System and method for monitoring cracking position of fracturing crack in drill hole

Abstract

The invention discloses a system for monitoring the cracking position of a fracturing crack in a drill hole, the system comprises a monitoring unit and a data analysis and processing unit, the monitoring unit comprises an end pipe structure, a temperature measurement optical fiber and a connecting pipe structure, the end pipe structure comprises an end pipe and a conical end, the connecting end of the end pipe is provided with a female head structure, and the female head structure is connected with the temperature measurement optical fiber. The invention further discloses a monitoring method for the cracking position of the fracturing crack in the drill hole, through the arrangement of the end pipe structure, the connecting pipe structure and the temperature measuring optical fiber exposed out of the outer side, on-way temperature distribution in the drill hole can be monitored, the temperature measuring optical fiber is arranged in the end pipe structure, the connecting pipe structure and the temperature measuring optical fiber exposed out of the outer side, and the monitoring accuracy of the cracking position of the fracturing crack in the drill hole is improved. According to the principle that the upstream and downstream on-way temperature of the crack can suddenly change, the cracking position of the crack in the drill hole is judged and controlled, and in the staged fracturing mode, whether the crack crossing phenomenon occurs in the fracturing process or not can be effectively judged by positioning the cracking position of the crack in the drill hole after hydraulic fracturing of different fracturing sections.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam hydraulic fracturing monitoring, and in particular provides a monitoring system and method for the cracking position of hydraulic fracturing cracks in a borehole. Background Art

[0002] As an effective measure to increase the permeability of coal seams, hydraulic fracturing technology has been widely used in the coal production industry. Its technical principle is to inject pressurized liquid into the coal body borehole with the help of a high-pressure pump to change the stress state of the coal body around the borehole. When the energy of the high-pressure liquid exceeds the minimum principal stress of the coal body around the borehole, the hole wall will crack and the main crack will expand. At the same time, with the expansion of the main cracks inside the coal body, the water pressure of the cracks penetrates to both sides, forming a seepage water pressure, causing the original joints and fissures to further expand at both ends. The expansion direction is generally parallel to the direction of the maximum principal stress, resulting in a certain angle between the expanded branch cracks and the original fracture surface, which is called a wing-shaped branch crack. After hydraulic fracturing of the coal seam, the crack density in the coal body increases, and the connectivity of the fracture network is improved; on the whole, a fracture network of original joints and fissures, wing-shaped branch cracks and hydraulic main fractures is formed, which improves the permeability of the coal seam, and is beneficial to coal seam gas extraction and mine gas prevention and control. According to the current classification of coal seam hydraulic fracturing technology, it can be divided into full-segment hydraulic fracturing technology and staged hydraulic fracturing technology. Full-segment hydraulic fracturing is to implement full-hole segment fracturing in one go for the entire fracturing borehole; staged hydraulic fracturing is to divide the fracturing borehole into several fracturing sections, and fracturing each fracturing section in a certain order. In comparison, staged hydraulic fracturing produces more cracks in the coal body, so its coal seam permeability enhancement effect is relatively good.

[0003] When hydraulic fracturing a coal seam in sections, control holes are generally arranged at a certain distance on both sides of the fracturing hole to control the expansion range of the cracks around the fracturing borehole. During the fracturing process, when the coal body cracks around the fracturing hole expand to the control hole and are interconnected with the control hole, high-pressure liquid will flow out of the control hole, and the fracturing of the fracturing section can be stopped at this time. By moving the fracturing device in the fracturing hole to the next fracturing section and starting fracturing, when water flows in the control hole, it means that the fracturing of the fracturing section is completed, and the cycle is repeated until all the fracturing sections in the fracturing hole are hydraulically fractured. Analysis shows that the fractures generated by each fracturing section may have a "series" phenomenon in the segmented hydraulic fracturing technology, that is, the fractures generated by the rear fracturing section and the fractures generated by the front fracturing section intersect, so that the high-pressure liquid in the rear fracturing section enters the fractures of the front fracturing section, and then directly connects with the control hole, resulting in a shorter fracture generated by the fracturing section, thereby reducing the coal seam permeability enhancement effect of the fracturing section. At present, there is no corresponding monitoring method for the "seamless fracture" phenomenon that may occur in staged fracturing technology. It can only be analyzed by observing and analyzing the changing pattern of injection pressure during the fracturing process, and its accuracy is questionable. Summary of the invention

[0004] To solve the above problems, the present invention provides a monitoring system and method for the cracking position of hydraulic fractures in a borehole. The distributed optical fiber temperature measurement technology is used to lay temperature measurement optical fibers in the control borehole to measure the temperature changes at different positions in the borehole to analyze and determine the cracking position of hydraulic fractures in the control borehole, thereby providing guidance for subsequent coal seam fracturing. The principle is that after the hydraulic fracture is connected to the control borehole, the temperature upstream and downstream of the cracking position will change suddenly.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a monitoring system for the cracking position of a fracturing crack in a borehole, comprising a monitoring unit and a data analysis and processing unit, wherein the monitoring unit comprises a terminal tube structure, a temperature measuring optical fiber and a connecting tube structure, wherein the terminal tube structure comprises a terminal tube and a tapered terminal, and the tapered terminal is integrally formed at the forward end of the terminal tube, a female structure is provided at the connecting end of the terminal tube, a temperature measuring optical fiber is installed between the tapered terminal and the female structure, an optical fiber exposure window is provided on the outer surface of the terminal tube, and the middle section of the temperature measuring optical fiber is arranged in the optical fiber exposure window;

[0006] The connecting tube structure comprises a connecting tube, one end of which is provided with a female head structure, and the other end of which is provided with a male head structure matching the female head structure, a temperature measuring optical fiber is installed between the male head structure and the female head structure, an optical fiber exposure window is provided on the outer surface of the connecting tube, and the middle section of the temperature measuring optical fiber is arranged in the optical fiber exposure window;

[0007] The end pipe structure and the connecting pipe structure are both provided with air flow channels inside;

[0008] The data analysis and processing unit comprises a connecting line, a host and a display screen. The temperature measuring optical fiber is connected to the host through the connecting line, and the display screen is assembled on the host.

