Double-sleeve equipment for closed circulation heat removal of geothermal well single well

Abstract

The invention belongs to the technical field of geothermal well construction, and particularly relates to double-sleeve equipment for geothermal well single-well closed circulation heat removal. The limiting centralizing frame and the coaxial centralizing frame can fix the position of the inner heat preservation casing pipe relative to the outer casing pipe, and the concentricity of the double casing pipes is guaranteed. Due to the design of the multifunctional float shoe, double operations of cement well cementation and circulating working medium circulation can be achieved, and the well completion process of a traditional geothermal well is simplified. The inner casing and the outer casing can be assembled on the ground and descend into a well at the same time, one-time casing descending operation is reduced, the construction efficiency is improved, the construction cost is reduced, and the labor intensity of constructors is reduced. Based on the design, one-time casing running operation of the medium-deep geothermal well can be achieved, the problems of concentricity of the inner casing and the outer casing, floating and sinking of the inner heat preservation casing due to density and the like can be effectively solved, the construction efficiency is remarkably improved, the construction strength is reduced, the construction period is shortened, and the well completion efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of geothermal well construction, and in particular relates to a double-casing device used for closed-cycle heat extraction in a single geothermal well. Background Art

[0002] With the transformation of the global energy structure and the increasing urgency of environmental protection, geothermal energy, as a clean and renewable energy form, is gradually gaining attention and favor. Geothermal energy has significant advantages such as ubiquity, continuous stability, low development cost, and environmental friendliness. It is a zero-carbon or near-zero-carbon, green and clean renewable energy with broad prospects for development and utilization. Geothermal energy can be divided into water-taking type and heat-taking type according to the heat extraction method. Water-taking geothermal energy mainly mines underground hot water and extracts heat energy from underground hot water for power generation, heating, bathing, etc. It has high heat exchange efficiency, flexible application, continuous supply, is not affected by seasonal changes, and has stable and reliable operation. However, geothermal fluid resources are limited, re-injection is difficult, and it is easy to cause damage to the underground rock structure; heat extraction geothermal uses underground high-temperature rocks or geothermal fluids as heat sources, and uses the heat exchange fluid in the casing, generally softened clean water, to carry underground heat energy to the surface by heat conduction and heat convection, and then adjusts to the user's required temperature through plate heat exchangers, heat pump units, etc. This heat extraction technology is also called "heat extraction without water extraction" underground heat exchange technology. Its main advantages are: 1) High efficiency and energy saving. The ground source heat pump system uses the constant temperature of the underground for heat exchange, and its energy efficiency ratio (COP) is usually higher than that of traditional air conditioning and heating systems; 2) Green and environmentally friendly. The system does not burn fossil fuels during operation. , reducing the emission of greenhouse gases and other pollutants, not extracting underground hot water, and having minimal impact on the environment; 3) Strong stability, the underground temperature is relatively stable and is not affected by extreme weather outside; 4) Low maintenance cost, the main components of the system are located indoors, avoiding the erosion of bad weather, and there are fewer moving parts, reducing the need for wear and maintenance, and low long-term operating costs; 5) Long life, the underground part of the ground source heat pump system has a design life of up to 50 years, and the above-ground part can reach more than 30 years, far exceeding the life of conventional air conditioning and heating equipment; 6) Renewability, ground source heat pumps utilize almost unlimited geothermal energy, which is a renewable energy utilization method and meets the requirements of sustainable development.

[0003] The single-well closed-cycle heat extraction technology requires the creation of a closed-cycle environment, mainly by using an outer casing and an inner insulation casing to establish a closed-cycle space. The specific process is: first, after the drilling work is completed, the outer casing is lowered; after the outer casing is lowered into the well, special cementing cement (high thermal conductivity) is injected for cementing; after cementing is completed, the insulation inner pipe is lowered. In order to ensure the concentricity of the outer casing and the insulation inner pipe, it is necessary to lower the centralizer at specific intervals to ensure the formation of a closed-cycle environment for the circulating medium (softened clean water) to exchange heat and circulate. The entire casing lowering process needs to be repeated twice, and it is also necessary to continuously lower the centralizer to adjust the concentricity of the inner and outer pipes, which prolongs the construction period. For drilling work, the longer the construction period, the higher the drilling cost, and repeated casing lowering operations increase the labor intensity of construction personnel. In order to solve the above problems, it is necessary to develop a casing structure that can be lowered once and automatically adjust the concentricity of the inner and outer casings. The double casing structure can theoretically achieve the purpose of one-time lowering, automatic adjustment of the concentricity of the inner and outer casings, shorten the construction period, and reduce labor intensity.

