Enhanced geothermal development system and method

Abstract

The invention provides an enhanced terrestrial heat development system which comprises a production casing, a middle pipe arranged in the production casing and a center pipe arranged in the middle pipe, the middle pipe is configured to be telescopic under the action of internal pressure at a horizontal well section, and sliding sealing pieces are arranged at the toe end of the middle pipe and between the middle pipe and the production casing. And a telescopic closed space is formed among the production casing, the middle pipe, the packer located at the horizontal well section and the sliding sealing piece. Under the action of continuous filling of the heat exchange working medium, the pressure in the middle pipe is increased and the middle pipe extends, so that the size of the closed space is increased, the pressure in the closed space is reduced, and the heat storage fluid in the stratum enters the closed space under the action of pressure difference and indirectly contacts with the heat exchange working medium in the middle pipe for heat exchange. On the basis of avoiding the arrangement of a power unit at the bottom of the well, the forced convection of the heat storage fluid, namely the rapid heat supplement of the heat storage of the near wellbore zone, is realized.

Description

Technical Field

[0001] The present invention relates to the field of geothermal energy development, and in particular to an enhanced geothermal development system and method. Background Art

[0002] Geothermal energy is a green, low-carbon, renewable energy source characterized by large reserves, widespread distribution, clean and environmentally friendly operation, and stable and reliable performance. It is a key area of ​​current and future energy development, offering enormous socioeconomic benefits and significant strategic significance. With the continued escalation of environmental protection requirements, the limitations of the "pumping and recharging" development model are becoming increasingly apparent. Ensuring "heat extraction without water extraction" and improving underground heat extraction efficiency have become key to current geothermal development.

[0003] A prior art method for geothermal development involves installing a power unit at the bottom of the well and transmitting energy to it via cables, converting electrical energy into kinetic energy for forced convection of the heat storage fluid. However, this method has certain limitations. First, due to the confined space within the well, the size of the power unit and its associated tools is limited, and the displacement and lift provided by a small power unit cannot meet production requirements. Second, the structure of the downhole pipe strings is relatively complex, and well entry operations are difficult. Third, during the production process, any problems with the downhole power unit require the entire downhole pipe string to be removed and then inspected and repaired item by item, significantly increasing production and operating costs. Fourth, the equipment investment and the electricity costs required for production are prohibitive.

[0004] In view of this, there is an urgent need for a geothermal development system that can meet the requirement of “taking heat without taking water” without installing a power unit at the bottom of the well, and realize rapid heat replenishment of heat storage near the wellbore. Summary of the Invention

[0005] One object of the present invention is to provide an enhanced geothermal development system and method to achieve rapid heat replenishment of heat storage near the wellbore without installing a power unit at the bottom of the well.

[0006] According to the present invention, an enhanced geothermal development system is provided, comprising: a production casing, an intermediate pipe arranged in the production casing, and a center pipe arranged in the intermediate pipe, wherein the intermediate pipe is constructed to be retractable under the action of internal pressure in the horizontal well section, and a sliding seal is provided at the toe end of the intermediate pipe between the intermediate pipe and the production casing, and a retractable closed space is formed between the production casing, the intermediate pipe, the packer located in the horizontal well section, and the sliding seal. Under the action of continuous filling of the heat exchange medium, the pressure inside the intermediate pipe increases and the pipe is elongated, so that the closed space is also elongated synchronously, thereby reducing the pressure in the closed space, and the heat storage fluid in the formation enters the closed space under the action of the pressure difference and indirectly contacts and exchanges heat with the heat exchange medium in the intermediate pipe.

[0007] In a preferred embodiment, after the intermediate pipe discharges the heat exchange medium that has completed heat exchange to the outside of the well through the central pipe, the internal pressure is reduced and reset, thereby causing the volume of the enclosed space to shrink and the internal pressure to increase. The heat storage fluid that has completed heat exchange in the enclosed space is discharged from the enclosed space and returned to the formation under the action of the pressure difference.

[0008] In a preferred embodiment, the production casing is provided with a first one-way valve for absorbing the heat storage fluid into the enclosed space and a second one-way valve for discharging the heat storage fluid into the formation.

