Single-well structure for exploration and extraction of deep geothermal energy, method for constructing underground heat exchange tank, and power generation method

Abstract

The present invention relates to an ultra-deep well hydroelectric power generation method using a density difference between cold water and hot water in geothermal energy, solving the problems that conventional geothermal energy utilization mostly uses a water pump to extract underground hot water for use, and a water turbine cannot be used to generate power from geothermal energy. The method comprises the following steps: S1, drilling an exploration and extraction well; S2, generating a bottom hole crack; S3, deploying a central pipe; and S4, injecting cold water between the central pipe and a casing pipe, wherein after the cold water is heated by a hot dry rock formation at the bottom of the exploration and extraction well, hot water rises from the central pipe, a specific gravity difference between the hot water and the cold water is used to form a water head difference between the inside and outside of the central pipe, and the hot water conveyed by the central pipe to the ground surface impacts a water turbine to generate power. In the present invention, a heat extraction point is the hot dry rock formation, reducing the impact on groundwater, breaking through the inertial thinking that conventional power generation by water turbines requires using the gravitational potential energy of water flow, and providing a brand-new hydroelectric power generation manner of water flowing from bottom to top.

Description

A single-well structure for deep geothermal energy exploration and extraction, a method for constructing underground heat exchange pools, and a power generation method thereof. Technical Field

[0001] This invention belongs to the field of energy and relates to a structure and method for the exploration and extraction of deep geothermal energy, particularly to a single-well structure for deep geothermal energy exploration and extraction, a method for constructing underground heat exchange pools, and a method for generating electricity from them. Background Technology

[0002] Geothermal energy is a type of energy originating from within the Earth and is a clean, renewable energy source. Humans have utilized geothermal energy for a long time, for example, through hot spring bathing, medical purposes, heating, building greenhouses for crops, aquaculture, and drying grains. The most traditional method of using geothermal energy is to explore shallow geothermal layers and extract the groundwater heated by these layers. While low-temperature geothermal energy is widely distributed, traditional geothermal energy exploration and extraction typically targets high-temperature groundwater, with limited utilization and a lack of effective methods for utilizing the geothermal energy in deep, dry, hot rock formations.

[0003] Currently, the mainstream power generation methods generally use steam turbines or water turbines. Steam turbines generate electricity by heating water at high temperatures into high-temperature, high-pressure steam, which is then injected into the turbine blades to rotate and generate electricity. Traditional thermal power plants and nuclear power plants both use steam turbines. Water turbines typically involve building dams at locations with significant river drops, utilizing the potential energy of the water flow to impact the turbine blades and generate electricity.

[0004] Traditional geothermal energy utilization requires pumping water from underground hot water to the surface for use. The pumping process itself consumes energy. Therefore, traditional geothermal energy for power generation generally uses geothermal energy to heat water and uses steam turbines to generate electricity. It is difficult to use water turbines to generate electricity from geothermal energy.

[0005] During the operation of deep exploration and production well power generation systems, the underground hot dry rock layer, as the core area of ​​heat exchange, plays a crucial role in transferring heat. Its contact surface with water directly affects the efficiency and stability of the entire power generation system. However, the geothermal energy wells in the hot dry rock layer are deep. If drilling directly into the hot dry rock layer for heat exchange is carried out, the water storage space at the bottom of the hot dry rock layer is small, and conventional fracturing methods for the hot dry rock layer cannot be implemented. This results in insufficient heat in the return water of the well, reducing the efficiency of the entire power generation system. Summary of the Invention

[0006] The purpose of this invention is to address the problem that traditional geothermal energy utilization mainly involves pumping underground hot water, which cannot be used to generate electricity from geothermal energy using turbines. This invention proposes a single-well structure for deep geothermal energy exploration and extraction, a method for constructing underground heat exchange pools, and a method for generating electricity from geothermal energy. The invention utilizes a single well to explore and extract deep dry hot rock layers underground, and uses the difference in specific gravity between hot and cold water to generate a head difference as the driving force for water flow, thereby driving a turbine to generate electricity.

[0007] The technical solution adopted by this invention to solve its technical problem is: a single-well structure for deep geothermal energy exploration and extraction using a pipe-in-pipe structure, including a vertically downward-opening exploration and extraction well, wherein a casing for reinforcement is installed in the upper part of the well wall, the casing depth is 70-90% of the exploration and extraction well depth, a central pipe is installed in the center of the casing, the central pipe wall is provided with a heat insulation layer, a cold water injection channel is formed between the inner wall of the casing and the outer wall of the central pipe, and a hot water rising channel is formed inside the central pipe, the bottom end of the exploration and extraction well is drilled to a dry hot rock layer, and the exploration and extraction well has cracks in a section of the dry hot rock layer below the casing.

[0008] This is a single-well structure. Water is injected externally into the central pipe, while hot water is extracted internally. The central pipe is insulated to reduce heat loss. In this device, the casing protects the wellbore. Due to the large drilling depth of this structure, the lower part of the exploration / production well penetrates deep into the rock strata. The casing reinforces and protects the more porous sections of the upper rock strata. During the fracturing process, the upper part of the exploration / production well is protected by the casing, preventing crack formation; cracks only appear in the lower section of the exploration / production well where there is no casing. The bottom of the central pipe has an open structure. Cracks are artificially created at the lower end of the exploration / production well in the dry, hot rock strata to improve heat exchange efficiency. Room-temperature water is pumped into the well from the surface through a cold water injection channel. It flows through the network of artificially created cracks, absorbing heat from the dry, hot rock and heating up. Subsequently, the hot water, due to its lower density, rises rapidly to the surface along the hot water rising channel inside the central pipe, completing the heat extraction process. This cycle repeats itself, enabling the efficient development and utilization of deep geothermal resources while maintaining the stability and sustainability of the underground environment.

