A method and apparatus for detecting the natural frequency of the rock at the bottom of a borehole while drilling

Abstract

The application discloses a while-drilling ultrasonic device and method for detecting the inherent frequency of hole bottom rock, which comprises a drill bit, a detection ultrasonic unit, a power ultrasonic unit, an external control device and the like; the detection ultrasonic unit is arranged in the form of a short section near the drill bit, contains a multi-array transducer and an echo information processing and entropy weight-Topsis dynamic weighting algorithm module, and through three-dimensional sweep frequency logic in the circumferential sector-by-sector, radial hierarchical and axial layered mode, sequentially carries out db4 wavelet denoising and FFT transformation on the echo signal to extract a resonance peak, and then calculates a weighted average frequency through the dynamic weighting algorithm; the power ultrasonic unit receives the frequency instruction to adjust vibration parameters in real time. The application realizes accurate detection of the inherent frequency of the whole space of the hole bottom, dynamically distinguishes the importance difference of rock blocks on rock breaking efficiency, improves the frequency matching degree and energy consumption efficiency of ultrasonic rock breaking, and has strong adaptability, supports original installation and later modification of various adjustable frequency ultrasonic rock breaking devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rock drilling and ultrasonic detection, and particularly relates to a while-drilling ultrasonic device and method for detecting the natural frequency of rock at a hole bottom. BACKGROUND

[0002] In the ultrasonic-assisted rock breaking technology system, the matching degree between the vibration frequency output by the adjustable frequency rock breaking device and the natural frequency of the rock at the hole bottom is a core factor determining the rock breaking efficiency and energy consumption level. Existing research has shown that when the vibration frequency of the rock breaking device and the natural frequency of the rock reach or approach the resonance state, significant stress concentration effects will occur in the rock, which can greatly reduce the rock breaking energy consumption and improve the rock breaking efficiency. Therefore, accurate detection of the natural frequency of the rock at the hole bottom is the basis for achieving efficient ultrasonic rock breaking.

[0003] The existing detection technology for the natural frequency of the rock at the hole bottom near the drill bit still has many defects that are difficult to overcome, which seriously restricts the application effect of the ultrasonic-assisted rock breaking technology. For example, in the patent technologies with publication numbers CN107780946A and CN103982131B, although the natural frequency and other parameters of the rock in front of the drill bit have been detected by a single ultrasonic probe, which provides a feasible idea for while-drilling acquisition of the mechanical properties of the rock in the near-drill-bit region, the vibration energy range of the adjustable frequency rock breaking device generally presents three-dimensional spatial distribution characteristics, and the range of action generally covers the hole bottom region in the radial direction, axial direction more than 10 cm and circumferential direction 360°. The detection range of the existing single ultrasonic probe is mainly focused on the local region of the hole bottom pointed by the probe, and there is further optimization space in matching with the actual three-dimensional full-space range of the action of the adjustable frequency rock breaking device. The difference in the coverage range may make the obtained natural frequency parameters of the rock unable to completely reflect the overall natural frequency characteristics of the rock in the rock breaking device action region.

[0004] In addition, the rock at the hole bottom generally presents a stepped distribution characteristic of “broken zone, fractured zone and intact zone” in the radial and axial directions, and the rock breaking states and physical and mechanical properties of different regions are significantly different, and their influence weights on the rock breaking efficiency are also different. However, the existing while-drilling detection technology does not distinguish the breaking states of the rock, and uses a homogenized average algorithm to calculate the natural frequency of the rock at the hole bottom, without giving different weights according to the breaking degrees of different regions, so that the final output frequency result is seriously deviated from the actual natural frequency of the key rock breaking region. The deviation of the detection frequency as the core basis for the frequency adjustment of the device further leads to insufficient real-time matching degree of the frequency adjustment of the device, and the representativeness and effectiveness of the detection data are also greatly reduced.

[0005] Therefore, there is an urgent need for a natural frequency detection technology that can realize full-space three-dimensional detection of the bottom of the hole, accurately distinguish the characteristics of the rock broken area, and efficiently link with the adjustable frequency rock breaking equipment, to solve the problems of narrow detection range, insufficient frequency representation, poor adaptability and other problems in the prior art. SUMMARY

[0006] In view of the defects of the prior art that the detection range of the rock natural frequency at the bottom of the hole is limited, the frequency error is large due to not distinguishing the rock breaking state, and the adaptability is poor, the present application provides a while-drilling ultrasonic device and method for detecting the natural frequency of rock at the bottom of the hole, which realizes accurate detection of the natural frequency of the full-space at the bottom of the hole, dynamically distinguishes the importance of rock blocks, and efficiently links with the adjustable frequency rock breaking equipment, improves the frequency matching degree of ultrasonic rock breaking, and reduces the energy consumption of rock breaking.

[0007] The technical scheme adopted by the present application to solve its technical problems is: a while-drilling ultrasonic device for detecting the natural frequency of rock at the bottom of the 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 near-drill-bit rock natural frequency core detection module, which is fixed in the form of a short section near the drill bit; the power ultrasonic unit is a rock breaking core vibration module, which is used to receive external control device instructions to adjust the vibration parameters;

[0009] The drill bit surface is embedded with a pressure sensor for collecting drilling pressure data, and the drill bit is circumferentially provided with a water outlet, which is in communication 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, the water pipe passes through the detection ultrasonic unit, and finally branches at the drill bit and is connected with the water outlet for water injection to remove residual drill cuttings at the bottom of the hole during the detection preparation stage;

[0010] The external control device is internally provided with a lithology 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 the parameters.

