CN111237146A - Geothermal branch well constant temperature difference power generation system - Google Patents

Abstract

The invention provides a geothermal multilateral well constant temperature difference power generation system which comprises a main shaft sleeve, wherein the main shaft sleeve penetrates through an overburden stratum and a high-temperature geothermal rock stratum; a plurality of branch wells are distributed on the side wall of the main shaft casing, and a main shaft gathering and transmitting cable is arranged in the main shaft casing; a constant temperature difference power generation cylinder group is arranged in each branch well and is connected with a main shaft gathering and transmission cable through a wiring branch well male joint and a main shaft cable female joint; the bottom of the main shaft gathering and transmission cable is provided with a clamping mechanism, and the clamping mechanism is seated on the inner wall of the main shaft sleeve to ensure that the main shaft gathering and transmission cable is in a straightening state; the top is connected with a ground power collection and transmission control center; the ground power collection and transmission control center is networked with an external power transmission grid. The invention has simple and feasible design, can improve the utilization of geothermal resources to the maximum extent by adopting the branch wells, provides stable electric energy supply, and realizes the underground thermoelectric power generation because each branch well section does not influence each other.

Description

A thermostatic differential power generation system for geothermal branch wells

technical field

The invention belongs to the technical field of geothermal power generation, and in particular relates to a constant temperature difference power generation system for geothermal branch wells.

Background technique

Huge thermal energy is stored inside the earth, which is about 50,000 times the energy of global oil and gas resources. With the increasing shortage of traditional fossil energy, geothermal resources, as a kind of clean energy with huge reserves, pollution-free and renewable, meet the needs of the modern industrial society. More and more attention has been paid to the development and utilization of geothermal resources, and it has become a new energy source. Hot spots for development and research.

The primary way of development and utilization of geothermal resources is drilling. With the continuous development of drilling equipment capacity, depth and breadth of geothermal development, geothermal wells are generally drilled to a depth of more than one kilometer. In many areas, only three or four kilometers can be drilled to obtain high-grade geothermal resources, and the construction cost is relatively high.

Geothermal power generation is the most important way of geothermal utilization. The main methods of geothermal power generation are steam type geothermal power generation and hot water type geothermal power generation. The steam type geothermal power generation method is simple, but the dry steam geothermal resources are very limited. big. In recent years, the manufacturing technology and process of thermoelectric power generation materials have been continuously improved, and thermoelectric power generation technology has gradually emerged. Thermoelectric power generation materials use the principle of the Seebeck effect to generate electricity. When different temperatures are applied on both sides of the thermoelectric power generation unit composed of N-type semiconductor and P-type semiconductor, an electromotive force will be generated between the thermoelectric power generation units, so that the thermal energy is directly converted. converted into electrical energy. During the power generation process of the thermoelectric power generation material, as the temperature difference increases, the output power of the thermoelectric power generation device increases accordingly. Generally speaking, the temperature of geothermal energy thermal fluid or heat source is relatively stable, so the best way to increase the temperature difference is to reduce the temperature of the cold end face of the thermoelectric power generation device.

The Chinese patent application with application number 201610496310.6 discloses a cold-source dry-hot rock thermoelectric power generation system of the formation itself. The part of the thermoelectric power generation module in contact with the exposed dry hot rock reservoir is the high-temperature hot end, and the downhole thermoelectric power generation module is directly connected to the wellbore. The contact part is the low temperature cold end, and the underground thermoelectric power generation module, the positive wire, the ground load and the negative wire are connected in sequence to form a closed circuit. This invention does not occupy additional ground area, but the power generation capacity and power generation efficiency are not high.