[0009] Further, the terminal tube structure also includes an air outlet, a bracket mounting plate and an optical fiber bracket, the outer circumferential surface of the terminal tube is provided with an air outlet at one end of a tapered terminal, a filter is installed in the air outlet, the inner surface of the terminal tube is evenly fixed with a bracket mounting plate, and the optical fiber bracket is fixedly installed on the inner end of the bracket mounting plate, and the temperature measuring optical fiber passes through the optical fiber bracket, the inner surface of the optical fiber bracket is provided with a through groove connected to the optical fiber exposed window, and the temperature measuring optical fiber is arranged in the optical fiber exposed window after passing through the through groove;

[0010] The internal structure of the connecting pipe structure is the same as the internal structure of the end pipe structure.

[0011] Furthermore, the female head structure includes an interface female head, a track groove, a terminal tube sealing ring groove and a fixing hole. The interface female head is fixedly installed in the middle of the connecting end of the terminal tube, and the interface female head is arranged at one end of the temperature measuring optical fiber. The inner surface of the interface female head is provided with a ventilation hole connected to the airflow channel, the inner surface of the connecting end of the terminal tube is symmetrically provided with a track groove, and the inner end of the inner surface of the track groove is provided with a fixing hole that passes through the terminal tube, and the terminal tube sealing ring groove is opened on the end face of the connecting end of the terminal tube.

[0012] Furthermore, the male head structure includes a connecting rod, a connecting tube, an interface male head, a limit spring and a connecting tube sealing ring groove. The inner surface of the other end of the connecting tube is symmetrically fixedly installed with a connecting rod, the inner surface of the connecting rod is provided with a step groove, and the connecting tube is fixedly installed in the step groove, the interface male head is assembled in the connecting tube, and the interface male head is arranged at the other end of the temperature measuring optical fiber, a limit spring is fixedly installed between the inner surface of the outer end of the connecting rod and the outer surface of the connecting tube, the outer surface of the outer end of the connecting rod is integrally formed with a connecting tooth matching the fixing hole, and the connecting tube sealing ring groove is provided on the other end face of the connecting tube.

[0013] Furthermore, it also includes a quick disassembler, which includes an upper gear plate and a lower gear plate, both of which are L-shaped structures, a movable groove is opened on the upper surface of the vertical rod of the lower gear plate, and the lower surface of the vertical rod of the upper gear plate is movably assembled in the movable groove, a spring is installed between the lower surface of the vertical rod of the upper gear plate and the inner surface of the movable groove, the lower surface of the cross bar of the upper gear plate is integrally formed with upper convex teeth matching the fixing holes, and the upper surface of the cross bar of the lower gear plate is integrally formed with lower convex teeth matching the fixing holes.

[0014] A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole, using a monitoring system for the cracking position of a hydraulic fracturing crack in a borehole as described above, specifically comprises the following steps:

[0015] S1, constructing a fracturing borehole and a control borehole according to the coal seam hydraulic fracturing plan, and constructing a control borehole on both sides of the fracturing borehole;

[0016] S2, before hydraulic fracturing the fracturing boreholes, the monitoring units in the monitoring system are lowered into the two control boreholes one by one, and the monitoring distance is equal to the control borehole depth;

[0017] S3, the monitoring unit is connected with the data analysis and processing unit to form a complete temperature measurement system;

[0018] S4, start the temperature measurement system to monitor the temperature distribution along the control boreholes, and detect the operating status of the monitoring system by injecting high-pressure gas into the control boreholes;

[0019] S5, fracturing the first section of the coal seam by staged hydraulic fracturing, and monitoring the temperature of the control boreholes on both sides thereof along the process by using a monitoring system;

[0020] S6, control the determination and analysis of cracking positions in the borehole;

[0021] S7, stop fracturing and move the fracturing device to the second fracturing section in the fracturing borehole, and at the same time inject high-pressure gas into the control borehole connected to the fracturing crack to clean up the water in the borehole;

[0022] S8, fracturing the second section of the fracturing borehole, monitoring the temperature along the two control boreholes during the fracturing process, and determining whether a "seamless cracking" situation occurs when cracks appear;

[0023] S9, after determining the fracturing position of the third section, repeat steps S6 to S8 until the fracturing of the fracturing borehole is completed.

[0024] Furthermore, in step S2, the process of lowering the monitoring units in the monitoring system into the two control boreholes one by one is as follows:

[0025] First, lower the end pipe structure into the control drill hole, and dock the connecting pipe structure in turn. Before docking, place a sealing ring in the sealing ring groove of the end pipe. Then, when connecting, hold the end pipe with one hand and the connecting pipe with the other hand, align the connecting teeth and the male interface of the connecting pipe with the track groove and the female interface of the end pipe, and dock them with force. When the connecting teeth of the connecting pipe and the fixing hole of the end pipe are docked with each other, the docking of the end pipe and the connecting pipe is completed;

[0026] The same applies to the butt joint between the connecting pipes until the end pipe is lowered to the deepest point of the control borehole;

[0027] Monitoring units were placed in both control boreholes.