[0009] Preferably, both the sleeve and the central tube are made of stainless steel.

[0010] Preferably, the insulation layer is an aerogel insulation layer.

[0011] Preferably, the bottom of the central pipe is 0.5-2 meters higher than the bottom of the exploration well.

[0012] Preferably, the inner diameter of the sleeve is 0.8-1.5 meters, and the outer diameter of the central tube does not exceed 60% of the inner diameter of the sleeve.

[0013] Preferably, the depth of the exploration well is 3000-10000 meters.

[0014] Preferably, the cracks in the dry, hot rock layer are artificially formed using a splitting method.

[0015] Preferably, the cracks in the dry hot rock layer are formed using controlled blasting or hydraulic fracturing techniques.

[0016] A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction includes the following steps:

[0017] Drilling from the surface into the underground hot and dry rock layer to a predetermined depth to form an exploration and production well with a channel;

[0018] For the dry hot rock layer area at the bottom of the exploration and production well, multiple bottom blasting techniques are used to carry out blasting and splitting operations to expand the space of the dry hot rock layer at the bottom of the well, increase the water storage space at the bottom of the exploration and production well, increase the contact area between the water and the dry hot rock, and form a stable heat exchange pool.

[0019] Preferably, the multiple bottom hole blasting technology includes:

[0020] S1. Place explosives in the dry, hot rock layer at the bottom of the exploration well and detonate them to flush out the gravel at the bottom of the exploration well with high-pressure water.

[0021] S2. Place explosives again in the dry hot rock layer at the bottom of the exploration well, cover the explosives with 5-10 meters of soil, detonate, and then use high-pressure water to flush out the gravel at the bottom of the exploration well.

[0022] S3. Following step S2, after multiple blasts at the bottom of the exploration well and high-pressure water jetting to remove the debris, the space within the blasted area at the bottom of the well is scanned. Once it is confirmed that the water storage space meets design requirements, the underground heat exchange pool is constructed. The underground heat exchange pool constructed using this method expands the dry, hot rock layer through multiple bottom blasts, increasing the water storage space at the bottom of the heat extraction well and enlarging the contact area between the water and the dry, hot rock, forming a stable heat exchange pool. This method effectively improves heat exchange efficiency and ensures the stable and efficient operation of the surface generator unit.

[0023] Preferably, the predetermined depth is 3000-10000 meters, and the borehole diameter from the surface to the underground hot dry rock layer is 600-1000 mm. A geothermal well at a depth of 3000-10000 meters will not affect the surface after an explosion, and the temperature of the hot dry rock layer at this depth is sufficient to generate electricity using the hydrodynamic force (head difference) generated by the difference in specific gravity between hot and cold water. A borehole diameter of 600-1000 mm allows for the use of existing drilling rigs.

[0024] Preferably, after drilling vertically from the surface to the underground hot dry rock layer to a predetermined depth, a casing is installed from the surface to a depth of 70-80% of the well bottom, and wall protection is performed between the casing and the well wall. This arrangement allows for cementing between the casing and the well wall, ensuring borehole stability, preventing surface environmental interference, and avoiding borehole collapse.

[0025] Preferably, the explosive is a high-temperature and high-pressure resistant composite explosive, the composition of which, by mass percentage, includes: 60%-80% high-energy explosive matrix, 10%-20% heat-resistant binder, 1%-5% desensitizer, 5%-15% oxidizer, and 2%-10% plasticizer. In the blasting and extraction of high-temperature geothermal wells, due to the high ambient temperature (potentially exceeding 200℃ or even higher) and the possible presence of high pressure and water-bearing conditions, it is necessary to select explosives that are high-temperature resistant, water-resistant, and have good stability. The high-temperature and high-pressure resistant composite explosive of this technical solution can remain stable at temperatures from 200℃ to 500℃ or even higher, without spontaneous combustion or failure; its temperature resistance range can reach over 300℃, and some formulations can withstand temperatures of 500℃ or even higher; and it has high explosive power and good stability.

[0026] Preferably, the high-energy explosive matrix comprises one or a combination of several of RDX, octogen, and hexanitrohexaazaisowulzane; the heat-resistant binder comprises one or a combination of several of fluororubber, silicone rubber, and ceramics; the desensitizing agent comprises one or a combination of two of paraffin wax and graphite; the oxidizing agent comprises one or a combination of two of ammonium nitrate and ammonium perchlorate; and the plasticizer comprises one or a combination of two of dioctyl sebacate and dioctyl phthalate.

[0027] Preferably, the high-temperature and high-pressure resistant composite explosive comprises, by mass percentage, 75% octogen, 12% fluororubber, 3% graphite, 7% ammonium perchlorate, and 3% dioctyl sebacate.

[0028] Preferably, the high-temperature and high-pressure resistant composite explosive further includes nano-alumina, wherein the nano-alumina comprises 1-2% by weight. For extreme heat resistance adjustments, the plasticizer can be reduced to 2%, the binder increased to 18%, and the addition of 1%-2% nano-alumina can improve thermal stability.

