Dry hot rock geothermal well fluid nitrogen multi-stage fracturing system and fracturing method

Abstract

The application discloses a dry hot rock geothermal well liquid nitrogen multistage fracturing system and a fracturing method, and belongs to the technical field of geothermal well fracturing. The dry hot rock geothermal well liquid nitrogen multistage fracturing system comprises a sleeve, an upper setting packer, a lower setting packer and a liquid supply device, and further comprises a separation structure comprising a plurality of setting strips, a sealed cavity formed between the upper setting packer, the lower setting packer and the outer wall of the sleeve and the well wall, and a plurality of mutually isolated separation cavities separated by the plurality of setting strips; the liquid supply device sequentially introduces liquid nitrogen into each separation cavity through a switching valve, when the hydraulic pressure value of the liquid nitrogen in one of the separation cavities reaches a predetermined value, the switching valve is switched to introduce liquid nitrogen into the next separation cavity; and a filtration mechanism is used for pumping and filtering the liquid nitrogen, and then conveying the filtered liquid nitrogen to the liquid supply device. The dry hot rock geothermal well liquid nitrogen multistage fracturing system can prevent fine rock particles generated during fracturing of the rock stratum of the geothermal well from blocking the pores of the rock stratum, thereby improving the permeability of the rock stratum.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal well fracturing, in particular to a dry hot rock geothermal well liquid nitrogen multi-stage fracturing system and a fracturing method. BACKGROUND

[0002] As a new type of energy with great potential, dry hot rock geothermal resources have become the focus of research and development because of their rich reserves, wide distribution, clean and pollution-free, and renewable advantages. Liquid nitrogen fracturing technology, as a new waterless fracturing method, has brought a new solution to the development of dry hot rock geothermal resources.

[0003] Liquid nitrogen is colorless and odorless, has extremely stable chemical properties, is extremely inert, and does not contain water phase, which fundamentally avoids the reservoir damage problems such as water sensitivity and water lock caused by the presence of water phase. Moreover, liquid nitrogen has the characteristics of ultra-low temperature, which can form a large temperature difference with the high-temperature dry hot rock reservoir and produce strong thermal shock. This thermal shock can promote the rapid expansion of the initial fracture in the rock and even induce new fractures, thereby improving the fracturing effect of the reservoir.

[0004] The core components of the existing liquid nitrogen fracturing system include a perfusion head and a liquid supply device. When in use, the perfusion head is lowered into the geothermal well, and the upper and lower seat seals on the perfusion head form a sealed cavity in the geothermal well. Then, the liquid supply device injects high-pressure liquid nitrogen into the sealed cavity, which, by virtue of the mechanical mechanism of liquid nitrogen cooling and fracturing rock and the mechanism of liquid nitrogen fracturing, performs fracturing on the rock formation in the geothermal well. However, in this process, when the liquid nitrogen is just injected into the geothermal well, the temperature of the liquid nitrogen is below zero, while the surface temperature of the rock in the geothermal well is very high. When the liquid nitrogen contacts the high-temperature rock in the rock formation, there is a large temperature difference between the surface of the high-temperature rock and the liquid nitrogen, which can cause the surface layer of the rock to crack and generate fine rock particles. These particles can easily block the pores in the rock formation, thereby reducing the permeability of the rock formation. The reduction of the permeability of the rock formation hinders the flow of underground hot water, which reduces the water yield of the geothermal well and further reduces the exploitation efficiency of geothermal resources to some extent. SUMMARY

[0005] The present application aims to overcome the problems in the prior art and provides a dry hot rock geothermal well liquid nitrogen multi-stage fracturing system, which can improve the permeability of the rock formation during fracturing and thus improve the exploitation efficiency of geothermal resources.

[0006] The present application provides a dry hot rock geothermal well liquid nitrogen multi-stage fracturing system, which comprises a sleeve, an upper seat seal, a lower seat seal and a liquid supply device. The sleeve has a gap between the sleeve and the well wall of the geothermal well. The liquid supply device is used to provide liquid nitrogen, and further comprises:

[0007] The partition structure comprises a plurality of setting strips which are uniformly distributed along the circumference of the sleeve and are in contact with the well wall, and the upper setting device, the lower setting device, the outer wall of the sleeve and the well wall form a sealed cavity, and the plurality of setting strips divide the sealed cavity into a plurality of mutually isolated partition cavities;

[0008] The switching valve is in communication with the liquid supply device and each partition cavity, and the liquid supply device sequentially supplies liquid nitrogen into each partition cavity through the switching valve. When the liquid pressure value of the liquid nitrogen in one of the partition cavities reaches a predetermined value, the switching valve switches to supply liquid nitrogen into the next partition cavity, so as to perform liquid nitrogen fracturing on the well wall region facing each partition cavity.