[0011] Further, the detection ultrasonic unit comprises a detection ultrasonic short section, an echo information processing module, an algorithm processing module, a monitoring and control module and a data transmission module, the modules of the detection ultrasonic unit are electrically connected to realize orderly transmission of signals and data; the detection ultrasonic short section is a hollow columnar structure, internally provided with a mechanical disc, a middle rod, a fixed shaft, an electric push rod and an array element transducer; the mechanical disc has at least two and is arranged in parallel along the axial direction of the detection ultrasonic short section; the diameter of the mechanical disc is smaller than the diameter of the drill bit, and is parallel to the end face of the drill bit;

[0012] The middle rod is coaxially arranged in the center of each mechanical disc and is fixedly connected with the detection ultrasonic short section at both ends; the electric push rod corresponds to the mechanical disc, and the output end of the electric push rod is connected with the mechanical disc to drive the mechanical disc to move along the middle rod in the axial direction;

[0013] The fixed shaft is coaxially fixed in the inner cavity of the detection ultrasonic short section and passes through each mechanical disc, and the fixed shaft is hollow inside to accommodate the water pipe of the cooling and chip removal system;

[0014] A plurality of radial telescopic rods are uniformly distributed on the mechanical disc in the radial direction, the fixed end of the radial telescopic rod is fixedly connected with the center of the mechanical disc, and the telescopic end of the radial telescopic rod is fixedly connected with an array element bearing block; the array element transducer is arranged on the array element bearing block;

[0015] The position sensing sensor is embedded in the array element bearing block 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 and is adjusted to the optimal emission angle through echo intensity feedback.

[0016] Further, a sound insulation short section is arranged between the detection ultrasonic unit and the power ultrasonic unit, the two ends of the sound insulation short section are fixedly connected with the detection ultrasonic unit and the power ultrasonic unit respectively, and a plurality of sound insulation grooves are arranged in the sound insulation short section; for isolating the vibration interference generated when the power ultrasonic unit works.

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

[0018] The isolation plate is an arc plate, the curvature of the arc plate is matched with the curvature of the outer wall of the detection ultrasonic short section, and a retractable sealing curtain is arranged around the edge of the arc plate, the arc plate is connected with the outer wall of the detection ultrasonic short section through the retractable sealing curtain; the two ends of the arc plate are provided with auxiliary push rods close to the inner side of the detection ultrasonic short section, the retractable direction of the auxiliary push rod is consistent with that of the radial telescopic rod, and a reset spring and a micro pressure sensor are arranged in the auxiliary push rod; the reset spring is used to reset the arc plate and the retractable sealing curtain when the array element transducer is retracted, and the micro pressure sensor is used to detect the contact pressure between the arc plate and the hole wall to determine the contact state with the hole wall.

[0019] Further, the input end of the echo information processing module is electrically connected with the array element transducer of the detection ultrasonic short section, and the output end is electrically connected with the algorithm processing module, for receiving the echo signal collected by the array element transducer, and sequentially executing db4 wavelet base noise reduction, time domain truncation and fast Fourier transform on the echo signal, extracting the frequency points with amplitude ≥80% of the maximum amplitude and duration ≥3 pulse periods as the resonance peaks, and determining 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 transducer collected by the position-aware sensor, control the emission timing of the multiple array element transducers through an electronic delay algorithm, realize the focusing of the ultrasonic beam at the specified rock block, and simultaneously call the lithology parameter library of the external control device, combine the amplitude stability, spectral dispersion, and the radial position coefficient and axial depth coefficient corresponding to the array element spatial position output by the echo information processing module, and calculate the final weighted average frequency through a dynamic weighting algorithm combining the entropy weight method and the TOPSIS algorithm.

[0021] The data transmission module has a bidirectional data transmission function, which transmits the collected data and processing results of each module of the detection ultrasonic unit to the external control device, and transmits the instructions of the external control device to the detection ultrasonic unit and the power ultrasonic unit.

[0022] Further, the monitoring and control module is the core coordination component of the detection ultrasonic unit, the input end of which is electrically connected with the pressure sensor, the position-aware sensor and the micro pressure sensor respectively, and the output end is electrically connected with the data transmission module; the monitoring and control module 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 through the data transmission module, so that the external control device triggers the switching of the drilling mode and the detection mode based on the data.

[0023] Further, the sweep frequency parameter of the array element transducer is set as: the sweep frequency range is 20kHz-50kHz, and the frequency step is 1kHz; and the array element transducers on each mechanical disc form a ring array, and perform sweep frequency in the order of the circumferential sector mode, the radial hierarchical mode and the axial layer mode; wherein, the circumferential sector mode is to divide the circumferential non-shielding sector, each sector corresponds to at least two array element transducers, and the angle interval between sectors is 45°-90°; the radial hierarchical mode is to divide the radial telescopic rod into levels; and the axial layer mode is to divide the axial spacing of the mechanical disc into layers, 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.

[0024] The application further discloses a while-drilling ultrasonic method for detecting the inherent frequency of bottom rock, and the while-drilling ultrasonic device for detecting the inherent frequency of bottom rock.

[0025] S1, drilling and triggering determination: the drill rod drives the drill bit to drill normally, the pressure sensor collects the drilling pressure data in real time, the collected data is summarized by the monitoring and control module and then transmitted to the external control device through the data transmission module; the external control device 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 monitoring and control module sends a detection preparation instruction;

[0026] S2, detection preparation: after receiving the detection preparation instruction, the monitoring and control module feeds back the confirmation signal to the external control device through the data transmission module; the external control device issues an execution instruction to control the power ultrasonic unit to stop vibrating, and at the same time controls the cooling and chip removal system to start, with a low flow rate of 5-10 L / min through the water pipe and water outlet to inject water to the hole bottom to remove residual rock debris on the hole bottom;

