A combined monitoring method and system for fracturing hole inspection, fiber optic grating, and distributed acoustics.

Abstract

This invention discloses a combined monitoring method and system for fracturing borehole inspection, fiber optic grating, and distributed acoustic sensors, belonging to the field of mining and strata control technology. The method includes: before fracturing, inserting a wireless transmission borehole inspection lens into the borehole to acquire borehole wall images; implementing fracturing using a one-way valve assembly and a high-pressure pump; after fracturing, scanning the borehole wall images again to quantitatively identify fractures; subsequently, laying a sensing cable integrating distributed acoustic sensors and fiber optic grating sensors within the borehole; and using sealing slurry to solidify the borehole and surrounding rock into a single unit, forming an in-situ monitoring unit. Static strain response is monitored through the fiber optic grating, and microseismic wave fields are recorded using the distributed acoustic sensors, enabling long-term monitoring and dynamic early warning of fracture development and roof failure during fracturing and mining operations in adjacent areas. This invention achieves secondary utilization of fracturing boreholes, enabling quantitative evaluation of fracturing effects and accurate early warning of roof disasters.

Description

Technical Field

[0001] This invention relates to the field of mining and rock strata control technology, and in particular to a method and system for joint monitoring of fracturing hole inspection, fiber optic grating, and distributed acoustics. Background Technology

[0002] Coal, as a core component of my country's energy structure, relies heavily on the stable control of the roof strata for safe and efficient underground mining. Hydraulic fracturing technology, as an effective method, alters the stress state of the surrounding rock mass using high-pressure water, artificially creating weak surfaces to weaken the rock mass's mechanical properties. It is widely used for roof stress relief, rockburst prevention, and stress distribution optimization. However, in current engineering practice, evaluating the fracturing effect often faces significant challenges. Current evaluation methods mainly rely on indirect parameters such as pumping pressure and flow rate during construction, or on macroscopic mine pressure manifestations on the roadway surface after construction. These methods cannot directly and deeply probe the true expansion morphology, spatial distribution, and effective influence range of the fracture network within the rock mass, resulting in significant ambiguity and lag in the judgment of fracturing effects. This fails to provide accurate data support for subsequent optimization of fracturing parameters and mining layout. Furthermore, fracturing boreholes are often directly grouted and sealed or abandoned after construction, failing to utilize these valuable borehole resources deep within the rock mass. This not only causes significant engineering waste but also increases the overall operating costs of the mine. Although technologies such as borehole inspection, fiber optic grating sensing, and distributed acoustic sensing have their own applications in the field of coal mine monitoring, each single technology has monitoring blind spots. For example, borehole inspection can only provide static visual information, fiber optic gratings are limited to point measurements, and although distributed acoustic sensing has a wide coverage, it is difficult to quantify static strain. There is a lack of an integrated solution that can organically combine the above technologies and realize full life cycle monitoring. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for joint monitoring of fracturing hole inspection, fiber optic grating, and distributed acoustics. By integrating an inspection lens and fiber optic sensing cable into the borehole and using sealing slurry to solidify the fiber optic cable with the surrounding rock, abandoned fracturing holes are transformed into permanent monitoring units, thereby realizing quantitative evaluation of the fracturing effect of the roof and long-term dynamic early warning of roof stability.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a method for joint monitoring of fracturing borehole inspection, fiber optic grating, and distributed acoustics, comprising the following steps: Step S1, borehole wall inspection before fracturing: drilling a borehole into the top plate to form a borehole, inserting a wireless transmission borehole inspection lens integrated on the drill rod into the borehole at the location to be fracturing, and acquiring an image of the borehole wall before fracturing; after inserting a one-way valve assembly into the target fracturing rock layer location within the borehole, starting a high-pressure pump to fracture the target fracturing rock layer.

[0005] Step S2, Borehole wall inspection after fracturing: After the fracturing operation is completed, the image data of the fracturing rock strata is scanned again by the wireless transmission borehole inspection lens during the drill rod retraction process, and the wireless transmission borehole inspection lens is removed from the borehole; the images before and after fracturing are processed to quantitatively identify the propagation trajectory and complexity of the fracturing-induced fractures.

[0006] Step S3: Forming a monitoring unit: A sensing cable integrating a distributed acoustic sensor and a fiber Bragg grating sensor is laid inside the borehole to form a monitoring unit; the measuring point position of the fiber Bragg grating sensor and the spatial channel of the distributed acoustic sensor are precisely aligned on the absolute depth coordinates of the borehole; the monitoring function of the sensing cable is activated, and static or quasi-static strain data of the borehole's axial and radial directions are collected through the fiber Bragg grating sensor, and dynamic vibration and sound wave signals along the entire length of the borehole are collected through the distributed acoustic sensor.

[0007] Step S4, Consolidating the optical fiber with the surrounding rock: Injecting sealing slurry into the borehole to seal it, so that the borehole and the surrounding rock are consolidated into one, realizing long-term reliable coupling between the sensing cable and the surrounding rock, and transforming the borehole into a downhole in-situ monitoring unit.

