A downhole heating system for single-well production

Abstract

This invention relates to a downhole heating system for single-well production, comprising a double-walled pipe, a heating rod, a first one-way valve assembly, and a second one-way valve assembly. The double-walled pipe has an inner channel and an outer channel, extending from the wellhead to the working formation. A gas inlet is located at the top of the inner channel, and a gas outlet at the bottom. A liquid outlet is located at the top of the outer channel, and a liquid inlet at the bottom. The heating rod is disposed inside the inner channel and located in the working formation. The first one-way valve assembly is disposed in the inner channel, below the heating rod, and restricts fluid flow from the gas outlet to the gas inlet. The second one-way valve assembly is disposed in the outer channel, at the liquid inlet, and restricts fluid flow from the liquid outlet to the liquid inlet. Compared with existing technologies, this system, through structural innovation and modular integration of downhole heating and downhole fluid return capabilities, significantly extends the service life of the downhole heating device and improves the process efficiency of single-well injection and production.

Description

Technical Field

[0001] This invention relates to the field of mineral extraction technology, and in particular to an underground heating system for single-well mining. Background Technology

[0002] Traditional underground mineral resource development employs mining methods, extracting ore to the surface for processing. This method is influenced by ore layer depth, hydrogeological conditions, and tectonic environment, and generates a large amount of waste during development. In contrast, in-situ mining is a new type of resource utilization method, with its core equipment being an underground heater. The design of the heater is crucial for in-situ mineral mining because economic efficiency is prioritized throughout the entire process, directly affecting the mining cycle and efficiency.

[0003] Downhole heaters have complex structures and must be deployed in conjunction with downhole processes. Due to the complex working conditions downhole, the size of traditional heaters is limited, thus requiring a modular and compact design.

[0004] Currently, traditional downhole heaters typically have a lifespan of only a few months, and their installation and maintenance are cumbersome. Maintenance requires opening the wellhead, lowering the formation temperature to ambient, and performing complex procedures, significantly extending the mining cycle.

[0005] In in-situ mining of solid minerals such as oil shale and oil-rich coal, as well as in the thermal recovery of heavy oil and oil sands, single-well huff and puff processes are frequently employed. This requires not only in-situ downhole heating but also in-situ fluid drainage. Traditional processes involve installing injection and production casings in a single well, placing higher demands on the limited wellbore space and increasing operational complexity. Currently, while in-situ wellhead fluid drainage is relatively common, it is still not possible to simultaneously perform in-situ heating and fluid drainage using the same downhole tool, limiting process integration and efficiency. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a downhole heating system for single-well production. Through structural innovation, it modularly integrates downhole heating and downhole fluid return capabilities, greatly extending the service life of the downhole heating device and improving the process efficiency of single-well injection and production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A downhole heating system for single-well production includes:

[0009] A double-walled tube has an inner channel and an outer channel, and extends from the wellhead to the working formation; the inner channel has a gas inlet at the top and a gas outlet at the bottom; the outer channel has a liquid outlet at the top and a liquid inlet at the bottom.

[0010] A heating rod is disposed inside the inner channel and located in the working layer;

[0011] A first one-way valve assembly is disposed in the inner channel, located below the heating rod, to restrict fluid from flowing from the outlet to the inlet;

[0012] A second check valve assembly is disposed in the outer channel and at the inlet, the second check valve assembly restricting fluid from flowing from the outlet to the inlet.

[0013] In one possible implementation, a spiral baffle is provided on the outer edge of the heating rod, which guides the fluid in the inner channel to flow around the heating rod.

[0014] In one possible implementation, the spiral baffle includes a high-density section and a low-density section, the high-density section being located at one end near the gas inlet.

[0015] In one possible implementation, the first one-way valve assembly includes a Tesla valve.

[0016] In one possible implementation, a mudguard is provided at the outlet end of the Tesla valve.

[0017] In one possible implementation, multiple liquid inlets are provided and are arranged at annular intervals at the ends of the outer channel;

[0018] The second one-way valve assembly includes multiple resilient one-way valves, which are installed at the liquid inlet.