The Chinese patent application with the application number of 201810524089.X discloses a U-shaped tube heat exchange closed circulation downhole thermoelectric power generation system. Under the action of the downhole diverter, a part of the cold fluid is diverted into the oil casing annular flow channel. The temperature of part of the cold fluid will gradually increase during the rising process; the other part of the cold fluid will continue to flow downward into the U-tube heat exchanger, after absorbing the heat transferred by the formation hot fluid, the temperature will increase, and it will become a circulating hot fluid and flow out. ground. The thermoelectric power generation module generates electric energy under the action of the temperature difference, and inputs the electric energy into the electric energy transmission module through the connecting cable. This invention can provide stable electric power supply, but increasing the temperature difference by means of water cooling requires more electric power and larger investment.

The Chinese patent application with the application number of 201810524090.2 discloses a dual-well closed-circulation downhole thermoelectric power generation system and method. The system will not affect the subsequent utilization of the produced fluid, but needs to drill through the A wellbore and the B wellbore of the same formation at the same time, The development cost is relatively large, and only medium and low temperature geothermal resources can be used, and the utilization rate of geothermal resources is not very high.

Therefore, there is an urgent need for a geothermal power generation system that can make full use of geothermal resources, consume less electric power, have high power generation efficiency, and provide stable power supply.

SUMMARY OF THE INVENTION

In order to overcome the above problems, the present invention provides a constant temperature difference power generation system for geothermal multilateral wells. The present invention does not need to inject fluid as the cold end face of the temperature difference power generation, and directly improves the power generation efficiency through a constant temperature difference power generation system. Multilateral wells can maximize the utilization of geothermal resources, reduce the number of development wells, reduce development costs, and provide stable power supply. The design is simple and feasible, and the on-site operation is also simple and convenient.

The specific technical solutions are:

A thermostatic differential power generation system for a geothermal branch well, comprising a main wellbore casing, the main wellbore casing penetrating an overlying stratum and a high-temperature geothermal rock layer;

A plurality of branch wells are distributed on the side wall of the main wellbore casing, and the main wellbore gathering and transmission cables are arranged in the main wellbore casing; each branch well is provided with a constant temperature difference generator set, and the constant temperature difference generator set is connected through the male joint of the branch well. , The main wellbore cable female connector is connected with the main wellbore gathering and transmission cable;

The bottom of the main wellbore gathering and transmission cable is provided with a clamping mechanism, and the clamping mechanism is seated on the inner wall of the main wellbore casing, so that the main wellbore gathering and transmission cable is in a straight state;

The top is connected to the ground power collection and transmission control center; the ground power collection and power transmission control center is connected to the external transmission grid.

The constant temperature difference generating tube group includes a plurality of temperature difference generating tubes, each of which includes an outer tube, the outer tube is a closed cylinder, and the outer tube is equipped with a male connector and a female connector which can be connected in sequence to form a constant temperature difference generating tube group;

One end of the thermoelectric generator is a cable male connector, and the other end is a cable female connector;

The outer cylinder is also provided with a cryogenic liquid cylinder, and the outer cylinder and the cryogenic liquid cylinder are coaxial; the annular cavity between the outer cylinder and the cryogenic liquid cylinder is provided with a thermoelectric power generation module and a thermoelectric refrigeration module; the thermoelectric refrigeration module and the thermoelectric power generation module are arranged The modules are alternately placed in sequence and isolated by isolation blocks; the area of the thermoelectric power generation module is larger than that of the thermoelectric refrigeration module;

The low temperature liquid cylinder is a sealed structure, and the outer wall is connected with the low temperature end of the thermoelectric power generation chip, and is also connected with the thermoelectric refrigeration module;

There is a certain gap between the constant temperature difference generator set and the high-temperature geothermal rock formation, and the gap is a heat-conducting liquid.