[0009] In a preferred embodiment, it also includes a ground heat exchange and injection control component connected to the central pipe and the intermediate pipe, which is used to inject heat exchange medium into the annulus between the intermediate pipe and the central pipe, and is also used to recover the heat exchange medium that has completed heat exchange from the central pipe.

[0010] In a preferred embodiment, the central pipe is provided with a central pipe valve near the ground heat exchange and injection control assembly.

[0011] In a preferred embodiment, the intermediate pipe in the horizontal well section is constructed to consist of an oil pipe and a telescopic oil pipe arranged in intervals.

[0012] In a preferred embodiment, the first end of the intermediate pipe close to the wellhead is configured as an opening, and the second end of the intermediate pipe is configured as a closed end.

[0013] In a preferred embodiment, the first end and the second end of the central tube are both configured to be open.

[0014] In a preferred embodiment, the production casing, the intermediate pipe and the central pipe are first extended downward from the vertical well section to the horizontal well section, and then extended in the horizontal direction in the horizontal well section.

[0015] The present invention also provides an enhanced geothermal development method, which specifically comprises the following steps:

[0016] S1. Injecting a heat exchange medium into the intermediate tube so that the heat exchange medium fills the annulus between the intermediate tube and the center tube and the center tube, thereby causing the intermediate tube to extend under the action of the continuously injected heat exchange medium;

[0017] S2. As the intermediate tube extends, the pressure inside the enclosed space decreases. Under the action of the pressure difference, the heat storage fluid in the formation enters the enclosed space and indirectly contacts and exchanges heat with the heat exchange medium in the intermediate tube.

[0018] S3. The heat exchange medium that has completed heat exchange is discharged out of the well through the central pipe to reduce the pressure inside the intermediate pipe and reset it, thereby causing the closed space to shrink and the internal pressure to increase. The heat storage fluid that has completed heat exchange is discharged from the closed space under the action of the pressure difference and returns to the formation.

[0019] The present invention has at least the following technical effects:

[0020] According to the present invention, a production casing, an intermediate pipe disposed within the production casing, and a center pipe disposed within the intermediate pipe are provided. Because the intermediate pipe is configured to expand and contract under internal pressure in the horizontal well section, a sliding seal is provided at the toe of the intermediate pipe between the intermediate pipe and the production casing. Furthermore, a retractable enclosed space is formed between the production casing, the intermediate pipe, the packer located in the horizontal well section, and the sliding seal. Furthermore, as the intermediate pipe is continuously filled with heat exchange fluid, the internal pressure within the intermediate pipe increases and the enclosed space expands, thereby simultaneously expanding and reducing the pressure within the enclosed space. Heat storage fluid in the formation enters the enclosed space under the action of the pressure differential and indirectly contacts and exchanges heat with the heat exchange fluid within the intermediate pipe. On the one hand, it can realize the forced convection circulation of the heat storage fluid in the underground heating layer, providing a guarantee for the rapid heat replenishment in the area near the wellbore; on the other hand, it can replace the power unit at the bottom of the well by setting an injection control device on the ground, so that energy can be transferred through the circulation of the heat exchange working fluid and the reciprocating motion of the intermediate pipe. During the production process, the internal circulation of the heat exchange working fluid and the forced convection circulation of the heat storage fluid are never in direct contact, ensuring "heat is taken without water".

[0021] According to the present invention, after the intermediate pipe discharges the heat exchange medium that has completed heat exchange to the outside of the well through the central pipe, the internal pressure of the intermediate pipe decreases and resets, thereby causing the volume of the closed space to shrink and the internal pressure to increase. The heat storage fluid that has completed heat exchange in the closed space is discharged from the closed space and returned to the formation under the action of the pressure difference, so that energy is transferred through the circulation of the heat exchange medium and the reciprocating motion of the intermediate pipe. The internal circulation of the heat exchange medium and the forced convection circulation of the heat storage fluid are always independent of each other and have no direct contact, thereby ensuring that "heat is taken but no water is taken" during the production process.

