different materials due to different expansion amounts is reduced, and the fatigue life of the connection part is improved.
[0009] As a preferred, the multiple dynamic sealing mechanism includes, from inside to outside: A metal sealing ring is arranged in the annular groove structure formed on the connecting end face of the two heat exchange pipe sections, and is made of a metal material with excellent plasticity. The metal sealing ring is configured to be plastically deformed under the action of axial pre-tightening force to form a first static metal seal. The ring is plastically deformed by applying a large axial pre-tightening force during installation to fill all microscopic irregularities and achieve static metal sealing. The metal seal is resistant to high temperature and aging, and has stable performance; An elastic polymer sealing ring is arranged outside the metal sealing ring to provide dynamic sealing following the expansion and deformation of the pipe body. When the metal sealing ring slightly shifts due to temperature changes or produces a small gap due to pressure fluctuations, the elastic body automatically expands under the action of medium pressure or relies on its own elastic force to rebound, tightly adheres to the sealing surface, compensates for the gap, and ensures the continuity of the seal; A hot melt sealing glue layer is filled in the annular space between the sealing sleeve and the heat exchange pipe section, and is configured to melt and solidify under the action of downhole temperature to form a third all-around covering seal; In the welding process, the heat provided by the welding heat source melts the hot-melt sealant layer into a fluid, penetrates into any small defects that may exist in the previous two seals, and solidifies after cooling to form a third all-around, dead-angle-free, wrapped seal, greatly improving the reliability and safety of the seal.
[0010] Preferably, the inner wall of the sealing sleeve and the outer wall of the heat exchange pipe segment are provided with a limiting step structure that engages with each other, for bearing the axial load generated by the downhole pressure and converting part of the axial force into radial force.
[0011] Preferably, the contact surface of the sealing sleeve and the heat exchange pipe segment are metallurgically combined by welding.
[0012] The main function of the limiting step structure is mechanical bearing, for bearing the axial load generated by the huge external pressure in the well, preventing the pipe segment from being squeezed and deformed inward, thereby protecting the aforementioned sealing material from being crushed; the contact surface of the sealing sleeve and the heat exchange pipe segment are metallurgically combined by welding, forming a permanent connection with a strength comparable to that of the base material, solidifying the entire assembly into a whole.
[0013] A gradient sealing connection method for a segmented medium-deep geothermal heat exchanger, the method is applied to the connection structure described above, comprising the following steps: S1: Based on the geological survey data of the target geothermal well, the rock thermal conductivity and ground stress gradient in different depth intervals are determined, and the heat exchange pipe segments of different materials, wall thicknesses and structural parameters are designed and prepared accordingly; S2: Process the end of the two adjacent heat exchange pipe segments to be connected to form a clean and smooth butt joint surface and a groove for accommodating the sealing mechanism, and place the sealing sleeve on one of the pipe segments; S3: Install the components of the multiple dynamic sealing mechanism in sequence to the pretreated butt joint area; S4: Move the sealing sleeve to the butt joint position and apply an axial pre-tightening force to cause plastic deformation of the metal sealing ring, completing the preliminary sealing connection; S5: Inject hot-melt sealant into the annular space through the pre-installed injection hole on the sealing sleeve, and then weld the sealing sleeve and the heat exchange pipe segment into a whole through the ring welding process to form a sealing structure; S6: Perform local annealing heat treatment on the welded connection part to eliminate welding residual stress.
[0014] Preferably, step S3 specifically includes: First, press the metal sealing ring into the groove at the butt joint end of the heat exchange pipe segment; Then install the elastic polymer sealing ring in the annular gap outside the metal sealing ring; Finally, the solid hot melt sealant preform is placed in the designated annular receiving groove on the inside of the sealing sleeve.
[0015] As preferred, the ring welding process in step S5 adopts narrow gap heat input control welding technology, and the pre-assembled elastic polymer sealing ring and hot melt sealant are actively cooled and protected during the welding process to prevent high-temperature failure.
