Enhanced geothermal development system and method with self-cleaning underground filter device

Abstract

The invention relates to an enhanced geothermal development system and method with a self-cleaning underground filter device, and belongs to the technical field of geothermal energy development. The invention discloses an enhanced terrestrial heat development system and method with a self-cleaning underground filtering device. The enhanced terrestrial heat development system comprises a fluid circulation injection and production system, a self-cleaning underground filtering system and a ground heat exchange system. The fluid circulation injection and production system comprises a water injection well, an artificial heat reservoir, a production well, a ground fluid migration pipeline and a water injection pump. The self-cleaning underground filtering system comprises a self-cleaning underground filtering device, an external direct-current power supply, a sewage treatment device, a sewage transportation pipeline, a filter element temperature monitor and a filter element self-cleaning mode control device; the ground heat exchange system comprises a ground heat exchange device. The internal temperature of the filter material is changed through the Peltier effect so as to change the porosity of the filter material, and the self-cleaning of the porous heat-sensitive material filter element is realized by controlling the flow of fluid in the porous channel of the filter element under the condition that the pressure difference at the two ends of the filter material is relatively unchanged.

Description

Technical Field

[0001] The present invention relates to an enhanced geothermal development system and method with a self-cleaning underground filtering device, belonging to the technical field of geothermal energy development. Background Art

[0002] An enhanced geothermal system is the main way to extract geothermal energy from high-temperature rock masses in deep formations. The traditional EGS heat extraction system mainly consists of an injection well, a production well, an artificial heat reservoir, a ground heat exchange system, and a ground fluid circulation device. It uses hydraulic fracturing technology to create an artificial heat reservoir in dense hot dry rock, and the fractures in the artificial heat reservoir connect the injection well and the production well. Fluids are injected into the formation through the injection wellbore, heat exchange occurs in the artificial heat reservoir, and then the heat-carrying fluid is produced through the production well. The heat energy is converted into electrical energy in the ground heat exchange system. The condensed circulating working fluid is recycled to the injection well for heat exchange after passing through the sewage treatment device. The enhanced geothermal system has the advantages of high heat extraction, long service life, large heat energy utilization area, and high economic benefits. Therefore, it has been widely regarded in geothermal development in recent years due to its high economic value and has great application prospects in the development of deep geothermal energy. However, since fractures are the main flow and heat exchange channels of fluids in the formation during the development of hot dry rock, the rock on the fracture surface will exfoliate with temperature changes and fluid erosion. Using a ground fluid cleaning device will cause rock debris to damage the wellbore and ground heat extraction devices during fluid migration, while using a traditional underground filtering device will face the problems of filter element blockage and failure and difficult replacement of filtering facilities. These phenomena will lead to a decrease in the heat exchange efficiency of the system and an increase in the failure rate. Summary of the Invention

[0003] The purpose of the present invention is to provide an enhanced geothermal development system and method with a self-cleaning underground filtering device in view of the problems existing in the prior art.

[0004] The technical solution provided by the present invention to solve the above technical problems is: an enhanced geothermal development system with a self-cleaning underground filtering device, including a fluid circulation injection-production system, a self-cleaning underground filtering system, and a ground heat exchange system;

[0005] The fluid circulation injection-production system includes an injection well, an artificial heat reservoir, a production well, a ground fluid transfer pipeline, and an injection pump. The injection well and the production well are both installed in the geothermal layer, and the injection well is connected to the production well through an artificial heat reservoir placed in the geothermal layer. The injection pump is arranged at the wellhead part of the injection well and is connected to the ground fluid transfer pipeline;

[0006] The self-cleaning underground filtration system includes a self-cleaning underground filtration device, an external DC power supply, a sewage treatment device, a sewage migration pipeline, a filter element temperature monitor, and a filter element self-cleaning mode control device. The self-cleaning underground filtration device is installed in the wellbore of a production well, and its hot end is connected to the external DC power supply; the sewage treatment device is connected to the ground part of the production well through the sewage migration pipeline, and the filter element self-cleaning mode control device is connected to the self-cleaning underground filtration device through the filter element temperature monitor;

[0007] The ground heat exchange system includes a ground heat exchange device, and the ground heat exchange device is respectively connected to the ground fluid migration pipeline and the ground part of the production well.

