Multi-dimensional loading visualization system and method for improving penetration and pressure relief of rotary drilling

Abstract

The present application relates to coal seam permeability improvement and pressure relief technical field, and disclose a kind of multi-dimensional loading visual counter-rotating drilling into permeability improvement and pressure relief experimental system and method, the system includes counter-rotating drilling experiment platform, mobile control component, counter-rotating drilling drive component, drill pipe spacing adjusting component, intelligent sensing component, safety protection component, coal sample holder, stress control component, mechanical response and hole fracture evolution monitoring component, data acquisition and control component;The present application can simulate real in-situ stress environment, and combine built-in grating fiber, acoustic emission sensor group array and external DIC visual equipment, synchronously real-time capture the three-dimensional stress evolution characteristics inside coal sample under drilling disturbance and the macroscopic crack propagation law of surface;The present application can multi-dimensionally represent the pressure relief mechanism of counter-rotating drilling, provide accurate data and equipment support for the parameter optimization of in-situ coal seam gas extraction and pressure relief permeability improvement.

Description

Technical Field

[0001] This invention belongs to the field of coal seam permeability enhancement and pressure relief technology, specifically a multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system and method. Background Technology

[0002] my country has a vast geographical distribution and large reserves of coal. However, the heterogeneity, low permeability, and low gas saturation of coal seams often limit the efficiency of coalbed methane extraction. Furthermore, with increasing mining depth, the high-stress environment further reduces coal seam permeability, increasing the difficulty of gas drainage and exacerbating dynamic disasters such as coal and gas outbursts. In engineering, measures such as borehole decompression, deep-hole pre-fracturing controlled blasting, high-pressure water injection, hydraulic fracturing, and hydraulic slotting are commonly used to improve permeability and relieve pressure in coal seams.

[0003] For borehole pressure relief, traditional drilling techniques have certain limitations. For example, large-diameter single-auger drilling mainly relies on the rotation of a single drill rod to achieve slag removal and drilling. The construction is relatively simple, but the borehole trajectory is difficult to control precisely due to the influence of the drill string's own weight and formation stress. In addition, the drill string is at risk of breakage, which seriously reduces the pressure relief range and gas extraction efficiency. Raised shaft drilling can effectively control the borehole trajectory and the straightness of the hole, but it has disadvantages such as long construction period, complex equipment disassembly and transportation, and high consumption of manpower and material resources.

[0004] The currently developed counter-rotating drilling method can simultaneously drill two parallel boreholes, which not only allows for precise control of the borehole trajectory but also effectively breaks down the stress concentration on the borehole wall formed by traditional single-hole drilling, significantly increasing the pressure relief range of the coal seam. Simultaneously, the two drill rods rotating in opposite directions, combined with large helical blades, greatly enhance the slag removal capacity, effectively reducing the risks of drill bit pressure and jamming, and significantly improving the safety and stability of borehole construction. Many scholars have conducted research on the pressure relief characteristics of this method from a numerical simulation perspective. However, in actual drilling processes, due to the heterogeneous characteristics of coal and rock, interfacial frictional resistance, drilling spacing, and other factors, numerical simulation data cannot accurately reflect the actual mechanical evolution mechanism during counter-rotating drilling. Currently, there is still a lack of experimental equipment to simulate the internal stress changes and external fracture evolution of coal samples during counter-rotating drilling under real geological conditions. Summary of the Invention

[0005] To address the aforementioned technical deficiencies, this invention provides a multi-dimensional loading and visualization-based counter-rotating drilling permeability enhancement and pressure relief experimental system and method. It uses a simulated counter-rotating drilling experimental platform as the main body, combined with a visualized large-size coal sample holder to simulate the multi-dimensional geostress environment of the sample. Furthermore, it incorporates grating optical fibers, DIC visualization equipment, and an array of acoustic emission sensors to characterize the permeability enhancement and pressure relief mechanism of counter-rotating drilling from multiple dimensions. This invention can simulate the evolution of stress and strain around the borehole and the mechanism of internal fracture propagation in coal samples under different counter-rotating drilling parameters, thereby providing scientific data support for actual permeability enhancement and pressure relief engineering in the field.

[0006] This invention is achieved through the following technical solution: A multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system includes a counter-rotating drilling experimental platform, a motion control component, a counter-rotating drilling drive component, a drill rod spacing adjustment component, an intelligent sensing component, a safety protection component, a coal sample holder, a stress control component, a mechanical response and pore fracture evolution monitoring component, and a data acquisition and control component. The counter-rotating drilling experimental platform includes a sliding movable frame; the movement control component drives the movable frame to move horizontally; the counter-rotating drilling drive component is connected to two parallel auger drill rods and provides counter-rotating power to the two auger drill rods; the drill rod spacing adjustment component is connected between the two auger drill rods to adjust the spacing between them; the intelligent sensing component identifies the working characteristics of the auger drill rods during drilling; the safety protection component is linked with the intelligent sensing component to intervene and protect against transient impacts or overloads that may occur during equipment operation. The coal sample holder is used to hold the coal sample, aligning the drilling direction of the auger with the coal sample. The stress control component applies a load to the coal sample through the coal sample holder to simulate the in-situ stress environment. The mechanical response and pore fracture evolution monitoring component captures the stress and strain characteristics inside the coal sample under drilling disturbance in real time by embedding a grating fiber in the coal sample. Combined with an external DIC visualization device and an acoustic emission sensor array, it characterizes the macroscopic displacement and fracture spatial evolution of the coal sample surface and interior. The data acquisition and control component is used for closed-loop control of the operation of each unit of the equipment, as well as real-time data acquisition, processing, and analysis.

[0007] Furthermore, the motion control component includes an X-axis servo motor, a first transmission wheel, a second transmission wheel, and an X-axis transmission screw; the X-axis servo motor is fixedly connected to the support frame, and its output end is connected to the first transmission wheel; the first transmission wheel is connected to the second transmission wheel via a synchronous belt, and the second transmission wheel rotates coaxially with the X-axis transmission screw; both ends of the X-axis transmission screw are connected to the support frame via fixed brackets, and the X-axis transmission screw is provided with a screw nut that is threaded to it; a screw nut bracket sleeved on the outside of the screw nut is fixedly connected to the lower end of the movable frame; a thrust sensor is connected between the screw nut bracket and the lower end of the movable frame for real-time measurement of the horizontal thrust during the drilling process.

[0008] Furthermore, the counter-rotating drilling drive assembly includes a spindle servo motor, a dynamic torque sensor, a seventh transmission gear, an eighth transmission gear, a fourth transmission wheel, a tenth transmission gear, a ninth transmission gear, a sixth transmission wheel, a fifth transmission wheel, a third transmission wheel, and a first transmission shaft. The output end of the spindle servo motor is connected to the first transmission shaft in sequence via a flexible coupling and a dynamic torque sensor. The seventh transmission gear is fixedly sleeved on the first transmission shaft. The seventh transmission gear meshes with the eighth transmission gear, and the eighth transmission gear, the fourth transmission wheel, and the tenth transmission gear are coaxially fixed on the second transmission shaft. When the seventh transmission gear rotates, it drives the second transmission shaft to rotate in the opposite direction. The tenth transmission gear meshes with the ninth transmission gear, and the ninth transmission gear and the sixth transmission wheel are coaxially fixed on the third transmission shaft. The sixth transmission wheel is connected to the fifth transmission wheel via a synchronous belt, and the fourth transmission wheel is connected to the third transmission wheel via a synchronous belt. The fifth and third transmission wheels are respectively connected to the corresponding auger drill rods.

[0009] Furthermore, the safety protection components include a magnetic particle slip coupler and an adaptive anti-seize module; there are two magnetic particle slip couplers, whose input ends are connected to the third and fifth transmission wheels respectively, their output ends are connected to the corresponding auger rod, and their control ends are connected to the PLC controller via wires; the adaptive anti-seize module is built into the PLC controller, and extracts the first derivative of the torque using a five-point cubic smoothing algorithm based on the signal from the dynamic torque sensor.

[0010] Furthermore, the drill pipe spacing adjustment assembly includes positive and negative threaded screws, two sets of drill pipe straightening brackets, a reducer, and a closed-loop stepper motor. The drill pipe straightening brackets are slidably connected to the movable frame. The positive and negative threaded screws pass through the two sets of drill pipe straightening brackets and are connected to the movable frame at both ends. One end of the screw is connected to the output end of the reducer via a flexible coupling. The input port of the reducer is connected to the closed-loop stepper motor. The positive and negative threaded screws have a first threaded section and a second threaded section with opposite directions of rotation. The nut seats at the bottom of the two sets of drill pipe straightening brackets are respectively connected to the first threaded section and the second threaded section. Each set of drill pipe straightening brackets supports a corresponding spiral drill pipe above it.