[0016] As preferred, step S1 further comprises: Different heat conductive filling materials are selected for inner tubes of heat exchange pipe segments of different depths, wherein the heat conductive filling material of the inner tube of the deep segment is higher than that of the shallow segment.
[0017] The beneficial effects of the present application are: 1. The gradient thermal resistance structure of the present application matches different depth segments of the heat exchanger with local rock layer thermal-mechanical properties; the low thermal conductivity material of the shallow segment effectively reduces the loss during the upward process of the heat flow; the high thermal conductivity material and high thermal conductivity filler of the deep segment strengthen the heat extraction capacity; the inner and outer cooperation improves the system net heat extraction efficiency; 2. The present application provides metal plastic sealing, elastomer dynamic sealing, hot melt glue all-around sealing, mechanical step pressure resistance, and metallurgical welding sealing through the multiple dynamic sealing mechanisms combined with mutual interlocking and welding connection structure; the connection part not only can withstand extreme static pressure, but also can adapt to the alternating stress caused by the downhole thermal cycle, and the sealing reliability and structural life are higher than those of the traditional single connection method, avoiding the risk of leakage; 3. The segmented differential design avoids "excessive consumption" or "insufficient performance" of materials; lower-cost materials are used in non-critical segments, and high-performance materials are used in critical segments, achieving optimized material allocation, reducing initial investment; at the same time, higher efficiency and longer fault-free operation time reduce operating costs and improve the overall economy of the project; 4. The connection method provided by the present application decomposes the complex sealing and connection process into a standardized process that can be accurately controlled, ensuring consistency and high quality of on-site construction, and is suitable for large-scale popularization and application. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 A three-dimensional structure schematic diagram of the segmented middle-deep geothermal heat exchanger gradient sealing connection structure of the present application is shown. Figure 2 A sectional three-dimensional structure schematic diagram of the segmented middle-deep geothermal heat exchanger gradient sealing connection structure of the present application is shown. Figure 3 A sectional plane structure schematic diagram of the segmented middle-deep geothermal heat exchanger gradient sealing connection structure of the present application is shown. Figure 4The first local structure schematic diagram of the segmented middle-deep geothermal heat exchanger gradient sealing connection structure is shown. Figure 5 The second local structure schematic diagram of the segmented middle-deep geothermal heat exchanger gradient sealing connection structure is shown. The figure mark explanation: 1, heat exchange pipe segment; 2, gradient sealing connection assembly; 21, sealing sleeve; 22, multiple dynamic sealing mechanism; 2201, metal sealing ring; 2202, elastic polymer sealing ring; 2203, hot melt sealing glue; 3, inner tube filling material; 4, limiting step structure. DETAILED DESCRIPTION
[0019] The application will be further described below in combination with the drawings and examples.
[0020] Please refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 , the application provides an embodiment: the segmented middle-deep geothermal heat exchanger gradient sealing connection structure, comprising: At least two segments of heat exchange pipe segments 1 made of different materials and / or different wall thicknesses are arranged in sequence along the depth direction of the geothermal well, the material selection and structure parameters of the heat exchange pipe segments 1 are adaptively designed based on the thermal conductivity of the rock stratum and the ground stress gradient in the depth interval where the heat exchange pipe segments 1 are located; the heat exchange pipe segments 1 include an inner tube and an outer sleeve coaxially arranged; the outer diameter of the inner tube is slightly smaller than the inner diameter of the outer sleeve, and the outer wall of the inner tube is tightly attached to the inner wall of the outer sleeve; The gradient sealing connection assembly 2 is used to connect two adjacent heat exchange pipe segments 1 to form a complete wellbore, and the gradient sealing connection assembly 2 includes a sealing sleeve 21 coaxially arranged outside the butt joint end of the two heat exchange pipe segments 1, and a multiple dynamic sealing mechanism 22 arranged between the sealing sleeve 21 and the heat exchange pipe segments 1; The multiple dynamic sealing mechanism 22 is configured to maintain the static sealing strength and dynamic sealing followability of the connection when the heat exchange pipe segments 1 produce axial expansion and contraction due to changes in downhole temperature and pressure; The inner tube filling material 3 is filled in the inner tube of the heat exchange pipe segment 1, and the thermal conductivity thereof is configured to form synergy with the outer sleeve material of the corresponding depth segment.