[0009] Preferably, the switching valve comprises a driving mechanism and a rotating sleeve, the rotating sleeve is rotationally connected in the sleeve and is coaxially arranged with the sleeve, the rotating sleeve is provided with a first liquid passage and a second liquid passage, the first liquid passage is in communication with the liquid supply device, the second liquid passage is in communication with the filtering mechanism, the side wall of the sleeve is provided with a plurality of third liquid passages, each third liquid passage is in communication with one partition cavity, the driving mechanism is connected with the rotating sleeve, and the driving mechanism is used to drive the rotating sleeve to rotate around its own axis when the liquid pressure value in the partition cavity reaches a predetermined value, so as to sequentially connect the first liquid passage and the second liquid passage with different third liquid passages.

[0010] Preferably, the driving mechanism comprises a fixed disc, a sliding rod and a transmission mechanism, the fixed disc is fixedly connected with the inner wall of the sleeve, the liquid supply device is in communication with the first liquid passage through the inner cavity of the sleeve, the fixed disc is provided with a sliding hole in the axial direction of the sleeve, the sliding rod is slidingly connected in the sliding hole, the sliding rod is provided with a first spring outside, and the lower end of the sliding rod is connected with 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, the sliding rod reciprocates along the axial direction of the sleeve under the action of the liquid pressure of the liquid nitrogen and the elastic force of the first spring, so as to drive the rotating sleeve to intermittently rotate through the transmission mechanism, so as to sequentially connect the first liquid passage with each third liquid passage.

[0011] Preferably, the sliding hole is a special-shaped hole, the outer wall of the sliding rod matches the sliding hole, and the sliding hole can limit the rotation of the sliding rod relative to the sleeve. The transmission mechanism comprises a cam groove and a driving slider, the cam groove is arranged on the inner wall of the rotating sleeve, and the driving slider is connected to the bottom end of the sliding rod and is slidingly connected in the cam groove. When the sliding rod drives the driving slider to reciprocate along the axial direction of the sleeve, the driving slider drives the rotating sleeve to intermittently rotate through the cam groove.

[0012] Preferably, the cam groove comprises a plurality of vertical grooves and a plurality of inclined grooves, the plurality of vertical grooves and the plurality of inclined grooves are arranged on the inner wall of the rotating sleeve, the plurality of vertical grooves and the plurality of inclined grooves are arranged in a spaced and connected manner, the length direction of the plurality of vertical grooves is parallel to the axial direction of the rotating sleeve, the distance between the bottom of the head end of the vertical groove and the center of the sliding rod is greater than the distance between the bottom of the tail end of the previous inclined groove and the center of the sliding rod, the distance between the bottom of the tail end of the vertical groove and the center of the sliding rod is less than the distance between the bottom of the head end of the next inclined groove and the center of the sliding rod, and the driving sliding block is in sliding connection with the bottoms of the plurality of vertical grooves and the plurality of inclined grooves.

[0013] Preferably, the bottom end of the sliding rod is provided with a sliding cavity in the radial direction of the sliding rod, the driving sliding block is in sliding connection with the sliding cavity, a second spring is arranged in the sliding cavity, and the second spring is used for applying an elastic force to the driving sliding block towards the inner wall of the rotating sleeve. Under the action of the elastic force of the second spring, the driving sliding block abuts against the bottom of the vertical groove or the bottom of the inclined groove.

[0014] Preferably, when the rotating sleeve rotates, the third liquid passage connected with the first liquid passage and the third liquid passage connected with the second liquid passage are opposite to each other with respect to the central axis of the sleeve.

[0015] Preferably, the liquid supply device comprises a pressurizing pump and a plurality of liquid nitrogen containers, the plurality of liquid nitrogen containers are in communication with the pressurizing pump through a reversing valve, the pressurizing pump is in communication with the inner cavity of the sleeve, the plurality of liquid nitrogen containers each contain liquid nitrogen, and the liquid nitrogen in the plurality of liquid nitrogen containers has a predetermined temperature gradient.

