A geothermal experimental device with switchable heat extraction scheme

Abstract

The present application relates to the technical field of geothermal energy research equipment, in particular to a geothermal experimental device with switchable heat extraction scheme. The device comprises a sand box, a constant temperature circulating water tank communicated with the sand box, a water injection pipe and a water outlet pipe longitudinally installed in the sand box, the sand box is provided with a sand-filled thermal reservoir, an upper water storage layer and a lower water storage layer; a sleeve pipe is horizontally installed in the sand-filled thermal 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 pipe, a sleeve pipe side opening is arranged on the other side of the sleeve pipe; two converters axially movable are installed in the inner cavity of the sleeve pipe, full-through heat extraction ports and half-through heat extraction ports are arranged on the side wall of the converters. By axially moving the converters, the water injection pipe and the water outlet pipe can be connected with different heat extraction ports, so that flexible switching of different heat extraction schemes can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal energy research equipment, in particular to a geothermal experimental device capable of switching heat extraction schemes. BACKGROUND

[0002] Developing new stable clean energy is more and more valued by energy workers. Geothermal energy, as an important part of new energy, has many advantages such as wide distribution, less affected by climate, large resource quantity, etc. According to whether the geothermal heat exchanger will extract high-temperature underground water in the formation, the medium-deep geothermal heat exchanger can be divided into heat conduction type geothermal heat exchanger and pumping type geothermal heat exchanger. The main difference between the two is that the heat conduction type geothermal system achieves "heat taking without water taking". This system uses a closed wellbore for geothermal well, that is, geothermal energy can only heat the circulating water in the well through the heat conduction of the wellbore wall, and does not use underground water as the circulating medium, which will not affect the underground water. Common heat conduction type geothermal heat exchangers include single-well downhole heat exchanger and U-shaped well downhole heat exchanger. The geothermal well used in pumping type geothermal development contains a water filter pipe, which will directly extract high-temperature underground water from the aquifer through a submersible pump during operation to heat on the ground. The circulating medium is underground water. This direct heat exchange method obtains a higher single-well heat exchange capacity, but it will affect the underground water resources. In the field of geothermal energy research and teaching, it is often necessary to switch between different types of heat exchangers to study the heat taking temperature, heat taking efficiency and other working parameters of different types of heat exchangers in the same geothermal environment. For large-scale field experiments, not only the initial investment is large, but also it is affected by geographical environment and open-air operation, and it is not easy to change the working conditions for multi-influence factor exploration. The indoor geothermal experimental device has a certain migration ability, is not affected by the geographical environment during use, and has low investment and can artificially set the experimental environment parameters. However, the existing indoor geothermal experimental device can only simulate one heat taking scheme, and cannot explore the adaptability of the 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 thermal reservoir, you need to prepare more than three experimental devices, which requires a large test site and high experimental cost. For example, the Chinese patent 2020112547838 discloses a rock fracture flow and heat exchange test device and method, and the authorization announcement number is CN112326728B. The heat exchange test device measures the pump arranged on the water supply mechanism; the drainage mechanism is communicated with the water outlet of the fracture, and the water outlet of the fracture is arranged at the top of the rock sample; the detection end of the first temperature sensor is fixedly arranged at the water inlet of the rock sample, the detection end of the second temperature sensor is fixedly arranged at the water outlet of the rock sample, the detection end of the third temperature sensor is arranged in the confining pressure chamber, and the detection ends of the plurality of fourth temperature sensors are arranged on the side wall of the rock sample; the metering pump, the first temperature sensor, the second temperature sensor, the third temperature sensor and the plurality of fourth temperature sensors are connected with 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, it still has only one working condition, and cannot change the working condition for multi-influence factor research. SUMMARY

[0003] The geothermal experimental device with switchable heat extraction schemes provided by the application has a reasonable structure and is convenient to use, can simulate three different heat extraction schemes and switch flexibly, and is used for researching adaptability of different types of downhole heat exchangers to different heat reservoirs.