[0008] A further technical solution is that a high thermal conductivity material layer is provided on the outer wall of the injection well, and an adiabatic material layer is provided on the outer wall of the production well.

[0009] A further technical solution is that anti-corrosion layers are provided on the inner walls of the injection well and the production well.

[0010] A further technical solution is that a first throttle valve is provided on the ground fluid migration pipeline, a second throttle valve is provided on the ground part of the production well, and a third throttle valve and a third pressure gauge are provided on the sewage migration pipeline.

[0011] A further technical solution is that a first thermometer and a first pressure gauge are provided on the ground part of the injection well.

[0012] A further technical solution is that a second thermometer, a second pressure gauge, and a flow rate monitor are provided on the ground part of the production well.

[0013] A further technical solution is that the self-cleaning underground filtration device includes a columnar heat conduction device, a semiconductor thermoelectric element, a heat-conducting ceramic plate, a porous thermosensitive material filter element, a filter device housing, and an adiabatic material layer, which are sequentially wrapped from the inside to the outside.

[0014] A further technical solution is that a conical cuttings buffer device is provided at the bottom of the self-cleaning underground filtration device 8. The conical cuttings buffer device includes a conical filter screen, a smooth sleeve, a metal cylinder, and a connecting device. The upper end of the conical filter screen is connected to the bottom of the self-cleaning underground filtration device 8, and the lower end is connected to the upper end of the metal cylinder. The outer wall of the metal cylinder is fixed in the smooth sleeve through the connecting device.

[0015] An enhanced geothermal development method with a self-cleaning underground filtration device specifically includes the following steps:

[0016] Step 1: Install the downhole self-cleaning system. Install the conical filter screen in the artificial heat storage section of the production well, and install the self-cleaning filter element above the conical filter screen. After the installation is completed, calculate the initial filter element porosity φ of the self-cleaning underground filtration system 0 , and open the corresponding valves and injection pumps to develop geothermal energy;

[0017] Step 2: Monitor the temperature of the filter element and the measured flow rate Q in real time through the filter element temperature monitor and the flow rate monitor respectively 2 ;

[0018] Step 3: Calculate the theoretical flow rate Q based on the real-time temperature of the filter element 1 , and compare the measured flow rate Q 2 with the theoretical flow rate Q 1 . If the ratio of the two is less than 50%, then proceed to the next step to start the self-cleaning of the filter element;

[0019] Step 4: Start the self-cleaning mode of the filter element. Open the second throttle valve at the sewage treatment pipeline, and at the same time close the first throttle valve connecting the wellhead and the ground heat processor to change the fluid flow direction. Then turn on the external power supply and use the Peltier effect to change the temperature of the filter element to lower the temperature of the filter element;

[0020] Step 5: At the same time, calculate the theoretical flow rate Q of the filter element in real time 1 , and compare the measured flow rate Q 2 with the theoretical flow rate Q 1 . If the ratio of the two is less than or equal to 95%, then increase the output current in gradient until the ratio of the two is greater than 95%, and then proceed to the next step;

[0021] Step 6: Disconnect the ground power supply, close the valve at the sewage pipeline, open the valve connecting to the ground heat treatment system, and at the same time inject a certain amount of working fluid into the injection well through the injection pump, the volume of which is the same as the volume of the sewage collected by the sewage processor, and resume production to complete the self-cleaning of a porous filter element.

