Device for exchanging geothermal energy with an aquifer which is near the surface, and thermal power station comprising at least one such device

Abstract

The invention relates to a device for exchanging geothermal energy with an aquifer which is near the surface for an operation in a thermal power station using an exploitation well (1) for conveying groundwater out of the aquifer (3) through at least one exploitation line (7) and using an injection well (4) for injecting the conveyed groundwater into the aquifer (3) through at least one injection line (9), wherein the at least one exploitation line (7) and the at least one injection line (9) are connected together via a primary line (17) in order to transfer water. The invention is characterized in that the exploitation well (1) has at least one horizontal exploitation section (6) at the aquifer-side end (12) thereof, the at least one exploitation section (6) is operatively connected to at least one exploitation line (7) in order to convey water out of the aquifer (3), and a filter tube (2) is arranged within the at least one exploitation section (6).

Description

[0001] Designation: Device for exchanging geothermal energy with a near-surface aquifer and thermal power plant with at least one such device

[0002] The invention relates to a device according to the preamble of patent claim 1 and to a thermal power plant with at least one such geothermal duplicate.

[0003] Near-surface geothermal energy refers to the use of geothermal energy from depths of up to 400 meters. A geothermal doublet consists of a production well for groundwater extraction and an injection well for returning the cooled water from a near-surface aquifer. A geothermal doublet is the central element of a geothermal plant, although the number of production wells does not necessarily have to be the same as the number of injection wells for returning the groundwater. In a geothermal doublet, groundwater is extracted from groundwater-bearing rock layers, so-called near-surface aquifers, from which heat is extracted in a thermal power plant via a heat exchanger and / or a heat pump.For reasons of water management and water balance within the aquifer, it is then planned that water extracted via the production well is returned to the same aquifer via an injection well at a certain distance from the production well.

[0004] In principle, a large number of devices according to the preamble of patent claim 1 are already known. For example, DE 10 2016 002 255 A1 describes how water is extracted from a shaft of a flooded underground mine to utilize the geothermal energy stored therein, a portion of the geothermal energy is extracted from the water via a heat exchanger, and the water is then returned to the flooded underground mine via another shaft.

[0005] Further devices according to the preamble of patent claim 1 are also known from DE 10 2008 057 943 A1, DE 10 2015 002 744 B4, CH 703 613 A1 and DE 103 43 544 A1.

[0006] Typically, a geothermal doublet consists of two vertical wells drilled at a corresponding distance, one used as a production well and the other as an injection well. Since an aquifer can be used to a maximum depth of 400 meters for near-surface geothermal energy or closed systems, one vertical well can extract water from the aquifer to a maximum depth of 400 meters, with the effective withdrawal area corresponding to the height of the aquifer, usually several tens of meters. Expansion can be achieved through multiple vertical production wells. However, this type of upscaling requires a larger area at the surface, meaning the space required for it cannot be used for other purposes. While it is possible to drill production and injection wells from a single well site, deviated wells can open up a wider user horizon.However, further upscaling of vertical wells drilled this deep requires additional vertical wells at the surface, meaning that in this case, the space required by the upscaling cannot be used for other purposes. Furthermore, the capacity increase from an additional well is only a factor of 2 compared to the original well.

[0007] It is therefore an object of the invention to provide a device according to the preamble of patent claim 1, which allows upscaling without requiring additional surface area. Furthermore, it is an object of the invention to provide a thermal power plant with such a device.

[0008] With regard to the device, this object is achieved by a device having all the features of patent claim 1. With regard to the thermal power plant, this object is achieved by a thermal power plant having all the features of patent claim 12. Advantageous embodiments of the invention can be found in the subclaims.