[0021] In this invention, at least two heat exchange tube segments 1, made of different materials and / or with different wall thicknesses, are sequentially arranged along the depth direction of the geothermal well. The material selection and structural parameters of the heat exchange tube segments 1 are designed for compatibility based on detailed geological survey data of the thermal conductivity of the rock strata and the stress gradient in their respective depth range, thereby optimizing cost and performance while ensuring safety. The gradient sealing connection assembly 2 is used to connect two adjacent heat exchange tube segments 1 to form a complete and continuous pressure boundary. This assembly is a sealing sleeve 21 coaxially sleeved on the outside of the mating end of the two heat exchange tube segments 1. Within the annular space between the sealing sleeve 21 and the heat exchange tube segment 1, a... Multiple dynamic sealing mechanisms 22 are provided; these mechanisms are specifically configured to not only provide static sealing strength in the initial state, but also maintain effective contact of the sealing surface when the heat exchange tube section 1 undergoes axial expansion and contraction due to changes in downhole temperature and pressure, i.e., they have dynamic sealing following capability, which is the key to ensuring long-term sealing; the inner tube filling material 3 is filled in the inner tube of the heat exchange tube section 1; its thermal conductivity is selected to form a synergistic effect with the outer tube material of the corresponding depth section. High thermal conductivity filling material is used in the deep section to enhance heat exchange, and low thermal conductivity filling material is used in the shallow section to assist in heat preservation, together optimizing the heat exchange efficiency throughout the entire well depth range and reducing ineffective heat loss.
[0022] Furthermore, at least two heat exchange tube sections 1 include a shallow section, a medium-deep section, and a deep section; The outer casing of the shallow section (0-500m) is made of alloy steel with low thermal conductivity, and its wall thickness is determined based on the shallow geological pressure and corrosion protection requirements; its core function is heat preservation to reduce heat loss of the upward working fluid. The outer casing of the medium-deep section (500-1500m) is made of alloy steel with medium thermal conductivity and high strength. Its wall thickness is reinforced based on the gradient stress in this depth range. It is optimized through finite element analysis to ensure that it can withstand huge external pressure without adding unnecessary cost and weight due to over-design. The outer casing of the deep section (1500-2000m and below) is made of special alloy steel with high thermal conductivity, ultra-high strength and high corrosion resistance. Its wall thickness is determined based on the maximum ground stress and high temperature creep performance. Its inner and outer walls can be coated with high-performance anti-corrosion coatings, and the annular gap between the inner and outer pipes can be filled with a high thermal conductivity medium for efficient and safe geothermal absorption in extreme environments.
[0023] Furthermore, the gradient sealing connection assembly 2 is specifically disposed between the shallow section and the intermediate-deep section, and between the intermediate-deep section and the deep section; The thermal expansion coefficient of the sealing sleeve 21 is between that of the heat exchange tube section 1 connected to its two ends, and is used to form a thermal stress transition zone. When the temperature changes, it can reduce the shear stress generated at the connection due to the different expansion of pipe sections of different materials, thereby improving the fatigue life of the connection.