[0022] A further technical solution is that the calculation formula for the initial filter element porosity φ 0 is:

[0023] φ 0 = 1(1 - φ s )(1 - α T (T 0 - T s ))

[0024] In the formula: φ s is the porosity of the porous self-cleaning filter element at normal temperature, a dimensionless constant; φ 0 is the porosity of the porous self-cleaning filter element at the initial ground temperature, a dimensionless constant; T sis the ambient temperature, in °C, when selecting the porous self-cleaning filter element; T 0 is the temperature of the filter element when placing the self-cleaning filter element, in °C; α T is the coefficient of thermal expansion of the porous thermosensitive material filter element, in K -1 .

[0025] Beneficial effects of the present invention: The self-cleaning underground filtration system of the present invention is installed in the upper wellbore of the artificial heat storage area underground of the heat exchange fluid production well. A semiconductor material capable of generating the Peltier effect is installed inside the filter material. By changing the internal temperature of the filter material through the Peltier effect, its porosity is changed. Under the condition that the pressure difference at both ends of the filter material remains relatively unchanged, by controlling the fluid flow rate in the porous channels of the filter element, self-cleaning of the porous thermosensitive material filter element is achieved, preventing smaller rock particles from accumulating inside the filter material and blocking the filter element. There is a conical cuttings buffer area outside the filter element to block larger cuttings. Through the multiphase fluid flow mechanism, the cuttings are precipitated in the bottom hole cuttings precipitation area, avoiding damage to the inner wall of the wellbore and the ground heat exchange facilities caused by larger cuttings, thereby improving the heat exchange efficiency and service life of the system. Description of the Drawings

[0026] Figure 1 is the overall structure diagram of the fluid circulation injection-production system, self-cleaning underground filtration system, and ground heat exchange system;

[0027] Figure 2 is the transverse sectional view of the self-cleaning underground filtration device;

[0028] Figure 3 is the vertical sectional view of the self-cleaning underground filtration device;

[0029] Figure 4 is the structural schematic diagram of the conical cuttings buffer device;

[0030] Figure 5 is the optimized flow chart of the filter element self-cleaning mode.

[0031] As shown in the figure: 1 - geothermal layer; 2 - injection well; 3 - external power supply; 4 - artificial heat storage; 5 - production well; 6 - ground heat exchange device; 7 - ground fluid migration pipeline; 8 - self-cleaning underground filtration system; 9 - sewage treatment device; 10 - first thermometer; 11 - first pressure gauge; 12 - second thermometer; 13 - second pressure gauge; 14 - flow monitoring meter; 15 - first throttle valve; 16 - second throttle valve; 17 - third throttle valve; 18 - filter element temperature monitor; 19 - filter element self-cleaning mode control device; 20 - injection pump; 21 - heat insulation material layer; 22 - high thermal conductivity material layer; 23 - third pressure gauge; 24 - columnar heat conduction device; 25 - semiconductor thermoelectric element; 26 - heat-conducting ceramic plate; 27 - porous thermosensitive material filter element; 28 - filter device housing; 29 - heat insulation material layer; 30 - conical filter screen; 31 - smooth sleeve; 32 - metal cylinder; 33 - connecting device. Detailed implementation manner

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] As Figure 1 shown, an enhanced geothermal development system with a self-cleaning underground filtration device provided by the present invention includes a fluid circulation injection and production system, a self-cleaning underground filtration system, and a ground heat exchange system;

[0034] The fluid circulation injection and production system includes an injection well 2, an artificial heat storage 4, a production well 5, a ground fluid migration pipeline 7, and an injection pump 20. The injection well 2 and the production well 5 are both installed in the geothermal layer 1. The injection well 2 is connected to the production well 5 through the artificial heat storage 4 placed in the geothermal layer 1. The injection pump 20 is arranged at the wellhead part of the injection well 2 and is connected to the ground fluid migration pipeline 7;

[0035] Among them, the artificial heat storage 4 is obtained by artificial hydraulic fracturing, directly connecting the fluid injection and production wells, and providing a flow channel for fluid migration;

