Horizontal well carbon dioxide fracturing-heat extraction-utilization integrated method and device

Abstract

The present specification relates to the technical field of geothermal energy development and utilization, and particularly relates to a horizontal well carbon dioxide fracturing-heat extraction-utilization integrated method and device, comprising: injecting fracturing fluid in a supercritical state into an injection well to fracture a geothermal reservoir to form a fracture; injecting nanofluid formed by mixing the fracturing fluid in a supercritical state and heat-conducting nanoparticles into the fracture of the geothermal reservoir through the injection well to absorb heat energy of the geothermal reservoir; and transporting the nanofluid after absorbing the heat energy of the geothermal reservoir to a ground heat extraction system through a production well to collect heat energy generated by expansion of the nanofluid. The present specification fractures the geothermal reservoir by using fracturing fluid in a supercritical state, improves the permeability of the geothermal reservoir, and ensures that the geothermal resources can flow and be extracted more efficiently. By combining heat-conducting nanoparticles and fracturing fluid in a supercritical state to form nanofluid, the heat energy extraction efficiency is greatly improved, and efficient utilization of geothermal resources is realized.

Description

Technical Field

[0001] The embodiments of this invention relate to the field of geothermal energy development and utilization technology, specifically to an integrated method and apparatus for horizontal well carbon dioxide fracturing-heat extraction-utilization. Background Technology

[0002] Hot dry rock is a clean energy source with abundant resources and unique advantages, possessing enormous development and utilization potential. Buried at depths greater than 3 km and with temperatures greater than or equal to 180℃, it is a high-temperature, dense rock mass containing little or no water. Its advantages lie in its stability, high efficiency, and lack of limitation due to seasonality, climate, or diurnal variations, making it environmentally friendly. The development method for hot dry rock involves the following steps: First, high-pressure water is injected into the underground reservoir through injection wells. The injection of high-pressure water forces the rock to fracture, forming a permeable, multi-scale artificial fracture network structure. Next, a low-temperature heat extraction medium is injected into the hot dry rock reservoir with the artificial fracture network through injection wells. After sufficient heat exchange with the high-temperature rock mass, it is extracted from the ground through production wells. Finally, the extracted heat energy is converted into electrical energy through a surface power generation system, realizing the utilization of geothermal energy and power generation.

[0003] Currently, the fracturing methods used in horizontal well geothermal development of hot dry rock primarily employ high-intensity pump injection, which easily leads to localized stress concentration and rapid release of hydraulic energy in a short period. This results in only a single main fracture, making it difficult to activate and connect natural fractures to form a three-dimensional fracture network. Consequently, the heat exchange area within the reservoir is small, the inter-well communication capacity is poor, and the injected fluid leakage is severe, resulting in low production flow rate, rapid temperature drop, low heat extraction power, and short operational life. Furthermore, the use of water as the heat extraction medium in existing horizontal well geothermal development methods for hot dry rock has many shortcomings. During fracturing, due to its low viscosity, water easily flows through existing fractures, making it difficult to form new fractures or fully expand existing ones. This limits fracturing efficiency and may not effectively cover large areas of the heat source rock layer. In addition, under high-temperature conditions, water reacts chemically with the rock, potentially leading to mineral precipitation, especially the formation of silicate deposits. This can cause fracture blockage, thereby reducing the permeability of the entire geothermal reservoir and affecting the flow of subsequent circulating working fluids and heat extraction. Furthermore, water has a high specific heat capacity, meaning it needs to absorb a significant amount of heat to raise its temperature. However, its density change is relatively small, resulting in limited heat exchange efficiency. Under high temperature and pressure conditions, water readily undergoes chemical reactions with minerals in rocks, which is also a major factor limiting its thermal energy extraction efficiency and can lead to equipment corrosion and crack blockage. Simultaneously, water is prone to phase change under high temperature and pressure, transforming from a liquid to a gaseous state. The volume change resulting from this phase change complicates fluid control within the system and may lead to a decrease in circulation efficiency.

[0004] Therefore, overcoming the problems of existing hot dry rock development methods, such as the inability to form a three-dimensional fracture network, easy chemical reactions, and poor permeability of geothermal reservoirs, and proposing a hot dry rock horizontal well geothermal development method with high heat extraction and circulation efficiency is a key issue that urgently needs to be addressed. Summary of the Invention

[0005] The purpose of the embodiments in this specification is to provide an integrated method and device for horizontal well carbon dioxide fracturing, heat extraction, and utilization, so as to overcome the problems in the geothermal development method of hot dry rock horizontal wells, such as the inability to form a three-dimensional fracture network, easy occurrence of chemical reactions, and poor permeability of geothermal reservoirs, and improve the heat extraction efficiency and circulation efficiency of hot dry rock horizontal well geothermal development.

[0006] On one hand, the embodiments of this specification provide an integrated method for horizontal well carbon dioxide fracturing-heat extraction-utilization. The method includes: injecting supercritical fracturing fluid into an injection well to fracture a geothermal reservoir to form fractures; injecting a nanofluid formed by mixing the supercritical fracturing fluid with thermally conductive nanoparticles into the fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir; and transporting the nanofluid after absorbing the thermal energy of the geothermal reservoir to a surface heat extraction system through a production well to collect the thermal energy generated by the expansion of the nanofluid.

