Terrestrial heat experimental device capable of switching heat extraction scheme

Abstract

The invention relates to the technical field of geothermal energy research equipment, in particular to a geothermal experimental device capable of switching heat extraction schemes. Comprising a sand box, a constant-temperature circulating water tank communicated with the sand box, a water injection pipe and a water outlet pipe, wherein the water injection pipe and the water outlet pipe are longitudinally mounted in the sand box; the sand box is provided with a sand-filled heat storage layer, an upper water storage layer and a lower water storage layer; a transversely-arranged sleeve is installed in the sand-filled heat reservoir, the lower ends of the water injection pipe and the water outlet pipe are fixedly connected to the outer side wall of the sleeve, and a sleeve side opening is formed in the other side of the sleeve. Two converters capable of axially moving are installed in an inner cavity of the sleeve, and a full-through heat removal opening and a semi-through heat removal opening are formed in the side wall of each converter. The water injection pipe and the water outlet pipe are in butt joint with different heat supplying and taking openings by axially moving the converter, so that flexible switching of different heat taking schemes can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of geothermal energy research equipment, in particular to a geothermal experimental device with switchable heat extraction schemes. Background Art

[0002] The development of new stable clean energy is increasingly valued by energy workers. Geothermal energy, as an important component of new energy, has many advantages such as wide distribution, little impact from climate, and large resources. According to whether the geothermal heat exchanger will extract high-temperature groundwater in the formation, the medium-deep geothermal heat exchanger can be divided into thermal conductivity geothermal heat exchanger and mining and irrigation geothermal heat exchanger. The main difference between the two is that the thermal conductivity geothermal system achieves "taking heat but not water". This type of system uses geothermal wells as closed wellbores, that is, geothermal energy can only heat the circulating water in the well through heat conduction of the wellbore wall. It does not use groundwater as the circulating medium and will not affect the groundwater. Common thermal conductivity geothermal heat exchangers include single-well downhole heat exchangers and U-well downhole heat exchangers. The geothermal wells used in mining and irrigation geothermal development contain water filter pipes. During operation, high-temperature groundwater in the aquifer will be directly extracted by a submersible pump and sent to the ground for heat exchange. The circulating medium is groundwater. This direct heat exchange method obtains a higher single-well heat exchange capacity, but it will affect groundwater resources. In the field of geothermal energy research and teaching, it is necessary to frequently switch between different types of heat exchangers to study the working parameters such as heating temperature and heating efficiency of different types of heat exchangers under the same geothermal environment. For large-scale field experiments, not only is the initial investment large, but it is also restricted by the geographical environment and the influence of open-air operations. It is not easy to change the working conditions to explore multiple influencing factors. Indoor geothermal experimental devices have a certain migration ability, are not affected by the geographical environment when in use, require little investment, and can manually set experimental environment parameters. However, the existing indoor geothermal experimental devices can only simulate one heat extraction scheme, and cannot explore the adaptability of three downhole heat exchangers to different thermal reservoirs. If you want to explore the development effect of different downhole heat exchangers for a certain type of heat storage, you need to prepare more than three experimental equipment at the same time, which requires a larger test site and high experimental costs. For example, Chinese patent 2020112547838 discloses "A rock fracture diversion heat exchange test device and method", and the authorization announcement number is CN112326728B. The metering pump of the heat exchange test device is set on the water supply mechanism; the drainage mechanism is connected to the water outlet of the fracture, and the water outlet of the fracture is set at the top of the rock sample; the detection end of the first temperature sensor is fixedly set at the water inlet of the rock sample, the detection end of the second temperature sensor is fixedly set at the water outlet of the rock sample, the detection end of the third temperature sensor is set in the confining pressure chamber, and the detection ends of several fourth temperature sensors are set on the side wall of the rock sample; the metering pump, the first temperature sensor, the second temperature sensor, the third temperature sensor and several fourth temperature sensors are all connected to the controller. The device truly simulates the convective heat transfer process of rock fractures and improves the calculation accuracy of the convective heat transfer coefficient. However, there is only one working condition, and there is still a problem that the working condition cannot be changed to study multiple influencing factors. Summary of the invention

