Liquid nitrogen multi-stage fracturing system and fracturing method for hot dry rock geothermal well

Abstract

The invention discloses a liquid nitrogen multi-stage fracturing system and method for a hot dry rock geothermal well, and belongs to the technical field of geothermal well fracturing. The liquid nitrogen multi-stage fracturing system for the hot dry rock geothermal well comprises a sleeve, an upper setting device, a lower setting device and a liquid supply device, and further comprises a separation structure comprising a plurality of setting strips, a sealing cavity is formed among the upper setting device, the lower setting device, the outer wall of the sleeve and the well wall, and the multiple setting strips divide the sealing cavity into a plurality of mutually isolated separation cavities; the liquid supply device sequentially introduces liquid nitrogen into each separation cavity through a switching valve, and when the hydraulic value of the liquid nitrogen in one separation cavity reaches a preset value, the switching valve is switched to introduce the liquid nitrogen into the next separation cavity; the suction filtration mechanism is used for sucking and filtering liquid nitrogen and then conveying the filtered liquid nitrogen to the liquid supply device. According to the liquid nitrogen multi-stage fracturing system for the hot dry rock geothermal well, when a rock stratum of the geothermal well is fractured, generated fine rock particles are prevented from blocking holes of the rock stratum, and therefore the permeability of the rock stratum is improved.

Description

Technical Field

[0001] This invention relates to the field of geothermal well fracturing technology, specifically to a liquid nitrogen multi-stage fracturing system and fracturing method for dry hot rock geothermal wells. Background Technology

[0002] Hot dry rock geothermal resources, as a highly promising new energy source, stand out among numerous energy options due to their abundant reserves, wide distribution, clean and pollution-free nature, and renewable nature, making them a focal area for research and development. Liquid nitrogen fracturing technology, as an emerging waterless fracturing method, has brought new solutions to the development of hot dry rock geothermal resources.

[0003] Liquid nitrogen is colorless and odorless, chemically extremely stable, and highly inert. It contains no aqueous phase, fundamentally avoiding reservoir damage issues such as water sensitivity and water lock-up that can occur due to the presence of an aqueous phase. Furthermore, liquid nitrogen's ultra-low temperature properties create a significant temperature difference with the high-temperature, dry rock reservoir, generating a powerful thermal shock. This thermal shock can rapidly expand initial fractures within the rock and even induce new fractures, thus improving the effectiveness of reservoir fracturing.

[0004] The core components of existing liquid nitrogen fracturing systems include an injection head and a liquid supply device. During operation, the injection head is lowered into the geothermal well. The upper and lower setting devices on the injection head create a sealed cavity within the well. High-pressure liquid nitrogen is then injected into this cavity through the liquid supply device. The system utilizes the mechanical mechanism of liquid nitrogen cooling and fracturing the rock, along with the fracturing mechanism itself, to fracture the rock formations within the well. However, when the liquid nitrogen is first injected into the well, its temperature is below zero degrees Celsius, while the surface temperature of the rock within the well is extremely high. This creates a significant temperature difference between the liquid nitrogen and the hot rock surface, causing the rock surface to fracture and produce fine rock particles. These particles can easily clog the pores within the rock formation, reducing its permeability. Reduced permeability hinders the flow of geothermal water, decreasing the well's output and consequently reducing the efficiency of geothermal resource extraction. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems in the prior art and provide a liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells, which can improve the permeability of the rock formations during fracturing of geothermal wells, thereby improving the extraction efficiency of geothermal resources.

[0006] This invention provides a liquid nitrogen multi-stage fracturing system for hot dry rock geothermal wells, including a sleeve, an upper setter, a lower setter, and a liquid supply device. A gap is left between the sleeve and the wellbore wall of the geothermal well. The liquid supply device is used to provide liquid nitrogen. The system also includes: The partition structure includes multiple setting strips, which are evenly distributed along the circumference of the sleeve on the outer wall of the sleeve and are all in contact with the well wall. The upper setting device, the lower setting device, the outer wall of the sleeve and the well wall form a sealing cavity, and the multiple setting strips divide the sealing cavity into multiple mutually isolated partition cavities. A switching valve is connected to the liquid supply device and to each compartment. The liquid supply device sequentially introduces liquid nitrogen into each compartment through the switching valve. When the hydraulic pressure of the liquid nitrogen in one compartment reaches a predetermined value, the switching valve switches to introduce liquid nitrogen into the next compartment, thereby performing liquid nitrogen fracturing on the well wall area facing each compartment. A filtration mechanism is connected to the liquid supply device. Each compartment after liquid nitrogen injection is sequentially connected to the filtration mechanism through the switching valve. The filtration mechanism is used to draw in and filter the liquid nitrogen, and then transport the filtered liquid nitrogen to the liquid supply device.