[0004] To achieve the above object, the application adopts the following technical scheme:

[0005] The geothermal experimental device with switchable heat extraction schemes comprises a sand box provided with a sand-filled heat reservoir, a constant-temperature circulating water tank in communication with an inner cavity of the sand box, a water injection pipe and a water outlet pipe vertically installed in the sand box, an upper water storage layer arranged above the sand-filled heat reservoir in the sand box, and a lower water storage layer arranged below the sand-filled heat reservoir, wherein the upper water storage layer is isolated from the sand-filled heat reservoir by an upper sand-prevention screen plate, and the lower water storage layer is isolated from the sand-filled heat reservoir by a lower sand-prevention screen plate; a sleeve pipe is horizontally arranged in the sand-filled heat reservoir, lower ends of the water injection pipe and the water outlet pipe are fixedly connected to an outer sidewall of the sleeve pipe and are in communication with the sleeve pipe, a sleeve pipe side opening is arranged on the other side of the sleeve pipe, and the sleeve pipe side opening is coaxially arranged with the water injection pipe or the water outlet pipe; the inner cavity of the sleeve pipe is provided with a first converter and a second converter which are axially movable, the first converter and the second converter are cylindrical structures with outer walls matched with the inner wall of the sleeve pipe and inner ends open and outer ends closed, full-through heat extraction openings and half-through heat extraction openings are arranged on the sidewall of the cylindrical structure, the half-through heat extraction openings are in communication with the inner cavity of the sleeve pipe by penetrating the sidewall on one side of the cylindrical structure, the full-through heat extraction openings penetrate the two sidewalls of the cylindrical structure, and baffles are fixedly arranged in the inner cavity of the cylindrical structure on both sides of the full-through heat extraction openings; the constant-temperature circulating water tank is in communication with the lower water storage layer of the sand box through a water supply pipe and is in communication with the upper water storage layer of the sand box through a water return pipe.

[0006] Through the scheme, the experimental device can simulate three different heat extraction schemes and switch flexibly, is used for researching adaptability of different types of downhole heat exchangers to different heat reservoirs, has a reasonable structure, and is convenient to use.

[0007] Preferably, the inner wall of the sleeve pipe is provided with internal threads, the outer wall of the first converter and the second converter is provided with external threads matched with the internal threads, and a rotating handle is fixedly installed at the outer end of the first converter and the second converter.

[0008] Through the scheme, the rotating handle can be used to drive the first converter and the second converter to axially move in the sleeve pipe, so that different heat extraction schemes are switched.

[0009] Preferably, the sleeve pipe is a straight pipe penetrating through both ends of the sand box, and the first converter and the second converter are symmetrically arranged at both ends of the sleeve pipe.

[0010] The first converter and the second converter are driven to move towards each other by rotating handles at two ends of the sand box, and different heat taking schemes are switched.

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

[0012] According to the scheme, the first converter and the second converter can be driven to move at the same side of the sand box, and different heat taking schemes are switched.

[0013] Preferably, the inner wall of the sleeve is provided with an axially extending sliding rail, the outer wall of the first converter and the second converter is provided with a sliding groove matched with the sliding rail, the outer end of the first converter and the second converter is coaxially installed with a screw rod through a sliding sleeve, the screw rod is installed at the outer end of the sleeve through thread cooperation, and the outer end of the screw rod is fixedly installed with a rotating handle.

[0014] According to the scheme, the first converter and the second converter will not rotate when moving axially, and accurate positioning is facilitated when switching the heat taking scheme.

[0015] Preferably, the inner cavity of the sleeve is a polygonal structure, the first converter and the second converter are polygonal cylindrical structures matched with the inner cavity of the sleeve, the outer end of the first converter and the second converter is coaxially installed with a screw rod through a sliding sleeve, the screw rod is installed at the outer end of the sleeve through thread cooperation, and the outer end of the screw rod is fixedly installed with a rotating handle.

[0016] According to the scheme, the converter is matched with the sleeve closely, the sealing effect is good, and the converter will not rotate when moving axially, and accurate positioning is facilitated when switching the heat taking scheme.