[0003] The purpose of the present invention is to provide a geothermal experimental device with a reasonable structure, easy to use and switchable heat extraction schemes, which can simulate three different heat extraction schemes and switch flexibly, and is used for studying the adaptability of different types of downhole heat exchangers to different thermal reservoirs.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A geothermal experimental device with switchable heat extraction schemes described in the present invention comprises a sand box provided with a sand-filled heat reservoir, a constant temperature circulating water tank connected to the inner cavity of the sand box, and a water injection pipe and a water outlet pipe longitudinally installed in the sand box, wherein an upper water storage layer is provided above the sand-filled heat reservoir in the sand box, and a lower water storage layer is provided below the sand-filled heat reservoir, the upper water storage layer and the sand-filled heat reservoir are isolated by an upper sand-proof sieve plate, and the lower water storage layer and the sand-filled heat reservoir are isolated by a lower sand-proof sieve plate; a transversely arranged casing is installed in the sand-filled heat reservoir, the lower ends of the water injection pipe and the water outlet pipe are fixedly connected to the outer side wall of the casing and are connected to the casing, a casing side opening is provided on the other side of the casing, and the casing side opening is connected to the injection pipe The water pipe or the water outlet pipe is coaxially arranged; the inner cavity of the sleeve is equipped with an axially movable first converter and a second converter, the first converter and the second converter are cylindrical structures whose outer walls adapt to the inner wall of the sleeve and are open at the inner end and closed at the outer end; the side wall of the cylindrical structure is provided with a full-through heat extraction port and a semi-through heat extraction port, the semi-through heat extraction port penetrates the side wall of one side of the cylindrical structure and is connected to the inner cavity of the sleeve, the full-through heat extraction port penetrates the two symmetrical side walls of the cylindrical structure, and partitions are fixedly arranged in the inner cavity of the cylindrical structure and on both sides of the full-through heat extraction port; the constant temperature circulating water tank is connected to the lower water storage layer of the sand box through the water supply pipe and is connected to the upper water storage layer of the sand box through the return pipe.

[0006] Through this scheme, the experimental device can simulate three different heat extraction schemes and switch them flexibly, which is used to study the adaptability of different types of downhole heat exchangers to different thermal reservoirs. It has a reasonable structure and is easy to use.

[0007] Preferably, the inner wall of the sleeve is provided with an internal thread, the outer walls of the first converter and the second converter are provided with external threads adapted to the internal thread, and the outer ends of the first converter and the second converter are fixedly mounted with rotating handles.

[0008] According to the present solution, the first converter and the second converter can be driven to move axially in the sleeve by rotating the handle, thereby switching between different heat extraction solutions.

[0009] Preferably, the casing is a straight tube that passes through both ends of the sand box, and the first converter and the second converter are symmetrically arranged at both ends of the casing.

[0010] According to the present solution, the first converter and the second converter are driven to move toward each other by rotating handles at both ends of the sand box to switch between different heat extraction solutions.

[0011] Preferably, the sleeve is a U-shaped tube, and the first converter and the second converter are respectively arranged at two ends of the sleeve.

[0012] Through this solution, the first converter and the second converter can be driven to move on the same side of the sand box to switch to different heat extraction solutions.

[0013] Preferably, the inner wall of the sleeve is provided with an axially extending slide rail, the outer walls of the first converter and the second converter are provided with slide grooves adapted to the slide rail, the outer ends of the first converter and the second converter are coaxially mounted with screws through sliding sleeves, the screws are mounted on the outer end of the sleeve through threaded fitting, and a rotating handle is fixedly mounted on the outer end of the screw.

[0014] According to this solution, the first converter and the second converter will not rotate when they move axially, which is conducive to accurate positioning when switching the heat extraction scheme.

[0015] Preferably, the inner cavity cross-section of the sleeve is a polygonal structure, the first converter and the second converter are polygonal cylindrical structures adapted to the inner cavity of the sleeve, the outer ends of the first converter and the second converter are coaxially installed with a screw through a sliding sleeve, the screw is installed at the outer end of the sleeve through threaded fitting, and a rotating handle is fixedly installed at the outer end of the screw.