[0009] The device according to the invention for exchanging geothermal energy or thermal energy with a near-surface aquifer for operation in a thermal power plant has a production borehole for extracting groundwater from a near-surface aquifer and an injection borehole for returning or injecting the extracted groundwater back into the near-surface aquifer. The at least one production line is connected to the at least one injection line for conveying water via a primary line. According to the invention, the production borehole has at least one horizontal production string at its aquifer-side end, wherein the production strings are operatively connected to at least one production line for extracting water from the aquifer, and wherein a filter pipe is arranged within each production string.In practice, the production well will be designed as a vertical shaft, which usually has a solid shaft bottom. Within this shaft, one or more horizontal production strings can be inserted into the aquifer to extract the groundwater. A key feature of the invention is that just one horizontal production string is sufficient to increase the capacity of the production well by an order of magnitude, i.e. by a factor of 10, or even more, compared to a state-of-the-art vertical borehole. The crucial factor here is that at least one production string can be driven over 100 meters into the aquifer, and from this, over 100 meters of groundwater can be extracted. The greater the number of production strings, the greater the capacity of the entire device and thus the amount of heat that can be extracted from or added to the groundwater in a thermal power plant.This requires no additional vertical drilling besides the single vertical shaft, so that additional surface space is not required when scaling up the system. The horizontal production strings, located on one or more levels, are collectively referred to as horizontal wells.

[0010] The individual production strings can be designed in either a wet or dry configuration within the shaft. In a wet configuration, the groundwater extracted via the production strings is collected at the bottom of the shaft and conveyed to the surface via at least one production line. However, the groundwater collected in the shaft floor comes into contact with the oxygen and other gases contained in the air, so that the likelihood of ochre formation within the at least one production line can increase with its service life, depending on the mineralization of the groundwater.

[0011] The device according to the invention is advantageously suitable, on the one hand, for extracting geothermal energy from an aquifer to supply heat to heat consumers, such as private households, but also commercial and industrial facilities. On the other hand, the device according to the invention can also be used for cooling. In this case, both private households and commercial and industrial facilities, such as energy-intensive data centers or the like, can be cooled.

[0012] According to a first advantageous embodiment of the invention, the injection well has at least one horizontal injection string at its aquifer-side end, wherein the at least one injection string is operatively connected to at least one injection line for introducing water into the aquifer, and wherein a filter pipe is arranged within the at least one injection string. According to this embodiment of the invention, the injection well has an identical design to the production well, i.e., it is mirrored. This is particularly advantageous because the injection well has at least the same capacity for incoming water as the production well has for water to be extracted. Advantageously, however, the injection well has a greater capacity to ensure that the water extracted from the aquifer is always introduced.Thus, a separate capacity adjustment is not necessary. In this embodiment of the invention, too, it is provided that the injection borehole is not designed as a simple vertical borehole. Rather, this injection borehole is then also designed as a vertically designed injection shaft, in which at least one horizontal injection string returns the groundwater to the aquifer. In this respect, the injection borehole also has a horizontal well—equivalent to the production well—in which, however, the groundwater is returned via the at least one injection string. In this embodiment of the invention, it can also be provided that the injection strings of the injection borehole return the groundwater to the same aquifer at different heights within the injection shaft.This measure also increases the absorption capacity of the injection well, so that no further injection well needs to be drilled at the surface during upscaling, which also minimizes the area required for the injection well at the surface, so that the saved area is available for other purposes.

[0013] The production well, with the at least one production line and the at least one production string, forms a first separate horizontal filter well, and the injection well, with the at least one injection line and the at least one injection string, forms a second separate horizontal filter well. These two separate horizontal filter wells form a geothermal doublet. Both the production well and the injection well can be designed as a shaft.

[0014] According to a further advantageous embodiment of the invention, however, it is provided that the groundwater extracted from the aquifer through one horizontal well or through the production borehole is pumped to the injection borehole in the absence of external oxygen. In this case, a dry installation is implemented, if possible, in which the groundwater extracted via each horizontal production line is pumped directly to the injection borehole via a pipe system in the absence of external oxygen. The advantage of a dry installation is that the entire groundwater extraction and return process can take place in the absence of external oxygen, which significantly minimizes the problem of calcification within the pipe system and thus significantly increases the service life of the pipe system.