[0007] On another front, embodiments of this specification provide an integrated horizontal well carbon dioxide fracturing-heat extraction-utilization device. The device includes: a fracturing module for injecting supercritical fracturing fluid into an injection well to fracture the geothermal reservoir and form fractures; an absorption module for injecting a nanofluid formed by mixing supercritical fracturing fluid with thermally conductive nanoparticles into the fractures of the geothermal reservoir via the injection well to absorb the thermal energy of the geothermal reservoir; and a collection module for transporting the nanofluid after absorbing the thermal energy of the geothermal reservoir to a surface heat extraction system via a production well to collect the thermal energy generated by the expansion of the nanofluid.

[0008] In another aspect, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor performs the above-described integrated horizontal well carbon dioxide fracturing-heat extraction-utilization method.

[0009] As can be seen from the technical solutions provided in the embodiments of this specification above, the embodiments of this specification can inject supercritical fracturing fluid into an injection well to fracture the geothermal reservoir and form fractures; a nanofluid formed by mixing supercritical fracturing fluid with thermally conductive nanoparticles is injected into the fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir; the nanofluid after absorbing the thermal energy of the geothermal reservoir is transported to a surface heat extraction system through a production well to collect the heat energy generated by the expansion of the nanofluid. Compared with existing methods, the embodiments of this specification, which use supercritical fracturing fluid to fracture the geothermal reservoir, can improve the permeability of the geothermal reservoir, ensuring that geothermal resources can flow and be extracted more efficiently. By combining thermally conductive nanoparticles with supercritical fracturing fluid to form a nanofluid, the thermal energy extraction efficiency is greatly improved, promoting the efficient utilization of geothermal resources. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below.

[0011] Figure 1 This is a flowchart of an integrated method for horizontal well carbon dioxide fracturing-heat extraction-utilization provided in the embodiments of this specification;

[0012] Figure 2 This is a structural diagram of an integrated method for horizontal well carbon dioxide fracturing, heat extraction, and utilization provided in the embodiments of this specification;

[0013] Figure 3 This is a schematic diagram of a steering method based on a temporary plugging agent provided in the embodiments of this specification;

[0014] Figure 4 This is a schematic diagram illustrating a staged fracturing of a geothermal reservoir using sand plugs, as provided in the embodiments of this specification.

[0015] Figure 5 This is a schematic diagram of the structural composition of an integrated horizontal well carbon dioxide fracturing-heat extraction-utilization device provided in the embodiments of this specification;

[0016] Figure 6 This is a schematic diagram of the structural composition of the computer device provided in the embodiments of this specification.

[0017] The reference numerals in the above figures are as follows:

[0018] 1. Caprock; 2. Geothermal reservoir; 3. Working fluid; 4. Cement; 5. Development area; 6. Insulated casing; 7. Circulating pump; 8. First-stage turbine; 9. High-pressure manifold; 10. Compressor; 11. First-stage generator; 12. First-stage heat exchanger; 13. Second-stage generator; 14. Gas-liquid separator; 15. Second-stage turbine; 16. Second-stage heat exchanger; 17. Condenser; 18. Condensate; 19. Adsorption refrigeration unit; 20. Mixing pump; 21. Injection well; 22. Production well; 23. Fracture; 24. Temporary plugging agent; 25. Fractured geothermal reservoir section; 26. Sand plug; 27. Unfractured geothermal reservoir section; 28. Horizontal well fracturing string. Detailed Implementation

[0019] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0020] Figure 1 This is a flowchart of an integrated method for horizontal well carbon dioxide fracturing, heat extraction, and utilization. In practice, the method includes the following steps:

[0021] S101: Injecting supercritical fracturing fluid into the injection well to fracture the geothermal reservoir and create fractures.

[0022] By injecting fracturing fluid in a supercritical state into the injection well, the geothermal reservoir is fractured to form fractures, thus achieving fracturing of the geothermal reservoir.

[0023] Reference Figure 2 The caprock 1 is located above the geothermal reservoir 2. A geothermal reservoir refers to a stratum, rock mass, or structural zone buried underground with effective porosity and permeability, containing geothermal fluids that can be developed and utilized. These geothermal fluids can be steam or hot water, storing geothermal energy through convection and enrichment of the heat-carrying fluid. The caprock is a protective layer located above the geothermal reservoir, sealing it off to prevent the oil and gas within from escaping upwards. A suitable development area 5 for geothermal development can be selected within the geothermal reservoir 2. Specifically, the permeability, porosity, and other parameters of the geothermal reservoir can be evaluated to determine the fluidity and exploitability of the geothermal fluids, thereby selecting a suitable geothermal reservoir area as the development area; details will not be elaborated further here.

[0024] In some embodiments, sCO2 can be injected into the injection well as a fracturing fluid in a supercritical state to fracture the geothermal reservoir in stages; the proppant concentration in the fracturing fluid in a supercritical state can be increased to a preset concentration threshold to form a sand plug; the sand plug is used to prevent the backflow of the fracturing fluid in a supercritical state within the fractured geothermal reservoir section.

[0025] By using supercarbonyl chloride (sCO2) as the fracturing fluid, the low viscosity, high fluidity, and simultaneous gas and liquid properties of sCO2 in its supercritical state are fully utilized, significantly enhancing the conductivity and permeability of geothermal reservoirs and ensuring more efficient flow and extraction of geothermal resources. Using sand plugs for staged fracturing effectively isolates fractured and unfractured geothermal reservoir segments, preventing backflow of fracturing fluid and inter-segment interference, ensuring independent fracturing operations for each segment. Furthermore, staged fracturing allows for more uniform and widespread fracturing of the geothermal reservoir, effectively avoiding incomplete fracturing. Finally, the use of sand plugs eliminates the need for complex mechanical isolation tools or repeated downhole operations, significantly reducing operation time and equipment usage, and lowering overall operating costs.