[0028] Further, in step S4, the process of injecting high-pressure gas into the control borehole to detect the operating status of the monitoring system is as follows:

[0029] Start the monitoring system to monitor the temperature distribution along the two control boreholes. After the monitoring system stabilizes for 5 minutes, disconnect the connecting line from the connecting pipe, install a reducer at the end of the connecting pipe to connect it to the compressed air pipeline in the tunnel through the air duct, and pressurize the connected pipe with pressurized air. The pressurized air reaches the end pipe through each section of the connecting pipe, enters the control borehole from the air outlet, and is finally pressed out from the orifice of the control borehole. Disconnect after 10 minutes of compressed air, reconnect the main unit to the connecting pipe through the connecting line, and start the monitoring system to check the changes in the monitored temperature of each section in the control borehole. The purpose is to change the temperature in the borehole through compressed air and to test the reliability of the temperature measurement system.

[0030] Furthermore, in step S6, the specific method for determining and analyzing the crack position in the control borehole is:

[0031] When it is monitored during the fracturing process that the temperature of a certain section in a certain control borehole changes significantly and the injection pressure continues to decrease, and water flows in the control borehole, it proves that the fracturing borehole has been interconnected with the control borehole through the fracturing crack. The crack position in the control borehole is judged according to the temperature distribution along the control borehole. The crack is the water supply point. The judgment is based on the principle that the temperature along the upstream and downstream of the water supply point will suddenly change. If the control borehole is an upward borehole, the temperature on the downstream side of the water supply point will drop significantly, and the temperature on the upstream side will not change or change very little. If the borehole is a downward borehole, the temperature on the downstream side of the water supply point will not change or change very little, and the temperature on the upstream side will drop significantly.

[0032] The downstream side of the water supply point is the interval between the crack opening and the control borehole opening, and the upstream side is the interval between the crack opening and the control borehole bottom.

[0033] Further, in step S8, the method for determining whether a "seamless crack" situation occurs when cracks occur is:

[0034] When it is monitored during the second-section fracturing process that the temperature of a certain section in a certain controlled borehole has changed significantly and the injection pressure continues to decrease, and water flows in the controlled borehole, the position of the fracturing cracks formed by the second-section fracturing in the controlled borehole is determined. If the cracking position of the controlled borehole during the second-section fracturing process is the same as the cracking position of the controlled borehole during the first fracturing process, it can be determined and analyzed that a "seamless cracking" phenomenon has occurred. Based on the analysis results, it is determined whether the next fracturing position needs to be adjusted, and corresponding adjustments are made based on the judgment results.

[0035] The beneficial effects of using the present invention are:

[0036] 1. The present invention can effectively complete the docking of the end tube structure and the connecting tube structure, as well as the docking between the temperature measuring optical fibers, by setting the female head structure and the male head structure, so that the monitoring unit can be smoothly placed in the control borehole. At the same time, each section of the temperature measuring optical fiber is partially arranged on the surface of the end tube structure and the connecting tube structure, which can effectively monitor the temperature distribution along the control borehole, and then judge the cracking position in the control borehole according to the temperature change during the hydraulic fracturing process.

[0037] 2. In the subsequent hydraulic fracturing process of staged hydraulic fracturing, the temperature change measured by the monitoring unit can be used to determine the subsequent cracking position in the controlled borehole. When the cracking position is the same as the cracking position in the previous hydraulic fracturing, it can be determined that the "seam-to-seam" phenomenon has occurred during the fracturing process, thereby realizing an effective monitoring method for the "seam-to-seam" phenomenon with high accuracy. At the same time, the fracturing parameters between the fracturing sections in the fracturing borehole can be adjusted according to the occurrence of the "seam-to-seam" phenomenon, thereby reducing and avoiding the occurrence of the "seam-to-seam" phenomenon in the subsequent fracturing process.

[0038] 3. The present invention designs the end tube structure and the connecting tube structure, and arranges an optical fiber bracket and an airflow channel inside. The optical fiber bracket supports and protects the temperature measuring optical fiber, and the airflow channel can circulate air. After completing a fracturing operation, high-pressure air can be pressed along the airflow channel to clean out the accumulated water in the control borehole, thereby making the control borehole in a state of temperature balance, so that the monitoring unit can effectively monitor the temperature change in the next fracturing operation, thereby ensuring the accuracy of the judgment of the crack position in the control borehole. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a stereoscopic diagram of the end tube structure in the first embodiment of the present invention.

[0040] Figure 2 This is a front view of the end tube structure in the first embodiment of the present invention.

[0041] Figure 3 For the present invention Figure 2 Cross-sectional view along the AA direction.

[0042] Figure 4 For the present invention Figure 2 Cross-sectional view along the BB direction.

[0043] Figure 5 For the present invention Figure 2 Cross-sectional view along CC direction.

[0044] Figure 6 For the present invention Figure 2 Cross-sectional view along the DD direction.

[0045] Figure 7 For the present invention Figure 1 A partial enlarged view of part a.

[0046] Figure 8 This is one of the three-dimensional views of the connecting pipe structure in the first embodiment of the present invention.

[0047] Fig. 9 This is the second stereoscopic diagram of the connecting pipe structure in the first embodiment of the present invention.

[0048] Fig.10 For the present invention Figure 8 A partial enlarged view of part b.

[0049] Fig.11 It is a three-dimensional diagram of the quick disassembler in the first embodiment of the present invention.

[0050] Fig.12 This is a front cross-sectional view of the quick disassembler in the first embodiment of the present invention.

[0051] Fig.13 It is a structural diagram of the second embodiment of the present invention.