[0027] S3, three-dimensional sweep frequency detection: the device switches to the detection mode, the monitoring and control module calls the pre-stored drill bit diameter and shape information, combines the actual scene drill bit action radius and the ultrasonic rock breaking influence depth in the lithology parameter library to determine the axial block thickness of the hole bottom rock, and constructs a three-dimensional model of the hole bottom rock;

[0028] By controlling the axial extension and retraction of the mechanical disc along the middle rod, the axial spacing of the adjacent two mechanical discs is consistent with the axial block length; by controlling the extension of the radial telescopic rod, the array element transducer and the array element carrier block are moved beyond the drill bit radius, and in the moving process, the array element carrier block first hits the isolation plate, and then the auxiliary push rod drives the extendable sealing curtain to move to the hole wall; when the micro pressure sensor detects that the fitting pressure reaches the preset pressure threshold, the radial telescopic rod stops extending;

[0029] The single array element transducer is independently deflected, and according to the real-time feedback of the echo intensity at each deflection angle by the echo information processing module, the array element transducer is adjusted to the transmission angle when the echo intensity reaches the maximum value;

[0030] Then, the array element transducers of the annular array execute sweep frequency in turn according to the three-dimensional model of the hole bottom rock in the frequency range of 20 kHz-50 kHz, with a frequency step of 1 kHz, 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 the single array element transducer receives the echo signal of the rock block in the corresponding sector;

[0031] S4, signal processing and frequency calculation: the echo information processing module executes db4 wavelet base denoising, time domain truncation and FFT transformation on the echo signal received by each array element transducer in turn, extracts the frequency domain spectrum of each rock block, and selects the resonance peak to determine the inherent frequency of each block;

[0032] The algorithm processing module calls the unit energy consumption rock breaking efficiency in the external control device lithology parameter library, combines the amplitude stability, spectral dispersion and position sensing sensor collected radial position coefficient and axial depth coefficient output by the echo information processing module, calculates the weight of each rock block through the dynamic weighting algorithm combined with the entropy weight method and the TOPSIS algorithm, and calculates the final weighted average frequency 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, and 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 frequencies of three consecutive detections, calculates the frequency difference between adjacent two detections, and triggers the lithology early warning if the difference of any time is greater than the preset frequency mutation threshold. After the lithology early warning is triggered, the algorithm processing module automatically loads the parameter library in the external control device that is adapted to the new lithology, recalibrates the axial spacing of the mechanical disc, the extension length of the radial telescopic rod, and the sweep frequency logic of the array transducer. When the frequency difference to be detected is less than or equal to the preset frequency mutation threshold, the lithology early warning is released, the power ultrasonic unit is restarted, and the drilling is resumed.

[0035] Further, the core quantitative indicators of the dynamic weighting algorithm combined with the entropy weight method and the TOPSIS algorithm in step S4 include five positive indicators, which are rock breaking efficiency per unit energy consumption η, amplitude stability S, spectral dispersion degree D, radial position coefficient R, and axial depth coefficient Z, respectively.

[0036] Each positive indicator is calculated by 、 、 、 、 .

[0037] In the above formulas, V i is the resonance rock breaking velocity of the rock block under the corresponding lithology; E i is the rock breaking energy consumption for breaking the block; V i and E i are obtained from the lithology parameter library of the external control device 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 spectral 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 obtained from the lithology parameter library of the external control device.

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

[0039] S41, data standardization: standardize the block measured indicators to the interval [0, 1] according to the positive indicator formula .

[0040] wherein: x ij is the original data of the i th rock block on the j th index; min(x j ) is the minimum value of all blocks on the j th index; max(x j ) is the maximum value of all blocks on the j th index; y ij is the normalized value of the i th rock block on the j th index, ranging from [0, 1];

[0041] 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;

[0042] The index probability distribution calculation formula is: ;

[0043] wherein, p ij is the probability of the i th block in the j th index; ε is a minimum value, taking 10 −10 ; n is the total number of rock blocks;

[0044] The information entropy calculation formula is: wherein, k = 1 / lnn;

[0045] The objective index weight calculation formula is: wherein is the total of the proportion of effective information of all indexes, ensuring .

[0046] S43, a weighted standardization matrix is constructed: ;

[0047] wherein, V ij is the weighted standardization value of the i th block on the j th index; y ij is the normalized value of the i th block on the j th index, ranging from [0, 1]; is the objective weight of the j th index;

[0048] S44, the TOPSIS algorithm is used to calculate the block closeness degree: the positive ideal solution , the negative ideal solution , the Euclidean distance of the block to the ideal solution is calculated

[0049] , and the closeness degree is ;

[0050] wherein, is the optimal value of the j th index; is the worst value of the j th index; is the spatial distance between the i th block and the optimal block; is the spatial distance of the ith block and the worst block; C i is the closeness of the ith block, ranging from [0, 1];

[0051] S45, weight normalization and frequency calculation: through the block weight, the final weighted average frequency is calculated;

[0052] The block weight calculation formula is: ;

[0053] The final weighted average frequency calculation formula is: ;

[0054] In the formula, is the maximum weight of the ith block; is the natural frequency of the ith rock block.

[0055] The beneficial effects of the present application are:

[0056] (1) The present application realizes full coverage detection of the three-dimensional space at the hole bottom through the cooperative design of mechanical disc axial extension, ultra-radius extension of radial extension rods, and small-angle deflection of array element transducers, combined with the sweep frequency logic of circumferential sector by sector, radial grading, and axial layering, effectively distinguishes the hierarchical distribution of the broken zone, the fractured zone, and the complete zone of the rock at the hole bottom, obtains the block spatial position information through the position sensing sensor built in the array element bearing block, gives different blocks different weights through the dynamic weighting algorithm, avoids the frequency deviation caused by homogenization averaging, improves the representativeness and accuracy of frequency detection, and solves the problem of limited detection range of the prior art, matching the actual action area of the adjustable frequency rock breaking equipment.