[0016] Preferably, the stationary disc is provided with an annular groove, the annular groove is coaxially arranged with the rotating sleeve, the suction filtration mechanism is in communication with the annular groove, and the second liquid passage is in communication with the annular groove.

[0017] The application further discloses a method for liquid nitrogen fracturing by using the dry hot rock geothermal well liquid nitrogen multi-stage fracturing system.

[0018] The sleeve is lowered into a pre-fracturing position in the geothermal well, and then the liquid nitrogen with a certain pressure is supplied to the switching valve by using the liquid supply device. The liquid nitrogen is first guided to the first separated cavity through the switching valve, so that the rock layer of the well wall region towards the first separated cavity is fractured.

[0019] The liquid pressure value of the liquid nitrogen in the first separated cavity is detected, and when the liquid pressure value of the liquid nitrogen in the first separated cavity reaches a predetermined value, the switching valve is switched to be in communication with the second separated cavity, so that the well wall region towards the second separated cavity is fractured by the liquid nitrogen. At the same time, the first separated cavity is in communication with the suction filtration mechanism through the switching valve, and the suction filtration mechanism performs suction filtration on the liquid nitrogen in the first separated cavity.

[0020] In this way, the rock layers of the whole well wall are cyclically fractured until the permeability of the rock layers of the whole well wall reaches the design requirement.

[0021] Compared with the prior art, the beneficial effects of the present application are: when the dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of the present application is working, liquid nitrogen is first introduced into a separate cavity through a switching valve to fracture the rock layer of the well wall region facing the separate cavity; when the pressure value of the liquid nitrogen in the separate cavity reaches a predetermined value, the switching valve is switched to communicate with the next separate cavity to perform liquid nitrogen fracturing on the well wall region facing it, and the suction and filtration mechanism performs suction and filtration on the liquid nitrogen in the previous separate cavity to remove the fine rock particles generated by the fracturing of the rock layer in this region. In this way, fine rock particles can be prevented from being squeezed into the rock layer pores when liquid nitrogen is injected again in the subsequent process. In this way, the system can perform multiple cycle fracturing on the entire well wall. Since part of the separate cavity is always in contact with liquid nitrogen during the fracturing process, the overall temperature of the rock layer around the well can be reduced through heat conduction, reducing the temperature difference between the liquid nitrogen and the surface of the remaining rock layer during subsequent fracturing, thereby reducing the generation of fine rock particles. Combined with the continuous filtration effect of the suction and filtration mechanism, rock particle blockage of rock layer pores can be prevented to the greatest extent, the permeability of the rock layer can be effectively improved, and the efficiency of geothermal resource exploitation can be improved.

[0022] When the pressure value in the separate cavity into which liquid nitrogen is injected reaches a predetermined value, the driving mechanism drives the rotating sleeve to rotate one station, so that the first liquid passage and the second liquid passage are respectively communicated with different third liquid passages. This design realizes the simultaneous fracturing of one separate cavity and the synchronous suction and filtration of liquid nitrogen in another separate cavity, and through the cyclic and alternating fracturing and filtration process, the generation of rock particles is inhibited and the blockage of pores is prevented, and the permeability of the rock layer is ultimately improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the present application;

[0024] Figure 2 is a structural schematic diagram of the present application in the first working state;

[0025] Figure 3 is a structural schematic diagram of the present application in the first working state;

[0026] Figure 4 is a structural schematic diagram of the present application in the first working state;

[0027] Figure 5 is a structural schematic diagram of the present application in the first working state;

[0028] Figure 6 is a structural schematic diagram of the present application in the first working state;

[0029] BRIEF DESCRIPTION OF DRAWINGS

[0030] 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

[0031] 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.

[0032] 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.

[0033] The working principle of the above embodiments is briefly described below:

[0034] In use, the sleeve 101 is lowered into a pre-fracturing position in the geothermal well 1, and then the liquid nitrogen is supplied to the switching valve 106 by the liquid supply device, and the liquid nitrogen is first supplied to the first separation chamber 105 through the switching valve 106, so as to permeate the rock layer of the well wall region to which the first separation chamber 105 is directed. Under the low-temperature cold impact, high-pressure driving effect and volume expansion effect of the liquid nitrogen, the rock layer fissure is expanded, so as to fracture the rock layer of the region. In this process, the hydraulic detector 902 is used to detect the hydraulic pressure value of the liquid nitrogen in the pipeline 901 in real time. The hydraulic pressure value of the liquid nitrogen in the first separation chamber 105 is proportional to the pressure value of the liquid nitrogen output by the liquid supply device. With the continuous injection of the liquid nitrogen in the first separation chamber 105, the real-time hydraulic pressure value of the liquid nitrogen in the first separation chamber 105 slowly increases, and the hydraulic pressure value of the liquid nitrogen in the pipeline 901 also slowly increases. When the hydraulic pressure value of the liquid nitrogen in the first separation chamber 105 reaches a predetermined value, the hydraulic pressure value of the liquid nitrogen in the pipeline 901 also reaches a certain hydraulic pressure value. At this time, the switching valve 106 is switched to be in communication with the next separation chamber 105 (i.e., the second separation chamber 105), so as to perform liquid nitrogen fracturing on the well wall region to which the next separation chamber 105 is directed. At the same time, the previous separation chamber 105 (i.e., the first separation chamber 105) is in communication with the suction filter mechanism through the switching valve 106, and the suction filter mechanism sucks the liquid nitrogen in the previous separation chamber 105. A large amount of fine rock particles generated during the fracturing of the rock layer are sucked into the suction filter mechanism together with the liquid nitrogen. The suction filter mechanism filters the liquid nitrogen mixed with the fine rock particles, and delivers the filtered liquid nitrogen to the liquid supply device for repeated use. In this way, the geothermal well 1 is cyclically fractured, and in this process, the fine rock particles generated during the fracturing of the rock layer can be prevented from blocking the pores of the rock layer, and the rock layer of the fracturing position of the geothermal well 1 can be ensured to have liquid nitrogen at all times. Under the cooling effect of the liquid nitrogen, the temperature difference between the rock surface and the liquid nitrogen during subsequent fracturing can be reduced, so as to prevent the rock surface layer from being broken due to the large temperature difference during subsequent fracturing, and to inhibit the generation of fine rock particles.

[0035] The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system can prevent the fine rock particles generated during the fracturing of the rock layer of the geothermal well 1 from blocking the pores of the rock layer, so as to improve the permeability of the rock layer and the efficiency of the exploitation of geothermal resources.

[0036] On the basis of the above embodiment, the cyclic liquid nitrogen fracturing and suction filtering of the rock layer of the geothermal well 1 are realized, so as to inhibit the generation of fine rock particles and prevent the fine rock particles from blocking the pores of the rock layer.

[0037] As Figures 1-5As shown in the figure, the switching valve 106 comprises a driving mechanism and a rotating sleeve 201, the rotating sleeve 201 is rotationally connected to the sleeve 101 and coaxially arranged in 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 communicated with the liquid supply device, the second liquid passage hole 203 is communicated with the suction filtering mechanism, the sleeve 101 is provided with a plurality of third liquid passage holes 204 on the side wall, each third liquid passage hole 204 is communicated with one of the separated cavities 105, the driving mechanism is connected with the rotating sleeve 201, and the driving mechanism is used to drive the rotating sleeve 201 to rotate around its own axis when the hydraulic pressure value in the separated cavity 105 reaches a predetermined value, so that the first liquid passage hole 202 and the second liquid passage hole 203 are sequentially communicated with different third liquid passage holes 204.

[0038] The driving mechanism drives the rotating sleeve 201 to rotate, so that the first liquid passage hole 202 on the rotating sleeve 201 is communicated with one of the third liquid passage holes 204 on the side wall of the sleeve 101, and the second liquid passage hole 203 on the rotating sleeve 201 is communicated with another third liquid passage hole 204 on the side wall of the sleeve 101. The liquid nitrogen supplied by the liquid supply device is injected into one of the separated cavities 105 through the first liquid passage hole 202 and the corresponding third liquid passage hole 204, and the well wall area facing the separated cavity 105 is fractured by liquid nitrogen; at the same time, the liquid nitrogen in another separated cavity 105 which has been injected with liquid nitrogen is sucked into the suction filtering mechanism through the third liquid passage hole 204 and the second liquid passage hole 203. When the liquid nitrogen pressure value in the separated cavity 105 reaches a predetermined value, the driving mechanism drives the rotating sleeve 201 to rotate one station, so that the first liquid passage hole 202 is communicated with the next third liquid passage hole 204 (fracturing the area facing the new separated cavity 105), and the second liquid passage hole 203 is synchronously communicated with the next third liquid passage hole 204 (sucking and filtering the liquid nitrogen in the previous separated cavity 105). Through the cycle, the liquid nitrogen fracturing and suction filtering of the geothermal well 1 rock stratum are alternately performed, so as to inhibit the generation of fine rock particles and prevent the rock stratum pores from being blocked by the fine rock particles.