[0024] Further, the multiple dynamic sealing mechanism 22 includes, from inside to outside, in order: The metal sealing ring 2201 is arranged in the annular groove structure opened on the connecting end face of the two heat exchange pipe sections 1, and is made of a metal material with excellent plasticity. The metal sealing ring 2201 is configured to be plastically deformed under the action of axial pre-tightening force to form the first static metal seal. The ring is plastically deformed by applying a large axial pre-tightening force during installation to fill all micro irregularities and achieve static metal sealing. The metal seal is resistant to high temperature and aging, and has stable performance. The elastic polymer sealing ring 2202 is arranged outside the metal sealing ring 2201 and is used to provide dynamic sealing following the expansion and deformation of the pipe body. When the metal sealing ring 2201 slightly shifts due to temperature changes or produces a small gap due to pressure fluctuations, the elastic body automatically expands under the action of medium pressure or relies on its own elastic force to rebound, tightly adheres to the sealing surface, compensates for the gap, and ensures the continuity of the seal. The hot melt sealing glue 2203 layer is filled in the annular space between the sealing sleeve 21 and the heat exchange pipe section 1 and is configured to melt and solidify under the action of downhole temperature to form the third all-around covering seal. During welding, the heat provided by the welding heat source melts the hot melt sealing glue 2203 layer into a fluid, penetrates into any micro defects that may exist in the previous two seals, and solidifies after cooling to form a third all-around, dead-angle-free covering seal, greatly improving the reliability and safety of the seal.
[0025] Further, the inner wall of the sealing sleeve 21 and the outer wall of the heat exchange pipe section 1 are provided with a limiting step structure 4 that engages with each other, for bearing the axial load generated by downhole pressure and converting part of the axial force into radial force.
[0026] Further, the contact surface of the sealing sleeve 21 and the heat exchange pipe section 1 is metallurgically combined by welding.
[0027] The main function of the limiting step structure 4 is mechanical bearing, for bearing the axial load generated by the huge external pressure in the well, preventing the pipe section from being squeezed and deformed inward, thereby protecting the aforementioned sealing material from being crushed; the contact surface of the sealing sleeve 21 and the heat exchange pipe section 1 is metallurgically combined by welding to form a permanent connection with a strength comparable to that of the base material, solidifying the entire assembly into one body.
[0028] A gradient sealing connection method for a segmented medium-deep geothermal heat exchanger, the method is applied to the connection structure described above, and includes the following steps: S1: Based on the geological survey data of the target geothermal well, the rock thermal conductivity and ground stress gradient of different depth intervals are determined, and the heat exchange pipe section 1 with different materials, wall thickness and structure parameters is designed and prepared; S2: The end of the two adjacent heat exchange pipe sections 1 to be connected is processed to form a clean and smooth butt joint surface and a groove for accommodating the sealing mechanism, and the sealing sleeve 21 is sleeved on one of the pipe section ends; S3: Assembling the components of the multiple dynamic sealing mechanism 22 in sequence to the pretreated butt joint area; S4: Moving the sealing sleeve 21 to the butt joint position, applying axial pre-tightening force to make the metal sealing ring 2201 plastically deform, and completing the preliminary sealing connection; S5: Injecting hot melt sealant 2203 into the annular space through the pre-installed glue injection hole on the sealing sleeve 21, and then welding the sealing sleeve 21 and the heat exchange pipe section 1 into a whole through ring welding process to form a sealing structure; S6: Local annealing heat treatment is performed on the welded connection part to eliminate the welding residual stress.
[0029] Further, step S3 specifically includes: First, press the metal sealing ring 2201 into the groove at the butt joint end of the heat exchange pipe section 1; Then install the elastic polymer sealing ring 2202 in the annular gap outside the metal sealing ring 2201; Finally, place the solid hot melt sealant 2203 preformed part into the designated annular receiving groove inside the sealing sleeve 21.
[0030] Further, the ring welding process in step S5 uses narrow gap heat input control welding technology, and the elastic polymer sealing ring 2202 and hot melt sealant 2203 assembled in advance are actively cooled and protected during the welding process to prevent high temperature failure.
[0031] Further, step S1 also includes: Select different thermal conductivity filling materials for the inner tubes of heat exchange pipe sections 1 at different depths, wherein the thermal conductivity of the filling material 3 in the deep section is higher than that in the shallow section.
