Enhanced single well local open type geothermal system

Abstract

The utility model provides an enhanced single well local open type geothermal system, which relates to the technical field of geothermal systems and comprises a main shaft and branch shafts. A central pipe is arranged in the main shaft, an annulus is formed by the inner wall of the main shaft and the outer wall of the central pipe, the bottom of the annulus is communicated with the bottom of an inner cavity of the central pipe, a packer is arranged in the annulus and divides the annulus into an upper annular cavity and a lower annular cavity, and the upper annular cavity is communicated with the lower annular cavity. A communicating hole communicating with the upper annular cavity and a first perforation hole communicating with the lower annular cavity are formed in the wall part of the main shaft; one end of the branch shaft is connected to the communicating hole of the main shaft, a second perforation hole is formed in the wall of the branch shaft, and a water passing channel is formed between the second perforation hole and the first perforation hole. The heat taking efficiency can be improved.

Description

Technical Field

[0001] This utility model relates to the field of geothermal system technology, and more specifically, to an enhanced single-well locally open geothermal system. Background Technology

[0002] Single-well geothermal systems are one of the commonly used methods for developing geothermal energy. They mainly extract heat from underground through a single well to provide it for heating systems.

[0003] In related technologies, existing single-well geothermal systems typically employ a closed system consisting of a wellbore and a central pipe. In this system, when fluid flows in from the annulus between the wellbore and the central pipe and takes heat, it directly enters the central pipe and returns to the surface. However, since the heat extraction process relies on heat conduction between the wellbore and the rock strata, the contact area between the wellbore and the rock strata is limited by the size of the wellbore, which results in limited heat extraction efficiency for the entire single-well geothermal system. Utility Model Content

[0004] The problem this invention addresses is: how to improve the heat extraction efficiency of a single-well geothermal system.

[0005] To address the aforementioned problems, this utility model provides an enhanced single-well locally open geothermal system.

[0006] This utility model provides an enhanced single-well partially open geothermal system, including a main well and branch wells. The main well contains a central pipe, and the inner wall of the main well and the outer wall of the central pipe form an annulus. The bottom of the annulus communicates with the bottom of the inner cavity of the central pipe. A packer is provided in the annulus, dividing it into an upper annulus and a lower annulus. The wall of the main well has a connecting hole communicating with the upper annulus and a first perforation communicating with the lower annulus. One end of the branch well is connected to the connecting hole of the main well, and the wall of the branch well has a second perforation, forming a water passage between the second perforation and the first perforation.

[0007] Optionally, it also includes a rock formation, the main wellbore and the branch wellbore extending into the rock formation, the rock formation including a reservoir fracturing zone located between the main wellbore and the branch wellbore, and the water passage including fractures formed in the reservoir fracturing zone.

[0008] Optionally, the branch wellbore gradually slopes downward from the connecting end to the free end.

[0009] Optionally, the first perforation is located in the lower part of the wall of the main wellbore, and the second perforation is located in the lower part of the wall of the branch wellbore.

[0010] Optionally, the first perforation is located on the side of the main wellbore closer to the branch wellbore, and the second perforation is located on the side of the branch wellbore closer to the main wellbore.

[0011] Optionally, the main shaft wall is provided with a plurality of first perforations, which are arranged sequentially at intervals in the vertical direction; the branch shaft wall is provided with a plurality of second perforations, which are arranged in a horizontal direction in a one-to-one correspondence with the plurality of first perforations, and water passages are formed between the horizontally opposite first perforations and second perforations.

[0012] Optionally, the branch wellbore includes a branch casing and a branch cementing sheath disposed around the periphery of the branch casing, and the second perforation sequentially penetrates the wall of the branch casing and the wall of the branch cementing sheath.

[0013] Optionally, the main wellbore includes a main casing and a main cementing sheath disposed around the main casing. The connecting hole sequentially penetrates the wall of the main casing and the wall of the main cementing sheath. The first perforation sequentially penetrates the wall of the main casing and the wall of the main cementing sheath. The connecting end of the branch wellbore is located in the connecting hole. The branch casing is connected to the main casing, and the branch cementing sheath is connected to the main cementing sheath.