[0022] According to the present invention, a first one-way valve for sucking the heat storage fluid into the enclosed space and a second one-way valve for discharging the heat storage fluid into the formation are provided on the production casing. The heat storage fluid can be sucked into and discharged from the enclosed space through the first one-way valve and the second one-way valve respectively, so that the heat storage fluid can realize forced convection circulation between the enclosed space and the formation, which is convenient for heat exchange with the heat exchange working medium during the circulation process, ensuring that "heat is taken but no water is taken" during the production process.

[0023] According to the present invention, a ground heat exchange and injection control assembly connected to a central tube and an intermediate tube is provided. The central tube can be used to inject heat exchange medium into the annulus between the intermediate tube and the central tube, and is also used to recover the heat exchange medium from the central tube, thereby facilitating the internal circulation of the heat exchange medium.

[0024] According to the present invention, a central tube valve is provided near the ground heat exchange and injection control assembly through the central tube, which can facilitate the control of the heat exchange medium entering or exiting the intermediate tube, thereby facilitating the internal circulation of the heat exchange medium.

[0025] According to the present invention, the intermediate pipe in the horizontal well section is constructed to be composed of an oil pipe and a retractable oil pipe arranged at intervals, so that the intermediate pipe can be retracted and contracted under the action of its internal pressure, thereby facilitating the formation of a retractable closed space between the intermediate pipe and the packer and sliding seal located in the horizontal well section. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The overall structure of the enhanced geothermal development system according to the present invention is schematically shown, wherein the intermediate pipe is in a reset state;

[0027] Figure 2 The overall structural diagram of the enhanced geothermal development system according to the present invention is schematically shown, wherein the intermediate pipe is in an extended state.

[0028] As shown in the figure:

[0029] Production casing-3

[0030] Intermediate pipe-4

[0031] Center tube-5

[0032] Sliding seals-12

[0033] Packer-6

[0034] Enclosed space-s

[0035] First one-way valve-7

[0036] Completion pipe section-8

[0037] Second one-way valve 11

[0038] Enhanced Geothermal Development System-100

[0039] Ground heat exchange and injection control components-1

[0040] Center pipe valve-2

[0041] YouTube-9

[0042] Retractable oil hose-10

[0043] In this application, all drawings are schematic drawings, which are only used to illustrate the principles of the present invention and are not drawn to scale. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] In the description of the present invention, it should be understood that the terms "inside", "outside", "axial", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0046] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features.

[0047] In the present invention, unless otherwise expressly specified or limited, the terms "connection" and "fixed" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0048] like Figure 1 As shown, the enhanced geothermal development system 100 of the present invention includes: a production casing 3, an intermediate pipe 4 disposed within the production casing 3, and a central pipe 5 disposed within the intermediate pipe 4. The production casing 3, the intermediate pipe 4, and the central pipe 5 all extend downward from a vertical well section to a horizontal well section, and then extend horizontally within the horizontal well section. The intermediate pipe 4 in the horizontal well section is configured to be retractable under the influence of internal pressure. Specifically, when the internal pressure of the intermediate pipe 4 increases to a certain level, the portion of the intermediate pipe 4 in the horizontal well section can extend horizontally. When the internal pressure of the intermediate pipe 4 decreases to a certain level, the portion of the intermediate pipe 4 in the horizontal well section can retract and return to its original position.

[0049] A sliding seal 12 is installed at the toe of the intermediate pipe 4, between the intermediate pipe 4 and the production casing 3. A retractable, enclosed space s is formed between the production casing 3, the intermediate pipe 4, the packer 6 located in the horizontal well section, and the sliding seal 12. During the extension and retraction of the intermediate pipe 4, the sliding seal 12 maintains the sealed space s. A heat exchange medium can be injected into the interior of the intermediate pipe 4 through its first end near the wellhead. Optionally, the heat exchange medium is a fluid medium suitable for heat exchange and energy extraction, such as water or gas.

[0050] The first end of the intermediate pipe 4, near the wellhead, is open, and the second end of the intermediate pipe 4 is closed. Both the first and second ends of the central pipe 5 are open. After a heat exchange medium is injected into the annulus between the intermediate pipes 4 and 5 through the first end of the intermediate pipe 4, near the wellhead, the heat exchange medium can flow down to the second end of the intermediate pipe 4 and into the interior of the central pipe 5 through the opening at the second end of the central pipe 5. It then flows from the interior of the central pipe 5 along the central pipe 5 toward its first end. The heat exchange medium will fill the annulus between the intermediate pipes 4 and 5 and the intermediate pipe 4.