[0052] The reference numerals include: 1. terminal tube structure, 1001. terminal tube, 1002. tapered terminal, 1003. air outlet, 1004. filter screen, 1005. bracket mounting plate, 1006. optical fiber bracket, 1007. female interface, 1008. track groove, 1009. sealing ring groove of terminal tube, 1010. fixing hole, 1011. ventilation hole, 2. temperature measuring optical fiber, 3. connecting tube structure, 3001. connecting tube, 3002. connecting rod, 3003. connecting cylinder, 3004. male interface, 3005. limit spring, 3006. connecting Connecting teeth, 3007, connecting pipe sealing ring groove, 4, quick disassembler, 4001, upper toothed disc, 4002, lower toothed disc, 4003, upper convex teeth, 4004, lower convex teeth, 4005, spring, 5, fracturing drilling, 6, left control hole, 7, right control hole, 8, front hole sealer, 9, rear hole sealer, 10, fracturing pipe, 11, fracturing hole, 12, high-pressure hose, 13, high-pressure pump, 14, liquid inlet pipe, 15, liquid return pipe, 16, water tank, 17, connecting line, 18, host, 19, display screen, 20, injection pipe, 21, manual pressure pump. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Embodiment 1

[0055] Reference Figures 1 to 10 A monitoring system for the cracking position of a fracturing crack in a borehole includes a monitoring unit and a data analysis and processing unit. The monitoring unit includes an end tube structure 1, a temperature measuring optical fiber 2 and a connecting tube structure 3. The end tube structure 1 includes an end tube 1001 and a tapered end 1002, and the tapered end 1002 is integrally formed at the forward end of the end tube 1001. A female structure is provided at the connecting end of the end tube 1001. A temperature measuring optical fiber 2 is assembled between the tapered end 1002 and the female structure. An optical fiber exposure window is provided on the outer surface of the end tube 1001, and the middle section of the temperature measuring optical fiber 2 is provided in the optical fiber exposure window.

[0056] The tapered end 1002 can reduce the resistance of the end tube structure 1 to movement in the controlled borehole, and is made of stainless steel.

[0057] The optical fiber exposure window is provided to expose the temperature measuring optical fiber 2 and contact the external environment, so as to accurately monitor the temperature of the external environment. The length of the optical fiber exposure window is set to 500 mm, and the length of the optical fiber exposure window can be changed according to actual needs.

[0058] One end of the temperature measuring optical fiber 2 located in the terminal tube structure 1 is fixed at the forward end, and the other end is arranged on the female head structure.

[0059] The temperature measuring optical fiber 2 is mainly composed of an insulating skin and an optical fiber line. The temperature measuring optical fiber 2 is the main component of the monitoring unit. The temperature measuring optical fiber 2 can integrate transmission and temperature sensing. It has the advantages of excellent optical properties, high tensile strength, corrosion resistance, high waterproofness, no metal medium, good pressure resistance, high reliability, and long service life.

[0060] The connecting tube structure 3 includes a connecting tube 3001, one end of which is provided with a female head structure, and the other end of the connecting tube 3001 is provided with a male head structure matching the female head structure, a temperature measuring optical fiber 2 is installed between the male head structure and the female head structure, an optical fiber exposure window is opened on the outer surface of the connecting tube 3001, and the middle section of the temperature measuring optical fiber 2 is arranged in the optical fiber exposure window.

[0061] Two ends of the temperature measuring optical fiber 2 in the connecting tube structure 3 are respectively arranged on the male head structure and the female head structure.

[0062] The male structure of the connecting tube structure 3 is docked with the female structure of the end tube structure 1 to complete the connection between the end tube structure 1 and the connecting tube structure 3. The docking between the connecting tube structures 3 is also achieved by docking the male structure with the female structure, and at the same time, the connection of multiple sections of temperature measuring optical fiber 2 can be achieved.

[0063] Wind channels are provided inside the end pipe structure 1 and the connecting pipe structure 3 to achieve air circulation.

[0064] like Fig.13 As shown, the data analysis and processing unit includes a connecting line 17 , a host 18 and a display screen 19 . The temperature measuring optical fiber 2 is connected to the host 18 via the connecting line 17 , and the display screen 19 is mounted on the host 18 .

[0065] The connecting line 17 is a temperature-sensitive optical cable, one end of which is connected to the female connector structure in the outermost connecting tube structure 3 , and the other end is connected to the host 18 .

[0066] The host 18 is used to analyze the signal transmitted by the temperature measuring optical fiber 2 and convert it into corresponding data for analysis and processing, and the data can be saved and exported.

[0067] The display screen 19 is used to display the temperature value of each section of the temperature measuring optical fiber 2 and control the cracking position of the crack in the borehole.

[0068] Specifically, if Figures 1 to 6 As shown, the end tube structure 1 also includes an air outlet 1003, a bracket mounting plate 1005 and an optical fiber bracket 1006. The outer peripheral surface of the end tube 1001 is installed with a conical end 1002, and an air outlet 1003 is opened at one end. The air outlet 1003 is equipped with a filter 1004. The inner surface of the end tube 1001 is evenly fixed with a bracket mounting plate 1005, and the optical fiber bracket 1006 is fixedly installed on the inner end of the bracket mounting plate 1005, and the temperature measuring optical fiber 2 passes through the optical fiber bracket 1006. The inner surface of the optical fiber bracket 1006 is provided with a through groove connected to the optical fiber exposed window, and the temperature measuring optical fiber 2 is arranged in the optical fiber exposed window after passing through the through groove.

[0069] The space between the terminal tube 1001 and the bracket mounting plate 1005 and the optical fiber bracket 1006 is the wind channel, and the air outlet 1003 is connected to the wind channel. A filter 1004 is arranged on the air outlet 1003 to prevent impurities such as coal slag in the control borehole from entering the interior of the terminal tube 1001. The filter 1004 is made of stainless steel.

[0070] The bracket mounting plate 1005 cooperates with the optical fiber bracket 1006 to place the temperature measuring optical fiber 2.

[0071] The diameter of the end tube 1001 is 20-30 mm and the length is 800-1500 mm.

[0072] The internal structure of the connecting pipe structure 3 is the same as the internal structure of the end pipe structure 1 .

