While-drilling ultrasonic device and method for detecting inherent frequency of hole bottom rock

Abstract

The invention discloses a while-drilling ultrasonic device and method for detecting inherent frequency of hole bottom rock. The while-drilling ultrasonic device comprises a drill bit, a detection ultrasonic unit, a power ultrasonic unit, external control equipment and the like. The detection ultrasonic unit is arranged near a drill bit in a short section mode and comprises a multi-array-element transducer and an echo information processing and entropy weight-Topsis dynamic weighting algorithm module, db4 wavelet noise reduction and FFT transformation are sequentially carried out on echo signals through circumferential sector-by-sector, radial grading and axial layering three-dimensional frequency sweeping logic so as to extract formants, and the detection ultrasonic unit is used for detecting the ultrasonic signals. Calculating a weighted average frequency through a dynamic weighting algorithm; the power ultrasonic unit receives the frequency instruction and adjusts vibration parameters in real time. According to the device and the method, the hole bottom full-space inherent frequency is accurately detected, the importance difference of rock blocks on the rock breaking efficiency is dynamically distinguished, the frequency matching degree and the energy consumption efficiency of ultrasonic rock breaking are improved, the adaptability is high, and original factory installation and later transformation of various frequency-adjustable ultrasonic rock breaking equipment are supported.

Description

Technical Field

[0001] This invention relates to the fields of rock drilling technology and ultrasonic testing technology, and in particular to a drilling ultrasonic device and method for detecting the natural frequency of rock at the bottom of a borehole. Background Technology

[0002] In ultrasonic-assisted rock breaking technology, the matching degree between the vibration frequency output of the tunable rock breaking device and the natural frequency of the rock at the bottom of the borehole is the core factor determining rock breaking efficiency and energy consumption. Existing research has clearly shown that when the vibration frequency of the rock breaking device resonates with or is close to resonating with the natural frequency of the rock, a significant stress concentration effect occurs within the rock, which can greatly reduce rock breaking energy consumption and improve rock breaking efficiency. Therefore, accurate detection of the natural frequency of the rock at the bottom of the borehole is fundamental to achieving efficient ultrasonic rock breaking.

[0003] Existing technologies for detecting the natural frequencies of rocks near the drill bit bottom still suffer from numerous insurmountable shortcomings, severely limiting the application effectiveness of ultrasonic-assisted rock breaking technology. For example, while patents CN107780946A and CN103982131B have achieved the detection of parameters such as the natural frequencies of rocks in front of the drill bit using a single ultrasonic probe, providing a feasible approach for obtaining the mechanical properties of rocks near the drill bit during drilling, the vibration energy of tunable frequency rock breaking equipment typically exhibits a three-dimensional spatial distribution, generally covering the bottom area of ​​the hole with radial and axial extensions exceeding 10 cm and a circumferential radius of 360°. Existing detection methods using a single ultrasonic probe primarily focus on the local area at the bottom of the hole pointed to by the probe, leaving room for further optimization in terms of matching with the actual three-dimensional full-space range of the tunable frequency rock breaking equipment. This difference in coverage may prevent the acquired natural frequency parameters from fully reflecting the overall natural frequency characteristics of the rock within the area of ​​action of the rock breaking equipment.

[0004] Furthermore, the rock at the bottom of the borehole generally exhibits a stepped distribution pattern of "fractured zone, fractured zone, and intact zone" in both radial and axial directions. The rock fracture state and physical and mechanical properties differ significantly in different regions, and their influence on rock-breaking efficiency also varies. However, current drilling monitoring technology does not differentiate between rock fracture states, using a homogenized averaging algorithm to calculate the natural frequency of the rock at the bottom of the borehole without assigning differentiated weights based on the degree of fracture in different regions. This results in the final output frequency significantly deviating from the actual natural frequency of the key rock-breaking areas. Since the detected frequency is the core basis for equipment frequency tuning, this deviation further leads to insufficient real-time matching of equipment frequency tuning, and a substantial reduction in the representativeness and effectiveness of the detected data.

[0005] Therefore, there is an urgent need for a natural frequency detection technology that can achieve full three-dimensional spatial coverage detection at the bottom of the borehole, accurately distinguish the characteristics of rock fracture areas, and efficiently link with frequency-adjustable rock breaking equipment, in order to solve the problems of narrow detection range, insufficient frequency representativeness, and poor adaptability of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as limited detection range of natural frequencies of rocks at the bottom of the borehole, large frequency errors due to failure to distinguish rock fragmentation states, and poor adaptability, this invention provides a drilling ultrasonic device and method for detecting the natural frequencies of rocks at the bottom of the borehole. This enables accurate detection of natural frequencies throughout the entire borehole space, dynamic differentiation of the importance of rock fragments, and efficient linkage with adjustable frequency rock breaking equipment, thereby improving the frequency matching degree of ultrasonic rock breaking and reducing rock breaking energy consumption.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a hole, comprising a drill bit, a detection ultrasonic unit, a power ultrasonic unit, an external control device, a drill rod, and a cooling and chip removal system; the drill rod is coaxially connected to the power ultrasonic unit, the detection ultrasonic unit, and the drill bit in sequence along the axial direction;

[0008] The detection ultrasonic unit is a core detection module for the natural frequency of rock near the drill bit, which is fixed near the drill bit in the form of a short section; the power ultrasonic unit is a core vibration module for rock breaking, used to receive instructions from external control equipment to adjust vibration parameters;

[0009] The drill bit surface is equipped with a pressure sensor for collecting drilling pressure data, and the drill bit is provided with a water outlet around its circumference, which is connected to the cooling and chip removal system. The cooling and chip removal system includes a water pipe arranged along the central axis of the drill rod. The water pipe passes through the ultrasonic detection unit and finally branches at the drill bit and connects with the water outlet, which is used to inject water to remove residual rock cuttings at the bottom of the hole during the detection preparation stage.

[0010] The external control device has a built-in lithological parameter library and a dual ultrasonic system control unit for controlling the start and stop of the detection ultrasonic unit and the power ultrasonic unit and adjusting their parameters.

[0011] Furthermore, the ultrasonic detection unit includes an ultrasonic detection subsection, an echo information processing module, an algorithm processing module, a monitoring and control module, and a data transmission module. The modules of the ultrasonic detection unit are electrically connected to achieve orderly signal and data transmission. The ultrasonic detection subsection has a hollow cylindrical structure, internally containing a mechanical disk, a central rod, a fixed shaft, an electric push rod, and an array transducer. There are at least two mechanical disks, arranged parallel to each other along the axial direction of the ultrasonic detection subsection. The diameter of the mechanical disk is smaller than the drill bit diameter and parallel to the drill bit end face.

[0012] The central rod is coaxially inserted through the center of each mechanical disk, and its two ends are fixedly connected to the ultrasonic testing section; the electric push rod corresponds to each mechanical disk, and the output end of the electric push rod is connected to the mechanical disk to drive the mechanical disk to move along the central rod axis;

[0013] The fixed shaft is coaxially fixed to the inner cavity of the detection ultrasonic short section and passes through each mechanical disk. The interior of the fixed shaft is hollow to accommodate the water pipes of the cooling chip removal system.

[0014] The mechanical disk has several radial telescopic rods evenly distributed along its radial direction. The fixed end of each radial telescopic rod is fixedly connected to the center of the mechanical disk, and the telescopic end of each radial telescopic rod is fixedly connected to an array element support block. The array element transducer is disposed on the array element support block.