[0016] Through this solution, the converter and the sleeve are closely matched and have a good sealing effect, and the converter will not rotate when moving axially, which is conducive to accurate positioning when switching the heat extraction scheme.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the experimental device can simulate three different heat extraction schemes and switch them flexibly, and is used to study the adaptability of different types of downhole heat exchangers to different thermal reservoirs; in one sand filling experiment, the heat extraction effects of three downhole heat exchangers can be simulated at the same time, and the pumping and reinjection heat supplement experiment can also be carried out after simulating the limit of single-well heat extraction without water extraction, which effectively saves experimental costs and equipment space; the hot water in the constant temperature water tank is injected from bottom to top into the sand-filled thermal reservoir through a circulating pump, so that the sand-filled thermal reservoir forms a geothermal gradient with low top and high bottom, which restores the thermal reservoir environment of the heat exchanger in the geothermal well to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of an embodiment of the present invention;

[0019] Figure 2 for Figure 1 A schematic diagram of the top view of the structure of the embodiment;

[0020] Figure 3 is a schematic diagram of a top view of the structure of another embodiment;

[0021] Figure 4 is a schematic diagram of a three-dimensional structure of a second converter with external threads;

[0022] Figure 5 It is a schematic diagram of a half-section structure of a casing with internal threads;

[0023] Figure 6 It is a schematic diagram of the cross-sectional structure of the sleeve and the second converter using the matching slide rail and slide groove.

[0024] Figure 7 It is a schematic diagram of the three-dimensional structure of the second converter with a slide slot. DETAILED DESCRIPTION

[0025] 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.

[0026] like Figure 1 As shown, the geothermal experimental device with a switchable heat extraction scheme described in the present invention includes a sand box 2 provided with a sand-filled heat reservoir 1, a constant temperature circulating water tank 13 connected to the inner cavity of the sand box 2, a water injection pipe 21 and a water outlet pipe 19 longitudinally installed in the sand box 2, and the sand box 2 can be a rectangular box or a circular or elliptical box, and a thermal insulation layer is attached to the outer wall of the sand box 2. An upper water storage layer 18 is provided above the sand-filled heat reservoir 1 in the sand box 2, and a lower water storage layer 9 is provided below. The upper water storage layer 18 is isolated from the sand-filled heat reservoir 1 by an upper sand-proof screen plate 81, and the lower water storage layer 9 is isolated from the sand-filled heat reservoir 1 by a lower sand-proof screen plate 8. When in use, the sand-filled thermal reservoir 1 is filled with sand and gravel, and the upper sand-proof screen plate 81 and the lower sand-proof screen plate 8 have sufficient strength to support the weight of the sand-filled thermal reservoir 1, and the upper sand-proof screen plate 81 and the lower sand-proof screen plate 8 allow water to flow through while blocking the sand and gravel in the sand-filled thermal reservoir 1 to prevent the sand and gravel from leaking into the upper water storage layer 18 and the lower water storage layer 9.

[0027] like Figure 1 , Figure 2As shown, a transversely arranged casing 4 is installed in the sand-filled thermal reservoir 1, and the casing 4 is made of a steel pipe or a stainless steel pipe with good thermal conductivity. The outer end of the casing 4 is welded and fixed to the side wall of the sand box 2; the lower ends of the water injection pipe 21 and the water outlet pipe 19 are fixedly connected to the outer wall of the casing 4 and communicated with the casing 4. A casing side opening 42 is provided on the other side of the casing 4, and the casing side opening 42 is coaxially arranged with the water injection pipe 21 or the water outlet pipe 19. Two casing side openings 42 are provided on the casing 4, as shown in FIG. Figure 5 As shown, one of the casing side openings 42 is coaxial with the water injection pipe 21, and the other is coaxial with the water outlet pipe 19. The upper ends of the water injection pipe 21 and the water outlet pipe 19 extend above the upper water storage layer 18 through the upper sand control screen plate 81.