[0014] Optionally, the thermal conductivity of the central tube is less than or equal to 0.02 W / (m·K), the thermal conductivity of the main casing and the branch casing are both greater than or equal to 35 W / (m·K) and less than or equal to 45 W / (m·K), and the thermal conductivity of the main cementing sheath and the branch cementing are both greater than or equal to 2 W / (m·K).

[0015] Optionally, the main shaft wall is provided with a plurality of the communicating holes, which are arranged sequentially at intervals along the circumference of the main shaft; a plurality of branch shafts are provided, which are respectively connected to the plurality of communicating holes of the main shaft.

[0016] The beneficial effects of this enhanced single-well partially open geothermal system are as follows: the main well wall is provided with a connecting hole that communicates with the upper annular cavity, and one end of the branch well is connected to the connecting hole of the main well, so that the branch well can communicate with the upper annular cavity through the connecting hole. At the same time, the main well wall is provided with a first perforation that communicates with the lower annular cavity, and the branch well wall is provided with a second perforation. A water passage is formed between the second perforation and the first perforation, so that the branch well can communicate with the lower annular cavity through the water passage. In this way, the upper annular cavity, the branch well, the water passage, the lower annular cavity, and the inner cavity of the central pipe can be connected in sequence. When the fluid enters the upper annular cavity, the fluid does not flow directly from the upper annular cavity to the lower annular cavity, but instead flows from the upper annular cavity around the branch well and the water passage and then back to the lower annular cavity. Compared with the existing single-well closed system, the existence of the branch well and the water passage can relatively increase the heat exchange path and contact area, and can exchange more heat from the bottom layer, thereby improving the heat extraction efficiency. One end of the branch well is connected to the connecting hole of the main well. In this way, the branch well and the main well can form a "one well, multiple sections" composite well structure. It is still a single well system. Compared with the injection-production-opening system, it can reduce the number of wells drilled in the rock formation, thereby reducing drilling costs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an enhanced single-well partially open geothermal system according to an embodiment of the present invention;

[0018] Figure 2 This is a partially enlarged view of the enhanced single-well partially open geothermal system according to an embodiment of this utility model.

[0019] Explanation of reference numerals in the attached figures:

[0020] 1. Main wellbore; 11. Connecting hole; 12. First perforation; 13. Main casing; 14. Main cementing sheath; 2. Branch wellbore; 21. Second perforation; 22. Branch casing; 23. Branch cementing sheath; 3. Center tube; 4. Annulus; 41. Upper annulus; 42. Lower annulus; 5. Packer; 6. Formation; 61. Reservoir fracturing zone; 62. Main borehole; 63. Branch borehole. Detailed Implementation

[0021] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Although some embodiments of this utility model are shown in the drawings, it should be understood that this utility model can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this utility model. It should be understood that the drawings and embodiments of this utility model are for illustrative purposes only and are not intended to limit the scope of protection of this utility model.

[0022] In the attached diagram, the Z-axis represents the vertical direction, i.e., the up-down position, with the positive direction of the Z-axis representing upward and the negative direction representing downward. The Y-axis represents the left-right position, with the positive direction of the Y-axis representing the left and the negative direction representing the right. It should be noted that the aforementioned representations of the Z-axis and Y-axis are merely for ease of description and simplification of the present invention, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0023] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this utility model are only used to distinguish different devices, modules, or units, and are not used to limit the order of functions performed by these devices, modules, or units or their interdependencies.

[0024] It should be noted that the terms "one" and "multiple" used in this utility model are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0025] This invention provides an enhanced single-well locally open geothermal system, which will be described in detail below with reference to specific embodiments.