[0017] Compared with the prior art, the experimental device can simulate three different heat taking schemes and switch flexibly, is used for researching adaptability of different types of downhole heat exchangers to different thermal reservoirs, can simultaneously simulate heat taking effects of three downhole heat exchangers in one sand filling experiment, can also simulate a water pumping and recharge heat supplement experiment after a single well heat taking and no water taking limit, and effectively saves experimental cost and equipment space, and hot water in the constant temperature water tank is injected into the sand filling thermal reservoir from bottom to top through the circulating pump, so that the sand filling thermal reservoir forms a geothermal gradient of low on the top and high on the bottom, and the thermal reservoir environment of the heat exchanger in the geothermal well is restored to the maximum extent. BRIEF DESCRIPTION OF DRAWINGS

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

[0019] Figure 2 It is a structural schematic view of an embodiment of the present application; Figure 1

[0020] ​Figure 3 is a top view structural schematic diagram of another embodiment;

[0021] Figure 4 is a perspective view structural schematic diagram of a second converter with external threads;

[0022] Figure 5 is a half-section view structural schematic diagram of a sleeve with internal threads;

[0023] Figure 6 is a section view structural schematic diagram of a sleeve and a second converter using a sliding rail and a sliding groove.

[0024] Figure 7 is a perspective view structural schematic diagram of a second converter with a sliding groove. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0026] As shown in Figure 1 , the geothermal experimental device with switchable heat extraction scheme comprises a sand box 2 provided with a sand-filled thermal reservoir 1, a constant-temperature circulating water tank 13 in communication with 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. The sand box 2 can be a rectangular box or a circular or elliptical box, and a heat preservation layer is attached to the outer wall of the sand box 2. 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 and the sand-filled thermal reservoir 1 are isolated by an upper sand prevention screen plate 81, and the lower water storage layer 9 and the sand-filled thermal reservoir 1 are isolated by a lower sand prevention screen plate 8. In use, the sand-filled thermal reservoir 1 is filled with sand, the upper sand prevention screen plate 81 and the lower sand prevention screen plate 8 have sufficient strength to support the weight of the sand-filled thermal reservoir 1, and the upper sand prevention screen plate 81 and the lower sand prevention screen plate 8 allow water flow while preventing sand in the sand-filled thermal reservoir 1 from leaking into the upper water storage layer 18 and the lower water storage layer 9.

[0027] As shown in Figure 1 , Figure 2As shown, the sand-filled thermal reservoir 1 is provided with a transversely arranged casing 4 made of steel pipe or stainless steel pipe with good heat conduction effect. The outer end of the casing 4 is welded to the side wall of the sand box 2, and the lower end of the water injection pipe 21 and the water outlet pipe 19 are fixedly connected to the outer side wall of the casing 4 and communicate with the casing 4. A casing side opening 42 is arranged on the other side of the casing 4, which is coaxially arranged with the water injection pipe 21 or the water outlet pipe 19, and two casing side openings 42 are arranged on the casing 4, as shown in Figure 5 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 81.