[0028] A first converter 15 and a second converter 151 which can move axially are installed in the inner cavity of the sleeve 4. The first converter 15 and the second converter 151 are cylindrical structures whose outer walls are adapted to the inner wall of the sleeve 4 and whose inner ends are open and outer ends are closed. A full-through heat outlet 7 and a semi-through heat outlet 6 are arranged on the side wall of the cylindrical structure. The semi-through heat outlet 6 penetrates the side wall of one side of the cylindrical structure and is connected to the inner cavity of the cylindrical structure. When the semi-through heat outlet 6 is connected to the pipe mouth of the water injection pipe 21 or the pipe mouth of the water outlet pipe 19 connected to the sleeve 4, the water injection pipe 21 or the water outlet pipe 19 can be connected to the inner cavity of the cylindrical structure; the full-through heat outlet 7 penetrates the two symmetrical side walls of the cylindrical structure, and a partition 12 is fixedly arranged in the inner cavity of the sleeve 4 and on both sides of the full-through heat outlet 7. The through heat extraction port 7 is symmetrically formed with two side openings on both sides of the cylindrical structure. When one of the openings of the through heat extraction port 7 is connected to the pipe opening of the water injection pipe 21 or the pipe opening of the water outlet pipe 19 connected to the casing 4, it is equivalent to extending the lower end opening of the water injection pipe 21 or the water outlet pipe 19 through the rotating cylindrical structure to the sand-filled heat reservoir 1 below it. Figure 1 As shown, when the second converter 151 moves axially in the casing 4, the interface between the water injection pipe 21 and the casing 4 has three states. One is docking with the semi-through heat extraction port 6 at the right end of the second converter 151, so that the water injection pipe 21 is connected to the inner cavity of the second converter 151, and is connected to the inner cavity of the casing 4 through the opening at the right end of the second converter 151; the second is docking with the full-through heat extraction port 7 in the middle of the second converter 151, so that the lower end of the water injection pipe 21 passes through the second converter 151 and the casing 4 and extends to the sand-filled thermal reservoir 1; the third state is that the interface between the water injection pipe 21 and the casing 4 is blocked by the side wall at the left end of the second converter 151, so that the water injection pipe 21 becomes a blind pipe with a closed lower end. Similarly, due to the axial movement of the first converter 15, the interface between the water outlet pipe 19 and the casing 4 also has the above three states, which will not be repeated here.

[0029] The constant temperature circulating water tank 13 is connected to the lower water storage layer 9 of the sand box 2 through the water supply pipe 131, and is connected to the upper water storage layer 18 of the sand box 2 through the water return pipe 132. A water pump is connected in series to the water supply pipe 131 or the water return pipe 132, and the hot water in the constant temperature circulating water tank 13 is injected into the lower water storage layer 9 by the water pump, and the hot water in the lower water storage layer 9 gradually fills the entire sand box 2, and the water in the upper water storage layer 18 flows back to the constant temperature circulating water tank 13 through the water return pipe 132. During the circulation of hot water in the sand box 2, a geothermal gradient with low temperature at the top and high temperature at the bottom is formed, forming a simulated underground thermal reservoir environment.

[0030] In addition, in order to accurately measure the temperature in this simulated geothermal environment, e.g. Figure 1 , Figure 2 As shown, a plurality of temperature sensors 11 may be arranged in the flask 2 . Figure 1 In the embodiment, 16 temperature measuring zones are distributed on both sides of the casing 4 inside the sand-filled thermal reservoir 1, and 4 temperature sensors 11 are vertically distributed on each temperature measuring zone. The temperature sensors 11 are connected to a temperature recorder to monitor the temperature change of the reservoir through the temperature recorder.

[0031] In order to realize the axial movement of the first converter 15 and the second converter 151 in the casing 4 and accurately dock the water outlet pipe 19 or the water injection pipe 21, as shown in FIG. Figure 4 , Figure 5 As shown, as an embodiment of the present invention, the inner wall of the sleeve 4 is provided with an internal thread, the outer wall of the first converter 15 and the second converter 151 is provided with an external thread adapted to the internal thread, and the outer ends of the first converter 15 and the second converter 151 are fixedly mounted with a rotating handle 5. The first converter 15 or the second converter 151 can be driven to rotate by the rotating handle 5 to simultaneously move the first converter 15 or the second converter 151 axially. Of course, in order to accurately judge the rotation angle of the first converter 15 or the second converter 151 and whether it has moved to the docking position, a scale can be set on the sand box 2, and the distance between the rear end of the first converter 15 or the second converter 151 and the side wall of the sand box 2 is used to judge whether the axial movement is in place, and at the same time, the azimuth symbol is marked on the rotating handle 5 to judge whether the docking port on the side wall of the first converter 15 or the second converter 151 is facing the outlet pipe 19 or the injection pipe 21.