[0039] As a preferred solution, as Figures 2-5As shown in the figure, the driving mechanism comprises a fixed disc 301, a slide rod 302 and a transmission mechanism, the fixed disc 301 is fixedly connected with the inner wall of the sleeve 101, the liquid supply device is communicated with the first liquid hole 202 through the inner cavity of the sleeve 101, the fixed disc 301 is provided with a sliding hole along the axial direction of the sleeve 101, the slide rod 302 is slidingly connected in the sliding hole, the slide rod 302 is externally provided with a first spring 303, the lower end of the slide rod 302 is connected with the inner wall of the rotating sleeve 201 through the transmission mechanism, when the liquid supply device intermittently supplies liquid nitrogen into 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 slide rod 302 reciprocates along the axial direction of the sleeve 101, thereby driving the rotating sleeve 201 to intermittently rotate through the transmission mechanism, so that the first liquid hole 202 is sequentially communicated with each third liquid hole 204. When the liquid supply device passes a certain pressure of liquid nitrogen into the inner cavity of the sleeve 101, the slide rod 302 is driven to move along the axial direction of the sleeve 101 to the side close to the third liquid hole 204 by the liquid nitrogen pressure, and the first spring 303 is compressed. Since the partition cavity 105 is communicated with the inner cavity of the sleeve 101 through the third liquid hole 204 and the first liquid hole 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, the slide rod 302 continuously moves to the side close to the third liquid hole 204, and the compression amount of the first spring 303 increases. 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 to the side away from the third liquid hole 204, so that the slide rod 302 completes an axial reciprocating motion in the sleeve 101. The slide rod 302 drives the rotating sleeve 201 to rotate one station through the transmission mechanism, the driving mechanism only relies on the pressure of the liquid supply device to intermittently supply liquid nitrogen into the inner cavity of the sleeve 101 to drive the rotating sleeve 201 to intermittently rotate, realizes the switching of the fracturing and filtration positions in the geothermal well 1, does not need an additional power device, and can improve the working reliability and persistence of the fracturing system in harsh working conditions.

[0040] As a preferred solution, as Figure 2 and Figure 5As shown in the figure, the sliding hole is a special-shaped hole, the outer wall of the sliding rod 302 matches the sliding hole, the sliding hole can limit the rotation of the sliding rod 302 relative to the sleeve 101, the transmission mechanism includes a cam groove 401 and a driving slider 402, the cam groove 401 is arranged on the inner wall of the rotating sleeve 201, the driving slider 402 is connected to the bottom end of the sliding rod 302, the driving slider 402 is slidingly connected in the cam groove 401, when the sliding rod 302 drives the driving slider 402 to reciprocate along the axial direction of the sleeve 101, the driving slider 402 drives the rotating sleeve 201 to intermittently rotate through the cam groove 401. Since the sliding hole on the fixed disc 301 is a special-shaped hole, the sliding hole can limit the rotation of the sliding rod 302 relative to the fixed disc 301; and the fixed disc 301 is fixedly connected to the inner wall of the sleeve 101, therefore, 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 in the axial direction and does not rotate. Since the driving slider 402 at the bottom end of the sliding rod 302 is slidingly connected in 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 of the fracturing and filtration positions in the geothermal well 1.

