Dry heat single pump geothermal system and construction method thereof

Abstract

The present invention relates to the field of geothermal energy utilization, in particular to a dry heat type single pump geothermal system. It includes an underground heat exchange system, and a ground heat exchange system connected and matched with the underground heat exchange system. The underground heat exchange system includes a water supply well device and a water supply well device. The underground ends of the water supply well device and the water supply well device both extend into the underground dry hot rock layer that has been treated by fracturing. The water supply well device is used to inject water into the underground dry hot rock layer that has been treated by fracturing. The water supply well device is used to lift and transport the hot water that has undergone heat exchange to the ground for use. The underground dry hot rock layer that has been treated by fracturing is used to receive and store water from the water supply well device and realize heat exchange. There is no need to consider the geographical location limitation like a hydrothermal geothermal system. The geothermal system is not limited by the geographical location, and there is no need to consider the restriction condition of whether there is natural hot water underground when selecting the site for the system. It has strong versatility.

Description

Technical Field

[0001] The present invention relates to the field of geothermal energy utilization, and in particular to related technologies for realizing efficient conversion and utilization of underground rock thermal energy, especially a dry heat single pump geothermal system and a construction method thereof. Background Art

[0002] Geothermal heat is an energy resource generated by nuclear fission inside the earth. The temperature of each layer of the earth is very different. On average, the temperature rises by 3°C for every 100 meters below the surface. In geothermal anomaly areas, the temperature increases faster with depth. When a well in the North China Plain of China was drilled to 1,000 meters, the temperature was 46.8°C; when it was drilled to 2,100 meters, the temperature rose to 84.5°C. Another well, 5,000 meters deep, had a bottom temperature of 180°C. According to various data, the temperature of the bottom of the crust and the upper mantle is about 1,100°C~1,300°C, and the core is about 4,100°C~6,600°C. The temperature of lava ejected from volcanoes on the earth is as high as 1,200°C~1,300°C, and the temperature of natural hot springs is mostly above 60°C, and some are even as high as 100°C~140°C.

[0003] In summary, the earth is a huge heat reservoir, which contains huge thermal energy. This heat seeps out of the surface, so there is geothermal energy. Geothermal energy is a clean energy and a renewable energy source, and its development prospects are very broad. At present, there are many geothermal heating products and technologies in society. The existing geothermal heating systems on the market are generally divided into two categories:

[0004] One type is to use heating equipment to achieve heating, which has three disadvantages: it will inevitably accumulate a large number of equipment, consume a lot of electricity, and inevitably cause the circuit capacity to increase.

[0005] The other type is the hydrothermal geothermal system, which has the prerequisite that there must be natural hot springs underground, that is, there must be natural geothermal fields formed underground, so its resource limitations are relatively large. According to statistics, geothermal resources brought out of the ground by water only account for 1% of the world, while 99% of the area is water-free dry hot area. Therefore, the dry hot geothermal system has a broader application prospect in terms of space and resources.

[0006] Therefore, how to effectively utilize the geothermal energy existing in the underground dry hot rocks in the water-free dry hot zone to achieve efficient energy utilization is a difficult problem that urgently needs to be solved in the industry, and it is also an important influencing factor in promoting the rational development and utilization of geothermal energy. Summary of the invention

[0007] The technical solution adopted by the present invention to solve one of the above-mentioned technical problems is: a dry heat single pump geothermal system, including an underground heat exchange system, and a ground heat exchange system connected and coordinated with the underground heat exchange system, the underground heat exchange system including a water supply well device and at least one water supply well device, the water supply well device and the water supply well device are arranged at an interval, the underground ends of the water supply well device and the water supply well device both extend into the underground dry hot rock layer that has been fractured, the water supply well device is used to inject water into the underground dry hot rock layer that has been fractured, the water supply well device is used to lift and transport the hot water that has undergone heat exchange to the ground for use, the underground dry hot rock layer that has been fractured is used to receive and store water from the water supply well device and realize heat exchange, the bottom end of the water supply well device is lower than the bottom end of the water supply well device and has a height difference, the above-ground water inlet end of the water supply well device and the above-ground water outlet end of the water supply well device are respectively sealed and connected with the outlet end and the inlet end of the heat exchanger in the ground heat exchange system.

