Improved heat exchanger for horizontal wells with perforated rectangular wing vortex finder and method of installation

Abstract

The present application relates to a kind of perforated rectangular wing vortexer horizontal well improved heat exchanger and setting method, and heat exchanger includes heat exchange well, heat exchange well uses the structure of single main well-four horizontal branch well, is made of main well and horizontal branch well;Main well is vertical shaft, bottom is closed, and horizontal branch well is drilled in geothermal reservoir position;Perforated rectangular wing vortexer structure is installed at horizontal branch well outside interval certain interval;Heat exchange well uses the form of casing, fluid working medium enters heat exchange well from outer tube to flow to the bottom of main well, fluid working medium enters inner tube from the opening of horizontal branch well inner tube, and via inner tube, fluid working medium flows out heat exchange well, and energy conversion processing is carried out, and low temperature fluid working medium is reciprocated again.The present application saves drilling cost, increases the heat exchange range of heat reservoir transverse, achieves the purpose of heat extraction without water;Heat exchange efficiency between horizontal well and heat reservoir is improved;Horizontal well interior is mixed by inner tube wall and outer tube wall heat transfer working medium fully, and it is convenient for the heat transfer working medium in pipe to be fully and evenly heat exchanged.

Description

Technical Field

[0001] This invention belongs to the field of heat exchanger performance optimization technology, specifically relating to an improved coaxial casing heat exchanger for horizontal wells with a multi-branch perforated rectangular winged vortex generator. Background Technology

[0002] For the most conventional EGS system, an EGS consists of two or more well systems connected by thermal reservoirs formed naturally or through hydraulic fracturing. However, traditional well (or multi-well) fracturing for reservoir creation suffers from problems such as difficulties in downhole connectivity, leakage of circulating working fluid, the presence of dominant channels in fractures, the potential for inducing microseismic events, and excessively high drilling costs and risks. These issues have prevented geothermal energy extraction from achieving its expected goals and represent a bottleneck in the current development of hot dry rock, necessitating the search for new breakthroughs.

[0003] Currently, engineering pilot projects for single-well circulating geothermal systems have been carried out in some overseas regions. However, the heat exchange area of ​​coaxial casing heat exchange projects is limited, resulting in insufficient development of medium-deep geothermal resources. In the field of heat exchanger performance optimization, existing technologies have disclosed the impact of installing typical torsional turbulence generators on the thermal-hydraulic performance of pipes with constant wall temperatures, and have also disclosed the use of triangular fins to enhance turbulence near the circular pipe wall. However, few researchers have combined the torsional degree of the vortex generator, the shape of the fins, and the degree of perforation in the research and development of vortex generators.

[0004] Existing technology discloses a geothermal well and a medium-deep geothermal heat exchange system. The geothermal well includes a heat exchange well and a water outlet well. The water outlet well is vertically positioned, with its lower end extending into the underground rock strata. The heat exchange well is horizontally positioned within the rock strata, with one end connected to the lower end of the water outlet well and the other end bent upwards and penetrating the surface. The upper end of the water outlet well connects to the inlet of the heat exchanger, and the upper end of the heat exchange well connects to the outlet of the heat exchanger. However, this increases drilling costs. Existing technology also discloses a through-flow vortex generator, including a central rod with two or more small fins arranged on it. The fins and the central rod have an angle, and the angle between all fins and the same side of the central rod is less than 90°. The free ends of the fins have notches. However, this technology has not yet been applied to geothermal heat exchange pipes to enhance the heat exchange efficiency of geothermal systems.