[0028] The inner cavity of the casing 4 is provided with an axially movable first converter 15 and a second converter 151, which are cylindrical structures with outer wall matched with the inner wall of the casing 4 and open inner end and closed outer end. The side wall of the cylindrical structure is provided with a full-through heat extraction port 7 and a half-through heat extraction port 6. The half-through heat extraction port 6 penetrates the side wall of one side of the cylindrical structure to communicate with the inner cavity of the cylindrical structure, and when the half-through heat extraction port 6 is docked with the pipe opening of the water injection pipe 21 or the water outlet pipe 19 connected to the casing 4, it can communicate the water injection pipe 21 or the water outlet pipe 19 with the inner cavity of the cylindrical structure. The full-through heat extraction port 7 penetrates the two symmetrical side walls of the cylindrical structure, and the two sides of the full-through heat extraction port 7 are fixedly provided with a baffle 12 in the inner cavity of the casing 4. The full-through heat extraction port 7 forms two side openings on the two sides of the cylindrical structure, and one of the openings of the full-through heat extraction port 7 is equivalent to extending the lower end opening of the water injection pipe 21 or the water outlet pipe 19 to the sand-filled thermal reservoir 1 below the cylindrical structure when it is docked with the pipe opening of the water injection pipe 21 or the water outlet pipe 19 connected to the casing 4, as shown in Figure 1 As shown, when the second converter 151 moves axially in the casing 4, there are three states of the interface between the water injection pipe 21 and the casing 4. One is that the half-through heat extraction port 6 at the right end of the second converter 151 is docked, so as to communicate the water injection pipe 21 with the inner cavity of the second converter 151, and communicate with the inner cavity of the casing 4 through the opening at the right end of the second converter 151; the second is that the full-through heat extraction port 7 in the middle of the second converter 151 is docked, so as to make the lower end of the water injection pipe 21 extend to the sand-filled thermal reservoir 1 through the second converter 151 and the casing 4; 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 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 tank 2 through a water supply pipe 131 and to the upper water storage layer 18 of the sand tank 2 through a 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 water pump is used to inject hot water in the constant-temperature circulating water tank 13 into the lower water storage layer 9, and the hot water in the lower water storage layer 9 gradually fills the entire sand tank 2, and the water in the upper water storage layer 18 returns to the constant-temperature circulating water tank 13 through the water return pipe 132. During the circulation of the hot water in the sand tank 2, a geothermal gradient with low temperature on the top and high temperature on the bottom is formed, and a simulated underground hot reservoir environment is formed.

[0030] In addition, in order to accurately measure the temperature in the simulated geothermal environment, a plurality of temperature sensors 11 can be arranged in the sand tank 2, as shown in Figure 1 、 Figure 2 Figure 1 In the embodiment, 16 temperature measuring belts are arranged on both sides of the casing pipe 4 in the sand-filled hot reservoir 1, and 4 temperature sensors 11 are vertically arranged on each temperature measuring belt. The temperature sensors 11 are connected to a temperature recorder, and the temperature change of the reservoir is monitored 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 pipe 4 and the accurate butt joint of the water outlet pipe 19 or the water injection pipe 21, as shown in Figure 4 、 Figure 5 as an embodiment of the present application, the inner wall of the casing pipe 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 matched with the internal thread, and a rotating handle 5 is fixedly installed at the outer end of the first converter 15 and the second converter 151. The rotating handle 5 drives the rotation of the first converter 15 or the second converter 151, which simultaneously moves axially. Of course, in order to accurately determine the angle of rotation of the first converter 15 or the second converter 151 and whether it moves to the butt joint position, a scale can be arranged on the sand tank 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 tank 2 is used to determine whether the axial movement is in place. Meanwhile, the direction symbol is marked on the rotating handle 5 to determine whether the butt joint port on the side wall of the first converter 15 or the second converter 151 is directed to the water outlet pipe 19 or the water injection pipe 21.

[0032] As a further improvement of the present application, as shown in Figure 2 the casing pipe 4 is a straight pipe penetrating through both ends of the sand tank 2, and the first converter 15 and the second converter 151 are symmetrically arranged at both ends of the casing pipe 4. In this embodiment, the first converter 15 and the second converter 151 need to be adjusted at both ends of the sand tank 2 when switching the heat extraction state in the experiment.

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

[0034] As shown in the drawings, Figure 6 , Figure 7 As shown, as a further improved embodiment of the present application, 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 wall of the first converter 15 and the second converter 151 is provided with a sliding groove 152 matched with the slide rail 41, and the outer end of the first converter 15 and the second converter 151 is coaxially mounted with a screw rod 51 through a sliding sleeve 153. One end of the sliding sleeve 153 is fixedly welded at the center of the end cover of the outer end of the first converter 15 or the second converter 151, and the other end of the sliding sleeve 153 is provided with a center hole in the center. The inner end of the screw rod 51 is provided with a ring groove matched with the center hole, and the ring groove is clamped in the center hole of the sliding sleeve 153. The screw rod 51 is mounted at the outer end of the sleeve 4 through threaded cooperation, and the outer end of the screw rod 51 is fixedly mounted with a rotating handle 5. When the rotating handle 5 rotates, it drives the screw rod 51 to rotate, and when the screw rod 51 rotates, it moves axially relative to the sleeve 4, pushing the sliding sleeve 153 to move axially. Since the sliding sleeve 153 and the screw rod 51 are connected through the ring groove and the center hole, when the screw rod 51 rotates, the ring groove rotates in the center hole, so that the rotation of the screw rod 51 can only push the first converter 15 or the second converter 151 to move axially and cannot make it rotate. Therefore, in this embodiment, only a scale is arranged on the side wall of the sand box 2 at the outer end or near the outer end of the sleeve 4, and the distance of the screw rod 51 extending into the sleeve 4 shown by the scale can be used to determine whether the first converter 15 or the second converter 151 is moved to the appropriate position.

