阅读说明：本技术 一种换热工质可回收式同井采热方法 (Heat exchange working medium recyclable same-well heat recovery method ) 是由 雷宏武 蔡雨娜 白冰 崔银祥 于 2020-10-15 设计创作，主要内容包括：本发明属于地热开发技术领域,具体涉及一种换热工质可回收式同井采热方法；其实施系统包括穿过盖层连通至目标热储层的井筒,用于开采的潜水泵和用于注入的增压泵、换热设备、缓冲储罐和井口密封法兰,可先根据需要设置对储层增渗改造的环节,如设置人工裂缝及其内填充的支撑剂；实施过程包括通过连通至目标热储层的井筒向目标热储层注入一定量低温换热工质后焖井,使注入的换热工质在地热储层中向外运移,并与储层充分换热,然后通过同一井筒回抽注入的换热工质实现地热采出；解决了现有地热能资源采热系统长期运行改变原地下水分布、换热效率低的问题。(The invention belongs to the technical field of geothermal development, and particularly relates to a heat exchange working medium recyclable same-well heat recovery method; the implementation system comprises a shaft penetrating through a cover layer and communicated to a target thermal reservoir, a submersible pump for mining, a booster pump for injection, heat exchange equipment, a buffer storage tank and a wellhead sealing flange, and links for enhancing and modifying the reservoir, such as setting artificial cracks and proppants filled in the artificial cracks, can be set according to needs; the implementation process comprises the steps of injecting a certain amount of low-temperature heat exchange working medium into a target thermal reservoir through a shaft communicated to the target thermal reservoir, stewing the well, enabling the injected heat exchange working medium to move outwards in the geothermal reservoir and fully exchange heat with the reservoir, and pumping the injected heat exchange working medium back through the same shaft to realize geothermal extraction; the problems that the existing geothermal energy resource heat collection system runs for a long time to change the original site water drainage distribution and the heat exchange efficiency is low are solved.)

1. A heat exchange working medium recoverable heat recovery method for the same well is characterized by comprising the following steps:

step one, arranging a single well system

A shaft (3) is built on rock, a submersible pump (14) is arranged in the shaft (3), a sealing flange (6) is fixedly connected to the wellhead of the shaft (3), and the submersible pump (14) is arranged below the water level (15) in the shaft (3);

step two, selectively arranging artificial fractures (4) in the target geothermal reservoir (2) according to the permeability of the target geothermal reservoir (2), and selectively filling proppants (5) in the artificial fractures (4) if the artificial fractures (4) are arranged;

step three, arranging an overground heat exchange energy supply part

The overground heat exchange energy supply part comprises a booster pump (10), heat exchange or power generation equipment (8) and a buffer storage tank (9), wherein the booster pump (10) is connected with the heat exchange or power generation equipment (8) through a first pipeline (11), the heat exchange or power generation equipment (8) is connected with the buffer storage tank (9) through a fourth pipeline (17), a second pipeline (18) is further arranged on the booster pump (10), the second pipeline (18) penetrates through a sealing flange (6) and extends into the shaft (3), meanwhile, the heat exchange or power generation equipment (8) is further connected with a submersible pump (14) through a third pipeline (19), and valves (16) are arranged on the first pipeline (11), the second pipeline (18), the third pipeline (19) and the fourth pipeline (17);

step four, implementing a heat collecting process:

injecting: opening valves (16) on a first pipeline (11), a second pipeline (18) and a fourth pipeline (17), starting a booster pump (10) to inject low-temperature heat exchange media in heat exchange or power generation equipment (8) and a buffer storage tank (9) into a target geothermal reservoir (2) through a shaft (3) through the first pipeline (11) and the second pipeline (18), and stopping injecting and closing the valves (16) after the injection amount of the low-temperature heat exchange media reaches a preset value so that the wellhead of the shaft (3) is in a sealed state;

well stewing: starting stewing, and opening a valve (16) on a third pipeline (19) to unseal the shaft (3) after the stewing time reaches a preset value;

and (3) stoping: and (3) pumping equivalent high-temperature heat exchange medium from the target geothermal reservoir (2) through the shaft (3) by using the submersible pump (14) to heat exchange or power generation equipment (8) for heat exchange or power generation.