[0029] Preferably, in the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the high-temperature resistant ceramic cartridge is filled with a heat-insulating material, which includes gel or glass fiber.

[0030] Preferably, when placing the high-temperature and high-pressure resistant composite explosive, the high-temperature ceramic cartridge and the high-temperature electric detonator are slowly lowered to the target depth using a drill pipe; the position of the high-temperature ceramic cartridge is precisely located using logging tools; and the ignition charge inside the electric detonator is activated by an electric current, thereby detonating the high-temperature and high-pressure resistant composite explosive. Specifically, the high-temperature electric detonator is connected to the high-temperature and high-pressure resistant composite explosive, and the lead of the high-temperature electric detonator is connected to the ground detonation device through a high-temperature cable (coated with fluororubber) to send a current signal and detonate the explosive, which is very safe.

[0031] A method for ultra-deep well hydroelectric power generation in a single well for deep geothermal energy exploration and extraction includes the following steps:

[0032] S1, exploration well drilling: According to the geological exploration report, the drilling rig is used to drill vertically downward from the surface to the dry hot rock layer at the predetermined depth to form a vertical well channel. During the drilling process, stainless steel casing with matching diameter is installed in the 75% depth range from the surface to the well bottom for wall protection.

[0033] S2, create cracks at the bottom of the well. After the exploration well reaches the predetermined depth, seal and split the dry hot rock layer at the bottom of the well. Use controlled blasting or hydraulic fracturing technology to artificially create cracks in the dry hot rock layer to expand the heat exchange area and improve the heat energy collection efficiency.

[0034] S3, Deploy the central pipe. Deploy a stainless steel central pipe in the center of the exploration and production well. The bottom of the stainless steel central pipe is higher than the bottom of the exploration and production well, and the height difference is 3% to 10% of the depth of the exploration and production well. The upper end of the central pipe is connected to the water turbine.

[0035] S4. Cold water is injected between the central pipe and the casing. After the cold water is heated by the dry hot rock layer at the bottom of the exploration well, the hot water rises from the central pipe. The difference in specific gravity between the hot water and the cold water creates a head difference between the inside and outside of the central pipe. The hot water transported to the surface by the central pipe impacts the turbine to generate electricity.

[0036] In this scheme, surface cold water injection utilizes gravity flow, requiring no power. After the cold water is heated at the bottom of the well, the density of the hot water decreases, causing it to rise from the central pipe. The density difference between the cold and hot water generates a sufficient head difference, ensuring adequate flow velocity within the central pipe to drive the turbine blades and generate electricity. Compared to traditional geothermal power generation, this application utilizes dry, hot rock layers as the extraction point, reducing the impact on groundwater. It uses underground thermal energy as its energy source, leveraging the density difference between cold and hot water to generate a head difference that powers the turbine. This approach to clean and renewable geothermal energy breaks away from the traditional thinking that hydroelectric power generation requires the high potential energy of flowing water, providing a novel method of hydroelectric power generation from bottom to top. Furthermore, this application utilizes both the thermal and kinetic energy of deep geothermal energy, achieving a better and more comprehensive utilization of geothermal energy.

[0037] Preferably, in S1, the depth of the exploration well is 3000-10000 meters.

[0038] Preferably, in S2, the bottom area is the area below the bottom end of the stainless steel casing.

[0039] Preferably, in S3, the outer wall of the stainless steel central tube has an insulation layer. The insulation layer is set on the outer wall of the stainless steel central tube, while the inner wall of the stainless steel central tube is a stainless steel tube wall with a low resistance coefficient, which reduces flow resistance and reduces head loss.

[0040] Preferably, the insulation layer is an aerogel insulation layer.

[0041] As a preferred embodiment, in S3, a heating device is connected to the turbine outlet.

[0042] As a preferred embodiment, in S4, the hot water transported to the ground surface by the central pipe first enters the water turbine for kinetic energy utilization, and then enters the heat-using device for thermal energy utilization.

[0043] This invention employs a single-well heat extraction system within a pipe, with open-type heat extraction at the well bottom. Cracks are artificially created in the lower section of the exploratory well's dry, hot rock layer, or a large-capacity underground heat exchange pool is constructed using multiple blasting methods to improve heat exchange efficiency. This achieves efficient development and utilization of deep geothermal resources while maintaining the stability and sustainability of the underground environment. The extraction point is a dry, hot rock layer, minimizing impact on groundwater. Using underground thermal energy as the energy source, the head difference generated by the density difference between hot and cold water is used to drive a water turbine for power generation. This invention breaks away from the traditional thinking that water turbine power generation requires utilizing the high potential energy of water flow, providing a novel method of hydroelectric power generation from bottom to top. Attached Figure Description

[0044] The invention will now be further described with reference to the accompanying drawings.

[0045] Figure 1 is a schematic diagram of an exploration well structure according to the present invention.

[0046] Figure 2 is a schematic diagram of the upper section of the exploration well of the present invention.

[0047] Figure 3 is a schematic diagram of the structure of the heat exchange pool at the bottom of the exploration well of the present invention.

[0048] Figure 4 is a schematic diagram of a single-well power generation method for deep geothermal energy exploration and extraction according to the present invention.