[0073] A bracket mounting plate 1005 and an optical fiber bracket 1006 are also provided in the connecting tube structure 3 for placing the temperature measuring optical fiber 2, and the middle part of the temperature measuring optical fiber 2 is arranged in the optical fiber exposure window on the connecting tube 3001 through a through groove. An airflow channel is also formed in the connecting tube 3001. When the end tube structure 1 is connected to the connecting tube structure 3, the airflow channel will also be connected.

[0074] Specifically, if Figure 1 and Figure 7 As shown, the female head structure includes an interface female head 1007, a track groove 1008, a terminal tube sealing ring groove 1009 and a fixing hole 1010. The interface female head 1007 is fixedly installed in the middle of the connecting end of the terminal tube 1001, and the interface female head 1007 is arranged at one end of the temperature measuring optical fiber 2. The inner surface of the interface female head 1007 is provided with a ventilation hole 1011 connected to the wind flow channel, the inner surface of the connecting end of the terminal tube 1001 is symmetrically provided with a track groove 1008, and the inner end of the inner surface of the track groove 1008 is provided with a fixing hole 1010 that penetrates the terminal tube 1001, and the terminal tube sealing ring groove 1009 is opened on the end face of the connecting end of the terminal tube 1001.

[0075] The female connector structure on the end tube structure 1 is the same as that on the connecting tube structure 3 .

[0076] Specifically, if Figures 8 to 10 As shown, the male head structure includes a connecting rod 3002, a connecting tube 3003, an interface male head 3004, a limit spring 3005 and a connecting tube sealing ring groove 3007. The inner surface of the other end of the connecting tube 3001 is symmetrically fixedly installed with the connecting rod 3002, the inner surface of the connecting rod 3002 is provided with a step groove, and the connecting tube 3003 is fixedly installed in the step groove, the interface male head 3004 is assembled in the connecting tube 3003, and the interface male head 3004 is arranged at the other end of the temperature measuring optical fiber 2, a limit spring 3005 is fixedly installed between the inner surface of the outer end of the connecting rod 3002 and the outer surface of the connecting tube 3003, the outer surface of the outer end of the connecting rod 3002 is integrally formed with a connecting tooth 3006 matching the fixing hole 1010, and the connecting tube sealing ring groove 3007 is provided on the other end face of the connecting tube 3001.

[0077] For the female head structure and the male head structure, the track groove 1008 in the female head structure is used to guide the connecting teeth 3006 on the connecting rod 3002 to move to the fixing hole 1010. The connecting teeth 3006 will be stuck in the fixing hole 1010 under the elastic force of the limit spring 3005, completing the connection between the end tube structure 1 and the connecting tube structure 3 or the two connecting tube structures 3.

[0078] The limit spring 3005 in the male head structure is always in a compressed state, ensuring that the connecting teeth 3006 are tightly combined with the fixing hole 1010 to prevent the connection from falling off, and the connecting rod 3002 has bending ability.

[0079] The track groove 1008, the fixing hole 1010 and the connecting rod 3002 are all provided one at the top and one at the bottom. In practical applications, four or more can be evenly provided to increase the stability of the pipeline connection.

[0080] The sealing ring groove 1009 of the end pipe and the sealing ring groove 3007 of the connecting pipe are used to place the sealing ring, so as to increase the air tightness between the pipes after the adjacent pipes are connected.

[0081] A cross-shaped bracket is fixedly installed on the inner surface of the connecting tube 3003, and the interface male head 3004 is installed on the cross-shaped bracket.

[0082] When the end tube structure 1 is connected to the connecting tube structure 3 or two connecting tube structures 3, the interface male head 3004 will be connected to the interface female head 1007 at the same time to complete the connection of different sections of the temperature measuring optical fiber 2, and through Fig.10 It can be seen that the outer peripheral surface of the interface male head 3004 is provided with a groove corresponding to the position of the ventilation hole 1011 to ensure the communication of the internal space when the end pipe structure 1 and the connecting pipe structure 3 or the two connecting pipe structures 3 are connected.

[0083] In the structures of the end pipe structure 1 and the connecting pipe structure 3, unless otherwise specified, both can be made of resin or plastic with relatively strong strength and relatively small mass.

[0084] Specifically, if Fig.11 and Fig.12 As shown, it also includes a quick disassembler 4, which includes an upper toothed disc 4001 and a lower toothed disc 4002. Both the upper toothed disc 4001 and the lower toothed disc 4002 are L-shaped structures. A movable groove is provided on the upper surface of the vertical rod of the lower toothed disc 4002, and the lower surface of the vertical rod of the upper toothed disc 4001 is movably assembled in the movable groove. A spring 4005 is arranged between the lower surface of the vertical rod of the upper toothed disc 4001 and the inner surface of the movable groove. The lower surface of the cross bar of the upper toothed disc 4001 is integrally formed with upper convex teeth 4003 matching the fixing holes 1010, and the upper surface of the cross bar of the lower toothed disc 4002 is integrally formed with lower convex teeth 4004 matching the fixing holes 1010.

[0085] In the quick dismantling device 4, except for the spring 4005 which is made of metal, the rest of the structures are made of plastic.

[0086] Under the action of the moving groove and the spring 4005 , the upper toothed disc 4001 can make a loud movement on the lower toothed disc 4002 .

[0087] When disassembling the pipeline, the upper protruding teeth 4003 and the lower protruding teeth 4004 of the quick disassembly tool 4 are aligned with the connecting teeth 3006 on the pipeline, and the quick disassembly tool 4 is pressed hard to push the connecting teeth 3006 out of the fixing holes 1010, and then the connecting pipe structure 3 is pulled out to complete the disassembly of the pipeline.