[0015] In an advantageous embodiment of the invention, the individual production lines are combined in a common production line in which the extracted groundwater is conveyed to the surface and further to the injection well.

[0016] To enable further upscaling of the entire geothermal doublet, a particularly advantageous embodiment of the invention provides for at least one horizontal production string to be provided at different heights of the production well or production shaft within the aquifer. This embodiment of the invention extracts groundwater from different levels, i.e., different heights of the aquifer, and further increases the groundwater extraction rate without increasing the surface area required. This measure therefore further increases the amount of heat that can be extracted from the geothermal doublet in a thermal power plant without requiring additional surface area.The extracted groundwater is returned to the same aquifer via the injection well, so that the groundwater level and thus the water balance remain unaffected and, overall, no groundwater is extracted from the aquifer.

[0017] According to a further embodiment of the invention, the production well or production shaft and the injection well are spaced at least ten times apart from each other by the depth of the production well and the injection well. This measure ensures that the groundwater returned via the injection well has the opportunity to reabsorb the heat extracted from the geothermal energy in the aquifer by the thermal power plant before it reaches the production well again and can be fed back into the thermal power plant for further heat extraction. Cooling of the aquifer is thus effectively prevented. To enable efficient heat extraction without generating cooling of the entire aquifer over a longer period of time, the minimum distance between the production well and injection well or shaft must be determined using a calculation model adapted to the geology of the aquifer location.If the distance is sufficient, the geothermal energy will supply the aquifer with sufficient heat energy, effectively preventing the aquifer from cooling down.

[0018] In principle, the number of horizontal injection strings within the injection borehole or vertical injection shaft can be configured to correspond to the number of horizontal production strings of the horizontal well(s) of the production borehole, so that the extraction and absorption capacity is equal. However, it is advantageous if the number of horizontal injection strings within the injection borehole is greater than the number of horizontal production strings of the horizontal well(s) of the production borehole, as the extracted groundwater can be returned without additional pressure, thus minimizing equipment costs by eliminating the need for pumps within the injection area.

[0019] According to another advantageous embodiment of the invention, the horizontal production strings and / or the horizontal injection strings have a length of more than 10 meters, preferably more than 50 meters, and particularly preferably more than 100 meters. Upscaling can also be achieved by varying the length of the production strings, so that a larger quantity of groundwater can be pumped to the thermal power plant and a larger amount of heat can be extracted there without requiring additional space at the surface. The corresponding length-related design of the injection strings, which must be able to absorb the returned groundwater, aims in the same direction. By varying the length of the individual production and injection strings, it is easily possible to adapt the geothermal duplicate or the thermal power plant to the heat consumers.In principle, it is even possible to subsequently increase the capacity of the geothermal duplicate or thermal power plant by installing additional horizontal production and injection lines.

[0020] According to a further aspect of the invention, the horizontal production lines and / or the horizontal injection lines are equipped with filter pipes. This allows groundwater to penetrate into the filter pipes of the production lines and exit from the filter pipes of the injection lines, thus enabling simple and safe extraction and return of the groundwater.

[0021] To remove potentially larger particles from the groundwater, the filter pipes are supported in a bed of gravel or glass beads, preferably as the bed and / or filter material. These materials are particularly well-suited to retaining particles, and the use of glass beads, especially as a filter material, allows for significantly more effective particle removal than using gravel. In addition, the grain size of the gravel or the size of the glass beads is adapted to the groundwater flow velocity in the aquifer to enable particularly effective extraction and recirculation of the groundwater.

[0022] According to a further advantageous embodiment of the invention, it is provided that by means of the feed pumps within the device, in particular within the at least one feed line and the at least one injection line, an overpressure is maintained or the water is pumped through the at least one feed line and the at least one injection line at a pressure to be determined or adjusted in order to avoid or minimize precipitation and clogging within the at least one feed line and the at least one injection line.