[0049] In the diagram: 1. Exploration well, 2. Casing, 3. Central pipe, 4. Insulation layer, 5. Cold water injection channel, 6. Hot water rising channel, 7. Dry hot rock layer, 8. Crack, 9. Water turbine, 10. Heat exchange pool. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Among them, Embodiment 1 does not involve the exploration and extraction of a single-well structure, Embodiments 2-8 involve the explosives used in the construction of underground heat exchange pools, Embodiments 9-10 involve the construction method of underground heat exchange pools, and Embodiment 11 involves the method of generating electricity from a single well using deep geothermal energy.

[0051] Example 1: A single-well structure for deep geothermal energy exploration and extraction using a pipe-in-pipe structure, as shown in Figure 1. This device includes a vertically downward-opening exploration well 1, with a depth of 3000-10000 meters. A casing 2 is installed in the upper section of the well wall of the exploration well 1, with a depth of 75% of the depth of the exploration well 1. A central pipe 3 is located at the center of the casing 2. Both the casing 2 and the central pipe 3 are made of stainless steel. An insulation layer 4, which is an aerogel insulation layer, is installed on the inner or outer wall of the central pipe. A cold water injection channel 5 is formed between the inner wall of the casing 2 and the outer wall of the central pipe 3, and a hot water rising channel 6 is formed inside the central pipe 3. The bottom of the exploration well 1 is drilled to a dry hot rock layer 7. Cracks 8 are present in the dry hot rock layer 7 below the bottom of the casing 2 in the lower section of the exploration well 1. The cracks in the dry hot rock layer are artificially formed using a fracturing method, employing controlled blasting or hydraulic fracturing technology.

[0052] In this example, the inner diameter of the sleeve is 1 meter, and the outer diameter of the central tube is 0.4 meters. The bottom end of the central tube is about 1 meter higher than the bottom end of the sleeve.

[0053] In this example, the drilling configuration involved using a 1-meter diameter drilling rig to drill vertically downwards from the surface to a predetermined depth, forming a vertical wellbore several kilometers deep. During this process, to ensure borehole stability and prevent interference from the surface environment, stainless steel casing of matching diameter was installed for wall protection within 75% of the depth range from the surface to the bottom.

[0054] Downhole layout: After reaching the target depth, precise sealing and fracturing operations are carried out in specific areas at the bottom of the well (dry hot rock layers). Multiple fractures are artificially created using controlled blasting or hydraulic fracturing technology to expand the heat exchange area and improve the efficiency of heat energy collection.

[0055] Heat exchange system: A 400 mm outer diameter stainless steel central pipe is deployed inside the well, with its bottom located approximately 1 meter above the drilling end. The pipe integrates a high-efficiency aerogel insulation layer, serving as a channel for hot water to rise. The annular space between the outer side of this pipe and the casing is designed as a cold water injection channel, forming a closed-loop circulation system. Based on the natural convection principle of hot water rising and cold water sinking, continuous heat energy exchange is achieved between the deep underground dry hot rock and surface water.

[0056] Working principle: During system operation, ambient temperature water is pumped from the surface into the well through the inlet. It flows through a network of fractures created by artificial splitting, absorbing heat from the dry, hot rock and heating up. Subsequently, the hot water, due to its decreased density, rapidly rises to the surface along the interior of the stainless steel central tube, completing the heat extraction process. This cycle repeats continuously, achieving efficient development and utilization of deep geothermal resources while maintaining the stability and sustainability of the underground environment.

[0057] Example 2: This example describes the preparation of a high-temperature and high-pressure resistant composite explosive. The components of the high-temperature and high-pressure resistant composite explosive, by mass percentage, include: 60% high-energy explosive matrix, 10% heat-resistant binder, 5% desensitizer, 15% oxidizer, and 10% plasticizer. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is a gel.

[0058] In this embodiment, the high-energy explosive matrix is ​​RDX, the heat-resistant binder is fluororubber, the desensitizing agent is paraffin wax, the oxidizing agent is ammonium nitrate, and the plasticizer is dioctyl sebacate.

[0059] Example 3: This example describes the preparation of a high-temperature and high-pressure resistant composite explosive. The components of this high-temperature and high-pressure resistant composite explosive, by mass percentage, include: 70% high-energy explosive matrix, 15% heat-resistant binder, 3% desensitizer, 6% oxidizer, and 6% plasticizer. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is glass fiber.

[0060] In this embodiment, the high-energy explosive matrix is ​​octogen, the heat-resistant binder is silicone rubber, the desensitizer is graphite, the oxidant is ammonium perchlorate, and the plasticizer is dioctyl phthalate.

[0061] Example 4: This example describes the preparation of a high-temperature and high-pressure resistant composite explosive. The components of this high-temperature and high-pressure resistant composite explosive, by mass percentage, include: 75% high-energy explosive matrix, 10% heat-resistant binder, 1% desensitizer, 10% oxidizer, and 4% plasticizer. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is a gel.

[0062] In this embodiment, the high-energy explosive matrix is ​​hexanitrohexaazaisowulzane, the heat-resistant binder is ceramic, the desensitizer is an equal volume combination of paraffin and graphite, the oxidant is an equal volume combination of ammonium nitrate and ammonium perchlorate, and the plasticizer is an equal volume combination of dioctyl sebacate and dioctyl phthalate.

