Circulating heat collecting method and circulating heat collecting system for branch horizontal well

Abstract

The invention discloses a circulating heat collecting method and system for a branch horizontal well. The circulating heat collecting method for the branch horizontal well comprises the steps that the branch horizontal well is drilled; an injection pipe is put into the vertical well section, so that an extraction channel is formed between the injection pipe and the wall surface of the vertical well section; a packer is installed at the lower end of the injection pipe so that the extraction channel and the horizontal well section can be sealed and separated; hydraulic fracture forming is carried out on the wall face of the vertical well section above the packer, and volume fracture net fracture forming is carried out on the wall face of the upper side of the horizontal well section, so that a volume fracture net is communicated with a hydraulic fracture; after the heat recovery fluid is injected into the injection pipe, the two ends of a first heat exchange channel of a heat exchange driving device communicate with the upper end of the recovery channel and the injection pipe correspondingly; the heat of the hot dry rock reservoir can be exchanged to the heat storage medium flowing through the second heat exchange channel of the heat exchange driving device, so that the heat collection area is increased, and the heat collection efficiency is improved.

Description

Technical Field

[0001] This application belongs to the technical field of energy extraction, and specifically relates to a cyclic heat extraction method and system for a branched horizontal well. Background Art

[0002] With the rapid development of the global economy, the contradiction between fossil energy's environmental pollution and the low-carbon demand has become increasingly prominent. Efficiently developing clean energy to assist energy transformation has become the energy development strategy of countries around the world. Geothermal energy comes from the thermal energy of the earth's core, mantle, and crust inside the earth, releases energy through the decay of radioactive elements, and forms sustainable and periodic clean energy. Geothermal resource types include: hydrothermal geothermal, hot dry rock, magmatic geothermal, and geopressured geothermal. Among them, shallow hydrothermal geothermal and deep hot dry rock are the main geothermal resources in China. The hydrothermal geothermal reservoir contains hot water and steam and is developed by drilling to extract fluids. The hot dry rock reservoir has a low permeability and needs to create fractures through volume fracturing or hydraulic fracturing to form a heat exchange channel.

[0003] Currently, the development methods for hot dry rock geothermal resources are single-wellbore cyclic heat extraction and dual-well injection-production cyclic heat extraction systems. Single-wellbore cyclic heat extraction means drilling a vertical well, horizontal well, or branched well in the geothermal reservoir. Fluids are injected through the tubing and produced from the casing, and the volume of the circulating fluid is the total volume of the tubing and the annulus between the tubing and the casing in the wellbore. The multi-well injection-production cyclic heat extraction system means arranging multiple wells horizontally or vertically in the geothermal reservoir, and the wells are interconnected through hydraulic fractures, volume fractures, or reservoir matrix. Fluids flow in the wellbore, fractures, and matrix to achieve reservoir heat exchange, and the volume of the circulating fluid is the sum of the volume of the wellbore and fractures or the volume of the wellbore and the matrix between the wells. Although both systems can effectively extract the heat energy of hot dry rock, the effective circulating fluid volume of the single-wellbore cyclic heat extraction system is small and the heat extraction area is limited. The economic benefits, heat extraction area, and heat extraction efficiency of the multi-well injection-production cyclic heat extraction system are limited by the fracture length and the area of the matrix region. That is to say, the traditional heat extraction system has the defect of low heat extraction efficiency. Summary of the Invention

[0004] In view of the above defects or deficiencies, this application provides a cyclic heat extraction method and system for a branched horizontal well, aiming to solve the technical problem of low heat extraction efficiency of the traditional heat extraction system.

[0005] To achieve the above object, this application provides a cyclic heat extraction method for a branched horizontal well, which includes:

[0006] Drill a branched horizontal well, where the branched horizontal well includes a vertical well section and at least two horizontal well sections extending circumferentially outward from the vertical well section respectively;

[0007] Lower an injection pipe into the vertical well section so that a production channel is formed between the injection pipe and the wall surface of the vertical well section;

[0008] A packer is installed at the lower end of the injection pipe to isolate the production channel from the horizontal well section;

[0009] Hydraulic fractures are created on the wall of the vertical well section above the packer, and volume fracture networks are created on the wall above the horizontal well section, so that the volume fracture networks are connected to the hydraulic fractures;

[0010] After injecting the heat extraction fluid into the injection pipe, the two ends of the first heat exchange channel of the heat exchange drive device are connected to the upper end of the extraction channel and the injection pipe respectively;

[0011] The heat exchange drive device is controlled to drive the heat recovery fluid to flow through the volume fracture network, the hydraulic fracture, the upper end of the production channel, the first heat exchange channel and the injection pipe in sequence and circulate, so that the heat of the hot dry rock reservoir can be exchanged to the heat storage medium flowing through the second heat exchange channel of the heat exchange drive device.

[0012] In an embodiment of the present application, hydraulically fracturing the wall of the vertical well section above the packer includes:

[0013] Obtain the thickness of hot dry rock reservoir;

[0014] If the thickness of the hot rock reservoir is less than a predetermined thickness, hydraulic fracturing is performed on the wall of the vertical well section located above the hot rock reservoir to generate hydraulic fractures;

[0015] If the thickness of some hot rock reservoirs is greater than or equal to a preset thickness, hydraulic fracturing is performed on the wall surface of the corresponding hot rock reservoir in the vertical well section to generate hydraulic fractures.