[0026] Reference Figure 2 and Figure 3 For development area 5 between injection well 21 and production well 22, development area 5 can be pre-divided into segments. Geothermal reservoir segmentation involves dividing the development area of ​​a geothermal reservoir into multiple relatively independent segments based on its geological characteristics, thermal performance, and development needs. Segmentation allows for better understanding and control of the geothermal reservoir's characteristics, improving the efficiency of geothermal energy extraction. Geothermal reservoir segmentation methods can include division by stratigraphy, lithology, and geothermal temperature. Division by stratigraphy can divide the development area of ​​a geothermal reservoir into different segments based on the sedimentary sequence and lithological characteristics of the strata. Division by lithology can divide the development area of ​​a geothermal reservoir into different segments based on the type and properties of the rocks. Typically, the lithology of a geothermal reservoir is dominated by sandstone layers with a sand-to-mud ratio greater than 0.5, representing a relatively aquifer or geothermal reservoir. The caprock lithology is dominated by mudstone layers with a sand-to-mud ratio less than 0.5, representing a relatively impermeable layer or insulating layer. Geothermal reservoirs can be divided into different sections based on their geothermal temperature. For example, based on instantaneous geothermal well data, reservoirs can be divided into low-temperature single-layer structures and medium-low-temperature double-layer structures.

[0027] After segmenting the geothermal reservoir development area, the geothermal reservoir section in development area 5 can be fractured sequentially. The purpose of sequential fracturing of the geothermal reservoir section in development area 5 is to improve the permeability of the geothermal reservoir, allowing the fracturing fluid to flow more effectively through the formation, thereby increasing the release and recovery rate of thermal energy. sCO2 has low viscosity and high fluidity, enabling it to rapidly penetrate into the micro-fractures in the geothermal reservoir under high pressure, promoting fracturing. Therefore, sCO2 can be used as a fracturing fluid. (Refer to...) Figure 2 , Figure 3 and Figure 4 sCO2 can be continuously injected into injection well 21 using a horizontal well fracturing string 28. Cement 4 can be used to reinforce injection well 21 to ensure stability during sCO2 injection. Injection well 21 includes a horizontal section and a vertical section, with the horizontal section containing the horizontal well fracturing string 28. The horizontal well fracturing string 28 continuously presses the geothermal reservoir section between injection well 21 and production well 22 with high-pressure sCO2. As sCO2 is continuously injected, the pressure on the geothermal reservoir section increases. When the pressure exceeds the fracturing strength of the geothermal reservoir rock, the rock fractures, generating fractures 23. The fluidity of sCO2 allows it to distribute evenly and extend fractures 23, forming a preliminary fracture network. sCO2's ability to combine with gas and liquid allows it to penetrate development zone 5 more effectively, promoting the extension of fractures 23.

[0028] After fracturing a geothermal reservoir section, the concentration of proppant in the fracturing fluid can be gradually increased to form sand plugs. The proppant supports the fractures formed after fracturing the geothermal reservoir section, preventing fracture closure and thus maintaining fracture conductivity. The sand plug's function is to isolate the fractured and unfractured sections, preventing flow interference of the fracturing fluid between them. (Refer to...) Figure 4 Ceramsite sand can be used as a proppant. By gradually increasing the proportion of ceramsite sand to a preset concentration threshold, the ceramsite sand accumulates between the fractured geothermal reservoir section 25 and the unfractured geothermal reservoir section 27 in the injection well 21, forming a dense sand plug 26. The high concentration of ceramsite sand can block the connection between the injection well 21 and the development area 5, preventing backflow of fracturing fluid during subsequent fracturing processes and ensuring that the unfractured geothermal reservoir section 27 remains undisturbed. The sand plug 26, through its sealing effect, prevents fracturing fluid in the fractured geothermal reservoir section 25 from flowing back into the injection well 21, ensuring independent development of the next fracturing section. Simultaneously, the sand plug 26 can improve the efficiency of fracturing operations, reduce the mutual influence between the fractured geothermal reservoir section 25 and the unfractured geothermal reservoir section 27, and promote the formation of a fracture network.

[0029] In some embodiments, a temporary plugging agent may be injected into the injection well to seal the fractured geothermal reservoir section.

[0030] By using a temporary plugging agent to form a temporary barrier within the fractures of a fractured geothermal reservoir segment, the fracture network is further expanded, eventually forming multiple fracture segments and improving the overall permeability of the geothermal reservoir.

[0031] Reference Figure 3 and Figure 4 After the sand plug 26 is formed, a temporary plugging agent 24 can be injected through injection well 21 to seal the fractures in the fractured geothermal reservoir section 25. The temporary plugging agent can be, for example, an agent with acrylamide (AM) as the main monomer, supplemented with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA) as functional monomers. AMPS contains -SO3- groups, exhibiting strong salt resistance and stability under high temperature and high salinity conditions. The -COO- groups in acrylic acid have water-absorbing and swelling capabilities, enhancing the sealing performance of the gel. Injecting the temporary plugging agent 24 through injection well 21 seals the fractures in the fractured geothermal reservoir section 25, diverting the sCO2 fracturing fluid to the unfractured reservoir section. Once the sand plug 26 is formed, the injected temporary plugging agent 24 seals the fractures in the fractured geothermal reservoir section 25, thereby preventing fracturing fluid from entering the fractures of the fractured geothermal reservoir section 25. This plugging is temporary. When the pressure of the fracturing fluid reaches a certain level, the temporary plugging agent will be forced open, allowing the fracturing fluid to be redirected to the unfractured geothermal reservoir section 27, further expanding the fracture network of development area 5.