[0008] Preferably, the water supply well device includes a water supply well, in which a water supply pipe is installed, and a water inlet sealing end cover with an exhaust valve is screwed on the ground water inlet port of the water supply pipe. The outlet end of the heat exchanger is sealed and connected with the inside of the water supply pipe through an outlet pipe, and a water collecting tank is installed at the end of the outlet pipe. The water collecting tank is used to receive water from the outlet pipe of the heat exchanger and inject it into the water supply pipe. The water collecting tank is connected with the inside of the water supply pipe through an injection pipe, and a flow control valve is installed on the injection pipe; it also includes a constant pressure water injection mechanism for auxiliary maintenance.

[0009] Preferably, the constant-pressure water injection mechanism includes a water injection pump, the water outlet end of the water injection pump is connected to the inside of the water supply pipe, the water inlet end of the water injection pump is connected to an external water source, an electromagnetic control valve is installed on the water injection pump, and a pressure sensor connected to the electromagnetic control valve is installed in the water supply pipe, and the pressure sensor is used to detect the pressure inside the water supply pipe.

[0010] The constant-pressure water injection mechanism is mainly turned on when the water collection tank cannot be naturally filled to the water supply well and the pressure sensor detects that the internal pressure is greater than the set value. After being turned on, the water injection pump can be used to pressurize the water to continue injecting water into the water supply well. If the pressure in the well gradually increases, this is generally caused by a slight blockage in the filter screen in the well. At this time, the pressurized water injection by the water injection pump can assist in clearing the blockage position of the filter screen, thereby clearing and maintaining the slight blockage, avoiding the tedious operations of manual backflow and well washing and maintenance, and can effectively reduce the occurrence rate of failures and extend the service life.

[0011] Preferably, the water supply well device includes a water supply well, a water supply pipe is installed in the water supply well, a submersible pump is installed in the water supply pipe, a water outlet sealing end cover with an exhaust valve is installed at the ground port of the water supply pipe, and a water inlet pipeline is sealably installed at the water inlet port of the heat exchanger, and the lower end of the water inlet pipeline is sealably connected to the inside of the water supply pipe.

[0012] Preferably, the inner diameter of the water supply pipe is at least twice the inner diameter of the water supply pipe, the interval between the centerline axis of the water supply pipe and the water supply pipe is not less than 500m, and the angle between the line connecting the bottom center of the water supply pipe and the bottom center of the water supply pipe and the horizontal line is 15°-60°, and the angle is the same as the downward dip angle of the formation.

[0013] A small-drill-distance directional fracturing operation is performed in the fracturing hot dry rock formation to connect the interior of the bottom end of the water supply well device with the interior of the bottom end of the water supply well device. This design, as a backup solution of the present application, can effectively increase the water supply volume. In a subsequent alternative solution, an electromagnetic control switch for controlling the opening size of the small-drill-distance directional fracturing section can be installed at the upper port.

[0014] Before working, the local heating system needs to inject sufficient water into the water supply well through the water collecting tank and the water injection pump, so that the water can flow into the underground hot dry rock layer that has been fractured and make the underground hot dry rock layer that has been fractured in a saturated state. At this time, the underground rock layer that has been fractured will form a backup water storage area.

[0015] When the system is working, the submersible pump is started to pump water, and a negative pressure siphon state will gradually form in the well during the pumping process. After stable operation, the submersible pump can be used alone to achieve single pump operation, effectively reducing the power loss of electrical equipment and playing a role in high efficiency and energy saving. There is no need to rely on a large number of heating equipment like other equipment of existing products, resulting in huge consumption of electricity.