[0016] In the embodiment of the present application, performing volume fracture network fracture creation on the wall surface on the upper side of the horizontal well section includes:

[0017] forming perforations extending upward in a vertical direction on the wall surface on the upper side of the horizontal well section, wherein the horizontal length of the horizontal well section is greater than the horizontal length of the hydraulic fracture;

[0018] The perforations are subjected to volume fracturing to form a volume fracture network, and the volume fracture network formed by the perforations extending out of the hydraulic fracture portion of the horizontal well section is connected to the side of the hydraulic fracture facing away from the vertical well section.

[0019] In the embodiment of the present application, after the injection pipe is lowered into the vertical well section, the following steps are further included:

[0020] Insulating cement slurry is injected into the wellhead of the branch well and allowed to flow through the entire horizontal well section.

[0021] In an embodiment of the present application, the cyclic heat recovery method of the branched horizontal well further includes:

[0022] The control supply device replenishes the heat extraction fluid into the injection pipe at preset time intervals.

[0023] In the embodiment of the present application, the cyclic heat extraction method for the branched horizontal well further includes:

[0024] When it is detected that the temperature of the heat extraction fluid flowing out of the upper end of the production channel is lower than the target temperature, the branched well is controlled to be closed until the temperature of the hot dry rock reservoir resumes to the preset temperature.

[0025] In the embodiment of the present application, the heat extraction fluid is supercritical carbon dioxide.

[0026] In addition, the present application also provides a cyclic heat extraction system for a branched horizontal well. The cyclic heat extraction system for the branched horizontal well is applied to the cyclic heat extraction method for the branched horizontal well as described above, and includes:

[0027] An injection pipe that can extend into the vertical well section, and a production channel is formed between the injection pipe and the wall surface of the vertical well section;

[0028] A plugging device is installed at the lower end of the injection pipe to seal off the production channel from the horizontal well section;

[0029] A heat exchange driving device having a first heat exchange channel and a second heat exchange channel. The two ends of the first heat exchange channel are respectively communicated with the upper end of the production channel and the injection pipe, and a heat storage medium is provided in the second heat exchange channel; the heat exchange driving device is used to drive the heat extraction fluid to flow through the volume fracture network, the hydraulic fracture network, the upper end of the production channel, the first heat exchange channel and the injection pipe in sequence and circulate, so that the heat of the hot dry rock reservoir can be exchanged to the heat storage medium flowing through the second heat exchange channel.

[0030] In the embodiment of the present application, a heat exchanger and a high-pressure pump are sequentially connected in series on the first heat exchange channel from the inlet end to the outlet end, and a second heat exchange channel is provided in the heat exchanger.

[0031] In the embodiment of the present application, the heat exchange driving device further includes a replenishment device arranged between the heat exchanger and the high-pressure pump, and the replenishment device is used to replenish the heat extraction fluid into the injection pipe.

[0032] Through the above technical solutions, the cyclic heat extraction method for the branched horizontal well provided by the embodiment of the present application has the following beneficial effects:

[0033] After being injected through the injection pipe, the lower-temperature heat production fluid flows through the horizontal well section and then into the volume fracture network and hydraulic fractures. In the volume fracture network and hydraulic fractures, the lower-temperature heat production fluid fully exchanges heat with the hot dry rock reservoir, causing the heat production fluid temperature to rise. The higher-temperature heat production fluid, having completed the heat exchange, then flows through the upper end of the extraction channel and the first heat exchange channel. The higher-temperature heat production fluid exchanges heat with the heat storage medium in the second heat exchange channel of the heat exchange drive device, thereby transferring heat from the hot dry rock reservoir to the heat storage medium in the second heat exchange channel, thereby extracting heat from the hot dry rock reservoir. After the higher-temperature heat production fluid exchanges heat with the heat storage medium in the second heat exchange channel, its temperature decreases. The lowered temperature heat production fluid is then reinjected into the injection pipe and circulated in a preset flow direction, achieving cyclic heat production and improving heat production efficiency.

[0034] This application uses a packer to isolate the production channel from the horizontal well section, allowing the heat recovery fluid to flow in a predetermined direction and preventing it from entering the horizontal well section through the production channel after heat recovery is completed. By forming an interconnected network of volume fractures and hydraulic fractures, the heat recovery area is increased and the heat recovery efficiency is improved.

[0035] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the embodiments of the present application, but do not constitute a limitation on the embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without inventive work. In the drawings:

[0037] Figure 1 This is a schematic diagram of the steps of a cyclic heat recovery method for a branched horizontal well according to an embodiment of the present application;

[0038] Figure 2 This is a schematic structural diagram of a branched horizontal well circulation heat recovery system according to an embodiment of the present application;

[0039] Figure 3 This is a schematic structural diagram of a branched horizontal well circulation heat recovery system according to another embodiment of the present application;

[0040] Figure 4 This is a schematic diagram of a simulated heat recovery temperature field of a cyclic heat recovery method for branched horizontal wells according to an embodiment of the present application;

[0041] Figure 5 This is a schematic diagram of the heat extraction temperature field of a traditional branch horizontal well.