[0032] For a single geothermal reservoir segment, fracturing can be used to create fractures. Next, the proppant concentration is increased to a preset threshold to generate a sand plug. Finally, a temporary plugging agent is injected to seal the geothermal reservoir segment. The above steps are repeated for each geothermal reservoir segment to complete the fracturing of the entire geothermal reservoir, forming a fracture network.

[0033] S102: A nanofluid formed by mixing supercritical fracturing fluid with thermally conductive nanoparticles is injected into the fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir.

[0034] By injecting a nanofluid formed by mixing supercritical fracturing fluid with thermally conductive nanoparticles into the fractures of the geothermal reservoir through the injection well, thermal energy in the geothermal reservoir is obtained.

[0035] In some embodiments, sCO2 can be used as a fracturing fluid in a supercritical state, CuO nanoparticles can be used as thermally conductive nanoparticles, and the sCO2 nanofluid formed by the mixture of the two can be injected into the injection well to expand the fractures of the geothermal reservoir; the sCO2 nanofluid formed by the mixture of the fracturing fluid in a supercritical state and the thermally conductive nanoparticles can be injected into the expanded fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir.

[0036] By combining CuO nanoparticles with sCO2, the thermal conductivity of sCO2 fluid is significantly enhanced, resulting in higher heat transfer efficiency. The Brownian motion of CuO nanoparticles strengthens the convective heat transfer mechanism, especially under high temperature and high pressure conditions, which greatly improves the efficiency of heat extraction and significantly promotes the efficient utilization of geothermal resources.

[0037] Compared to water-based fluids, sCO2 has lower viscosity and higher permeability, enabling rapid and uniform fracture propagation and heat transfer. Furthermore, as a circulating fluid and heat extraction medium, sCO2 nanofluids do not cause formation or pore blockage, allowing for long-term stable operation. (Reference) Figure 2 After fracturing the entire development zone 5, sCO2 and CuO nanoparticles can be mixed to form sCO2 nanofluid, which is then injected into the fractures of development zone 5 as the heat extraction medium 3. The sCO2 nanofluid can effectively penetrate into the fractures and pores of development zone 5, thereby rapidly and uniformly expanding the fractures through the pressure and velocity carried by the sCO2 nanofluid. Combining CuO nanoparticles with sCO2 can effectively improve heat extraction efficiency. CuO nanoparticles have extremely high thermal conductivity, far exceeding that of basic fluids (such as water or CO2). By adding CuO nanoparticles to the sCO2 fluid, the thermal conductivity of the sCO2 fluid can be significantly improved. Furthermore, the Brownian motion of CuO nanoparticles in the sCO2 fluid can enhance the convective heat transfer mechanism, especially under high temperature and high pressure conditions, where the addition of CuO nanoparticles enhances the thermal conductivity of sCO2. CuO nanoparticles exhibit good chemical stability under high temperature and high pressure conditions and are not prone to adverse reactions with sCO2 or the chemical components in the geothermal reservoir. This stability allows CuO nanoparticles to maintain their thermal conductivity in CO2 fluid for a long time without performance degradation or agglomeration.

[0038] S103: The nanofluid that has absorbed geothermal reservoir heat energy is transported to the surface heat extraction system through the production well to collect the heat energy generated by the expansion of the nanofluid.

[0039] By transporting the nanofluid that has absorbed geothermal energy from the reservoir to a surface heat extraction system via a production well, the heat energy generated by the expansion of the nanofluid is collected, thus realizing the utilization of thermal energy in the geothermal reservoir.

[0040] In some embodiments, the surface heat extraction system includes a power generation system and a heating system; the step of transporting the sCO2 nanofluid after absorbing geothermal reservoir heat energy to the surface heat extraction system via a production well includes: transporting the sCO2 nanofluid after absorbing geothermal reservoir heat energy to the power generation system via a production well; transporting the sCO2 nanofluid output from the power generation system to the heating system; and injecting supercritical CO2 fracturing fluid into an injection well to fracture the geothermal reservoir to form fractures, including: compressing the cooled CO2 fracturing fluid output from the heating system to a supercritical state; and injecting the compressed supercritical CO2 fracturing fluid into an injection well to fracture the geothermal reservoir to form fractures.

[0041] By using sCO2 nanofluids for power generation and heating, and by recompressing the heated sCO2 nanofluids to generate sCO2, greenhouse gas emissions are significantly reduced, laying the foundation for the recycling of CO2.

[0042] Reference Figure 2 After the sCO2 nanofluid 3 is injected into the fractures of development zone 5, it circulates and absorbs a certain amount of heat within the zone. It can then be returned to the surface via production well 22. Production well 22 includes horizontal and vertical sections. The sCO2 nanofluid 3, after circulating and absorbing heat in development zone 5, reaches the surface sequentially through both the horizontal and vertical sections of production well 22. The temperature of the sCO2 nanofluid reaching the surface typically exceeds 200°C. Upon reaching the surface, the sCO2 nanofluid is first transported to a power generation system to convert geothermal energy into electrical energy. The sCO2 nanofluid output from the power generation system is then transported to a heating system to utilize its residual heat energy for district heating. The heating system outputs low-temperature CO2 fracturing fluid separated from the sCO2 nanofluid. This cooled CO2 fracturing fluid can be compressed to a supercritical state and then injected into the injection well to fracture the geothermal reservoir.