[0008] Step S5, Monitoring the fracturing effect in adjacent areas: When new fracturing operations are carried out in the area surrounding the downhole in-situ monitoring unit, the fiber optic grating sensor is used to record the static strain response caused by adjacent fracturing, and the influence range and degree of stress disturbance are quantitatively evaluated; the distributed acoustic sensor is used to record the microseismic wave field induced by adjacent fracturing, and the expansion range and direction of the fracture network are determined by the seismic source location.

[0009] Step S6: Long-term monitoring of roof fracture during mining: The fiber optic grating sensor is used to monitor the trend of rock mass strain and to provide early warning of roof instability through strain growth rate and sudden changes; the distributed acoustic sensor is used to capture acoustic emission and microseismic signals emitted by the activation and connection of existing hydraulic fracturing cracks and the generation of new fractures in the roof under mining stress, and to depict the fracture development zone and roof fracture line through the spatiotemporal evolution of event frequency, energy and location.

[0010] Step S7: Verification of multiple monitoring methods: Use the strain distribution data of the fiber optic grating sensor to identify strain concentration areas and gradient bands; use the data of the distributed acoustic sensor to locate the position and energy of micro-fracture events; perform spatial superposition analysis of the dense area of ​​micro-fracture events and strain concentration area, and combine with the original fractures identified in the image data to delineate the effective boundary of the hydraulic fracturing fracture field and the range of rock mass damage, so as to achieve dynamic early warning.

[0011] Furthermore, in step S2, the method for processing the images before and after fracturing includes image segmentation and feature extraction, tracking the expansion trajectory of the crack through a skeletonization algorithm, and quantitatively characterizing the complexity of the crack using fractal dimension.

[0012] Furthermore, in step S3, the sensing cable is made of glass fiber reinforced plastic (GFRP) optical cable, the GFRP optical cable is wrapped with a cladding layer on the outside, and the distributed acoustic sensor and the fiber optic grating sensor are integrated inside.

[0013] Furthermore, the sensor cable is laid in the borehole in one of the following ways: the sensor cable is wrapped around the outside of the PVC pipe; or, the sensor cable is laid on the inner wall of the PVC pipe and solidified by grouting to prevent the sensor cable from being damaged by the shearing action of the rock strata.

[0014] Furthermore, in step S4, the consolidation of the sensing cable with the surrounding rock is achieved by using precast concrete blocks, specifically including: a groove is formed on the outer surface of a pre-made cylindrical concrete block, the sensing cable is fixedly installed in the groove and sealed with encapsulating adhesive; a set of sensing devices is installed in one of the cylindrical concrete blocks, and the previous set of optical fiber sensing lines passes through the groove of the next set of cylindrical concrete blocks; multiple cylindrical concrete blocks are arranged at intervals and stored in a sleeve, and the sealing slurry is used to fill the sleeve to achieve a tight fit between the sleeve and the surrounding rock.

[0015] Furthermore, in steps S5 and S6, the acoustic signals recorded by the distributed acoustic sensors are distinguished by signal source. The signal source distinction is based on the timing of signal occurrence, spatial location, waveform spectrum characteristics, and strain response mode of the fiber optic grating sensor, so as to identify whether the signal source is adjacent fracturing operations or mining-induced fracture in this area.

[0016] Furthermore, in step S6, the microseismic event is located based on the monitoring data of the distributed acoustic sensor. Specifically, the microseismic source is located by utilizing the dense spatial sampling channels of the distributed acoustic sensor and detecting the time difference between the arrival of longitudinal and transverse waves in different channels.

[0017] Furthermore, the roof fracture law is inverted based on the acoustic signals monitored by the distributed acoustic sensors. Specifically, this includes: using the background noise recorded by the distributed acoustic sensors, calculating the virtual seismic response between channels through noise cross-correlation technology, continuously monitoring the spatiotemporal changes of seismic wave velocity in the virtual seismic response, identifying areas of significant decrease in seismic wave velocity as damaged areas and potential fracture areas of the roof rock mass, thereby dynamically inverting the formation process and location of the roof fracture line.

[0018] Secondly, the present invention provides a combined monitoring system for fracturing borehole inspection—fiber optic grating—distributed acoustic imaging to implement the method described above, comprising: a borehole inspection module, including a wireless transmission borehole inspection lens integrated on the drill pipe, the front end of the wireless transmission borehole inspection lens being provided with a lens protective housing for acquiring images of the borehole inner wall; a fracturing module, including a one-way valve group and a high-pressure pump, the one-way valve group being disposed on the drill pipe and fed into the target fracturing rock layer in the borehole, the high-pressure pump being connected to the one-way valve group to perform fracturing operations; an integrated sensing unit, including a sensing cable, the sensing cable integrating the distributed acoustic sensor and the fiber optic grating sensor, the sensing cable being laid in the borehole and coupled to the surrounding rock through the sealing slurry; and a data processing and evaluation unit, signal-connected to the integrated sensing unit, configured to perform fusion analysis on the strain data acquired by the fiber optic grating sensor and the acoustic data acquired by the distributed acoustic sensor, execute joint monitoring and evaluation steps, and output quantitative evaluation results.