[0035] In addition, as a further improvement of the present application, the inner cavity of the sleeve 4 is a polygonal structure, the outer end of the sleeve 4 is provided with an internal thread or a fixedly connected internal thread sleeve, the first converter 15 and the second converter 151 are polygonal cylindrical structures matched with the inner cavity of the sleeve 4, the outer end of the first converter 15 and the second converter 151 is coaxially mounted with a screw rod 51 through a sliding sleeve 153, and the screw rod 51 is mounted at the outer end of the sleeve 4 through threaded cooperation. The outer end of the screw rod 51 is fixedly mounted with a rotating handle 5.

[0036] In the preparation process, the sand box 2 is filled with sand, the constant temperature circulating water tank 13 is opened and set to the required temperature, the formation water circulating pump 16 is opened, the heated circulating water enters the lower water storage layer 9, flows into the sand-filled thermal reservoir 1 through the lower sand control screen 8, seeps upward in the sand-filled thermal reservoir 1 and conducts heat, the circulating water enters the upper water storage layer 18 through the upper sand control screen 81 and is pumped into the constant temperature water tank 13 for heating again, and the cycle is repeated until the reservoir temperature remains unchanged, and the circulating pump is stopped. Otherwise, the reservoir temperature cannot reach the required standard, or the heating is uneven, and good experimental results cannot be obtained.

[0037] In the experiment, the switching of the heat extraction interface is achieved by rotating the handle 5 to push the converter, as shown in Figure 1 As the first heat extraction scheme, if the experiment simulates the water pumping and recharging heat extraction process, in this experimental state, water is required to be injected into the sand-filled thermal reservoir 1 from one wellhead while heat is extracted 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 the first converter 15 and the second converter 151 are both sliding rail and groove matched with the sleeve 4, the left rotating handle 5 is rotated to push the second converter 151 to move axially, and the scale on the sleeve 4 is observed to indicate when the full-through heat extraction port 7 on the second converter 151 is connected with the pipe opening of the water injection pipe 21, and the rotating handle is stopped; then, the right rotating handle is rotated to push the first converter 15 to move axially, and the scale on the sleeve 4 is observed to indicate when the full-through heat extraction port on the first converter 15 is connected with the pipe opening of the water outlet pipe 19, and the rotating handle is stopped. Of course, for the embodiment in which the first converter 15 and the second converter 151 are both thread matched with the sleeve 4, after the rotating handle 5 is rotated and the scale on the sleeve 4 is observed to indicate that it has moved axially to the right position, the direction mark on the rotating handle 5 is also observed to determine that the direction of the full-through heat extraction port 7 is upward and connected with the pipe opening of the water injection pipe 21 or the water outlet pipe 19.

[0038] After the first converter 15 and the second converter 151 are both moved to the right position, 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, and the produced hot water enters the water injection pipe 21 again through the external circulating pump to form a water pumping and recharging cycle.