[0043] In some embodiments, the power generation system includes a first expansion component and a second expansion component; the heating system includes a heat exchange component. The step of transporting the sCO2 nanofluid, after absorbing geothermal reservoir heat energy, to the power generation system via a production well includes: transporting the sCO2 nanofluid to the first expansion component to collect the heat energy generated by the expansion of the sCO2 nanofluid; transporting the nanofluid output from the first expansion component to the second expansion component to mix the sCO2 nanofluid with water; and collecting the heat energy generated by the expansion of the sCO2 nanofluid again based on the latent heat of phase change of water. The step of transporting the sCO2 nanofluid output from the power generation system to the heating system includes: transporting the sCO2 nanofluid output from the second expansion component to the heating system to use the remaining heat energy of the sCO2 nanofluid for district heating.

[0044] By collecting the heat energy generated by the primary and secondary expansion of sCO2 nanofluids, and using the remaining heat energy of the sCO2 nanofluids after secondary expansion for district heating, geothermal energy can be fully utilized, greatly improving the overall utilization rate of geothermal energy.

[0045] The first expansion component includes at least a circulation pump 7, a first-stage turbine 8, a high-pressure manifold 9, a compressor 10, and a first-stage generator 11. (Refer to...) Figure 2 After the sCO2 nanofluid 3 is injected into the fracture of the development area 5, it circulates and absorbs a certain amount of heat within the development area 5 before being returned to the surface via the production well 22. The tubing of the production well 22 is encased in an insulated sleeve 6, which effectively reduces heat loss during the return journey, improving thermal efficiency and extending the wellbore's lifespan. The temperature of the sCO2 nanofluid reaching the surface typically exceeds 200°C. Upon reaching the surface, the sCO2 nanofluid first passes through the circulation pump 7 and enters the compressor 10 for preheating and pressurization. Then, it enters the first-stage turbine 8 through the high-pressure manifold 9. During expansion, the pressure of the sCO2 nanofluid rapidly decreases, driving the turbine blades of the first-stage turbine 8 to rotate, which in turn drives the first-stage generator 11 to convert mechanical energy into electrical energy. During this process, the temperature and pressure of the sCO2 nanofluid decrease significantly, but a large amount of residual heat is still retained. The CO2 then enters the waste heat recovery system for further utilization.

[0046] The second expansion component includes at least a primary heat exchanger 12, a secondary generator 13, a gas-liquid separator 14, and a secondary turbine 15. (Refer to...) Figure 2After the initial expansion and power generation of the sCO2 nanofluid, the waste heat of the sCO2 nanofluid can be transferred to water using the first-stage heat exchanger 12. The water receiving the waste heat from the sCO2 nanofluid can then be converted into high-temperature, high-pressure steam using the gas-liquid separator 14. The steam and sCO2 nanofluid can then be fed together into the second-stage turbine 15, utilizing the latent heat of phase change of the steam and the heat from the sCO2 nanofluid for secondary expansion and power generation. During phase change (e.g., from liquid to gas), steam releases or absorbs a large amount of heat; this heat is called the latent heat of phase change. Feeding the steam and sCO2 nanofluid together into the second-stage turbine 15 fully utilizes their combined heat to drive the turbine blades of the second-stage turbine 15, which in turn drives the second-stage generator 13 to convert mechanical energy into electrical energy. The latent heat released by the steam during phase change and the remaining heat from the sCO2 nanofluid work together to power the second-stage generator 13, thereby increasing the output power of the second-stage turbine 15.

[0047] The heat exchange components include at least a secondary heat exchanger 16. (Refer to...) Figure 2 After the sCO2 nanofluid undergoes secondary expansion for power generation, a secondary heat exchanger 16 can be used to transfer the waste heat of the sCO2 nanofluid to the district heating system, utilizing the 50℃ to 100℃ waste heat of the sCO2 nanofluid to provide heating energy to users in the area. The secondary heat exchanger 16 can effectively transfer the waste heat from the sCO2 nanofluid to the circulating water or steam of the district heating system, thereby increasing the temperature of the district heating system. Secondary heat exchangers typically feature high efficiency, corrosion resistance, and high temperature resistance, ensuring the stability and reliability of the waste heat transfer process. Utilizing the waste heat from sCO2 nanofluid for heating can significantly reduce energy consumption and carbon emissions, improving energy utilization efficiency. Furthermore, using the waste heat from sCO2 nanofluid for heating can reduce heating costs and improve economic benefits.

[0048] In some embodiments, the ground heating system further includes a separation system; the step of compressing the cooled fracturing fluid output from the heating system to a supercritical state includes: transporting the sCO2 nanofluid output from the heating system to the separation system to output the cooled CO2 fracturing fluid; and compressing the cooled CO2 fracturing fluid to a supercritical state.

[0049] By recompressing the expanded sCO2 nanofluid to generate sCO2, greenhouse gas emissions are significantly reduced, laying the foundation for the recycling of CO2.

[0050] After transferring the waste heat of the sCO2 nanofluid to the district heating system, the sCO2 nanofluid can be fed into a separation system. The separation system can be used to separate low-temperature CO2, CuO nanoparticles, and the water mixed within them. The condensate 18 separated in the separation system can be returned to the gas-liquid separator 14, and the low-temperature CO2 separated in the separation system can be compressed to a supercritical state to generate sCO2.