[0011] Furthermore, the intelligent sensing component consists of an acoustic emission monitoring unit, a visual monitoring unit, and a wireless temperature measurement unit; The acoustic emission monitoring unit includes a high-frequency acoustic emission sensor mounted on the drill rod straightening support. The acoustic emission sensor is connected to a computer and a PLC controller via a preamplifier and a multi-channel acoustic emission acquisition instrument. The visual monitoring unit includes an industrial camera mounted in front of the coal sample holder and a visual image processing unit built into the computer. The industrial camera is used to continuously acquire image features of the borehole section of the auger drill rod and transmit them to the computer. The wireless temperature measurement unit consists of a thin-film thermocouple. The thin-film thermocouple is installed in a miniature wire groove behind the cutting edge of the drill bit at the front end of the auger drill rod and is covered with a wear-resistant coating. Its compensating wire is laid in the central through hole of the auger drill rod, and the non-contact transmission of the thermal load signal is achieved through a signal receiving device on the drill rod straightening support.

[0012] Furthermore, the stress control component includes a stress control console, which is equipped with a servo pressurizer, a loading controller, a hydraulic station, a hydraulic control valve platform, a loading cylinder, a cylinder head, and a flat pressure head. The loading cylinder is used to store the pressurizing medium. The servo pressurizer is connected to the loading controller, which is used to adjust and output the system pressure of the hydraulic station in real time. The oil inlet of the hydraulic control valve platform is connected to the hydraulic station, and its oil outlet is connected to each loading cylinder through multiple independent branch pipes. Each loading cylinder has a cylinder head at its output end, and a square flat pressure head is connected to the end of the cylinder head. A pressure sensor is sandwiched between the cylinder head and the flat pressure head, and the flat pressure head is in contact with the surface of the coal sample. The pressure sensor is led out from the sealed joint on the side wall of the loading cylinder through a signal line and connected to the loading controller.

[0013] Furthermore, the mechanical response and pore / crack evolution monitoring component includes a grating fiber monitoring unit, an external DIC visualization monitoring unit, and an acoustic emission sensor array; The coal sample holder includes a sample fixing frame. The sample holder wall has through holes and is fitted with high-voltage fiber optic sealing connectors. U-shaped grooves are formed on the pressure-bearing end faces of the upper and rear faces of the sample holder base where they contact the coal sample. The grating fiber monitoring unit includes multiple sets of grating fibers and a fiber optic demodulator. Each grating fiber is surrounded by a protective tube, embedded in the U-shaped groove, and extends into the coal sample. It exits the cavity through the sealing connector and is connected to the fiber optic demodulator via an optical signal line. The multiple sets of grating fibers are arranged in a three-dimensional spatial arrangement with equal or variable spacing along the central axis, radial direction, and transverse direction of the counter-rotating borehole inside the sample. Each set of grating fibers integrates multiple grating measurement points. The external DIC visualization monitoring unit includes an industrial camera and an illumination source; the lenses of the industrial camera and the illumination source are directly facing the observation port on the sample holder. The acoustic emission sensor array uses an ultra-thin flexible piezoelectric film probe, which is directly laid between the end face of the flat pressure head and the coal sample to capture stress waves generated by internal cracks in the coal sample in real time. The acquired signal is led out through the sample holder housing via a data cable, passes through a preamplifier, and is connected to the acoustic emission data acquisition instrument.

[0014] Furthermore, the data acquisition and control components include a computer, a data acquisition unit, a control cabinet, and data cables; the control cabinet houses a PLC controller; the motion control component, the counter-rotating drilling drive component, the drill rod spacing adjustment component, the intelligent sensing component, the safety protection component, the stress control component, and the mechanical response and hole fracture evolution monitoring component are all connected to the data acquisition unit via data cables; the computer is connected to both the data acquisition unit and the PLC controller.

[0015] A multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental method, based on the aforementioned experimental system, includes the following steps: S1. Experimental preparation: Prepare a cubic coal sample. On the side of the coal sample facing the transparent observation port, spray a white primer evenly and create randomly distributed black speckles to meet the recognition requirements of the DIC digital image correlation method. Arrange grating optical fibers inside the coal sample and connect the components. Turn on the external lighting source and industrial camera, focus and calibrate the speckle image on the sample surface. S2. Sample stress setting: Stress is applied to the coal sample through the stress control component. After the pressure sensor reaches the preset stress level, the system automatically enters the pressure holding state. At this time, the data acquisition device is turned on to record the initial center wavelength of the current grating fiber and use this as the stress-strain baseline before drilling. S3. Setting parameters for counter-rotating drilling equipment: Input the axis spacing of the counter-rotating drill rods on the computer control interface. The drill rod spacing adjustment component will start and automatically stop adjusting after the spacing between the two auger drill rods reaches the set value. Set the auger drill rod thrust and drilling speed on the computer control interface. The counter-rotating drilling drive component and the movement control component will start synchronously, driving the two auger drill rods to cut into the coal sample in opposite directions for drilling and slag removal.

[0016] S4. Data Measurement: At the instant the drill bit cuts and disturbs the coal sample, the built-in grating optical fiber senses the micro-strain around the borehole in real time. The data acquisition unit acquires the wavelength signal of the grating optical fiber at high frequency and converts it into a three-dimensional stress-strain dynamic curve along the transverse / longitudinal direction inside the coal sample. Simultaneously, the industrial camera, triggered by the same mechanism, continuously captures speckle deformation images of the coal sample surface at a high frame rate through the observation port. The DIC software is used to calculate in real time the evolution characteristics of the displacement field of the coal body around the borehole and the generation and propagation process of macroscopic cracks. At the same time, during the drilling process, the axial resistance and the torque and speed of the main shaft during the advancement of the movable frame are captured in real time, and the computer generates the thrust / torque / speed curves as a function of time. Meanwhile, the temperature parameters at the cutting point during the drilling process, the slag discharge images at the borehole mouth acquired in real time by the industrial camera, the volume flow rate and particle size distribution characteristics of the sample particles, and the coal and rock media characteristics identified by the spectrum captured by the acoustic emission sensor array are all generated and recorded in real time by the computer after being processed by the data acquisition unit. S5. Safety Protection System: The PLC controller operates an adaptive anti-seize drill module in real time, as well as temperature-torque over-limit protection: when the first derivative of the torque exceeds the set first-level slope threshold, the feed rate of the auger drill rod is automatically reduced and the drilling speed is increased; when the volumetric flow rate or temperature of the coal sample particles is abnormal, the PLC controller automatically reduces the excitation current of the magnetic powder slip coupler in the safety protection component, actively inducing controlled slip to alleviate the impact load; if its first derivative value continuously exceeds the set second-level slope threshold, the system automatically switches to high-frequency disturbance mode, outputs pulse torque to the counter-rotating drilling drive component, and resumes slag discharge; if the situation does not improve after the above adjustments, the system triggers a forced protection program, the PLC controller controls the equipment to stop, the movable frame retracts, and the auger drill rod exits the coal sample; S6. Data Analysis of Pressure Relief Mechanism: After drilling reaches the predetermined depth, drilling stops, the experiment ends, the system is depressurized, the auger drill rod is withdrawn, and the industrial camera is turned off; finally, the drill rod torque / thrust data, coal sample stress / strain, deformation, acoustic emission characteristic parameters, and fracture propagation images recorded in the computer are exported, and the pressure relief range and permeability enhancement mechanism of the coal sample after counter-rotating drilling under the current parameters are comprehensively analyzed.