2. The heat exchange working medium recoverable same-well heat recovery method according to claim 1, characterized in that two or more sets of single-well systems share one set of above-ground heat exchange energy supply part, so that the two or more sets of single-well systems alternately perform the injection-soaking-recovery process of step four on the same energy supply unit.

3. The heat exchange working medium recoverable same well heat recovery method according to claim 1, characterized in that in the first step, the well bore (3) is communicated to the target geothermal reservoir (2) through the cover layer (1).

4. The heat recovery method for the same well with the recoverable heat exchange working medium according to claim 3, characterized in that in the step one, the well bore (3) is well-cased or well-uncased, wherein when the well bore (3) is well-cased, the well bore (3) is connected with the stratum by a high heat conduction casing, and the casing between the well bore (3) and the target geothermal reservoir (2) is subjected to perforation treatment.

5. The heat exchange working medium recoverable same well heat recovery method according to claim 4, characterized in that in the first step, the sealing flange (6) is provided with a sealing joint for connecting a pipeline.

6. The heat exchange working medium recoverable same well heat recovery method according to claim 5, characterized in that in the second step, if the rock is dense magma rock with geothermal resource existence of dry thermal rock type, artificial fractures (4) need to be formed in the target geothermal reservoir (2) through excitation means, and if the rock is sedimentary rock with higher permeability with geothermal resource existence of hydrothermal type, additional artificial fractures (4) do not need to be manufactured, and propping agent (5) does not need to be filled.

7. The heat exchange working medium recoverable same well heat recovery method according to claim 6, characterized in that in step three, one end of a third pipeline (19) is communicated with the submersible pump (14), and the other end of the third pipeline passes through the sealing flange (6) and is communicated with the heat exchange or power generation equipment (8).

8. The heat recovery method of the same well with the recoverable heat exchange working medium according to claim 7, characterized in that the well bore (3) in the first step is a vertical well, a horizontal well or a well with any angle.

9. A heat exchange working fluid as claimed in claim 8 which is recoverableThe heat recovery method of the same well is characterized in that the low-temperature heat exchange medium in the fourth step is water and CO₂Or other heat exchange working media.

10. A heat exchange working medium recoverable heat recovery method for the same well as defined in claim 9, characterized in that the heat exchange or power generation apparatus (8) is a heat exchange apparatus when heat recovery is used for heating, and the heat exchange or power generation apparatus (8) is a power generation apparatus capable of converting heat energy into electric energy when heat recovery is used for power generation.

Technical Field

The invention belongs to the technical field of geothermal development, and particularly relates to a heat exchange working medium recyclable same-well heat recovery method.

Background

Geothermal energy is a green, low-carbon, sustainable and renewable energy source, and has the characteristics of large reserves, wide distribution, stability, reliability and the like, and the development of the geothermal energy is increasingly paid attention and supported by countries in the world. According to the occurrence state of geothermal energy, the geothermal energy can be divided into a hydrothermal type geothermal energy resource, a dry-hot rock type geothermal energy resource and a shallow geothermal energy resource. Different types of geothermal energy resources are developed in different ways, a multi-well heat extraction-recharge mode is generally adopted for geothermal reservoirs with good stratum connectivity and permeability, and for geothermal reservoirs with poor connectivity and permeability, an enhanced geothermal system is established by manual excitation means such as artificial fracturing and the like so as to realize geothermal extraction (such as dry hot rock type geothermal resources) or a single-well heat extraction system is adopted. Regardless of the heat collection mode, the final aim is to realize the geothermal energy collection with high efficiency and low cost, and the damage to the original environment is avoided as much as possible.