[0023] The thermal power plant according to the invention is equipped with at least one device as described above. Such a thermal power plant can extract or supply significantly more heat from the groundwater than when used with a geothermal doublet with a normal vertical well, so that significantly more consumers can obtain heat energy from the thermal power plant or supply it to the thermal power plant. Thus, for example, significantly more households in a residential area can be supplied with heat energy or cooled, or significantly more heat energy can be used for industrial purposes, both for heating and cooling. Upscaling is also possible, since horizontal production strings can be inserted at different heights within the vertical production borehole or the production shaft within the horizontal well.In the same way, the groundwater can be returned via the injection well with corresponding horizontal injection lines without increasing the area required on the surface.

[0024] It has also proven advantageous for the thermal power plant to have at least one heat exchanger and / or at least one heat pump in order to extract or supply thermal energy from the groundwater extracted between the production well and the injection well. For this purpose, the extracted groundwater is fed to the heat exchanger and / or the heat pump via a primary line, wherein a liquid is heated or cooled in a secondary line coupled to the heat exchanger and / or the heat pump, and the supplied or extracted thermal energy is passed on to consumers via the secondary line. Therefore, the at least one heat exchanger and / or the at least one heat pump is operatively connected on the one hand to the primary line and on the other hand to a closed secondary line for transferring thermal energy, wherein the secondary line is operatively connected to consumers.

[0025] Since the use of geothermal energy is a CO2-free and renewable form of energy, it makes sense to keep the entire energy use process CO2-free in order to make the operation of the geothermal duplicate plant and the thermal power plant as emission-free as possible. Therefore, it makes sense to use electricity generated from renewable sources, such as photovoltaic or wind turbines, to operate at least one heat pump.

[0026] By using geothermal doublets with horizontal wells, the capacity of the thermal power plant can be significantly increased, as significantly more groundwater can be extracted and returned from the aquifer in a smaller area than with vertical wells. This allows the thermal power plant to have significantly more groundwater available, from which significantly more thermal energy can be extracted. The thermal power plant can be easily adapted to demand by varying the number of horizontal production and injection lines or by connecting additional geothermal doublets with horizontal wells to the thermal power plant.

[0027] As already described, it is possible to run the entire process in opposite directions and use the geothermal doublet for both heating and cooling. For cooling, heat is extracted from the fluid in the secondary line in a heat exchanger and / or a heat pump and fed to the groundwater via the primary line. For heating, heat energy from the primary line is fed to the secondary line via a heat exchanger and / or a heat pump, which can then supply heat to consumers.

[0028] Further objects, advantages, features, and possible applications of the present invention will become apparent from the following description of the exemplary embodiments with reference to the drawings. All described and / or illustrated features, individually or in any meaningful combination, constitute the subject matter of the present invention, regardless of their summary in the claims or their reference back to them.

[0029] They show:

[0030] Figure 1: a first embodiment of a thermal power plant according to the invention with a first embodiment of a device according to the invention for operation in the thermal power plant,

[0031] Figure 2: a second embodiment of a thermal power plant according to the invention with a second embodiment of a device according to the invention for operation in the thermal power plant and

[0032] Figure 3: a third embodiment of a thermal power plant according to the invention with a third embodiment of a device according to the invention for operation in the thermal power plant.

[0033] Figure 1 shows a first embodiment of a thermal power plant according to the invention, in which a first embodiment of a geothermal doublet according to the invention is used in dry installation.