[0004] In view of this, the inventor hopes to design a double-casing device for closed-cycle heat extraction in a single geothermal well. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems existing in the traditional technology and to provide a double-casing device for closed-cycle heat extraction in a single geothermal well.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a double-casing device for closed-cycle heat extraction of a single geothermal well, comprising an outer casing, an inner thermal insulation casing, a limit-rightening frame, a coaxial righting frame, a multifunctional floating shoe, an inner hexagonal screw, a spring fixing screw, a compression spring, a semi-ball valve, a tension spring and a dovetail plate; the inner part of the outer casing is installed with the inner thermal insulation casing, the limit-rightening frame, the coaxial righting frame and the dovetail plate from top to bottom, the limit-rightening frame is fixedly connected to the inner thermal insulation casing, the coaxial righting frame is installed on the outside of the limit-righting frame, the dovetail plate is connected to the inner wall of the outer casing through a tension spring, the bottom end of the outer casing is installed with a multifunctional floating shoe, the interior of the multifunctional floating shoe is installed with a spring supporting plate through an inner hexagonal screw, the spring supporting plate is installed with a compression spring through a spring fixing screw, and a semi-ball valve is installed at one end of the compression spring away from the spring supporting plate.

[0008] Furthermore, in the above-mentioned double-casing equipment for closed-cycle heat extraction in a single geothermal well, at least three limit grooves are evenly distributed in an circumferential direction on the inner side of the upper end of the outer casing, and the upper end of the outer casing is provided with an internal thread A, and an upper thickening ring is provided at the thread; the lower end of the outer casing is provided with an external thread A, and a lower thickening ring is provided at the thread; both thickening rings are provided with chamfers for reducing friction resistance when the outer casing is lowered into the well and flow resistance during grouting and cementing; the outer casings are fixedly connected to each other by threads.

[0009] Furthermore, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single geothermal well, the inner insulation casing is divided into three layers along the radial direction, the inner layer is a pressure-resistant layer, the middle layer is a heat-insulating filling material, and the outer layer is a shaping layer; the outer side of the upper end of the inner insulation casing is provided with an external thread B for fixed connection with a limit-limiting uprighting frame, and the outer side of the lower end is provided with a reducing groove A that cooperates with the coaxial uprighting frame, the inner side of the upper part of the reducing groove is provided with an internal thread B, and the outer side of the lower end is provided with an external thread C except for the lowermost inner insulation casing; The inner insulation casings are fixedly connected by threads; when cementing is carried out, a high pressure will be generated on the inner insulation casing, and the pressure-resistant layer is made of high-strength steel, which can prevent the damage to the inner insulation casing as a whole caused by high pressure; the middle layer is an insulation filling material, which plays a role in insulation and heat insulation; the outer layer is a shaping layer, which determines the overall shape of the inner insulation casing; at the same time, the combined installation of the inner insulation casing, the limit righting frame, the coaxial righting frame, and the multi-functional floating shoe can achieve the same diameter up and down, ensuring the smoothness of the circulation of the circulating working medium.

[0010] Furthermore, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single geothermal well, an inner thread C is provided on the inner side of the connecting ring of the limit and righting frame, and at least three limit frames are evenly distributed in the circumferential direction on the outer side; the limit frame is in the shape of a triangle which can improve the axial limit capacity, and the limit frame as a whole is thick in the middle and thin on both sides, thereby reducing the circulation resistance of the circulating working medium; a limit block is provided at the end of the limit frame, and the limit block is tightly matched with the limit groove of the outer casing; when the outer casings are connected to each other, the limit block will be completely blocked to play a limiting role, and at this time, the upper part of the inner insulation casing can only be centered due to the existence of the limit and righting frame.