The above-mentioned single well heat recovery system can be further divided into two types, open type and closed type, wherein the open type single well heat recovery system usually extracts the heat exchange medium in the target heat storage directly through the recovery well without injection, which causes adverse effects such as groundwater level drop and ground subsidence caused thereby on the original stratum, and recently, patent CN 110131781 proposes a heat recovery technique using a packer to make the injection water flow from the upper screen pipe of the shaft to the hydrous heat storage layer and then flow into the shaft again through the lower screen pipe, which attempts to change the groundwater flow direction by manual design, and has low feasibility; the closed single-well heat recovery system is a relatively isolated system, a heat exchange medium only moves in a continuous and closed shaft, is not in direct contact with a reservoir layer and reservoir layer water, and only absorbs heat through heat conduction of a well wall, and the system can be further subdivided into a coaxial closed heat recovery system, a multi-pipeline closed heat recovery system and a U-shaped closed heat recovery system. On the basis, on the premise of not increasing the cost, a technical method which can avoid part of adverse effects caused by heat collection and can improve the heat collection efficiency is significant.

Disclosure of Invention

In order to overcome the problems, the invention provides a heat exchange working medium recyclable same-well heat recovery method, which solves the problems that the existing geothermal energy resource heat recovery system is operated for a long time to change the original groundwater distribution and the heat exchange efficiency is low.

A heat exchange working medium recoverable same-well heat recovery method comprises the following steps:

step one, arranging a single well system

A shaft 3 is built on rock, a submersible pump 14 is arranged in the shaft 3, a sealing flange 6 is fixedly connected to the wellhead of the shaft 3, and the submersible pump 14 is arranged below the water level 15 in the shaft 3;

step two, selectively arranging artificial fractures 4 in the target geothermal reservoir 2 according to the permeability of the target geothermal reservoir 2, and selectively filling proppants 5 in the artificial fractures 4 if the artificial fractures 4 are arranged;

step three, arranging an overground heat exchange energy supply part

The overground heat exchange energy supply part comprises a booster pump 10, heat exchange or power generation equipment 8 and a buffer storage tank 9, wherein the booster pump 10 is connected with the heat exchange or power generation equipment 8 through a first pipeline 11, the heat exchange or power generation equipment 8 is connected with the buffer storage tank 9 through a fourth pipeline (17), a second pipeline 18 is further arranged on the booster pump 10, the second pipeline 18 penetrates through a sealing flange 6 and extends into the shaft 3, meanwhile, the heat exchange or power generation equipment 8 is further connected with a submersible pump 14 through a third pipeline 19, and valves 16 are arranged on the first pipeline 11, the second pipeline 18, the third pipeline 19 and the fourth pipeline 17;

step four, implementing a heat collecting process:

injecting: opening valves 16 on a first pipeline 11, a second pipeline 18 and a fourth pipeline 17, starting a booster pump 10 to inject low-temperature heat exchange media in a heat exchange or power generation device 8 and a buffer storage tank 9 into a target geothermal reservoir 2 through a shaft 3 through the first pipeline 11 and the second pipeline 18, and stopping injecting and closing the valves 16 after the injection amount of the low-temperature heat exchange media reaches a preset value so that the wellhead of the shaft 3 is in a sealed state;

well stewing: starting to soak the well, and opening a valve 16 on a third pipeline 19 to unseal the well shaft 3 after the soaking time reaches a preset value;

and (3) stoping: and pumping equivalent high-temperature heat exchange medium from the target geothermal reservoir 2 through the shaft 3 by using the submersible pump 14 to heat exchange or power generation equipment 8 for heat exchange or power generation.

And two or more single well systems share one set of ground heat exchange energy supply part, so that the injection, well stewing and recovery processes of the step four are alternately carried out on the same energy supply unit by the two or more single well systems.

In the first step, a shaft 3 penetrates through the cover layer 1 to be communicated to a target geothermal reservoir 2.