[0032] In the process of work, the specific implementation of the sectional middle-deep geothermal heat exchanger gradient sealing connection structure needs to be based on the geological survey data of the target geothermal well; first, according to the rock thermal conductivity and ground stress gradient of different depth intervals (such as shallow section 0-500m, middle-deep section 500-1500m, deep section 1500m and below), design and prepare adaptive heat exchange pipe section 1; the outer sleeve pipe of the shallow section adopts low thermal conductivity alloy steel, and the pipe wall thickness meets the requirements of geological pressure and corrosion prevention; the middle-deep section selects medium thermal conductivity high strength alloy steel, and the wall thickness is optimized by finite element analysis to resist gradient ground stress; the deep section adopts high thermal conductivity, ultra-high strength and corrosion-resistant special alloy steel, and the wall thickness is determined combined with high temperature creep performance; each section is filled with outer sleeve pipe material with coordinated thermal conductivity, such as filling high thermal conductivity material in deep section to strengthen heat extraction, and filling low thermal conductivity material in shallow section to reduce heat loss; then, the end of the adjacent heat exchange pipe section 1 is cleaned, smoothed and processed with a sealing groove, and the sealing sleeve 21 is sleeved on the end of the pipe section, laying a foundation for subsequent sealing connection; The installation of the gradient sealing connection assembly 2 needs to strictly follow the assembly sequence of the multiple dynamic sealing mechanism 22; first, press the plastic metal sealing ring 2201 into the heat exchange pipe section 1 butt joint end groove, make it plastic deformation by axial pre-tightening force, form the first static metal seal; then, install the elastic polymer sealing ring 2202 in the annular gap outside the metal sealing ring 2201, use its elastic deformation ability to adapt to the axial expansion and contraction of the pipe body, realize dynamic sealing compensation; finally, place the solid hot melt sealing glue 2203 preform in the inner annular receiving groove of the sealing sleeve 21; after moving the sealing sleeve 21 to the butt joint position, inject the hot melt sealing glue 2203 through the glue injection hole, use the welding heat source to make it melt and penetrate into the small defects of the previous two seals, and solidify to form the third all-around covering seal after cooling; the limiting step structure 4 between the inner wall of the sealing sleeve 21 and the outer wall of the heat exchange pipe section 1 can bear axial load and convert it into radial force, cooperate with the ring welding process to form a whole structure with metallurgical bonding, ensure the mechanical strength and sealing reliability of the connection; The whole connection method needs the system to perform the whole process from design to verification; step S1 determines the parameters of each depth interval based on the geological data, prepares the heat exchange pipe section 1 and selects the inner tube filling material 3; step S2 completes the pretreatment and preloading of the sealing sleeve 21; step S3 sequentially assembles the multiple dynamic sealing mechanism 22 components; step S4 deforms the metal sealing ring 2201 through the axial pre-tightening force to achieve preliminary sealing; step S5 adopts the narrow gap heat input control welding technology, actively cools and protects the elastic polymer sealing ring 2202 and the hot melt sealing glue 2203 during the welding process, prevents high temperature failure, and welds the sealing sleeve 21 and the pipe section into a whole through ring welding; step S6 performs local annealing heat treatment on the welded part to eliminate residual stress; and finally the formed connection structure not only meets the static sealing strength requirement, but also can maintain dynamic sealing followability in the expansion and contraction of the pipe body caused by the change of downhole temperature and pressure, and ensure the long-term efficient and reliable operation of the medium-deep geothermal heat exchanger.