The thermoelectric power generation module includes a plurality of sets of thermoelectric power generation chips, and the thermoelectric power generation chip set includes a power generation hot end insulating heat receiving member, a power generation hot end metal conductor group, a power generation cold end metal conductor group, a power generation cold end insulation and heat release member, a power generation module negative electrode, a power generation module The positive electrode and thermoelectric power generation semiconductor group; the power generation hot end insulating heat receiving member is in close contact with the outer cylinder, and the power generation cold end insulation heat release member is in direct contact with the low temperature liquid cylinder; the thermoelectric power generation semiconductor group consists of several groups of N-type semiconductors and P-type semiconductors alternately formed into Pair arrangement; one end of the thermoelectric power generation semiconductor group is placed in the insulating and heat-receiving member of the power generation hot end, and the other end is placed in the power generation cold end insulation and heat release member; in the thermoelectric power generation semiconductor group, the N-type semiconductor of the first group of thermoelectric power generation semiconductor groups The cold end is connected to the negative electrode of the power generation module through a wire; the N-type semiconductor hot end and the P-type semiconductor hot end of the first group of thermoelectric power generation semiconductor groups are connected by the first conductor in the metal conductor group of the power generation hot end; the first group of thermoelectric power generation semiconductor group The cold end of the P-type semiconductor is connected with the cold end of the N-type semiconductor of the second group of thermoelectric power generation semiconductor groups through the first conductor of the metal conductor group of the power generation cold end; Structure; the P-type semiconductor cold end of the last group of thermoelectric power generation semiconductor group is connected to the positive electrode of the power generation module through a wire.

The thermoelectric refrigeration module includes a refrigeration chip set, and the refrigeration chip set includes a refrigeration hot end insulating and heating component, a refrigeration hot end metal conductor group, a refrigeration cold end metal conductor group, a refrigeration cold end insulating heat release component, a refrigeration module negative pole, a refrigeration module positive pole, a thermoelectric Refrigeration semiconductor group; the insulating and heat-receiving member of the cooling hot end is in close contact with the outer cylinder, and the insulating and heat-releasing member of the cooling cold end is in direct contact with the low-temperature liquid cylinder; the thermoelectric refrigeration semiconductor group consists of a group of N-type semiconductors and P-type semiconductors alternately arranged in pairs; One end of the thermoelectric refrigeration semiconductor group is placed in the cooling hot end insulating heat receiving member, and the other end is placed in the refrigeration cold end insulating heat releasing member; in the thermoelectric refrigeration semiconductor group, the N-type semiconductor hot end is connected to the positive electrode of the refrigeration module through a wire; thermoelectric refrigeration The N-type semiconductor cold end and the P-type semiconductor cold end of the semiconductor group are connected through the cooling cold end metal conductor group; the P-type semiconductor hot end of the thermoelectric refrigeration semiconductor group is connected to the negative electrode of the refrigeration module through a wire.

The positive pole of the power generation module of the thermoelectric power generation module is connected to the positive pole of the refrigeration module of the thermoelectric refrigeration module through a wire, and the negative pole of the power generation module of the thermoelectric power generation module is connected to the negative pole of the refrigeration module of the thermoelectric refrigeration module through a wire.

The main wellbore cable female connector is connected to the main wellbore gathering and transmission cable through the upper connector and the lower connector; the side interface is connected to the branch well male connector.

The branch and the main well form an included angle of 30°-60°; the branch wells are distributed around the main well in a spiral manner.

Compared with the prior art, the beneficial effects of the present invention are:

1. The present invention adopts the method of geothermal multilateral wells to realize downhole heat extraction and power generation, avoiding potential environmental problems in the traditional geothermal production process.

2. The geothermal multilateral well described in the present invention is composed of a vertical well casing cementing main wellbore and n spirally distributed inclined open-hole lateral wells by following the petroleum engineering drilling technology, which can maximize the utilization of geothermal resources without additional Occupy the ground area, reduce the cost of ground power generation devices, reduce the number of development wells, and reduce development costs.

3. The constant temperature difference power generation subsystem of the present invention includes a constant temperature difference power generation tube group and a geothermal rock formation in n branch wellbores, and the constant temperature difference power generation tube group mainly includes a thermoelectric power generation module, a thermoelectric refrigeration module, and a low temperature liquid cylinder. A constant temperature difference is generated between the high-temperature geothermal heat and the low-temperature liquid of the well, which can stably realize the interactive transformation of electric energy and cold energy, without causing pollution, with long service life and easy control.