[0007] Preferably, the switching valve includes a drive mechanism and a rotating sleeve. The rotating sleeve is rotatably connected inside the sleeve and coaxially arranged with the sleeve. The rotating sleeve is provided with a first liquid passage hole and a second liquid passage hole. The first liquid passage hole communicates with the liquid supply device, and the second liquid passage hole communicates with the suction filtration mechanism. The side wall of the sleeve is provided with a plurality of third liquid passage holes, each of which communicates with a partition cavity. The drive mechanism is connected to the rotating sleeve and is used to drive the rotating sleeve to rotate around its own axis when the hydraulic pressure value in the partition cavity reaches a predetermined value, so that the first liquid passage hole and the second liquid passage hole communicate sequentially with different third liquid passage holes.

[0008] Preferably, the driving mechanism includes a fixed plate, a sliding rod, and a transmission mechanism. The fixed plate is fixedly connected to the inner wall of the sleeve. The liquid supply device communicates with the first liquid passage hole through the inner cavity of the sleeve. The fixed plate is provided with a sliding hole along the axial direction of the sleeve. The sliding rod is slidably connected in the sliding hole. A first spring is provided outside the sliding rod. The lower end of the sliding rod is connected to the inner wall of the rotating sleeve through the transmission mechanism. When the liquid supply device intermittently supplies liquid nitrogen into the inner cavity of the sleeve, under the action of the liquid nitrogen pressure and the elastic force of the first spring, the sliding rod reciprocates along the axial direction of the sleeve, thereby driving the rotating sleeve to rotate intermittently through the transmission mechanism, so that the first liquid passage hole communicates with each third liquid passage hole in sequence.

[0009] Preferably, the sliding hole is an irregularly shaped hole, and the outer wall of the sliding rod matches the sliding hole. The sliding hole can restrict the rotation of the sliding rod relative to the sleeve. The transmission mechanism includes a cam groove and a drive slider. The cam groove is located on the inner wall of the rotating sleeve, and the drive slider is connected to the bottom end of the sliding rod. The drive slider is slidably connected in the cam groove. When the sliding rod drives the drive slider to reciprocate along the axial direction of the sleeve, the drive slider drives the rotating sleeve to rotate intermittently through the cam groove.

[0010] Preferably, the cam groove includes multiple vertical grooves and multiple inclined grooves. The multiple vertical grooves and multiple inclined grooves are all provided on the inner wall of the rotating sleeve. The multiple vertical grooves and multiple inclined grooves are spaced apart and connected end to end. The length direction of the multiple vertical grooves is parallel to the axial direction of the rotating sleeve. The distance from the bottom of the first end of the vertical groove to the axis of the slide rod is greater than the distance from the bottom of the last end of the inclined groove to the axis of the slide rod. The distance from the bottom of the last end of the vertical groove to the axis of the slide rod is less than the distance from the bottom of the first end of the inclined groove to the axis of the slide rod. The driving slider is slidably connected to the bottom of the multiple vertical grooves and the bottom of the inclined grooves.

[0011] Preferably, the bottom end of the slide rod is provided with a sliding cavity along the radial direction of the slide rod, the drive slider is slidably connected in the sliding cavity, and a second spring is provided in the sliding cavity. The second spring is used to apply an elastic force toward the inner wall of the rotating sleeve to the drive slider. Under the action of the elastic force of the second spring, the drive slider abuts against the bottom of the vertical groove or the bottom of the inclined groove.

[0012] Preferably, when the rotating sleeve rotates, the third liquid passage connected to the first liquid passage and the third liquid passage connected to the second liquid passage are symmetrical with respect to the central axis of the sleeve.

[0013] Preferably, the liquid supply device includes a pressure pump and multiple liquid nitrogen chambers. The multiple liquid nitrogen chambers are connected to the pressure pump through a reversing valve. The pressure pump is connected to the inner cavity of the sleeve. Each of the multiple liquid nitrogen chambers contains liquid nitrogen, and the liquid nitrogen in the multiple liquid nitrogen chambers has a predetermined temperature gradient.

[0014] Preferably, the fixed plate is provided with an annular groove, the annular groove is coaxially arranged with the rotating sleeve, the suction filtration mechanism is connected to the annular groove, and the second liquid passage hole is connected to the annular groove.