[0017] The beneficial effects of this invention compared to the prior art are as follows: 1. This invention involves three-dimensionally arranging multiple sets of grating optical fibers at equal or varying intervals along the centerline, radial direction, and axial direction of the counter-rotating borehole inside the sample, with each set integrating multiple grating measurement points. To ensure stable signal transmission under high stress, a U-shaped groove is installed on the pressure-bearing end face of the pressure head in contact with the coal sample, along with a fiber optic protective tube. This ensures non-destructive, in-situ, and real-time measurement of the transverse / longitudinal stress and strain evolution characteristics within the coal sample during drilling. Simultaneously, industrial cameras and illumination sources are arranged at multiple angles outside the observation window, and the displacement field distribution and macroscopic fracture evolution characteristics of the loaded coal sample surface are acquired in real-time using digital image correlation (DIC). An array of acoustic emission sensors is deployed on the coal sample surface to capture stress waves generated by internal fractures during drilling in real time. A time-of-arrival (TOA) positioning algorithm is used to continuously calculate the three-dimensional spatial coordinates of the acoustic emission sources for fracture initiation and propagation within the coal sample. Simultaneously, multi-source spatiotemporal feature fusion is performed on acoustic emission three-dimensional spatial signals, strain data measured by fiber optic gratings, and external displacement field data from DIC to reconstruct and dynamically map the internal fracture propagation and stress damage process of coal and rock under pressure relief disturbance, achieving full-scale closed-loop comprehensive monitoring of three-dimensional dynamic damage. This allows for a systematic study of the evolution of the borehole stress field, pressure relief range, and macroscopic fracture propagation characteristics under different drilling conditions, providing multi-dimensional data support for the pressure relief mechanism of counter-rotating drilling.

[0018] 2. This invention employs a large-size cubic visual gripper with a square opening penetrating the housing on the feed end face. This provides a feed channel for the auger drilling and also serves as an observation window for the DIC visualization monitoring components. The gripper is equipped with loading cylinders on all four sides and a multi-channel independently adjustable hydraulic control system. Computer-controlled automatic stress loading of the sample achieves closed-loop control of the stress loading system. Simultaneously, multi-dimensional dynamic disturbance loading can be performed, enabling low-frequency cyclic loading and unloading or transient impact loading. The overall process is simple to operate, ensuring that the stress around the sample closely approximates the actual coal seam. Furthermore, placing a pressure sensor between the cylinder head and the flattening head effectively eliminates interference from the attenuation of force in the hydraulic transmission pipe, achieving real-time and accurate sensing and feedback of in-situ stress loading on the coal sample.

[0019] 3. This invention achieves automatic and precise adjustment of the auger drill rod spacing through the coordinated use of a closed-loop stepper motor, a right-angle reducer, and forward and reverse lead screws in the drill rod spacing adjustment system. Simply inputting the drill rod spacing into the IPC host computer allows the system to automatically adjust and precisely shift the drill rod spacing, significantly shortening experimental preparation time and avoiding errors caused by manual adjustment, thus improving experimental efficiency. In terms of mechanical transmission, the use of multiple gear transmission groups of different diameters, three sets of transmission shafts, a vertical shaft support, and a servo motor in the counter-rotating drilling drive system precisely achieves synchronous reverse rotation of the counter-rotating drill rod, effectively reducing the meshing tangential force on the tooth surface and providing a good mechanical buffer against sudden load changes during drilling, ensuring the stability of the experimental equipment and extending its service life. Simultaneously, by connecting it with a thrust sensor and a spindle dynamic torque sensor, and effectively integrating it through a PLC controller, real-time and accurate acquisition and dynamic closed-loop control of drilling parameters (thrust, torque, and speed) are achieved, providing a reliable experimental platform and data support for in-depth understanding of the optimization of counter-rotating drilling process parameters.

[0020] 4. This invention, by integrating an acoustic emission monitoring unit, a visual monitoring unit, and a wireless temperature measurement unit, can accurately identify the hardness and fragmentation state of the medium during the cutting process, quantify the slag discharge flow rate and particle size, and record the microsecond-level temperature changes of the cutting edge. This provides a highly sensitive, accurate, and sufficient predictive database for the subsequent safety protection system. Furthermore, this system, in conjunction with the safety protection system, can proactively identify unexpected situations such as chipping, jamming, and drill bit seizure during drilling. Before the drill rod torque reaches its destructive limit, the system can detect abnormal data from the intelligent sensing system and proactively identify the risk of drill bit seizure. The PLC controller quickly intervenes in the magnetic powder slip coupler, actively inducing controlled slip and simultaneously activating the adaptive anti-screwing module. Without stopping the machine, this flexibly reduces transient impact loads, greatly ensuring the safe operation of the experimental equipment. Attached Figure Description

[0021] Figure 1 This is a front view of the overall structure of the experimental system; Figure 2 A schematic diagram showing the connection between the first and second transmission wheels; Figure 3 A schematic diagram showing the connection between the fourth and third transmission wheels; Figure 4 A top view of the drill pipe straightening support and the positive and negative threaded screws; Figure 5 This is a schematic diagram of the transmission structure of the ninth and tenth transmission gears. Figure 6 Top view of the sample fixing frame; Figure 7 Diagram of the fiber optic grating assembly; Figure 8This is a schematic diagram of the stress control component connection; Figure 9 This is a schematic diagram showing the connection of the data acquisition and control components.

[0022] In the picture: 1—Support frame; 3—X-axis servo motor; 4—First transmission wheel; 5—Second transmission wheel; 6—Fixed frame; 7—X-axis transmission screw; 8—Screw nut bracket; 9—Connecting plate; 10—Guide rail; 11—Slider; 12—Thrust sensor; 13—Modible frame; 14—Main spindle servo motor; 15—Flexible coupling; 16—Dynamic torque sensor; 17—Seventh transmission gear; 18—Eighth transmission gear; 19—Ninth transmission gear; 20—Tenth transmission gear; 21—Fourth transmission wheel; 22—Sixth transmission wheel; 23—Third transmission wheel; 24—Fifth transmission wheel; 25—First transmission shaft; 26—Second transmission shaft; 27—Third transmission shaft; 28—Synchronous belt; 29—Drill pipe straightening bracket; 30—Positive and negative thread screw; 31— Vertical shaft support; 32—nut seat; 33—reducer; 34—closed-loop stepper motor; 35—auger drill rod; 36—universal wheel; 37—magnetic powder slip coupler; 38—thin-film thermocouple; 39—signal receiving device; 40—acoustic emission sensor; 41—sample fixing frame; 42—observation port; 43—servo pressurizer; 44—loading controller; 45—hydraulic station; 46—hydraulic control valve platform; 47—pressure sensor; 48—sealing joint; 49—oil pipe; 50—loading cylinder; 51—cylinder head; 52—flattening head; 53—stress control console; 54—serpentine silicone heating wire; 55—acoustic emission sensor array; 56—preamplifier; 57—acoustic emission acquisition instrument; 58—U-shaped groove; 59—high-pressure fiber optic sealing joint; 61—Fiber optic grating; 62—Grate measuring point; 63—Industrial camera; 64—Light source; 65—Data cable; 66—Data acquisition unit; 67—Control cabinet; 68—PLC controller; 69—Computer. Detailed Implementation

[0023] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto. Example 1

[0024] See Figures 1 to 9This embodiment proposes a multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system, including a counter-rotating drilling experimental platform, a movement control component, a counter-rotating drilling drive component, a drill rod spacing adjustment component, an intelligent sensing component, a safety protection component, a large square visual coal sample holder, a stress control component, a mechanical response and pore fracture evolution monitoring component, and a data acquisition and control component.

[0025] The counter-rotating drilling experimental platform includes a support frame 1 and a movable frame 13; the movable frame 13 is located above the support frame 1; the support frame 1 is a frame structure, mainly used to support the moving control components, and universal wheels 36 are installed at the four corners of the bottom of the support frame 1 to facilitate the overall movement and positioning of the experimental system.

[0026] The aforementioned mobile control component is mainly used to drive the movable frame 13 to move horizontally; the aforementioned counter-rotating drilling drive component uses the movable frame 13 as a carrier, connects to two parallel spiral drill rods 35, and provides counter-rotating power to the two spiral drill rods 35; the aforementioned drill rod spacing adjustment component is used to adjust the spacing between the two spiral drill rods 35; the aforementioned intelligent sensing component is mainly used to identify the working condition characteristics of the drill rods during drilling; the aforementioned safety protection component is linked with the intelligent sensing component to intervene and protect against transient impacts or overloads that may occur during equipment operation; the aforementioned large square visual coal sample holder... The holder is used to place large coal samples, including a sample fixing frame 41; the stress control component adds load to the coal sample through a visualized coal sample holder to simulate the in-situ stress environment; the mechanical response and pore fracture evolution monitoring component captures the stress and strain characteristics inside the coal sample under drilling disturbance in real time through a built-in grating optical fiber 61, and combines it with an external DIC visualization device and an acoustic emission sensor array 55 to characterize the macroscopic displacement and fracture spatial evolution law of the coal sample surface and interior; the data acquisition and control component is used for closed-loop control of the operation of each unit of the equipment, as well as real-time data acquisition, processing and analysis.