[0026] like Figure 1 and Figure 2 As shown in the figure, an enhanced single-well partially open geothermal system provided by this utility model embodiment includes a main wellbore 1 and a branch wellbore 2; the main wellbore 1 is provided with a central pipe 3, the inner wall of the main wellbore 1 and the outer wall of the central pipe 3 form an annulus 4, the bottom of the annulus 4 is connected to the bottom of the inner cavity of the central pipe 3, a packer 5 is provided in the annulus 4, the packer 5 divides the annulus 4 into an upper annulus 41 and a lower annulus 42, the wall of the main wellbore 1 is provided with a connecting hole 11 communicating with the upper annulus 41 and a first perforation 12 communicating with the lower annulus 42; one end of the branch wellbore 2 is connected to the connecting hole 11 of the main wellbore 1, the wall of the branch wellbore 2 is provided with a second perforation 21, and a water passage is formed between the second perforation 21 and the first perforation 12.

[0027] Specifically, to ensure the bottom of the annulus 4 is connected to the bottom of the inner cavity of the central tube 3, the lower end of the central tube 3 can be set higher than the lower end of the main wellbore 1. This allows fluid in the bottom of the annulus 4 (i.e., the bottom of the lower annulus 42) to bypass the lower end of the central tube 3 and enter the inner cavity of the central tube 3, thus achieving communication between the bottom of the annulus 4 and the bottom of the inner cavity of the central tube 3. It should be noted that the packer 5, used to control fluid flow and isolate the medium, is a commonly used device in geothermal systems; its specific structure will not be specified further here.

[0028] In this embodiment, the main shaft 1 has a connecting hole 11 on its wall that communicates with the upper annular cavity 41. One end of the branch shaft 2 is connected to the connecting hole 11 of the main shaft 1, allowing the branch shaft 2 to communicate with the upper annular cavity 41 through the connecting hole 11. Simultaneously, the main shaft 1 has a first perforation 12 on its wall that communicates with the lower annular cavity 42, and the branch shaft 2 has a second perforation 21 on its wall. A water passage is formed between the second perforation 21 and the first perforation 12, allowing the branch shaft 2 to communicate with the lower annular cavity 42 through the water passage. Thus, the upper annular cavity 41, the branch shaft 2, the water passage, the lower annular cavity 42, and the inner cavity of the central pipe 3 can be sequentially connected. When fluid enters the upper annular cavity 41, the fluid does not flow directly from the upper annular cavity 41 to the lower annular cavity 42, but instead flows from the upper annular cavity 41 around the branch shaft 2 and the water passage before returning to the lower annular cavity 42 (the fluid flow direction is referenced). Figure 1 (As shown by the arrow) Compared to existing single-well closed systems, the presence of branch wellbore 2 and water passage can relatively increase the heat exchange path and contact area, enabling more heat to be extracted from the bottom layer, thereby improving heat extraction efficiency. One end of branch wellbore 2 is connected to the connecting hole 11 of main wellbore 1. In this way, branch wellbore 2 and main wellbore 1 can form a "one well, multiple sections" composite wellbore structure, which is still a single-well system. Compared to well-injection-production open system, it can reduce the number of wells drilled in rock formation 6, thereby reducing drilling costs.

[0029] Optionally, such as Figure 1 and Figure 2 As shown, the enhanced single-well locally open geothermal system also includes a rock stratum 6, the main wellbore 1 and the branch wellbore 2 extending into the rock stratum 6, the rock stratum 6 including a reservoir fracturing zone 61 located between the main wellbore 1 and the branch wellbore 2, and the water passage including fractures formed in the reservoir fracturing zone 61.

[0030] Specifically, the rock stratum 6 may contain a main wellbore 62 and a branch wellbore 63 connected to the main wellbore 62. The main wellbore 1 is located in the main wellbore 62, and the branch wellbore 2 is located in the branch wellbore 63. It should be noted that fractures can be formed by hydraulic fracturing. Hydraulic fracturing refers to the technique of injecting fracturing fluid into the rock stratum 6 using a high-pressure pump set to form and extend fractures, followed by the filling of proppant to maintain the open state of the fractures. For the specific method of fracture formation, fracturing can be performed from the first perforation 12, so that the formed fracture connects the first perforation 12 and the second perforation 21; fracturing can also be performed from the second perforation 21, so that the formed fracture connects the first perforation 12 and the second perforation 21; or fracturing can be performed simultaneously from the first perforation 12 and the second perforation 21, so that the formed fracture connects the first perforation 12 and the second perforation 21.