[0016] The combination of the three elements and the small-drilling-distance directional fracturing design as a backup solution can better achieve negative pressure siphoning and save energy:

[0017] This system provides a pressure difference by setting a height difference between the lower ends of the water supply well and the water supply well; the underground inclination angle provides the gravity component of the water flow and the crack direction to form a water flow guide; the inner diameter difference between the water supply well and the water supply well is further coordinated with the height difference to ensure the pressure difference effect; finally, the water flow resistance is reduced through directional fracturing with a small drilling distance, and the submersible pump is better coordinated for water supply to achieve a good negative pressure siphon, ensure the water supply rate, and reduce the energy consumption of the submersible pump.

[0018] The construction method of the dry heat single pump geothermal system includes the following steps:

[0019] S1: Conduct geophysical exploration to determine the target rock formation;

[0020] S2: Drilling and logging a well to form a water supply well;

[0021] S3: Hydraulic fracturing connects hot dry rock formations;

[0022] S4: well layout;

[0023] The well layout distance is calculated and the location of subsequent water supply wells is determined;

[0024] S5: Drilling and completing wells;

[0025] Form a water well;

[0026] S6: Install water supply pipe assembly and water supply pipe assembly, and the underground heat exchange system is formed;

[0027] S7: Connect the underground heat exchange system with the ground heat exchange system to form a dry heat type single pump geothermal system.

[0028] Preferably, the method for determining the target rock formation described in S1 comprises the following steps:.

[0029] Preliminary determination of project feasibility based on geophysical exploration results;

[0030] Confirming the geophysical exploration results through exploration wells ultimately determines the feasibility of the project;

[0031] Through stress testing of the target rock formation, well layout design is carried out according to the stress test results;

[0032] Fracturing connection.

[0033] Preferably, the method in S2 comprises the following steps: obtaining the actual stratum structure and lithology by drilling and observing rock cuttings.

[0034] The beneficial effects of the present invention are embodied in:

[0035] First of all, there is no need to consider the geographical limitations like the hydrothermal geothermal system. The geothermal system is not restricted by geographical location, and there is no need to consider whether there is natural hot water underground when selecting the system site. It has strong versatility and directly uses dry hot rock layers to achieve geothermal energy exchange. The method used is to directly inject water from the ground to achieve underground heat exchange and then achieve heating.

[0036] Secondly, the system adopts multiple means to effectively improve the heat exchange efficiency through negative pressure siphoning, reduce the power loss of external power supply equipment, and achieve good energy-saving effects while achieving efficient heat exchange.

[0037] Third, the system is designed with the problem of later fault maintenance in mind. The pre-designed unblocking device can effectively prevent system blockage and can perform effective pre-cleaning after a slight blockage occurs in the system, reducing the system failure rate and maintenance frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or components are generally identified by similar reference numerals. In the drawings, the elements or components are not necessarily drawn according to the actual scale.

[0039] Figure 1 It is a schematic diagram of the well location arrangement of the present invention.

[0040] Figure 2 It is a structural schematic diagram of the present invention.

[0041] In the figure, 1. water supply well; 2. water supply pipe; 3. water inlet sealing end cover; 4. heat exchanger; 5. water outlet pipeline; 6. water collecting tank; 7. water injection pipe; 8. flow control valve; 9. water injection pump; 10. water supply well; 11. water supply pipe; 12. submersible pump; 13. water outlet sealing end cover; 14. water inlet pipeline; 15. small drilling distance directional fracturing; 16. underground hot dry rock formation treated by fracturing. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0043] like Figure 1-2 As shown in, a dry heat type single pump geothermal system includes an underground heat exchange system and a ground heat exchange system connected to and coordinated with the underground heat exchange system, wherein the underground heat exchange system includes a water supply well device and at least one water supply well device, wherein the water supply well device and the water supply well device are spaced apart, and the underground ends of the water supply well device and the water supply well device both extend into an underground dry hot rock layer 16 that has been fractured, wherein the water supply well device is used to inject water into the underground dry hot rock layer 16 that has been fractured, and the water supply well device is used to lift and transport the hot water that has undergone heat exchange to the ground for utilization, wherein the underground dry hot rock layer 16 that has been fractured is used to receive and store water from the water supply well device and to realize heat exchange, wherein the bottom end of the water supply well device is lower than the bottom end of the water supply well device and has a height difference, and the above-ground water inlet end of the water supply well device and the above-ground water outlet end of the water supply well device are respectively sealed and connected with the outlet end and the inlet end of the heat exchanger 4 in the ground heat exchange system.