[0011] Furthermore, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single geothermal well, the coaxial straightening frame is provided with an inner straightening ring that cooperates with the variable diameter groove A in the inner insulation casing and an outer straightening ring that fits with the outer casing. The upper end of the outer straightening ring is provided with a chamfer for reducing the flow resistance of the circulating working fluid. At least three straightening arms are provided between the inner and outer straightening rings. The straightening arms are thick in the middle and thin on both sides as a whole, thereby reducing the circulation resistance of the circulating working fluid. When the inner insulation casings are connected to each other, the inner straightening ring will be axially limited by the two inner insulation casings, and the outer diameter of the outer straightening ring is the same as the inner diameter of the outer casing. Under the action of the straightening arm, the inner insulation casing is straightened so that the inner insulation casing and the outer casing remain coaxial.

[0012] Further, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single well of a geothermal well, the outer side of the upper end of the multifunctional floating shoe is provided with an internal thread D for fixed connection with the outer casing, and the inner side of the upper end is provided with a reducing groove B for plugging and fixing with the inner insulation casing. The inner side of the outer wall of the multifunctional floating shoe is uniformly distributed with at least one tension spring fixing ring in the circumferential direction, and the lower end of the tension spring fixing ring is provided with a guide fillet; the inner wall of the multifunctional floating shoe is uniformly distributed with a number of dovetail grooves that are closely matched with the dovetail plate in the circumferential direction, and the outer side of the dovetail groove is provided with a drag reduction fillet A for guiding and reducing the resistance of the circulating working medium; the lower half of the multifunctional floating shoe includes two opposing frustum structures, the upper frustum is reduced in diameter, and the diameter of the lower frustum is gradually expanded to be able to cooperate with the hemispherical valve to form a one-way valve; the lower end of the multifunctional floating shoe is provided with a drag reduction fillet B for reducing the resistance of the lower casing and the return resistance of the cementing cement, and the bottom of the lower end of the multifunctional floating shoe is provided with two symmetrical grooves and a blind hole, and the grooves and blind holes can fix the spring support plate, thereby providing support force for the compression spring.

[0013] Furthermore, in the above-mentioned double-casing equipment for closed-cycle heat extraction from a single geothermal well, a tension spring fixing ring is provided on the outer side of the dovetail plate, and the tension spring fixing ring as a whole has a narrow outer diameter and a wide inner diameter structure, and is tightly matched with the dovetail groove on the multifunctional float shoe; when cementing the well, the dovetail plate and the dovetail groove are in a closed state under the action of the tension spring; when a thermal cycle is carried out after the cementing is completed, the tension spring is further stretched under the action of pressure until it is broken, and at this time the dovetail plate falls into the annulus of the multifunctional float shoe under the action of gravity, and at this time the dovetail groove is in an open state.

[0014] Furthermore, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single geothermal well, the main function of the lower part of the multifunctional floating shoe is to guide and cement the casing string. After the casing string is put into the well, cementing operations are first performed. The upper frustum, lower frustum, hemispherical valve, compression spring, and spring support plate cooperate to realize the function of a one-way valve. When cementing cement is injected from the inner insulation casing to the bottom of the well, due to the structural shape characteristics of the dovetail plate and the dovetail groove, the dovetail plate will tightly adhere to the dovetail groove under the action of radial pressure. At this time, the axial pressure of the cementing cement will be transmitted to the hemispherical valve and the compression spring. The compression spring Further compression opens the one-way valve; the cementing cement returns along the bottom of the multifunctional float shoe to the annular channel between the well wall and the outer casing string. When all the cementing cement completely closes the annular channel, the pressure is removed, the compression spring rebounds, and the lower truncated cone is closed to prevent the cementing cement from flowing back; the main function of the upper part of the multifunctional float shoe is to provide a circulation channel for the circulating working medium. After the cementing operation is completed, when the softened cold water enters the annular channel between the outer casing and the inner insulation casing, the dovetail plate is separated from the dovetail groove under the action of the liquid column pressure, and the dovetail groove channel is opened to realize the circulation heat exchange of the circulating working medium.

[0015] Furthermore, in the above-mentioned double-casing equipment for closed-loop heat extraction in a single geothermal well, the cement cementing circulation path is: cement is injected from the inner insulation casing, passing through a one-way valve composed of a hemispherical valve, a compression spring and a spring support plate. Under the action of axial pressure, the one-way valve opens, and the cement slurry passes through the bottom of the multi-functional floating shoe and rises along the annular channel between the outer casing string and the well wall to perform cementing.