[0031] In this optional embodiment, by creating cracks in the rock layer 6 as water passages, the contact area between the water passages and the rock layer 6 can be effectively increased, resulting in higher heat extraction efficiency. In addition, as water passages, cracks allow fluid to flow from the second perforation 21 to the first perforation 12. Compared to fluid directly permeating through the rock layer 6, the flow process is smoother and losses during passage are reduced. Furthermore, the simple form of the cracks avoids the use of additional pipes, thereby helping to reduce material costs.

[0032] Optionally, such as Figure 1 and Figure 2 As shown, the branch wellbore 2 gradually slopes downward from the connecting end to the free end.

[0033] It should be noted that the connecting end is the end of the branch wellbore 2 that is connected to the main wellbore 1, and the free end is the end of the branch wellbore 2 that is not connected to the main wellbore 1.

[0034] In rock stratum 6, geothermal temperature typically increases with depth. In this optional embodiment, by gradually tilting the branch wellbore 2 downwards from the connecting end to the free end, the entire branch wellbore 2 is relatively biased towards the depth of rock stratum 6, thereby obtaining more heat and further improving heat extraction efficiency. In addition, the main wellbore 1 and the branch wellbore 2 do not have curved pipe sections, which simplifies the structure of the entire geothermal system and reduces construction difficulty and risk.

[0035] Optionally, such as Figure 1 and Figure 2 As shown, the packer 5 can be located at a lower position in the annulus 4, and the connecting hole 11 is adjacent to the packer 5 and located above the packer 5. For example, the height of the packer 5 in the annulus 4 is less than 1 / 3 of the height of the annulus 4. With this arrangement, the position of the connecting hole 11 can be closer to the depth of the rock stratum 6, and correspondingly, the entire branch wellbore 2 can also be closer to the depth of the rock stratum 6, thereby further improving the heat extraction efficiency.

[0036] Optionally, such as Figure 1 and Figure 2 As shown, the first perforation 12 is located in the lower part of the wall of the main shaft 1, and the second perforation 21 is located in the lower part of the wall of the branch shaft 2.

[0037] In this optional embodiment, the first perforation 12 is located in the lower part of the wall of the main shaft 1, and the second perforation 21 is located in the lower part of the wall of the branch shaft 2, which can make the water passage deeper, thereby increasing the heat obtained by the fluid flowing through the water passage.

[0038] Optionally, such as Figure 1 and Figure 2 As shown, the first perforation 12 is located on the side of the main wellbore 1 near the branch wellbore 2, and the second perforation 21 is located on the side of the branch wellbore 2 near the main wellbore 1.

[0039] In this optional embodiment, the first perforation 12 is located on the side of the main shaft 1 near the branch shaft 2, and the second perforation 21 is located on the side of the branch shaft 2 near the main shaft 1. This allows the first perforation 12 and the second perforation 21 to be closer together, which makes the construction of the water passage easier and reduces the construction difficulty.

[0040] Optionally, such as Figure 2 As shown, the main shaft 1 has a plurality of first perforations 12 on its wall, which are arranged at intervals in the vertical direction; the branch shaft 2 has a plurality of second perforations 21 on its wall, which are arranged in a horizontal direction in a one-to-one correspondence with the plurality of first perforations 12, and water passages are formed between the horizontally opposite first perforations 12 and second perforations 21.

[0041] The multiple first perforations 12 and multiple second perforations 21 refer to two or more perforations. This embodiment does not limit the specific number and can select them according to actual needs.

[0042] In this optional embodiment, a plurality of first perforations 12 are arranged sequentially at intervals in the vertical direction, and a plurality of second perforations 21 are arranged opposite to the plurality of first perforations 12 in the horizontal direction. Water passages are formed between the horizontally opposite first perforations 12 and second perforations 21, that is, multiple water passages are formed between the plurality of first perforations 12 and the plurality of second perforations 21, so that fluid can flow from the plurality of second perforations 21 to the plurality of first perforations 12 through the multiple water passages. This can promote fluid flow and reduce flow resistance. In addition, the multiple water passages can further increase the contact area with the rock stratum 6, thereby further improving the heat extraction efficiency.