In the first step, the shaft 3 is well-cemented by a sleeve or non-well-cemented by a sleeve, wherein the shaft 3 is connected with the stratum by a high heat-conducting sleeve when the shaft 3 is well-cemented by the sleeve, and the sleeve between the shaft 3 and the target geothermal reservoir 2 is perforated.

And arranging a sealing joint for connecting a pipeline on the sealing flange 6 in the first step.

If the rock in the second step is compact magma rock with hot rock type geothermal resources, an artificial fracture 4 needs to be formed in the target geothermal reservoir 2 through an excitation means; if the rock is a high-permeability sedimentary rock (such as sandstone or limestone) with the existence of hydrothermal geothermal resources, the artificial fracture 4 does not need to be additionally manufactured, and the propping agent 5 does not need to be filled.

And in the third step, one end of a third pipeline 19 is communicated with the submersible pump 14, and the other end of the third pipeline passes through the sealing flange 6 and is communicated with the heat exchange or power generation equipment 8.

The heat exchange or power generation equipment 8 is heat exchange equipment when heat collection is used for heating, and the heat exchange or power generation equipment 8 is power generation equipment capable of converting heat energy into electric energy when heat collection is used for power generation.

The well shaft 3 in the step one is a vertical well, a horizontal well or a well with any angle.

The low-temperature heat exchange medium in the fourth step is water and CO₂Or other heat exchange working media.

The invention has the beneficial effects that:

the heat exchange working medium recyclable same-well heat recovery method provided by the invention has multiple advantages: (1) compared with the traditional single-well heat exchange technology, the heat exchange range is not only on the well wall, but also expanded to the stratum around the shaft, and the heat exchange area is obviously expanded; (2) the heat exchange working medium and the geothermal reservoir fully exchange heat through the soaking process, so that the heat exchange effect is effectively improved; (3) the injection amount and the extraction amount are controlled to be basically consistent, so that damages such as underground water level reduction, ground settlement and the like to an original place layer in the heat extraction process are avoided to a great extent; (4) the heat exchange working medium can be recovered, so that the using amount of the heat exchange working medium is reduced; (5) through the alternate heat extraction of a plurality of single wells, the flow of the well mouth is ensured to reach the preset target, and the stable and continuous energy supply is realized.

Drawings

FIG. 1 is a vertical cross-sectional view of a single well system and an above-ground heat exchange power supply section of the present invention;

FIG. 2 is a schematic view of an implantation process of the present invention;

figure 3 is a schematic view of the present invention during the soaking process;

FIG. 4 is a schematic view of the recovery process of the present invention;

FIG. 5 is a partial horizontal cross-sectional view of the single well system and above-ground heat exchange and energy supply system of example 2;

FIG. 6 is a schematic representation of the wellhead flow rate over time for two wellbores as described in example 2.

In the figure, 1, a cover layer, 2, a target heat storage layer, 3, a shaft, 31, an injection state shaft, 32, a recovery state shaft, 4, an artificial fracture, 5, a propping agent, 6, a sealing flange, 7, a residential area, 8, a heat exchange or power generation device, 9, a buffer storage tank, 10, a booster pump, 11, a first pipeline, 12, a terrestrial heat flow, 13, a heat exchange medium flow direction, 14, a submersible pump, 15, a water level, 16, a valve, 17, a fourth pipeline, 18, a second pipeline, 19, a third pipeline, 20 and a fifth pipeline.