[0051] In some embodiments, the separation system includes a condensation component and a refrigeration component. The step of delivering the sCO2 nanofluid output from the heating system to the separation system to output cooled CO2 fracturing fluid; and compressing the cooled CO2 fracturing fluid to a supercritical state, includes: delivering the sCO2 nanofluid output from the heating system to the condensation component to condense and separate CO2 fracturing fluid, CuO heat-generating nanoparticles, and water; and delivering the CO2 fracturing fluid output from the condensation component to the refrigeration component to cool the CO2 fracturing fluid and compress the cooled CO2 fracturing fluid to a supercritical state. After compressing the cooled CO2 fracturing fluid to a supercritical state, the step further includes: injecting the supercritical sCO2 fracturing fluid mixed with CuO heat-generating nanoparticles to form an sCO2 nanofluid into the fractures of the geothermal reservoir via the injection well to absorb the thermal energy of the geothermal reservoir.

[0052] By using a separation system to separate low-temperature CO2 fracturing fluid and compressing it to a supercritical state, the sCO2 fracturing fluid can be mixed with CuO nanoparticles to form sCO2 nanofluid, which is then injected into the fractures of the geothermal reservoir. This achieves the recycling of CO2, greatly reduces greenhouse gas emissions, and effectively improves resource utilization efficiency.

[0053] The separation system includes at least a condensing component and a refrigeration component. The condensing component includes at least a condenser 17. The refrigeration component includes at least an adsorption refrigeration unit 19. (Refer to...) Figure 2After transferring the waste heat of the sCO2 nanofluid to the district heating system, the sCO2 nanofluid can be fed into condenser 17. Condenser 17 can be used to separate low-temperature CO2, CuO nanoparticles, and the water mixed therewith. The condensate 18 separated from condenser 17 can be sent back to gas-liquid separator 14, and the low-temperature CO2 separated from condenser 17 can be sent to adsorption refrigeration unit 19. During the condensation and separation of low-temperature CO2, CuO nanoparticles, and water, the mixture of sCO2 nanofluid and water vapor is fed into condenser 17. By lowering the temperature, the water vapor condenses into liquid water, and the CuO nanoparticles no longer dissolve in the low-temperature CO2, thus achieving the separation of the three components. After secondary expansion for power generation, district heating, and condensation, the CO2 temperature is close to ambient temperature. CO2 obtained by condensation and separation can be compressed to a supercritical state to generate sCO2 through an adsorption refrigeration device 19. Then, sCO2 and CuO nanoparticles can be remixed using a mixing pump 20 to generate sCO2 nanofluid, which is used as heat extraction medium 3 and transported back to the cracks in the development area 5 to absorb the heat energy of the geothermal reservoir again and start the recycling process again.

[0054] By injecting supercritical fracturing fluid into an injection well, the geothermal reservoir is fractured to form fractures. A nanofluid, formed by mixing the supercritical fracturing fluid with thermally conductive nanoparticles, is then injected into the fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir. The nanofluid, after absorbing the thermal energy of the geothermal reservoir, is then transported to a surface heat extraction system through a production well to collect the heat energy generated by the expansion of the nanofluid, thus realizing the integration of geothermal reservoir fracturing, heat extraction, and utilization.

[0055] Based on the above-described integrated method for horizontal well carbon dioxide fracturing, heat extraction, and utilization, this specification also proposes embodiments of an integrated device for horizontal well carbon dioxide fracturing, heat extraction, and utilization. For example... Figure 5 As shown, the integrated horizontal well carbon dioxide fracturing-heat extraction-utilization device may specifically include the following modules:

[0056] The fracturing module 501 can be used to inject fracturing fluid in a supercritical state into the injection well to fracture the geothermal reservoir and form fractures.

[0057] The absorption module 502 can be used to inject a nanofluid formed by mixing fracturing fluid in a supercritical state with thermally conductive nanoparticles into the fractures of the geothermal reservoir through the injection well, so as to absorb the thermal energy of the geothermal reservoir.

[0058] The collection module 503 can be used to transport the nanofluid that has absorbed geothermal reservoir heat energy to the surface heat extraction system through the production well, so as to collect the heat energy generated by the expansion of the nanofluid.

[0059] In some embodiments, the fracturing module 501 can be specifically used to inject fracturing fluid in a supercritical state into an injection well to fracture the geothermal reservoir in stages; increase the proppant concentration in the supercritical fracturing fluid to a preset concentration threshold to form a sand plug; the sand plug is used to prevent backflow of the supercritical fracturing fluid in the fractured geothermal reservoir section. In some embodiments, the fracturing module 501 can also be used to inject a temporary plugging agent into the injection well to seal the fractured geothermal reservoir section.

[0060] In some embodiments, the absorption module 502 can be specifically used to inject a nanofluid formed by mixing fracturing fluid in a supercritical state with thermally conductive nanoparticles into an injection well to expand the fractures in the geothermal reservoir; the nanofluid formed by mixing fracturing fluid in a supercritical state with thermally conductive nanoparticles is injected into the expanded geothermal reservoir fractures through the injection well to absorb the thermal energy of the geothermal reservoir.