[0033] Through the above steps, the gradient thermal resistance structure of the present application matches the heat-power characteristics of the local stratum at different depths of the heat exchanger; the low thermal conductivity material of the shallow section effectively reduces the loss during the upward process of the heat flow; the high thermal conductivity material and the high thermal conductivity filler of the deep section strengthen the heat extraction capacity; the inner and outer cooperation improves the system net heat extraction efficiency; the present application provides metal plastic sealing, elastomer dynamic sealing, hot melt glue all-around sealing, mechanical step pressure resistance and metallurgical welding sealing through the multiple dynamic sealing mechanism 22 combined with mutual interlocking and welding connection structure; the connection part not only can withstand extreme static pressure, but also can adapt to the alternating stress caused by the downhole thermal cycle, the sealing reliability and the structure life are higher than those of the traditional single connection mode, and the leakage risk is avoided; the segmented differential design avoids the "excessive consumption" or "insufficient performance" of the material; the lower cost material is used in the non-critical section, and the high-performance material is used in the critical section, realizing the optimal allocation of the material and reducing the initial investment; at the same time, the higher efficiency and longer failure-free operation time reduce the operation cost and improve the overall economy of the project; the connection method provided by the present application decomposes the complex sealing and connection process into a standardized process which can be accurately controlled, guarantees the consistency and high quality of the on-site construction, and is suitable for large-scale popularization and application.
[0034] The embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.
Claims
1. A sectional middle-deep geothermal heat exchanger gradient sealing connection structure, characterized in that: The application relates to a heat exchange pipe for a geothermal well. The heat exchange pipe comprises at least two heat exchange pipe sections (1) made of different materials and / or having different wall thicknesses, which are arranged in sequence along the depth direction of the geothermal well, the materials and structural parameters of the heat exchange pipe sections (1) being adaptively designed based on the thermal conductivity of the rock stratum and the stress gradient at the depth interval of the heat exchange pipe sections (1); the heat exchange pipe section (1) comprises an inner pipe and an outer sleeve which are coaxially arranged; the outer diameter of the inner pipe is slightly smaller than the inner diameter of the outer sleeve, and the outer wall of the inner pipe is tightly attached to the inner wall of the outer sleeve; a gradient sealing connection assembly (2) is arranged between the two heat exchange pipe sections (1) to form a complete wellbore; the gradient sealing connection assembly (2) comprises a sealing sleeve (21) which is coaxially arranged outside the abutting end of the two heat exchange pipe sections (1), and a plurality of dynamic sealing mechanisms (22) which are arranged between the sealing sleeve (21) and the heat exchange pipe sections (1); the plurality of dynamic sealing mechanisms (22) are configured to maintain the static sealing strength and dynamic sealing followability of the connection part when the heat exchange pipe sections (1) are axially stretched or contracted due to the change of the temperature and pressure in the well; an inner pipe filling material (3) is filled in the inner pipe of the heat exchange pipe section (1), and the thermal conductivity of the inner pipe filling material (3) is configured to be coordinated with the material of the outer sleeve at the corresponding depth section.
2. The graded seal connection structure of the segmented middle-deep geothermal heat exchanger according to claim 1, characterized in that: The at least two heat exchange pipe sections (1) comprise a shallow layer section, a medium-deep layer section and a deep layer section; the outer sleeve of the shallow layer section (0-500m) is made of low-thermal-conductivity alloy steel, and the wall thickness of the outer sleeve is determined based on the shallow geological pressure and corrosion prevention requirements; the outer sleeve of the medium-deep layer section (500-1500m) is made of medium-thermal-conductivity and high-strength alloy steel, and the wall thickness of the outer sleeve is reinforced based on the gradient stress at the depth interval; the outer sleeve of the deep layer section (1500-2000m and below) is made of high-thermal-conductivity, super-high-strength and high-corrosion-resistance special alloy steel, and the wall thickness of the outer sleeve is determined based on the maximum stress and high-temperature creep performance.
3. The graded seal connection structure of the segmented middle-deep geothermal heat exchanger according to claim 2, characterized in that: The gradient sealing connection assembly (2) is arranged between the shallow layer section and the medium-deep layer section, and between the medium-deep layer section and the deep layer section; the material thermal expansion coefficient of the sealing sleeve (21) is between the thermal expansion coefficients of the materials of the heat exchange pipe sections (1) connected at the two ends of the sealing sleeve (21), and the sealing sleeve (21) is used for forming a thermal stress transition zone.