Detailed Description

A heat exchange working medium recoverable same-well heat recovery method comprises the following steps:

step one, arranging a single well system

Building a shaft 3 on the rock, arranging a submersible pump 14 in the shaft 3, fixedly connecting a sealing flange 6 at the wellhead of the shaft 3, and arranging the submersible pump 14 below the water level (15) in the shaft 3;

step two, setting artificial fractures 4 in the target geothermal reservoir 2 according to the permeability selectivity of the geothermal reservoir 2, and optionally filling proppants 5 in the artificial fractures 4 if the artificial fractures 4 are set;

step three, arranging an overground heat exchange energy supply part

The ground heat exchange and energy supply part comprises a booster pump 10 for regulating and controlling injection, heat exchange or power generation equipment 8 (heat exchange equipment if geothermal energy is used for heating residents and power generation equipment if geothermal energy is used for generating electricity) and a buffer storage tank 9, wherein the booster pump 10 is connected with the heat exchange or power generation equipment 8 through a first pipeline 11, the heat exchange or power generation equipment 8 is connected with the buffer storage tank 9 through a fourth pipeline 17, a second pipeline 18 is further arranged on the booster pump 10, the second pipeline 18 penetrates through a sealing joint on a sealing flange 6 and extends into a shaft 3, meanwhile, the heat exchange or power generation equipment 8 is also connected with a submersible pump 14 through a third pipeline 19, and valves 16 are arranged on the first pipeline 11, the second pipeline 18, the third pipeline 19 and the fourth pipeline 17 and are controlled by the valves 16 to be communicated or not;

step four, implementing a heat collecting process:

injecting: opening valves 16 on a first pipeline 11, a second pipeline 18 and a fourth pipeline 17, starting a booster pump 10 to inject low-temperature heat exchange media in a heat exchange or power generation device 8 and a buffer storage tank 9 into a target geothermal reservoir 2 through a shaft 3 through the first pipeline 11 and the second pipeline 18, and stopping injecting and closing the valves 16 after the injection amount of the low-temperature heat exchange media reaches a preset value so that the wellhead of the shaft 3 is in a sealed state; the preset value of the injection amount is obtained through calculation or pilot test, so that the injection amount of the heat exchange medium can meet the heat exchange or power generation requirements under a certain working condition;

well stewing: determining the stewing time length according to actual conditions such as permeability, heat energy grade and the like of the target geothermal reservoir 2, starting stewing, and opening a valve 16 on a third pipeline 19 to unseal the shaft 3 after the stewing time length reaches a preset value; when the heat exchange or power generation needs are fixed, the higher the permeability and the heat energy grade of the geothermal reservoir are, the shorter the soaking time is, and vice versa;

and (3) stoping: a submersible pump 14 is utilized to pump a substantially equal amount of high temperature heat exchange medium from the target geothermal reservoir 2 through the wellbore 3 into the heat exchange or power generation equipment 8 for heat exchange or power generation.

And two or more single well systems share one set of ground heat exchange energy supply part, so that the injection, well stewing and recovery processes of the step four are alternately carried out on the same energy supply unit by the two or more single well systems.

In the first step, a shaft 3 penetrates through the cover layer 1 to be communicated to a target geothermal reservoir 2.

In the first step, the shaft 3 is well-cemented by a sleeve or non-well-cemented by a sleeve, wherein the shaft 3 is connected with the stratum by a high heat-conducting sleeve when the shaft 3 is well-cemented by the sleeve, and the sleeve between the shaft 3 and the target geothermal reservoir 2 is perforated.

And arranging a sealing joint for connecting an inlet pipeline and an outlet pipeline on the sealing flange 6 in the first step.

If the rock in the second step is compact magma rock with dry hot rock type geothermal resources, an artificial fracture 4 needs to be formed in a geothermal reservoir, namely the target geothermal reservoir 2, by means of excitation means such as hydraulic fracturing, and a propping agent 5 can be filled in the rock according to actual requirements to prevent the artificial fracture 4 from being closed; if the rock is a high-permeability sedimentary rock (such as sandstone or limestone) in the presence of hydrothermal geothermal resources, additional artificial fractures 4 do not need to be manufactured, and the proppant 5 does not need to be filled.

And in the third step, one end of a third pipeline 19 is communicated with the submersible pump 14, and the other end of the third pipeline passes through a sealing joint on the sealing flange 6 and is communicated with the heat exchange or power generation equipment 8.