[0063] Example 5: This example describes the preparation of a high-temperature and high-pressure resistant composite explosive. The components of this high-temperature and high-pressure resistant composite explosive, by mass percentage, include: 80% high-energy explosive matrix, 10% heat-resistant binder, 1% desensitizer, 5% oxidizer, 3% plasticizer, and 1% nano-alumina. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is glass fiber.

[0064] In this embodiment, the high-energy explosive matrix is ​​an equal volume combination of RDX, octogen, and hexanitrohexaazaisowulzane; the heat-resistant binder is an equal volume combination of fluororubber, silicone rubber, and ceramics; the desensitizer is an equal volume combination of paraffin wax and graphite; the oxidant is an equal volume combination of ammonium nitrate and ammonium perchlorate; and the plasticizer is an equal volume combination of dioctyl sebacate and dioctyl phthalate.

[0065] Example 6: This example describes the preparation of a high-temperature and high-pressure resistant composite explosive. The components of this high-temperature and high-pressure resistant composite explosive, by mass percentage, include: 65% high-energy explosive matrix, 20% heat-resistant binder, 3% desensitizer, 8.5% oxidizer, 2% plasticizer, and 1.5% nano-alumina. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is glass fiber.

[0066] In this embodiment, the high-energy explosive matrix is ​​an equal volume combination of RDX, octogen, and hexanitrohexaazaisowulzane; the heat-resistant binder is an equal volume combination of fluororubber, silicone rubber, and ceramics; the desensitizer is an equal volume combination of paraffin wax and graphite; the oxidant is an equal volume combination of ammonium nitrate and ammonium perchlorate; and the plasticizer is an equal volume combination of dioctyl sebacate and dioctyl phthalate.

[0067] Example 7: The high-temperature and high-pressure resistant composite explosive of this example comprises, by mass percentage, 75% octogen, 12% fluororubber, 3% graphite, 3% ammonium perchlorate, 3% dioctyl sebacate, and 2% nano-alumina. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is glass fiber.

[0068] Example 8: The high-temperature and high-pressure resistant composite explosive of this example comprises, by mass percentage, 65% octogen, 18% fluororubber, 5% graphite, 8% ammonium perchlorate, 2% dioctyl sebacate, and 2% nano-alumina. During the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the cartridge is filled with a heat-insulating material. In this example, the heat-insulating material is glass fiber.

[0069] The temperature resistance test data of the high-temperature and high-pressure resistant composite explosives prepared in Examples 2-8 above are as follows:

[0070] Example 9: This example describes a method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction, including the following steps:

[0071] The process involves drilling from the surface into the underground hot dry rock layer to a predetermined depth, forming a well with a channel. Specifically, a 1-meter diameter drilling rig is used to drill vertically downwards from the surface to the predetermined depth, creating a vertical well channel up to 5000 meters deep. The borehole diameter from the surface to the underground hot dry rock layer is 600mm. After drilling vertically to the predetermined depth, casing is installed from the surface to 70% of the well bottom depth, and wall protection is applied between the casing and the well wall. Wall protection involves injecting cement between the casing and the well wall to cement the well, ensuring borehole stability, preventing surface environmental interference, and avoiding borehole collapse.

[0072] For the dry, hot rock strata at the bottom of a heat extraction well, multiple bottom-hole blasting techniques are used to carry out blasting and fracturing operations, expanding the space of the dry, hot rock strata at the bottom of the well, increasing the water storage space at the bottom of the heat extraction well, increasing the contact area between the water and the dry, hot rock, and forming a stable heat exchange pool. The multiple bottom-hole blasting techniques include:

[0073] S1. Place explosives in the dry hot rock layer at the bottom of the heating well, detonate them, and use a drilling rig to flush out the debris in the well with high-pressure water after the explosion.

[0074] S2. Explosives are placed again in the dry, hot rock layer at the bottom of the well. A 5-meter-thick layer of soil is placed on top of the explosives to cover them, and then detonated. After the blast, a drilling rig is used again to flush out the backfill soil and gravel from the well using high-pressure water. Covering the explosives with a 5-10 meter thick layer of soil prevents upward pressure release after the explosion, which could affect the splitting effect. Granite typically has a compressive strength of 100-300 MPa, requiring a second explosive detonation to generate a pressure of approximately 300 MPa. Due to the small blast radius, the energy diffuses around the well wall, creating an expansion effect that pulverizes the dry, hot rock into approximately 2 cm of gravel. A certain number of cracks and fissures will appear in the inner rock layers.

[0075] S3. After five blasts at the bottom of the heating well and the removal of the rubble using high-pressure water following step S2, an ultrasonic borehole and trenching monitoring instrument is used to scan the space within the blast area at the bottom of the heating well. Once it is confirmed that the water storage space meets the design requirements, the construction of the underground heat exchange pool 10 is completed. As shown in Figure 3.

[0076] When placing the high-temperature and high-pressure resistant composite explosive, the high-temperature ceramic cartridge and the high-temperature electric detonator are slowly lowered to the target depth using drill pipe; the position of the high-temperature ceramic cartridge is precisely located using logging tools; and the ignition charge inside the electric detonator is activated by an electric current, thereby detonating the high-temperature and high-pressure resistant composite explosive. Specifically, the high-temperature electric detonator is connected to the high-temperature and high-pressure resistant composite explosive, and the lead of the high-temperature electric detonator is connected to the ground detonation device through a high-temperature cable (coated with fluororubber) to send a current signal and detonate the explosive.