[0061] In some embodiments, the collection module 503 can be specifically used to transport the nanofluid, after absorbing geothermal reservoir heat energy, to the power generation system via a production well; transport the nanofluid output from the power generation system to a heating system; and inject supercritical fracturing fluid into an injection well to fracture the geothermal reservoir, including: compressing the cooled fracturing fluid output from the heating system to a supercritical state; and injecting the supercritical fracturing fluid into the injection well to fracture the geothermal reservoir. In some embodiments, the collection module 503 can also be used to transport the nanofluid to a first expansion component to collect the heat energy generated by the expansion of the nanofluid; transport the nanofluid output from the first expansion component to a second expansion component to mix the nanofluid with water; collect the heat energy generated by the expansion of the nanofluid again based on the latent heat of phase change of water; and transport the nanofluid output from the second expansion component to a heat exchange component to use the remaining heat energy of the nanofluid for district heating. In some embodiments, the collection module 503 can also be used to transport the nanofluid output from the heating system to the separation system to output cooled fracturing fluid; and compress the cooled fracturing fluid to a supercritical state. The collection module 503 can also be used to transport the nanofluid output from the heating system to a condensation component to condense and separate fracturing fluid, heat-extracting nanoparticles, and water; transport the fracturing fluid output from the condensation component to a cooling component to cool the fracturing fluid and compress the cooled fracturing fluid to a supercritical state; and inject the nanofluid formed by mixing the supercritical fracturing fluid with the heat-extracting nanoparticles into the fractures of the geothermal reservoir via the injection well to absorb the thermal energy of the geothermal reservoir.

[0062] It should be noted that the units, devices, or modules described in the above embodiments can be implemented by computer chips or physical entities, or by products with certain functions. For ease of description, the above devices are described by dividing them into various modules according to their functions. Of course, in implementing this specification, the functions of each module can be implemented in one or more software and / or hardware, or the module that implements the same function can be implemented by a combination of multiple sub-modules or sub-units, etc. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection between the devices or units shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0063] As can be seen from the above, the integrated horizontal well carbon dioxide fracturing-heat extraction-utilization device provided in the embodiments of this specification can fracture geothermal reservoirs with fracturing fluid under supercritical conditions, thereby improving the permeability of geothermal reservoirs and ensuring that geothermal resources can flow and be extracted more efficiently. By combining thermally conductive nanoparticles with fracturing fluid under supercritical conditions to form nanofluids, the thermal energy extraction efficiency is greatly improved, promoting the efficient utilization of geothermal resources.

[0064] This specification also provides a computer device for an integrated method of horizontal well carbon dioxide fracturing-heat extraction-utilization, including a processor and a memory for storing processor-executable instructions. Specifically, the processor can execute the following steps according to the instructions: injecting supercritical fracturing fluid into an injection well to fracture the geothermal reservoir and form fractures; injecting a nanofluid formed by mixing the supercritical fracturing fluid with thermally conductive nanoparticles into the fractures of the geothermal reservoir via the injection well to absorb the thermal energy of the geothermal reservoir; and transporting the nanofluid after absorbing the geothermal reservoir's thermal energy to a surface heat extraction system via a production well to collect the heat energy generated by the expansion of the nanofluid.

[0065] To execute the above instructions more accurately, please refer to... Figure 6 As shown in the embodiments of this specification, another specific electronic device is also provided, wherein the electronic device includes a network communication port 601, a processor 602 and a memory 603, and the above structures are connected by internal cables so that the various structures can perform specific data interaction.

[0066] The processor 602 can be specifically used to inject supercritical fracturing fluid into an injection well to fracture the geothermal reservoir and form fractures; to inject a nanofluid formed by mixing supercritical fracturing fluid with thermally conductive nanoparticles into the fractures of the geothermal reservoir through the injection well to absorb the thermal energy of the geothermal reservoir; and to transport the nanofluid that has absorbed the thermal energy of the geothermal reservoir to a surface heat extraction system through a production well to collect the thermal energy generated by the expansion of the nanofluid.

[0067] The memory 603 can be used to store the corresponding instruction program.

[0068] In this embodiment, the network communication port 601 can be a virtual port bound to different communication protocols, thereby enabling the sending or receiving of different data. For example, the network communication port can be a port responsible for web data communication, a port responsible for FTP data communication, or a port responsible for email data communication. Furthermore, the network communication port can also be a physical communication interface or communication chip. For example, it can be a wireless mobile network communication chip, such as GSM or CDMA; it can also be a Wi-Fi chip; or it can be a Bluetooth chip.

[0069] In this embodiment, the processor 602 can be implemented in any suitable manner. For example, the processor can take the form of a microprocessor or processor and a computer-readable medium storing computer-readable program code (e.g., software or firmware) executable by the (micro)processor, logic gates, switches, application-specific integrated circuits (ASICs), programmable logic controllers, and embedded microcontrollers, etc. This specification is not limiting.

[0070] In this embodiment, the memory 603 includes volatile memory and non-volatile memory. The memory 603 can include multiple layers. In digital systems, anything that can store binary data can be a memory; in integrated circuits, a circuit with storage function but no physical form is also called a memory, such as RAM, FIFO, etc.; in a system, a storage device with a physical form is also called a memory, such as a memory stick, TF card, etc.