4. The main wellbore gathering and transmission cable subsystem of the present invention is connected to all the branch well power generation subsystems and transmits electric energy to the ground electric energy gathering and transmission control center, so that each branch well section forms a closed thermoelectric power generation subsystem, which can make full use of Geothermal resources provide a stable power supply without affecting each other.

To sum up, the present invention is simple and feasible in design, the use of branch wells can maximize the utilization of geothermal resources, provide stable power supply, and each branch well section does not affect each other, and realizes downhole thermoelectric power generation.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the main well top view of the present invention;

3 is a schematic structural diagram of a thermoelectric generator tube of the present invention;

4 is a schematic structural diagram of a thermoelectric power generation module of the present invention;

5 is a schematic structural diagram of a thermoelectric refrigeration module of the present invention;

FIG. 6 is a schematic structural diagram of a branch well cable joint of the present invention.

Detailed ways

The specific technical solutions of the present invention are described with reference to the embodiments.

As shown in Figures 1 and 2, a thermostatic differential power generation system for a geothermal branch well includes a main wellbore casing 3, and the main wellbore casing 3 penetrates the overlying stratum 1 and the high-temperature geothermal rock layer 2;

A plurality of branch wells are distributed on the side wall of the main wellbore casing 3. The main wellbore casing 3 is provided with a main wellbore gathering and transmission cable 4; Connect with the main wellbore gathering and transmission cable 4 through the wiring branch well male connector 7 and the main wellbore cable female connector 5;

The bottom of the main wellbore gathering and transmission cable 4 is provided with a clamping mechanism 10, and the clamping mechanism 10 is seated on the inner wall of the main wellbore casing 3, so that the main wellbore gathering and transmission cable 4 is in a straight state;

The top is connected to the ground power collection and transmission control center 11 ; the ground power collection and power transmission control center 11 is connected to the external transmission network 13 .

The high-temperature geothermal rock layer 2 is buried several kilometers deep, and the overlying stratum 1 is a thermal insulation layer such as sedimentary rock or soil covered by the high-temperature geothermal rock layer 2 and above to the surface. reservoir temperature. The main wellbore is formed by drilling and casing 3 is cemented, and the open-hole section of the branch well is formed by window sidetracking or hydraulic jet drilling. According to the drilling method of the lateral wells, the diameter of the wellbore is about 80-200mm and the length is about 20-200m. The axis of the lateral wellbore and the main wellbore form an included angle of 30°-60°, which is convenient for the constant temperature difference generator tube group 6 to withstand its own weight. Under the action, it entered the branch wellbore smoothly. The wellbore of the lateral well is distributed in a spiral manner, which is conducive to the maximum development of geothermal rock energy.

As shown in FIG. 3 , the constant temperature difference generator set 6 includes a plurality of thermoelectric generators, each of which includes an outer cylinder 105 , the outer cylinder 105 is a closed cylinder, and the outer cylinder 105 is equipped with a male connector 107 and a female cylinder 105 . The joints 106 can be sequentially connected to form the constant temperature difference generator set 6;

One end of the thermoelectric generator is a cable male connector 108, and the other end is a cable female connector 109;

The constant temperature difference generator set 6 is composed of a plurality of thermoelectric generators, each of which is a cylinder with a length of 10m, and can be formed into a diameter of 80-200mm according to needs. Lengthen to form a thermoelectric generator set of about 200m.

The outer cylinder 105 is made of high-temperature and corrosion-resistant materials to prevent the outer cylinder 105 from being corroded by the liquid in the high-temperature geothermal rock formation 2; A thermoelectric power generation module 102 and a thermoelectric power generation module 103 are arranged in the annular cavity between the cylinder 105 and the cryogenic liquid cylinder 101; The area is larger than the area of the thermoelectric refrigeration module 103; the power generation energy is much larger than the refrigeration energy, the interactive transformation of electric energy and cold energy can be stably realized, no pollution is caused, the service life is long, and it is easy to control.