[0042] Description of Reference Numerals

[0043] 11 Vertical well section 30 Injection pipe

[0044] 111 Production channel 40 Packer

[0045] 12 Horizontal well section 50 Heat exchange driving device

[0046] 13 Hydraulic fracture 51 First heat exchange channel

[0047] 14 Volume fracture network 52 Heat exchanger

[0048] 21 Hot dry rock reservoir 53 High-pressure pump

[0049] 22 Overlying impermeable layer 54 Recharge equipment

[0050] 23 Underlying impermeable layer Detailed Embodiment

[0051] The following describes in detail the specific embodiments of the present application with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present application, and are not intended to limit the present application.

[0052] The following describes the cyclic heat extraction method and cyclic heat extraction system of the branched horizontal well of the present application with reference to the accompanying drawings.

[0053] As Figures 1 to 3 shown, the present application provides a cyclic heat extraction method for a branched horizontal well. Among them, the cyclic heat extraction method for a branched horizontal well includes:

[0054] Step S10, drilling a branched horizontal well, where the branched horizontal well includes a vertical well section 11 and at least two horizontal well sections 12 respectively extending circumferentially outward from the vertical well section 11;

[0055] The vertical well section 11 extends in the vertical direction. The vertical well section 11 is drilled downward from the ground through the formation until it reaches the predetermined hot dry rock reservoir 21. The function of the vertical well section 11 is to provide a stable entry point for the subsequent horizontal well section 12 and provide support for the structure of the entire branched horizontal well. The horizontal well section 12 extends circumferentially outward from the vertical well section 11, and the horizontal well section 12 can increase the contact area with the hot dry rock reservoir 21, thereby improving the extraction efficiency.

[0056] Step S20, lowering an injection pipe 30 into the vertical well section 11 so that a production channel 111 is formed between the injection pipe 30 and the wall surface of the vertical well section 11;

[0057] Injecting pipe 30 is lowered into the vertical well section 11. The injecting pipe 30 is located at the middle position of the vertical well section 11, so that a production channel 111 is formed between the injecting pipe 30 and the wall surface of the vertical well section 11. By arranging the injecting pipe 30, the heat extraction fluid can be injected from the injecting pipe 30 into the branched horizontal well. By arranging the production channel 111, the heat extraction fluid can flow out of the branched horizontal well from the production channel 111 after heat extraction is completed.

[0058] Step S30: Install a packer 40 at the lower end of the injecting pipe 30 to isolate the production channel 111 from the horizontal well section 12.

[0059] Step S40: Create a hydraulic fracture 13 on the wall surface of the vertical well section 11 above the packer 40, and create a volumetric fracture network 14 on the upper wall surface of the horizontal well section 12, so that the volumetric fracture network 14 is connected to the hydraulic fracture 13.

[0060] The packer 40 is located at the lower end of the injecting pipe 30 and is within the production channel 111. By arranging the packer 40 to isolate the production channel 111 from the horizontal well section 12, after the heat extraction fluid is injected from the injecting pipe 30, it can only enter the horizontal well section 12, then flow through the volumetric fracture network 14 and the hydraulic fracture 13, and then flow out through the production channel 111, rather than flowing directly out of the production channel 111 without passing through the volumetric fracture network 14 and the hydraulic fracture 13. Also, by arranging the packer 40, it can prevent the heat extraction fluid from flowing back into the horizontal well section 12 from the production channel 111 after flowing through the volumetric fracture network 14 and the hydraulic fracture 13. That is to say, by arranging the packer 40, the heat extraction fluid can only flow according to Figure 2 the preset flow direction shown by the arrow in the figure, preventing the heat extraction fluid from entering the horizontal well section 12 from the production channel 111 after heat extraction is completed, and also preventing the heat extraction fluid that has not undergone heat extraction from flowing out of the production channel 111.

[0061] Perform hydraulic fracturing on the wall surface of the vertical well section 11 above the packer 40 to form a hydraulic fracture 13, and perform volumetric fracturing on the upper wall surface of the horizontal well section 12 to form a volumetric fracture network 14. The direction of the volumetric fracture network 14 is vertically upward, and the length of the volumetric fracture network 14 runs through the entire hot dry rock reservoir 21. Part of the volumetric fracture network 14 is connected to the hydraulic fracture 13 to form a large-area heat extraction channel.

[0062] Step S50: After injecting the heat extraction fluid into the injecting pipe 30, connect the two ends of the first heat exchange channel 51 of the heat exchange driving device 50 to the upper end of the production channel 111 and the injecting pipe 30 respectively.

[0063] Step S60: Control the heat exchange driving device 50 to drive the heat extraction fluid to flow through the volume fracture network 14, hydraulic fracture 13, the upper end of the production channel 111, the first heat exchange channel 51, and the injection pipe 30 in sequence for circulating flow, so that the heat of the hot dry rock reservoir 21 can be exchanged to the heat storage medium flowing through the second heat exchange channel of the heat exchange driving device 50.