When the heat collection is used for heating, the heat exchange or power generation equipment 8 is heat exchange equipment, and specifically comprises the following components: a plate heat exchanger unit, a threaded pipe heat exchanger unit or a heating and heating heat exchanger unit of the texas ligin energy-saving technology limited company and the like of the Shandong Huanjin New energy technology limited company;

the heat exchange or power generation equipment 8 is power generation equipment capable of converting thermal energy into electrical energy when heat is collected for power generation.

The well bore 3 in the first step can be any angle well including a vertical well and a horizontal well.

The heat exchange medium in the fourth step can be water or CO₂Or other heat exchange working media.

And the buffer storage tank 9 in the step two is used for adjusting the problem of surplus or shortage of flow in the injection and production process.

The invention is further described below with reference to the accompanying drawings.

Example 1

In the embodiment, the heat is used for heating residents, so that the heat exchange or power generation equipment 8 in the ground heat exchange and energy supply part is heat exchange equipment.

As shown in fig. 1, 2 and 3, an implementation system of a heat exchange working medium recoverable same-well heat recovery technology relies on that an underground heat recovery part, namely a single-well system, comprises a shaft 3 which penetrates through a cover layer 1 and is communicated with a target geothermal reservoir 2, a sealing flange 6, artificial fractures 4 which are arranged and proppants 5 filled in the artificial fractures 4 are selected according to the permeability of the reservoir, namely if the artificial fractures are compact rock pulp rocks occurring in a dry-hot-rock geothermal resource, artificial fractures need to be formed in the geothermal reservoir through excitation means such as hydraulic fracturing, and the proppants need to be filled in the artificial fractures to prevent the closure of the artificial fractures, and if the artificial fractures are high-permeability sedimentary rocks occurring in a hydrothermal geothermal resource (such as sandstone or limestone), additional artificial fractures and filled proppants are not required in general cases; the sealing flange 6 is fixed at the wellhead at the top of the shaft 3;

the ground heat exchange energy supply part comprises a booster pump 10 for regulating and controlling injection, a submersible pump 14 for pumping, a heat exchange device 8 and a buffer storage tank 9, wherein the booster pump 10 is connected with the heat exchange device 8 through a first pipeline 11, the heat exchange device 8 is connected with the buffer storage tank 9 through a fourth pipeline 17, the submersible pump 14 is connected with the heat exchange device 8 through a third pipeline 19, a second pipeline 18 is further arranged on the booster pump 10, the second pipeline 18 penetrates through a sealing joint on a sealing flange 6 and extends into the shaft 3, and valves 16 are arranged on the first pipeline 11, the second pipeline 18, the third pipeline 19 and the fourth pipeline 17, and whether the booster pump is communicated or not is controlled by the valves 16.

This embodiment illustrates a flow of implementing the heat exchange working medium recoverable heat recovery method in a single well, and as shown in fig. 1, the injection process of the heat recovery technology operation in the same well is shown, in the injection process, the valve 16 on the first pipeline 11, the second pipeline 18 and the fourth pipeline 17 is opened to heat exchange or power generation equipment 8, the booster pump 10 is used to inject the low-temperature heat exchange medium in the heat exchange or power generation equipment 8 and the buffer storage tank 9 into the target geothermal reservoir 2 through the wellbore 3, and the injected low-temperature heat exchange medium is injected into the target geothermal reservoir 2 through the wellbore 3The medium carries out limited migration in the target geothermal reservoir 2 through the primary pore fractures or artificial fractures 4, the main flow direction is shown as the flow direction 13 of the heat exchange medium, and exchanges heat with the target geothermal reservoir 2, when the injection amount of the low-temperature heat exchange medium reaches a preset value, the injection is stopped and the valve 16 is closed, determining the soaking time length according to the characteristics of the actual geothermal reservoir permeability, geothermal energy grade and the like, wherein the soaking process is shown as figure 2, in the soaking process, the injected low-temperature heat exchange medium is further slowly moved in the geothermal reservoir 2 under the high pressure of a well head to obtain more heat, after the soaking is finished, as shown in fig. 3, the valve 16 on the third conduit 19 is opened to the heat exchange or power generation device 8, and the high-temperature heat exchange medium in the target geothermal reservoir 2 is recovered to the heat exchange or power generation equipment 8 through the submersible pump 14 for heat exchange and heating, and low-temperature water or CO is obtained after heat exchange.₂Stored in buffer tank 9 for use in the next injection process.