[0019] Furthermore, the integrated sensing unit also includes a PVC pipe, with the sensing cable wound around the outside of the PVC pipe or laid on the inner wall of the PVC pipe; or, the integrated sensing unit also includes a plurality of spaced cylindrical concrete blocks and a sleeve, with grooves for accommodating the sensing cable formed on the outer surface of the cylindrical concrete blocks, the grooves being sealed with encapsulating adhesive, and the plurality of cylindrical concrete blocks being stored in the sleeve.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention innovatively constructs a three-dimensional monitoring system of "peeping imaging + fiber optic grating + distributed acoustics" through a joint monitoring method of fracturing borehole inspection - fiber optic grating - distributed acoustics. The method first uses a wireless transmission borehole inspection lens to perform in-situ scanning of the borehole wall before and after fracturing, and combines image processing algorithms to directly obtain the true propagation trajectory and complexity of the crack, solving the problem of the blindness of the traditional evaluation method that only relies on pumping parameters to infer the crack morphology; then, by laying a sensing cable integrating distributed acoustic sensors and fiber optic grating sensors in the same borehole, and using sealing slurry to consolidate the optical fiber with the surrounding rock, the secondary development and utilization of borehole resources is realized. This method can not only quantify the static strain field changes generated by fracturing, but also capture the dynamic micro-vibration signals induced by crack propagation in real time. Through the mutual verification of multi-source data, the accuracy of the evaluation of the roof fracturing effect and the reliability of the early warning of roof instability are significantly improved.

[0021] (2) This invention provides flexible and diverse sensor cable deployment and consolidation schemes, especially the precast concrete block deployment structure. By opening grooves on the surface of the cylindrical concrete block and encapsulating the sensor cable, it not only effectively protects the fragile fiber optic sensor from mechanical damage in the downhole construction environment, but also ensures tight coupling between the sensor and the surrounding rock through the cooperation of the sleeve and the sealing grout. This structural design ingeniously solves the problem of poor fiber optic survival and poor coupling effect in soft or broken coal and rock masses, ensuring the stable operation of the monitoring system and the acquisition of high signal-to-noise ratio signals under long-term mining stress environment.

[0022] (3) This invention also proposes an integrated fracturing hole inspection-fiber grating-distributed acoustic joint monitoring system, which organically integrates the borehole inspection module, the high-pressure fracturing module, and the integrated sensing unit. This system utilizes the dense spatial sampling channels of the distributed acoustic sensors for high-precision microseismic source localization, and uses background noise cross-correlation technology to invert the roof fracture pattern. Combined with static strain data from the fiber grating, it can accurately depict the fracture development zone and the roof fracture line from both spatiotemporal dimensions. Through this deeply integrated hardware and software system architecture, it achieves full-process coverage from construction monitoring to long-term early warning, significantly improving the intelligent level of coal mine roof management. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the planar layout of the boreholes and monitoring units during the working face mining process of this invention.

[0024] Figure 2 yes Figure 1 The cross-sectional diagram along the AA direction shows the distribution of boreholes along the working face advance direction.

[0025] Figure 3 yes Figure 1 The cross-sectional diagram along the BB direction shows the distribution of boreholes along the working face.

[0026] Figure 4 This is a schematic diagram illustrating the working principle of a fracturing inspection lens scanning a single borehole.

[0027] Figure 5 This is a schematic diagram of the arrangement of sensor cables wrapped around the outside of PVC pipes.

[0028] Figure 6 yes Figure 5 A partially enlarged structural diagram.

[0029] Figure 7 yes Figure 5 A cross-sectional view along the CC direction.

[0030] Figure 8This is a schematic diagram of the arrangement of sensor cables inside PVC pipes.

[0031] Figure 9 yes Figure 8 A partially enlarged structural diagram.

[0032] Figure 10 yes Figure 8 A cross-sectional view along the DD direction.

[0033] Figure 11 This is a structural diagram showing the sensor cables arranged using precast concrete blocks.

[0034] Figure 12 yes Figure 11 A partially enlarged structural diagram.

[0035] Figure 13 yes Figure 11 A cross-sectional view along the EE direction.

[0036] Figure 14 This is a flowchart of the monitoring method of the present invention.

[0037] Label Descriptions: 1. Drill Hole; 2. Drill Rod; 3. Wireless Transmission Drill Hole Viewing Lens; 4. Lens Protective Housing; 5. One-Way Valve Assembly; 6. High-Pressure Pump; 7. Distributed Acoustic Sensor; 8. Fiber Optic Grating Sensor; 9. PVC Pipe; 10. Sealing Grout; 11. Surrounding Rock; 12. Cylindrical Concrete Block; 13. Sealing Adhesive; 14. Sleeve; 15. Level Roadway; 16. Goaf; 17. Working Face; 18. Target Fracturing Rock Layer; 19. Hydraulic Fracturing; 20. Drill Rig; 21. DAS Cable for In-situ Rock Block; 22. DAS Cable for Forward Rock Block; 23. FBG Cable for In-situ Rock Block; 24. FBG Cable for Forward Rock Block; 25. Sealing Device; 26. Adapter; 27. Plug. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0039] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0040] In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] In the description of the invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] like Figure 1 , Figure 2 and Figure 3 As shown, this invention provides an application scenario layout for a combined monitoring method of fracturing hole inspection, fiber optic grating, and distributed acoustics. In a horizontal roadway 15 of a coal mine, a drilling rig 20 drills a borehole 1 of a specific diameter into the roof at a certain length and angle. The borehole 1 penetrates the target fracturing rock layer 18 and extends into the surrounding rock 11. As the working face 17 advances during the mining process, a goaf 16 is formed behind it. Hydraulic fractures 19 are formed inside the fracturing rock layer, and the expansion pattern of these fractures directly affects the stability of the roof.