[0015] The array element carrier block is equipped with a position sensing sensor, which is used to collect the spatial coordinates of the array element transducer in real time and transmit them to the algorithm processing module; the array element transducer has an angle deflection function, which is adjusted to the optimal transmission angle through echo intensity feedback.

[0016] Furthermore, a sound-insulating section is provided between the detection ultrasonic unit and the power ultrasonic unit. The two ends of the sound-insulating section are fixedly connected to the detection ultrasonic unit and the power ultrasonic unit, respectively. Several sound-insulating grooves are opened inside the sound-insulating section to isolate the vibration interference generated by the power ultrasonic unit during operation.

[0017] Furthermore, an isolation plate corresponding to each array element transducer is provided on the outer wall of the detection ultrasonic short section at the position of each array element transducer;

[0018] The isolation plate is an arc-shaped plate, the curvature of which matches the curvature of the outer wall of the ultrasonic testing section. A retractable sealing curtain is provided around the edge of the isolation plate, and the isolation plate is connected to the outer wall of the ultrasonic testing section through the retractable sealing curtain. Auxiliary push rods are provided on the inner side of both ends of the isolation plate near the ultrasonic testing section. The extension and retraction direction of the auxiliary push rods is consistent with that of the radial extension rod, and a return spring and a miniature pressure sensor are provided inside the auxiliary push rods. The return spring is used to drive the isolation plate and the retractable sealing curtain to return to their original positions when the array transducer retracts. The miniature pressure sensor is used to detect the contact pressure between the isolation plate and the hole wall to determine the contact state with the hole wall.

[0019] Furthermore, the input end of the echo information processing module is electrically connected to the array element transducer of the ultrasonic short section, and the output end is electrically connected to the algorithm processing module. It is used to receive the echo signal collected by the array element transducer, and sequentially perform db4 wavelet basis noise reduction, time domain truncation and fast Fourier transform on the echo signal. After extracting the frequency domain spectrum, the frequency points with amplitude ≥ 80% of the maximum amplitude and duration ≥ 3 pulse periods are selected as resonance peaks to determine the natural frequency of each rock block.

[0020] The algorithm processing module is configured to: based on the real-time spatial position of the array element transducers collected by the position sensing sensor, control the emission timing of the multi-array element transducers through an electronic delay algorithm to achieve focusing of the ultrasonic beam at a specified rock segment; simultaneously call the lithological parameter library of the external control device, and combine the amplitude stability, spectral dispersion, and radial position coefficient and axial depth coefficient corresponding to the spatial position of the array element output by the echo information processing module, calculate the final weighted average frequency through a dynamic weighting algorithm combining the entropy weighting method and the TOPSIS algorithm;

[0021] The data transmission module has a bidirectional data transmission function. On the one hand, it transmits the collected data and processing results of each module of the detection ultrasound unit to the external control device. On the other hand, it transmits the instructions of the external control device to the detection ultrasound unit and the power ultrasound unit.

[0022] Furthermore, the monitoring and control module is the core coordinating component of the ultrasonic detection unit. Its input end is electrically connected to the pressure sensor, position sensing sensor, and miniature pressure sensor, respectively, and its output end is electrically connected to the data transmission module. The monitoring and control module is used to synchronously collect and summarize the real-time data of each sensor, and feed the summarized data back to the external control device through the data transmission module. The external control device triggers the switching between drilling mode and detection mode based on the data.

[0023] Furthermore, the sweep frequency parameters of the array element transducers are set as follows: the sweep frequency range is 20kHz-50kHz, and the frequency step is 1kHz; and the array element transducers on each mechanical disk form a ring array, and the sweep frequency is performed in the order of circumferential sector-by-sector mode, radial graded mode, and axial layered mode; wherein, the circumferential sector-by-sector mode is divided according to the unobstructed sector around the drill bit, each sector corresponds to at least 2 array element transducers, and the angle interval between sectors is 45°-90°; the radial graded mode is graded according to the extension length of the radial telescopic rod; the axial layered mode is layered according to the axial spacing of the mechanical disks, and each layer corresponds to the axial block of the rock at the bottom of the hole, and the block thickness is consistent with the axial spacing of the mechanical disks.

[0024] This invention also discloses a drilling ultrasonic method for detecting the natural frequency of rock at the bottom of a borehole, based on the aforementioned drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole, comprising the following steps:

[0025] S1. Drilling and Trigger Judgment: The drill rod drives the drill bit to drill normally. The pressure sensor collects drilling pressure data in real time. After being summarized by the monitoring and control module, the data is transmitted to the external control device through the data transmission module. The external control device compares the data. When it is determined that the real-time drilling pressure is greater than or equal to the preset drilling pressure threshold, the real-time drilling speed is less than or equal to the preset drilling speed threshold, and this state lasts for a preset time, it sends a detection preparation command to the monitoring and control module.

[0026] S2. Detection Preparation: After receiving the detection preparation instruction, the monitoring and control module sends a confirmation signal to the external control device through the data transmission module. The external control device issues an execution instruction to stop the vibration of the power ultrasonic unit and simultaneously controls the cooling chip removal system to start, injecting water into the bottom of the hole at a low flow rate of 5-10L / min through the water pipe and outlet to remove residual rock chips.

[0027] S3, 3D frequency sweep detection: The device switches to detection mode, and the monitoring and control module calls the pre-stored drill bit diameter and shape information. Combined with the actual drill bit action radius and the ultrasonic rock breaking influence depth in the lithology parameter library, the axial block thickness of the rock at the bottom of the hole is determined, and a 3D model of the rock at the bottom of the hole is constructed.

[0028] By controlling the mechanical disc to extend and retract along the central rod axis, the axial distance between two adjacent mechanical discs is made consistent with the axial segment length; by controlling the extension of the radial telescopic rod, the array element transducer and array element support block are driven to move in a direction exceeding the drill bit radius. During the movement, the array element support block first touches the isolation plate, and then the telescopic sealing curtain is driven to move to the hole wall through the auxiliary push rod; when the micro pressure sensor detects that the contact pressure reaches the preset pressure threshold, the radial telescopic rod stops extending.

[0029] Each array element transducer deflects independently. The echo information processing module provides real-time feedback on the echo intensity at each deflection angle, and adjusts the array element transducer to the emission angle when the echo intensity reaches its maximum value.

[0030] Subsequently, the array element transducers of the ring array perform frequency sweeping according to the three-dimensional rock model at the bottom of the hole, with a frequency range of 20kHz-50kHz and a frequency step of 1kHz, in the order of circumferential sector mode, radial hierarchical mode, and axial layer mode. At the same time, the algorithm processing module controls the transmission timing of each array element transducer through electronic delay technology, so that the ultrasonic beam is accurately focused on the corresponding rock block, and each array element transducer receives the echo signal of the rock block in its corresponding sector.

[0031] S4. Signal Processing and Frequency Calculation: The echo information processing module sequentially performs db4 wavelet basis noise reduction, time domain truncation, and FFT transformation on the echo signals received by each array element transducer to extract the frequency domain spectrum of each rock block and screen the resonance peaks to determine the inherent frequency of each block.

[0032] The algorithm processing module calls the unit energy consumption rock breaking efficiency in the lithology parameter library of the external control equipment, and combines the amplitude stability, spectrum dispersion and radial position coefficient and axial depth coefficient output by the echo information processing module with the radial position coefficient and axial depth coefficient collected by the position sensing sensor. The weight of each rock block is calculated by a dynamic weighting algorithm that combines the entropy weight method and the TOPSIS algorithm. The final weighted average frequency is calculated based on the inherent frequency of each block and the corresponding weight.