[0077] The parameters used and the resulting heat exchange pools for each blast are as follows:

[0078] Example 10: This example describes a method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction, including the following steps:

[0079] The process involves drilling vertically from the surface into the hot, dry rock layer to a predetermined depth, forming a well with a channel. Specifically, a 1-meter diameter drilling rig (equivalent to a 10,000-meter drilling rig) is used to drill vertically downwards from the surface to the predetermined depth, creating a vertical well channel up to 8,000 meters deep. The borehole diameter from the surface to the hot, dry rock layer is 600mm. After drilling to the predetermined depth, casing is installed from the surface to 80% of the well bottom depth, and wall protection is applied between the casing and the well wall. This wall protection involves injecting cement between the casing and the well wall to cement the well, ensuring borehole stability, preventing surface environmental interference, and avoiding borehole collapse.

[0080] For the dry, hot rock strata at the bottom of a heat extraction well, multiple bottom-hole blasting techniques are used to carry out blasting and fracturing operations, expanding the space of the dry, hot rock strata at the bottom of the well, increasing the water storage space at the bottom of the heat extraction well, increasing the contact area between the water and the dry, hot rock, and forming a stable heat exchange pool. The multiple bottom-hole blasting techniques include:

[0081] S1. Place explosives in the dry hot rock layer at the bottom of the heating well, detonate them, and use a drilling rig to flush out the debris in the well with high-pressure water after the explosion.

[0082] S2. Explosives are placed again in the dry, hot rock layer at the bottom of the well. A 10-meter-thick layer of soil is placed over the explosives to cover them, and then the explosion is detonated. After the explosion, a drilling rig is used again to flush out the backfill soil and gravel from the well using high-pressure water. Covering the explosives with a 5-10-meter-thick layer of soil prevents upward pressure release after the explosion, which could affect the splitting effect. Granite typically has a compressive strength of 100-300 MPa, requiring a second explosion to generate a pressure of approximately 300 MPa. Due to the small blast radius, the energy diffuses around the well wall, creating an expansion effect that pulverizes the dry, hot rock into approximately 2-cm gravel. A certain number of cracks and fissures will appear in the inner rock layers.

[0083] S3. Following step S2, after 11 blasts at the bottom of the heating well and high-pressure water jetting to remove the rubble, an ultrasonic borehole and trenching monitoring instrument is used to scan the space within the blast area at the bottom of the heating well. Once it is confirmed that the water storage space meets the design requirements, the underground heat exchange pool 10 is constructed. As shown in Figure 3.

[0084] When placing the high-temperature and high-pressure resistant composite explosive, the high-temperature ceramic cartridge and the high-temperature electric detonator are slowly lowered to the target depth using drill pipe; the position of the high-temperature ceramic cartridge is precisely located using logging tools; and the ignition charge inside the electric detonator is activated by an electric current, thereby detonating the high-temperature and high-pressure resistant composite explosive. Specifically, the high-temperature electric detonator is connected to the high-temperature and high-pressure resistant composite explosive, and the lead of the high-temperature electric detonator is connected to the ground detonation device through a high-temperature cable (coated with fluororubber) to send a current signal and detonate the explosive.

[0085] The parameters used and the resulting heat exchange pools for each blast are as follows:

[0086] As can be seen from the above embodiments, the underground heat exchange pool for deep geothermal well power generation manufactured using the method of the present invention employs multiple bottom-hole blasting to expand the dry hot rock layer, increasing the water storage space at the bottom of the heat extraction well and increasing the contact area between the water and the dry hot rock, forming a stable heat exchange pool. This method can effectively improve heat exchange efficiency and ensure the stable and efficient operation of the surface generator unit. In the blasting and mining of high-temperature geothermal wells, due to the high ambient temperature and the possible presence of high pressure and water-bearing conditions, it is necessary to select explosives that are resistant to high temperatures, have strong water resistance, and good stability. The high-temperature and high-pressure resistant composite explosive of the present invention can remain stable at temperatures from 200°C to 500°C or even higher, without spontaneous combustion or failure; its temperature resistance range can reach over 300°C, and some formulations can withstand temperatures of 500°C or even higher; moreover, it has great explosive power and good stability.

[0087] Example 11: An ultra-deep well hydroelectric power generation method for deep geothermal energy exploration and extraction, as shown in Figure 4. This method includes the following steps:

[0088] S1, exploration well 1 drilling, using a drilling rig to drill vertically downwards from the surface to the predetermined depth of the dry hot rock layer 7, forming a vertical well channel, the exploration well depth is 3000-10000 meters; during the drilling process, stainless steel casing 2 with matching diameter is installed in the 75% depth range from the surface to the well bottom for wall protection.

[0089] S2, Create bottom cracks. After the exploration well reaches the predetermined depth, seal and split the dry hot rock layer in the bottom area of ​​the well. The bottom area is the area below the bottom of the stainless steel casing. Using controlled blasting or hydraulic fracturing technology, artificially create cracks in the dry hot rock layer to expand the heat exchange area and improve the heat energy collection efficiency.

[0090] S3, deploy the central pipe 3, deploy the stainless steel central pipe 3 in the center of the exploration well, the outer wall of the stainless steel central pipe 3 has an aerogel insulation layer 4; the bottom of the stainless steel central pipe 3 is higher than the bottom of the exploration well 1, the height difference is 3% to 10% of the depth of the exploration well, the upper end of the central pipe is connected to the water turbine 9, and the water turbine outlet is connected to the heating device.