[0057] (2) The present application designs a sound insulation nipple to isolate vibration interference, a telescopic sealing curtain to protect the detection environment, and a cooling and chip removal system to remove rock chips, which safeguards the stability and accuracy of the detection signal in multiple dimensions, providing a reliable data basis for frequency calculation; the data transmission module realizes the bidirectional linkage of the detection unit and the external control device, the power ultrasonic unit, real-time feedback of the detection results, and dynamic adjustment of the rock breaking vibration parameters, so that the rock breaking frequency and the rock natural frequency are accurately matched, the breaking energy consumption is significantly reduced, and the rock breaking efficiency is improved; the modules of the device are assembled in the form of a nipple, without changing the core structure of the original rock breaking equipment, adapting to various ultrasonic vibration rock breaking equipment with adjustable frequency function, supporting original factory installation and later modification, with wide application range and high automation degree. BRIEF DESCRIPTION OF DRAWINGS

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

[0059] Figure 2 is the structure schematic diagram for embodying the detection ultrasonic unit of the present application;

[0060] Figure 3 Fig. 1 is a structural schematic diagram for embodying the detection of the inner cavity of the ultrasonic short section according to the present application;

[0061] Figure 4 Fig. 2 is a local enlarged view of the A part in Fig. 1; Figure 3

[0062] Figure 5 Fig. 3 is a structural schematic diagram for embodying the detection of the surface of the ultrasonic short section according to the present application;

[0063] Figure 6 Fig. 4 is a schematic diagram for emitting ultrasonic waves to the three-dimensional model of the bottom rock according to the present application;

[0064] Figure 7 Fig. 5 is a flow chart of the method for detecting the natural frequency of the bottom rock according to the present application.

[0065] In the figure: 1, drill bit; 11, water outlet; 12, pressure sensor; 2, detection ultrasonic unit; 21, detection ultrasonic short section; 210, electric push rod; 211, array element transducer; 212, array element bearing block; 213, radial telescopic rod; 214, middle rod; 215, mechanical disc; 216, fixed shaft; 217, reset spring; 218, auxiliary push rod; 219, isolation plate; 220, telescopic sealing curtain; 221, micro pressure sensor; 22, echo information processing module; 23, algorithm processing module; 24, monitoring and control module; 25, data transmission module; 26, sound insulation short section; 3, power ultrasonic unit; 4, external control device; 5, drill pipe; 6, three-dimensional model of the bottom rock. DETAILED DESCRIPTION

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

[0067] The present application discloses a drilling ultrasonic device for detecting the natural frequency of the bottom rock.

[0068] Referring to Figures 1-6 A drilling ultrasonic device for detecting the natural frequency of the bottom rock, comprising 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 with the power ultrasonic unit 3, the sound insulation short section 26, the detection ultrasonic unit 2 and the drill bit 1 in sequence along the axial direction, and the components are rigidly connected through the drill stem coupling, and fluorine rubber sealing washers are arranged at the connection positions to prevent the drilling fluid from invading the internal circuit, thereby ensuring the stable operation of the modules under the complex working conditions in the well and avoiding the influence of liquid corrosion or short circuit on the detection and rock breaking operations.

[0069] ​The detection ultrasonic unit 2 is a near-bit rock inherent frequency core detection module, is fixed at the near-bit in the form of a short section, and is installed to maximize the shortening of a detection signal transmission path, reduce signal attenuation and interference, and improve detection response speed. 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, and the modules are electrically connected to realize orderly transmission of signals and data.

[0070] The power ultrasonic unit 3 is a rock breaking core vibration module, and comprises an adjustable frequency ultrasonic generator, an ultrasonic transducer, and an amplitude changer. The adjustable frequency range is 20 kHz-50 kHz. The core function is to receive instructions from the external control device 4 to dynamically adjust the vibration parameters, so that the output frequency and the rock inherent frequency at the bottom of the hole are matched in resonance or near resonance. According to the principle of ultrasonic resonance rock breaking, the energy consumption required for rock breaking is reduced, and the rock breaking efficiency is improved.

[0071] The drill bit 1 is embedded with a pressure sensor 12 on the surface. The pressure sensor 12 collects and transmits the drilling pressure data to the monitoring and control module 24 in real time. The drill bit 1 is circumferentially provided with a water outlet 11, which is in communication with the cooling and chip removal system, to ensure that the cooling and chip removal medium can uniformly cover the bottom of the hole, and to improve the chip removal effect.

[0072] The cooling and chip removal system comprises a water pipe arranged along the central axis of the drill rod 5. The water pipe penetrates the inner cavity of the fixed shaft 216 in the detection ultrasonic short section 21, and finally branches at the drill bit 1 and is connected with the water outlet 11. The water pipe is used to clear the residual rock chips at the bottom of the hole in the detection preparation stage by low-flow water injection. The low-flow design can avoid the change of the broken state of the rock at the bottom of the hole caused by the impact of high-pressure water flow, effectively clean the rock chip accumulation, ensure the smooth transmission path of the ultrasonic beam in the subsequent detection process, avoid the interference of the rock chip reflection with the echo signal, and further ensure the detection accuracy.

[0073] The external control device 4 is internally provided with a lithology parameter library and a dual-ultrasonic system control unit. The lithology parameter library stores parameters such as unit energy consumption rock breaking efficiency and ultrasonic rock breaking influence axial range of at least 10 common rock types. These parameters are pre-calibrated through indoor lithology breaking experiments to provide reliable data basis for the dynamic weighting algorithm. The dual-ultrasonic system control unit is used to control the start and stop and parameter adjustment of the detection ultrasonic unit 2 and the power ultrasonic unit 3, to realize the coordinated linkage of detection and rock breaking.