[0044] After using hydraulic fracturing to modify the internal structure of rock strata, its fracturing effect is currently difficult to quantitatively assess. Existing fracturing assessment methods mostly rely on indirect parameters such as pumping pressure and flow rate during the fracturing process, or on observations of surface mine pressure manifestations after fracturing. These methods cannot directly and accurately obtain the expansion morphology, spatial distribution, and effective influence range of the fracture network inside the rock mass after fracturing, resulting in ambiguity and lag in the judgment of fracturing effect, and failing to provide reliable data support for optimizing fracturing parameters and subsequent mining layout. Secondly, the boreholes used for fracturing are usually sealed with grouting or directly abandoned after construction, and the value of the boreholes excavated inside the rock mass is not fully utilized, resulting in a huge waste of borehole resources and increasing the overall cost of the mine. To address the aforementioned problems, this invention provides a joint monitoring method for fracturing hole inspection—fiber optic grating—distributed acoustics. Through three embodiments, namely, the sensing cable is wrapped around the outside of the PVC pipe 9, laid inside the PVC pipe 9, and passed through the groove of the precast concrete block, the specific implementation process of the joint monitoring method for fracturing hole inspection—fiber optic grating—distributed acoustics is described in detail.

[0045] Example 1: As Figure 14 As shown, this embodiment provides a joint monitoring method for fracturing borehole inspection—fiber optic grating—distributed acoustics. This method first uses a borehole inspection device with wireless transmission capabilities to acquire images of the borehole wall before and after fracturing. Then, an integrated sensor cable is laid within the same borehole and grouted to solidify it, forming a permanent downhole in-situ monitoring unit. For example... Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, the specific implementation steps for the case where the sensor cable is wrapped around the outside of the PVC pipe 9 are as follows.

[0046] Step S1 is the pre-fracturing borehole wall inspection stage. For example... Figure 1 , Figure 2 and Figure 3 As shown, a hole 1 of a specific diameter is drilled into the top plate at a certain length and angle. Figure 4 As shown, a wireless transmission borehole inspection lens 3 integrated on drill pipe 2 is inserted into the borehole 1 at the fracturing location to acquire an image of the borehole wall before fracturing. The front end of the wireless transmission borehole inspection lens 3 is equipped with a lens protective housing 4 to prevent damage caused by direct friction between the lens and the rock. After the one-way valve assembly 5 is inserted into the target fracturing rock layer 18 within the borehole 1, the high-pressure pump 6 is activated to fracture the target fracturing rock layer 18. During fracturing, the wireless transmission borehole inspection lens 3 remains inside the borehole 1, monitoring the changes in the rock layer state in real time during the initial fracturing stage.

[0047] Step S2 is the borehole wall inspection stage after fracturing. After the fracturing operation is completed, the image data of the fracturing rock strata is scanned again by the wireless transmission borehole inspection lens 3 during the retraction of drill pipe 2. The retraction speed of drill pipe 2 is controlled within an appropriate range to ensure that the lens can clearly capture the detailed features of the borehole wall after fracturing. The wireless transmission borehole inspection lens 3 is then removed from borehole 1. By processing the images before and after fracturing, the propagation trajectory and complexity of the fracturing-induced fractures are quantitatively identified. The image processing methods include image segmentation and feature extraction. The propagation trajectory of the fractures is tracked through a skeletonization algorithm, and the complexity of the fractures is quantitatively characterized using fractal dimension, thereby providing intuitive visual data support for subsequent fracturing effect evaluation.

[0048] Step S3 is the stage of forming a monitoring unit. For example... Figure 5 , Figure 6 and Figure 7 As shown, a sensing cable integrating a distributed acoustic sensor 7 and a fiber Bragg grating sensor 8 is laid inside the borehole 1 to form a monitoring unit. The sensing cable is made of glass fiber reinforced plastic (GFRP) optical cable, with an outer cladding covering the cable, and the distributed acoustic sensor 7 and fiber Bragg grating sensor 8 integrated inside. In this embodiment, a PVC pipe winding method is used, that is, the sensing cable is laid inside the borehole 1 by winding it around the outside of a PVC pipe 9. Figure 6 As shown, the sensing cable is spirally and uniformly wound around the outer wall of the PVC pipe 9, with consistent winding spacing to ensure uniform sensor distribution. During deployment, the measuring points of the fiber optic grating sensors 8 are precisely aligned with the spatial channels of the distributed acoustic sensors 7 on the absolute depth coordinates of the borehole 1. Then, the monitoring function of the sensing cable is activated. Specifically, the array of fiber optic grating sensors 8 in the sensing cable collects static or quasi-static strain data in the axial and radial directions of the borehole 1; and the distributed acoustic sensing fiber collects dynamic vibration and acoustic signals along the entire length of the borehole 1.