[0032] As a further improvement of the present invention, Figure 2 As shown, the sleeve 4 is a straight tube that passes through both ends of the sand box 2, and the first converter 15 and the second converter 151 are symmetrically arranged at both ends of the sleeve 4. In this embodiment, when switching the heat extraction state in the experiment, the first converter 15 and the second converter 151 need to be adjusted at both ends of the sand box 2 respectively.

[0033] As another embodiment of the present invention, Figure 3As shown, the sleeve 4 is a U-shaped tube, and the two ends of the U-shaped tube are two straight tubes arranged thereon, one end of the two straight tubes passes through the side wall of the sleeve 4 for installing the first converter 15 and the second converter 151, and the other ends of the two straight tubes are connected by an arc-shaped elbow. At this time, the first converter 15 and the second converter 151 are respectively arranged at the two ends of the sleeve 4 but are located on the same side of the sand box 2. When switching the heat extraction state in the experiment, the first converter 15 and the second converter 151 can be adjusted as long as they are on the same side of the sand box 2.

[0034] like Figure 6 , Figure 7 As shown, as another embodiment of the present invention that is further improved, the inner wall of the sleeve 4 is provided with an axially extending slide rail 41, and the outer end of the sleeve 4 is provided with an internal thread or a fixedly connected internal thread sleeve. The outer walls of the first converter 15 and the second converter 151 are provided with a slide groove 152 adapted to the slide rail 41, and the outer ends of the first converter 15 and the second converter 151 are coaxially mounted with a screw rod 51 through a sleeve 153, one end of the sleeve 153 is fixedly welded to the center of the end cover at the outer end of the first converter 15 or the second converter 151, and the center of the other end of the sleeve 153 is provided with a center hole, and the inner end of the screw rod 51 is provided with an annular groove adapted to the center hole, which is clamped in the center hole of the sleeve 153, and the screw rod 51 is installed at the outer end of the sleeve 4 through threaded matching, and the outer end of the screw rod 51 is fixedly installed with a rotating handle 5. When the rotating handle 5 rotates, the screw rod 51 is driven to rotate, and when the screw rod 51 rotates, it moves axially relative to the sleeve 4, pushing the sleeve 153 to move axially. Since the sleeve 153 is connected to the screw rod 51 through the annular groove and the center hole, the annular groove rotates in the center hole when the screw rod 51 rotates, so the rotation of the screw rod 51 can only push the first converter 15 or the second converter 151 to move axially without rotating it. Therefore, in this embodiment, as long as a scale is set on the outer end of the sleeve 4 or the side wall of the sand box 2 nearby, it can be judged whether the first converter 15 or the second converter 151 has moved to a suitable position according to the distance of the screw rod 51 extending into the sleeve 4 shown by the scale.

[0035] In addition, as a further improvement of the present invention, the inner cavity cross-section of the sleeve 4 is a polygonal structure, and an internal thread or an internal thread sleeve is fixedly connected to the outer end of the sleeve 4. The first converter 15 and the second converter 151 are polygonal cylindrical structures adapted to the inner cavity of the sleeve 4. The outer ends of the first converter 15 and the second converter 151 are coaxially installed with a screw 51 through a sliding sleeve 153. The screw 51 is installed on the outer end of the sleeve 4 through threaded cooperation, and a rotating handle 5 is fixedly installed on the outer end of the screw 51.

[0036] During the preparation process, first fill the sand box 2 with sand, open the constant temperature circulating water tank 13 and set it to the temperature required for the experiment, turn on the formation water circulation pump 16, and the heated circulating water enters the lower water storage layer 9, flows into the sand-filled thermal reservoir 1 through the lower sand-proof screen plate 8, and seeps upward in the sand-filled thermal reservoir 1 and conducts seepage heat transfer. The circulating water enters the upper water storage layer 18 through the upper sand-proof screen plate 81 and is then pumped into the constant temperature water tank 13 for reheating. This cycle is repeated until the reservoir temperature remains unchanged, and then the circulation pump is turned off to stop the circulation. Otherwise, the reservoir temperature will not meet the experimental standards, or the heating will be uneven, and good experimental results cannot be achieved.