[0033] S5. Parameter Adjustment and Lithology Early Warning: The monitoring and control module transmits the final weighted average frequency to the external control device through the data transmission module. The external control device controls the power ultrasonic unit to adjust the vibration frequency based on the final weighted average frequency.

[0034] The monitoring and control module records the weighted average frequency of three consecutive tests and calculates the frequency difference between two adjacent tests. If any difference exceeds the preset frequency mutation threshold, a lithology warning is triggered. After the lithology warning is triggered, the algorithm processing module automatically loads the parameter library adapted to the new lithology from the external control equipment and recalibrates the axial spacing of the mechanical disk, the extension length of the radial telescopic rod, and the frequency sweep logic of the array element transducer. When the frequency difference to be detected is ≤ the preset frequency mutation threshold, the lithology warning is lifted, the power ultrasonic unit restarts, and drilling resumes.

[0035] Furthermore, the core quantitative indicators of the dynamic weighted algorithm combining the entropy weight method and the TOPSIS algorithm in step S4 include five positive indicators, namely, rock breaking efficiency per unit energy consumption η, amplitude stability S, spectral dispersion D, radial position coefficient R, and axial depth coefficient Z.

[0036] Each positive indicator is respectively from , , , , Calculated;

[0037] In the above formulas, V i E represents the resonant rock-breaking velocity corresponding to rock fragmentation under the corresponding lithology. i V represents the rock-breaking energy consumption for fracturing this segment under the corresponding lithology. i With E i All parameters are derived from the lithological parameter library of external control equipment and were measured through indoor lithological fracturing experiments; σ is the standard deviation of the echo amplitude after noise reduction of rock blocks; Var is the variance of the frequency domain spectrum of rock blocks; r i r is the actual radial distance from the center of the rock block at the bottom of the hole to the center of the bottom of the hole; r0 is the main breaking radius of the drill bit; r i Data collected by a position sensing sensor; r0 represents pre-recorded drill bit parameters; z i z is the actual axial depth of the rock block center at the bottom of the borehole; z0 is the axial range affected by the ultrasonic rock-breaking energy of the corresponding lithology; z i Data is collected by a position sensing sensor; z0 comes from a lithological parameter library of an external control device.

[0038] Furthermore, the specific calculation method of the dynamic weighting algorithm in step S4 is as follows:

[0039] S41. Data Standardization: Standardize the measured indicators in the blocks according to the positive indicator formula. Standardize to the [0,1] interval;

[0040] In the formula: x ij For the i-th rock block, the original data for the j-th index; min(x j ) represents the minimum value of all blocks on the j-th index; max(x) j ) represents the maximum value of all blocks on the j-th index; y ij The value of the i-th rock fragment after standardization of the j-th index is in the range [0,1].

[0041] S42. Calculation of objective indicator weights using the entropy weight method: By calculating the probability distribution and information entropy of the indicators, the final objective indicator weights are obtained.

[0042] The formula for calculating the probability distribution of the index is: ;

[0043] In the formula, p ij Let be the probability of the i-th block in the j-th index; ε is the minimum value, taken as 10. −10 n represents the total number of rock fragments;

[0044] The formula for calculating information entropy is: Where, k = 1 / lnn;

[0045] The formula for calculating the weight of objective indicators is: ,in The sum of the percentage of valid information for all indicators, ensuring .

[0046] S43. Construct a weighted standardized matrix: ;

[0047] In the formula, V ij y is the weighted standardized value of the i-th block on the j-th indicator; ij The value of the i-th block after standardization of the j-th index is in the range [0,1]. Let be the objective weight of the j-th indicator;

[0048] S44. TOPSIS algorithm for calculating block proximity: determining the ideal solution. Negative ideal solution Calculate the Euclidean distance from the partition to the ideal solution.

[0049] Proximity: ;

[0050] In the formula, The optimal value for the j-th indicator; The worst value of the j-th indicator; Let be the spatial distance between the i-th block and the optimal block; C is the spatial distance between the i-th block and the worst block; i Let be the proximity of the i-th block, ranging from [0,1].

[0051] S45. Weight normalization and frequency calculation: Calculate the final weighted average frequency by dividing the weights into blocks.

[0052] The formula for calculating block weight is: ;

[0053] The final weighted average frequency is calculated using the following formula: ;

[0054] In the formula, Let be the final weight of the i-th block; Let be the natural frequency of the i-th rock fragment.

[0055] The beneficial effects of this invention are:

[0056] (1) This invention achieves full coverage detection of the three-dimensional space at the bottom of the hole by using the coordinated design of axial extension and retraction of the mechanical disk, over-radius extension of the radial telescopic rod and small-angle deflection of the array element transducer, combined with the frequency sweeping logic of circumferential sector-by-sector, radial gradation and axial layering. It effectively distinguishes the stepped distribution of rock fracture zone, fracture zone and intact zone at the bottom of the hole. The position sensing sensor built into the array element bearing block obtains the spatial position information of the blocks. Combined with the dynamic weighting algorithm, it assigns differentiated weights to different blocks, avoids frequency deviation caused by homogenization averaging, improves the representativeness and accuracy of frequency detection, solves the problem of limited detection range of the prior art, and matches the actual working area of ​​the adjustable frequency rock breaking equipment.

[0057] (2) The present invention designs a sound-insulating short section to isolate vibration interference, a retractable sealing curtain to protect the detection environment, and a cooling chip removal system to remove rock chips, which ensures the stability and accuracy of the detection signal from multiple dimensions and provides a reliable data basis for frequency calculation; the data transmission module realizes bidirectional linkage between the detection unit and external control equipment and power ultrasonic unit, and the detection results are fed back in real time and the rock breaking vibration parameters are dynamically adjusted so that the rock breaking frequency is accurately matched with the natural frequency of the rock, significantly reducing the energy consumption of crushing and improving the rock breaking efficiency; each module of the device is assembled in the form of a short section, without changing the core structure of the original rock breaking equipment, and is compatible with various ultrasonic vibration rock breaking equipment with adjustable frequency function. It supports original factory installation and later modification, has a wide range of applications and a high degree of automation. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention during drilling;

[0059] Figure 2 This is a schematic diagram illustrating the structure of the ultrasonic detection unit of the present invention;

[0060] Figure 3 This is a schematic diagram illustrating the structure of the present invention used to detect the intramural cavity of an ultrasonic short segment;

[0061] Figure 4 for Figure 3 A magnified view of part A in the middle;

[0062] Figure 5 This is a schematic diagram illustrating the structure of the present invention used for detecting the surface of an ultrasonic subsection;

[0063] Figure 6 This is a schematic diagram of the present invention used to emit ultrasonic waves onto a three-dimensional rock model at the bottom of a borehole;

[0064] Figure 7 This is a flowchart of the ultrasonic drilling bottom rock natural frequency detection method of the present invention.

[0065] In the diagram: 1. Drill bit; 11. Water outlet; 12. Pressure sensor; 2. Ultrasonic detection unit; 21. Ultrasonic detection sub; 210. Electric push rod; 211. Array element transducer; 212. Array element support block; 213. Radial telescopic rod; 214. Central rod; 215. Mechanical disk; 216. Fixed shaft; 217. Return spring; 218. Auxiliary push rod; 219. Isolation plate; 220. Telescopic sealing curtain; 221. Miniature pressure sensor; 22. Echo information processing module; 23. Algorithm processing module; 24. Monitoring and control module; 25. Data transmission module; 26. Sound insulation sub; 3. Power ultrasonic unit; 4. External control equipment; 5. Drill rod; 6. Three-dimensional model of the bottom rock. Detailed Implementation

[0066] The present invention will be further described in detail below with reference to the accompanying drawings.