[0074] The detection ultrasonic short section 21 is a hollow columnar structure made of 45 steel. The detection ultrasonic short section 21 is internally provided with a mechanical disc 215, a middle rod 214, a fixed shaft 216, an electric push rod 210, and an array element transducer 211.

[0075] The mechanical disc 215 is at least two, and two mechanical discs 215 are arranged in the embodiment and are arranged axially parallel to the detection ultrasonic short section 21; the diameter of the mechanical disc 215 is 5-15 mm smaller than the diameter of the drill bit 1, and is parallel to the end surface of the drill bit 1; the mechanical disc 215 avoids interference with the hole 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 middle rod 214 is coaxially arranged in the center of each mechanical disc 215, and the two ends are fixedly connected with the detection ultrasonic short section 21; 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, and the mechanical disc 215 drives the mechanical disc 215 to move axially along the middle rod 214;

[0077] 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 hollow to accommodate the water pipe of the cooling and chip removal system; and the fixed shaft 216 realizes efficient use of the structural space.

[0078] Eight radial telescopic rods 213 are uniformly distributed on each mechanical disc 215 in the radial direction; the radial telescopic rod 213 in the embodiment adopts an electric push rod; the fixed end of the radial telescopic rod 213 is fixedly connected with the center of the mechanical disc 215; and the telescopic end of the radial telescopic rod 213 is fixedly connected with the array element bearing block 212; the array transducer 211 is installed on the array element bearing block 212; the radial telescopic rod 213 can drive the array transducer 211 to extend to a direction beyond the radius of the drill bit 1, break through the limitation of the traditional detection range, and realize full coverage detection of the hole bottom in the radial direction.

[0079] The array element bearing block 212 is embedded with a position sensing sensor inside; the position sensing sensor is used for collecting the spatial coordinates of the array transducer 211 in real time and transmitting the spatial coordinates to the algorithm processing module 23; the array transducer 211 has a small angle deflection function of ±5°, which is used for adjusting to the optimal emission angle through the echo intensity feedback.

[0080] The sound insulation short section 26 is located between the detection ultrasonic unit 2 and the power ultrasonic unit 3, and the two ends are fixedly connected with the detection ultrasonic unit 2 and the power ultrasonic unit 3 respectively; a plurality of sound insulation grooves are uniformly arranged in the sound insulation short section 26; the sound insulation grooves are composed of a plurality of annular sound insulation grooves and a plurality of strip-shaped sound insulation grooves; the plurality of annular sound insulation grooves are uniformly arranged along the axial direction of the sound insulation short section 26; and the plurality of strip-shaped sound insulation grooves are arranged along the circumferential direction of the sound insulation short section 26; the cross section of the sound insulation groove is "U" type, and the sound insulation groove is filled with damping sound insulation material; through the double sound insulation design of the sound insulation groove and the damping material, the vibration energy generated during the operation of the power ultrasonic unit 3 can be effectively absorbed and blocked, the signal acquisition interference caused by the vibration transmission to the detection ultrasonic unit 2 is avoided, and the authenticity and reliability of the detection data are ensured.

[0081] The outer wall of the detection ultrasonic short section 21 is provided with an isolation plate 219 corresponding to the position of each array transducer 211. The isolation plate 219 is an arc-shaped plate, the curvature of which is matched with the curvature of the outer wall of the detection ultrasonic short section 21. A retractable sealing curtain 220 is arranged around the edge of the isolation plate 219. The isolation plate 219 is connected to the outer wall of the detection ultrasonic short section 21 through the retractable sealing curtain 220. The retractable sealing curtain 220 is made of fluororubber, has good corrosion resistance and stretchability, and can be used for a long time in a complex environment at the bottom of a hole. The core function of the retractable sealing curtain 220 is to cover the gap between the array transducer 211 and the hole wall, form a sealed protection space, and prevent rock debris or cooling liquid from entering and affecting the detection performance of the array transducer 211.

[0082] Auxiliary push rods 218 are arranged at both ends of the isolation plate 219 close to the inner side of the detection ultrasonic short section 21. The auxiliary push rod 218 is composed of a sleeve and a movable rod arranged in the sleeve. The sleeve of the auxiliary push rod 218 is fixedly installed in the detection ultrasonic short section 21. The end of the movable rod away from the sleeve is connected to the isolation plate 219. The extension direction of the auxiliary push rod 218 is consistent with the radial extension rod 213. A reset spring 217 and a micro pressure sensor 221 are arranged in the auxiliary push rod 218. The reset spring 217 is used to reset the isolation plate 219 and the retractable sealing curtain 220 when the array transducer 211 is retracted. The micro pressure sensor 221 is used to detect the contact pressure between the isolation plate 219 and the hole wall, and to judge 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 end of the echo information processing module 22 is electrically connected to the array transducer 211 of the detection ultrasonic short section 21, and the output end is electrically connected to the algorithm processing module 23, which is used to receive the echo signal collected by the array transducer 211. Considering that the hole bottom echo signal is easily affected by rock debris interference, vibration noise, etc., the algorithm processing module 23 sequentially performs db4 wavelet base noise reduction, time domain truncation and fast Fourier transform (FFT) on the echo signal. The db4 wavelet base has good time-frequency localization characteristics, can effectively separate the signal and the noise, the time domain truncation can remove invalid signal segments, and the FFT transform realizes the conversion of the time domain signal to the frequency domain spectrum. Then, the frequency points with an amplitude ≥80% of the maximum amplitude and a duration ≥3 pulse periods are selected as the resonance peaks to determine the natural frequency of each rock block. The selection standard can ensure the authenticity of the resonance peak, avoid misjudgment of transient interference signals as resonance peaks, and accurately determine 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-aware sensor, control the transmission timing of the multi-array element transducer 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 output by the echo information processing module 22, and the radial position coefficient and axial depth coefficient corresponding to the array element spatial position, and calculate the final weighted average frequency through the dynamic weighting algorithm combined with the entropy weight method and the TOPSIS algorithm.