The low temperature liquid cylinder 101 is a sealed structure, and the outer wall is connected to the low temperature end of the thermoelectric power generation chip 102, and is also connected to the thermoelectric refrigeration module 103;

There is a certain gap between the constant temperature difference generator tube group 6 and the high temperature geothermal rock formation 2, and the gap is filled with heat-conducting liquid.

The constant temperature difference generator tube group 6 is sequentially fed into the corresponding branch wellbore from the bottom according to the well design scheme, waiting to be connected with the main wellbore gathering and transmission cable 4. At the same time, due to the formation of temperature difference, the constant temperature difference generator tube group 6 has started to generate electricity, and all use When the cryogenic liquid cylinder 101 is refrigerated, the longer the constant temperature difference generator set 6 is in the well without external transmission, the lower the temperature of the cryogenic liquid cylinder 101, the greater the temperature difference formed by the constant temperature difference generator set 6, and the more power generation energy.

As shown in FIG. 4 , the thermoelectric power generation module 102 includes multiple sets of thermoelectric power generation chips, and the thermoelectric power generation chip set includes a power generation hot end insulation and heat receiving member 201, a power generation hot end metal conductor group 202, a power generation cold end metal conductor group 203, and a power generation cold end insulation The heat release member 204, the negative electrode 205 of the power generation module, the positive electrode 206 of the power generation module, and the thermoelectric power generation semiconductor group 207; The thermoelectric power generation semiconductor group 207 consists of several groups of N-type semiconductors and P-type semiconductors alternately and arranged in pairs; one end of the thermoelectric power generation semiconductor group 207 is placed in the power generation hot end insulation and heat receiving member 201, and the other end is placed in the power generation cold end insulation heat release In the component 204; in the thermoelectric power generation semiconductor group 207, the N-type semiconductor cold end of the first group of thermoelectric power generation semiconductor group is connected to the negative electrode 205 of the power generation module through a wire; the N-type semiconductor hot end and P-type semiconductor of the first group of thermoelectric power generation semiconductor group The hot end is connected by the first conductor in the metal conductor group 202 of the power generation hot end; the cold end of the P-type semiconductor of the first group of thermoelectric power generation semiconductor group and the cold end of the N-type semiconductor of the second group of thermoelectric power generation semiconductor group are connected by the cold end metal of the power generation cold end The first conductor of the conductor group 203 is connected; according to the circular connection, the N-type semiconductor and the P-type semiconductor are connected to form a series structure;

As shown in FIG. 5 , the thermoelectric cooling module 103 includes a cooling chip set, and the cooling chip set includes a cooling hot end insulating heat receiving member 301 , a cooling hot end metal conductor set 302 , a cooling cold end metal conductor set 303 , and a cooling cold end insulating heat releasing member 304, the negative electrode 306 of the refrigeration module, the positive electrode 305 of the refrigeration module, and the thermoelectric refrigeration semiconductor group 307; the cooling hot end insulating and heating member 301 is in close contact with the outer cylinder 105, and the cooling cold end insulating heat releasing member 304 is in direct contact with the low temperature liquid cylinder 101; thermoelectric refrigeration The semiconductor group 307 is composed of a group of N-type semiconductors and P-type semiconductors alternately arranged in pairs; one end of the thermoelectric refrigeration semiconductor group 307 is placed in the cooling and hot end insulating heat receiving member 301, and the other end is placed in the cooling cold end insulating heat releasing member 304 In the thermoelectric refrigeration semiconductor group 307, the N-type semiconductor hot end is connected to the anode 305 of the refrigeration module through a wire; the N-type semiconductor cold end and the P-type semiconductor cold end of the thermoelectric refrigeration semiconductor group 307 are connected by the refrigeration cold end metal conductor group 303; The P-type semiconductor hot end of the refrigeration semiconductor group 307 is connected to the negative electrode 306 of the refrigeration module through a wire.