[0015] This invention also discloses a method for liquid nitrogen fracturing using a liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells, comprising the following steps: The sleeve is lowered into the pre-fracturing position inside the geothermal well. Then, liquid nitrogen at a certain pressure is supplied to the switching valve using the liquid supply device. The liquid nitrogen is first passed to the first compartment through the switching valve, thereby fracturing the rock strata in the well wall area facing the first compartment. The hydraulic pressure value of liquid nitrogen in the first compartment is detected. When the hydraulic pressure value of liquid nitrogen in the first compartment reaches a predetermined value, the switching valve is switched to connect with the second compartment, thereby performing liquid nitrogen fracturing on the well wall area facing the second compartment. At the same time, the first compartment is connected to the filtration mechanism through the switching valve, and the filtration mechanism performs suction and filtration on the liquid nitrogen in the first compartment. This process is repeated until the permeability of the rock strata surrounding the geothermal well reaches the design requirements.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: When the liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells of this invention is working, liquid nitrogen is first introduced into a partitioned chamber through a switching valve to fracture the rock strata in the well wall area facing that partitioned chamber. When the pressure value of the liquid nitrogen in that partitioned chamber reaches a predetermined value, the switching valve switches to connect with the next partitioned chamber to perform liquid nitrogen fracturing in the well wall area it faces. Simultaneously, a filtration mechanism suctions and filters the liquid nitrogen in the previous partitioned chamber to remove free fine rock particles generated during rock fracturing in that area. In this way, it is possible to avoid fine rock particles being squeezed into the pores of the rock strata when liquid nitrogen is subsequently injected into the previous partitioned chamber. This process is repeated, and the system can perform multiple cyclic fracturing cycles around the entire geothermal well. Because some partitioned chambers remain in contact with liquid nitrogen throughout the fracturing process, heat conduction can reduce the overall temperature of the rock strata around the geothermal well, reducing the temperature difference between the liquid nitrogen and the remaining rock strata surfaces during subsequent fracturing, thereby reducing the generation of fine rock particles. Combined with the continuous filtration effect of the filtration mechanism, it can prevent rock particles from clogging the pores of the rock layer to the greatest extent, effectively improve the permeability of the rock layer, and thus improve the efficiency of geothermal resource extraction.

[0017] When the pressure inside the liquid nitrogen-injected compartment reaches a predetermined value, the drive mechanism rotates the rotating sleeve one position, connecting the first and second liquid passages to different third liquid passages. This design allows one compartment to perform fracturing operations while another compartment simultaneously performs liquid nitrogen suction and filtration. Through the alternating fracturing and filtration processes, the generation of rock particles is synergistically suppressed and their clogging of pores is prevented, ultimately improving the permeability of the rock formation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the internal structure of the first working state of the present invention; Figure 3 This is a schematic diagram of the AA surface of the present invention; Figure 4 This is a schematic diagram of the BB surface of the present invention; Figure 5 This is a schematic diagram of the internal structure of the second working state of the present invention; Figure 6 This is a schematic diagram of the liquid supply device of the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Geothermal well; 101. Sleeve; 102. Upper setting device; 103. Lower setting device; 104. Setting strip; 105. Separating chamber; 106. Switching valve; 201. Rotating sleeve; 202. First fluid passage; 203. Second fluid passage; 204. Third fluid passage; 301. Fixed plate; 302. Sliding rod; 303. First spring; 401. Cam groove; 402. Drive slider; 501. Vertical groove; 502. Inclined groove; 601. Sliding cavity; 602. Second spring; 701. Liquid nitrogen tank; 702. Pressurizing pump; 703. Reversing valve; 8. Annular groove; 901. Pipeline; 902. Hydraulic detector. Detailed Implementation

[0020] The following is in conjunction with the appendix Figures 1-6 The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] like Figures 1-6 As shown, the present invention provides a liquid nitrogen multi-stage fracturing system for a hot dry geothermal well, comprising a sleeve 101, an upper setter 102, a lower setter 103, a liquid supply device, and a hydraulic detector 902. A gap is left between the sleeve 101 and the well wall of the geothermal well 1. The upper setter 102 is located at the upper end of the sleeve 101, and the lower setter 103 is located at the lower end of the sleeve 101. The liquid supply device is used to provide liquid nitrogen at a predetermined pressure through the pipeline 901. The hydraulic detector 902 is used to detect the hydraulic pressure value of the liquid nitrogen in the pipeline 901 in real time. The system also includes a partition structure, a switching valve 106, and a filtration mechanism. The partition structure includes multiple setting strips 104, which are evenly distributed along the circumference of the sleeve 101 on the outer wall of the sleeve 101 and are all in contact with the well wall. The upper setter 102, lower setter 103, upper setter 104, lower setter 105, and lower setter 106 are all located at the lower end of the sleeve 101. The liquid supply device is used to provide liquid nitrogen at a predetermined pressure through the pipeline 901. The hydraulic detector 902 is used to detect the hydraulic pressure value of the liquid nitrogen in the pipeline 901 in real time. The system also includes a partition structure, a switching valve 106, and a filtration mechanism. The partition structure includes multiple setting strips 104, which are evenly distributed along the circumference of the sleeve 101 on the outer wall of the sleeve 101 and are all in contact with the well wall. The upper setter 102, lower setter 103, and lower setter 104 are all in contact with the well wall. The upper setter 102, lower setter 103, and lower setter 104 are all in contact with the A sealed cavity is formed between the outer wall of the device 103 and the sleeve 101 and the well wall. Multiple seated seals 104 divide the sealed cavity into multiple mutually isolated partition cavities 105. The switching valve 106 is connected to the liquid supply device and is connected to each partition cavity 105. The liquid supply device sequentially introduces liquid nitrogen into each partition cavity 105 through the switching valve 106. When the hydraulic pressure value of the liquid nitrogen in one partition cavity 105 reaches a predetermined value, the switching valve 106 switches to introduce liquid nitrogen into the next partition cavity 105, thereby performing liquid nitrogen fracturing on the well wall area facing each partition cavity 105. The filtration mechanism is connected to the liquid supply device. Each partition cavity 105 after liquid nitrogen injection is sequentially connected to the filtration mechanism through the switching valve 106. The filtration mechanism is used to draw and filter liquid nitrogen, and then transport the filtered liquid nitrogen to the liquid supply device.