[0051] After the heat exchange medium fills the annular space between the intermediate tube 4 and the central tube 5 and the intermediate tube 4, the heat exchange medium is continued to be injected into the intermediate tube 4. Since the opening at the second end of the central tube is in a closed state, the pressure inside the intermediate tube 4 increases and stretches under the action of continuous filling with the heat exchange medium, causing the closed space s to stretch synchronously, thereby reducing the pressure in the closed space s. Under the action of the pressure difference, the heat storage fluid in the formation enters the closed space s and indirectly contacts and exchanges heat with the heat exchange medium in the intermediate tube 4.

[0052] According to the present invention, a production casing 3, an intermediate pipe 4 disposed within the production casing 3, and a center pipe 5 disposed within the intermediate pipe 4 are provided. Because the intermediate pipe 4 is configured to be retractable under internal pressure in the horizontal well section, a sliding seal 12 is provided at the toe of the intermediate pipe 4 and between the intermediate pipe 4 and the production casing 3. A retractable enclosed space s is formed between the production casing 3, the intermediate pipe 4, the packer 6 located in the horizontal well section, and the sliding seal 12. Furthermore, as the intermediate pipe 4 is continuously filled with heat exchange fluid, the internal pressure increases and the enclosed space s simultaneously elongates, thereby reducing the pressure within the enclosed space s. Heat storage fluid in the formation enters the enclosed space s under the action of the pressure differential and indirectly contacts and exchanges heat with the heat exchange fluid within the intermediate pipe. On the one hand, it can realize the forced convection circulation of the heat storage fluid in the underground heating layer, providing a guarantee for the rapid heat replenishment in the area near the wellbore; on the other hand, it can replace the power unit at the bottom of the well by setting an injection control device on the ground, so that energy can be transferred through the circulation of the heat exchange working fluid and the reciprocating motion of the intermediate pipe 4. During the production process, the internal circulation of the heat exchange working fluid and the forced convection circulation of the heat storage fluid are never in direct contact, ensuring "heat extraction without water extraction".

[0053] In one or more embodiments, after the intermediate pipe 4 discharges the heat exchange medium that has completed heat exchange to the outside of the well through the central pipe 5, the internal pressure of the intermediate pipe 4 decreases and resets, so that the closed space s also shrinks and resets, and the internal pressure increases. The heat storage fluid that has completed heat exchange in the closed space s is discharged from the closed space s and returned to the formation under the action of the pressure difference.

[0054] According to the present invention, after the intermediate pipe 4 discharges the heat exchange medium that has completed heat exchange to the outside of the well through the central pipe 5, the internal pressure of the intermediate pipe 4 decreases and resets, so that the closed space s also shrinks and resets, and the internal pressure increases. The heat storage fluid that has completed heat exchange in the closed space s is discharged from the closed space s under the action of the pressure difference and returns to the formation. This process realizes the reset of the intermediate pipe 4 and the closed space s, and provides power for the discharge of the heat storage fluid that has completed heat exchange.

[0055] In one or more embodiments, the production casing 3 is provided with one or more first one-way valves 7 for drawing the heat storage fluid into the enclosed space s, and one or more second one-way valves 11 for discharging the heat storage fluid into the formation. Specifically, the horizontal well section has a completion tubing section 8, and the first one-way valve 7 and the second one-way valve 11 are provided on the production casing 3 via the completion tubing section 8.

[0056] According to the present invention, a first one-way valve 7 for sucking the heat storage fluid into the closed space s and a second one-way valve 11 for discharging the heat storage fluid into the formation are provided on the production casing 3. The heat storage fluid can be sucked into and discharged from the closed space s through the first one-way valve 7 and the second one-way valve 11 respectively, so that the heat storage fluid can realize forced convection circulation between the closed space s and the formation, thereby realizing rapid heat replenishment in the near-wellbore area.