[0034] The thermal power plant according to the invention in Figure 1 essentially consists of a heat pump 14 and a heat exchanger 13, which supply a plurality of heat consumers A with thermal energy via a secondary line 18. Both the heat exchanger 13 and the heat pump 14 are coupled to a geothermal doublet via a primary line 17. The geothermal doublet has a production section and an injection section, which are connected to one another by means of the primary line 17, wherein the primary line 17 is coupled to the thermal power plant or to the heat pump 14 and the heat exchanger 13 in such a way as to transfer the thermal energy of the groundwater pumped in the primary line to the thermal power plant. The production section essentially consists of a production borehole 1, which in the present exemplary embodiment is designed as a production shaft 10 arranged below the earth's surface 21.In the present case, two production lines 7 are arranged in the production shaft 10, which are each connected on the one hand to two production strings 6 arranged at an aquifer-side end 12 of the production lines 7 and on the other hand to the primary line 17.

[0035] In the present exemplary embodiment, two production strings 6 are arranged at two different heights in the production shaft 10, which protrude into an aquifer 3 and are designed to pump groundwater from the aquifer 3 via the production lines 7 to the primary line 17 in order to make thermal energy contained in the groundwater available to the thermal power plant by means of the heat pump 14 and the heat exchanger 13. The production strings 6 form a horizontal well 5, so that a horizontal well 5 with production strings 6 arranged at different heights is arranged in the production shaft 10 within the aquifer 3. The entire horizontal well 5 is arranged below the groundwater level 19 of the aquifer 3. As a result, larger quantities of groundwater can be made available to the thermal power plant from the aquifer 3 than with vertical wells known from the prior art.This makes it possible to supply significantly more groundwater to the thermal power plant and thus extract significantly more heat energy, which can be made available to a variety of heat consumers A without having to increase the surface area required. Filter pipes 2 are arranged within the extraction lines 6. To separate the groundwater to be extracted from particles, the filter pipes 2 are located in a bed of gravel.

[0036] 15 and / or glass beads 16 or similar filler material. In the present embodiment, both gravel 15 and glass beads 16 are used as fill material. However, this is only an example; in practice, each horizontal well 5 will be uniformly provided with a fill material, i.e., either gravel 15 or glass beads 16 or similar filler material, to accommodate the filter tubes 2. The use of glass beads

[0037] 16 is ideal for this purpose, as it can be cleaned of particles more easily than gravel. Depending on the local geology, both the filter size of the filter pipes 2 and the grain size of the fill material can be adjusted to prevent the filter pipes 2 from becoming filled with sand.

[0038] The groundwater from the aquifer 3 enters the filter pipe 2 located within the production line 6 via the gravel 15 or glass beads 16 or similar filling material and is then transported via the production line 7 into the primary line 17 of the thermal power plant. To pump the groundwater from the aquifer 3 into the primary line 17, a pump 20 is used in each production line 7. The pumps 20 pump the groundwater within the production line 7 through the device at a pressure to be determined in each case in order to avoid or minimize precipitation or clogging within the production line 7 and injection line 9.

[0039] In the primary line 17, the groundwater is now fed to the thermal power plant via the heat exchanger 13 and the heat pump 14 to extract the thermal energy contained in the groundwater. After the groundwater in the primary line 17 has passed through the heat exchanger 13 and the heat pump 14, the now cooled groundwater is fed further via the primary line 17 to the injection section, where it is returned to the aquifer 3.

[0040] In the present embodiment, the injection section consists of an injection borehole 4, which is designed as an injection shaft 11 located below the earth's surface 21. Within this injection shaft 11, horizontal injection strings 8 are also formed at different heights at an aquifer-side end 22 of the injection lines 9. Filter pipes 2 are arranged in these injection lines, which are also embedded in a bed of gravel 15 or glass beads 16. In the present embodiment, the number of production strings 6 is equal to the number of injection strings 8, so that the same capacity level prevails on both sides of the geothermal doublet. All production strings 6 and injection strings 8 are the same length.Of course, it is also possible to increase the number of injection strings 8 or their length in order to increase the absorption capacity on the injection side so that the performance of the feed pumps 20 in the feed area is sufficient to return the groundwater to the aquifer 3.