[0064] After the heat extraction fluid with a lower temperature is injected from the injection pipe 30, it flows through the horizontal well section 12 and then enters the volume fracture network 14 and the hydraulic fracture 13. In the volume fracture network 14 and the hydraulic fracture 13, the heat extraction fluid with a lower temperature fully exchanges heat with the hot dry rock reservoir 21, causing the temperature of the heat extraction fluid to rise. Then, the heat extraction fluid with a higher temperature after heat exchange flows through the upper end of the production channel 111 and the first heat exchange channel 51, and the heat extraction fluid with a higher temperature exchanges heat with the heat storage medium in the second heat exchange channel of the heat exchange driving device 50, thereby realizing the exchange of the heat of the hot dry rock reservoir 21 to the heat storage medium in the second heat exchange channel, so as to extract the heat in the hot dry rock reservoir 21. After the heat extraction fluid with a higher temperature exchanges heat with the heat storage medium in the second heat exchange channel, the temperature of the heat extraction fluid decreases. The heat extraction fluid with a decreased temperature is re-injected into the injection pipe 30 and circulates according to a preset flow direction to achieve cyclic heat extraction and improve the heat extraction efficiency.

[0065] In this application, the packer 40 is set to isolate the production channel 111 from the horizontal well section 12, so that the heat extraction fluid flows according to a preset flow direction, preventing the heat extraction fluid from entering the horizontal well section 12 from the production channel 111 after heat extraction. By forming the interconnected volume fracture network 14 and hydraulic fracture 13, the heat extraction area is increased and the heat extraction efficiency is improved.

[0066] Specifically, the heat extraction fluid with a higher temperature flows in the first heat exchange channel 51 of the heat exchange driving device 50, and the heat storage medium with a lower temperature flows in the second heat exchange channel, and heat can be exchanged and transferred between the first heat exchange channel 51 and the second heat exchange channel.

[0067] The branched horizontal well is not limited to having only two horizontal well sections 12. When the thickness of the hot dry rock reservoir 21 is large enough, the horizontal well sections 12 of the branched horizontal well can be multiple layers and multiple sections, and the corresponding hydraulic fractures 13 and volume fracture networks 14 are multiple groups, further expanding the heat extraction area.

[0068] In the embodiment of this application, creating a hydraulic fracture 13 on the wall surface of the vertical well section 11 above the packer 40 includes:

[0069] Step S41: Obtain the thickness of the hot dry rock reservoir 21;

[0070] Step S42: If the thickness of the hot rock reservoirs 21 is less than a preset thickness, hydraulic fracturing is performed on the wall of the vertical well section 11 above the hot dry rock reservoirs 21 to generate hydraulic fractures 13;

[0071] In step S43 , if the thickness of the hot rock reservoirs 21 is greater than or equal to a preset thickness, hydraulic fracturing is performed on the wall surface of the vertical well section 11 corresponding to the hot dry rock reservoirs 21 to generate hydraulic fractures 13 .

[0072] like Figure 2 As shown, the thickness of some hot rock reservoirs 21 is less than the preset thickness, indicating that the hot rock reservoirs 21 are relatively thin. In this case, hydraulic fracturing is performed on the wall of the vertical well section 11 above the hot rock reservoir 21 to generate hydraulic fractures 13, thereby expanding the area of the volume fracture network 14. Heat exchange between the heat recovery fluid and the hot rock reservoir 21 is achieved through the volume fracture network 14. At this time, the hydraulic fractures 13 do not play a heat recovery role, but only serve to receive the heat recovery fluid. Figure 2 As shown, there is an overlying impermeable layer 22 above the hot dry rock reservoir 21. If the thickness of some hot rock reservoirs 21 is less than a preset thickness, hydraulic fracturing is performed on the overlying impermeable layer 22 to generate hydraulic fractures 13.

[0073] like Figure 3 As shown, if the thickness of the hot dry rock reservoir 21 is greater than or equal to the preset thickness, it means that the hot dry rock reservoir 21 is relatively thick, then hydraulic fracturing is performed on the wall of the vertical well section 11 corresponding to the hot dry rock reservoir 21 to generate hydraulic fractures 13. At this time, the hydraulic fractures 13 can not only play a role in heat extraction, but also play a role in receiving heat extraction fluid.

[0074] The location of the hydraulic fracture 13 is determined according to the thickness of the hot dry rock reservoir 21 to determine a more suitable heat extraction scheme, thereby improving heat extraction efficiency.

[0075] Exemplarily, the preset thickness may be 5 m, 6 m, 7 m, 8 m, 9 m, 10 m, 11 m, 12 m, 13 m, 14 m or 15 m.

[0076] In the embodiment of the present application, creating the volume fracture network 14 on the wall surface on the upper side of the horizontal well section 12 includes:

[0077] Step S44: forming perforations extending vertically upward on the wall surface above the horizontal well section 12, wherein the horizontal length of the horizontal well section 12 is greater than the horizontal length of the hydraulic fracture 13;

[0078] In step S45 , volume fracturing is performed on the perforations to form a volume fracture network 14 , and the volume fracture network 14 formed by the perforations extending from the hydraulic fracture 13 in the horizontal well section 12 is connected to the side of the hydraulic fracture 13 facing away from the vertical well section 11 .