[0022] The working principle of the above embodiments is briefly described below: In operation, the fracturing system involves lowering the sleeve 101 into the pre-fracturing position within the geothermal well 1. Then, a liquid nitrogen supply device supplies liquid nitrogen at a certain pressure to the switching valve 106. The liquid nitrogen, through the switching valve 106, first flows to the first partition chamber 105, thereby penetrating the rock formation in the wellbore area facing that partition chamber 105. Under the effects of low-temperature cold impact, high-pressure driving, and volume expansion of the liquid nitrogen, the fractures in the rock formation are expanded, thus fracturing the rock formation in that area. During this process, the hydraulic pressure gauge 902 is used to monitor the real-time hydraulic pressure value of the liquid nitrogen in the pipeline 901. The hydraulic pressure value of the liquid nitrogen in the first partition chamber 105 is proportional to the pressure value of the liquid nitrogen output from the supply device. As liquid nitrogen is continuously injected into the partition chamber 105, the real-time hydraulic pressure value of the liquid nitrogen in the first partition chamber 105 will slowly increase. The hydraulic pressure of the liquid nitrogen in compartment 1 will also increase slowly. When the hydraulic pressure of the liquid nitrogen in compartment 105 reaches a predetermined value, the hydraulic pressure of the liquid nitrogen in pipe 901 will also reach a certain value. At this time, the switching valve 106 switches to connect with the next compartment 105 (i.e., the second compartment 105), so as to perform liquid nitrogen fracturing on the well wall area facing the next compartment 105. At the same time, the previous compartment 105 (the first compartment 105) is connected to the filtration mechanism through the switching valve 106. The filtration mechanism draws liquid nitrogen from the previous compartment 105. A large number of free fine rock particles generated during rock fracturing are drawn into the filtration mechanism along with the liquid nitrogen. The filtration mechanism filters the liquid nitrogen mixed with fine rock particles and delivers the filtered liquid nitrogen to the liquid supply device for reuse. This process is repeated to allow for cyclic fracturing of the entire circumference of geothermal well 1. During this process, it prevents the fine rock particles generated during fracturing from clogging the pores and ensures that there is always liquid nitrogen in the rock strata at the fracturing location of geothermal well 1. Under the cooling effect of liquid nitrogen, the temperature difference between the rock surface and liquid nitrogen during subsequent fracturing is reduced, thereby preventing the excessive temperature difference from exacerbating the fragmentation of the rock surface during subsequent fracturing and inhibiting the generation of fine rock particles.

[0023] The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells of the present invention can prevent the generated fine rock particles from clogging the pores of the rock layer when fracturing the rock layer of geothermal well 1, thereby improving the permeability of the rock layer and improving the extraction efficiency of geothermal resources.

[0024] Based on the above embodiments, in order to achieve liquid nitrogen fracturing and suction filtration of the geothermal well 1 rock formation, thereby suppressing the generation of fine rock particles and preventing fine rock particles from clogging the rock formation pores.

[0025] like Figures 1-5As shown, the switching valve 106 includes a drive mechanism and a rotating sleeve 201. The rotating sleeve 201 is rotatably connected inside the sleeve 101 and coaxially arranged with the sleeve 101. The rotating sleeve 201 is provided with a first liquid passage hole 202 and a second liquid passage hole 203. The first liquid passage hole 202 is connected to the liquid supply device, and the second liquid passage hole 203 is connected to the suction filtration mechanism. The side wall of the sleeve 101 is provided with a plurality of third liquid passage holes 204. Each third liquid passage hole 204 is connected to a partition cavity 105. The drive mechanism is connected to the rotating sleeve 201. The drive mechanism is used to drive the rotating sleeve 201 to rotate around its own axis when the hydraulic pressure value in the partition cavity 105 reaches a predetermined value, so that the first liquid passage hole 202 and the second liquid passage hole 203 are connected to different third liquid passage holes 204 in sequence.