[0041] As a preferred solution, as Figure 2 and Figure 5As shown in FIG. 4, the cam groove 401 comprises a plurality of vertical grooves 501 and a plurality of inclined grooves 502, which are arranged on the inner wall of the rotating sleeve 201. The plurality of vertical grooves 501 and the plurality of inclined grooves 502 are arranged in an alternating manner. The length direction of each vertical groove 501 is parallel to the axial direction of the rotating sleeve 201. The distance between the bottom of the first vertical groove 501 and the axis of the sliding rod 302 is greater than the distance between the bottom of the last inclined groove 502 and the axis of the sliding rod 302. The distance between the bottom of the last vertical groove 501 and the axis of the sliding rod 302 is less than the distance between the bottom of the first inclined groove 502 and the axis of the sliding rod 302. The driving sliding block 402 is in sliding connection with the bottoms of the vertical grooves 501 and the inclined grooves 502. When the sliding rod 302 reciprocates along the sleeve 101, the driving sliding block 402 slides in the vertical grooves 501 or the inclined grooves 502. Due to the alternating arrangement of the plurality of vertical grooves 501 and the plurality of inclined grooves 502, the driving sliding block 402 can sequentially slide from the vertical grooves 501 into the inclined grooves 502, and then from the inclined grooves 502 into the next vertical grooves 501. Because the distance between the bottom of the first vertical groove 501 and the axis of the sliding rod 302 is greater than the distance between the bottom of the last inclined groove 502 and the axis of the sliding rod 302, and the distance between the bottom of the last vertical groove 501 and the axis of the sliding rod 302 is less than the distance between the bottom of the first inclined groove 502 and the axis of the sliding rod 302, the structure of the cam groove 401 can limit the driving sliding block 402 to slide in only one direction, thereby driving the rotating sleeve 201 to rotate in one direction relative to the sleeve 101, avoiding the disorder of the fracturing and filtration positions in the geothermal well 1 caused by the reverse rotation of the rotating sleeve 201, and ensuring the efficiency and sustainability of the fracturing system.

[0042] As a preferred solution, as shown in FIG. 5, Figure 2 and Figure 5 As shown in FIG. 6, the bottom end of the sliding rod 302 is provided with a sliding cavity 601 in the radial direction of the sliding rod 302, and the driving sliding block 402 is in sliding connection with the sliding cavity 601. A second spring 602 is arranged in the sliding cavity 601, and is used to apply an elastic force to the driving sliding block 402 towards the inner wall of the rotating sleeve 201. Under the action of the elastic force of the second spring 602, the driving sliding block 402 abuts against the bottom of the vertical groove 501 or the inclined groove 502. The driving sliding block 402 can move in the radial direction of the rotating sleeve 201 in the sliding cavity 601, and the second spring 602 applies an elastic force to the driving sliding block 402 towards the inner wall of the rotating sleeve 201, so that the driving sliding block 402 always abuts against the bottom of the vertical groove 501 or the inclined groove 502. In combination with the special structure of the vertical groove 501 and the inclined groove 502, the reverse rotation of the rotating sleeve 201 can be further prevented, and the disorder of the fracturing and filtration positions in the geothermal well 1 can be avoided.

[0043] As a preferred solution, as shown in FIG. 7, Figure 4As shown in the figure, the third liquid passage 204 connected with the first liquid passage 202 and the third liquid passage 204 connected with the second liquid passage 203 are symmetrically opposite to the central axis of the sleeve 101 when the rotating sleeve 201 rotates. The third liquid passage 204 connected with the first liquid passage 202 and the third liquid passage 204 connected with the second liquid passage 203 are symmetrically distributed relative to the central axis of the sleeve 101 when the rotating sleeve 201 rotates. The symmetric design uniformly spaces the fracturing position and the filtration position in the geothermal well 1, ensures that the liquid nitrogen in the fracturing area has sufficient time to act on the rock formation (such as sufficient cooling to crack), thereby ensuring the fracturing effect of the geothermal well 1.

[0044] As a preferred solution, as shown in the figure, Figure 6 As shown in the figure, the liquid supply device includes a plurality of liquid nitrogen tanks 701 and a pressure pump 702, the plurality of liquid nitrogen tanks 701 are connected with the pressure pump 702 through a reversing valve 703, the pressure pump 702 is connected with the inner cavity of the sleeve 101, each of the plurality of liquid nitrogen tanks 701 contains liquid nitrogen, and the liquid nitrogen in the plurality of liquid nitrogen tanks 701 has a predetermined temperature gradient. The pressure pump 702 pressurizes the liquid nitrogen in the plurality of liquid nitrogen tanks 701 with a predetermined temperature gradient in sequence and then delivers the liquid nitrogen to the partition cavity 105 to fracture the rock formation in the geothermal well 1. The rock formation is gradually cooled by the liquid nitrogen with a gradient temperature, which can further reduce the temperature difference between the rock surface and the liquid nitrogen, thereby reducing the generation of fine rock particles.

[0045] As a preferred solution, as shown in the figure, Figure 3 As shown in the figure, the second liquid passage 203 is connected with the annular groove 8, and the filtration mechanism is connected with the annular groove 8. When the rotating sleeve 201 rotates relative to the fixed disc 301, the annular groove 8 can ensure that the second liquid passage 203 is always connected with the filtration mechanism, avoiding interruption of the filtration work during the rotation of the rotating sleeve 201, and ensuring the continuity of the filtration.