[0044] Preferably, the water supply well device includes a water supply well 1, in which a water supply pipe 2 is installed, and a water inlet sealing end cover 3 with an exhaust valve is screwed and installed at the ground water inlet port of the water supply pipe 2. The outlet end of the heat exchanger 4 is sealed and connected with the inside of the water supply pipe 2 through the outlet pipe 5, and a water collecting tank 6 is installed at the end of the outlet pipe 5. The water collecting tank 6 is used to receive water from the outlet pipe 5 of the heat exchanger 4 and inject it into the water supply pipe 2. The water collecting tank 6 is connected with the inside of the water supply pipe 2 through the injection pipe 7, and a flow control valve 8 is installed on the injection pipe 7; it also includes a constant pressure water injection mechanism for auxiliary maintenance.

[0045] Preferably, the constant-pressure water injection mechanism includes a water injection pump 9, the water outlet end of the water injection pump 9 is connected to the inside of the water supply pipe 2, and the water inlet end of the water injection pump 9 is connected to an external water source. An electromagnetic control valve is installed on the water injection pump 9, and a pressure sensor connected to the electromagnetic control valve is installed in the water supply pipe 2. The pressure sensor is used to detect the pressure inside the water supply pipe 2.

[0046] The constant-pressure water injection mechanism is mainly turned on when the water supply well 1 cannot be injected with water due to natural full filling through the water collecting tank 6 and when the pressure sensor detects that the internal pressure is greater than the set value. After being turned on, the water injection pump 9 can pressurize the water to continue injecting water into the water supply well 1. If the pressure in the well gradually increases slowly, this situation is generally caused by a slight blockage in the filter screen in the well. At this time, the pressurized water injection by the water injection pump 9 can assist in clearing the blockage position of the filter screen, thereby clearing and maintaining the slight blockage, avoiding the tedious operations of manual backflow and well washing and maintenance, and can effectively reduce the occurrence rate of failures and extend the service life.

[0047] Preferably, the water supply well device includes a water supply well 10, a water supply pipe 11 is installed in the water supply well 10, a submersible pump 12 is installed in the water supply pipe 11, a water outlet sealing end cover 13 with an exhaust valve is installed at the ground port of the water supply pipe 11, and a water inlet pipeline 14 is sealed and installed at the water inlet port of the heat exchanger 4, and the lower end of the water inlet pipeline 14 is sealed and connected to the inside of the water supply pipe 11.

[0048] Preferably, the inner diameter of the water supply pipe 2 is at least twice the inner diameter of the water supply pipe 11, the interval between the centerline axis of the water supply pipe 2 and the water supply pipe 11 is set to be no less than 500m, and the angle between the line connecting the bottom center of the water supply pipe 2 and the bottom center of the water supply pipe 11 and the horizontal line is 15°-60°, and the angle is the same as the downward dip angle of the formation.

[0049] A small-drill-distance directional fracturing 15 operation is performed in the fracturing hot dry rock formation to connect the interior of the bottom end of the water supply well device with the interior of the bottom end of the water supply well device. This design, as a backup solution of the present application, can effectively increase the water supply volume. In a subsequent alternative solution, an electromagnetic control switch for controlling the opening size of the small-drill-distance directional fracturing section can be installed at the upper port.

[0050] Before working, the local heating system needs to inject sufficient water into the water supply well 1 through the water collecting tank 6 and cooperate with the water injection pump 9 to allow the water to flow into the underground hot dry rock layer 16 that has been fractured and make the underground hot dry rock layer 16 that has been fractured in a saturated state. At this time, the underground rock layer that has been fractured will form a backup water storage area.