[0005] In summary, existing medium-deep geothermal heat exchange systems suffer from several drawbacks, including a small heat exchange range in single-well heat exchange technology, insufficient heat extraction without water extraction in enhanced geothermal systems, susceptibility to earthquakes induced by hydraulic fracturing technology, and low heat exchange efficiency within horizontal wells. Therefore, there is an urgent need to develop an improved coaxial casing heat exchanger for horizontal wells to effectively address these issues. Summary of the Invention

[0006] The purpose of this invention is to provide an improved coaxial casing heat exchanger for horizontal wells with multi-branch perforated rectangular winged vortex generators, in order to solve the problems of small heat exchange range of existing medium-deep single-well heat exchange technology, insufficient "heat extraction without water extraction" of enhanced geothermal systems, easy induction of earthquakes by hydraulic fracturing technology, and low heat exchange efficiency inside horizontal wells.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] An improved heat exchanger for a horizontal well with a perforated rectangular winged vortex generator includes a heat exchange well, wherein the heat exchange well adopts a single main well-four horizontal branch well structure, consisting of a main well 1 and horizontal branch wells 2.

[0009] The main well 1 is a vertical shaft with a sealed bottom, and a horizontal branch well 2 is drilled at the geothermal reservoir 4. A perforated rectangular winged vortex generator 3 is installed indirectly at certain intervals on the outside of the horizontal branch well 2.

[0010] The heat exchange well adopts the form of a casing. The working fluid enters the heat exchange well from the outer pipe and flows to the bottom of the main well 1. The working fluid enters the inner pipe from the opening of the inner pipe of the horizontal branch well 2, and then flows out of the heat exchange well through the inner pipe for energy conversion treatment. The low-temperature working fluid is then reused repeatedly.

[0011] Furthermore, the perforated rectangular winged vortex generator 3 is based on a rectangular plate of a certain thickness, with a circular hole of the same size as the outer diameter of the inner pipe of the horizontal branch well left at the center point of the rectangular plate; small triangular wings 13 of the same size, with an included angle of 45° and adjacent inclinations opposite are built at the four corners of the rectangular plate; symmetrical circular holes 12 with their centers located on the midline of the short sides are made between the central circular hole 11 and the two short sides; the perforated rectangular winged plate is twisted 90° with the midline of the short sides as the axis.

[0012] Furthermore, adjacent winglets are welded together.

[0013] A method for installing an improved heat exchanger for a horizontal well with a perforated rectangular vortex diffuser includes the following steps:

[0014] A. Preparation of the perforated rectangular vortex generator 3:

[0015] A1. First, prefabricate a rectangular steel plate with a torsion angle of 90°, then cut the rectangular plate into small triangular wings of the same size, and weld the small wings at a 45° angle to the horizontal.

[0016] A2. Determine the size of the central circular hole of the vortex generator and the size of the circular holes on both sides of the rectangular plate according to the inner and outer pipe diameters of the preset horizontal branch well.

[0017] B. Installation of vertical shafts:

[0018] B1. Vertical shaft outer pipe: The outer pipe of the vertical shaft is made of steel pipe with a thermal conductivity of 40-45 [W / m·k]. The bottom of the outer pipe is closed and the top is open. The opening of the horizontal well outer pipe is reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well outer pipe is 0.10-0.12m.

[0019] B2. Vertical shaft inner pipe: The inner pipe of the vertical shaft is made of a pipe with a thermal conductivity of 0.020-0.025 [W / m·k]. The bottom of the inner pipe is closed and the top is open. The opening of the horizontal well inner pipe is reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well inner pipe is 0.07-0.08m.

[0020] C. Placement of horizontal branch well 2:

[0021] C1. Horizontal branch well outer pipe: The outer pipe material of the horizontal branch well is steel pipe with a thermal conductivity of 40-45 [W / m·k]. One side of the outer pipe is open and the other side is closed. Four horizontal branch well outer pipes are placed according to the reserved opening positions of the horizontal well outer pipes. The radius of the horizontal well outer pipe is 0.08-0.09m.

[0022] C2. Horizontal branch well inner pipe: The inner pipe material of the horizontal branch well is selected with a thermal conductivity of 0.020-0.025 [W / m·k]. One side of the inner pipe is open and the other side is closed. Perforated rectangular winged vortex generators are arranged on the inner pipe at intervals of 0.1mm. Then, four horizontal branch well inner pipes are placed according to the reserved opening positions of the horizontal well inner pipe. The radius of the horizontal well inner pipe is 0.050-0.055m.

[0023] Further, in step A1, adjacent winglets are oriented in opposite directions.