[0026] The drive mechanism drives the rotating sleeve 201 to rotate, so that its first liquid passage hole 202 communicates with a third liquid passage hole 204 on the side wall of the sleeve 101, and at the same time, the second liquid passage hole 203 on the rotating sleeve 201 communicates with another third liquid passage hole 204 on the side wall of the sleeve 101. Liquid nitrogen supplied by the liquid supply device is injected into a partition cavity 105 through the first liquid passage hole 202 and the corresponding third liquid passage hole 204, and liquid nitrogen fracturing is performed on the well wall area facing the partition cavity 105; at the same time, liquid nitrogen in another partition cavity 105 that has been injected with liquid nitrogen is sucked into the filtration mechanism for filtration through its communicating third liquid passage hole 204 and second liquid passage hole 203. When the liquid nitrogen pressure in the partition chamber 105 reaches a predetermined value, the drive mechanism drives the rotating sleeve 201 to rotate one position, connecting the first liquid passage 202 with the next third liquid passage 204 (for fracturing the new partition chamber 105 towards the region), and simultaneously connecting the second liquid passage 203 with the next third liquid passage 204 (for filtration of liquid nitrogen in the previous partition chamber 105). Through this cycle, liquid nitrogen fracturing and filtration of the geothermal well 1 rock formation are alternated, thereby suppressing the generation of fine rock particles and preventing them from clogging the pores of the rock formation.

[0027] As a preferred option, such as Figures 2-5As shown, the driving mechanism includes a fixed plate 301, a sliding rod 302, and a transmission mechanism. The fixed plate 301 is fixedly connected to the inner wall of the sleeve 101. The liquid supply device communicates with the first liquid passage hole 202 through the inner cavity of the sleeve 101. The fixed plate 301 is provided with a sliding hole along the axial direction of the sleeve 101. The sliding rod 302 is slidably connected in the sliding hole. A first spring 303 is provided outside the sliding rod 302. The lower end of the sliding rod 302 is connected to the inner wall of the rotating sleeve 201 through the transmission mechanism. When the liquid supply device intermittently supplies liquid nitrogen to the inner cavity of the sleeve 101, under the action of the liquid nitrogen pressure and the elastic force of the first spring 303, the sliding rod 302 reciprocates along the axial direction of the sleeve 101, thereby driving the rotating sleeve 201 to rotate intermittently through the transmission mechanism, so that the first liquid passage hole 202 communicates with each third liquid passage hole 204 in sequence. When the liquid supply device introduces liquid nitrogen at a certain pressure into the inner cavity of the sleeve 101, the liquid nitrogen pressure drives the slide rod 302 to move axially along the sleeve 101 towards the side closer to the third liquid passage 204, and the first spring 303 is compressed. Since the partition cavity 105 is connected to the inner cavity of the sleeve 101 through the third liquid passage 204 and the first liquid passage 202, the liquid nitrogen pressure value in the partition cavity 105 is equal to the liquid nitrogen pressure value in the inner cavity of the sleeve 101; as the liquid nitrogen pressure value in the partition cavity 105 increases, the liquid nitrogen pressure value in the inner cavity of the sleeve 101 increases synchronously, and the slide rod 302 continues to move towards the side closer to the third liquid passage 204, increasing the compression of the first spring 303. When the liquid nitrogen pressure value in the partition cavity 105 reaches a predetermined value, the liquid supply device stops supplying liquid. At this time, the elastic force of the first spring 303 drives the slide rod 302 to move away from the third liquid passage 204, so that the slide rod 302 completes one axial reciprocating motion within the sleeve 101. The slide bar 302 drives the rotating sleeve 201 to rotate one position through the transmission mechanism. This drive mechanism only relies on the pressure of liquid nitrogen intermittently supplied to the inner cavity of the sleeve 101 by the liquid supply device to drive the rotating sleeve 201 to rotate intermittently, realizing the switching between fracturing and filtration positions in the geothermal well 1. No additional power device is required, which can improve the reliability and continuity of the fracturing system under harsh working conditions.