[0085] The entropy weight method can objectively calculate the weight based on index data, avoid the deviation of artificial subjective assignment, and the TOPSIS algorithm can quantify the importance by calculating the closeness of each block to the ideal solution, and the combination of the two can give different weights according to the characteristics of the rock block such as the broken state and the spatial position, solve the frequency deviation problem caused by the traditional homogenization average algorithm, and improve the representativeness and accuracy of the frequency detection.

[0086] 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.

[0087] The monitoring and control module 24 is the core coordination component of the detection ultrasonic unit 2, the input end of which is electrically connected with the pressure sensor 12, the position-aware sensor and the micro pressure sensor 221 respectively, 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, including the drilling pressure data, the array element spatial coordinate data, the isolation plate 219 adhesion pressure data, and the pre-recorded drill bit 1 diameter and shape information, and feeding back the summarized data to the external control device 4 through the data transmission module 25, so that the external control device 4 triggers the switching of the drilling mode and the detection mode based on the data, and ensures the rationality of the detection opportunity and the operation continuity.

[0088] The sweep frequency parameter of the array transducer 211 is set as: sweep frequency range 20kHz-50kHz, frequency step 1kHz; the parameter range matches the adjustable frequency range of the power ultrasonic unit 3, and the adaptability of the detection frequency and the rock breaking frequency is ensured. The array transducers 211 on each mechanical disc 215 form a ring array, and the sweep frequency is executed in the order of a circumferential sector-by-sector mode, a radial hierarchical mode and an axial layering mode; wherein the circumferential sector-by-sector mode is to divide the circumferential unobstructed sector of the drill bit 1, at least two array transducers 211 correspond to each sector, 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 layering 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. Through the three-dimensional sweep frequency logic of the circumferential, radial and axial directions, the fine detection of the full space of the bottom hole is realized, and the hierarchical distribution of the "broken zone, fractured zone and complete zone" of the bottom hole rock is effectively distinguished.

[0089] With reference to Figure 7 The application further discloses a while-drilling ultrasonic method for detecting the natural frequency of bottom hole rock, based on the ultrasonic while-drilling bottom hole rock natural frequency detection device, comprising the following steps:

[0090] S1, drilling and trigger determination: the drill pipe 5 drives the drill bit 1 to normally drill, the pressure sensor 12 collects the drilling pressure data in real time, the monitoring and control module 24 collects the data and then transmits the data to the external control equipment 4 through the data transmission module 25; the external control equipment 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 value, the real-time drilling speed is less than or equal to the preset drilling speed threshold value, and the state lasts for 0.5-2 seconds, the detection preparation instruction is sent to the monitoring and control module 24. The design basis of the trigger condition is that when the drilling pressure rises and the drilling speed drops, it usually indicates that the matching degree of the current rock breaking frequency and the natural frequency of the rock is insufficient, and the rock breaking efficiency is reduced, so the detection is started at this time to timely adjust the parameters, avoid invalid energy consumption, and the setting of lasting for 0.5-2 seconds can exclude the false triggering caused by instantaneous fluctuation, and ensure the reliability of the detection instruction.

[0091] S2, detection preparation: after the monitoring and control module 24 receives the detection preparation instruction, the monitoring and control module 24 feeds back the confirmation signal to the external control equipment 4 through the data transmission module 25; the external control equipment 4 sends the 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, so that water is injected into the bottom hole through the water pipe and the water outlet at a low flow rate of 5-10L / min, and the residual cuttings at the bottom hole are removed for 10-20s.

[0092] S3, three-dimensional sweep frequency detection: the device switches to the detection mode, 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 to determine the axial block thickness of the hole bottom rock, construct the three-dimensional model 6 of the hole bottom rock, and realize the accurate division of the detection area;

[0093] The control mechanical disc 215 moves axially along the shaft 214, so that the axial spacing of the adjacent two mechanical discs 215 is consistent with the axial block length; the radial telescopic rod 213 is controlled to extend, driving the array element transducer 211 and the array element bearing block 212 to move beyond the radius of the drill bit 1, and in the moving process, the array element bearing block 212 first collides with the isolation plate 219, and the isolation plate 219 drives the telescopic sealing curtain 220 to move to the hole wall; when the micro pressure sensor 221 detects that the adhesion pressure reaches the preset pressure threshold, the radial telescopic rod 213 stops extending.

[0094] The single array element transducer 211 is independently deflected, the echo intensity under each deflection angle is fed back in real time according to the echo information processing module 22, the array element transducer 211 is adjusted to the transmission angle when the echo intensity reaches the maximum value, and the echo acquisition quality is ensured;

[0095] Subsequently, the array element transducers 211 of the annular array execute sweep frequency in turn according to the circumferential sector mode, the radial hierarchical mode and the axial layer mode in sequence according to the three-dimensional model 6 of the hole bottom rock with the frequency range of 20 kHz-50 kHz and the frequency step of 1 kHz; meanwhile, 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 the single array element transducer 211 receives the echo signal of the rock block in the corresponding sector; the independent detection of the inherent frequency of each block is realized.

[0096] S4, signal processing and frequency calculation: the echo information processing module 22 executes db4 wavelet basis denoising, time domain truncation and FFT transformation on the echo signal received by each array element transducer 211 in turn, extracts the frequency domain spectrum of each rock block, and screens the resonance peak 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, combines the amplitude stability, spectral dispersion and position sensing sensor collected radial position coefficient and axial depth coefficient output by the echo information processing module 22, calculates the weight of each rock block through the dynamic weighting algorithm combined with the entropy weight method and the TOPSIS algorithm, and calculates the final weighted average frequency based on the inherent frequency of each block and the corresponding weight.