[0067] This invention discloses a drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole.

[0068] Reference Figures 1-6 A drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole includes a drill bit 1, a detection ultrasonic unit 2, a power ultrasonic unit 3, an external control device 4, a drill pipe 5, and a cooling and chip removal system. The drill pipe 5 is coaxially connected to the power ultrasonic unit 3, a sound insulation sub 26, the detection ultrasonic unit 2, and the drill bit 1 in sequence. All components are rigidly connected via drill collars, and fluororubber sealing gaskets are installed at the connections to prevent drilling fluid from entering the internal circuitry, ensuring stable operation of each module under complex downhole conditions and preventing interference with detection and rock breaking operations due to fluid corrosion or short circuits.

[0069] The ultrasonic detection unit 2 is a core module for detecting the natural frequency of rock near the drill bit. It is fixed near the drill bit in the form of a short section. This near-drill bit installation minimizes the signal transmission path, reduces signal attenuation and interference, and improves the detection response speed. The ultrasonic detection unit 2 includes an ultrasonic short section 21, an echo information processing module 22, an algorithm processing module 23, a monitoring and control module 24, and a data transmission module 25. These modules are electrically connected to achieve orderly signal and data transmission.

[0070] The power ultrasonic unit 3 is the core vibration module for rock breaking. It has a built-in adjustable frequency ultrasonic generator, ultrasonic transducer and amplitude transformer. The adjustable frequency range is 20kHz-50kHz. Its core function is to receive commands from the external control device 4 to dynamically adjust the vibration parameters so that the output frequency can resonate or nearly resonate with the natural frequency of the rock at the bottom of the hole. Based on the principle of ultrasonic resonance rock breaking, it reduces the energy consumption required for rock breaking and improves the rock breaking efficiency.

[0071] A pressure sensor 12 is embedded on the surface of the drill bit 1. The pressure sensor 12 collects drilling pressure data in real time and transmits it to the monitoring and control module 24. The drill bit 1 is provided with a water outlet 11 around its circumference. The water outlet 11 is connected to the cooling and chip removal system to ensure that the cooling and chip removal medium can evenly cover the bottom area of ​​the hole and improve the chip removal effect.

[0072] The cooling and chip removal system includes a water pipe arranged along the central axis of the drill rod 5. The water pipe passes through the inner cavity of the fixed shaft 216 inside the ultrasonic testing section 21 and finally branches at the drill bit 1 and connects to the water outlet 11. It is used to remove residual rock chips at the bottom of the hole by injecting water at a low flow rate during the testing preparation stage. The low flow rate design can avoid the change in the fracture state caused by the impact of high-pressure water flow on the rock at the bottom of the hole, while effectively cleaning up the rock chip accumulation, ensuring that the transmission path of the ultrasonic beam is unobstructed during the subsequent testing process, avoiding the interference of rock chip reflection with the echo signal, and thus ensuring the testing accuracy.

[0073] The external control device 4 has a built-in lithological parameter library and a dual ultrasonic system control unit. The lithological parameter library stores parameters such as unit energy consumption rock breaking efficiency and axial range of ultrasonic rock breaking influence for at least 10 common lithologies. These parameters are pre-calibrated through indoor lithological fracturing experiments, providing a reliable data basis for the dynamic weighted algorithm. The dual ultrasonic system control unit is used to control the start and stop of the detection ultrasonic unit 2 and the power ultrasonic unit 3 and to adjust the parameters, so as to realize the coordinated linkage of detection and rock breaking.

[0074] The ultrasonic testing subsection 21 is a hollow cylindrical structure made of No. 45 steel. Inside it are a mechanical disc 215, a central rod 214, a fixed shaft 216, an electric push rod 210, and an array element transducer 211.

[0075] There are at least two mechanical discs 215. In this embodiment, two mechanical discs 215 are provided and arranged parallel to each other along the axis of the detection ultrasonic sub-section 21. The diameter of the mechanical discs 215 is 5-15 mm smaller than the diameter of the drill bit 1 and is parallel to the end face of the drill bit 1. This avoids interference between the mechanical discs 215 and the borehole wall and ensures that the detection range of the array transducer 211 is accurately matched with the rock-breaking area of ​​the drill bit 1.

[0076] The central rod 214 is coaxially inserted through the center of each mechanical disk 215, and its two ends are fixedly connected to the ultrasonic testing section 21. The electric push rod 210 corresponds to each mechanical disk 215, and the output end of the electric push rod 210 is connected to the mechanical disk 215, driving the mechanical disk 215 to move along the axial direction of the central rod 214.

[0077] The fixed shaft 216 is coaxially fixed to the inner cavity of the ultrasonic testing section 21 and passes through each mechanical disk 215. The fixed shaft 216 is hollow inside to accommodate the water pipes of the cooling chip removal system, thus achieving efficient utilization of the structural space.

[0078] Eight radial telescopic rods 213 are evenly distributed along the radial direction on each mechanical disk 215. In this embodiment, the radial telescopic rods 213 are electric actuators. The fixed end of the radial telescopic rods 213 is fixedly connected to the center of the mechanical disk 215, and the telescopic end of the radial telescopic rods 213 is fixedly connected to the array element support block 212. The array element transducer 211 is installed on the array element support block 212. The radial telescopic rods 213 can drive the array element transducer 211 to extend in a direction exceeding the radius of the drill bit 1, breaking through the limitations of traditional detection range and realizing full radial coverage detection of the bottom of the hole.

[0079] The array element carrier block 212 is equipped with a position sensing sensor to collect the spatial coordinates of the array element transducer 211 in real time and transmit them to the algorithm processing module 23; the array element transducer 211 has a small angle deflection function of ±5°, which is used to adjust to the optimal transmission angle through echo intensity feedback.

[0080] The sound insulation section 26 is located between the detection ultrasonic unit 2 and the power ultrasonic unit 3. Its two ends are fixedly connected to the detection ultrasonic unit 2 and the power ultrasonic unit 3, respectively. Several sound insulation grooves are evenly opened in the circumferential direction inside the sound insulation section 26. The sound insulation grooves are composed of several annular sound insulation grooves and strip sound insulation grooves. The several annular sound insulation grooves are evenly arranged along the axial direction of the sound insulation section 26, and the several strip sound insulation grooves are arranged along the circumferential direction of the sound insulation section 26. The cross-section of the sound insulation groove is "U" shaped, and the groove is filled with damping sound insulation material. Through the dual sound insulation design of the sound insulation groove and the damping material, the vibration energy generated by the power ultrasonic unit 3 during operation can be effectively absorbed and blocked, avoiding signal acquisition interference caused by vibration transmission to the detection ultrasonic unit 2, and ensuring the authenticity and reliability of the detection data.

[0081] At the locations of each array element transducer 211 on the outer wall of the ultrasonic testing sub-section 21, an isolation plate 219 corresponding to the array element transducer 211 is provided. The isolation plate 219 is an arc-shaped plate, the curvature of which matches the curvature of the outer wall of the ultrasonic testing sub-section 21. A retractable sealing curtain 220 is provided around the edge of the isolation plate 219. The isolation plate 219 is connected to the outer wall of the ultrasonic testing sub-section 21 through the retractable sealing curtain 220. The retractable sealing curtain 220 is made of fluororubber, which has good corrosion resistance and elasticity, and can be used for a long time in complex environments at the bottom of the borehole. Its core function is to cover the gap between the array element transducer 211 and the borehole wall, forming a sealed protective space to prevent rock debris or coolant from entering and affecting the detection performance of the array element transducer 211.