The positive electrode 206 of the power generation module of the thermoelectric power generation module 102 is connected to the positive electrode 305 of the cooling module of the thermoelectric cooling module 103 through a wire, and the negative electrode 205 of the power generation module of the thermoelectric power generation module 102 is connected to the negative electrode 306 of the cooling module of the thermoelectric cooling module 103 through a wire.

The thermoelectric cooling module 103 continuously generates cold energy under a stable power supply, and the cryogenic liquid cylinder 101 can continue to cool; at the same time, the thermoelectric power generation module 102 continuously generates electric energy under a constant temperature difference, and the power generation energy is much greater than the cooling energy.

As shown in FIG. 6 , the main wellbore cable female connector 5 is connected to the main wellbore gathering and transmission cable 4 through the upper connector 401 and the lower connector 402 ; the side port 403 is connected to the branch well male connector 7 .

The male connector 7 of the branch shaft is picked up by the downhole robot and sent to the main wellbore cable female connector 5. When the male and female connectors are engaged, the anti-dropping clamping mechanism of the female connector is automatically locked, and the locking mechanism can be unlocked by the ground control downhole robot. At the same time, the joint has the function of controlling electric energy input or feedback, and can detect the power generation state of the branch well. Once the power generation efficiency of the branch well is low, the collection of electric energy can be suspended.

The main wellbore cable joint mechanism composed of the main wellbore cable female joint 5 and the branch well male joint 7 is assembled in series on the ground and then lowered into the predetermined well depth, the main wellbore cable power is turned on, and the 10 clamping mechanisms at the bottom of the main wellbore cable are controlled to be sealed at the bottom of the main wellbore cable. On the inner wall of the main wellbore casing 3, the cable is pulled to make the main wellbore gathering and transmission cable 4 in a straight state, avoiding bending and breaking of the bottom hole cable, and facilitating the positioning and mating connection of the main wellbore cable female connector 5 and the branch well male connector 7.

The system works as follows:

The main wellbore of the geothermal branch well 12 is formed by drilling, and the main wellbore casing 33 is set for cementing, and the open-hole section of the branch well is formed by window sidetracking or hydraulic jet drilling. The constant temperature difference generator set 6 is sequentially fed into the corresponding branch wellbore from the bottom, and the high temperature geothermal rock layer 2 provides a heat source for the thermoelectric power generation module 102 and becomes the high temperature hot end of the thermoelectric power generation module 102 . The refrigerating liquid in the low temperature liquid cylinder 101 provides a cold source for the thermoelectric power generation module 102 and becomes the low temperature cold end of the thermoelectric power generation module 102 . The thermoelectric power generation module 102 generates electrical energy under the action of the temperature difference between the temperature of the refrigerant liquid of the low temperature liquid cylinder 101 and the temperature of the high temperature geothermal rock formation 2 . Most of the electric energy is transmitted to the main wellbore gathering and transmission cable 4 , and a small part of the electric energy is output to the adjacent thermoelectric refrigeration module 103 for continuous refrigeration of the cryogenic liquid cylinder 101 . Multiple main wellbore cable joint mechanisms are assembled in series on the ground and then run down to a predetermined well depth, turn on the power supply of the main wellbore gathering and transmission cable 4, and control the bottom clamping mechanism 10 of the main wellbore gathering and transmission cable 4 to be seated on the inner wall of the main wellbore casing 3, The pulling main wellbore gathering and transmission cable 4 is in a straightened state. Run the downhole robot from the wellhead, pick up and pair and install the branch well male connector 7 into the main wellbore cable female connector 5 from the bottom branch well and lock it. In this way, each branch well male joint 7 is installed to the main wellbore gathering and transmission cable 4 in turn, so as to realize that the electric energy of the constant temperature difference generator tube group 6 of the branch well is transmitted to the main wellbore gathering and transmission cable 4, and then aggregated to the ground power collection and transmission control center 11. And boost to the external transmission grid 13 .

To sum up, the present invention uses geothermal branch wells without occupying additional ground area, reducing the cost of ground power generation devices, reducing the number of development wells, reducing development costs, greatly reducing initial investment and post-maintenance costs, and the entire process is simple in operation and engineering. The difficulty is low, the degree of dependence on the environment is small, and the utilization of geothermal resources can be maximized.