[0051] When the system is working, the submersible pump 12 is started to pump water, and a negative pressure siphon state will gradually form in the well during the pumping process. After the operation is stable, the submersible pump 12 can be used alone to achieve single pump operation, effectively reducing the power loss of electrical equipment and achieving high efficiency and energy saving. There is no need to rely on a large number of heating equipment like other equipment of existing products, which consumes a lot of electricity.

[0052] The combination of the three elements and the small-drilling-distance directional fracturing design as a backup solution can better achieve negative pressure siphoning and save energy:

[0053] This system provides a pressure difference by setting a height difference between the lower ends of the water supply well 1 and the water supply well 10; the inclination of the underground rock formation provides the gravity component of the water flow and the direction of the cracks to form a water flow guide; the inner diameter difference between the water supply well 1 and the water supply well 10 is further coordinated with the height difference to ensure the pressure difference effect; finally, the small drilling distance directional fracturing 15 is used to reduce the water flow resistance, better cooperate with the submersible pump 12 to realize good negative pressure siphoning for water supply, ensure the water supply rate, and reduce the energy consumption of the submersible pump 12.

[0054] The construction method of the dry heat single pump geothermal system includes the following steps:

[0055] S1: Conduct geophysical exploration to determine the target rock formation;

[0056] S2: drilling and logging a well to form a water supply well 1;

[0057] S3: Hydraulic fracturing connects hot dry rock formations;

[0058] S4: well layout;

[0059] The well layout distance is obtained according to the calculation, and the location of the subsequent water supply well 10 is determined;

[0060] S5: Drilling and completing wells;

[0061] forming a water well 10;

[0062] S6: Install the water supply pipe 2 assembly and the water supply pipe 11 assembly, and the underground heat exchange system is formed;

[0063] S7: Connect the underground heat exchange system with the ground heat exchange system to form a dry heat type single pump geothermal system.

[0064] Preferably, the method for determining the target rock formation described in S1 comprises the following steps:.

[0065] Preliminary determination of project feasibility based on geophysical exploration results;

[0066] Confirming the geophysical exploration results through exploration wells ultimately determines the feasibility of the project;

[0067] Through stress testing of the target rock formation, well layout design is carried out according to the stress test results;

[0068] Fracturing connection.

[0069] Preferably, the method in S2 comprises the following steps: obtaining the actual stratum structure and lithology by drilling and observing rock cuttings.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention. For those skilled in the art, any replacement, improvement or change made to the implementation mode of the present invention falls within the protection scope of the present invention.