[0082] Auxiliary push rods 218 are provided on the inner sides of the isolation plate 219 near the detection ultrasonic subsection 21 at both ends. The auxiliary push rod 218 consists of a sleeve and a movable rod passing through the sleeve. The sleeve of the auxiliary push rod 218 is fixedly installed inside the detection ultrasonic subsection 21. The end of the movable rod away from the sleeve is connected to the isolation plate 219. The extension and retraction direction of the auxiliary push rod 218 is consistent with that of the radial extension rod 213. The auxiliary push rod 218 is equipped with a return spring 217 and a miniature pressure sensor 221. The return spring 217 is used to drive the isolation plate 219 and the retractable sealing curtain 220 to return to their original positions when the array transducer 211 retracts. The miniature pressure sensor 221 is used to detect the contact pressure between the isolation plate 219 and the hole wall and to determine the contact state with the hole wall. When the pressure reaches a preset threshold, it is determined that the contact is in place.

[0083] The input of the echo information processing module 22 is electrically connected to the array element transducer 211 of the ultrasonic sub-section 21, and the output is electrically connected to the algorithm processing module 23, used to receive the echo signal collected by the array element transducer 211. Considering that the bottom echo signal is easily affected by rock cuttings, vibration noise, etc., the algorithm processing module 23 performs db4 wavelet basis noise reduction, time domain truncation, and fast Fourier transform (FFT) on the echo signal in sequence. The db4 wavelet basis has good time-frequency localization characteristics and can effectively separate the signal from the noise. The time domain truncation can eliminate invalid signal segments, and the FFT transform realizes the conversion of the time domain signal to the frequency domain spectrum. Then, frequency points with amplitude ≥ 80% of the maximum amplitude and duration ≥ 3 pulse periods are selected as resonance peaks to determine the natural frequency of each rock block. This selection criterion can ensure the authenticity of the resonance peaks and avoid misjudging instantaneous interference signals as resonance peaks, thereby accurately determining the natural frequency of each rock block.

[0084] The algorithm processing module 23 is configured to: based on the real-time spatial position of the array element transducer 211 collected by the position sensing sensor, control the transmission timing of the multi-array element transducer 211 through an electronic delay algorithm to achieve the focusing of the ultrasonic beam at the specified rock segment; at the same time, call the lithological parameter library of the external control device 4, combine the amplitude stability, spectral dispersion, and radial position coefficient and axial depth coefficient corresponding to the spatial position of the array element output by the echo information processing module 22, and calculate the final weighted average frequency through a dynamic weighting algorithm combining the entropy weighting method and the TOPSIS algorithm.

[0085] Entropy weighting can objectively calculate weights based on index data, avoiding bias from subjective human assignment. The TOPSIS algorithm can quantify the importance of each block by calculating its closeness to the ideal solution. The combination of the two can assign differentiated weights based on the characteristics of rock blocks such as their fracture state and spatial location, solving the frequency deviation problem caused by traditional homogenization averaging algorithms and improving the representativeness and accuracy of frequency detection.

[0086] The data transmission module 25 has a bidirectional data transmission function. On the one hand, it transmits the collected data and processing results of each module of the detection ultrasound unit 2 to the external control device 4. On the other hand, it transmits the instructions of the external control device 4 to the detection ultrasound unit 2 and the power ultrasound unit 3.

[0087] The monitoring and control module 24 is the core coordinating component of the ultrasonic detection unit 2. Its input end is electrically connected to the pressure sensor 12, the position sensing sensor, and the miniature pressure sensor 221, respectively, and its output end is electrically connected to the data transmission module 25. The monitoring and control module 24 is used to synchronously collect and summarize the real-time data of each sensor, including drilling pressure data, array element spatial coordinate data, isolation plate 219 bonding pressure data, and pre-recorded drill bit 1 diameter and shape information. The summarized data is fed back to the external control device 4 through the data transmission module 25. The external control device 4 triggers the switching between drilling mode and detection mode based on the data to ensure the rationality of the detection timing and the continuity of operation.

[0088] The sweep frequency parameters of the array element transducer 211 are set as follows: the sweep frequency range is 20kHz-50kHz, and the frequency step is 1kHz. The parameter range matches the adjustable frequency range of the power ultrasonic unit 3 to ensure the compatibility between the detection frequency and the rock breaking frequency. The array element transducers 211 on each mechanical disk 215 form a ring array and perform the sweep frequency in the order of circumferential sector-by-sector mode, radial graded mode, and axial layered mode. Among them, the circumferential sector-by-sector mode is divided according to the unobstructed sector of the drill bit 1, and each sector corresponds to at least 2 array element transducers 211, with an angle interval of 45°-90° between sectors; the radial graded mode is graded according to the extension length of the radial telescopic rod 213; the axial layered mode is layered according to the axial spacing of the mechanical disk 215, and each layer corresponds to the axial block of the rock at the bottom of the hole, with the block thickness consistent with the axial spacing of the mechanical disk 215. By using three-dimensional frequency scanning logic in the circumferential, radial and axial directions, the system achieves refined detection of the entire space at the bottom of the borehole, effectively distinguishing the stepped distribution of the rock at the bottom of the borehole into "fractured zone, fractured zone and intact zone".

[0089] Reference Figure 7 The present invention also discloses a drilling ultrasonic method for detecting the natural frequency of bottom rock, based on the above-mentioned ultrasonic drilling bottom rock natural frequency detection device, comprising the following steps:

[0090] S1. Drilling and Trigger Detection: Drill rod 5 drives drill bit 1 to drill normally. Pressure sensor 12 collects drilling pressure data in real time. After being summarized by monitoring and control module 24, the data is transmitted to external control device 4 through data transmission module 25. External control device 4 compares the data. When it is determined that the real-time drilling pressure is greater than or equal to the preset drilling pressure threshold and the real-time drilling speed is less than or equal to the preset drilling speed threshold, and this state lasts for 0.5-2 seconds, it sends a detection preparation command to monitoring and control module 24. The design basis of this trigger condition is: when the drilling pressure increases and the drilling speed decreases, it usually indicates that the current rock breaking frequency is not well matched with the natural frequency of the rock, and the rock breaking efficiency is reduced. At this time, starting the detection can adjust the parameters in time to avoid ineffective energy consumption. The setting of 0.5-2 seconds can eliminate false triggering caused by instantaneous fluctuations and ensure the reliability of the detection command.

[0091] S2. Detection preparation: After receiving the detection preparation instruction, the monitoring and control module 24 sends a confirmation signal to the external control device 4 through the data transmission module 25. The external control device 4 issues an execution instruction to control the power ultrasonic unit 3 to stop vibrating and at the same time controls the cooling chip removal system to start, injecting water into the bottom of the hole at a low flow rate of 5-10L / min through the water pipe and water outlet for 10-20 seconds to remove residual rock chips from the bottom of the hole.

[0092] S3, Three-dimensional frequency sweep detection: The device switches to detection mode, and the monitoring and control module 24 calls the pre-stored diameter and shape information of drill bit 1. Combined with the actual scene, the radius of action of drill bit 1 and the ultrasonic rock breaking influence depth in the lithology parameter library, the axial block thickness of the rock at the bottom of the hole is determined, and a three-dimensional model 6 of the rock at the bottom of the hole is constructed to achieve accurate division of the detection area.