[0036] The self-cleaning underground filtration system includes a self-cleaning underground filtration device 8, an external DC power supply 3, a sewage treatment device 9, a sewage migration pipeline, a filter element temperature monitor 18, and a filter element self-cleaning mode control device 19. The self-cleaning underground filtration device 8 is installed in the wellbore of the production well 5, and its hot end is connected to the external DC power supply 3. The sewage treatment device 9 is connected to the ground part of the production well 5 through the sewage migration pipeline. The filter element self-cleaning mode control device 19 is connected to the self-cleaning underground filtration device 8 through the filter element temperature monitor 18;

[0037] The ground heat exchange system includes a ground heat exchange device 6, and the ground heat exchange device 6 is respectively connected to the ground fluid transportation pipeline 7 and the ground part of the production well 5.

[0038] During the specific operation of this embodiment, the injection well 2 and the production well 5 are connected through the artificial heat storage 4 in the formation, and on the ground, the system ground fluid is transported through the ground fluid transportation pipeline 7.

[0039] As Figure 1 shown, in this embodiment, a high thermal conductivity material layer 22 is provided on the outer wall of the injection well 2 to improve the heat extraction capacity of the system; an adiabatic material layer 21 is provided on the outer wall of the production well 5 to prevent the fluid in the wellbore from releasing heat to the formation.

[0040] In this embodiment, in order to reduce the corrosion and damage of the fluid to the system facilities, therefore, the preferred implementation is that anti-corrosion layers are provided on the inner walls of the injection well 2 and the production well 5.

[0041] As Figure 1 shown, in this embodiment, for the convenience of system operation, the preferred implementation is that a first throttle valve 15 is provided on the ground fluid transportation pipeline 7, a second throttle valve 16 is provided on the ground part of the production well 5, a third throttle valve 17 and a third pressure gauge 23 are provided on the sewage transportation pipeline, a first thermometer 10 and a first pressure gauge 11 are provided on the ground part of the injection well 2, and a second thermometer 12, a second pressure gauge 13, and a flow rate monitoring table 14 are provided on the ground part of the production well 5.

[0042] As Figure 2 and Figure 3 shown, in this embodiment, the self-cleaning underground filtering device 8 includes a columnar heat conduction device 24, a semiconductor thermoelectric element 25, a heat-conducting ceramic plate 26, a porous thermosensitive material filter element 27, a filter device housing 28, and an adiabatic material layer 29, which are sequentially wrapped and arranged from the inside to the outside.

[0043] Among them, the N-type semiconductor material and the P-type semiconductor material form a group of semiconductor thermoelectric elements. Each ring of thermoelectric elements from top to bottom is connected at the bottom end. The second pin of the first group of thermoelectric elements from top to bottom is connected to the first pin of the second group of thermoelectric elements, and the second pin of the second group is connected to the third pin of the third group, and so on. The hot end part of the semiconductor thermoelectric element is connected to the columnar heat conduction device in a ring shape, the cold end part is connected to the ceramic plate 6, and the porous thermosensitive material filter element 5 is connected. The hot end pin of the semiconductor thermoelectric element 25 is externally connected to the columnar heat-conducting material, and the cold end is in a ring shape and is attached to the inside of the porous self-cleaning filter element around the columnar heat-conducting material;

[0044] As Figure 1 and Figure 4As shown, a conical debris buffer device is provided at the bottom of the self-cleaning underground filtering device 8. The conical debris buffer device includes a conical filter screen 30, a smooth sleeve 31, a metal cylinder 32, and a connecting device 33. The upper end of the conical filter screen 30 is connected to the bottom of the self-cleaning underground filtering device 8, and the lower end is connected to the upper end of the metal cylinder 32. The outer wall of the metal cylinder 32 is fixed in the smooth sleeve 31 through the connecting device 33. There is no seal between the smooth sleeve 31 and the metal cylinder 32. The debris drained by the conical filter screen 30 is transported through the annular space between the smooth sleeve 31 and the metal cylinder 32 to the bottom of the well for precipitation.