[0024] Further, in step A2, the radius of the central circular hole 11 is 50mm.

[0025] Furthermore, the inner tube is 0.5m shorter than the outer tube.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. Compared with the traditional dual-well EGS, this invention saves the drilling cost of dual vertical wells and avoids the problems of large water loss, fracturing fluid pollution of deep geological environment, and earthquake induction caused by hydraulic fracturing technology.

[0028] 2. Compared with ordinary coaxial casing heat exchange wells, it increases the lateral heat exchange range of the thermal reservoir, making full use of the thermal reservoir, so that the heat exchange range of a single-well heat exchange well is close to that of a traditional dual-well EGS system.

[0029] 3. It reduces the uncertainty of hydraulic fracturing-assisted EGS, fully achieving the goal of "extracting heat without extracting water";

[0030] 4. The application of the horizontal well vortex generator produces local turbulence at the vortex generator wing, which reduces the boundary layer thickness of the heat transfer medium and increases the convective heat transfer coefficient between the flowing medium and the outer wall of the heat exchange tube, thus greatly improving the heat transfer efficiency between the horizontal well and the thermal reservoir.

[0031] 5. The application of small holes and rectangular plate torsion angle in the horizontal well turbulence generator results in obvious vortex phenomena in the horizontal well. The occurrence of vortex phenomena allows the heat transfer medium near the inner and outer pipe walls of the horizontal well to be fully mixed, which facilitates the heat transfer medium in the pipe to exchange heat fully and evenly. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 Schematic diagram of an improved coaxial casing heat exchanger for a four-branch horizontal well.

[0034] Figure 2 Front view of a perforated rectangular vortex generator structure;

[0035] Figure 3 Top view of a perforated rectangular vortex generator structure;

[0036] Figure 4 Right view of a perforated rectangular vortex generator structure;

[0037] Figure 5 Front view of the internal casing structure of a horizontal well;

[0038] Figure 6 Right view of the internal casing structure of a horizontal well;

[0039] Figure 7 Top view of the internal casing structure of a horizontal well;

[0040] Figure 8 Fluid velocity contour plot;

[0041] Figure 9 Fluid streamline diagram;

[0042] Figure 10 Fluid temperature diagram;

[0043] Figure 11 Fluid pressure drop diagram.

[0044] In the diagram, 1. Main well 2. Horizontal branch well 3. Perforated rectangular vortex generator with wing 4. Thermal reservoir 5. Fluid outflow 6. Inner pipe wall 7. Fluid inflow 8. Outer pipe wall 9. Cement layer 10. Rock stratum 11. Central circular hole 12. Circular hole 13. Triangular wing Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments:

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0047] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0048] like Figures 1-7 As shown, the present invention relates to an improved horizontal well heat exchanger with a perforated rectangular winged vortex generator, comprising a heat exchange well, which is composed of a main well and horizontal branch wells.

[0049] The main well 1 is a vertical shaft, and horizontal branch wells are drilled at the geothermal reservoir 4. This invention adopts a structure of a single main well and four horizontal branch wells. Perforated rectangular winged vortex generators 3 are indirectly installed at certain intervals on the outer side of each horizontal branch well 2.

[0050] The heat exchanger of this invention adopts the form of a casing. The working fluid enters the heat exchange well from the outer pipe and flows to the bottom of the main well 1. Since the bottom of the main well is closed, the working fluid enters the inner pipe from the opening of the inner pipe of the horizontal branch well 2, and then flows out of the heat exchange well through the inner pipe for energy conversion. The low-temperature working fluid is then reused repeatedly, giving full play to the "heat extraction without water extraction" technology of the single-well heat exchange well.

[0051] The perforated rectangular winged vortex generator 3 is based on a rectangular plate of a certain thickness. A circular hole of the same size as the outer diameter of the inner pipe of the horizontal branch well is left at the center point of the rectangular plate. Triangular wings 13 of the same size, with an included angle of 45° and adjacent inclinations opposite are built at the four corners of the rectangular plate. Adjacent wings are welded together. Symmetrical circular holes 12 with their centers located on the midline of the short sides are made between the central circular hole 10 and the two short sides. The perforated rectangular winged plate is twisted 90° with the midline of the short sides as the axis.