[0019] In one possible implementation, a double-walled tube located above the heating rod is an installation pipe section, and a liquid extraction device is provided inside the installation pipe section. The liquid extraction device provides pressure to the outer channel to pump the fluid from the inlet to the outlet.

[0020] In one possible implementation, a sealing cavity is provided in the inner channel corresponding to the installation pipe section;

[0021] The liquid extraction device is sealed inside the sealed cavity, and a connecting pipe is provided in the outer channel, which connects to the inner channel above and below the sealed cavity.

[0022] In one possible implementation, the liquid extraction device includes:

[0023] Electric motor;

[0024] A drive shaft, which is connected to the motor for transmission; and

[0025] Turbine blades, which are mounted on the drive shaft;

[0026] The inner channel has a liquid extraction port and a liquid pumping port that connect to the outer channel. A solenoid valve is sealed inside the outer channel to switch the connection state of the outer channel. The solenoid valve is located between the liquid extraction port and the liquid pumping port.

[0027] In one possible implementation, the drive shaft is a hollow shaft, and the connecting circuit of the heating rod extends upward through the drive shaft.

[0028] The present invention has the following advantages due to the adoption of the above technical solutions:

[0029] The system utilizes a dual-layer structure with an inner channel (for gas injection / cable laying) and an outer channel (for fluid return), achieving modular integration of heating and extraction functions. This simplifies downhole equipment layout and avoids process interference. Simultaneously, the double-walled tubing extends from the wellhead to the working formation, forming an integrated flow channel, reducing leakage risk and extending service life. Compared to existing technologies, this system, through structural innovation and modular integration of downhole heating and fluid return capabilities, significantly extends the service life of the downhole heating unit and improves the process efficiency of single-well injection and production.

[0030] The heating rod is set in the working layer of the inner channel, and its outer edge is innovatively equipped with a spiral baffle. The airflow path is optimized by high / low density section partitioning design, which not only improves heating efficiency but also avoids heat accumulation. The one-way valve assembly adopts a combination design of Tesla valve and flexible valve. The former uses the principle of fluid dynamics to achieve one-way isolation without mechanical force, while the latter ensures smooth liquid return through multi-valve ring arrangement. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating the specific principle structure of a downhole heating system according to one embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the specific structure of a double-walled tube according to one embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram showing the flow direction of gas in a heating rod according to one embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram showing the flow direction of gas in the first one-way valve assembly according to an embodiment of the present invention.

[0035] Figure 5 This is a schematic diagram showing the flow direction of liquid in the heating rod region according to one embodiment of the present invention;

[0036] Figure 6This is a schematic diagram showing the flow direction of liquid in the region of the first one-way valve assembly in one embodiment of the present invention;

[0037] Figure 7 This is a schematic diagram of the specific structure of the liquid extraction device in another embodiment of the present invention;

[0038] Figure 8 This is a schematic diagram of the specific structure of the sealing cavity in one embodiment of the present invention;

[0039] Figure label:

[0040] 1. Double-walled tube; 11. Inner channel; 111. Gas inlet; 112. Gas outlet; 12. Outer channel; 121. Liquid outlet; 122. Liquid inlet;

[0041] 2. Heating rod; 21. Spiral baffle;

[0042] 3. First one-way valve assembly; 31. Mudguard;

[0043] 4. Second check valve assembly;

[0044] 5. Liquid extraction device; 51. Motor; 52. Drive shaft; 53. Turbine blades;

[0045] 6. Sealed cavity; 61. Liquid extraction port; 62. Pump inlet;

[0046] 7. Connect pipes. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," "third," "fourth," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0049] Currently, traditional downhole heaters typically have a lifespan of only a few months, and their installation and maintenance are cumbersome. Maintenance requires opening the wellhead, lowering the formation temperature to ambient, and performing complex procedures, significantly extending the mining cycle.