[0027] Specifically, the movable frame 13 has a connecting plate 9 with a hollow center at the bottom. The connecting plate 9 is fixed to the upper end of the support frame 1. Two rows of linear guide rails 10 are fixed horizontally above the connecting plate 9. A slider 11 is provided above the guide rails 10. The movable frame 13 moves above the support frame 1 by sliding the slider 11 with the guide rails 10. The sample fixing frame 41 is located at the upper right side of the movable frame 13 and is used to place the sample.

[0028] The aforementioned motion control component mainly consists of an X-axis servo motor 3, a first transmission wheel 4, a second transmission wheel 5, and an X-axis transmission screw 7. The X-axis servo motor 3 is fixedly connected to the support frame 1, and its output end is connected to the first transmission wheel 4. The first transmission wheel 4 is connected to the second transmission wheel 5 via a synchronous belt, and the second transmission wheel 5 rotates coaxially with the X-axis transmission screw 7. Both ends of the X-axis transmission screw 7 are connected to the support frame 1 via fixed brackets 6. The X-axis transmission screw 7 is provided with a screw nut that has a threaded fit with it. A screw nut bracket 8 sleeved on the outside of the screw nut is fixedly connected to the lower end of the movable frame 13. A thrust sensor 12 is connected between the screw nut bracket 8 and the lower end of the movable frame 13 for real-time measurement of the horizontal thrust during the drilling process.

[0029] The counter-rotating drilling drive assembly mainly consists of a spindle servo motor 14, a dynamic torque sensor 16, a seventh transmission gear 17, an eighth transmission gear 18, a fourth transmission wheel 21, a tenth transmission gear 20, a ninth transmission gear 19, a sixth transmission wheel 22, a fifth transmission wheel 24, a third transmission wheel 23, a first transmission shaft 25, and a magnetic powder slip coupler 37. The output end of the spindle servo motor 14 is connected to the first transmission shaft 25 in sequence through a flexible coupling 15 and a dynamic torque sensor 16. The seventh transmission gear 17 is fixedly sleeved on the first transmission shaft 25. On a drive shaft 25, a flexible coupling 15 with a serpentine spring rotates coaxially with it. This flexible coupling 15 is used to compensate for minor axial, radial, and angular deviations, and also to absorb the impact load generated when the motor starts or when the drill bit hits the sample. The seventh drive gear 17 meshes with the eighth drive gear 18. The eighth drive gear 18, the fourth drive wheel 21, and the tenth drive gear 20 are coaxially fixed on the second drive shaft 26. When the seventh drive gear 17 rotates, it drives the second drive shaft 26 and its related components to rotate in the opposite direction. The tenth transmission gear 20 meshes with the ninth transmission gear 19, and the ninth transmission gear 19 is coaxially fixed to the sixth transmission wheel 22 on the third transmission shaft 27. Due to the meshing and reversing action of the gears, the rotation direction of the third transmission shaft 27 (i.e., the sixth transmission wheel 22) is always opposite to the rotation direction of the second transmission shaft 26 (i.e., the fourth transmission wheel 21). The sixth transmission wheel 22 and the fourth transmission wheel 21 are parallel in space. The sixth transmission wheel 22 is connected to the fifth transmission wheel 24 via a synchronous belt 28, and the fourth transmission wheel 21 is connected to the third transmission wheel 23 via a synchronous belt 28. A vertical shaft support 31 is fixed at the upper end of the movable frame 13 to support the transmission between the gears. The fifth transmission wheel 24 and the third transmission wheel 23 are respectively connected to the corresponding spiral drill rod 35 via a magnetic powder slip coupler 37.

[0030] Each transmission gear and drive wheel is circumferentially fixed to its corresponding transmission shaft via a flat key and axially fixed via axial limiting components. The transmission ratio between the tenth transmission gear 20 and the ninth transmission gear 19 is 1:1 to ensure absolute synchronization of their speeds. The diameters of the ninth transmission gear 19 and the tenth transmission gear 20 are significantly larger than those of the other gears. This increases the center distance between the second transmission shaft 26 and the third transmission shaft 27, providing ample space for the subsequent parallel synchronous belt assembly and auger drill rod 35, avoiding structural interference. Furthermore, the large diameter design reduces the tangential force at this core stress point during meshing, improving the gear's load-bearing capacity and fatigue life. Its larger moment of inertia also acts as a buffer during sudden changes in drilling load, significantly improving the stability of equipment operation.

[0031] The drill pipe spacing adjustment assembly mainly consists of two auger drill pipes 35, positive and negative threaded screws 30, two sets of drill pipe straightening supports 29, a reducer 33, a closed-loop stepper motor 34, two guide rails, and a slider. The guide rails are fixed to the upper end of the movable frame 13. Each set of drill pipe straightening supports 29 has a slider at its bottom, which is slidably mounted on the guide rail to realize the movement of the drill pipe straightening supports 29. The positive and negative threaded screws 30 are inserted below the two sets of drill pipe straightening supports 29, and both ends are connected to the movable frame 13. One end of the screw is connected to the output end of the reducer 33 through a flexible coupling 15. The input port of the reducer 33 is connected to the closed-loop stepper motor 34 to realize the adjustment of the distance between the two auger drill pipes 35. The speed reduction and torque increase characteristics of the machine 33 amplify the driving torque of the closed-loop stepper motor 34, improving the fine-tuning accuracy of the rotation of the forward and reverse threaded screws 30 and the self-locking stability of the system when stationary. The forward and reverse threaded screws 30 have a first thread section and a second thread section with opposite directions of rotation. The nut seats 32 at the bottom of the two sets of drill rod straightening brackets 29 are respectively connected to the first thread section and the second thread section. When the forward and reverse threaded screws 30 rotate, the two sets of drill rod straightening brackets 29 are driven by the different directions of rotation of the threads, causing them to move synchronously towards the center or away from both sides along the transverse guide rail, thereby achieving symmetrical adjustment of the distance between the two spiral drill rods 35. Each set of drill rod straightening brackets 29 supports one spiral drill rod 35 above it.

[0032] The safety protection component consists of a magnetic particle slip coupler 37 and an adaptive anti-seize module. There are two magnetic particle slip couplers 37, whose input ends are connected to the third transmission wheel 23 and the fifth transmission wheel 24 respectively, and whose output ends are connected to the corresponding auger drill rod 35. The control end is connected to a PLC controller 68 via a wire. The torque transmission stiffness is dynamically adjusted in real time by regulating the excitation current to buffer transient impact loads during drilling. The adaptive anti-seize module is built into the PLC controller 68 and extracts the first derivative of the torque using a five-point cubic smoothing algorithm based on the signal from the dynamic torque sensor 16. When the first derivative exceeds the set first-order slope threshold for m consecutive sampling periods, the PLC controller 68 automatically reduces the feed rate of the X-axis servo motor through the internal PID regulator, while the spindle servo motor slightly increases the drilling speed. If the first derivative value exceeds the set second-order slope threshold for m consecutive periods, the system automatically switches to high-frequency disturbance mode, the spindle servo motor outputs pulse torque and resumes slag discharge. If the situation does not improve after the above adjustments, the system triggers a forced protection program, the PLC controller 68 controls the equipment to stop, the movable frame retracts, and the auger drill rod 35 exits the coal sample.

[0033] The intelligent sensing component consists of an acoustic emission monitoring unit, a visual monitoring unit, and a wireless temperature measurement unit. The acoustic emission monitoring unit mainly includes a high-frequency acoustic emission sensor 40 installed on the drill pipe straightening support 29. The breaking sound signal generated by the drill pipe cutting end is transmitted to the acoustic emission sensor 40 through the auger drill pipe 35. The acoustic emission sensor 40 is connected to the computer 69 and PLC controller 68 in sequence through the preamplifier 56 and the multi-channel acoustic emission acquisition instrument 57. By analyzing the spectral characteristics of the acoustic emission signal, the hardness and breaking state of the cutting medium are identified. When the precursor of the impact of hard foreign objects is detected, it is linked with the magnetic powder slip coupler 37 to actively induce slip to buffer the mechanical load and prevent equipment damage.

[0034] The visual monitoring unit includes an industrial camera 63 installed in front of the sample fixing frame 41 and a vision image processing unit (CV) built into the computer 69. The industrial camera 63 is used to continuously acquire image features of the borehole section of the auger rod 35 and transmit them to the computer 69. The computer vision (CV) image processing unit extracts the volume flow rate and particle size distribution characteristics of the discharged sample particles in real time and makes a joint judgment with the data of the adaptive anti-seize module: when a sharp drop in the slag discharge rate or intermittent gushing is detected, the system intervenes in advance, actively induces controlled slip through the excitation current of the magnetic powder slip coupler 37, and starts the adaptive anti-seize module to restore slag discharge.