4. The graded seal connection structure of the segmented middle-deep geothermal heat exchanger according to claim 1, characterized in that: The plurality of dynamic sealing mechanisms (22) comprise, from inside to outside, a metal sealing ring (2201) which is arranged in a ring-shaped groove structure formed on the connecting end surface of the two heat exchange pipe sections (1) and is made of a metal material with excellent plasticity, the metal sealing ring (2201) being configured to be plastically deformed under the action of axial pre-tightening force to form a first static metal seal; an elastic polymer sealing ring (2202) which is arranged outside the metal sealing ring (2201) and is used for providing dynamic sealing which follows the stretching and deformation of the pipe body; and a hot-melt sealing glue (2203) layer which is filled in the annular space between the sealing sleeve (21) and the heat exchange pipe section (1) and is configured to be melted and solidified under the action of the downhole temperature to form a third all-around covering seal. 5. The segmented intermediate-depth geothermal heat exchanger gradient seal connection structure of claim 1, wherein: The inner wall of the sealing sleeve (21) and the outer wall of the heat exchange pipe section (1) are provided with a limiting step structure (4) which engages with each other, for bearing axial load generated by downhole pressure and converting part of the axial force into radial force.
6. The graded seal connection structure of a segmented intermediate-deep geothermal heat exchanger according to claim 1, characterized in that: The contact surface of the sealing sleeve (21) and the heat exchange pipe section (1) are metallurgically combined by welding.
7. A method of making a gradient seal connection for a segmented intermediate-depth geothermal heat exchanger, the method comprising: The method is applied to the connecting structure as claimed in any one of claims 1-6, comprising the following steps: S1: Based on the geological survey data of the target geothermal well, the rock thermal conductivity and the ground stress gradient in different depth intervals are determined, and the heat exchange pipe section (1) with different materials, wall thicknesses and structure parameters is designed and prepared; S2: The end of the two adjacent heat exchange pipe sections (1) to be connected is processed to form a clean and smooth butt joint surface and a groove for accommodating the sealing mechanism, and the sealing sleeve (21) is sleeved on one of the pipe sections; S3: The components of the multiple dynamic sealing mechanism (22) are sequentially installed in the pretreated butt joint area; S4: Move the sealing sleeve (21) to the butt joint position, apply axial pre-tightening force to make the metal sealing ring (2201) plastically deform, and complete the preliminary sealing connection; S5: Inject hot-melt sealant (2203) into the annular space through the pre-installed glue injection hole on the sealing sleeve (21), and then weld the sealing sleeve (21) and the heat exchange pipe section (1) into a whole through the ring welding process to form a sealing structure; S6: Local annealing heat treatment is performed on the welded connection part to eliminate the welding residual stress.
8. The method of gradient sealing connection for a segmented intermediate-depth geothermal heat exchanger according to claim 7, characterized in that: Step S3 specifically includes: First, press the metal sealing ring (2201) into the groove of the heat exchange pipe section (1) butt joint end; Then install the elastic polymer sealing ring (2202) in the annular gap outside the metal sealing ring (2201); Finally, place the solid hot-melt sealant (2203) preformed part into the designated annular receiving groove inside the sealing sleeve (21).
9. The method of gradient sealing connection for a segmented intermediate-depth geothermal heat exchanger according to claim 7, characterized in that: The ring welding process in step S5 uses narrow gap heat input control welding technology, and the elastic polymer sealing ring (2202) and hot-melt sealant (2203) assembled in advance are actively cooled and protected during the welding process.
10. The method of making a gradient seal connection for a segmented intermediate- to deep geothermal heat exchanger according to claim 7, wherein: Step S1 further includes: Different thermal conductivity filling materials are selected for the inner tubes of heat exchange pipe sections (1) at different depths, wherein the thermal conductivity of the filling material (3) in the deep section is higher than that in the shallow section.