[0079] likeFigure 2 As shown, perforations are formed on the upper wall of the horizontal well section 12, extending vertically upward. Volumetric fractures are then applied to the perforations to form a large-area volumetric fracture network 14. Furthermore, the horizontal length of the horizontal well section 12 is greater than the horizontal length of the hydraulic fracture 13, so that the volumetric fracture network 14 formed by the perforations in the portion of the horizontal well section 12 extending beyond the hydraulic fracture 13 is connected to the side of the hydraulic fracture 13 facing away from the vertical well section 11. In other words, the volumetric fracture network 14 formed by the perforations in the portion of the horizontal well section 12 extending beyond the hydraulic fracture 13 is connected to the hydraulic fracture 13 from the side, increasing the contact area between the volumetric fractures 13. Furthermore, heat recovery fluid can enter the hydraulic fracture 13 from the side through the volumetric fracture network 14, making the flow of the heat recovery fluid more conducive to entering the production channel 111, thereby improving heat recovery efficiency.

[0080] In the embodiment of the present application, after the injection pipe 30 is lowered into the vertical well section 11, the following steps are further included:

[0081] Insulation cement slurry is injected into the wellhead of the branch well, and the insulation cement slurry is allowed to flow through the entire horizontal well section 12.

[0082] By injecting thermal insulation cement slurry into the wellhead of a branch well, the branch well can be insulated, reducing heat loss during the circulation of the heat recovery fluid, thereby improving heat recovery efficiency. In addition, injecting thermal insulation cement slurry into the branch well can improve the structural stability of the branch well, cementing the branch well, making the branch well more stable and reliable, and improving the safety of the branch well.

[0083] In an embodiment of the present application, the cyclic heat recovery method of the branched horizontal well further includes:

[0084] The supply device is controlled to replenish the heat recovery fluid into the injection pipe 30 at preset time intervals.

[0085] To ensure efficient heat extraction, the branched horizontal well's circulating heat extraction system regularly controls the supply device to replenish the heat extraction fluid into the injection pipe 30 at preset time intervals. This process is achieved through a precise time control mechanism to ensure the fluidity and temperature stability of the heat extraction fluid, thereby maximizing the efficiency of heat energy extraction. The operating status of the supply device and the flow rate of the heat extraction fluid will be monitored in real time and adjusted according to actual needs to maintain optimal energy transmission and heat exchange. At the same time, the system will also set an alarm mechanism to ensure timely maintenance and adjustments in the event of a failure in the supply device or insufficient supply of heat extraction fluid, ensuring the stability and reliability of the entire branched horizontal well's circulating heat extraction system.

[0086] In an embodiment of the present application, the cyclic heat recovery method of the branched horizontal well further includes:

[0087] When it is detected that the temperature of the heat extraction fluid flowing out of the upper end of the heat extraction channel 111 is lower than the target temperature, control is performed to close the branch well until the temperature of the hot dry rock reservoir 21 resumes to the preset temperature.

[0088] When it is detected that the temperature of the heat extraction fluid flowing out of the upper end of the heat extraction channel 111 is lower than the target temperature, the system will immediately activate the emergency response mechanism to control the closing of the branch well to prevent the further output of the low-temperature heat extraction fluid. This measure can effectively avoid the waste of thermal energy. After closing the branch well, the system will enter the monitoring and evaluation stage, obtain the temperature data of the hot dry rock reservoir 21 in real time, and analyze its recovery status. During this process, the system will make full use of the temperature information collected by the sensors to regularly evaluate the temperature of the hot dry rock reservoir 21. Once it is detected that the temperature of the hot dry rock reservoir 21 resumes to the preset target temperature, the branch well will be reopened to resume the normal flow of the heat extraction fluid. In addition, the system will also record the data of the entire process, including temperature changes, closing and opening times, etc., for later analysis and optimization of the operation strategy to ensure the safety and efficiency of future heat extraction operations.

[0089] In the embodiment of the present application, the heat extraction fluid is supercritical carbon dioxide.

[0090] The heat conduction efficiency of supercritical carbon dioxide in the supercritical state is higher than that of traditional heat conduction media such as water, and it can transfer heat more effectively, thereby improving the overall thermal energy collection efficiency. Compared with water, supercritical carbon dioxide maintains the supercritical state at a lower pressure, reducing the equipment load and risk. Carbon dioxide is a relatively environmentally friendly fluid. Using it as the heat conduction media can reduce the negative impact on the environment, and at the same time can also promote the recycling of carbon dioxide to a certain extent, contributing to addressing climate change issues. Supercritical carbon dioxide has a high energy density and can store and transfer more thermal energy in a relatively small volume, thereby improving the heat extraction efficiency. During the process of obtaining thermal energy, using supercritical carbon dioxide can achieve the recycling of carbon dioxide, reduce the loss and replenishment demand of the heat extraction fluid, and improve the economy of the system.