[0091] S4. Cold water is injected through the cold water injection channel 5 between the central pipe and the casing. After being heated by the dry hot rock layer 7 at the bottom of the exploration well, the hot water rises through the hot water rising channel 6 inside the central pipe. Utilizing the density difference between the hot and cold water, a head difference is created inside and outside the central pipe. The hot water transported to the surface through the central pipe first enters the water turbine for kinetic energy utilization, and then enters the heat-using device for thermal energy utilization. This embodiment can be adapted to the exploration well with the structure shown in Figure 1. This embodiment can also be adapted to the exploration well with a heat exchange pool 10 built at the bottom as shown in Figure 3.

[0092] Taking a stainless steel sleeve with a diameter of 1 meter and a central pipe with a diameter of 0.4 meters as an example, the surface cold water injection temperature is 20℃, and the central pipe output hot water is 100℃.

[0093] Methods for generating electricity using the density difference between hot and cold water in deep exploration and production wells:

[0094] The density of water changes with temperature; the density of water at 100℃ and 20℃ is 0.958 g / cm³. 3 and 0.998g / cm 3 The difference in head between the inside and outside of the stainless steel central pipe is primarily determined by pressure. Under the same atmospheric pressure, the pressure of the two types of water will differ due to their different densities. However, in practical applications, we are more concerned with the head difference between the two types of water under different conditions, rather than the absolute head value. If a specific head difference needs to be calculated, other factors such as pipe friction and flow velocity must also be considered.

[0095] In this example, the water columns inside and outside the stainless steel central tube generate the same pressure at the same depth at point A at the bottom of the stainless steel central tube. Therefore: ΔP 100=0.958 × 9.8 × h 100 ΔP 20 =0.998 × 9.8 × h 20

[0096] Where ΔP 100 h is the pressure of water at 100℃ inside the central pipe at point A. 100 ΔP represents the height of the water at 100°C inside the central pipe. 20 h is the water pressure at 20℃ inside the central pipe at point A. 20 Let H be the height of the water at 20°C outside the central pipe. Since the pressure is the same at point A, we have: 0.958 × 9.8 × h 100 =0.998 × 9.8 × h 20

[0097] Solving the above equation yields: h 100 = (0.998 / 0.958)×h 20 ≈1.043×h 20

[0098] This means that under the same pressure, the height difference of water at 100°C is approximately 1.043 times that of water at 20°C. If the height of water at 20°C is known, the height of water at 100°C can be calculated using the above ratio, and the head difference between the hot and cold water inside and outside the central pipe can be calculated accordingly.

[0099] As shown above, for every 1000 meters of depth in a deep exploration well, there is a head difference of 43 meters. Assuming the stainless steel central pipe is 4000 meters deep, the flow resistance within the pipe is related to the pipe material, pipe diameter, pipe linearity, and water flow velocity. Given the pipe material and diameter, and considering that the pipe in this example is straight, the greater the water flow velocity, the greater the flow resistance. When the flow resistance and the head difference reach equilibrium, the water flow velocity within the pipe reaches its maximum. The head difference between the hot and cold water is approximately 172 meters, and the maximum flow rate of a 400mm stainless steel central pipe can reach 1.72 cubic meters per second. A generator can generate 34,400 kilowatt-hours of electricity in one day.

Claims

1. A single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure, comprising a vertically downward-opened exploration and production well, characterized in that: The upper part of the exploration well is equipped with a casing for reinforcement. The casing depth is 70-90% of the exploration well depth. A central tube is set in the center of the casing. The wall of the central tube is equipped with a heat insulation layer. A cold water injection channel is formed between the inner wall of the casing and the outer wall of the central tube. A hot water rising channel is formed inside the central tube. The bottom of the exploration well is drilled to a dry hot rock layer. The exploration well has cracks in a section of the dry hot rock layer below the casing.

2. The single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: Both the sleeve and the central tube are made of stainless steel.

3. The single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The insulation layer is an aerogel insulation layer.

4. The single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The bottom of the central pipe is 0.5-2 meters higher than the bottom of the exploration and production well.

5. A single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The inner diameter of the sleeve is 0.8-1.5 meters, and the outer diameter of the central tube does not exceed 60% of the inner diameter of the sleeve.

6. A single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The depth of the exploration well is 3,000-10,000 meters.

7. A single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The cracks in the dry, hot rock layer were artificially created using a splitting method.

8. A single-well structure for deep geothermal energy exploration and production using a pipe-in-pipe structure as described in claim 1, characterized in that: The cracks in the dry, hot rock layer were formed using controlled blasting or hydraulic fracturing techniques.

9. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction, characterized in that, Includes the following steps: Drilling from the surface into the underground hot and dry rock layer to a predetermined depth to form an exploration and production well with a channel; For the dry hot rock layer area at the bottom of the exploration and production well, multiple bottom blasting techniques are used to carry out blasting and splitting operations to expand the space of the dry hot rock layer at the bottom of the well, increase the water storage space at the bottom of the exploration and production well, increase the contact area between the water and the dry hot rock, and form a stable heat exchange pool.

10. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 9, characterized in that, The multiple bottom-hole blasting technology includes: S1. Place explosives in the dry, hot rock layer at the bottom of the exploration well and detonate them to flush out the gravel at the bottom of the exploration well with high-pressure water. S2. Place explosives again in the dry hot rock layer at the bottom of the exploration well, cover the explosives with 5-10 meters of soil, detonate, and then use high-pressure water to flush out the gravel at the bottom of the exploration well. S3. After multiple blasts at the bottom of the exploration well and the removal of the rubble from the bottom of the exploration well using high-pressure water following steps S2, the space within the blasting area at the bottom of the exploration well is scanned. Once it is confirmed that the water storage space meets the design requirements, the construction of the underground heat exchange pool is completed.

11. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 9, characterized in that, The predetermined depth is 3000-10000 meters, and the diameter of the borehole from the surface to the underground dry hot rock layer is 600-1000 mm.

12. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 9, characterized in that, After drilling vertically from the surface to the underground hot dry rock layer to the predetermined depth, a casing is installed from the surface to a depth of 70-80% of the bottom of the exploration and production well, and a protective wall treatment is carried out between the casing and the well wall.

13. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 10, characterized in that, The explosive is a high-temperature and high-pressure resistant composite explosive, and the components of the high-temperature and high-pressure resistant composite explosive include, by mass percentage: 60%-80% high-energy explosive matrix, 10%-20% heat-resistant binder, 1%-5% desensitizer, 5%-15% oxidizer, and 2%-10% plasticizer.

14. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 13, characterized in that, The high-energy explosive matrix comprises one or a combination of several of RDX, octogen, and hexanitrohexaazaisowulzane; the heat-resistant binder comprises one or a combination of several of fluororubber, silicone rubber, and ceramics; the desensitizing agent comprises one or a combination of two of paraffin wax and graphite; the oxidizing agent comprises one or a combination of two of ammonium nitrate and ammonium perchlorate; and the plasticizer comprises one or a combination of two of dioctyl sebacate and dioctyl phthalate.

15. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 14, characterized in that, The high-temperature and high-pressure resistant composite explosive comprises, by mass percentage, 75% octogen, 12% fluororubber, 3% graphite, 7% ammonium perchlorate, and 3% dioctyl sebacate.

16. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 13, characterized in that, The high-temperature and high-pressure resistant composite explosive also includes nano-alumina, with the nano-alumina comprising 1-2% by weight.

17. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to any one of claims 14-16, characterized in that, In the preparation of the high-temperature and high-pressure resistant composite explosive, the uniformly mixed components are loaded into a high-temperature resistant ceramic cartridge, and the high-temperature resistant ceramic cartridge is filled with a heat-insulating material, which includes gel or glass fiber.

18. A method for constructing an underground heat exchange pool for a single well used in deep geothermal energy exploration and extraction according to claim 17, characterized in that, When placing high-temperature and high-pressure resistant composite explosives, the high-temperature ceramic cartridge and the high-temperature electric detonator are slowly lowered to the target depth using a drill pipe; the position of the high-temperature ceramic cartridge is precisely located using logging tools; and the ignition charge inside the electric detonator is activated by an electric current, thereby detonating the high-temperature and high-pressure resistant composite explosives.

19. A method for ultra-deep well hydroelectric power generation using a single well for deep geothermal energy exploration and extraction, characterized in that, Includes the following steps: S1, exploration well drilling: According to the geological exploration report, the drilling rig is used to drill vertically downward from the surface to the dry hot rock layer at the predetermined depth to form a vertical well channel. During the drilling process, stainless steel casing with matching diameter is installed in the 75% depth range from the surface to the well bottom for wall protection. S2, create cracks at the bottom of the well. After the exploration well reaches the predetermined depth, seal and split the dry hot rock layer at the bottom of the well. Use controlled blasting or hydraulic fracturing technology to artificially create cracks in the dry hot rock layer to expand the heat exchange area and improve the heat energy collection efficiency. S3, Deploy the central pipe. Deploy a stainless steel central pipe in the center of the exploration and production well. The bottom of the stainless steel central pipe is higher than the bottom of the exploration and production well, and the height difference is 3% to 10% of the depth of the exploration and production well. The upper end of the central pipe is connected to the water turbine. S4. Cold water is injected between the central pipe and the casing. After the cold water is heated by the dry hot rock layer at the bottom of the exploration well, the hot water rises from the central pipe. The difference in specific gravity between the hot water and the cold water creates a head difference between the inside and outside of the central pipe. The hot water transported to the surface by the central pipe impacts the turbine to generate electricity.

20. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water based on geothermal energy, as described in claim 19, characterized in that: In S1, the depth of the exploration well is 3000-10000 meters.

21. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water based on geothermal energy, as described in claim 19, characterized in that: In S2, the bottom area is the area below the bottom of the stainless steel casing.

22. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water in geothermal energy according to claim 19, characterized in that: In S3, the outer wall of the stainless steel central tube has an insulation layer.

23. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water in geothermal energy according to claim 22, characterized in that: The insulation layer is an aerogel insulation layer.

24. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water at geothermal energy, as described in claim 19, is characterized in that: In S3, a heating device is connected to the water turbine outlet.

25. A method for ultra-deep well hydroelectric power generation utilizing the density difference between hot and cold water in geothermal energy according to claim 24, characterized in that: In S4, the hot water delivered to the surface by the central pipe first enters the water turbine for kinetic energy utilization, and then enters the heat-using device for thermal energy utilization.

Images