[0049] Step S4 is the stage of consolidating the optical fiber with the surrounding rock. Sealing grout 10 is injected into borehole 1 to seal the borehole. For example... Figure 7 As shown, the grouting process proceeds gradually from the deep part of borehole 1 to the shallow part, ensuring that the PVC pipe 9 is tightly bonded to the surrounding rock 11, so that borehole 1 and surrounding rock 11 are solidified into one, realizing long-term reliable coupling between the sensing cable and surrounding rock 11, thereby transforming the abandoned fracturing borehole into a permanent downhole in-situ monitoring unit.

[0050] Step S5 is the monitoring stage for fracturing effects in adjacent areas. When new fracturing operations are carried out in the area surrounding the downhole in-situ monitoring unit, the adjacent fracturing areas can be monitored through the constructed downhole in-situ monitoring unit. Fiber optic grating sensor 8 is used to record the static strain response caused by adjacent fracturing to quantitatively evaluate the range and degree of stress disturbance. Simultaneously, distributed acoustic sensor 7 is used to record the microseismic wave field induced by adjacent fracturing. By locating the seismic source, the expansion range and direction of the fracture network are determined, and its connectivity with the rock mass in the monitored area is assessed.

[0051] Step S6 is the long-term monitoring stage for roof fracture during mining operations. For example... Figure 1 and Figure 2 As shown, during the process of the longwall face 17 in the mine continuously approaching the borehole monitoring area, fiber optic grating sensors 8 are used to monitor the trend changes in rock mass strain, and roof instability is predicted by the strain growth rate and sudden changes. At the same time, distributed acoustic sensors 7 are used to capture the acoustic emission and microseismic signals emitted by the activation and connection of existing hydraulic fracturing cracks and the generation of new fractures in the roof under the action of mining stress. The spatiotemporal evolution of event frequency, energy and location is used to depict the fracture development zone and the roof fracture line.

[0052] In this process, microseismic events are located based on the monitoring data of the distributed acoustic sensor 7. Specifically, the microseismic source is located by using the dense spatial sampling channels of the distributed acoustic sensor 7 and detecting the time difference between the arrival of longitudinal and transverse waves in different channels.

[0053] The acoustic signals recorded by the distributed acoustic sensor 7 are distinguished by signal source. The signal source distinction is based on the signal occurrence timing, spatial location, waveform spectrum characteristics and strain response mode of the fiber optic grating sensor 8, so as to identify whether the signal source is adjacent fracturing operations or mining-induced fracture in this area.

[0054] The roof fracture pattern is inverted based on the acoustic signals monitored by the distributed acoustic sensor 7. Specifically, this includes: using the background noise recorded by the distributed acoustic sensor 7, calculating the virtual seismic response between channels through noise cross-correlation technology, continuously monitoring the spatiotemporal changes of seismic wave velocity in the virtual seismic response, identifying areas with significant decreases in seismic wave velocity as damaged areas and potential fracture areas of the roof rock mass, thereby dynamically inverting the formation process and location of the roof fracture line.

[0055] Step S7 is the mutual verification stage of multiple monitoring methods. Data acquired by the wireless transmission borehole viewing camera 3, fiber optic grating sensor 8, and distributed acoustic sensor 7 are mutually verified. Using strain distribution data from fiber optic grating sensor 8, strain concentration zones and gradient zones inside and outside the fracturing influence zone are identified. Data from distributed acoustic sensor 7 is used to locate the position and energy of micro-fracture events generated in the rock mass under mining stress, inverting the spatial distribution of the fracture network and the roof fracture law. The dense areas of micro-fracture events and strain concentration zones are spatially superimposed and analyzed for mutual verification, jointly delineating the effective boundary of the fracturing fracture field and the range of rock mass damage. Combined with the original fractures identified in the image data, the temporal evolution law of rock mass stability reflected by strain and acoustic data during the mining process is analyzed to achieve dynamic early warning.

[0056] Example 2: This example provides another method for laying sensor cables; the remaining steps are the same as in Example 1. For example... Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 8 , Figure 9 and Figure 10 As shown, the specific implementation steps for the case where the sensor cable is laid inside the PVC pipe 9 are as follows.

[0057] The implementation methods of steps S1 and S2 are the same as in Example 1. First, a borehole 1 with a certain length and angle is drilled into the top plate to form a specific diameter. The borehole wall images before and after fracturing are obtained using a wireless transmission drilling peep lens 3. The crack information is identified through binarization processing, image segmentation and feature extraction.