[0045] In this embodiment, an enhanced geothermal development system is established in the hot dry rock formation. The orientations of the injection well 2 and the production well 5 are reasonably arranged, and a self-cleaning underground filtering device 8 is installed in the production well 5 shaft. A circulating working fluid flow channel is established through the artificial heat reservoir 4 and the ground fluid transport pipeline 7. A certain amount of working fluid is injected into the injection well 2 through the injection pump 20. The throttle valves at the ground fluid transport pipeline 7 and the production well 5 wellhead are opened, the readings of each instrument are checked, and the instrument is zeroed to ensure the normal operation of the instrument.

[0046] During the operation of the geothermal system, the filter element self-cleaning module in the ground current control device records the values of the pressure gauge and the filter element temperature monitor 18 located at the production wellhead, and generates the theoretical flow rate Q under the clean state of the filter element. 1 , and at the same time synchronizes the actual flow rate Q recorded by the flow rate monitor at the production wellhead. 2 , and performs secondary processing on the data. When the ratio of the actual flow rate Q 2 to the theoretical flow rate Q 1 is less than 50%, it means that the filter element of the downhole filtering device is significantly blocked. At this time, the ground current control device will close the throttle valve at the production well 5 wellhead, open the throttle valve located at the sewage transport pipeline, so that the working fluid flows to the sewage collection and treatment device 9. At the same time, the ground DC power supply is connected to generate the Peltier effect, so that the semiconductor thermoelectric element cools the porous thermosensitive material filter element, and controls the production pressure difference at the wellhead to keep it unchanged. When the temperature decreases, the porous material skeleton shrinks, the porosity of the porous material filter element increases, and the production pressure difference remains unchanged. The dirt blocking the filter element is carried by the fluid to the sewage collection and treatment device under the scouring of the fluid. As the self-cleaning time increases, the current magnitude is increased in a gradient. At this time, the flow rate and the filter element temperature at the production well wellhead show dynamic changes. When the ratio of the actual flow rate Q 2 to the theoretical flow rate Q 1 is greater than 95%, the ground current control device will control the opening of the throttle valve at the production well 5 wellhead, close the throttle valve at the sewage transport pipeline, disconnect the DC power supply, and inject a certain amount of circulating working fluid into the injection well 2 to make the enhanced geothermal system return to the normal production mode, completing one self-cleaning of the porous filter element of the thermosensitive material.

[0047] An enhanced geothermal development method with a self-cleaning underground filtration device in this embodiment specifically includes the following steps:

[0048] Step 1: Install the downhole self-cleaning system. Install the conical filter screen in the artificial heat storage section of the production well, and install the self-cleaning filter element above the conical filter screen. After installation, calculate the initial filter element porosity φ of the self-cleaning underground filtration system 0 , and open the corresponding valves and injection pumps to carry out geothermal energy development;

[0049] The initial filter element porosity φ 0 The calculation formula is:

[0050] φ 0 =1(1 - φ s )(1 - α T (T 0 -T s ))

[0051] In the formula: φ s is the porosity of the porous self-cleaning filter element at room temperature, a dimensionless constant; φ 0 is the porosity of the porous self-cleaning filter element at the initial geothermal temperature, a dimensionless constant; T s is the ambient temperature when selecting the porous self-cleaning filter element, °C; T 0 is the filter element temperature when placing the self-cleaning filter element, °C; α T is the thermal expansion coefficient of the porous thermosensitive material filter element, K -1 ;

[0052] Step 2: Real-time monitor the temperature of the filter element and the measured flow rate Q through the filter element temperature monitor 18 and the flow rate monitor 14 respectively 2 ;

[0053] Step 3: Calculate the theoretical flow rate Q based on the real-time temperature of the filter element, and compare the measured flow rate Q 1 with the theoretical flow rate Q 2 . If the ratio of the two is less than 50%, then proceed to the next step to start the filter element self-cleaning; 1