[0046] As a preferred solution, as shown in the figure, Figure 1 As shown in the figure, the upper packer 102, the lower packer 103 and the plurality of packer strips 104 are detachably connected with the side wall of the sleeve 101. The upper packer 102, the lower packer 103 and the plurality of packer strips 104 are detachably connected with the side wall of the sleeve 101, which facilitates the maintenance and replacement of the upper packer 102, the lower packer 103 and the packer strips 104, thereby ensuring the reliability of the fracturing system.

[0047] The application also discloses a method for liquid nitrogen fracturing by using the dry hot rock geothermal well liquid nitrogen multi-stage fracturing system.

[0048] The sleeve 101 is lowered to a pre-fracturing position in the geothermal well 1, and then a certain pressure of liquid nitrogen is supplied to the switching valve 106 by means of the liquid supply device, and the liquid nitrogen is first guided to the first partition chamber 105 through the switching valve 106, so as to fracture the rock stratum of the well wall region to which the first partition chamber 105 is directed;

[0049] The liquid pressure value of the liquid nitrogen in the first partition chamber 105 is detected, and when the liquid pressure value of the liquid nitrogen in the first partition chamber 105 reaches a predetermined value, the switching valve 106 is switched to be in communication with the second partition chamber 105, so as to perform liquid nitrogen fracturing on the well wall region to which the second partition chamber 105 is directed, and at the same time, the first partition chamber 105 is in communication with the suction filtering mechanism through the switching valve 106, and the suction filtering mechanism performs suction filtering on the liquid nitrogen in the first partition chamber 105;

[0050] In this way, the rock stratum of the whole well wall of the geothermal well 1 is cyclically fractured until the permeability of the rock stratum of the whole well wall of the geothermal well 1 reaches the design requirement.

[0051] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application.

Claims

1. A dry hot rock geothermal well liquid nitrogen multi-stage fracturing system comprising a sleeve, an upper packer, a lower packer and a liquid supply, the sleeve leaving a gap between the sleeve and the well wall of the geothermal well, the liquid supply being for providing liquid nitrogen, characterised in that, Also comprising: a partition structure comprising a plurality of setting-off strips, the plurality of setting-off strips are uniformly distributed along the circumference of the sleeve and are in contact with the well wall, the upper setting-off device, the lower setting-off device, the outer wall of the sleeve and the well wall form a sealed cavity, and the plurality of setting-off strips divide the sealed cavity into a plurality of mutually isolated partition cavities; a switching valve in communication with the liquid supply device and each partition cavity, the liquid supply device sequentially supplies liquid nitrogen into each partition cavity through the switching valve, when the liquid pressure value of the liquid nitrogen in one of the partition cavities reaches a predetermined value, the switching valve switches to supply liquid nitrogen into the next partition cavity, thereby fracturing the well wall region facing each partition cavity with liquid nitrogen; and a suction filtration mechanism in communication with the liquid supply device, each partition cavity after being injected with liquid nitrogen is sequentially connected to the suction filtration mechanism through the switching valve, the suction filtration mechanism is used to suck and filter the liquid nitrogen, and then deliver the filtered liquid nitrogen to the liquid supply device; the switching valve comprises a driving mechanism and a rotating sleeve, the rotating sleeve is rotationally connected in the sleeve and coaxially arranged with the sleeve, the rotating sleeve is provided with a first liquid passage and a second liquid passage, the first liquid passage is in communication with the liquid supply device, the second liquid passage is in communication with the suction filtration mechanism, the side wall of the sleeve is provided with a plurality of third liquid passages, each third liquid passage is in communication with one partition cavity, the driving mechanism is connected with the rotating sleeve, and the driving mechanism is used to drive the rotating sleeve to rotate around its own axis when the liquid pressure value in the partition cavity reaches a predetermined value, so that the first liquid passage and the second liquid passage are sequentially connected with different third liquid passages.

2. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 1, wherein, the driving mechanism comprises a fixed disc, a sliding rod and a transmission mechanism, the fixed disc is fixedly connected with the inner wall of the sleeve, the liquid supply device is connected with the first liquid passage through the inner cavity of the sleeve, the fixed disc is provided with a sliding hole in the axial direction of the sleeve, the sliding rod is slidingly connected in the sliding hole, the sliding rod is provided with a first spring outside, and the lower end of the sliding rod is connected with 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, the sliding rod reciprocates along the axial direction of the sleeve under the action of the liquid pressure of the liquid nitrogen and the elastic force of the first spring, thereby driving the rotating sleeve to intermittently rotate through the transmission mechanism, so that the first liquid passage is sequentially connected with each third liquid passage.

3. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 2, wherein, the sliding hole is a special-shaped hole, the outer wall of the sliding rod matches the sliding hole, and the sliding hole can limit the rotation of the sliding rod relative to the sleeve, the transmission mechanism comprises a cam groove and a driving slider, the cam groove is arranged on the inner wall of the rotating sleeve, and the driving slider is connected with the bottom end of the sliding rod and slidingly connected in the cam groove, when the sliding rod drives the driving slider to reciprocate along the axial direction of the sleeve, the driving slider drives the rotating sleeve to intermittently rotate through the cam groove.

4. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 3, wherein, the cam groove comprises a plurality of vertical grooves and a plurality of inclined grooves, the plurality of vertical grooves and the plurality of inclined grooves are arranged on the inner wall of the rotating sleeve, the plurality of vertical grooves and the plurality of inclined grooves are arranged in a spaced and connected manner, the length direction of the plurality of vertical grooves is parallel to the axial direction of the rotating sleeve, the distance between the groove bottom of the head end of the vertical groove and the axis of the sliding rod is greater than the distance between the groove bottom of the tail end of the previous inclined groove and the axis of the sliding rod, the distance between the groove bottom of the tail end of the vertical groove and the axis of the sliding rod is less than the distance between the groove bottom of the head end of the next inclined groove and the axis of the sliding rod, and the driving slider is slidingly connected with the groove bottoms of the plurality of vertical grooves and the plurality of inclined grooves.

5. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 4, wherein, The bottom end of the slide rod is provided with a slide cavity in the radial direction of the slide rod, the driving slide block is slidably connected in the slide cavity, the slide cavity is provided with a second spring, the second spring is used for applying an elastic force to the driving slide block towards the inner wall of the rotating sleeve, and under the action of the elastic force of the second spring, the driving slide block abuts against the groove bottom of the vertical groove or the groove bottom of the inclined groove.

6. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 1, wherein, The third liquid passage communicated with the first liquid passage and the third liquid passage communicated with the second liquid passage are opposite to the central axial plane of the sleeve in symmetry when the rotating sleeve rotates.

7. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 1, wherein, The liquid supply device comprises a pressurizing pump and a plurality of liquid nitrogen bins, the plurality of liquid nitrogen bins are communicated with the pressurizing pump through a reversing valve, the pressurizing pump is communicated with the inner cavity of the sleeve, the plurality of liquid nitrogen bins each contain liquid nitrogen, and the liquid nitrogen in the plurality of liquid nitrogen bins has a predetermined temperature gradient.

8. The dry hot rock geothermal well liquid nitrogen multi-stage fracturing system of claim 2, wherein, The fixed disc is provided with an annular groove coaxially arranged with the rotating sleeve, the suction filter mechanism is communicated with the annular groove, and the second liquid passage is communicated with the annular groove.

9. A method for liquid nitrogen fracturing using the dry hot rock geothermal well liquid nitrogen multi-stage fracturing system according to claim 1, characterized in that, The method comprises the following steps: The sleeve is lowered into a pre-fracturing position in the geothermal well, then the liquid nitrogen with a certain pressure is supplied to the switching valve by the liquid supply device, the liquid nitrogen is first communicated to the first separated cavity through the switching valve, so as to fracture the rock stratum of the well wall region towards which the first separated cavity is directed; The liquid pressure value of the liquid nitrogen in the first separated cavity is detected, when the liquid pressure value of the liquid nitrogen in the first separated cavity reaches a predetermined value, the switching valve is switched to be communicated with the second separated cavity, so as to perform liquid nitrogen fracturing on the well wall region towards which the second separated cavity is directed, at the same time, the first separated cavity is communicated with the suction filter mechanism through the switching valve, and the suction filter mechanism performs suction filtration on the liquid nitrogen in the first separated cavity; The rock stratum of the whole well wall of the geothermal well is cyclically fractured until the permeability of the rock stratum of the whole well wall of the geothermal well reaches a design requirement.

Images