[0035] The wireless temperature measurement unit consists of a thin-film thermocouple 38, which is installed in a miniature wire groove behind the cutting edge of the drill bit at the front end of the auger rod 35 and covered with a wear-resistant coating. Its compensating wire is laid in the central through-hole of the auger rod 35, and non-contact transmission of the thermal load signal is achieved through the signal receiving device 39 on the drill rod straightening bracket 29. When the temperature exceeds the limit, the PLC controller 68 adjusts the magnetic powder slip coupler 37 in conjunction to reduce the excitation current, thereby cutting off the rigid torque transmission and suppressing frictional heat generation from the drill bit.

[0036] The shell of the sample holder 41 is made of high-strength steel, and its interior is a multi-dimensional pressure chamber for large cubic samples. The walls of the pressure chamber are integrated with serpentine silicone heating wires 54 to provide a high-precision constant temperature or variable temperature loading environment for the coal sample to simulate the temperature field of deep in-situ coal seams. A square opening is provided on the drilling side end face, which penetrates the shell. The square opening is coaxial with the counter-rotating drill bit and serves as the feed channel during the spiral drilling process. It also serves as the observation port 42 for the subsequent DIC visualization monitoring component.

[0037] The stress control assembly includes a stress control console 53, which is equipped with a servo pressurizer 43, a loading controller 44, a hydraulic station 45, a hydraulic control valve platform 46, a loading cylinder 50, a cylinder head 51, and a flattening head 52. The loading cylinder 50 is used to store the pressurizing medium. The servo pressurizer 43 is connected to the loading controller 44, which can perform multi-dimensional dynamic disturbance loading to adjust and output the system pressure of the hydraulic station 45 in real time, realizing low-frequency cyclic loading and unloading or transient impact loading. The oil inlet of the hydraulic control valve platform 46 is connected to the hydraulic station 45, and its oil outlet is connected to multiple independent branch pipes (oil supply pipes 49). Each loading cylinder 50 is connected to a separate loading cylinder 50 for independent servo pressure regulation of the loading channels in different directions. Each loading cylinder 50 has a cylinder head 51 at its output end, and a square flat head 52 is connected to the end of the cylinder head 51. A high-frequency pressure sensor 47 is sandwiched between the cylinder head 51 and the flat head 52, and the flat head 52 is in contact with the surface of the coal sample. The pressure sensor 47 is led out from the sealing joint 48 on the side wall of the loading cylinder 50 through a signal line and connected to the loading controller 44 for real-time feedback of the in-situ loading stress, so as to realize closed-loop servo control of each loading cylinder 50, thereby providing a stable stress environment for the coal sample.

[0038] The mechanical response and pore fracture evolution monitoring component includes a grating fiber monitoring unit, an external DIC visualization monitoring unit, and an acoustic emission sensor array 55, which are used to characterize the macroscopic displacement and fracture spatial evolution of the coal sample surface and interior. The grating fiber monitoring unit includes multiple sets of grating fibers 61 and a fiber optic demodulator; the sample holder 41 has a through hole on its wall and is fitted with a high-voltage fiber optic sealing connector 59; the flat pressure head 52 on the upper and rear ends of the sample holder 41 base has a U-shaped groove 58 on the pressure end face that is in contact with the coal sample; the grating fiber 61 is surrounded by a protective tube, embedded in the U-shaped groove 58 and extends into the coal sample, is led out of the cavity through the sealing connector 48, and is connected to the fiber optic demodulator through an optical signal line to convert the optical signal into the deformation of the coal sample, and finally the stress data of the coal sample is calculated by computer software; the multiple sets of grating fibers 61 are arranged in three dimensions with equal or variable spacing in the center axis, radial and transverse directions of the counter-rotating borehole inside the sample, and each set of grating fibers 61 integrates multiple grating measuring points 62 to obtain the stress and strain evolution characteristics of the coal sample in the transverse and longitudinal directions under drilling disturbance in real time. The external DIC visualization monitoring unit includes an industrial camera 63 and an illumination source 64; the lenses of the industrial camera 63 and the illumination source 64 are facing the transparent observation port 42. The industrial camera 63 equipped in this system acquires the displacement field distribution and macroscopic fracture evolution characteristics of the surface of the loaded coal sample in real time through digital image correlation (DIC) and displays them on the computer 69.

[0039] The acoustic emission sensor array 55 employs an ultra-thin flexible piezoelectric film probe, which is directly installed between the end face of the pressure head 52 and the coal sample to capture stress waves generated by internal cracks in the coal sample in real time. The acquired signals are led out through the sample holder 41 housing via a data cable 65, passed through a preamplifier 56, and connected to the acoustic emission data acquisition instrument 57. During drilling, the computer 69 receives multi-channel acoustic emission signals in real time and uses a time-of-arrival (TOA) positioning algorithm to continuously calculate the three-dimensional spatial coordinates of the acoustic emission sources for the initiation and propagation of internal cracks in the coal sample. By fusing the three-dimensional spatial signals of acoustic emission, strain data measured by the fiber optic grating array, and external displacement field data from the DIC, the propagation of internal cracks and stress damage processes in the coal and rock under pressure relief disturbance are reconstructed and dynamically mapped, achieving full-scale closed-loop comprehensive monitoring of three-dimensional dynamic damage.

[0040] The data acquisition and control components mainly consist of a computer 69, a data acquisition unit 66, a control cabinet 67, a data cable 65, and various sensors and servo motors connected to them. The control cabinet 67 houses a PLC controller 68, which has a built-in adaptive anti-seize module. The thrust sensor 12, dynamic torque sensor 16, thin-film thermocouple 38, acoustic emission sensor 40, pressure sensor 47, grating fiber optic cable 61, and industrial camera 63 are all connected to the data acquisition unit 66 via the data cable 65. The X-axis servo motor 3, spindle servo motor 14, closed-loop stepper motor 34, acoustic emission sensor 40, magnetic powder slip coupler 37, and signal receiving device 39 are all connected to the data acquisition unit 66 and the PLC controller 68 via the data cable 65. The computer 69 is connected to both the data acquisition unit 66 and the PLC controller 68. The computer 69 has a built-in computer vision (CV) image processing unit and digital image correlation (DIC) method, which can simultaneously display the acoustic emission characteristics, temperature characteristics, and image characteristics of the auger drill pipe orifice section during the drilling process, as well as the stress data, displacement field data, and grating fiber stress-strain data converted by the fiber optic demodulator during the counter-rotating drilling process. All of these are processed and displayed on the computer in real time. The screw speed and feed rate are set on the computer, and the motor parameters are controlled by the PLC controller 68 to drive the equipment. The computer displays the torque and thrust of the auger drill pipe 35 in real time during the drilling process. At the same time, the screw spacing is also set by the computer 69, and the equipment adjusts itself automatically.

[0041] The working process of a multi-dimensional loading visualization counter-rotating drilling penetration enhancement and pressure relief experimental system includes the following steps: S1. Experimental Preparation: Prepare a large-sized cubic raw coal sample. On the side of the sample facing the transparent observation port 42, uniformly spray white primer and create randomly distributed black speckle patterns to meet the recognition requirements of the DIC digital image correlation method. Pre-drill micro-holes along the predetermined counter-rotating drilling axis, radial, and lateral positions. Insert the grating optical fiber 61, wrapped in a protective sleeve, into the micro-holes and grout with epoxy resin. Then, embed the grating optical fiber 61 into the pre-drilled U-shaped groove 58 on the end face of the flat pressure head 52, and finally connect it to the external data acquisition unit 66 through the sealed joint 48 on the side wall of the loading cylinder 50. After installing the remaining components, perform a self-test on the relevant circuitry of the equipment and confirm that it is correct. Turn on the external illumination source 64 and the industrial camera 63, focus, and calibrate the speckle image on the sample surface.

[0042] S2. Sample Stress Setting: Check and confirm the connection status of each hydraulic pipeline, sensor data line, and PLC controller 68. Input the set stress parameters into the loading controller 44. The servo pressurizer 43 and the hydraulic control valve platform 46 work together to drive the loading cylinders 50 in four directions to apply stress. After the pressure sensor 47 reaches the preset stress level, the system automatically enters the pressure holding state. At this time, turn on the data acquisition device 66 to record the initial center wavelength of the current grating fiber 61, and use this as the stress-strain baseline before drilling.