The constant temperature difference generator set of the present invention combines a thermoelectric power generation module with a thermoelectric refrigeration module, utilizes a high-performance thermoelectric power generation module to fully develop geothermal resources, and at the same time, based on the thermoelectric refrigeration module, does not need to inject additional cold fluid to ensure the temperature at both ends of the thermoelectric power generation module. It can realize the direct conversion of thermal energy to electric energy, improve the power generation efficiency, and has great application potential and development prospects.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as herein, are not to be taken in an idealized or overly formal sense. explain.

Those of ordinary skill in the art can understand that the components of the apparatus in the embodiment may be distributed in the apparatus of the embodiment according to the description of the embodiment, or may be located in one or more apparatuses different from the embodiment with corresponding changes. The components of the above-mentioned embodiments may be combined into one component, or may be further divided into multiple sub-components.

Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be modified. Or equivalent replacements, without departing from the spirit and scope of the present invention, any modifications or partial replacements shall be included in the scope of the claims of the present invention.

Claims (6)

1. The geothermal multilateral well constant temperature difference power generation system is characterized by comprising a main well casing (3) in a main well, wherein the main well casing (3) penetrates through an overburden (1) and a high-temperature geothermal rock stratum (2);

a plurality of branch wells are distributed on the side wall of the main shaft casing (3), and a main shaft gathering and transmission cable (4) is arranged in the main shaft casing (3); a constant-temperature difference power generation cylinder group (6) is arranged in each branch well, and the constant-temperature difference power generation cylinder group (6) is connected with a main shaft gathering and transmission cable (4) through a wiring branch well male joint (7) and a main shaft cable female joint (5);

the bottom of the main shaft gathering and transmission cable (4) is provided with a clamping mechanism (10), and the clamping mechanism (10) is seated on the inner wall of the main shaft casing (3) to ensure that the main shaft gathering and transmission cable (4) is in a straightened state;

the top is connected with a ground power collection and transmission control center (11); the ground power collection and transmission control center (11) is connected with an external power transmission grid (13) in a network.

2. The geothermal branch well constant temperature difference power generation system according to claim 1, wherein the constant temperature difference power generation barrel group (6) comprises a plurality of temperature difference power generation barrels, each temperature difference power generation barrel comprises an outer barrel (105), the outer barrel (105) is a closed cylinder, the outer barrel (105) is provided with a male connector (107) and a female connector (106), and the male connector and the female connector can be sequentially connected to form the constant temperature difference power generation barrel group (6);

one end of the thermoelectric generation cylinder is a cable male joint (108), and the other end is a cable female joint (109);

a low-temperature liquid cylinder (101) is also arranged in the outer cylinder (105), and the outer cylinder (105) and the low-temperature liquid cylinder (101) have the same axial lead; a thermoelectric power generation module (102) and a thermoelectric refrigeration module (103) are arranged in an annular cavity between the outer cylinder (105) and the low-temperature liquid cylinder (101); the thermoelectric refrigeration modules (103) and the thermoelectric power generation modules (102) are alternately arranged in sequence and are isolated by the isolation blocks (104); the area of the thermoelectric power generation module (102) is larger than that of the thermoelectric cooling module (103);

the low-temperature liquid cylinder (101) is of a sealing structure, and the outer wall of the low-temperature liquid cylinder is connected with the low-temperature end of the thermoelectric generation chip (102) and also connected with the thermoelectric refrigeration module (103);

a certain gap is formed between the constant temperature difference power generation cylinder group (6) and the high-temperature geothermal rock stratum (2), and heat-conducting liquid is filled in the gap.