[0093] The mechanical disk 215 is controlled to move axially along the central rod 214, so that the axial distance between two adjacent mechanical disks 215 is consistent with the axial segment length; the radial telescopic rod 213 is controlled to extend, driving the array element transducer 211 and the array element support block 212 to move in a direction exceeding the radius of the drill bit 1. During the movement, the array element support block 212 first touches the isolation plate 219, and the isolation plate 219 drives the retractable sealing curtain 220 to move to the hole wall; when the micro pressure sensor 221 detects that the contact pressure reaches the preset pressure threshold, the radial telescopic rod 213 stops extending.

[0094] Each array element transducer 211 deflects independently. Based on the real-time feedback of the echo intensity at each deflection angle from the echo information processing module 22, the array element transducer 211 is adjusted to the emission angle when the echo intensity reaches its maximum value, ensuring the quality of echo acquisition.

[0095] Subsequently, the array element transducers 211 of the ring array perform frequency sweep according to the three-dimensional rock model 6 at the bottom of the borehole, with a frequency range of 20kHz-50kHz and a frequency step of 1kHz, in the order of circumferential sector mode, radial hierarchical mode, and axial layer mode; at the same time, the algorithm processing module 23 controls the transmission timing of each array element transducer 211 through electronic delay technology, so that the ultrasonic beam is accurately focused on the corresponding rock block, and each array element transducer 211 receives the echo signal of the rock block in its corresponding sector; thus realizing the independent detection of the inherent frequency of each block.

[0096] S4. Signal processing and frequency calculation: The echo information processing module 22 performs db4 wavelet basis noise reduction, time domain truncation, and FFT transformation on the echo signal received by each array element transducer 211 in sequence, extracts the frequency domain spectrum of each rock block, and filters the resonance peaks to determine the inherent frequency of each block.

[0097] The algorithm processing module 23 calls the unit energy consumption rock breaking efficiency in the lithology parameter library of the external control device 4, and combines the amplitude stability, spectrum dispersion and radial position coefficient and axial depth coefficient output by the echo information processing module 22 with the position sensing sensor to calculate the weight of each rock block through a dynamic weighting algorithm that combines the entropy weight method and the TOPSIS algorithm. Based on the inherent frequency of each block and the corresponding weight, the final weighted average frequency is calculated.

[0098] Among them, the core quantitative indicators of the dynamic weighted algorithm combining the entropy weight method and the TOPSIS algorithm include five positive indicators, namely, rock breaking efficiency per unit energy consumption η, amplitude stability S, spectral dispersion D, radial position coefficient R, and axial depth coefficient Z.

[0099] Each positive indicator is respectively from , , , , The calculation shows that the larger the index value, the higher the importance of the corresponding rock fragment to the resonant rock breaking, and the greater the weight allocation.

[0100] In the above formulas, V i To correspond to the resonant rock-breaking velocity of rock fragmentation under lithology, E i To correspond to the rock-breaking energy consumption of fracturing this segment under the lithological conditions, V i With E i All parameters are from the lithological parameter library of external control device 4, and were measured through indoor lithological fracturing experiments; σ is the standard deviation of the echo amplitude after noise reduction of rock blocks, and the data comes from the echo information processing module 22; Var is the variance of the frequency domain spectrum of rock blocks, and the data comes from the echo information processing module 22; r i r is the actual radial distance from the center of the rock block at the bottom of the hole to the center of the bottom of the hole, r0 is the main breaking radius of the drill bit, r i Data is collected by a position sensing sensor; r0 represents pre-recorded drill bit parameters; z i z0 represents the actual axial depth of the rock block center at the bottom of the borehole, and z0 represents the axial range affected by the ultrasonic rock-breaking energy of the corresponding lithology. i The position sensing sensor collects z0, which comes from the lithological parameter library of the external control device 4.

[0101] The specific calculation method of the dynamic weighting algorithm is as follows:

[0102] S41. Data Standardization: Standardize the measured indicators in the blocks according to the positive indicator formula. Standardize to the [0,1] interval;

[0103] In the formula: x ij For the i-th rock block, the original data for the j-th index; min(x j ) represents the minimum value of all blocks on the j-th index; max(x) j ) represents the maximum value of all blocks on the j-th index; y ij These are the standardized values, ranging from [0,1].

[0104] S42. Entropy weight method for calculating objective indicator weights: By calculating the probability distribution and information entropy of the indicators, the objective indicator weights are finally obtained, ensuring the objectivity of weight allocation.

[0105] The formula for calculating the probability distribution of the index is: ;

[0106] In the formula, p ij Let be the probability of the i-th block in the j-th index; ε is the minimum value, taken as 10. −10 n represents the total number of rock fragments;

[0107] The formula for calculating information entropy is: Where, k = 1 / lnn;

[0108] The formula for calculating the weight of objective indicators is: ,in The sum of the percentage of valid information for all indicators, ensuring .

[0109] S43. Construct a weighted standardized matrix: ;

[0110] In the formula, V ij y is the weighted standardized value of the i-th block on the j-th indicator; ij The value of the i-th block after standardization of the j-th indicator is obtained by processing the original indicator data through the positive indicator standardization formula, and its range is [0,1]. The objective weight of the j-th indicator is calculated using the entropy weight method;

[0111] S44. TOPSIS algorithm for calculating block proximity: determining the ideal solution. Negative ideal solution Calculate the Euclidean distance from the partition to the ideal solution.

[0112] Proximity: ;

[0113] In the formula, The optimal value for the j-th indicator; The worst value of the j-th indicator; Let be the spatial distance between the i-th block and the optimal block; C is the spatial distance between the i-th block and the worst block; i Let be the proximity of the i-th block, ranging from [0,1].

[0114] S45. Weight normalization and frequency calculation: By dividing the weights into blocks, the final weighted average frequency is calculated. This frequency can more accurately reflect the inherent frequency characteristics of the key rock breaking area at the bottom of the borehole.

[0115] The formula for calculating block weight is: ;

[0116] The final weighted average frequency is calculated using the following formula: ;

[0117] In the formula, Let be the final weight of the i-th block; Let be the natural frequency of the i-th rock fragment.

[0118] S5. Parameter adjustment and lithological early warning: The monitoring and control module 24 transmits the final weighted average frequency to the external control device 4 through the data transmission module 25. The external control device 4 controls the power ultrasonic unit 3 to adjust the vibration frequency based on the final weighted average frequency, so as to achieve a precise match between the rock breaking frequency and the natural frequency of the rock.

[0119] The monitoring and control module 24 records the weighted average frequency of three consecutive detections and calculates the frequency difference between two adjacent detections. If any difference exceeds the preset frequency change threshold, a lithology warning is triggered. This design can promptly identify changes in lithology at the bottom of the borehole and avoid frequency mismatch caused by changes in lithology.

[0120] After the lithology warning is triggered, the algorithm processing module 23 automatically loads the parameter library adapted to the new lithology from the external control device 4, and recalibrates the axial spacing of the mechanical disk 215, the extension length of the radial telescopic rod 213, and the frequency sweep logic of the array element transducer 211 to ensure that the detection parameters are adapted to the new lithology. When the frequency difference between two consecutive detections is ≤ the preset frequency mutation threshold, the lithology warning is lifted, the power ultrasonic unit 3 is restarted, and drilling resumes, ensuring the continuity and stability of the operation.