[0091] In addition, the present application further provides a cyclic heat extraction system for a branched horizontal well. The cyclic heat extraction system for a branched horizontal well is applied to the cyclic heat extraction method for a branched horizontal well as described above, and includes an injection pipe 30, a plugging device, and a heat exchange driving device 50: The injection pipe 30 can extend into the vertical well section 11, and a production channel 111 is formed between the injection pipe 30 and the wall surface of the vertical well section 11; The plugging device is installed at the lower end of the injection pipe 30 to isolate the production channel 111 from the horizontal well section 12; The heat exchange driving device 50 has a first heat exchange channel 51 and a second heat exchange channel. Two ends of the first heat exchange channel 51 are respectively communicated with the upper end of the production channel 111 and the injection pipe 30, and a heat storage medium is arranged in the second heat exchange channel; The heat exchange driving device 50 is used to drive the heat extraction fluid to flow through the volume fracture network 14, the hydraulic fracture network, the upper end of the production channel 111, the first heat exchange channel 51, and the injection pipe 30 in sequence and circulate, so that the heat of the hot dry rock reservoir 21 can be exchanged to the heat storage medium flowing through the second heat exchange channel.

[0092] The injection pipe 30 is lowered into the vertical well section 11, and the injection pipe 30 is located at the middle position of the vertical well section 11, so that a production channel 111 is formed between the injection pipe 30 and the wall surface of the vertical well section 11. By arranging the injection pipe 30, the heat extraction fluid can be injected into the branched horizontal well from the injection pipe 30, and by arranging the production channel 111, the heat extraction fluid can flow out of the branched horizontal well from the production channel 111 after heat extraction. The packer 40 is installed at the lower end of the injection pipe 30 to isolate the production channel 111 from the horizontal well section 12. By arranging the packer 40, the heat extraction fluid can only flow according to Figure 2 the preset flow direction shown by the arrow in the figure, preventing the heat extraction fluid from entering the horizontal well section 12 from the production channel 111 after heat extraction, and also preventing the heat extraction fluid that has not undergone heat extraction from flowing out of the production channel 111.

[0093] After the heat extraction fluid with a lower temperature is injected from the injection pipe 30, it flows through the horizontal well section 12 and then enters the volume fracture network 14 and the hydraulic fracture 13. In the volume fracture network 14 and the hydraulic fracture 13, the heat extraction fluid with a lower temperature exchanges heat fully with the hot dry rock reservoir 21, so that the temperature of the heat extraction fluid rises; Then, the heat extraction fluid with a higher temperature after heat exchange flows through the upper end of the production channel 111 and the first heat exchange channel 51, and the heat extraction fluid with a higher temperature exchanges heat with the heat storage medium in the second heat exchange channel of the heat exchange driving device 50, thereby realizing the exchange of the heat of the hot dry rock reservoir 21 to the heat storage medium in the second heat exchange channel, so as to collect the heat in the hot dry rock reservoir 21. After the heat extraction fluid with a higher temperature exchanges heat with the heat storage medium in the second heat exchange channel, the temperature of the heat extraction fluid decreases. The heat extraction fluid with a decreased temperature is re-injected into the injection pipe 30 and circulates according to the preset flow direction to realize cyclic heat extraction and improve the heat extraction efficiency.

[0094] In the embodiment of the present application, a heat exchanger 52 and a high-pressure pump 53 are successively connected in series on the first heat exchange channel 51 from the inlet end to the outlet end, and a second heat exchange channel is arranged in the heat exchanger 52.

[0095] A second heat exchange channel is arranged in the heat exchanger 52, and a heat storage medium with a lower temperature flows through the second heat exchange channel. After the heat extraction fluid exchanges heat with the hot dry rock reservoir 21, its temperature rises. After the heat extraction fluid with a higher temperature exchanges heat with the heat storage medium in the second heat exchange channel, the temperature of the heat extraction fluid decreases. The high-pressure pump 53 injects the heat extraction fluid with a reduced temperature back into the injection pipe 30 again and circulates according to a preset flow direction to achieve cyclic heat extraction and improve the heat extraction efficiency. By arranging the heat exchanger 52 to exchange heat with the heat extraction fluid, heat collection is realized. By arranging the high-pressure pump 53, the flow of the circulating heat extraction fluid is promoted to ensure the effective transfer and utilization of heat. The high-pressure pump 53 helps maintain the pressure of the entire system, ensures the system operates in an efficient state, and at the same time prevents problems such as precipitation of the heat extraction fluid.

[0096] In the embodiment of the present application, the heat exchange driving device 50 further includes a replenishment device 54 arranged between the heat exchanger 52 and the high-pressure pump 53, and the replenishment device 54 is used to replenish the heat extraction fluid into the injection pipe 30.

[0097] To ensure the efficient progress of the heat extraction process, the cyclic heat extraction system of the branched horizontal well will regularly control the replenishment device to deliver the heat extraction fluid into the injection pipe 30 at preset time intervals. This process is achieved through an accurate time control mechanism to ensure the fluidity and temperature stability of the heat extraction fluid, thereby maximizing the efficiency of heat energy collection.