[0039] As a second heat extraction scheme, if the experiment simulates a U-shaped well heat extraction process, in this experimental state, water is injected from one wellhead into the casing 4, and after heat exchange through the casing 4, heat is extracted from the other wellhead; at this time, the injection pipe 21 and the outlet pipe 19 simulate the injection wellhead and the heat extraction wellhead, respectively. Rotate the left rotating handle 5 to push the second converter 151 to move axially, and observe the scale on the casing 4 at the same time. When the half-through heat extraction port 6 on the second converter 151 is connected with the pipe opening of the injection pipe 21, stop the rotating handle. Then, rotate the right rotating handle to push the first converter 15 to move axially, and observe the scale on the casing 4 at the same time. When the half-through heat extraction port on the first converter 15 is connected with the pipe opening of the outlet pipe 19, stop the rotating handle. Cold water is injected from the injection pipe 21, and hot water enters the inner cavity of the casing 4 through the half-through heat extraction port 6 on the second converter 151, exchanges heat with the sand-filled thermal reservoir 1 through the outer wall of the casing 4, and the heat-exchanged hot water is produced from the outlet pipe 19 through the half-through heat extraction port on the first converter 15, and the produced hot water enters the injection pipe 21 through the external circulating pump to form a U-shaped well heat extraction without water extraction cycle.

[0040] As a third heat extraction scheme, if the experiment simulates a single-well heat extraction without water extraction process, in this experimental state, water is injected from one wellhead, and after heat exchange through the well wall, heat is extracted from the same wellhead; at this time, one of the injection pipe 21 and the outlet pipe 19 can be selected as a simulated well. Figure 1 In the embodiment, the injection pipe 21 is used as a simulated well, a thinner pipe is inserted into the injection pipe 21 as a single-well outlet pipe 211, the second converter 151 is pushed to move axially by rotating the left rotating handle 5, and when the lower end of the injection pipe 21 is neither connected with the half-through heat extraction port 6 nor connected with the full-through heat extraction port 7, but is blocked by the side wall of the second converter 151, it is indicated that the second converter 151 has been moved to the right position. At this time, cold water is injected from the annulus between the injection pipe 21 and the single-well outlet pipe 211, and the hot water after heat exchange between the lower end of the injection pipe 21 and the sand-filled thermal reservoir 1 is produced from the single-well outlet pipe 211. Temperature measuring points are arranged at the inlet of the injection pipe 21 and the outlet of the single-well outlet pipe 211, and are connected with a temperature recorder, so as to monitor the inlet and outlet water temperatures in real time.

[0041] In the above process, the temperature recorder monitors and records the temperature of the reservoir and the inlet and outlet temperatures 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 the specification belong to the prior art known to those skilled in the art.

[0043] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A geothermal experimental device with switchable heat extraction scheme, comprising a sand box (2) with a sand-filled thermal reservoir (1), a constant-temperature circulating water tank (13) communicating with the inner cavity of the sand box (2), a water injection pipe (21) and a water outlet pipe (19) installed longitudinally inside the sand box (2), characterized in that, The sand box (2) has an upper water storage layer (18) above the sand-filled thermal reservoir (1) and a lower water storage layer (9) below it. 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 horizontally arranged sleeve (4) is installed in the sand-filled thermal reservoir (1), and the water injection pipe (21) and water outlet pipe (19) are also present. The lower end is fixedly connected to the outer wall of the sleeve (4) and communicates with the sleeve (4). A sleeve side opening (42) is provided on the other side of the sleeve (4). The sleeve side opening (42) is coaxially arranged with the water inlet pipe (21) or the water outlet pipe (19). The inner cavity of the sleeve (4) is equipped with an axially movable first converter (15) and a second converter (151). The first converter (15) and the second converter (151) are adapted to the outer wall of the sleeve. (4) A cylindrical structure with an inner wall and an open inner end and a closed outer end. The side wall of the cylindrical structure is provided with a full-through heat extraction port (7) and a semi-through heat extraction port (6). The semi-through heat extraction port (6) penetrates one side wall of the cylindrical structure and connects to the inner cavity of the cylindrical structure. The full-through heat extraction port (7) penetrates the two symmetrical side walls of the cylindrical structure. In the inner cavity of the cylindrical structure, partitions (12) are fixedly provided 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 the water supply pipe (131) and to the upper water storage layer (18) of the sand box (2) through the return water pipe (132). 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 threads. The outer ends of the first converter (15) and the second converter (151) are fixedly installed with rotating handles (5).

2. The geothermal experimental device with switchable heat extraction scheme according to claim 1, characterized in that, The sleeve (4) is a straight pipe that runs 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).

3. The 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 located at both ends of the sleeve (4).

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