[0058] Step S3 is the stage of forming a monitoring unit. For example... Figure 8 , Figure 9 and Figure 10 As shown, a sensing cable integrating a distributed acoustic sensor 7 and a fiber Bragg grating sensor 8 is laid inside the borehole 1 to form a monitoring unit. The sensing cable is made of glass fiber reinforced plastic (GFRP) optical cable, with an outer cladding covering the cable, and the distributed acoustic sensor 7 and fiber Bragg grating sensor 8 integrated internally. Unlike Embodiment 1, the sensing cable is laid on the inner wall of a PVC pipe 9 and fixed within the borehole 1 by grouting. Figure 9As shown, the sensing cable is laid close to the inner wall of the PVC pipe 9, avoiding the risk of cable loosening that may result from external entanglement. This method provides physical protection through the PVC pipe 9 to prevent the sensing cable from being damaged by rock shearing. The measuring point positions of the fiber optic grating sensor 8 and the spatial channel of the distributed acoustic sensor 7 are precisely aligned on the absolute depth coordinates of the borehole 1. Then, the monitoring function of the sensing cable is activated. Specifically, the axial and radial static or quasi-static strain data of the borehole 1 are collected through the array of fiber optic grating sensors 8 in the sensing cable; and dynamic vibration and sound wave signals along the entire length of the borehole 1 are collected through the distributed acoustic sensing fiber.

[0059] Step S4 is the stage of consolidating the optical fiber with the surrounding rock. Sealing slurry 10 is injected into the borehole 1 and the PVC pipe 9 to seal the borehole. For example... Figure 10 As shown, the grouting process can achieve a tight fit between the PVC pipe 9 and the surrounding rock 11, so that the borehole 1 and the surrounding rock 11 are solidified into one, so as to achieve long-term reliable coupling between the optical fiber and the surrounding rock 11, thereby transforming the abandoned fracturing borehole into a permanent downhole in-situ monitoring unit.

[0060] The implementation methods for steps S5 to S7 are the same as in Example 1. Fiber Bragg grating sensor 8 and distributed acoustic sensor 7 are used to monitor the fracturing effect in adjacent areas, conduct long-term monitoring of crack development and roof failure during mining operations, and verify the cross-validation of multiple monitoring methods. Utilizing the dense spatial sampling channels of the distributed acoustic sensor 7, the microseismic source is located by detecting the time difference between the arrival of P-waves and S-waves in different channels; the acoustic signals recorded by the distributed acoustic sensor 7 are differentiated by signal source; and the virtual seismic response is calculated using background noise cross-correlation technology to invert the roof failure pattern.

[0061] Example 3: This example provides a consolidation method based on precast concrete blocks, suitable for scenarios with high requirements for coupling quality. The remaining steps are basically the same as in Example 1. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 11 , Figure 12 and Figure 13 As shown, the specific implementation steps for the case where the sensor cable passes through the groove of the precast concrete block are as follows.

[0062] The implementation methods of steps S1 and S2 are the same as in Example 1. First, a borehole 1 with a certain length and angle is drilled into the top plate to form a specific diameter. The borehole wall images before and after fracturing are obtained using a wireless transmission drilling peep lens 3. The crack propagation trajectory is identified through binarization processing, image segmentation and feature extraction.

[0063] Step S3 is the stage of forming a monitoring unit. For example... Figure 11 , Figure 12 and Figure 13 As shown, a sensing cable integrating a distributed acoustic sensor 7 and a fiber Bragg grating sensor 8 is laid inside the borehole 1 to form a monitoring unit. The sensing cable is made of glass fiber reinforced plastic (GFRP) optical cable, with an outer cladding covering the cable and the distributed acoustic sensor 7 and fiber Bragg grating sensor 8 integrated inside. A groove is formed on the outer surface of a pre-fabricated cylindrical concrete block 12, and the sensing cable integrating the distributed acoustic sensor 7 and fiber Bragg grating sensor 8 is fixedly installed in the groove and sealed with encapsulating adhesive 13. Figure 12 As shown, a set of sensing devices is installed in one of the cylindrical concrete blocks 12, with the previous set of fiber optic sensing lines passing through the grooves of the next set of cylindrical concrete blocks 12, and the monitoring devices do not interfere with each other. Multiple cylindrical concrete blocks 12 are arranged at intervals and all are stored in a sleeve 14. The measuring point positions of the fiber optic grating sensors 8 and the spatial channels of the distributed acoustic sensors 7 are precisely aligned on the absolute depth coordinates of the borehole 1. Then, the monitoring function of the sensing cable is activated. Specifically, the axial and radial static or quasi-static strain data of the borehole 1 are collected through the fiber optic grating sensor 8 array in the sensing cable; and dynamic vibration and acoustic signals along the entire length of the borehole 1 are collected through the distributed acoustic sensing fibers.

[0064] Step S4 is the stage of consolidating the optical fiber with the surrounding rock. Sealing slurry 10 is injected into the borehole 1 and the outside of the sleeve 14 to seal the borehole. For example... Figure 13 As shown, the grouting process achieves a tight fit between the sleeve 14 and the surrounding rock 11, solidifying the borehole 1 and the surrounding rock 11 into a single unit. This ensures long-term reliable coupling between the surrounding rock 11 and the optical fiber, thereby transforming the abandoned fracturing borehole into a permanent downhole in-situ monitoring unit. The cylindrical concrete block 12, a rock-like material, is used because the mechanical properties of concrete and rock are similar, which improves strain transfer efficiency and enhances detection accuracy.