[0057] In one or more embodiments, the enhanced geothermal development system 100 described in the present invention also includes a ground heat exchange and injection control component 1 connected to the central pipe 5 and the intermediate pipe 4, which is used to inject heat exchange fluid into the annulus between the intermediate pipe 4 and the central pipe 5, and is also used to recover the heat exchange fluid from the central pipe 5.

[0058] According to the present invention, a ground heat exchange and injection control assembly 1 connected to a central pipe 5 and an intermediate pipe 4 is provided. The central pipe 1 can be used to inject heat exchange medium into the annulus between the intermediate pipe 4 and the central pipe 5, and is also used to recover the heat exchange medium from the central pipe 5, thereby realizing internal circulation of the heat exchange medium.

[0059] In one or more embodiments, the central pipe 5 is provided with a central pipe valve 2 near the ground heat exchange and injection control assembly 1 .

[0060] According to the present invention, a central pipe valve 2 is provided near the ground heat exchange and injection control assembly 1 through the central pipe 5, which can control the heat exchange medium to enter or discharge the intermediate pipe 4, and is used to adjust the circulation process of the heat exchange medium.

[0061] In one or more embodiments, the intermediate pipe 4 in the horizontal well section is constructed to consist of an oil pipe 9 and a telescopic oil pipe 10 arranged at intervals.

[0062] According to the present invention, the intermediate pipe 4 in the horizontal well section is constructed to be composed of an oil pipe 9 and a retractable oil pipe 10 arranged at intervals, so that the intermediate pipe 4 can be retracted under the action of its internal pressure, thereby facilitating the formation of a retractable closed space s between the production casing 3, the intermediate pipe 4 and the packer 6 and the sliding seal 12 located in the horizontal well section.

[0063] Based on the above-mentioned enhanced geothermal development system 100, the present invention further provides an enhanced geothermal development method, which specifically includes the following steps:

[0064] S1. Inject a heat exchange medium into the intermediate pipe 4 so that the heat exchange medium fills the annulus between the intermediate pipe 4 and the central pipe 5 and the central pipe 5, thereby causing the intermediate pipe 4 to extend under the action of the continuously injected heat exchange medium. Specifically, the heat exchange medium is injected into the annulus between the intermediate pipe 4 and the central pipe 5 through the surface heat exchange and injection control device 1. The heat exchange medium flows down the annulus to the bottom of the well at the target heat extraction layer, and after filling the annulus, it flows up the central pipe 5 to the wellhead. During this process, the central pipe valve 2 is in the closed state, and the intermediate pipe 4 extends under the pressure of the heat exchange medium inside it.

[0065] S2. As the intermediate tube 4 extends, the volume of the enclosed space s increases, and the pressure inside it decreases. Under the pressure differential, the heat storage fluid in the formation enters the enclosed space s and exchanges heat with the heat exchange medium in the intermediate tube 4. Specifically, the intermediate tube 4 extends under the pressure of the heat exchange medium therein, and the volume of the enclosed space s increases and the pressure inside it decreases as the intermediate tube 4 extends. Under the pressure differential, the heat storage fluid in the formation then passes through the first one-way valve 7 into the enclosed space s and indirectly exchanges heat with the heat exchange medium in the intermediate tube 4. During this process, the central tube valve 2 is closed.

[0066] S3. The heat exchange medium that has completed heat exchange is discharged out of the well through the central pipe 5, so that the internal pressure of the intermediate pipe 4 is reduced and reset, thereby causing the closed space s to retract and reset and the internal pressure to increase. The heat storage fluid that has completed heat exchange is discharged from the closed space s under the action of the pressure difference and returned to the formation. Specifically, after the intermediate pipe 4 is extended to the preset position (i.e., the longest state of the intermediate pipe 4), the injection of heat exchange medium is stopped, and the central pipe valve 2 is opened. The heat exchange medium is discharged along the central pipe 5 to the surface heat exchange and injection control device 1. The internal pressure of the intermediate pipe 4 is reduced and it automatically retracts and resets. The closed space s then retracts and resets synchronously and the internal pressure increases. The heat storage fluid that has completed heat exchange is discharged from the closed space s under the action of the pressure difference and returned to the formation. When the intermediate pipe 4 is fully reset (i.e., the telescopic oil pipe 10 and the sliding sealing device 12 are restored to their initial positions), the central pipe valve 2 is closed. Subsequently, the heat exchange medium that has completed heat exchange completes heat exchange in the ground heat exchange and injection control device 1, and is then injected again into the annulus between the intermediate pipe 4 and the central pipe 5 to start the next cycle.