[0052] The present invention discloses a method for installing a perforated rectangular vortex vortex generator in a horizontal well, comprising the following steps:

[0053] 1. Preparation of the perforated rectangular vortex generator 3:

[0054] 11. First, prefabricate a rectangular steel plate with a torsion angle of 90°, then cut the rectangular plate into triangular winglets 13 of the same size, and weld the winglets at a 45° angle to the horizontal (adjacent winglets tend to opposite directions);

[0055] 12. Determine the size of the central circular hole of the vortex generator and the size of the circular holes on both sides of the rectangular plate according to the inner and outer pipe diameters of the preset horizontal branch well 2. Generally, the radius of the central circular hole is 50mm.

[0056] Because it is used for the development of medium-deep geothermal energy, the heat exchange well is too large. The placement process of the heat exchange well is divided into the following two steps:

[0057] 2. Placement of vertical shafts:

[0058] 21. Vertical shaft outer pipe: The outer pipe of the vertical shaft is made of steel pipe with a thermal conductivity of 40-45 [W / m·k]. The bottom of the outer pipe is closed and the top is open. The opening of the horizontal well outer pipe is reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well outer pipe is 0.10-0.12m.

[0059] 22. Vertical Shaft Inner Tubing: The inner tubing of the vertical shaft is made of a material with a thermal conductivity of 0.020-0.025 [W / m·K]. The bottom of the inner tubing is sealed, while the top is open. The opening for the horizontal well inner tubing is pre-reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well inner tubing is 0.07-0.08m. Generally, the inner tubing length is 0.5m shorter than the outer tubing length.

[0060] 3. Placement of horizontal branch well 2:

[0061] 31. Horizontal branch well outer pipe: The outer pipe material of the horizontal branch well 2 is steel pipe with a thermal conductivity of 40-45 [W / m·k]. One side of the outer pipe is open and the other side is closed. Then, four horizontal branch well outer pipes are placed according to the reserved opening positions of the horizontal well outer pipes. The radius of the horizontal well outer pipe is 0.08-0.09m.

[0062] 32. Horizontal Branch Well Inner Pipe: The inner pipe of the horizontal branch well is made of a pipe with a thermal conductivity of 0.020-0.025 [W / m·K]. One side of the inner pipe is open, and the other side is closed. Perforated rectangular winged vortex generators are arranged on the inner pipe at 0.1mm intervals. Four horizontal branch well inner pipes are then placed according to the positions of the pre-reserved openings in the horizontal well inner pipe. The radius of the horizontal well inner pipe is 0.050-0.055m. Generally, the length of the inner pipe is 0.50m shorter than the length of the outer pipe.

[0063] Numerical simulation of the inner casing of a horizontal well

[0064] To verify the effectiveness of increasing the heat exchange efficiency of the horizontal branch pipe, this invention conducted a numerical simulation of the horizontal branch pipe. A 1m long heat exchange well and rock strata were plotted, and the fluid inside the heat exchange pipe was water. For rock strata 10, the parameters of the inner and outer pipes and the working fluid were assigned. This simulation adopted the TH coupling model. In the laminar flow physics field, the inlet velocity was 0.4m / s and the outlet pressure was set to 1.4e6pa. In the solid-fluid heat exchange physics field, the initial temperature of the solid domain was set to 105℃, and the initial temperatures of the working fluid, inner and outer pipes and vortex generator were set to 20℃.

[0065] like Figure 8-11 As shown, the presence of the torsion between the winglet and the rectangular plate causes a surge in fluid velocity at the winglet tip and within the tube, resulting in localized turbulence inside the horizontal tube. This significantly reduces the fluid boundary layer and enhances the convective heat transfer coefficient. The presence of perforations also creates pronounced vortices within the tube, promoting fluid mixing and increasing the volume of fluid in contact with the heat exchange wall.