[0041] The cooled groundwater is pumped into injection lines 9 via the primary line 17. An injection pump (not shown here) can also be used for pumping to return the cooled groundwater under pressure to aquifer 3 if the capacity of the pumping pumps 20 in the pumping area is insufficient to return the groundwater to aquifer 3.

[0042] The injection lines 9 lead the cooled groundwater into the filter pipes 2, which are located in the horizontal injection lines 8, from where they feed the groundwater directly back into the aquifer 3.

[0043] Within the injection section, the filter pipes 2 and the injection strings 8 are also arranged at different heights within the injection shaft 11 and also within the aquifer 3, so that the previously large amount of groundwater extracted from the aquifer 3 can also be easily made available to the aquifer 3 again. In this respect, the injection strings 8 form a separate horizontal filter well 5', analogous to the production strings 6.

[0044] As can be seen from Figure 1, the entire extraction of groundwater in the extraction section and the return of groundwater in the injection section take place in the absence of external oxygen and external gas, thus significantly minimizing the problem of ochre contamination and significantly increasing the overall service life of the pipeline system. In principle, other or further technically known measures, such as the use of electrical potentials or—as already described—overpressure in the system, can also be used to minimize ochre contamination in the pipeline system of the geothermal doublet.

[0045] Figure 2 shows a second embodiment of a thermal power plant according to the invention, in which a second embodiment of a geothermal doublet according to the invention is used in a dry installation. The part of the thermal power plant located above the earth's surface 21 corresponds to that of the embodiment shown in Figure 1, with a plurality of consumers A being supplied with heat.

[0046] However, the parts of the geothermal doublet located below the earth's surface 21 differ in some details. The production area, like the exemplary embodiment in Figure 1, includes a horizontal well 5 arranged in a production borehole 10 formed as a vertical shaft 10, with four horizontal production strings 6 arranged at an aquifer-side end 12 of the production lines 7. However, in the exemplary embodiment in Figure 2, each individual production string 6 is connected to a separate production line 7, with all four production lines 7 flowing into the primary line 17 of the thermal power plant. The entire horizontal well 5 is located below the groundwater level 19 of the aquifer 3.

[0047] Here, too, filter pipes 2 are arranged within the production lines 6, which are embedded in a fill of gravel 15 and / or glass beads 16 or similar fill material. In this exemplary embodiment, both gravel 15 and glass beads 16 are used as the fill. However, this is only an example; in practice, each horizontal well 5 will be uniformly provided with a fill material, i.e., either gravel 15 or glass beads 16 or similar fill material, to accommodate the filter pipes 2.

[0048] The groundwater from the aquifer 3 enters the filter pipe 2 located within the production line 6 via the gravel 15 or glass beads 16 or similar filling material and is then transported via the production line 7 into the primary line 17 of the thermal power plant. A separate pump 20 is used in each of the four production lines 7 to pump the groundwater from the aquifer 3 into the primary line 17.

[0049] In the primary line 17, the groundwater is now fed to the thermal power plant via the heat exchanger 13 and the heat pump 14, as in the embodiment shown in Figure 1, to extract the thermal energy contained in the groundwater. After the groundwater in the primary line 17 has passed through the heat exchanger 13 and the heat pump 14, the now cooled groundwater is fed further via the primary line 17 to the injection section, where it is returned to the aquifer 3.

[0050] In the present exemplary embodiment, the injection section consists of an injection borehole 4, which is designed as an injection shaft 11 arranged below the earth's surface 21. Within this injection shaft 11, four horizontal injection strings 8 are now also formed at different heights at an aquifer-side end 22 of the injection lines 9. Filter pipes 2 are arranged in these horizontal injection strings, which are also embedded in a bed of gravel 15 or glass beads 16. In the present exemplary embodiment, the number of production strings 6 is equal to the number of injection strings 8, so that the same capacity level prevails on both sides of the geothermal doublet, with each injection string 8 being connected to the primary line 17 via a separate injection line 9. In this exemplary embodiment, too, all production strings 6 and injection strings 8 are of the same length.Of course, it is also possible to increase the number of injection strings 8 or their length in order to increase the absorption capacity on the injection side, so that the performance of the feed pumps 20 in the feed area is sufficient to return the groundwater to the aquifer 3. In this respect, the injection strings 8, analogous to the feed strings 6, also form a separate horizontal filter well 5'.