[0037] During the experiment, the switching of the heat extraction interface is achieved by rotating the handle 5 to push the converter, such as Figure 1 As shown; as a simulation experiment of the first heat extraction scheme, if the experiment simulates the process of pumping and recharging for heat extraction, in this experimental state, it is required to inject water into the sand-filled thermal reservoir 1 from one wellhead while extracting heat from another wellhead; at this time, the water injection pipe 21 and the water outlet pipe 19 simulate the water injection wellhead and the heat extraction wellhead respectively. For the embodiment in which both the first converter 15 and the second converter 151 use the slide rail and the slide groove to cooperate with the casing 4, turn the left rotating handle 5 to push the second converter 151 to move axially, and observe the scale indication on the casing 4 at the same time. When the full-through heat extraction port 7 on the second converter 151 is docked with the nozzle of the water injection pipe 21, stop the rotating handle; then, turn the right rotating handle to push the first converter 15 to move axially, observe the scale indication on the casing 4, and stop the rotating handle when the full-through heat extraction port on the first converter 15 is docked with the nozzle of the water outlet pipe 19. Of course, for the embodiment in which both the first converter 15 and the second converter 151 use threads to cooperate with the sleeve 4, after rotating the handle 5 and observing that the scale on the sleeve 4 indicates that it has moved axially into place, it is also necessary to observe the direction mark on the rotating handle 5 to determine that the direction of the full-through heat extraction port 7 is facing upward and docking with the pipe mouth of the water injection pipe 21 or the water outlet pipe 19.

[0038] After the first converter 15 and the second converter 151 are moved into place, cold water is injected into the sand-filled thermal reservoir 1 from the water injection pipe 21, and hot water is produced from the water outlet pipe 19. The produced hot water enters the water injection pipe 21 through an external circulation pump to form a pumping and recharging cycle.

[0039] As a simulation experiment of the second heat extraction scheme, if the experiment simulates the U-shaped well heat extraction process, in this experimental state, it is required to inject water into the casing 4 from one wellhead, and then extract heat from another wellhead after heat exchange through the casing 4; at this time, the water injection pipe 21 and the water outlet pipe 19 simulate the water injection wellhead and the heat extraction wellhead respectively. Turn the left rotating handle 5 to push the second converter 151 to move axially, and observe the scale indication on the casing 4 at the same time. When the semi-through heat extraction port 6 on the second converter 151 is docked with the pipe mouth of the water injection pipe 21, stop the rotating handle; then, turn the right rotating handle to push the first converter 15 to move axially, observe the scale indication on the casing 4, and stop the rotating handle when the semi-through heat extraction port on the first converter 15 is docked with the pipe mouth of the water outlet pipe 19. Cold water is injected from the water injection pipe 21, and hot water enters the inner cavity of the casing 4 from the semi-through heat extraction port 6 on the second converter 151, and exchanges heat with the sand-filled heat reservoir 1 through the outer wall of the casing 4. The hot water after heat exchange is produced from the water outlet pipe 19 through the semi-through heat extraction port on the first converter 15. The produced hot water enters the water injection pipe 21 again through an external circulation pump to form a U-shaped well heat extraction without water extraction circulation.

[0040] As a simulation experiment of the third heat extraction scheme, if the experiment simulates the process of extracting heat from a single well without taking water, in this experimental state, it is required to inject water from a wellhead, and then extract heat from the same wellhead after heat exchange through the well wall; at this time, one of the water injection pipe 21 and the water outlet pipe 19 can be selected as the simulation well. Figure 1 In the embodiment, the water injection pipe 21 is used as a simulated well, and a thinner pipe is inserted into the water injection pipe 21 as a single-well water outlet pipe 211. The second converter 151 is pushed to move axially by turning the rotating handle 5 on the left side. When the scale on the casing 4 indicates that the pipe opening at the lower end of the water injection pipe 21 is neither connected to the semi-through heat extraction port 6 nor to the full-through heat extraction port 7, but is pushed to block the side wall of the second converter 151, it means that the second converter 151 is pushed to move into place. At this time, cold water is injected into the annulus between the water injection pipe 21 and the single-well water outlet pipe 211. The hot water after heat exchange with the sand-filled thermal reservoir 1 at the lower end of the water injection pipe 21 through the side wall of the water injection pipe 21 is produced from the single-well water outlet pipe 211. Temperature measuring points are provided at the inlet of the water injection pipe 21 and the outlet of the single-well water outlet pipe 211 and connected to temperature recorders to monitor the inlet and outlet water temperatures in real time.