[0028] As a preferred option, such as Figure 2 and Figure 5As shown, the sliding hole is an irregularly shaped hole, and the outer wall of the sliding rod 302 matches the sliding hole. The sliding hole can restrict the rotation of the sliding rod 302 relative to the sleeve 101. The transmission mechanism includes a cam groove 401 and a drive slider 402. The cam groove 401 is provided on the inner wall of the rotating sleeve 201, and the drive slider 402 is connected to the bottom end of the sliding rod 302. The drive slider 402 is slidably connected in the cam groove 401. When the sliding rod 302 drives the drive slider 402 to reciprocate along the axial direction of the sleeve 101, the drive slider 402 drives the rotating sleeve 201 to rotate intermittently through the cam groove 401. Because the sliding hole on the fixed plate 301 is an irregularly shaped hole, it can restrict the rotation of the sliding rod 302 relative to the fixed plate 301. Since the fixed plate 301 is fixedly connected to the inner wall of the sleeve 101, when the liquid nitrogen pressure in the inner cavity of the sleeve 101 and the elastic force of the first spring 303 drive the sliding rod 302 to reciprocate, the sliding rod 302 only moves axially and does not rotate. Furthermore, because the driving slider 402 at the bottom end of the sliding rod 302 is slidably connected to the cam groove 401 on the inner wall of the rotating sleeve 201, the cooperation between the driving slider 402 and the cam groove 401 can drive the rotating sleeve 201 to rotate, thereby realizing the switching between fracturing and filtration positions in the geothermal well 1.

[0029] As a preferred option, such as Figure 2 and Figure 5As shown, the cam groove 401 includes multiple vertical grooves 501 and multiple inclined grooves 502. The multiple vertical grooves 501 and multiple inclined grooves 502 are all provided on the inner wall of the rotating sleeve 201. The multiple vertical grooves 501 and multiple inclined grooves 502 are spaced apart and connected end to end. The length direction of the multiple vertical grooves 501 is parallel to the axial direction of the rotating sleeve 201. The distance from the bottom of the first end of the vertical groove 501 to the axis of the slide rod 302 is greater than the distance from the bottom of the last end of the inclined groove 502 to the axis of the slide rod 302. The distance from the bottom of the last end of the vertical groove 501 to the axis of the slide rod 302 is less than the distance from the bottom of the first end of the inclined groove 502 to the axis of the slide rod 302. The driving slider 402 is slidably connected to the bottom of the multiple vertical grooves 501 and the bottom of the inclined grooves 502. When the slide rod 302 reciprocates along the axial direction of the sleeve 101, the drive slider 402 slides within the vertical groove 501 or inclined groove 502 of the cam groove 401. Since multiple vertical grooves 501 and multiple inclined grooves 502 are spaced apart and connected end-to-end, the drive slider 402 can slide sequentially from the vertical groove 501 into the inclined groove 502, and then from the inclined groove 502 into the next vertical groove 501. Furthermore, because the distance between the beginning of the vertical groove 501 and the axis of the slide rod 302 is greater than the corresponding distance between the end of the previous inclined groove 502, and the distance between the end of the vertical groove 501 and the axis of the slide rod 302 is less than the corresponding distance between the beginning of the next inclined groove 502, this cam groove 401 structure restricts the drive slider 402 to slide only in a single direction, thereby driving the rotating sleeve 201 to rotate unidirectionally relative to the sleeve 101. This prevents the rotating sleeve 201 from reversing, which could cause confusion in the fracturing and filtration positions within the geothermal well 1, ensuring the efficiency and continuity of the fracturing system.

[0030] As a preferred option, such as Figure 2 and Figure 5 As shown, the bottom end of the slide rod 302 is provided with a sliding cavity 601 along the radial direction of the slide rod 302. The driving slider 402 is slidably connected in the sliding cavity 601. A second spring 602 is provided in the sliding cavity 601. The second spring 602 is used to apply an elastic force to the driving slider 402 toward the inner wall of the rotating sleeve 201. Under the action of the elastic force of the second spring 602, the driving slider 402 abuts against the bottom of the vertical groove 501 or the bottom of the inclined groove 502. The driving slider 402 can move radially along the rotating sleeve 201 in the sliding cavity 601. The second spring 602 applies an elastic force to the driving slider 402 toward the inner wall of the rotating sleeve 201, so that the driving slider 402 always abuts against the bottom of the vertical groove 501 or the inclined groove 502. The special structure of the vertical groove 501 and the inclined groove 502 can further prevent the rotating sleeve 201 from reversing, avoiding confusion in the fracturing and filtration positions in the geothermal well 1.

[0031] As a preferred option, such as Figure 4As shown, when the rotating sleeve 201 rotates, the third liquid passage 204 connected to the first liquid passage 202 and the third liquid passage 204 connected to the second liquid passage 203 are symmetrical with respect to the central axis of the sleeve 101. This symmetrical design ensures that the fracturing position and the filtration position within the geothermal well 1 are evenly spaced, guaranteeing that the liquid nitrogen in the fracturing zone has sufficient time to interact with the rock formation (e.g., sufficient cooling to induce fracturing), thereby ensuring the fracturing effect of the geothermal well 1.