[0050] In in-situ mining of solid minerals such as oil shale and oil-rich coal, as well as in the thermal recovery of heavy oil and oil sands, single-well injection-output processes are frequently employed. This requires not only in-situ downhole heating but also in-situ fluid drainage. Traditional processes involve installing injection and production casings in a single well, placing higher demands on the limited well space and increasing operational difficulty. Currently, although in-situ fluid drainage at the wellhead is relatively common, it is not yet possible to simultaneously perform in-situ heating and fluid drainage using the same downhole tool, limiting process integration and efficiency. To address the above technical problems, this invention provides a downhole heating system for single-well mining. Through structural innovation, it modularly integrates downhole heating and downhole fluid return capabilities, significantly extending the service life of the downhole heating device and improving the process efficiency of single-well injection-production. The technical solution of this invention will be described in detail below with specific examples.

[0051] Reference Figure 1 as well as Figure 2 As shown, the present invention relates to a downhole heating system for single-well mining, comprising a double-walled pipe 1, a heating rod 2, a first one-way valve assembly 3, and a second one-way valve assembly 4.

[0052] The double-walled pipe 1 has an inner channel 11 and an outer channel 12, extending from the wellhead to the working formation. The inner channel 11 has a gas inlet 111 at the top and a gas outlet 112 at the bottom. The outer channel 12 has a liquid outlet 121 at the top and a liquid inlet 122 at the bottom.

[0053] The heating rod 2 is located inside the inner channel 11 and is situated in the working layer.

[0054] The first one-way valve assembly 3 is disposed in the inner channel 11, below the heating rod 2, and restricts the flow of fluid from the outlet 112 to the inlet 111. The second one-way valve assembly 4 is disposed in the outer channel 12 and at the inlet 122, and restricts the flow of fluid from the outlet 121 to the inlet 122.

[0055] It should be noted that the piping connection of this system adopts double-walled pipe 1, which extends continuously from the underground to the working formation. Among them, the inner channel 11 is mainly used for laying cables and gas injection, and heating rods 2 are installed in the inner channel 11 located in the working formation.

[0056] For example, when using this system for single-well production, it is necessary to first close the connection channel of the well outlet 121, connect the gas inlet 111 at the top of the inner channel 11 through the ground equipment, and inject gas into the inner channel 11. During gas injection, the gas enters the inner channel 11 from the gas inlet 111 and gradually enters the working formation. After being heated by the heating rod 2, the gas is ejected from the gas outlet 112 and enters the formation pores and fractures to achieve downhole gas injection heating.

[0057] As the well is heated, the oil-rich coal in the reservoir undergoes pyrolysis, producing liquid that is stored in the formation pores and fractures. When extraction is required, heating is stopped, and the connection channel of the liquid outlet 121 on the surface is opened. Because the first one-way valve assembly 3 is located in the inner channel 11, it restricts the flow of fluid from the gas outlet 112 to the gas delivery port 111. The pressure inside the well will drive the liquid inside the well to open the liquid one-way valve and be extracted to the surface along the outer layer of the double-walled heated guide pipe.

[0058] Repeated heating and extraction operations enable in-situ pyrolysis of oil-rich coal in a single-well injection-output process. Two in-situ processes are implemented simultaneously within the same unit without interference, significantly improving the efficiency of in-situ extraction. Compared to existing technologies, this system, through structural innovation and modular integration of downhole heating and fluid return capabilities, greatly extends the service life of the downhole heating unit and enhances the process efficiency of single-well injection-production.

[0059] In one embodiment, more preferably, in order to optimize the heating efficiency of the heating rod 2 on the gas, a spiral baffle 21 is provided on the outer edge of the heating rod 2, and the spiral baffle 21 guides the fluid in the inner channel 11 to flow around the heating rod 2.

[0060] In this embodiment, the spiral baffle 21 specifically includes a high-density section and a low-density section, with the high-density section located at one end near the gas inlet 111.

[0061] It should be noted that, as the gas flows from one end of the heating rod 2 to the other end under the guidance of the spiral baffle 21, the gas heated by the front end of the heating rod 2 will cause heat to accumulate at the end when it enters the end of the heating rod 2. Therefore, it is necessary to speed up the gas escape from the end of the heating rod 2. Dividing the gas into high-density and low-density sections can optimize the heating effect of the heating rod 2 and avoid heat accumulation at the end of the heating rod 2.

[0062] In one embodiment, the overall structure of the first one-way valve assembly 3 is further refined, and the first one-way valve assembly 3 includes a Tesla valve.