[0054] φ 1 =1-(1 - φ 0 )(1 - α T (T 1 -T 0 ))

[0055]

[0056]

[0057] In the formula: φ 0is the porosity of the porous self-cleaning filter element at the initial ground temperature, a dimensionless constant; α T is the coefficient of thermal expansion of the porous thermosensitive material filter element, K -1 ; φ 1 is the porosity of the porous self-cleaning filter element at the current temperature, a dimensionless constant; T 1 is the ambient temperature at which the porous self-cleaning filter element is currently located, °C; K 1 is the theoretical permeability of the filter element calculated from the filter element temperature, m 2 ; A is the cross-sectional area of the self-cleaning filter element, m 2 ; ΔP is the wellhead pressure difference, Pa; S is the specific surface area of the porous self-cleaning filter element at the initial ground temperature, m 2 / m 3 ;

[0058] Step 4: Start the self-cleaning mode of the filter element, open the second valve at the sewage treatment pipeline, and at the same time close the first valve connecting the wellhead and the ground heat processor, change the fluid flow direction, and turn on the external power supply to change the temperature of the filter element using the Peltier effect to reduce the temperature of the filter element;

[0059] Step 5: At the same time, calculate the theoretical flow rate Q of the filter element in real time 1 , and compare the measured flow rate Q 2 with the theoretical flow rate Q 1 . If the ratio of the two is less than or equal to 95%, then increase the output current in gradient until the ratio of the two is greater than 95%, and then proceed to the next step;

[0060] Step 6: Disconnect the ground power supply, close the valve at the sewage pipeline, open the valve connecting to the ground heat treatment system, and at the same time inject a certain amount of working fluid into the injection well through an injection pump, the volume of which is the same as the volume of sewage collected by the sewage treatment device, resume production, and complete one self-cleaning of the porous filter element.

[0061] As mentioned above, it is not any form of limitation to the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to form equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An enhanced geothermal development system with a self-cleaning underground filtration device, characterized in that: It includes fluid circulation injection and production system, self-cleaning underground filtration system and ground heat exchange system; The fluid circulation injection and production system comprises an injection well (2), an artificial heat reservoir (4), a production well (5), a surface fluid transport pipeline (7), and an injection pump (20); the injection well (2) and the production well (5) are both installed in a geothermal layer (1); the injection well (2) is connected to the production well (5) via the artificial heat reservoir (4) disposed in the geothermal layer (1); the injection pump (20) is disposed at the wellhead portion of the injection well (2) and is connected to the surface fluid transport pipeline (7); The self-cleaning underground filtration system comprises a self-cleaning underground filtration device (8), an external DC power supply (3), a sewage treatment device (9), a sewage transport pipeline, a filter element temperature monitor (18), and a filter element self-cleaning mode control device (19); the self-cleaning underground filtration device (8) is installed in the wellbore of the production well (5), and its hot end is connected to the external DC power supply (3); the sewage treatment device (9) is connected to the ground part of the production well (5) through the sewage transport pipeline, and the filter element self-cleaning mode control device (19) is connected to the self-cleaning underground filtration device (8) through the filter element temperature monitor (18); The ground heat exchange system comprises a ground heat exchange device (6), and the ground heat exchange device (6) is respectively connected to a ground fluid transport pipeline (7) and the ground part of a production well (5).

2. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 1, characterized in that: The outer wall of the water injection well (2) is provided with a high thermal conductivity material layer (22), and the outer wall of the production well (5) is provided with a thermal insulation material layer (21).

3. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 2, characterized in that: The inner walls of the water injection well (2) and the production well (5) are both provided with an anti-corrosion layer.

4. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 1, characterized in that: The surface fluid transport pipeline (7) is provided with a first throttle valve (15), the surface part of the production well (5) is provided with a second throttle valve (16), and the sewage transport pipeline is provided with a third throttle valve (17) and a third pressure gauge (23).

5. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 1, characterized in that: A first temperature gauge (10) and a first pressure gauge (11) are provided on the surface of the injection well (2).

6. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 5, characterized in that: A second temperature gauge (12), a second pressure gauge (13), and a flow monitoring gauge (14) are provided on the surface of the production well (5).

7. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 1, characterized in that: The self-cleaning underground filtering device (8) comprises a columnar heat conduction device (24), a semiconductor temperature difference element (25), a heat-conducting ceramic plate (26), a porous heat-sensitive material filter element (27), a filtering device housing (28), and a heat-insulating material layer (29) which are sequentially wrapped from the inside to the outside.

8. The enhanced geothermal development system with a self-cleaning underground filtration device according to claim 7, characterized in that: A conical rock debris buffer is provided at the bottom of the self-cleaning underground filtering device (8), and the conical rock debris buffer comprises a conical filter screen (30), a smooth sleeve (31), a metal cylinder (32), and a connecting device (33). The upper end of the conical filter screen (30) is connected to the bottom of the self-cleaning underground filtering device (8), and the lower end is connected to the upper end of the metal cylinder (32). The outer wall of the metal cylinder (32) is fixed in the smooth sleeve (31) via the connecting device (33).

9. An enhanced geothermal development method with a self-cleaning underground filtration device, characterized in that: The method adopts an enhanced geothermal development system with a self-cleaning underground filtration device as described in any one of claims 1 to 8, and specifically comprises the following steps: Step 1: Install the underground self-cleaning system, install the conical filter (30) in the artificial heat storage section of the production well, and install the self-cleaning filter element on the upper part of the conical filter (30). After the installation is completed, calculate the initial filter element porosity φ0 of the self-cleaning underground filtration system, and open the corresponding valve and water injection pump (20) to carry out geothermal energy development; Step 2, respectively monitoring the temperature of the filter element and the measured flow rate Q2 in real time through the filter element temperature monitor (18) and the flow rate monitoring meter (14); Step 3: Calculate the theoretical flow rate Q1 according to the real-time temperature of the filter element, and compare the measured flow rate Q2 with the theoretical flow rate Q1. If the ratio of the two is less than 50%, proceed to the next step to start the filter element self-cleaning; Step 4: The filter element self-cleaning mode is started, the second throttle valve (16) at the sewage treatment pipeline is opened, and the first throttle valve (15) connecting the wellhead and the ground heat exchange device (6) is closed at the same time, the fluid flow direction is changed, and the external power supply (3) is turned on, and the filter element temperature is changed by using the Peltier effect, so that the filter element temperature is reduced; Step 5: Calculate the theoretical flow rate Q1 of the filter element in real time, and compare the measured flow rate Q2 with the theoretical flow rate Q1. If the ratio of the two is less than or equal to 95%, increase the output current gradually until the ratio of the two is greater than 95%, and then proceed to the next step; Step 6: disconnect the ground power supply, close the valve at the sewage pipe, open the valve connected to the ground heat treatment system, and at the same time inject a certain amount of working fluid into the injection well (2) through the water injection pump (20), the volume of which is the same as the volume of sewage collected by the sewage treatment device (9), resume production, and complete the self-cleaning of the porous filter element.

10. The enhanced geothermal development method with a self-cleaning underground filtration device according to claim 9, characterized in that: The calculation formula of the initial filter element porosity φ0 is: φ0=1(1-φ s )(1-a T (T0-T s )) Where: φ s is the porosity of the porous self-cleaning filter element at room temperature, a dimensionless constant; φ0 is the porosity of the porous self-cleaning filter element at the initial ground temperature, a dimensionless constant; T s is the ambient temperature when selecting the porous self-cleaning filter element, ℃; T0 is the filter element temperature when the self-cleaning filter element is placed, ℃; α T is the thermal expansion coefficient of the porous thermal sensitive material filter element; the thermal expansion coefficient of the rock, K -1 .

Images