[0071] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0072] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0073] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0074] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0075] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A horizontal well carbon dioxide fracturing-heat extraction-utilization integrated method, characterized in that, The method comprises: injecting carbon dioxide in a supercritical state into an injection well to fracture the geothermal reservoir through a horizontal well section of the injection well to form fractures; wherein the method comprises: dividing a development area of the geothermal reservoir into a plurality of relatively independent sections according to geological characteristics, thermal reservoir performance and development requirements of the geothermal reservoir; and fracturing the geothermal reservoir sections of the development area one by one; injecting a nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles into the fractures of the geothermal reservoir through the horizontal well section of the injection well to absorb thermal energy of the geothermal reservoir; wherein the method comprises: injecting the nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles into the injection well to expand the fractures of the geothermal reservoir; and injecting the nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles into the expanded fractures of the geothermal reservoir through the horizontal well section of the injection well to absorb thermal energy of the geothermal reservoir; the thermally conductive nanoparticles comprise CuO nanoparticles; the CuO nanoparticles are used to enhance convective heat transfer through Brownian motion in the nanofluid; transporting the nanofluid after absorbing thermal energy of the geothermal reservoir to a surface heat extraction system through a production well to collect thermal energy generated by expansion of the nanofluid; the surface heat extraction system comprises a power generation system, a heating system and a separation system; the separation system comprises a condensing component and a refrigeration component; the transporting the nanofluid after absorbing thermal energy of the geothermal reservoir to the surface heat extraction system through the production well comprises: transporting the nanofluid after absorbing thermal energy of the geothermal reservoir to the power generation system to convert thermal energy of the nanofluid into electrical energy; transporting the nanofluid output by the power generation system to the heating system to use residual thermal energy of the nanofluid for regional heating; transporting the nanofluid output by the heating system to the condensing component to separate out carbon dioxide, heat extraction nanoparticles and water by condensation; transporting the carbon dioxide output by the condensing component to the refrigeration component to cool the carbon dioxide and compress the cooled carbon dioxide to a supercritical state; and injecting the nanofluid formed by mixing the carbon dioxide in the supercritical state and the CuO nanoparticles into the fractures of the geothermal reservoir through the horizontal well section of the injection well to absorb thermal energy of the geothermal reservoir.

2. The method of claim 1, wherein, The method comprises: injecting a fracturing fluid in a supercritical state into an injection well to fracture the geothermal reservoir through a horizontal well section of the injection well; increasing a concentration of proppants in the fracturing fluid in the supercritical state to a preset concentration threshold to form a sand plug; the sand plug is used to prevent backflow of the fracturing fluid in the supercritical state in the fractured geothermal reservoir section.

3. The method of claim 2, wherein, The method further comprises: injecting a temporary plugging agent into the injection well to plug the fractured geothermal reservoir section.

4. The method of claim 1, wherein, The method comprises: compressing the cooled carbon dioxide output by the heating system to a supercritical state; Carbon dioxide compressed to a supercritical state is injected into an injection well to form fractures in a geothermal reservoir by fracturing a horizontal well section of the injection well.

5. The method of claim 4, wherein, The power generation system comprises a first expansion component and a second expansion component; and the heating system comprises a heat exchange component; The nanofluid after absorbing heat energy of the geothermal reservoir is transported to the power generation system through a production well, comprising: The nanofluid is transported to the first expansion component to collect heat energy generated by expansion of the nanofluid; The nanofluid output by the first expansion component is transported to the second expansion component to mix the nanofluid and water; Based on latent heat of phase change of water, heat energy generated by expansion of the nanofluid is collected again; The nanofluid output by the power generation system is transported to the heating system, comprising: The nanofluid output by the second expansion component is transported to the heat exchange component to use residual heat energy of the nanofluid for regional heating.

6. A horizontal well carbon dioxide fracturing-heat extraction-utilization integrated device, characterized in that, The device comprises: A fracturing module for injecting carbon dioxide in a supercritical state into an injection well to form fractures in a geothermal reservoir by fracturing a horizontal well section of the injection well; wherein the development area of the geothermal reservoir is divided into multiple relatively independent sections according to the geological characteristics, thermal reservoir performance and development requirements of the geothermal reservoir; and the geothermal reservoir sections of the development area are fractured one by one; An absorption module for injecting nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles into the fractures of the geothermal reservoir through the horizontal well section of the injection well to absorb heat energy of the geothermal reservoir; wherein the nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles is injected into the injection well to expand the fractures of the geothermal reservoir; and the nanofluid formed by mixing carbon dioxide in a supercritical state and thermally conductive nanoparticles is injected into the expanded fractures of the geothermal reservoir through the horizontal well section of the injection well to absorb heat energy of the geothermal reservoir; the thermally conductive nanoparticles comprise CuO nanoparticles; and the CuO nanoparticles are used to strengthen convective heat transfer through Brownian motion in the nanofluid. The collecting module is used for conveying the nanofluid after absorbing the heat energy of the geothermal reservoir to the ground heat extraction system via the production well to collect the heat energy generated by the expansion of the nanofluid; the ground heat extraction system comprises a power generation system, a heating system and a separation system; the separation system comprises a condensing component and a refrigeration component; the conveying of the nanofluid after absorbing the heat energy of the geothermal reservoir to the ground heat extraction system via the production well comprises: conveying the nanofluid after absorbing the heat energy of the geothermal reservoir to the power generation system via the production well to convert the heat energy of the nanofluid into electric energy; conveying the nanofluid output by the power generation system to the heating system to use the residual heat energy of the nanofluid for regional heating; conveying the nanofluid output by the heating system to the condensing component to separate out carbon dioxide, heat extraction nanoparticles and water by condensation; conveying the carbon dioxide output by the condensing component to the refrigeration component to cool the carbon dioxide and compress the cooled carbon dioxide to a supercritical state; and conveying the nanofluid formed by mixing the carbon dioxide in the supercritical state with CuO nanoparticles into the cracks of the geothermal reservoir via the horizontal well section of the injection well to absorb the heat energy of the geothermal reservoir.

7. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to realize the method of any one of claims 1-5.

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