[0063] A Tesla valve is a fluid control device that requires no mechanical movement. It utilizes fluid dynamics and flow path design to achieve unidirectional flow isolation, offering advantages such as simple structure, excellent sealing, and no mechanical wear. Proposed by American engineer Clarence Lee Tesla, it is commonly used in industrial pipelines requiring backflow prevention or unidirectional flow.

[0064] In this embodiment, a mudguard 31 is provided at the outlet end of the Tesla valve to block foreign objects.

[0065] In one embodiment, the overall structure of the second one-way valve assembly 4 is further refined. Multiple inlet ports 122 are provided and are annularly spaced at the ends of the outer channel 12. The second one-way valve assembly 4 includes multiple resilient one-way valves, which are correspondingly installed at the inlet ports 122. Specifically, the resilient one-way valves are commonly used one-way valve components, achieving unidirectional flow via springs.

[0066] Reference Figure 3 , Figure 4 , Figure 5 as well as Figure 6 As shown, the present invention also provides a specific operating method:

[0067] Step 1: First, close the connection channel of the wellhead outlet 121. The surface equipment then injects nitrogen gas into the well through the inner channel 11, with an injection volume of 400m³. 3 / h, power is supplied to heating rod 2, and the gas temperature at outlet 112 is 600℃, achieving downhole gas injection heating. See details... Figure 3 as well as Figure 4 The figure shows the flow trajectory of the gas.

[0068] Step 2: After 30 days of downhole heating, the oil-rich coal in the reservoir undergoes pyrolysis, producing 120m³ of... 3 The liquid, stored in the formation pores and fractures, is heated and the connection channel of the wellhead outlet 121 is opened. Because the first one-way valve assembly 3 is located in the inner channel 11, it restricts the flow of fluid from the gas outlet 112 to the gas delivery port 111. The pressure inside the well will drive the liquid inside the well to open the liquid one-way valve and be extracted to the surface along the outer layer of the double-walled heated guide pipe. See details. Figure 5 as well as Figure 6 The image shows the flow trajectory of the liquid.

[0069] Step 3: Repeat steps 1-2 to achieve the in-situ pyrolysis single-well huff and puff process for oil-rich coal. The two in-situ processes are implemented in the same unit without interference, greatly improving the efficiency of in-situ mining.

[0070] Reference Figure 7 as well as Figure 8As shown, the present invention also provides a downhole heating system. Based on the above scheme, specifically, a section of double-walled pipe 1 located above the heating rod 2 is an installation pipe section. A pumping device 5 is installed in the installation pipe section. The pumping device 5 provides pressure to the external channel 12 to pump the fluid from the inlet 122 to the outlet 121.

[0071] It should be noted that in some working scenarios, the working layer may not have sufficient pressure to drive the liquid upward from the working layer. In order to deal with this situation, this embodiment provides a liquid pumping device 5 to provide pressure to the external channel 12 and pump the fluid from the inlet 122 to the outlet 121.

[0072] With the integration of the pumping device 5, operators can select the appropriate drainage method according to the actual needs of the site. If drainage can be carried out autonomously through natural pressure difference, it can be done directly through the second one-way valve assembly 4. If the pressure difference is small, the pumping device 5 is activated to provide pressure to the external channel 12, pumping the fluid from the inlet 122 to the outlet 121. This structure makes the system more flexible, allowing operators to adjust the drainage method according to actual needs during operation.

[0073] In one embodiment, the overall structure of the liquid extraction device 5 is further refined. The inner channel 11 corresponding to the installation pipe section is provided with a sealing cavity 6, and the liquid extraction device 5 is sealed in the sealing cavity 6. The outer channel 12 is provided with a connecting pipe 7, which connects to the inner channel 11 above and below the sealing cavity 6.

[0074] It should be noted that all the components of the system are installed in the inner channel 11 of the double-walled pipe 1. The installation of the liquid extraction device 5 will occupy a large part of the inner channel 11. In order to avoid affecting the flow of gas, a connecting pipe 7 is installed in the corresponding installation pipe section to optimize the smooth flow of gas.