[0043] Optionally, such as Figure 2 As shown, the branch wellbore 2 includes a branch casing 22 and a branch cementing sheath 23 disposed around the branch casing 22. The second perforation 21 passes through the wall of the branch casing 22 and the wall of the branch cementing sheath 23 in sequence.

[0044] In this optional embodiment, the inner cavity of the branch wellbore 2 can be separated from the rock formation 6 by the branch casing 22 and the branch cementing sheath 23, so that fluid is less likely to flow into the rock formation 6 from outside the second perforation 21, thereby reducing fluid loss.

[0045] Furthermore, the bottom opening of the branch casing 22 is provided with a base plate, which covers the bottom opening of the branch casing 22. This can improve the isolation effect between the inner cavity of the branch wellbore 2 and the rock strata 6 and reduce fluid loss.

[0046] Optionally, such as Figure 2 As shown, the main wellbore 1 includes a main casing 13 and a main cementing sheath 14 disposed around the main casing 13. The connecting hole 11 passes through the wall of the main casing 13 and the wall of the main cementing sheath 14 in sequence. The first perforation 12 passes through the wall of the main casing 13 and the wall of the main cementing sheath 14 in sequence. The connecting end of the branch wellbore 2 is located in the connecting hole 11. The branch casing 22 is connected to the main casing 13, and the branch cementing sheath 23 is connected to the main cementing sheath 14.

[0047] In this optional embodiment, the branch casing 22 is connected to the main casing 13, and the branch cementing sheath 23 is connected to the main cementing sheath 14. This allows the main wellbore 1 and the branch wellbore 2 to form an integrated structure, improving the overall integrity of the wellbore structure and helping to further reduce fluid loss.

[0048] Optionally, the thermal conductivity of the central tube 3 is less than or equal to 0.02 W / (m·K), the thermal conductivity of the main casing 13 and the branch casing 22 are both greater than or equal to 35 W / (m·K) and less than or equal to 45 W / (m·K), and the thermal conductivity of the main cementing sheath 14 and the branch cementing sheath are both greater than or equal to 2 W / (m·K).

[0049] In this optional embodiment, the thermal conductivity of the central tube 3 is less than or equal to 0.02 W / (m·K), which ensures that the fluid does not lose heat when passing through the inner cavity of the central tube 3, thereby improving the heat extraction efficiency. The thermal conductivity of the main cementing sheath 14 and the branch cementing sheath are both greater than or equal to 2 W / (m·K), which is high and can enhance the heat transfer capacity to the high-temperature rock formation 6, thereby improving the heat extraction efficiency. The thermal conductivity of the main casing 13 and the branch casing 22 are both greater than or equal to 35 W / (m·K) and less than or equal to 45 W / (m·K), which is greater than that of the rock formation 6 and the cementing sheath. This ensures that the heat transferred from the cementing sheath is not lost and maximizes the heating of the injected fluid.

[0050] Optionally, such as Figure 1 As shown, the main shaft 1 has a plurality of connecting holes 11 on its wall, and the plurality of connecting holes 11 are arranged sequentially at intervals along the circumference of the main shaft 1; the branch shafts 2 are provided in a plurality of manner, and the plurality of branch shafts 2 are respectively connected to the plurality of connecting holes 11 of the main shaft 1.

[0051] The multiple connecting holes 11 refer to two or more connecting holes 11. This embodiment does not limit the specific number, and it can be determined according to factors such as the target heat extraction, the thermal reservoir conditions, and the target investment amount.

[0052] In this optional embodiment, multiple branch wells 2 are respectively connected to multiple connecting holes 11 of the main well 1, and the multiple connecting holes 11 are arranged sequentially at intervals along the circumference of the main well 1. That is to say, the multiple branch wells 2 are radially distributed around the main well 1, which can make more effective use of the heat of the rock strata 6 around the main well 1.

[0053] Although the present invention has been disclosed above, its protection scope is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the protection scope of the present invention.