[0088] Embodiment 2

[0089] like Fig.13 As shown, a method for monitoring the cracking position of a hydraulic fracturing crack in a borehole, using a monitoring system for the cracking position of a hydraulic fracturing crack in a borehole according to any one of claims 1 to 5, specifically comprises the following steps:

[0090] S1, constructing a fracturing borehole 5 and a control borehole according to the coal seam hydraulic fracturing plan, and constructing a control borehole on both sides of the fracturing borehole 5;

[0091] The control holes on both sides are the left control hole 6 and the right control hole 7, and the distance to the fracturing hole 5 is the same, generally 20-50m, which can be selected according to the site conditions;

[0092] The depth of the fracturing borehole 5 is the same as that of the control borehole, which is generally at least 30m less than the length of the coal mining face (the distance from the return air lane to the intake air lane), and the hole diameter is also the same, which is generally 75-108mm;

[0093] S2, before hydraulic fracturing the fracturing borehole 5, the monitoring units in the monitoring system are lowered into the two control boreholes one by one, and the monitoring distance is equal to the control borehole depth;

[0094] The process of lowering the monitoring units in the monitoring system into the two control boreholes one by one is as follows:

[0095] First, lower the end pipe structure 1 into the control borehole, and dock the connecting pipe structure 3 in turn. Before docking, place a sealing ring in the sealing ring groove 1009 of the end pipe. Then, when connecting, hold the end pipe 1001 with one hand and the connecting pipe 3001 with the other hand, align the connecting teeth 3006 and the interface male head 3004 of the connecting pipe 3001 with the track groove 1008 and the interface female head 1007 of the end pipe 1001, and dock them with force. When the connecting teeth 3006 of the connecting pipe 3001 and the fixing holes 1010 of the end pipe 1001 are docked with each other, the docking of the end pipe 1001 and the connecting pipe 3001 is completed;

[0096] The connection between the connecting pipes 3001 is similarly carried out until the end pipe 1001 is lowered to the deepest point of the control borehole;

[0097] When lowering the end pipe structure 1 and the connecting pipe structure 3, ensure that the temperature measuring optical fiber 2 exposed outside the pipes does not contact the hole wall to prevent friction loss;

[0098] Monitoring units were placed in both control boreholes;

[0099] S3, the monitoring unit is connected with the data analysis and processing unit to form a complete temperature measurement system;

[0100] After the detection units in the two control boreholes are placed, the display screen 19, the host 18 and the connecting line 17 of the data analysis and processing unit are connected to the connecting pipe structure 3 respectively;

[0101] Two control drillings can share a host computer 18 and display screen 19 via a connecting line 17;

[0102] S4, start the temperature measurement system to monitor the temperature distribution along the control boreholes, and detect the operating status of the monitoring system by injecting high-pressure gas into the control boreholes;

[0103] The process of injecting high pressure gas into the control borehole to detect the operating status of the monitoring system is as follows:

[0104] Start the monitoring system to monitor the temperature distribution along the two control boreholes. After the monitoring system is stable for 5 minutes, disconnect the connecting line 17 from the connecting pipe 3001, install a reducer at the end of the connecting pipe 3001 to connect it to the compressed air pipeline in the lane through the air duct, and pressurize the connecting pipe 3001 with pressurized air;

[0105] The pressurized air passes through the connecting pipes 3001 of each section to the end pipe 1001, and enters the control borehole through the air outlet 1003, and finally is pressed out from the orifice of the control borehole;

[0106] After 10 minutes of compressed air, disconnect the connection, reconnect the host 18 to the connecting pipe 3001 through the connecting line 17, and start the monitoring system to check the changes in the monitored temperature of each section in the control borehole. The purpose is to change the temperature in the borehole by compressed air and test the reliability of the temperature measurement system;

[0107] S5, fracturing the first section of the coal seam by staged hydraulic fracturing, and monitoring the temperature of the control boreholes on both sides thereof along the process by using a monitoring system;

[0108] The front sealer 8, the fracturing tube 10, the injection tube 20, the rear sealer 9 and the fracturing tube 10 are lowered into the fracturing borehole 5 respectively until the front sealer 8 reaches the deepest part of the fracturing borehole 5, and a fracturing hole 11 is provided on the fracturing tube 10 between the front sealer 8 and the rear sealer 9;

[0109] Then, the liquid injection pipe 20 is connected to the manual pressure pump 21, and the manual pressure pump 21 is used to inject high-pressure liquid into the two hole sealers to complete the hole sealing;

[0110] Then, the fracturing pipe 10, the high-pressure hose 12, the high-pressure pump 13, the liquid inlet pipe 14, the liquid return pipe 15 and the water tank 16 are connected in sequence. After the connection is completed, the high-pressure pump 13 is started to inject high-pressure liquid into the fracturing borehole 5 to start hydraulic fracturing of the coal body, and the temperature changes along the two control boreholes are monitored during the fracturing process;

[0111] S6, control the determination and analysis of cracking positions in the borehole;

[0112] When it is monitored during the fracturing process that a certain section of the temperature in a certain control borehole changes significantly and the injection pressure continues to decrease, and water flows in the control borehole, it proves that the fracturing borehole 5 is connected to the control borehole through the fracturing crack;

[0113] The crack position in the control borehole is determined based on the temperature distribution along the control borehole. The crack is the water supply point. The temperature along the upstream and downstream of the water supply point will suddenly change. If the control borehole is an upward borehole, the temperature on the downstream side of the water supply point will drop significantly, and the temperature on the upstream side will not change or change very little. If the borehole is a downward borehole, the temperature on the downstream side of the water supply point will not change or change very little, and the temperature on the upstream side will drop significantly.