Example 2

In the embodiment, the heat is extracted for heating residents.

On the basis of embodiment 1, this embodiment illustrates an implementation process of implementing the heat exchange working medium recoverable heat recovery method for the resident heating in two wells. As shown in fig. 4, in order to establish a heat recovery method of the same well with heat exchange working medium capable of recovering heat, in which two wells coordinate and alternately perform injection, soaking and recovery processes to ensure stable and continuous total heat produced, two single well systems are established, wherein well bores 3 in the two single well systems are a first well bore 31 and a second well bore 32 respectively, and the first well bore 31 and the second well bore 32 share a set of ground heat exchange and heating part;

assuming that the total injection amount and the total extraction amount of the two well bores in each injection-soaking-recovery cycle are equal, and the mass is recorded as M. The injection rates are all v, the extraction rates are all 1/2v, the injection duration is t ═ M/v, the extraction duration is 2t, the soaking duration is t, and stable and continuous extraction heat can be realized through the following processes: (1) the capacity of a buffer storage tank 9 is 2M, firstly, a booster pump 10 injects a low-temperature heat exchange medium with the total amount of M into a target geothermal reservoir 2 below a second shaft 32 at a constant speed v, and the time is t; (2) closing the second wellbore 32; (3) after the soaking time is long, the second shaft 32 is not opened, high-temperature heat exchange medium with the total amount of M is extracted from the target geothermal reservoir 2 below the second shaft 32 at a constant speed of 1/2v, the time is consumed for 2t, meanwhile, low-temperature heat exchange medium with the total amount of M is injected into the target geothermal reservoir 2 below the first shaft 31 at a constant speed of v through the first shaft 31 by the booster pump 10, the time is consumed for t, then the first shaft 31 is closed, and the soaking time is long; (4) repeating the processes (1) to (3) on the second wellbore 32, unsealing the first wellbore 31, and uniformly extracting the total amount of M high-temperature heat exchange medium from the target geothermal reservoir 2 below the first wellbore 31 at a speed of 1/2v, wherein the time is 2 t; (5) repeating processes (3) - (4) for the first wellbore 31. The flow-time diagram corresponding to the above operation flow is shown in fig. 5, and the working state shown in fig. 4 is between 2t and 3t in fig. 5. The extracted heat energy is heat exchanged via the heat exchanging device 8 and is heated to the residential area 7 through the fifth pipeline 20.

Fig. 4 and fig. 5 are more visual to show how the alternating injection and soaking mining process of the two wells in the embodiment 2 realizes continuous wellhead mining, and compared with the traditional single-well heat exchange technology, the heat exchange range is not only on the well wall, but also expanded to the stratum around the well shaft, and the heat exchange area is obviously expanded; the heat exchange working medium and the geothermal reservoir fully exchange heat through the soaking process, so that the heat exchange effect is effectively improved;

the injection amount and the extraction amount are controlled to be basically consistent, so that damages such as underground water level reduction, ground settlement and the like to an original place layer in the heat extraction process are avoided to a great extent; the heat exchange working medium can be recovered, so that the using amount of the heat exchange working medium is reduced; through the alternate heat extraction of a plurality of single wells, the flow of the well mouth is ensured to reach the preset target, and the stable and continuous energy supply is realized.