[0075] In this embodiment, the liquid extraction device 5 specifically includes a motor 51, a drive shaft 52, and a turbine blade 53. The motor 51 is fixedly installed in the inner channel 11 by a mounting base. In the corresponding installation pipe section, the mounting base and the bottom of the installation pipe section form a sealed cavity 6. The drive shaft 52 is installed in the sealed cavity 6 and is connected to the motor 51 through the mounting base. The turbine blade 53 is disposed on the drive shaft 52.

[0076] The inner channel 11 has a liquid extraction port 61 and a pumping port 62 that connect to the outer channel 12 on its pipe wall. The outer channel 12 is sealed with a solenoid valve that switches the connection state of the corresponding outer channel 12. The solenoid valve is located between the liquid extraction port 61 and the pumping port 62.

[0077] In this embodiment, in order to further optimize the arrangement of the connection circuit, the drive shaft 52 is a hollow shaft, and the connection circuit of the heating rod 2 extends upward to the well through the drive shaft 52.

[0078] For example, when single-well heating is required, the connection channel of the well outlet 121 is closed first, and the surface equipment injects nitrogen into the well through the inner channel 11 to supply power to the heating rod 2, thereby realizing downhole gas injection heating; when drainage is required, the motor 51 and the solenoid valve are started through the surface switch. The motor 51 drives the turbine fan blades to extract the static underground liquid to the surface. The liquid enters the outer channel 12 from the inlet 122. After reaching the installation section, because the solenoid valve blocks the current connection of the outer channel 12, the liquid enters from the extraction port 61 and enters the upper outer channel 12 again through the pump port 62 until it is pumped to the surface.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A downhole heating system for application in single well production, characterized in that, include: A double-walled tube, having an inner channel and an outer channel, extends from the wellhead to the working formation; An air inlet is provided at the top of the inner channel, and an air outlet is provided at the bottom. The outer channel is provided with an outlet at the top and an inlet at the bottom. A heating rod is disposed inside the inner channel and located at the working layer. A double-walled pipe section above the heating rod is an installation pipe section. A liquid extraction device is disposed inside the installation pipe section. The liquid extraction device provides pressure to the outer channel to pump the fluid from the inlet to the outlet. A sealed cavity is provided in the inner channel corresponding to the installation pipe section. The liquid extraction device is sealed inside the sealed cavity. A connecting pipe is disposed in the outer channel, and the connecting pipe connects to the inner channel above and below the sealed cavity. A liquid extraction port and a pumping port are disposed on the pipe wall of the inner channel, which communicate with the outer channel. A solenoid valve is sealed inside the outer channel to switch the communication state corresponding to the outer channel. The solenoid valve is located between the liquid extraction port and the pumping port. A first one-way valve assembly is disposed in the inner channel, located below the heating rod, to restrict fluid from flowing from the outlet to the inlet; A second check valve assembly is disposed in the outer channel and at the inlet, the second check valve assembly restricting fluid from flowing from the outlet to the inlet.

2. The downhole heating system according to claim 1, characterized in that, The outer edge of the heating rod is provided with a spiral baffle, which guides the fluid in the inner channel to flow around the heating rod.

3. The downhole heating system according to claim 2, characterized in that, The spiral baffle includes a high-density section and a low-density section, with the high-density section located at one end near the gas inlet.

4. The downhole heating system according to claim 1, characterized in that, The first one-way valve assembly includes a Tesla valve.

5. The downhole heating system according to claim 4, characterized in that, The outlet end of the Tesla valve is equipped with a mudguard.

6. The downhole heating system according to claim 1, characterized in that, The liquid inlet is provided in multiple ways and is arranged in a ring at intervals at the end of the outer channel; The second one-way valve assembly includes multiple resilient one-way valves, which are installed at the liquid inlet.

7. The downhole heating system according to claim 1, characterized in that, The liquid extraction device includes: Electric motor; A drive shaft, which is connected to the motor for transmission; and Turbine blades are mounted on the drive shaft.

8. The downhole heating system according to claim 7, characterized in that, The drive shaft is a hollow shaft, and the connection circuit of the heating rod extends upward through the drive shaft.

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