[0067] While the present invention has been described with reference to preferred embodiments, various modifications may be made and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various technical features described in the various embodiments may be combined in any manner, provided no structural conflicts exist. The present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. An enhanced geothermal development system comprising: A production casing, an intermediate pipe disposed in the production casing, and a central pipe disposed in the intermediate pipe, wherein the intermediate pipe is configured to be retractable under the action of internal pressure in a horizontal well section. At the toe end of the intermediate pipe, a sliding seal is provided between the intermediate pipe and the production casing, and a retractable closed space is formed between the production casing, the intermediate pipe, the packer located in the horizontal well section, and the sliding seal. As the intermediate pipe is continuously filled with the heat exchange medium, the pressure inside it increases and the pipe stretches, causing the enclosed space to stretch synchronously, thereby reducing the pressure inside the enclosed space. The heat storage fluid in the formation enters the enclosed space under the action of the pressure difference and indirectly contacts the heat exchange medium in the intermediate pipe for heat exchange.

2. The enhanced geothermal development system according to claim 1, characterized in that: After the intermediate pipe discharges the heat exchange medium that has completed heat exchange to the outside of the well through the central pipe, the internal pressure of the intermediate pipe decreases and resets, thereby causing the volume of the enclosed space to shrink and the internal pressure to increase. The heat storage fluid that has completed heat exchange in the enclosed space is discharged from the enclosed space under the action of the pressure difference and returns to the formation.

3. The enhanced geothermal development system according to claim 2, characterized in that: The production casing is provided with a first one-way valve for absorbing the heat storage fluid into the enclosed space and a second one-way valve for discharging the heat storage fluid into the formation.

4. The enhanced geothermal development system according to claim 3, characterized in that: It also includes a ground heat exchange and injection control component connected to the central pipe and the intermediate pipe, which is used to inject heat exchange medium into the annulus between the intermediate pipe and the central pipe, and is also used to recover the heat exchange medium that has completed heat exchange from the central pipe.

5. The enhanced geothermal development system according to claim 4, characterized in that: The central pipe is provided with a central pipe valve near the ground heat exchange and injection control assembly.

6. The enhanced geothermal development system according to claim 1, characterized in that: The intermediate pipe in the horizontal well section is constructed to consist of an oil pipe and a telescopic oil pipe arranged at intervals.

7. The enhanced geothermal development system according to claim 1, characterized in that: The first end of the intermediate pipe close to the wellhead is configured as an opening, and the second end of the intermediate pipe is configured as a closed end.

8. The enhanced geothermal development system according to claim 4, characterized in that: The first end and the second end of the central tube are both configured to be open.

9. The enhanced geothermal development system according to claim 1, characterized in that: The production casing, the intermediate pipe and the central pipe are first extended downward from the vertical well section to the horizontal well section, and then extended in the horizontal direction in the horizontal well section.

10. An enhanced geothermal development method comprising the following steps: S1. Injecting a heat exchange medium into the intermediate tube so that the heat exchange medium fills the annulus between the intermediate tube and the center tube and the center tube, thereby causing the intermediate tube to extend under the action of the continuously injected heat exchange medium; S2. As the intermediate tube extends, the pressure inside the enclosed space decreases. Under the action of the pressure difference, the heat storage fluid in the formation enters the enclosed space and indirectly contacts and exchanges heat with the heat exchange medium in the intermediate tube. S3. The heat exchange medium that has completed heat exchange is discharged out of the well through the central pipe to reduce the pressure inside the intermediate pipe and reset it, thereby causing the closed space to shrink and the internal pressure to increase. The heat storage fluid that has completed heat exchange is discharged from the closed space under the action of the pressure difference and returns to the formation.

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