[0066] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. An improved heat exchanger for a horizontal well with a perforated rectangular vortex generator, characterized in that: It includes a heat exchange well, which adopts a single main well-four horizontal branch well structure, consisting of a main well (1) and horizontal branch wells (2); The main well (1) is a vertical shaft with a closed bottom, and a horizontal branch well is drilled at the location of the geothermal reservoir (4); a perforated rectangular winged vortex generator (3) is indirectly installed at a certain interval on the outside of the horizontal branch well (2). The heat exchange well adopts the form of a casing. The working fluid enters the heat exchange well from the outer pipe and flows to the bottom of the main well (1). The working fluid enters the inner pipe from the opening of the inner pipe of the horizontal branch well (2) and then flows out of the heat exchange well through the inner pipe for energy conversion treatment. The low temperature working fluid is then reused repeatedly. The perforated rectangular winged vortex generator (3) is based on a rectangular plate of a certain thickness. A circular hole of the same size as the outer diameter of the inner pipe of the horizontal branch well is left at the center point of the rectangular plate. Triangular wings (13) of the same size, with an included angle of 45° and adjacent inclinations opposite are built at the four corners of the rectangular plate. Symmetrical circular holes (12) with the center located on the center line of the short sides are made between the central circular hole (11) and the two short sides. The perforated rectangular winged plate is twisted 90° with the center line of the short sides as the axis. The radius of the central circular hole (11) is 50mm.

2. The improved horizontal well heat exchanger with a perforated rectangular winged vortex generator according to claim 1, characterized in that: Adjacent winglets are welded together.

3. The method for installing a perforated rectangular vortex vortex generator in a horizontal well according to claim 1, characterized in that, Includes the following steps: A. Preparation of the perforated rectangular vortex generator (3): A1. First, prefabricate a rectangular steel plate with a torsion angle of 90°, then cut the rectangular plate into small triangular wings of the same size, and weld the small wings at a 45° angle to the horizontal. A2. Determine the size of the central circular hole of the vortex generator and the size of the circular holes on both sides of the rectangular plate according to the inner and outer pipe diameters of the preset horizontal branch well. B. Installation of vertical shafts: B1. Vertical shaft outer pipe: The outer pipe of the vertical shaft is made of steel pipe with a thermal conductivity of 40-45W / m•k. The bottom of the outer pipe is closed and the top is open. The opening of the horizontal well outer pipe is reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well outer pipe is 0.10-0.12m. B2. Vertical shaft inner pipe: The inner pipe of the vertical shaft is made of a pipe with a thermal conductivity of 0.020-0.025 W / m•k. The bottom of the inner pipe is closed and the top is open. The opening of the horizontal well inner pipe is reserved according to the location of the surveyed thermal reservoir. The radius of the vertical well inner pipe is 0.07-0.08m. C. Placement of horizontal branch well (2): C1. Horizontal branch well outer pipe: The outer pipe material of the horizontal branch well (2) is steel pipe with a thermal conductivity of 40-45W / m•k. One side of the outer pipe is open and the other side is closed. Then, according to the reserved position of the horizontal well outer pipe opening, four horizontal branch well outer pipes are placed. The radius of the horizontal well outer pipe is 0.08-0.09m. C2. Inner pipe of horizontal branch well: The inner pipe of the horizontal branch well (2) is made of a pipe with a thermal conductivity of 0.020-0.025 [W / m•k]. One side of the inner pipe is open and the other side is closed. Perforated rectangular winged vortex generators are arranged on the inner pipe at intervals of 0.1mm. Then, four inner pipes of horizontal branch wells are placed according to the reserved opening positions of the inner pipe of the horizontal well. The inner pipe radius of the horizontal well is 0.050-0.055m.

4. The method for installing a perforated rectangular vortex vortex generator in a horizontal well according to claim 3, characterized in that: Step A1: Adjacent winglets are inclined in opposite directions.

5. The method for installing a perforated rectangular vortex vortex generator in a horizontal well according to claim 3, characterized in that: Step A2, the radius of the central circular hole (11) is 50mm.

6. The method for installing a perforated rectangular vortex vortex generator in a horizontal well according to claim 3, characterized in that: The inner tube is 0.5m shorter than the outer tube.

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