[0041] In the above process, the temperature recorder monitors and records the temperature in the reservoir and at the inlet and outlet of the working fluid in real time. By inverting the recorded temperature data, the temperature distribution in the reservoir can be obtained.

[0042] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A geothermal experimental device with switchable heat extraction schemes, comprising a sand box (2) provided with a sand-filled heat reservoir (1), a constant temperature circulating water tank (13) connected to the inner cavity of the sand box (2), a water injection pipe (21) and a water outlet pipe (19) longitudinally installed in the sand box (2), characterized in that: An upper water storage layer (18) is arranged above the sand-filled thermal reservoir (1) in the sand box (2), and a lower water storage layer (9) is arranged below the sand-filled thermal reservoir (1); the upper water storage layer (18) is isolated from the sand-filled thermal reservoir (1) by an upper sand-proof screen plate (81), and the lower water storage layer (9) is isolated from the sand-filled thermal reservoir (1) by a lower sand-proof screen plate (8); a transversely arranged casing (4) is installed in the sand-filled thermal reservoir (1); the lower ends of the water injection pipe (21) and the water outlet pipe (19) are fixedly connected to the outer wall of the casing (4) and communicated with the casing (4); a casing side opening (42) is arranged on the other side of the casing (4); the casing side opening (42) is arranged coaxially with the water injection pipe (21) or the water outlet pipe (19); an axially movable first rotating shaft is installed in the inner cavity of the casing (4); The first converter (15) and the second converter (151) are cylindrical structures whose outer walls are adapted to the inner wall of the sleeve (4) and whose inner ends are open and whose outer ends are closed. A full-through heat extraction port (7) and a semi-through heat extraction port (6) are arranged on the side wall of the cylindrical structure. The semi-through heat extraction port (6) penetrates the side wall of one side of the cylindrical structure and is connected to the inner cavity of the cylindrical structure. The full-through heat extraction port (7) penetrates the symmetrical two side walls of the cylindrical structure. A partition plate (12) is fixedly arranged in the inner cavity of the cylindrical structure and on both sides of the full-through heat extraction port (7). The constant temperature circulating water tank (13) is connected to the lower water storage layer (9) of the sand box (2) through a water supply pipe (131) and is connected to the upper water storage layer (18) of the sand box (2) through a water return pipe (132).

2. A geothermal experimental device with switchable heat extraction scheme according to claim 1, characterized in that: The inner wall of the sleeve (4) is provided with an internal thread, the outer walls of the first converter (15) and the second converter (151) are provided with external threads adapted to the internal thread, and the outer ends of the first converter (15) and the second converter (151) are fixedly mounted with a rotating handle (5).

3. A geothermal experimental device with switchable heat extraction scheme according to claim 1 or 2, characterized in that: The casing (4) is a straight pipe that passes through both ends of the sand box (2), and the first converter (15) and the second converter (151) are symmetrically arranged at both ends of the casing (4).

4. A geothermal experimental device with switchable heat extraction scheme according to claim 1, characterized in that: The sleeve (4) is a U-shaped tube, and the first converter (15) and the second converter (151) are respectively arranged at two ends of the sleeve (4).

5. A geothermal experimental device with switchable heat extraction scheme according to claim 1, characterized in that: The inner wall of the sleeve (4) is provided with an axially extending slide rail (41), and the outer walls of the first converter (15) and the second converter (151) are provided with slide grooves (152) adapted to the slide rail (41). The outer ends of the first converter (15) and the second converter (151) are coaxially mounted with a screw rod (51) via a sliding sleeve (153), and the screw rod (51) is mounted on the outer end of the sleeve (4) via threaded engagement, and a rotating handle (5) is fixedly mounted on the outer end of the screw rod (51).

6. A geothermal experimental device with switchable heat extraction scheme according to claim 1, characterized in that: The inner cavity cross-section of the sleeve (4) is a polygonal structure. The first converter (15) and the second converter (151) are polygonal cylindrical structures adapted to the inner cavity of the sleeve (4). The outer ends of the first converter (15) and the second converter (151) are coaxially mounted with a screw rod (51) via a sliding sleeve (153). The screw rod (51) is mounted on the outer end of the sleeve (4) via threaded engagement. A rotating handle (5) is fixedly mounted on the outer end of the screw rod (51).

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