[0121] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A logging-while-drilling ultrasonic device for detecting the natural frequency of a borehole bottom rock, characterized by: The application relates to a drilling device, which comprises a drill bit (1), a detection ultrasonic unit (2), a power ultrasonic unit (3), an external control device (4), a drill rod (5) and a cooling and chip removal system; the drill rod (5) is coaxially connected with the power ultrasonic unit (3), the detection ultrasonic unit (2) and the drill bit (1) in sequence along an axial direction; The detection ultrasonic unit (2) is a near-drill-bit rock inherent frequency core detection module and is fixed in a short section form near the drill bit; the power ultrasonic unit (3) is a rock breaking core vibration module and is used for receiving an instruction of the external control device (4) to adjust vibration parameters; A pressure sensor (12) is embedded on the surface of the drill bit (1) and is used for collecting drilling pressure data; a water outlet (11) is arranged in a circumferential direction of the drill bit (1); the water outlet (11) is communicated with the cooling and chip removal system; the cooling and chip removal system comprises a water pipe arranged along the central axis of the drill rod (5); the water pipe passes through the detection ultrasonic unit (2) and is finally branched at the drill bit (1) and connected with the water outlet (11) to inject water to remove residual rock debris at the bottom of a hole in a detection preparation stage; The external control device (4) is internally provided with a lithology parameter library and a double-ultrasonic system control unit used for controlling the start and stop of the detection ultrasonic unit (2) and the power ultrasonic unit (3) and parameter adjustment.

2. The drillable ultrasonic device for detecting the natural frequency of the rock at the borehole bottom according to claim 1, characterized in that: The detection ultrasonic unit (2) comprises a detection ultrasonic short section (21), an echo information processing module (22), an algorithm processing module (23), a monitoring and control module (24) and a data transmission module (25); the modules of the detection ultrasonic unit (2) are electrically connected to realize ordered signal and data transmission; the detection ultrasonic short section (21) is a hollow column structure and internally provided with mechanical discs (215), a middle rod (214), a fixed shaft (216), an electric push rod (210) and an array element transducer (211); the mechanical discs (215) are arranged in parallel along the axial direction of the detection ultrasonic short section (21) and at least two; the diameter of the mechanical disc (215) is smaller than the diameter of the drill bit (1) and parallel to the end surface of the drill bit (1); The middle rod (214) is coaxially arranged in the center of each mechanical disc (215) and fixedly connected with the detection ultrasonic short section (21) at both ends; the electric push rod (210) corresponds to the mechanical disc (215) one by one; the output end of the electric push rod (210) is connected with the mechanical disc (215) to drive the mechanical disc (215) to move along the middle rod (214) in the axial direction; The fixed shaft (216) is coaxially fixed in the inner cavity of the detection ultrasonic short section (21) and passes through each mechanical disc (215); the fixed shaft (216) is internally hollow to accommodate the water pipe of the cooling and chip removal system; A plurality of radial telescopic rods (213) are uniformly distributed on the mechanical disc (215) in the radial direction; the fixed ends of the radial telescopic rods (213) are fixedly connected with the center of the mechanical disc (215); the telescopic ends of the radial telescopic rods (213) are fixedly connected with array element bearing blocks (212); the array element transducer (211) is arranged on the array element bearing block (212). The array element bearing block (212) is internally embedded with a position sensing sensor for real-time collection of spatial coordinates of the array element transducer (211) and transmission to the algorithm processing module (23); the array element transducer (211) has an angle deflection function and is adjusted to an optimal emission angle through echo intensity feedback.

3. The drillable ultrasonic device of claim 2, wherein: The detection ultrasonic unit (2) and the power ultrasonic unit (3) are provided with a sound insulation nipple (26), the two ends of the sound insulation nipple (26) are fixedly connected with the detection ultrasonic unit (2) and the power ultrasonic unit (3), and a plurality of sound insulation grooves are formed in the sound insulation nipple (26); for isolating the vibration interference generated when the power ultrasonic unit (3) works.

4. The drillable ultrasonic device of claim 3, wherein: Corresponding to the positions of the array element transducers (211), the outer wall of the detection ultrasonic nipple (21) is provided with isolation plates (219) corresponding to the array element transducers (211); The isolation plate (219) is an arc plate, the curvature of which is matched with the curvature of the outer wall of the detection ultrasonic nipple (21), and a retractable sealing curtain (220) is arranged around the edge of the isolation plate (219), the isolation plate (219) is connected with the outer wall of the detection ultrasonic nipple (21) through the retractable sealing curtain (220); the two ends of the isolation plate (219) are provided with auxiliary push rods (218) close to the inner side of the detection ultrasonic nipple (21), the retractable direction of the auxiliary push rod (218) is consistent with the radial retractable rod (213), and the auxiliary push rod (218) is internally provided with a reset spring (217) and a micro pressure sensor (221); the reset spring (217) is used for driving the isolation plate (219) and the retractable sealing curtain (220) to reset when the array element transducer (211) is retracted, and the micro pressure sensor (221) is used for detecting the adhesion pressure of the isolation plate (219) and the hole wall to judge the contact state with the hole wall.

5. The drillable ultrasonic device for detecting the natural frequency of the rock at the borehole bottom according to claim 4, characterized in that: The input end of the echo information processing module (22) is electrically connected with the array element transducer (211) of the detection ultrasonic nipple (21), and the output end is electrically connected with the algorithm processing module (23), for receiving the echo signal collected by the array element transducer (211), and sequentially performing db4 wavelet base noise reduction, time domain truncation and fast Fourier transform on the echo signal, extracting frequency points with an amplitude greater than or equal to 80% of the maximum amplitude and a duration greater than or equal to 3 pulse periods as resonance peaks to determine the natural frequency of each rock block; The algorithm processing module (23) is configured to: based on the real-time spatial position of the array element transducer (211) collected by the position sensing sensor, control the emission timing of the multiple array element transducers (211) through an electronic delay algorithm, realize the focusing of the ultrasonic beam at the specified rock block; at the same time, call the lithology parameter library of the external control device (4), combine the amplitude stability, spectral dispersion degree and the corresponding radial position coefficient and axial depth coefficient of the array element spatial position output by the echo information processing module (22), and calculate the final weighted average frequency through a dynamic weighting algorithm combining the entropy weight method and the TOPSIS algorithm. The data transmission module (25) has a bidirectional data transmission function, which transmits the collected data and processing results of each module of the detection ultrasonic unit (2) to the external control device (4) and transmits the instructions of the external control device (4) to the detection ultrasonic unit (2) and the power ultrasonic unit (3).

6. The drillable ultrasonic device for detecting the natural frequency of the rock at the borehole bottom according to claim 5, characterized in that: The monitoring and control module (24) is a core coordination component of the detection ultrasonic unit (2), and the input end is electrically connected with the pressure sensor (12), the position sensing sensor and the micro pressure sensor (221), and the output end is electrically connected with the data transmission module (25); the monitoring and control module (24) is used for synchronously collecting and summarizing the real-time data of each sensor, and feeding back the summarized data to the external control device (4) through the data transmission module (25), and triggering the switching of the drilling mode and the detection mode based on the data by the external control device (4).

7. The drillable ultrasonic device of claim 6, wherein: The sweep frequency parameters of the array element transducer (211) are set as follows: the sweep frequency range is 20kHz-50kHz, and the frequency step is 1kHz; and the array element transducers (211) on each mechanical disc (215) form a ring array, and perform sweep frequency in the order of a circumferential sector mode, a radial hierarchical mode and an axial layer mode; wherein, the circumferential sector mode is to divide the circumferential non-shielding sector of the drill bit (1), each sector corresponds to at least two array element transducers (211), and the angle interval between sectors is 45°-90°; the radial hierarchical mode is to divide according to the extension length of the radial telescopic rod (213); and the axial layer mode is to divide according to the axial spacing of the mechanical disc (215), each layer corresponds to the axial block of the bottom rock, and the block thickness is consistent with the axial spacing of the mechanical disc (215).