[0098] The following is a cyclic heat extraction method for a branched horizontal well in an embodiment of the present application

[0099] 1. Based on geological exploration data, clarify the burial depth, reservoir thickness, reservoir porosity, reservoir permeability, well points of the branched well, horizontal section position of the branched well, horizontal section length of the branched well, half-length of the hydraulic fracture 13, width of the hydraulic fracture 13, conductivity of the hydraulic fracture 13, and conductivity of the volumetric fracture network 14; divide the reservoir thickness and top and bottom positions of the development area to ensure accurate drilling of the branched well.

[0100] 2. Determine the wellhead position of the branched well to ensure that the bottom of the vertical well section 11 is 10 m - 15 m away from the bottom of the target reservoir, the horizontal well section 12 is 15 m - 20 m away from the bottom of the target reservoir, and the horizontal well section 12 has at least two segments and is in the same plane.

[0101] 3. Use a drill bit to drill a vertical wellbore of the branch well at the wellhead of the branch well, passing through the overlying impermeable layer 22 until 10 m - 15 m above the underlying impermeable layer 23 (the value taken from numerical simulation is 15 m). Place a casing, inject heat-insulating cement slurry and lower an injection pipe 30, complete well cementing, and a production channel 111 is formed between the injection pipe 30 and the wall surface of the vertical well section 11.

[0102] 4. Place a drill bit and a geosteering tool in the branch well, perform deviation control and drilling of the horizontal well section 12. The drilling length of the horizontal well section 12 is 1500 m, and the horizontal wellbore is 15 m - 20 m away from the bottom of the target reservoir (the value taken from numerical simulation is 20 m).

[0103] 5. Place a packer 40 in the production channel 111, with the packer 40 being 10 m - 15 m away from the top of the target reservoir (the value taken from numerical simulation is 15 m). The position of the packer 40 changes with the change of the position of the hydraulic fracture 13.

[0104] 6. Use a perforating tool to perforate the area from above the packer 40 to the upper part of the reservoir to form perforations, and at the same time perforate upward on the upper side of the horizontal well section 12 to form perforations.

[0105] 7. Use water and supercritical carbon dioxide as fracturing fluids, perform hydraulic fracturing in the vertical well section 11 and volume fracturing in the horizontal well section 12 to create a hydraulic fracture 13 and a volume fracture network 14 respectively. The hydraulic fracture 13 and the volume fracture network 14 are vertically connected, and the volume fracture network 14 penetrates the entire hot dry rock reservoir 21 to form a heat extraction channel with inter-connected fractures. When the hot dry rock reservoir 21 is too thin (thickness less than 5 m), the hydraulic fracture 13 can also be located in the overlying impermeable layer 22 to ensure that the volume fracture network 14 penetrates the entire hot dry rock reservoir 21 (at this time, the hydraulic fracture 13 does not play a role in heat extraction but only serves to receive fluids).

[0106] 8. Connect a high-pressure pump 53, a heat exchanger 52, and a supply device 54 to each other on the ground using a high-pressure pipe manifold.

[0107] 9. A high-pressure pump 53 is used to inject supercritical carbon dioxide into the injection pipe 30. The supercritical carbon dioxide flows into the horizontal well section 12 and then enters the volumetric fracture network 14; the supercritical carbon dioxide fills the volumetric fracture network 14 and exchanges heat with the hot dry rock reservoir 21 sufficiently, and then flows into the hydraulic fracture 13; the supercritical carbon dioxide fills the hydraulic fracture 13 and continuously exchanges heat with the hot dry rock reservoir 21, and then flows from the hydraulic fracture 13 into the production channel 111 and then flows to the ground; the produced fluid flows through the heat exchanger 52, exchanges heat with the second heat exchange channel in the heat exchanger 52, and then circulates the cooled supercritical carbon dioxide into the high-pressure pump 53 for cyclic heat extraction again; the recharge device 54 is used to supplement supercritical carbon dioxide to the hot dry rock reservoir 21 regularly to ensure sufficient cyclic heat extraction fluid until the temperature of the produced fluid is lower than the preset temperature, and the well is temporarily shut down until the temperature of the hot dry rock reservoir 21 recovers.

[0108] Please refer to Figure 4 and Figure 5 , Figure 4 is a schematic diagram of the simulated heat extraction temperature field of the cyclic heat extraction method for a branched horizontal well according to an embodiment of the present application; Figure 5 is a schematic diagram of the heat extraction temperature field of a traditional branched horizontal well. The above fluid circulation steps are used for simulation tests. By comparing the cyclic heat extraction method for the branched horizontal well proposed in the present application with the heat extraction of the traditional branched well, the numerical simulation results show that the heat extraction area of the cyclic heat extraction system for the branched horizontal well proposed in the present application is much larger than that of the traditional branched well, and the heat extraction efficiency and economic benefits are high.