[0065] The implementation methods for steps S5 to S7 are the same as in Example 1. Fiber Bragg grating sensor 8 and distributed acoustic sensor 7 are used to monitor the fracturing effect in adjacent areas, conduct long-term monitoring of crack development and roof fracture during mining, and verify the interaction of multiple monitoring methods. Utilizing the dense spatial sampling channels of the distributed acoustic sensor 7, microseismic source location is achieved by detecting the time difference between P-waves and S-waves arriving at different channels; the acoustic signals recorded by the distributed acoustic sensor 7 are differentiated by signal source; and virtual seismic responses between channels are calculated using background noise cross-correlation technology. The spatiotemporal changes in seismic wave velocity in the virtual seismic response are continuously monitored, and areas of significant decrease in seismic wave velocity are identified as damaged areas and potential fracture zones in the roof rock mass, thereby dynamically reversing the formation process and location of the roof fracture line.

[0066] Example 4: As an example, the present invention also provides a fracturing hole inspection-fiber grating-distributed acoustic joint monitoring system for implementing the aforementioned method.

[0067] The system includes a borehole inspection module, a fracturing module, an integrated sensing unit, and a data processing and evaluation unit. The borehole inspection module includes a wireless transmission borehole inspection lens 3 integrated on the drill rod 2. The front end of the wireless transmission borehole inspection lens 3 is provided with a lens protective housing 4 for acquiring images of the inner wall of the borehole 1.

[0068] The fracturing module includes a one-way valve assembly 5 and a high-pressure pump 6. The one-way valve assembly 5 is mounted on the drill pipe 2 and fed into the target fracturing rock layer 18 in the borehole 1. The high-pressure pump 6 is connected to the one-way valve assembly 5 to carry out fracturing operations.

[0069] The integrated sensing unit includes the sensing cable, which integrates the distributed acoustic sensor 7 and the fiber optic grating sensor 8. The sensing cable is laid in the borehole 1 and is coupled to the surrounding rock 11 through the sealing grout 10.

[0070] Depending on different engineering requirements, the integrated sensing unit can be configured in three different ways. In the first configuration, the integrated sensing unit also includes a PVC pipe 9, with the sensing cable wound around the outside of the PVC pipe 9, as shown in Embodiment 1. In the second configuration, the sensing cable is laid on the inner wall of the PVC pipe 9, as shown in Embodiment 2. This method effectively prevents the sensing cable from being damaged by rock shear. In the third configuration, the integrated sensing unit also includes multiple spaced cylindrical concrete blocks 12 and sleeves 14. The outer surface of each cylindrical concrete block 12 has grooves for accommodating the sensing cable, and these grooves are sealed with sealing adhesive 13. Multiple cylindrical concrete blocks 12 are stored within the sleeves 14, as shown in Embodiment 3. This configuration improves strain transfer efficiency and detection accuracy by leveraging the similarity between the mechanical properties of the concrete material and the surrounding rock.

[0071] The data processing and evaluation unit is signal-connected to the integrated sensing unit and is configured to perform fusion analysis on the strain data collected by the fiber optic grating sensor 8 and the acoustic data collected by the distributed acoustic sensor 7, execute joint monitoring and evaluation steps, and output quantitative evaluation results.