Claims

1. An enhanced single-well locally open geothermal system, characterized in that, The well includes a main shaft (1) and a branch shaft (2); the main shaft (1) is provided with a central pipe (3), the inner wall of the main shaft (1) and the outer wall of the central pipe (3) form an annulus (4), the bottom of the annulus (4) is connected to the bottom of the inner cavity of the central pipe (3), a packer (5) is provided in the annulus (4), the packer (5) divides the annulus (4) into an upper annulus (41) and a lower annulus (42), the wall of the main shaft (1) is provided with a connecting hole (11) communicating with the upper annulus (41) and a first perforation (12) communicating with the lower annulus (42); one end of the branch shaft (2) is connected to the connecting hole (11) of the main shaft (1), the wall of the branch shaft (2) is provided with a second perforation (21), and a water passage is formed between the second perforation (21) and the first perforation (12).

2. The enhanced single-well locally open geothermal system according to claim 1, characterized in that, It also includes a rock stratum (6), the main wellbore (1) and the branch wellbore (2) extending into the rock stratum (6), the rock stratum (6) including a reservoir fracturing zone (61) located between the main wellbore (1) and the branch wellbore (2), the water passage including fractures formed in the reservoir fracturing zone (61).

3. The enhanced single-well locally open geothermal system according to claim 1, characterized in that, The branch wellbore (2) gradually slopes downward from the connecting end to the free end.

4. The enhanced single-well locally open geothermal system according to claim 3, characterized in that, The first perforation (12) is located in the lower part of the wall of the main shaft (1), and the second perforation (21) is located in the lower part of the wall of the branch shaft (2).

5. The enhanced single-well locally open geothermal system according to claim 4, characterized in that, The first perforation (12) is located on the side of the main wellbore (1) near the branch wellbore (2), and the second perforation (21) is located on the side of the branch wellbore (2) near the main wellbore (1).

6. The enhanced single-well locally open geothermal system according to claim 5, characterized in that, The main shaft (1) has a plurality of first perforations (12) on its wall, and the plurality of first perforations (12) are arranged at intervals in the vertical direction; the branch shaft (2) has a plurality of second perforations (21) on its wall, and the plurality of second perforations (21) and the plurality of first perforations (12) are arranged opposite each other in the horizontal direction, and the water passages are formed between the horizontally opposite first perforations (12) and second perforations (21).

7. The enhanced single-well locally open geothermal system according to claim 1, characterized in that, The branch wellbore (2) includes a branch casing (22) and a branch cementing sheath (23) disposed around the branch casing (22). The second perforation (21) passes through the wall of the branch casing (22) and the wall of the branch cementing sheath (23) in sequence.

8. The enhanced single-well locally open geothermal system according to claim 7, characterized in that, The main wellbore (1) includes a main casing (13) and a main cementing sheath (14) disposed around the main casing (13). The connecting hole (11) passes through the wall of the main casing (13) and the wall of the main cementing sheath (14) in sequence. The first perforation (12) passes through the wall of the main casing (13) and the wall of the main cementing sheath (14) in sequence. The connecting end of the branch wellbore (2) is located in the connecting hole (11). The branch casing (22) is connected to the main casing (13), and the branch cementing sheath (23) is connected to the main cementing sheath (14).

9. The enhanced single-well locally open geothermal system according to claim 8, characterized in that, The thermal conductivity of the central tube (3) is less than or equal to 0.02 W / (m·K), the thermal conductivity of the main casing (13) and the thermal conductivity of the branch casing (22) are both greater than or equal to 35 W / (m·K) and less than or equal to 45 W / (m·K), and the thermal conductivity of the main cementing sheath (14) and the thermal conductivity of the branch cementing are both greater than or equal to 2 W / (m·K).

10. The enhanced single-well locally open geothermal system according to claim 1, characterized in that, The main shaft (1) has a plurality of connecting holes (11) on its wall, and the plurality of connecting holes (11) are arranged sequentially at intervals along the circumference of the main shaft (1); the branch shafts (2) are provided in a plurality of manner, and the plurality of branch shafts (2) are respectively connected to the plurality of connecting holes (11) of the main shaft (1).

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