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

[0099] Each positive indicator is calculated by 、 、 、 、 The greater the indicator value is, the higher the importance of the corresponding rock block to the resonance rock breaking is, and the greater the weight distribution is.

[0100] In the above formula, V i is the resonance rock breaking speed of the rock block corresponding to the rock property, E i is the rock breaking energy consumption for breaking the block, V i and E i are obtained from the rock property parameter library of the external control device 4 and are measured through indoor rock breaking experiments; σ is the standard deviation of the echo amplitude of the rock block after noise reduction, and the data is obtained from the echo information processing module 22; Var is the spectral variance of the rock block, and the data is obtained from the echo information processing module 22; 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, and 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 rock property, z i is collected by the position sensing sensor, and z0 is obtained from the rock property 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: normalize the measured indicators of the block to the [0, 1] interval according to the positive indicator formula

[0103] In the formula, x ij is the original data of the i-th rock block on the j-th indicator; min(x j ) is the minimum value of all blocks on the j-th indicator; max(x j ) is the maximum value of all blocks on the j-th indicator; y ij is the normalized value, ranging from 0 to 1;

[0104] S42, entropy weight method to calculate the objective indicator weight: by calculating the indicator probability distribution and information entropy, the objective indicator weight is finally obtained, ensuring the objectivity of the weight distribution. ​

[0105] The index probability distribution calculation formula is: ;

[0106] In the formula, p ij is the probability of the ith block in the jth index; ε is a minimum value, which is 10 −10 ; n is the total number of rock blocks;

[0107] The information entropy calculation formula is: , wherein k=1 / lnn;

[0108] The objective index weight calculation formula is: , wherein is the sum of the proportions of effective information of all indexes, and is ensured .

[0109] S43, a weighted standardized matrix is constructed: ;

[0110] In the formula, V ij is the weighted standardized value of the ith block in the jth index; y ij is the standardized value of the ith block in the jth index, which is obtained by processing the original index data through the positive index standardization formula, and the range is [0, 1]; is the objective weight of the jth index, which is calculated by the entropy weight method;

[0111] S44, the TOPSIS algorithm is used to calculate the block closeness: the positive ideal solution , the negative ideal solution , the Euclidean distance of the block to the ideal solution is calculated

[0112] , and the closeness is ;

[0113] In the formula, is the optimal value of the jth index; is the worst value of the jth index; is the spatial distance between the ith block and the optimal block; is the spatial distance between the ith block and the worst block; C i is the closeness of the ith block, and the range is [0, 1];

[0114] S45, weight normalization and frequency calculation: through the block weight, the final weighted average frequency is calculated, which can more accurately reflect the inherent frequency characteristics of the key region of rock breaking at the bottom of the hole;

[0115] The block weight calculation formula is: ;

[0116] The calculation formula of the final weighted average frequency is: ;

[0117] In the formula, is the maximum weight of the i th block; is the natural frequency of the i th rock block.

[0118] S5, parameter adjustment and lithology 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, and 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 realize accurate matching of the rock breaking frequency and the natural frequency of the rock;

[0119] The monitoring and control module 24 records the weighted average frequencies of three consecutive detections, calculates the frequency difference between adjacent two detections, and triggers the lithology early warning if the difference of any time is greater than the preset frequency mutation threshold; this design can identify the change of the bottom lithology in time, and avoid the frequency mismatch caused by the change of the lithology;

[0120] After the lithology early warning is triggered, the algorithm processing module 23 automatically loads the parameter library in the external control device 4 that is adapted 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, so as to ensure that the detection parameters are adapted to the new lithology; when the frequency difference of two consecutive detections is less than or equal to the preset frequency mutation threshold, the lithology early warning is released, the power ultrasonic unit 3 is restarted, the drilling is resumed, and the continuity and stability of the operation are ensured.

[0121] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. A drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole, characterized in that: It includes 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 to the power ultrasonic unit (3), the detection ultrasonic unit (2), and the drill bit (1) in sequence along the axial direction; The detection ultrasonic unit (2) 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 (3) is a core vibration module for breaking rocks, which is used to receive instructions from external control equipment (4) to adjust vibration parameters; The drill bit (1) is fitted with a pressure sensor (12) to collect drilling pressure data, and 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. 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 ultrasonic detection unit (2) and finally branches at the drill bit (1) and connects with the water outlet (11) to inject water to remove residual rock cuttings at the bottom of the hole during the detection preparation stage. The external control device (4) has a built-in lithological parameter library and a dual ultrasonic system control unit for controlling the start-up and shutdown of the detection ultrasonic unit (2) and the power ultrasonic unit (3) and adjusting the parameters. The ultrasonic detection unit (2) includes an ultrasonic detection subsection (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 ultrasonic detection unit (2) are electrically connected to achieve orderly transmission of signals and data. The ultrasonic detection subsection (21) is a hollow columnar structure, with a mechanical disk (215), a central rod (214), a fixed shaft (216), an electric push rod (210), and an array element transducer (211) inside. There are at least two mechanical disks (215), which are arranged parallel to each other along the axial direction of the ultrasonic detection subsection (21). The diameter of the mechanical disk (215) is smaller than the diameter of the drill bit (1) and is parallel to the end face of the drill bit (1). The central rod (214) is coaxially inserted through the center of each mechanical disk (215), and both ends are fixedly connected to the detection ultrasonic short section (21); the electric push rod (210) corresponds one-to-one with the mechanical disk (215), and the output end of the electric push rod (210) is connected to the mechanical disk (215) to drive the mechanical disk (215) to move along the axial direction of the central rod (214); The fixed shaft (216) is coaxially fixed to the inner cavity of the detection ultrasonic subsection (21) and passes through each mechanical disk (215). The fixed shaft (216) is hollow inside to accommodate the water pipe of the cooling chip removal system. The mechanical disk (215) has a plurality of radial telescopic rods (213) evenly distributed along the radial direction. The fixed end of the radial telescopic rod (213) is fixedly connected to the center of the mechanical disk (215). The telescopic end of the radial telescopic rod (213) is fixedly connected to an array element support block (212). The array element transducer (211) is disposed on the array element support block (212). 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 an angle deflection function and is adjusted to the optimal emission angle through echo intensity feedback. A sound insulation section (26) is provided between the detection ultrasonic unit (2) and the power ultrasonic unit (3). The two ends of the sound insulation section (26) are fixedly connected to the detection ultrasonic unit (2) and the power ultrasonic unit (3) respectively. Several sound insulation grooves are opened inside the sound insulation section (26) to isolate the vibration interference generated by the power ultrasonic unit (3) during operation. The outer wall of the detection ultrasonic short section (21) is provided with an isolation plate (219) corresponding to the position of each array element transducer (211); The isolation plate (219) is an arc-shaped plate, the curvature of which matches the curvature of the outer wall of the ultrasonic testing 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 section (21) through the retractable sealing curtain (220). Auxiliary push rods (218) are provided at both ends of the isolation plate (219) near the inner side of the ultrasonic testing section (21). The extension and retraction direction of the auxiliary push rods (218) is consistent with the radial extension rod (213). A reset spring (217) and a miniature pressure sensor (221) are provided inside the auxiliary push rods (218). The reset spring (217) is used to drive the isolation plate (219) and the retractable sealing curtain (220) to reset 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.