[0016] Furthermore, in the above-mentioned double-casing device for closed-loop heat extraction in a single geothermal well, the heat conversion circulation path of the softened cold water is: cold water is injected from the outer casing, and passes through the high-temperature formation during the cold water injection process. The high-temperature formation transfers heat to the cold water, thereby increasing the temperature of the cold water, and then enters the inner insulation casing through the dovetail groove. The inner insulation casing can greatly reduce the heat exchange between hot water and cold water, reduce the energy loss of high-temperature hot water, and finally returns to the wellhead.

[0017] The beneficial effects of the present invention are:

[0018] 1. In the present invention, double casings are lowered into the well at the same time, which reduces one casing lowering operation, improves construction efficiency, reduces construction costs, and reduces the labor intensity of construction personnel.

[0019] 2. The position-limiting and righting frames and the coaxial righting frames in the present invention can fix the position of the inner thermal insulation sleeve relative to the outer sleeve, thereby ensuring the concentricity of the double sleeves.

[0020] 3. The multifunctional floating shoe of the present invention is reasonably designed, and can realize the dual operation of cementing and circulating working medium, simplifying the traditional geothermal well completion process: lowering outer casing - cementing - lowering inner casing.

[0021] 4. The present invention can realize the one-time casing operation of medium-deep geothermal wells, and can effectively solve the problems of concentricity of inner and outer casings, floating and sinking of inner insulation casing due to density reasons, etc., significantly improve construction efficiency, reduce construction intensity, shorten construction period, and improve well completion efficiency.

[0022] Of course, any product implementing the present invention does not necessarily need to achieve all of the above advantages at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0024] Figure 1 It is an overall cross-sectional view of the present invention;

[0025] Figure 2 It is a three-dimensional schematic diagram of the outer sleeve of the present invention;

[0026] Figure 3 It is a cross-sectional view of the inner thermal insulation sleeve of the present invention;

[0027] Figure 4 It is a three-dimensional schematic diagram of the position limiting and righting frame of the present invention;

[0028] Figure 5 It is a three-dimensional schematic diagram of the coaxial straightening frame of the present invention;

[0029] Figure 6 It is a three-dimensional cross-sectional view of the multifunctional floating shoe of the present invention;

[0030] Figure 7 It is a three-dimensional schematic diagram of the dovetail plate of the present invention;

[0031] Figure 8 A schematic diagram of the cement cementing circulation trajectory of the present invention;

[0032] Fig. 9 It is a schematic diagram of the circulating heat exchange trajectory of the circulating working fluid of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, the present embodiment provides a double-casing device for closed-cycle heat extraction of a single geothermal well, comprising an outer casing 1, an inner insulation casing 2, a limit righting frame 3, a coaxial righting frame 4, a multifunctional floating shoe 5, an inner hexagon screw 6, a spring fixing screw 8, a compression spring 9, a semi-ball valve 10, a tension spring 11 and a dovetail plate 12; the inner casing 1 is provided with the inner insulation casing 2, the limit righting frame 3, the coaxial righting frame 4 and the dovetail plate 12 from top to bottom, the limit righting frame 3 is fixedly connected to the inner insulation casing 2, the coaxial righting frame 4 is installed on the outer side of the limit righting frame 3, the dovetail plate 12 is connected to the inner wall of the outer casing 1 through the tension spring 11, the bottom end of the outer casing 1 is provided with a multifunctional floating shoe 5, the inner part of the multifunctional floating shoe 5 is provided with a spring support plate 7 through an inner hexagon screw 6, the spring support plate 7 is provided with a compression spring 9 through a spring fixing screw 8, and the end of the compression spring 9 away from the spring support plate 7 is provided with a semi-ball valve 10.

[0035] like Figure 2As shown, at least three limiting grooves 101 are evenly distributed in an circumferential direction on the inner side of the upper end of the outer casing 1, the upper end of the outer casing 1 is provided with an internal thread A102, and an upper thickening ring 103 is provided at the thread; the lower end of the outer casing 1 is provided with an external thread A106, and a lower thickening ring 105 is provided at the thread; both thickening rings are provided with chamfers 104 for reducing friction resistance when the outer casing is lowered into the well and flow resistance during grouting and cementing; the outer casings 1 are fixedly connected to each other by threads.