[0071] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A dry heat type single pump geothermal system, comprising an underground heat exchange system and a ground heat exchange system connected and matched with the underground heat exchange system, characterized in that: The underground heat exchange system comprises a water supply well device and at least one water supply well device, the water supply well device and the water supply well device are arranged at intervals, the underground ends of the water supply well device and the water supply well device both extend into the underground hot dry rock layer treated by fracturing, the water supply well device is used to inject water into the underground hot dry rock layer treated by fracturing, the water supply well device is used to lift and transport the hot water that has undergone heat exchange to the ground for use, the underground hot dry rock layer treated by fracturing is used to receive and store water from the water supply well device and realize heat exchange, the bottom end of the water supply well device is lower than the bottom end of the water supply well device and has a height difference, the above-ground water inlet end of the water supply well device and the above-ground water outlet end of the water supply well device are respectively sealed and connected with the outlet end and the inlet end of the heat exchanger in the ground heat exchange system; The water supply well device comprises a water supply well, in which a water supply pipe is installed, a water inlet sealing end cap with an exhaust valve is screwed and installed at the ground water inlet port of the water supply pipe, the outlet end of the heat exchanger is sealed and connected with the inside of the water supply pipe through the outlet pipe, a water collecting tank is installed at the end of the outlet pipe, the water collecting tank is used to receive water from the outlet pipe of the heat exchanger and inject it into the water supply pipe, the water collecting tank is connected with the inside of the water supply pipe through the injection pipe, and a flow control valve is installed on the injection pipe; it also comprises a constant pressure water injection mechanism for auxiliary maintenance; the constant pressure water injection mechanism comprises a water injection pump, the water outlet end of the water injection pump is connected with the inside of the water supply pipe, the water inlet end of the water injection pump is connected with an external water source, an electromagnetic control valve is installed on the water injection pump, a pressure sensor connected with the electromagnetic control valve is installed in the water supply pipe, and the pressure sensor is used to detect the pressure inside the water supply pipe; The small-drill-distance directional fracturing operation for connecting the inside of the bottom end of the water supply well device with the inside of the bottom end of the water supply well device is carried out in the fracturing hot dry rock layer, which can effectively increase the water supply amount; an electromagnetic control switch for controlling the opening size is installed at the upper port of the small-drill-distance directional fracturing section; before the operation, a sufficient amount of water is injected into the water supply well through a water collecting tank and a water injection pump, so that the water flows into the underground hot dry rock layer treated by the fracturing and makes the underground hot dry rock layer treated by the fracturing in a saturated state, and the underground rock layer treated by the fracturing will form a spare water storage area; When the system is working, the submersible pump is started to pump water. During the pumping process, a negative pressure siphon state will gradually form in the well. After stable operation, the submersible pump can be used alone to achieve single pump operation, reducing the power loss of electrical equipment and achieving energy saving. The system provides a pressure difference by setting the height difference between the lower ends of the water supply well and the water supply well. The underground inclination angle provides the gravity component of the water flow and the direction of the cracks to form a water flow guide. The inner diameter difference between the water supply well and the water supply well is further coordinated with the height difference to ensure the pressure difference effect. Finally, directional fracturing with a small drilling distance is used to reduce water flow resistance, better cooperate with the submersible pump to supply water to achieve a good negative pressure siphon, ensure the water supply rate, and reduce the energy consumption of the submersible pump.

2. The dry heat single pump geothermal system according to claim 1, characterized in that: The water supply well device includes a water supply well, a water supply pipe is installed in the water supply well, a submersible pump is installed in the water supply pipe, a water outlet sealing end cover with an exhaust valve is installed at the ground port of the water supply pipe, and a water inlet pipeline is sealably installed at the water inlet port of the heat exchanger, and the lower end of the water inlet pipeline is sealably connected to the inside of the water supply pipe.

3. The dry heat single pump geothermal system according to claim 2, characterized in that: The inner diameter of the water supply pipe is at least twice the inner diameter of the upper water pipe, the interval between the centerline axis of the water supply pipe and the upper water pipe is not less than 500m, the angle between the line connecting the bottom center of the water supply pipe and the bottom center of the upper water pipe and the horizontal line is 15°-60°, and the angle is the same as the downward dip angle of the formation.

4. A construction method for a dry heat type single pump geothermal system, applied to the dry heat type single pump geothermal system according to claim 3, characterized in that: The steps include: S1: Conduct geophysical exploration to determine the target rock formation; S2: Drilling and logging a well to form a water supply well; S3: Hydraulic fracturing connects hot dry rock formations; S4: well layout: the well layout distance is calculated and the location of the subsequent water supply well is determined; S5: digging wells and forming wells; forming water supply wells; S6: Install water supply pipes and water pipes, and the underground heat exchange system is formed; S7: Connect the underground heat exchange system with the ground heat exchange system to form a dry heat type single pump geothermal system.

5. The construction method according to claim 4, characterized in that: The method for determining the target rock formation described in S1 includes the following steps: preliminarily determining the feasibility of the project based on the geophysical exploration results; Confirming the geophysical exploration results through exploration wells ultimately determines the feasibility of the project; Through stress testing of the target rock formation, well layout design is carried out according to the stress test results; Fracturing connection.

6. The construction method according to claim 5, characterized in that: The method in S2 comprises the following steps: the actual formation structure and lithology are known by actual drilling and observation of rock cuttings.

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