[0032] As a preferred option, such as Figure 6 As shown, the liquid supply device includes a pressurizing pump 702 and multiple liquid nitrogen tanks 701. The multiple liquid nitrogen tanks 701 are connected to the pressurizing pump 702 via a reversing valve 703. The pressurizing pump 702 is connected to the inner cavity of the sleeve 101. Each of the multiple liquid nitrogen tanks 701 contains liquid nitrogen, and the liquid nitrogen within the multiple liquid nitrogen tanks 701 has a predetermined temperature gradient. The pressurizing pump 702 sequentially pressurizes the liquid nitrogen with the predetermined temperature gradient in the multiple liquid nitrogen tanks 701 and then delivers it to the partition chamber 105 to fracture the rock formations within the geothermal well 1. By gradually cooling the rock formations with liquid nitrogen at a gradient temperature, the temperature difference between the rock surface and the liquid nitrogen can be further reduced, thereby reducing the generation of fine rock particles.

[0033] As a preferred option, such as Figure 3 As shown, the fixed plate 301 is provided with an annular groove 8, which is coaxially arranged with the rotating sleeve 201. The filtration mechanism is connected to the annular groove 8, and the second liquid passage 203 is connected to the annular groove 8. The annular groove 8 on the fixed plate 301 ensures that the second liquid passage 203 is always connected to the filtration mechanism when the rotating sleeve 201 rotates relative to the fixed plate 301, preventing the rotation of the rotating sleeve 201 from interrupting the filtration operation and ensuring the continuity of filtration.

[0034] As a preferred option, such as Figure 1 As shown, the upper setting device 102, lower setting device 103, and multiple setting strips 104 are all detachably connected to the side wall of the sleeve 101. This detachable connection facilitates maintenance and replacement of the upper setting device 102, lower setting device 103, and setting strips 104, thereby ensuring the reliability of the fracturing system.

[0035] This invention also discloses a method for liquid nitrogen fracturing using a liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells, comprising the following steps: The sleeve 101 is lowered into the pre-fracturing position in the geothermal well 1. Then, liquid nitrogen at a certain pressure is supplied to the switching valve 106 using the liquid supply device. The liquid nitrogen is first passed to the first partition chamber 105 through the switching valve 106, thereby fracturing the rock strata in the well wall area facing the first partition chamber 105. The hydraulic pressure value of liquid nitrogen in the first partition chamber 105 is detected. When the hydraulic pressure value of liquid nitrogen in the first partition chamber 105 reaches a predetermined value, the switching valve 106 switches to connect with the second partition chamber 105, thereby performing liquid nitrogen fracturing on the well wall area facing the second partition chamber 105. At the same time, the first partition chamber 105 is connected to the filtration mechanism through the switching valve 106, and the filtration mechanism performs suction and filtration on the liquid nitrogen in the first partition chamber 105. This process is repeated until the permeability of the rock strata surrounding Geothermal Well 1 reaches the design requirements.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A multi-stage liquid nitrogen fracturing system for a hot dry geothermal well, comprising a sleeve, an upper setter, a lower setter, and a liquid supply device, wherein a gap is left between the sleeve and the wellbore of the geothermal well, and the liquid supply device is used to supply liquid nitrogen, characterized in that, Also includes: The partition structure includes multiple setting strips, which are evenly distributed along the circumference of the sleeve on the outer wall of the sleeve and are all in contact with the well wall. The upper setting device, the lower setting device, the outer wall of the sleeve and the well wall form a sealing cavity, and the multiple setting strips divide the sealing cavity into multiple mutually isolated partition cavities. A switching valve is connected to the liquid supply device and to each compartment. The liquid supply device sequentially introduces liquid nitrogen into each compartment through the switching valve. When the hydraulic pressure of the liquid nitrogen in one compartment reaches a predetermined value, the switching valve switches to introduce liquid nitrogen into the next compartment, thereby performing liquid nitrogen fracturing on the well wall area facing each compartment. A filtration mechanism is connected to the liquid supply device. Each compartment after liquid nitrogen injection is sequentially connected to the filtration mechanism through the switching valve. The filtration mechanism is used to draw in and filter the liquid nitrogen, and then transport the filtered liquid nitrogen to the liquid supply device.

2. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 1, characterized in that, The switching valve includes a drive mechanism and a rotating sleeve. The rotating sleeve is rotatably connected inside the sleeve and coaxially arranged with the sleeve. The rotating sleeve is provided with a first liquid passage hole and a second liquid passage hole. The first liquid passage hole is connected to the liquid supply device, and the second liquid passage hole is connected to the suction filtration mechanism. The side wall of the sleeve is provided with a plurality of third liquid passage holes, each of which is connected to a partition cavity. The drive mechanism is connected to the rotating sleeve and is used to drive the rotating sleeve to rotate around its own axis when the hydraulic pressure value in the partition cavity reaches a predetermined value, so that the first liquid passage hole and the second liquid passage hole are connected to different third liquid passage holes in sequence.

3. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 2, characterized in that, The driving mechanism includes a fixed plate, a sliding rod, and a transmission mechanism. The fixed plate is fixedly connected to the inner wall of the sleeve. The liquid supply device communicates with the first liquid passage hole through the inner cavity of the sleeve. The fixed plate is provided with a sliding hole along the axial direction of the sleeve. The sliding rod is slidably connected in the sliding hole. A first spring is provided outside the sliding rod. The lower end of the sliding rod is connected to the inner wall of the rotating sleeve through the transmission mechanism. When the liquid supply device intermittently supplies liquid nitrogen into the inner cavity of the sleeve, under the action of the liquid nitrogen pressure and the elastic force of the first spring, the sliding rod reciprocates along the axial direction of the sleeve, thereby driving the rotating sleeve to rotate intermittently through the transmission mechanism, so that the first liquid passage hole communicates with each third liquid passage hole in sequence.

4. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 3, characterized in that, The sliding hole is an irregularly shaped hole, and the outer wall of the sliding rod matches the sliding hole. The sliding hole can restrict the rotation of the sliding rod relative to the sleeve. The transmission mechanism includes a cam groove and a drive slider. The cam groove is located on the inner wall of the rotating sleeve, and the drive slider is connected to the bottom end of the sliding rod. The drive slider is slidably connected in the cam groove. When the sliding rod drives the drive slider to reciprocate along the axial direction of the sleeve, the drive slider drives the rotating sleeve to rotate intermittently through the cam groove.

5. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 4, characterized in that, The cam groove includes multiple vertical grooves and multiple inclined grooves. The multiple vertical grooves and multiple inclined grooves are all located on the inner wall of the rotating sleeve. The multiple vertical grooves and multiple inclined grooves are spaced apart and connected end to end. The length direction of the multiple vertical grooves is parallel to the axis of the rotating sleeve. The distance from the bottom of the first end of the vertical groove to the axis of the slide rod is greater than the distance from the bottom of the last end of the inclined groove to the axis of the slide rod. The distance from the bottom of the last end of the vertical groove to the axis of the slide rod is less than the distance from the bottom of the first end of the inclined groove to the axis of the slide rod. The driving slider is slidably connected to the bottom of the multiple vertical grooves and the bottom of the inclined grooves.

6. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 5, characterized in that, The bottom end of the slide rod is provided with a sliding cavity along the radial direction of the slide rod. The drive slider is slidably connected in the sliding cavity. A second spring is provided in the sliding cavity. The second spring is used to apply an elastic force toward the inner wall of the rotating sleeve to the drive slider. Under the action of the elastic force of the second spring, the drive slider abuts against the bottom of the vertical groove or the bottom of the inclined groove.

7. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 2, characterized in that, When the rotating sleeve rotates, the third liquid passage connected to the first liquid passage and the third liquid passage connected to the second liquid passage are symmetrical with respect to the central axis of the sleeve.

8. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 1, characterized in that, The liquid supply device includes a pressure pump and multiple liquid nitrogen chambers. The multiple liquid nitrogen chambers are connected to the pressure pump through a reversing valve. The pressure pump is connected to the inner cavity of the sleeve. Each of the multiple liquid nitrogen chambers contains liquid nitrogen, and the liquid nitrogen in the multiple liquid nitrogen chambers has a predetermined temperature gradient.

9. The liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 3, characterized in that, The fixed plate is provided with an annular groove, which is coaxially arranged with the rotating sleeve. The suction filtration mechanism is connected to the annular groove, and the second liquid passage is connected to the annular groove.

10. A method for liquid nitrogen fracturing using the liquid nitrogen multi-stage fracturing system for dry hot rock geothermal wells as described in claim 1, characterized in that, Includes the following steps: The sleeve is lowered into the pre-fracturing position inside the geothermal well. Then, liquid nitrogen at a certain pressure is supplied to the switching valve using the liquid supply device. The liquid nitrogen is first passed to the first compartment through the switching valve, thereby fracturing the rock strata in the well wall area facing the first compartment. The hydraulic pressure value of liquid nitrogen in the first compartment is detected. When the hydraulic pressure value of liquid nitrogen in the first compartment reaches a predetermined value, the switching valve is switched to connect with the second compartment, thereby performing liquid nitrogen fracturing on the well wall area facing the second compartment. At the same time, the first compartment is connected to the filtration mechanism through the switching valve, and the filtration mechanism performs suction and filtration on the liquid nitrogen in the first compartment. This process is repeated until the permeability of the rock strata surrounding the geothermal well reaches the design requirements.

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