[0036] like Figure 3 As shown, the inner insulation sleeve 2 is divided into three layers along the radial direction, the inner layer is a pressure-resistant layer 205, the middle layer is an insulation filling material 206, and the outer layer is a shaping layer 207; the outer side of the upper end of the inner insulation sleeve 2 is provided with an external thread B201 for fixed connection with the limiting and righting frame 3, and the outer side of the lower end is provided with a reducing groove A203 that cooperates with the coaxial righting frame 4, the upper inner side of the reducing groove 203 is provided with an internal thread B202, and the outer side of the lower end except for the lowermost inner insulation sleeve 2 is provided with an external thread C204; the inner insulation sleeves 2 are fixedly connected by threads.

[0037] like Figure 4 As shown, there is an internal thread C301 on the inner side of the connecting ring of the limiting and righting frame 3, and at least three limiting frames 302 are evenly distributed in the circumferential direction on the outer side; the limiting frame 302 is in the shape of a triangle which can improve the axial limiting capacity, and the limiting frame 302 as a whole is thick in the middle and thin on both sides, thereby reducing the circulation resistance of the circulating working medium; a limiting block 303 is provided at the end of the limiting frame 302, and the limiting block 303 is tightly matched with the limiting groove 101 of the outer sleeve 1; when the outer sleeves 1 are connected to each other, the limiting block 303 will be completely blocked to play a limiting role, and at this time, the upper part of the inner insulation sleeve 2 can only be centered due to the existence of the limiting and righting frame 3.

[0038] like Figure 5 As shown, the coaxial straightening frame 4 is provided with an inner straightening ring 403 cooperating with the reducing groove A203 in the inner insulation sleeve 2 and an outer straightening ring 401 fitted with the outer sleeve 1, and the upper end of the outer straightening ring 401 is provided with a chamfer for reducing the flow resistance of the circulating working medium, and at least three straightening arms 402 are provided between the inner straightening ring 403 and the outer straightening ring 401. The straightening arms 402 are thick in the middle and thin on both sides as a whole, thereby reducing the circulation resistance of the circulating working medium; when the inner insulation sleeves 2 are connected to each other, the inner straightening ring 403 will be axially limited by the two inner insulation sleeves 2, and the outer diameter of the outer straightening ring 401 is the same as the inner diameter of the outer sleeve 1. Under the action of the straightening arms 402, the inner insulation sleeve 2 is straightened so that the inner insulation sleeve 2 and the outer sleeve 1 remain coaxial.

[0039] like Figure 6As shown, the outer side of the upper end of the multifunctional floating shoe 5 is provided with an internal thread D501 for fixing with the outer casing 1, and the inner side of the upper end is provided with a reducing groove B511 for plugging and fixing with the inner insulation casing 2. The inner side of the outer wall of the multifunctional floating shoe 5 is evenly distributed with at least one tension spring fixing ring 502 in the circumferential direction, and the lower end of the tension spring fixing ring 502 is provided with a guide fillet 503; the inner wall of the multifunctional floating shoe 5 is evenly distributed with a plurality of dovetail grooves 509 that are closely matched with the dovetail plate 12 in the circumferential direction, and the outer side of the dovetail groove 509 is provided with a guide for guiding and reducing the resistance of the circulating working medium. Drag reduction fillet A510; the lower half of the multifunctional floating shoe 5 includes two opposing frustum structures, the upper frustum 504 is reduced in diameter, and the lower frustum 505 is gradually expanded in diameter to form a one-way valve in cooperation with the hemispherical valve 10; the lower end of the multifunctional floating shoe 5 is provided with a drag reduction fillet B506 for reducing the resistance of the casing and the resistance of the cementing cement, and the bottom of the lower end of the multifunctional floating shoe 5 is provided with two symmetrical grooves 507 and a blind hole 508, the grooves 507 and the blind hole 508 can fix the spring support plate 7, thereby providing support force for the compression spring 9.