[0114] The downstream side of the water supply point is the interval between the crack opening and the control borehole opening, and the upstream side is the interval between the crack opening and the control borehole bottom;

[0115] S7, stop fracturing and move the fracturing device to the second fracturing section in the fracturing borehole 5, and at the same time inject high-pressure gas into the control borehole connected to the fracturing crack to clean up the water in the borehole;

[0116] After determining the cracking position of the crack in the controlled borehole, stopping the fracturing of the first section of the fracturing borehole 5, and moving the sealer to the second fracturing section of the fracturing borehole 5;

[0117] Before moving, the two sealers are first depressurized, and then the fracturing pipe 10 is disassembled in sequence until the sealers reach the second section fracturing position;

[0118] In addition, the control borehole with cracks needs to be compressed air. The air compression step is the same as step S4 to reduce the water accumulation in the control borehole. After the air compression, the temperature of the control borehole is monitored for 10-20 minutes along the way. After the temperature is stable, the second section fracturing is started.

[0119] S8, fracturing the second section of the fracturing borehole 5, monitoring the temperature along the two control boreholes during the fracturing process, and determining whether a "seamless cracking" situation occurs when cracks appear;

[0120] Perform second-stage fracturing on the fracturing borehole 5 according to steps S5, S6 and S7;

[0121] When it is monitored during the second-stage fracturing process that a certain section of the temperature in a certain controlled borehole has changed significantly and the injection pressure continues to decrease, and water flows in the controlled borehole, the position of the fracturing cracks formed by the second-stage fracturing in the controlled borehole is determined. If the cracking position of the controlled borehole during the second-stage fracturing process is the same as the cracking position of the controlled borehole during the first fracturing process, it can be determined and analyzed that a "seamless cracking" phenomenon has occurred. According to the analysis results, it is determined whether the next fracturing position needs to be adjusted, and corresponding adjustments are made according to the judgment results;

[0122] S9, after determining the fracturing position of the third section, repeat steps S6 to S8 until the fracturing of the fracturing borehole 5 is completed;

[0123] The fracturing parameters between the fracturing sections in the fracturing borehole 5 are gradually adjusted to reduce and avoid the "seam-by-seam" phenomenon, and then the fracturing section division method is promoted and applied.

[0124] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, many changes can be made in the specific implementation methods and application scopes based on the ideas of the present invention. As long as these changes do not deviate from the concept of the present invention, they all belong to the protection scope of the present invention.

Claims

1. A monitoring system for the cracking position of hydraulic fracturing cracks in a borehole, characterized by: It includes a monitoring unit and a data analysis and processing unit. The monitoring unit includes a terminal tube structure, a temperature measuring optical fiber and a connecting tube structure. The terminal tube structure includes a terminal tube and a tapered terminal, and the tapered terminal is integrally formed at the forward end of the terminal tube. The connecting end of the terminal tube is provided with a female structure. A temperature measuring optical fiber is installed between the tapered terminal and the female structure. An optical fiber exposure window is provided on the outer surface of the terminal tube, and the middle section of the temperature measuring optical fiber is provided in the optical fiber exposure window. The connecting tube structure comprises a connecting tube, one end of which is provided with a female head structure, and the other end of which is provided with a male head structure matching the female head structure, a temperature measuring optical fiber is installed between the male head structure and the female head structure, an optical fiber exposure window is provided on the outer surface of the connecting tube, and the middle section of the temperature measuring optical fiber is arranged in the optical fiber exposure window; The end pipe structure and the connecting pipe structure are both provided with air flow channels inside; The data analysis and processing unit comprises a connecting line, a host and a display screen. The temperature measuring optical fiber is connected to the host through the connecting line, and the display screen is assembled on the host.

2. A monitoring system for the cracking position of a hydraulic fracturing crack in a borehole according to claim 1, characterized in that: The terminal tube structure also includes an air outlet, a bracket mounting plate and an optical fiber bracket. The outer circumferential surface of the terminal tube is provided with an air outlet at one end of a tapered terminal, and a filter is installed in the air outlet. The inner surface of the terminal tube is evenly fixed with a bracket mounting plate, and the optical fiber bracket is fixedly installed on the inner end of the bracket mounting plate, and the temperature measuring optical fiber passes through the optical fiber bracket. The inner surface of the optical fiber bracket is provided with a through groove connected to the optical fiber exposed window, and the temperature measuring optical fiber is arranged in the optical fiber exposed window after passing through the through groove; The internal structure of the connecting pipe structure is the same as the internal structure of the end pipe structure.

3. A monitoring system for the cracking position of a hydraulic fracturing crack in a borehole according to claim 1, characterized in that: The female head structure includes an interface female head, a track groove, a terminal tube sealing ring groove and a fixing hole. The interface female head is fixedly installed in the middle of the connecting end of the terminal tube, and the interface female head is arranged at one end of the temperature measuring optical fiber. The inner surface of the interface female head is provided with a ventilation hole connected to the airflow channel, the inner surface of the connecting end of the terminal tube is symmetrically provided with a track groove, and the inner end of the inner surface of the track groove is provided with a fixing hole that penetrates the terminal tube, and the terminal tube sealing ring groove is provided on the end face of the connecting end of the terminal tube.

4. A monitoring system for the cracking position of a hydraulic fracturing crack in a borehole according to claim 1, characterized in that: The male head structure includes a connecting rod, a connecting tube, an interface male head, a limit spring and a connecting tube sealing ring groove. The inner surface of the other end of the connecting tube is symmetrically fixedly installed with a connecting rod, the inner surface of the connecting rod is provided with a step groove, and the connecting tube is fixedly installed in the step groove, the interface male head is assembled in the connecting tube, and the interface male head is arranged at the other end of the temperature measuring optical fiber, a limit spring is fixedly installed between the inner surface of the outer end of the connecting rod and the outer surface of the connecting tube, the outer surface of the outer end of the connecting rod is integrally formed with connecting teeth matching the fixing hole, and the connecting tube sealing ring groove is provided on the other end face of the connecting tube.