[0109] In the description of the present application, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0110] In the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or communicable with each other; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0111] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0112] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting this application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A cyclic heat extraction method for a branched horizontal well, characterized in that, The cyclic heat recovery method of the branch horizontal well includes: Drilling a branch horizontal well, wherein the branch horizontal well comprises a vertical well section (11) and at least two horizontal well sections (12) extending circumferentially outward from the vertical well section (11); An injection pipe (30) is lowered into the vertical well section (11) to form a production channel (111) between the injection pipe (30) and the wall of the vertical well section (11); A packer (40) is installed at the lower end of the injection pipe (30) to isolate the production channel (111) from the horizontal well section (12); Performing hydraulic fractures (13) on the wall surface of the vertical well section (11) above the packer (40), and performing volume fracture network (14) on the wall surface above the horizontal well section (12), so that the volume fracture network (14) is connected to the hydraulic fractures (13); After injecting the heat extraction fluid into the injection pipe (30), the two ends of the first heat exchange channel (51) of the heat exchange drive device (50) are connected to the upper end of the extraction channel (111) and the injection pipe (30) respectively; The heat exchange driving device (50) is controlled to drive the heat recovery fluid to flow sequentially through the volume fracture network (14), the hydraulic fracture (13), the upper end of the production channel (111), the first heat exchange channel (51) and the injection pipe (30) and to circulate the fluid, so that the heat of the hot dry rock reservoir (21) can be exchanged with the heat storage medium flowing through the second heat exchange channel of the heat exchange driving device (50).

2. The cyclic heat extraction method for a branched horizontal well according to claim 1, wherein The hydraulic fracture (13) is performed on the wall of the vertical well section (11) above the packer (40) and includes: Obtaining the thickness of the hot dry rock reservoir (21); If the thickness of the hot rock reservoirs (21) is less than a predetermined thickness, hydraulic fracturing is performed on the wall of the vertical well section (11) above the hot rock reservoirs (21) to generate hydraulic fractures (13); If the thickness of the plurality of hot rock reservoirs (21) is greater than or equal to a preset thickness, hydraulic fracturing is performed on the wall surface of the vertical well section (11) corresponding to the hot dry rock reservoir (21) to generate hydraulic fractures (13).

3. The cyclic heat extraction method for a branched horizontal well according to claim 1, wherein The method of creating a volume fracture network (14) on the upper wall surface of the horizontal well section (12) includes: Perforations extending upward in a vertical direction are formed on the wall surface on the upper side of the horizontal well section (12), wherein the length of the horizontal well section (12) in the horizontal direction is greater than the length of the hydraulic fracture (13) in the horizontal direction; The perforations are subjected to volume fracturing to form a volume fracture network (14), and the volume fracture network (14) formed by the perforations of the horizontal well section (12) extending beyond the hydraulic fracture (13) is connected to the side of the hydraulic fracture (13) facing away from the vertical well section (11).

4. The cyclic heat extraction method for a branched horizontal well according to claim 1, characterized in that, After the injection pipe (30) is lowered into the vertical well section (11), the method further comprises: Insulating cement slurry is injected into the wellhead of the branch well, and the insulating cement slurry is made to flow through the entire horizontal well section (12).

5. The cyclic heat extraction method for a branched horizontal well according to any one of claims 1 to 4, characterized in that The branch horizontal well circulation heat recovery method further includes: The supply device is controlled to replenish the heat extraction fluid into the injection pipe (30) at preset time intervals.

6. The cyclic heat extraction method for a branched horizontal well according to any one of claims 1 to 4, characterized in that, The branch horizontal well circulation heat recovery method further includes: In the case where the temperature of the heat extraction fluid flowing out of the upper end of the self-extraction channel (111) is lower than the target temperature, the control closes the branch well until the temperature of the hot dry rock reservoir (21) resumes to the preset temperature.

7. The cyclic heat extraction method for a branched horizontal well according to any one of claims 1 to 4, characterized in that, The heat extraction fluid is supercritical carbon dioxide.

8. A cyclic heat extraction system for a branched horizontal well, characterized in that, The circulating heat extraction system of the branch horizontal well is applied to the circulating heat extraction method of the branch horizontal well according to any one of claims 1 to 7, and includes: An injection pipe (30) that can extend into the vertical well section (11), and a heat extraction channel (111) is formed between the injection pipe (30) and the wall surface of the vertical well section (11); A plugging device is installed at the lower end of the injection pipe (30) to isolate the heat extraction channel (111) from the horizontal well section (12); A heat exchange driving device (50) having a first heat exchange channel (51) and a second heat exchange channel. The two ends of the first heat exchange channel (51) are respectively communicated with the upper end of the heat extraction channel (111) and the injection pipe (30), and a heat storage medium is arranged in the second heat exchange channel; the heat exchange driving device (50) is used to drive the heat extraction fluid to flow through the volume fracture network (14), the hydraulic fracture network, the upper end of the heat extraction channel (111), the first heat exchange channel (51) and the injection pipe (30) in sequence and circulate, so that the heat of the hot dry rock reservoir (21) can be exchanged to the heat storage medium flowing through the second heat exchange channel.

9. The cyclic heat extraction system for a branched horizontal well according to claim 8, wherein A heat exchanger (52) and a high-pressure pump (53) are serially connected in sequence from the inlet end to the outlet end on the first heat exchange channel (51), and the second heat exchange channel is arranged in the heat exchanger (52).

10. The cyclic heat extraction system for a branched horizontal well according to claim 9, characterized in that, The heat exchange driving device (50) further includes a supply device (54) arranged between the heat exchanger (52) and the high-pressure pump (53), and the supply device (54) is used to supply the heat extraction fluid into the injection pipe (30).

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