[0051] Here, too, the cooled groundwater is pumped into injection lines 9 via the primary line 17. An injection pump (not shown here) can also be used for pumping to ensure that the cooled groundwater is returned to aquifer 3 under pressure if the performance of the feed pumps 20 in the pumping area is not sufficient to return the groundwater to aquifer 3.

[0052] Since the embodiment of Figure 2 also shows a completed dry installation of the geothermal duplicate, this counteracts the problem of ochre infestation of the pipeline system - as in the embodiment of Figure 1.

[0053] In contrast to the exemplary embodiments in Figures 1 and 2, the exemplary embodiment in Figure 3 shows a geothermal doublet in a wet installation. The part of the thermal power plant located above the earth's surface 21 corresponds to that of the two previously described exemplary embodiments, with a plurality of consumers A being supplied with heat.

[0054] However, the parts of the geothermal doublet located below the earth's surface 21 differ in some details. The production area, like the previously described embodiments, includes a horizontal well 5 arranged in a production borehole 10 formed as a vertical shaft 10 with four horizontal production strings 6 arranged at an aquifer-side end 12 of the production lines 7. However, in the embodiment shown in Figure 3, each individual production string 6 flows directly into the production shaft 10, in which the groundwater collects. Here, too, the entire horizontal well 5 is located below the groundwater level 19 of the aquifer 3. Two production lines 7, each equipped with a production pump 20, dip into the groundwater collected in the production shaft 10 and pump the groundwater into a common primary line 17 of the thermal power plant, from where it is fed back into an injection area.In this embodiment, this is also designed as a wet well installation and consists of an injection shaft 11 designed as an injection borehole 4. Four horizontal injection lines 8 are inserted into the injection shaft 11, which open directly into the injection shaft 11. Two injection lines 9 lead from the primary line 17 into the injection shaft 11, into which the groundwater pumped by the feed pumps 20 is collected, where the groundwater level 19 is also established. From the injection shaft 11, the groundwater is returned to the aquifer via the injection lines 8.

[0055] Here, too, both the production strings 6 and the injection strings 8 have filter pipes 2, which are embedded in a fill material that can be formed from gravel 15 and / or glass beads 16 or similar fill material. In the present exemplary embodiment, both gravel 15 and glass beads 16 are used as the fill material. However, this is only an example; in practice, each horizontal well 5, 5' will be uniformly provided with a fill material, i.e., either gravel 15 or glass beads 16 or similar fill material, to accommodate the filter pipes 2. The use of glass beads 16 is recommended because they can be cleaned of particles more easily than gravel. A wet-well installation of the geothermal doublet is generally recommended when the groundwater flowing in the aquifer 3 has a mineralization that makes rock formation in the pipe system of the geothermal doublet unlikely.

[0056] Although the systems shown in Figures 1 to 3 have been described here for extracting thermal energy from aquifer 3, it is also possible to use the system for cooling by introducing thermal energy into aquifer 3 after the water extracted from the aquifer has been heated via heat exchanger 13 or heat pump 14.