2. The drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole according to claim 1, characterized in that: The input end of the echo information processing module (22) is electrically connected to the array element transducer (211) of the detection ultrasonic subsection (21), and the output end is electrically connected to the algorithm processing module (23). It is used to receive the echo signal collected by the array element transducer (211), and to perform db4 wavelet basis noise reduction, time domain truncation and fast Fourier transform on the echo signal in sequence. 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. 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 the electronic delay algorithm to realize the focusing of the ultrasonic beam at the specified rock block; at the same time, call the lithological parameter library of the external control device (4), combine the amplitude stability, spectrum 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 the dynamic weighting algorithm combining the entropy weight method and the TOPSIS algorithm; 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).

3. The drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole according to claim 2, characterized in that: 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, and feed the summarized data 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.

4. The drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole according to claim 3, characterized in that: 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 disk (215) 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 of the drill bit (1) circumferentially, each sector corresponds to at least 2 array element transducers (211), and the angular interval between sectors is 45°-90°; 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), 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 disk (215).

5. A drilling ultrasonic method for detecting the natural frequency of rock at the bottom of a borehole, characterized in that, A drilling ultrasonic device for detecting the natural frequency of rock at the bottom of a borehole, as described in claim 4, comprises the following steps: S1. Drilling and Trigger Judgment: The drill rod (5) drives the drill bit (1) to drill normally. The pressure sensor (12) collects the drilling pressure data in real time. After being summarized by the monitoring and control module (24), the data is transmitted to the external control device (4) through the data transmission module (25). The external control device (4) compares the data. When it is determined that the real-time drilling pressure is ≥ the preset drilling pressure threshold, the real-time drilling speed is ≤ the preset drilling speed threshold, and the state lasts for a preset time, it sends a detection preparation command to the monitoring and control module (24). 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 the outlet to remove residual rock chips 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 consecutive tests and calculates the frequency difference between two adjacent tests. If any difference is greater than the preset frequency mutation threshold, a lithology warning is triggered. After the lithology warning is triggered, the algorithm processing module (23) automatically loads the parameter library adapted to the new lithology in 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). When the frequency difference to be detected is less than or equal to the preset frequency mutation threshold, the lithology warning is lifted, the power ultrasonic unit (3) is restarted, and drilling resumes.

6. The drilling ultrasonic method for detecting the natural frequency of rock at the bottom of a borehole according to claim 5, characterized in that: In step S4, the core quantitative indicators of the dynamic weighted algorithm combining the entropy weight method and the TOPSIS algorithm include five positive indicators: unit energy consumption rock breaking efficiency η, amplitude stability S, spectral dispersion D, radial position coefficient R, and axial depth coefficient Z. Each positive indicator is respectively from , , , , Calculated; 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 were obtained from the lithological parameter library of the 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; 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 The data is collected by a position sensing sensor; z0 comes from the lithological parameter library of an external control device (4).

7. The drilling ultrasonic method for detecting the natural frequency of rock at the bottom of a borehole according to claim 6, characterized in that, The specific calculation method of the dynamic weighting algorithm in step S4 is as follows: S41. Data Standardization: Standardize the measured indicators in the blocks according to the positive indicator formula. Standardize to the [0,1] interval; 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 segment after standardization of the j-th index is in the range [0,1]. S42. Entropy weight method for calculating objective indicator weights: By calculating the probability distribution and information entropy of the indicators, the final objective indicator weights are obtained. The formula for calculating the probability distribution of the index is: ; 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; The formula for calculating information entropy is: Where, k = 1 / lnn; The formula for calculating the weight of objective indicators is: ,in The sum of the percentage of valid information for all indicators, ensuring ; S43. Construct a weighted standardized matrix: ; 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; 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. Proximity: ; 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]. S45. Weight normalization and frequency calculation: Calculate the final weighted average frequency by dividing the weights into blocks. The formula for calculating block weight is: ; The final weighted average frequency is calculated using the following formula: ; In the formula, Let be the final weight of the i-th block; Let be the natural frequency of the i-th rock fragment.

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