[0040] like Figure 7 As shown, a tension spring fixing ring 121 is provided on the outer side of the dovetail plate 12. The tension spring fixing ring 121 has a narrow outer diameter and a wide inner diameter as a whole, and is tightly matched with the dovetail groove 509 on the multifunctional float shoe 5. When cementing, the dovetail plate 12 and the dovetail groove 509 are in a closed state under the action of the tension spring. When thermal cycling is performed after cementing is completed, the tension spring 11 is further stretched under the action of pressure until it is broken. At this time, the dovetail plate falls into the annulus of the multifunctional float shoe 5 under the action of gravity, and the dovetail groove 509 is in an open state.

[0041] like Figure 8 and Fig. 9As shown, the main function of the lower part of the multifunctional floating shoe 5 is to guide the casing string and cementing. When the casing string is put into the well, cementing operation is first performed. The upper truncated platform 504, the lower truncated platform 505, the semi-ball valve 10, the compression spring 9, and the spring support plate 7 cooperate to realize the function of a one-way valve. When the cementing cement is injected from the inner insulation casing 2 to the bottom of the well, due to the structural shape characteristics of the dovetail plate 12 and the dovetail groove 509, the dovetail plate 12 will be tightly attached to the dovetail groove 509 under the action of radial pressure. At this time, the axial pressure of the cementing cement will be transmitted to the semi-ball valve 10 and the compression spring 9, and the compression spring 9 will be further compressed. The one-way valve is opened; the cementing cement returns along the bottom of the multifunctional float shoe 5 to the annular channel between the well wall and the outer casing string. When all the cementing cement completely closes the annular channel, the pressure is removed, the compression spring 9 rebounds, and the lower truncated cone 505 is closed to prevent the cementing cement from flowing back; the main function of the upper part of the multifunctional float shoe 5 is to provide a circulation channel for the circulating working medium. After the cementing operation is completed, when the softened cold water enters the annular channel between the outer casing 1 and the inner insulation casing 2, under the action of the liquid column pressure, the dovetail plate 12 is separated from the dovetail groove 509, and the dovetail groove 509 channel is opened to realize the circulation heat exchange of the circulating working medium.

[0042] In this embodiment, the cement cementing circulation path is: cement is injected from the inner insulation casing 2, passing through the one-way valve composed of the semi-ball valve 10, the compression spring 9 and the spring support plate 7. Under the action of axial pressure, the one-way valve opens, and the cement slurry passes through the bottom of the multifunctional float shoe 5 along the annular channel between the outer casing string and the well wall to perform cementing.

[0043] In this embodiment, the heat conversion circulation path of the softened cold water is: the cold water is injected from the outer casing, and passes through the high-temperature formation during the cold water injection process. The high-temperature formation transfers heat to the cold water, increasing the temperature of the cold water, and then enters the inner insulation casing 2 through the dovetail groove 509. The inner insulation casing 2 can greatly reduce the heat exchange between hot water and cold water, reduce the energy loss of high-temperature hot water, and finally return to the wellhead.

[0044] A specific application of this embodiment is: the inner and outer casings are lowered into the well at the same time. In order to meet the limit requirements of the inner insulation casing, the upper end of the outer casing is designed with a limit groove. The limit blocks on the limit straightening frame are connected and fixed between the outer casings to axially limit and radially straighten the inner insulation casing. The inner insulation casing is made completely coaxial with the outer casing in cooperation with the coaxial straightening frame to meet the requirements of cementing from the inner insulation casing. In the actual construction process, because a double casing device for closed-loop heat extraction in a single well of a geothermal well can realize one-time casing lowering and automatically adjust the concentricity of the inner and outer casings, it can greatly shorten the construction period, reduce labor intensity, improve well completion efficiency, and reduce construction costs.

[0045] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A double-casing device for closed-loop heat extraction in a single geothermal well, characterized in that: The invention comprises an outer sleeve (1), an inner thermal insulation sleeve (2), a position limiting and righting frame (3), a coaxial righting frame (4), a multifunctional floating shoe (5), an inner hexagon screw (6), a spring fixing screw (8), a compression spring (9), a hemispherical valve (10), a tension spring (11) and a dovetail plate (12); the inner thermal insulation sleeve (2), the position limiting and righting frame (3), the coaxial righting frame (4) and the dovetail plate (12) are installed from top to bottom inside the outer sleeve (1); the position limiting and righting frame (3) is fixedly connected to the inner thermal insulation sleeve (2); ... The shaft straightening frame (4) is installed on the outer side of the limit straightening frame (3), the dovetail plate (12) is connected to the inner wall of the outer sleeve (1) through a tension spring (11), a multifunctional floating shoe (5) is installed at the bottom end of the outer sleeve (1), a spring support plate (7) is installed inside the multifunctional floating shoe (5) through a hexagon socket screw (6), the spring support plate (7) is installed through a spring fixing screw (8) and a compression spring (9), and a semi-ball valve (10) is installed at one end of the compression spring (9) away from the spring support plate (7).

2. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 1, characterized in that: At least three limiting grooves (101) are evenly distributed in an circumferential direction on the inner side of the upper end of the outer casing (1); the upper end of the outer casing (1) is provided with an internal thread A (102), and an upper thickening ring (103) is provided at the thread; the lower end of the outer casing (1) is provided with an external thread A (106), and a lower thickening ring (105) is provided at the thread; both thickening rings are provided with chamfers (104) for reducing friction resistance when the outer casing is lowered into the well and flow resistance during grouting and cementing; the outer casings (1) are fixedly connected to each other by threads.

3. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 2, characterized in that: The inner thermal insulation sleeve (2) is divided into three layers along the radial direction, the inner layer is a pressure-resistant layer (205), the middle layer is a thermal insulation filling material (206), and the outer layer is a shaping layer (207); the outer side of the upper end of the inner thermal insulation sleeve (2) is provided with an external thread B (201) for fixed connection with the limit straightening frame (3), and the outer side of the lower end is provided with a reducing groove A (203) for matching with the coaxial straightening frame (4); the inner side of the upper part of the reducing groove (203) is provided with an internal thread B (202), and the outer side of the lower end except the bottommost inner thermal insulation sleeve (2) is provided with an external thread C (204); the inner thermal insulation sleeves (2) are fixedly connected by threads.

4. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 3 is characterized in that: The inner side of the connecting ring of the limiting and righting frame (3) is provided with an internal thread C (301), and the outer side is circumferentially evenly distributed with at least three limiting frames (302); the limiting frame (302) is in the shape of a triangle which can improve the axial limiting capacity, and the limiting frame (302) as a whole is thick in the middle and thin on both sides, thereby reducing the circulation resistance of the circulating working medium; a limiting block (303) is provided at the end of the limiting frame (302), and the limiting block (303) is tightly matched with the limiting groove (101) of the outer sleeve (1); when the outer sleeves (1) are connected to each other, the limiting block (303) will be completely blocked to play a limiting role, and at this time, the upper part of the inner thermal insulation sleeve (2) can only be centered due to the existence of the limiting and righting frame (3).

5. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 4, characterized in that: The coaxial straightening frame (4) is provided with an inner straightening ring (403) matched with the diameter-changing groove A (203) in the inner thermal insulation sleeve (2) and an outer straightening ring (401) fitted with the outer sleeve (1); the upper end of the outer straightening ring (401) is provided with a chamfer for reducing the flow resistance of the circulating working medium; at least three straightening arms (402) are provided between the inner straightening ring (403) and the outer straightening ring (401); the straightening arms (402) are thick in the middle and thin at both sides as a whole, thereby reducing the circulation resistance of the circulating working medium; when the inner thermal insulation sleeves (2) are connected to each other, the inner straightening ring (403) will be axially limited by the two inner thermal insulation sleeves (2); the outer diameter of the outer straightening ring (401) is the same as the inner diameter of the outer sleeve (1); under the action of the straightening arms (402), the inner thermal insulation sleeve (2) is straightened so that the inner thermal insulation sleeve (2) and the outer sleeve (1) remain coaxial.