[0072] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A combined monitoring method for fracturing hole inspection, fiber optic grating, and distributed acoustic monitoring, comprising the following steps: Step S1, Pre-fracturing borehole wall inspection: Drill a borehole (1) into the top plate, send the wireless transmission borehole inspection lens (3) integrated on the drill rod (2) into the borehole (1) to obtain the image of the borehole wall before fracturing, and use the one-way valve group (5) and high pressure pump (6) to fracture the target fracturing rock layer (18) in the borehole (1); Step S2, Hole wall inspection after fracturing: The drill rod (2) is retracted to drive the wireless transmission borehole inspection lens (3) to scan the rock layer image after fracturing again, and the images before and after fracturing are processed to quantitatively identify the crack propagation trajectory and complexity. Step S3: Forming a monitoring unit: The sensing cable integrating the distributed acoustic sensor (7) and the fiber optic grating sensor (8) is laid in the borehole (1), and the measuring point of the fiber optic grating sensor (8) is precisely aligned with the spatial channel of the distributed acoustic sensor (7) on the depth coordinate. Step S4, Consolidating the optical fiber and the surrounding rock: Injecting sealing slurry (10) into the borehole (1) to consolidate and couple the sensing cable with the surrounding rock (11), and converting the borehole (1) into a downhole in-situ monitoring unit; Step S5, monitoring the fracturing effect in adjacent areas: the fiber optic grating sensor (8) is used to record the static strain response caused by adjacent fracturing to evaluate stress disturbance, and the distributed acoustic sensor (7) is used to record the microseismic wave field to determine the range of the fracture network. Step S6: Long-term monitoring of roof breakage during mining: The fiber optic grating sensor (8) is used to monitor strain changes and warn of roof instability, and the distributed acoustic sensor (7) is used to capture acoustic emission and micro-vibration signals to delineate the roof breakage line; Step S7: Cross-verification of multiple monitoring methods: Overlay analysis of the dense micro-fracture event area and the strain concentration area, combined with the original fracture image to delineate the boundary of the pressure fracturing fracture field, to achieve dynamic early warning; In step S2, the method for processing images before and after fracturing includes image segmentation and feature extraction, tracking the propagation trajectory of the crack through a skeletonization algorithm, and quantitatively characterizing the complexity of the crack using fractal dimension. In step S3, the sensing cable is made of glass fiber reinforced plastic (GFRP) optical cable. The GFRP optical cable is wrapped with a cladding layer on the outside and integrates the distributed acoustic sensor (7) and the fiber optic grating sensor (8) inside. In step S4, the consolidation of the sensing cable with the surrounding rock (11) is achieved by using precast concrete blocks. Specifically, the outer surface of the precast cylindrical concrete block (12) is provided with a groove, and the sensing cable is fixedly installed in the groove and sealed with encapsulating glue (13). A set of sensing devices is installed in one of the cylindrical concrete blocks (12), and the previous set of optical fiber sensing lines passes through the groove of the next set of cylindrical concrete blocks (12). Multiple cylindrical concrete blocks (12) are arranged at intervals and stored in a sleeve (14), and the sealing slurry (10) is used to fill the sleeve (14) to achieve a tight fit between the sleeve (14) and the surrounding rock (11). In steps S5 and S6, the acoustic signals recorded by the distributed acoustic sensor (7) are distinguished by signal source. The signal source distinction is based on the occurrence time sequence, spatial location, waveform spectrum characteristics and strain response mode of the fiber optic grating sensor (8) to identify the source of the signal source as either adjacent fracturing operations or mining-induced fracture in this area. In step S6, the micro-seismic event is located based on the monitoring data of the distributed acoustic sensor (7). Specifically, the micro-seismic source is located by using the dense spatial sampling channels of the distributed acoustic sensor (7) and detecting the time difference between the arrival of longitudinal and transverse waves in different channels.

2. The fracturing hole inspection-fiber grating-distributed acoustic joint monitoring method according to claim 1, characterized in that, The sensor cable is laid out in the borehole (1) in one of the following ways: The sensing cable is wrapped around the outside of the PVC pipe (9); Alternatively, the sensing cable may be laid on the inner wall of a PVC pipe (9) and solidified by grouting to prevent the sensing cable from being damaged by rock shearing.

3. The fracturing hole inspection-fiber grating-distributed acoustic joint monitoring method according to claim 1, characterized in that, Based on the acoustic signals monitored by the distributed acoustic sensor (7), the roof fracture law is inverted, specifically including: using the background noise recorded by the distributed acoustic sensor (7), calculating the virtual seismic response between channels through noise cross-correlation technology, continuously monitoring the spatiotemporal changes of seismic wave velocity in the virtual seismic response, identifying the area of ​​significant decrease in seismic wave velocity as the damage area and potential fracture area of ​​the roof rock mass, thereby dynamically inverting the formation process and location of the roof fracture line.

4. A fracturing hole inspection-fiber grating-distributed acoustic joint monitoring system for implementing the method of claim 1, characterized in that, include: The drilling observation module includes the wireless transmission drilling observation lens (3) integrated on the drill rod (2), and the front end of the wireless transmission drilling observation lens (3) is provided with a lens protective shell (4) for acquiring images of the inner wall of the drill hole (1); The fracturing module includes a one-way valve assembly (5) and a high-pressure pump (6). The one-way valve assembly (5) is mounted on the drill rod (2) and fed into the target fracturing rock layer (18) in the borehole (1). The high-pressure pump (6) is connected to the one-way valve assembly (5) to carry out fracturing operations. An integrated sensing unit includes the sensing cable, which integrates the distributed acoustic sensor (7) and the fiber optic grating sensor (8). The sensing cable is laid in the borehole (1) and is coupled to the surrounding rock (11) through the sealing slurry (10). The data processing and evaluation unit is signal-connected to the integrated sensing unit and is configured to perform fusion analysis on the strain data collected by the fiber optic grating sensor (8) and the acoustic data collected by the distributed acoustic sensor (7), execute joint monitoring and evaluation steps, and output quantitative evaluation results.

5. The fracturing hole inspection-fiber grating-distributed acoustic joint monitoring system according to claim 4, characterized in that, The integrated sensing unit also includes a PVC pipe (9), and the sensing cable is wound around the outside of the PVC pipe (9) or laid on the inner wall of the PVC pipe (9); or, the integrated sensing unit also includes a plurality of spaced cylindrical concrete blocks (12) and sleeves (14), the outer surface of the cylindrical concrete blocks (12) is provided with grooves for accommodating the sensing cable, the grooves are sealed with encapsulating glue (13), and the plurality of cylindrical concrete blocks (12) are stored in the sleeves (14).

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