8. A method of detecting the natural frequency of the rock at the bottom of a borehole while drilling using ultrasonic waves, characterized in that, The method comprises the following steps: S1, drilling and triggering determination: the drill pipe (5) drives the drill bit (1) to drill normally, the pressure sensor (12) collects the drilling pressure data in real time, the collected data is summarized by the monitoring and control module (24) and then transmitted to the external control device (4) through the data transmission module (25); the external control device (4) compares the data, and when it is determined that the real-time drilling pressure is greater than or equal to the preset drilling pressure threshold, the real-time drilling speed is less than or equal to the preset drilling speed threshold, and the state lasts for a preset time, the detection preparation instruction is sent to the monitoring and control module (24); S2, detection preparation: after receiving the detection preparation instruction, the monitoring and control module (24) feeds back the confirmation signal to the external control device (4) through the data transmission module (25); the external control device (4) sends an execution instruction to control the power ultrasonic unit (3) to stop vibrating, and controls the cooling and chip removal system to start at the same time, and water is injected to the bottom of the hole through the water pipe and the water outlet at a low flow rate of 5-10L / min to remove the residual cuttings at the bottom of the hole; S3, Three-dimensional frequency sweep detection: The device switches to the detection mode, and the monitoring and control module (24) calls the pre-stored drill bit (1) diameter and shape information, combines the actual scene drill bit (1) action radius and the ultrasonic rock breaking influence depth in the lithology parameter library, determines the axial block thickness of the rock at the bottom of the hole, and constructs a three-dimensional model of the rock at the bottom of the hole (6). By controlling the mechanical disk (215) to extend and retract along the central rod (214), the axial distance between two adjacent mechanical disks (215) is made consistent with the axial block length; by controlling the extension of the radial telescopic rod (213), the array element transducer (211) and the array element support block (212) are driven to move in a direction exceeding the radius of the drill bit (1). During the movement, the array element support block (212) first touches the isolation plate (219), and then the telescopic sealing curtain (220) is driven to move to the hole wall through the auxiliary push rod (218); when the micro pressure sensor (221) detects that the contact pressure reaches the preset pressure threshold, the radial telescopic rod (213) stops extending; Each array element transducer (211) deflects independently. Based on the echo information processing module (22) providing real-time feedback on the echo intensity at each deflection angle, the array element transducer (211) is adjusted to the emission angle when the echo intensity reaches its maximum value. Subsequently, the array element transducers (211) of the ring array perform frequency sweep according to the three-dimensional rock model (6) at a frequency range of 20kHz-50kHz and a frequency step of 1kHz, in the order of circumferential sector mode, radial hierarchical mode, and axial layer mode; at the same time, the algorithm processing module (23) controls the transmission timing of each array element transducer (211) through electronic delay technology, so that the ultrasonic beam is accurately focused on the corresponding rock block, and each array element transducer (211) receives the echo signal of the rock block in its corresponding sector; S4. Signal processing and frequency calculation: The echo information processing module (22) sequentially performs db4 wavelet basis noise reduction, time domain truncation, and FFT transformation on the echo signal received by each array element transducer (211), extracts the frequency domain spectrum of each rock block, and filters the resonance peaks to determine the inherent frequency of each block. The algorithm processing module (23) calls the unit energy consumption rock breaking efficiency in the lithology parameter library of the external control device (4), and combines the amplitude stability, spectrum dispersion and radial position coefficient and axial depth coefficient output by the echo information processing module (22) with the dynamic weighting algorithm combining the entropy weight method and the TOPSIS algorithm to calculate the weight of each rock block, and calculates the final weighted average frequency based on the inherent frequency of each block and the corresponding weight. S5. Parameter adjustment and lithological early warning: The monitoring and control module (24) transmits the final weighted average frequency to the external control device (4) through the data transmission module (25). The external control device (4) controls the power ultrasonic unit (3) to adjust the vibration frequency based on the final weighted average frequency. The monitoring and control module (24) records the weighted average frequency of three continuous detections, calculates the frequency difference of two adjacent detections, and triggers the lithology warning if the difference of any time is greater than the preset frequency mutation threshold; after the lithology warning is triggered, the algorithm processing module (23) automatically loads the parameter library in the external control device (4) that adapts to the new lithology, recalibrates the axial spacing of the mechanical disc (215), the extension length of the radial telescopic rod (213), and the sweep frequency logic of the array transducer (211); when the frequency difference to be detected is less than or equal to the preset frequency mutation threshold, the lithology warning is removed, the power ultrasonic unit (3) is restarted, and drilling is resumed.

9. The method of claim 8, wherein: The core quantitative index of the dynamic weighting algorithm combined with the entropy weight method and the TOPSIS algorithm in step S4 includes five positive indexes, which are rock breaking efficiency per unit energy consumption η, amplitude stability S, spectral dispersion D, radial position coefficient R, and axial depth coefficient Z, respectively. The forward indicators are calculated respectively by , , , , . V i is the resonant rock breaking velocity corresponding to the rock block under the lithology; E i is the rock breaking energy consumption for breaking the block under the lithology; V i and E i are both from the lithology parameter library of the external control device (4), and are measured by indoor lithology breaking experiments; σ is the standard deviation of the echo amplitude of the rock block after noise reduction; Var is the frequency domain spectrum variance of the rock block; r i is the actual radial distance from the center of the rock block at the bottom of the hole to the center of the hole bottom; r0 is the main breaking radius of the drill bit; r i is collected by the position sensing sensor; r0 is the pre-recorded drill bit parameter; z i is the actual axial depth of the center of the rock block at the bottom of the hole; z0 is the axial range affected by the ultrasonic rock breaking energy corresponding to the lithology; z i is collected by the position sensing sensor; z0 is from the lithology parameter library of the external control device (4).

10. The method of claim 9, wherein the step of detecting the natural frequency of the rock at the borehole bottom is performed by a downhole ultrasonic tool. The specific calculation method of the dynamic weighting algorithm in step S4 is as follows: S41, data standardization: the block measured indicators are standardized to the interval [0, 1] according to the positive index formula . where: x ij is the original data of the ith rock patch on the jth index; min(x j ) is the minimum value of all patches on the jth index; max(x j ) is the maximum value of all patches on the jth index; y ij is the normalized value of the ith rock patch on the jth index, ranging from [0, 1]. S42, entropy weight method is used to calculate the objective index weight: by calculating the index probability distribution and information entropy, the objective index weight is finally obtained; The index probability distribution calculation formula is: ; In the formula, p ij is the probability of the ith block in the jth index; ε is a minimum value, taking 10 −10 ; n is the total number of rock blocks; The information entropy calculation formula is: wherein, k = 1 / lnn; The objective index weight calculation formula is: Wherein is the sum of the proportion of all effective information of the indexes, ensuring ; S43, constructing a weighted standardized matrix: ; In the formula, V ij is the weighted normalized value of the ith block on the jth index; y ij is the normalized value of the ith block on the jth index, ranging from [0, 1]; is the objective weight of the jth index; S44, TOPSIS algorithm calculates the block closeness: determine the positive ideal solution , negative ideal solution , calculate the Euclidean distance of the block to the ideal solution , the closeness is ; wherein, is the optimal value of the jth index; is the worst value of the jth index; is the spatial distance between the ith patch and the optimal patch; is the spatial distance between the ith patch and the worst patch;C i is the closeness of the ith patch, ranging from [0, 1]; S45, weight normalization and frequency calculation: the final weighted average frequency is calculated through the block weight; The piecewise weight calculation formula is: ; The final weighted average frequency is calculated as follows: ; wherein is the maximum weight of the ith block; is the natural frequency of the ith rock block.

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