[0057] List of reference symbols

[0058] 1 production well

[0059] 2 filter tube

[0060] 3 Aquifer

[0061] 4 injection wells

[0062] 5 horizontal wells

[0063] 6 conveyor string

[0064] 7 Conveying line

[0065] 8 Injection line

[0066] 9 Injection line

[0067] 10 production shaft

[0068] 11 Injection shaft

[0069] 12 aquifer end

[0070] 13 heat exchangers

[0071] 14 Heat pump

[0072] 15 gravel

[0073] 16 glass balls

[0074] 17 Primary line

[0075] 18 Secondary line

[0076] 19 Groundwater level

[0077] 20 feed pump

[0078] 21 Earth's surface

[0079] 22 aquifer end

[0080] A heat consumer

Claims

Patent claims 1. Device for exchanging geothermal energy with a near-surface aquifer for operation in a thermal power plant, having a production borehole (1) for pumping groundwater from the aquifer (3) through at least one production line (7) and an injection borehole (4) for injecting the pumped groundwater into the aquifer (3) through at least one injection line (9), wherein the at least one production line (7) is connected to the at least one injection line (9) for conveying water via a primary line (17), characterized in that the production borehole (1) has at least one horizontal production line (6) at its aquifer-side end (12), wherein this at least one production line (6) is operatively connected to at least one production line (7) for pumping water out of the aquifer (3), and wherein a filter pipe (2) is arranged within the at least one production line (6).

2. Device according to claim 1, characterized in that the injection bore (4) has at least one horizontal injection string (8) at its aquifer-side end (22), wherein the injection strings (8) are operatively connected to at least one injection line (7) for introducing water into the aquifer (3), and wherein a filter pipe (2) is arranged within each injection string (8).

3. Device according to one of the preceding claims, characterized in that a) the production bore (1) with the at least one production line (7) and the at least one production line (6) forms a first horizontal filter well (5) and b) the injection bore (4) with the at least one injection line (9) and the at least one injection line (8) forms a second horizontal filter well (5').

4. Device according to claim 3, characterized in that the two horizontal filter wells (5, 5') form a geothermal doublet.

5. Device according to one of the preceding claims, characterized in that the production bore (1) is designed as a first shaft (10) and the injection bore (4) as a second shaft (11) is formed.

6. Device according to one of the preceding claims, characterized in that the groundwater extracted from the aquifer (3) through the production borehole (1) is conveyed to the injection borehole (4) under exclusion of external oxygen.

7. Device according to one of the preceding claims, characterized in that the production borehole (1) has at least two horizontal production strings (6) which are arranged at different heights of the production borehole (1) within the aquifer (3).

8. Device according to one of the preceding claims, characterized in that the production bore (1) and the injection bore (4) have a minimum distance of ten times the depth of the production bore (1) and the injection bore (4) from each other.

9. Device according to one of the preceding claims, characterized in that the horizontal conveyor lines (6) and / or the horizontal injection lines (8) have a length of greater than 10 meters, preferably greater than 50 meters and particularly preferably greater than 100 meters.

10. Device according to one of the preceding claims, characterized in that the filter tubes (2) are stored in a bed, wherein gravel or glass beads are used as bed material and / or filter material.

11. Device according to one of the preceding claims, characterized in that feed pumps (20) are arranged for conveying the water within the feed bore (1), in particular within the at least one feed line (7), and / or within the injection bore (4), in particular within the at least one injection line (9).

12. Device according to claim 11, characterized in that by means of the feed pumps (20) an overpressure is maintained within the device, in particular within the at least one delivery line (7) and the at least one injection line (9), or the water is pumped through the at least one delivery line (7) and the at least one injection line (9) at a pressure to be determined or adjusted.

13. Thermal power plant with at least one device according to one of the preceding claims.

14. Thermal power plant according to claim 13, characterized in that it has at least one heat exchanger (13) and / or at least one heat pump (14) in order to extract or supply thermal energy from the groundwater extracted between the production borehole (1) and the injection borehole (4).

15. Thermal power plant according to claim 13 or 14, characterized in that the at least one heat exchanger (13) and / or the at least one heat pump (14) is operatively connected on the one hand to the primary line (17) and on the other hand to a closed secondary line (18) for transmitting thermal energy, wherein the secondary line (18) is operatively connected to heat consumers (A).

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