6. The double-casing equipment for closed-cycle heat extraction in a single geothermal well according to claim 5, characterized in that: The outer side of the upper end of the multifunctional floating shoe (5) is provided with an internal thread D (501) for fixed connection with the outer sleeve (1), and the inner side of the upper end is provided with a reducing groove B (511) for plugging and fixing with the inner insulation sleeve (2). The inner side of the outer wall of the multifunctional floating shoe (5) is circumferentially evenly distributed with at least one tension spring fixing ring (502), and the lower end of the tension spring fixing ring (502) is provided with a guide fillet (503); the inner wall of the multifunctional floating shoe (5) is circumferentially evenly distributed with a plurality of dovetail grooves (509) that are tightly matched with the dovetail plate (12), and the outer side of the dovetail groove (509) is provided with a reducing groove for guiding the circulating working medium and reducing drag. The multifunctional floating shoe (5) comprises a resistance fillet A (510); the lower half of the multifunctional floating shoe (5) comprises two opposing frustum structures, the upper frustum (504) is of reduced diameter, and the lower frustum (505) is gradually enlarged in diameter to form a one-way valve in cooperation with the hemispherical valve (10); the lower end of the multifunctional floating shoe (5) is provided with a resistance reduction fillet B (506) for reducing the resistance of the casing and the resistance of the cementing cement; the bottom of the lower end of the multifunctional floating shoe (5) is provided with two symmetrical grooves (507) and a blind hole (508); the grooves (507) and the blind hole (508) can fix the spring support plate (7), thereby providing a supporting force for the compression spring (9).

7. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 6, characterized in that: A tension spring fixing ring (121) is provided on the outer side of the dovetail plate (12). The tension spring fixing ring (121) has a narrow outer diameter and a wide inner diameter as a whole, and is tightly matched with the dovetail groove (509) on the multifunctional float shoe (5). When cementing the well, the dovetail plate (12) and the dovetail groove (509) are in a closed state under the action of the tension spring. When thermal cycling is performed after cementing is completed, the tension spring (11) is further stretched under the action of pressure until it is broken. At this time, the dovetail plate falls into the annulus of the multifunctional float shoe (5) under the action of gravity, and the dovetail groove (509) is in an open state.

8. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 7, characterized in that: The main function of the lower part of the multifunctional floating shoe (5) is to guide the casing string and cement the well. When the casing string is put into the well, the cementing operation is first performed. The upper truncated platform (504), the lower truncated platform (505), the semi-ball valve (10), the compression spring (9), and the spring support plate (7) cooperate to realize the function of a one-way valve. When the cementing cement is injected from the inner insulation casing (2) to the bottom of the well, due to the structural shape characteristics of the dovetail plate (12) and the dovetail groove (509), the dovetail plate (12) will tightly adhere to the dovetail groove (509) under the action of radial pressure. At this time, the axial pressure of the cementing cement will be transmitted to the semi-ball valve (10) and the compression spring (9), and the compression spring (9) will further compress the well. The one-way valve is opened after the compression; the cementing cement returns to the annular passage between the well wall and the outer casing string along the bottom of the multifunctional float shoe (5); when all the cementing cement completely seals the annular passage, the pressure is removed, the compression spring (9) rebounds, and the lower truncated plate (505) is sealed to prevent the cementing cement from flowing back; the main function of the upper part of the multifunctional float shoe (5) is to provide a circulation passage for the circulating medium; after the cementing operation is completed, when the softened cold water enters the annular passage between the outer casing (1) and the inner insulation casing (2), the dovetail plate (12) is separated from the dovetail groove (509) under the action of the liquid column pressure, and the dovetail groove (509) passage is opened, thereby realizing the circulation heat exchange of the circulating medium.

9. The double-tube equipment for closed-cycle heat extraction in a single geothermal well according to claim 8, characterized in that: The cement cementing circulation path is as follows: cement is injected from the inner insulation casing (2), passes through a one-way valve composed of a semi-ball valve (10), a compression spring (9) and a spring support plate (7), and under the action of axial pressure, the one-way valve opens, and the cement slurry passes through the bottom of the multifunctional floating shoe (5) and rises along the annular channel between the outer casing string and the well wall to perform cementing.

10. The double-casing equipment for closed-cycle heat extraction in a single geothermal well according to claim 9, characterized in that: The heat conversion circulation path of the softened cold water is as follows: the cold water is injected from the outer casing, passes through the high-temperature formation during the cold water injection process, and the high-temperature formation transfers heat to the cold water, thereby increasing the temperature of the cold water. The cold water then enters the inner insulation casing (2) through the dovetail groove (509). The inner insulation casing (2) can significantly reduce the heat exchange between hot water and cold water, reduce the energy loss of high-temperature hot water, and finally returns to the wellhead.

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