[0043] S3. Setting parameters for the counter-rotating drilling equipment: Input the axis spacing of the counter-rotating drill rods on the computer 69 control interface. The drill rod spacing adjustment component starts and automatically stops adjusting after the spacing between the two auger drill rods 35 reaches the set value. Set the thrust and drilling speed of the auger drill rods 35 on the computer 69 control interface; the counter-rotating drilling drive component, the spindle servo motor 14 and the X-axis servo motor 3 start synchronously, driving the two auger drill rods 35 in opposite directions of rotation to cut into the interior of the high-pressure sample for drilling and slag removal.

[0044] S4. Data Measurement: At the instant the drill bit cuts and disturbs the coal sample, the built-in grating optical fiber 61 senses the micro-strain around the borehole in real time. The data acquisition unit 66 acquires the wavelength signal of the grating optical fiber 61 at high frequency and simultaneously converts it into a three-dimensional stress-strain dynamic curve along the transverse / longitudinal direction inside the coal sample. Simultaneously triggered, the industrial camera 63 continuously captures speckle deformation images of the coal sample surface at a high frame rate through the transparent observation port 42. The DIC software is used to calculate in real time the evolution characteristics of the displacement field of the coal body around the borehole and the generation and propagation process of macroscopic cracks. At the same time, during the drilling process, the thrust sensor 12 captures the axial resistance of the moving frame 13 during the advancement process in real time, and the dynamic torque sensor 16 captures the torque and speed of the spindle in real time. The computer 69 generates a thrust / torque / speed curve with respect to time. At the same time, the temperature parameters at the cutting point during the drilling process, the slag discharge images at the borehole mouth acquired in real time by the industrial camera 63, the volume flow rate and particle size distribution characteristics of the sample particles, and the coal and rock media characteristics identified by the spectrum captured by the acoustic emission sensor 40 are all generated and recorded in real time by the computer after being processed by the data acquisition unit.

[0045] S5. Safety Protection System: The PLC controller 68 operates an adaptive anti-seize drill module in real time, and provides temperature-torque over-limit protection: when the first derivative of the torque exceeds the set first-level slope threshold, the feed rate of the auger drill rod 35 is automatically reduced and the drilling speed is increased; when the volumetric flow rate of the sample particles or the temperature displayed by the thin-film thermocouple 38 is abnormal, the PLC controller 68 automatically reduces the excitation current of the magnetic powder slip coupler 37, actively inducing controlled slip to alleviate the impact load; if its first derivative value continuously exceeds the set second-level slope threshold, the system automatically switches to high-frequency disturbance mode, the spindle servo motor 14 outputs pulse torque and resumes slag discharge; if the situation does not improve after the above adjustments, the system triggers a forced protection program, the PLC controller 68 controls the equipment to stop, the movable frame retracts, and the auger drill rod exits the coal sample.

[0046] S6. Data Analysis of Pressure Relief Mechanism: After drilling reaches the predetermined depth, drilling stops, the experiment ends, the system is depressurized, the drill rod is withdrawn, and the camera is turned off. Finally, the drill rod torque / thrust data, coal sample stress / strain, deformation, acoustic emission characteristic parameters, and fracture propagation images recorded in computer 69 are exported. The pressure relief range and permeability enhancement mechanism of the coal sample after counter-rotating drilling under the current parameters are comprehensively analyzed.

[0047] S7. Multi-parameter comparison experiment: Change the axial spacing of the counter-rotating drill rod, drilling rate, thrust, and loading stress, and repeat the above steps. Through multiple sets of experiments, quantitatively analyze the coal seam decompression response mechanism under different parameters and stress coupling effects, and provide optimal parameter configuration for the actual counter-rotating decompression and permeability enhancement process in the field. Example 2

[0048] This embodiment provides an experimental method for optimizing the anti-seize and slag removal characteristics and drilling parameters in counter-rotating drilling. The specific experimental steps are as follows: S1. Sample Preparation and System Initialization: Fix the soft coal seam sample onto the counter-rotating drilling experimental platform, turn on the IPC host computer and set the drill rod spacing. The PLC controller 68 controls the closed-loop stepper motor 34 to automatically adjust the two spiral drill rods 35 to the preset spacing. Focus and calibrate the industrial camera 63, and perform self-checks on the relevant circuits of the equipment to confirm that there are no errors.

[0049] S2. Verification of Drill Seizure Induction and Adaptive Protection: To simulate extreme drill seizure conditions, drilling parameters of "high feed rate and low spindle speed" were set on the IPC host computer. After the experiment started, the volumetric flow rate of coal slag carried out by the auger rod 35 was much lower than the rate of coal powder production from the drill bit, and the coal powder in the hole quickly accumulated and compacted. At this time, the information from the IPC host computer showed obvious anomalies, that is, the thrust and torque curves showed typical drill seizure characteristics of a slow rise in the early stage and an exponential surge in the later stage. The volumetric flow rate of particles extracted in real time by the computer vision (CV) image processing unit dropped, and the cutting edge temperature rose. At this time, the PLC controller 68 immediately triggered the adaptive safety protection component: reducing the excitation current of the magnetic powder slip coupler 37, actively inducing the transmission system to generate controlled slip, and flexibly cutting off the rigid impact load; at the same time, the internal PID regulator automatically reduced the feed rate of the X-axis servo motor 3 and increased the drilling speed of the spindle servo motor 14 slightly. This effectively verified the device's predictive and flexible protection capabilities under special working conditions.

[0050] S3. Drilling Parameter Optimization: After the experiment stops, the equipment is reset and shut down. After replacing the sample with one of the same specifications, different drill pipe feed rates and rotation speeds are set on the IPC host computer for orthogonal testing. When the optimal feed rate and rotation speed are set, the thrust and torque curves, slag discharge volume flow rate, acoustic emission, and temperature displayed in real time on the IPC host computer are all in a stable state. This is the optimal parameter for counter-rotating drilling that balances high cutting efficiency and safety. Example 3

[0051] This embodiment provides a study on the effect of different drill pipe spacing on pressure relief and permeability enhancement in counter-rotating drilling of coal seams. The specific experimental steps are as follows: S1. Experimental Preparation: Prepare a large-sized cubic raw coal sample. Evenly spray white primer onto the end face facing the observation port 42 and create randomly distributed black speckles to meet the recognition requirements of the DIC digital image correlation method. Install optical fiber 61 around a pre-drilled hole inside the coal sample and safely lead the signal line to the data acquisition unit 66. Turn on the external lighting source 64 and industrial camera 63. After checking and confirming that all equipment connections are correct, turn on the equipment.

[0052] S2. Parameter Setting: Activate the stress control system, set the axial stress during drilling to 9 MPa, and the remaining stresses to 18 MPa. Maintain constant pressure after the stress field around the coal sample reaches equilibrium. Five sets of experiments were conducted, with the axial spacing of the counter-rotating drill rods set to 20 mm, 40 mm, 60 mm, 80 mm, and 100 mm, respectively. First, the experiment with a drill spacing of 20 mm was conducted. The drill rod spacing was set using computer 69, and the experiment began after the equipment was ready.

[0053] S3. Drilling and Data Monitoring: The counter-rotating drill rod rotation speed is set to 120 r / min, and the axial feed speed is 5 mm / s. The PLC controller 68 controls the spindle servo motor 14 and the X-axis servo motor 3 to operate synchronously, and the drill rod begins to cut into the coal sample. During drilling, the computer 69 displays monitoring data in real time, including the three-dimensional stress-strain dynamic curve inside the coal sample, the evolution of the displacement field of the coal body around the borehole, and images of fracture generation and propagation.

[0054] S4. Experimental Data Analysis: After the counter-rotating drill reached the predetermined depth, drilling stopped, and the drilling stage ended. Subsequently, the stress control system was depressurized, the counter-rotating drill rod was withdrawn, and external equipment such as industrial cameras were turned off. Finally, the drill rod torque / thrust data, coal sample stress / strain, deformation, acoustic emission characteristic parameters, and fracture propagation images recorded in computer 69 were exported. A comprehensive analysis was conducted on the depressurization range and permeability enhancement effect on the coal sample when the counter-rotating drill rod spacing was 20 mm.