3. The geothermal multilateral well constant-temperature-difference power generation system according to claim 2, wherein the thermoelectric power generation module (102) comprises a plurality of thermoelectric power generation chips, and the thermoelectric power generation chip group comprises a power generation hot-end insulated heated component (201), a power generation hot-end metal conductor group (202), a power generation cold-end metal conductor group (203), a power generation cold-end insulated heat-releasing component (204), a power generation module cathode (205), a power generation module anode (206) and a thermoelectric power generation semiconductor group (207); the power generation hot end insulated heating component (201) is in close contact with the outer cylinder (105), and the power generation cold end insulated heat release component (204) is in direct contact with the low-temperature liquid cylinder (101); the thermoelectric power generation semiconductor group (207) is formed by alternately arranging a plurality of groups of N-type semiconductors and P-type semiconductors in pairs; one end of the thermoelectric power generation semiconductor group (207) is arranged in the power generation hot end insulating and heating component (201), and the other end is arranged in the power generation cold end insulating and heat releasing component (204); in the thermoelectric power generation semiconductor group (207), the cold end of an N-type semiconductor of a first thermoelectric power generation semiconductor group is externally connected with the negative electrode (205) of the power generation module through a lead; the N-type semiconductor hot end and the P-type semiconductor hot end of the first thermoelectric power generation semiconductor group are connected through a first conductor in the power generation hot end metal conductor group (202); the cold ends of the P-type semiconductors of the first group of thermoelectric power generation semiconductor groups are connected with the cold ends of the N-type semiconductors of the second group of thermoelectric power generation semiconductor groups through a first conductor of a power generation cold end metal conductor group (203); connecting the N-type semiconductor and the P-type semiconductor into a series structure according to the cyclic connection; the P-type semiconductor cold ends of the last group of thermoelectric power generation semiconductor groups are externally connected with the anode (206) of the power generation module through wires.

4. The geothermal multilateral well constant-temperature-difference power generation system according to claim 3, wherein the thermoelectric refrigeration module (103) comprises a refrigeration chip set, and the refrigeration chip set comprises a refrigeration hot-end insulated heated component (301), a refrigeration hot-end metal conductor set (302), a refrigeration cold-end metal conductor set (303), a refrigeration cold-end insulated heat-release component (304), a refrigeration module cathode (306), a refrigeration module anode (305) and a thermoelectric refrigeration semiconductor set (307); the refrigeration hot end insulated heating component (301) is in close contact with the outer cylinder (105), and the refrigeration cold end insulated heat-releasing component (304) is in direct contact with the low-temperature liquid cylinder (101); the thermoelectric cooling semiconductor group (307) is formed by arranging a group of N-type semiconductors and P-type semiconductors in pairs alternately; one end of the thermoelectric refrigeration semiconductor group (307) is arranged in the refrigeration hot-end insulated heated component (301), and the other end is arranged in the refrigeration cold-end insulated heat-release component (304); in the thermoelectric refrigeration semiconductor group (307), the hot end of an N-type semiconductor is externally connected with the positive electrode (305) of the refrigeration module through a lead; the N-type semiconductor cold end and the P-type semiconductor cold end of the thermoelectric refrigeration semiconductor group (307) are connected through a refrigeration cold end metal conductor group (303); the P-type semiconductor hot end of the thermoelectric refrigeration semiconductor group (307) is externally connected with the refrigeration module cathode (306) through a lead;

the positive pole (206) of the power generation module (102) is externally connected with the positive pole (305) of the refrigeration module of the thermoelectric refrigeration module (103) through a lead, and the negative pole (205) of the power generation module of the thermoelectric power generation module (102) is externally connected with the negative pole (306) of the refrigeration module of the thermoelectric refrigeration module (103) through a lead.

5. A geothermal multilateral well constant temperature difference power generation system according to claim 1, characterized in that the main wellbore cable female joint (5) is connected to the main wellbore gathering and transportation cable (4) through an upper joint (401) and a lower joint (402); the side interface (403) is connected with a branch well male connector (7).

6. The geothermal multilateral well constant temperature difference power generation system of claim 1, wherein the branch forms an angle of 30-60 ° with the main well; the lateral wells are distributed around the main well in a spiral manner.

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