5. A monitoring system for the cracking position of a hydraulic fracturing crack in a borehole according to claim 2, characterized in that: It also includes a quick disassembler, which includes an upper gear plate and a lower gear plate, both of which are L-shaped structures, a movable groove is opened on the upper surface of the vertical rod of the lower gear plate, and the lower surface of the vertical rod of the upper gear plate is movably assembled in the movable groove, a spring is installed between the lower surface of the vertical rod of the upper gear plate and the inner surface of the movable groove, the lower surface of the cross bar of the upper gear plate is integrally formed with upper convex teeth matching the fixing holes, and the upper surface of the cross bar of the lower gear plate is integrally formed with lower convex teeth matching the fixing holes.

6. A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole, using a monitoring system for the cracking position of a hydraulic fracturing crack in a borehole as claimed in any one of claims 1 to 5, specifically comprising the following steps: S1, constructing a fracturing borehole and a control borehole according to the coal seam hydraulic fracturing plan, and constructing a control borehole on both sides of the fracturing borehole; S2, before hydraulic fracturing the fracturing boreholes, the monitoring units in the monitoring system are lowered into the two control boreholes one by one, and the monitoring distance is equal to the control borehole depth; S3, the monitoring unit is connected with the data analysis and processing unit to form a complete temperature measurement system; S4, start the temperature measurement system to monitor the temperature distribution along the control boreholes, and detect the operating status of the monitoring system by injecting high-pressure gas into the control boreholes; S5, fracturing the first section of the coal seam by staged hydraulic fracturing, and monitoring the temperature of the control boreholes on both sides thereof along the process by using a monitoring system; S6, control the determination and analysis of cracking positions in the borehole; S7, stop fracturing and move the fracturing device to the second fracturing section in the fracturing borehole, and at the same time inject high-pressure gas into the control borehole connected to the fracturing crack to clean up the water in the borehole; S8, fracturing the second section of the fracturing borehole, monitoring the temperature along the two control boreholes during the fracturing process, and determining whether "seamless cracking" occurs when cracks appear; S9, after determining the fracturing position of the third section, repeat steps S6 to S8 until the fracturing of the fracturing borehole is completed.

7. A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole according to claim 6, characterized in that: In step S2, the process of lowering the monitoring units in the monitoring system into the two control boreholes one by one is as follows: First, lower the end pipe structure into the control drill hole, and dock the connecting pipe structure in turn. Before docking, place a sealing ring in the sealing ring groove of the end pipe. Then, when connecting, hold the end pipe with one hand and the connecting pipe with the other hand, align the connecting teeth and the male interface of the connecting pipe with the track groove and the female interface of the end pipe, and dock them with force. When the connecting teeth of the connecting pipe and the fixing hole of the end pipe are docked with each other, the docking of the end pipe and the connecting pipe is completed; The same applies to the butt joint between the connecting pipes until the end pipe is lowered to the deepest point of the control borehole; Monitoring units were placed in both control boreholes.

8. A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole according to claim 6, characterized in that: In step S4, the process of injecting high-pressure gas into the control borehole to detect the operating status of the monitoring system is as follows: Start the monitoring system to monitor the temperature distribution along the two control boreholes. After the monitoring system stabilizes for 5 minutes, disconnect the connecting line from the connecting pipe, install a reducer at the end of the connecting pipe to connect it to the compressed air pipeline in the tunnel through the air duct, and pressurize the connected pipe with pressurized air. The pressurized air reaches the end pipe through each section of the connecting pipe, enters the control borehole from the air outlet, and is finally pressed out from the orifice of the control borehole. Disconnect after 10 minutes of compressed air, reconnect the main unit to the connecting pipe through the connecting line, and start the monitoring system to check the changes in the monitored temperature of each section in the control borehole. The purpose is to change the temperature in the borehole through compressed air and to test the reliability of the temperature measurement system.

9. A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole according to claim 6, characterized in that: In step S6, the specific method of determining and analyzing the crack position in the control borehole is: When it is monitored during the fracturing process that the temperature of a certain section in a certain control borehole changes significantly and the injection pressure continues to decrease, and water flows in the control borehole, it proves that the fracturing borehole has been interconnected with the control borehole through the fracturing crack. The crack position in the control borehole is judged according to the temperature distribution along the control borehole. The crack is the water supply point. The judgment is based on the principle that the temperature along the upstream and downstream of the water supply point will suddenly change. If the control borehole is an upward borehole, the temperature on the downstream side of the water supply point will drop significantly, and the temperature on the upstream side will not change or change very little. If the borehole is a downward borehole, the temperature on the downstream side of the water supply point will not change or change very little, and the temperature on the upstream side will drop significantly. The downstream side of the water supply point is the interval between the crack opening and the control borehole opening, and the upstream side is the interval between the crack opening and the control borehole bottom.

10. A method for monitoring the cracking position of a hydraulic fracturing crack in a borehole according to claim 6, characterized in that: In step S8, the method for determining whether a "seam-through" situation occurs when cracks occur is: When it is monitored during the second-section fracturing process that the temperature of a certain section in a certain control borehole changes significantly and the injection pressure continues to decrease, and water flows in the control borehole, the position of the fracturing cracks formed by the second-section fracturing in the control borehole is determined. If the cracking position of the control borehole during the second-section fracturing process is the same as the cracking position of the control borehole during the first fracturing process, it can be determined and analyzed that a "seamless cracking" phenomenon has occurred. Based on the analysis results, it is determined whether the next fracturing position needs to be adjusted, and corresponding adjustments are made based on the judgment results.

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