[0055] S5. Multi-parameter comparison: Reset the experimental system (replace with new samples of the same specifications), and adjust the axial spacing of the counter-rotating drill rods to 40 mm, 60 mm, 80 mm, and 100 mm respectively, repeating the above experimental steps in sequence. Finally, compare the five sets of data, quantitatively analyze the influence of different drill rod spacings on the pressure relief range and the degree of fracture development and penetration, and deeply reveal the control mechanism of the counter-rotating drill rod spacing on the borehole pressure relief range, thereby obtaining the optimal spacing parameters. Example 4

[0056] This embodiment provides a study on the influence of coal seam stress on pressure relief and permeability enhancement during counter-rotating drilling. The specific experimental steps are as follows: S1. Experimental Preparation: Prepare a large-sized cubic raw coal sample. Evenly spray white primer onto the end face facing the observation port 42 and create randomly distributed black speckles to meet the recognition requirements of the DIC digital image correlation method. Lay out a grating optical fiber 61 inside the coal sample and safely lead the signal line to the data acquisition unit 66. Then, turn on the external lighting source 64 and the industrial camera 63, and start the data acquisition unit 66 to acquire the initial reference data from various sensors. After checking and confirming that all equipment connections are correct, turn on the equipment.

[0057] S2. Parameter Setting: To study the stress relief and fracture propagation evolution laws of counter-rotating drilling under uniform and non-uniform stress conditions, two sets of stress loading control experiments were set up. For the uniform stress experiment, the sample was set to be subjected to uniform stress in all directions, and the stress on all four sides of the coal sample was set to 10 MPa using the stress control console 53. For the non-uniform stress experiment, the stress on both horizontal sides and the vertical stress were set to 20 MPa, and the stress at the top of the coal sample was set to 10 MPa. First, the uniform stress experiment simulation was carried out, with the stress set to 10 MPa. After the stress field reached equilibrium, the pressure was kept constant. At the same time, the spacing of the counter-rotating drill rods was set to 60 mm using computer 69. After the equipment was ready, the drilling experiment began.

[0058] S3. Drilling and Data Monitoring: The rotational speed of the counter-rotating drill rod is set to 120 r / min, and the axial feed rate is 5 mm / s. The PLC controller 68 controls the spindle servo motor 14 and the X-axis servo motor 3 to operate synchronously, and the drill rod begins to cut into the coal sample. During drilling, the computer 69 displays monitoring data in real time, including the three-dimensional stress-strain dynamic curve inside the coal sample, the evolution of the displacement field of the coal body around the borehole, and images of fracture generation and propagation.

[0059] S4. Experimental Data Analysis: After drilling reaches the predetermined depth, drilling stops, and the drilling stage ends. Subsequently, the stress control system is depressurized, the counter-rotating drill rod is withdrawn, and external industrial cameras and other equipment are turned off. Finally, the drill rod torque / thrust data, coal sample stress / strain, deformation, acoustic emission characteristic parameters, and fracture propagation images recorded in computer 69 are exported to comprehensively analyze the perforation depressurization range and permeability enhancement effect under the current uniform stress state.

[0060] S5. Multi-parameter comparison: Replace with a new sample, adjust the stress to conduct a non-uniform stress experiment simulation, and repeat the above experimental steps. Compare and analyze the two sets of data, and quantitatively analyze the differences in the stress relief range, stress-strain direction changes, and asymmetric crack propagation characteristics caused by counter-rotating drilling under uniform and non-uniform stress conditions, thereby revealing the correspondence between stress distribution characteristics and the stress relief range of counter-rotating drilling and the enhanced penetration mechanism.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multi-dimensional loading and visualization counter-rotating drilling permeability enhancement and pressure relief experimental system, characterized in that, It includes a counter-rotating drilling experimental platform, a motion control component, a counter-rotating drilling drive component, a drill rod spacing adjustment component, an intelligent sensing component, a safety protection component, a coal sample holder, a stress control component, a mechanical response and pore fracture evolution monitoring component, and a data acquisition and control component; The counter-rotating drilling experimental platform includes a sliding movable frame (13); the movement control component is used to drive the movable frame (13) to move horizontally; the counter-rotating drilling drive component is connected to two parallel auger drill rods (35) and is used to provide counter-rotating power to the two auger drill rods (35); the drill rod spacing adjustment component is connected between the two auger drill rods (35) and is used to adjust the spacing between the two auger drill rods (35); the intelligent sensing component is used to identify the working condition characteristics of the auger drill rods (35) during drilling; the safety protection component is linked with the intelligent sensing component and is used to intervene in transient impacts or overloads that occur during equipment operation. The coal sample holder is used to place the coal sample so that the drilling direction of the auger rod (35) is aligned with the coal sample. The stress control component adds load to the coal sample through the coal sample holder to simulate the in-situ stress environment. The mechanical response and pore fracture evolution monitoring component captures the stress and strain characteristics inside the coal sample under drilling disturbance in real time by embedding a grating fiber (61) in the coal sample, and combines it with the external DIC visualization equipment and acoustic emission sensor array (55) to characterize the macroscopic displacement and fracture space evolution law of the coal sample surface and interior. The data acquisition and control component is used for closed-loop control of the operation of each unit of the equipment, as well as real-time data acquisition, processing and analysis. The drill pipe spacing adjustment assembly includes a positive and negative threaded screw (30), two sets of drill pipe straightening brackets (29), a reducer (33), and a closed-loop stepper motor (34). The drill pipe straightening bracket (29) is slidably connected to the movable frame (13). The positive and negative threaded screw (30) passes under the two sets of drill pipe straightening brackets (29) and is connected to the movable frame (13) at both ends. One end of the screw is connected to the output end of the reducer (33) through a flexible coupling. The input port of the reducer (33) is connected to the closed-loop stepper motor (34). The positive and negative threaded screw (30) has a first thread section and a second thread section with opposite directions of rotation. The nut seat (32) at the bottom of the two sets of drill pipe straightening brackets (29) is respectively connected to the first thread section and the second thread section. Each set of drill pipe straightening brackets (29) supports a corresponding spiral drill pipe (35).

2. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 1, characterized in that, The aforementioned motion control component includes an X-axis servo motor (3), a first transmission wheel (4), a second transmission wheel (5), and an X-axis transmission screw (7); the X-axis servo motor (3) is fixedly connected to the support frame (1), and its output end is connected to the first transmission wheel (4); the first transmission wheel (4) is connected to the second transmission wheel (5) via a synchronous belt, and the second transmission wheel (5) rotates coaxially with the X-axis transmission screw (7); both ends of the X-axis transmission screw (7) are connected to the support frame (1) via a fixed frame (6), and the X-axis transmission screw (7) is provided with a screw nut that is threaded to it, and a screw nut bracket (8) sleeved on the outside of the screw nut is fixedly connected to the lower end of the movable frame (13); a thrust sensor (12) is connected between the screw nut bracket (8) and the lower end of the movable frame (13) for real-time measurement of the horizontal thrust during the drilling process.

3. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 1, characterized in that, The counter-rotating drilling drive assembly includes a spindle servo motor (14), a dynamic torque sensor (16), a seventh transmission gear (17), an eighth transmission gear (18), a fourth transmission wheel (21), a tenth transmission gear (20), a ninth transmission gear (19), a sixth transmission wheel (22), a fifth transmission wheel (24), a third transmission wheel (23), and a first transmission shaft (25). The output end of the spindle servo motor (14) is connected to the first transmission shaft (25) in sequence through a flexible coupling and the dynamic torque sensor (16). The seventh transmission gear (17) is fixedly sleeved on the first transmission shaft (25). The seventh transmission gear (17) meshes with the eighth transmission gear (18). (18) The fourth transmission wheel (21) and the tenth transmission gear (20) are coaxially fixed on the second transmission shaft (26); when the seventh transmission gear (17) rotates, it drives the second transmission shaft (26) to rotate in the opposite direction; the tenth transmission gear (20) meshes with the ninth transmission gear (19), and the ninth transmission gear (19) and the sixth transmission wheel (22) are coaxially fixed on the third transmission shaft (27); the sixth transmission wheel (22) is connected to the fifth transmission wheel (24) through a synchronous belt in two upward transmission, and the fourth transmission wheel (21) is connected to the third transmission wheel (23) through a synchronous belt in three upward transmission. The fifth transmission wheel (24) and the third transmission wheel (23) are respectively connected to the corresponding spiral drill rod (35).

4. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 3, characterized in that, The safety protection components include a magnetic powder slip coupler (37) and an adaptive anti-seize module; there are two magnetic powder slip couplers (37), whose input ends are connected to the third transmission wheel (23) and the fifth transmission wheel (24) respectively, their output ends are connected to the corresponding auger rod (35), and their control ends are connected to the PLC controller (68) through wires; the adaptive anti-seize module is built into the PLC controller (68), and extracts the first derivative of the torque using the signal from the dynamic torque sensor (16) and a five-point cubic smoothing algorithm.

5. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 1, characterized in that, The intelligent sensing component consists of an acoustic emission monitoring unit, a visual monitoring unit, and a wireless temperature measurement unit. The acoustic emission monitoring unit includes a high-frequency acoustic emission sensor (40) installed on the drill rod straightening support (29). The high-frequency acoustic emission sensor (40) is connected to the computer (69) and PLC controller (68) in sequence through a preamplifier (56) and a multi-channel acoustic emission acquisition instrument (57). The visual monitoring unit includes an industrial camera (63) installed in front of the coal sample holder and a visual image processing unit built into the computer (69). The industrial camera (63) is used to continuously acquire image features of the borehole section of the auger drill rod (35) and transmit them to the computer (69). The wireless temperature measurement unit is composed of a thin-film thermocouple (38). The thin-film thermocouple (38) is installed in the miniature wire groove behind the cutting edge of the drill bit at the front end of the auger drill rod (35) and is covered with a wear-resistant coating. Its compensation wire is laid in the central through hole of the auger drill rod (35). The non-contact transmission of the thermal load signal is realized through the signal receiving device (39) on the drill rod straightening support (29).

6. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 5, characterized in that, The stress control assembly includes a stress control console (53), which is equipped with a servo pressurizer (43), a loading controller (44), a hydraulic station (45), a hydraulic control valve platform (46), a loading cylinder (50), a cylinder head (51), and a flattening head (52). The loading cylinder (50) is used to store the pressurizing medium. The servo pressurizer (43) is connected to the loading controller (44), which is used to adjust and output the system pressure of the hydraulic station (45) in real time. The inlet end of the hydraulic control valve platform (46) is connected to... The hydraulic station (45) has its oil outlet connected to each loading cylinder (50) via multiple independent branch pipes. Each loading cylinder (50) has a cylinder head (51) at its output end. The end of the cylinder head (51) is connected to a square flat head (52), and a pressure sensor (47) is sandwiched between the cylinder head (51) and the flat head (52). The flat head (52) is attached to the surface of the coal sample. The pressure sensor (47) is led out from the sealing joint (48) on the side wall of the loading cylinder (50) via a signal line and connected to the loading controller (44).

7. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 6, characterized in that, The mechanical response and pore evolution monitoring component includes a grating fiber monitoring unit, an external DIC visualization monitoring unit, and an acoustic emission sensor array (55). The coal sample holder includes a sample fixing frame (41), the sample fixing frame (41) has a through hole and a high-voltage fiber optic sealing connector (59) installed on its wall surface; the flat pressure head (52) on the upper end face and the rear end face of the sample fixing frame (41) has a U-shaped groove (58) on the pressure end face that is in contact with the coal sample; the grating fiber monitoring unit includes multiple sets of grating fibers (61) and a fiber optic demodulator; the grating fiber (61) is covered with a protective tube, embedded in the U-shaped groove (58) and extends into the interior of the coal sample, is led out of the cavity through the sealing connector (48), and is connected to the fiber optic demodulator through an optical signal line; the multiple sets of grating fibers (61) are arranged in three dimensions with equal or variable spacing in the center axis, radial and transverse directions of the counter-rotating borehole inside the sample, and each set of grating fibers (61) integrates multiple grating measurement points (62). The external DIC visualization monitoring unit includes an industrial camera (63) and an illumination source (64); the lenses of the industrial camera (63) and the illumination source (64) are directly facing the observation port (42) on the sample fixing frame (41). The acoustic emission sensor array (55) uses an ultra-thin flexible piezoelectric film probe, which is directly laid between the end face of the flat pressure head (52) and the coal sample to capture stress waves generated by internal cracks in the coal sample in real time. The acquired signal is led out through the sample fixing frame (41) via the data line (65), passes through the preamplifier (56), and is connected to the multi-channel acoustic emission acquisition instrument (57).

8. The multi-dimensional loading visualization counter-rotating drilling permeability enhancement and pressure relief experimental system according to claim 7, characterized in that, The data acquisition and control components include a computer (69), a data acquisition unit (66), a control cabinet (67), and a data cable (65); a PLC controller (68) is placed inside the control cabinet (67); the motion control component, the counter-rotating drilling drive component, the drill rod spacing adjustment component, the intelligent sensing component, the safety protection component, the stress control component, and the mechanical response and hole fracture evolution monitoring component are all connected to the data acquisition unit (66) via the data cable (65); the computer (69) is connected to both the data acquisition unit (66) and the PLC controller (68).

9. A multi-dimensional loading and visualization method for counter-rotating drilling to enhance penetration and relieve pressure, characterized in that, Based on the experimental system of claim 8, and comprising the following steps: S1. Experimental preparation: Prepare a cubic coal sample. On the side of the coal sample facing the transparent observation port (42), spray a white primer evenly and make randomly distributed black speckles to meet the recognition requirements of the DIC digital image correlation method. Arrange grating optical fibers (61) inside the coal sample and connect each component. Turn on the external lighting source (64) and industrial camera (63) to focus and calibrate the speckle image on the sample surface. S2, Sample stress setting: Stress is applied to the coal sample through the stress control component. After the pressure sensor (47) reaches the preset stress level, the system automatically enters the pressure holding state. At this time, the data acquisition device (66) is turned on to record the initial center wavelength of the current grating fiber (61) and use it as the stress and strain baseline before drilling. S3. Setting parameters for counter-rotating drilling equipment: Input the axial spacing of the counter-rotating drill rods on the computer (69) control interface. The drill rod spacing adjustment component starts and automatically stops adjusting after the spacing between the two spiral drill rods (35) reaches the set value. Set the thrust and drilling speed of the spiral drill rods (35) on the computer (69) control interface. The counter-rotating drilling drive component and the movement control component start synchronously, driving the two spiral drill rods (35) to cut into the coal sample in opposite directions for drilling and slag removal. S4. Data Measurement: At the instant the drill bit cuts and disturbs the coal sample, the built-in grating fiber (61) senses the micro-strain around the hole in real time. The data acquisition unit (66) acquires the wavelength signal of the grating fiber (61) at high frequency and converts it into a three-dimensional stress-strain dynamic curve along the transverse / longitudinal direction inside the coal sample. Simultaneously, the industrial camera (63) is triggered to continuously capture speckle deformation images of the coal sample surface at a high frame rate through the observation port (42). The evolution characteristics of the displacement field of the coal body around the borehole and the generation of macroscopic cracks are calculated in real time using DIC software. The process of expansion; at the same time, during the drilling process, the axial resistance of the moving frame (13) and the torque and speed of the main shaft are captured in real time, and the thrust / torque / speed curves with respect to time are generated on the computer (69); at the same time, the temperature parameters of the cutting point, the slag discharge images of the borehole collected in real time by the industrial camera (63), the volume flow rate and particle size distribution characteristics of the sample particles, and the coal and rock media characteristics identified by the acoustic emission sensor array (55) are all generated and recorded in real time on the computer (69) after being processed by the data acquisition device; S5, Safety Protection System: The PLC controller (68) operates the adaptive anti-seize drill module in real time, and temperature-torque over-limit protection: that is, when the first derivative of the torque exceeds the set first-level slope threshold, the feed rate of the auger rod (35) is automatically reduced and the drilling speed is increased; when the volume flow rate or temperature of the coal sample particles is abnormal, the PLC controller (68) automatically reduces the excitation current of the magnetic powder slip coupler (37) in the safety protection component, and actively induces the generation of controlled slip to alleviate the impact load; if its first derivative value continuously exceeds the set second-level slope threshold, the system automatically switches to the high-frequency disturbance mode, outputs pulse torque to the counter-rotating drilling drive component and resumes slag discharge; if the situation does not improve after the above adjustment, the system triggers the forced protection program, the PLC controller (68) controls the equipment to stop, the movable frame moves backward, and the auger rod exits the coal sample; S6. Data analysis of pressure relief mechanism: After drilling reaches the predetermined depth, drilling stops, the experiment ends, the system is depressurized, the auger drill rod (35) is withdrawn, and the industrial camera (63) is turned off; finally, the drill rod torque / thrust data, coal sample stress / strain, deformation, acoustic emission characteristic parameters and crack propagation image recorded in the computer (69) are exported, and the pressure relief range and permeability enhancement mechanism of the coal sample after counter-rotating drilling under the current parameters are comprehensively analyzed.

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